The ecological significance of dissolved organic carbon in acidified waters
AMBIO: A Journal of the Human Environment, 1993
The ecological significance of dissolved organic carbon in acidified waters. A Kullberg, KH Bisho... more The ecological significance of dissolved organic carbon in acidified waters. A Kullberg, KH Bishop, A Hargeby, M Jansson, RC Petersen Jr Ambio. Stockholm 22:55, 331-337, 1993. Acidification, liming and other anthropogenic ...
Pigmentation in the freshwater isopod Asellus aquaticus (Crustacea) differed between habitats in ... more Pigmentation in the freshwater isopod Asellus aquaticus (Crustacea) differed between habitats in two Swedish lakes. In both lakes, isopods had lighter pigmentation in stands of submerged vegetation, consisting of stoneworts (Chara spp.), than in nearby stands of reed (Phragmites australis). Experimental crossings of light and dark isopods in a common environment showed that pigmentation had a genetic basis and that genetic variance was additive. Environmental effects of diet or chromatophore adjustment to the background had minor influence on pigmentation, as shown by laboratory rearing of isopods on stonewort or reed substrates, as well as analyses of stable isotope ratios for isopods collected in the field. In both study lakes, the average phenotype became lighter with time (across generations) in recently established stonewort stands. Taken together, these results indicate that altered phenotype pigmentation result from evolutionary responses to local differences in natural selection. Based on the assumption of two generations per year, the evolutionary rate of change in pigmentation was 0.08 standard deviations per generation (haldanes) over 20 generations in one lake and 0.22 haldanes over two generations in the other lake. This genetic change occurred during an episode of population growth in a novel habitat, a situation known to promote adaptive evolution. In addition, stonewort stands constitute large and persistent patches, characteristics that tend to preserve local adaptations produced by natural selection. Results from studies on selective forces behind the adaptive divergence suggest that selective predation from visually oriented predators is a possible selective agent. We found no indications of phenotype-specific movements between habitats. Mating within stonewort stands was random with respect to pigmentation, but on a whole-lake scale it is likely that mating is assortative, as a result of local differences in phenotype distribution.
Miljökonsekvenser av markavvattning och dikesrensning : En kunskapssammanställning
Målet med denna litteratursammanställning har varit att göra en kritisk granskning av nationell o... more Målet med denna litteratursammanställning har varit att göra en kritisk granskning av nationell och internationell forskningslitteratur vad gäller i) produktionshöjande effekter av markavvattning i jordbruksmark och skogsmark, ii) påverkan av markavvattning och dikesrensning på vattenkemi, särskilt närsalter, pesticider i jordbruksmark och metaller i skogsmark, iii) effekter av markavvattning på biota i vattendrag, iv) effekter av möjliga åtgärder för att minska negativ miljöpåverkan på vattenförekomster av markavvattning och dikesrensning. Mycket av åtgärderna för att minska läckaget av närsalter och andra ämnen från jord- och skogsbruk hänger samman med olika produktionssystem och vilka brukningsmetoder som används, men detta faller utanför syftet med denna sammanställning. I Sverige är arealen mark som påverkats av markavvattning ungefär lika stor inom skogsbruket som inom jordbruket. Man räknar med att ca 1,2 miljoner åkermark har väl fungerande dränering, och att över 1,5 miljoner hektar torvmark har dikats för skogsproduktion. Detta har varit en av flera faktorer som bidragit till den kraftiga produktionshöjningen som skett under 1900-talet inom både jordbruket och skogsbruket. Denna omfattande markavvattning har dock lett till stora negativa miljökonsekvenser. Direkta effekter ser vi i form av försvunna habitat och därmed en kraftigt minskad biodiversitet i våra produktionslandskap där vissa arters överlevnad i Sverige är direkt hotad. Andra effekter är indirekta i form av ökat läckage av kväve, fosfor, pesticider och metaller till våra vatten. Det är dock mer eller mindre omöjligt att kvantifiera hur stor del av denna ökade belastning på svenska vattenförekomster som beror på enbart markavvattningen, eftersom den ofta är en förutsättning för att marken ska kunna användas till odling idag. Troligen blir den än viktigare i ett framtida förändrat klimat. Det finns relativt god kunskap om effekten av ett antal åtgärder som kan vidtas för att minska läckaget från den dikade jordbruksmarken, bl.a. reglerbar dränering, skyddszoner, våtmarker och dammar, fosfordammar, bioreaktorer och denitrifikations-väggar. Ytterligare undersökningar som underlag för utformning och tillämpning skulle behövas vad gäller återanvändning av dräneringsvatten, avfasade strandzoner, filter för fosforsorption, etappvis dikesrensning och att planera dikesrensning på landskapsnivå. När det gäller åtgärder inom skogsbruket tycks underlaget för att föreslå skyddsåtgärder i samband med dikesrensning vara tunt. Litteraturen tyder på att slamfickor och sedimentations-dammar inte har någon större effekt på transporten av finkorniga jordpartiklar, vilka orsakar de mest negativa effekterna om de sedimenterar i vattendrag nedströms det dikade området. Väl utformade