Florida Bay Project Profiles: Groundwater and Nutrients in Florida Bay

Question: Where is groundwater discharge taking place in Florida Bay? Does this inflow of groundwater contribute to an excess of nutrients in Florida Bay surface waters?

Project: Groundwater discharge from the limestone bedrock of Florida Bay may be one way nutrients are entering the bay’s surface waters. When present in certain concentrations, these nutrients can promote the excessive growth of microscopic algae (phytoplankton) in the water column which results in ecological changes in the environment including reduced water clarity. Four extensive surveys of Florida Bay have been conducted since early 1997. During each survey, several dozen stations were sampled to determine how much groundwater discharge was occurring in that location. Natural tracer elements (radon, methane, and radium) were used because they have been shown to be present in higher concentrations in groundwater than in bay surface waters. These elements are also relatively easy to measure even at low concentrations. Water samples were collected from each site to determine the levels of the nutrients, phosphorus, and nitrogen. Seagrasses and macroalgae (seaweed) were collected from some stations for analysis of the nitrogen isotope, N15.

Findings to Date: There are distinct differences in tracer patterns, indicating that seasonal differences in groundwater discharge exist. In the summertime, discharge was most evident on the bayside of the Upper Keys, and in the wintertime, it was most evident in the north central to northwestern bay. One

possible reason for this seasonal switching is enhanced flushing from the keys during the summer which is the wet season. Groundwater discharge in the nearshore waters of the keys may be rich in nitrogen since concentrations of this nutrient were moderate to high at sample sites in these areas. Seagrass and macroalgal samples from nearshore sites also showed enriched nitrogen 15 levels perhaps due to sewage input from human habitation. Groundwater may also be a pathway for phosphorus to enter the bay since concentrations of this nutrient were high in the north bay where the tracer signals were strong.

Status: Funded through 1999.

Restoration Impacts: Understanding the role of nutrient loading from groundwater is important for scientists involved in developing computer models which predict water quality and groundwater flow patterns in Florida Bay.

Funding Source: NOAA

Related Profiles:

• FBPP 100 • FBPP 109

• FBPP 110 • FBPP 111

• FBPP 112 • FBPP 113

January 07, 2009 This page last modified: July 16, 2001
January 07, 2009 This page last modified: July 16, 2001	Water Quality Groundwater and Nutrients in Florida Bay Florida Bay Project Profile - 93 *Question:* Where is groundwater discharge taking place in Florida Bay? Does this inflow of groundwater contribute to an excess of nutrients in Florida Bay surface waters? *Project:* Groundwater discharge from the limestone bedrock of Florida Bay may be one way nutrients are entering the bay’s surface waters. When present in certain concentrations, these nutrients can promote the excessive growth of microscopic algae (phytoplankton) in the water column which results in ecological changes in the environment including reduced water clarity. Four extensive surveys of Florida Bay have been conducted since early 1997. During each survey, several dozen stations were sampled to determine how much groundwater discharge was occurring in that location. Natural tracer elements (radon, methane, and radium) were used because they have been shown to be present in higher concentrations in groundwater than in bay surface waters. These elements are also relatively easy to measure even at low concentrations. Water samples were collected from each site to determine the levels of the nutrients, phosphorus, and nitrogen. Seagrasses and macroalgae (seaweed) were collected from some stations for analysis of the nitrogen isotope, N15. *Findings to Date:* There are distinct differences in tracer patterns, indicating that seasonal differences in groundwater discharge exist. In the summertime, discharge was most evident on the bayside of the Upper Keys, and in the wintertime, it was most evident in the north central to northwestern bay. One possible reason for this seasonal switching is enhanced flushing from the keys during the summer which is the wet season. Groundwater discharge in the nearshore waters of the keys may be rich in nitrogen since concentrations of this nutrient were moderate to high at sample sites in these areas. Seagrass and macroalgal samples from nearshore sites also showed enriched nitrogen 15 levels perhaps due to sewage input from human habitation. Groundwater may also be a pathway for phosphorus to enter the bay since concentrations of this nutrient were high in the north bay where the tracer signals were strong. *Status:* Funded through 1999. *Restoration Impacts:* Understanding the role of nutrient loading from groundwater is important for scientists involved in developing computer models which predict water quality and groundwater flow patterns in Florida Bay. *Funding Source:* NOAA *Related Profiles:* • FBPP 100 • FBPP 109 • FBPP 110 • FBPP 111 • FBPP 112 • FBPP 113 fbpp 63
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Water Quality

Groundwater and Nutrients in Florida Bay