Biosolids and distillery effluent amendments to Irish short rotation coppiced willow plantations: Impacts on overland flow and surface water quality

It's necessary to determine risks of pollution arising from amendment of organic by-products (OBs) to energy crops. The impact of applying two OBs on the quality of overland flow (OLF) from plantations of short rotation coppiced willow was assessed. Municipal biosolids (BS) and distillery effluent (DE) were spread annually on six 0.1174ha treatment plots at rates of 100% (W-BS100, W-DE100), 50% (W-BS50, W-DE50) and 0% (W-BS0, W-DE0). The 100% rate was the maximum load of 15t Pha−1 as per the current Irish regulation based on crop uptake of P. Surface flows were sampled over 18 months and tested for pH, electrical conductivity, NO3−, PO43−, total P, K, Cu, Cd, Cr, Pb, Ni, and Zn. Results showed NO3−, Cu, Cd, Cr, Pb, Ni, and Zn concentrations in OLF were well below quality standard limits set out in European Union (EU) drinking water (DW) and surface water (SW) regulation. For P–PO43− and K, concentrations in OLF exceeded these limits. There were treatment responses for all OLF species, except P and Ni; in some cases there were large increases in OLF concentration as OB treatment rate increased. There was build-up in soil-P, -K and in heavy metals (HMs) following application of BS, but not distillery effluent (DE). Results suggest increased OB application could result in increased export from plots treated with OBs. Despite high PO43− and K OLF concentrations, the occurrence of OLF was rare and volumes lost from plots were low; actual exports of nutrient and HMs by this pathway were small. It was unlikely OLF streams transported particulate matter far from plots, and no preferential flow routes were available to the OLF streams. For these reasons, the OLF encountered during experiments did not pose any serious threat to the quality of nearby surface waters.