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.