Impact of a power plant on a subtropical estuarine environment

move generally seaward and to decompose where it sinks to the bottom, we might continue to ignore it though its presence in London's river would be as unwelcome as litter in London's streets. But when it can be shown that some portion of it is being returned for final breakdown to those reaches that are chronically short of dissolved oxygen it becomes important to ascertain the quantities involved. It is possible that the concentration of rubbish between Bugsby's and Halfway Reaches is as much a cause of oxygen depletion as the

unfortunate geographical coincidence of silt and sewage effluents. P. A. BOARD Central Electricity Research Laboratories, Kelvin Avenue, Leatherhead, Surrey, UK

Inglis, C. C. & Allen, F. H. (1957). Proc. Instn. Cir. Engrs., 7, 827. Hancock, D. A., Drinnan, R. E. & Harris, W; N. 0956). J. mar. biol. Ass., UK, 35, 307. Reitzenstein, E. von (1913). Abh. dtsch. Seefisch Vet., 12, I.

Impact of a Power Plant

a

Esmarine Environment The development of electricity generating stations around Biscayne Bay, Florida, has resulted in a considerable discharge of cooling water into this subtropical sea. The impact of this on the biology of the area has been studied for the last four years by a team of scientists; this report summarizes their general conclusions. Due to increasing population in Miami and Dade County coupled with increasing power demands, two fossil fuel and two nuclear plants were recently constructed on the shore of Biscayne Bay, a shallow subtropical bay approximately 15 km south of Miami (Fig. l). Scientists have conducted a four-year multidisciplinary study of the plant's environmental impact (Bader et al., 1972), part of which has already been described by Roessler (1971) and by Thorhaug and Fernandez (1973). At first the effluent was discharged into Biscayne Bay just south of the plant location, resulting in persistent

temperatures up to 5°C above the ambient temperature (Roessler, 1971, Fig. 2). To reduce recirculation of heated water to the plant, to provide better cooling of the effluent, and to decrease the impact on the biota, a second canal was built to Card Sound, a rectangular body of water (5 km × 3 km) south of Biscayne Bay. Studies were conducted for a year prior to the discharge of the effluent into the Sound.

Circulation The general circulation pattern of the water adjacent to Turkey Point is to the NNE on flood and SSW on ebbtides, with winds occasionally producing other patterns. The bay is approximately 2-3 m deep with a shallow sill 1-2 m deep on the western shoreline. Card Sound is 3-4 m deep. Tidal exchange via small inlets between barrier islands from the eastern boundary is poorly developed as demonstrated by the wet-dry seasonal salinity contrasts between the bay and ocean. The interior western portion chiefly exchanges with Biscayne Bay to the north and Barnes Sound to the south (Lee, 1972: Lee & Rooth, 1972).

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166

Map of Florida showinglocation of study area. The letter

'A' indicates the original exit point for the effluentcanal, as discussed in this paper. The letter 'B' indicates the new exit point in Card Sound, opened February 14, 1972.

The study area was found to be typical of subtropical tidal estuaries having low concentrations of dissolved nitrogen and phosphorus (Gerchakov et al., 1973), The concentrations of these nutrients in the fresh water run-off to the bay are low. The discharge water from the power plant showed small increases in salinity, nitrate, nitrite, silicate, phosphate and slight depletion of oxygen compared to the intake water. In addition, total dissolved organic carbon and dissolved iron, copper and zinc concentrations were higher in the effluent water (Gerchakov et al., 1973). The trace transition metal biogeochemistry of South Biscayne Bay appears to be anomalous when compared to previously studied coastal areas. Concentrations of these metals are generally lower in Biscayne Bay sediments (Table 1) and biota (Segar & Gilio, unpublished) than have been reported for sediments and the same or similar species of organisms from other environments. However, dissolved concentrations of these metals in the water column appear to be normal or perhaps somewhat higher than would be expected

