Lake Plankton Research Articles

The effects of salinity on plankton and benthic communities in the Great Salt Lake, Utah, USA: a microcosm experiment

Saline lakes change in size and salinity because of natural climate variability and especially from inflow diversions, which threaten life in these waters. We conducted a microcosm experiment in 12 L containers using organisms from the Great Salt Lake to determine how salinities ranging from 10 to 275 g·L−1influenced the ecosystem. After 30 days, brine shrimp (Artemia franciscana) were nearly absent in salinities of 10 g·L−1(where fish survived) and >225 g·L−1. As salinities increased from 75 to 225 g·L−1, final masses decreased 60% and their total biomass decreased fourfold. Copepod and rotifer biomasses were negligible at salinities >50 g·L−1. Brine fly (Ephydra gracilis) final biomass decreased 45% as salinity increased from 50 to 250 g·L−1. When Artemia and other grazers were abundant, phytoplankton chlorophyll levels were near 4.0 μg·L−1, but when grazing rates declined at higher salinities, phytoplankton chlorophyll increased to 130 μg·L−1. Mean periphyton chlorophyll levels showed the reverse pattern. Denitrification decreased total N concentrations during the experiment, resulting in final N:P ratios indicative of algal nitrogen limitation. The microcosm experiment demonstrated the strong influence of salinity on the entire ecosystem and highlighted the need for careful management of salt lakes to maintain appropriate salinities.

Biogeochemical specifics of sapropel formation in Cisbaikalian undrained lakes (exemplified by Lake Ochki)

The biogeochemistry of organic lacustrine sediments (sapropels) has been poorly studied in Siberia. In this paper we show the specifics of sapropel formation caused by low pH and mineralization of water by the example of Lake Ochki in Cisbaikalia. The main sources of organic matter are zoo- and phytoplankton, which concentrate mostly basic chemical elements and also some alkaline, alkali-earth, and chalcophile elements and move them to the sediment. The calculated enrichment factors (EF) have shown that the lake plankton is strongly enriched with phosphorus and chalcophile elements. The calculations have also revealed a great contribution of the plankton to the elemental composition of sapropel (Mebio, %): P (-100), Cd (57), Br (45), Hg (40), Se and Na (30), Zn (23), K (21), and Ca (15). Elements are rather uniformly distributed throughout the 3.2m thick sapropel layer. Lithophile elements (Al, Sc, Ti, Y, Zr, Nb) and LREE are mostly from a terrigenous source. The high contents of mobile elements (Cd, Sb, Sn, Pb, Zn) in the upper part of sapropel are probably due to anthropogenic factors. The high Cu and Zn contents in some sapropel layers are probably related to the inflow of deep-level groundwaters, and the elevated contents of Hg, Cd, and Sb might have been caused by forest fires.

Spatial heterogeneity in a deep artificial lake plankton community revealed by PCR-DGGE fingerprinting

To explore the spatial heterogeneity of plankton communities in a deep artificial lake (Songhua Lake, China), samples were collected at seven sites. Samples were investigated by denaturing gradient gel electrophoresis (DGGE) analysis of the PCR-amplified 16S and 18S rRNA genes and specific bands were sequenced. Cluster analysis of the DGGE profiles revealed that all of the samples grouped into two distinct clusters, in accordance with sampling site; while in each cluster, the divergence of sub-clusters correlated with sampling depth. Sequence analysis of selected dominant DGGE bands revealed that most sequenced phylotypes (84%) exhibited ≥97% similarity to the closest sequences in GenBank, and were affiliated with ten common freshwater plankton phyla (Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, Bacillariophyta, Pyrrophyta, Cryptophyta, Ciliophora, Stramenopiles, and Rotifera). Several of these groups are also found worldwide, indicating the cosmopolitan distribution of the phylotypes. The relationships between DGGE patterns and environmental factors were analyzed by redundancy analysis (RDA). The results suggested that, total nitrogen, nitrate, nitrite, ammonia, and CODMn concentrations, and water temperature were strongly correlated with the variation in plankton composition.

