Determination of trace metal concentrations in soil profiles of municipal waste dumps in Nigeria

The concentrations of trace metals (Cd, Pb, Cu, Cr, Fe, Ni, Zn and Co) were studied in soil profiles of eight municipal waste dump sites in Warri metropolis. The results indicate that concentrations of trace metals varied widely among the different dumpsites and decreased with depths in a studied soil profile. The accumulation pattern for the heavy metals in the soil profiles follows the order: Fe > Pb > Mn > Co > Cr > Zn > Ni > Cu > Cd. The concentrations of metals found in these sites was below the Canadian remediation criteria for land for agricultural, residential and commercial/industrial purposes except for the cadmium levels in some sites that exceeded criterion values for agricultural and residential. In such sites, remedial actions are required before any form of chosen development can take place. The levels of heavy metals found in these dump sites were higher than that of the control site. The examined metals showed no significant correlation with soil physicochemical properties at the surface horizon, which is suggestive evidence that these metals arise from anthropogenic input.     

Tracing the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain,India: a source identification perspective

Arsenic contamination in groundwater is of increasing concern because of its high toxicity and widespread occurrence. This study is an effort to trace the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain of India through major ion chemistry, arsenic speciation, sediment grain-size analyses, and multivariate statistical techniques. The study focuses on the distinction between the contributions of natural weathering and anthropogenic inputs of arsenic with its spatial distribution and seasonal variations in the plain of the state Bihar of India. Thirty-six groundwater and one sediment core samples were collected in the pre-monsoon and post-monsoon seasons. Various graphical plots and statistical analysis were carried out using chemical data to enable hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies, and factors controlling groundwater quality. Results suggest that the groundwater is characterized by slightly alkaline pH with moderate to strong reducing nature. The general trend of various ions was found to be Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ > NH₄ ⁺; and HCO₃ ⁻ > Cl⁻ > SO₄ ²⁻ > NO₃ ⁻ > PO₄ ³⁻ > F⁻ in both seasons. Spatial and temporal variations showed a slightly higher arsenic concentration in the pre-monsoon period (118 μg/L) than in the post-monsoon period (114 μg/L). Results of correlation analyses indicate that arsenic contamination is strongly associated with high concentrations of Fe, PO₄ ³⁻, and NH₄ ⁺ but relatively low Mn concentrations. Further, the enrichment of arsenic is more prevalent in the proximity of the Ganges River, indicating that fluvial input is the main source of arsenic. Grain size analyses of sediment core samples revealed clay (fine-grained) strata between 4.5 and 7.5 m deep that govern the vertical distribution of arsenic. The weathering of carbonate and silicate minerals along with surface-groundwater interactions, ion exchange, and anthropogenic activities seem to be the processes governing groundwater contamination, including with arsenic. Although the percentage of wells exceeding the permissible limit (50 μg/L) was less (47%) than that reported in Bangladesh and West Bengal, the percentage contribution of toxic As(III) to total arsenic concentration is quite high (66%). This study is vital considering that groundwater is the exclusive source of drinking water in the region and not only makes situation alarming but also calls for immediate attention.     

Southwest monsoon influences the water quality and waste assimilative capacity in the Mandovi estuary (Goa state,India)

The monsoon-dominated Mandovi estuary is located in Goa state – a global tourist destination along the centralwest coast of India. In addition to factor analyses of water quality data, the water quality index (WQI), trophic state index (TSI) and percentage of freshwater volume in the estuary are calculated in order to infer the general waste assimilative capacity and prevailing water quality conditions. Factor analysis showed a dominance of PO₄–P, NO₂–N, NH₃–N, total suspended solids (TSS) and turbidity during southwest (SW) monsoon relative to other seasons. The WQI suggested that an increase in nutrients, turbidity and TSS during SW monsoon increase the WQI values beyond 2, rendering the water at some locations slightly polluted. During pre-monsoon, considerable increase in the WQI is observed at all the upstream stations rendering slightly polluted water at these stations. The TSI showed an average value of 46.95 during SW monsoon, 42.43 during post-monsoon and 48.42 during the pre-monsoon seasons, suggesting better productivity level during pre-monsoon, followed by SW monsoon, but the least during the post-monsoon. All the seasons, however, indicated a mesotrophic condition in the estuary and the assimilative capacity of the estuary is found to be in good to fairly good state (pre-monsoon?相似文献   

