Bioscience

1. Sedimentary remains of aquatic plants, both vegetative (turions, leaves, spines) and reproductive (fruits, seeds, pollen), may provide a record of temporal changes in the submerged vegetation of lakes. An independent assessment of the degree to which these remains reflect past floristic change is, however, rarely possible. 2. By exploiting an extensive series of historical plant records for a small shallow lake we compare plant macrofossil (three cores) and pollen (one core) profiles with the documented sequence of submerged vegetation change since c. 1750 AD. The data set is based on 146 site visits with 658 observations including 42 taxa classified as aquatic, spanning 250 years.

To assess the similarity, not only in community structure, but also in the factors that shape cladoceran assemblages, we analysed the contemporary zooplankton populations and their sub-fossil remains in 39 shallow UK and Danish lakes. Contemporary zooplankton populations sampled from both the lake edge and the open water in August were compared with surficial sediment assemblages. The sedimentary assemblage data combined counts of both ephippial and chitinous remains in order to provide some

CITATIONS 25 READS 57 5 authors, including: Some of the authors of this publication are also working on these related projects: colonization of periglacial habitats, recently uncovered due to the retreating ice sheet in Western Greenland, by clones of obligately asexual water flea populations. View project

colonization of periglacial habitats, recently uncovered due to the retreating ice sheet in Western Greenland, by clones of obligately asexual water flea populations. View project SUMMARY 1. To correctly interpret chironomid faunas for palaeoenvironmental reconstruction, it is essential that we improve our understanding of the relative influence of ecosystem variables, biotic as well as physicochemical, on chironomid larvae. To address this, we analysed the surface sediments from 39 shallow lakes (29 Norfolk, U.K., 10 Denmark) for chironomid head capsules, and 70 chironomid taxa (including Chaoborus) were identified. 2. The shallow lakes were selected over large environmental gradients of aquatic macrophytes, total phosphorus (TP) and fish communities. Redundancy analysis (RDA) identified two significant variables that explained chironomid distribution: macrophyte species richness (P < 0.001) and TP (P < 0.005). Generalised linear models (GLM) identified specific taxa that had significant relationships with both these variables. Macrophyte percentage volume infested (PVI) and species richness were significant in classifying the lake types based on chironomid communities under T W I N S P A N T W I N S P A N analysis, although other factors, notably nutrient concentrations and fish communities, were also important, illustrating the complexities of classifying shallow lake ecosystems. Lakes with plant species richness >10 all had relatively diverse (Hill's N2) chironomid assemblages, and lakes with Hill's N2 >10 all had TP <250 lg L )1 and total fish densities <2 fish per m 2 . 3. Plant density (PVI), and perhaps more importantly species richness, were primary controls on the distribution of chironomid communities within these lakes. This clearly has implications for palaeoenvironmental reconstructions using zoobenthos remains (i.e. chironomids) and suggests that they could be used to track changes in benthic ⁄ pelagic production and could be used as indicators of changing macrophyte habitat. 4. Measuring key biological gradients, in addition to physicochemical gradients, allowed the major controls on chironomid distribution to be assessed more directly, in terms of plant substrate, food availability, competition and predation pressure, rather than implying indirect mechanisms through relationships with nutrients. Many of these variables, notably macrophyte abundance and species richness, are not routinely measured in such studies, despite their importance in determining zoobenthos in temperate shallow lakes. 5. When physical, chemical and ecological gradients are considered, as is often the case with palaeo-reconstructions rather than training sets chosen to maximise one gradient, complex relationships exist, and attempting to reconstruct a single trophic variable quantitatively may not be appropriate or reliable.

1. Quantitative palaeolimnology has traditionally sought to quantify species-environment relationships to use alterations in biological assemblages to reflect past environmental change. Transfer functions have used regression techniques, such as weighted averaging, to define taxon optima and tolerance for a single chemical or biological variable.2. Cladoceran assemblages and their sub-fossil remains in shallow lakes are shaped by a combination of interacting factors. Partial constrained ordination of sub-fossil cladoceran assemblages from 39 shallow lakes (29 in Norfolk, U.K. and 10 in Denmark) indicated that both zooplanktivorous fish (ZF) density and submerged macrophyte abundance significantly influenced community composition. These dual structuring forces precluded the use of a transfer function as one of the key assumptions of this approach was not met, namely that environmental variables apart from the variable being modelled have negligible influence on species distribution or that there is a linear relationship between the two. Separate transfer functions for ZF and macrophyte abundance were developed but had poor performance diagnostics with low bootstrapped r2, high root mean square error of prediction (RMSEP) and large bias.3. To obviate the problem of multiple structuring forces a multivariate regression tree (MRT) was employed, which allows for more than one explanatory variable within a model. The MRT analysis defined six groups with discrete ranges of ZF and macrophyte densities. The technique identified critical values or ‘break points’ in ZF and macrophyte abundances which result in significant alterations in the sub-fossil cladoceran assemblage. In addition, the MRT groups had different summer mean values for chlorophyll-a, Secchi depth, total phosphorus and nitrate-nitrogen.4. The predictive abilities of the model were assessed by comparing the observed versus predicted MRT group membership. In general group membership was reliably predicted, suggesting sub-fossil cladoceran assemblages reliably reflect ZF and macrophyte density in shallow lakes. For a relatively small number of sites there were differences between the observed and predicted MRT group membership. These failures of prediction may result, at least in part, from the disparity of the time period represented by the environmental data and the surface sediment cladoceran assemblage.

