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Effects of pollution upon the benthos of Belfast Lough
Marine Pollution Bulletin Koeman, J. H., Bothof, Th., De Vries, R., Van Veltzen-Blad, H. & Vos, J. G. (1972). The impact of persistent pollutants on piscivorous and molluscivorous birds. TNO-nieuws, 27, 561-569. Mendola, J. T., Risebrough, R. W. & Blondel, J. (1977). Contamination
de l'avifauneCamarguaisepar des residuosorganochlores.Environm. Pollut., 13,21-31. Olsson, M., Jensen, S. & Renberg, L. (1973). PCB in coastal areas of the Baltic. PCB Conf. II, 4E, 59-68. National Swedish Environment ProtectionBoard 1973. Presst. I., Jefferies, D. J. & Moore, N. W. (1970). Polychlorinated biphenyls in wild birds in Britain and their avian toxicity.Environm. Pollut., 1, 3-26. Renberg, L., SundstrOm,G. & Reutergardh, L. (1978). Polychlorinated terphenyls (PCT) in Swedish White-tailedEagles and in Grey Seals a preliminarystudy. Chemosphere, 7, 477--482. Risebrough, R. W., Reiche,P., Peakall, D. B., Herman, S. G. & Kirven, M. N. (1968). Polychlorinatedbiphenyls in the global ecosystem.
Nature, Lond., 2211, 1098-1102. Sitrkk~i, J., Hattula, M. L., Janatuinen, J., Paasivirta, J. & Palokangas, R. (1978). Chlorinated hydrocarbons and mercury in birds of Lake Paijanne, Finland - 1972-74. Pest. Monit. J., 12, 26-34. Vermeer, K. & Reynolds, L. M. (1970). Organochlorine residues in aquatic birds in the Canadian Prairie Provinces. Can. Field-Nat., 84, 117-130. Vermeer, K. & Peakall, D. B. (1977). Toxic chemicals in Canadian fisheating birds. Mar. Pollut. Bull., 8,205-210. Viviani, R., Crisetig, G., Cortesi, P. & Carpene, E. (1974). R+sidus de polychlorobiphenyls (PCB) et de pesticides chiores dans ies poissons et les oiseaux du delta du Po. Rev. int. Oceanogr. Med., 35/36, 79-90. Zitko, V., Hutzinger, O., Jamieson, W. D. & Choi, P. M. K. (1972). Polychlorinated terphenyls in the environment. Bull. environm. contain. ToxicoL, 7,200-201. Zitko, V. (1974). Trends of PCB and DDT in fish and aquatic birds. Proc. Int. Conf. Transp. Persist. Chem. Aquat. Ecosyst., Ill 61-11164, Ottawa, Canada.
MarinePollutionBulletin,Vol.11,pp.80-83 PergamonPressLtd. 1980.PrintedinGreatBritain.
Effects of Pollution upon the Benthos of Belfast Lough JAMES G. PARKER Department o f Agriculture (N. L ), Fisheries Research Laboratory, Coleraine, N. Ireland BT513RL Prefiminary results of a study of the benthos of Belfast Lough are described. An outline of the rationale and approach and a description of the major trends in the fauna is presented along with an assessment of the principal environmental influences. The gross effects of pollution are confined to the docks area.
Belfast Lough is the receiving water for the domestic and industrial waste water of the city of Belfast and of the industries and towns which surround the lough (Fig. 1). Belfast is the capital city (pop. > 360000) of Northern Ireland and is the largest commercial port in the province. Reports from early this century (Local Government Board for Ireland, 1904) recognised the possibility that the consumption of mussels (Mytilus edulis) from Belfast Lough had resulted in cases of enteric fever; the collection of mussels from the lough was subsequently prohibited. At about the same time, the Royal Commission on Sewage Disposal 0908) was given evidence that the enrichment of Belfast Lough by raw sewage had resulted in the growth of large amounts of Ulva sp. which caused a nuisance around the shores as it decayed. A large amount of sewage effluent still enters the lough at the landward end. The majority of the Belfast population is served by sewage treatment works which provide primary treatment only. Furthermore, the Belfast sewerage is a combined system which carries both foul sewage and stormwater. Because of overloading of the system, untreated sewage frequently enters the tidal waters of the River Lagan which consequently suffers serious contamination by faecal matter (Parker et al., 1979). Crude sewage from Bangor is discharged close to the defined southern limit (Orlock Point) of the lough. Cooling water and process wastewater are discharged to the lough from the manufacture of man-made fibres, fertilizers, bleaches, dyes 80
and from power stations. A new oil-fired power station located at Kilroot Point is nearing completion; one of the largest oil jetties in Europe, projecting over 1 km into the lough, has been constructed to convey the fuel oil to this station. An oil refinery lies on the southern shore of the lough close to the city. The discharge of waste water in Northern Ireland is controlled by the Water Act (NI), 1972. In addition to the wastes which are discharged into the lough there is a sludge dumping site outside the entrance to the lough. The sludge dumped here is mainly primary sewage sludge but some industrial waste is also disposed of in this way. Under licence from the Dumping at Sea Act, 1974, the amount of sludge which may be dumped is limited to 220000 wet tonnes p.a. (DOE, 1977), although the amount dumped is somewhat less than this figure. As well as being an important navigational water, the outer lough supports a limited commercial fishery for cod and whiting; there is a locally important scallop (Pecten maximus) fishery off the mouth of the lough. Parts of the lough have considerable amenity value with sea angling, bathing and sailing being popular at various sites. The effects of pollution upon the ecology of Belfast Lough have not been investigated previously, unlike the other major industrialized estuaries and bays of the UK. This paper reports the preliminary results of benthic studies in Belfast Lough which have the objective of determining to what extent pollution is responsible for the spatial pattern of benthic life. The lough has some unique features when compared with the receiving waters for discharges from other major industrialized regions of the UK. In particular, its waters are almost fully marine, and the bottom slopes gradually to --, 20 m where it meets the North Channel, near the northern limit of the Irish Sea. Belfast Lough is defined as the area lying to the landward of a line drawn from Black Head to Orlock Point (Irish Coast Pilot, 1968), whilst the
