Date of Award

2014

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Tammi L Richardson

Second Advisor

Erik M Smith

Abstract

Stormwater detention ponds are a common approach to managing stormwater runoff in coastal South Carolina. While effective at preventing flooding, they can be sites of intense phytoplankton blooms that result from excess nutrients inputs. This can lead to water quality degradation within ponds from oxygen depletion, fish kills, health concerns from harmful algal blooms (HABs), and water quality deterioration in adjacent coastal waters when pond discharges. The most common management practice to rid the ponds of excess phytoplankton biomass is the addition of copper-based algaecides. While temporarily effective, these algaecides require regular re-application and lead to artificial cycles of productivity and decomposition within the ponds. The installation of water column aerators (fountains or bubblers) have been proposed as an alternative to control phytoplankton biomass by breaking down thermal stratification and oxygenating the bottom waters which could promote benthic nutrient sequestration and enhance denitrification. The use and effectiveness of aerators has never been researched in the shallow ponds typical of coastal South Carolina.

For this thesis, a Before-After-Control-Impact (BACI) experimental design was used to quantify the effects of aeration on water quality in stormwater ponds near Myrtle Beach, SC. Sets of two ponds in two residential developments were sampled for nutrients, phytoplankton biomass, community composition, and rates of primary productivity over two years. Aerators were installed in one pond of each pair after the first year. We hypothesized that aeration would 1) increase bottom water dissolved oxygen concentrations and thereby increase nutrient retention in sediments and enhance nitrification leading to reduction in water column nutrients and phytoplankton biomass; and 2) increased mixing would shift phytoplankton community composition from potentially harmful cyanobacteria and dinoflagellates towards a community dominated by diatoms. While aeration did enhance mixing and bottom water dissolved oxygen concentrations, overall it had no significant effect on nutrient concentrations, rates of primary productivity, phytoplankton biomass or significantly alter phytoplankton community composition. This research has important implications for developing best management practices and improving coastal water quality in South Carolina as all of these ponds flow directly or indirectly into the coastal zone and are thus potential sources of both chemical and biological pollutants.

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