översilningsområden kan vara effektiva, enligt finska undersökningar, men detbehövs studier av hur sådana kan skapas och utformas för att få effekt i områden med de förhållanden som råder i Sverige. Andra åtgärder som behöver undersökas är användningen av så kallade ”silt fences” för att avskärma områden där vatten grumlas, eller styra grumligt vatten över markområden och därigenom öka sedimenteringen av partiklar innan vattnet når vattendrag. Forskning av relevans för åtgärdsprogram relaterade till markavvattning ochdikesrensning pågår i Sverige inom bl.a. följande områden: Mekanismer bakom ökade transporter av kvicksilver i samband med skogsbruk och markavvattning, liksom effekter på kvicksilvers rörlighet av höjda grundvattennivåer i samband med att våtmarker återskapas (SLU, Stockholms Universitet, Umeå universitet). Dikesrensningens effekter på transporten av suspenderat material och kvicksilver i skogsområden (bl.a. IVL). Effekten av rester av bekämpningsmedel på organismlivet i vatten (SLU). Dikens betydelse för fosfortransport som länk mellan fält och vattendrag (SLU). Kalkfilter i brunnar och kalkfilterbäddar (KTH och olika företag). Effekter av integrerade skyddszoner (HS Halland). Metodik för bestämning av dikens status och stöd för planering av åtgärder (SLU). Sedimentation i tvåstegsdiken (Linköpings universitet, Jordbruksverket och SLU)
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
Does a long-term oscillation in nitrogen concentration reflect climate impact on submerged vegeta... more Does a long-term oscillation in nitrogen concentration reflect climate impact on submerged vegetation and vulnerability to state shifts in a shallow lake? Á Oikos 115: 334 Á348. Various ecosystems, including shallow lakes, are suggested to possess alternative stable state dynamics. The response of such systems to environmental change is non-linear and not fully reversible, which calls for identification of feedback mechanisms and subtle changes connected to structural stability. Here, we used a 25-year data series on water chemistry to make inferences on processes prior to a recent shift from a clear to a turbid state in Lake Tåkern, Sweden. Before the shift, annual concentration of total organic nitrogen (TON) described a cyclic pattern, with a periodicity of eight years. Annual TON was negatively correlated with the magnitude of a summer decline in calcium carbonate, treated as a proxy of the seasonal production of submerged vegetation. Cross-correlations of TON and the north Atlantic oscillation (NAO) indicated a possible connection to climate. The strongest correlation was obtained by a three-year lag of the NAO index. Using a set of linear time series models, the most parsimonious model was a 3 rd order autoregressive model with NAO, delayed three years, as a covariate. Analyses of seasonality indicated that the delayed NAO signal was strongly correlated with summer TON. Also, the autocorrelation function was very similar for these two time series, and autoregressive models including NAO as a covariate were strongly supported (sum of Akaike weights 0/0.93). These results indicate that climate may have contributed to the regime shift through lowered macrophyte production at the time of the shift, and therefore most likely also a depleted resilience of the clear water state. The delayed effect of climate is suggested to result from indirect and inter-year dependent response of submerged vegetation to fish kills during harsh winters.
Rapid adaptive divergence between ecotypes of an aquatic isopod inferred from F ST ��� Q ST analysis
Molecular Ecology, 2009
Divergent natural selection is often thought to be the principal factor driving phenotypic differ... more Divergent natural selection is often thought to be the principal factor driving phenotypic differentiation between populations. We studied two ecotypes of the aquatic isopod Asellus aquaticus which have diverged in parallel in several Swedish lakes. In these lakes, isopods from reed belts along the shores colonized new stonewort stands in the centre of the lakes and rapid phenotypic changes in size and pigmentation followed after colonization. We investigated if selection was likely to be responsible for these observed phenotypic changes using indirect inferences of selection (F(ST)-Q(ST) analysis). Average Q(ST) for seven quantitative traits were higher than the average F(ST) between ecotypes for putatively neutral markers (AFLPs). This suggests that divergent natural selection has played an important role during this rapid diversification. In contrast, the average Q(ST) between the different reed ecotype populations was not significantly different from the mean F(ST). Genetic drift could therefore not be excluded as an explanation for the minor differences between allopatric populations inhabiting the same source habitat. We complemented this traditional F(ST)-Q(ST) approach by comparing the F(ST) distributions across all loci (n = 67-71) with the Q(ST) for each of the seven traits. This analysis revealed that pigmentation traits had diverged to a greater extent and at higher evolutionary rates than size-related morphological traits. In conclusion, this extended and detailed type of F(ST)-Q(ST) analysis provides a powerful method to infer adaptive phenotypic divergence between populations. However, indirect inferences about the operation of divergent selection should be analyzed on a per-trait basis and complemented with detailed ecological information.
