Design and demonstration of a distributed sensor array for predicting water flow and nitrate flux in the Santa Fe Basin

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0609968Graham Watersheds are dynamic. Consequently, answers to critical sciencequestions about watersheds require observations of watershed characteristics and depend ondeveloping new engineering capabilities to sample data at high temporal frequency and spatialdensity; to assess the optimal frequency and density of sampling; and to analyze those data for theimprovement of mechanistic understanding of processes. Examples of fundamental timedependentcharacteristics of watersheds that require improved sampling and analyticalcapabilities 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. Thisproposed work develops new engineering approaches to address science questions about thespatial 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 flowmixtures and nitrate loads; and the feasibility of using surrogate measures for estimating basinscale nitrate dynamics in space and time. The engineering approaches are two-pronged. (1)Commercially available nitrate, conductivity, temperature, and pressure sensors will be installedin an array that will sample at sub-daily frequencies and communicate via cell phone technologyin real time to a central computer. (2) Existing data will be used to develop a probabilisticalgorithm based on information theory to identify minimum spatial and temporal spacing ofsampling necessary to reduce uncertainty to a prescribed level; this algorithm will be validatedwith the newly collected data.The study site is the Santa Fe River watershed in north-central Florida. The Santa FeRiver is a major tributary to the Suwannee River which has been cited as a potential location forCUAHSI-CLEANER WATer and Environmental Research Systems Network. The Santa FeRiver has similar characteristics to the Suwannee River Basin, but at a smaller scale, making it anideal test-bed for developing new sampling and analytical capabilities required to advancewatershed science and engineering. Both rivers cross the Cody escarpment, which marks theboundary between geologically confined and unconfined portions of the Floridan aquifer, and thechange from a surface water to ground water dominated system. The entire region is undergoinga transition from minimal anthropogenic impact to multiple stressors from land-use practicesincluding population increase and consumptive use, proposed water diversions, and acceleratingdevelopment making predictive basin-scale science essential.Broader Impacts. Development of the sensor network and probabilistic algorithm represent agood 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-shelfsensors, and outside users will be welcome to test instrumentation at these sites. The probabilisticalgorithms to be developed as part of the work will be sufficiently generic that they will be usefulfor planning sensor deployments in any watershed. This generic characteristic will make themuseful for analyses of the uncertainty of predictability of variables in addition to nitrate. Humanresources will be impacted through support of two PhD-level graduate students (and a postdoctoral researcher). Data collected and collated for the work will be archived in an ArcHydrogeodatabase to be made available to non-local researchers. These data will also be demonstratedfor use in AP Environmental Science classes at the high school level, Environmental Science andHydrologic courses at the college level, and as a an interactive exhibit at the Florida Museum ofNatural History in Gainesville.