Characterisation of European Marine Sites The Severn Estuary (possible) Special Area of Conservation Special Protection Area Marine Biological Association Occasional publication No. 13 Cover Photograph – Aerial view of the Severn Bridge: with kind permission of Martin Swift Site Characterisation of the South West European Marine Sites Severn Estuary pSAC, SPA W.J. Langston∗1, B.S.Chesman1, G.R.Burt1, S.J. Hawkins1, J. Readman2 and 3 P.Worsfold April 2003 A study carried out on behalf of the Environment Agency, English Nature and the Countryside Council for Wales by the Plymouth Marine Science Partnership ∗ 1(and address for correspondence): Marine Biological Association, Citadel Hill, Plymouth PL1 2PB (email: [email protected]): 2Plymouth Marine Laboratory, Prospect Place, Plymouth; 3PERC, Plymouth University, Drakes Circus, Plymouth ACKNOWLEDGEMENTS Thanks are due to members of the steering group for advice and help during this project, notably Mark Taylor, Mark Wills and Roger Covey of English Nature and Nicky Cunningham, Peter Jonas and Roger Saxon of the Environment Agency (South West Region). Helpful contributions and comments from the Countryside Council for Wales and EA personnel from Welsh, Midlands and South West Regions are also gratefully acknowledged. It should be noted, however, that the opinions expressed in this report are largely those of the authors and do not necessarily reflect the views of EA, EN or CCW. © 2003 by Marine Biological Association of the U.K., Plymouth Devon All rights reserved. No part of this publication may be reproduced in any form or by any means without permission in writing from the Marine Biological Association. ii Plate 1: Some of the operations which may cause disturbance or deterioration to key interest features of the Severn Estuary pSAC, SPA 1-3: Process Industries at Severnside 5: Sewage Treatment 4: The Rhondda valley - historically the epicentre of coal mining in South Wales 6: (right) Agricultural run-off 1&5: Ian Britton, Freefoto.com 2 &3: EA 5: Wales Tourist board photo gallery 6: MBA iii Plate 2: Some of the Interest Features and habitats of the Severn Estuary pSAC, SPA 1: Severn Mudflats 2: Saltpans, Bridgwater Bay 3: (right) Bewicks Swan Cygnus columbianus bewickii 4: Twaite shad Alosa fallax 5: Allis shad Allosa alosa 1: Dr Peter French, University of London 2: English Nature (www.oursouthwest.com) 3: Tim Watts 4: fishing-in-kite-country.co.uk 5: Willy Van Cammeren iv 1. EXECUTIVE SUMMARY The Environment Agency (EA), English Nature (EN) and Countryside Council for Wales (CCW) are currently undertaking investigative work in order to review permissions required under regulation 50 of the Conservation (Natural Habitats &c.) Regulations, 1994. Phase 1 of this exercise is the characterisation of designated European marine sites. In the South-West these sites include the Severn Estuary possible Special Area of Conservation (pSAC), Special Protection Area (SPA). This project, undertaken by the Plymouth Marine Science Partnership (PMSP), (comprising Marine Biological Association (MBA), University of Plymouth (UoP) and Plymouth Marine Laboratory (PML)), has two main objectives. Firstly, to characterise the site in terms of water quality, both current and over recent years (up to 2002), and to identify areas where conditions might result in effects on habitats and species for which the site was designated. Secondly, to consider permissions, activities and sources, either alone or in combination which have, or are likely to have, a significant effect on the site. Site characterisation has been accomplished by review of published literature and unpublished reports, together with interrogation of raw data sets, notably that of the EA (this does not include recent compliance data and other forms of self-monitoring for Integrated Pollution Control sites, which was not available). Some of the key findings are: The unique physical features of the Estuary dominate sediment distributions and composition, which are, in turn, the main components governing distributions of organisms. Much of the sub-tidal Severn mud is impoverished in terms of biota and even some sandy areas may be impoverished because of extreme mobility of silts at spring tides. Because physical conditions dominate, for the majority of biological communities, there is little unequivocal evidence of additional impact due to contaminants across the Estuary as a whole. Individual populations may have been impacted, close to major discharges, though most evidence is correlative rather than mechanistic. Metals have traditionally been a major concern in the Estuary, because of smelting and other metal industries. Cd, As, Cr and Hg probably originate mainly from industrial sources around the Estuary whilst Cu, Zn and