Biosolids and distillery effluent amendments to Irish Miscanthus plantations: Impacts on overland flow and surface water quality

There are plans to use Irish energy crop plantations as repositories of organic by-products (OBs). It is first necessary to determine the risk of surface-water (SW) pollution from amendment of OBs to energy crops under typical Irish conditions. Therefore, the impact of application of two OBs on the quality of overland flow (OLF) emanating from plantations of Miscanthus × giganteus was assessed. Municipal biosolids (BS) and distillery effluent (DE) were spread annually (for four years) on six 0.1174 ha plots at “100%”, “50%” and “0%” treatment rates. The 100% rate was the maximum P-load of 15 t ha−1 allowed by regulation. Surface flows were sampled over 25 months and tested for pH, electrical conductivity, NO3−, P, K, Cu, Cd, Cr, Pb, Ni, and Zn. Results were compared to drinking-water (DW) and SW quality limits; total exports were used to assess risk to SW. The concentrations of nitrate and heavy metals were within DW limits. Concentrations of PO43− were above limits in all cases; K in OLF from M-DEx plots was above DW limits (in some cases). Despite high concentrations, all exports were relatively small, as OLF events were rare and involved small volumes. There was correlation between OB treatment and increases in OLF concentration in some cases, implying higher applications could result in larger exports. Results imply very low SW quality risks exist in areas that are not prone to OLF (at treatment rates and plot scales used). It is recommended further work is conducted to assess risks at catchment scales, particularly for P-loss.