Water Treatment Residuals and Biosolids Long-Term Co-Applications Effects to Semi-Arid Grassland Soils and Vegetation

Water treatment residuals (WTRs) and biosolids are byproducts from municipal water treatment processes. Both byproducts have been studied separately for land application benefi ts. Th ere are possible environmental benefi ts of WTRs and biosolids co-application but these studies are limited. Our objectives were to determine relative long-term (13-15 yr) eff ects of a single and short-term (2-4 yr) eff ects of repeated WTR-biosolids co-applications on soil chemistry, microbiology, and plant community structure in a Colorado semiarid grassland. Only relative changes associated between co-applications were studied, as we assumed WTR application would only occur if used as a management practice. Th ree WTR rates (5, 10, and 21 Mg ha -1 ) were surface co-applied (no incorporation) with a single biosolids rate (10 Mg ha -1 ) once in 1991 (long-term plots) and again in 2002 (short-term plots). Soil 0- to 8-, 8- to 15-, and 15- to 30-cm depth pH, electrical conductivity (EC), NO 3 -N, NH 4 -N, total C, and total N were not aff ected by WTR application in 2004, 2005, or 2006. Ammonium-bicarbonate diethylenetriaminepentaacetic acid (AB-DTPA)- extractable soil Al was unaff ected by WTR application, but extractable P and Mo decreased with increasing WTR rate because of WTR adsorption. Plant tissue P and Mo content decreased with specifi c plant species and years due to adsorption to WTR; no defi ciency symptoms were observed. Plant community composition and cover were largely unaff ected by WTR application. Soil microbial community structure was unaff ected by WTR co-application rate (total ester-linked fatty acid methyl ester (EL-FAME) concentrations ranged from 33.4 to 54.8 nmol g -1 soil), although time since biosolids-WTR application aff ected a subset of microbial community fatty acids including markers for Gram-positive and Gram-negative bacteria. Overall, WTR-biosolids co-applications did not adversely aff ect semiarid grassland ecosystem dynamics. Abbreviations: AB-DTPA, ammonium-bicarbonate diethylenetriaminepentaacetic acid; EC, electrical conductivity; EL-FAME, ester-linked fatty acid methyl ester; PCA, principal component analysis; WTR, water treatment residual.