Decadal patterns of anthropogenic salinisation in typical mountain streams in northeastern China: Increased rates and sources

Freshwater salinisation: unravelling causes, adaptive mechanisms, ecological impacts, and management strategies

Freshwater salinisation is a growing problem worldwide, affecting surface and groundwater resources. Compared with other global environmental issues, freshwater salinisation has been studied extensively in North America, Australia, and Europe but less so in South America, Asia, and Africa. Both the natural and anthropogenic sources can contribute for freshwater salinisation, through the concentration of dissolved salts in water rising above its normal levels. This review provides a comprehensive assessment of the causes of freshwater salinisation, the impacts on freshwater communities and ecosystem functions, the adaptive mechanisms for survival in an increasingly saline environment, and the management strategies available to control freshwater salinisation. Many human activities contribute to freshwater salinisation, including road salt use, agricultural practices, resource extraction, reservoir construction, and climate change. Aquatic organisms have evolved mechanisms to survive in increasingly saline environments, but excessive salinity can lead to mortality and non-lethal effects. Such effects can have cascading impacts on the structure and function of aquatic communities and ecosystem services. Therefore, monitoring programmes and chemical fingerprinting are needed to identify highly salinised areas, determine how various human activities contribute to freshwater salinisation, and implement management strategies. Furthermore, current research on freshwater salinisation has been limited to a few regions of the world. It is essential to expand the research further into exploring the impacts of salinisation on freshwater resources in unexplored geographic areas of the world that are mainly impacted by climate change scenarios.

Increasing anthropogenic salinisation leads to declines in community diversity, functional diversity and trophic links in mountain streams

Anthropogenic salinisation is becoming an increasing global issue for freshwater ecosystems, leading to serious biodiversity loss and ecosystem degradation. While the effect of anthropogenic salinisation on freshwater ecosystems has been intensively studied in recent years, most studies focus on salinisation effects on the individual or single groups of organisms without considering the effect on the ecosystem levels, such as diversity and trophic links. Therefore, we conducted a long-term field survey from May 2009 to August 2016 at 405 sites in northeast China to investigate the effect of a gradient of salinisation on community diversity, functional diversity and trophic links in mountain streams. Samples of water chemistry, periphyton, macroinvertebrates and fish were collected. Our results showed that as anthropogenic salinisation increased, Ca²⁺, Mg²⁺, HCO₃^- and SO₄^2- exhibited significant increases (p < 0.05). These increased ions caused decreases in taxonomic evenness and biotic integrity, but an increase in the beta diversity for periphyton and macroinvertebrates, and a slight increase in the evenness of fish. The increased salinisation resulted in the extirpation of salt-sensitive taxa and declines in macroinvertebrate functional richness and functional redundancy, which consequently led to simplified trophic links. Our results implied that if salt-tolerant taxa in high salinisation sites were not functionally redundant with less tolerant taxa, alterations of their functional composition probably decrease the stability of ecosystem functions. Overall, our study suggests that the ongoing anthropogenic salinisation is posing serious threats to biodiversity and trophic links in river ecosystems, and should be considered in future river restoration and biodiversity conservation.