7636 - Laserfiche WebLink

Home Browse Search

20 RESTORATION OF AQUATIC ECOSYSTEMS removing timber from a bottomland hardwood wetland or prevent- ing the construction of levees and tide gates on a coastal marsh. Pres- ervation also implies management (e.g., weed and pest control) of the aquatic ecosystem to maintain its natural functions and charac- teristics. Preservation is sometimes mistakenly linked to mitigation via the assumption that a preserved aquatic ecosystem at one loca- tion will offset or mitigate the losses of displaced aquatic functions at another. Although such preservation may prevent further losses, it cannot compensate for losses already incurred. Preservation is dis- tinct from restoration and creation in that the functions and charac- teristics of the preserved ecosystem are presumed to exist, more or less, in their desired states. This is not to say that the aquatic ecosys- tem has not been subject to changes over the years but that the eco- system is performing in an acceptable manner not requiring reclama- tion or rehabilitation. Whether restored, created, rehabilitated, mitigated, or preserved, most, if not all, aquatic ecosystems subject to the pressures of large human populations need to be managed. Management is the ma- nipulation of an ecosystem to ensure the maintenance of one or more functions or conditions. In the case of preserved, created, or restored aquatic ecosystems, management activities should be directed toward maintaining all functions and characteristics. This is distinct from the management of an aquatic ecosystem for more limited objectives. Controlling water levels in a wetland for duck production is a lim- ited management objective. Another limited objective is releasing water from a reservoir to maintain in-stream flows for trout- fishing. These activities generally ignore the needs of other organisms and bias an ecosystem's characteristics in support of a desired single function. However, management of an aquatic ecosystem need not be limited in scope. Controlled burns of mesic prairies will prevent the intro- duction of weedy plant species and increase plant and habitat diver- sity. The management strategy of using beaver to build dams to prevent stream-bank erosion (Spencer, 1985) may also aid the resto- ration process when, for example, the beavers graze on woody veg- etation and the beaver ponds trap nutrients and sediments (Seton, 1929; Naiman, 1988). Selectively restoring a river meander or a chemical characteristic of a lake is not restoring the aquatic ecosystem unless that is the only significant aspect that has -been degraded. To restore the aquatic ecosystem, all functions and characteristics must be considered, an approach that may in practice be difficult to achieve. However, the term restoration should be applied only to those activities directed to rebuilding an entire ecosystem: reconstructing topography without