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

Abstract

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)], NO 3 : SRP, and NO 3 : NH 4 C 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.

Riparian Corridors: A New Conceptual Framework for Assessing Nitrogen Buffering Across Biomes

“…Based on existing published data, we forecast that denitrification is not significant in riparian zones along low stream order streams under Mediterranean, arid or arctic climate due to low water availability and/or short residence time of water and solutes (Jones et al, 2005;Bernal et al, 2007;Mu et al, 2017;Poblador et al, 2017). Therefore, we forecast that in Mediterranean and arid regions, denitrification rates are consistently low compared to more humid catchments (Holmes et al, 1996;Bernal et al, 2007;Harms and Grimm, 2010;Lupon et al, 2015;Poblador et al, 2017). Yet, the capacity for denitrification can rapidly increase once waterlogged conditions develop in riparian zones (Harms et al, 2009).…”

Responses of trace gases to hydrologic pulses in desert floodplains

“…Thus, inter‐annual variation in sediment delivery to floodplains may contribute to longer‐term patterns in emission of trace gases from desert floodplains. However, peak annual soil microbial biomass occurs during the monsoon season [ Harms and Grimm , 2008], and biomass is positively related to accumulated precipitation [ Harms and Grimm , 2010], suggesting that the substrate‐limitation mechanism does not explain seasonal‐scale patterns.…”

“…Relationships between emissions of CO 2 , CH 4 , and NO from floodplains of the San Pedro River and multiple attributes of the hydrologic cycle illustrate strong interactions of the hydrologic cycle and the biogeochemical processes that produce these gases. Because desert floodplains undergo seasonal and inter‐annual shifts in biogeochemical dynamics due to dominant climate drivers [ Harms and Grimm , 2010], observations from these ecosystems may be used to anticipate general ecosystem responses to altered hydrologic regimes. In particular, droughts are expected to interact with the size of subsequent storms or floods to stimulate microbial processes that turn over soil C and N or generate abiotic conditions conducive to gaseous efflux, resulting in elevated emissions of gaseous C and NO following larger hydrologic pulses.…”

“…Desert floodplains receive hydrologic pulses that vary in size and frequency [ Harms and Grimm , 2010; Jacobs et al , 2007]. Precipitation inputs to floodplains provide small pulses of variable frequency, whereas floods are large inputs of water that may also vary in frequency, but are generally constrained to time periods of highest precipitation.…”

Red Swamp Crawfish (Procambarus clarkii) Discovered in the San Pedro River, Arizona: A New Invader in a Threatened Ecosystem

“…A section of the river and its riparian zone was protected as the San Pedro Riparian Natural Conservation Area, which is critical habitat for riparian vegetation and migratory songbirds (Skagen et al, 1998;Stromberg et al, 2006). While the riparian zone of the San Pedro River has been well studied, studies in the river itself are limited largely to biogeochemical dynamics (e.g., Meixner et al, 2007;Harms and Grimm, 2010). The river hosts a large population of non-native virile crayfish, in addition to the non-native black bullhead catfish (Ameiurus melas), channel catfish (Ictalurus punctatus), flathead catfish (Pylodictis olivarus), western mosquitofish (Gambusia affinis), green sunfish (Lepomis cyanellus), common carp (Cyprinus carpio), and American bullfrog (Lithobates catesbeianus; United States Geological Survey, http://nas.…”