The role and use of wetlands

“Over 90% of the wetlands in New Zealand have been drained since European settlement, predominantly to create farmland. Wetlands now have a degree of protection under the Resource Management Act.”

“Wetlands are very effective at filtering and cleaning water pollution ^[13], (often from agricultural runoff from the farms that replaced the wetlands in the first place). To replace these wetland ecosystem services enormous amounts of money have been spent on water purification plants and remediation measures”

http://en.wikipedia.org/wiki/Wetland