Objective: Develop a framework to guide county planners and conservationists through the process of prioritizing locations for potential multi-beneficial wetland restoration to capture and control non-point pollution loads from agricultural landscapes.
Author: Laura Flessner; NOAA Coastal Fellow - Association of State Floodplain Managers & The Nature Conservancy
Publication Date: October 14, 2014
Non-point source pollution does not have a single contributor to be held liable for regulating runoff. Therefore, the responsibility to capture and control non-point source runoff requires a cooperative effort between land owners, municipalities, and other key stakeholders. In 2010, the Wisconsin Administrative Codes regarding allowable phosphorus levels in surface waters as well as the performance standards and prohibitions (pdf) that farmers must comply with were made more stringent ("Wisconsin's phosphorous rule"). These changes have motivated counties within the Sheboygan River watershed to more effectively reduce phosphorus discharge from major non-point source contributors like agricultural fields and urban developments.
One example of how these changes in phosphorous regulations are motivating action on the local level is the City of Plymouth, Wisconsin (Figure 1). Located in Sheboygan County just fifteen miles west of Lake Michigan, the city is at the center of a landscape dominated by agriculture, with urban land uses making up about 4% (WI, DNR) of total land cover. Land use changes have caused loss of wetlands, woodlands, and riparian vegetation buffers. Agricultural and urban development has resulted in the loss of about 41% of the original wetlands in the Mullet River watershed and the removal of riparian vegetation and stream cover. Of high concern to city officials is the Mullet River, a tributary to the Sheboygan River which flows into Lake Michigan. The city is seeking alternative ways to manage and control non-point source pollution which is a major contributor of phosphorous to the Mullet River. The city is interested in identifying locations where wetlands can be restored to filter pollution in upstream tributaries, ultimately helping reduce pollution issues for Lake Michigan. In addition to improved water quality, city officials are interested in prioritizing restoration sites based on the potential for wetlands to provide multiple ecosystem services such as surface water storage and flood risk reduction.
Figure 1. Study Area Map (PDF)
Courtesy of: Laura Flessner, The Nature Conservancy
To address these expressed needs, the Association of State Floodplain Managers (ASFPM), The Nature Conservancy (TNC), and NOAA Coastal Services Center (NOAA, CSC), partnered with the Sheboygan County Planning and Conservation Office and the City of Plymouth to identify priority locations for wetland restoration that have the potential to provide the multiple benefits of both nutrient capture and flood reduction within the Mullet Creek watershed. This framework was based on the multi-objective management (MOM) approach to coastal landuse planning and management outlined in the ASFPM's No Adverse Impact (NAI) Toolkit. NAI is an approach to management that emphasizes the "do no harm" principle, by encouraging natural resource managers to anticipate the both beneficial and adverse impacts of any management strategy (Mauriello et al., 2007). This framework was also informed by high resolution landuse and soils data layers from The Nature Conservancy. This case study provides guidance on how others within the region can replicate a similar multi-beneficial function assessment.
Identifying areas where wetlands could be restored with relative ease and developing a framework for prioritizing them based on their ability to store flood waters and capture nutrients was the goal of this study. To understand the rationale behind the previously mentioned framework, the criteria used to prioritize parcels for wetland restoration in Sheboygan County based on their potential to reduce flood risks and capture nutrients must be defined and describe briefly. These criteria are:
- Wetland Characteristics
- Potentially Restorable Wetlands
- Connectivity to the River or Floodplain
- Precipitation Intensity and Frequency
- Best Management Practices
1. Wetland Characteristics
Example of a flourishing wetland.
Courtesy of: The Nature Conservancy
Wetlands are defined as areas where water covers the soil, or is present either at or near the surface of the soil all year or for varying periods of time during the year, including during the growing season. Wetlands vary widely because of regional and local differences in soils, topography, climate, hydrology, water chemistry, vegetation, and other factors, including human disturbance (Wisconsin Wetlands Association). The types of functions a wetland can perform include flood abatement, water quality, wildlife habitat, fish habitat, heritage values, floral diversity, and shoreline protection.
Due to their storage capacity and ability to slow the speed of flood waters, wetlands can help reduce the severity of floods and associated damage in downstream areas. The ability of a wetland to reduce downstream flooding depends on its size, position within the watershed, topography, and vegetation. This study assessed all of these factors when determining which areas have the most likely potential to provide multiple benefits in the Mullet sub-watershed.
