Date of Award

5-2022

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Toxicology

Committee Chair/Advisor

Dr. Sarah A. White

Committee Member

Dr. William H. J. Strosnider

Committee Member

Dr. Mark A. Schlautman

Committee Member

Dr. Peter Van den Hurk

Abstract

Excessive phosphorus (P) accumulation and internal P cycling processes within surface waters can contribute to eutrophication, which poses a risk to aquatic ecosystem health and clean water availability. The development of low-cost methods for removing P from water is imperative to reduce the environmental impacts of P pollution. Floating treatment wetlands (FTWs) are a type of modified constructed wetland that can be installed within existing water containment infrastructure, where plants facilitate nutrient removal by direct contact with the water column. FTW plants demonstrate peak growth and nutrient uptake periods in the summer months, though some nutrients, notably P, can be re-released from plant tissues when the plants senesce during winter months. Some management practices recommend annual or seasonal harvest of plant tissues to prevent nutrient release from senescing tissues during the fall and winter months. But the degree to which nutrient release occurs is highly debated in the literature. During these winter months, nutrient removal can be supplemented by other remediation technologies, such as iron oxide (Fe-oxide) based P sorption filters and denitrifying pine bark bioreactors. However, the degree to which design and treatment order affect P removal within these supplemental treatments is not well characterized.

The goal of this research was to 1) quantify the P uptake and release patterns during fall and winter senescence to assess the subsequent spring regrowth potential for plants that have overwintered in FTWs, and 2) assess the P remediation contribution of an Fe-oxide sorption filter within a supplemental treatment train to the FTW mesocosms. Two mesocosm-scale FTW experiments were conducted to characterize plant growth in Juncus effusus and Pontederia cordata plants, plant tissue P accumulation, and the P remediation contribution of supplemental treatments over both a fall and spring season.

These experiments showed that plant senescence induced only a small amount of P export from the P. cordata treatments, but the J. effusus treatments maintained a higher P removal rate, higher survivability, and regrew earlier in the spring after overwintering. Additionally, when P removal by plant treatments slowed during senescence and winter dormancy, combining treatment technologies helped maintain P removal during seasons where plant nutrient uptake was limited. The use of supplemental P remediation methods in conjunction with FTWs will help to optimize year-round nutrient management and help potential users assess the design and lifespan of FTWs and Fe-oxide-based sorption filters for treating P-enriched waters.

These experiments showed that with proper plant selection, the passive management style of overwintering FTWs allows greater opportunity for plants to fix nutrients within their tissues during subsequent growing seasons. Understanding nutrient cycling patterns in plants and how best to maintain nutrient removal year-round is a critical step in helping agricultural operations, stormwater managers, and water treatment facilities improve FTW design and management practices to maximize nutrient removal.

Available for download on Monday, January 09, 2023

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