State Water Resources Research Institute Program

Project ID: 2008MD166B
Title: The biodiversity effect: Do plant species mixtures perform better than monocultures in runoff treatment wetlands?
Project Type: Research
Start Date: 3/01/2008
End Date: 2/28/2009
Congressional District: 5th and 8th Congressional District of Maryland
Focus Categories: Treatment, Wetlands, Water Quality
Keywords: agricultural and urban runoff, non-point source pollution, treatment wetlands, plant biodiversity
Principal Investigator: Baldwin, Andrew
Federal Funds: $ 30,899
Non-Federal Matching Funds: $ 63,146
Abstract: Problem: Nutrients from agricultural and urban runoff (i.e., non-point source pollution) may cause eutrophication, toxic algae blooms, and other ecological impacts in downstream waters, such as the Chesapeake Bay. Numerous studies have examined the effectiveness of constructed wetlands for removing a wide range of water constituents, and the importance of wetland vegetation for nutrient uptake and promoting microbial transformation of nitrogen is well-established. However, surprisingly little systematic research has been conducted on the role of different vegetation types in treatment effectiveness. In particular, almost nothing is known about the role of plant diversity in water treatment.

Extensive research published in the ecology literature during the last decade indicates that a number of ecosystem functions are promoted by higher numbers of coexisting plant species (higher diversity) but no one has applied this fundamental science to the engineering of constructed wetland systems, the subject of our proposed research. To our knowledge, this proposed research will be the first to apply biodiversity-ecosystem function science to ecologically-engineered water treatment systems such as runoff treatment wetlands.

Objectives: The overall goal of this research is to understand how the treatment of agricultural or urban runoff using wetlands is affected by the diversity of planted species. Specific objectives are to:

  1. Create experimental treatment wetland mesocosms (simulating both surface and subsurface flow wetland configurations) containing different plant diversity treatments, and relate diversity treatments to removal of nutrients from water; and
  2. Develop a set of recommendations for planting wetlands to improve runoff water quality and calculate removal rate coefficients for use in designing future runoff treatment wetlands.

Methods: Experimental greenhouse mesocosms will be planted with monocultures or mixtures of two and three plant species. There will be five replicates of each treatment in a randomized block design. Water containing dissolved nutrients (nitrate, ammonium, and phosphate) at concentrations simulating typical ranges for runoff will be pumped into the mesocosms. Vegetation will be monitored non-destructively on a monthly basis. Influent and effluent water will also be monitored on a monthly basis for ortho-phosphate, ammonium, and nitrate. Other environmental variables such as temperature, soil redox potential, and light will be monitored regularly and related to treatment effectiveness. At the end of the growing season above- and belowground biomass will be harvested, sorted by species, dried, weighed, and analyzed for total nitrogen and phosphorus. Removal rate coefficients will be calculated for each treatment, and concentration- and mass-based nutrient removal rates will be compared using analysis of variance (ANOVA) (including repeated measures and covariance analysis where appropriate).

As the first systematic study of the application of biodiversity-ecosystem function science to water quality improvement, the results of this research will be of interest to applied ecologists and environmental scientists, engineers, and managers studying or developing solutions to manage runoff water quality.

Progress/Completion Report, PDF

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