In addition to the ecosystem services they provide, wetlands have also been shown to be a valuable resource. A 2011 wetland valuation study in Delaware suggested that the potential cost of replacing the natural nutrient removal services of a healthy wetland with additional municipal water treatment would cost $85 per pound ($188/kg) removed of nitrogen and phosphorus combined. This accumulated to an avoided cost of $9,670,000 for the entire 3,132 acre study area, or approximately $3,080/wetland acre (Delaware Department of Natural Resources and Environmental Control, 2011). Further making the case for the value that wetlands provide in the region, in 2012 the Wisconsin Wetlands Association commissioned a study by Earth Economics that found that Wisconsin's wetlands are worth between $3.2 billion to $152 billion in benefits every year. Learn more in the Rapid Assessment of the Economic Value of Wisconsin's Wetlands report.
Nearly half of Wisconsin's original 10 million acres of wetlands have been drained or developed. In recent decades, progress has been made in wetland protection and restoration, but there is still much more to do.
2. Potentially Restorable Wetlands
Although nearly half of Wisconsin's original 10 million acres of wetlands have been drained, filled, or developed, not all of that wetland acreage is lost forever. Three basic characteristics are used to determine candidate locations for wetland restoration which include:
- Soil type that indicates wetlands could have existed there previously (≥ 85% hydric)
- Land not currently mapped as a wetland
- Land currently identified in a use that is compatible with restoration techniques like agriculture
For this study, a Potentially Restorable Wetlands data set was shared with project partners by The Nature Conservancy and used as the unit of analysis.
3. Connectivity to the River or Floodplain:
Riverine areas, floodplains, and wetlands are extremely interconnected landscape features. Together these landscape features, help to mitigate the effects of agricultural development. Rivers are natural conveyance channels that allow largely quantities of water to flow freely throughout the landscape. When water levels are high or an extreme precipitation event occurs, floodplains provide critical additional storage for excess water. Populated with resilient vegetation, healthy and functioning floodplains stabilize soils, catch sediments before they run into stream channels, and cleanse water of pollutants as it filters through the underlying soils. Finally, wetlands act as the kidneys of the landscape, sponging up water where it falls and cleaning it as it percolates into the ground. These landscape features normally exist as a naturally occurring system which function more efficiently together. As a result, wetland connectivity to rivers and floodplains is a critical factor when determining a wetland's ability to reduce flood risks and capture nutrients ("Flood Protection;" ASFPM, 2008). This study used multiple criteria to measure potential wetland restorations sites' connectivity to the Mullet River and the floodplain including but not limited to: connectivity to the floodplain and headwaters, and whether or not the area was incapable of growing crops due to the frequent presence of excess water.
4. Precipitation Intensity and Frequency
Projected Change in Wisconsin Precipitation Events.
Courtesy of: WICCI
For the purpose of this study, data on precipitation intensity and frequency was used to determine run-off scenarios. Run-off from agricultural fields is a primary contributor of phosphorous and other nutrients into surface waters. Both time of year and intensity of rainfall can amplify the amount of nutrients getting washed into surface waters. Projections show that winter and spring precipitation may increase more significantly. Warmer temperatures will lead to less precipitation falling as snow, and more falling as rain. This increased precipitation combined with land use changes that are more susceptible to runoff like urban developments or agricultural fields can increase pollutants in our waterways and exacerbate flooding. Increases in the frequency and intensity of heavy downpours have been already been observed in the Northeast and Midwest, and these trends are expected to become more severe in coming years (Melilo et al., 2014). Read more...
To learn more about these projected changes, Wisconsin Climate Change Initiative (WICCI) climate scientists have "down-scaled" global climate models to project how Wisconsin's climate has been changing and how it might change in the years to come. Preliminary runoff estimations derived from increased precipitation scenarios for the Sheboygan River basin suggest that even small increases in rainfall can have significant impacts on local and downstream accumulated phosphorus loads. The Nature Conservancy's Climate Wizard also provides climate information.
5. Best Management Practices
Best management practice (BMP) is a general term for an action that has shown to provide soil conservation and water quality benefits. BMPs are voluntary actions, meaning landowners and managers can self-select what practices they would like to employ. With respect to agricultural landscapes, best management practices can be divided into three categories:
Avoiding-type BMPs work to prevent pollution from agricultural development and farming. A few common examples are: crop rotation, contour buffer strips, planting cover crops, and implementing nutrient management practices.
Controlling BMPs attempt to control the amount or reduce the risk of pollution from agricultural landscapes. Some examples are: conservation tillage, rotational grazing, terracing, and planting vegetation in riparian areas.
Trapping BMPs are designed to capture pollutants near their source in an effort to reduce the extent to which they proliferate a watershed. Some examples are: planting filter strips and field borders, constructing sediment control basins, and restoring wetlands.
