113
estuary
largely lost to science. Botanical material arrived safely at Kew and results
were published by the botanist of the expedition and later director of Kew's
Gardens J.D. Hooker in six volumes between 1847 and 1860, which established his scientific reputation. Hooker discovered diatoms in net samples,
bottom sediments and alive in sea ice; these were studied by the well-known
German microscopist Christian Ehrenberg.
erosion loosening, dissolution, or wearing away of the Earth's crust and transportation by natural agencies. The term is sometimes restricted by excluding transportation or weathering.
erratic (geol.) transported rock fragment, deposited at some distance from its
place of origin and generally resting on bedrock or sediment of different
lithology. The term is generally applied to fragments transported by glaciers
or floating ice (-7glaciomarine sediments and -7ice rafting). Erratics range in size
from pebbles to house-size blocks and occur either free or as part of a sediment.
erythrocruorin high molecular weight extracellular hemoglobin molecules, occurring, for instance, in Annelida.
esophagus (or oesophagus) part of the alimentary canal between pharynx and
stomach, passing the food along by peristaltic contraction.
estuarine zone the estuarine part of a sea area. -7estuary.
estuary a semi-enclosed coastal body of water that has a free connection with
the open sea and within which seawater is mixed with freshwater from land.
Important physical processes are the effects of vertical stratification because of
the salinity differences and the longitudinal and vertical mixing by turbulence. This turbulence may be caused by the tides, but also by current shear.
Estuaries are classified by their origin (coastal plain estuaries, lagoonal
estuaries, fjords, faultblock estuaries), by the type of mixing (saltwedge, partially mixed, and well-mixed estuaries), and by the tidal range (microtidal:
tidal range 0-2 m; mesotidal: tidal range 2-4 m, macrotidal: tidal range
more than 4 m). Mixing is largely dominated by the interaction of river outflow and the tides. Estuarine sediments may show a large variation of sands,
silts, muds, and shell or other carbonate deposits. The sediment can be supplied by rivers as bottom load or suspended load, or from coastal seas by
inflow along the bottom. Less important sources are shore erosion, and
organisms. Sedimentation is often highly irregular: during exceptional
floods or storms more sediment may be deposited in a few days than during
many years of normal conditions. In tidal estuaries usually a turbidity maximum develops, so that a zone of muddy sediments and high suspended
estuary
largely lost to science. Botanical material arrived safely at Kew and results
were published by the botanist of the expedition and later director of Kew's
Gardens J.D. Hooker in six volumes between 1847 and 1860, which established his scientific reputation. Hooker discovered diatoms in net samples,
bottom sediments and alive in sea ice; these were studied by the well-known
German microscopist Christian Ehrenberg.
erosion loosening, dissolution, or wearing away of the Earth's crust and transportation by natural agencies. The term is sometimes restricted by excluding transportation or weathering.
erratic (geol.) transported rock fragment, deposited at some distance from its
place of origin and generally resting on bedrock or sediment of different
lithology. The term is generally applied to fragments transported by glaciers
or floating ice (-7glaciomarine sediments and -7ice rafting). Erratics range in size
from pebbles to house-size blocks and occur either free or as part of a sediment.
erythrocruorin high molecular weight extracellular hemoglobin molecules, occurring, for instance, in Annelida.
esophagus (or oesophagus) part of the alimentary canal between pharynx and
stomach, passing the food along by peristaltic contraction.
estuarine zone the estuarine part of a sea area. -7estuary.
estuary a semi-enclosed coastal body of water that has a free connection with
the open sea and within which seawater is mixed with freshwater from land.
Important physical processes are the effects of vertical stratification because of
the salinity differences and the longitudinal and vertical mixing by turbulence. This turbulence may be caused by the tides, but also by current shear.
Estuaries are classified by their origin (coastal plain estuaries, lagoonal
estuaries, fjords, faultblock estuaries), by the type of mixing (saltwedge, partially mixed, and well-mixed estuaries), and by the tidal range (microtidal:
tidal range 0-2 m; mesotidal: tidal range 2-4 m, macrotidal: tidal range
more than 4 m). Mixing is largely dominated by the interaction of river outflow and the tides. Estuarine sediments may show a large variation of sands,
silts, muds, and shell or other carbonate deposits. The sediment can be supplied by rivers as bottom load or suspended load, or from coastal seas by
inflow along the bottom. Less important sources are shore erosion, and
organisms. Sedimentation is often highly irregular: during exceptional
floods or storms more sediment may be deposited in a few days than during
many years of normal conditions. In tidal estuaries usually a turbidity maximum develops, so that a zone of muddy sediments and high suspended