Assessing the impacts of land spreading water treatment residuals on the anecic earthworm Lumbricus terrestris, soil microbial activity and porewater chemistry.

Abstract

Water treatment residuals (WTRs), by-products of drinking water clarification, are increasingly recycled to land to promote circular economy and reduce disposal costs, yet there is a lack of published literature on their effects on soil ecology. In the present study, the effects of WTRs on earthworm growth, soil respiration, and soil porewater chemistry are investigated throughout a seven-week outdoor mesocosm trial. WTRs derived from both aluminium and iron coagulants were applied to a loam soil at 0-20 % (w/w). Additionally, soil from a field that had received long-term WTR applications and that of an adjacent non-treated reference field were included in the study. Earthworm mass increase was significantly higher in all but one laboratory treated soils when compared to the control. Furthermore, a linear regression model can be used to predict increases in weekly soil respiration based on the application rates of both Al and Fe WTRs. In addition, a significant increase in soil respiration was observed from the treated farm soils during the first four weeks of the trial. Measured sodium, magnesium, potassium and iron porewater concentrations were higher in the treated farm soils than reference site soil in a majority of samples, although these differences may be related to land management. Laboratory treated soils had elevated porewater arsenic concentrations (e.g. ~17 µg L-1 in controls vs ~62 µg L-1 in the 20 % w/w Al WTR treatment in week 1), while porewater nickel concentrations were respectively elevated and lowered in Al WTR and Fe WTR amended samples. Overall, observed disturbances to soil ecology were determined to be minimal. This article is protected by copyright. All rights reserved.