Stream ecosystems can be sensitive to watershed urbanization, but less is known about how streams respond to urbanization in semi-arid cities. To characterize how urbanization and altered salinity regimes affect stream chemistry and microbial activity, I conducted (1) a mesocosm experiment to investigate how press versus pulse salinity regimes altered biogeochemical cycles in stream sediments and (2) a field survey of streams in Reno, Nevada. The mesocosm experiment results revealed that the press salinity regime caused the greatest fluxes in ammonium and potassium from exposed stream sediments, while microbial activity rates were not affected. Results from the field survey demonstrated that the heterogenous underlying lithology of Reno imparted a stronger signal on stream chemistry than watershed urbanization in paired sites. The results of this work characterize the wide temporal and spatial variability in how stream chemistry and microbial activity respond to urbanization and altered salinity regimes in a semi-arid city
