The extent and variability of storm-induced temperature changes in lakes measured with long-term and high-frequency data

The intensity and frequency of storms are projected to increase in many regions of the world because of climate change. Storms can alter environmental conditions in many ecosystems. In lakes and reservoirs, storms can reduce epilimnetic temperatures from wind-induced mixing with colder hypolimnetic waters, direct precipitation to the lake's surface, and watershed runoff. We analyzed 18 long-term and high-frequency lake datasets from 11 countries to assess the magnitude of wind- vs. rainstorm-induced changes in epilimnetic temperature. We found small day-to-day epilimnetic temperature decreases in response to strong wind and heavy rain during stratified conditions. Day-to-day epilimnetic temperature decreased, on average, by 0.28 degrees C during the strongest windstorms (storm mean daily wind speed among lakes: 6.7 +/- 2.7 m s(-1), 1 SD) and by 0.15 degrees C after the heaviest rainstorms (storm mean daily rainfall: 21.3 +/- 9.0 mm). The largest decreases in epilimnetic temperature were observed >= 2 d after sustained strong wind or heavy rain (top 5(th) percentile of wind and rain events for each lake) in shallow and medium-depth lakes. The smallest decreases occurred in deep lakes. Epilimnetic temperature change from windstorms, but not rainstorms, was negatively correlated with maximum lake depth. However, even the largest storm-induced mean epilimnetic temperature decreases were typicallyPeer reviewe

The effects of hypoxia on zooplankton population estimates and migration in lakes

Many zooplankton species typically exhibit diel vertical migration (DVM), where zooplankton migrate from the hypolimnion to the epilimnion of lakes at night. Zooplankton exhibit this behavior to avoid visual predators and UV radiation by remaining in the bottom waters during the day and ascending to the surface waters to feed on phytoplankton at night. However, hypoxic conditions in the hypolimnion of lakes mayinterfere with DVM and force zooplankton to increase diel horizontal migration (DHM) to find predation refuge in littoral zones. Climate change and eutrophication are expected to increase the prevalence and severity of hypoxic conditions worldwide and thereby possibly alter zooplankton migration patterns. We hypothesize that hypoxia will force zooplankton to shift their migration patterns from predominantly DVM to DHM to avoid oxygen-depleted bottom waters. To test our hypothesis, we are conducting a standardized global sampling program to test whether pelagic, full water column estimates of zooplankton are greater at night versus the day under hypolimnetic hypoxic versus oxic conditions. Participants are aiming to sample at least one lake with an oxic hypolimnion and one lake with a hypoxic hypolimnion during the thermally-stratified period at midday and midnight. With our global dataset (currently expecting about 60 lakes in 22 countries), our goal is to improve our understanding of how global change may alter zooplankton migration behavior and patterns in lakes.info:eu-repo/semantics/publishedVersio

Dormant eggs of a calanoid copepod from tropical brackish aquaculture ponds

International audienceMany Asian aquaculture farms cultivate copepods as live-feed for aquaculture species, as copepod nutritional and behavioural qualities are usually higher than those of traditional live-feeds (i.e., Artemia and rotifers). The most convenient method to use zooplankton in aquaculture as live feed involves dormant eggs. In this study, to establish whether the copepod species of the tropical Taiwanese ponds exhibit quiescence of their eggs, several sediment samples were collected from the ponds and incubated at low temperature. After 3 months of cold incubation, several nauplii of Acartia bilobata Abraham, 1970 hatched from the sediment at high temperature over several days. Further investigations need to be conducted to understand the origin of the dormancy (i.e., induced originally in the field or in the laboratory). Nevertheless, it is the first reported case of dormant eggs in calanoid copepods in tropical regions. The present study will certainly find some interest in tropical aquaculture as our results showed that long-term storage of tropical calanoid copepod eggs is possible, even if collected directly from the sediment without sorting the eggs

Effets de la contamination chimique : des organismes en danger ?

Le présent fascicule a pour objectif d’apporter les éléments de réponse disponibles pour l’estuaire de la Seine sur ce questionnement. Dans la première partie écotoxicologie. Les effets de la contamination chimique à différents niveaux d’organisation biologique, sur les organismes présents dans l’estuaire de la Seine, seront présentés dans la deuxième partie puis synthétisés dans notion d’analyse du risque environnemental

Scientists' Warning to Humanity : Rapid degradation of the world's large lakes

Large lakes of the world are habitats for diverse species, including endemic taxa, and are valuable resources that provide humanity with many ecosystem services. They are also sentinels of global and local change, and recent studies in limnology and paleolimnology have demonstrated disturbing evidence of their collective degradation in terms of depletion of resources (water and food), rapid warming and loss of ice, destruction of habitats and ecosystems, loss of species, and accelerating pollution. Large lakes are particularly exposed to anthropogenic and climatic stressors. The Second Warning to Humanity provides a framework to assess the dangers now threatening the world's large lake ecosystems and to evaluate pathways of sustainable development that are more respectful of their ongoing provision of services. Here we review current and emerging threats to the large lakes of the world, including iconic examples of lake management failures and successes, from which we identify priorities and approaches for future conservation efforts. The review underscores the extent of lake resource degradation, which is a result of cumulative perturbation through time by long-term human impacts combined with other emerging stressors. Decades of degradation of large lakes have resulted in major challenges for restoration and management and a legacy of ecological and economic costs for future generations. Large lakes will require more intense conservation efforts in a warmer, increasingly populated world to achieve sustainable, high-quality waters. This Warning to Humanity is also an opportunity to highlight the value of a long-term lake observatory network to monitor and report on environmental changes in large lake ecosystems. (C) 2020 The Authors. Published by Elsevier B.V. on behalf of International Association for Great Lakes Research.Peer reviewe