Lead and cadmium in urban allotment and garden soils and vegetables in the United Kingdom

In order to assess the intake of lead and cadmium by consumers of home grown vegetables in urban areas, replicated experimental plots of uniform size, comprising summer and winter crops, were established in 94 gardens and allotments in nine towns and cities in England.The geometric mean lead and cadmium concentrations for the soils (n = 94) were 217 g g^–1 (ranging from 27 to 1,676 g g^–1) and 0.53 g g^–1 (<0.2–5.9 g g^–1), respectively. Compared with agricultural soils, the garden and allotment soils contained elevated levels of lead but not cadmium.Lead concentrations in the vegetables ranged from <0.25 g g^–1 to 16.7 g g^–1 dry weight and cadmium concentrations ranged from <0.025 g g^–1 to 10.4 g g^–1 dry weight. Lead concentrations were higher than reported background levels, although <1% exceeded the statutory limit for saleable food in the UK (1 g g^–1 fresh weight). Cadmium concentrations were generally similar to background levels.     

Temporal variation and distribution of trace metals in freshwater and fish from Calabar River, S.E. Nigeria

An investigation on the abundance and distribution of trace metals (Fe, Cu, Zn, Mn, Cr, Cd and Pb) in water, and nine species of fish samples from Calabar river was carried out in 1992. The concentrations of iron (6000–7240gl^–1), zinc (4910–7230gl^–1), and cadmium (3–7gl^–1) showed moderate pollution while those of copper (420–630gl^–1), manganese (23–48gl^–1), chromium (<10–20gl^–1) and lead (<1–10gl^–1) in water were well below WHO permissible levels. Significant seasonal changes (0.001p0.25) were obtained for iron, copper, zinc, manganese and cadmium in water. Furthermore, iron, zinc and cadmium showed statistically significant spatial changes (0.005p0.10). Of the nine fish species studied, no statistically significant relationship between body weight and the concentrations of the metals was observed. The concentrations of the metals per mean total body weight apparently decreases in the order Fe>Zn>Cu>Mn>Pb>Cd=Cr and were within the limits that were safe for consumption.     

Effects of light intensity on nitrate and nitrite uptake and excretion by Chaetoceros curvisetus

Michaelis-Menten uptake kinetics were observed at all light intensities. With constant illumination, the V_max and K₁ in nitrate uptake over the natural light intensity range of 0 to 2000 E were 0.343 g-at NO₃–N(g)^-1 at protein-N h^-1 and 26 E, respectively. Nitrate uptake was inhibited at higher light intensities. The K_s for nitrate uptake did not vary as a function of light intensity remaining relatively constant at 0.62 g-at NO₃–N 1^-1. With intermittent illumination, the V_mzx for light intensity in nitrate uptake over a light intensity range of 0 to 5000 E was 0.341 g-at NO₃–N(g)^-1-at protein-N h^-1. No inhibition of nitrate uptake was observed at higher than natural light intensities. Chaetoceros curvisetus will probably never experience light inhibition of nitrate uptake under natural conditions.     

Background levels of soil beryllium in several countries

Beryllium and aluminium contents in uncontaminated soils from six countries are reported. The means and ranges of beryllium in the surface soils were as follows: 1.43(0.20–5.50)g g^–1 in Thailand (n=28), 0.7 (0.31–1.03) g g^–1 in Indonesia (n=12), 0.99(0.82–1.32) g g^–1 in New Zealand (n=3), 0.58(0.08-1.68)g g^–1 in Brazil (n=16), 3.52(2.49–4.97)g g^–1 in the former Yugoslavia (n=10), and 1.56(1.01–2.73) g g^–1 in the former USSR (n=8). The mean and range of beryllium contents of the surface soils in Japan (1.17(0.27–1.95)g g^–1 n=27) are situated within the values of the soils from these countries except for the Yugoslav soils derived from limestones. The mean of the mean beryllium contents of the surface soils in all these countries is 1.42 g g^–1 which will be used as a tentative average content of beryllium in uncontaminated surface soils, except for the soils derived from parent materials high in beryllium content. The beryllium contents of the subsoils were higher than those of the surface soils in New Zealand and Yugoslavia as is the case with Japan. The correlation coefficient between the contents of beryllium and aluminium in all the soil samples (n=113) including surface soils and subsoils was 0.505 (p < 0.001).     

