Abstract
Human appropriation of water resources may induce water stress in freshwater ecosystems when ecosystem needs are not met. Intensive abstraction and regulation cause river ecosystems to shift towards non-natural flow regimes, which might have implications for their water quality, biological structure and functioning. We performed a meta-analysis of published studies to assess the potential effects of water stress on nutrients, microcontaminants, biological communities (bacteria, algae, invertebrates and fish), and ecosystem functions (organic matter breakdown, gross primary production and respiration). Despite the different nature of the flow regime changes, our meta-analysis showed significant effects of human-driven water stress, such as significant increases in algal biomass and metabolism and reduced invertebrate richness, abundance and density and organic matter decomposition. Water stress also significantly decreased phosphate concentration and increased the concentration of pharmaceutical compounds. The magnitude of significant effects was dependent on climate, rainfall regime, period of the year, river size and type of water stress. Among the different causes of water stress, flow regulation by dams produced the strongest effects, followed by water abstraction and channelization.
Highlights
The use of water resources is one of the strongest manifestations of nature-human cross-linkages[1] and is likely to increase due to the rising human population, climate change and land use changes[2]
Most of the collected data were obtained in summer (34.4%), a large amount consisted of annual records
Most of the data were from nutrient-poor systems (59.5%) and the majority was not affected by waste water treatment plants (WWTP) effluents (95%)
Summary
The use of water resources is one of the strongest manifestations of nature-human cross-linkages[1] and is likely to increase due to the rising human population, climate change and land use changes[2]. In these situations, altered flow regimes subsequently affect water quality and biodiversity This human-driven water stress (HDWS) differs from naturally-occurring water stress of intermittent or temporary rivers, which characteristically show a decreased or interrupted flow for given period(s) of the year[10]. Natural flow decrease or cessation in temporary rivers follows characteristic spatial patterns depending on the intensity of the dry period[16], whereas changes in the flow regimes produced by HDWS. The concentration of nutrients and pollutants may follow particular patterns[25,26], with reduced peak flows affecting in-stream habitats and sediment transport[17,27,28] This could in turn affect the composition, abundance and diversity of biological communities, the common directions of these effects are still unclear[29,30,31]. This variability might be due to the described environmental conditions and to the few cases described in most papers that make the intensity and prevalence of effects difficult to generalise
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