Environmental Engineering Reference
In-Depth Information
2. SUPRATIDAL AND INTERTIDAL ENVIRONMENTS
In contrast to wave-dominated shorelines, which coarsen landward, tidal flats in
general coarsen seaward parallel to an increase in tidal energy. In tide-
dominated shorelines, a typical tidal-flat profile in a landward direction consists
of a lower intertidal sand flat, a middle intertidal mixed (sand and mud) flat, and
an upper intertidal mud flat. Landward of the mud flat, supratidal salt marshes
may be present (
Figs. 1 and 2
;
Dalrymple, 2010; Klein, 1977
). The intertidal
zone represents an extremely harsh ecosystem in which few species are able
to inhabit the entire tidal range and, accordingly, different animal communities
live in different areas within the tidal flat (
Reise, 1985
). Benthic faunas in supra-
tidal to intertidal settings are mostly controlled by the interplay of (1) salinity,
(2) sediment mobility and hydrodynamic energy, (3) time of exposure to sub-
aerial conditions, (4) temperature, (5) substrate type, and (6) food supply.
Salinity strongly controls the type of organisms and associated biogenic
structures of tidal flats, the emplacement of which may range from the open
shoreline to the fluvio-estuarine transition, encompassing highly variable salini-
ty conditions, from fully marine to brackish water and freshwater (see
M
ยด
ngano
and Buatois, 2004b
). Even in the case of tidal flats directly facing the open
sea, salinity fluctuations may be significant. Periodical fluctuations in salinity
are typically related to periodical emersions and submersions of the intertidal
zone, in combination with wind and solar radiation. In addition, seasonal
FIGURE 2
Integrated sedimentological and ichnological model for intertidal to supratidal environ-
ments.
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