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Baseline studies of delaware ocean outfall sites
Volume 7/Number 2/February 1976 sorb petroleum. Whatever the source of scatter, the important relationship is the increase in Macoma balthica mortality as the concentration of oil in the sediment and in the animal's tissue increases. The data from day 44 further suggest that duration of exposure also plays a role in determining mortality rate. Conclusions A significant increase in M. balthica mortality has been shown to accompany an application of crude oil to sediments which approximates the stranding of a light oil slick. We suspect that this relationship between M. balthica mortality and the concentration of oil in the top 1 cm of sediment is a result of the animal's deposit feeding habit. Thus we hypothesize that other deposit feeding species of the genus Macoma will have similar potential as indicators of oil pollution. If our hypothesis is correct, Macoma may prove to be a valuable indicator, since it has wide geographic distribution. Macoma balthica itself is circumarctic and occurs in numerous regions of present or contemplated petroleum production and transport.
This work was supported by a grant from the U.S. Environmental Protection Agency and is contribution number 193 from the Institute of Marine Science, University of Alaska.
D. G. SHAW A. J. PAUL L. M. CHEEK H. M. FEDER lnsn'tute o f Marine Science University o f Alaska Fairbanks, A K 99701 U.S.A.
Brafield, A. E. & Newell, G. E. (1961). J. mar. biol. Ass. U.K., 41, 81-87. Butler, P., Andr6n, L. E., Bonde, G. J., Jernelov, A. B. & Reish, D. J. (1972). In: A Guide to Marine Pollution. (Goldberg, E. D. (ed.) New York: Gordon & Breach pp. 147-160. Coan, E. V. (1971). Veliger, 14 (Suppl.), 44-46. Snedecor, G. W. (1956). Statistical Methods Applied to Experiments in Agriculture and Biology, 5th edn., Ames: Iowa State College Press, 534 pp.
Baseline Studies of Delaware Ocean Outfall Sites A quarterly sampling programme was conducted during 1 9 7 3 - 1 9 7 4 off the coast of Delaware to provide an environmental baseline for two ocean sewage ouffalls. Extensive physical measurements and water quality data, together with biological data (fish, invertebrates, bacteriological samples), were collected. Based on this research the design of sewage treatment for one of the outfalls was improved. The world's coastal zones continue to be the target of man's activities ranging from recreation to heavy industry. At the present time recreation in Delaware's coastal zone is more valuable than heavy industry. In Sussex County, tourism, together with increasing pressure from heavy industry, will place a huge load on sewage facilities. Without adequate facilities, amenity values would decline rapidly. To anticipate this problem, a sewage system was authorized for Sussex County. Two sites were chosen for the construction of facilities and associated ocean outfalls (Fig.l). The Henlopen site at the mouth of Delaware Bay would provide a maximum discharge of 1.9 × 106 ma/day (291 M.G.D.) of secondary (or better) treated sewage. The Bethany site is approximately 3 0 k m south of Cape Henlopen and would provide a maximum discharge of 0.94 X l0 s ma/day (25 M.G.D.) of similarly treated effluent. This study was undertaken for several reasons. First, a physical, chemical, and biological baseline was needed in order to assess the environmental impact of the outfalls when they become operational. Second, seasonal field measurements of currents, circulation, and density structure, treated in detail by Ditmars (1974), were of value in evaluating possible outfall locations at each site. In addition, system configurations, near-field, and far-field mixing performances based on Ditmars' work were of
potential value in designing the specific configuration of the outfall. By influencing the design and location of the system this study has the potential for reducing the probability of environmental degradation. The purpose of this account is to briefly summarize the rationale for the sampling regime and the choice of chemical and biological parameters, as well as summarizing the results of the biological studies, especially of fish and invertebrates. Environmental Background The Henlopen site is dominated topographically by Hen and Chickens Shoal, which is maintained by ebb tide currents. The abrupt beach slope yields to a shallow, flat bottom (9 m), which rises on the shoal and in turn drops off steeply into a series of depressions ( 2 0 - 3 0 m). At the Bethany site the abrupt beach slope grades gradually to a shallow bottom ( 9 - 1 2 m), marked with slight sloughs and ridges. Sediment at both sites is mainly medium sand (<0.5 ram) although the deeper bottom at the Henlopen site contains cobbles, small boulders, and pockets of silt. These nearshore sites were similar in temperature (3-21°C), salinity (27-31 ~oo), and dissolved oxygen (3.4-9.3 ppm) of the bottom water throughout the study. Sampling Regime Sampling for this project was designed to provide a view of seasonal, diurnal, and tidal variations of the physical, chemical, and biological parameters. The physical measurements (Ditmars,1974) were of predictive value in choosing outfall configurations and locations. Chemical and biological data are described in detail by Maurer et al. (1974). Chemical studies included background 31
Marine Pollution Bulletin
I
75~10 '
DEL A W A R E B A Y
-58*50'
CAP
PA. ( ~39" ,D.
.ENLOPE.
