Water Resources Research Act Program

Details for Project ID 2018LA120B

Ecological Consequences of Low-Level Sodium Inputs in Riparian Zones on Decomposition Processes and Inputs to Freshwater Ecosystems

Institute: Louisiana
Year Established: 2018 Start Date: 2018-03-01 End Date: 2019-02-28
Total Federal Funds: $11,000 Total Non-Federal Funds: $25,855

Principal Investigators: Natalie Clay, Sally Entrekin, Michelle Evans-White

Abstract: Rising salinity in soils and freshwater is a global problem that threatens both agriculture and riparian and stream ecosystems. The effects of toxic levels of sodium are fairly well understood, but we know little about how low-level increases in salinization impact riparian and stream ecosystems and communities therein. High-pulse or press sodium additions have led to desertification in terrestrial ecosystems and loss of diversity and ecosystem function in aquatic ecosystems. High-level increases in salts in freshwater are common, particularly where road salting is widespread, but low-level, sub-lethal increases in sodium may be more prevalent, yet less understood. Agriculture is a major nonpoint source contributor for sodium to riparian and aquatic ecosystems. Increased salinity of ground and surface water can then cause a positive feedback on the salinity of water available to agriculture for irrigation when irrigation water is pulled from these sources. Specifically, increased salinization of irrigation water reduces yield, increases desertification, and further contributes to the rising sodium in adjacent riparian and stream ecosystems. However, impacts of low-level increases are less understood. Riparian ecosystems adjacent to agriculture serve as the main interface between processes like runoff and salinization from agriculture to stream ecosystems. Although increased salinization in freshwater ecosystems typically leads to decreased productivity and detritivore diversity, increased sodium in terrestrial ecosystems can have a stimulatory effect on plant consumers. However, whether this occurs in riparian ecosystems and how it impacts inputs from riparian zones to streams remains unknown. This project will test three main pathways by which low-level sodium additions to riparian systems could impact water quality. 1) Increased salt deposition in riparian soils will increase sodium in freshwater through runoff. 2) Increased salt in riparian soils will stimulate decomposer community activity thereby increasing breakdown of litter and increasing dissolved organic matter in freshwater resulting in lowered water quality. 3) Increased salt in riparian soils will lead to increased riparian vegetation uptake of salt. Increased concentrations of salts in leaves will stimulate decomposer activity and result in increased dissolved organic matter in stream ecosystems. This project will use riparian soil mesocosms to determine how nonpoint source sodium increases like those from agriculture can impact processes in riparian ecosystems that influence water quality. Specifically, this project will measure sodium and dissolved organic carbon content of leachate from riparian soil mesocosms after 3 months to determine how slight to moderate risk of causing detrimental soil salinization NaCl irrigation water levels (0.5 g/l) impact water quality. This project will quantify the impacts of each of the above three pathways using mesocosms. This project will thus provide valuable information on how low-level increases in sodium impact riparian ecosystems, some of the most threatened ecosystems, and the subsequent impacts on water quality driven by processes at the riparian-stream interface. Understanding impacts of low-level sodium increases is essential as demand for freshwater resources increase for both human consumption and agriculture.