Consequences of an ecosystem state shift for nitrogen cycling in a desert stream

Cessation of cattle grazing has resulted in the reestablishment wetlands some streams U.S. Southwest. Decades prevented vascular plant growth Sycamore Creek (Arizona, U.S.A.), resulting stream reaches dominated by diatoms and filamentous green algae. Establishment plants can profoundly modify ecosystem processes; yet, effects on nitrogen (N) cycling remain unexplored. We examined consequences this state shift N N-limited desert stream. compared results from whole-reach ammonium-N stable isotope (15NH4+) tracer additions conducted before (pre-wetland state) 13 yr after (wetland free-range removal watershed. Water column estimations showed that in-stream uptake storage were higher pre-wetland than wetland state. turnover was also state, indicating assimilated retained for shorter time biomass. In addition, mostly driven assimilatory regardless considered. trends mechanistically explained fact dominant primary compartments (i.e., algae diatoms) had rates those plants). Overall, show composition dominance producers induced cessation within stream-riparian corridor changes processing a intense fast recycling to prevalence retention biomass producers.