Download Approved Sampling Plan

SEDIMENT OXYGEN DEMAND MEASUREMENTS
1
INTRODUCTION
A critical component of water quality models is the sediment oxygen demand
(SOD). HydroQual, and its predecessor organization Hydroscience, have been measuring
SOD and sediment flux and incorporating it into water quality models for over twentyfive years. Applications include models where measured SOD is directly incorporated,
such as for the Qachita River in Arkansas and Louisiana (July 1992) and state-of-the-art
sediment flux models such as developed for the Chesapeake Bay for the U.S. Army
Corps of Engineers (February 1991). SOD analysis is under the general direction of
Dr.Dominic DiToro. Dr. DiToro is a recognized expert on sediment flux processes and
modeling. Publications include "Sediment Oxygen Demand Model: Methane and
Ammonia
Oxidation,"
(Journal
of
Environmental
Engineering,
ASCE,
September/October, 1991) and "A Diagenic Oxygen Equivalents Model of Sediment
Oxygen Demand," (Sediment Oxygen Demand, Processes, Modeling & Measurement,
University of Georgia Institute of Natural Resources, 1986).
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SAMPLING PROCEDURES
SOD measurements are performed in the laboratory using sediment cores.
HydroQual has found the core technique to generally be more effective than in-situ
methods. Performing SOD measurements in the laboratory allows better analytical
control, allows low water column dissolved oxygen concentrations to be adjusted to
avoid SOD inhibition, and allows replicates to be performed on the same core by
reaerating and repeating the experiment.
Sediment cores are collected using four inch inner diameter plexiglass core tubes
having a beveled lower edge to aid in core tube penetration. Core tubes are manufactured
by Aquatic Research Innovations, Seattle, Washington. Use of these relatively large
diameter core tubes minimizes possible wall effects which could disturb the sediment
sample and also maximizes test sensitivity and availability of overlying sample water for
a given depth of overlying water. Cores are collected upstream of the sampler to
minimize disturbance of the sediment sample. Core tubes are pressed into the sediment
such that, as nearly as possible, 6 inches of overlying water is retained in the core tube
above the core sample. A rubber end cap is then placed on top of the core tube to create a
vacuum which prevents the core sample from slipping downward and the core sample is