Parallelism and historical contingency during rapid ecotype divergence in an isopod
Journal of Evolutionary Biology, 2009
Recent studies on parallel evolution have focused on the relative role of selection and historica... more Recent studies on parallel evolution have focused on the relative role of selection and historical contingency during adaptive divergence. Here, we study geographically separate and genetically independent lake populations of a freshwater isopod (Asellus aquaticus) in southern Sweden. In two of these lakes, a novel habitat was rapidly colonized by isopods from a source habitat. Rapid phenotypic changes in pigmentation, size and sexual behaviour have occurred, presumably in response to different predatory regimes. We partitioned the phenotypic variation arising from habitat ('selection': 81–94%), lake ('history': 0.1–6%) and lake × habitat interaction ('unique diversification': 0.4–13%) for several traits. There was a limited role for historical contingency but a strong signature of selection. We also found higher phenotypic variation in the source populations. Phenotype sorting during colonization and strong divergent selection might have contributed to these rapid changes. Consequently, phenotypic divergence was only weakly influenced by historical contingency.
The importance of lake ecosystems for waterfowl remains a topic of debate. In order to assess how... more The importance of lake ecosystems for waterfowl remains a topic of debate. In order to assess how temporal variations in lake features, specifically shifts between alternative stable states, may interact with the waterfowl fauna, we performed a long-term (22 years) study of the shallow Lake Krankesjön, southern Sweden. Lower total numbers of waterfowl occurred during periods with low macrophyte cover and turbid water, than when submersed macrophytes flourished and the water was clear. Some specific functional groups of waterfowl, such as herbivores, invertebrate, and fish feeders, showed a positive relation to clear water and high macrophyte cover. Hence, our data suggest that some migratory waterfowl may select lakes based on water quality, thereby adjusting their large-scale migratory routes. On the other hand, omnivorous waterfowl exhibited their highest abundances during turbid conditions. Furthermore, waterfowl not primarily relying on food from the lake showed no response to fluctuations in turbidity or macrophyte cover, but followed regional trends in population dynamics. In our study lake, L. Krankesjön, we estimated that waterfowl remove less than 3% of the macrophyte biomass during a stable clear-water state with lush macrophyte beds. However, during transition periods between alternative stable states, when macrophyte biomass is lower and the plants already stressed, the consumption rate of waterfowl may have a stronger effect on lake ecosystem functioning.
The genomics of phenotypically differentiated Asellus aquaticus cave, surface stream and lake ecotypes
Molecular Ecology
Organisms well suited for the study of ecotype formation have wide distribution ranges, where the... more Organisms well suited for the study of ecotype formation have wide distribution ranges, where they adapt to multiple drastically different habitats repeatedly over space and time. Here we study such ecotypes in a Crustacean model, Asellus aquaticus, a commonly occurring isopod found in freshwater habitats as diverse as streams, caves and lakes. Previous studies focusing on cave vs. surface ecotypes have attributed depigmentation, eye loss and prolonged antennae to several south European cave systems. Likewise, surveys across multiple Swedish lakes have identified the presence of dark‐pigmented "reed" and light‐pigmented "stonewort" ecotypes, which can be found within the same lake. In this study, we sequenced the first draft genome of A. aquaticus, and subsequently use this to map reads and call variants in surface stream, cave and two lake ecotypes. In addition, the draft genome was combined with a RADseq approach to perform a quantitative trait locus (QTL) mapping study using a laboratory bred F2 and F4 cave × surface intercross. We identified genomic regions associated with body pigmentation, antennae length and body size. Furthermore, we compared genome‐wide differentiation between natural populations and found several genes potentially associated with these habitats. The assessment of the cave QTL regions in the light–dark comparison of lake populations suggests that the regions associated with cave adaptation are also involved with genomic differentiation in the lake ecotypes. These demonstrate how troglomorphic adaptations can be used as a model for related ecotype formation.
Alternative Stable States in Shallow Lakes: What Causes a Shift?
Ecological Studies, 1998
Lake TE5;kern and Lake Krankesjon, two shallow, moderately eutrophic, calcium-rich lakes in south... more Lake TE5;kern and Lake Krankesjon, two shallow, moderately eutrophic, calcium-rich lakes in southern Sweden have shifted between turbid and clearwater states several times during the past decades (Fig. 26.1). Lake Krankesjon shifted from a clearwater state with abundant submerged vegetation to a turbid state with sparse vegetation during the mid-1970s (Karlsson et al., 1976) and back to a clearwater state during 1985. Today, the lake is in the clearwater state, with abundant submerged vegetation dominated by Charophyta (Blindow et al., 1993; Fig. 26.2). Both shifts coincided with deviations from the average water level. During the mid-1970s, the water level during spring and summer was about 15 cm higher than average, whereas it was about 10 cm lower than average during 1983-1985 (Blindow, 1992).
