1. We studied the effects of increased water temperatures (0–4.5 °C) and nutrient enrichment on t... more 1. We studied the effects of increased water temperatures (0–4.5 °C) and nutrient enrichment on the stoichiometric composition of different primary producers (macrophytes, epiphytes, seston and sediment biofilm) and invertebrate consumers in 24 mesocosm ecosystems created to mimic shallow pond environments. The nutrient ratios of primary producers were used as indicative of relative nitrogen (N) or phosphorus (P) limitation. We further used carbon stable isotopic composition (δ13C) of the different primary producers to elucidate differences in the degree of CO2 limitation.2. Epiphytes were the only primary producer with significantly higher δ13C in the enriched mesocosms. No temperature effects were observed in δ13C composition of any primary producer. Independently of the treatment effects, the four primary producers had different δ13C signatures indicative of differences in CO2 limitation. Seston had signatures indicating negligible or low CO2 limitation, followed by epiphytes and sediment biofilm, with moderate CO2 limitation, while macrophytes showed the strongest CO2 limitation. CO2 together with biomass of epiphytes were the key variables explaining between 50 and 70% of the variability in δ13C of the different primary producers, suggesting that epiphytes play an important role in carbon flow of temperate shallow lakes.3. The ratio of carbon to chlorophyll a decreased with increasing temperature and enrichment in both epiphytes and seston. The effects of temperature were mainly attributed to changes in algal Chl a content, while the decrease with enrichment was probably a result of a higher proportion of algae in the seston and epiphytes.4. Macrophytes, epiphytes and seston decreased their C : N with enrichment, probably as an adaptation to the different N availability levels. The C : N of epiphytes and Elodea canadensis decreased with increasing temperature in the control mesocosms. Sediment biofilm was the only primary producer with lower C : P and N : P with enrichment, probably as a result of higher P accumulation in the sediment.5. Independently of nutrient level and increased temperature effects the four primary producers had significantly different stoichiometric compositions. Macrophytes had higher C : N and C : P and, together with epiphytes, also the highest N : P. Seston had no N or P limitation, while macrophytes and epiphytes may have been P limited in a few mesocosms. Sediment biofilm indicated strong N deficiency.6. Consumers had strongly homeostatic stoichiometric compositions in comparison to primary producers, with weak or no significant treatment effects in any of the groups (insects, leeches, molluscs and crustaceans). Among consumers, predators had significantly higher N content and lower C : N than grazers.
Retrospective investigations using carbon and nitrogen stable isotope composition of archived mat... more Retrospective investigations using carbon and nitrogen stable isotope composition of archived material have a great potential for describing past effects of anthropogenic ecosystem alterations or natural shifts in ecosystems. In this study, we examined the effects of two commonly used preservation substances of freshwater invertebrates, ethanol and lugol, on δ13C and δ15N of various planktonic and benthic taxa. For both isotopes, the average effect of fixation in ethanol was stronger than in lugol, and the effects on δ13C were stronger than on δ15N (average ± SD: 1.18 ± 0.94 and −0.47 ± 0.99 for δ13C ethanol and lugol fixed samples, respectively, and 0.39 ± 0.68 and 0.17 ± 0.77 for δ15N, respectively). The changes in the isotopic composition were not dependent on the initial isotopic composition of each taxon, but were related with concomitant changes in the carbon or nitrogen content. Application of a mass balance correction equation to the fixed samples resulted in a significantly lower average effect of fixation in ethanol (0.01 ± 0.59 and 0.44 ± 0.65 for δ15N and δ13C, respectively), while corrections had little effect for lugol fixed samples (0.24 ± 0.53 and −0.39 ± 0.85, respectively). For both isotopes and fixatives, corrections resulted in linear relationships between fixed vs. control samples, with slopes and intercepts not significantly different from 1 and 0, respectively. Therefore, mass balance correction of stable isotopes in fixed invertebrates is recommended for minimising the effects of fixation.
In order to evaluate the need for using scale acidification to remove carbonates prior to stable ... more In order to evaluate the need for using scale acidification to remove carbonates prior to stable isotope analysis, we compared acidified and non-acidified scales of six freshwater fish species (perch, roach, rudd, pike, tench and bream) with contrasting mineral content in their scales. Fish samples were taken from six lakes with variable trophic conditions, ranging from oligotrophic to hypertrophic, and differing in CO2 concentrations. The scale mineral content of the six species studied ranged between 31.8 and 61.3% dry weight (DW) in tench and perch, respectively. The elemental composition was characterised by high amounts of phosphorus, varying from 4.5 to 9.1% DW. The mineral fraction was dominated by apatite (range 24.4–49.2% DW), carbonates constituted a very small proportion of the total carbon content (average ± SD: 5.5 ± 1.7%). The average effect of acidification was very small for all species (average ± SD: 0.181 ± 0.122 and −0.208 ± 0.243 for carbon and nitrogen, respectively), albeit significant for five out of the six species (excepting tench that had the lowest mineral content). Linear regression slopes between acidified and untreated scales did not differ significantly from one for almost all the species and isotopes. The effects of acidification on the two isotopes were correlated with the relative carbonate content as well as with the CO2 concentration for carbon and total phosphorus for nitrogen. We conclude that the need for scale acidification depends on the different species and on the system studied, although in most cases the acidification effect will be biologically irrelevant. However, dual analysis of acidified and untreated scales may provide useful information on differences in stable isotope composition of dissolved inorganic carbon and on phytoplankton carbon fractionation generated by varying levels of CO2 availability.
1. Variations in the light regime can affect the availability and quality of food for zooplankton... more 1. Variations in the light regime can affect the availability and quality of food for zooplankton grazers as well as their exposure to fish predation. In northern lakes light is particularly low in winter and, with increasing warming, the northern limit of some present-day plankton communities may move further north and the plankton will thus receive less winter light.2. We followed the changes in the biomass and community structure of zooplankton and phytoplankton in a clear and a turbid shallow lake during winter (November–March) in enclosures both with and without fish and with four different light treatments (100%, 55%, 7% and <1% of incoming light).3. In both lakes total zooplankton biomass and chlorophyll-a were influenced by light availability and the presence of fish. Presence of fish irrespective of the light level led to low crustacean biomass, high rotifer biomass and changes in the life history of copepods. The strength of the fish effect on zooplankton biomass diminished with declining light and the effect of light was strongest in the presence of fish.4. When fish were present, reduced light led to a shift from rotifers to calanoid copepods in the clear lake and from rotifers to cyclopoid copepods in the turbid lake. Light affected the phytoplankton biomass and, to a lesser extent, the phytoplankton community composition and size. However, the fish effect on phytoplankton was overall weak.5. Our results from typical Danish shallow eutrophic lakes suggest that major changes in winter light conditions are needed in order to have a significant effect on the plankton community. The change in light occurring when such plankton communities move northwards in response to global warming will mostly be of modest importance for this lake type, at least for the rest of this century in an IPCC A2 scenario, while stronger effects may be observed in deep lakes.
1. Fish community structure and habitat distribution of the abundant species roach, perch and ruf... more 1. Fish community structure and habitat distribution of the abundant species roach, perch and ruffe were studied in Lake Nordborg (Denmark) before (August 2006) and after (August 2007) aluminium treatment to reduce internal phosphorus loading. 2. Rapid changes in fish community structure, abundance and habitat distribution occurred following a decline in in-lake phosphorus concentrations from 280 to 37 lg P L )1 and an increase in Secchi depth transparency from 1.1 to 1.9 m (August). The proportion of perch in overnight gill net catches increased, whilst roach decreased, and the average weight of all key species increased. 3. The habitat distribution of perch and roach changed from a high proportion in the upper pelagic and littoral zones in 2006, towards enhanced proportions in the deeper pelagic and profundal zone in 2007. The abundance of large-bodied zooplankton increased and the abundance of benthic invertebrates decreased in the same period, suggesting that the habitat shift was not induced by food limitation. 4. Ruffe shifted from the littoral and upper profundal zones towards the deep profundal zone, likely reflecting an increased predation risk in the littoral zone and better oxygen conditions in the deep profundal. 5. Our results indicate that enhanced risk of predation in the upper pelagic and the littoral zones and perhaps improved oxygen concentrations in the deeper profundal zone at decreasing turbidity are responsible for the observed habitat shift. The results indicate that fish respond rapidly to changes in nutrient state, both in terms of community structure and habitat use.