-
REHOBOTI
BEACH
R E H O BOTH BAY
A TL A N TIC 0 CEAIV
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BETHANY BEACH
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INDIAN R I V E R INLET
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•7
•8
•9
6
5•4
ol
2
3
• 38"30'
38°30 '
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I
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I
2 3 4 5
KILOMETERS
75*00' I
Fig. 1 Location m a p o f sampling sites.
levels of salinity, dissolved oxygen, B.O.D., hardness, chlofinity, nutrients (organic nitrogen, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, phosphate), total organic carbon, heavy metals (copper, chromium, silver, zinc, lead, nickel, cadmium, mercury, arsenic), and pesticides in the water column. In addition, analyses of the background levels of some heavy metals and pesticides were made on sediments, fish, and invertebrate samples. Since millions of gallons of fresh water would be exported to each outfall site daily, significant local alteration of the normal salinity regime would be a potential problem. This change could affect the fish or benthic fauna. Particulate matter associated with the effluent could affect B.O.D., total organic carbon, and dissolved oxygen. A secondary treated sewage effluent would still have high levels of nutrients and pesticides associated with it, so an indication of background levels was necessary. Various heavy metals have been shown to be associated with sewage sludge (Gross, 1972; Watling et al., 1974) dump sites and may also prove to be present in high levels in a sewage effluent. Biological studies included baseline information on bacteria (total coliform, faecal coliform, and faecal streptococcus), macroscopic benthic invertebrates, and fish. Background bacteria levels and normal variations were important to assess any bacterial introduction through the 32
outfall. Each of the chemical parameters has a potential effect on the benthic and fL~la communities, and baseline data were necessary to assess the impact of the outfalls on species composition, evenness of distribution, and species richness.
Methods Twelve stations (3 replicates/station) were sampled quarterly (July and October 1973, January and April 1974) at each site with a 0.1 m 2 Petersen grab (Fig.l). Samples were washed through a 1.0 mm mesh screen and the residue retained on the screen was preserved in 10% formalin buffered with hexamethylenamine for laboratory analysis. Two 10 min otter trawl tows (mouth 6 m, 7.6 cm stretch mesh net, 2.5 cm stretch mesh bag) were taken at each site per quarterly sampling period. In addition, 10m in otter trawl tows were made every 4 h over 2 4 h in August, October, December 1973 and January and April 1974. Fish were identified and counted immediately and the length was measured to the nearest millimetre. Top and bottom water samples providing the basis for chemical and bacteriological analyses were also collected every 4 h during the same 24 h sampling periods. Results Bacteria Seasonal 24 h studies provided top and bottom water samples for seasonal and diurnal baseline counts of total coliform, faecal coliform, and faecal streptococcus (No./10Oml). Levels were generally low at both sites ( < 2 / 1 0 0 m l) with occasional pulses of higher bacteriological activity at each site. There were no seasonal or diurnal trends noted. Total coliform varied from < 2 - 3 8 0 0 colonies/100 ml at the Bethany site and < 2 - 2 0 0 at the Henlopen site. Faecal coliform remained uniformly low at the Bethany site (<2) and rather low at the Henlopen site ( < 2 - 8 ) . Faecal streptococcus ranged from < 2 - 5 0 at the Henlopen site and < 2 - 1 0 6 at the Bethany site. Preliminary indications are that bacterial levels may be somewhat higher at the Bethany site on some occasions, due to short pulses of bacterial activity an order of magnitude higher than that noted at the Henlopen site.
Fish Otter trawl hauls throughout the year at the Henlopen site yielded 1384 individuals of 25 species. An average haul yielded 48 individuals of six species with a scaled diversity (H) of 0.572 (0 = skewed, 1 = even) (Fager, 1972). Seasonally, the highest number of species was sampled in the fall (12); the number of individuals/haul was highest in the spring (81). Diurnal trends showed a larger number of individuals at night (58) than during the day (44) with no differences in the number of species taken. The red hake, Urophysis chuss, and the silver hake, Merluccius bilinearis, together comprised 52.3% of the total catch at the Henlopen site. The Bethany site yielded 971 individuals of 26 species. An average haul yielded 40 individuals of eight species with a scaled diversity (H) of 0.602. Seasonally, the highest number of species was sampled in summer and fall (11). The number of individuals/haul was also highest in summer (55) and fall (57). Diurnal variation showed no differences between day and night in the number of species sampled, but the number of individuals/haul was higher at night (58)
Volume 7/Number 2/February 1976 than during the day. The sea robin, Prionotus carolinus; the windowpane, Scophthalmus aquosus; the spot, Leiostomus xanthurus; and the red hake, Urophysis chuss; together accounted for 54% of the catch at the Bethany site. Macroscopic benthic invertebrates 9051 individuals of 68 species were collected from the Henlopen site. Abundance patterns were seasonal with 4622 individuals taken in july, 1956 in October, 1560 in January, and 913 in April. Annelids (83 species) comprised 49.4% of the fauna, arthropods (49 species) 29.2%, molluscs (15 species) 8.9%, ectoprocts (10 species) 6.0%, cnidarians (5 species) 3.0%, rhynchocoels (3 species) i.8%, and echinoderms (3 species)