Example of buffers on farmland.
Courtesy of: USDA Forest Service
Of the many BMPs highlighted here, the framework described in this case study focused solely on wetland restoration. Although other practices like planting filter and buffer strips were initially considered, the resolution of the data available for the Mullet River watershed was not high enough to gather meaningful results from these smaller areas. As a result, they were eventually dropped from the study. As you now know, wetland restoration was the appropriate BMP to analyze for this framework because it provides both ecosystems services that project partners expressed interest in, but this may not be the case for all communities. Others that attempt to implement this framework will likely need to alter some of the criteria and data inputs to reflect their specific concerns and the BMP selected to address them. The options shown here are not comprehensive, many more BMPs are being implemented within the region daily. Read More...
In Sheboygan County, the actions taken to identify priority areas for wetland restoration can be generalized into a 6-step process documented in the interactive work flow below.
For the purpose of this study, a multi-benefit functional assessment was created by project partners to evaluate runoff analyses completed using OpenNSPECT (NSPECT). These analyses were calibrated with local land use data and runoff coefficients to determine areas of high nutrient contribution within the study area and thus areas that might benefit most from wetland restoration. Following the multi-benefit functional assessment, NSPECT was rerun using a "what if" management scenario that assumed that all PRW found to provide both flood abatement and water quality protection services were restored to fully functioning wetlands. To learn more about this process, click on each step of the work flow below. Or reference the extended methodology, here...
For a detailed description of the process used to identify priority locations for wetland restoration in Sheboygan County, please reference the extended case study here...
The results and framework derived from this functional assessment can be employed in three primary ways: 1. they can be integrated into on-going projects, 2. they can be used as planning and education tools, and 3. they can act as the foundation for further research. Using the results of this analysis can help to ensure that they are implemented in the long term.
1. Integrate Research into On-Going Projects:
The results of this study will be used to inform an ongoing project in the region lead by TNC and other partners which aims to target agricultural fields for management of soil and phosphorus loss. The estimated runoff data from this analysis can be used in combination with outputs of SnapPlus (Soil Nutrient Application Planner), a nutrient management planning software, to produce watershed maps showing those fields most in need of management. The recommended PRW sites identified in this study will provide a multi-beneficial management option for landowners.
As the SnapPlus project progresses, the TNC Wisconsin project team will work closely with Sheboygan County, the City of Plymouth, landowners, and other key stakeholders to discuss how the results of these analyses can be implemented effectively in future assessments, planning, and projects. The recommendations here can also be combined with the outputs of the 2009 functional assessment of existing wetlands to help inform restoration and conservation opportunities on a broader scale.
2. Encourage No Adverse Impact Through Community-Wide Education and Planning:
The findings of this research will not bring about any significant reduction in flood risk or nutrient capture if they are never implemented. Stakeholder education is necessary to cause a change in their behaviors and attitudes towards land use and management. The results of this study can be used immediately as a tool to educate land owners and decision makers on the potential benefits of and ideal locations for wetland restoration. Both the hot spot (Figure 6) and parcel prioritization (Figure 8, PDF) maps simply and effectively highlight the areas that have the potential to provide the most benefits if restored. A starting point would be to get into contact with the individuals, organizations, and decision makers who own parcels that were highly prioritized. By taking the time to educate them on the study, the previously mentioned regulations, the potential benefits of wetland restoration, and on government funded cost share programs for wetland restoration projects, land owners and decision makers could be encouraged to voluntarily implement wetland restoration projects.
B. Plan and Manage for Multiple-Objectives:
Integrating the findings of this functional assessment into future plans will help to ensure that city planners and other local decision makers are managing the landscape for mutliple objectives and maximizing on the potential benefits. Specifically, this analysis can help stakeholders prioritize where to work within the Mullet watershed by identifying where PRWs are situated within the study area which have the potential to provide the biggest benefit for the investment. The results found here can also be combined with the City of Plymouth's 20 year development projections to explicitly determine areas where future development pressure may inhibit significant PRW sites (Figure 9). Visualizing this relationship will help stakeholders start thinking about opportunities to avoid growth to protect valuable PRW.
3. Expand Research to Address Additional Best Management Practices:
The primary goal of this study was to provide a replicable framework that can be used to guide the prioritization of restoration of potentially restorable wetlands (PRWs) at a watershed scale. That said, the framework described here could be adapted to evaluate the effectiveness of other best management practices, like filter strips, riparian buffers, and terracing. Going forward, this framework could guide the evaluation of many best management practices and provide insight on their effectiveness. Research of this nature is necessary for making informed management decisions, and will ultimately result in better management overall.