Using Regional Net Precipitation to Infer Sustainable Net Groundwater Exchanges in Florida Lakes
Abstract
The long-term balance between net precipitation and net groundwater exchange that maintains water levels in thousands of seepage lakes in Florida is explored in detail for a representative lake in the southern end of the State's Central Lake District and then regionally using remote sensing. The water budget of Lake Starr includes the longest continuous record of lake evaporation measured using the energy-budget approach in the southeastern United States. The 15-year budget period includes historic wet and dry extremes in the annual rainfall. Monthly lake evaporation at Lake Starr is used to quantify net precipitation - rainfall minus lake evaporation - between August 1996 and July 2011. Results contradict the prevailing conclusion that lakes in the mid-peninsula of Florida receive a long-term average surplus of net precipitation, and reveal instead a sizeable net precipitation deficit of about -25 cm/yr. Net groundwater exchange, the difference between groundwater inflow and lake leakage, was derived from the lake water budget and was examined for its ability to balance the net precipitation deficit monthly, annually, and cumulatively for 15 years. The Lake Starr water budget indicates that current net groundwater exchanges, which are adversely affected by groundwater pumping, are unable to sustain the lake level under conditions of average annual rainfall. In 10 of the 15 years, net groundwater exchanges were either too small to offset the precipitation deficit or were negative, meaning leakage losses exceeded the groundwater inflow to the lake. Net groundwater exchanges did balance the net precipitation deficit for a time period when hurricanes and El Niño-influenced climate patterns produced above-average rainfall. Annual average net precipitation results for Lake Starr were compared to remote-sensing based estimates of annual average net precipitation to lakes spanning the three degrees of latitude of the Central Lake District. Results indicate that a net precipitation deficit occurs at lakes throughout the District, and becomes increasingly negative with distance southward by 10 cm or more. These deficits emphasize the crucial role of net groundwater inflow for maintaining seepage lake levels, and the vulnerability of these lakes to pumping effects that can reduce groundwater inflow and increase lake leakage. The regional distribution of net precipitation in the Central Lake District, together with lakebed leakance data, further suggest that net groundwater exchanges are comparatively more positive at lakes in the southern part of the district, and that lakes in the northern part of the district lakes are comparatively leakier.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.H11D1206L
- Keywords:
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- 1818 HYDROLOGY / Evapotranspiration;
- 1830 HYDROLOGY / Groundwater/surface water interaction;
- 1876 HYDROLOGY / Water budgets