Draft wetland research plan JP:012202 p.1
Effect of alternate seeding and maintenance strategies on the structure and function of constructed wetlands: Proposed Jones farm wetland restoration research
Background:
Roughly 86% of the wetlands in the continental United States have been drained or altered in the last two centuries (stat cited in McKenna 2003). Concern over the loss of wetland habitat and of ecological services provided by wetlands has resulted in legislative efforts at both state and federal levels to create and restore wetlands. On one hand, there are inducement programs such as the Conservation Reserve Enhancement Program (CREP) that provide farmers with an economic incentive to convert marginally productive wet areas into wetlands (a carrot approach). On the other hand, legislative requirements associated with the “no net wetland loss” policy force developers to “remediate” wetland destruction by either creating wetlands or paying others to do so (a stick approach). In the mid-west much of the restoration effort has focused on converting marginal farmland to wetlands. The guidelines for what constitutes a successful wetland restoration vary with these programs. Conservationists and ecological scientists have also suggested a broad range of criteria for appraising success (e.g. Ewel 1987). The issue of what constitutes ecological success raises a range of interesting research questions and opportunities to test ecological theory (Bradshaw 1987, Ehrenfeld and Toth 1997, Holl et al. 2003). The research we propose here will address the efficacy of alternate seeding and maintenance strategies on the structure and function of the wetlands created on former farmland.
Objectives and assessment of wetland restoration have been diverse:
The fact that wetland creation is motivated by diverse objectives has important implications for efforts to appraise the success of a particular project. Stated objectives include developing habitat for particular animal species (often waterfowl), providing habitat for native native plants and animals, removing sediments from surface waters, and processing and immobilizing nutrients and/or toxins in surface and ground water. Those concerned with the functional value of wetlands increasingly emphasize the importance of a landscape-scale approach to restoration that considers the position of the restored wetland within the watershed, proximity and degree of connection with other ecosystems, and adjacent land use (e.g. Crumpton 2001, Ehrenfeld and Toth 1997, Hobbs and Norton 1996, Holl et al. 2003, Kentula 2000, Palmeri and Trepel 2002, Vellidis et al. 2003, Zedler 2000).
In spite of the expressed need to address multiple objectives at multiple scales, restoration projects still typically focus on achieving just one or two of the objectives listed above while ignoring others. For instance, in agricultural landscapes, the primary objective of wetland creation/restoration is often to remove nutrients, sediments, and/or synthetic organics from rivers (e.g. Mitsch et al. 1995) from uplands and/or directly from agricultural fields (e.g., Crumpton 2001, Zedler 2003). Since restoration objectives vary, a range of criteria have been offered to appraise success (e.g. Kentula 2000). In some circumstances, wetlands designed to maximize benefits for one set of objectives may actually decrease the value for others. For instance, choices designed solely to maximize habit for particular species of waterfowl may result in wetlands with poor water quality (Crumpton 2001). The intent of the proposed research is to evaluate the effect of alternate initiation and management strategies using variables that that assess success in terms of both habitat value and ecosystem function.
Need to assess impact of alternate construction and management practices:
Construction and management approaches are obviously crucial to outcome and vary considerably. Ecological theory suggests that alternate stable communities may occur as a result of even small differences in management and random events that occur over the course of the restoration efforts (Hobbs and Norton 1996). At one extreme are the numerous restoration projects that simply create saturated hydrological conditions by moving earth and altering drainage and then rely entirely on natural recruitment to seed and populate the site with wetland species. This approach typically results in a species composition that differs significantly from natural wetlands of the region and in reduced overall species diversity (Seabloom and van der Valk 2003). A second, slightly more management intense approach, is to seed the site with inexpensive (and oftentimes invasive) monocultures or mixes of plant species such as Typha or Phaelaris. These low intensity practices are common for both remediation and CREP projects conducted on former agricultural fields.
At the other extreme of construction and management intensity are wetlands that are carefully and sometimes sequentially planted and stocked so as to achieve diverse assemblages of native species. Few controlled experiments have been conducted to compare the structure and function of similar sites subject to different planting and management strategies [JP: there may be a bunch out there – I did not look hard]. One unreplicated study was conducted in which a single riparian marsh was planted with 13 native species and a second was vegetated through natural recruitment alone. After 2 years, researchers found that while species diversity differed in the two sites, the marshes did not exhibit differences in nutrient retention (Nairn and Mitsch 2000).
The proposed research at the Jones Farm is designed to assess alternate management strategies. Specifically, we propose to assess the impact of three alternate seeding/management practices: 1) Natural recruitment with selective weeding, 2) One time planting with selective weeding, 3) Multiple plantings with selective weeding. Details of these treatments and of variables used to trace response are described below under “experimental design”.
What do we measure to assess restoration efforts?
