Quantification of deep drainage flux and drainage water quality characterization below the root zone of a short rotation coppice of willow and poplar receiving municipal treated wastewater irrigation in the lower foothills natural subregion of Alberta.

摘要

Short rotation coppice is a type of bio-energy that involves the management of woody species to be harvested for energy purposes. Short rotation coppice in combination with municipal treated wastewater irrigation offers various benefits, mainly a low cost form of both nutrients and irrigation water. However, wastewater contains plant essential nutrients that can impact groundwater if the systems are mismanaged, i.e. nitrate. To prevent soil salinization from occurring in the root zone, a leaching fraction (LF) is applied. Leaching fraction is the fraction of surface infiltrated water that drains past the root zone. The research objectives involve quantifying and qualifying drainage in a fine textured soil below a SRC with wastewater irrigation system. Drainage was estimated under the wastewater irrigated soil and non-irrigated soil (control) using two methods, the soil water balance and a model based on the chloride mass balance by Rose et al (1979). The drainage in 2010 and 2011 using the water balance was -9.2 and 28 cm, respectively, and the model results were -18.5 and 11.7 cm, respectively. Drainage quality was monitored over 2010 and 2011 for nitrate-N, orthophosphate-P and other solutes using soil solution samplers and a transport model by Schoups and Hopmans (2002). Solute loading rates to groundwater were greater under the wastewater irrigated soil than the control. Nitrate-N in the soil solution at 150 cm below ground surface for both monitoring years never exceeded either the potable water guidelines (10 mg L-1), however, these years had relatively low irrigation amounts and the Schoups and Hopman (2002) model predicted soil solution nitrate-N concentration in exceedance of potable water guidelines at LF's above about 0.55. Based on the findings from this research, it is recommended to use a LF between 0.2 and 0.5 to protect groundwater users, prevent soil salinization and utilize the large supply of municipal treated wastewater available.