Macrophyte Associated Invertebrates and the Effect of Habitat Permanence
Oikos, 1990
... The Asellus and Gammarus in each wad were counted alive. ... The exclosures/enclosures were 2... more ... The Asellus and Gammarus in each wad were counted alive. ... The exclosures/enclosures were 2 m high net cages constructed of PVC net (1.1 x 1.3 mm mesh) thread on two iron rings (60 cm diameter) and stretched as the iron rings were nailed to two wooden laths. ...
Effects of pH, humic substances and animal interactions on survival and physiological status of A... more Effects of pH, humic substances and animal interactions on survival and physiological status of Asellus aquaticus L. and Gammarus pulex (L.
We estimated total lake plant biomass and primary net production in two shallow Swedish lakes tha... more We estimated total lake plant biomass and primary net production in two shallow Swedish lakes that differ in nutrient loading and plant form dominance. In clearwater Lake Krankesjö n (10 mg chlorophyll a L 21), submerged macrophytes contributed more than phytoplankton and epiphyton to the estimated plant biomass. Estimated net primary production during May to September was 90-130, 1.2, and 14 g C m 22 for phytoplankton, epiphyton, and submerged macrophytes, respectively. In turbid Lake Bö rringesjö n (60-80 mg chlorophyll a L 21), primary production by submerged macrophytes and periphyton was negligible. Although gross primary production of phytoplankton was high close to the water surface, estimated areal net primary production during May to September was low, 240 to +25 g C m 22 , as a result of self-shading and high respiration. Grazing pressure from zooplankton rarely exceeded 15% d 21 in both lakes, indicating that phytoplankton production was not limited by grazing. Low gross epiphyton production could result from high grazing by macroinvertebrates and thus higher trophic transfer efficiency through the benthic than through the pelagic food web. Provided that conditions in Lake Bö rringesjö n reflect previous turbid state conditions in Lake Krankesjö n, our results may explain why a shift to a clearwater state was followed by increased biomass of higher trophic levels. Our results also support the paradox of enrichment hypothesis, which predicts lower productivity at high nutrient loading. Contrary to former investigations, we found lower production at a higher nutrient loading already at the trophic level of primary producers. * tot-N 5 total nitrogen; tot-P 5 total phosphorus. Chemical parameters: Mean values for samples taken during June to September of 1988-1997 (Lake Krankesjö n) and 1998-2003 (Lake Bö rringesjö n, as well as calcium values in Lake Krankesjö n). Values for calcium (both lakes) and nitrogen and phosphorus (Lake Bö rringesjö n) were obtained from the Swedish University for Agricultural Sciences, Uppsala.
Facilitation of clear-water conditions in shallow lakes by macrophytes: differences between charophyte and angiosperm dominance
Hydrobiologia, 2013
ABSTRACT A number of mechanisms result in a feedback between water clarity and macrophytes and, c... more ABSTRACT A number of mechanisms result in a feedback between water clarity and macrophytes and, consequently, the occurrence of alternative stable states in shallow lakes. We hypothesize that bottom-up mechanisms and interactions within the benthic food web are more important in a charophyte-dominated clear-water state, while top-down mechanism and interactions in the planktonic food web prevail at angiosperm dominance. Charophytes, which dominate at lower nutrient concentrations and develop higher densities than most angiosperms, can have a higher influence on sedimentation, resuspension, and water column nutrients. During dominance of dense sub-merged vegetation like charophytes, zooplankton can be hampered by low food quality and quantity and by high predation pressure from juvenile fish, which in turn are favoured by the high refuge potential of this vegetation. Grazing pressure from zooplankton on phytoplankton can therefore be low in charophytes, but the main feedback in angiosperm-dominated ecosystems. Charophytes offer a higher surface than most angiosperms to periphyton, which favors benthic invertebrates. These support macrophytes by grazing periphyton and constitute a central link in a trophic cascade from fish to periphyton and macrophytes. To test these hypotheses, more experiments and field measurements comparing the effect of charophytes and angiosperms on water clarity are needed.
A simple trickle chamber for rearing aquatic invertebrates
Hydrobiologia, 1986
A chamber for laboratory rearing of aquatic invertebrates is described. The animals are reared in... more A chamber for laboratory rearing of aquatic invertebrates is described. The animals are reared in plastic dishes, through which a recirculating water volume is passed. The design ensures identical water quality in a high number of parallels. The chamber is constructed for rearing the freshwater amphipod Gammarus pulex, but can be used in studies of growth, reproduction etc. of other
The ecological significance of dissolved organic carbon in acidified waters
AMBIO: A Journal of the Human Environment, 1993
The ecological significance of dissolved organic carbon in acidified waters. A Kullberg, KH Bisho... more The ecological significance of dissolved organic carbon in acidified waters. A Kullberg, KH Bishop, A Hargeby, M Jansson, RC Petersen Jr Ambio. Stockholm 22:55, 331-337, 1993. Acidification, liming and other anthropogenic ...
