Tamar Estuary
The Tamar estuary is a coastal plain estuary located to the west of Plymouth, a south-western city in England (Grabemann et al., 1997). The Tamar extends from North Cornwall flowing for approximately 100 km towards the south, while amassing water discharge from its two major tributaries, the river Tavy and the river Lynher along the way (Miller, 1999). It has a catchment area of approximately 1700 km 2 (Evans et al., 1993) but together with its two tributaries, the Tamar has a total catchment area of 1.5 x 10 9 m2 (Butler & Tibbitts, 1972). The estuary is tidal for only about 31 km from the Weir head to the mouth at Plymouth Sound (see map) where it discharges into the ocean (Grabemann et al., 1997).
The Tamar estuary experiences a semi-diurnal tidal effect (Uncles & Stephens, 2001) with tidal ranges of 6.5m at springs and 1.5m at neaps (Miller, 1999). At the mouth, it has mean and spring ranges of 2.2 and 4.7 m (Uncles & Stephens, 2001). During spring tides, there is the occurrence of strong tidal pumping of fresh water in the central reaches and also in the lower reaches of the estuary (Uncles & Lewis, 2001) resulting in a flux of suspended sediment to the estuarine bed (Uncles et al., 1985).
There is the presence of turbidity maximum zone (TMZ) where maximum suspended particulate matter (SPM) in the estuary is observed (Uncles & Stephens, 1989; Grabemann et al., 1997). The turbidity maximum commonly occurs in the upper mid estuarine region, usually in the salinity range 1 -5.
The estuary is subject to a number of anthropogenic influences including run off form historic mining sites and discharges from sewage works
Mining metaliferrous deposits (Cu, Pb, Ag, Fe, As, Zn) have occurred over the last nine centauries with the 19 th century being the most active period, particularly for Cu and As, hence the Tamar is subject to metal contamination as a result of runoff from disused sites as well as acid mine drainage from various mine adits along the Tamar valley (Gunnislake).
The Tamar is also subject to point and diffuse sources of nutrients N and P. The diffuse sources being a result of agricultural land use over the general catchment area whereas point sources are due to sewage inputs mainly located in the lower Tamar estuary. For more comprehensive information of these and other chemical inputs and their impacts please refer to Langston et al., (2003).
References
Langston W. J., Chesman B. S., Burt G.R., Hawkins S. J., Readman J., Worsfold P., (2003). Site Characterisation of the South West European Marine Sites, Plymouth Sound and Estuaries cSAC, SPA. MBA Occasional Publication No 9. Available for downloading from the MBA website
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