NONPOINT SOURCE PHOSPHORUS CONTRIBUTION FROM NURSERIES IN THE UPPER COHANSEY WATERSHED, NEW JERSEY
Nonpoint sources are a major cause of stream impairment in New Jersey, especially for phosphorus. Nurseries are the fastest growing agricultural sector in the state, but little information has been available on their effect on water quality. The Upper Cohansey Watershed in southern
New Jersey contains a considerable nursery industry and a phosphorus-impaired river reach. It is anticipated that a total maximum daily load (TMDL) will be established for phosphorus in the near future.
Weekly grab water samples were collected from October 2001 - July 2003, then biweekly
through January 2004, at four stream stations. Stations 1 and 2 were on a tributary immediately upstream and downstream of a nursery, respectively, while Station 3 was nearby on the Cohansey River. Station 4 was located upstream to provide background (but not pristine) information. Analyses
performed included total phosphate-phosphorus (TP), filtered (“soluble”) reactive phosphate-phosphorus (FP), pH, TKN, ammonium, nitrite, nitrate, and, for 6 months, chlorophyll a. Additionally, soil samples were collected from 6 points in each of 3 nursery fields and 2 forested
areas, at 3 depths (0–10, 10–30, and 30–50 cm). Soils were Matapeake B and Chillum B silt loams. Sediment samples were collected from 4 points at each of 4 stream locations, at the same 3 depths.
Nutrient concentrations were elevated at Stations 1–3 relative to Station
4; Station 2 typically had the highest concentrations. Mean concentrations of TP at Stations 1–4, respectively, were 0.075, 0.096, 0.073, and 0.049 mg/L. Of 97 TP analyses at each station, 14, 22, 23, and 10% exceeded the stream water standard (0.10 mg/L).
On average, FP accounted
for only 30% of TP at the 4 stations; the correlation between FP and TP was strong (R2 = 0.68–0.85). TP also showed a good correlation (R2 = 0.50) with total suspended solids (20 samples) and with rainfall in the preceding 36 hours. The soil TP was correlated with
electrical conductivity and finer particles, but not organic matter. The average TP in forest soils was 336 mg/kg (dry weight) compared to 906 mg/kg in nursery field soils and 1293 mg/kg in stream sediments.
Overall, the results suggest that nursery fields contribute elevated
levels of nutrients to adjacent waters. Most of the phosphate in the stream samples was associated with particles, indicating that soil erosion may be the major contributor to elevated phosphorus levels.
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