Pigmentation in the freshwater isopod Asellus aquaticus (Crustacea) differed between habitats in ... more Pigmentation in the freshwater isopod Asellus aquaticus (Crustacea) differed between habitats in two Swedish lakes. In both lakes, isopods had lighter pigmentation in stands of submerged vegetation, consisting of stoneworts (Chara spp.), than in nearby stands of reed (Phragmites australis). Experimental crossings of light and dark isopods in a common environment showed that pigmentation had a genetic basis and that genetic variance was additive. Environmental effects of diet or chromatophore adjustment to the background had minor influence on pigmentation, as shown by laboratory rearing of isopods on stonewort or reed substrates, as well as analyses of stable isotope ratios for isopods collected in the field. In both study lakes, the average phenotype became lighter with time (across generations) in recently established stonewort stands. Taken together, these results indicate that altered phenotype pigmentation result from evolutionary responses to local differences in natural selection. Based on the assumption of two generations per year, the evolutionary rate of change in pigmentation was 0.08 standard deviations per generation (haldanes) over 20 generations in one lake and 0.22 haldanes over two generations in the other lake. This genetic change occurred during an episode of population growth in a novel habitat, a situation known to promote adaptive evolution. In addition, stonewort stands constitute large and persistent patches, characteristics that tend to preserve local adaptations produced by natural selection. Results from studies on selective forces behind the adaptive divergence suggest that selective predation from visually oriented predators is a possible selective agent. We found no indications of phenotype-specific movements between habitats. Mating within stonewort stands was random with respect to pigmentation, but on a whole-lake scale it is likely that mating is assortative, as a result of local differences in phenotype distribution.
Miljökonsekvenser av markavvattning och dikesrensning : En kunskapssammanställning
Målet med denna litteratursammanställning har varit att göra en kritisk granskning av nationell o... more Målet med denna litteratursammanställning har varit att göra en kritisk granskning av nationell och internationell forskningslitteratur vad gäller i) produktionshöjande effekter av markavvattning i jordbruksmark och skogsmark, ii) påverkan av markavvattning och dikesrensning på vattenkemi, särskilt närsalter, pesticider i jordbruksmark och metaller i skogsmark, iii) effekter av markavvattning på biota i vattendrag, iv) effekter av möjliga åtgärder för att minska negativ miljöpåverkan på vattenförekomster av markavvattning och dikesrensning. Mycket av åtgärderna för att minska läckaget av närsalter och andra ämnen från jord- och skogsbruk hänger samman med olika produktionssystem och vilka brukningsmetoder som används, men detta faller utanför syftet med denna sammanställning. I Sverige är arealen mark som påverkats av markavvattning ungefär lika stor inom skogsbruket som inom jordbruket. Man räknar med att ca 1,2 miljoner åkermark har väl fungerande dränering, och att över 1,5 miljoner hektar torvmark har dikats för skogsproduktion. Detta har varit en av flera faktorer som bidragit till den kraftiga produktionshöjningen som skett under 1900-talet inom både jordbruket och skogsbruket. Denna omfattande markavvattning har dock lett till stora negativa miljökonsekvenser. Direkta effekter ser vi i form av försvunna habitat och därmed en kraftigt minskad biodiversitet i våra produktionslandskap där vissa arters överlevnad i Sverige är direkt hotad. Andra effekter är indirekta i form av ökat läckage av kväve, fosfor, pesticider och metaller till våra vatten. Det är dock mer eller mindre omöjligt att kvantifiera hur stor del av denna ökade belastning på svenska vattenförekomster som beror på enbart markavvattningen, eftersom den ofta är en förutsättning för att marken ska kunna användas till odling idag. Troligen blir den än viktigare i ett framtida förändrat klimat. Det finns relativt god kunskap om effekten av ett antal åtgärder som kan vidtas för att minska läckaget från den dikade jordbruksmarken, bl.a. reglerbar dränering, skyddszoner, våtmarker och dammar, fosfordammar, bioreaktorer och denitrifikations-väggar. Ytterligare undersökningar som underlag för utformning och tillämpning skulle behövas vad gäller återanvändning av dräneringsvatten, avfasade strandzoner, filter för fosforsorption, etappvis dikesrensning och att planera dikesrensning på landskapsnivå. När det gäller åtgärder inom skogsbruket tycks underlaget för att föreslå skyddsåtgärder i samband med dikesrensning vara tunt. Litteraturen tyder på att slamfickor och sedimentations-dammar inte har någon större effekt på transporten av finkorniga jordpartiklar, vilka orsakar de mest negativa effekterna om de sedimenterar i vattendrag nedströms det dikade området. Väl utformade översilningsområden kan vara effektiva, enligt finska undersökningar, men detbehövs studier av hur sådana kan skapas och utformas för att få effekt i områden med de förhållanden som råder i Sverige. Andra åtgärder som behöver