Rivers and associated floodplains have been vitally linked to civilization throughout history for food production. In order to make farming easier and more productive, rivers have been diverted and floodplains have been deforested and drained or leveed to provide fertile land. A major consequence of the widespread use of floodplains and adjacent uplands for agriculture has been the generation of large sediment loads in associated streams and rivers. As a result, much sediment has been deposited on streambeds and floodplains with negative consequences for aquatic habitat and floodplain vegetation. More recently, impoundments have become commonplace for energy production and water storage and levees continue to be built to provide space for development as well as for farming. Globally, it is estimated that, at a minimum, 75% of total floodplain area has been lost.
Floodplain function is dependent on connectivity between the river and its riparian area. Unfortunately, many anthropogenic impacts eliminate or reduce that connectivity so that key functions such as water filtration are much reduced at the landscape level. Similarly, alterations in hydroperiod caused by human activity often drive changes in composition and productivity of vegetation communities as those species adapted to the former conditions decline and are replaced by others.
Additional impacts include fragmentation of riparian vegetation communities and stimulation of invasive non-native plant invasion. Fragmentation often results in reduced habitat quality while successful invasion by non-native species may cause major alterations in community composition, structure, and function. While ecological restoration of floodplains has attracted widespread interest, economic constraints have primarily limited restoration applications to localized areas. However, notable exceptions include restoration of the portions of the Pantanal River Basin in South America and the Kissimmee River Corridor in Florida, USA.
More recently, urbanization has led to significant and growing impacts on floodplains in many parts of the world. As catchments become developed, the concomitant rise in impervious surface drives major increases in runoff volume and velocity. As a result, rising limbs during flood events become much steeper, a condition that is often associated with higher in-channel velocities. Higher flow velocity increases the rate of channel incision resulting in a lowered groundwater table and reduced connectivity between the stream and floodplain. In addition, urbanization stimulates loadings of nutrients (particularly, nitrogen) and causes a considerable degree of water pollution in general.
Further anthropogenic impacts include channelization of river systems. Channelization has benefited farming and waterborne transportation by reducing flooding and removing obstacles to barge and other water traffic. However, water quality has suffered in many instances since there is again less opportunity for river waters to contact floodplain surfaces and undergo pollutant reduction.
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