Structural estuaries

Structural estuaries are formed by neotectonic (within the Quaternary period or past 1.8 My BP) processes such as faulting, volcanism, postglacial rebound, and isostacy that have occurred since the Pleistocene. 

Quivira, M.P. (1995) Structural estuaries. In Geomorphology and Sedimentology of Estuaries. Developments in Sedimentology 53 (Perillo, GM.E., ed.), pp. 227-239, Elsevier Science, New York. 

Johnson, J.W., Eagleson, P.S. (1966). Sediment problems at coastal structures. Estuary and coastline hydrodynamics. 462-488, A.T. Ippen, ed. McGraw-HiU New York. 

Brown SS, Gaston GR, Rakocinski CF, Heard RW. 2000. Effects of sediment contaminants and environmental gradients on macrobenthic community trophic structure in Gulf of Mexico estuaries. Estuaries 23 411M24. 

Particular attention has been focused on the toxic effects of aromatic hydrocarbons because these chemicals have proven highly carcinogenic to humans and marine life. Of greatest concern are the PAHs, which are toxic to the benthos at the ppb level. The most common compounds are shown in Figure 28.20 their structures are based on fused aromatic rings. These high-molecular-weight compoimds are very nonpolar and, hence, have low solubilities. Once in seawater, they tend to adsorb onto particles and become incorporated in the sediments. The toxicity of PAHs is enhanced by photochemical reaction with UV radiation. Photo-activated toxicity is especially problematic in shallow-water sediments, such as found in estuaries. 

Estuarine A term used to describe structures, organisms, sediments, and other features associated with estuaries. 

Many of the previous morphological classifications of estuaries provided by Fairbridge (1980) and others fail to make any connection with the prior structure and relief in which an estuary has formed (Perillo, 1995). A more recent modification of this classification system uses an approach that better encompasses the spectrum and diversity of estuarine systems (figure 2.5 Perillo, 1995). It also provides a genetically based linkage of primary and secondary estuaries based on classification of the shoreline (see Shepard, 1973), which considers the prior structure from which an estuary has formed. This morphogenetic... 

Primary estuaries are formed from terrestrial and/or tectonic processes with minimal changes from the sea that have essentially preserved their original characteristics. The four categories within primary estuaries are former fluvial valleys, former glacial valleys, river dominated, and structural. 

The abundance and ratios of important elements in biological cycles (e.g., C, H, N, O, S, and P) provide the basic foundation of information on organic matter cycling. For example, concentrations of total organic carbon (TOC) provide the most important indicator of organic matter since approximately 50% of most organic matter consists of C. As discussed in chapter 8, TOC in estuaries is derived from a broad spectrum of sources with very different structural properties and decay rates. Consequently, while TOC provides essential information on spatial and temporal dynamics of organic matter it lacks any specificity to source or age of the material. 

Figure 9.15 Chemical structures of some of the important sterols used as biomarkers in estuaries (e.g., /3-sistosterol, stigmasterol, campesterol, brassicasterol, and cholesterol).

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