Biogeochemistry and effects of copper,manganese and zinc added to enclosures in Island Billabong,Magela Creek,northern Australia

Three large plastic enclosures (5 m diam, volume 40 m³) were used to study the effects of copper, manganese and zinc, on the phytoplankton community in Island billabong, a floodplain billabong (waterhole) situated in the Magela Creek in tropical northern Australia. Copper was added to one enclosure, and manganese and zinc to another, to give initial concentrations around ten times the normal wet season values. The enclosures and the billabong were monitored over a ten week period towards the end of the dry season, with the enclosures allowed to stabilise for four weeks before the metals were added.The control enclosure adequately simulated the temperature and pH changes in the billabong. The trends in conductivity, dissolved oxygen and major ion concentrations were similar in the enclosure and the billabong, with the minor differences observed attributed to either epiphytic growth on the enclosure walls (influenced dissolved oxygen, pH and bicarbonate concentration) or ingress of sulphate-rich groundwater into the billabong (influenced sulphate concentration and conductivity). Major differences in both the composition of species and the size of the phytoplankton populations were observed between the three enclosures and between the control enclosure and the billabong. This variability reflects the great natural variability in the phytoplankton communities in tropical lentic systems, and means that enclosures are unlikely to adequately simulate the biological communities in the billabongs.The control enclosure appeared to simulate quite well the longer term changes in total concentration and speciation of the three metals (copper, manganese & zinc) in the billabong. The mean concentrations of copper and zinc were similar in the two systems, although the mean concentration of manganese in the billabong was almost double that in the enclosure, possibly due to ingress of manganese-enriched groundwater. Particulate forms dominated the speciation of copper and manganese. There was considerable short term variation in both total metal concentration and speciation in both the enclosure and the billabong. This variability appears to be a feature of these small tropical waterbodies.The added heavy metals were found to have minimal detrimental effect on the phytoplankton community in each metal-loaded enclosure. The high natural variability in the phytoplankton community in these tropical systems will make it difficult to separate natural changes from those caused by low level contamination from mining operations should this occur.All three metals were rapidly removed from the water column, so that by the end of the six week period, only ca. 5% of each added metal remained in the water column. Association with the particulate matter (phytoplankton, abiotic particulate matter and MnO_x in enclosure 2) followed by sedimentation was the major removal pathway. Epiphytes growing on the enclosure walls appeared to have a minor influence (<10% of the total amount of metal added) on the removal of the added metals. For copper, uptake by phytoplankton followed by sedimentation was the major (65%) removal process. Manganese and zinc, added together, were found to influence each other. The major manganese removal process (60%) was rapid (ca. 3 days) involving bacterial oxidation and sedimentation of the MnO_x formed. This material appeared to have little influence on the behaviour of zinc, possibly because other particulate matter competed more effectively for the zinc. A further 30% of the added manganese was removed via initial adsorption to other particulate matter, possibly phytoplankton. Approximately one third of this adsorbed manganese (10% of the total added) appeared to undergo delayed oxidation some 8 days after the initial additions, and the heavier particles settled out more rapidly. This path was responsible for removing the major amount (ca. 60%) of the added zinc. We hypothesis that the sorbed zinc inhibited the bacterial oxidation of the manganese. A further 25% of the zinc was removed in association with a burst of phytoplankton activity. The occurrence of bursts in the phytoplankton activity, when populations can increase very substantially and then decrease again, all within the space of a day, appears to be an important mechanism for removing copper and zinc from the water column in these tropical water bodies     

Overview of trace metal contamination in the Scheldt estuary and effect of regulatory measures

