Damming effect on the distribution of mercury in Wujiang River

Seasonal changes in total mercury concentrations in surface water were observed for the Wujiang River, with higher values at the time of greater flow. The total mercury in this river was mostly associated with suspended particles, particulate mercury accounting for 84% of the total mercury flux on average during the high flow period, and 52% of the total mercury flux on average in the low flow period. Significant losses of Hg from the water were observed in the downstreams of the reservoir. In addition, the concentrations of particulate mercury in the downstreams of reservoir appeared to have been enhanced by sediment re-suspension and shoreline erosion caused by flood discharge, while the filtered portion decreased. These observations suggested that reservoirs played an important role in controlling the transport and fate of mercury in the Wujiang River.     

“Source to Sink”: A Review of Tectonics-Erosion-Sedimentation Interactions in the Analogue Experiments of Accretionary WedgeEI北大核心CSCD

It is believed that the tectonics-erosion-sedimentation interaction in the analogue experiments was essentially improved by the theory of “from source to sink”. In particular, the widespread uplift and exhumation in the western China occurred in Cenozoic can be considered to be a typical natural laboratory in the world. Here we review our current understanding from tectonic sandbox models of tectonics-erosion-sedimentation and their interactions, as well as from natural laboratory. As we known, there are widespread erosion occurred predominantly at hinterland of the accretionary wedge, in contrast to the sedimentation occurred widely at foreland of the wedge. Therefore, fold-and-thrust belts with low syntectonic sedimentation and erosion would evolve in a self-similar fashion to produce a narrow accretionary wedge, while high syntectonic sedimentation and erosion would produce accretionary wedge with very active hinterland thrusts, and a large width. Furthermore, the critically tapered wedge model suggests that the crust-scale thrust-and-fold belts under a horizontal compressive force would come into a self-similar growth of a forward-tapering wedge when it reaches a critical taper angle of the combined angles of the base dip and the wedge slope. Such a process has important influence on the tectonics-erosion- sedimentation and their interactions both in accretionary wedges and their analogue experiments. Although there is a significant similarity between the analogue experiments and natural accretionary wedges in the surface processes of tectonics- erosion-sedimentation and their interactions, it is difficult to get more universal parameters between them. It should be noted that sandbox models of the accretionary wedges in the natural laboratory would improve significantly our understanding of the theory of the tectonics-erosion-sedimentation interactions and “from source to sink”. © 2018, Science Press. All right reserved.     

Evidence for Tibetan Plateau Uplift in Qaidam Basin before Eocene-Oligocene Boundary and Its Climatic Implications

Geometry analysis of the Hongsanhan (红三旱) Section in the northwestern Qaidam basin illustrates the typical growth strata in the Xiaganchaigou (下干柴沟) Formation. The age and sedimentation rates of the Xiaganchaigou and the Shangganchaigou (上干柴沟) formations were determined by the high-resolution magnetostratigraphy. This result shows that the growth strata began to form at ca. 38.0 Ma and increased sedimentation rates occurred at ca. 37.0 Ma. The uplift of the Tibetan plateau before the Eocene-Oligocene boundary is confirmed, which enables us to better understand the relationship between climatic changes and the tectonic uplift. This uplift event could have resuited in the regional drying by blocking the moisture and contributed to the Eocene-Oligocene boundary global cooling event due to the declining atmospheric CO2 concentrations by increased weathering of the mountains.     

Late Cenozoic Chemical Weathering and Environmental Changes Recorded in the Co Ngoin Sediments,Central Qinghai-Tibet Plateau

