Shallow Water Habitats

Measurements of bottom characteristics of estuaries and coastal marine waters are necessary to understand benthic community structure and function.  Sediment grain size influences the spatial distribution of benthic macrofauna and nekton. Fine-grained sediments can adsorb contaminants, creating a source of potential impairment to benthic communities.  Particulate and dissolved organic matter and nutrients found in sediments can mediate the concentrations of DO, organic contaminants, and metals, and reflect the degree of eutrophication in the overlying water column. 

Physical disturbance, such as resuspension, advection of surface water through sandy sediment, and changes in the water column chemistry may allow sediment dissolved or particulate nutrients to become an additional nutrient source leading to potential eutrophication, phytoplankton blooms, and hypoxia of estuarine and coastal marine waters. Finally, sediment contaminant measurements can provide insights on factors that might limit biological assemblages and lead to potential human health effects. 

It is important that a sampling program be designed to allow for characterization of any relevant variability, e.g., spatial, temporal, or down-core, in bottom characteristics.  New acoustic methods and photographic techniques make it possible to characterize bed sediment characteristics and biogenic structure over large spatial scales.  In shallow water habitats, samples for sediment grain size, organic content, and pore water or exchangeable nutrients at specific sites may be collected directly with small Plexiglas cores, by subsampling larger cores or sediment grabs, and by use of pore water samplers

Sediment grain size analyses are typically completed in the laboratory, although methods have been developed that allow for rapid assessment.  The quantity and quality of sediment organic matter can be estimated using measures of total volatile solids, total organic carbon, total nitrogen and chlorophyll a. 

Sampling and analytical methods for total volatile solids are presented in Standard Methods (APHA 1992). Methods for analyzing soil and sediment porewater and exchangeable dissolved nutrients are described in Methods of Soil Analysis, Soil Science Society of America (1996).  The method for analyzing sediment chlorophyll is presented in Anderson et al. (2003) but modified to reduce freezing time in extractant to 24 hours instead of 72 hours.

For additional details on sampling bottom characteristics refer to the following:

American Public Health Association (APHA). 1992.  Standard methods for the examination of waters and wastewater. American Public Health Association, American Water Works Association, and Water Pollution Control Federation. 18th edition, Washington, DC.

Anderson, I.C., McGlathery, K. J., and Tyler, A. C. (2003). Microbial mediation of reactive nitrogen transformations in a temperate lagoon. Mar. Ecol. Prog. Ser. 246:73-84.

Bale, A. J. and A. J. Kenny. 2005. Sediment Analysis and Characterization. Chapter 2 in Eleftheriou, A. and A. McIntyre. (eds.) Methods for the Study of Marine Benthos. 3rd Edition.  Blackwell Scientific, Oxford, London.

Gibson , G.R., M. L. Bowman, J. Gerritsen and B. D. Snyder. 2000. Estuarine and Coastal Marine Waters: Bioassessment and Biocriteria Technical Guidance. EPA 822-B-00-024. U.S. Environmental Protection Agency, Office of Water, Washington, DC. (sections 3.4 and 6.4)

Smith, C. J. and H. Rumohr.  2005. Imaging Techniques. Chapter 3 in Eleftheriou, A. and A. McIntyre. (eds.) Methods for the Study of Marine Benthos. 3rd Edition.  Blackwell Scientific, Oxford, London.