Soil animal detritivores play an important role in facilitating decomposition processes but littl... more Soil animal detritivores play an important role in facilitating decomposition processes but little information is available on how the quality of dietary resources affects their stoichiometry of carbon (C) nitrogen (N) and phosphorus (P), and turnover of C and N. This study investigated how a fungal diet, Fusarium culmorum, with a low N content and imbalanced amino acid (AA) composition affected the physiology of three soil-dwelling collembolans (Folsomia candida, Protaphorura fimata and Proisotoma minuta) in comparison to a control diet, Saccharomyces cerevisiae, with a high N content and balanced AA composition. We compared the elemental composition of animals, their growth rates and tissue replacement of C and N. We also measured the individual AA δ13C to investigate the extent that Collembola may rely on endogenous sources to compensate for scarcity of essential AAs. The results showed that animal&amp;#x27;s N content tracked closely the composition of their diets, decreasing from around 10 to 7% N from the high to low N diet. They also had a significant increase of C and a decrease of P. P. fimata was less affected than F. candida and P. minuta. The total incorporation of C and N in the animals due to growth and tissue replacement decreased from 11–17 to 6–12% DM d−1 on the high and low N diet respectively with P. fimata experiencing the smallest change. Essential AAs δ13C did not always match perfectly between Collembola species and their diets; particularly on the low N diet. Isotope patterns of AAs indicate that bacteria may have been the alternative source of essential AAs. While the results of this study cannot be extrapolated directly to the dynamics of Collembola populations in the field, they serve to demonstrate their flexibility in adapting physiologically to the temporal and spatial patchiness of the soil environment.
It has been demonstrated that plant roots can take up small amounts of low-molecular weight (LMW)... more It has been demonstrated that plant roots can take up small amounts of low-molecular weight (LMW) compounds from the surrounding soil. Root uptake of LMW compounds have been investigated by applying isotopically labelled sugars or amino acids but not labelled organic matter. We tested whether wheat roots took up LMW compounds released from dual-labelled (13C and 15N) green manure by analysing for excess 13C in roots. To estimate the fraction of green manure C that potentially was available for root uptake, excess 13C and 15N in the primary decomposers was estimated by analysing soil dwelling Collembola that primarily feed on fungi or microfauna. The experimental setup consisted of soil microcosm with wheat and dual-labelled green manure additions. Plant growth, plant N and recoveries of 13C and 15N in soil, roots, shoots and Collembola were measured at 27, 56 and 84 days. We found a small (<1%) but significant uptake of green manure derived 13C in roots at the first but not the two last samplings. About 50% of green manure C was not recovered from the soil-plant system at 27 days and additional 8% was not recovered at 84 days. Up to 23% of C in collembolans derived from the green manure at 56 days (the 27 days sampling was lost). Using a linear mixing model we estimated that roots or root effluxes provided the main C source for collembolans (54−79%). We conclude that there is no solid support for claiming that roots assimilated green manure derived C due to very small or no recoveries of excess 13C in wheat roots. During the incubation the pool of green manure derived C available for root uptake decreased due to decomposition. However, the isotopic composition in Collembola indicated that there was a considerable fraction of green manure derived C in the decomposer system at 56 days thus supporting the premise that LMW compounds containing C from the green manure was released throughout the incubation.
1Physiological mechanisms such as allocation and release of nutrients are keys to understanding a... more 1Physiological mechanisms such as allocation and release of nutrients are keys to understanding an animal's adaptation to a particular habitat. This study investigated how two detrivores with contrasting life-history traits allocated carbon (C) and nitrogen (N) to growth, reproduction and metabolism. As model organisms we used the collembolans, Proisotoma minuta (Tullberg 1871) and Protaphorura fimata (Gisin 1952).2To estimate allocations of C and N in tissue, we changed the isotopic composition of the animal's yeast diets when they became sexually mature and followed isotope turnover in tissue, growth and reproduction for 28 days. In addition, we measured the composition of C, N and phosphorus (P) to gain complementary information on the stoichiometry underlying life-history traits and nutrient allocation.3For P. minuta, the smallest and most fecund of the two species, the tissue turnover of C and N were 13% and 11% day−1, respectively. For P. fimata, the equivalent rates were 5% and 4% d−1, respectively. Protaphorura fimata had the lowest metabolic rate relative to total body mass but the highest metabolic rates relative to reproductive investment. Adult P. fimata retained approximately 17% of the nutrient reserves acquired while a juvenile and adult P. minuta about 11%. N and P contents of total tissue were significantly higher in P. minuta than in P. fimata, suggesting that tissue turnover was correlated with high protein-N and RNA-P.4Our results suggest that the lower metabolism and nutritional requirements by P. fimata than P. minuta is an adaptation to the generally low availability and quality of food in its natural habitat.5The methodological approach we implemented tracking mass balance, isotope turnover and elemental composition is promising for linking nutrient budgets and life-history traits in small invertebrates such as Collembola.Physiological mechanisms such as allocation and release of nutrients are keys to understanding an animal's adaptation to a particular habitat. This study investigated how two detrivores with contrasting life-history traits allocated carbon (C) and nitrogen (N) to growth, reproduction and metabolism. As model organisms we used the collembolans, Proisotoma minuta (Tullberg 1871) and Protaphorura fimata (Gisin 1952).To estimate allocations of C and N in tissue, we changed the isotopic composition of the animal's yeast diets when they became sexually mature and followed isotope turnover in tissue, growth and reproduction for 28 days. In addition, we measured the composition of C, N and phosphorus (P) to gain complementary information on the stoichiometry underlying life-history traits and nutrient allocation.For P. minuta, the smallest and most fecund of the two species, the tissue turnover of C and N were 13% and 11% day−1, respectively. For P. fimata, the equivalent rates were 5% and 4% d−1, respectively. Protaphorura fimata had the lowest metabolic rate relative to total body mass but the highest metabolic rates relative to reproductive investment. Adult P. fimata retained approximately 17% of the nutrient reserves acquired while a juvenile and adult P. minuta about 11%. N and P contents of total tissue were significantly higher in P. minuta than in P. fimata, suggesting that tissue turnover was correlated with high protein-N and RNA-P.Our results suggest that the lower metabolism and nutritional requirements by P. fimata than P. minuta is an adaptation to the generally low availability and quality of food in its natural habitat.The methodological approach we implemented tracking mass balance, isotope turnover and elemental composition is promising for linking nutrient budgets and life-history traits in small invertebrates such as Collembola.
Lake Redó, a dimictic oligotrophic mountain lake, was monitored for two complete years from July ... more Lake Redó, a dimictic oligotrophic mountain lake, was monitored for two complete years from July 1996 to July 1998. The main seasonal variations in the physical, chemical and biological parameters are described, with special emphasis on the comparison of external forcing (weather and atmospheric deposition) with internal lake dynamics. Annual mean air temperature was estimated to be 3.6 °C. The duration of ice cover on the lake was 4.5 months in 1996/97 and 5.8 months in 1997/98. The lake water was very ionpoor (mean annual conductivity 12 µS cm -1 ); however, ion concentrations in the lake were higher than in the precipitation, the differences being due mainly to Ca 2+ and bicarbonates originating in the catchment. NH 4 + was the main ion in the precipitation, with an average concentration of 17 µM, while in the lake it was always below 3 µM. However, the concentration of dissolved inorganic nitrogen always exceeded that of soluble reactive phosphorus by two or three orders of magnitude, so the latter is likely to be the limiting nutrient for phytoplankton growth. Four main production episodes were identified, occurring during spring and autumn overturn, in the upper hypolimnion during summer stratification, and under the ice at the beginning of the ice-covered period. The highest chlorophyll-a concentrations (1.2-2.2 µg l -1 ) were attained during spring overturn; concentrations of chlorophyll-c were high during both spring and autumn overturn, while chlorophyll-b was comparatively important in the upper hypolimnion during the stratification period. Daphnia pulicaria was the most abundant macrozooplankton species; its abundance was highest during the icecovered period, when its biomass was comparable to the measured sestonic particulate carbon concentration. The Daphnia maximum was associated with higher concentrations of NH 4 + and dissolved organic carbon, suggesting that it may play an important role in the pelagic biogeochemical compartment of the lake under ice. Winter respiration rates for the lake were estimated to be 339 mg O 2 m -2 d -1 for 1996/97 and 281 mg O 2 m -2 d -1 for 1997/98.