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Fig. 1 Belfast L o u g h showing m a i n t o p o g r a p h i c a l features and s a m p l i n g sites (e); arrowed sites contained no benthic macrofauna. Top inset shows c o n t o u r s o f % s i l t / c l a y and areas with M z < 0 . 2 m m . L o w e r inset shows areas with 104 specimens per m 2.
harbour lies to the landward of a line from Carrickfergus to Grey Point. In this paper, the waters lying between these limits are referred to as the outer lough, while the harbour installations in the immediate vicinity of Belfast are referred to as the docks.
Methods During December 1976, a 0.1 m 2 sample of sediment was taken using a Valeport-Hunter grab (Hunter & Simpson, 1976) from each of 41 sampling sites on Belfast Lough (Fig. 1); five of the sites were within the docks area. Sampling positions were timed by means of a Decca Navigator. A 5 cm depth core (10 cm 2 area) of sediment was taken from the undisturbed grab sample and was preserved in industrial methylated spirit. The granulometry of this sub-sample was analysed subsequently by sieving and pipette analysis (Buchanan, 1971); the graphic mean (Mz), inclusive graphic standard deviation (o-t), inclusive graphic skewness (Ski) and graphic kurtosis (/Ca) were determined according to Folk (1974). The bulk of the sediment from each grab sample was washed through a 0.5 mm screen and the retained fraction was preserved in 5070formalin in seawater. The fauna was sorted initially into major taxonomic groups and identification to species level is now in progress. During the sampling programme, the salinity and temperature of the surface (0.5 m) and bottom water was measured in situ
using an EIL MC5/2 salinity and temperature measuring bridge. Associations within and between physical, chemical and biological data were analysed by correlation matrix. The depth of each site and its distance from Belfast were included in the data matrix. The latter gives a crude measure of the distance of each site from the main source of pollution. Localized, possibly important, sources of pollution are ignored at present.
Results and Discussion Physical and chemical fact ors Figure 1 shows the main topographical features of the lough. Although strong tidal currents of up to 2 m s- ~flow past the mouth of the lough, the currents within the lough seldom exceed 0.5 m s-~ at spring tides. Midway between Kilroot Point and Grey Point there is a more-or-less rotary clockwise tidal stream with a spring tide flow of not more than 0.5 m s -~ in any direction (Irish Coast Pilot, 1968). Evidently, these weak tidal streams promote the settlement of fine sedimentary particles. The range of values for siltclay content (< 63 ~m) was 0.4°7o to 85.9070, and the mean silt-clay content over all sites was 32.9°7o. The median grain size (Mz) varied between 0.02 and 1.35 mm. There was a considerable patchiness underlying the main trends of sediment distribution shown in Fig. 1. There were clear horizontal and vertical gradients of 81
Marine Pollution Bulletin 3[i AMPHIPODA
TABLE 1
Thecompositionof BelfastLoughbenthicfauna, December1976 Taxonomic 070of specimens Mean nos. group in group per0.1 m 2 Polychaeta 41.1 389 Oligochaeta 16.4 155 Isopoda 13.3 126 Amphipoda 13.3 126 Pelecypoda 6.9 65 Cumacea 3.7 35 Cirripedia 2.5 24 Ostracoda 1.5 13 Sipunculida Ophiuroidea Anthozoa Decapoda Gastropoda Mysidacea Echinoidea
total 5 °70
each < 10 per0.1 m 2
salinity and temperature within the lough. In the tidal waters of the River Lagan (Parker et al., 1979) and the docks area, the surface salinity was influenced strongly by the freshwater flow. Proceeding seawards, the surface layer (1 m) of the river became gradually more saline. The minimum salinity of water at 1 m depth leaving the docks area was 17.0°700. The minimum salinity recorded in the bottom water of the docks area was ~28o700. The distribution of surface salinities in the harbour area, excluding the docks, indicated that fresh water from the River Lagan has little influence on the lough. Surface salinlties in the harbour area were usually >31 °7oo. In the outer lough the surface salinity reached >33%o; here, the distribution of salinity was more homogeneous than in the inner lough. A small but significant (P<0.01) vertical salinity gradient was present in the lough. Bottom salinity was on average 0.4°7oo higher than the surface salinity, the difference becoming less marked towards the seaward end of the lough. Associated with the salinity gradients were highly significant (P<0.001) gradients of temperature. During the sampling programme, the bottom temperature at the seawards end of the lough was up to 3°C higher than that of the harbour area. Clearly, this temperature gradient may have major consequences for the reproductive cycles of the benthic communities. The effect of salinity, however, is likely to be minimal except for communities within the docks complex.
