The effect of irrigation with wastewaters on the abundance of bio-indicators in established short rotation coppice willow plantations

Abstract

This study investigated the effect of irrigation with wastewaters on the abundance of earthworms, mites and springtails in established short rotation coppice willow plantations. The study examined two different sites in Northern Ireland over two consecutive irrigation periods in 2012 and 2013. Site one (8,100m2) was located at Culmore, Co. Derry and was irrigated with primary treated effluent from a nearby wastewater treatment plant at a rate of 30m3/ha/d. Site two (23,700m2) was located at Hillsborough, Co. Down and was irrigated at variable rates (18, 34 and 44 m3/ha/d) with dairy parlour washings from an on-site farm. Earthworms were extracted by a combination of chemical extraction (mustard solution) and hand-sorting. Mites and springtails were extracted using Berlese-Tullgren funnels. Earthworms proved to be useful bio-indicators to monitor the impact of irrigation with dairy wastewater at site two since their abundance significantly decreased at the highest irrigation rates used at this site (i.e. 34 and 44 m3/ha/day). The abundance of earthworms was not significantly affected by irrigation with municipal wastewater at site one. A variety of earthworm species were recovered in sites one and two (n=8 and n=11, respectively) but the majority of these were present in low numbers. Acid-tolerant earthworm species occurred in greatest numbers at both sites. The abundance of mites and springtails was not affected by irrigation with wastewater in sites one or two, regardless of application rate. Previous land-use significantly affected the abundance of earthworms and mites at site one. A greater abundance of earthworms was observed in plots that had been previously planted with grassland prior to SRC willow conversion in 2010, while a greater abundance of mites was observed in plots that had been previously planted with poplar. No interaction factor was evident between previous cropping history and irrigation.