Freshwater Runoff and Salinity
Intertidal sand and mudflats are sensitive to increased rainfall and thus an increased
freshwater input. This may cause scouring of intertidal areas, changes in intertidal
creeks and possibly a reduction in salinity in localised areas. Salinity is an important
variable which influences the populations of intertidal and subtidal areas, especially in
estuaries where it is the dominant factor (McLusky, 1989). On open coasts it is less
important but it may have a significant local influence.
The physiological affects of salinity change are well described (e.g. McLusky, 1989)
and species in intertidal areas are adapted to tolerate changes in salinity by
osmoregulation, reducing oxygen consumption and reducing metabolic activity to conserve
energy (Brown, 1983) or by moving seaward if they are mobile. Thus salinity gradients over
intertidal mud and sandflats will produce zonation in the fauna. In extreme cases of
run-off and freshwater dilution, euryhaline species such as Macoma balthica, Corophium
volutator, Nereis diversicolor, Hydrobia ulvae and brackish oligochaete species
may become permanently established at the top of beaches.