An experimental demonstration of the critical depth principle

AbstractSverdrup's critical depth hypothesis, which has had an almost canonical status in biological oceanography, has recently been challenged as a universal explanation for the formation of oceanic spring blooms, and several alternative hypotheses have been proposed. Arguments pro and contra alternative explanations have so far relied on theoretical considerations and purely observational data. In this paper, we propose that mesocosm experiments with natural plankton communities could make important contributions to the resolution of the issue. We first briefly review the foundations of the critical depth concept and derive an approximate relationship that relates optically scaled critical depth (=“critical optical depth”, i.e. the product of the light attenuation coefficient and the critical depth) to light-dependent phytoplankton production in the mixed surface layer. We describe how this relationship can be used to scale experimental mesocosms such that they reproduce ambient light conditions of natural water columns from the surface down to the critical depth and beyond. We illustrate the power of the approach with a mesocosm study in which we experimentally controlled the onset of the spring bloom of a lake plankton community through the manipulation of optically scaled mixed-layer depth. This experiment may be the first experimental demonstration of the critical depth principle acting on a natural plankton community. Compensation light intensity (=minimum average mixed-layer light intensity required to trigger a bloom of the ambient plankton community) could be constrained to be somewhat above 3.2 moles PAR m−2 d−1, corresponding to a critical optical depth of 10.5. We compare these numbers to estimates from marine systems and end with a discussion of how experiments could be designed to (i) more accurately determine the critical depth in a given system and (ii) resolve among competing hypotheses for vernal bloom onset.

High diversity of protistan plankton communities in remote high mountain lakes in the European Alps and the Himalayan mountains.

We analyzed the genetic diversity (V4 region of the 18S rRNA) of planktonic microbial eukaryotes in four high mountain lakes including two remote biogeographic regions (the Himalayan mountains and the European Alps) and distinct habitat types (clear and glacier-fed turbid lakes). The recorded high genetic diversity in these lakes was far beyond of what is described from high mountain lake plankton. In total, we detected representatives from 66 families with the main taxon groups being Alveolata (55.0% OTUs97%, operational taxonomic units), Stramenopiles (34.0% OTUs97%), Cryptophyta (4.0% OTUs97%), Chloroplastida (3.6% OTUs97%) and Fungi (1.7% OTUs97%). Centrohelida, Choanomonada, Rhizaria, Katablepharidae and Telonema were represented by <1% OTUs97%. Himalayan lakes harbored a higher plankton diversity compared to the Alpine lakes (Shannon index). Community structures were significantly different between lake types and biogeographic regions (Fisher exact test, P < 0.01). Network analysis revealed that more families of the Chloroplastida (10 vs 5) and the Stramenopiles (14 vs 8) were found in the Himalayan lakes than in the Alpine lakes and none of the fungal families was shared between them. Biogeographic aspects as well as ecological factors such as water turbidity may structure the microbial eukaryote plankton communities in such remote lakes.

Contrasting pelagic plankton in temperate Irish lakes: the relative contribution of heterotrophic, mixotrophic, and autotrophic components, and the effects of extreme rainfall events

The mobilisation of energy from allocthonous carbon by heterotrophic bacterioplankton can be proportionally more important than autotrophic production in humic lakes. Moreover, increasing levels of dissolved organic carbon (DOC) in many aquatic systems linked to increases in precipitation, which in turn may be related to changing climate, mean that this heterotrophic component of the food web may play an increasing role in the overall transfer and production of energy, particularly within peatland catchments. While such catchments are common in the temperate northwest Atlantic regions of Europe, studies describing the seasonal dynamics of the heterotrophic, mixotrophic, and autotrophic components of their aquatic food webs are rare. In this study, the biomass of these pelagic components was enumerated over 1 year in 2 oligotrophic lakes, both situated in peatland catchments in the west of Ireland but with contrasting DOC concentrations. Bacterial biomass dominated the pelagic food web of the more humic lake, Lough Feeagh, while autotrophic phytoplankton biomass was greatest in the clearwater lake, Lough Guitane. The biomass of potentially mixotrophic flagellates was also slightly larger in the Lough Guitane, while phagotrophic ciliate biomass was comparable between the 2 lakes. An extreme precipitation event led to a significant increase in bacterial biomass while simultaneously depressing autotrophic production for several months in the humic lake. Extreme precipitation in the clearwater lake also depressed autotrophic production but did not give rise to significant increases in bacterial biomass. This quantification of autotrophic, mixotrophic, and heterotrophic components provides a vital first step in understanding how pelagic communities contribute to net ecosystem productivity, and thus how Irish peatland lakes may be affected by projected climate changes.