undersökas är användningen av så kallade ”silt fences” för att avskärma områden där vatten grumlas, eller styra grumligt vatten över markområden och därigenom öka sedimenteringen av partiklar innan vattnet når vattendrag. Forskning av relevans för åtgärdsprogram relaterade till markavvattning ochdikesrensning pågår i Sverige inom bl.a. följande områden: Mekanismer bakom ökade transporter av kvicksilver i samband med skogsbruk och markavvattning, liksom effekter på kvicksilvers rörlighet av höjda grundvattennivåer i samband med att våtmarker återskapas (SLU, Stockholms Universitet, Umeå universitet). Dikesrensningens effekter på transporten av suspenderat material och kvicksilver i skogsområden (bl.a. IVL). Effekten av rester av bekämpningsmedel på organismlivet i vatten (SLU). Dikens betydelse för fosfortransport som länk mellan fält och vattendrag (SLU). Kalkfilter i brunnar och kalkfilterbäddar (KTH och olika företag). Effekter av integrerade skyddszoner (HS Halland). Metodik för bestämning av dikens status och stöd för planering av åtgärder (SLU). Sedimentation i tvåstegsdiken (Linköpings universitet, Jordbruksverket och SLU)
All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.
Does a long-term oscillation in nitrogen concentration reflect climate impact on submerged vegeta... more Does a long-term oscillation in nitrogen concentration reflect climate impact on submerged vegetation and vulnerability to state shifts in a shallow lake? Á Oikos 115: 334 Á348. Various ecosystems, including shallow lakes, are suggested to possess alternative stable state dynamics. The response of such systems to environmental change is non-linear and not fully reversible, which calls for identification of feedback mechanisms and subtle changes connected to structural stability. Here, we used a 25-year data series on water chemistry to make inferences on processes prior to a recent shift from a clear to a turbid state in Lake Tåkern, Sweden. Before the shift, annual concentration of total organic nitrogen (TON) described a cyclic pattern, with a periodicity of eight years. Annual TON was negatively correlated with the magnitude of a summer decline in calcium carbonate, treated as a proxy of the seasonal production of submerged vegetation. Cross-correlations of TON and the north Atlantic oscillation (NAO) indicated a possible connection to climate. The strongest correlation was obtained by a three-year lag of the NAO index. Using a set of linear time series models, the most parsimonious model was a 3 rd order autoregressive model with NAO, delayed three years, as a covariate. Analyses of seasonality indicated that the delayed NAO signal was strongly correlated with summer TON. Also, the autocorrelation function was very similar for these two time series, and autoregressive models including NAO as a covariate were strongly supported (sum of Akaike weights 0/0.93). These results indicate that climate may have contributed to the regime shift through lowered macrophyte production at the time of the shift, and therefore most likely also a depleted resilience of the clear water state. The delayed effect of climate is suggested to result from indirect and inter-year dependent response of submerged vegetation to fish kills during harsh winters.
Rapid adaptive divergence between ecotypes of an aquatic isopod inferred from F ST ��� Q ST analysis
Molecular Ecology, 2009
Divergent natural selection is often thought to be the principal factor driving phenotypic differ... more Divergent natural selection is often thought to be the principal factor driving phenotypic differentiation between populations. We studied two ecotypes of the aquatic isopod Asellus aquaticus which have diverged in parallel in several Swedish lakes. In these lakes, isopods from reed belts along the shores colonized new stonewort stands in the centre of the lakes and rapid phenotypic changes in size and pigmentation followed after colonization. We investigated if selection was likely to be responsible for these observed phenotypic changes using indirect inferences of selection (F(ST)-Q(ST) analysis). Average Q(ST) for seven quantitative traits were higher than the average F(ST) between ecotypes for putatively neutral markers (AFLPs). This suggests that divergent natural selection has played an important role during this rapid diversification. In contrast, the average Q(ST) between the different reed ecotype populations was not significantly different from the mean F(ST). Genetic drift could therefore not be excluded as an explanation for the minor differences between allopatric populations inhabiting the same source habitat. We complemented this traditional F(ST)-Q(ST) approach by comparing the F(ST) distributions across all loci (n = 67-71) with the Q(ST) for each of the seven traits. This analysis revealed that pigmentation traits had diverged to a greater extent and at higher evolutionary rates than size-related morphological traits. In conclusion, this extended and detailed type of F(ST)-Q(ST) analysis provides a powerful method to infer adaptive phenotypic divergence between populations. However, indirect inferences about the operation of divergent selection should be analyzed on a per-trait basis and complemented with detailed ecological information.
