An enzymatic mechanism on sediment N and P release in arid-region lakes under various saline conditions

Arid-region lakes are facing complex water management challenges due to interactive effects of nutrient pollution and salinity variations. However, the effects of salinity gradients on sediment extracellular enzyme activities and nutrient release dynamics remain unclear. This study investigated sediment alkaline phosphatase (APA) and urease (UA) activities, along with soluble reactive phosphorus (SRP) and ammonium fluxes at the sediment-water interface, across three lakes spanning freshwater to brackish conditions in the arid region of Central Asia. Results showed that sediment APA was significantly inhibited by combined effects of high salinity and SRP concentrations. Conversely, sediment UA demonstrated negligible sensitivity to salinity variations, being primarily regulated by sediment organic matter content. Nutrient release from sediments in freshwater lake (Lake Bosten) were significantly higher than in brackish lakes (Lake Sayram and Lake Ulungur). While the involvement of other environmental factors cannot be ruled out, our findings suggest that high salinity may limit sediment nutrient release, potentially through inhibiting enzyme activity or affecting ion exchange. Consequently, the ongoing climatic wetting trend in arid Xinjiang could potentially lead to a reduction in lake salinity, which might consequently promote the release of nutrients from sediments. Hence, heightened vigilance against the potential adverse environmental impacts on these lakes is warranted.