Ni are predominantly riverine in origin with additional inputs from trade and sewage discharges. Concentrations in sediments are commonly above interim sediment quality guidelines over much of the Estuary, but only occasionally exceed probable effects levels. Bioaccumulation of metals occurs widely in invertebrates, though the ecological significance is still uncertain. Hydrocarbon compounds, including PAHs, are present, locally, in elevated concentrations. Sources include a combination of fossil fuel combustion, shipping, urban run-off, STW and various point-source and diffuse discharges from industrialised areas. Local coal and oil bearing strata also contribute, though the principal component appears to be anthropogenic. Moderately high levels of PAHs are present in sediments from much of the system and for some individual PAHs concentrations occasionally exceed probable effects levels. This may have consequences for benthic fish species and invertebrates. A number of synthetic organic compounds may be present, locally, in elevated concentrations. In the past, monitoring has indicated several pesticide and herbicide v EQS exceedences in rivers entering the Severn Estuary. It would appear that currently, exceedences in the Severn Estuary occur rarely, if at all. However, there is very little robust data with which to characterise the threats to the European marine site from the majority of these compounds. If such threats do occur, these would be expected to be largely localised issues. Only occasionally are elevated levels indicated (e.g. DDT, dieldrin and endrin in sediments; DDT, lindane and dieldrin in eels; dieldrin, triazines and endosulphan in water). Rivers probably introduce the largest loadings (particularly those from catchment areas with intensive agriculture) but there are indications that high pesticide concentrations sometimes occur in discharges. PCB contamination is related to past industrial usage and production (at Newport on the Usk). Sediments close to river mouths and docks are classified as being ‘heavily contaminated’ but decrease at offshore sites. PCBs in eel tissue are elevated in the lower reaches of industrialised catchments in south Wales. Although other fish from Cardigan Bay and the Severn Estuary do not appear to be seriously contaminated, high concentrations have been found in marine mammals from these locations. Data on organotins are surprisingly scarce: however, analysis of dredge spoils in and around the pSAC suggest there may be localised reservoirs of TBT near major conurbations such as Newport and Cardiff, and presumably elsewhere. There are indications of inputs from a number of outfalls thoughout the region. Nutrient levels and loadings in the Severn Estuary are considered significant in UK terms. However, high turbidity means that algal productivity is generally low, except in localised hotspots. Eutrophication is therefore not a major issue within the pSAC. Intermittent oxygen sags occur in low salinity regions of the Severn and in some of the principal rivers feeding the Estuary. These probably originate from the high densities of suspendable solids and associated particulate organic matter, perhaps enhanced by discharge outfalls. Anomalously high concentrations of tritium in sediments and benthic biota in the Cardiff area have been attributed primarily to an industrial discharge. Remedial action has been initiated and an application for a revised discharge has been made. Whilst not a threat to humans, the bioavailability, assimilation pathways and effects of organically-bound tritium on marine life require further investigation. Evidence from loadings, concentration data and EQS compliance frequencies indicates continuing improvements in water quality for the major contaminants (e.g. Cd). The balance of evidence indicates that these may coincide with biological improvements, though the extent to which these events are linked remains uncertain. The persistence and behaviour of sediment-bound contaminants, and their potential combined effects, gives rise to the greatest uncertainty about recovery. The purported decline in eel and Twaite shad populations (and several other fish species) appears to run contrary to the general perception of recovery. It has yet to be established whether the causes are related to water quality or other factors within, or even outside, the pSAC (e.g. fishing pressures, natural variability of stocks). These principal findings are discussed in detail, together with implications for key habitats and species. A major challenge is to establish a more reliable integrated means of assessing future changes in the biology and chemistry of the pSAC. Recommendations are made which may improve understanding of the system and assist Regulatory Authorities