Watersheds are dynamic. Consequently, answers to critical science questions about watersheds require observations of watershed characteristics and depend on developing new engineering capabilities to sample data at high temporal frequency and spatial density; to assess the optimal frequency and density of sampling; and to analyze those data for the improvement of mechanistic understanding of processes. Examples of fundamental timedependent characteristics of watersheds that require improved sampling and analytical capabilities include the magnitude of mass of water, nutrients, sediments, and energy in stores; the residence time in the stores; fluxes between the stores; and flowpaths among the stores. This proposed work develops new engineering approaches to address science questions about the spatial and temporal variability of regulators of nitrate load in watersheds; how geologic setting, land use and terrain influence loading and delivery dynamics; the relationship between flow mixtures and nitrate loads; and the feasibility of using surrogate measures for estimating basin scale nitrate dynamics in space and time. The engineering approaches are two-pronged. (1) Commercially available nitrate, conductivity, temperature, and pressure sensors will be installed in an array that will sample at sub-daily frequencies and communicate via cell phone technology in real time to a central computer. (2) Existing data will be used to develop a probabilistic algorithm based on information theory to identify minimum spatial and temporal spacing of sampling necessary to reduce uncertainty to a prescribed level; this algorithm will be validated with the newly collected data. The study site is the Santa Fe River watershed in north-central Florida. The Santa Fe River is a major tributary to the Suwannee River which has been cited as a potential location for CUAHSI-CLEANER WATer and Environmental Research Systems Network. The Santa Fe River has similar characteristics to the Suwannee River Basin, but at a smaller scale, making it an ideal test-bed for developing new sampling and analytical capabilities required to advance watershed science and engineering. Both rivers cross the Cody escarpment, which marks the boundary between geologically confined and unconfined portions of the Floridan aquifer, and the change from a surface water to ground water dominated system. The entire region is undergoing a transition from minimal anthropogenic impact to multiple stressors from land-use practices including population increase and consumptive use, proposed water diversions, and accelerating development making predictive basin-scale science essential. Broader Impacts. Development of the sensor network and probabilistic algorithm represent a good initial test at a small scale of how to develop water and environmental research networks. The communication ports will be configured for testing of any newly developed or off-the-shelf sensors, and outside users will be welcome to test instrumentation at these sites. The probabilistic algorithms to be developed as part of the work will be sufficiently generic that they will be useful for planning sensor deployments in any watershed. This generic characteristic will make them useful for analyses of the uncertainty of predictability of variables in addition to nitrate. Human resources will be impacted through support of two PhD-level graduate students (and a post doctoral researcher). Data collected and collated for the work will be archived in an ArcHydro geodatabase to be made available to non-local researchers. These data will also be demonstrated for use in AP Environmental Science classes at the high school level, Environmental Science and Hydrologic courses at the college level, and as a an interactive exhibit at the Florida Museum of Natural History in Gainesville.
