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The response of wetland quality indicators to human disturbance indicators across the United States
Citation:
Herlihy, A., J. Sifneos, G. Lomnicky, A. Nahlik, M. Kentula, T. Magee, M. Weber, AND A. Trebitz. The response of wetland quality indicators to human disturbance indicators across the United States. ENVIRONMENTAL MONITORING AND ASSESSMENT. Springer, New York, NY, 191:296, (2019). https://doi.org/10.1007/s10661-019-7323-5
Impact/Purpose:
A team of scientists associated with EPA investigated the response of indicators of wetland quality to indicators of human disturbance at a continental scale by analyzing data from the 2011 National Wetland Condition Assessment (NWCA). Wetland responses were studied using vegetation condition, soil chemistry and water chemistry data. Observations of human disturbance in and around the randomly chosen sample site documented ditching, damming, filling, hardening, vegetation replacement, and vegetation removal. Landscape-level disturbance (agriculture, development, road and population density) was quantified using GIS data within 200, 500, and 1000-m circular buffers around each site. Major findings were: - Among the three buffer sizes, landscape disturbances were highly correlated and had similar relationships with the response indictors. - Disturbance-response models built using only GIS-landscape data or only field-level data generally explained only a small portion of the pattern in the response variables, whereas, models using both types of disturbance data were better at predicting wetland responses. - The vegetation condition multimetric index (VMMI) had the strongest relationship to the disturbances assessed. Percent agriculture and ditching were the disturbance variables most associated with the VMMI. - National models of wetland responses to soil and water chemistry, and percent cover of alien plant species were not significant, but, it was possible to build significant models predicting presence/absence of alien species and presence of lead in wetland soils above/below the NWCA background concentration of 35 mg/kg. These results provide the first look at the major disturbance factors associated with wetland condition at a national scale. This study also contributes to work being done under SSWR Task 3.01A, subtask 1.1.
Description:
We analyzed data from 1138 wetland sites sampled in 2011 across the conterminous United States as part of the National Wetland Condition Assessment (NWCA) to investigate the response of indicators of wetland quality to indicators of human disturbance at a continental scale. Wetland response indicators were a multimetric index of vegetation condition (VMMI), percent relative cover of alien plant species, soil lead and phosphorus, and water column total nitrogen and total phosphorus. Site-level disturbance indices were generated from field observations of numerous disturbance from 13 plots within a circular 140-m radius area around the randomly chosen site. Summary indices were calculated representing disturbances for ditching, damming, filling, hardening, vegetation replacement, and vegetation removal. Landscape-level disturbance associated with agricultural and urban land cover, roads, and human population were based on GIS data layers quantified in 200, 500, and 1000-m circular buffers around each sample site. Among these three buffer sizes, the landscape disturbance indicators were highly correlated and had similar relationships with the response indictors. Consequently, only the 1000-m buffer data were used for subsequent analyses. Disturbance-response models built using only landscape or only site-level disturbance variables generally explained a small portion of the variance in the response variables (R2<0.2), whereas, models using both types of disturbance data were better at predicting wetland responses. The VMMI was the response variable with the strongest relationship to the disturbances assessed in the NWCA (national model R2=0.251). National multiple regression models for the soil and water chemistry, and percent alien cover responses to disturbance indices were not significant. Logistic regression modeling was more informative, resulting in significant national and wetland subpopulation-specific models predicting site presence/absence of alien species and/or the concentration of lead in wetland soils above background.
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DOI: The response of wetland quality indicators to human disturbance indicators across the United States