The sensitivity of phytoplankton in Loch Leven (U.K.) to changes in nutrient load and water temperature

1. Loch Leven is a shallow, eutrophic lake in Scotland, U.K. It has experienced much change over the 30 years that it has been studied; this has primarily been due to reduced nutrient loads to the lake through active catchment management. Its recovery has been slow and, therefore, we used a phytoplankton community model (PROTECH) to test its sensitivity to changing nutrient loads and water temperature.
2. PROTECH was initialized to simulate the observed phytoplankton community in 1995 and was then repeatedly run through a combination of step-wise changes in water temperature and nutrient load (two treatments were simulated for nutrient load: one changing both nitrate and phosphorus, and one changing just phosphorus). The effect on total chlorophyll- a concentration, cyanobacteria abundance and phytoplankton diversity was examined.
3. Whilst changes in temperature had little effect, variations in the nutrient load produced a range of responses. Increasing only the phosphorus load caused a large increase in Anabaena abundance and total chlorophyll- a concentration. However, the opposite response was recorded when nitrate load was changed as well, with Anabaena increasing its biomass under reduced nutrient load scenarios.
4. The key factor determining the type of response appeared to be nitrogen availability. Anabaena , a nitrogen fixer, could exploit the phosphorus resource of Loch Leven under limiting nitrogen conditions, allowing it to dominate under most of the scenarios tested apart from those supplying extra nitrogen to the lake. The model predictions agree with the observed data, which show that Anabaena continues to dominate the summer phytoplankton bloom in Loch Leven despite the considerable reduction in phosphorus supply from the catchment. This research provides a possible explanation for this.     

Diurnal changes in the vertical distribution of phytoplankton in hypertrophic Lake Kasumigaura,Japan

The daily vertical migration of five species;Microcystis aeruginosa (Kütz.) Trevis,Anabaena spiroides Klebahn f.crassa (L.) Elenkin,Aphanizomenon flos-aquae (L.) Ralfs,Melosira granulata (E). Ralfs, andCoscinodiscus lacustris Grun. was studied using a close-interval water sampler on a calm summer day in Lake Kasumigaura. Many colonies ofMicrocystis were observed at the middle of the water column (approx. 1.5 m depth) in the afternoon, and at the surface in the early morning.Anabaena occurred mostly in the upper layer whileAphanizomenon tended to be uniformly distributed. The difference in migration patterns suggests thatMicrocystis is superior toAnabaena andAphanizomenon in obtaining both light and nutrients from this lake. Among diatoms,Melosira remained at the bottom of the water column throughout day and night, but Coscinodiscus was uniformly distributed.     

Warming promotes cold-adapted phytoplankton in temperate lakes and opens a loophole for Oscillatoriales in spring

The effects of the recent warming trend in many northern temperate lakes on the species composition of spring phytoplankton remain poorly understood, especially because a recent change in nutrients has complicated efforts, and previous studies have defined spring according to the calendar. We analysed data from 1979 to 2004 from Lake Müggelsee (Berlin, Germany), using physical and biological parameters to define the spring period. We show that a change in timing of spring plankton events in warm years led to the paradox of lower mean water temperatures during the growth period, favouring cold-adapted diatoms over cyanobacteria, and within the diatoms, some cold-adapted centric forms over pennate forms. Under high P : Si ratios, the increased time between phytoplankton and cladoceran peaks opened a loophole for filamentous cyanobacteria (Oscillatoriales) in warm years to establish dominance after the diatoms, which are silicate limited. Therefore, the warming trend promotes filamentous cyanobacteria, a well-known nuisance in eutrophic lakes, and surprisingly, cold-adapted diatoms.     

