Article // Implications of the Nexus Approach When Assessing Water and Soil Quality as a Function of Solid and Liquid Waste Management

By Johan Bouma (Soil Science, Wageningen University). — The Nexus approach is valuable when screening the overwhelming number of publications on water, waste, and soils by: (1) focusing on linkages and trade-offs between the three constituting elements, (2) being a source for inter- and transdisciplinary research, and (3) facilitating communication. To be most effective, the elements should have a comparable degree of detail, and linkages should be expressed in terms of ecosystem services to cover impacts beyond the local. Solid and liquid wastes are well defined in terms of properties, generation, and characterization processes. Regional water regimes can be expressed by widely available hydrological models in which, however, the soil component is usually poorly represented. Unsaturated flow in the soil is crucial for the integration of solid waste (compost), increasing the organic content, and for disposal and purification of liquid waste, the latter either on the surface or in subsurface seepage beds for on-site waste disposal from septic tanks. Every soil has a characteristically different unsaturated flow regime that is insufficiently known at this time. Generation of compost from urban waste is increasing worldwide, offering potential opportunities for soil quality improvement, and successful application of liquid waste to soil cannot only benefit agriculture through irrigation but is also a contribution to groundwater supply and erosion control.