1.8%. A measure of evenness (SDN) (Fager, 1972) was used to evaluate the distribution of individuals over the species. This is a scaled value between 0.0-1.0 (0=skewed, 1 = even). The mean scaled SDN for the 12 stations at this site were generally low ranging from 0.238 to 0.382. Variation in evenness between the 12 stations was considerable, however. The characteristic fauna at the Henlopen site occurred in two distinct sediment types. The shoal, a well-sorted fine sand, was dominated by the amphipod, Parahaustorius longimerus, other species of Haustoridae, and the bivalves, Spisula solidissima and Tellina agilis. The deeper stations east of the shoal contained mixed course sand, pebbles, shell debris, and small pockets of silt. The fauna associated with this bottom consisted of infaunal species (Tharyx acutus and Aricidea cerruti) and epifaunal species (Mytilus edulis and Unciola serrata). Mytilus edulis was a dominant species in terms of number and occurrence throughout most of the year. In order to determine something about the structure of the community a dominance index (McNaughton, 1967) was applied to the data. The index reflected the large Mytilus edulis recruitment in July at the Henlopen site, with the highest mean value of 0.83. When the species were ranked by numbers of individuals, the two most abundant species (Mytilus edulis and Parahaustorius longimerus) in July represented 83% of the fauna. During the other three quarters, between 13 and 16 species were necessary to duplicate this percentage. During these quarters the dominance index declined (0.72 in October, 0.65 in January, and 0.67 in April) indicating less dominance by one or two species. The fauna of the Henlopen site was dominated by important estuarine species and rarely included species commonly collected in offshore areas of the continental shelf. 6239 individuals of 181 species were collected from the Bethany site throughout the course of the study. Abundance patterns were roughly seasonal with 1956 in July, 2454 in October, 899 in January, and 878 in April. Annelids (79 species) comprised 44% of the fauna, arthropods (59 species) 33%, molluscs (21 species) 11.7%, ectoprocts (9 species) 5%, cnidarians (4 species) 2.2%, rhynchocoels (5 species) 2.8%, echinoderms (1 species) 0.6%, and protozoans (1 species) 0.6%. The evenness (SDN) of the distribution of individuals at each station was used. The mean SDN values for the 12 stations varied between 0.503 and 0.522 indicating a rather
even distribution seasonally. Variation between stations in scaled SDN values was great however. The benthic assemblage at the Bethany site was characteristic of a medium sand fauna. The bivalves, T. agilis and S. solidissima; the amphipod, Protohaustorius wigleyi; and the polychaetes, Nephtys spp.; were important species. The polychaete, Spiophanes bombyx, and the archiannelid, Polygordius sp., which were previously collected in great numbers offshore (30 km) (Maurer et al., 1975), were also found to be important at this nearshore site. The dominance value for this site was rather low and constant (0.57-0.63) throughout the year.
Discussion a n d Conclusions Ditmars (1974) recommended that the outfall proposed for the Henlopen site can be placed outside the shoal, where a high level of mixing of the discharge could be achieved over a wide range of receiving water conditions. Proximity to swimming beaches and reduced circulation inside the shoal made this area an unlikely choice for the outfall. Ditmars' work showed that the Bethany site would result in less rapid flushing of the diluted effluent from the area. This fmding necessitated some alteration of design of the outfall proposed for this site. Analysis of fish data shows that numbers of individuals and evenness varies on a diurnal basis and that species composition varies tremendously seasonally. Greater abundance in night m day hauls was probably due to net avoidance. An example of the importance to the fauna of species present only seasonally can be seen in the Henlopen site fish data. The red hake, the most numerous fish taken, was present throughout the year; while the silver hake, second in importance numerically, was taken only during late winter and early spring. The importance of a year-long study as a minimum baseline for evaluation of future environmental degradation is emphasized by these results. Sampling should include 2 4 h studies or should be standardized with respect to time and tide. The benthic fauna presents an interesting contrast between the two sites which are both near-shore and only 3 0 k m apart. The influence of Delaware Bay on the Henlopen site can be seen in the fauna as well as the sediment. Strong ebb tide currents deposit both fine sand and large cobbles in this area. The larger substrates present a settling area for mussel larvae, which probably originate from a Delaware Bay source. These blue mussels provide an area for epifaunal crabs and worms, which in turn attract fish. The Bethany site had a more homogeneous sediment type (medium sand) which favoured a largely infaunal assemblage, including some species also important 30 km from shore. Environments with highly predictable fluctuations in chemical parameters, such as the continental shelf are often inhabited by species with a narrow ability to adapt to change (Slobodkin & Sanders, 1969). The lower flushing rate of the Bethany site might therefore combine with small fluctuations in salinity, nutrients, and trace metals from the outfall to adversely affect the portion of the fauna found also on the outer shelf. On this basis it was decided that the treatment of sewage at the Bethany site had to be improved over that initially planned. This approach will hopefully reduce the potential for environmental damage. 33
MarinePollutionBulletin This research was supported by the County Engineer, Sussex County, Delaware, under the management of Mr.William Henry and Mr. Roger Truitt. Chemical analyses were performed by the Technical Services Division of the Delaware Department of Natural Resources and Environmental Control (DNREC) under the coordination of their Director, Dr. Harry Otto, and the supervision of their Chief Chemist, Mr. Charles J'Anthony. We owe thanks to the crew of the R. V. Delaware, DNREC's vessel, and to our own crews aboard the R. V. Skimmer and the R. V. Wolverine. Many technicians and staff aided in sorting and processing biotic and sediment samples. Our colleague, Dr. Les Watling, aided in the identification of arthropods, and Dr. Jack Ditmars, the Project Manager, facilitated our task in many ways.