Genotypic variation in element concentrations in brown rice from Yunnan landraces in China

The mineral elements present in brown rice play an important physiological role in global human health. We investigated genotypic variation of eight of these elements (P, K, Ca, Mg, Fe, Zn, Cu, and Mn) in 11 different grades of brown rice on the basis of the number and distance coefficients of 282 alleles for 20 simple sequence repeat (SSR) markers. Six-hundred and twenty-eight landraces from the same field in Yunnan Province, one of the largest centers of genetic diversity of rice (Oryza sativa L.) in the world, formed our core collection. The mean concentrations (mg kg⁻¹) of the eight elements in brown rice for these landraces were P (3,480) > K (2,540) > Mg (1,480) > Ca (157) > Zn (32.8) > Fe (32.0) > Cu (13.6) > Mn (13.2). Mean P concentrations in brown rice were 6.56 times total soil P, so the grains are important in tissue storage of P, but total soil K is 7.82 times mean K concentrations in brown rice. The concentrations of the eight elements in some grades of brown rice, on the basis of the number and distance coefficients of alleles for 20 SSR markers for the landraces, were significantly different (P < 0.05), and further understanding of the relationship between mineral elements and gene diversity is needed. There was large variation in element concentrations in brown rice, ranging from 2,160 to 5,500 mg P kg⁻¹, from 1,130 to 3,830 mg K kg⁻¹, from 61.8 to 488 mg Ca kg⁻¹, from 864 to 2,020 mg Mg kg⁻¹, from 0.40 to 147 mg Fe kg⁻¹, from 15.1 to 124 mg Zn kg⁻¹, from 0.10 to 59.1 mg Cu kg⁻¹, and from 6.7 to 26.6 mg Mn kg⁻¹. Therefore, germplasm evaluations for Ca, Fe, and Zn concentrations in rice grains have detected up to sevenfold genotypic differences, suggesting that selection for high levels of Ca, Fe, and Zn in breeding for mass production is a feasible approach. Increasing the concentrations of Ca, Fe, and Zn in rice grains will help alleviate chronic Ca, Zn, and Fe deficiencies in many areas of the world.     

Distribution and mobility of metals in agricultural soils near a copper smelter in South China

The distribution and mobility of heavy metals in the paddy soils surrounding a copper smelting plant in south China was investigated. We assessed the degree of metal contamination using an index of geoaccumulation. The metals were divided into two groups: (1) Cu, Zn, Pb and Cd, whose concentrations were heavily affected by anthropogenic inputs, and (2) Ni, Co and Cr, which were mainly of geochemical origin. Concentrations of Cu, Cd, Zn, and Pb in the polluted soils were higher than the Chinese soil quality criteria. The chemical partitioning patterns of Pb, Zn and Cu indicated that Pb was largely associated with the residual and NH₂OH HCl extractable fractions. In contrast, Cd was predominantly associated with the MgCl₂ extractable fraction. A large proportion of Cu was bound to the acidic H₂O₂ extractable fractions, while Zn was predominantly found in the residual phase. The fraction of mobile species, which potentially is the most harmful to the environment, was found to be elevated compared to unpolluted soils in which heavy metals are more strongly bound to the matrix. The mobility of the metals was studied by water extraction using a modification of Tessier’s procedure, and the order of mobility was Zn > Cd > Cu  > Pb.     