Uptake of dissolved organic matter by larval stage of the crown-of-thorns starfish Acanthaster planci

The life-history of the crown-of thorns starfish (Acanthaster planci) includes a planktotrophic larva that is capable of feeding on particulate food. It has been proposed, however, that particulate food (e.g. microalgae) is scarce in tropical water columns relative to the nutritional requirements of the larvae of A. planci, and that periodic shortages of food play an important role in the biology of this species. It has also been proposed that non-particulate sources of nutrition (e.g. dissolved organic matter, DOM) may fuel part of the nutritional requirements of the larval development of A. planci as well. The present study addresses the ability of A. planci larvae to take up several DOM species and compares rates of DOM uptake to the energy requirements of the larvae. Substrates transported in this study have been previously reported to be transported by larval asteroids from temperate and antarctic waters. Transport rates (per larval A. planci) increased steadily during larval development and some substrates had among the highest mass-specific transport rates ever reported for invertebrate larvae. Maximum transport rates (J _max ⁱⁿ) for alanine increased from 15.5 pmol larva^–1 h^–1 (13.2 pmol g^–1 h^–1) for gastrulas (J _max ⁱⁿ=38.7 pmol larva^–1 h^–1 or 47.4 pmol g^–1 h^–1) to 35.0 pmol larva^–1 h^–1 (13.1 pmol g^–1 h^–1) for early brachiolaria (J _max ⁱⁿ just prior to settlement=350.0 pmol larva^–1 h^–1 or 161.1 pmol g^–1 h^–1) at 1 M substrate concentrations. The instantaneous metabolic demand for substrates by gastrula, bipinnaria and brachiolaria stage larvae could be completely satisfied by alanine concentrations of 11, 1.6 and 0.8 M, respectively. Similar rates were measured in this study for the essential amino acid leucine, with rates increasing from 11.0 pmol larva^–1 h^–1 (or 9.4 pmol g^–1 h^–1) for gastrulas (J _max ⁱⁿ=110.5 pmol larva^–1 h^–1 or 94.4 pmol g^–1 h^–1) to 34.0 pmol larva^–1 h^–1 (or 13.0 pmol g^–1 h^–1) for late brachiolaria (J _max ⁱⁿ=288.9 pmol larva^–1 h^–1 or 110.3 pmol g^–1 h^–1) at 1 M substrate concentrations. The essential amino acid histidine was transported at lower rates (1.6 pmol g^–1 h^–1 at 1 M for late brachiolaria). Calculation of the energy contribution of the transported species revealed that larvae of A. planci can potentially satisfy 0.6, 18.7, 29.9 and 3.3% of their total energy requirements (instantaneous energy demand plus energy added to larvae as biomass) during embryonic and larval development from external concentrations of 1 M of glucose, alanine, leucine and histidine, respectively. These data demonstrate that a relatively minor component of the DOM pool in seawater (dissolved free amino acids, DFAA) can potentially provide significant amounts of energy for the growth and development of A. planci during larval development.     

Environmental Accumulation of Airborne Fluorides in Romania

The nature and extent of pollution from an aluminium smelter and a fertiliser factory in Romania were studied. These are large industrial complexes, and both types of industry are known to release fluorides into the atmosphere. In grass samples collected from around the aluminium smelter, the maximum fluoride levels were found to be 4023mgkg^–1 and 162mgkg^–1 in unwashed and washed grass samples respectively, and 89mgkg^–1 in soils. For the fertiliser factory, the maximum levels in washed grasses were found to be 207mgkg^–1, and 11mgkg^–1 in the soils. In both locations, these maximum values were obtained in samples collected from within 200m of the factory limits, and compare with regional background levels of less than 10mgkg^–1 for grasses and 2mgkg^–1 for soils. The high fluoride levels of fluoride in the grasses are sufficient to give cause for concern for the effects that these could have on the local population and on grazing animals.     