Benthicfauna Around 40 000 specimens were obtained from the benthic sampling programme and their distribution into major taxa is shown in Table 1. Three sampling sites in the docks area were devoid of benthic macrofauna (Fig. 1) undoubtedly as a consequence of the anaerobic and sulphide-rich nature of the sediment. Those sites within the docks which supported a benthic fauna were dominated by Oligochaeta, Peioscolex benedeni being prominent among this group. The polychaetes Nereis diversicolor, N. virens, Polydora ciliata and Capitella capitata also occurred. At the seawards end of the docks, Nephtys hombergii, Spio filicornis, Heteromastus filiformis, Scoioplos armiger and Tharyx sp. were also present. Ampelisca brevicornis (Amphipoda), Pseudocuma longicornis and Diastylis sp. (Cumacea) were also found in the docks area along with a small number of bivalve molluscs. 82
.
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.
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I I. 5 10 Distance from Belfast
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Fig. 2 Regressionof numbers of amphipods on distance from Belfast (r = correlationcoefficient).
Polychaeta dominated the fauna of 19 sampling sites. The distribution of the polychaetes showed a significant (P < 0.1) positive correlation with Ka but not with any other environmental factor. The Oligochaeta were next in order of abundance and dominated 11 sampling sites. Many oligochaete species are able to tolerate a wide range of salinities and often thrive in estuarine sediments which are rich in organic matter. The distribution of oligochaetes was not significantly associated with salinity in this study. However, the abundance of oligochaetes decreased significantly with distance from Belfast (P<0.1), with depth (P<0.01) and with surface temperature (P<0.1). Work in progress, but not reported here, indicates that elevated levels of readily oxidizable organic matter occur in the vicinity of Belfast. It may be that the oligochaetes are able to utilize this energy source where it is abundant. The lower oxygen tensions which are usually associated with a high content of organic matter may preclude some marine species, reducing the competition against oligochaetes. However there was no evidence of an inverse relationship between the distribution of Oligochaeta and other groups so there is no strong evidence of a biological control upon the oligochaetes. The Isopoda were third in order of abundance mainly as a result of a very high number of juveniles at one sampling site; the distribution of this group was not significantly associated with the physical and. chemical factors. Amphipoda were slightly less abundant than isopods but they dominated six sampling sites. The Amphipoda was the only faunal group showing a significant positive correlation (P<0.1) with salinity. Amphipods increased in abundance with temperature (P < 0.1) and with the distance from Belfast (P < 0.01) (see Fig. 2) but not with depth. The remaining groups were each represented by less than 103 specimens m -2. The most important of these numerically was the Pelecypoda which, in common with the Amphipoda, showed a very significant (P<0.01) positive correlation with the distance from Belfast. The numbers of pelecypods increased also with depth (P < 0.1), with water temperature (P<0.1) and with the sediment factors al (P<0.01) and Kc (P<0.01). The Ophiuroidea increased significantly in numbers with distance from Belfast (P<0.01), depth (P<0.1) and water temperature (P<0.01). This group was negatively correlated ( P < 0.1) with silt-clay content.
Volume 11/Number 3/March 1980
Previous papers have discussed the long-term changes in the fauna of polluted estuaries. For example, Gray (1976) studied the fauna of the Tees Estuary and found that the species richness of Pelecypoda had declined markedly when compared with earlier records (Alexander et al., 1935), possibly as a result of pollution. The survey of Belfast Lough followed the rationale proposed by Moore (1971) who emphasized the need for a knowledge of spatial distribution patterns in benthic ecosystems as a prerequisite for temporal studies. Only the major trends in the physical and chemical environment and in the distribution of faunal groups of Belfast Lough are presented here. Additional information on levels of heavy metals, organic matter and redox potential along with a consideration of individual species distributions may help to determine the extent to which pollution measurably affects the benthic life. The fauna in the docks area suffers from the gross effects of pollution whereas in the outer lough the fauna is subjected to diffusely distributed pollutants. It may be postulated that in the harbour area pollution is a dominant ecofactor for the benthic population. A long-term study is now in progress at selected sites in this area in order to determine the role of pollution in temporal trends in the benthic fauna. I thank Dr D. A. Stewart, Biometrics Division, Department of Agriculture (N.I.) for carrying out the correlation analyses, and Ms N. Howard and Mr I. Moffett for technical assistance.
