Pollutant runoff yields in the Yamato-gawa River, Japan, to be applied for EAH books of municipal wastewater intending pollutant discharge reduction

SummaryA Social Experiment Program to decrease municipal wastewater pollutant discharge by “soft interventions” in households and to improve river water quality was conducted in the Yamato-gawa River Basin, Japan. Environmental accounting housekeeping (EAH) books of municipal wastewater were prepared mainly for dissemination purpose to be applied during the Social Experiment Program. The EAH books are table format spreadsheets to estimate pollutant discharges. Pollutant load per capita flowing into water body (PLCwb) and pollutant runoff yields from sub-river basins to the river mouth are indispensable parameters for their preparation. In order to estimate the pollutant runoff yields of the pollutants, BOD, TN and TP, a concept of pollutant runoff yield from upper monitoring point, MPn, to lower monitoring point, MPn+1 (Rmn(n+1)), and that from corresponding sub-river basin (Rd(n+1)(n+1)) was introduced in this paper. When proportion of the pollutant runoff yields, pn (=Rmn(n+1)/Rd(n+1)(n+1)), was equal to 1.0 in all the river sections, which was determined based on the simulation results of Rm and Rd, pollutant runoff yield from sub-river basin n to the monitoring point nearest to the river mouth, Ryn7, were estimated to be 0.3–66.8% for BOD, 25.8–75.8% for TN and 18.9–78.5% for TP. The EAH books of municipal wastewater were prepared by adopting the estimated pollutant runoff yields, Ryn7. The EAH books were thought to be distributed widely, however, they did not seem to be used by many ordinary citizens in the Social Experiment Program in February, 2010, judging from the small number of website visitor counter and less responses from people. Possible reasons for less usage than expected were considered to be unsuccessful negotiation with the official organizations of the Social Experiment Program on the EAH books utilization as official tools and some difficulties in using the EAH books for ordinary people.

Research highlights
► Pollutant runoff yields from sub-river basins to the river mouth were estimated.
► Pollutant runoff yields were estimated with those from the upper and corresponding river basins.
► Pollutant runoff yields were 0.3–67% for BOD, 26–76% for TN and 19–79% for TP.
► The EAH books of municipal wastewater were prepared with estimated pollutant runoff yields.
► The EAH books did not seem to be used by many ordinary people in the Social Experiment Program.