Speciation of heavy metals in sediments from the Scheldt estuary,Belgium

A simple three-step sequential extraction procedure was applied to study the speciation of heavy metals in sediment from Scheldt estuary, and their relationship to sediment grain size and organic matter content. The sedimentary metal content was fractionated into carbonate and exchangeable, metals bound to organic matter and residual fractions. Sedimentary total metal content was also determined using an industrial microwave (ETHOS 900) HF/HNO₃ extraction method. The extracts were analysed for metals using inductively coupled plasma atomic emission spectrometry. The bioavailable fraction (exchangeable and metals bound to organic matter) comprised less than the other forms. Residue metals were the dominant form of metals in almost all studied sites. The average total metal content for the studied sites decreased in the order Fe>Cr>Cu>Co>Zn>Pb>Cd. Based on average values for the studied sites, the highest bioavailable metals in sediments were Cd (38%) from Westkapelle, Zn (17%) from Yerseke, Co (12%) from Domburg, Cr (9%) from Vlissingen, Fe and Pb each (2%) from Yerseke, and Cu (1%) from Domburg. Metal recovery was good, with<10% difference between the total metal recovered through the extractant steps and the total metal determined using HF/HNO₃ extract.     

In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O₂ m⁻² h⁻¹ (~11.7 mg C m⁻² h⁻¹) while from the sediment it was 6.08 mmol O₂ m⁻² h⁻¹ (~70.8 mg C m⁻² h⁻¹). When the ice was present O₂ export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)⁻¹ h⁻¹ while those from the benthos were up to 1.53 mg C (mg Chl-a)⁻¹ h⁻¹. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.     

Heavy metal speciation,leaching and toxicity status of a tropical rain-fed river Damodar,India

Speciations of metals were assessed in a tropical rain-fed river, flowing through the highly economically important part of the India. The pattern of distribution of heavy metals (Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn) were evaluated in water and sediment along with mineralogical characterization, changes with different water quality parameters and their respective health hazard to the local population along the Damodar River basin during pre-monsoon and post-monsoon seasons. The outcome of the speciation analysis using MINTEQ indicated that free metal ions, carbonate, chloride and sulfate ions were predominantly in anionic inorganic fractions, while in cationic inorganic fractions metal loads were negligible. Metals loads were higher in sediment phase than in the aqueous phase. The estimated values of I_geo in river sediment during both the seasons showed that most of the metals were found in the I_geo class 0–1 which represents unpolluted to moderately polluted sediment status. The result of partition coefficient indicated the strong retention capability of Cr, Pb, Co and Mn, while Cd, Zn, Cu and Ni have resilient mobility capacity. The mineralogical analysis of sediment samples indicated that in Damodar River, quartz, kaolinite and calcite minerals were dominantly present. The hazard index values of Cd, Co and Cr were >?1 in river water, which suggested potential health risk for the children. A combination of pragmatic, computational and statistical relationship between ionic species and fractions of metals represented a strong persuasion for identifying the alikeness among the different sites of the river.     

Geochemistry of leachates from the El Fraile sulfide tailings piles in Taxco, Guerrero, southern Mexico