Rotifer Invasion? On Appearance and Abundance of Tropical Species in Lakes of North-Eastern Poland

ABSTRACT: Trichocerca simoneae De Smet described in 1989 has since been found in tropical and subtropical areas, but was not recorded in Poland before World War II. A bibliography of Polish rotifers by Wiszniewski (1953), although very comprehensive, does not refer to T. simoneae. However, in the studies of plankton of the dystrophic lake, i.e. humic one with water rich in humic acids, acidic pH and brown coloured, carried out in the years 1998–2000, the species dominated. Here, studies in 39 small, inter-forest lakes of north-eastern Poland revealed T. simoneae in 15 of them, often at high densities, up to ca 6000 ind L-1. The possible reasons for this ‘invasion’ are: (1) zooplankton communities in dystrophic lakes are unsaturated with biotic interactions too weak to exclude invaders; CCA and RDA analyses showed that T. simoneae preferred habitats with low number of zooplankton species of low density and dystrophic lakes seem to offer such habitats; (2) long-term deposition of rotifer resting eggs is pro...

Cross‐taxon congruence in lake plankton largely independent of environmental gradients

Groups of organisms often have congruent patterns of diversity or community structure due to similar environmental requirements. However, ecological interactions across trophic levels may also promote congruence independent of environmental drivers through selective predation, niche partitioning, or facilitation. We examined congruence between phytoplankton and zooplankton communities using 20 years of monitoring data from 17 Danish lakes, most of which were subject to external nutrient loading reduction after a period of eutrophication. Linear mixed effect models and partial Mantel tests were used to elucidate the extent to which congruence in genus richness and composition was driven by environmental factors. Congruence not explained by environmental controls might indicate ecological interactions across trophic levels of lake plankton. Genus richness and composition of phyto‐ and zooplankton were significantly congruent. Environmental factors had limited power to explain the genus richness of phyto‐ and zooplankton (R2: 6% and 12%, respectively). Including richness of the reciprocal group among the predictors markedly improved each respective model and explanatory power (R2: 11% and 17%, respectively). Similarly, a large proportion of the congruence in genus composition was independent of environmental dissimilarity (Mantel r: 0.29 and partial Mantel r after accounting for environmental control: 0.17). The strength of the congruence varied among different groups of phyto‐ and zooplankton, likely reflecting that the different zooplankton groups differ in their grazing size spectra and thus in the strength of their coupling with the phytoplankton assemblages. Remarkably, congruence with phytoplankton was strongest for the smallest group of zooplankton, rotifers, which graze on a limited size spectrum of phytoplankton. Moreover, congruence was stronger in low‐nutrient lakes, suggesting that the strength of the interactions between the two groups weakens with eutrophication. This is likely due to changes in trophic dynamics, where enhanced fish predation on large‐bodied zooplankton with increasing nutrient levels results in reduced zooplankton grazing control of phytoplankton assemblages.

The effects of local, buffer zone and geographical variables on lake plankton metacommunities

Lake plankton metacommunities are affected by their surrounding multidimensional landscape. Hence, understanding mechanisms shaping lake plankton communities requires considering not only local or geographical drivers, but also drivers at buffer zone level, indicating fluxes of nutrients and organic compounds. We investigated the effects of local, buffer zone (characterised via remote sensing) and geographical level variables on the phyto- and zooplankton community composition in 100 lakes distributed over five watersheds in Finland. We examined the community variation at two spatial scales using redundancy analysis with variation partitioning. Among watersheds, phyto- and zooplankton showed a small spatial imprint in their metacommunity structure, suggesting weak dispersal limitation. Environmental drivers explained negligible shares of the community variation, indicating weak species sorting. However, within single watersheds, larger fractions of the variation in communities were explained by the effects of multi-scale variables, suggesting that communities may be structured by species sorting and mass effects. Groups of variables exerted a relatively equal influence on the community composition. Including buffer zone variables into models increased the explained community variation by one-third. Due to the unique effects of the buffer zone on plankton composition, remotely sensed buffer zone variables may serve as useful proxies in analyses of lake plankton metacommunities.