Loss of Mercury from Sea Water Sir, A recent report by N. Glickstein (Mar. Pollut. Bull., 10, 157) discussed the potential loss of mercury from sea water by volatilization and adsorption onto the walls of the container. This study was made to bring to the attention of marine ecotoxicologists that these mechanisms are significant and must be borne in mind during experimental studies of the effect of contaminated sea water on marine organisms. It is perhaps useful to note that similar problems have been encountered by marine chemists in the collection and preservation of sea water samples prior to analysis, and in the storage of standard solutions of low concentrations (e.g. Carr & Wilkniss, 1973; Feldman, 1974; Bothner & Robertson, 1975; Carron&Agemian, 1977). Although we have no argument with the results of this study, we feel that they do not accurately reflect the relative importance of the mechanisms which influence the removal of mercury from the sea. We also consider that the real environment is more closely simulated in the laboratory or field experimental system using sea water which is not subjected to the rigourous prefiltration and UV irradiation procedure described by Glickstein. Recent studies by this laboratory of the movement and transfer of inorganic mercury in large (100 m 3) plastic experimental enclosures (Topping, 1977) have shown that
The opinions expressed in this paper are the author's and are not necessarily those of the Department of Agriculture.
Alexander, W. B., Southgate, B. A. & Bassindale, R. (1935). Survey of the River Tees. Part II. The estuary chemical and biological. Technical Paper on Water Pollution Research No. 5, 71 pp. Her Majesty's Stationery Office, London. Buchanan, J. B. (1971). Measurement of the physical and chemical environment. Sediment. In Methods f o r the Study o f Marine Benthos, N. A. Holme & A. D. Mc l ntyre (eds.). Blackwell, Oxford. Department of the Environment. (1977). Monitoring the marine environment of the United Kingdom. The first report of the marine pollution monitoring management group 1975-76, Pollut. Rep. No. 2. Folk, R. L. (1974). Petrology o f Sedimentary Rocks. 182 pp. Hemphill, Austin, Texas. Gray, J. S. (1976). The fauna of the polluted River Tees Estuary. Estuar. coast, mar. Sci., 1,203-223. Hunter, B. & Simpson, A. E. (1976). A benthic grab designed for easy operation and durability. J. mar. bioL Ass. U.K., 56, 951-957. Irish Coast Pilot. (1968). l l t h edition. Hydrographer of the Navy, London. Local Government Board for Ireland (1904). Report on the Shell-fish Layings on the Irish Coast as Respects their Liability to Sewage Contamination. Her Majesty's Stationery Office, Dublin. Moore, P. G. (1971). Ecological survey strategy. Mar. Pollut. Bull., 2, 37-39. Parker, J. G., Damoglou, A. P. & Stewart, D. A. (1979). The distribution of faecal bacteria in the estuary of the River Lagan. Rec. agric. Res. Dept. Agric. Nth Ir., 27, 43-51. Royal Commission on Sewage Disposal. (1908). Methods o f Treating and Disposing o f Sewage. Appendix 1: Minutes o f Evidence, la. 591. Her Majesty's Stationery Office.
(i) Following the addition of inorganic mercury to sea water there is a period of 12-24 h during which the mercury is rapidly converted from a dissolved or 'reactive' form into a state requiring oxidation prior to extraction from the water, and which probably represents association with particulate material. Twenty-four hours after addition of mercury to 1 /tg Hg 1_ ~, only 30o70 of the mercury was still in the reactive form. (ii) Loss of mercury by volatilization represents a small proportion ( < 5 °70)of the added mercury over the whole experiment. Laboratory studies have shown that losses to the atmosphere are directly related to the concentration of 'reactive' mercury i.e. the significance of this pathway of loss rapidly decreases after addition of inorganic mercury. (iii) Loss of mercury by adsorption onto the walls of the plastic enclosure over the first 5 days of the experiment represented < 5°10ofthemercuryaddedtothebags. (iv) The main mechanisms by which mercury was lost from the bags was through the settlement of particulate material with which the mercury had become associated. There was a close relationship between mercury loss and the carbon content of the settlement material. Bothner, M. H. & Robertson, D. E. (1975). Mercury contamination of sea water samples stored in polyethylene containers. Analyt. Chem., 47, (3) 592-595. Carr, R. A. & Wilkniss, P. E. (1973). Mercury: short-term storage of natural waters. Envir. Sci. TechnoL, 7, 62-63.
