Wetland degradation and loss in the rapidly urbanizing area of Portland, Oregon

Abstract

An inventory was conducted of small (≤2 ha) freshwater wetlands composed of some combination of open water and emergent marsh in the metropolitan area of Portland, Oregon to (1) document changes in the wetland resource since the National Wetlands Inventory (NWI) was conducted (1981/1982 aerial photograph dates) and (2) identify patterns in wetland loss and degradation over a 10-year period in a rapidly urbanizing area. Wetlands identified on NWI maps were visited during summer 1992, and data on the location, wetland type, and surrounding land use or the cause of loss were collected. Of the 233 wetlands identified by NWI in 1981/1982, approximately 40% had been destroyed by human activities or were missing due to drought. Although conversion to urban land uses was the predominant cause of wetland loss from human activities, agricultural conversion accounted for about 31%. Drier-end wetlands (e.g., seasonally flooded) were missing from the landscape most frequently. Of the 141 wetlands still existing, 25% were severely degraded by human activities. Approximately half of those wetlands not severely degraded were affected by noise, and about 40% were disturbed, primarily by grazing and littering. We suggest that because land uses change quickly in rapidly urbanizing areas, leading to increased pressures to convert wetlands, resource agencies and urban planners should conduct similar inventories in other metropolitan areas. Then, demographic projections could be used in conjunction with information on patterns in wetland loss to identify and prioritize areas for wetland protection before development takes place.