Environmental Geochemistry of Soils and Waters of Susaki Area, Korinthos, Greece

Soil and water samples were collected from the Susaki area of Korinthos and analysed for heavy metals in order to evaluate their environmental impact. The geology of the studied area includes ultrabasic rocks and Neogene and Quaternary deposits whereas magnesite veins are found within the ultrabasic rocks. In the north part of the studied area post volcanic emissions of H₂S, CO₂ and H₂O vapor continue to the present day. All the samples were analysed for heavy metals by the ICP method. The element ranges (in g g^–1) for soil samples are: Cu 11–63, Pb 5–256, Zn 21–604, Ni 183–2665, Co 12–124, Mn 456–1434, As 5–104, Sr 44–730, V 21–84, Cr 163–2346, Ba 48–218, Zr 3–41, Y 3–13. The metals Pb, Zn, Ni, Co, Cr, Fe, Cu, Mn, As and Sr are enriched in the Susaki soils. The element ranges for water samples are: Cu 65–103ppb, Pb<10ppb, Zn<5ppb, Ni 21–163ppb, Co 2–12ppb, As<30ppb, Cr<20ppb, Ba 36–785ppb, Sb<10ppb, W<10ppb, Bi<30ppb, Mn 0.0–0.9 g g^–1, Fe 0.01–0.22 g g^–1, Na 843–3076 g g^–1, K 98–278 g g^–1, Si 39–65 g g^–1, P 0.1–0.2 g g^–1. There is a natural pollution of soils with elevated concentrations of Ni, Co, Mn, Fe and Cr due to the presence of ultrabasic rocks. Another natural case of As pollution of soils is due to the volcanic activity and the geothermal field in the area. The geochemical data of ground waters and also the ¹⁸, D data showed a mixing in different proportions between sea water and meteoric water.     

Seasonal and depth related variation in the photosynthesis–irradiance response of<Emphasis Type="Italic"> Ecklonia radiata</Emphasis> (Phaeophyta,Laminariales) at West Island,South Australia

The photosynthesis–irradiance response of Ecklonia radiata (C. Agardh) J. Agardh, a common kelp in the temperate southern hemisphere, was investigated in situ throughout the year and across a depth profile at West Island, South Australia. Temperature and irradiance environment altered throughout the year, varying at 3 m between 14–20°C and 279–705 mol photons m^–2 s^–1. Photosynthetic capacity (P_m) varied throughout the year between 177–278 mol O₂ g^–1 dry wt h^–1 at 3 m and 133–348 mol O₂ g^–1 dry wt h^–1 at 10 m. The irradiance required for sub-saturation of photosynthesis (E_k) varied between 97–152 and 81–142 mol photons m^–2 s^–1 for 3 m and 10 m respectively, and the respiration rate varied between 15–36 and 13–20 mol O₂ g^–1 dry wt h^–1 for 3 m and 10 m. A clear seasonal change in photokinetic parameters was detected and provided strong evidence for a seasonal acclimation response. During winter an increase in the efficiency of light utilisation at low irradiance () was accompanied by a decrease in both E_k and that required for photosynthetic compensation. P_m also increased during the winter and autumn months and respiratory requirements decreased. These changes enable E. radiata to display an optimal photosynthetic performance throughout the year despite significant changes in the surrounding environment.Communicated by P.W. Sammarco, Chauvin     

Particulate organic carbon and nitrogen in the adjacent seas of the Pacific Ocean

