Reduced additions to river phosphorus for three years following implementation of a lawn fertilizer ordinance

Abstract

Water quality data collected weekly from May to September 2008–2010 show statistically significant reductions in total phosphorus (TP), dissolved phosphorus (DP), and soluble molybdate-reactive phosphorus (SRP) following implementation of a municipal ordinance limiting the application of lawn fertilizers containing phosphorus (P). No reductions were seen at an upstream control river site not affected by the ordinance. Nontarget analytes including nitrate, silica, colored dissolved organic matter, specific conductance, and pH did not change systematically at experimental sites as did P. The data were compared with a multiyear historical dataset at weekly and subweekly resolution that preceded the ordinance. Mean concentrations of the 3 P analytes were lower than those of the reference period in 43 of 45 comparisons, and statistically significant reductions were observed in one or more of these analytes from June to September, but not in May. A statistical model that incorporated temporal effects, stream flow, and variations at the upstream control site detected highly significant effects of time period (pre- or postordinance) for P, but typically no significant effects for nontarget analytes. The average reductions compared to reference conditions from June to September at 3 sites affected by the ordinance ranged from 24 to 52% for SRP, 23 to 35% for DP, and 11 to 23% for TP.