A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In this paper, we present the weathering history and paleoclimatic changes in the last 2.8 Ma based on studies of high-resolution temporal distributions of Sr, Rb and Zr concentrations, Rb/Sr and Zr/Rb ratios and δ ^13C and TOC for the Co Ngoin sediments, in combination with the sediment properties, grain size distribution and clay mineralogy. The sedimentary records indicate three environmental stages in the last 2.8Ma. At the core depth of 197-170m (about 2.8-2.5Ma), low-intensity chemical weathering in the Co Ngoin catchment was experienced under warm-dry to cool-wet climate conditions with relatively low Sr concentration and high Rb/Sr and Zr/Rb ratios. The sudden occurrence of both subalpine coniferous forest and coarses and and gravel sediments in the Co Ngoin core reflects a strong tectonic uplift. The high Sr concentrations and low Rb/Sr and Zr/Rb ratios reflect a relatively strong chemical weathering between 2.5Ma and 0.8Ma (at the core depth of 170-38.5m) under a temperate/cool and wet climate, characterized by mud and silt with fine sand, probably indicating a stable process of denudation and planation of the plateau. Above the depth of 38.5m (about 0.8-0Ma), the coarsening of sediments indicates a strong tectonic uplift and a relatively low intensity of chemical weathering as supported by the record of sediments having relatively low Sr concentrations and high Rb/Sr and Zr/Rb ratios. Since then, the plateau has taken the shape of the modern topographic pattern above 4000m a.s.l.     

Manganese Abnormity in Holocene Sediments of the Bohai Sea

Manganese abnormity has been observed in the Holocene sediments of the mud area of Bohai Sea. On the basis of grain size, chemical composition, heavy mineral content and accelerator mass spectrometry (AMS) 14C dating of foraminifer, relationships between manganese abnormity and sedimentation rates, material source, hydrodynamic conditions are probed. Manganese abnormity occurred during the Middle Holocene when sea level and sedimentation rates were higher than those at present. Sedimentary hiatus was not observed when material sources and hydrodynamic conditions were quite similar. Compared with the former period, the latter period showed a decrease in reduction environment and an inclination toward oxidation environment with high manganese content, whereas provenance and hydrodynamic conditions showed only a slight change. From the above observations, it can be concluded that correlation among manganese abnormity, material source, and hydrodynamic conditions is not obvious. Redox environment seems to be the key factor for manganese enrichment, which is mainly related to marine authigenic process.     

Origin of Phosphate-bearing Carbonate Concretions in the Upper Triassic Lacustrine Black Shales of the Southern Ordos Basin,China

Carbonate concretions are conspicuous in organic-rich shales and are generally related to decomposition of organic matter.The black shales from the Chang 7 Member of the Upper Triassic Yanchang Formation of the southern Ordos Basin host abundant carbonate concretions,which provide a unique record of depositional and early diagenetic conditions of the paleo-lake sediments.However,little attention has been given to the genesis and growth processes of the concretions in these lacustrine petroleum source rocks.New petrographic observations and geochemical analysis show that the concretions are composed of calcite,phosphate fossil fragments,K-NH_4-feldspar,quartz,bitumen,and minor Fedolomite.Phosphate minerals,mainly carbonate fluorapatite (CFA),show pervasive replacement by calcite,most of which contains phosphorus,ranging in concentration from 0.26 to 2.35 wt%.This suggests that the phosphate minerals are the precursors for concretion growth.Positiveδ~(13)C (+5.6 to+12.4‰V-PDB) signatures and the absence of pyrite indicate that microbial methanogenesis was the dominant driver for concretion growth,rather than bacterial sulfate reduction.Quartz,bitumen,and Fe-dolomite are the last cements that occurred,at deep burial depths and high temperatures.The formation of phosphate minerals might have been induced by upwelling of phosphate-enriched deep water in the Late Triassic paleolake,which promoted phytoplankton blooms and further enrichment of organic matter.Extremely slow sedimentation rates of fine-grained detrital minerals,relative to dead organism accumulation,led to the high permeabilities of the organic-rich sediments and rapid concretion growth during shallow burial.The close association of phosphate-bearing carbonate concretions and organic-rich shales reflects that upwelling played a critical role in the formation of the high-quality petroleum source rocks in the Triassic paleo-Ordos lake.     

