Highest composition dissimilarity among phytoplankton communities at intermediate environmental distances across high-altitude tropical lakes

Tropical high-altitude lakes are vital freshwater ecosystems for the functioning and dynamics of tropical high-altitude wetlands called páramos, found at over 3300 m above sea level. They play a major role in the hydrogeological cycle and provide important hydrological services such as water storage, and yet they are understudied. Describing the patterns and processes of community composition in these lakes is required to better understand the consequences of their degradation by human activities. In this study we tested the geographical and environmental components of distance–decay relationships in the phytoplankton structure across 24 tropical high-altitude lakes from Southern Ecuador. Phytoplankton composition at the phyla level showed high among-lake variation in the tropical high-altitude lakes from Tres Lagunas. We found no links, however, between the geographic distance and phytoplankton composition. On the contrary, we observed some environmentally related patterns of community structure like redox potential, altitude, water temperature, and total phosphorus. The absence of support for the distance–decay relationship observed here can result from a conjunction of local niche-based effects and dispersal limitations. Phytoplankton community composition in the Tres Lagunas system or any other ecosystem may be jointly regulated by niche-based and neutral forces that still need to be explored. Despite not proving a mechanistic explanation for the observed patterns of community structure, we hope our findings provide understanding of these vulnerable and vital ecosystems. More studies in tropical high-altitude lakes are urgently required

Antecedent lake conditions shape resistance and resilience of a shallow lake ecosystem following extreme wind storms

Extreme wind storms can strongly influence short-term variation in lake ecosystem functioning. Climate change is affecting storms by altering their frequency, duration, and intensity, which may have consequences for lake ecosystem resistance and resilience. However, catchment and lake processes are simultaneously affecting antecedent lake conditions which may shape the resistance and resilience landscape prior to storm exposure. To determine whether storm characteristics or antecedent lake conditions are more important for explaining variation in lake ecosystem resistance and resilience, we analyzed the effects of 25 extreme wind storms on various biological and physiochemical variables in a shallow lake. Using boosted regression trees to model observed variation in resistance and resilience, we found that antecedent lake conditions were more important (relative importance = 67%) than storm characteristics (relative importance = 33%) in explaining variation in lake ecosystem resistance and resilience. The most important antecedent lake conditions were turbidity, Schmidt stability, %O2 saturation, light conditions, and soluble reactive silica concentrations. We found that storm characteristics were all similar in their relative importance and results suggest that resistance and resilience decrease with increasing duration, mean precipitation, shear stress intensity, and time between storms. In addition, we found that antagonistic or opposing effects between the biological and physiochemical variables influence the overall resistance and resilience of the lake ecosystem under specific lake and storm conditions. The extent to which these results apply to the resistance and resilience of different lake ecosystems remains an important area for inquiry

Phytoplankton responses to repeated pulse perturbations imposed on a trend of increasing eutrophication

While eutrophication remains one of the main pressures acting on freshwater ecosystems, the prevalence of anthropogenic and nature-induced stochastic pulse perturbations is predicted to increase due to climate change. Despite all our knowledge on the effects of eutrophication and stochastic events operating in isolation, we know little about how eutrophication may affect the response and recovery of aquatic ecosystems to pulse perturbations. There are multiple ways in which eutrophication and pulse perturbations may interact to induce potentially synergic changes in the system, for instance, by increasing the amount of nutrients released after a pulse perturbation. Here, we performed a controlled press and pulse perturbation experiment using mesocosms filled with natural lake water to address how eutrophication modulates the phytoplankton response to sequential mortality pulse perturbations; and what is the combined effect of press and pulse perturbations on the resistance and resilience of the phytoplankton community. Our experiment showed that eutrophication increased the absolute scale of the chlorophyll-a response to pulse perturbations but did not change the proportion of the response relative to its pre-event condition (resistance). Moreover, the capacity of the community to recover from pulse perturbations was significantly affected by the cumulative effect of sequential pulse perturbations but not by eutrophication itself. By the end of the experiment, some mesocosms could not recover from pulse perturbations, irrespective of the trophic state induced by the press perturbation. While not resisting or recovering any less from pulse perturbations, phytoplankton communities from eutrophying systems showed chlorophyll-a levels much higher than non-eutrophying ones. This implies that the higher absolute response to stochastic pulse perturbations in a eutrophying system may increase the already significant risks for water quality (e.g., algal blooms in drinking water supplies), even if the relative scale of the response to pulse perturbations between eutrophying and non-eutrophying systems remains the same

Chytrid epidemics may increase genetic diversity of a diatom spring-bloom

Contrary to expectation, populations of clonal organisms are often genetically highly diverse. In phytoplankton, this diversity is maintained throughout periods of high population growth (that is, blooms), even though competitive exclusion among genotypes should hypothetically lead to the dominance of a few superior genotypes. Genotype-specific parasitism may be one mechanism that helps maintain such high-genotypic diversity of clonal organisms. Here, we present a comparison of population genetic similarity by estimating the beta-dispersion among genotypes of early and peak bloom populations of the diatom Asterionella formosa for three spring-blooms under high or low parasite pressure. The Asterionella population showed greater beta-dispersion at peak bloom than early bloom in the 2 years with high parasite pressure, whereas the within group dispersion did not change under low parasite pressure. Our findings support that high prevalence parasitism can promote genetic diversification of natural populations of clonal hosts

Antecedent lake conditions shape resistance and resilience of a shallow lake ecosystem following extreme wind storms