Seasonally, dissolved and particulate metal concentrations in the Scheldt estuary were assessed over a period of 4 years (1995–1998). High quality data were obtained following stringent analytical protocols for each step: sampling, sample treatment, sample storage and analysis. Of the 5 trace metals, Ni showed the most conservative behaviour, while Cd and Cu were clearly transferred from the particulate to the dissolved phase in the middle estuary. A substantial part of the particulate metals entering the estuarine system are lost through sedimentation. General seasonal patterns are the following: lower concentrations in spring and higher ones in winter (sometimes late fall/early winter) for dissolved metals, while in summer a pronounced rise of the longitudinal concentration profile is observed for the particulate metals. A comparison of the trace metal concentrations (dissolved and particulate) at the mouth of the estuary in 1995–1998 with those from 1981 to 1983, reveal reductions between 30 and 58%. Reductions based on direct emission measurements for almost the same period suggest reductions (dissolved + particulate) between 42 and 64%. Biomagnification (BMF) is the accumulation of a compound through the food-chain. It is in our case expressed as the ratio of the metal concentration in the organism (g g^–1, d.w.)/the metal concentration in total suspended matter (g g^–1, d.w.). Almost all BMF-values of Periwinkle, Nereis diversicolor and Macoma balthica (3 bottom organisms in the Scheldt estuary) are negative meaning that these organisms contain less heavy metals than the particulate suspended matter. For all organisms log BMFs for Pb, respectively Ni, are around –1.8, respectively –0.7. For Cd, Periwinkle shows slight enrichment (0.05) and for Cu even more (0.45), while negative values were observed for Nereis diversicolour and Macoma balthica. The latter organisms are more enriched in Zn (–0.09) than Periwinkle (–0.43).     

The behaviour of copper and zinc in the Scheldt estuary

The behaviour of copper and zinc in the Scheldt estuary, both in the particulate and the dissolved phase, is discussed for the period 1982–1983. The longitudinal particulate copper and zinc profiles fall below the dilution line, which is attributed to mixing and mobilization processes. In the dissolved phase both metals show a production region in the end member of the estuary, for copper a pronounced mid estuarine maximum is observed. Study of the metal speciation suggested that organic ligands might keep heavy metals in solution, especially in area of intensive production, and promote the subsequent export of these metals downstream the estuary.     

Ammonium formation in cape timiris (Mauritania) upwelling

Ammonium formation was studied in two consecutive years by following a newly upwelled ammonium-free ‘parcel’ of water with a drogue. High concentrations (> 2 μg-at. NH₄-N l^?1) were found at the end of each study. The relative importance of WP-2 net mesozooplankton excretion on the ammonium values is greater before the phytoplanktonic bloom (35–48%) than during it (10–16%). From carbon grazing estimates, it is shown that other herbivore excretion does not take the place of WP-2 mesozooplankton and because of synchronous variations of chlorophyll with dissolved organic nitrogen, and bacterial activity with ammonium, it is suggested that much of the ammonium is produced from phytoplankton decay or nitrogen excretion during the bloom.     

Use of dissolved carbohydrates by planktonic bacteria in a mesotrophic lake

Dissolved carbohydrates comprise one of the largest pools of labile organic matter readily available for bacterial use in pelagic ecosystems. Despite this fact, very little is known about use of dissolved carbohydrates by planktonic bacteria. We studied use of total dissolved carbohydrates (TDCHO) by planktonic bacteria in mesotrophic Lake Constance, Germany, from April until August 1992. We examined the decrease of TDCHO over time together with the increase of bacterial numbers in 1-m filtered lake water incubated at in situ temperature in the dark. TDCHO analyses were done after hydrolysis by sulfuric acid as free monosaccharides and oxidation by periodate to formaldehyde with 3-methyl-2-benzothiazolinone-hydrazon-hypochloride (MBTH). Preliminary tests showed that hydrolysis by sulfuric acid gave higher yields than hydrolysis by HCl. Our results show that TDCHO are readily used by bacteria and compose substantial fractions of the C requirements for their growth. Concentrations of TDCHO varied between 1.7 and 5.5 m (glucose equivalents), and use rates varied between 0.47 and 3.43 g C liter^–1 h^–1. Highest rates of TDCHO use occurred during the phytoplankton spring bloom, during the clear-water phase in June, and during a phytoplankton bloom in August. Ratios of use of TDCHO/bacterial biomass production varied between 0.17 and 3.05. During the spring bloom, TDCHO and total dissolved amino acids (TDAA) were used in equal amounts. During the clear-water phase at chlorophyll a concentrations <3 g liter^–1, however, bacteria only consumed TDCHO and excreted amino acids. The growth efficiency based on the consumption of TDCHO and TDAA varied between 16 and 21% during the phytoplankton spring bloom and was 35% during the clear-water phase. Correspondence to: M. Simon     

