ALLGSB_RESBSED_MAY08.SHP: Processed continuous resistivity profile (CRP) data below the sediment water interface from Great South Bay on Long Island, New York, collected by the U.S. Geological Survey from May 19 to May 22, 2008

An investigation of submarine aquifers adjacent to the Fire Island National Seashore and Long Island, New York, was conducted to assess the importance of submarine groundwater discharge (SGD) as a potential nonpoint source of nitrogen delivery to Great South Bay. More than 200 kilometers (km) of continuous resistivity profiling (CRP) data were collected to image the fresh-saline groundwater interface in sediments beneath the bay. In addition, groundwater sampling was performed at sites (1) along the northern shore of Great South Bay, particularly in Patchogue Bay, that were representative of the developed Long Island shoreline, and (2) at sites on and adjacent to Fire Island, a 50-km-long barrier island on the southern side of Great South Bay. Other field activities included sediment coring, stationary electrical resistivity profiling, and surveys of in-situ pore water conductivity. The onshore and offshore shallow hydrostratigraphy of the Great South Bay shorelines, particularly the presence and nature of submarine confining units, appears to exert primary control on the dimensions and chemistry of the submarine groundwater flow and discharge zones. Sediment coring has shown that the confining units commonly consist of drowned and buried peat layers likely deposited in salt marshes. Based on CRP data, low-salinity groundwater extends from 10 to 100 meters (m) offshore along much of the northern and southern shores of Great South Bay, especially off the mouths of tidal creeks, and beneath shallow flats to the north of Fire Island adjacent to modern salt marshes. Human modifications of much of the shoreline and nearshore areas along the northern shore of the bay, including filling of salt marshes, construction of bulkheads and piers, and dredging of navigation channels, has substantially altered the natural hydrogeology of the bay's shorelines by truncating confining units and increasing recharge near the shore in filled areas. Better understanding of the nature of SGD along developed and undeveloped shorelines of embayments such as this could lead to improved models and mitigation strategies for nutrient overenrichment of estuaries. For more information on the surveys involved in this project, see http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2008-007-FA and http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2008-037-FA.本研究针对美国纽约州长岛及火岛国家海岸邻近的海底含水层开展调查，旨在评估海底地下水排泄（submarine groundwater discharge, SGD）作为氮素非点源输入大南湾的潜在重要性。研究采集了超过200公里的连续电阻率剖面法（continuous resistivity profiling, CRP）数据，用于成像大南湾下方沉积物中的淡水-咸水地下水界面。此外，研究团队分别在两类点位开展地下水采样：其一为大南湾北海岸（尤其帕乔格湾）的代表性点位，可代表开发改造后的长岛海岸线；其二为大南湾南侧长50公里的障壁岛火岛之上及其邻近区域的点位。其他野外工作还包括沉积物取芯、固定式电阻率剖面测量以及原位孔隙水电导率调查。大南湾岸线（尤其是海底隔水层的赋存状态与特征）的陆上与近岸浅层水文地层学，似乎是控制海底地下水流与排泄区规模及化学特征的核心影响因素。沉积物取芯结果显示，海底隔水层通常由被淹没且埋藏的泥炭层构成，这类泥炭层大概率形成于古盐沼沉积环境。基于CRP数据分析结果，低盐度地下水沿大南湾多数南北岸向海延伸10至100米，尤其分布于潮汐河口外侧以及火岛北侧毗邻现代盐沼的浅滩下方。该湾北海岸的多数岸线及近岸区域已受到人类活动显著改造，包括盐沼填埋、驳岸与码头修建以及航道疏浚，这类活动通过破坏隔水层以及提升填埋区域近岸的地下水补给量，大幅改变了该湾岸线的自然水文地质条件。若能更深入地理解此类海湾开发与未开发岸线的SGD特征，将有助于优化河口湾营养物过富营养化的模拟模型与缓解策略。如需了解本项目涉及的调查详情，请访问以下链接：http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2008-007-FA 与 http://woodshole.er.usgs.gov/operations/ia/public_ds_info.php?fa=2008-037-FA。