Environmental Cleanup and Restoration

CE/ESR 410/510

Glossary of Sediment Terminology

Acid-volatile sulfide (AVS). Defined operationally as the sulfide component of the sediment that will dissolve in acid within 1 hr and then is stripped off as gaseous H2S (hydrogen sulfide). AVS tens to bind up toxic metal in a very insoluble and biologically unavailable form.

Adsorption. The process whereby chemicals (either natural or pollutant) attach to the surface of particles. For example, heavy metals commonly adsorb to clay particles and to natural organic particles.

Anaerobic. Pertaining to microbes that live in the absence of oxygen. Also refers to conditions favorable to these organisms. Similar in meaning to anoxic, but anaerobic properly refers to microbes and their ecology whereas anoxic is simply a description of chemical conditions. Aerobic is the antonym of anerobic and refers to organisms that require oxygen.

Anoxic. An environment devoid of measurable oxygen. Many sediments are anoxic below the sediment-water interface. Oxic implies some measurable or otherwise significant amounts of free oxygen.

Benthos. Collective term for sediment and the organisms that dwell there. Adjective: benthic

Benthic-pelagic coupling. The cycling of nutrients between the bottom sediments and overyling water column. Pelagic refers to deep water, especially in the ocean.

Biogenically reworked zone. The depth zone, within a sediment, that is actively burrowed by benthic organisms. Also called the zone of bioturbation.

Biota. Refers collectively to all the living things in a system.

Detritus. Particulate material that enters into a marine or aquatic system. If derived from decaying organic matter it is organic detritus. Many invertebrate organisms in the sediments are detritus feeder, so detritus is a vital part of the food chain. Detritus can eventually break down into humic material.

Diffusion. The net movement of units of a substance from areas of higher concentration to areas of lower concentration of that substance

Dissolved organic matter. Dissolved molecules derived from degradation of dead organisms or excretion of molecules synthesized by organisms

Disturbance. A rapid change in an environment that greatly alters a previously persistent biological community

Diversity. A parameter describing, in combination, the species richness and evenness of a collection of species. Diversity is often used as a synonym for species richness

Dredge Spoils. During a dredging operation, the dredged sediments to be disposed of are referred to as spoils. They may returned to the water in an area away from the dredging zone (in-water spoil disposal) or they may be placed on dry land (upland spoil disposal). Both methods have environmental and engineering advantages and disadvantages.

Environmental stress. Variously defined as (a) an environmental change to which an organism cannot acclimate and (b) an environmental change that increases the probability of death

Estuary. A semienclosed body of water that has a free connection with the open sea and within which seawater is diluted measurably with freshwater that is derived from land drainage

Epibenthic (epifaunal or epifloral). Living on the surface of the bottom (see Infauna)

foc - Fraction Organic Carbon. The fraction of the sediment that is organic matter, expressed in terms of carbon (MW = 12.00) a dry weight basis. For example foc = 0.02 means that a dried sediment sample is 2% organic carbon by weight. I.e., 1 kg of dry sediment contains 20 g of organic carbon, and inorganic carbon (carbonate minerals like calcite) is not included.

Humic material. Naturally occurring organic matter that comes from decayed plant tissues. Humic material is a good adsorbent of toxic metals and hydrophobic organic compounds, hence it reduces their toxicity by binding them.

Hydrophobic organic compounds (HOC). Organic compounds that "fear" being in the water; in other words, compounds that have a very low solubility in water and therefore more likely found adsorbed to surfaces and partitioned into natural organic (humic) matter. HOCs also tend to accumulate in fatty tissues and thus may become bioconcentrated in the food chain.

Infauna. Living within a soft sediment and being large enough to displace sedimentary grains Adj: infaunal. Compare to interstitial.

Interstitial. Living in the pore spaces among sedimentary grains in a soft sediment (not large enough to significantly displace them. Also refers to the water found in those pores, as in "interstitial chemistry"

Lipids. Oily or fatty components of living tissues. Many hydrophobic organic compounds tend to partition out of water and into lipids, leading to bioaccumulation.

Partitioning. The tendency of a chemical to be divided or "partitioned" between the solid phase and the liquid phase of the sediment. The coefficient that quantifies the extent of this porcess is called the partition coefficient (often designated by Kp or Kd).

Redox-potential discontinuity. That depth below the sediment-water interface marking the transition from chemically oxidative to reducing processes.

Resuspension. The mixing of sediments back up into suspension in the water column. May be caused by natural currents (rivers, wind shear, tides) or by human activities (dredging, boat propellers, ship anchors).

Sediment quality criteria. Guidelines developed by regulatory agencies that specify what constitutes a sediment that is sufficiently contaminated that some sort of protective or cleanup action must be taken. SQCs can be based on chemical composition or on the results of bioassays.

Seston. Particles suspended in the water; particulate matter. Seston can include nonliving material (minerals and detritus) as well as living organisms (plankton).

Spoils. See Dredge spoils.

Suspension feeder. An organism that feeds by capturing particles suspended in the water column.

Total Organic Carbon (TOC). The concentration of organic matter in the sediment, expressed in terms of carbon (MW = 12.00) a dry weight basis (usually g/kg or mg/kg).

Toxicity Testing. In the context of sediments, any of a variety of tests in which one or more organisms that typically inhabit the benthos are exposed to sediments containing known or suspected toxic contaminants. A common standard test is to expose the benthic amphipod Ampelisca abdita to sediments for 10 days, and then determine the survival rates compared to a population exposed to uncontaminated control sediments. That would be an acute toxicity test. Longer exposures would be used to determine chronic toxicity.

Xenobiotic. Refers to chemicals that are biologically active but that are "foreign" to the system. Usually refers to synthetic chemicals such as pesticides and such.