The pattern of water flow in a river can affect the abundance of plants and animals and the food web that supports fisheries. Severe floods that scour the riverbed can potentially displace or kill plants and animals, however, little is known about how floods (or droughts) or the timing of these across years affects the complexity and diversity of food webs. Some work suggests that river flow is a stronger determinant than the quantity of plant production on the flow of energy through the food web, but little is known about how the quality of plant food affects food chains and biodiversity. The study will provide fundamental information on how the timing of floods and droughts across years influences water quality (nitrate inputs to rivers), primary production, and the production of animals higher in the food web, such as fish. The researchers will produce a synthesis of research in hydrology and ecology to improve the management of arid land rivers. This work will reach across fundamental knowledge to education, from kindergarten to graduate levels. The project will have numerous broader impacts including training of several undergraduates, graduate students, and a postdoc. Researchers will work with a non-profit group to integrate project findings into an existing citizen science program on river drying sponsored by The Nature Conservancy, and develop an environmental education program for grades K-5. Finally, the research team will establish an innovative open source, distributed graduate seminar on application of statistical methods in ecology.

Researchers will study streams spanning a gradient in the timing of rainfall to examine the role of changing hydrologic regimes in altering nitrogen supply, energy supply and food web structure in arid land streams. This proposal will: 1) Quantify the effect of food quality, energy supply and energetic efficiencies on trophic structure, 2) Quantify the effects of time between floods on stimulation of plant production and trophic structure, and 3) Quantify the effect of changes in flow regime on trophic structure via direct mortality, shifts in plants at the base of the food web, and the structure of the food web. Proposed research activities include characterization of the hydrologic regime, analysis of food webs across a hydroclimate gradient, and manipulation of nitrogen supply. Extreme event statistics and spectral analyses will characterize properties of flood intervals and flow regime shifts across 12 study sites spanning a gradient in timing of rainfall and hydrologic variation (monsoon vs. winter precipitation dominance) in Arizona. Derived hydrologic metrics will be used in combination with measures of ecosystem metabolism, N supply, secondary consumer energetic efficiencies, resource stoichiometry, and the proportion of autochthonous energy sources as predictor variables of food chain length and trophic structure to understand the mechanisms linking energetics and hydrology to food chain length. This comparative study includes 12 streams within the same biogeographic province that feature an algal-dominated food source and similar ecosystem size (1st-3rd order streams). Additionally researchers will conduct a nitrogen enrichment experiment in 6 streams to disentangle the indirect effects of water flow on nitrogen cycling versus the direct effects on plants and animals.