DON MAURER JEFF C. TINSMAN WAYNE LEATHEM PETER KINNER
Field Station, College o f Marine Studies, University o f Delaware, Lewes, D E 19958, U.S.A. Ditmars, J. D. (1974). Physical aspects of baseline studies for the environmental assessment of Sussex County ocean outfalls. Rept. to the Sussex Co. Eng., 58 pp. Fager, E. W. (1972). Diversity: a sampling study. Am. Nat., 106, 239-310. Gross, M. G. (1972). Marine waste deposits near New York. Mar. Pollut. Bull., 3 (4), 61-63. Maurer, D., Tinsman, J. C., Leathem, W. & Kinner, P. (1974). Baseline study of Sussex County, Delaware ocean outfalls. Rept. to the Sussex Co. Eng., 287 pp. Maurer, D., Kinner, P., Leathern, W. &Watling, L. (1975). Benthic faunal assemblages off the Delmarva Peninsula. Estuar. coast. Mar. Sci., (in press). Slobodkin, L. B. & Sanders, H. L. (1969). On the contribution of environmental predictability to species diversity. Brookhaven Symposia in Biology. Number 22, pp. 82-95. Wafting, L., Leathern, W., Kinner, P., Wethe, C. & Manrer, D. (1974). Evaluation of sludge dumping off Delaware Bay.Mar. Pollut. Bull., 5 (3), 39-42.
Mercury in Plankton From a Polluted Norwegian Fjord Plankton of mixed composition has been collected from Sorfjorden and Hardangerfj~rden, on the west coast of Norway and analysed for total mercury by flameless atomic absorption. Different methods of decomposing the samples prior to analysis were tested, showing no significant variations in the recovery of mercury. The high levels of mercury (0.52-25.21 ppm dry weight) are apparently associated with a source of industrial pollution. Indications of higher mercury concentrations in phytoplankton than in zooplankton were noticed and suggest a lack of food chain amplification within the lower trophic levels. The growing concern about the occurrence of mercury in the marine environment has led to intensified research to establish levels of mercury at different trophic levels in the sea. Investigations have been concentrated on organisms directly used in the human diet (West66, 1966; Klein & Goldberg, 1970; Burton & Leatherland, 1971) and less attention has been paid to the biomass at the lower end of the marine food chains. However, the uptake mechanisms of mercury and the transformation reactions that may take place in an aquatic ecosystem have been reported (Davis & Ferguson, 1972; Fagerstr6m & Jernel6v, 1972). Analyses of mercury in plankton collected in the open ocean (Knauer & Martin, 1972) and in estuaries (Cocoros et al., 1973) revealed no significant differences in concentrations and the values found were low (about 0.2 ppm dry weight). In this paper the results of analyses for total mercury in mixed phyto- and zooplankton samples from Sort}¢rden and Hardangert~¢rden, West Norway are reported. For comparison a plankton sample from the south-west African coast was also analysed. Material a n d M e t h o d s The samples were collected in August 1972 using a 34
nylon net (25/~m), equipped with a fibre glass bucket. All the samples were obtained by oblique near surface ( 0 - 1 0 m) hauls and the samples were frozen immediately after collection. We analysed 0.05-0.25 g wet plankton and calculated the concentration of mercury on a dry basis (80°C), using the wet: dry ratio determined on another portion of the sample. Aqueous plankton solutions (see below) were analysed for mercury by flameless AA using a Techtron AA 4/5 spectrophotometer and Model 62 mercury cell (Stux & Rothery, 1971). Dilute standards were made up from a 5 0 p p m Hg stock solution in a range from 0 to 0.2/ag Hg/30 ml. The sensitivity of the determination was 0.5 ng Hg/ml for 1% absorption, the detection limit was 3 ng absolute or 0.1 ng Hg/ml. The relative deviation of 6 replicate determinations of 0.1/ag Hg was 4.5% and the reagent blank was below detection. Due to the uncertainty of how the various methods of decomposing biological material affects the recovery of mercury in the samples, the following methods of sample attack were compared: (1) Modified official A.O.A.C. method (Analytical Methods Committee, 1965) (2) 50% H2 02-conc.H2 SO4 (3) cone. HNO3-conc. H2SO4 in a P.T.F.E. bomb (Paus, 1972) (4) cone. HNO3 (Scobbie, 1971) (5) 6% v/v KMnO4-conc. HzSO4 (Lindstedt, 1970). The results (Table 1) show that the recovery of mercury using different methods of sample attack is reasonably consistent. Only method 2 gave a complete decomposition of fatty substances in the samples, although the merury concentration did not increase, implying that the fats do not contain much mercury (see also Omang, 1973).
