Nutrient Exchange in Western Long Island Sound through the Highly Urbanized East River Tidal Strait

Hypoxia reoccurs annually between June and September in the western and central regions of Long Island Sound (LIS), an urban estuary located off the US east coast. It has been long assumed that a major cause of the hypoxia is eutrophication from large New York City wastewater inputs, but new results suggest that this may not be the driving factor. While it is known that some nutrients are imported into WLIS through the East River Tidal Strait, the net exchange at this boundary remains unknown, though it is critically needed information in the management of LIS hypoxia. Furthermore, inputs from other boundaries (e.g. rivers, atmosphere, central LIS) are also important factors for nutrient loading. To constrain the exchange between WLIS and the East River, water samples were collected during 4 transects at a cross-section of WLIS in the spring, summer and winter (high and low river flow conditions) to resolve temporal variability of carbon, nitrogen, and phosphorous constituents over a complete tidal cycle. By pairing these measurements with water current data collected from an Acoustic Doppler Current Profiler, a variety of regimes were identified. This high-resolution pairing of physical and chemical observations to constrain nutrient fluxes is transferable to other estuaries.