83
de l'avifauneCamarguaisepar des residuosorganochlores.Environm. Pollut., 13,21-31. Olsson, M., Jensen, S. & Renberg, L. (1973). PCB in coastal areas of the Baltic. PCB Conf. II, 4E, 59-68. National Swedish Environment ProtectionBoard 1973. Presst. I., Jefferies, D. J. & Moore, N. W. (1970). Polychlorinated biphenyls in wild birds in Britain and their avian toxicity.Environm. Pollut., 1, 3-26. Renberg, L., SundstrOm,G. & Reutergardh, L. (1978). Polychlorinated terphenyls (PCT) in Swedish White-tailedEagles and in Grey Seals a preliminarystudy. Chemosphere, 7, 477--482. Risebrough, R. W., Reiche,P., Peakall, D. B., Herman, S. G. & Kirven, M. N. (1968). Polychlorinatedbiphenyls in the global ecosystem.
Nature, Lond., 2211, 1098-1102. Sitrkk~i, J., Hattula, M. L., Janatuinen, J., Paasivirta, J. & Palokangas, R. (1978). Chlorinated hydrocarbons and mercury in birds of Lake Paijanne, Finland - 1972-74. Pest. Monit. J., 12, 26-34. Vermeer, K. & Reynolds, L. M. (1970). Organochlorine residues in aquatic birds in the Canadian Prairie Provinces. Can. Field-Nat., 84, 117-130. Vermeer, K. & Peakall, D. B. (1977). Toxic chemicals in Canadian fisheating birds. Mar. Pollut. Bull., 8,205-210. Viviani, R., Crisetig, G., Cortesi, P. & Carpene, E. (1974). R+sidus de polychlorobiphenyls (PCB) et de pesticides chiores dans ies poissons et les oiseaux du delta du Po. Rev. int. Oceanogr. Med., 35/36, 79-90. Zitko, V., Hutzinger, O., Jamieson, W. D. & Choi, P. M. K. (1972). Polychlorinated terphenyls in the environment. Bull. environm. contain. ToxicoL, 7,200-201. Zitko, V. (1974). Trends of PCB and DDT in fish and aquatic birds. Proc. Int. Conf. Transp. Persist. Chem. Aquat. Ecosyst., Ill 61-11164, Ottawa, Canada.
MarinePollutionBulletin,Vol.11,pp.80-83 PergamonPressLtd. 1980.PrintedinGreatBritain.
Effects of Pollution upon the Benthos of Belfast Lough JAMES G. PARKER Department o f Agriculture (N. L ), Fisheries Research Laboratory, Coleraine, N. Ireland BT513RL Prefiminary results of a study of the benthos of Belfast Lough are described. An outline of the rationale and approach and a description of the major trends in the fauna is presented along with an assessment of the principal environmental influences. The gross effects of pollution are confined to the docks area.
Belfast Lough is the receiving water for the domestic and industrial waste water of the city of Belfast and of the industries and towns which surround the lough (Fig. 1). Belfast is the capital city (pop. > 360000) of Northern Ireland and is the largest commercial port in the province. Reports from early this century (Local Government Board for Ireland, 1904) recognised the possibility that the consumption of mussels (Mytilus edulis) from Belfast Lough had resulted in cases of enteric fever; the collection of mussels from the lough was subsequently prohibited. At about the same time, the Royal Commission on Sewage Disposal 0908) was given evidence that the enrichment of Belfast Lough by raw sewage had resulted in the growth of large amounts of Ulva sp. which caused a nuisance around the shores as it decayed. A large amount of sewage effluent still enters the lough at the landward end. The majority of the Belfast population is served by sewage treatment works which provide primary treatment only. Furthermore, the Belfast sewerage is a combined system which carries both foul sewage and stormwater. Because of overloading of the system, untreated sewage frequently enters the tidal waters of the River Lagan which consequently suffers serious contamination by faecal matter (Parker et al., 1979). Crude sewage from Bangor is discharged close to the defined southern limit (Orlock Point) of the lough. Cooling water and process wastewater are discharged to the lough from the manufacture of man-made fibres, fertilizers, bleaches, dyes 80
and from power stations. A new oil-fired power station located at Kilroot Point is nearing completion; one of the largest oil jetties in Europe, projecting over 1 km into the lough, has been constructed to convey the fuel oil to this station. An oil refinery lies on the southern shore of the lough close to the city. The discharge of waste water in Northern Ireland is controlled by the Water Act (NI), 1972. In addition to the wastes which are discharged into the lough there is a sludge dumping site outside the entrance to the lough. The sludge dumped here is mainly primary sewage sludge but some industrial waste is also disposed of in this way. Under licence from the Dumping at Sea Act, 1974, the amount of sludge which may be dumped is limited to 220000 wet tonnes p.a. (DOE, 1977), although the amount dumped is somewhat less than this figure. As well as being an important navigational water, the outer lough supports a limited commercial fishery for cod and whiting; there is a locally important scallop (Pecten maximus) fishery off the mouth of the lough. Parts of the lough have considerable amenity value with sea angling, bathing and sailing being popular at various sites. The effects of pollution upon the ecology of Belfast Lough have not been investigated previously, unlike the other major industrialized estuaries and bays of the UK. This paper reports the preliminary results of benthic studies in Belfast Lough which have the objective of determining to what extent pollution is responsible for the spatial pattern of benthic life. The lough has some unique features when compared with the receiving waters for discharges from other major industrialized regions of the UK. In particular, its waters are almost fully marine, and the bottom slopes gradually to --, 20 m where it meets the North Channel, near the northern limit of the Irish Sea. Belfast Lough is defined as the area lying to the landward of a line drawn from Black Head to Orlock Point (Irish Coast Pilot, 1968), whilst the