Effects of recent climate change on phytoplankton phenology in a temperate lake

1. A number of long-term studies have shown that spring biological events have advanced in recent decades and that this is a response to climate change. In lentic systems, changes in phytoplankton phenology have been attributed to various directly climate-related processes including changes in the onset and duration of thermal stratification, earlier ice-break up and increased water temperature. Both indirect climatic drivers and non-climate drivers such as elevated grazing pressure and nutrient enrichment can also affect phenology.
2. This study investigated whether phenological trends in phytoplankton could be detected in a relatively short time series in a shallow, ice-free, polymictic lake with a high annual discharge and whether any such trends could be causally explained.
3. It was found that the centre of gravity of the spring chlorophyll a bloom advanced significantly by 1.6 days per year over a 15-year period. This was accompanied by a significant increase in water temperature of 0.12 °C per year which is high compared to published rates of change over longer time series. No direct effects of ice cover, stratification or water discharge rates could be linked to the advancement of the spring bloom. Instead, the shift in timing was attributed to an advance in the timing of the dominant spring diatom, Aulacoseira spp., instigated by a temperature-driven increase in replication rate leading to an earlier onset of silica (SiO₂) limitation.     

Sensitivity and responses of diatoms to climate warming in lakes heavily influenced by humans

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A bioassay to assess the potential effects of sediment resuspension on phytoplankton community composition

A laboratory assay (SAGA or Sediment Algal Growth Assay) was developed to assess the potential impact of sediment resuspension on the structure of phytoplankton communities, and to evaluate the effectiveness of various sediment treatments in decreasing the abundance of blue-green algae in the event of sediment resuspension during storms. In assays with sediment from eutrophic Akanoi Bay, Lake Biwa, Japan, 7–11 species of phytoplankton seeded from the sediments grew during the 3-week assay indicating that sediment resuspension has the potential to increase both phytoplankton biomass and species diversity. Treatment of sediments with Ca(NO3)2 substantially decreased phytoplankton biomass (measured as chlorophyll concentration) in assays with sediments from Akanoi Bay and the North Basin of Lake Biwa. Further, among various oxidation treatments of sediments, Ca(NO3)2 was most effective in decreasing or preventing filamentous blue-green algal growth in N- and P-replete media. In contrast, when sediments were added to P-limited phytoplankton dominated by green algae and diatoms, no growth of blue-green algae occurred regardless of sediment treatment. This revised version was published online in June 2006 with corrections to the Cover Date.     

Storm impacts on phytoplankton community dynamics in lakes

In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short‐term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well‐developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short‐ and long‐term. We summarize the current understanding of storm‐induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions.     

Nutrient balances and phytoplankton dynamics in two agriculturally loaded shallow lakes

The impact of agriculture was estimated on two shallow, eutrophic lakes, Lake Kotojärvi and Lake Villikkalanjärvi in southern Finland. The main emphasis was on phosphorus and nitrogen budgets and on the phytoplankton dynamics. Special attention was paid to internal P loading and blue-green algal blooms. The mean Tot-P load from agricultural land was 1.2 kg ha^-1 a^-1 in both basins and Tot-N loads were 19 kg ha^-1 a^-1 in L. Villikkalanjärvi and 12 kg ha^-1 a^-1 in L. Kotojärvi. The Tot-P input to L. Kotojärvi was on an average 0.62 g m^-2 a^-1 (per lake surface area), and the Tot-N input 9.1 g m^-2 a^-1. The corresponding inputs to L. Villikkalanjärvi were 3.1 and 57 g m^-2 a^-1, respectively. The annual variation followed the runoff volumes. About half of the Tot-P and one third of the Tot-N load was retained in L. Kotojärvi. In L. Villikkalanjärvi the retention was only 24% for Tot-P and 19% for Tot-N. The difference was very probably due to a longer theoretical retention time in L. Kotojärvi. In L. Villikkalanjärvi the mean concentration of Tot-P was 120 µg 1^-1 and that of Tot-N 1700 µg 1^-1 and the corresponding figures in L. Kotojärvi 67 and 990 µg 1^-1, respectively. The mean chlorophyll a concentration was, however, higher in L. Kotojärvi (26 µg 1^-1) than in L. Villikkalanjärvi (20 µg 1^-1). This was probably due to an internal P load in L. Kotojärvi: in 1988 the internal load of dissolved P was estimated to be as much as twofold the external load. In L. Villikkalanjärvi the internal dissolved P load was only up to 50% of the external input. In L. Kotojärvi the high internal P load coupled with a low DIN:DIP ratio resulted in a strong blue-green algal bloom in the summer of 1988. In L. Villikkalanjärvi blue-green algae were observed only in small amounts. Even in August 1990, when the DIN:DIP ratio was low enough to favor the occurrence of blue-green algae, they contributed only up to 10–15% of the total phytoplankton biomass.     

