Thousands of hectares of forested wetlands were converted to emergent, scrub-shrub, and nonvegetated wetlands. These losses were nearly offset by the conversion of forested wetlands to scrub-shrub wetlands. The net gain of thousands of hectares of freshwater emergent wetlands is similarly deceptive. Most of these gains, however, resulted from construction of ponds on uplands not used for agricultural production, but additional thousands of hectares were built on former agricultural lands. This category also experienced gains from converted forested wetlands and scrub-shrub wetlands.
Some functions tend to be compatible, such as flood control and water purification.
Other functions tend to be incompatible, such as flood control and food chain support. In addition, wetlands of a given type do not have the same effectiveness in performing a given function. For example, the effectiveness of a given forested wetland for flood control depends on its size, shape, location in the watershed, and so forth. Because wetlands are constantly being affected by disturbance, their effectiveness in performing functions constantly changes. Uplands can and do perform some of the functions performed by wetlands, such as sediment trapping.