Kinetics of Hydrothermal Reactions of Minerals in Near-critical and Supercritical Water

This work presents new experimental results on the kinetics of mineral dissolution in near-critical and supercritical water in a temperature range (T) from 25 to 400℃ and a constant pressure of 23 MPa. Kinetic experiments were carried out by using a flow reactor (packed bed reactor) of an open system. The dissolution rates of albite and magnetite were measured under these experimental conditions. Na, Al and Si release rates for albite dissolution in water were measured as a function of the temperature and flow velocity in the reaction system. The maximum release rates of Na, AI and Si of albite dissolution in the hydrothermal flow systems under different flow velocities were always obtained at 300℃, that is to say, the maximum albite dissolution rates in the flow systems, regardless of different flow rates, were repeatedly measured at 300℃. Results indicate a wide fluctuation in albite dissolution rates occurring close to the critical point of water. The dissolution rates increased when the temperatu     

A preliminary study on the distribution characteristics of nutrients （N, P, Si, C） in the Wujiang River Basin

The distribution of nutrients (N, P, Si, C) in the Wujiang River surface water was studied during the high-flow and low-flow periods in 2002. The results showed that nitrate nitrogen (NO3-N) is the main form of dissolved inorganic nitrogen (DIN) in the Wujiang River Basin. It accounts for about 90% of DIN. The average NO3-N concentrations in the mainstream are 147.5 μM in the high-flow period and 158.0 μM in the low-flow period, respectively. The average concentrations of total phosphorus (TP) are 6.43 μM in the high-flow period and 4.18 μM in the low-flow period, respectively. Of the various forms of phosphorus, particulate phosphorus (PP) has the highest percentage ( 62.9%) of TP in the high-flow period. In the low-flow period, however, phosphate is the main form of phosphorus, which accounts for 49% of TP. With the Wujiangdu Reservoir as the boundary, the concentrations of DIN and phosphorus in the upper reaches are different from those in the lower reaches of the Wujiang River. As a whole, the concentrations of DIN and phosphorus are both higher in the low-flow period than in the high-flow period. The spatial and temporal variations of DIN and phosphorus concentrations suggested that DIN and phosphorus come from agricultural and domestic wastewaters and groundwaters and that the Wujiangdu Reservoir has an important impact on the concentrations and distribution of DIN and phosphorus in the Wujiang River. The distribution patterns of dissolved silica (DSi) and dissolved organic carbon (DOC) are similar. Both of them maintain no change in the whole course of the river and their concentrations (with the exception of the reservoir itself) are higher in the high-flow period than in the low-flow period. The average DSi and DOC concentrations in the mainstream are 85.4, 84.6 μM in the high-flow period and 60.8, 53.9 μM in the low-flow period, respectively. The concentrations of nutrients in most of the major tributaries are lower than in the mainstream. This suggested that the contributions of most tributaries are relatively small but importance should be attached to the influence of some individual tributaries such as the Qingshuijiang River and the Weng'an River on the mainstream.     

Mercury in river sediments, floodplains and plants growing thereon in the drainage area of the Idrija mine, Slovenia

Half a millennium mercury production at Idrija is reflected in increased mercury contents in all environmental segments. The bulk of roasting residues from the middle of the 19th century to 1977 was discharged directly into the Idrijca River, and the material was carried at high waters to the Soca River and farther into the Adriatic Sea. It has been estimated that 45500 tons of mercury were emitted into the environment during the operating period of the mine, which ceased production in 1994. In the lower reaches of the Idrijca the riverine deposits with high mercury contents have been, and will be in the future a source of mercury polluted sediment. Stream sediments were monitored at the same locations along the Idrijca and Soca rivers （70 kin） every 5 years since 1991 （1991-2005）. Grain size distribution was determined by dry sieving and fractions for geochemical analysis were prepared （〈0.04 and 〈0.125 mm）. Soils on river terraces were sampled at 5 localities in the lower course of Idrijca. At two locations of the terrace profiles the samples of averaged meadow forage and plantain （Plantago lanceolata） were collected within a 50-meters radius. We found that there was no decrease in mercury concentration in active river sediments during the last 20 years. Upstream from the Idrija Town the mercury concentrations in active river sediments vary from 1 to 10 mg/kg （average 3.3 mg/kg）. From Idrija to Spodnja Idrija the mercury concentrations increase extremely and vary greatly （32-4,121 mg/kg, the average is 734 mg/kg）. From Spodnja ldrija to the Idrijca-Soca confluence is the average 218 mg/kg, and 57 mg/kg downstream in the Soca River sediments.     

