The effectiveness and restoration potential of riparian ecotones for the management of nonpoint source pollution, particularly nitrate

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Abstract
The interface found where rivers meet terrestrial systems is an ecotone that has a profound influence on the movement of water and waterborne contaminants. Maintaining or restoring ecotone functions and characteristics such as natural near stream vegetation and channel morphology are important means to safeguard water quality in agricultural landscapes. A riparian buffer zone of 20 to 30 m width can remove up to 100% of incoming nitrate. Denitrification is the major pathway of removal and rates depend on nitrate loadings, carbon availability, and hydrology. Denitrification occurs throughout the year as long as subsurface hydrology is intact, whereas plant uptake of nitrogen is limited to seasonal removal. Nitrate removal is favored in forested areas with subsurface flow and is less in grassed areas with surface flow. The balance between surface and subsurface flows and the redox conditions that result are critical to nitrate removal in riparian ecotones. Surface retention of nutrients and sediment is a function of slope length and gradient, vegetation density, and flow rates. Plant communities play a major role in nitrogen cycling by acting as a source of carbon for denitrifying bacteria, direct uptake of nutrients, and creating oxidized rhizospheres where nitrification can occur. Restoration of riparian zones requires knowledge of the area's hydrology and ecology, as well as clear goals for the project. Restoration of riparian zones for water quality improvement may provide higher economic benefits than allocating the same land to crops. While it is possible to restore the functions of natural floodplain systems, existing restoration techniques are in their infancy and success cannot be guaranteed, especially given the extent of hydrological modification that has occurred in most developed countries.