Trophic-niche differentiation is often cited as a main factor in structuring zooplankton assembla... more Trophic-niche differentiation is often cited as a main factor in structuring zooplankton assemblages, although field evidence for this is rarely presented. The study was based on a survey of 29 Pyrenean lakes with altitudes ranging between 1,875 and 2,990 m carried out during July and August 2000. Because of the oligotrophic nature of these lakes, we aimed to confirm that food partitioning is a major factor in shaping zooplankton assemblages. We analysed the amino acid composition of six cladocera and seven copepod species. A discriminant analysis showed that each species could be distinguished according to its amino acid composition. A negative relationship between amino acid differentiation and co-occurrence among the cladocera and cyclopoid copepod was observed. In contrast, calanoids did not show any relationship and were characterised by a high amino acid differentiation between species. As the differences in the amino acid composition among zooplankton species indicate distinct food sources, the relationship found indicates that trophic-niche differentiation plays a key role in determining the assemblage of these zooplankton communities. Therefore exploitative competition, either at present or in the past by driving co-evolutionary histories, has been a significant factor in structuring the cladocera and cyclopoid communities in these oligotrophic lakes.
The paper presents the first comprehensive account of congener profiles of polycyclic aromatic hy... more The paper presents the first comprehensive account of congener profiles of polycyclic aromatic hydrocarbons (PAHs) in intertidal bivalve mollusks [Meretrix meretrix, Macoma birmanica, and Sanguilonaria (Soletellina) acuminata] of Sunderban mangrove wetland (India). The main aim of this work was to use the bivalves as bioindicators of the contamination of the 16 USEPA PAH. The PAH profile in bivalves is largely dominated by a petrogenic fingerprint, with over-imposition of pyrolytic PAH sources, as evidenced by diagnostic molecular ratios. Bioaccumulation factors (BAF) of individual compounds from the sediments were calculated, and it reveals overall higher values in the visceral mass of the bivalves. S acuminata showed significantly higher levels of PAHs, especially the high molecular weight (HMW) PAHs, compared to the other two species as a sensitive indicator of trace organic stress in future monitoring programs.
1. A survey of c. 350 remote high altitude and high latitude lakes from 11 different mountain reg... more 1. A survey of c. 350 remote high altitude and high latitude lakes from 11 different mountain regions was undertaken to explore species distribution across Europe at a scale not previously attempted.2. Lakes were sampled for planktonic crustaceans, rotifers, littoral invertebrates and sub-fossil chironomids, diatoms and cladocerans. Each lake was characterised in terms of water chemistry, morphology, catchment attributes and geographical location.3. Separate twinspan analyses were undertaken on diatom, chironomid, planktonic crustacean, littoral invertebrate and cladoceran (chydorids only) data to classify sites according to taxonomic composition. For most datasets there was a spatial component to the classification with distinct geographical groups emerging – Norway and Scotland, Finland and Central/Eastern Europe.4. Constrained ordination methods were employed to examine how species responded to a range of environmental factors, which were aggregated into a series of component groups – proximal environment (the chemical, trophic and physical attributes of the lake), catchment characteristics and geographical location. Several key environmental gradients were identified, which explained significant levels of the variance across several of the biological groups including dissolved organic carbon (chironomids, planktonic crustaceans), temperature (chironomids and littoral invertebrates), chloride/sea-salt (littoral invertebrates, diatoms and rotifers), lake morphology (all groups), calcium/pH (diatoms), nitrate (chydorids, littoral invertebrates, rotifers and planktonic crustaceans) and fish (littoral invertebrates). In some cases these statistical relationships are likely to represent direct ecological constraints and, in others, it is probable that the environmental variable is acting as a surrogate for some other attribute or process.5. Variance partitioning was undertaken to quantify how much of the variation in each biological group could be uniquely attributed to variables representing the proximal environment, catchment characteristics and geographical location. For most groups the location of the lake tends to explain the greatest variation in species composition across the Lake Districts. The proximal environment was also important but, with the exception of diatoms, secondary to location. Therefore, a strong geographical signal emerged from the analyses. Three distinct limno-regions were identified; Nordic (Scotland and Norway), Sub-Arctic (Northern Finland) and Alpine (Pyrenees, the Alps and Eastern Europe ranges).6. Our results have implications for the development of regionalisation schemes based on biological responses to environmental gradients; (i) lake ‘types’ based on environmental factors cannot be extrapolated throughout Europe, even within the relatively narrow gradients found in remote mountain lakes, (ii) biotic response to large-scale variations in environmental conditions, such as those that could be expected with climate change, is likely to vary according to regions because of the biogeographical differences among them.
The integrated assessment models that drive atmospheric pollutant emission reduction policies wit... more The integrated assessment models that drive atmospheric pollutant emission reduction policies within Europe, under the Convention on Long-range Transboundary Air Pollution, work at the scale of the EMEP grid (50 ¥ 50 km). Critical loads are used to link anthropogenic deposition to adverse effects for individual ecosystems within each grid cell. The critical loads have two aspects, ecosystem area and the ecosystem specific critical load. The presence of highly acid-sensitive ecosystems within these grid cells can lead to very low critical loads of acidity which provide emission targets that are difficult to achieve: these cells are known as "binding grid squares". Since mountain lakes are highly sensitive to environmental change, their inclusion in critical loads assessments might be expected to result in lower EMEP scale critical loads. The combination of mountain lakes data with those from other ecosystems already included Aquat. Sci. 67 (2005) 252 -262 Aquatic Sciences in the integrated modelling shows unexpected results. The average accumulated exceedance of critical loads of acidity may increase with either the presence of significant mountain lake catchment areas within grid cells or the presence of highly acidified clusters of sites. These circumstances occur in only a small number of grid cells. Furthermore, the relatively low sensitivity of mountain lakes to acidification in some regions means that their inclusion in EMEP scale models would lead to a relaxation of emission abatement requirements because of an increase in the area of ecosystems not exceeding critical loads and a decrease in AAE. Hence the potential effects of the inclusion of mountain lake critical loads of acidity in EMEP scale models vary greatly on a regional basis.
1. Species assemblages of diatoms, rotifers, chydorids, planktonic crustaceans and chironomids we... more 1. Species assemblages of diatoms, rotifers, chydorids, planktonic crustaceans and chironomids were studied in 235 alpine lakes in the Alps, Pyrenees, Tatras (Western Carpathians), Retezat (Southern Carpathians) and Rila Mountains (Balkans).2. For all taxonomic groups we found a hierarchical structure in the community assemblage using distinct scales of lake clustering (number of k-means groups) based on species composition similarity (Hellinger distance). We determined the optimal partition in assemblage types (i.e. number of lake clusters) for each taxonomic group by maximising the sum of the taxon indicative value (IndVal) and performed discriminant analyses, using environmental variables not conditioned by geographical patterns. Relevant environmental variables differed among and within taxonomic groups. Therefore the assemblages respond to a complex environmental mosaic, with the exception of diatom assemblages, which followed an acid–base gradient.3. The significant environmental variables could be grouped into four general factors: lake size, tropho-dynamic status, acid–base balance and ice-cover duration (i.e., altitudinal gradient). Lake size was significant for the highest number of assemblage types; however, the most significant factor differed among taxonomic groups: acid–base balance for diatoms, lake size for rotifers, ice-cover duration for chydorids and planktonic crustaceans and tropho-dynamic status for chironomids. No single environmental typology accounted for the assemblage structure of all taxonomic groups.4. However, defining ecological thresholds as values within environmental gradients at which the rate of change in assemblages is accelerated relative to points distant from that threshold, we were able to find specific threshold values for each of the four main general environmental factors identified, which were relevant across several taxonomic groups: 3 ha for lake area; 0.6 mg L−1 for dissolved organic carbon; 190 days for ice-cover duration and 200 μeq L−1 for acid neutralising capacity. Above and below these values ecosystem organisation change substantially. They have direct applications in establishing lake typologies for environmental quality and biodiversity conservation programmes, and in improving predictions about global change impacts.