V o l u m e 1 1 / N u m b e r 3 / M a r c h 1980
I
Sediment
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Oil M z < 0-2mm %silt-clay
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Fig. 1 Belfast L o u g h showing m a i n t o p o g r a p h i c a l features and s a m p l i n g sites (e); arrowed sites contained no benthic macrofauna. Top inset shows c o n t o u r s o f % s i l t / c l a y and areas with M z < 0 . 2 m m . L o w e r inset shows areas with 104 specimens per m 2.
harbour lies to the landward of a line from Carrickfergus to Grey Point. In this paper, the waters lying between these limits are referred to as the outer lough, while the harbour installations in the immediate vicinity of Belfast are referred to as the docks.
Methods During December 1976, a 0.1 m 2 sample of sediment was taken using a Valeport-Hunter grab (Hunter & Simpson, 1976) from each of 41 sampling sites on Belfast Lough (Fig. 1); five of the sites were within the docks area. Sampling positions were timed by means of a Decca Navigator. A 5 cm depth core (10 cm 2 area) of sediment was taken from the undisturbed grab sample and was preserved in industrial methylated spirit. The granulometry of this sub-sample was analysed subsequently by sieving and pipette analysis (Buchanan, 1971); the graphic mean (Mz), inclusive graphic standard deviation (o-t), inclusive graphic skewness (Ski) and graphic kurtosis (/Ca) were determined according to Folk (1974). The bulk of the sediment from each grab sample was washed through a 0.5 mm screen and the retained fraction was preserved in 5070formalin in seawater. The fauna was sorted initially into major taxonomic groups and identification to species level is now in progress. During the sampling programme, the salinity and temperature of the surface (0.5 m) and bottom water was measured in situ
using an EIL MC5/2 salinity and temperature measuring bridge. Associations within and between physical, chemical and biological data were analysed by correlation matrix. The depth of each site and its distance from Belfast were included in the data matrix. The latter gives a crude measure of the distance of each site from the main source of pollution. Localized, possibly important, sources of pollution are ignored at present.
Results and Discussion Physical and chemical fact ors Figure 1 shows the main topographical features of the lough. Although strong tidal currents of up to 2 m s- ~flow past the mouth of the lough, the currents within the lough seldom exceed 0.5 m s-~ at spring tides. Midway between Kilroot Point and Grey Point there is a more-or-less rotary clockwise tidal stream with a spring tide flow of not more than 0.5 m s -~ in any direction (Irish Coast Pilot, 1968). Evidently, these weak tidal streams promote the settlement of fine sedimentary particles. The range of values for siltclay content (< 63 ~m) was 0.4°7o to 85.9070, and the mean silt-clay content over all sites was 32.9°7o. The median grain size (Mz) varied between 0.02 and 1.35 mm. There was a considerable patchiness underlying the main trends of sediment distribution shown in Fig. 1. There were clear horizontal and vertical gradients of 81
Marine Pollution Bulletin 3[i AMPHIPODA
TABLE 1
Thecompositionof BelfastLoughbenthicfauna, December1976 Taxonomic 070of specimens Mean nos. group in group per0.1 m 2 Polychaeta 41.1 389 Oligochaeta 16.4 155 Isopoda 13.3 126 Amphipoda 13.3 126 Pelecypoda 6.9 65 Cumacea 3.7 35 Cirripedia 2.5 24 Ostracoda 1.5 13 Sipunculida Ophiuroidea Anthozoa Decapoda Gastropoda Mysidacea Echinoidea
total 5 °70
each < 10 per0.1 m 2
salinity and temperature within the lough. In the tidal waters of the River Lagan (Parker et al., 1979) and the docks area, the surface salinity was influenced strongly by the freshwater flow. Proceeding seawards, the surface layer (1 m) of the river became gradually more saline. The minimum salinity of water at 1 m depth leaving the docks area was 17.0°700. The minimum salinity recorded in the bottom water of the docks area was ~28o700. The distribution of surface salinities in the harbour area, excluding the docks, indicated that fresh water from the River Lagan has little influence on the lough. Surface salinlties in the harbour area were usually >31 °7oo. In the outer lough the surface salinity reached >33%o; here, the distribution of salinity was more homogeneous than in the inner lough. A small but significant (P<0.01) vertical salinity gradient was present in the lough. Bottom salinity was on average 0.4°7oo higher than the surface salinity, the difference becoming less marked towards the seaward end of the lough. Associated with the salinity gradients were highly significant (P<0.001) gradients of temperature. During the sampling programme, the bottom temperature at the seawards end of the lough was up to 3°C higher than that of the harbour area. Clearly, this temperature gradient may have major consequences for the reproductive cycles of the benthic communities. The effect of salinity, however, is likely to be minimal except for communities within the docks complex.