1. Seasonal relationships between macrophyte and phytoplankton populations may alter considerably as lakes undergo eutrophication. Understanding of these changes may be key to the interpretation of ecological processes operating over longer (decadal-centennial) timescales.2. We explore the seasonal dynamics of macrophytes (measured twice in June and August) and phytoplankton (measured monthly May–September) populations in 39 shallow lakes (29 in the U.K. and 10 in Denmark) covering broad gradients for nutrients and plant abundance.3. Three site groups were identified based on macrophyte seasonality; 16 lakes where macrophyte abundance was perennially low and the water generally turbid (‘turbid lakes’); 7 where macrophyte abundance was high in June but low in August (‘crashing’ lakes); and 12 where macrophyte abundance was high in both June and August (‘stable’ lakes). The seasonal behaviour of the crashing and turbid lakes was extremely similar with a consistent increase in nutrient concentrations and chlorophyll-a over May–September. By contrast in the stable lakes, seasonal changes were dampened with chlorophyll-a consistently low (<10–15 μg L−1) over the entire summer. The crashing lakes were dominated by one or a combination of Potamogeton pusillus, Potamogeton pectinatus and Zannichellia palustris, whereas Ceratophyllum demersum and Chara spp. were more abundant in the stable lakes.4. A long-term loss of macrophyte species diversity has occurred in many shallow lakes affected by eutrophication. One common pathway is from a species-rich plant community with charophytes to a species-poor community dominated by P. pusillus, P. pectinatus and Z. palustris. Such compositional changes may often be accompanied by a substantial reduction in the seasonal duration of plant dominance and a greater tendency for incursions by phytoplankton. We hypothesise a slow-enacting (10–100 s years) feedback loop in nutrient-enriched shallow lakes whereby increases in algal abundance are associated with losses of macrophyte species and hence different plant seasonal strategies. In turn such changes may favour increased phytoplankton production thus placing further pressure on remaining macrophytes. This study blurs the distinction between so-called turbid phytoplankton-dominated and clear plant-dominated shallow lakes and suggests that plant loss from them may be a gradual process.

Concentrations are reported of hexabromocyclododecanes (HBCDs) and tetrabromobisphenol-A (TBBP-A) in water (n ) 27), sediment (n ) 9), and fish samples (n ) 30) from nine English lakes. Seasonal variation in concentrations in water is minimal. Concentrations of TBBP-A range from 140 to 3200 pg L -1 (water), 330 to 3800 pg g -1 dry weight (sediment), and <0.29 to 1.7 ng g -1 lipid weight (fish). Those of ΣHBCDs range between 80 and 270 pg L -1 (water), 880 and 4800 pg g -1 dry weight (sediment), and 14 and 290 ng g -1 lipid weight (fish). Aqueous concentrations of ΣHBCDs and TBBP-A are significantly positively correlated, indicating a common source. Average (σ n "freely-dissolved" phase proportions are 47 ( 4.7% (ΣHBCDs) and 61 ( 2.9% (TBBP-A). Average field-derived bioaccumulation factors are 5900, 1300, 810, and 2100 for R-, -, γ-, and ΣHBCDs, respectively. Tetrabromocyclododecadienes are detected in all sediments, with pentabromocyclododecenes present in some. This suggests HBCD degrades via sequential loss of HBr. The δ-HBCD meso form was quantified in 43% of fish samples (1.0-11% ΣHBCDs). Its absence from temporally and spatially consistent water and sediment samples suggests it is formed via bioisomerization. While HBCD chiral signatures are racemic in water and sediment, our data reveal enantiomeric enrichment of (-)R-HBCD and (+)γ-HBCD in fish.

