Processed continuous resistivity profile data collected in Manhasset Bay on Long Island, New York on May 16, 2008

An investigation of coastal groundwater systems was performed along the north shore of Long Island, New York during May 2008 to constrain nutrient delivery to Northport Harbor and Manhasset Bay by delineating locations of likely groundwater discharge. The embayments are bounded by steep moraines and are underlain by thick fine-grained sediments deposited in proglacial lakes during the last ice age. Beach sand and gravel overlie the glacial deposits along the coast. The continuous resistivity profiling (CRP) surveys that were conducted indicate the existence of low-salinity groundwater in shore-parallel bands, typically 25 to 50 meters wide, along the shorelines of both bays. Piezometer sampling and seepage meter deployments in intertidal and subtidal areas of the two bays confirmed the presence and discharge of brackish and low-salinity groundwater. The large tidal ranges (up to 3 meters), and the steep onshore topography and hydraulic gradients are important variables controlling coastal groundwater discharge in these areas. For more information on the survey involved in this project, see http://quashnet.er.usgs.gov/data/2008/08007/.

2008年5月，研究团队于美国纽约州长岛北岸开展沿海地下水系统调查，旨在通过划定潜在地下水排泄点位，限定输入至北港港（Northport Harbor）与曼哈塞特湾（Manhasset Bay）的营养盐通量。该两处海湾以陡峭的冰碛丘陵为界，末次冰期冰前湖沉积形成的厚层细粒沉积物构成了其基底；沿海区域的海滩砂与砾石覆盖于上述冰川沉积层之上。本次开展的连续电阻率剖面法（Continuous Resistivity Profiling, CRP）勘测结果显示，两处海湾的岸线沿线存在与岸线平行的低盐度地下水带，宽度通常为25至50米。对两处海湾潮间带与潮下带区域的孔隙水压计采样及渗流计布设工作，证实了半咸水与低盐度地下水的存在及其排泄过程。该区域的大型潮差（可达3米）、陡峭的陆上地形与水力梯度，是控制沿海地下水排泄的关键影响因素。如需了解本项目所涉勘测的更多细节，请访问：http://quashnet.er.usgs.gov/data/2008/08007/