This work was supported by a grant from the U.S. Environmental Protection Agency and is contribution number 193 from the Institute of Marine Science, University of Alaska.
D. G. SHAW A. J. PAUL L. M. CHEEK H. M. FEDER lnsn'tute o f Marine Science University o f Alaska Fairbanks, A K 99701 U.S.A.
Brafield, A. E. & Newell, G. E. (1961). J. mar. biol. Ass. U.K., 41, 81-87. Butler, P., Andr6n, L. E., Bonde, G. J., Jernelov, A. B. & Reish, D. J. (1972). In: A Guide to Marine Pollution. (Goldberg, E. D. (ed.) New York: Gordon & Breach pp. 147-160. Coan, E. V. (1971). Veliger, 14 (Suppl.), 44-46. Snedecor, G. W. (1956). Statistical Methods Applied to Experiments in Agriculture and Biology, 5th edn., Ames: Iowa State College Press, 534 pp.
Baseline Studies of Delaware Ocean Outfall Sites A quarterly sampling programme was conducted during 1 9 7 3 - 1 9 7 4 off the coast of Delaware to provide an environmental baseline for two ocean sewage ouffalls. Extensive physical measurements and water quality data, together with biological data (fish, invertebrates, bacteriological samples), were collected. Based on this research the design of sewage treatment for one of the outfalls was improved. The world's coastal zones continue to be the target of man's activities ranging from recreation to heavy industry. At the present time recreation in Delaware's coastal zone is more valuable than heavy industry. In Sussex County, tourism, together with increasing pressure from heavy industry, will place a huge load on sewage facilities. Without adequate facilities, amenity values would decline rapidly. To anticipate this problem, a sewage system was authorized for Sussex County. Two sites were chosen for the construction of facilities and associated ocean outfalls (Fig.l). The Henlopen site at the mouth of Delaware Bay would provide a maximum discharge of 1.9 × 106 ma/day (291 M.G.D.) of secondary (or better) treated sewage. The Bethany site is approximately 3 0 k m south of Cape Henlopen and would provide a maximum discharge of 0.94 X l0 s ma/day (25 M.G.D.) of similarly treated effluent. This study was undertaken for several reasons. First, a physical, chemical, and biological baseline was needed in order to assess the environmental impact of the outfalls when they become operational. Second, seasonal field measurements of currents, circulation, and density structure, treated in detail by Ditmars (1974), were of value in evaluating possible outfall locations at each site. In addition, system configurations, near-field, and far-field mixing performances based on Ditmars' work were of
potential value in designing the specific configuration of the outfall. By influencing the design and location of the system this study has the potential for reducing the probability of environmental degradation. The purpose of this account is to briefly summarize the rationale for the sampling regime and the choice of chemical and biological parameters, as well as summarizing the results of the biological studies, especially of fish and invertebrates. Environmental Background The Henlopen site is dominated topographically by Hen and Chickens Shoal, which is maintained by ebb tide currents. The abrupt beach slope yields to a shallow, flat bottom (9 m), which rises on the shoal and in turn drops off steeply into a series of depressions ( 2 0 - 3 0 m). At the Bethany site the abrupt beach slope grades gradually to a shallow bottom ( 9 - 1 2 m), marked with slight sloughs and ridges. Sediment at both sites is mainly medium sand (<0.5 ram) although the deeper bottom at the Henlopen site contains cobbles, small boulders, and pockets of silt. These nearshore sites were similar in temperature (3-21°C), salinity (27-31 ~oo), and dissolved oxygen (3.4-9.3 ppm) of the bottom water throughout the study. Sampling Regime Sampling for this project was designed to provide a view of seasonal, diurnal, and tidal variations of the physical, chemical, and biological parameters. The physical measurements (Ditmars,1974) were of predictive value in choosing outfall configurations and locations. Chemical and biological data are described in detail by Maurer et al. (1974). Chemical studies included background 31
Marine Pollution Bulletin
I
75~10 '
DEL A W A R E B A Y
-58*50'
CAP
PA. ( ~39" ,D.
.ENLOPE.
