SEDIMENT GRAIN SIZE ANALYSIS IN LONG ISLAND MARSH CORES

Hofstra University’s Fall 2019 Sedimentation class embarked on a project to corroborate the results of a study initiated by The Nature Conservancy (TNC), in partnership with Northwell Health, to use medical imaging to evaluate saltmarsh health and assess how excess nitrogen pollution affects root growth and subsequent marsh architecture. TNC is using computer-aided tomography (CT) to measure the saltmarshes’ initial condition and long-term response to a dramatic water quality improvement project planned in western Hempstead Bay, NY. Chronic nutrient loading is known to impact the way that marsh grasses grow, and compromise the integrity of marsh peat. The main source of nutrients to western Hempstead Bay is slated to be “shut off” through treatment upgrades and connection to an ocean outfall. Saltmarsh cores from high marsh and low marsh habitats in four marshes were imaged by CT at a rapid and high-resolution approach to quantify roots, rhizomes, peat, and soil particle densities. Hofstra’s Sedimentation class conducted a traditional sieve analysis of the coarse fraction of the cores to evaluate the CT scan results. Marshes in the study include two that will experience dramatic water quality improvements from the planned water quality restoration project (Lawrence and North Greensedge Marshes); a high nutrient control (Pelham Bay Cove) and a low nutrient control (Bass Creek). We decided as a class to analyze the Lawrence Marsh cores because that site is suspected to be the most affected by the nearby water treatment facility (in East Rockaway), and the Bass Creek cores because it is a protected marshland exposed to lower levels of nitrogen and serving as our low nutrient control. This study has confirmed the validity of this sediment analysis method by affirming the presence of higher concentrations of sand where they were suggested in the cores by the CT scans.