Influences of land use and stream size on particulate and dissolved materials in a small Amazonian stream network

We investigated the influences of forest or pasture land use and stream size on particulate and dissolved material concentrations in a network of second to third order streams in Rondônia, in the Brazilian Amazon. During the dry season, a second order stream originating in pasture had lower concentrations of dissolved oxygen and nitrate, higher concentrations of chlorophyll, total suspended solids, particulate organic carbon, particular organic nitrogen, ammonium, and phosphate than a second order stream originating in forest. Where the second order forest stream exited forest and entered pasture, concentrations of dissolved oxygen dropped from 6 mg/L to almost 0 mg/L and nitrate concentrations dropped from 12 M to 2 M over a reach of 2 km. These changes indicated a strong influence of land use. During the rainy season, differences among reaches of all particulate and dissolved materials were diminished. Concentrations of oxygen, chlorophyll, total suspended solids, particulate organic carbon and nitrogen, nitrate, ammonium, and phosphate in the third order pasture stream more closely resembled the second order forest stream than the second order pasture stream, suggesting that conditions in the channels of larger pasture streams more strongly control concentrations of these materials. If this pattern is widespread in stream networks of regions that consist of a mosaic of forest and pasture lands, it may have important consequences for understanding the effects of deforestation on larger rivers of the Amazon Basin. This would indicate that the effects of forest clearing on the concentrations of many suspended and dissolved materials will be most easily detected in very small streams but potentially difficult to detect in larger streams and rivers.     

Colloidal organic carbon and trace metal (Cd, Fe, and Zn) releases by diatom exudation and copepod grazing

Colloidal macromolecular organic compounds are important intermediaries between solution and particle phases and play a critical role in the biogeochemistry of trace metals and organic carbon. The releases of colloidal organic carbon and trace metals (Cd, Fe, and Zn) mediated by copepod grazing and decomposition, and direct diatom exudation, were examined using a radiotracer approach. The colloidal phase was operationally defined in this study as the size fraction between 5 kDa and 0.2 μm and the dissolved phase as the ≤0.2 μm filter passing phase. About 13-60% of dissolved carbon exuded by the diatom Thalassiosira pseudonana was partitioned into the colloidal phase, and this fraction increased considerably as the diatom cells grew older. A lower fraction of dissolved ¹⁴C (12-23%) excreted by the copepods Acartia erythraea was detected in the colloidal phase compared to carcass (13-35%) and feces decomposition (21-34%). In contrast to carbon, a lower fraction of regenerated dissolved Cd (1-11%) and Zn (0-20%) from copepods and diatoms was consistently detected in the colloidal phases. Copepod excretion and carcass decomposition resulted in more colloidal Fe (51-91%) than diatom exudation (46-62% for Thalassiosira weissflogii, and 3-33% for T. pseudonana) and copepod feces decomposition (16-30%). Copepod (Calanus sinicus) grazing reduced the colloidal fraction of dissolved ¹⁴C, although a higher concentration of the diatom's (T. weissflogii) carbon was regenerated into the dissolved phase. The grazing of these copepods did not have any influence on the colloidal metal partitioning. The release of trace metals and carbon was enhanced by a higher density of copepod's grazing. Thus, different biological processes (grazing, excretion, exudation, and decomposition) may contribute differently to the production and dynamics of colloidal carbon and metals in planktonic systems.     