in unpolluted coastal waters (Segar, unpublished). The extremely low concentrations of metals in the sediments appear to be due to the absence of a clay mineral suite. The sediments consist of fine quartz and carbonate debris with considerable quantities of organic matter. Fraetionation studies have shown that most of the trace metal load appears to be associated with the organic matter and very little with the quartz, carbonate or sulphide minerals (Segar & Pellenbarg, 1973). Thus the sediments of South Biscayne Bay will not act as a permanent sink for trace metals, including radionuelides, that may be added as contaminants. The metals would be released during bacterial decay of the organic matter in the sediments. Those metals with insoluble sulphides may be expected to be held in the solid phase of the sediments while active decay and sulphide production are taking place. However, resuspension and oxidation of the sediments by physical and biological processes is frequent in this shallow location and these sulphides would not remain permanently held in the sedimentary phase. In addition metals may be transported from the sediments through Thalassia back into the water column and detritus (see below). It is apparent that because of this anomalous sedimentary complex the recycling of metals within the Biscayne Bay ecosystem may be significantly more rapid and involve a larger proportion of the total metal load than clay mineral dominated environments. Indeed, preliminary data show that the fossil fuel burning, Turkey Point plant increases the dissolved concentration of certain metals in the cooling water during entrainment. In addition, exceptionally high concentrations of nickel, copper and vanadium have been found in the sediments immediately adjacent to the Bay outfall of the Turkey Point plant when compared to less affected sediments outside the thermal plume area (Segar & Pellenbarg, 1973). The sediments of the entire Turkey Point study area have also been found to contain significantly higher concentrations of copper, lead, cadmium, zinc, vanadium, nickel and iron, but not of silver, than the very similar sediments from the undisturbed Card Sound area a few miles to the south (Table 1). TABLE 1 Concentration of metals in sediments(ppm)* Deep Deep Near Card Turkey Sea Sea Shore Sound Point Element Carbonates Clays Sediments Florida Florida V Fe Cd Pb Ag Zn Cu Ni

20 9,000 9 35 30 30

120 65,000 0.42 80 0.11 165 250 225

130 20 48 55

24 1,900 0.07 1 0.5 4 2 <2

52 2,600 0.2 3 0.4 12 11 25

* From Segar and PeUenbarg, 1973.

Vegetation In the near shore marine subtropics and tropics the dominant plant community is often that composed of turtle grass (Thalassia) and associated macrophytes (Voss & Voss, 1955). This is true of South Biscayne Bay and Card Sound, where the Thalassia and the red epiphytes dominate (Humm, 1965), being particularly numerous in the fall. In areas where the standing crop

of Thalassia is low, green algae, particularly Halimeda and Penicillus, dominate. This entire community produces an abundance of plant material. Thalassia alone produces up to 40 g dry wt/m2/day or about 14,600 of dry wt/m2]yr. The red epiphytes are dominated by Laurencia poitei which produces approximately 6 g dry wt/m2/day or 2,190 dry wt/m2/yr. The other green algae add about 2 g/m2/day of organic material. Using a combination of aerial photography, field observations and control studies, it has been estimated that in the area of Turkey Point, prior to opening the effluent canal, the Thalassia community produced about 17,500 g dry wt/m2/yr. On the average, at any time, the standing crop of Thalassia blades would have amounted to approximately 165 g dry wt/m 2 of which 62 g would have been carbon, 17 g proteins and about 1 g lipids (Table 2). TABLE 2 Chemicalanalysisof Thalassia blades at TurkeyPoint Average g dry wt/m2 Carbon g dry wt/m2 Lipids g dry wt/m2 Protein g dry wt/m2 Iron ~g/m2 Cobalt/~g/m2 Nickel/zg/m2

165.4 62-9* 1.2* 17.0" 7,443 t 66.2t 661"6t

Z~aiOdCm~•~ iu~mmm g~2 2 /zg/a/xg/mm2 Lead

330-8,t 2,481 132"35 148.9t

* From Bauersfeldet al., 1969. 3"From Segar & Gilio,unpublished. There must be a very rapid cycling of organic and inorganic materials since the Thalassia blades have a turnover rate of about three weeks. Since the sum of nitrate and nitrite content of the water is about 3 mg/m3, it appears that an appreciable portion of the total nitrogen of the system is contained in the grass blades and roots. The nutrient dynamics of the turtle grass are not clear. Eel grass (Zostera) obtains most of its nitrate and phosphate from the sediments (McRoy et aL, 1970, 1972) acting as a pumping system: sediment-plant-watersediment. There are preliminary indications that Thalassia may function in a similar manner. Trace metal studies have shown that an appreciable fraction of the ecosystem content of most metals is also found in the grass. It has been hypothesized that the grass may pump trace metals from the sediments out into the water and detritus food chain (Segar et al., 1972, 1973). When the first effluent canal was opened at Turkey Point, persistent isotherms developed. The Thalassia community disappeared in an area of about 9.3 ha off the mouth of the canal, 5°C above ambient. In an area of approximately 30 ha, 3 to 4°C above ambient, the Thalassia community declined by about 50~o and the important macroalgae, Halimeda and Penicillus, fell to about 30~o of the former population. As a result of this modification, selected entities in the animal population increased temporarily. This was due to feeding on the dying plant material. After exploiting this food many motile forms departed with the nutrients gained from the detritus. This, coupled with strong currents from the effluent, removed a considerable portion of the nutrients from the area. The denuded area then became covered with blue-green algae. 167

Increased temperature is not necessarily detrimental to a subtropical ecosystem; control and limitation is the essential factor. For example, in the areas where a +3°C isotherm was maintained the macroalgae and grass populations fell markedly in the summer as temperatures exceeded 31 °C. However, during the winter months Thalassia rebounded. Comparatively speaking the +2°C isotherm was extremely productive, exceeding that of the control stations outside the obvious influence of the thermal plume. This may be due to a number of factors, the increased availability of nitrogen via decaying detritus, modification of circulation and elevated winter temperatures, etc. Regardless of the reason it does indicate that with sufficient understanding and adequate control, man's activities normally detrimental to the environment can be put to productive use.

