Grantee Research Project Results
Transient Biogeochemical Cycling and Sediment Oxygen DemandEPA Grant Number: F5A20168
Title: Transient Biogeochemical Cycling and Sediment Oxygen Demand
Investigators: Bryant, Lee D.
Institution: Virginia Tech
EPA Project Officer: Packard, Benjamin H
Project Period: July 1, 2005 through June 30, 2008
Project Amount: $111,172
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
This research focuses on the impact of transient lacustrine processes on biogeochemical sediment-water fluxes and sediment oxygen demand in lakes and reservoirs.
Sediment oxygen demand (SOD), which governs dissolved oxygen (DO) depletion in lakes and reservoirs, is largely controlled by oxygen availability and microbial degradation of organic matter. Organic loading of thermally stratified lakes and reservoirs may lead to significant depletion of DO in the bottom (hypolimnetic) water, resulting in the release of chemical species from sediments, decreased water quality, and increased drinking-water treatment costs. The dynamic nature of lacustrine processes (e.g., sediment-laden hydraulic inflows, differential settling of terrigenous material and organic detritus, and variable near-sediment oxygen concentrations) has been established; however, the degree to which SOD and sediment-water fluxes are specifically impacted by spatial and temporal variations in these processes needs further investigation. Hypolimnetic oxygenation systems (e.g., bubble-plume diffusers), used increasingly by drinking water and hydropower utilities to replenish DO while preserving stratification, can also impact SOD and biogeochemical cycling via diffuser-induced mixing and increased oxygen concentration gradients. Little work has been done to quantify oxygen penetration into sediments, “diffuser-induced” SOD, and soluble chemical fluxes at the sediment-water interface as a result of diffuser use. The objective of this research is to investigate and quantify the effects of variations in sediment loading, mineral and organic matter composition of influent sediments, and oxygen availability on biogeochemical cycling and SOD.
A network of measurements based on a comprehensive reservoir sampling grid will be performed. Sediment, porewater, and water column data will be collected prior to, during, and following both sediment loading and diffuser use to isolate the influences of sediment distribution, nutrient loading, and oxygen availability on SOD and chemical fluxes. Specific experimental objectives are to elucidate the effects of sedimentation rate on SOD and to quantify biological and chemical SOD fractions as a function of oxygen availability and sediment composition. Building on recent work that models sediment diagenesis during unsteady-state conditions, data obtained in-situ and in the laboratory will be used to extend an existing sediment model and incorporate the transient processes characterized in this research.
Through this research, the effects of variable sediment accumulation and oxygen concentration on SOD and soluble chemical fluxes will be quantified. This study will enable correct estimates of “diffuser-induced” SOD to be made that will facilitate appropriate design of hypolimnetic oxygenation systems. Understanding the impacts that transient lacustrine processes have on sediments and the overlying water column is crucial for accurately quantifying SOD, optimizing water quality, and enhancing our ability to manage lakes and reservoirs.