Particulate organic carbon (POC) and nitrogen in sea water were measured in samples collected in the adjacent seas of the Pacific Ocean during the cruises of T. S. Oshoro-Maru (1969, 1970) and the R. V. Hakuho-Maru (KH-70-4, KH-72-1). High values were obtained in the northern North Pacific and the Bering Sea, the concentration of particulate carbon in the upper 50-m layer ranged from 35 to 550 g Cl^-1. In the deep waters of these area, values above 50 g Cl^-1 were frequently observed. The lowest values in the surface layer and deeper layers were obtained in the Japan Sea (23 gCl^-1) and in the South China Sea (7 g Cl^-1) respectively. A consistent minimum was located in the intermediate waters (100–400 m) throughout the entire region studied. Variation with depth was generally irregular with marked peak values in different layers. The POC distribution consited of these peak values and a relatively uniform background concentration. These background values slightly decreased with increasing depth and were different locally. Correlation analysis between carbon concentration and apparent oxygen utilization (AOU) of ambient water for the samples in the Japan Sea and the Sulu Sea showed that there was no systematic decrease of particulate carbon with increasing AOU. In these areas, the carbon concentration scattered in the higher AOU domain ranged from 10–100 g Cl^-1. These observations support the conception that downward transport of particulate matter from the overlying surface layer in the adjacent seas of the Pacific Ocean may be fairly rapid.     

Geochemistry of an arsenic anomaly in St. Elizabeth, Jamaica

A soil arsenic anomaly with concentrations up to 400g As g^–1 was discovered near Maggotty, St. Elizabeth, during an islandwide geochemical survey of Jamaica. Detailed sampling and chemical analysis of soil samples confirmed the arsenic levels and led to a better definition of the size of the anomaly. The area exceeding the 95th percentile (>65g As g^–1) of the islandwide concentrations has been determined to be at least 10km². The anomalous values may be the result of an ancient hot spring environment which was responsible for the introduction and deposition of Fe–As–S as pyrite and arsenopyrite in the limestone bedrock, which were subsequently oxidised and weathered to yield the arsenic rich soils. These soils were also enhanced in elements such as Sb, Fe and Co. Despite the high soil arsenic content, the arsenic concentration in the surface water is low and there seems to be no immediate health risk to the residents. The area, however, does present a potential hazard with changing land use.     

Seasonal photosynthetic characteristics of Ascoseira mirabilis (Ascoseirales,Phaeophyceae) from King George Island,Antarctica

Monthly variation in photosynthesis, dark respiration, chlorophyll a content and carbon: nitrogen (C:N) ratios in different lamina sections of adult plants of Ascoseira mirabilis Skottsberg from King George Island, Antarctica, was investigated between September 1993 and February 1994. Light saturated net photosynthesis (P _max) showed maximum values in September (12 to 25 mol O₂ g^-1 fr wt h^-1), and decreased towards the summer to values ranging between 2.0 and 5.0 mol O₂ g^-1. In the distal section, however, a second optimum occurred in December (25 mol O₂ g^-1 fr wt h^-1). Dark respiration rates were also highest in October and November and decreased strongly in December to February (6.0 and 1.0 mol O₂ g^-1 fr wt h^-1, respectively). Gross photosynthesis exhibited high values between September and December. Concomitant with the seasonal decrease of photosynthetic efficiency () from mean values of 1.2 mol O₂ g^-1 fr wt h^-1 (mol photons cm^-2 s^-1)^-1 in September to 0.3 mol O₂ g^-1 fr wt h^-1 (mol photons cm^-2 s^-1)^-1 in January, the initial light saturating point (I _k) gradually increased from 19 to 60 mol photons m^-2 s^-1. Likewise C:N ratios were low in spring (12 to 13) and increased in summer (20). In general, the photosynthetic parameters P _max, gross photosynthesis, and Chl a concentrations were significantly higher in the distal section of the thallus. In contrast, C:N ratios were lower in the distal section of the lamina. The results show that photosynthesis obviously strongly supports growth of the alga in late winter to spring, as it does in some morphologically related brown algae from temperate and polar regions. The question whether growth is additionally powered     

