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Technical Note: Flow and Nutrient Contributions from Groundwater to a Drainage Ditch in a Beef Cattle Ranch in the Lake Okeechobee Basin, Florida

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASABE. 55(1): 167-174. (doi: 10.13031/2013.41253) @2012
Authors:   D. Goswami, S. Shukla, W. D. Graham
Keywords:   Dupuit equation, Groundwater flow, Nitrogen, Nutrient loading, Phosphorus

Pastures in beef cattle ranches are identified as one of the major land uses that contribute phosphorus (P) and nitrogen (N) loadings to Lake Okeechobee (LO), Florida. A study was conducted to quantify flow, P, and N contributions from groundwater to a 170 m ditch section within a beef cattle ranch located in the LO basin from June 2005 to May 2009. Groundwater depths and total N (TN) and total P (TP) concentrations measured in five wells, installed on each side (bank) of the ditch section, were combined with the ditch stage and N and P concentrations to quantify groundwater flow and nutrient loads. The Dupuit equation was used to estimate the groundwater flow to and from the ditch. The average net groundwater flow to the ditch section, estimated from a range (low and high) of saturated hydraulic conductivity (Ksat) values, ranged from 765 to 1,729 m3 per year. Annual groundwater flow contributions were positive (to the ditch) for all four years, while the groundwater nutrient contributions were positive for three years and negative (from the ditch) for one year (drought year). Average net annual TP loads to the ditch section ranged from 0.1 (low) to 0.2 (high) kg, while TN loads ranged from 2.1 (low) to 4.5 (high) kg. Extrapolating the results from this study to the LO basin indicated that groundwater was a major contributor of TP loads to the lake.

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