Total gaseous mercury （TGM） in the atmosphere of southern Tibetan Plateau, China

Total gaseous mercury （TGM） concentrations in the atmosphere of southern Tibetan Plateau, China, were measured continuously during the Tibetan Plateau mercury vapor campaign from March to November 2005. The half-hourly mean TGM concentration in Lhasa was higher than that at the Nam Co station and both are higher than the known global background level. Field observations showed that TGM concentrations exhibited dramatic increases during period of agricultural and seasonal combustion of plant and dry grass incineration. TGM concentrations correlate well with the three meteorological parameters： mean dew point, relative humidity and the mixing ratio of water and vapour. From this study, we found that southern Tibetan Plateau is affected by human activities with TGM. Because of high sea level and less industry in our observed sites,     

Phytoplankton blooms and nitrogen productivity in San Francisco Bay

San Francisco Bay has been considered an HNLC or HNLG (high nutrient low chlorophyll or low growth) region with nonlimiting concentrations of inorganic nutrients yet low standing stocks of phytoplankton. Most of the studies leading to this conclusion come from the South Bay and little is known about nutrient processes and phytoplankton productivity in the northern and central parts of the estuary. Data collected over 3 yr (1999–2003) in Suisun, San Pablo, and Central Bays describe the availability of dissolved inorganic nitrogen (DIN), silicate, and phosphate and the seasonal variability in phytoplankton abundance. Rate measurements of fractionated nitrogen productivity provide the relative contributions of different forms of DIN (ammonium and nitrate) and different sized phytoplankton to the development of seasonal phytoplankton blooms. Regional differences in bloom dynamics are observed with Suisun Bay, the least saline, highest nutrient, most turbid region having less phytoplankton biomass and productivity than San Pablo and Central Bays, except in the abnormally wet spring of 2000. Spring blooms in San Francisco Bay are driven primarily by high rates of nitrate uptake by larger phytoplankton cells following a period of increased ammonium uptake that depletes the ambient ammonium. The smaller occasional fall blooms are apparently flueled mostly by ammonium uptake by small sized phytoplankton. The data suggest that the HNLC condition in the northern and central parts of San Francisco Bay is due primarily to light availability modulated by the interaction between ammonium and nitrate, and the relative amounts of the two forms of the DIN pool available to the phytoplankton.     

Nutrient limitation of phytoplankton growth in Georgia nearshore waters

Nutrient enrichment experiments were conducted to investigate the utilization of dissolved organic and inorganic nitrogen by marine phytoplankton in Georgia coastal waters. Natural populations of marine phytoplankton, enriched with different concentrations of ammonium chloride and other plant nutrients, were grown under controlled temperature and irradiance conditions until the populations reached “stationary phase.” Results showed that (1) phytoplankton are limited by DIN up to ca. 20μM, when another nutrient (phosphate or silicate) becomes limiting, (2) very little naturally-occurring DON is directly utilized for growth, (3) very little DON is indirectly made available for growth over time periods of days to ca. 1 week, and (4) trace metals and vitamins do not significantly limit phytoplankton growth.     

Drought effects on pelagic properties in the shallow and turbid Patos Lagoon, Brazil

