Influence of the hydrologic regime on resource availability in a semi-arid stream-riparian corridor

The hydrologic regime of an ecosystem directly affects ecological processes by controlling water availability, but may also have indirect effects by influencing resource availability. To clarify interactions between the hydrologic regime and resource availability, we quantified the timescales over which precipitation and discharge correlated with abundance of dissolved carbon, nitrogen, and phosphorus in the stream-riparian corridor of the San Pedro River, a large desert river. We hypothesized that the hydrologic regime drives regimes of resource availability during flushing events caused by variation in source areas of run-off generation. We also hypothesized that seasonal droughts may result in accumulation of resources within the catchment. Such accumulations would contribute to high solute concentrations in receiving waters following dry periods. To test these hypotheses, we compiled seasonal datasets over 4-6 years and used regression analyses to determine the temporal extents at which solute concentrations and transformations were correlated with precipitation and stream discharge. Concentrations of most biologically reactive solutes were unrelated to precipitation or discharge, suggesting overlapping influences of myriad biological and transport processes probably operating on event or shorter timescales. Concentration of phosphate [soluble reactive phosphate (SRP)], NO₃^-: SRP, and NO₃^-: NH₄⁺ in the stream were positively correlated with precipitation abundance over weeks and up to 2 months, supporting the flushing hypothesis. Microbial processes in floodplain soils responded to precipitation and discharge, suggesting that biological processes may mediate relationships between hydrology and resource availability. In this large, semi-arid catchment, resource availability is linked to hydrology via hydrologic transport, flowpath characteristics, and biotic processing.