Copper contamination in the Patuxent River,Maryland

Copper contamination was studied in the Patuxent River, Maryland, which flows from the western shore of the Chesapeake Bay. The only heavy industry on this river is a coal-fired power plant situated 35 km from the river mouth. The plant uses river water for cooling purposes and had been implicated in early studies as a source of localized copper pollution from copper: nickel condenser tubing. Average cooling water usage exceeded average natural river flow over the study period by a factor of 3. This investigation showed high levels of both dissolved and particulate copper at this point source, with a high ratio of particulate: dissolved copper at the point of discharge. A copper budget achieved through comparison of industrial intake/outflow data showed that when natural river flow was considered, output from this single point source could conservatively account for a total copper concentration in the river of 6.7 g 1^–1 above background. This considerably exceeded the measured figure of 2.6 g 1^–1 (relative to the upstream station). Part of this discrepancy was probably due to copper deposition close to the power plant. Although copper concentrations declined downstream from this source, they still remained high in absolute terms and were comparable with a much more heavily industrialized river system. Even at the river mouth, copper concentration remained elevated and it was speculated that anti-fouling paints associated with heavy recreational boat traffic may be particularly responsible for this.     

Heavy metals in the Rosetta estuary of the Nile and the adjoining Mediterranean waters: evidence of removal of dissolved heavy metals from waters as a result of possible binding to suspended matter

The Rosetta estuary was partially separated from the Rosetta branch of the Nile by Edfina Barrage, which controls the Nile discharge into the Mediterranean Sea. The study area covers the Rosetta estuary (lotic environment) and the adjoining seawaters (lentic environment) to investigate the local and seasonal distribution of dissolved and particulate copper and zinc, as well as dissolved cadmium in this estuary and to illustrate its influence on the distribution of these metal forms in the inshore seawaters. Besides, emphasis on the removal of dissolved heavy metals from waters by their adsorption onto suspended matter (SM) was also considered. Contrary to particulate copper (PCu), the vertical values of dissolved copper (DCu) decreased generally with depth. Planktonic scavenging and regeneration processes might determine the vertical profiles of the copper forms. The copper data suggest that the surface sources of DCu exceeded the bottom sources, contrary to the sources of PCu. The markedly high and maximum seasonal averages of DCu in the estuary and inshore seawater in July inspite of the high uptake in summer possibly reflect higher amounts of humic materials. The lowest seasonal average value of DCu in the inshore seawater in January suggests removal of copper in presence of maximum value of SM during highest discharge. The highest regional average of DCu at the estuarine mouth coincided with desorption process during mixing of the fresh and salt waters. The vertical values of dissolved zinc (DZn) and particulate zinc (PZn) showed irregular variations and their high concentrations in the surface of the estuarine and inshore seawater indicate possible land-based sources. The high bottom DZn values, however, resulted from its contribution from the interstitial water of the sediments. The data suggest that the surface sources of DZn exceeded the bottom sources and PZn showed the opposite trend in the open sea area. In the estuary, the maximum seasonal average value of DZn accompanied by the lowest seasonal average of PZn in April inspite of the high uptake in spring suggest that desorption was the dominant process. The minimum regional averages of both zinc forms at the estuarine opening and the highest average of PZn near Edfina Barage are correlated with the amounts of SM, which decreased toward the estuarine mouth. The vertical values of dissolved cadmium (DCd) were much lower in the estuary than the other metals. They showed in both environments irregular variations with depth. The bottom maximum value of DCd can be attributed mainly to contamination from the sediments. There was a distinct seasonal variation of DCd. The minimum seasonal average value of DCd in the estuary in April seems to be caused by its specific binding to living plankton found in abundance. The minimum regional average of DCd value was found at the estuarine mouth. The decrease in Cd concentration due to removal from dissolved state is most pronounced in the early stage of mixing. The correlation coefficients of DCd were positive with salinity and negative with SM, indicating that Cd increased seaward. Statistical correlation between Cd and Zn concludes that the factors affecting their distribution are generally the same.     