1. Palaeolimnology and contemporary ecology are complementary disciplines but are rarely combined. By reviewing the literature and using a case study, we show how linking the timescales of these approaches affords a powerful means of understanding ecological change in shallow lakes.2. Recently, palaeolimnology has largely been pre-occupied with developing transfer functions which use surface sediment-lake environment datasets to reconstruct a single environmental variable. Such models ignore complex controls over biological structure and can be prone to considerable error in prediction. Furthermore, by reducing species assemblage data to a series of numbers, transfer functions neglect valuable ecological information on species’ seasonality, habitat structure and food web interactions. These elements can be readily extracted from palaeolimnological data with the interpretive assistance of contemporary experiments and surveys. For example, for one shallow lake, we show how it is possible to infer long-term seasonality change from plant macrofossil and fossil diatom data with the assistance of seasonal datasets on macrophyte and algal dynamics.3. On the other hand, theories on shallow lake functioning have generally been developed from short-term (<1–15 years) studies as opposed to palaeo-data that cover the actual timescales (decades–centuries) of shallow lake response to stressors such as eutrophication and climate change. Palaeolimnological techniques can track long-term dynamics in lakes whilst smoothing out short-term variability and thus provide a unique and important means of not only developing ecological theories, but of testing them.4. By combining contemporary ecology and palaeolimnology, it should be possible to gain a fuller understanding of changing ecological patterns and processes in shallow lakes on multiple timescales.

The palaeoecological potential of fish scales was assessed by comparing contemporary population data with scale remains obtained from littoral (n = 10) and open water (n = 10) surface sediment samples in two English shallow lakes, Selbrigg Pond and Cockshoot Broad. Scales and/or scale fragments were present, in low numbers (<20 per 100 cm3 wet sediment) in 34 of 40 sediment samples. In accordance with fish population data, higher densities of scale remains were found in Selbrigg compared to Cockshoot, and in littoral compared to open water samples. Taxonomic difficulties, exacerbated by scale fragmentation, made it impossible to assign the majority of remains to individual species. Most remains could, however, be placed into one of two groups: (i) percids – represented by both scales and scale fragments; and (ii) cyprinids – largely represented by scale fragments. To allow comparison of fish population and sedimentary scale data, both were converted to percentages of the aggregate percid–cyprinid total. Whole scales recovered were almost exclusively percid (45 of 48), thus bore little resemblance to the contemporary fish data. Nevertheless, percentages of scale fragments (Selbrigg: 34 and 66%; Cockshoot: 13 and 87% percid and cyprinid, respectively) and of whole scales and fragments combined (Selbrigg: 54 and 46%; Cockshoot: 46 and 54% percid and cyprinid, respectively) reflected the presence of the numerically dominant fish groups and the broad inter-site differences in their relative abundance (Selbrigg: 36 and 64%; Cockshoot: 10 and 90% percid and cyprinid, respectively). A running mean of scales per sediment volume indicated that some 400 cm3 of sediment was required to accurately characterise the remains present. This study suggests that, with the appropriate methodological considerations (e.g., collection of large sediment samples), fish scale remains may be used to determine the past presence–absence and relative abundance of percid and cyprinid species. As such, this technique may be a valuable supplementary tool for establishing longer-term changes in the fish communities of shallow lakes.

1. Shallow lakes are often cited as classic examples of systems that exhibit trophic cascades but, whilst they provide good model systems with which to test general ecological theory and to assess long-term community change, their food web linkages have rarely been resolved, so changes associated with the structure and dynamics of the ecological network as a whole are still poorly understood.2. We sought to redress this, and to demonstrate the potential benefits of integrating palaeolimnological and contemporary data, by constructing highly resolved food webs and stable isotope derived measures of trophic interactions and niche space, for the extant communities of two shallow U.K. lakes from different positions along a gradient of eutrophication. The contemporary surface sediment cladoceran and submerged macrophyte assemblages in the less enriched site, Selbrigg Pond, matched the palaeolimnological assemblages of the more enriched site, Felbrigg Hall Lake, in its more pristine state during the 1920s. Thus, Selbrigg was a temporal analogue for Felbrigg, from which the consequences of long-term eutrophication on food web structure could be inferred. These data represent the first steps towards reconstructing not only past assemblages (i.e. nodes within a food web), but also past interactions (i.e. links within a food web): a significant departure from much of the previous research in palaeolimnology.3. The more eutrophic food web had far fewer nodes and links, and thus a less reticulate network, than was the case for the more pristine system. In isotopic terms, there was vertical compression in δ15N range (NR) and subsequent increased overlap in isotopic niche space, indicating increased trophic redundancy within Felbrigg. This structural change, which was associated with a greater channelling of energy through a smaller number of nodes as alternative feeding pathways disappear, could lead to reduced dynamic stability, pushing the network towards further simplification. These changes reflected a general shift from a benthic-dominated towards a more pelagic system, as the plant-associated subweb eroded.4. Although these data are among the first of their kind, the palaeo-analogue approach used here demonstrates the huge potential for applying food web theory to understand how and why these ecological networks change during eutrophication. Furthermore, because of the rich biological record preserved in their sediments, shallow lakes represent potentially important models for examining long-term intergenerational dynamics, thereby providing a means by which models and data can be integrated on meaningful timescales – a goal that has long proved elusive in food web ecology.

