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Across the Northern hemisphere, chloride concentrations in lakes are increasing from decades of road salt use, threatening aquatic ecosystems. Zooplankton are sensitive to increasing chloride but few studies have considered how additional stressors, such as soft water or increasing lake temperatures interact with the negative effects of chloride. To determine the effects of increasing chloride and temperature on freshwater zooplankton and phytoplankton communities, we conducted a mesocosm experiment using 30 concentrations of chloride from ambient levels to 1500 mg L−1, ambient or warmed (+2.7°C) temperatures, and plankton from a softwater lake. We compared the results with current Canadian Water Quality Guidelines (CWQG) for chronic exposure to chloride. Although warming elicited little response, increasing chloride concentrations led to reduced zooplankton biomass and richness, even at concentrations below the CWQG, and an increase in cyanobacteria abundance, suggesting that policies regulating road salt application should be reevaluated to better protect aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The salinization of freshwaters is a global threat to aquatic biodiversity. We quantified variation in chloride (Cl−) tolerance of 19 freshwater zooplankton species in four countries to answer three questions: (1) How much variation in Cl− tolerance is present among populations? (2) What factors predict intraspecific variation in Cl− tolerance? (3) Must we account for intraspecific variation to accurately predict community Cl− tolerance? We conducted field mesocosm experiments at 16 sites and compiled acute LC50s from published laboratory studies. We found high variation in LC50s for Cl− tolerance in multiple species, which, in the experiment, was only explained by zooplankton community composition. Variation in species‐LC50 was high enough that at 45% of lakes, community response was not predictable based on species tolerances measured at other sites. This suggests that water quality guidelines should be based on multiple populations and communities to account for large intraspecific variation in Cl− tolerance. [ABSTRACT FROM AUTHOR]

G. Evelyn Hutchinson proposed that external control by climate limits the fundamental productivity and the possible diversity of ecological communities. These climatic drivers are currently changing as a result of human activity, which may herald a shift in the influence of climate on global ecosystems. Long-term records reveal a reduction in ice cover on northern lakes over the last several centuries. Hence, we explore whether inter-annual climatic variability, represented by ice cover, influences the productivity and diversity of zooplankton communities in long-term datasets for five lakes in Northern Wisconsin. We used a multilevel modeling approach to test three predictions: (1) density will increase, (2) diversity will increase, and (3) community composition will be altered. We found an inverse relationship between ice-off date and annual zooplankton density. Daphnia density, for example, was inversely related to ice-off date, with 10-fold variability across the gradient of ice-off dates in Northern Wisconsin. In contrast, we did not observe a consistent shift in diversity or community structure. Thus, from ice cover records of northern lakes we found support for Hutchinson’s idea that external climatic forces may regulate aquatic productivity; however, the response was numeric and we did not find evidence that lakes moved closer to maximum diversity on an inter-annual scale. [ABSTRACT FROM AUTHOR]

The role that climate plays in determining the temporal dynamics of freshwater zooplankton is poorly understood, despite its potential to synchronize population dynamics on a regional basis. We quantify the spatial synchrony of common zooplankton taxa among lakes in the Dorset, Ontario, area and investigate the climatic mechanisms responsible for these patterns at both annual and seasonal scales. We show that the dynamics of several taxa are characterized by similar patterns of abundance among lakes across the region, suggesting a synchronising effect of climate on zooplankton population abundances. Using multiple regression analyses to compare zooplankton dynamics with climatic and in-lake variables, we find that El Niño – Southern Oscillation (ENSO) events and ice cover variability are among the most important predictors of synchrony at annual and seasonal scales, particularly for Leptodiaptomus and Bosmina. Leptodiaptomus, a dominant herbivore in these lakes, had decreased abundances in years with earlier ice-off dates and shorter periods of ice cover. Secchi depth was also synchronous and appeared to respond to regional meteorological factors (spring temperature and precipitation, ice duration). A warming climate with the ability to modify ice and ENSO dynamics, as well as temperature and precipitation patterns, may also alter the structure and dynamics of zooplankton communities in north-temperate lakes. [ABSTRACT FROM AUTHOR]

Presents information on a study of the temporal coherence of annual abundances among populations of freshwater zooplankton in lakes in Ontario, Canada. Use of the intraclass correlation coefficient; Implications of the correlations; Identification of homogeneous and temporally coherent subsets of lakes for each species.