Attached and free-living bacteria: Production and polymer hydrolysis during a diatom bloom

Abundance, production and extracellular enzymatic activity of free-living and attached bacteria were measured during the development and collapse of a spring bloom in a eutrophic lake. Free-living bacteria accounted for most of the total bacterial production during the first part of the bloom. Their production had a significant positive correlation to chlorophyll (P < .01) and polysaccharide concentration (P < .02) and to potential -glucosidase and aminopeptidase activity (P < .05), suggesting that algal release of dissolved polymeric compounds provided an important carbon source for bacterial production. As the bloom collapsed, we observed a change in the activity and structure of the microbial community. The mean contribution of attached bacteria to total bacterial production increased from 12% during the first part of the bloom to 26% at the end. Also, the extracellular enzymatic activity of attached bacteria increased as the bloom collapsed and constituted up to 75% of the total hydrolytic activity. An estimated disparity between hydrolytic activity and the corresponding carbon demand of attached bacteria suggested a net release of dissolved organic compounds from organic particles via polymer hydrolysis by attached bacteria. Correspondence to: M. Middelboe     

The primary production of Amursky Bay (Sea of Japan) in the summer of 2008

In July 2015, the assimilation number (An) of phytoplankton in Amursky Bay was measured using optical dissolved oxygen sensors (Rinko). The primary production (PP) in the photic layer of Amursky Bay was calculated based on the measured An and chlorophyll vertical profiles obtained during a hydrochemical survey on August 23?28, 2008. The total production in the bay at that period was 840 tC/day. During a phytoplankton bloom, the excess production of biomass leading to the hypoxia of the bottom water was estimated to be approximately (1.0?2.0) × 10³ tC/day.     

The IRT1 protein from Arabidopsis thaliana is a metal transporter with a broad substrate range

The molecular basis for the transport of manganese across membranes in plant cells is poorly understood. We have found that IRT1, an Arabidopsis thaliana metal ion transporter, can complement a mutant Saccharomyces cerevisiae strain defective in high-affinity manganese uptake (smf1). The IRT1 protein has previously been identified as an iron transporter. The current studies demonstrated that IRT1, when expressed in yeast, can transport manganese as well. This manganese uptake activity was inhibited by cadmium, iron(II) and zinc, suggesting that IRT1 can transport these metals. The IRT1 cDNA also complements a zinc uptake-deficient yeast mutant strain (zrt1zrt2), and IRT1-dependent zinc transport in yeast cells is inhibited by cadmium, copper, cobalt and iron(III). However, IRT1 did not complement a copper uptake-deficient yeast mutant (ctr1), implying that this transporter is not involved in the uptake of copper in plant cells. The expression of IRT1 is enhanced in A. thaliana plants grown under iron deficiency. Under these conditions, there were increased levels of root-associated manganese, zinc and cobalt, suggesting that, in addition to iron, IRT1 mediates uptake of these metals into plant cells. Taken together, these data indicate that the IRT1 protein is a broad-range metal ion transporter in plants.     

Seasonal cycle of nitrogen and phytoplankton biomass in a well-mixed coastal system (Eastern English Channel)

The hydrological structure of the French coastal part of the eastern English Channel is strongly linked with tidal regimes and riverine input. Two distinct water masses are separated by a frontal area and drift along the coast in SW–NE direction. These two water masses are well-mixed during the entire year. We studied the seasonal dynamic of nitrogenous nutrients, chlorophyll a and organic particulate carbon and nitrogen at two stations, characteristic of these water masses, during the year 1994. Results show (i) a winter stock of nitrate and ammonium, (ii) a pre-bloom period corresponding to the use of ammonium, (iii) a high bloom period of short duration using nitrate, (iv) a post-bloom period with little phytoplanktonic activity probably limited by nutrients other than nitrogen and (v) an autumnal period of reconstitution of stock. The essential difference between the two stations is the importance of winter stock of nutrients and of bloom chlorophyll a concentration, with the coastal station richer than the offshore one. An assumption about the nitrogen available for new production in this area gives a value of 57% of the winter stock of inorganic nitrogen.     