Impact on animals The catch of animals correlated well with the data on benthic macroplants. Predictive models based on 350 species of animals caught with a 10-foot otter trawl over a period of two and a half years near the Turkey Point effluent indicate that maximum numbers of species and numbers of individuals of benthic macroinvertebrates and fishes will occur near 26°C. Fig. 2 presents an illustration of the predictive exclusion and optimal temperature model for molluscs and crustaceans. About half the species arc excluded at 33°C, 75% above 37°C. Laboratory studies on the macrophytes show an optimum near 28°C. Laboratory investigation on lethal temperature limits corroborated filed data on both plants and animals. __A

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Multiple regression analyses of dominant species of molluscs, echinoderms, and sponges indicated that the principle variables related to catch were vegetation and salinity. Those species most closely related to vegetation were near-shore forms, while those related most closely to salinity were offshore forms such as echinoderms, sponges, wormshell gastropods and the checkered pheasant shell. Analysis of variance of the mean number of animals per trawl drag (approximately 100/m2) indicated that areas elevated 4 to 5°C above ambient produced few specimens of those species of animals which comprised one per cent or more of the total number of macroanimals. Stations located in areas elevated between 3-4°C had low numbers of animals in the summer, but showed some recovery in winter; however, the average annual standing crop was lower than at control stations. At stations elevated between 2-3°C, the catches were low in summer, but high in winter and spring; this produced above average annual standing crops. At stations elevated less than 2°C, no statistical differences between controls and affected stations could be detected. Analysis of total numbers of individuals of major taxa comprising 80 species of fishes, 147 of molluscs, 66 of crustaceans, 23 of echinoderms and 22 of sponges, showed similar results to those found for the dominant indicator organisms. Preliminary results from studies of the Card Sound effluent canal, opened in February, 1972, indicated the effluent was 2°C above bay ambient and carried a considerable load of suspended matter. In the immediate area of the canal mouth, the macroplant community in

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approximately 2-3 ha disappeared. In the area where the water contained noticeably more suspended matter, the seagrasses decreased in production of dry weight blade material from 20 to 30% that in 1971. Control stations increased 10~o compared with 1971, probably due to a slightly warmer winter. However, the animal populations in 1972 at the affected stations were similar in abundance and diversity to those found prior to the canal mouth opening. We would like to acknowledge the primary support of the US Atomic Energy Commission and the Florida Power and Light Company with aid from Sea Grant (NOAA and NSF) and the Envirorunental Protection Agency. Other investigatorsinvolved in the total study included R. G. Bader, J. Bunt, D. de Sylva, E. Fefgnson-Wood, J. Fell, S. Gerchakov, T. Johnson, T. Lee, J. Michel, H. B. Moore, M. Reeve, C. Rooth with their students and technical staff. A. THORHAUG School o f Medicine D. SE~AR M. A. ROESSLER School o f Marine and Atmospheric Sciences, University o f Miami, Miami, Florida 33152, USA Bader, R. & Roessler, M. (eds.) (1972). An ecological study of South BiscayneBay and Card Sound, Florida. Progress Report to the US Atomic Energy Commission and Florida Power and Light Co. Bauersfeld, P., Kifer, R. R., Durrant, N. W. & Sykes, J. E. (1969). Nutrient content of turtle grass Thulassla testudinum. Proc. Intl. Seaweed Syrup., 6: 637--645.