The properties of constructed wetlands are assessed both to fulfill legislative requirements and as part of research and monitoring programs. In the case of legal compliance, success is most often assessed by documenting attributes of the plant community such as the presence and/or abundance of wetland indicator species (Kentula 2000). Soils, fauna and hydrologic conditions are also commonly used to assess compliance (Kentula 2000). With respect to research, a wide range field and laboratory techniques are available and have been applied to assessing wetland restoration. For instance, research variables used to trace development of restored wetlands include vegetation and wildlife (Wilson and Mitsch 1996), soil properties [e.g. /BishelMachung, 1996 #3602; Wilson, 1996 #3206], rates of sedimentation (Fennessy et al. 1994a, Harter and Mitsch 2003), aquatic ecosystem metabolism (Cronk and Mitsch 1994, McKenna 2003), macrophyte productivity (Fennessy et al. 1994b, McKenna 2003) above and belowground biomass (Miller and Zedler 2003), nutrient retention (Nairn and Mitsch 2000, Wilson and Mitsch 1996), and algal dynamics (Wu and Mitsch 1998). We propose to use many of these techniques to trace the development of our constructed wetlands (see list below).
Experimental Design:
Six hydrologically isolated wetland cells have been constructed. The restoration requirements associated with this project allow us to completely obliterate vegetation and change experimental designs at some time in the future (so long as we maintain the area as wetland).
Statistical considerations:
Six experimental units allows for two alternate experimental designs. In a regression type design we could select a single treatment and apply it at different levels to each cell. In an ANOVA type design we would compare among replicated treatments. One ANOVA option would be to construct two treatments (or a treatment and a control if you want to look at it that way) with three replicates per treatment. Although less statistically powerful, we have opted for and ANOVA approach that uses three treatments with duplicates for each treatment. Duplicate cells will be treated identically and will be systematically spaced apart from each other so as to minimize biases associated with preexisting soil conditions and edge effects [we need to discuss how to accomplish this].
[I suggest we get a statistician on board this project!]
Experimental treatments and manipulations for the first three years:
Treatments for first three years are designed to assess the effects of seeding and management practices and are outlined below:
1) Natural recruitment:
This treatment will not be planted or seeded.
Three dominant invasive wetland species, Typha,Phragmites and Phaelaris will be selectively weeded out for the first three years.
2) Planted/seeded one time:
This treatment will be planted and seeded once or twice at the start of the experiment.
We need to decide what species composition will be included in this treatment.
Invasives will be weeded out for first three years
3) Multiple staged plantings/seedings to maximize biodiversity
This treatment will be planted at several intervals.
Will the species list be the same for this as for treatment #2 or will treatment #2 be a subset?
Invasives will be weeded out
Experimental treatments and manipulations for future:
Invasibility (yr 4)
Maintain existing cells, but stop management and follow invasion
Do different treatments exhibit differences in invasibility once weeding stops?
Effect of prior management on nutrient retention characteristics (yr 5)
Deliver nutrients to treatments either in pulse or continuous additions
Do different wetlands exhibit differences in nutrient retention or in invasibility in response to nutrient addition?
Recovery from disturbance (e.g. fire, intense grazing?)
Response to variations in hydrology (?)
Variables used to trace wetland development/response:
Restoration effort
#people hours in collecting & planting
#people hours necessary to weed invasives
Estimated financial costs of planting (based on current market price of plants)
Population-level
Differences in populations among treatments
Community-level
Plant species composition, density and diversity
Animal species composition, density and diversity
Invasibility
#people hours necessary to remove plants
#invasives removed per unit time
Ecosystem-level (Biogeochemistry)
Soil/sediment
Soil organic matter
CEC
Total carbon
Redox potential
Sedimentation
Water column
Dissolved inorganic nutrients (NO3, NH4, PO4)
Total system metabolism (measured with in situ dissolved oxygen probes)
Emergent plants
Density
Biomass (above and belowground)
Other physical factors
Water column and sediment temperatures
Landscape-level
Spatial heterogeneity of plants and sediments within each cell
(Ahn and Mitsch 2002, BishelMachung et al. 1996, Bradshaw 1983, Cronk and Mitsch 1994, Crumpton 2001, Ehrenfeld 2000, Ehrenfeld and Toth 1997, Fennessy et al. 1994a, Fennessy et al. 1994b, Harter and Mitsch 2003, Hobbs and Norton 1996, Holl et al. 2003, Jordan et al. 1987, Kentula 2000, Lindig-Cisneros et al. 2003, McKenna 2003, Miller and Zedler 2003, Mitsch 1995, Mitsch et al. 1995, Mitsch et al. 2002, Mitsch and Wang 2000, Nairn and Mitsch 2000, Palmeri and Trepel 2002, Seabloom and van der Valk 2003, Spieles and Mitsch 2000, Vellidis et al. 2003, Wilson and Mitsch 1996, Wu and Mitsch 1998, Zedler 2000, Zedler 2003)
Bibliography
Note: In addition to cited literature, the references below include additional papers that seem relevant to this project. I have a number of these in .PDF format and could potentially post these for easy access if folks are interested.
