Restoration progress and flood disturbance at IDOT wetland mitigation sites.

Details

• Creators:
  Pociask, Geoffrey E. ; Matthews, Jeffrey W.
• Corporate Creators:
  Illinois Center for Transportation ; University of Illinois at Urbana-Champaign. Dept. of Civil and Environmental Engineering
• Corporate Contributors:
  United States. Federal Highway Administration
• Subject/TRT Terms:
  • Wetlands
  • Flood plains
  • Floods
  • Plants
  • Vegetation
  • Performance measurement
  • Restoration ecology
• Publication/ Report Number:
  FHWA-ICT-13-016 ; ICT-13-016 ; UILU-ENG-2013-2010
• Resource Type:
  Tech Report
• Geographical Coverage:
  Illinois
• Corporate Publisher:
  Illinois. Dept. of Transportation. Bureau of Materials and Physical Research
• Abstract:
  As required under Section 404 of the Clean Water Act and the Illinois Interagency Wetland Policy Act of 1989, the Illinois ; Department of Transportation (IDOT) has established wetlands at mitigation sites throughout Illinois to compensate for ; impacts to natural wetlands by road construction. One of the mechanisms for meeting regulatory obligations is to mitigate ; wetland impacts through restoration or creation of wetlands that provide functions similar to natural wetlands, under the ; federal policy goal of “no net loss” of wetland area and function. Progress toward restoring wetland functions is measured ; through the use of prescribed performance standards issued by state and federal regulatory agencies. In most cases, these ; performance standards contain measures of quality, health, and structure of wetland plant communities. ; The majority of extant Illinois wetlands and most IDOT wetland mitigation sites are located in floodplain areas and are ; exposed to varying degrees of flooding, depending on their location within a given watershed, their position within the ; floodplain setting, and their climate zone within the state. Among the major challenges in attaining vegetation-based ; performance standards at IDOT wetland mitigation projects are poor plant-community quality (e.g., low species richness) and ; mortality of planted trees. Although floodplain wetlands are supported by regular flooding, floods can also produce excessive ; sediment, cause ice damage, and result in prolonged inundation—leading to mortality in wetland plants, thereby interrupting ; expected trajectories of succession and progress toward achieving mitigation performance standards. ; In this study, we analyzed data collected by the Illinois Natural History Survey and the Illinois State Geological Survey ; during past and current site monitoring to examine the influence that flooding has on ecological mechanisms that lead to ; variation in the performance levels among a large number of floodplain compensatory mitigation wetlands. The goals of the ; analyses were to evaluate the influence that flooding has on (1) plant-community quality at the landscape scale and (2) ; species turnover within plant-community functional groups at wetland mitigation sites. For the first component of the analysis, ; we used simple linear regression to evaluate the influence of flooding on the levels of ten plant-community metrics. Results of ; linear regression analysis showed significant, inverse relationships between mean annual flood exposure and average levels ; of three of the ten plant-community metrics: species richness, floristic quality index (FQI), and proportion of perennial species. ; Also, we used hierarchical mixed models to evaluate the influence of flooding on loss and subsequent gain of species within ; seven species functional groups. Mixed models showed significant correlation of the loss of species within all species groups ; with magnitude of flood intensity in the same year, and the gain of non-hydrophytic, annual, and non-native species with ; magnitude of flood intensity in the preceding year. Results of this study indicate two general tendencies at IDOT wetland ; mitigation sites: (1) Higher average magnitudes of flooding will lead to decreased species richness, floristic quality, and ; proportion of perennials in floodplain settings and significantly decrease the likelihood of attaining performance standards ; based on these metrics; and (2) higher-magnitude floods will tend to disrupt succession by eliminating the species groups that ; are associated with higher-quality plant communities and allow more undesirable species to colonize in the year following ; flood disturbance. These tendencies highlight the importance of considering flood-disturbance regime, when evaluating the ; quality of plant communities in floodplain wetlands. ; Additionally, planted-tree counts and mapping were conducted to provide a baseline for future tree-survival studies at ; three sites. Potential future studies would track survivorship of each tree species in response to flood disturbance.
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• Format:
  PDF
• Funding:
  R27-114
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/26739/dot_26739_DS1.pdf
• File Type:
  [PDF - 1.52 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:79214e1d3e6d541ecdbf480e61b83fec0e7881eae13332121a10bc20e6a0ce4c