Lignocellulosic-based bioenergy and water quality parameters: a review

Abstract

High rates of crop residue removal as biofuel feedstocks could increase losses of nonpoint source pollutants, negatively affecting water quality. An alternative to residue removal can be growing dedicated bioenergy crops such as warm season grasses (WSGs) and short-rotation woody crops (SRWCs). Yet, our understanding of the implications of growing dedicated bioenergy crops on water quality is limited. Thus, we (i) synthesized and compared the impacts of crop residue removal, WSGs, and SRWCs on water quality parameters (i.e., sediment and nutrient runoff, and nutrient leaching) and (ii) identified research gaps for growing dedicated energy crops. Literature indicates that residue removal at rates >50% (residue retention up to 4.71 Mg ha−1) can increase runoff by 5–15 mm, sediment loss by 0.2–7 Mg ha−1, NO3–N by 0.58–1 kg ha−1, and sediment-associated C by 0.3–57 kg ha−1 per rainstorm event compared to no residue removal. Crop residue removal may also increase nutrient leaching. Studies on the impacts of growing WSGs as dedicated bioenergy crops at field scale on water quality parameters are few. However, WSGs when used as conservation buffers reduce losses of sediment by 66–97%, nutrients by 21–94%, and contaminants by 9–98%. This suggests that if WSGs were grown as dedicated bioenergy crops at larger scales, they could reduce losses of nonpoint source pollutants. Literature indicates that SRWCs can consistently reduce NO3–N leaching. More modeled than field data are available, warranting further field research on (i) field data collection from WSGs and SRWCs from marginal lands, (ii) growing monoculture or polyculture of WSGs, and (iii) large-scale production of energy crops. Overall, dedicated bioenergy crops, particularly WSGs, can reduce losses of nonpoint source pollutants compared to residue removal and be an important strategy to improve water quality if grown at larger scales.