The Salinity of the Water Retained in the Muddy Foreshore of an Estuary

Abstract

IT has been shown by Reid (1930) that the salinity of the water retained in a sandy foreshoreat low tide may be considerablyhigher than that of , a stream of brackish water flowing over it. A few similar observations have been made on the salinity of the water held in the muddy foreshore of the estuary of the River Tees.The mud banks exposed at low tide are very soft and glutinous, and contain a high percentage of organic matter derived largely from sewage and industrial wastes with which the estuary is polluted.At low tide, a small hole, some 6 inches deep, was dug in the mud, about 3 feet from the water's edge, and the water which slowly percolated into it was removed in a pipette and filtered. A sample of estuary water was taken at the same time a few feet offshore and the salinity of both samples was determined. The results are shown in the following table, where the average salinity at high water near the estuary bottom at the, stations sampled is also given :- It seems probable that non-burrowing animals living in an estuary are. subjected to greater variations and to lower minimum values of salinity than are burrowing forms at the same distance from the sea. It has been observed that, both in the clean, sandy estuary of the Tay, and in the polluted, muddy estuary of the Tees, burrowing marine animals are, on the whole, relatively more abundant in the central part of the estuary than-

Salinity variation in interstitial water of sand at Kames Bay, Millport, with reference to the distribution of Nereis diversicolor

“…34, 1955 5 parts per mille at 35 m to 16%0at 100m (that is, salinities of 9 and 29%0 respectively). These values were maintained beneath nearly fresh overflowingstream water during low tide (at 100m the flowingsurface stream had a chloride of 2'4%0)' Such a situation has been repeatedly observed in estuarine environments (Reid, 193°, 1932;Alexander, Southgate &Bassindale, 1932). The broad distribution of N. diversicolorcontrasted, however, with the narrow zonal grouping reported by.Watkin, and seemed possibly related to the wide zone of freshwater influence.…”

Size in relation to salinity in fossil and recent euryhaline ostracods

“…In the River Tamar the effect of the tide is very strong, carrying large quantities of fine grade material in suspension, some of which is left behind as it retreats. Amongst the suspension could be ostracod larvae some of which could be stranded by the tide but continue to exist in the interstitial water which in an estuary at low tide is more saline than the water above it (Reid, 1930(Reid, , 1932Alexander, Southgate & Bassindale, 1932). When the larvae become strong enough they would be able to migrate downstream to more saline conditions with the help of later tides.…”

Salinity and Faunal Distribution in the Pocasset River, Massachusetts1

“…These regions are not sharply separated and may move cithcr up or downstream tidally or seasonally (Rlcxander, Southgatc, and Bassindale 1935 ) . In the gradient estuary, the minimum number of species occurs in the middle reaches, the zone of maximum salinity variation ( Remane 1934;Alexander et al 1935 ) .…”

“…Perhaps even more important than salinity fluctuations per se is the rate of change in salinity (Alexander et al 1935). Therefore, the distribution of both marinc and freshwater species in an estuary may be determined, not primarily by the salinity gradient, but by the rate and magnitude of salinity change.…”

“…Published data on this question have been obtained from interstitial water from intertidal sediments during the exposed phase of the tide (Alexander et al 1932;Reid 1930Reid , 1932Smith 1955Smith , 1956. Smith (1956) has been able to show both spatial and regional differences in sediment salinities in his study of the gradient-typo Tamar Estuary.…”