Date of Award
Ph.D. in Biological Science
Marjorie M Holland
Gregg R. Davidson
Agricultural activities are major sources of non-point pollutants causing eutrophication. Constructed wetlands are used as a best management practice for sequestration of nutrients from agricultural runoff. This dissertation focuses on the influence of vegetation on bacterial community structure, microbial enzyme activities, and phosphorus retention capacity of constructed wetland systems. A greenhouse experiment was conducted using unvegetated or vegetated mesocosms with Juncus effusus, Carex lurida or Dichanthelium acuminatum var. acuminatum in monoculture or mixed culture.
To study the influence of vegetation on the bacterial community structure and microbial enzyme activities, sediment samples were taken from monoculture mesocosms in the greenhouse. β-1,4-glucosidase, phosphatase, and N-acetylglucosaminidase activities were similar for all the samples. Phenol oxidase and peroxidase activities were higher in the unvegetated sediments. Bacterial communities were dominated by Acidobacteria, Proteobacteria and Firmicutes groups. Fewer sequences affiliated with the Firmicutes and Alphaproteobacteria were recovered from unvegetated sediments. Mesocosms were later dosed in August 2007 with 2.5mg/L of phosphorus to study the influence of vegetation on microbial enzyme activities in phosphorus-loaded wetlands. Sediment samples were collected on days 1, 14, 28, 42 and 56 after dosing. The results from this study show that the presence of plants can have a negative impact on the activity of phosphatase, phenol oxidase and peroxidase enzymes.
To study phosphorus retention rates, mesocosms in the greenhouse were dosed with 2.5 mg/L of phosphorus for six months in 2008 and 2009. This was followed by a decomposition experiment to study the release of phosphorus due to plant senescence. The net removal rate was highest for mixed culture (82% in 2008 and 77% in 2009) and C. lurida in monoculture (82% in 2008 and 80% in 2009). Vegetated mesocosms (except for monoculture of D. acuminatum) showed higher removal rate compared to unvegetated mesocosms. Results recommend the use of J. effusus and C. lurida (either grown as monoculture or mixed culture) as plants that could be used for the efficient removal of phosphorus in constructed wetlands. This information indicates that a focused selection of plants can improve the effectiveness of constructed wetlands.
Menon, Rani, "Influence of vegetation on sediment bacterial community structure, microbial enzyme activities and phosphorus retention in constructed freshwater wetlands" (2011). Electronic Theses and Dissertations. 1347.