The effect of a 7-mo drought (La Niña 1988) was evaluated on pelagic properties in the large Patos Lagoon (30°12′–32°12′S, 50°40′–52°15′W). From December 1987 to December 1988, surface water was sampled along the longitudinal axis of the lagoon for temperature (10–29°C), salinity (0–31.4), dissolved inorganic phosphate (0.02–4.73 μM), nitrate (0.05–66.25 μM), nitrite (0.01–3.54 μM), ammonium (0.09–33.19 μM), silicate (1.11–359.20 μM), phytoplankton chlorophylla (chl; 0.4–41.2 mg m^?3), primary production (gross PP 1.72–161.82 mg C m³ h^?1; net PP 0.04–126.19 mg C m³ h^?1), and species composition and abundance (42–4,961 ind ml^?1). In the wet season the whole system acted as a river and light availability limited phytoplankton growth. During the drought from February to August monthly freshwater runoff was low and the inflow of marine water to the southern sector generated spatial variability of the analyzed properties and five functional areas were recognized. The northernmost Guaíba River (1) presented low light availability and phytoplankton chl concentration compared to the northern limnetic area (2) (chl mean 13.3 μg I^?1; max 41.2 μg I^?1; gross PP mean 52.6 mg C m³ h^?1), which acted as a biological filter removing dissolved inorganic nutrients. Silicate concentration was strongly diminished in this area due to diatom uptake (Aulacoseira granulata, 9,330 cells ml^?1). In the northern limnetic and central oligohaline (3) areas, phytoplankton biomass was controlled by light but nitrogen also played a limiting role. In the southern area (4) that is under marine influence, low chl concentration (mean 4.5 μg I^?1) and gross PP (mean 28.1 mg C m³ h^?1) coincided with co-limitation of nitrogen and light while the channel to the ocean (5) was strongly light limited. This study demonstrated that low light and high silicate input had a buffer effect at Patos Lagoon, hampering negative expression of cultural eutrophication. The main effect during the drought period occurred in the northern limnetic region, where low silicate values due to diatom uptake led to higher cyanobacteria abundance, and enhanced mineralization occurred in the central oligohaline lagoon. Increased rainfall resulted in light limitation and decreasing primary production in the entire freshwater lagoon, and the adjacent coastal region benefited from nutrient enrichment.     

Iron Budget and Its Correlations with Macronutrients in the Inshore Waters of the Aegean Sea

Macronutrients and micronutrients were measured during the phytoplankton bloom period and then seasonally monitored after the bloom in the polluted Izmir Bay. Iron and the macronutrients (phosphate, ammonium, nitrate, nitrite, and silicate) were abundant in the waters of the inner and middle sections of Izmir Bay. The iron concentration decreased exponentially from the eutrophic inner bay to the oligotrophic outer bay. Suboxic–anoxic processes and the resuspension dynamics in the sediment were the most important factor in the control of iron, ammonium, and phosphate enrichment in the bay beside the anthropogenic activities. The biological removal of Fe in the inner and middle bay and nonbiological removal in the outer bay were effective in controlling iron concentration in Izmir Bay. The nitrate, nitrite, and ammonium nitrogen (N) and Si decreased to critical levels in the middle and outer bay at the end of the summer as long as the concentration of phosphate was high. The N/P ratios in the bay suggested that N might be the controlling nutrient for phytoplankton growth particularly in the middle and outer bay throughout summer. Furthermore, Si was also able to have controlling impact probably on diatom growth during autumn and winter in the inner and middle bay and in the early spring in the outer bay. The N/Si/Chelex labile Fe ratios implied that the iron could be a critical controlling nutrient for phytoplankton growth during early April in the outer bay unless the other macronutrients were low.     

The Influence of Coastal Nutrients on Phytoplankton Productivity in a Shallow Low Inflow Estuary,Drakes Estero,California (USA)

Seasonal wind-driven upwelling along the U.S. West Coast supplies large concentrations of nitrogen to surface waters that drives high primary production. However, the influence of coastal upwelled nutrients on phytoplankton productivity in adjacent small estuaries and bays is poorly understood. This study was conducted in Drakes Estero, California, a low inflow estuary located in the Point Reyes National Seashore and the site of an oyster mariculture facility that produces 40 % of the oysters harvested in California. Measurements of nutrients, chlorophyll a, phytoplankton functional groups, and phytoplankton carbon and nitrogen uptake were made between May 2010 and June 2011. A sea-to-land gradient in nutrient concentrations was observed with elevated nitrate at the coast and higher ammonium at the landward region. Larger phytoplankton cells (>5 μm diameter) were dominant within the outer and middle Estero where phytoplankton primary productivity was fueled by nitrate and f-ratios were >0.5; the greatest primary production rates were in the middle Estero. Primary production was lowest within the inner Estero, where smaller phytoplankton cells (<5 μm) were dominant, and nitrogen uptake was dominated by ammonium. Phytoplankton blooms occurred at the outer and middle Estero and were dominated by diatoms during the spring and dry-upwelling seasons but dinoflagellates during the fall. Small flagellated algae (>2 μm) were dominant at the inner Estero where no blooms occurred. These results indicate that coastal nitrate and phytoplankton are imported into Drakes Estero and lead to periods of high new production that can support the oyster mariculture; a likely scenario also for other small estuaries and bays.     