Extreme wind storms can strongly influence short‐term variation in lake ecosystem functioning. Climate change is affecting storms by altering their frequency, duration, and intensity, which may have consequences for lake ecosystem resistance and resilience. However, catchment and lake processes are simultaneously affecting antecedent lake conditions which may shape the resistance and resilience landscape prior to storm exposure. To determine whether storm characteristics or antecedent lake conditions are more important for explaining variation in lake ecosystem resistance and resilience, we analyzed the effects of 25 extreme wind storms on various biological and physiochemical variables in a shallow lake. Using boosted regression trees to model observed variation in resistance and resilience, we found that antecedent lake conditions were more important (relative importance = 67%) than storm characteristics (relative importance = 33%) in explaining variation in lake ecosystem resistance and resilience. The most important antecedent lake conditions were turbidity, Schmidt stability, %O2 saturation, light conditions, and soluble reactive silica concentrations. We found that storm characteristics were all similar in their relative importance and results suggest that resistance and resilience decrease with increasing duration, mean precipitation, shear stress intensity, and time between storms. In addition, we found that antagonistic or opposing effects between the biological and physiochemical variables influence the overall resistance and resilience of the lake ecosystem under specific lake and storm conditions. The extent to which these results apply to the resistance and resilience of different lake ecosystems remains an important area for inquiry.EU‐ITN MANTELMarie Sklodowska‐Curiehttps://aslopubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2Flno.11859&file=lno11859-sup-0001-Supinfo1.docxhttps://aslopubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2Flno.11859&file=lno11859-sup-0002-Supinfo2.doc

Highest Composition Dissimilarity among Phytoplankton Communities at Intermediate Environmental Distances across High-Altitude Tropical Lakes

Tropical high-altitude lakes are vital freshwater ecosystems for the functioning and dynamics of tropical high-altitude wetlands called páramos, found at over 3300 m above sea level. They play a major role in the hydrogeological cycle and provide important hydrological services such as water storage, and yet they are understudied. Describing the patterns and processes of community composition in these lakes is required to better understand the consequences of their degradation by human activities. In this study we tested the geographical and environmental components of distance–decay relationships in the phytoplankton structure across 24 tropical high-altitude lakes from Southern Ecuador. Phytoplankton composition at the phyla level showed high among-lake variation in the tropical high-altitude lakes from Tres Lagunas. We found no links, however, between the geographic distance and phytoplankton composition. On the contrary, we observed some environmentally related patterns of community structure like redox potential, altitude, water temperature, and total phosphorus. The absence of support for the distance–decay relationship observed here can result from a conjunction of local niche-based effects and dispersal limitations. Phytoplankton community composition in the Tres Lagunas system or any other ecosystem may be jointly regulated by niche-based and neutral forces that still need to be explored. Despite not proving a mechanistic explanation for the observed patterns of community structure, we hope our findings provide understanding of these vulnerable and vital ecosystems. More studies in tropical high-altitude lakes are urgently required

Life under ice in Lake Onego (Russia) - an interdisciplinary winter limnology study

This special issue of Inland Waters focuses on recent under-ice research in Lake Onego, Russia. Compared to open waters, research on ice-covered lakes is sparse because of the demanding work environment and logistics in the field (Kirillin et al. 2012). In the past, large lakes in particular, such as the European Lakes Onego (61°36′10.52″N, 35°34′22.42″E) and Ladoga (61°00′0.00″N, 31°00′0.00″E), were not typically studied during their ice-cover periods. Today, however, substantial concerns exist about the potential effects of rapid climate warming and the resulting reduction in ice cover in high latitude lakes. Subsequently, scientific interest in boreal lakes has strongly increased (Brown and Duguay 2010). At the same time, these lakes are important for drinking water, transport, hydropower, and recreation (Rukhovets and Filatov 2010, Magnuson and Lathrop 2014) and represent outstanding biological resources. Therefore, the sustainable use of water and conservation of biodiversity in Lakes Ladoga and Onego were declared a high priority in 2013 by the Russian Security Council (http://kremlin.ru/events/president/news/19655). Given these circumstances, a better understanding of the role of ice cover on ecological characteristics of these large lakes is required. Lake Onego, a lake of glacial-tectonic origin located in Karelia (Russia), offers a fascinating place for such studies. As the second largest lake on the European continent (9600 km2, 292 km3; Filatov and Rukhovets 2012), Lake Onego is ice covered for several months each winter, which strongly influences its characteristics, including the occurrence of endemic species. Excellent research infrastructure, collaboration opportunities, and expertise in winter limnology (Jonas et al. 2003) are available from the Northern Water Problems Institute, Karelian Research Center of the Russian Academy of Sciences (NWPI-KRC-RAS; http://nwpi.krc.karelia.ru/e/), located on the shore of Lake Onego in Petrozavodsk. The Limnology Center of the Swiss Federal Institute of Technology Lausanne (LIMNC-EPFL; https://www.epfl.ch/research/domains/limnc/) was proposed to launch a research initiative supported by the Fondation pour l’Etude des Eaux du Leman (FEEL). Hence, we designed a multidisciplinary project on Lake Onego during late winter and spring from 2015 to 2017 to investigate physical, geochemical, and biological under-ice processes in this seasonally ice-covered lake. Additional fields of research included hydrology, paleolimnology, and remote sensing. The LIMNC-EPFL and the NWPI-KRC-RAS jointly implemented this project. The following 7 publications on Lake Onego are the outcome of this multidisciplinary project. We consider this contribution a first step toward a more integrated understanding of winter limnological processes and hope to stimulate follow-up investigations on these fascinating aquatic systems

Understanding the key ecological traits of cyanobacteria as a basis for their management and control under expected environmental change

International audienc