Leachates from the El Fraile tailings impoundment (Taxco, Mexico) were monitored every 2 months from October 2001 to August 2002 to assess the geochemical characteristics. These leachates are of interest because they are sometimes used as alternative sources of domestic water. Alternatively, they drain into the Cacalotenango creek and may represent a major source of metal contamination of surface water and sediments. Most El Fraile leachates show characteristics of Ca–SO₄, (Ca+Mg)–SO₄, Mg–SO₄ and Ca–(SO₄+HCO₃) water types and are near-neutral (pH=6.3–7.7). Some acid leachates are generated by the interaction of meteoric water with tailings during rainfall events (pH=2.4–2.5). These contain variable levels of SO₄ ²⁻ (280–29,500 mg l⁻¹) and As (<0.01–12.0 mg l⁻¹) as well as Fe (0.025–2352 mg l⁻¹), Mn (0.1–732 mg l⁻¹), Zn (<0.025–1465 mg l⁻¹) and Pb (<0.01–0.351 mg l⁻¹). Most samples show the highest metal enrichment during the dry seasons. Leachates used as domestic water typically exceed the Mexican Drinking Water Guidelines for sulfate, hardness, Fe, Mn, Pb and As, while acidic leachates exceed the Mexican Guidelines for Industrial Discharge Waters for pH, Cu, Cd and As. Speciation shows that in near-neutral solutions, metals exist mainly as free ions, sulfates and bicarbonates, while in acidic leachates they are present as sulfates and free ions. Arsenic appears as As^(V) in all samples. Thermodynamic and mineralogical evidence indicates that precipitation of Fe oxides and oxyhydroxides, clay minerals and jarosite as well as sorption by these minerals are the main processes controlling leachate chemistry. These processes occur mainly after neutralization by interaction with bedrock and equilibration with atmospheric oxygen.     

Assessment of the chemical components of Famenin groundwater,western Iran

The Faminin area in the semi-arid Hamadan state, western Iran is facing a serious deficiency in groundwater resources due to an increasing demand associated with rapid population growth and agricultural development. The chemical composition of 78 well samples throughout the Faminin area was determined with the aim of evaluating the concentration of the background ions and identifying the major hydrogeochemical processes that control the groundwater chemistry. The similarity between rock and groundwater chemistries in the recharge area indicates a significant rock-water interaction. The hydrochemical types Na–HCO₃ and Na–SO₄ are the predominate forms in the groundwater, followed by water types Ca–HCO₃ and Na–Cl. The high values of electrical conductivity and high concentrations of Na⁺, Cl⁻, SO₄²⁻ and NO₃⁻ in the groundwater appeared to be caused by the dissolution of mineral phases and would appeared to be caused by anthropogenic activities, such as intense agricultural practices (application of fertilizers, irrigation practice), urban and industrial waste discharge, among others.     

Modification of light utilization for skeletal growth by water flow in the scleractinian coral <Emphasis Type="Italic">Galaxea fascicularis</Emphasis>

In this study, we tested the hypothesis that the importance of water flow for skeletal growth (rate) becomes higher with increasing irradiance levels (i.e. a synergistic effect) and that such effect is mediated by a water flow modulated effect on net photosynthesis. Four series of nine nubbins of G. fascicularis were grown at either high (600 μE m⁻² s⁻¹) or intermediate (300 μE m⁻² s⁻¹) irradiance in combination with either high (15–25 cm s⁻¹) or low (5–10 cm s⁻¹) flow. Growth was measured as buoyant weight and surface area. Photosynthetic rates were measured at each coral’s specific experimental irradiance and flow speed. Additionally, the instantaneous effect of water flow on net photosynthetic rate was determined in short-term incubations in a respirometric flowcell. A significant interaction was found between irradiance and water flow for the increase in buoyant weight, the increase in surface area, and specific skeletal growth rate, indicating that flow velocity becomes more important for coral growth with increasing irradiance levels. Enhancement of coral growth with increasing water flow can be explained by increased net photosynthetic rates. Additionally, the need for costly photo-protective mechanisms at low flow regimes could explain the differences in growth with flow.     

