Influence of Discharge Magnitude on Phosphorus Transport Characteristics in a Variable Land-Use Watershed
Abstract
Mill Creek, a watershed in the karst terrain of the Nashville Basin, has exceeded regulatory levels for siltation, nutrient load, and pathogens, and failed to reach adequate dissolved oxygen concentrations. Phosphatic calcarenite in the Hermitage limestone and Bigby limestone units may provide a natural source of phosphorus in the watershed; similar deposits elsewhere were historically mined for phosphate. Other potential sources include agricultural and residential contributions from fertilizers and waste disposal. Grab samples were collected under variable flow conditions over an 18-month period in Mill Creek's upper, middle, and lower reaches, dominated respectively by agricultural, suburban, and urban land uses. Tangential flow filtration and/or syringe filters were used to assess the particulate contribution to phosphorus load in several size ranges (>0.65µm, 0.65µm - 0.45µm, 0.45µm - 0.11µm and <0.11µm). Filtered and unfiltered samples were analyzed for total and reactive phosphate by spectrophotometer. In all three land use regions, the phosphorus load was dominated by orthophosphate, and phosphate loads increased with increasing discharge. Phosphate loads also increased downstream suggesting additional contributions from urban and suburban runoff, especially during high flow events. Under high flow conditions, a greater proportion of the phosphorus is associated with particulate material greater than 0.65 µm. This trend becomes more pronounced downstream.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2006
- Bibcode:
- 2006AGUSM.B33A..07S
- Keywords:
-
- 0414 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0793;
- 1615;
- 4805;
- 4912);
- 0469 Nitrogen cycling;
- 0470 Nutrients and nutrient cycling (4845;
- 4850);
- 0483 Riparian systems (0744;
- 1856);
- 0496 Water quality