Ahn C, Mitsch WJ. 2002. Scaling considerations of mesocosm wetlands in simulating large created freshwater marshes. Ecological Engineering 18: 327-342.
BishelMachung L, Brooks RP, Yates SS, Hoover KL. 1996. Soil properties of reference wetlands and wetland creation projects in Pennsylvania. Wetlands 16: 532-541.
Bradshaw AD. 1983. The reconstruction of ecosystems. Journal of Applied Ecology 20: 1-17.
Bradshaw AD. 1987. Restoration: an acid test for ecology. Pages 23-29 in Jordan WRI, Gilpin ME, Aber JD, eds. Restoration Ecology: A Synthetic Approach to Ecological Research. Cambridge, UK. Cambridge University Press.
Cronk JK, Mitsch WJ. 1994. Aquatic metabolism in 4 newly constructed fresh-water wetlands with different hydrologic inputs. Ecological Engineering 3: 449-468.
Crumpton WG. 2001. Using wetlands for water quality improvement in agricultural watersheds; the importance of a watershed scale approach. Water Sci. Technol. 44: 559-564.
Ehrenfeld JG. 2000. Evaluating wetlands within an urban context. Ecol. Eng. 15: 253-265.
Ehrenfeld JG, Toth LA. 1997. Restoration ecology and the ecosystem perspective. Restoration Ecology 5: 307-317.
Ewel JJ. 1987. Restoration is the ultimate test of ecological theory. Pages 31-33 in Jordan WRI, Gilpin ME, Aber JD, eds. Restoration Ecology: A Synthetic Approach to Ecological Research. Cambridge, UK. Cambridge University Press.
Fennessy MS, Brueske CC, Mitsch WJ. 1994a. Sediment deposition patterns in restored fresh-water wetlands using sediment traps. Ecological Engineering 3: 409-428.
Fennessy MS, Cronk JK, Mitsch WJ. 1994b. Macrophyte productivity and community-development in created fresh-water wetlands under experimental hydrological conditions. Ecological Engineering 3: 469-484.
Harter SK, Mitsch WJ. 2003. Patterns of short-term sedimentation in a freshwater created marsh. Journal of Environmental Quality 32: 325-334.
Hobbs RJ, Norton DA. 1996. Towards a conceptual framework for restoration ecology. Restoration Ecology 4: 93-110.
Holl KD, Crone EE, Schultz CB. 2003. Landscape restoration: Moving from generalities to methodologies. Bioscience 53: 491-502.
Jordan WRI, Gilpin ME, Aber JD. 1987. Restoration ecology: ecological restoration as a technique for basic research. Pages 342 in Jordan WRI, Gilpin ME, Aber JD, eds. Restoration Ecology: A Synthetic Approach to Ecological Research. Cambridge, UK. Cambridge University Press.
Kentula ME. 2000. Perspectives on setting success criteria for wetland restoration. Ecol. Eng. 15: 199-209.
Lindig-Cisneros R, Desmond J, Boyer KE, Zedler JB. 2003. Wetland restoration thresholds: Can a degradation transition be reversed with increased effort? Ecol. Appl. 13: 193-205.
McKenna JE. 2003. Community metabolism during early development of a restored wetland. Wetlands 23: 35-50.
Miller RC, Zedler JB. 2003. Responses of native and invasive wetland plants to hydroperiod and water depth. Plant Ecology 167: 57-69.
Mitsch WJ. 1995. Restoration of our lakes and rivers with wetlands - an important application of ecological engineering. Water Science and Technology 31: 167-177.
Mitsch WJ, Cronk JK, Wu XY, Nairn RW, Hey DL. 1995. Phosphorus retention in constructed fresh-water riparian marshes. Ecological Applications 5: 830-845.
Mitsch WJ, Lefeuvre JC, Bouchard V. 2002. Ecological engineering applied to river and wetland restoration. Ecological Engineering 18: 529-541.
Mitsch WJ, Wang NM. 2000. Large-scale coastal wetland restoration on the Laurentian Great Lakes: Determining the potential for water quality improvement. Ecological Engineering 15: 267-282.
Nairn RW, Mitsch WJ. 2000. Phosphorus removal in created wetland ponds receiving river overflow. Ecological Engineering 14: 107-126.
Palmeri L, Trepel M. 2002. A GIS-based score system for siting and sizing of created or restored wetlands: Two case studies. Water Resour. Manag. 16: 307-328.