Influence of uraniferous black shales on cadmium,molybdenum and selenium in soils and crop plants in the Deog-Pyoun-g area of Korea

The influence of naturally occurring uraniferous black shales on cadmium, molybdenum and selenium concentrations in soils and plants is examined. The possible implications of element concentrations to animal and human health are considered for the Deog-Pyoung area. Geochemical surveys have been undertaken within 13 river tributary valleys in the area underlain by uraniferous black shales and black slates or grey chlorite schists. Sampling of rocks, soils and plants has been carried out along transect lines within each valley. Samples were analysed for trace elements by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and for uranium by Neutron Activation Analysis (NAA). Soil pH, cation exchange capacity, loss on ignition and particle size distribution have been measured for selected samples. Average trace element concentrations of the Okchon uraniferous black shales were 6.3 μg g⁻¹ Cd, 136 μg g⁻¹ Mo and 8.6 μg g⁻¹ Se. Soils derived from these rocks tend to reflect their extreme geochemical composition. Trace element concentrations in alluvial soils derived in part from these black shales averaged 1.2 μg g⁻¹ Cd, 20 μg g⁻¹ Mo and 1.5 μg g⁻¹ Se. Trace element concentrations in plants were found to be influenced by those of soils. Cadmium accumulated in tobacco leaves up to 46 μg g⁻¹ (D.M.) and leafy plants such as lettuce contain up to 0.5 μg g⁻¹ Se (D.M.). In addition to total concentrations in soils, soil pH is a major factor influencing uptake of Mo into crop plants and soil texture for Se. Concentrations of trace elements in plants also varied between plant species. The relative concentrations of Cd were found to vary in the order tobacco > lettuce > red pepper > rice grain. Elevated concentrations of Cd in crop plants and in tobacco may possibly have deleterious effects on human health in this area. The low Cu:Mo ratio in rice stalk of 2.65:1 may be associated with disturbed Cu metabolism in ruminant animals which regularly consume this material.     

Photolytical property of L(+)-α-phenylglycine in aqueous solution

A wide range of pharmaceutical compounds have been identified in the environment, and their existence is a topic of growing concern, both for human and ecological health. The work described here has investigated the photolytic properties of L(+)-α-phenylglycine (L-α-PG-H) in aqueous solution as it can be degraded by photo-catalysis. In 266 nm laser flash photolysis of aqueous solution of L-α-PG-H saturated with nitrogen, two transient absorption bands are observed at 280–330 nm and 450–800 nm, respectively, due to L-α-PG-H radical cation and hydrated electrons (e_aq⁻). Then e_aq⁻ reacts with L-α-PG-H to form the L-α-PG-H radical anion. Decaying rate constants of e_aq⁻ observed at 720 nm is to be 8.9 × 10⁸ dm³ mol⁻¹ s⁻¹. The rate constant for oxidation of L-α-PG-H by SO₄ ⁻ is calculated as 4.5 × 10⁸ and 4.3 × 10⁸ s⁻¹ mol⁻¹ dm³, respectively. The dissociation constants (pKa) of L-α-PG-H is 3. Excited triplet of L-α-PG-H in solution is formed by laser flash photolysis. The quench rate constant of L-α-PG-H excited triplet (k _s) is determined to be 1.3 × 10⁷ dm³ mol⁻¹ s⁻¹ and k ₀ is equal to 1.7 × 10⁵ s⁻¹.     

Cadmium, zinc and copper accumulation in the squid Illex argentinus from the Southwest Atlantic Ocean

 The levels and burdens of Cd, Zn, Cu and Hg were measured in the dorsal mantle, digestive gland and gonads of the squid Illex argentinus, from the Southwest Atlantic Ocean. Mature and immature individuals of both sexes were analysed. Correlations of heavy metal concentrations and burdens with sex and food habits were studied. The highest metal levels were found, particularly for Cd, in the digestive gland, which attained a concentration of up to 270 μg g⁻¹ (wet weight). Dorsal mantle and gonads exhibited the same order of metal enrichment: Zn>Cu>Cd. Zinc and Cu levels were higher in ovaries than in testes and varied with the stage of maturation. The dorsal mantle exhibited the lowest heavy metal concentrations. Mercury levels were below the detection limit of the method in all the tissues analysed. Received: 7 September 1999 / Accepted: 9 March 2000     

Multivariate statistical techniques for the evaluation of spatial and temporal variations in water quality of the Mahanadi river–estuarine system (India) – a case study