-
REHOBOTI
BEACH
R E H O BOTH BAY
A TL A N TIC 0 CEAIV
RIVER
BETHANY BEACH
38°4d -
INDIAN R I V E R INLET
,2
,, jo
•7
•8
•9
6
5•4
ol
2
3
• 38"30'
38°30 '
! 0
I
75¢,10'
I
2 3 4 5
KILOMETERS
75*00' I
Fig. 1 Location m a p o f sampling sites.
levels of salinity, dissolved oxygen, B.O.D., hardness, chlofinity, nutrients (organic nitrogen, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, phosphate), total organic carbon, heavy metals (copper, chromium, silver, zinc, lead, nickel, cadmium, mercury, arsenic), and pesticides in the water column. In addition, analyses of the background levels of some heavy metals and pesticides were made on sediments, fish, and invertebrate samples. Since millions of gallons of fresh water would be exported to each outfall site daily, significant local alteration of the normal salinity regime would be a potential problem. This change could affect the fish or benthic fauna. Particulate matter associated with the effluent could affect B.O.D., total organic carbon, and dissolved oxygen. A secondary treated sewage effluent would still have high levels of nutrients and pesticides associated with it, so an indication of background levels was necessary. Various heavy metals have been shown to be associated with sewage sludge (Gross, 1972; Watling et al., 1974) dump sites and may also prove to be present in high levels in a sewage effluent. Biological studies included baseline information on bacteria (total coliform, faecal coliform, and faecal streptococcus), macroscopic benthic invertebrates, and fish. Background bacteria levels and normal variations were important to assess any bacterial introduction through the 32
outfall. Each of the chemical parameters has a potential effect on the benthic and fL~la communities, and baseline data were necessary to assess the impact of the outfalls on species composition, evenness of distribution, and species richness.
Methods Twelve stations (3 replicates/station) were sampled quarterly (July and October 1973, January and April 1974) at each site with a 0.1 m 2 Petersen grab (Fig.l). Samples were washed through a 1.0 mm mesh screen and the residue retained on the screen was preserved in 10% formalin buffered with hexamethylenamine for laboratory analysis. Two 10 min otter trawl tows (mouth 6 m, 7.6 cm stretch mesh net, 2.5 cm stretch mesh bag) were taken at each site per quarterly sampling period. In addition, 10m in otter trawl tows were made every 4 h over 2 4 h in August, October, December 1973 and January and April 1974. Fish were identified and counted immediately and the length was measured to the nearest millimetre. Top and bottom water samples providing the basis for chemical and bacteriological analyses were also collected every 4 h during the same 24 h sampling periods. Results Bacteria Seasonal 24 h studies provided top and bottom water samples for seasonal and diurnal baseline counts of total coliform, faecal coliform, and faecal streptococcus (No./10Oml). Levels were generally low at both sites ( < 2 / 1 0 0 m l) with occasional pulses of higher bacteriological activity at each site. There were no seasonal or diurnal trends noted. Total coliform varied from < 2 - 3 8 0 0 colonies/100 ml at the Bethany site and < 2 - 2 0 0 at the Henlopen site. Faecal coliform remained uniformly low at the Bethany site (<2) and rather low at the Henlopen site ( < 2 - 8 ) . Faecal streptococcus ranged from < 2 - 5 0 at the Henlopen site and < 2 - 1 0 6 at the Bethany site. Preliminary indications are that bacterial levels may be somewhat higher at the Bethany site on some occasions, due to short pulses of bacterial activity an order of magnitude higher than that noted at the Henlopen site.
Fish Otter trawl hauls throughout the year at the Henlopen site yielded 1384 individuals of 25 species. An average haul yielded 48 individuals of six species with a scaled diversity (H) of 0.572 (0 = skewed, 1 = even) (Fager, 1972). Seasonally, the highest number of species was sampled in the fall (12); the number of individuals/haul was highest in the spring (81). Diurnal trends showed a larger number of individuals at night (58) than during the day (44) with no differences in the number of species taken. The red hake, Urophysis chuss, and the silver hake, Merluccius bilinearis, together comprised 52.3% of the total catch at the Henlopen site. The Bethany site yielded 971 individuals of 26 species. An average haul yielded 40 individuals of eight species with a scaled diversity (H) of 0.602. Seasonally, the highest number of species was sampled in summer and fall (11). The number of individuals/haul was also highest in summer (55) and fall (57). Diurnal variation showed no differences between day and night in the number of species sampled, but the number of individuals/haul was higher at night (58)
Volume 7/Number 2/February 1976 than during the day. The sea robin, Prionotus carolinus; the windowpane, Scophthalmus aquosus; the spot, Leiostomus xanthurus; and the red hake, Urophysis chuss; together accounted for 54% of the catch at the Bethany site. Macroscopic benthic invertebrates 9051 individuals of 68 species were collected from the Henlopen site. Abundance patterns were seasonal with 4622 individuals taken in july, 1956 in October, 1560 in January, and 913 in April. Annelids (83 species) comprised 49.4% of the fauna, arthropods (49 species) 29.2%, molluscs (15 species) 8.9%, ectoprocts (10 species) 6.0%, cnidarians (5 species) 3.0%, rhynchocoels (3 species) i.8%, and echinoderms (3 species)
