Quantifying ecological responses to amplified water level fluctuations in standing waters: an experimental approach.
Abstract
Global freshwater demand is increasing dramatically, with water withdrawal rates more than tripling in the last five decades. Consequently, alteration of water level regimes, particularly in the form of amplified water level fluctuations (WLF), is rapidly becoming one of the major disturbances of aquatic ecosystems globally. However, even though the impacts of WLF are likely to be strongest in littoral zones, little is known about their effects on the structure and functioning of littoral assemblages in standing water systems. We established an experiment in large outdoor pond mesocosms to examine the effects of WLF on littoral assemblages and explore the potential for development of ecological indicators of WLF. Water level fluctuations reduced benthic algal biomass and the density and taxonomic distinctness of benthic invertebrate assemblages. Both the taxonomic and trophic structure of benthic assemblages were altered significantly in ponds with WLF and homogenized along the depth gradient. Synthesis and applications. Our results indicate that water level fluctuations (WLF) can reduce considerably the productivity and biological diversity of lake littoral zones. Given that the problem is likely to be exacerbated by predicted increases in climatic variability and enhanced demand for water and hydropower, our findings have important implications for the conservation and management of global aquatic biodiversity. We identified several specific ways that WLF modify littoral assemblages along the depth gradient. This ability to identify separate pressures is an important requirement of robust ecological assessment tools. This study confers potential for development of ecological indicators of WLF in standing waters, provides indication of sampling strategies to be employed and demonstrates the need to mitigate the most extreme water withdrawals. Our results indicate that water level fluctuations (WLF) can reduce considerably the productivity and biological diversity of lake littoral zones. Given that the problem is likely to be exacerbated by predicted increases in climatic variability and enhanced demand for water and hydropower, our findings have important implications for the conservation and management of global aquatic biodiversity. We identified several specific ways that WLF modify littoral assemblages along the depth gradient. This ability to identify separate pressures is an important requirement of robust ecological assessment tools. This study confers potential for development of ecological indicators of WLF in standing waters, provides indication of sampling strategies to be employed and demonstrates the need to mitigate the most extreme water withdrawals.