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Document: Assessment of environmental services of CREP wetlands in Iowa and the midwestern corn belt (Doc-372)

372
Authors
Otis, D. L., W. G. Crumpton, D. Green, A. K. Loan-Wilsey, R. L. McNeely, K. L. Kane, R. Johnson, T. Cooper, and M. Vandever
Year
2010
Title
Assessment of environmental services of CREP wetlands in Iowa and the midwestern corn belt
Document Type
Report
Report Number
3
Abstract
This final project report is a compendium of 3 previously submitted progress reports and a 4th report for work accomplished from August – December, 2009. Our initial primary objective (Progress Report I) was prediction of environmental services provided by the 27 Iowa Conservation Reserve Enhancement Program (CREP) wetland sites that had been completed by 2007 in the Prairie Pothole Region of northcentral Iowa. The sites contain 102.4 ha of wetlands and 377.4 ha of associated grassland buffers. Mass balance models were constructed for each of the 27 wetlands and used to simulate nitrate removal performance across a representative range in hydraulic loading rate and temperature. Models predicted that nitrate mass removal could range from 200 – 3,000 kg/ha/y, depending on hydraulic and nitrate loading rates. The greatest benefit of wetlands for mass nitrate reduction will be found in those extensively row-cropped and tile-drained areas where the nitrate concentrations and loading rates are highest. With respect to wildlife habitat value, USFWS models predicted that the 27 wetlands would provide habitat for 136 pairs of 6 species of ducks, 48 pairs of Canada Geese, and 839 individuals of 5 grassland songbird species of special concern. Wildlife Habitat Relational Models developed by the Iowa Gap Analysis program predicted that the existing CREP wetlands would provide habitat for 192 wildlife species, including 13 species of amphibians, 115 species of birds, 41 species of mammals and 23 species of reptiles. Approximately 30% of these species are listed in the Iowa Wildlife Action Plan as Species of Greatest Conservation Need. Seed mixtures in planted buffers surrounding the wetlands had slight variances but were dominated by 5 native grasses and 10 native forbs from local ecotypes. Field assessment in 2007 of community vegetation in the buffers of a sample of the sites suggested that the first few years after seeding provided an environment suitable for opportunistic annuals, mostly native but not originally seeded. After the initial emergence of these ruderal species, evidence suggests seeded natives became established, providing greater canopy cover. Average canopy cover of seeded and not-seeded grasses varied between fields from 44% greater cover by seeded grasses to 35% greater cover from not-seeded grasses. Our focus in the 2nd phase of the project (Progress Report II and III) shifted to comparative pre- versus post-construction analysis of potential wildlife habitat value in alternative CREP wetland sites within a watershed. Specifically, the 4 hypothesized position types were: tile-zone (TZ), breakpoint (BP), upstream floodplain (USFP), and downstream floodplain (DSFP). (Existing CREP sites would be classified as BP position type.) We used several metrics of predicted wildlife response: species richness, cumulative species habitat value (CHSV), grassland bird density, and waterfowl breeding success, to compare potential habitat value in the 4 landscape positions. We constrained our analysis by considering only bird, mammal, amphibian, and reptile species that were classified as Species of Greatest Conservation Need (SGCN) in the Iowa DNR Wildlife Action Plan. Average species richness generally increased significantly as landscape position moved lower in the watershed, but the largest predicted increases between preto post-construction occurred in TZ and BP locations. Average differences in a metric of site habitat value (CSHV) among position types and between pre- and post-construction times were significant for all taxonomic groups. CSHV increased significantly for all taxonomic groups as the landscape position moved lower in the drainage area. For all taxonomic groups except mammals, there were also significant differences among position types in the net change in CHSV between pre- and post-construction. Bird and reptile habitat increased significantly only in USFP and DSFP sites, and there were no significant net changes in mammal habitat in any position type. A significant increase in amphibian habitat occurred only in DSFP sites. For all species combined, there were significant average increases in habitat in USFP and DSFP sites, no significant increase in BP sites, and a marginally significant increase in TZ sites. The total increase in habitat value was about the same in USFP and DSFP sites, and the smallest increase was in BP sites. The majority of increased habitat value was associated with bird species. Predicted densities of 3 of 4 modeled grassland bird species tended to increase as position type moved lower in the watershed. For all position types, post-project average densities of 3 of 4 species also were greater than the corresponding pre-project average, but smallest increases were consistently in BP sites. The predicted number of breeding waterfowl pairs and recruits differed by landscape position for mallards, blue‐winged teal, and total ducks. Floodplain sites had about twice the numbe
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