An approach to quantifying the grey water footprint of agricultural productions in basins with impaired environment

Abstract

Grey water footprint (GWF) is an indicator that converts the pollution loads to the equivalent freshwater volume in water footprint (WF) assessment. The conventional application of GWF is to account the embedded water required for the assimilation of pollution loads discharged by production processes. However, this research highlights a deficiency in GWF accounting and proposes an integrated methodology to reinforce GWF to consider the regional environmental concerns in the WF of agricultural productions. This methodology has three main consecutive steps. First, the soil and water assessment tool (SWAT) is used for basin simulation. Second, the WFs of agricultural productions are assessed by the modeling outcomes and according to the conventional approach of GWF accounting. In the third step, an amendment is introduced in WF assessment for accounting the embedded freshwater required for environmental enhancement. This amendment develops multiple-pollutant GWF assessment and increases the WFs of agricultural productions in environmentally impaired basins. This approach is verified in Zrebar Lake basin where farmlands are the main non-point sources and the lake experiences eutrophication. Here, the average WFs of rain-fed and irrigated crops are increased 8.9% and 5.8%, respectively by the developed methodology. In addition, the average ratio of GWF to WF of crops grows from 1.3% to 7.6% and the water pollution level increases more than 5.3 times in basin for WF sustainability assessment. This enhancement in the quantification of GWF is mainly due to the fact that the majority of the GWF of crops in the study area is related to nitrogen pollution loads, while phosphorous reduction is more critical for eutrophication control. Thus, this approach enables the multiple-pollutant GWF to consider the impacts of both pollution loads and ecological impairment in the WF of products. This perspective can promote GWF as an environmental indicator and extend its application for decision-making.