Benthicfauna Around 40 000 specimens were obtained from the benthic sampling programme and their distribution into major taxa is shown in Table 1. Three sampling sites in the docks area were devoid of benthic macrofauna (Fig. 1) undoubtedly as a consequence of the anaerobic and sulphide-rich nature of the sediment. Those sites within the docks which supported a benthic fauna were dominated by Oligochaeta, Peioscolex benedeni being prominent among this group. The polychaetes Nereis diversicolor, N. virens, Polydora ciliata and Capitella capitata also occurred. At the seawards end of the docks, Nephtys hombergii, Spio filicornis, Heteromastus filiformis, Scoioplos armiger and Tharyx sp. were also present. Ampelisca brevicornis (Amphipoda), Pseudocuma longicornis and Diastylis sp. (Cumacea) were also found in the docks area along with a small number of bivalve molluscs. 82
.
._~
°
•
•
•. 2
6 ~ •
~
•
o
.
0
---
I I. 5 10 Distance from Belfast
:
I 15 km
I 20
Fig. 2 Regressionof numbers of amphipods on distance from Belfast (r = correlationcoefficient).
Polychaeta dominated the fauna of 19 sampling sites. The distribution of the polychaetes showed a significant (P < 0.1) positive correlation with Ka but not with any other environmental factor. The Oligochaeta were next in order of abundance and dominated 11 sampling sites. Many oligochaete species are able to tolerate a wide range of salinities and often thrive in estuarine sediments which are rich in organic matter. The distribution of oligochaetes was not significantly associated with salinity in this study. However, the abundance of oligochaetes decreased significantly with distance from Belfast (P<0.1), with depth (P<0.01) and with surface temperature (P<0.1). Work in progress, but not reported here, indicates that elevated levels of readily oxidizable organic matter occur in the vicinity of Belfast. It may be that the oligochaetes are able to utilize this energy source where it is abundant. The lower oxygen tensions which are usually associated with a high content of organic matter may preclude some marine species, reducing the competition against oligochaetes. However there was no evidence of an inverse relationship between the distribution of Oligochaeta and other groups so there is no strong evidence of a biological control upon the oligochaetes. The Isopoda were third in order of abundance mainly as a result of a very high number of juveniles at one sampling site; the distribution of this group was not significantly associated with the physical and. chemical factors. Amphipoda were slightly less abundant than isopods but they dominated six sampling sites. The Amphipoda was the only faunal group showing a significant positive correlation (P<0.1) with salinity. Amphipods increased in abundance with temperature (P < 0.1) and with the distance from Belfast (P < 0.01) (see Fig. 2) but not with depth. The remaining groups were each represented by less than 103 specimens m -2. The most important of these numerically was the Pelecypoda which, in common with the Amphipoda, showed a very significant (P<0.01) positive correlation with the distance from Belfast. The numbers of pelecypods increased also with depth (P < 0.1), with water temperature (P<0.1) and with the sediment factors al (P<0.01) and Kc (P<0.01). The Ophiuroidea increased significantly in numbers with distance from Belfast (P<0.01), depth (P<0.1) and water temperature (P<0.01). This group was negatively correlated ( P < 0.1) with silt-clay content.
Volume 11/Number 3/March 1980
Previous papers have discussed the long-term changes in the fauna of polluted estuaries. For example, Gray (1976) studied the fauna of the Tees Estuary and found that the species richness of Pelecypoda had declined markedly when compared with earlier records (Alexander et al., 1935), possibly as a result of pollution. The survey of Belfast Lough followed the rationale proposed by Moore (1971) who emphasized the need for a knowledge of spatial distribution patterns in benthic ecosystems as a prerequisite for temporal studies. Only the major trends in the physical and chemical environment and in the distribution of faunal groups of Belfast Lough are presented here. Additional information on levels of heavy metals, organic matter and redox potential along with a consideration of individual species distributions may help to determine the extent to which pollution measurably affects the benthic life. The fauna in the docks area suffers from the gross effects of pollution whereas in the outer lough the fauna is subjected to diffusely distributed pollutants. It may be postulated that in the harbour area pollution is a dominant ecofactor for the benthic population. A long-term study is now in progress at selected sites in this area in order to determine the role of pollution in temporal trends in the benthic fauna. I thank Dr D. A. Stewart, Biometrics Division, Department of Agriculture (N.I.) for carrying out the correlation analyses, and Ms N. Howard and Mr I. Moffett for technical assistance.