With the aim to determine the contribution of development and reproduction to the variability in ... more With the aim to determine the contribution of development and reproduction to the variability in the elemental composition of zooplankton, we measured the carbon (C), hydrogen (H), nitrogen (N), and phosphorus (P) elemental composition of the planktonic crustacean assemblage in an alpine lake for a whole seasonal cycle. The species included three distinct living modes: a cladoceran, Daphnia pulicaria; a cyclopoid copepod, Cyclops abyssorum; and a calanoid copepod, Diaptomus cyaneus. For the three species, reproduction was the main cause of elemental variability. Adult females of the three species lost from 32% to 48% of their initial absolute C and H content during reproduction, which corresponded to a similar decrease in their lipid and carbohydrate content. The N content did not change in any of the three species, nor did the protein and chitin content. Daphnia and Diaptomus lost 35% and 56%, respectively, of their initial absolute P content during reproduction, whereas the P content of Cyclops did not change. The three species stored energy compounds under unfavorable conditions for later use in offspring production, but only Diaptomus and Daphnia mobilized stored P. Corresponding stoichiometric changes with reproduction included a decrease in C : N ratio for the three species; an increase in N : P ratio for Daphnia adult females and adults of Diaptomus; and a C : P ratio increase in Diaptomus females and decline in Cyclops females. Differences in C : P ratio changes corresponded with differences in allocation to their respective reproductive tissues. Diaptomus males and Daphnia females did not change their C : P ratio with reproduction.
The process-oriented catchment-scale model MAGIC was used to simulate water chemistry at Lake Red... more The process-oriented catchment-scale model MAGIC was used to simulate water chemistry at Lake Redó, a high mountain lake in the Central Pyrenees, Spain. Data on lakewater and atmospheric deposition chemistry for the period 1984-1998 were used to calibrate the model, which was then used to reconstruct past and to provide forecasts for three hypothetical future scenarios of deposition. Forecast scenarios considered several combinations of changes in S and N deposition due to abatement strategies, and in base cation deposition due to climate-induced changes in air-mass trajectories from northern Africa. Scenario 1 assumed constant deposition of base cations at the present level plus the expected decrease in S and N deposition resulting from reduced emissions; scenario 2 (best case) assumed an increase in base cation deposition plus the same decrease in S and N deposition as in scenario 1; scenario 3 (worst case) assumed a decrease in base cation deposition plus no decrease in S and N deposition. The hindcast indicated that during the past 140-year period changes in lake water chemistry have been significant for a remote mountain catchment, although no substantial acidification has occurred. In this regard Lake Redó can be described as a "non-sensitive lake" maintaining a reference condition. The forecasts indicated changes that do not affect this status, but the trends, even if slight, were different between scenarios. A slight decline in the surface water ANC is predicted by Scenario 3. The N budget indicates an unusually low retention in the catchment, which may result in enhanced sensitivity to further increased N deposition. Some of the discrepancy between modelled and measured Ca 2+ in lake water during 1984-98 could be explained by changes in rainfall amounts and by increased weathering rates due to increases in air temperature.
1. The complex terrain and heterogeneous nature of the mountain environment coupled with remotene... more 1. The complex terrain and heterogeneous nature of the mountain environment coupled with remoteness from major centres of human activity makes mountains challenging locations for meteorological investigations. Mountainous areas tend to have more varied and more extreme weather than lowlands.2. The EMERGE program has the primary aim of assessing the status of remote mountain and sub-arctic lakes throughout Europe for the first time. In this study, we describe the main features of the climate, ice-cover durations and recent temperature trends of these areas. The main weather characteristics of European mountain and sub-arctic lakes are their cold temperatures and year-round precipitation. Mean annual temperatures are generally close to 0 °C, and maximum summer temperatures reasonably close to 10 °C.3. Maritime versus continental settings determine the main differences in annual-temperature range among lake districts (10.5 °C in Scotland to 26.7 °C in Northern Finland), and a similar factor for ice-cover duration. Radiation ranges from low (120 W m−2) in the high latitude sub-arctic and high (237 W m−2) in the southern ranges of the Pyrenees and Rila. Similarly, precipitation is high in the main Alpine chain (250 cm year−1 in the Central Southern Alps) and low in the continental sub-arctic (65 cm year−1 in Northern Finland).4. The main temporal patterns in air temperature follow those of the adjacent lowlands. All the lake districts warmed during the last century. Spring temperature trends were highest in Finland; summer trends were weak everywhere; autumn trends were strongest in the west, in the Pyrenees and western Alps; while winter trends varied markedly, being high in the Pyrenees and Alps, low in Scotland and Norway and negative in Finland.5. Two new, limnological case studies on Lake Redon, in the Pyrenees, highlight the sensitivity of remote lakes to projected changes in the global climate. These two case studies involve close linkages between extreme chemical-precipitation events and synoptic wind-patterns, and between thermocline behaviour and features of the large-scale circulation.6. Individual lakes can be ultra-responsive to climate change. Even modest changes in future air temperatures will lead to major changes in lake temperatures and ice-cover duration and hence probably affect their ecological status.
An integrated study encompassing the distribution of organochlorine compounds (OC) in water, food... more An integrated study encompassing the distribution of organochlorine compounds (OC) in water, food web (chironomids, terrestrial insects, cladocerans, mollusks, and cyanobacteria), and fish (brown trout) from a high mountain lake (Redon, Pyrenees) is reported. OC distributions in these compartments have been determined to assess their transport routes into fish. Food diets have been estimated by analysis of fish stomach content and food web stable isotopes (δ 13 C and δ 15 N). OCs with octanol-water partition coefficient (K ow ) higher than 10 6 showed lower concentrations in food than expected from theoretical octanol-water partition, indicating that the distribution of these compounds does not reach equilibrium within the life span of the food web organisms (ca. 1 year). On the other hand, the degree of biomagnification in fish increased with K ow , except in the case of the largest compound analyzed (seven chlorine substituents, PCB #180). OC exchange at fish gill and gut has been evaluated using a fugacity model based on the water, food, and fish concentrations. All compounds exhibited a net gill loss and a net gut uptake. A pseudostationary state was only achieved for compounds with log(K ow ) < 6. Calculation of fish average residence times for the compounds in apparent steady state gave values of days to a few weeks for HCHs, 1 year for HCB and 4,4′-DDE, and 2-3 years for 4,4′-DDT and PCB#28 and PCB#52. Residence times longer than one decade were found for the more chlorinated PCB.
Polycyclic aromatic hydrocarbons (PAH) were measured in bulk atmospheric deposition collected in ... more Polycyclic aromatic hydrocarbons (PAH) were measured in bulk atmospheric deposition collected in three remote areas of Europe during 1997-1998. Mean total PAH fluxes over a period of 18 months were 1560 ( 750 and 1150 ( 630 ng m -2 mo -1 in the Pyrenees and the Alps, respectively. In the Caledonian mountains (Scandinavia) the observed mean fluxes were 1900 ( 940 ng m -2 mo -1 (6 month collection). Similar qualitative PAH compositions (p values <0.05) in the bulk atmospheric deposition have been observed between sites, which are dominated by the more volatile parent compounds. The main differences between lakes are related to the high molecular weight compounds. Atmospheric deposition of PAH to these remote sites appears to be independent of their concentrations in the atmosphere, which are similar between sites (in the range of 1.8-3.0 ng‚m -3 ), being controlled mainly by particle deposition, followed by precipitation and air temperature. A multilevel regression model including these three variables accounted for 74% of the total variability in total PAH bulk deposition; however, the contribution of each variable in the model is compound and site-dependent. The deposition of high molecular weight PAH depends more on particle deposition and precipitation, whereas air temperature is the main factor controlling the deposition fluxes of the low molecular weight PAH.
