Effects of Streamside Management Zones on Nutrient Movement Following Forestland Application of Biosolids.

Biosolids, materials resulting from domestic sewage treatment, are commonly applied to agricultural land, increasing amended land’s fertility by releasing nutrients to the soil. As the amount of agricultural land available for biosolids application decreases due to land conversion, wastewater treatment plant managers are seeking alternative application sites, such as forestland, which could also benefit forest managers seeking inexpensive alternatives to conventional fertilizers. Streamside management zones (SMZs), acting as a buffer between managed areas and streams, have been used to intercept and attenuate nutrients lost from a site, addressing concerns over leaching and runoff of nutrients released from biosolids. We treated planted loblolly pine (Pinus taeda) stands adjacent to three intermittent streams with anaerobically digested biosolids at a rate of 224 kg ha-1 of plant available nitrogen (PAN) maintaining a 15 m untreated SMZ. Treated stands on one side of each stream were paired with untreated stands on the opposite streamside. We found significantly elevated nitrate outside the SMZ at a concentration below 1.5 mg L-1 and no significant differences between control and treatment for nitrate inside the SMZ measured using lysimeters placed at 60 cm deep. We found no significant treatment effect on ammonium concentration in soil solution at 60 cm deep measured using lysimeters. We found significantly elevated nitrogen in extracts from ion exchange membranes placed in the shallow soil outside the SMZ immediately following biosolids application which declined to near control levels within a year. Nitrogen was not elevated adjacent to streams throughout the study period. Intermittent and perennial streams downstream of the treatment sites showed no significant change. Our results indicate that a 15 m SMZ protects adjacent streams from subsurface nitrogen movement.