1.8%. A measure of evenness (SDN) (Fager, 1972) was used to evaluate the distribution of individuals over the species. This is a scaled value between 0.0-1.0 (0=skewed, 1 = even). The mean scaled SDN for the 12 stations at this site were generally low ranging from 0.238 to 0.382. Variation in evenness between the 12 stations was considerable, however. The characteristic fauna at the Henlopen site occurred in two distinct sediment types. The shoal, a well-sorted fine sand, was dominated by the amphipod, Parahaustorius longimerus, other species of Haustoridae, and the bivalves, Spisula solidissima and Tellina agilis. The deeper stations east of the shoal contained mixed course sand, pebbles, shell debris, and small pockets of silt. The fauna associated with this bottom consisted of infaunal species (Tharyx acutus and Aricidea cerruti) and epifaunal species (Mytilus edulis and Unciola serrata). Mytilus edulis was a dominant species in terms of number and occurrence throughout most of the year. In order to determine something about the structure of the community a dominance index (McNaughton, 1967) was applied to the data. The index reflected the large Mytilus edulis recruitment in July at the Henlopen site, with the highest mean value of 0.83. When the species were ranked by numbers of individuals, the two most abundant species (Mytilus edulis and Parahaustorius longimerus) in July represented 83% of the fauna. During the other three quarters, between 13 and 16 species were necessary to duplicate this percentage. During these quarters the dominance index declined (0.72 in October, 0.65 in January, and 0.67 in April) indicating less dominance by one or two species. The fauna of the Henlopen site was dominated by important estuarine species and rarely included species commonly collected in offshore areas of the continental shelf. 6239 individuals of 181 species were collected from the Bethany site throughout the course of the study. Abundance patterns were roughly seasonal with 1956 in July, 2454 in October, 899 in January, and 878 in April. Annelids (79 species) comprised 44% of the fauna, arthropods (59 species) 33%, molluscs (21 species) 11.7%, ectoprocts (9 species) 5%, cnidarians (4 species) 2.2%, rhynchocoels (5 species) 2.8%, echinoderms (1 species) 0.6%, and protozoans (1 species) 0.6%. The evenness (SDN) of the distribution of individuals at each station was used. The mean SDN values for the 12 stations varied between 0.503 and 0.522 indicating a rather
even distribution seasonally. Variation between stations in scaled SDN values was great however. The benthic assemblage at the Bethany site was characteristic of a medium sand fauna. The bivalves, T. agilis and S. solidissima; the amphipod, Protohaustorius wigleyi; and the polychaetes, Nephtys spp.; were important species. The polychaete, Spiophanes bombyx, and the archiannelid, Polygordius sp., which were previously collected in great numbers offshore (30 km) (Maurer et al., 1975), were also found to be important at this nearshore site. The dominance value for this site was rather low and constant (0.57-0.63) throughout the year.
Discussion a n d Conclusions Ditmars (1974) recommended that the outfall proposed for the Henlopen site can be placed outside the shoal, where a high level of mixing of the discharge could be achieved over a wide range of receiving water conditions. Proximity to swimming beaches and reduced circulation inside the shoal made this area an unlikely choice for the outfall. Ditmars' work showed that the Bethany site would result in less rapid flushing of the diluted effluent from the area. This fmding necessitated some alteration of design of the outfall proposed for this site. Analysis of fish data shows that numbers of individuals and evenness varies on a diurnal basis and that species composition varies tremendously seasonally. Greater abundance in night m day hauls was probably due to net avoidance. An example of the importance to the fauna of species present only seasonally can be seen in the Henlopen site fish data. The red hake, the most numerous fish taken, was present throughout the year; while the silver hake, second in importance numerically, was taken only during late winter and early spring. The importance of a year-long study as a minimum baseline for evaluation of future environmental degradation is emphasized by these results. Sampling should include 2 4 h studies or should be standardized with respect to time and tide. The benthic fauna presents an interesting contrast between the two sites which are both near-shore and only 3 0 k m apart. The influence of Delaware Bay on the Henlopen site can be seen in the fauna as well as the sediment. Strong ebb tide currents deposit both fine sand and large cobbles in this area. The larger substrates present a settling area for mussel larvae, which probably originate from a Delaware Bay source. These blue mussels provide an area for epifaunal crabs and worms, which in turn attract fish. The Bethany site had a more homogeneous sediment type (medium sand) which favoured a largely infaunal assemblage, including some species also important 30 km from shore. Environments with highly predictable fluctuations in chemical parameters, such as the continental shelf are often inhabited by species with a narrow ability to adapt to change (Slobodkin & Sanders, 1969). The lower flushing rate of the Bethany site might therefore combine with small fluctuations in salinity, nutrients, and trace metals from the outfall to adversely affect the portion of the fauna found also on the outer shelf. On this basis it was decided that the treatment of sewage at the Bethany site had to be improved over that initially planned. This approach will hopefully reduce the potential for environmental damage. 33
MarinePollutionBulletin This research was supported by the County Engineer, Sussex County, Delaware, under the management of Mr.William Henry and Mr. Roger Truitt. Chemical analyses were performed by the Technical Services Division of the Delaware Department of Natural Resources and Environmental Control (DNREC) under the coordination of their Director, Dr. Harry Otto, and the supervision of their Chief Chemist, Mr. Charles J'Anthony. We owe thanks to the crew of the R. V. Delaware, DNREC's vessel, and to our own crews aboard the R. V. Skimmer and the R. V. Wolverine. Many technicians and staff aided in sorting and processing biotic and sediment samples. Our colleague, Dr. Les Watling, aided in the identification of arthropods, and Dr. Jack Ditmars, the Project Manager, facilitated our task in many ways.