Parallelism and historical contingency during rapid ecotype divergence in an isopod
Journal of Evolutionary Biology, 2009
Recent studies on parallel evolution have focused on the relative role of selection and historica... more Recent studies on parallel evolution have focused on the relative role of selection and historical contingency during adaptive divergence. Here, we study geographically separate and genetically independent lake populations of a freshwater isopod (Asellus aquaticus) in southern Sweden. In two of these lakes, a novel habitat was rapidly colonized by isopods from a source habitat. Rapid phenotypic changes in pigmentation, size and sexual behaviour have occurred, presumably in response to different predatory regimes. We partitioned the phenotypic variation arising from habitat ('selection': 81–94%), lake ('history': 0.1–6%) and lake × habitat interaction ('unique diversification': 0.4–13%) for several traits. There was a limited role for historical contingency but a strong signature of selection. We also found higher phenotypic variation in the source populations. Phenotype sorting during colonization and strong divergent selection might have contributed to these rapid changes. Consequently, phenotypic divergence was only weakly influenced by historical contingency.
The importance of lake ecosystems for waterfowl remains a topic of debate. In order to assess how... more The importance of lake ecosystems for waterfowl remains a topic of debate. In order to assess how temporal variations in lake features, specifically shifts between alternative stable states, may interact with the waterfowl fauna, we performed a long-term (22 years) study of the shallow Lake Krankesjön, southern Sweden. Lower total numbers of waterfowl occurred during periods with low macrophyte cover and turbid water, than when submersed macrophytes flourished and the water was clear. Some specific functional groups of waterfowl, such as herbivores, invertebrate, and fish feeders, showed a positive relation to clear water and high macrophyte cover. Hence, our data suggest that some migratory waterfowl may select lakes based on water quality, thereby adjusting their large-scale migratory routes. On the other hand, omnivorous waterfowl exhibited their highest abundances during turbid conditions. Furthermore, waterfowl not primarily relying on food from the lake showed no response to fluctuations in turbidity or macrophyte cover, but followed regional trends in population dynamics. In our study lake, L. Krankesjön, we estimated that waterfowl remove less than 3% of the macrophyte biomass during a stable clear-water state with lush macrophyte beds. However, during transition periods between alternative stable states, when macrophyte biomass is lower and the plants already stressed, the consumption rate of waterfowl may have a stronger effect on lake ecosystem functioning.
The genomics of phenotypically differentiated Asellus aquaticus cave, surface stream and lake ecotypes
Molecular Ecology
Organisms well suited for the study of ecotype formation have wide distribution ranges, where the... more Organisms well suited for the study of ecotype formation have wide distribution ranges, where they adapt to multiple drastically different habitats repeatedly over space and time. Here we study such ecotypes in a Crustacean model, Asellus aquaticus, a commonly occurring isopod found in freshwater habitats as diverse as streams, caves and lakes. Previous studies focusing on cave vs. surface ecotypes have attributed depigmentation, eye loss and prolonged antennae to several south European cave systems. Likewise, surveys across multiple Swedish lakes have identified the presence of dark‐pigmented "reed" and light‐pigmented "stonewort" ecotypes, which can be found within the same lake. In this study, we sequenced the first draft genome of A. aquaticus, and subsequently use this to map reads and call variants in surface stream, cave and two lake ecotypes. In addition, the draft genome was combined with a RADseq approach to perform a quantitative trait locus (QTL) mapping study using a laboratory bred F2 and F4 cave × surface intercross. We identified genomic regions associated with body pigmentation, antennae length and body size. Furthermore, we compared genome‐wide differentiation between natural populations and found several genes potentially associated with these habitats. The assessment of the cave QTL regions in the light–dark comparison of lake populations suggests that the regions associated with cave adaptation are also involved with genomic differentiation in the lake ecotypes. These demonstrate how troglomorphic adaptations can be used as a model for related ecotype formation.
Alternative Stable States in Shallow Lakes: What Causes a Shift?
Ecological Studies, 1998
Lake TE5;kern and Lake Krankesjon, two shallow, moderately eutrophic, calcium-rich lakes in south... more Lake TE5;kern and Lake Krankesjon, two shallow, moderately eutrophic, calcium-rich lakes in southern Sweden have shifted between turbid and clearwater states several times during the past decades (Fig. 26.1). Lake Krankesjon shifted from a clearwater state with abundant submerged vegetation to a turbid state with sparse vegetation during the mid-1970s (Karlsson et al., 1976) and back to a clearwater state during 1985. Today, the lake is in the clearwater state, with abundant submerged vegetation dominated by Charophyta (Blindow et al., 1993; Fig. 26.2). Both shifts coincided with deviations from the average water level. During the mid-1970s, the water level during spring and summer was about 15 cm higher than average, whereas it was about 10 cm lower than average during 1983-1985 (Blindow, 1992).