1. We studied the effects of increased water temperatures (0–4.5 °C) and nutrient enrichment on t... more 1. We studied the effects of increased water temperatures (0–4.5 °C) and nutrient enrichment on the stoichiometric composition of different primary producers (macrophytes, epiphytes, seston and sediment biofilm) and invertebrate consumers in 24 mesocosm ecosystems created to mimic shallow pond environments. The nutrient ratios of primary producers were used as indicative of relative nitrogen (N) or phosphorus (P) limitation. We further used carbon stable isotopic composition (δ13C) of the different primary producers to elucidate differences in the degree of CO2 limitation.2. Epiphytes were the only primary producer with significantly higher δ13C in the enriched mesocosms. No temperature effects were observed in δ13C composition of any primary producer. Independently of the treatment effects, the four primary producers had different δ13C signatures indicative of differences in CO2 limitation. Seston had signatures indicating negligible or low CO2 limitation, followed by epiphytes and sediment biofilm, with moderate CO2 limitation, while macrophytes showed the strongest CO2 limitation. CO2 together with biomass of epiphytes were the key variables explaining between 50 and 70% of the variability in δ13C of the different primary producers, suggesting that epiphytes play an important role in carbon flow of temperate shallow lakes.3. The ratio of carbon to chlorophyll a decreased with increasing temperature and enrichment in both epiphytes and seston. The effects of temperature were mainly attributed to changes in algal Chl a content, while the decrease with enrichment was probably a result of a higher proportion of algae in the seston and epiphytes.4. Macrophytes, epiphytes and seston decreased their C : N with enrichment, probably as an adaptation to the different N availability levels. The C : N of epiphytes and Elodea canadensis decreased with increasing temperature in the control mesocosms. Sediment biofilm was the only primary producer with lower C : P and N : P with enrichment, probably as a result of higher P accumulation in the sediment.5. Independently of nutrient level and increased temperature effects the four primary producers had significantly different stoichiometric compositions. Macrophytes had higher C : N and C : P and, together with epiphytes, also the highest N : P. Seston had no N or P limitation, while macrophytes and epiphytes may have been P limited in a few mesocosms. Sediment biofilm indicated strong N deficiency.6. Consumers had strongly homeostatic stoichiometric compositions in comparison to primary producers, with weak or no significant treatment effects in any of the groups (insects, leeches, molluscs and crustaceans). Among consumers, predators had significantly higher N content and lower C : N than grazers.
Retrospective investigations using carbon and nitrogen stable isotope composition of archived mat... more Retrospective investigations using carbon and nitrogen stable isotope composition of archived material have a great potential for describing past effects of anthropogenic ecosystem alterations or natural shifts in ecosystems. In this study, we examined the effects of two commonly used preservation substances of freshwater invertebrates, ethanol and lugol, on δ13C and δ15N of various planktonic and benthic taxa. For both isotopes, the average effect of fixation in ethanol was stronger than in lugol, and the effects on δ13C were stronger than on δ15N (average ± SD: 1.18 ± 0.94 and −0.47 ± 0.99 for δ13C ethanol and lugol fixed samples, respectively, and 0.39 ± 0.68 and 0.17 ± 0.77 for δ15N, respectively). The changes in the isotopic composition were not dependent on the initial isotopic composition of each taxon, but were related with concomitant changes in the carbon or nitrogen content. Application of a mass balance correction equation to the fixed samples resulted in a significantly lower average effect of fixation in ethanol (0.01 ± 0.59 and 0.44 ± 0.65 for δ15N and δ13C, respectively), while corrections had little effect for lugol fixed samples (0.24 ± 0.53 and −0.39 ± 0.85, respectively). For both isotopes and fixatives, corrections resulted in linear relationships between fixed vs. control samples, with slopes and intercepts not significantly different from 1 and 0, respectively. Therefore, mass balance correction of stable isotopes in fixed invertebrates is recommended for minimising the effects of fixation.
In order to evaluate the need for using scale acidification to remove carbonates prior to stable ... more In order to evaluate the need for using scale acidification to remove carbonates prior to stable isotope analysis, we compared acidified and non-acidified scales of six freshwater fish species (perch, roach, rudd, pike, tench and bream) with contrasting mineral content in their scales. Fish samples were taken from six lakes with variable trophic conditions, ranging from oligotrophic to hypertrophic, and differing in CO2 concentrations. The scale mineral content of the six species studied ranged between 31.8 and 61.3% dry weight (DW) in tench and perch, respectively. The elemental composition was characterised by high amounts of phosphorus, varying from 4.5 to 9.1% DW. The mineral fraction was dominated by apatite (range 24.4–49.2% DW), carbonates constituted a very small proportion of the total carbon content (average ± SD: 5.5 ± 1.7%). The average effect of acidification was very small for all species (average ± SD: 0.181 ± 0.122 and −0.208 ± 0.243 for carbon and nitrogen, respectively), albeit significant for five out of the six species (excepting tench that had the lowest mineral content). Linear regression slopes between acidified and untreated scales did not differ significantly from one for almost all the species and isotopes. The effects of acidification on the two isotopes were correlated with the relative carbonate content as well as with the CO2 concentration for carbon and total phosphorus for nitrogen. We conclude that the need for scale acidification depends on the different species and on the system studied, although in most cases the acidification effect will be biologically irrelevant. However, dual analysis of acidified and untreated scales may provide useful information on differences in stable isotope composition of dissolved inorganic carbon and on phytoplankton carbon fractionation generated by varying levels of CO2 availability.
1. Variations in the light regime can affect the availability and quality of food for zooplankton... more 1. Variations in the light regime can affect the availability and quality of food for zooplankton grazers as well as their exposure to fish predation. In northern lakes light is particularly low in winter and, with increasing warming, the northern limit of some present-day plankton communities may move further north and the plankton will thus receive less winter light.2. We followed the changes in the biomass and community structure of zooplankton and phytoplankton in a clear and a turbid shallow lake during winter (November–March) in enclosures both with and without fish and with four different light treatments (100%, 55%, 7% and <1% of incoming light).3. In both lakes total zooplankton biomass and chlorophyll-a were influenced by light availability and the presence of fish. Presence of fish irrespective of the light level led to low crustacean biomass, high rotifer biomass and changes in the life history of copepods. The strength of the fish effect on zooplankton biomass diminished with declining light and the effect of light was strongest in the presence of fish.4. When fish were present, reduced light led to a shift from rotifers to calanoid copepods in the clear lake and from rotifers to cyclopoid copepods in the turbid lake. Light affected the phytoplankton biomass and, to a lesser extent, the phytoplankton community composition and size. However, the fish effect on phytoplankton was overall weak.5. Our results from typical Danish shallow eutrophic lakes suggest that major changes in winter light conditions are needed in order to have a significant effect on the plankton community. The change in light occurring when such plankton communities move northwards in response to global warming will mostly be of modest importance for this lake type, at least for the rest of this century in an IPCC A2 scenario, while stronger effects may be observed in deep lakes.
1. Fish community structure and habitat distribution of the abundant species roach, perch and ruf... more 1. Fish community structure and habitat distribution of the abundant species roach, perch and ruffe were studied in Lake Nordborg (Denmark) before (August 2006) and after (August 2007) aluminium treatment to reduce internal phosphorus loading. 2. Rapid changes in fish community structure, abundance and habitat distribution occurred following a decline in in-lake phosphorus concentrations from 280 to 37 lg P L )1 and an increase in Secchi depth transparency from 1.1 to 1.9 m (August). The proportion of perch in overnight gill net catches increased, whilst roach decreased, and the average weight of all key species increased. 3. The habitat distribution of perch and roach changed from a high proportion in the upper pelagic and littoral zones in 2006, towards enhanced proportions in the deeper pelagic and profundal zone in 2007. The abundance of large-bodied zooplankton increased and the abundance of benthic invertebrates decreased in the same period, suggesting that the habitat shift was not induced by food limitation. 4. Ruffe shifted from the littoral and upper profundal zones towards the deep profundal zone, likely reflecting an increased predation risk in the littoral zone and better oxygen conditions in the deep profundal. 5. Our results indicate that enhanced risk of predation in the upper pelagic and the littoral zones and perhaps improved oxygen concentrations in the deeper profundal zone at decreasing turbidity are responsible for the observed habitat shift. The results indicate that fish respond rapidly to changes in nutrient state, both in terms of community structure and habitat use.