Shifting states,shifting services: Linking regime shifts to changes in ecosystem services of shallow lakes

1. Shallow lakes can shift between stable states as a result of anthropogenic or natural drivers. Four common stable states differ in dominant groups of primary producers: submerged, floating, or emergent macrophytes or phytoplankton. Shifts in primary producer dominance affect key supporting, provisioning, regulating, and cultural ecosystem services supplied by lakes. However, links between states and services are often neglected or unknown in lake management, resulting in conflicts and additional costs.
2. Here, we identify major shallow lake ecosystem services and their links to Sustainable Development Goals (SDGs), compare service provisioning among the four ecosystem states and discuss potential trade‐offs.
3. We identified 39 ecosystem services potentially provided by shallow lakes. Submerged macrophytes facilitate most of the supporting (86%) and cultural (63%) services, emergent macrophytes facilitate most regulating services (60%), and both emergent and floating macrophytes facilitate most provisioning services (63%). Phytoplankton dominance supports fewer ecosystem services, and contributes most to provisioning services (42%).
4. The shallow lake ecosystem services we identified could be linked to 10 different SDGs, notably zero hunger (SDG 2), clean water and sanitation (SDG 6), sustainable cities and communities (SDG 11), and climate action (SDG13).
5. We highlighted several trade‐offs (1) among ecosystem services, (2) within ecosystem services, and (3) between ecosystem services across ecosystems. These trade‐offs can have significant ecological and economic consequences that may be prevented by early identification in water quality management.
6. In conclusion, common stable states in shallow lakes provide a different and diverse set of ecosystem services with numerous links to the majority of SDGs. Conserving and restoring ecosystem states should account for potential trade‐offs between ecosystem services and preserving the natural value of shallow lakes.

     

Increased risk of cyanobacterial blooms in northern high‐latitude lakes through climate warming and phosphorus enrichment

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Long-term changes in phytoplankton, zooplankton and salmon related to climate

Recently, large‐scale changes in the biogeography of calanoid copepod crustaceans have been detected in the northeastern North Atlantic Ocean and adjacent seas. Strong biogeographical shifts in all copepod assemblages were found with a northward extension of more than ° in latitude of warm‐water species associated with a decrease in the number of colder‐water species. These changes were attributed to regional increase in sea surface temperature. Here, we have extended these studies to examine long‐term changes in phytoplankton, zooplankton and salmon in relation to hydro‐meteorological forcing in the northeast Atlantic Ocean and adjacent seas. We found highly significant relationships between (1) long‐term changes in all three trophic levels, (2) sea surface temperature in the northeastern Atlantic, (3) Northern Hemisphere temperature and (4) the North Atlantic Oscillation. The similarities detected between plankton, salmon, temperature and hydro‐climatic parameters are also seen in their cyclical variability and in a stepwise shift that started after a pronounced increase in Northern Hemisphere Temperature anomalies at the end of the 1970s. All biological variables show a pronounced change which started after circa 1982 for euphausiids (decline), 1984 for the total abundance of small copepods (increase), 1986 for phytoplankton biomass (increase) and Calanus finmarchicus (decrease) and 1988 for salmon (decrease). This cascade of biological events led to an exceptional period, which is identified after 1986 to present and followed another shift in large‐scale hydro‐climatic variables and sea surface temperature. This regional temperature increase therefore appears to be an important parameter that is at present governing the dynamic equilibrium of northeast Atlantic pelagic ecosystems with possible consequences for biogeochemical processes and fisheries.     

