RECOVER MAP 3.1.3.3 Coastal Gradients - Nutrient Concentrations in Groundwater Along the Mangrove Ecotone Region of Shark River Slough

Introduction Concentrations of nitrogen and phosphorus are often higher in groundwater than in surface water. Seawater intrudes along the entire coastline of the southern Everglades (Fig 1). This brackish groundwater contains concentrations of total phosphorus (TP) as high as 2 M (Price et al. 2006), with higher groundwater TP concentrations with increasing salinity. The occurrence of the brackish groundwater corresponds with the mangrove ecotone along the coastal Everglades, and suggests that the mangroves may be utilizing this high TP groundwater as a nutrient source. The goal of the Comprehensive Everglades Restoration Plan (CERP) is to restore the natural quantity, quality, timing, and distribution of flows into the Everglades. CERP is expected to restore the freshwater flows across Tamiami Trail and the northern boundary of ENP. The additional supply of freshwater to Shark Slough is expected to move the brackish groundwater closer towards the coastline, thereby moving the nutrient rich groundwater closer to the coast. The ecological implications for the movement of the brackish groundwater are currently unknown. This project directly addresses Hypothesis 9.2.4.4 in the "Assessment Strategy of the Monitoring and Assessment Plan" (RECOVER 2005): Sea level and freshwater flow as determinants of production, organic matter accretion, and resilience of coastal mangrove forests. Objectives The goal of this study is to determine the concentrations of both total and dissolved nutrients (nitrogen, phosphorus, and carbon) in groundwater and sediment water within the mangrove ecotone region of Shark River Slough. Samples will be collected from existing USGS wells. Many of these wells were sampled in 2003 and the nutrient concentrations in these wells were published in Price et al (2006). This additional sampling and analysis will determine if the nutrient concentrations in the brackish groundwater beneath the Shark River Slough region has changed since 2003. The data collected in this study will also provide background information on groundwater concentrations of nutrients within the mangrove ecotone, prior to the increase of freshwater flows across Tamiami Trail.

引言
地下水中的氮、磷浓度通常高于地表水。佛罗里达大沼泽地南部的全部海岸线均受海水入侵影响（图1）。该微咸地下水中的总磷（Total Phosphorus, TP）浓度最高可达2 M（Price等，2006），且地下水TP浓度随盐度升高而升高。微咸地下水的分布与大沼泽地沿海的红树林交错带（mangrove ecotone）一致，这表明红树林可能将这种高TP地下水作为养分来源。
《大沼泽地综合修复计划》（Comprehensive Everglades Restoration Plan, CERP）的目标是恢复流入大沼泽地的水流的自然数量、质量、时序与分布格局。该计划预计将修复穿过塔米亚米小径（Tamiami Trail）以及大沼泽地国家公园（Everglades National Park, ENP）北部边界的淡水径流。向鲨鱼泥潭（Shark Slough）额外补给淡水，预计将使微咸地下水更靠近海岸线，进而将富养分地下水推向近海区域。目前，微咸地下水移动所带来的生态影响尚不明确。本项目直接针对《监测与评估计划评估策略》（RECOVER 2005）中的假说9.2.4.4：作为沿海红树林生产力、有机质积累与恢复力决定因素的海平面与淡水径流。

研究目标
本研究旨在测定鲨鱼河泥潭（Shark River Slough）红树林交错带内地下水与沉积物水中的总态与溶解态养分（氮、磷、碳）浓度。样品将从现有美国地质调查局（United States Geological Survey, USGS）井中采集。其中多数井已于2003年完成采样，其养分浓度数据已发表于Price等（2006）的研究。本次补充采样与分析，将用于确认2003年以来鲨鱼河泥潭区域下方微咸地下水中的养分浓度是否发生变化。本研究采集的数据还将为塔米亚米小径淡水补给增加前的红树林交错带地下水养分浓度提供背景参考数据。