Given the widespread degradation of freshwater habitats, assessing the distributions of species that may be negatively or positively impacted should be of general interest. However, determining distributions of freshwater organisms that are small and patchily distributed and attached or sedentary is particularly problematic, as it is time consuming, inaccurate, and nearly impossible when the focal species is rare. Here we illustrate the use of indirect sampling approaches to survey the distribution of the rare freshwater bryozoan Lophopus crystallinus, a priority species in the UK Biodiversity Action Plan [Anonymous, 1999. UK Biodiversity Group Tranche 2 Action Plans. Invertebrates, vol. 4. Environment Agency, Peterborough, pp. 437–439.]. By utilising two complementary methods for sampling bryozoan propagules (statoblasts), namely the collection of debris samples and sediment cores, we achieved an efficient and integrative sampling of habitats across spatial and temporal scales. Analysis of 154 debris samples, encompassing 62 rivers and lakes, identified at least 16 new populations while analysis of 26 sediment cores provided evidence of current or very recent (in the last 10–20 years) occurrence in a further six localities. These results represent a more than 10-fold increase in the current recorded distribution of the species in the UK. Logistic regression analysis provided evidence that L. crystallinus is generally found in lowland sites and is tolerant of eutrophication. Our study exemplifies how integrative and indirect sampling approaches can greatly aid in assessing the conservation status of rare aquatic species and reveals, in this case, that the focal species is less rare than previously appreciated.

The potential of palaeolimnological methods for establishing reference conditions and restoration targets for lakes has been recognised for some time, and has received renewed interest in recent years with the introduction of the EU Water Framework Directive. This paper considers some of the issues associated with the role of lake sediments in establishing reference conditions and defining recovery targets. We discuss the problem of attributing variation in the sediment record to human activity rather than to natural causes or random variability, and the need for the concepts of pristine and reference conditions to be differentiated. We address the question of expressing quantitatively the degree of change that has taken place between the reference and the present day and the problem of accounting for changes that may have taken place between the reference and the present, such as climate change, that may limit the use of the reference condition as a restoration target. Finally we consider the use of past habitat structure and inferred ecological functioning as targets for restoration, and the potential role that multi-proxy palaeoecological studies can play in defining such targets.

The annual flood pulse in the Okavango Delta (Botswana), has a major influence on water chemistry and habitat. We explore spatial and temporal patterns in a suite of chemical variables, analysed from 98 sample points, across four regions, taken at different stages of the flood cycle. The major pattern in water chemistry is characterised by an increasing gradient in ionic concentration from deep-water sites in the Panhandle to more shallow, distal regions to the south. Concentrations of cations, anions, dissolved organic carbon, and SiO2 are significantly higher in the seasonally inundated floodplains than in permanently flooded regions. Several variables (including Na and total nitrogen) significantly increase from low flood to high flood, while others (including HCO3, SiO2, and Cl) increase in concentration, initially between low flood and flood expansion, before declining at maximum flood extent. Redundancy analysis (RDA) revealed that hydrological variables (water depth, flow velocity, flood frequency, and hydroperiod class) significantly explain 17% variation in surface water chemistry. Predictions of increasing flood volume in the near future may result in a decline in alkalinity and dilution of DOC. Our study provides an important baseline from which to monitor future change in the Delta.

Aphandra natalia (Balslev and Henderson) Barfod, an economically important fibre producing palm, is common in rainforest on low terraces along the Pastaza and Urituyacu rivers in Amazonian Peru. The aim of this study was to investigate the spatial distribution and environmental preferences of Aphandra in old-growth terrace forest to which it is limited in this region.

Abstract We assembled data on the diversity of tree species, genera, families, and orders in 13 large-scale forest inventory plots across the tropics. Each plot included at least 16 ha where every individual≥ 1 cm in stem diameter was censused, providing a much more thorough measure of α-diversity than the typical 0.1-or 1-ha inventories. Amazonian and Southeast Asian plots had more than 1000 tree species, double the highest prior estimate of α-diversity.

Eleven species of palms occur at altitudes of I 000-2 800 m in the Maquipucuna reserve and adjacent areas in the Ecuadorian Andes. Of these, at least five have lower upper altitudinal limits in Maquipucuna than elsewhere in Ecuador, possibly due to the Massenerhebung effect. Nine species represent Andean elements, while two species represent lowland elements. The species vary from abundant to very rare in the area. The palms provide edible fruits, palm heart, and leaves for Palm Sunday.

Aim This study uses a high-resolution simulation of the Last Glacial Maximum (LGM) climate to assess:(1) whether LGM climate still affects the geographical species richness patterns in the European tree flora and (2) the relative importance of modern and LGM climate as controls of tree species richness in Europe.