A Mass Balance Study of Application of Municipal Waste Water to Forests in Michigan

Abstract

AbstractA mass balance study of the effects of secondary municipal waste water on phosphorus and nitrogen cycling was conducted in 1976 and 1977 on three 1.2‐ha plots in a late successional, sugar maple (Acer saccharum Marsh.)‐beech (Fagus grandifolia Ehrh.) forest in southern Michigan. The treatments included an unirrigated control plot and 5‐ and 10‐cm/week waste water application plots. The 10‐cm/week site was deliberately overloaded hydraulically. Chloride concentrations at the 150‐cm depth on the waste water application plots did not approach input concentrations until the end of the 1976 irrigation season. Thus, 1977 data are emphasized in mass balance calculations. About 96% of the added inorganic nitrogen from 5 cm/week of waste water application leached past the root zone. Application of 10 cm/week waste water increased inorganic nitrogen “retention” on a mass balance basis to 69% of input apparently as a result of denitrification under anaerobic conditions in the water‐logged soils. However, the 10‐cm/week application resulted in nitrate concentrations approaching those of waste water input concentrations during peak runoff periods. The 10‐cm/week application also resulted in death of trees in the lower areas of the forest where water tended to pool. Phosphorus retention by the system was 96.5% at an application rate of 5 cm/week but decreased to 66% when the irrigation rate was increased to 10 cm/week as a result of runoff losses. Changes in soils included increased available phosphorus and exchangeable magnesium and potassium in the top 15 cm of soil and increased sodium and chloride concentrations throughout the 150‐cm depth sampled.