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Determining the sources of water and hydrogen sulfide in Suwannee Springs and White Springs, Florida

Project Chief: Scott McBride
Collaboration: Suwannee River Water Management District
Period of Project: FY 2012-2014

Problem Statement

Click to enlarge - Water-quality sampling at SuwanneeSprings

Water-quality sampling at Suwannee Springs

Minimum flows and levels (MFLs) for springs, rivers, and lakes are required by the State of Florida to protect water resources from significant harm. MFLs also provide important information for water supply planning and permitting criteria for consumptive water use. Information on sources of groundwater and solutes is critical for establishing effective MFLs for springs. The Suwannee River Water Management District (SRWMD) is currently working on setting MFLs for two springs in the upper Suwannee River basin (SRB) - Suwannee Springs and White Springs. These two springs, whose water source likely is the upper Floridan aquifer, contain hydrogen sulfide. During low-flow conditions, when the proportion of groundwater flow to springs is high, the presence of sulfides and other contaminants of concern could have adverse effects on water quality and biota in spring runs and in the Suwannee River. Two possible sources of hydrogen sulfide in groundwater in this area are reduction of sulfate from the dissolution of gypsum at depth, and the decomposition and reduction of organic matter in groundwater. Previous investigations have attributed the presence of hydrogen sulfide in the Upper Floridan aquifer in the upper SRB to the reduction of sulfate from the dissolution of gypsum in areas where the UFA is overlain by a thick sequence of confining material of the Hawthorn Group, but there are knowledge gaps in understanding the flow system that are hampering water management.

Objectives

The main objective of this study is to assess the source(s) of groundwater and hydrogen sulfide in Suwannee Springs and White Springs in the upper Suwannee River basin.

Approach

Several novel age-dating, geochemical and isotopic tracer techniques have been developed since previous investigations were conducted in the 1960s and 1970s and could provide new insights into the sources of water and solutes to the springs. Information on the age distribution of spring waters not only has important implications for determining sources of water but also for estimating recharge rates to aquifers, improving groundwater model calibration, and assessing historical records of contaminant loading to aquifers. The combination of age-dating techniques with other natural environmental tracers can be highly effective in understanding current and past flow conditions.

Spring water and groundwater samples were collected during low-flow and high-flow conditions and analyzed for a combination of naturally occurring isotopic and other chemical tracers along with groundwater age-dating tracers to determine sources of water and hydrogen sulfide to Suwannee Springs and White Springs. This study used several isotopic tracers including strontium, sulfur, and isotopes (oxygen and hydrogen). Water samples also were analyzed for sulfur hexafluoride and tritium (which have an atmospheric origin) to estimate the groundwater age (the time elapsed since recharge to the aquifer). These tracers have an effective dating range of about 50 years. Lumped parameter mixing models were used to estimate groundwater ages and mixing fractions of young and old water.

It is possible that groundwater flowing toward White Springs is originating from the east side of the Suwannee River. Therefore, water samples also were collected from Bell Spring, which is located east of White Springs. Anecdotal information suggests that water flowing from this spring originates from the intermediate aquifer. The use of strontium isotopes along with major ion chemistry would provide more definitive information as to its source of water. The isotopic and other chemical data collected during the study will be interpreted using geochemical and lumped-parameter models (NETPATH, TracerLPM) and statistical techniques.

Additional information on sources of water and solutes were obtained from the collection and analysis of water samples for major ions, nutrients, and dissolved gases. The pH, specific conductance, dissolved oxygen, and temperature were measured in the field either by inserting the multiparameter sonde directly into the spring vent, or through a closed flow-through sampling chamber. Hydrogen sulfide was measured using a portable spectrophotometer.

Results

[Results are not yet available]

Information Product

Results will be published as a journal article.

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