Soil animal detritivores play an important role in facilitating decomposition processes but littl... more Soil animal detritivores play an important role in facilitating decomposition processes but little information is available on how the quality of dietary resources affects their stoichiometry of carbon (C) nitrogen (N) and phosphorus (P), and turnover of C and N. This study investigated how a fungal diet, Fusarium culmorum, with a low N content and imbalanced amino acid (AA) composition affected the physiology of three soil-dwelling collembolans (Folsomia candida, Protaphorura fimata and Proisotoma minuta) in comparison to a control diet, Saccharomyces cerevisiae, with a high N content and balanced AA composition. We compared the elemental composition of animals, their growth rates and tissue replacement of C and N. We also measured the individual AA δ13C to investigate the extent that Collembola may rely on endogenous sources to compensate for scarcity of essential AAs. The results showed that animal&amp;#x27;s N content tracked closely the composition of their diets, decreasing from around 10 to 7% N from the high to low N diet. They also had a significant increase of C and a decrease of P. P. fimata was less affected than F. candida and P. minuta. The total incorporation of C and N in the animals due to growth and tissue replacement decreased from 11–17 to 6–12% DM d−1 on the high and low N diet respectively with P. fimata experiencing the smallest change. Essential AAs δ13C did not always match perfectly between Collembola species and their diets; particularly on the low N diet. Isotope patterns of AAs indicate that bacteria may have been the alternative source of essential AAs. While the results of this study cannot be extrapolated directly to the dynamics of Collembola populations in the field, they serve to demonstrate their flexibility in adapting physiologically to the temporal and spatial patchiness of the soil environment.
It has been demonstrated that plant roots can take up small amounts of low-molecular weight (LMW)... more It has been demonstrated that plant roots can take up small amounts of low-molecular weight (LMW) compounds from the surrounding soil. Root uptake of LMW compounds have been investigated by applying isotopically labelled sugars or amino acids but not labelled organic matter. We tested whether wheat roots took up LMW compounds released from dual-labelled (13C and 15N) green manure by analysing for excess 13C in roots. To estimate the fraction of green manure C that potentially was available for root uptake, excess 13C and 15N in the primary decomposers was estimated by analysing soil dwelling Collembola that primarily feed on fungi or microfauna. The experimental setup consisted of soil microcosm with wheat and dual-labelled green manure additions. Plant growth, plant N and recoveries of 13C and 15N in soil, roots, shoots and Collembola were measured at 27, 56 and 84 days. We found a small (<1%) but significant uptake of green manure derived 13C in roots at the first but not the two last samplings. About 50% of green manure C was not recovered from the soil-plant system at 27 days and additional 8% was not recovered at 84 days. Up to 23% of C in collembolans derived from the green manure at 56 days (the 27 days sampling was lost). Using a linear mixing model we estimated that roots or root effluxes provided the main C source for collembolans (54−79%). We conclude that there is no solid support for claiming that roots assimilated green manure derived C due to very small or no recoveries of excess 13C in wheat roots. During the incubation the pool of green manure derived C available for root uptake decreased due to decomposition. However, the isotopic composition in Collembola indicated that there was a considerable fraction of green manure derived C in the decomposer system at 56 days thus supporting the premise that LMW compounds containing C from the green manure was released throughout the incubation.
1Physiological mechanisms such as allocation and release of nutrients are keys to understanding a... more 1Physiological mechanisms such as allocation and release of nutrients are keys to understanding an animal's adaptation to a particular habitat. This study investigated how two detrivores with contrasting life-history traits allocated carbon (C) and nitrogen (N) to growth, reproduction and metabolism. As model organisms we used the collembolans, Proisotoma minuta (Tullberg 1871) and Protaphorura fimata (Gisin 1952).2To estimate allocations of C and N in tissue, we changed the isotopic composition of the animal's yeast diets when they became sexually mature and followed isotope turnover in tissue, growth and reproduction for 28 days. In addition, we measured the composition of C, N and phosphorus (P) to gain complementary information on the stoichiometry underlying life-history traits and nutrient allocation.3For P. minuta, the smallest and most fecund of the two species, the tissue turnover of C and N were 13% and 11% day−1, respectively. For P. fimata, the equivalent rates were 5% and 4% d−1, respectively. Protaphorura fimata had the lowest metabolic rate relative to total body mass but the highest metabolic rates relative to reproductive investment. Adult P. fimata retained approximately 17% of the nutrient reserves acquired while a juvenile and adult P. minuta about 11%. N and P contents of total tissue were significantly higher in P. minuta than in P. fimata, suggesting that tissue turnover was correlated with high protein-N and RNA-P.4Our results suggest that the lower metabolism and nutritional requirements by P. fimata than P. minuta is an adaptation to the generally low availability and quality of food in its natural habitat.5The methodological approach we implemented tracking mass balance, isotope turnover and elemental composition is promising for linking nutrient budgets and life-history traits in small invertebrates such as Collembola.Physiological mechanisms such as allocation and release of nutrients are keys to understanding an animal's adaptation to a particular habitat. This study investigated how two detrivores with contrasting life-history traits allocated carbon (C) and nitrogen (N) to growth, reproduction and metabolism. As model organisms we used the collembolans, Proisotoma minuta (Tullberg 1871) and Protaphorura fimata (Gisin 1952).To estimate allocations of C and N in tissue, we changed the isotopic composition of the animal's yeast diets when they became sexually mature and followed isotope turnover in tissue, growth and reproduction for 28 days. In addition, we measured the composition of C, N and phosphorus (P) to gain complementary information on the stoichiometry underlying life-history traits and nutrient allocation.For P. minuta, the smallest and most fecund of the two species, the tissue turnover of C and N were 13% and 11% day−1, respectively. For P. fimata, the equivalent rates were 5% and 4% d−1, respectively. Protaphorura fimata had the lowest metabolic rate relative to total body mass but the highest metabolic rates relative to reproductive investment. Adult P. fimata retained approximately 17% of the nutrient reserves acquired while a juvenile and adult P. minuta about 11%. N and P contents of total tissue were significantly higher in P. minuta than in P. fimata, suggesting that tissue turnover was correlated with high protein-N and RNA-P.Our results suggest that the lower metabolism and nutritional requirements by P. fimata than P. minuta is an adaptation to the generally low availability and quality of food in its natural habitat.The methodological approach we implemented tracking mass balance, isotope turnover and elemental composition is promising for linking nutrient budgets and life-history traits in small invertebrates such as Collembola.
Lake Redó, a dimictic oligotrophic mountain lake, was monitored for two complete years from July ... more Lake Redó, a dimictic oligotrophic mountain lake, was monitored for two complete years from July 1996 to July 1998. The main seasonal variations in the physical, chemical and biological parameters are described, with special emphasis on the comparison of external forcing (weather and atmospheric deposition) with internal lake dynamics. Annual mean air temperature was estimated to be 3.6 °C. The duration of ice cover on the lake was 4.5 months in 1996/97 and 5.8 months in 1997/98. The lake water was very ionpoor (mean annual conductivity 12 µS cm -1 ); however, ion concentrations in the lake were higher than in the precipitation, the differences being due mainly to Ca 2+ and bicarbonates originating in the catchment. NH 4 + was the main ion in the precipitation, with an average concentration of 17 µM, while in the lake it was always below 3 µM. However, the concentration of dissolved inorganic nitrogen always exceeded that of soluble reactive phosphorus by two or three orders of magnitude, so the latter is likely to be the limiting nutrient for phytoplankton growth. Four main production episodes were identified, occurring during spring and autumn overturn, in the upper hypolimnion during summer stratification, and under the ice at the beginning of the ice-covered period. The highest chlorophyll-a concentrations (1.2-2.2 µg l -1 ) were attained during spring overturn; concentrations of chlorophyll-c were high during both spring and autumn overturn, while chlorophyll-b was comparatively important in the upper hypolimnion during the stratification period. Daphnia pulicaria was the most abundant macrozooplankton species; its abundance was highest during the icecovered period, when its biomass was comparable to the measured sestonic particulate carbon concentration. The Daphnia maximum was associated with higher concentrations of NH 4 + and dissolved organic carbon, suggesting that it may play an important role in the pelagic biogeochemical compartment of the lake under ice. Winter respiration rates for the lake were estimated to be 339 mg O 2 m -2 d -1 for 1996/97 and 281 mg O 2 m -2 d -1 for 1997/98.
