Streamside management zones effectiveness for protecting water quality after forestland application of biosolids
Received for publication August 1, 2008. Biosolids, materials resulting from domestic sewage treatment, are surface applied to forest soils to increase phosphorus (P), nitrate, and ammonium availability. Retaining streamside management zones (SMZs) can limit nutrient pollution of streams. We delineated 15-m SMZs along three intermittent streams in an 18-yr-old Pinus taeda L. plantation. We applied biosolids at a rate of 1120 and 629 kg ha–1 of total nitrogen and total P outside the SMZ on one side of each of the streams while maintaining the other side of the stream as control. We collected water samples from the three treated and six reference streams and from the perennial stream upstream and downstream from the intermittent streams for 12 mo after treatment. Along transects perpendicular to the treated streams, we collected overland flow samples, soil solution samples at 60 cm, and extracts from ion exchange membranes (IEMs) placed in the surface soil. We observed significantly elevated P concentrations adjacent to the stream in overland flow during one period on the treated side of the stream. We found significantly elevated nitrate concentrations outside the SMZ in the treated-side soil solution samples, in which concentrations remained below 1.5 mg L–1. Phosphorus, nitrate, and ammonium concentrations outside the SMZ in treated-side IEM extracts showed significant increases after biosolids application, returning to near control levels after 1 yr. Phosphorus, nitrate, and ammonium concentrations in IEM extracts were not different adjacent to the streams. Stream P, nitrate, and ammonium concentrations showed few differences downstream from the treatment with concentrations below 1.5 mg L–1. Our results indicate that at 15 m, SMZ protected streams from P, nitrate, and ammonium pollution for the first year after biosolids application to adjacent loblolly pine plantations in the Virginia Piedmont.