Macrophyte Associated Invertebrates and the Effect of Habitat Permanence
Oikos, 1990
... The Asellus and Gammarus in each wad were counted alive. ... The exclosures/enclosures were 2... more ... The Asellus and Gammarus in each wad were counted alive. ... The exclosures/enclosures were 2 m high net cages constructed of PVC net (1.1 x 1.3 mm mesh) thread on two iron rings (60 cm diameter) and stretched as the iron rings were nailed to two wooden laths. ...
Effects of pH, humic substances and animal interactions on survival and physiological status of A... more Effects of pH, humic substances and animal interactions on survival and physiological status of Asellus aquaticus L. and Gammarus pulex (L.
We estimated total lake plant biomass and primary net production in two shallow Swedish lakes tha... more We estimated total lake plant biomass and primary net production in two shallow Swedish lakes that differ in nutrient loading and plant form dominance. In clearwater Lake Krankesjö n (10 mg chlorophyll a L 21), submerged macrophytes contributed more than phytoplankton and epiphyton to the estimated plant biomass. Estimated net primary production during May to September was 90-130, 1.2, and 14 g C m 22 for phytoplankton, epiphyton, and submerged macrophytes, respectively. In turbid Lake Bö rringesjö n (60-80 mg chlorophyll a L 21), primary production by submerged macrophytes and periphyton was negligible. Although gross primary production of phytoplankton was high close to the water surface, estimated areal net primary production during May to September was low, 240 to +25 g C m 22 , as a result of self-shading and high respiration. Grazing pressure from zooplankton rarely exceeded 15% d 21 in both lakes, indicating that phytoplankton production was not limited by grazing. Low gross epiphyton production could result from high grazing by macroinvertebrates and thus higher trophic transfer efficiency through the benthic than through the pelagic food web. Provided that conditions in Lake Bö rringesjö n reflect previous turbid state conditions in Lake Krankesjö n, our results may explain why a shift to a clearwater state was followed by increased biomass of higher trophic levels. Our results also support the paradox of enrichment hypothesis, which predicts lower productivity at high nutrient loading. Contrary to former investigations, we found lower production at a higher nutrient loading already at the trophic level of primary producers. * tot-N 5 total nitrogen; tot-P 5 total phosphorus. Chemical parameters: Mean values for samples taken during June to September of 1988-1997 (Lake Krankesjö n) and 1998-2003 (Lake Bö rringesjö n, as well as calcium values in Lake Krankesjö n). Values for calcium (both lakes) and nitrogen and phosphorus (Lake Bö rringesjö n) were obtained from the Swedish University for Agricultural Sciences, Uppsala.
Facilitation of clear-water conditions in shallow lakes by macrophytes: differences between charophyte and angiosperm dominance
Hydrobiologia, 2013
ABSTRACT A number of mechanisms result in a feedback between water clarity and macrophytes and, c... more ABSTRACT A number of mechanisms result in a feedback between water clarity and macrophytes and, consequently, the occurrence of alternative stable states in shallow lakes. We hypothesize that bottom-up mechanisms and interactions within the benthic food web are more important in a charophyte-dominated clear-water state, while top-down mechanism and interactions in the planktonic food web prevail at angiosperm dominance. Charophytes, which dominate at lower nutrient concentrations and develop higher densities than most angiosperms, can have a higher influence on sedimentation, resuspension, and water column nutrients. During dominance of dense sub-merged vegetation like charophytes, zooplankton can be hampered by low food quality and quantity and by high predation pressure from juvenile fish, which in turn are favoured by the high refuge potential of this vegetation. Grazing pressure from zooplankton on phytoplankton can therefore be low in charophytes, but the main feedback in angiosperm-dominated ecosystems. Charophytes offer a higher surface than most angiosperms to periphyton, which favors benthic invertebrates. These support macrophytes by grazing periphyton and constitute a central link in a trophic cascade from fish to periphyton and macrophytes. To test these hypotheses, more experiments and field measurements comparing the effect of charophytes and angiosperms on water clarity are needed.
A simple trickle chamber for rearing aquatic invertebrates
Hydrobiologia, 1986
A chamber for laboratory rearing of aquatic invertebrates is described. The animals are reared in... more A chamber for laboratory rearing of aquatic invertebrates is described. The animals are reared in plastic dishes, through which a recirculating water volume is passed. The design ensures identical water quality in a high number of parallels. The chamber is constructed for rearing the freshwater amphipod Gammarus pulex, but can be used in studies of growth, reproduction etc. of other
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