Separating effects of climatic drivers and biotic feedbacks on seasonal plankton dynamics: no sign of trophic mismatch

Summary Climate change may impact most strongly on temperate lake plankton communities in spring, when light availability and water temperature change rapidly due to thermal stratification. Effects of changing light and temperature on one food‐web component transfer to other components, producing a complex interplay between physical drivers and biotic feedbacks. Understanding this interplay is important, because altered climate regimes could result in phenological mismatch between the phytoplankton spring bloom and the timing of maximum food requirements of grazers. To separate direct effects of light and temperature on spring plankton dynamics from effects mediated through micro‐ and mesograzer feedbacks, we manipulated water temperature, stratification depth and presence/absence of the mesograzer Daphnia in lake mesocosms. In early spring, stratification depth and water temperature directly influenced the light supply to phytoplankton and the growth rates of all plankton groups. Subsequently, indirect effects, including light‐dependent food supply to grazers and temperature‐dependent grazing pressure, became increasingly important. Phytoplankton and Daphnia peaked earlier in warmer treatments and reached higher peaks when stratification depth was shallower. Ciliates responded positively to increased food density and higher temperature and subsequently affected the taxonomic composition, but not the total biomass, of phytoplankton. In the absence of Daphnia, phytoplankton did not enter a distinct clear water phase. When present, Daphnia caused an extended clear water phase, maintaining phytoplankton and ciliates at low levels throughout early summer and suppressing all direct effects of physical drivers on these plankton groups. Our Daphnia treatments mimicked the high and low fish predation settings of the largely descriptive, recently revised Plankton Ecology Group (PEG) model of seasonal plankton succession and explored their responses to climate change scenarios. The results largely support the PEG model, but attribute greater importance to early season temperature effects and later season grazing effects of Daphnia. In warmer treatments, the timing of phytoplankton and zooplankton peaks tended to be more closely coupled, and temperature did not affect the height of zooplankton peaks. In line with other experiments, these results do not support the widely held concern that warming may create a trophic mismatch between phytoplankton and zooplankton and reduce spring zooplankton production.

Cyanoprokaryota в планктоне рек и озер Омского Прииртышья (Россия)

Cyanoprokaryota в планктоне рек и озер Омского Прииртышья (Россия)

Species-specific separation of lake plankton reveals divergent food assimilation patterns in rotifers.

1. The analysis of functional groups with a resolution to the individual species level is a basic requirement to better understand complex interactions in aquatic food webs. Species-specific stable isotope analyses are currently applied to analyse the trophic role of large zooplankton or fish species, but technical constraints complicate their application to smaller-sized plankton.2. We investigated rotifer food assimilation during a short-term microzooplankton bloom in the East African soda lake Nakuru by developing a method for species-specific sampling of rotifers.3. The two dominant rotifers, Brachionus plicatilis and Brachionus dimidiatus, were separated to single-species samples (purity >95%) and significantly differed in their isotopic values (4.1‰ in δ13C and 1.5‰ in δ15N). Bayesian mixing models indicated that isotopic differences were caused by different assimilation of filamentous cyanobacteria and particles <2 μm and underlined the importance of species-specific sampling of smaller plankton compartments.4. A main difference was that the filamentous cyanobacterium Arthrospira fusiformis, which frequently forms blooms in African soda lakes, was an important food source for the larger-sized B. plicatilis (48%), whereas it was hardly ingested by B. dimidiatus. Overall, A. fusiformis was, relative to its biomass, assimilated to small extents, demonstrating a high grazing resistance of this species.5. In combination with high population densities, these results demonstrate a strong potential of rotifer blooms to shape phytoplankton communities and are the first in situ demonstration of a quantitatively important direct trophic link between rotifers and filamentous cyanobacteria.