Grazing and ingestion rates of nauplii,copepodids and adults of the marine planktonic copepod Calanus helgolandicus

The average grazing and ingestion rates of all stages of the marine planktonic copepod Calanus helgolandicus (Calanoida) from nauplius stage IV to adults were measured experimentally at 15°C in agitated cultures. The chain-forming diatom Lauderia borealis and the unarmoured dinoflagellate Gymnodinium splendens were offered as food. The food concentrations were close to natural conditions and ranged from 36 to 101 g of organic carbon per liter. The medium body weights expressed in g of organic carbon of almost all larval stages raised at 49 g C/1 were identical with the weight of the same stages caught in the Pacific Ocean off La Jolla, California, USA. In a log-log system, grazing and ingestion rates increased almost linearly with increasing body weight. Grazing rates ranged from 4 to 21 ml/day/nauplius stage IV to 286 ml to 773 ml/day/female. Ingestion rates increased from 0.2 g to 0.8 g C/day/nauplius stage IV to 18 g to 69 g C/day/female. Grazing and ingestion rates per unit body weight decreased gradually with increasing body weight. The daily ingested amount of food decreased from 292 to 481% of the body weight (g C) of nauplius stage V to 28–85% of the body weight of adult females. Grazing and ingestion performances of all stages increased with increasing particle size. Grazing rates decreased and ingestion rates increased with increasing food concentrations. The published data on food intake of the different age groups of C. helgolandicus show that the young stages of herbivorous planktonic copepods can play a major part in the consumption of phytoplankton in the sea due to their high grazing and ingestion rates.     

Sodium regulation in the shore crab Carcinus maenas as related to ambient salinity

The activity of Na–K-ATPase was measured in crude homogenates prepared from various organs (leg muscle, pincer muscle, heart, testes, digestive gland, hypodermis, gills 1–9) of shore crabs, Carcinus maenas L., acclimated to salinities ranging between 10 and 50 S (in steps of 10 S). In all salinities tested, Na–K-ATPase activity was highest in posterior gills 7–9 (10–12 mol P_i mg protein^-1 h^-1), followed by anterior gills 1–6 (ca. 2.5 mol P_i mg protein^-1 h^-1) and the other organs (in most cases far below 2mol P_i mg protein^-1 h^-1). In gills only, Na–K-ATPase activity was salinity-dependent, with the highest values in the lowest salinities and vice versa. In gills 7–9, Na–K-ATPase activity was increased more than threefold following a reduction in salinity from 50 to 10 S. Na–K-ATPase activity, expressed as percentage of total ATPase activity, amounted to 60–80% in gills, about 60% in hypodermis and 20–40% in the other organs. Ouabain, a specific inhibitor of Na–K-ATPase activity, reduced serum osmolalities in crabs kept at 9–10 S only when injected into the hemolymph (1 and 5 · 10^-5 M), but had no effect when dissolved in ambient water (10^-4 M). The results obtained underline that crustacean gills are the main organs for ionic regulation, and confirm the hypothesis of the central role of the Na–K-ATPase in active Na uptake as the basic mechanism of hyperregulation in dilute media. Reduction of serum osmolalities following injection of ouabain into the hemolymph confirms previous reports on localization of the sodium pump in the basolateral parts of epithelial cells.     

Feeding,growth and bioluminescence of the heterotrophic dinoflagellate Protoperidinium huberi