Spatial and temporal distributions of water quality using multivariate statistical techniques for the evaluation of nutrients (NO₂-N, NO₃-N, NH₄-N, PO₄-P, SiO₄-Si, total N, total P) in relation to some physico-chemical features (DO, BOD, TSS, TDS, SO₄²⁻, Cl⁻) were studied for 31 different stations of the Mahanadi river–estuarine system in the eastern part of India. The seasonal nutrient variations (except SiO₄-Si) exhibit higher values during monsoon season in unpolluted stations and the reverse trends for polluted stations, which are related to agricultural run-off and regional anthropogenic activities respectively. Silicate shows a well defined pattern of distribution with a higher concentration during the monsoon, which is slightly removed from the estuarine water of Mahanadi during the pre-monsoon season. The results of R-mode factor analyses revealed that anthropogenic contributions are responsible for the increase in nutrients and the decrease in DO and pH levels of the water. The magnitude of BOD with respect to total N and P demonstrates the intensity of organic pollution in the system. The removal of silicate in the saline system is clearly visible through factor analysis and the different mode of association of TSS is reflected seasonally. The relationships among the stations are highlighted by cluster analysis, represented in dendograms to categorize different levels of contamination.     

Hydrogeochemistry of the Coxilha das Lombas Aquifer, Brazil

The hydrogeochemical characterization of Coxilha das Lombas Aquifer, Brazil, was studied. Chemical characteristics from 23 groundwater samples and meteoric waters data from public registers were used. The ionic speciation and mineral dissolution/precipitation was calculated by EQ3/6 package software. The results showed low total dissolved solids (TDS) values and slightly acidic pH. The concentration of most abundant ions usually followed this trend Cl⁻>HCO₃ ⁺>SO₄ ²⁻>Na⁺. The characteristics of groundwaters and the chemistry similarity with the meteoric waters reflect their short residence time, due to high hydraulic conductivity, and low degree of water/rock interactions, due to sands composed mainly of quartz.     

Irradiance and temperature regulation of oxygenic photosynthesis and O2 consumption in a hypersaline cyanobacterial mat (Solar Lake, Egypt)

 Short-term effects of temperature and irradiance on oxygenic photosynthesis and O₂ consumption in a hypersaline cyanobacterial mat were investigated with O₂ microsensors in a laboratory. The effect of temperature on O₂ fluxes across the mat–water interface was studied in the dark and at a saturating high surface irradiance (2162 μmol photons m⁻² s⁻¹) in the temperature range from 15 to 45 °C. Areal rates of dark O₂ consumption increased almost linearly with temperature. The apparent activation energy of 18 kJ mol⁻¹ and the corresponding Q ₁₀ value (25 to 35 °C) of 1.3 indicated a relative low temperature dependence of dark O₂ consumption due to mass transfer limitations imposed by the diffusive boundary layer at all temperatures. Areal rates of net photosynthesis increased with temperature up to 40 °C and exhibited a Q ₁₀ value (20 to 30 °C) of 2.8. Both O₂ dynamics and rates of gross photosynthesis at the mat surface increased with temperature up to 40 °C, with the most pronounced increase of gross photosynthesis at the mat surface between 25 and 35 °C (Q ₁₀ of 3.1). In another mat sample, measurements at increasing surface irradiances (0 to 2319 μmol photons m⁻² s⁻¹) were performed at 25, 33 (the in situ temperature) and 40 °C. At all temperatures, areal rates of gross photosynthesis saturated with no significant reduction due to photoinhibition at high irradiances. The initial slope and the onset of saturation (E _k = 148 to 185 μmol photons m⁻² s⁻¹) estimated from P versus E _d curves showed no clear trend with temperature, while maximal photosynthesis increased with temperature. Gross photosynthesis was stimulated by temperature at each irradiance except at the lowest irradiance of 54 μmol photons m⁻² s⁻¹, where oxygenic gross photosynthesis and also the thickness of the photic zone was significantly reduced at 40 °C. The compensation irradiance increased with temperature, from 32 μmol photons m⁻² s⁻¹ at 25 °C to 77 μmol photons m⁻² s⁻¹ at 40 °C, due to increased rates of O₂ consumption relative to gross photosynthesis. Areal rates of O₂ consumption in the illuminated mat were higher than dark O₂ consumption at corresponding temperatures, due to an increasing O₂ consumption in the photic zone with increasing irradiance. Both light and temperature enhanced the internal O₂ cycling within hypersaline cyanobacterial mats. Received: 30 November 1999 / Accepted: 11 April 2000     