Predicting impacts of an invading copepod by ecological assessment in the animal’s native range

We assembled data from 11 years of observational research on zooplankton in subtropical Florida, USA, lakes to determine potential impacts of the copepod Arctodiaptomus dorsalis on biodiversity and biomass of co-occurring crustacean zooplankton. This synthesis provided insight into how the species might impact plankton in limnologically similar lakes that it invades outside of its native range. A. dorsalis recently was found in the Philippines, and it was suggested that it could invade lakes in Asia and reduce biodiversity. In 7 shallow eutrophic lakes in Florida, we found no relationship between relative biomass of A. dorsalis and number of species of crustacean zooplankton, and we were equally likely to find a similar-sized copepod Diaptomus floridanus in lakes with or without A. dorsalis. In Lake Okeechobee, where a 7-year dataset existed for crustacean zooplankton, we found no evidence that A. dorsalis impacts the biomass of cladocerans or other dominant copepods. Gut analysis and grazing experiments documented that A. dorsalis is capable of eating bacteria and nearly all phytoplankton taxa, including cyanobacteria. This ability to exploit a broad range of resources and to execute rapid escape maneuvers to avoid fish predation may explain why A. dorsalis often is dominant in shallow eutrophic lakes with high densities of omnivorous fish. We conclude that A. dorsalis will not negatively affect the biodiversity of plankton in similar lakes of Asia; instead, it may fill a vacant niche in lakes with high fish predation where other copepods cannot survive. Further research is needed to determine how A. dorsalis will influence the plankton in less enriched lakes where food resources may be limiting.

Light microscopical observations of the sigmoid species of the genus Cryptomonas Ehrenberg (Cryptophyceae) and their eventual pyrenoids

Several species of the genus Cryptomonas EHRENB. are characterized by the sigmoid (S-shaped) form of their cells under natural conditions. Such species were sampled and studied by the author for decades from the plankton of freshwater lakes, dam reservoirs, fishponds, and peat pools, from among littoral vegetation, as well as in small water bodies overgrown with vegetation. After application of optical microscopes on live or chemically treated specimens, they were measured and depicted. Four species known from literature are demonstrated to be easily determinable, namely Cryptomonas curvata, C. reflexa, C. marssonii, C. gracilis. Two new varieties are described. Cryptomonas borealis is shown as a transient species between straight and sigmoid cells. A special attention is given to the occurrence of pyrenoids and Maupas corpuscles within the cells. The new forma of C. cylindrica is pictured and described, with the antapex of the cells deformed differently from sigmoid species.

Intraspecific phenotypic variation in a fish predator affects multitrophic lake metacommunity structure

Contemporary insights from evolutionary ecology suggest that population divergence in ecologically important traits within predators can generate diversifying ecological selection on local community structure. Many studies acknowledging these effects of intraspecific variation assume that local populations are situated in communities that are unconnected to similar communities within a shared region. Recent work from metacommunity ecology suggests that species dispersal among communities can also influence species diversity and composition but can depend upon the relative importance of the local environment. Here, we study the relative effects of intraspecific phenotypic variation in a fish predator and spatial processes related to plankton species dispersal on multitrophic lake plankton metacommunity structure. Intraspecific diversification in foraging traits and residence time of the planktivorous fish alewife (Alosa pseudoharengus) among coastal lakes yields lake metacommunities supporting three lake types which differ in the phenotype and incidence of alewife: lakes with anadromous, landlocked, or no alewives. In coastal lakes, plankton community composition was attributed to dispersal versus local environmental predictors, including intraspecific variation in alewives. Local and beta diversity of zooplankton and phytoplankton was additionally measured in response to intraspecific variation in alewives. Zooplankton communities were structured by species sorting, with a strong influence of intraspecific variation in A. pseudoharengus. Intraspecific variation altered zooplankton species richness and beta diversity, where lake communities with landlocked alewives exhibited intermediate richness between lakes with anadromous alewives and without alewives, and greater community similarity. Phytoplankton diversity, in contrast, was highest in lakes with landlocked alewives. The results indicate that plankton dispersal in the region supplied a migrant pool that was strongly structured by intraspecific variation in alewives. This is one of the first studies to demonstrate that intraspecific phenotypic variation in a predator can maintain contrasting patterns of multitrophic diversity in metacommunities.

