Groundwater sources of "new" N for benthic microalgal production in the South Atlantic Bight

大陆架的生产力很高，具有生态和经济重要性。底栖微藻是这些地区的主要初级生产者。 多达6倍的水柱生物量的初级生产者被压缩成一层只有几毫米厚的沉积物表面。支持这种高度浓缩的BMA生物质的固定氮（N）的来源目前是未知的。 南卡罗来纳州大学最近对海底地下水流的研究表明，上涌的含盐地下水可能为南大西洋湾（SAB）的山脊-洼地生境提供高浓度的营养物质。 研究人员认为，地下水输入的固定氮到表层沉积物是N的主要来源，支持BMA生物量和生产的中间架地区的SAB。本项目的目的是确定固定氮的主要来源，支持BMA生物量在浅水架沃茨（30米）的表层沉积物，使用SAB作为一个领域。 第二个目标是应用新的和创新的方法来直接量化地下水输入的N到表层沉积物。 研究结果将充分记录的时空分布的BMA和浮游植物生物量和群落结构的SAB的中间架区域，并与所观察到的模式，地下水输入的固定N源，以及水文和气候条件。 这项研究将提供全额支持和学费为2名研究生，夏季支持本科生助理，并涉及高层次的本科生作为实验室实习生。 该研究小组还将与巴鲁克研究所和其他合作伙伴合作，开发一个“海洋校园”计划，以满足教师，学生和社区观众的需求。该项目还将为Girls Go for I.T.提供部分支持，一个旨在吸引中学女生从事信息技术职业的编程夏令营。和STEM领域的研究的具体目标是（1）量化的空间和时间变化的N通量与水动力交换和地下水向上流动（2）文件的空间和时间变化的BMA生物量和（3）测量三角洲15 N的固定氮源（井水，孔隙水和水柱铵和硝酸盐;沉积物），BMA和浮游植物。取样区域将限于南卡罗来纳州查尔斯顿海岸外SAB的10 - 30米等深线区域。将在现有地下水井场和大陆架其他区域收集样品。 在井场的每个地下水威尔斯井，水肺潜水员将从威尔斯井中收集液体，以确定井水无机营养物浓度（硝酸盐+亚硝酸盐、铵、正磷酸盐、硅）和井水铵和硝酸盐（如果存在）的15 N增量。在附近的沉积物中，将采集样品用于BMA生物量和群落组成、表面孔隙水无机营养物（硝酸盐+亚硝酸盐、铵、正磷酸盐、硅）、沉积物的C和N、沉积物粒度分析以及BMA、铵、硝酸盐（如果存在）和沉积物的δ 15 N。 将在4个深度地层中的每一个中进行样线调查，包括沿50 m样线沿着的5个采样位置。 潜水员将沿着每个断面以沿着10 m的间隔采集与上述井场相同的样品。 将收集水柱样本，用于浮游植物生物量和群落组成、无机营养物浓度（硝酸盐+亚硝酸盐、铵、正磷酸盐、硅）、悬浮物CHN、浮游植物的δ 15 N以及铵和硝酸盐的δ 15 N的HPLC测量。研究人员将利用热量作为示踪剂来绘制水动力交换的深度，并监测垂直地下水流的速度。该分析的结果还将使他们能够模拟保守示踪剂的运输，该示踪剂可以与观察到的营养浓度、BMA丰度和群落组成进行比较。

Continental shelves are highly productive, with both ecological and economic importance. Benthic microalgae (BMA) are key primary producers in these location. As much as 6x the water column biomass of primary producers is compressed into a layer only a few mm thick on the sediment surface. The source(s) of fixed nitrogen (N) supporting such highly concentrated BMA biomass is currently unknown. Recent studies of sub-seafloor groundwater flow at the University of South Carolina have demonstrated that upwelling saline groundwater likely supplies high concentrations of nutrients in the ridge-swale habitats in the South Atlantic Bight (SAB). The investigators suggest that groundwater input of fixed N into surficial sediments is the primary source of N supporting BMA biomass and production in the mid-shelf region of the SAB. The purpose of this project is to determine the primary source of fixed N supporting BMA biomass in the surface sediments of the shallow shelf waters (30 m), using the SAB as a field area. A secondary objective is to apply novel and innovative methods to directly quantify groundwater inputs of N into surficial sediments. Research results will fully document the spatio-temporal distributions of BMA and phytoplankton biomass and community structure in the mid-shelf region of the SAB and relate the observed patterns to groundwater inputs of fixed N sources as well as hydrographic and climatic conditions. This research will provide full support and tuition for 2 graduate students, summer support for undergraduate assistants, and involve upper level undergraduates as lab interns. The study team will also work with the Baruch Institute and other partners to develop an "Ocean Schoolyard" program to meet the needs of teachers, students, and community audiences. The project will also provide partial support for Girls Go for I.T., a coding summer camp designed to attract middle-school-aged girls to careers in I.T. and STEM fieldsThe specific objectives of the study are to (1) quantify spatial and temporal variations in N fluxes associated with hydrodynamic exchange and upward groundwater flow (2) document spatial and temporal variations in BMA biomass and (3) measure the delta15N of fixed nitrogen sources (well water, porewater and water column ammonium and nitrate; sediments), the BMA, and phytoplankton. The sampling area will be restricted to the 10 - 30 m isobath region of the SAB off the coast of Charleston, SC. Samples will be collected at both the existing groundwater well field and other regions of the shelf. At each of the groundwater wells in the well field, SCUBA divers will collect fluids from the wells to determine well water inorganic nutrient concentrations (nitrate + nitrite, ammonium, orthophosphate, silicon) and the delta 15N of well water ammonium and nitrate (when present). In nearby sediments, samples will be collected for BMA biomass and community composition, surface porewater inorganic nutrients (nitrate + nitrite, ammonium, orthophosphate, silicon), C and N of sediments, sediment grain size analysis, and delta 15N of BMA, ammonium, nitrate (when present), and sediments. Line transects, consisting of 5 sampling locations along a 50 m transect, will be conducted in each of the 4 depth strata. At 10 m intervals along each transect, divers will collect samples the same as above for the well field. Water column samples will be collected for HPLC measurements of phytoplankton biomass and community composition, inorganic nutrient concentrations (nitrate + nitrite, ammonium, orthophosphate, silicon), seston CHN, delta 15N of phytoplankton, and the delta 15N of ammonium and nitrate. The researchers will use heat as a tracer to map the depth of hydrodynamic exchange and monitor the rate of vertical groundwater flow. Results from that analysis will also allow them to then simulate transport of a conservative tracer that can be compared to observed nutrient concentrations to BMA abundance and community composition.