Mark Lucius, MS and Serge Thomas, Ph.D. Florida Gulf Coast University

Transcription

1 Mark Lucius, MS and Serge Thomas, Ph.D. Florida Gulf Coast University

2 Deployed 15 groundwater seepage meters in a wet detention pond on FGCU campus 1 year study Monthly sampling Analyzed flow rates Analyzed nutrient loading

3 To determine: Groundwater/surface water interactions Nutrient loading via groundwater Spatiotemporal variation Potential source of nutrients in well maintained pond Implications for pond management Implications for watershed protection Limited data in wet detention ponds Often treated as isolated systems

4 Poorly maintained, hyper-eutrophic stormwater pond Well maintained natural Lake or stormwater pond Coastal watershed

5 Subsurface flow of pore water

6 Wet detention pond, FGCU campus Located: 26 27'56.90"N, 81 46'54.01"W Adjacent to solar panel fields Fairly young (7 years), Approx. 1.5 acres

7 Steep sloping littoral zone in some areas Rocky in some areas Limited organic sediment High mesotrophic to Eutrophic (Carlson TSI) Naturally maintained; no fertilizers

8 Groundwater seepage meters Lee (1977) design 1

9 Meter Placement 15 seepage meters Three depth classes A: 0-1 m, B: 1-2 m, C: 2+ m Placement was limited to suitability Meters A5 A7 were only used during higher water levels

10 1 year study: March February 2014 Sampling Monthly bag deployment 24 hour period Bags collected, measured volumetrically Influxes sampled and frozen

11 Calculations Volumetric Flow: Correction coefficient = 1.25 (2,3,4) Surfer12 for interpolation Nutrient analysis TN Second derivative spectroscopy 5 TP EPA standard method for surface/wastewater 6

12 Mean seepage rate: 0.27±1.14 L m -2 d -1 Mean daily discharge (interpolated): 1223±2121 L d -1 or 0.23% of pond volume Total groundwater discharge: 5,354 m 3 or 858% of pond volume

13 Dry season (October-April) Wet season (June-September)

14 Schiffer,

15 Mean = 7.05 kg TN d -1 TN Mean concentrations TN: 2.83±2.96 mg l -1 TP: 0.28±0.23 mg l -1 Mean = 0.77 kg TP d -1 TP

16

17 Results

18 Bennet et al. 1992

19 Flux rates similar to natural lakes 7 Groundwater discharge and recharge both observed Significantly more flux overall in the dry season (p =0.031) Due to rain effects May be exacerbated by small sampling duration Significantly more flux in shallow meters (p < 0.001)

20 Nutrient concentrations elevated in groundwater discharge Significance of groundwater nutrient load is unknown Other sources not measured Full nutrient budget needed Source of elevated nutrients unknown May come from surrounding land use May be cause of elevated TSI

21 Sampling method may have impacted nutrient concentrations 7 Sampling seepage bags has been reported to elevate phosphorus concentrations Pore-water wells are a preferred alternative Concentrations still elevated Ponds engineered with surface runoff in mind Groundwater discharge loads may push ponds over pollutant removal capacity

22 The solar field pond: Did show groundwater discharge and recharge Showed more influx than efflux; contrary to typical belief Inflow carried nutrients As high as 17 mg TN L -1 and 1.14 mg TP L -1 Precedent for pond maintenance Groundwater connection cannot be overlooked May overload ponds Risks to neighboring systems and the watershed Responsible pond management and design is important!!

23 1. Lee DR A device for measuring seepage flux in lakes and estuaries. Limnology and Oceanography, 22: Murdoch, L.C., and Kelly, S.E., Factors affecting the performance of conventional seepage meters: Water Resources Research, v. 39, no. 6, p. SWC Asbury, C.E., The role of groundwater seepage in sediment chemistry and nutrient budgets in Mirror Lake, New Hampshire: Cornell University, Ph.D., 275 p. 4. Harvey, J.W., S.L. Krupa, C. Gefvert,, R. H. Mooney, J. Choi, S. A. King, and Giddings, J. B Interactions between surface water and ground water and effects on mercury transport in the northcentral Everglades. US Department of the Interior, US Geological Survey Open-File Reports 2000, 168: Bachman, R. W. and Canfield, D. E Use of an alternative method for monitoring total nitrogen concentrations in Florida Lakes. Hydrobiologia. 323: DEP - Standard methods for the examination of water and wastewater. Ch Belanger, T. V. and D. F. Mikutel On the use of seepage meters to estimate groundwater nutrient loading to lakes. Journal of American Water Resources Association, 21(2): Bennett MW A three-dimensional finite difference ground water flow model of western Collier County, Florida. Hydrogeology Division, Department of Research and Evaluation, South Florida Water Management District. Technical Publication Schiffer DM Hydrology of Central Florida Lakes A Primer. United States Geological Survey Circular. Technical Publication 1137.