Assessing the relative and attributable risk of stressors to wetland condition across the conterminous United States

We analyzed data from 967 randomly selected wetland sites across the conterminous United States (US) as part of the 2011 National Wetland Condition Assessment (NWCA) to investigate the relative and attributable risk of various stressors on wetland vegetation condition. Indicators of stress included six habitat stressors (damming, ditching, filling/erosion, hardening, vegetation removal, and vegetation replacement), and two soil stressors (phosphorus and heavy metals) that represent a wide range of human disturbance activities. Risk was evaluated nationally and within four aggregate ecoregions and four aggregate wetland types. Nationally, all of the stressors except soil heavy metals and phosphorus had a significant relative risk but values were always < 2 (a relative risk of two indicates that it’s twice as likely to have poor vegetation condition when the stressor is present relative to when it is absent). Within the different ecoregions or wetland types, no one stressor was consistently dominant. All of the stressors were associated with reduced (poor) vegetation condition in one or another of the subpopulations. Overall, hardening had the highest attributable and relative risks in the most different subpopulations. Attributable risks above 25% were observed for vegetation removal in the Coastal Plain, hardening and ditching in the West, and hardening in Estuarine Woody wetlands. Relative risks above 3 were noted for heavy metals and soil phosphorus in the Interior Plains, and vegetation removal, vegetation replacement, and damming in the Estuarine Woody wetlands. Relative and attributable risk were added to the data analyses tools used in the NWCA to improve the ability of survey results to assist managers and policy makers in setting priorities based on conditions observed on the ground. These analyses provide useful information to both individual site managers and regional-national policy makers.

Impact/Purpose

A team of scientists associated with EPA investigated the relative and attributable risk of various indicators of stress on wetland condition as indicated by vegetation status. Indicators of stress investigated were included six habitat stressor indicators (damming, ditching, filling/erosion, hardening, vegetation removal, and vegetation replacement), and two soil stressor indicators (phosphorus and heavy metals) that represent a wide range of human disturbance activities. The analysis was done at a continental scale by analyzing data from the 2011 National Wetland Condition Assessment (NWCA). Risk was evaluated nationally and within four aggregated ecoregions and four aggregated wetland types. Major findings were: - All of the habitat stressor indicators had a significant relative risk. - No stressor was consistently dominant among the various ecoregions and wetland types, while all stressor indicators were related to poor wetland condition in one or more of the ecoregions and/or wetland types. - Surface hardening had the highest attributable and relative risks in the most ecoregions and wetland types. Through the use of the concepts of relative and attributable risk managers can provide useful information to managers and policy makers as well as a way to set priorities for management actions in specific locales. This study also contributes to work being done under SSWR Task 3.01A, subtask 1.1.

Citation

Herlihy, A., Steve Paulsen, M. Kentula, T. Magee, A. Nahlik, AND G. Lomnicky. Assessing the relative and attributable risk of stressors to wetland condition across the conterminous United States. Springer, New York, NY, 191:320, (2019). [DOI: 10.1007/s10661-019-7313-7]

DOI: Assessing the relative and attributable risk of stressors to wetland condition across the conterminous United States