Isotopic composition (C & N) of the suspended particles and N uptake by phytoplankton in a shallow tropical coastal lagoon

The spatial distribution of the C/N ratios and variations in δ¹³C and δ¹⁵N of suspended particulate matter were used to characterise their source in Asia’s largest brackish water lagoon, Chilika, India. In addition, the significance of re-mineralised nutrients in the primary productivity of the shallow lagoon was also determined through quantification of the subsurface nitrogen uptake conditions at two relatively stable locations in the lagoon. The results indicated that the influence of terrestrial organic matter was the maximum in the northern sector and was relatively limited at the central and southern part of the lagoon. In situ ¹⁵N uptake experiments (daytime) under biogeochemically stable conditions revealed that the N uptake by phytoplankton ranged between 0.24 and 1.01?mM?m^?3?h^?1 during pre-monsoon and post-monsoon seasons. New production and regenerated production in the shallow lagoon was also estimated by calculating f-ratios (ratio of nitrate assimilation by phytoplankton to total nitrogenous nutrient assimilation, have been estimated), which varied from 0.52 in the post-monsoon to 0.38 in the pre-monsoon. Lowering of the f-ratio from post- to pre-monsoon indicated a dominance of mineralisation over the new production.     

Presence of Alexandrium catenella and paralytic shellfish toxins in finfish, shellfish and rock crabs in Monterey Bay, California, USA

The central California coast is a highly productive, biodiverse region that is frequently affected by the toxin-producing dinoflagellate Alexandrium catenella. Despite the consistent presence of A. catenella along our coast, very little is known about the movement of its toxins through local marine food webs. In the present study, we investigated 13 species of commercial finfish and rock crabs harvested in Monterey Bay, California for the presence of paralytic shellfish toxins (PSTs) and compared them to the presence of A. catenella and PSTs in sentinel shellfish over a 3-year period. Between 2003 and 2005, A. catenella was noted in 55% of surface water samples (n = 307) and reached a maximum concentration of 17,387 cells L⁻¹ at our nearshore site in Monterey Bay. Peak cell densities occurred in the month of July and were associated with elevated shellfish toxicity in the summers of 2004 and 2005. When A. catenella was present, particulate PSTs were detected 71% of the time and reached a maximum concentration of 962 ng STXeq L⁻¹. Of the 13 species tested, we frequently detected PSTs in Pacific sardines (Sardinops sagax; maximum 250 μg STXeq 100 g⁻¹), northern anchovies (Engraulis mordax; maximum 23.2 μg STXeq 100 g⁻¹), brown rock crabs (Cancer antennarius; maximum 49.3 μg STXeq 100 g⁻¹) and red rock crabs (C. productus; 23.8 μg STXeq 100 g⁻¹). PSTs were also present in one sample of Pacific herring (Clupea pallas; 13.3 μg STXeq 100 g⁻¹) and one sample of English sole (Pleuronectes vetulus; 4.5 μg STXeq 100 g⁻¹), and not detected in seven other species of flatfish tested. The presence of PSTs in several of these organisms reveals that toxins produced by A. catenella are more prevalent in California food webs than previously thought and also indicates potential routes of toxin transfer to higher trophic levels. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.