Nitrogen limitation of phytoplankton in a shallow embayment in northern Puget Sound

The effect of nutrient enrichments on natural phytoplankton assemblages was examined in six experiments conducted from June to October 1992. Short-term (4 d to 7 d) nutrient enrichment bioassays were incubated in situ in Padilla Bay, a slough-fed estuary in northern Puget Sound, Washington. Ammonium additions (15 μM) significantly (p<0.001) stimulated phytoplankton biomass accumulation during all six experiments. In two experiments, nitrate additions (15 μM) significantly stimulated accumulation of phytoplankton biomass during October, but not September. Addition of phosphate (1.0 μM) or silicate (15 μM) alone did not stimulate phytoplankton biomass accumulation during any of the experiments. In most experiments, phytoplankton response was greatest in combination treatments of ammonium and phosphate. Dissolved inorganic nutrient concentrations in the containers decreased during all incubations, but showed the greatest reduction in treatments receiving nitrogen. Dissolved inorganic nitrogen (DIN) to phosphate (PO₄ ^3?) ratios were below 16∶1 during all experiments, suggesting the potential for nitrogen limitation. In three experiments, the response of photosynthetic nanoplankton (<20 μm) to ammonium additions was compared to that of the total phytoplankton assemblages. Accumulation of nanoplankton biomass exceeded that of the total phytoplankton during two experiments in August but showed no significant response to ammonium additions in October. Results from the bioassays, the low DIN∶PO₄ ^3? ratios, and the reduction in nutrient concentrations in the containers provide evidence for potential nitrogen limitation of phytoplankton production during summer in Padilla Bay.     

Nutrient changes in the Mississippi River and system responses on the adjacent continental shelf

The Mississippi River system ranks among the world's top 10 rivers in freshwater and sediment inputs to the coastal ocean. The river contributes 90% of the freshwater loading to the Gulf of Mexico, and terminates amidst one of the United States' most productive fisheries regions and the location of the largest zone of hypoxia, in the western Atlantic Ocean. Significant increases in riverine nutrient concentrations and loadings of nitrate and phosphorus and decreases in silicate have occurred this century, and have accelerated since 1950. Consequently, major alterations have occurred in the probable nutrient limitation and overall stoichiometric nutrient balance in the adjacent continental shelf system. Changes in the nutrient balances and reduction in riverine silica loading to, the continental shelf appear to have led to phytoplankton species shifts offshore and to an increase in primary production. The phytoplankton community response, as indicated by long-term changes in biological uptake of silicate and accumulation of biologically bound silica in sediments, has shown how the system has responded to changes in riverine nutrient loadings. Indeed, the accumulation of biologically bound silica in sediments beneath the Mississippi River plume increased during the past two decades, presumably in response to, increased nitrogen loading. The duration, size, and severity of hypoxia has probably increased as a consequence of the increased primary production. Management alternatives directed at water pollution issues within the Mississippi River watershed may have unintended and contrasting impacts on the coastal waters of the northern Gulf of Mexico.     

Tidal Influences on Biotic and Abiotic Factors in the Seomjin River Estuary and Gwangyang Bay,Korea

To assess changes in abiotic and biotic factors between flood and ebb tides, we investigated the seasonal phytoplankton dynamics and environmental conditions along a salinity gradient at 14 stations in the Seomjin River estuary (SRE), Korea, and conducted bioassays to investigate the effect of nutrient addition (+N, +P, and +NP) on phytoplankton growth. Saltwater intrusion upstream was greatly dependent on the amount of freshwater discharge resulting from seasonal rainfall. There was a strong negative correlation between salinity and the nitrate+nitrite concentration (p?<?0.001), and between salinity and the silicate concentration (p?<?0.001), but no clear correlation between salinity and the ammonium concentration, or salinity and the phosphate concentration (p?>?0.01). This indicates that the N and Si loading increased as a result of freshwater input. The algal bioassays showed that high phytoplankton growth rates were usually recorded in response to the +NP treatment, but in the saltwater zone, the phytoplankton community also responded rapidly to the +N treatment, and to the +P treatment in the freshwater zone. The range of nutrient limitation depended on freshwater discharge. The seasonal and horizontal distribution of phytoplankton communities changed along the salinity gradient. The significant differences in abiotic factors between flood and ebb tides play important roles in controlling the biotic factors, including the occurrence of aquatic organisms including microalgae.     

