THE DEVELOPMENT OF AN INSTRUMENT TO MEASURE THE FLOW RATE AND NUTRIENT FLUX OF GROUNDWATER INTO COASTAL WATERS

Many coastal waters are receiving high loads of nutrients from anthropogenically-impacted groundwater that upwells in the intertidal zone. The temporal variability of submarine groundwater discharge (SGD)-derived nutrient flux is poorly understood and mostly likely large. To address this issue, we are developing and testing an automated sampler/analyzer for determining the nutrient composition and flux of groundwater entering coastal and estuarine regions. The sensing instrument consists of a battery-powered and programmable WS Ocean Systems, Inc. nutrient analyzer that is capable of time-series measurements over a period of days to weeks. The sampling port of this instrument can be connected to seepage meters and/or piezometers embedded in the intertidal sands, allowing for the nutrient analysis of SGD and interstitial waters. We have modified the instrument to inject food dye into a chamber that receives the flow of water from a seepage meter. The flow rate of SGD can be determined by using the optical spectrometer in the nutrient analyzer, which follows the dilution of the injected dye with time.