Toward predicting climate change effects on lakes: a comparison of 1656 shallow lakes from Florida and Denmark reveals substantial differences in nutrient dynamics, metabolism, trophic structure, and top-down control

Abstract

Rapid climate changes may potentially have strong impacts on the ecosystem structure and nutrient dynamics of lakes as well as implications for water quality. We used a space-for-time approach to elucidate such possible effects by comparing data from 1656 shallow lakes (mean depth <3 m) in north temperate Denmark (DK) and subtropical Florida (FL). The lakes were categorized into 7 total phosphorus (TP) classes within the range of 2 to 300 µg L −1. Physicochemical variables showed significant seasonal differences, which can be attributed to different sunlight regimes and temperatures. The FL lakes had overall higher fish biomasses (notably in the littoral zone) but a substantially lower zooplankton biomass and body mass of microcrustaceans, a much lower zooplankton:phytoplankton biomass ratio (lower grazing on phytoplankton), and a markedly lower biomass of benthic invertebrates, indicating much greater control of consumers by fish in the FL lakes. Accordingly, the summer phytoplankton biomass was higher in the FL lakes. Cyanobacteria in summer were proportionally more important in the FL lakes at all TP levels, whereas the proportion of dinophytes, chrysophytes, and cryptophytes was higher in the DK lakes at low TP. Submerged macrophytes occurred at higher TP (>100 µg L −1) in the FL lakes, but coverage was higher in the DK lakes at low TP. We also found lower oxygen saturation in the nutrient-rich FL lakes than in the DK lakes, suggesting lower net ecosystem production in the FL lakes. We discuss our results within the framework of climate warming.

Changes in Pelagic Fish Community Composition, Abundance, and Biomass along a Productivity Gradient in Subtropical Lakes

“…We found that species richness was significantly linearly related to lake productivity (expressed as Chla), which is in accordance with several studies from the temperate climate zone [7,39,40]. The relationship between species richness and environmental factors has been well studied in Europe [3,7,10,16,41,42]. Our results differ from those of [3], which showed a unimodal relationship with TP, and those of Helminen et al (2000) [43], which revealed a reduction in species number in eutrophic Finnish lakes that was attributed to oxygen deficiency.…”

Model‐based decomposition of environmental, spatial and species‐interaction effects on the community structure of common fish species in 772 European lakes

“…Other studies on freshwater invertebrates across large spatial scales suggest that, in addition to spatial factors, climatic gradients (e.g., temperature, precipitation) and ecosystem size are dominant predictors of species richness, community composition and average organismal size in lakes (Hayden et al., 2019; Meerhoff et al, 2012). Studies on processes of community assembly for fishes in freshwater lakes likewise identified dominant roles of abiotic filtering at large spatial scales (Brucet et al., 2013; Emmrich et al., 2014; Jeppesen et al., 2020). Fish population densities and population size structure are modified primarily by productivity of the ecosystems (Arranz et al., 2016; Brucet et al., 2013), and dispersal limitation of small fish species can affect local fish species occurrences (Mehner et al., 2014; Olden et al., 2001).…”

Brian Moss: the wizard of shallow lakes

“…He frequently told us that 'this Florida-Denmark comparison is really good stuff for understanding climate change effects on lakes-get it published!' It took a while, but now it is done (Jeppesen et al 2020), and we are very happy to be able to publish it in a special issue celebrating his legacy." Meryem Beklioğlu wrote: "As a young MSc graduate awarded a PhD scholarship from the Turkish government, I was searching for a supervisor to carry out my PhD on freshwater ecology but had no background and no idea who to study with.…”