Fate and movement of nitrogen and phosphorus in deep creek in the lower St. Johns river basis of northeast Florida

Christine M. Worthington, Chad M. Hutchinson


According to the St. Johns River Water Management District, approximately 36% of the pollutant load entering the lower St. Johns River basin is related to human activities. Deep Creek, a tributary in the lower St. Johns River basin, drains approximately 4,000 ha of irrigated cropland in and around Hastings through a system of tail water and drainage canals into Deep Creek. Objectives of this project were to measure water quality and aquatic plant density effects in Deep Creek. Water samples collected were analyzed for nitrate-nitrogen, ammonium-nitrogen, potassium and total phosphorus. Blue-green algae, chlorophyll a, dissolved oxygen, pH, specific conductivity and water temperature were measured at 23 sample sites on a weekly schedule in Oct. 2007. Total phosphorus concentration within Deep Creek at the 1st, 13th, and 15th sample locations were signifi cantly higher compared with all other sample sites at 896.4, 930.7, and 896.9 μg·L–1, respectively. A significant correlation between total phosphorus and chlorophyll a was observed. Chlorophyll a increased as total phosphorus increased. Alternatively, a signifi cant inverse relationship was observed as nitrate-nitrogen concentrations decreased, chlorophyll a increased. Continued data collection will further support Best Management Practices strategies for the Tri-County Agricultural Area of Northeast Florida.

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283