DON MAURER JEFF C. TINSMAN WAYNE LEATHEM PETER KINNER
Field Station, College o f Marine Studies, University o f Delaware, Lewes, D E 19958, U.S.A. Ditmars, J. D. (1974). Physical aspects of baseline studies for the environmental assessment of Sussex County ocean outfalls. Rept. to the Sussex Co. Eng., 58 pp. Fager, E. W. (1972). Diversity: a sampling study. Am. Nat., 106, 239-310. Gross, M. G. (1972). Marine waste deposits near New York. Mar. Pollut. Bull., 3 (4), 61-63. Maurer, D., Tinsman, J. C., Leathem, W. & Kinner, P. (1974). Baseline study of Sussex County, Delaware ocean outfalls. Rept. to the Sussex Co. Eng., 287 pp. Maurer, D., Kinner, P., Leathern, W. &Watling, L. (1975). Benthic faunal assemblages off the Delmarva Peninsula. Estuar. coast. Mar. Sci., (in press). Slobodkin, L. B. & Sanders, H. L. (1969). On the contribution of environmental predictability to species diversity. Brookhaven Symposia in Biology. Number 22, pp. 82-95. Wafting, L., Leathern, W., Kinner, P., Wethe, C. & Manrer, D. (1974). Evaluation of sludge dumping off Delaware Bay.Mar. Pollut. Bull., 5 (3), 39-42.
Mercury in Plankton From a Polluted Norwegian Fjord Plankton of mixed composition has been collected from Sorfjorden and Hardangerfj~rden, on the west coast of Norway and analysed for total mercury by flameless atomic absorption. Different methods of decomposing the samples prior to analysis were tested, showing no significant variations in the recovery of mercury. The high levels of mercury (0.52-25.21 ppm dry weight) are apparently associated with a source of industrial pollution. Indications of higher mercury concentrations in phytoplankton than in zooplankton were noticed and suggest a lack of food chain amplification within the lower trophic levels. The growing concern about the occurrence of mercury in the marine environment has led to intensified research to establish levels of mercury at different trophic levels in the sea. Investigations have been concentrated on organisms directly used in the human diet (West66, 1966; Klein & Goldberg, 1970; Burton & Leatherland, 1971) and less attention has been paid to the biomass at the lower end of the marine food chains. However, the uptake mechanisms of mercury and the transformation reactions that may take place in an aquatic ecosystem have been reported (Davis & Ferguson, 1972; Fagerstr6m & Jernel6v, 1972). Analyses of mercury in plankton collected in the open ocean (Knauer & Martin, 1972) and in estuaries (Cocoros et al., 1973) revealed no significant differences in concentrations and the values found were low (about 0.2 ppm dry weight). In this paper the results of analyses for total mercury in mixed phyto- and zooplankton samples from Sort}¢rden and Hardangert~¢rden, West Norway are reported. For comparison a plankton sample from the south-west African coast was also analysed. Material a n d M e t h o d s The samples were collected in August 1972 using a 34
nylon net (25/~m), equipped with a fibre glass bucket. All the samples were obtained by oblique near surface ( 0 - 1 0 m) hauls and the samples were frozen immediately after collection. We analysed 0.05-0.25 g wet plankton and calculated the concentration of mercury on a dry basis (80°C), using the wet: dry ratio determined on another portion of the sample. Aqueous plankton solutions (see below) were analysed for mercury by flameless AA using a Techtron AA 4/5 spectrophotometer and Model 62 mercury cell (Stux & Rothery, 1971). Dilute standards were made up from a 5 0 p p m Hg stock solution in a range from 0 to 0.2/ag Hg/30 ml. The sensitivity of the determination was 0.5 ng Hg/ml for 1% absorption, the detection limit was 3 ng absolute or 0.1 ng Hg/ml. The relative deviation of 6 replicate determinations of 0.1/ag Hg was 4.5% and the reagent blank was below detection. Due to the uncertainty of how the various methods of decomposing biological material affects the recovery of mercury in the samples, the following methods of sample attack were compared: (1) Modified official A.O.A.C. method (Analytical Methods Committee, 1965) (2) 50% H2 02-conc.H2 SO4 (3) cone. HNO3-conc. H2SO4 in a P.T.F.E. bomb (Paus, 1972) (4) cone. HNO3 (Scobbie, 1971) (5) 6% v/v KMnO4-conc. HzSO4 (Lindstedt, 1970). The results (Table 1) show that the recovery of mercury using different methods of sample attack is reasonably consistent. Only method 2 gave a complete decomposition of fatty substances in the samples, although the merury concentration did not increase, implying that the fats do not contain much mercury (see also Omang, 1973).