Processed continuous resistivity profile data collected in Manhasset Bay on Long Island, New York on May 17, 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 https://cmgds.marine.usgs.gov/fan_info.php?fan=2008-007-FA.

2008年5月，研究团队于纽约州长岛北岸开展海岸地下水系统调查，通过划定潜在地下水排泄点位，以限定北港港（Northport Harbor）与曼哈塞特湾（Manhasset Bay）的营养盐输入通量。上述海湾被陡峭冰碛所环绕，基底为末次冰期冰前湖沉积的厚层细粒沉积物；沿岸带的冰碛沉积物之上覆有海滩砂与砾石。本次开展的连续电阻率剖面（continuous resistivity profiling, CRP）测量显示，两处海湾沿岸均发育与岸线平行的低盐度地下水带，带宽通常为25~50米。对两处海湾潮间带与潮下带区域开展的测压管采样及渗流计布设工作，证实了微咸地下水与低盐度地下水的存在及其排泄过程。较大的潮差（可达3米）、陡峭的陆上地形与水力梯度，是控制该区域海岸地下水排泄的关键影响因子。如需了解本项目所涉调查的详细信息，请访问：https://cmgds.marine.usgs.gov/fan_info.php?fan=2008-007-FA