ABSTRACT
The return flows from irrigated agriculture (i.e., Irrigation Return Flows, IRF) are considered the major diffuse or ‘‘non-point’’ contributor to the pollution of surface and groundwater bodies.[1] This off-the-farm discharge (‘‘off-site’’ contamination) is inevitable since irrigated agriculture cannot survive if salts and other constituents accumulate in excessive amounts in the crop’s root zone (‘‘on-site’’ contamination), and so they must be reached and exported with the drainage waters.[2]
Thus, the major task concerning the viability and the long-term sustainability of irrigated agriculture is the attainment of a proper balance for optimizing crop production while minimizing both the ‘‘on-site’’ and the ‘‘off-site’’ environmental damages or impacts and, ultimately, finding an acceptable disposal of the IRF.[3,4]
As a consequence of this increasing ‘‘off-site’’ environmental problem, water pollution standards and emerging policies regulating the discharge of the IRF are being implemented in developed countries. The key policies for mitigating the negative environmental impacts of irrigation are incorporated in the Water Pollution Control Act in United States,[5] and in theNitrates, Habitats and Environmental Impact Assessment, and Water Framework directives in European Union.[6]
The degree of the ‘‘off-site’’ irrigation-induced pollution depends on the hydrogeological characteristics of the irrigated land and substrata, the agricultural production technologies used, and the water supply and drainage conveyance systems.[1] This article reviews these issues in IRF, describes the main components and chemical constituents of IRF, and summarizes recommended management practices aimed at reducing the off-site water quality impact from irrigated agriculture.