Trophic-niche differentiation is often cited as a main factor in structuring zooplankton assembla... more Trophic-niche differentiation is often cited as a main factor in structuring zooplankton assemblages, although field evidence for this is rarely presented. The study was based on a survey of 29 Pyrenean lakes with altitudes ranging between 1,875 and 2,990 m carried out during July and August 2000. Because of the oligotrophic nature of these lakes, we aimed to confirm that food partitioning is a major factor in shaping zooplankton assemblages. We analysed the amino acid composition of six cladocera and seven copepod species. A discriminant analysis showed that each species could be distinguished according to its amino acid composition. A negative relationship between amino acid differentiation and co-occurrence among the cladocera and cyclopoid copepod was observed. In contrast, calanoids did not show any relationship and were characterised by a high amino acid differentiation between species. As the differences in the amino acid composition among zooplankton species indicate distinct food sources, the relationship found indicates that trophic-niche differentiation plays a key role in determining the assemblage of these zooplankton communities. Therefore exploitative competition, either at present or in the past by driving co-evolutionary histories, has been a significant factor in structuring the cladocera and cyclopoid communities in these oligotrophic lakes.
The paper presents the first comprehensive account of congener profiles of polycyclic aromatic hy... more The paper presents the first comprehensive account of congener profiles of polycyclic aromatic hydrocarbons (PAHs) in intertidal bivalve mollusks [Meretrix meretrix, Macoma birmanica, and Sanguilonaria (Soletellina) acuminata] of Sunderban mangrove wetland (India). The main aim of this work was to use the bivalves as bioindicators of the contamination of the 16 USEPA PAH. The PAH profile in bivalves is largely dominated by a petrogenic fingerprint, with over-imposition of pyrolytic PAH sources, as evidenced by diagnostic molecular ratios. Bioaccumulation factors (BAF) of individual compounds from the sediments were calculated, and it reveals overall higher values in the visceral mass of the bivalves. S acuminata showed significantly higher levels of PAHs, especially the high molecular weight (HMW) PAHs, compared to the other two species as a sensitive indicator of trace organic stress in future monitoring programs.
1. A survey of c. 350 remote high altitude and high latitude lakes from 11 different mountain reg... more 1. A survey of c. 350 remote high altitude and high latitude lakes from 11 different mountain regions was undertaken to explore species distribution across Europe at a scale not previously attempted.2. Lakes were sampled for planktonic crustaceans, rotifers, littoral invertebrates and sub-fossil chironomids, diatoms and cladocerans. Each lake was characterised in terms of water chemistry, morphology, catchment attributes and geographical location.3. Separate twinspan analyses were undertaken on diatom, chironomid, planktonic crustacean, littoral invertebrate and cladoceran (chydorids only) data to classify sites according to taxonomic composition. For most datasets there was a spatial component to the classification with distinct geographical groups emerging – Norway and Scotland, Finland and Central/Eastern Europe.4. Constrained ordination methods were employed to examine how species responded to a range of environmental factors, which were aggregated into a series of component groups – proximal environment (the chemical, trophic and physical attributes of the lake), catchment characteristics and geographical location. Several key environmental gradients were identified, which explained significant levels of the variance across several of the biological groups including dissolved organic carbon (chironomids, planktonic crustaceans), temperature (chironomids and littoral invertebrates), chloride/sea-salt (littoral invertebrates, diatoms and rotifers), lake morphology (all groups), calcium/pH (diatoms), nitrate (chydorids, littoral invertebrates, rotifers and planktonic crustaceans) and fish (littoral invertebrates). In some cases these statistical relationships are likely to represent direct ecological constraints and, in others, it is probable that the environmental variable is acting as a surrogate for some other attribute or process.5. Variance partitioning was undertaken to quantify how much of the variation in each biological group could be uniquely attributed to variables representing the proximal environment, catchment characteristics and geographical location. For most groups the location of the lake tends to explain the greatest variation in species composition across the Lake Districts. The proximal environment was also important but, with the exception of diatoms, secondary to location. Therefore, a strong geographical signal emerged from the analyses. Three distinct limno-regions were identified; Nordic (Scotland and Norway), Sub-Arctic (Northern Finland) and Alpine (Pyrenees, the Alps and Eastern Europe ranges).6. Our results have implications for the development of regionalisation schemes based on biological responses to environmental gradients; (i) lake ‘types’ based on environmental factors cannot be extrapolated throughout Europe, even within the relatively narrow gradients found in remote mountain lakes, (ii) biotic response to large-scale variations in environmental conditions, such as those that could be expected with climate change, is likely to vary according to regions because of the biogeographical differences among them.
The integrated assessment models that drive atmospheric pollutant emission reduction policies wit... more The integrated assessment models that drive atmospheric pollutant emission reduction policies within Europe, under the Convention on Long-range Transboundary Air Pollution, work at the scale of the EMEP grid (50 ¥ 50 km). Critical loads are used to link anthropogenic deposition to adverse effects for individual ecosystems within each grid cell. The critical loads have two aspects, ecosystem area and the ecosystem specific critical load. The presence of highly acid-sensitive ecosystems within these grid cells can lead to very low critical loads of acidity which provide emission targets that are difficult to achieve: these cells are known as "binding grid squares". Since mountain lakes are highly sensitive to environmental change, their inclusion in critical loads assessments might be expected to result in lower EMEP scale critical loads. The combination of mountain lakes data with those from other ecosystems already included Aquat. Sci. 67 (2005) 252 -262 Aquatic Sciences in the integrated modelling shows unexpected results. The average accumulated exceedance of critical loads of acidity may increase with either the presence of significant mountain lake catchment areas within grid cells or the presence of highly acidified clusters of sites. These circumstances occur in only a small number of grid cells. Furthermore, the relatively low sensitivity of mountain lakes to acidification in some regions means that their inclusion in EMEP scale models would lead to a relaxation of emission abatement requirements because of an increase in the area of ecosystems not exceeding critical loads and a decrease in AAE. Hence the potential effects of the inclusion of mountain lake critical loads of acidity in EMEP scale models vary greatly on a regional basis.
1. Species assemblages of diatoms, rotifers, chydorids, planktonic crustaceans and chironomids we... more 1. Species assemblages of diatoms, rotifers, chydorids, planktonic crustaceans and chironomids were studied in 235 alpine lakes in the Alps, Pyrenees, Tatras (Western Carpathians), Retezat (Southern Carpathians) and Rila Mountains (Balkans).2. For all taxonomic groups we found a hierarchical structure in the community assemblage using distinct scales of lake clustering (number of k-means groups) based on species composition similarity (Hellinger distance). We determined the optimal partition in assemblage types (i.e. number of lake clusters) for each taxonomic group by maximising the sum of the taxon indicative value (IndVal) and performed discriminant analyses, using environmental variables not conditioned by geographical patterns. Relevant environmental variables differed among and within taxonomic groups. Therefore the assemblages respond to a complex environmental mosaic, with the exception of diatom assemblages, which followed an acid–base gradient.3. The significant environmental variables could be grouped into four general factors: lake size, tropho-dynamic status, acid–base balance and ice-cover duration (i.e., altitudinal gradient). Lake size was significant for the highest number of assemblage types; however, the most significant factor differed among taxonomic groups: acid–base balance for diatoms, lake size for rotifers, ice-cover duration for chydorids and planktonic crustaceans and tropho-dynamic status for chironomids. No single environmental typology accounted for the assemblage structure of all taxonomic groups.4. However, defining ecological thresholds as values within environmental gradients at which the rate of change in assemblages is accelerated relative to points distant from that threshold, we were able to find specific threshold values for each of the four main general environmental factors identified, which were relevant across several taxonomic groups: 3 ha for lake area; 0.6 mg L−1 for dissolved organic carbon; 190 days for ice-cover duration and 200 μeq L−1 for acid neutralising capacity. Above and below these values ecosystem organisation change substantially. They have direct applications in establishing lake typologies for environmental quality and biodiversity conservation programmes, and in improving predictions about global change impacts.