Short-term biogeochemical influence of a diatom bloom on the nutrient and trace metal concentrations in South San Francisco Bay microcosm experiments

Two laboratory microcosm experiments were conducted to mimic an annual spring diatom bloom in South San Francisco Bay by isolating the phytoplankton community from the benthic grazing pressure to induce a phytoplankton bloom. The purpose of these experiments was to isolate the impact of a spring diatom bloom on the nutrient and trace metal geochemical cycling. Microcosms were created in 2.5 L incubation bottles and subjected to one of 4 treatments (control, copper [Cu] addition, manganese [Mn] addition, and both Cu and Mn addition) to investigate the toxicity of Cu on the resident plankton and the potential antagonistic effects of Mn on reducing Cu toxicity. Dissolved macronutrient (nitrate + nitrite, phosphate, and silicate), and dissolved and particulate trace metal (Cu, Ni, Mn) concentrations were monitored in the grow-out incubations on a daily basis. Chlorophylla concentrations were also monitored over the course of the experiment and used to calculate diatom-specific growth rates. In the experiments containing ambient South San Francisco Bay surface waters, average specific growth rates were on the order of 1.1 d^?1. The induced diatom blooms resulted in significant removal of macronutrients from the microcosms over the course of the experiments. Our research supports previous suggestions that dissolved Ni and Cu concentrations in South San Francisco Bay have a very low biological availability as a result of organic chelation. Ni(EDTA)^2? has been found to be the dominant dissolved Ni species by other researchers and Cu speciation analyses from this study and others indicate that > 99% of the dissolved Cu in South San Francisco Bay is strongly chelated as CuL₁. The free cupric ion concentration was on the order of 10^?12 M. Marked removal of dissolved Mn was observed in the control treatments, well exceeding expected dissolved Mn removal by diatom uptake. Additions of 375 nM Cu resulted in the complete titration of the chelating ligand (L₁) concentrations. The elevated [Cu²⁺] (≈10^?8MM) appeared to have a toxic effect on the diatom community observed in the significant decreases in their specific growth rates (μ=0.4 d^?1). The suppression of dissolved Mn removal from solution was also observed in treatments spiked with high levels of dissolved Cu, providing support that Mn precipitation was due to biologically mediated oxidation not phytoplankton assimilation. The observed geochemical behavior in the concurrent Cu and Mn addition treatments provide evidence in support of Mn alleviation of Cu toxicity. The biological role in the ambient short-term biogeochemical cycling of Cu and Ni in South San Francisco Bay appears to be minimal due to the inert character of the organic ligand-metal complexes. A significant portion of the annual macronutrient and Mn cycling occurs as a result of spring diatom blooms in South San Francisco Bay.     

Nutrient enrichments and phytoplankton growth in the surface waters of the Louisiana Bight

Nitrate concentrations have increased twofold in the Mississippi River during the past three decades. The increased nitrogen loading to the Louisiana shelf has been postulated as a factor leading to eutrophication and the subsequent development of hypoxia west of the Mississippi River delta. While ratios of nitrogen:phosphorus and nitrogen:silica are relatively high in surface waters on the western Louisiana shelf, nitrogen has been posed as the ‘limiting’ nutrient in this region. Bioassays were performed with nutrient additions to surface waters collected from the Louisiana shelf to examine the potential for specific nutrient limitation. Experiments were conducted in March and September 1991, and May 1992. The growth responses of natural and cultured phytoplankton populations were determined by measuring the time course of in vivo and 3-(3,4 dichlorophenyl)-1, 1-dimethylurea (DCMU)-induced fluorescence, as well as initial and final chlorophylla concentrations. The results suggest that phosphate and silicate potentially limit phytoplankton growth during the winter-spring, particularly at low salinities. In late summer, in contrast, nitrogen limitation may be prominent at higher salinities.