Is Recovery of Large-Bodied Zooplankton after Nutrient Loading Reduction Hampered by Climate Warming? A Long-Term Study of Shallow Hypertrophic Lake Søbygaard, Denmark

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A two-decade (1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) time series of lake phyto-and zooplankton, water characteristics and climate in 17 Danish lakes was analysed to examine the long term changes and the effects of lake restoration efforts. The analyses of the pair-wise correlations across time series revealed a strong synchrony in climatic variables among the lakes. A significant, but weak increase in air temperature was observed and resulted in a corresponding increase in surface water temperature only in summer. Lake physico-chemical variables had weaker synchrony than climatic variables. Synchrony in water temperature and stratification was stronger than lake chemistry as the former is mostly affected by atmospheric energy flux. Synchrony in the taxonomic richness of the plankton groups and phytoplankton biomass was apparent, to a similar degree as observed for lake chemistry. The synchrony and the temporal trends in lake chemistry and plankton were more pronounced for the lakes with strong re-oligotrophication. Phytoplankton biomass decreased and plankton richness increased in these lakes, with a shift from Chlorophyta dominance towards more heterogeneous phytoplankton communities. Notably, a widespread significant positive trend in plankton richness was observed not only in lakes with strong re-oligotrophication but across all lakes. The widespread increase in plankton richness coincided with widespread decrease in phosphate and total nitrogen concentrations, as well as with the trends in climate indicating a likely joint effect of nutrient reduction and climate in driving lake plankton. However, temporal changes and synchrony as well as the recovery of richness and composition of lake plankton more coherently corresponded with the nutrient loading reduction across the Danish landscape, while the role of climate control of the lake plankton was less pronounced.

Section: Discussionsupporting

confidence: 86%

Long-Term Trends and Temporal Synchrony in Plankton Richness, Diversity and Biomass Driven by Re-Oligotrophication and Climate across 17 Danish Lakes

Özkan

Davidson

Bjerring

et al. 2016

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“…The nutrient loading reduction scenarios projected increased diatom dominance accompanied by an increase in the zooplankton/phytoplankton biomass ratio. As in [15], a higher proportion of small fish and enhanced fish predation with increasing warming were revealed. The simulations generally showed phytoplankton to benefit from a warmer climate and the fraction of cyanobacteria to increase and that a higher external loading reduction is necessary in a future warmer world to maintain the present ecological state.…”

Section: Temperate Climate Zonementioning

confidence: 85%

“…This was shown in an analysis of a comprehensive 23-year long data series from shallow Danish Lake Søbygård, which is in recovery after a major nutrient loading reduction [15]. Focus in this study was on changes in zooplankton.…”

Section: Temperate Climate Zonementioning

confidence: 92%

Lake Restoration and Management in a Climate Change Perspective: An Introduction

Jeppesen

Søndergaard

Liu

2017

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Lakes all around the globe are under severe pressure due to an increasing anthropogenic impact from a growing population in a more developed world. Accordingly, today, many lakes are highly eutrophic and suffer from severe blooms of often toxic cyanobacteria and may become even more eutrophic in the future unless strong lake management actions are taken. Recent research has further shown that global warming and subsequent changes in water use will further exacerbate the eutrophication process in lakes. There is therefore a growing demand for lake restoration and insight into sustainable lake management. The measures to be taken, however, depend on the climate and other local conditions. This special issue addresses lake restoration and management with special emphasis on the restoration of eutrophicated lakes within a climate change perspective. The papers included collectively highlight that the ongoing climate change affects lake water quality by (1) changes in external and internal nutrient loading; (2) higher frequency of extreme events (such as hurricanes); (3) temperature-induced changes in biota, biotic interactions; and (4) water level. Lower nutrient loading is therefore needed in a future warmer world to achieve the same ecological state as today. Several papers discuss lake restoration methods within a climate change perspective and show practical results, notably of various attempts of biomanipulation. Finally, some papers discuss the effects of other anthropogenic stressors and their interaction with climate.

“…With the increasing proportion of juveniles in the plankti-benthivorous fish population with rising temperatures, higher levels of fish zooplanktivory are to be expected, subsequently resulting in lower zooplankton:phytoplankton biomass ratios [10,67,68] as seen at high nutrient loading in the PCLake simulations. The recent data from the lake has shown an increase in the proportion of small fish, attributed to a higher temperature and a reduction in zooplankton size, but no decline in the zooplankton: chl.-a ratio [7]. Contradicting cross-latitude studies [69,70], the PCLake simulations show total fish biomass to decline with rising temperatures.…”

Section: Effects Of Increasing Temperatures and Reduced Nutrient Loadingmentioning

confidence: 97%

“…Cross-latitude studies have shown fish to play an essential structuring role, in particular in shallow lakes. In a warmer climate, small individuals tend to dominate the fish community and predation pressure on zooplankton increases [6,7]. This results in a lower zooplankton biomass and an increasing proportion of benthi-omnivorous fish and consequently greater resuspension of the sediment [8].…”

Section: Introductionmentioning

confidence: 99%

Climate Change Will Make Recovery from Eutrophication More Difficult in Shallow Danish Lake Søbygaard

Rolighed

Søndergaard

Bjerring

et al. 2016

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Abstract:Complex lake ecosystem models can assist lake managers in developing management plans counteracting the eutrophication symptoms that are expected to be a result of climate change. We applied the ecological model PCLake based on 22 years of data from shallow, eutrophic Lake Søbygaard, Denmark and simulated multiple combinations of increasing temperatures (0-6 • C), reduced external nutrient loads (0%-98%) with and without internal phosphorus loading. Simulations suggest nitrogen to be the main limiting nutrient for primary production, reflecting ample phosphorus release from the sediment. The nutrient loading reduction scenarios predicted increased diatom dominance, accompanied by an increase in the zooplankton:phytoplankton biomass ratio. Simulations generally showed phytoplankton to benefit from a warmer climate and the fraction of cyanobacteria to increase. In the 6 • C warming scenario, a nutrient load reduction of as much as 60% would be required to achieve summer chlorophyll-a levels similar to those of the baseline scenario with present-day temperatures.