With the aim to determine the contribution of development and reproduction to the variability in ... more With the aim to determine the contribution of development and reproduction to the variability in the elemental composition of zooplankton, we measured the carbon (C), hydrogen (H), nitrogen (N), and phosphorus (P) elemental composition of the planktonic crustacean assemblage in an alpine lake for a whole seasonal cycle. The species included three distinct living modes: a cladoceran, Daphnia pulicaria; a cyclopoid copepod, Cyclops abyssorum; and a calanoid copepod, Diaptomus cyaneus. For the three species, reproduction was the main cause of elemental variability. Adult females of the three species lost from 32% to 48% of their initial absolute C and H content during reproduction, which corresponded to a similar decrease in their lipid and carbohydrate content. The N content did not change in any of the three species, nor did the protein and chitin content. Daphnia and Diaptomus lost 35% and 56%, respectively, of their initial absolute P content during reproduction, whereas the P content of Cyclops did not change. The three species stored energy compounds under unfavorable conditions for later use in offspring production, but only Diaptomus and Daphnia mobilized stored P. Corresponding stoichiometric changes with reproduction included a decrease in C : N ratio for the three species; an increase in N : P ratio for Daphnia adult females and adults of Diaptomus; and a C : P ratio increase in Diaptomus females and decline in Cyclops females. Differences in C : P ratio changes corresponded with differences in allocation to their respective reproductive tissues. Diaptomus males and Daphnia females did not change their C : P ratio with reproduction.
The process-oriented catchment-scale model MAGIC was used to simulate water chemistry at Lake Red... more The process-oriented catchment-scale model MAGIC was used to simulate water chemistry at Lake Redó, a high mountain lake in the Central Pyrenees, Spain. Data on lakewater and atmospheric deposition chemistry for the period 1984-1998 were used to calibrate the model, which was then used to reconstruct past and to provide forecasts for three hypothetical future scenarios of deposition. Forecast scenarios considered several combinations of changes in S and N deposition due to abatement strategies, and in base cation deposition due to climate-induced changes in air-mass trajectories from northern Africa. Scenario 1 assumed constant deposition of base cations at the present level plus the expected decrease in S and N deposition resulting from reduced emissions; scenario 2 (best case) assumed an increase in base cation deposition plus the same decrease in S and N deposition as in scenario 1; scenario 3 (worst case) assumed a decrease in base cation deposition plus no decrease in S and N deposition. The hindcast indicated that during the past 140-year period changes in lake water chemistry have been significant for a remote mountain catchment, although no substantial acidification has occurred. In this regard Lake Redó can be described as a "non-sensitive lake" maintaining a reference condition. The forecasts indicated changes that do not affect this status, but the trends, even if slight, were different between scenarios. A slight decline in the surface water ANC is predicted by Scenario 3. The N budget indicates an unusually low retention in the catchment, which may result in enhanced sensitivity to further increased N deposition. Some of the discrepancy between modelled and measured Ca 2+ in lake water during 1984-98 could be explained by changes in rainfall amounts and by increased weathering rates due to increases in air temperature.
1. The complex terrain and heterogeneous nature of the mountain environment coupled with remotene... more 1. The complex terrain and heterogeneous nature of the mountain environment coupled with remoteness from major centres of human activity makes mountains challenging locations for meteorological investigations. Mountainous areas tend to have more varied and more extreme weather than lowlands.2. The EMERGE program has the primary aim of assessing the status of remote mountain and sub-arctic lakes throughout Europe for the first time. In this study, we describe the main features of the climate, ice-cover durations and recent temperature trends of these areas. The main weather characteristics of European mountain and sub-arctic lakes are their cold temperatures and year-round precipitation. Mean annual temperatures are generally close to 0 °C, and maximum summer temperatures reasonably close to 10 °C.3. Maritime versus continental settings determine the main differences in annual-temperature range among lake districts (10.5 °C in Scotland to 26.7 °C in Northern Finland), and a similar factor for ice-cover duration. Radiation ranges from low (120 W m−2) in the high latitude sub-arctic and high (237 W m−2) in the southern ranges of the Pyrenees and Rila. Similarly, precipitation is high in the main Alpine chain (250 cm year−1 in the Central Southern Alps) and low in the continental sub-arctic (65 cm year−1 in Northern Finland).4. The main temporal patterns in air temperature follow those of the adjacent lowlands. All the lake districts warmed during the last century. Spring temperature trends were highest in Finland; summer trends were weak everywhere; autumn trends were strongest in the west, in the Pyrenees and western Alps; while winter trends varied markedly, being high in the Pyrenees and Alps, low in Scotland and Norway and negative in Finland.5. Two new, limnological case studies on Lake Redon, in the Pyrenees, highlight the sensitivity of remote lakes to projected changes in the global climate. These two case studies involve close linkages between extreme chemical-precipitation events and synoptic wind-patterns, and between thermocline behaviour and features of the large-scale circulation.6. Individual lakes can be ultra-responsive to climate change. Even modest changes in future air temperatures will lead to major changes in lake temperatures and ice-cover duration and hence probably affect their ecological status.
An integrated study encompassing the distribution of organochlorine compounds (OC) in water, food... more An integrated study encompassing the distribution of organochlorine compounds (OC) in water, food web (chironomids, terrestrial insects, cladocerans, mollusks, and cyanobacteria), and fish (brown trout) from a high mountain lake (Redon, Pyrenees) is reported. OC distributions in these compartments have been determined to assess their transport routes into fish. Food diets have been estimated by analysis of fish stomach content and food web stable isotopes (δ 13 C and δ 15 N). OCs with octanol-water partition coefficient (K ow ) higher than 10 6 showed lower concentrations in food than expected from theoretical octanol-water partition, indicating that the distribution of these compounds does not reach equilibrium within the life span of the food web organisms (ca. 1 year). On the other hand, the degree of biomagnification in fish increased with K ow , except in the case of the largest compound analyzed (seven chlorine substituents, PCB #180). OC exchange at fish gill and gut has been evaluated using a fugacity model based on the water, food, and fish concentrations. All compounds exhibited a net gill loss and a net gut uptake. A pseudostationary state was only achieved for compounds with log(K ow ) < 6. Calculation of fish average residence times for the compounds in apparent steady state gave values of days to a few weeks for HCHs, 1 year for HCB and 4,4′-DDE, and 2-3 years for 4,4′-DDT and PCB#28 and PCB#52. Residence times longer than one decade were found for the more chlorinated PCB.
Polycyclic aromatic hydrocarbons (PAH) were measured in bulk atmospheric deposition collected in ... more Polycyclic aromatic hydrocarbons (PAH) were measured in bulk atmospheric deposition collected in three remote areas of Europe during 1997-1998. Mean total PAH fluxes over a period of 18 months were 1560 ( 750 and 1150 ( 630 ng m -2 mo -1 in the Pyrenees and the Alps, respectively. In the Caledonian mountains (Scandinavia) the observed mean fluxes were 1900 ( 940 ng m -2 mo -1 (6 month collection). Similar qualitative PAH compositions (p values <0.05) in the bulk atmospheric deposition have been observed between sites, which are dominated by the more volatile parent compounds. The main differences between lakes are related to the high molecular weight compounds. Atmospheric deposition of PAH to these remote sites appears to be independent of their concentrations in the atmosphere, which are similar between sites (in the range of 1.8-3.0 ng‚m -3 ), being controlled mainly by particle deposition, followed by precipitation and air temperature. A multilevel regression model including these three variables accounted for 74% of the total variability in total PAH bulk deposition; however, the contribution of each variable in the model is compound and site-dependent. The deposition of high molecular weight PAH depends more on particle deposition and precipitation, whereas air temperature is the main factor controlling the deposition fluxes of the low molecular weight PAH.
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Papers by Marc Ventura