Thursday, November 8, 2007 - 9:45 AM
347-5

Streamside Management Zone Effectiveness in Protecting Water Quality Following Forestland Application of Biosolids in the Virginia Piedmont.

W. A. Pratt, Forestry, Virginia Polytechnic Institute and State Univ, 228 Cheatham Hall, Dept of Forestry (0324), Blacksburg, VA 24061 and T.R. Fox, Department of Forestry, Virginia Polytechnic Institute and State Univ, 228 Cheatham Hall, Blacksburg, VA 24061.

Biosolids are the materials resulting from domestic sewage treatment, which have been processed to be safe for disposal by application to land. They release high concentrations of nitrogen and phosphorous to the soil, increasing the productivity of amended lands. As conventional fertilizer prices increase, biosolids may benefit forest managers seeking cheap alternatives. However, environmental concerns exist that nutrients from biosolids may leach or runoff from a site contributing to non-point source pollution. Streamside management zones (SMZ), acting as a buffer between managed areas and streams, have been used to intercept and attenuate nitrogen and phosphorous moving from a site. We treated planted loblolly pine (Pinus taeda) stands adjacent to three intermittent streams with anaerobically digested biosolids at a rate of 224 kg/ha of plant available N (PAN) maintaining a 15 m untreated SMZ. Untreated control stands on the opposite side of each stream were paired with each treated stream. We used suction lysimeters placed at a depth of 60 cm and ion exchange membranes placed in the forest floor and A horizon to evaluate spatial variation of nutrients across the SMZ. Nitrate-N concentration in soil solution collected using suction lysimeters decreased from 0.17 mg/L in the biosolids-amended areas to 0.10 mg/L in the adjacent SMZs, compared to values in the untreated control of 0.01 and 0.08 mg/L. Nitrate-N extracted from ion exchange membranes were similar, ranging from 2.2 mg/m2/day in biosolids-amended areas to 2.0 mg/m2/day in the adjacent SMZs, compared to control values of 0.92 and 0.79 mg/m2/day. We collected stream water samples from treated and untreated streams to evaluate cumulative treatment effect. Nitrate-N concentrations were 0.02 mg/L in treated streams and below detection levels in untreated streams. Early results indicate that nutrients may be moving through the soil, but nutrient concentration in streams show little response.