A hypothesis linking chrysophyte microfossils to lake carbon dynamics on ecological and evolutionary time scales

Chrysophyte algae are common in the plankton of oligotrophic lakes and produce a rich microfossil record of siliceous cysts and scales. Paleolimnological investigations and phytoplankton records suggest that chrysophyte populations are increasing in a wide range of boreal and arctic lakes, ultimately representing one component of the limnological response to contemporary global changes. However, the exact mechanisms responsible for widespread increases of chrysophyte populations remain elusive. We hypothesize that recent increases in chrysophytes are related to rising pCO2 in lakes, in part because these algae lack carbon concentrating mechanisms and therefore rely on diffusive entry of CO2 to Rubisco during photosynthesis. We assessed the abundance of modern sediment chrysophyte microfossils in relation to summer CO2 relative saturation in 46 New England (USA) lakes, revealing significant positive relationships for both cysts and scales. These observations imply that correlations between chrysophytes and limnological conditions including low pH, oligotrophy, and elevated dissolved organic matter are ultimately underscored by the high pCO2 associated with these conditions. In lakes where chrysophyte populations have expanded over recent decades, we infer that increasingly heterotrophic conditions with respect to CO2 have stimulated production by these organisms. This linkage is supported by the remarkable abundance and diversity of chrysophytes from middle Eocene lake sediments, deposited under atmospheric CO2 concentrations significantly higher than present. The Eocene assemblages suggest that any chrysophyte-CO2 connection borne out of results from modern and sub-recent sediments also operated on evolutionary time scales, and thus the absence of carbon concentrating mechanisms appears to be an ancient feature within the group. Chrysophyte microfossils may potentially provide important insights concerning the temporal dynamics of carbon cycling in aquatic ecosystems.

Subsidy quantity and recipient community structure mediate plankton responses to autumn leaf drop

Although ecologists appreciate the important contributions of cross‐ecosystem subsidies to a variety of ecological processes, relatively little is known about the ability of detrital subsidies from temperate forests (e.g., leaves and leaf leachates) to stimulate plankton in freshwater lakes and ponds, especially immediately after leaves fall. We hypothesized that subsidy quantity interacts with zooplankton community structure to determine how phytoplankton and zooplankton respond to leaf additions, predicting that phytoplankton would peak at intermediate levels of leaf addition due to a tradeoff between increasing nutrients and decreasing light, while Daphnia would continue to increase due to their ability to exploit increased microbes. To test this hypothesis, we manipulated the amount of freshly‐abscised sugar maple leaves added to artificial pond mesocosms with contrasting zooplankton community structures (with vs. without added Daphnia) in a factorial experiment and then monitored the responses of water chemistry, phytoplankton, and zooplankton to treatments over the next four weeks. Leaf additions increased total phosphorus (TP) concentrations but decreased pH, water clarity, and total nitrogen (TN) to TP ratios; the increases in TP and decreases in TN:TP were smaller in ponds with added Daphnia. Consistent with expectations, chlorophyll a increased following modest leaf additions in the ponds without Daphnia and decreased in response to the largest leaf addition in both zooplankton treatments, probably due to a lack of light. Daphnia increased with increasing leaf quantity in the +Daphnia ponds, as predicted. Surprisingly, the dominant copepods (mainly diaptomids) also increased with leaf quantity in the ponds without Daphnia. We conclude that modest leaf additions can stimulate phytoplankton and zooplankton in autumn, especially in small lakes and ponds surrounded by forest, and suggest that this “hot moment” (sensu McClain et al. 2003) for cross‐ecosystem studies be further evaluated in natural systems.

Plankton communities in oxbow lakes of the River Vistula (Oświęcim Basin) with bottom sediments heterogeneously contaminated with heavy metals

Abstract This study presents plankton communities (phytoplankton and zooplankton) in the three reservoirs of the River Vistula’s oxbow lake near Zator (Oświęcim Basin). Selected physicochemical parameters of the oxbow lake waters and the bottom sediments were analysed. Aquatic ecosystems in the investigated area have been heterogeneously contaminated with heavy metals (mostly by zinc, cadmium, lead and chromium), because of contaminated waters of the Vistula, and with manganese and iron. The highest differences were observed between Krajskie and Miejsce oxbow lakes among chlorides and the conductivity of the water and among Cr and Fe in the bottom sediments. This indicates a strong influence of the River Vistula. The plankton structure was different in each of the oxbow lakes. The index of taxa similarity showed also differences in the structure of plankton in oxbow lakes, which was convergent with the chemical parameters of oxbow lakes. The index of taxa similarity was similar for all three oxbow lakes only for one group of algae (Chlorophyta) and one group of plankton animals (Rotatoria). Lower similarity was shown between one oxbow lake impacted by the River Vistula (Krajskie) and another oxbow lake completely separated from the River Vistula (Oko).