Gerchakov, S. M., Segar, D. A. & Stearns, R. D. (1971). Some chemical and hydrologicalinv~.gafions in an area of thermal discharge into a tropical marine estuary. Third National Symposium on Radioecology, Oak Ridge, Tenn. Humm, H. J. (1964). Epiphytes of the seagram Thakt~ testudimm Konig in Florida. Bull. Mar. Sa. Gulf& Car&. 14(2): 306-341. Lee, T. Cm press). Effects of power plant dischat~ on exchange processes in shallow estuaries. Qmrt. J. F/a. Amd. $d. Lee, T. & Rooth, C. (1972). Exchat~ processes in shallow tidal estuaries. Sea Grant Spee. Bull. U. of Miami. McRoy, C. P., Barsdate, R. J. & Hebert, M. N. (1972). Phosphorus cycling in an eelgrass (Zostera marine L.) ecosystem. Llnmol. Oceanog., 17: 58--67. McRoy, C. P. & Barsdate, R. J. (1970). Phosphate absorption in eelgrass. Linmol. Oceanog., 15: 6-13. Reeve, M. R. (1972). Seasonal changes in the zooplankton of South Biscayne Bay and some problems of assessing the effects on the zooplankton of natural and artificial thermal and other fluctuations. Bull. Mar. Sci., 20(4): 894--921. Roessler, M. A. (1971). Environmental changes associated with a Florida power plant. Mar. Poll. Bull., 2(6): 87-90. Segar, D. A., Gilio, J. L. & Pellenbarg, R. E. (1972). Observations on the distribution of Ag, Cu, Co, Ni, Cd, Zn, Pb, Fe and V in a coastal ecosystem. Presented at Amer. Gcophys. Union Annual Meeting, San Francisco. Segar, D. A., Gilio, J. L. & Pellenbarg, R. E. (1973). Some aspects of the biogeochemicalcycles of trace metals in a subtropical estuary including ecosystem compartment models. Presented at Symposium on Environmental Biogeochemistry, Logan, Utah. Segar, D. A. & Pellenbarg, R. E. (to be submitted). Trace metals in carbonate organic rich sediments:effectsof industrialization and urbanization. Thorhaug, A. & Fernandez, M. (1973). Biological membranes as pollution indicators. Mar. Poll. Bull., 4(5): 70-73. Voss, G. L. & Voss, N. An ecological study of Soldier Key, Biscayne Bay, Florida. Bull. Mar. Sci. Gulf & Carib., 5(3): 203-229.

Effects of Red Mud on Marine Animals Red mud is a waste preduet in the reduetion of bauxite in the wedaetioa of ainmininm. The exact eompeeition of red mud depends on the semee of the bauxite and its

trcatwat ~

la~ineflea. TI~ variation has beca

respmm'Ne for eodiOi-~ reports abeut the damage caused by dmn#ag red mud at sea. At the 1972 meeting of the International Council for the Exploration of the Sea, Dethlefsen (1972) described the results of an experimental dumping of red mud in an area of the North Sea designated as a potential site for the disposal of large quantities of this waste from the German aluminium industry. After a careful consideration of the effects produced by the red mud on the fauna in the dumping area and of the effects produced by red mud in laboratory experiments, Dethlefsen concluded that it would be inadvisable to dispose of the waste at sea. For several years a similar waste had been dumped in the Bristol Channel on the west coast of the U K with the approval of scientists from the Ministry of Agriculture, Fisheries and Food. Following the closure of the factory this operation ceased in 1972, but during the six years of operation no effects on the fisheries in the area had been reported. In the light of the German decision it was considered necessary to conduct a careful reappraisal of the question of the disposal of red mud at sea and in particular to examine the reasons for the differences between the U K and German experience with this waste. This paper considers the importance of physical and chemical differences between red muds of different origin, of differences in interpretation of the observed effects of red mud in the laboratory and of differences in the dumping sites.

Physical and chemical characteristics of red mud Red mud is a by-product in the 'reduction' of bauxite to alumina by the Bayer process, and its physical and chemical composition depends upon the origin and treatment of the bauxite. Most of the crude bauxite ore is obtained by open quarrying although some underground mining is carried out. The ore is crushed and may be 'beneficiated' by washing before processing. Bauxites usually contain about 5-10~o reactive silica (SiO2) and 50-60% alumina. The alumina can occur as the trihydrate (gibbsite) A1203.3H20 or the monohydrate (bohmite) AI203.H20, and the bauxite can contain either of these forms or a mixture. The essential difference between the two forms is their solubility. The trihydrate can be extracted by digestion in a low-strength solution of caustic soda at boiling point, whereas the dissolution of the monohydrate requires steam pressures up to 180 lb/sq inch and concentrated caustic soda solutions. Bauxites also contain iron oxide (Fe203) and it is this that gives the ore and the red mud its reddish-brown colour. The proportion of iron oxide can vary from about 25~o in French ores and 15~o in Ghanaian ores to 2-3~o in South American ores. Other major impurities such as vanadium, arsenic, chromium and nickel can all occur in trace amounts. Following extraction of the aluminium with caustic soda, the silica (now present as sodium aluminium silicate) separates out and with the other insoluble residue forms the red mud slurry. In the German process this is thickened by filtration before disposal; in the U K the slurry was passed through a five-stage counter169