Quantifying the extent of human disturbance activities and anthropogenic stressors in wetlands across the conterminous United States: results from the National Wetland Condition Assessment

In 2011, the U.S. Environmental Protection Agency conducted the National Wetland Condition Assessment (NWCA) as part of the National Aquatic Resource Survey (NARS) program to determine the condition of wetlands across the continental U.S.A. Site selection was accomplished using a generalized random tessellated stratified (GRTS) probability design. We investigated the types, extent and magnitude of human activity as an indicator of potential disturbance on a sample of 1138 wetland sites representing a target population of 251,546 km2 of wetlands in the U.S. We developed five metrics representing categories of human activities, an overall Human Disturbance Activity Index (HDAI), and 6 indices of anthropogenic stress on wetland ecological functions to quantify human influences on wetlands. Based on repeat visit data, these metrics and indices were precise enough for regional assessment. Population estimates of the percentage of wetland area affected by varying levels of human activities and anthropogenic stress were made for the U.S. and for reporting groups classified by region and wetland types. Nationally, among the six stressor categories assessed, the percentage of wetland area having high levels of disturbance ranged from 10% due to filling/erosional activities to 27% due to vegetation removal activities. The proportion of wetland area with no signs of human disturbance activity (HDAI=0) within a 140 m diameter buffer area varied widely among the different wetland ecoregions/types we assessed. No visible human disturbance activity was evident in 70% of estuarine wetlands, but among non-estuarine wetlands, only 8% of the wetland area in the West, 15% of the Interior Plains, 22% of the Coastal Plains, and 36% of the Eastern Mountains and Upper Midwest were relatively undisturbed. The woody wetlands of the West were most highly stressed reporting group, with more than 75% of their wetland area subject to high levels of ditching, hardening, and vegetation removal. The NWCA offers a unique opportunity to quantify the type, intensity, and extent of human disturbance activities in and around wetlands and to assess their likely stress on wetland ecological functions at regional and continental scales.

Impact/Purpose

Wetlands are an integral component of our Nation’s aquatic resources, and provide abundant benefits to humans and their environment. The USEPA’s 2011 National Wetland Condition Assessment (NWCA), part of the National Aquatic Resource Surveys (NARS), was the nation’s first statistically-valid and policy-relevant assessment of condition of wetlands across the entire conterminous United States. Nationwide, many wetlands are under the continuing threat of resource extraction or draining to support development including building, farming, and human habitation as our population continues to grow. Anthropogenic disturbance in buffer areas surrounding wetlands has great potential to diminish the ecosystem services of wetlands that depend on critical ecological functions in those wetlands. Identifying, measuring and quantifying human disturbance is critical to assessing the amount and degree to which humans are potentially impairing wetlands across the landscape. In this manuscript, the authors used data collected from the NWCA to identify, quantify and evaluate human disturbances in wetlands and their buffer areas affecting wetland ecological processes (primarily hydrology and vegetation). Indicators were developed and scored from these observations to describe the type and magnitude of human activity and likely stress on wetland ecological functions. These indicators were then used to define the extent and degree of wetland area stressed nationally, and by ecoregion and wetland type. The measures of human disturbance activity we developed were used as a basis for setting criteria for defining least disturbed reference condition and also identifying the most disturbed sites for the NWCA. They were also used directly in the NWCA report as measures of the level of human disturbances in wetlands regionally and nationwide. This manuscript describes a unique and groundbreaking effort in quantifying the type, intensity and extent of human disturbance activities in and around wetlands, and assessing their likely stress on wetland ecological functions at continental scales. This manuscript and the indicators developed therein contribute to work being done under SSWR Task 3.01A, subtask 1.1.

Citation

Lomnicky, G., A. Herlihy, AND Phil Kaufmann. Quantifying the extent of human disturbance activities and anthropogenic stressors in wetlands across the conterminous United States: results from the National Wetland Condition Assessment. Springer, New York, NY, 191:324, (2019). [DOI: 10.1007/s10661-019-7314-6]

DOI: Quantifying the extent of human disturbance activities and anthropogenic stressors in wetlands across the conterminous United States: results from the National Wetland Condition Assessment