Shifts in Plankton, Nutrient and Light Relationships in Small Tundra Lakes Caused by Localized Permafrost Thaw

Tundra lakes located in the Mackenzie Delta uplands, NWT, Canada, are increasingly being affected by permafrost thaw in the form of shoreline retrogressive thaw slumping. This form of thaw-induced disturbance is used as a surrogate indicator of landscape-related disturbance linked to regional climate warming. We compared 22 lakes, half affected by thaw slumping and half unaffected, to determine whether water column nutrient concentrations, light availability, and plankton biomass differed between these two lake types. Total phosphorus (TP), total dissolved nitrogen (TDN), dissolved organic carbon (DOC), and chlorophyll a concentrations were higher in unaffected lakes than in slump-affected lakes. Absorbance related to water colour of both UV and photosynthetically active radiation in the water column was also higher in unaffected lakes, but bacterioplankton abundance was not different between lake types. UV light absorbance was found to be the best predictor of pelagic chlorophyll a concentrations in unaffected lakes, whereas TDN (and to a lesser extent TP) were the best predictors of pelagic chlorophyll a in slump-affected lakes. These findings indicate that slumping arising from permafrost thaw produces a shift in tundra lake nutrient, light, and phytoplankton relationships. Given the projections of continued warming, this result has significant implications for the future biogeochemical and ecological states of Arctic tundra lakes.

Plankton dynamics under different climatic conditions in space and time

Summary1. Different components of the climate system have been shown to affect temporal dynamics in natural plankton communities on scales varying from days to years. The seasonal dynamics in temperate lake plankton communities, with emphasis on both physical and biological forcing factors, were captured in the 1980s in a conceptual framework, the Plankton Ecology Group (PEG) model.2. Taking the PEG model as our starting point, we discuss anticipated changes in seasonal and long‐term plankton dynamics and extend this model to other climate regions, particularly polar and tropical latitudes. Based on our improved post‐PEG understanding of plankton dynamics, we also evaluate the role of microbial plankton, parasites and fish in governing plankton dynamics and distribution.3. In polar lakes, there is usually just a single peak in plankton biomass in summer. Lengthening of the growing season under warmer conditions may lead to higher and more prolonged phytoplankton productivity. Climate‐induced increases in nutrient loading in these oligotrophic waters may contribute to higher phytoplankton biomass and subsequent higher zooplankton and fish productivity.4. In temperate lakes, a seasonal pattern with two plankton biomass peaks – in spring and summer – can shift to one with a single but longer and larger biomass peak as nutrient loading increases, with associated higher populations of zooplanktivorous fish. Climate change will exacerbate these trends by increasing nutrient loading through increased internal nutrient inputs (due to warming) and increased catchment inputs (in the case of more precipitation).5. In tropical systems, temporal variability in precipitation can be an important driver of the seasonal development of plankton. Increases in precipitation intensity may reset the seasonal dynamics of plankton communities and favour species adapted to highly variable environments. The existing intense predation by fish on larger zooplankters may increase further, resulting in a perennially low zooplankton biomass.6. Bacteria were not included in the original PEG model. Seasonally, bacteria vary less than the phytoplankton but often follow its patterns, particularly in colder lakes. In warmer lakes, and with future warming, a greater influx of allochthonous carbon may obscure this pattern.7. Our analyses indicate that the consequences of climate change for plankton dynamics are, to a large extent, system specific, depending on characteristics such as food‐web structure and nutrient loading. Indirect effects through nutrient loading may be more important than direct effects of temperature increase, especially for phytoplankton. However, with warming a general picture emerges of increases in bacterivory, greater cyanobacterial dominance and smaller‐bodied zooplankton that are more heavily impacted by fish predation.