Feeding, growth and bioluminescence of the thecate heterotrophic dinoflagellate Protoperidinium huberi were measured as a function of food concentration for laboratory cultures grown on the diatom Ditylum brightwellii. Ingestion of food increased with food concentration. Maximum ingestion rates were measured at food concentrations of 600 g C l^-1 and were 0.7 g C individual^-1 h^-1 (1.8 D. brightwelli cells individual^-1 h^-1). Clearance rates decreased asymptotically with increasing food concentration. Maximum clearance rates at low food concentration were ca. 23 l ind^-1 h^-1, which corresponds to a volume-specific clearance rate of 5.9x10⁵ h^-1. Cell size of P huberi was highly variable, with a mean diameter of 42 m, but no clear relationship between cell size and food concentration was evident. Specific growth rates increased with food concentration until maximum growth rates of 0.7 d^-1 were reached at a food concentration of 400 g C l^-1 (1000 cells ml^-1). Food concentrations as low as 10 g C l^-1 of D. brightwellii (25 cells ml^-1) were able to support growth of P. huberi. The bioluminescence of P. huberi varied with its nutritional condition and growth rate. Cells held without food lost their bioluminescence capacity in a matter of days. P. huberi raised at different food concentrations showed increased bioluminescence capacity, up to food concentration that supported maximum growth rates. The bioluminescence of P. huberi varied over a diel cycle, and these rhythmic changes persisted during 48 h of continuous darkness, indicating that the rhythm was under endogenous control.     

Thallium in marine plankton

Concentrations of thallium in phytoplankton (0.02 to 0.8 g g^–1), zooplankton (0.03 to 0.5 g g^–1) and ichthyoplankton (0.1 g g^–1) from the central Pacific were comparable , as were the atomic ratios of thallium to calcium (3x10^–6) and to potassium (1x10^–6) in those organisms. These relatively constant ratios, plus the biounlimited ocean profile of thallium, indicate that it is rapidly cycled through plankton in the same manner as potassium, its principal biogeochemical analogue. The higher atomic ratios of thallium to potassium in pelagic clays (6x10^–6) and ferromanganese nodules (4x10^–3) suggest that both biological transport processes and abiotic transport processes influence this trace element's oceanic cycle.     

Effect of heavy metals (Zn,Hg, Cu,Cd, Pb,Ni) on the length growth of Mytilus edulis

The shortterm (10–22 d) effect of Zn, Hg, Cu, Cd, Pb, and Ni on the length growth of Mytilus edulis is studied. Significant reductions of growth rate was found at 0.3 g Hgl^-1, 3 g Cul^-1, 10 g Znl^-1, and 10 g Cdl^-1 added to the local sea water, while concentrations of up to 200 gl^-1 of Pb and Ni had no effect on the growth. With exposure to Cu and Zn, there was a linear reduction in growth rate with increasing metal concentration up to about 6 g Cul^-1 and 100 g Znl^-1. Above these levels, growth stopped with Cu, while with Zn it was stabilized at about 20% of control growth. When Hg and Cd were added, a curvilinear relationship between growth and metal concentration is indicated. With Hg, growth rate is nearly zero above 3–4 g Hgl^-1, while the growth rate was 50% of control after 10 d of exposure to 100 g Cdl^-1. At 2 g Cdl^-1 there was a significant stimulation of length increase. Observed EC₅₀-values for growth were 0.3–0.4 g Hgl^-1, 3–4 g Cul^-1, 60 g Znl^-1, and 100 g Cdl^-1.     

Influence of food concentration on the physiological energetics and growth ofOstrea edulis larvae

Feeding, respiration and growth rates of oyster (Ostrea edulis L.) larvae reared at five food levels were measured throughout the entire larval period. Energy budgets were derived as a function of alga (Isochrysis galbana Parke) food concentration. Ingestion rate (IR, cells h^-1) and oxygen consumption rate ( , nl h^-1) were almost isometric functions of larval size [ash-free dry weight, (AFDW, g)], characterized by the equations: IR=803.9 AFDW^1.13 and =4.85 AFDW^1.09. Ingested ration was directly correlated to cell concentration up to a maximum at 200 cells l^-1, with further increases failing to support higher ingestion rates. Likewise, growth rate linearly increased with food ration up to 100 cells l^-1 (max. growth efficiency,K ₁=25%) and reached a maximum at 200 cells l^-1 (growth rate=5.6 m d^-1), with further increases in food not supporting significantly faster growth. Maintenance ration was 2 to 3% daily dry weight (DW); optimum ration increased during larval development from 5 to 20% DW; maximum ration was 20% DW. During larval rearing, an increasing feeding schedule of 50, 100 and 200 cells l^-1 from Days 0, 5 and 10, respectively, is recommended.     