Hierarchical regulation of pelagic invertebrates in lakes of the northern Great Plains: a novel model for interdecadal effects of future climate change on lakes

Endorheic lakes of the northern Great Plains encompass a wide range of environmental parameters (e.g., salinity, pH, DOC, Ca, nutrients, depth) that vary 1000‐fold among sites and through the past 2000 years due to variation in basin hydrology and evaporative forcing. However, while many environmental parameters are known to individually influence zooplankton diversity and taxonomic composition, relatively little is known of the hierarchical relationships among potential controls or of how regulatory mechanisms may change in response to climate variation on diverse scales. To address these issues, we surveyed 70 lakes within a 100 000 km² prairie region to simulate the magnitude of environmental change expected to occur over 100–1000 years and to quantify the unique and interactive effects of diverse environmental parameters in regulating pelagic invertebrate community structure at that scale. Multivariate analyses showed that salinity was the principal correlate of changes in invertebrate composition among lakes, with a sequential loss of taxa between salinities of 4 and 50 g total dissolved solids L^?1 until one to two species predominated in highly saline systems. In contrast, changes in the concentrations of Ca²⁺ and other mineral nutrients exerted secondary controls of invertebrate assemblages independent of salinity, whereas lake depth provided a tertiary regulatory mechanism structuring species composition. In contrast to these large‐scale hierarchical patterns, seasonal surveys (May, July, September) of a subset of 21 lakes in each of 2003–2005 revealed that annual meteorological variation had no measurable effect on pelagic invertebrates, despite large differences in temperature, precipitation, and evaporation arising from regional droughts. Together these findings show that pelagic invertebrate communities in saline lakes are resilient to interannual variability in climate, but suggest that lakes of the northern Great Plains may provide a sensitive model to forecast centennial effects of future climate change.     

Biological responses to permafrost thaw slumping in Canadian Arctic lakes

1. Rapid environmental change occurring in high‐latitude regions has the potential to cause extensive thawing of permafrost. Retrogressive thaw slumps are a particularly spectacular form of permafrost degradation that can significantly impact lake–water chemistry; however, to date, the effects on aquatic biota have received little attention. 2. We used a diatom‐based palaeolimnological approach featuring a paired lake study design to examine the impact of thaw slumping on freshwater ecosystems in the low Arctic of western Canada. We compared biological responses in six lakes affected by permafrost degradation with six undisturbed, reference lakes. 3. Slump‐affected lakes exhibited greater biological change than the paired reference systems, although all systems have undergone ecologically significant changes over the last 200 years. Four of the six reference systems showed an increase in the relative abundance of planktonic algal taxa (diatoms and scaled chrysophytes), the earliest beginning about 1900, consistent with increased temperature trends in this region. 4. The response of sedimentary diatoms to thaw slumping was understandably variable, but primarily related to the intensity of disturbance and associated changes in aquatic habitat. Five of the slump‐affected lakes recorded increases in the abundance and diversity of periphytic diatoms at the presumed time of slump initiation, consistent with increased water clarity and subsequent development of aquatic macrophyte communities. Slump‐affected lakes generally displayed lower nutrient levels; however, in one system, thaw slumping, induced by an intense fire at the site in 1968, ostensibly led to pronounced nutrient enrichment that persists today. 5. Our results demonstrate that retrogressive thaw slumping represents an important stressor to the biological communities of lakes in the western Canadian Arctic and can result in a number of limnological changes. We also show that palaeolimnological methods are effective for inferring the timing and response of aquatic ecosystems to permafrost degradation. These findings provide the first long‐term perspective on the biological response to permafrost thaw, a stressor that will become increasingly important as northern landscapes respond to climate change.     

Global changes may be promoting a rise in select cyanobacteria in nutrient‐poor northern lakes

The interacting effects of global changes—including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes—are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient‐poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient‐poor Swedish lakes over 16 years (1998–2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon‐specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria.     

Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes

The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000. We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g⁻¹ vs. 107 μg g⁻¹, respectively) and soil TP (284 μg g⁻¹ vs. 145 μg g⁻¹). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites (2936 vs. 575 grams ash-free dry mass m⁻²). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats, diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate community. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

River connectivity and climate behind the long‐term evolution of tropical American floodplain lakes

This study presents the long‐term evolution of two floodplains lakes (San Juana and Barbacoas) of the Magdalena River in Colombia with varying degree of connectivity to the River and with different responses to climate events (i.e., extreme floods and droughts). Historical limnological changes were identified through a multiproxy‐based reconstruction including diatoms, sedimentation, and sediment geochemistry, while historical climatic changes were derived from the application of the Standardised Precipitation‐Evapotranspiration Index. The main gradients in climatic and limnological change were assessed via multivariate analysis and generalized additive models. The reconstruction of the more isolated San Juana Lake spanned the last c. 500 years. Between c. 1,620 and 1,750 CE, riverine‐flooded conditions prevailed as indicated by high detrital input, reductive conditions, and dominance of planktonic diatoms. Since the early 1800s, the riverine meander became disconnected, conveying into a marsh‐like environment rich in aerophil diatoms and organic matter. The current lake was then formed around the mid‐1960s with a diverse lake diatom flora including benthic and planktonic diatoms, and more oxygenated waters under a gradual increase in sedimentation and nutrients. The reconstruction for Barbacoas Lake, a waterbody directly connected to the Magdalena River, spanned the last 60 years and showed alternating riverine–wetland–lake conditions in response to varying ENSO conditions. Wet periods were dominated by planktonic and benthic diatoms, while aerophil diatom species prevailed during dry periods; during the two intense ENSO periods of 1987 and 1992, the lake almost desiccated and sedimentation rates spiked. A gradual increase in sedimentation rates post‐2000 suggests that other factors rather than climate are also influencing sediment deposition in the lake. We propose that hydrological connectivity to the Magdalena River is a main factor controlling lake long‐term responses to human pressures, where highly connected lakes respond more acutely to ENSO events while isolated lakes are more sensitive to local land‐use changes.     

Environmental factors favouring the formation of Microcystis aeruginosa hyperscums in a hypertrophic lake

Hyperscums are crusted buoyant mats of densely packed cyanobacteria, often decimeters thick, that persist for periods of weeks to months at the same site. In Hartbeespoort Dam, a hypertrophic lake in South Africa, hyperscums of the cyanobacterium Microcystis aeruginosa that cover more than a hectare and contain up to 2 tons of chlorophyll a typically form in winter and persist for 2–3 months. This paper reports on the environmental conditions that favour hyperscum formation.Reynolds & Walsby (1975) postulated that cyanobacterial bloom formation depended on the coincidence of three preconditions: a pre-existing population, a significant proportion of the organisms having positive buoyancy, and turbulent mixing that is too weak to overcome the tendency of the cells to float. This model of bloom formation is evaluated in the context of hyperscums, based on a case-study from Hartbeespoort Dam. We examine the occurrence of hyperscums and the dynamics of their formation and breakdown in relation to diurnal and seasonal changes in the wind regime and in relation to the population dynamics and buoyancy of Microcystis. We conclude that Reynolds and Walsby's preconditions are essential but not sufficient to explain hyperscum formation. The additional preconditions are prolonged low speed wind regime, suitable lake morphometry, large cyanobacterial standing crops, and high insolation. The rare co-occurrence of these conditions make hyperscums an uncommon phenomenon, but with increasing eutrophication worldwide the frequency and distribution of hyperscum occurrence are likely to increase.     

Diurnal changes in zooplankton respiration rates and the phytoplankton activity in two Chilean lakes

Phytoplankton spatial distribution patterns in the Abra of Bilbao (a semienclosed coastal body of water) and adjacent shelf waters have been studied during June–July 1983 and May–June 1984. Small naked dinoflagellates, cryptophyceans and an unidentified nanoplankton component, were a common feature in all surveys. In July 1983 a dense bloom of nanoplankton developed inside the Abra which, in contrast to the community in the adhacent waters, contained high densities of small diatoms, naked dinoflagellates, cryptophyceans and the Haptophyta Phaeocystis pouchetii. Microplankton was mainly composed of dinoflagellates in July 1983, and of diatoms in June 1983 and May–June 1984. Microplankton abundance was highest in May–June 1984 and decreased from the shelf to the Abra. A principal component analysis performed separately on each cruise revealed the differences in the structure of the phytoplankton community between the Abra of Bilbao and the adjacent shelf waters.