Characterisation of European Marine Sites Essex Estuaries European Marine Site Marine Biological Association Occasional Publication No. 17 Cover photograph: The River Blackwater at low tide, from the Promenade, Maldon, Essex. © Barry Samuels Site Characterisation of European Marine Sites Essex Estuaries European Marine Site B.S.Chesman, G.R.Burt & W.J. Langston 2006 A study carried out on behalf of English Nature By The Marine Biological Association, Citadel Hill, Plymouth PL1 2PB (Part of the Plymouth Marine Science Partnership) i ACKNOWLEDGEMENTS Thanks are due to members of the steering group for advice and help during this project, particularly Helen Wake and Michael Coyle (English Nature) and Daniel Bastreri (Environment Agency). We are also indebted to Ms L Noble, Mrs H Treadwell and the staff of the National Marine Biological Library (NMBL) for their assistance with literature surveys. It should be noted that the opinions expressed in this report are largely those of the authors and do not necessarily reflect the views of EN. Preferred citation Chesman, B.S., Burt, G.R. & Langston, W.J. (2006). Characterisation of the European Marine Sites: Essex Estuaries European Marine Site. Marine Biological Association of the United Kingdom Occasional Publication (17). pp 198. (2006) ISSN: 02602784 © 2006 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 1. EXECUTIVE SUMMARY This report provides an overview of water and sediment quality within the Essex Estuaries European Marine Site (EMS) and examines evidence for their influence on biological condition. Site characterisation has been accomplished by review of published literature and unpublished reports, together with interrogation of summary data sets for tidal waters provided by EA. Key findings are as follows: • Some of the more extensive water quality issues relate to hypernutrification1, notably in the Colne and Blackwater and perhaps to a lesser extent, in the Crouch & Roach. Associated influences on DO, turbidity etc. are difficult to establish though there is evidence of macroalgal proliferation in the Blackwater. • Concentrations and risks from water-borne, toxic contaminants appear to be mostly low, though few sites within the EMS have been monitored comprehensively. (Note: IPPC information, discharge data or riverine loadings were not available and therefore it is not possible to comment on sources). • Metals are unlikely to pose an acute threat to the site but some, such as Cu and Zn, could contribute to sub-lethal stress, in combination with other contaminants. Earlier evidence points to an important component from antifouling/ anticorrosion uses, particularly for Cu. STW could also contribute to the Zn loadings. Indications are that the risk of EQS excedence has declined during the last decade. Sediment levels are seldom above probable effects levels for any metal but are sometimes above threshold levels. Contamination in the area tends to be relatively low-level and widespread (reflected also in body burdens), with distributions influenced by variety of processes and inputs, both present-day and historical. For some contaminants, this probably includes a significant contribution from the Thames. • Investigations into the practice of managed retreat indicate that metals such as Fe, Mn and Cd may be released from sediments, whilst Pb, Cr and Cu may increase, following redox and salinity changes that accompany tidal inundation. • TBT threats are receding, generally, but residual contamination remains a concern near marinas, particularly in sediments. Also there are some anomalous TBT increases in the Blackwater. Further ecotoxicological investigations are needed. • There is a dearth of information on PAHs in the EMS. The little that is available indicates that PAH enrichment in sediment is consistent with an anthropogenic origin. Though not as high as those recorded in highly industrialised estuaries, concentrations may represent a chronic threat for benthic organisms (>TEL), notably in the Blackwater Estuary. • Risks from pesticides, herbicides, PCBs, and VOCs appear low, though the data are not sufficient for a rigorous assessment. Pesticides and herbicides in sediments generally indicate low level contamination, with occasional enrichment associated with both urban and agricultural inputs. Episodic pulses of high concentrations of pesticides and herbicides can occur following application to agricultural areas adjacent to tidal waters. This may have consequences for local flora and fauna, though detailed biological effects studies have not been carried out. In the past, sludge dumping and sources in the Thames estuary may have influenced levels of PCBs and DDT in sediment (and perhaps PCBs in biota) at coastal sites (Dengie). • Bradwell nuclear power station has been the main consented source of radionuclides to the EMS for 40 years, but ceased production in 2002. Monitoring 1 See Glossary iii of samples from the Blackwater Estuary, in 2003, indicated that, as in previous years the radiological impact from authorized disposals was relatively low. • Little information exists on endocrine disruption caused by oestrogens or xenoestrogens, except for flounder in the Crouch Estuary, where male fish display relatively low levels of feminization (some vitellogenesis but no ovotestis). There are no data for the Colne and Blackwater, or for invertebrates. • Recent bioaccumulation data are sparse and are largely restricted to mussel sampling at the West Mersea NMMP Shellfish site. Bioaccumulation is not considered a threat here, and the patchy historic data from other sites tend to indicate the same, though bioavailability of most contaminants tends to be above background. Targeted updates on metals, pesticides, PCBs and PAHs, using appropriate monitoring organisms, is suggested, alongside effects studies. • Invertebrate diversity in Essex Estuaries is considered good, although quantitative biodiversity indices have not been applied widely in the EMS. There are few examples of unambiguous links with environmental quality. One exception is decline and recovery of invertebrates in the Crouch Estuary from the effects of TBT pollution. There is no evidence to link the decline in saltmarsh extent (or condition) to water or sediment quality. Offshore, benthic communities tend to be impoverished due, largely, to the nature of the substrate. Despite historical dumping of sewage sludge in the Barrow and Black Deeps, impact on biota was minor. Because of the dispersive nature of the site, and net transport in a NE direction, significant community-level changes within the EMS, particularly estuaries, seem unlikely. • Since the submission of bird population baselines for the original SPA designations, internationally important levels of several of the major qualifying species have declined in two of the component estuaries of the EMS. A number of nationally important qualifying species and non-qualifying species also appear to have decreased over the period. It is uncertain whether these trends can be attributed solely to water quality although reduced freshwater inputs and changes to waste water treatment are cited by BTO as factors directly related to EA consents. • Biological response information, linked to WQ data, is sparse and disjointed for sites within the EMS. Bioassay and biomarker-type studies could provide important contextual information to inform the EMS assessment. Links with the broader biological consequences should also be investigated in the long-term by traditional benthic survey. It is recommended that a programme of harmonised chemical and biological effects monitoring be instigated at the earliest opportunity, focusing on priority contaminants and key biota of the EMS, particularly those which are of major dietary significance for dependent bird populations. • Review of the available chemical data for the area rarely raises concerns over acute toxicity within the EMS, though the possibility that combined pressures might impair performance of sensitive species and communities cannot be ruled out. At present the (limited) evidence probably does not justify expensive remedial action on sources. However, there is sufficient uncertainty to justify a more targeted and detailed programme of research to measure actual biological impacts at a variety of levels (community, population, biochemical, bioaccumulation in suitable indicators). If such studies indicate deleterious effects, which can be attributed to known causes, then the case for remedial action against key sources would be placed on a stronger, scientifically-sound basis. iv CONTENTS 1. EXECUTIVE SUMMARY ..................................................................................... iii 2. INTRODUCTION .....................................................................................................1 3. REFERENCE LISTS AND SOURCES OF INFORMATION .................................5 4. THE SITE: FEATURES AND THREATS ............................................................11 5. STUDIES ON BIOLOGICAL COMMUNITIES....................................................19 6. TRENDS IN WATER AND SEDIMENT QUALITY............................................41 6.1 Toxic contaminants.......................................................................................41 6.1.1 Metals................................................................................................41