Influence of three sediment types on copper toxicity to the polychaete Neanthes arenaceodentata

Adult male Neanthes arenaceodentata were exposed to 0.10±0.015 mg l^-1 copper in the seawater of a continuous-flow bioassay system in the presence of a sand, a mud, a mixture of the sand and mud, and no sediment, to assess the influence of sediment type on Cu-induced mortality. The sediment type did influence mortality. The time to 50% mortality was 7.8 days without sediment, 36.5 days with sand, 54.5 days with the mixture, and 50.0 days with mud. There was no threshold Cu body burden that caused death. The mean Cu concentration per gram of N. arenaceodentata (24 h after death) without sediment was 270 g, in sand 994 g, in the mixture 1047 g, and in mud 1464 g. The differences in the toxic responses are discussed.     

Unusual sources of aluminium and heavy metals in potable waters

Aluminium in water supplies derives from natural sources and from the use of Al₂(SO₄)₃ in water treatment. Heavy metals such as Pb, Cu, Zn and Cd can be added to water from pipework and solder. However, it is apparent that AI and other metals in potable waters can derive from deposits on pipe walls which can be subsequently mobilised when the supply and/or treatment process is changed. Concentrations of Al in domestic supply water of the Llanbrynmair area have been shown to increase from 1 g to 50 g L^–1 during its 18 km journey along the water main. Similarly, Pb concentrations in a public building in the Aberystwyth area are found to be extremely elevated due to the metal's mobilisation from encrustations occurring on the copper pipework.     

Photosynthetic characteristics of nanoplankton and picoplankton from the surface mixed layer

Nanoplankton and picoplankton primary production has been studied at two oceanic stations in the Porcupine Sea-bight and at one shelf station in the Celtic Sea. At both sites, low wind conditions in June and July 1985 resulted in greatly reduced vertical turbulent mixing and a secondary, temporary thermocline developed in what is usually a well-mixed surface layer; as a result, there was physical separation of the phytoplankton within two zones of the surface mixed layer. The photosynthetic characteristics of three size fractions (>5 m, <5 to >1 m and <1 to >0.2 m) of phytoplankton populations from the two zones have been measured. Phytoplankton was more abundant at the oceanic stations and chlorophyll a values were between 1.3 and 2.2 mg chlorophyll a m^-3, compared with 0.3 to 0.6 mg chlorophyll a m^-3 at the shelf station; at both stations, numbers of cyanobacteria were slightly higher in the lower zone of the surface mixed layer. There was no effect of the temporary thermocline on the vertical profiles of primary production and most phtosynthesis occurred in the surface 10 m. Photosynthetic parameters of the three size fractions of phytoplankton have been determined; there was considerable day-to-day variation in the measured photosynthetic parameters. Assimilation number (P _m ^B ) of all >5 m phytoplankton was lower for the deeper than for the surface populations, but there was little change in initial slope (a ^B ). The small oceanic nanoplankton (<5 to >1 m) showed changes similar to the >5 m phytoplankton, but the same size fraction from the shelf station showed changes that were more like those shown by the picoplankton (<1 m) viz, little change in P _m ^B but an increase in a ^B with depth. Values of a ^B were generally greater for the picoplankton fraction than for the larger phytoplankton, but values of adaptation parameter (I _k )(=P _m ^B /) were not always less. There was little evidence to support the hypothesis that these populations of picoplankton were significantly more adapted to low light conditions than the larger phytoplankton cells. When photosynthetic parameters of the picoplankton were normalised to cell number (P _m ^C /a ^C ) rather than chlorophyll a, P _m ^C was comparable to other published data for picoplankton, but a ^C was much lower. The maximum doubling time of the picoplankton at saturating irradiance is calculated to be ca. 8.5 h for the oceanic population and ca. 6.2 h for the shelf population.