The area off U.S. coast ("South Atlantic Bight" or SAB) is characterized by a broad,
relatively shallow continental shelf. The bottom is typically
composed of soft sediments (see the geomorphology
- Terrigenous sediments
- Biogenous sediments
- Hydrogenous sediments
Common taxa found in marine soft
diverse assemblage responsible for various geochemical transformations
also known as microphytobenthos
annelids (marine segmented
worms) and other worms
Worms tend to be
important in benthic / water column coupling. They contribute
significant to bioturbation
Some are suspension feeders, others deposit feeders
molluscs (clams, oysters,
...) and Gastropod
arthropods (crab, shrimp,
(sea stars, brittle stars,
sand dollars, sea cucumbers)
Numerous meiofaunal taxa:
(42-500 µm) that live between
sediment grains (up to 2 billion individual/m2) and feed on
detritus, bacteria, and protozoans.
Numerous taxa of demersal
benthic organisms which periodically emerge from the benthos and move
up into the water column" including ostracodes, copepods, and amphipods.
Do these benthic organisms affect the
coupling between sediment and the overlying water column?
Because organic matter produced in the water column above tends to
settle out, bacteria in bottom sediment are
important in remineralization
of organic molecules to inorganic forms) through aerobic respiration using
dissolved oxygen as electron acceptor and anaerobic processes
using a variety of inorganic species (i.e. nitrate, nitrite, manganese
and iron oxides, sulfate).
The vertical distributions of light and oxygen in sediment
Where is photosynthesis by benthic
microalgae the greastest and what is the consequence of this on the
distribution of oxygen with depth within the sediment?
determine the rate exchange of pore water (the water held in the
interstitial spaces between sediment particles) with the overlying
What factor determines what size
particles settle in a given area?
thought of as reduction of nitrate
to N2 with organic matter as the
electron donor (heterotrophic denitrification) though recently other
have been discovered.
availability from the
sediment to the water column is also tied in tightly with sediment
oxygen concentration because phosphate in
the presence of iron
will precipitate (i.e. insoluable) as iron phosphate
(FePO4) making less available.
of organic matter and nutrients on the shelf
- Planktonic production in overlying
shelf exchange of water from
are typical of some estuaries and move up and down the estuary over
tidal cycle. Flocculation (precipitation) of organic and
occurs as cations (e.g. Na+
with river silt, forming
larger clumps that settle toward the bottom ("salting out
The floc may further sorb inorganic and organic compounds (e.g.
phosphates and DOM) and be utilized by both planktonic animals and
benthic animals (both suspension feeders and deposit feeders).
is further enhanced by coupling
with salt marshes (i.e. export
decaying vegetation), and with intertidal
mudflats (sediments are usually black
due to reduced sulfides resulting in absorption
of heat that is released into estuary waters at high tide).
Salt marshes are defined by the presence of
plants that are distributed across an intertidal area. In
cordgrass (Spartina alterniflora), forms a near monoculture in
the lower marsh and is responsible for much of the marsh's
productivity. Salt marsh
systems are extremely
productive (both primary and secondary). Why are these systems so productive?
What determines to what degree this estuarine production influences the
benthic community offshore on the continential shelf?