Grimwood & Dixon (1997) reported on metal concentrations found by the Environment Agency in the water column, sediments and biota in 27 Sensitive Marine Areas (SMAs) in England, one of which was for Portland Harbour and the Fleet. Only data for water column concentrations of certain metals from two sites in Portland Harbour were available, relating to samples taken in 1994, >95 and >96. The limited data showed no increasing nor decreasing trend in metal concentrations at either site. Values given (in &micro;g l^-1) were mostly within the following ranges: zinc (1.1-6.6), copper (<0.5-1.6), nickel (0.3-6.5), and arsenic (<1-<2.5). No data was available for lead, chromium, vanadium, boron and iron. A risk assessment exercise indicated that for Portland and the Fleet, isolated concentrations of zinc occurred at levels exceeding the Environmental Quality Standard (EQS) of 5 &micro;g l^-1, and so could present potential risk of ecotoxicological effects to exposed organisms in the short term. However, in the long term, results indicated that levels of zinc were not at concentrations likely to pose significant risks to ecosystem structure and function, and limitations on the zinc EQS were highlighted in the report.

Parr et al (1998) reported on turbidity in English and Welsh waters, however, data were only available for sites at some distance to seawards of the Fleet. These results indicated that marine waters off Chesil Beach were in the highest category for light transmission (75-100%) in summer 1995, and the second highest (50-75%) in winter >95; and the lowest category for presence of chlorophyll a (0-1 &micro;g l^-1) in both summer and winter 1995.

Figure - Distribution of tracer released to mimic inputs from the Abbotsbury swannery after 10 tidal cycles (C12 from Westwater, Falconer and Lin 1999)

Figure - Distribution of tracer released to mimic stream inputs after 10 tidal cycles (C20 from Westwater, Falconer and Lin 1999)

Next Section                 References