EFFECT OF WATER TREATMENT RESIDUALS ON GROWTH AND PHOSPHORUS REMOVAL BY PLANTS ADAPTED FOR VEGETATIVE BUFFERS IN THE MID-ATLANTIC U.S.

Many soils in the Atlantic Coastal Plain are high in phosphorus (P) due to long term overapplication of manures and fertilizers. Phosphorus enrichment of lakes, streams and estuaries by surface and subsurface runoff from agricultural land has been implicated as a major cause of the degradation of water quality in this region. Therefore, stabilizing P in these soils and thus reducing P release to runoff waters will play a major role in alleviating many of the water quality problems faced today in the Atlantic Coastal Plain. One alternative that is currently being investigated is the use of drinking water treatment residuals (WTRs) to stabilize soil P and reduce P losses by runoff and leaching. We characterized five WTRs from the mid-Atlantic region for P sorption capacity and elemental composition. Based on the results of these analyses, one alum WTR was then selected for use in laboratory soil incubation studies and greenhouse experiments, the primary purpose of which was to identify the most suitable rates of WTRs for use in upcoming field studies. In the laboratory experiments the WTR was incorporated with three high P (> 100 mg P/kg) Delaware soils at four rates (0, 15, 30, and 60 g kg−1 = tons acre−1). The amount of total P desorbed from the amended soils was determined by equilibrating the soils for 48 h with 0.01 M CaCl2, followed by five consecutive 24 h extractions with an Fe-oxide filter strip. Phosphorus sorption in the WTR-amended soils was determined by equilibrating the soils for 48 h with a 75 mg L−1 P solution. The WTR we used was found to reduce the amount of total P desorbed from amended soils by 30–50%, and increased the amount of total P sorbed in the amended soils by 40–60%. In the greenhouse experiment, the alum WTR was incorporated with the same three soils used in the laboratory experiment at the same four rates. Orchardgrass was then grown in the amended soils and germination and early growth were evaluated. At the conclusion of the two-month greenhouse experiment, plants were visually rated, then harvested and dry matter production was determined. Elemental composition of all plants was determined by microwave digestion, and analysis of the digest by inductively coupled plasma emission spectroscopy (ICP). The alum WTR did not significantly reduce germination or plant dry weight at any application rate. Plant P concentrations were reduced at the highest WTR rates, although P deficiency was not observed at any application rate. Elevated extractable Cu levels were also found in the WTR and some WTR-amended soils, but no symptoms of Cu toxicity were observed.