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Human activities are affecting the environment at continental and global scales. An example of this is the Mississippi basin where there has been a large scale loss of wetlands and water quality deterioration over the past century. Wetland and riparian ecosystems have been isolated from rivers and streams. Wetland loss is due both to drainage and reclamation, mainly for agriculture, and to isolation from the river by levees, as in the Mississippi delta. There has been a decline in water quality due to increasing use of fertilizers, enhanced drainage and the loss of wetlands for cleaning water. Water quality has deteriorated throughout the basin and high nitrogen in the Mississippi river is causing a large area of hypoxia in the Gulf of Mexico adjacent to the Mississippi delta. Since the causes of these problems are distributed over the basin, the solution also needs to be distributed over the basin. Ecotechnology and ecological engineering offer the only ecologically sound and cost-effective method of solving these problems. Wetlands to promote nitrogen removal, mainly through denitrification but also through burial and plant uptake, offer a sound ecotechnological solution. At the level of the Mississippi basin, changes in farming practices and use of wetlands for nitrogen assimilation can reduce nitrogen levels in the River. There are additional benefits of restoration of wetland and riverine ecosystems, flood control, reduction in public health threats, and enhanced wildlife and fisheries. At the local drainage basin level, the use of river diversions in the Mississippi delta can address both problems of coastal land loss and water quality deterioration. Nitrate levels in diverted river water are rapidly reduced as water flows through coastal watersheds. At the local level, wetlands are being used to treat municipal wastewater. This is a cost-effective method, which results in improved water quality, enhanced wetland productivity and increased accretion. The problems in the Mississippi basin serves as an example for other watersheds in the Gulf of Mexico. This is especially important in Mexico, where there is a strong need for economical solutions to ecological problems. The Usumacinta delta–Laguna de Terminos regional ecosystem is an example where ecotechnological approaches offer realistic solutions to environmental problems. [Copyright &y& Elsevier]

River diversions within the Mississippi Delta deliver river water and associated sediments and nutrients to interior marshes that were previously isolated from river inputs by elevated levees. When isolated from river inputs, the marshes subside and deteriorate to open water, resulting in ecological and economic losses. River diversions are an ecological engineering method to reverse this trend by restoring controlled flows of river water through modified levees. This study compares the cost of constructing and operating the diversions with potential benefits to determine whether the diversions yield a net public benefit. The Caernarvon and Davis Pond river diversions were evaluated using emergy analysis to provide a common basis to quantify and compare economic and ecological costs and benefits. The analysis quantified high concentrations of natural resources inherent to deltas and demonstrated benefits produced by investing economic resources in river diversions to capture and utilize renewable resources. The diversions resulted in large net emergy yield ratios (33.2 and 9.36) that varied depending on the rate of marsh gain produced by the diversions. [Copyright &y& Elsevier]