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United States Department of Agriculture

Agricultural Research Service

Title: Agricultural land use and hydrology affect variability of shallow groundwater nitrate concentration in south Florida

Authors
item Ritter, A - ICIA, SPAIN
item Munoz-Carpena, R - UNIV. OF FLORIDA
item Bosch, David
item Schaffer, B - UNIV. OF FLORIDA
item Potter, Thomas

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 2006
Publication Date: August 30, 2007
Citation: Ritter, A., Munoz-Carpena, R., Bosch, D.D., Schaffer, B., Potter, T.L. 2007. Agricultural land use and hydrology affect variability of shallow groundwater nitrate concentration in south Florida. Hydrological Processes. 21:2464-2473 (DOI: 10.002/hyp.6483).

Interpretive Summary: The South Florida Miami-Dade area is undergoing the costliest environmental restoration project in history. Agriculture in the region competes for land and water resources with the restoration efforts and Miami’s urban sprawl. Understanding regional water quality interactions is critical to reducing a potentially negative impact to agriculture. A study was conducted in a 4-ha square field containing 0.9-ha of corn grown in the center and surrounded by fallow land. Shallow groundwater nitrate-nitrogen concentration was analyzed during a 3 year period. Detailed hydrological and crop data were recorded. The dataset was analyzed using a specialized time series statistical technique. The technique was able to evaluate the factors which had the greatest influence on groundwater quality, groundwater elevation, groundwater flow direction, and precipitation between sampling periods. Furthermore, a spatial structure across the field, matching land use, was found whereby the groundwater nitrate-nitrogen concentration in wells within the cornrows could be generally separated from those upgradient and downgradient of the crop strip. Fertilization, masked by soil/water/plant-delayed processes, had no discernible effect on groundwater nitrate-nitrogen levels.

Technical Abstract: South Florida’s Miami-Dade agricultural area is located between two federally protected natural areas, the Biscayne and Everglades National Parks, subject to the costliest environmental restoration project in history. Agriculture, an important economic activity in the region, competes for land and water resources with the restoration efforts and Miami’s urban sprawl. Understanding water quality interactions between agricultural land use and the shallow regional aquifer is critical to reduce the potentially negative impact to agriculture. A study was conducted in a 4-ha square field containing 0.9-ha of corn grown in the center and surrounded by fallow land. The corn crop was laid-out in a diagonal with rows oriented NW-SE along the dominant groundwater flow in the area. A network of 18 monitoring wells was distributed across the field. Shallow groundwater nitrate-nitrogen concentration was analyzed on samples collected from the wells biweekly during a 3 year period. Detailed hydrological (water table elevation, groundwater flow direction, rainfall) and crop (irrigation, fertilization, calendar) data were also recorded. Flow direction is locally affected by seasonal regional drainage through canal management exercised by the local water authority. The dataset was analyzed by dynamic factor analysis (DFA), a specialized time series statistical technique only recently applied in hydrology. In a first step, the observed nitrate variation was successfully described by 5 common trends representing the unexplained variability. By including the measured hydrological series as explanatory variables the trends were reduced to 3. The analysis yields a quantification of the effects of hydrological factors over local groundwater nitrate-nitrogen concentration. Furthermore, a spatial structure across the field, matching land use, was found in the trends whereby the groundwater nitrate-nitrogen concentration in wells within the cornrows could be generally separated from those upgradient and downgradient of the crop strip. Fertilization, masked by soil/water/plant-delayed processes, had no discernible effect on groundwater nitrate-nitrogen levels.

Last Modified: 10/22/2014
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