Loss of Mercury from Sea Water Sir, A recent report by N. Glickstein (Mar. Pollut. Bull., 10, 157) discussed the potential loss of mercury from sea water by volatilization and adsorption onto the walls of the container. This study was made to bring to the attention of marine ecotoxicologists that these mechanisms are significant and must be borne in mind during experimental studies of the effect of contaminated sea water on marine organisms. It is perhaps useful to note that similar problems have been encountered by marine chemists in the collection and preservation of sea water samples prior to analysis, and in the storage of standard solutions of low concentrations (e.g. Carr & Wilkniss, 1973; Feldman, 1974; Bothner & Robertson, 1975; Carron&Agemian, 1977). Although we have no argument with the results of this study, we feel that they do not accurately reflect the relative importance of the mechanisms which influence the removal of mercury from the sea. We also consider that the real environment is more closely simulated in the laboratory or field experimental system using sea water which is not subjected to the rigourous prefiltration and UV irradiation procedure described by Glickstein. Recent studies by this laboratory of the movement and transfer of inorganic mercury in large (100 m 3) plastic experimental enclosures (Topping, 1977) have shown that
The opinions expressed in this paper are the author's and are not necessarily those of the Department of Agriculture.
Alexander, W. B., Southgate, B. A. & Bassindale, R. (1935). Survey of the River Tees. Part II. The estuary chemical and biological. Technical Paper on Water Pollution Research No. 5, 71 pp. Her Majesty's Stationery Office, London. Buchanan, J. B. (1971). Measurement of the physical and chemical environment. Sediment. In Methods f o r the Study o f Marine Benthos, N. A. Holme & A. D. Mc l ntyre (eds.). Blackwell, Oxford. Department of the Environment. (1977). Monitoring the marine environment of the United Kingdom. The first report of the marine pollution monitoring management group 1975-76, Pollut. Rep. No. 2. Folk, R. L. (1974). Petrology o f Sedimentary Rocks. 182 pp. Hemphill, Austin, Texas. Gray, J. S. (1976). The fauna of the polluted River Tees Estuary. Estuar. coast, mar. Sci., 1,203-223. Hunter, B. & Simpson, A. E. (1976). A benthic grab designed for easy operation and durability. J. mar. bioL Ass. U.K., 56, 951-957. Irish Coast Pilot. (1968). l l t h edition. Hydrographer of the Navy, London. Local Government Board for Ireland (1904). Report on the Shell-fish Layings on the Irish Coast as Respects their Liability to Sewage Contamination. Her Majesty's Stationery Office, Dublin. Moore, P. G. (1971). Ecological survey strategy. Mar. Pollut. Bull., 2, 37-39. Parker, J. G., Damoglou, A. P. & Stewart, D. A. (1979). The distribution of faecal bacteria in the estuary of the River Lagan. Rec. agric. Res. Dept. Agric. Nth Ir., 27, 43-51. Royal Commission on Sewage Disposal. (1908). Methods o f Treating and Disposing o f Sewage. Appendix 1: Minutes o f Evidence, la. 591. Her Majesty's Stationery Office.
(i) Following the addition of inorganic mercury to sea water there is a period of 12-24 h during which the mercury is rapidly converted from a dissolved or 'reactive' form into a state requiring oxidation prior to extraction from the water, and which probably represents association with particulate material. Twenty-four hours after addition of mercury to 1 /tg Hg 1_ ~, only 30o70 of the mercury was still in the reactive form. (ii) Loss of mercury by volatilization represents a small proportion ( < 5 °70)of the added mercury over the whole experiment. Laboratory studies have shown that losses to the atmosphere are directly related to the concentration of 'reactive' mercury i.e. the significance of this pathway of loss rapidly decreases after addition of inorganic mercury. (iii) Loss of mercury by adsorption onto the walls of the plastic enclosure over the first 5 days of the experiment represented < 5°10ofthemercuryaddedtothebags. (iv) The main mechanisms by which mercury was lost from the bags was through the settlement of particulate material with which the mercury had become associated. There was a close relationship between mercury loss and the carbon content of the settlement material. Bothner, M. H. & Robertson, D. E. (1975). Mercury contamination of sea water samples stored in polyethylene containers. Analyt. Chem., 47, (3) 592-595. Carr, R. A. & Wilkniss, P. E. (1973). Mercury: short-term storage of natural waters. Envir. Sci. TechnoL, 7, 62-63.
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