Science Inventory

The National Wetland Condition Assessment


Kentula, M. The National Wetland Condition Assessment. 2016 National Mitigation and Ecosystem Banking Conference, Fort Worth, TX, May 10 - 13, 2016.


The first National Wetland Condition Assessment (NWCA) was completed by EPA in 2011. The results will be released to the public by the Office of Water in 2016. A team of scientists from ORD played a major role in designing the survey, analyzing the data, and reporting on the results of the assessment in cooperation with the Office of Water. The analysis team also developed quantitative national and regional definitions of least disturbed reference condition. This presentation provides a summary of the major results and examples of their utility to wetland mitigation and restoration. About 50% of the wetland area nationally was found to be in good biological condition while about 30% was in poor condition. The stressors with the greatest areal extent nationally were vegetation removal, hardening (e.g., roads, paths, extreme soil compaction), and ditching. A relative risk analysis indicated a strong relationship between high levels of nearly all the stressors measured (i.e., vegetation removal, hardening, ditching, damming, filling/erosion, and vegetation replacement) and poor biological condition. These results can be used by wetland restorationists as a quantitative definition and benchmark of least disturbed (reference) condition and context for evaluating restoration outcomes. In addition, NWCA results can guide development of restoration designs that address effects of stressors closely tied to poor condition. This research also contributes to work being done under SSWR task 3.01A, subtask 1.1.


The first National Wetland Condition Assessment (NWCA) was conducted in 2011 by the US Environmental Protection Agency (USEPA). Vegetation, algae, soil, water chemistry,and hydrologic data were collected at each of 1138 sites across the contiguous US. Ecological condition was assessed in relation to a disturbance gradient anchored by least (reference) and most disturbed sites identified using chemical, physical, and biological disturbance indices. A vegetation multimetric index (VMMI) indicated condition. Potential stressors to condition were incorporated into indices of hydrologic alteration, physical alteration and soil heavy metals, and a nonnative plant indicator. All 1138 sites sampled were placed along a quantitatively defined disturbance gradient customized by ecoregions used in reporting. The characteristics of the 277 sites identified as least disturbed were considered reference. Least disturbed sites are those with the best available condition given the current status of the landscape in which the site is located. Approximately 48±6% of the national wetland area was in good condition; 32±6% in poor condition as measured by the VMMI. Fair condition is the smallest by percent and total area nationally, in two of four regions, and by wetland type. A possible explanation of this pattern is that, we are doing a good job of protecting the best wetlands, while it’s harder to do the same for wetlands that are degraded to some degree. This results in those sites in the fair category drifting into the poor category. It also suggests more protection and restoration are needed for disturbed sites. The NWCA examined the relationship between relative extent of stressors and relative and attributable risk to identify emerging issues and prioritize management responses. Relative risk indicates the likelihood of having poor ecological condition when the magnitude of a stressor is high, while attributable risk estimates the proportion of the target population in poor ecological condition that could be improved if the effects of a stressor were reduced. Vegetation removal, hardening, and ditching had the greatest extent at high stressor levels, affecting 23-27% of the Nation’s wetland area.Those stressors with high relative risk were: vegetation removal, hardening (e.g., parking lots, severely compacted soil), ditching, damming, filling/erosion, vegetation replacement. The stressors with the highest attributable risk were vegetation removal, hardening and ditching. Large error bars indicate caution in drawing conclusions. Nationwide, more that 60% of the wetland area has low stressor levels related to non-native species, while 20% had high or very high levels. Approximately 11% of wetland area in the Coastal Plains, and Eastern Mountains and Upper Midwest had high or very high stressor levels for nonnative plants; the Interior Plains (46%) and West (72%) appear heavily influenced by nonnative plants. The total wetland area estimated to have high or very high nonnative stressor levels is similar for all NWCA ecoregions. The results from the 2011 NWCA can be used in wetland mitigation banking and restoration: As a quantitative definition of least disturbed(reference)condition; For evaluating restoration outcomes; and To prioritize restoration designs addressing effects of stressors tied to poor condition. The report on the 2011 NWCA is scheduled for completion in 2016. The 2016 NWCA will build on 2011 results and add reporting on trends.



Record Details:

Product Published Date: 07/26/2016
Record Last Revised: 07/26/2016
OMB Category: Other
Record ID: 322475