The influence of color,age, and sex on the content of zinc,copper, nickel,manganese, and lead in human hair

The hair of 132 healthy subjects between 6 and 40 yr old living in the Veneto region in Italy was analyzed by means of HPLC method in order to determine the presence of zinc, copper, nickel, manganese, and lead. The collected samples were subdivided on the basis of age (6–11 and 19–40 yr), and sex and color (black, red, brown, and blond). From the data some evident differences were emphasized. In female hair the content of metals was higher than in male hair independently of color. Blond hair gave the lowest concentration values of the elements studied independently of sex. The maximum amount of the metals was found generally in black hair, followed by red and brown hair. Age seems to have a different influence, with the copper element decreasing appreciably in brown and blond female hair as the age of the subjects increased.     

The effect of increased nitrogen load on phytoplankton in a phosphorus‐limited lake

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Predominance of phytoplankton-derived dissolved and particulate organic carbon in a highly eutrophic tropical coastal embayment (Guanabara Bay,Rio de Janeiro,Brazil)

We investigate the carbon dynamics in Guanabara Bay, an eutrophic tropical coastal embayment surrounded by the megacity of Rio de Janeiro (southeast coast of Brazil). Nine sampling campaigns were conducted for dissolved, particulate and total organic carbon (DOC, POC and TOC), dissolved inorganic carbon (DIC), partial pressure of CO₂ (pCO₂), chlorophyll a (Chl a), pheo-pigments and ancillary parameters. Highest DOC, POC and Chl a concentrations were found in confined-shallow regions of the bay during the summer period with strong pCO₂ undersaturation, and DOC reached 82 mg L^?1, POC 152 mg L^?1, and Chl a 800 μg L^?1. Spatially and temporally, POC and DOC concentrations varied positively with total pigments, and negatively with DIC. Strong linear correlations between these parameters indicate that the production of TOC translates to an equivalent uptake in DIC, with 85% of the POC and about 50% of the DOC being of phytoplanktonic origin. Despite the shallow depths of the bay, surface waters were enriched in POC and DOC relative to bottom waters in periods of high thermohaline stratification. The seasonal accumulation of phytoplankton-derived TOC in the surface waters reached about 105 g C m^?2 year^?1, representing between 8 and 40% of the net primary production. The calculated turnover time of organic carbon was 117 and 34 days during winter and summer, respectively. Our results indicate that eutrophication of coastal bays in the tropics can generate large stocks of planktonic biomass and detrital organic carbon which are permanently being produced and partially degraded and buried in sediments.     

Seasonal changes in bacterial and phytoplankton biomass in a subantarctic coastal area (Kerguelen Islands)

The seasonal variations of bacterial and phytoplanktonic biomass were studied during several pluri-annual surveys in the subantarctic Morbihan Bay (Kerguelen Islands, 49 ° 20 S; 70 ° 10 E). Large interannual variation was observed. Phytoplanktonic biomass showed moderate values during winter and autumn. They increased sharply in spring, reaching a maximum value of about 1 mg C l^–1 corresponding to an important depletion of nutrients. A second phytoplanktonic bloom of similar amplitude occurred in late summer. During algal blooms which were roughly associated with optimal values of solar irradiation for the first one and with the highest temperatures for the second one, phytoplanktonic material represented near 100% of particulate and living carbon. Bacteria showed maximal abundance (0.2 to 0.7 mg C l^–1) during summer or autumn. Their relative abundance, which represented less than 1% of the living biomass in spring and summer, can reach more than 95% in autumn and winter.     

The occurrence and behaviour of phosphate fractions in Izmir Bay, Aegean Sea

The area around Izmir Bay (Turkey) is heavily urbanized and receives, therefore, high concentrations of phosphate originating from industrial and municipal inputs. During the surveys between April 1993 and July 1994, the total phosphate concentrations were highest in the Inner Bay (6.45 M and 5.59 M in the surface and bottom water, respectively) where very dense anthropogenic pollution occurs. The total phosphate value gradually decreased towards the Outer Bay where 0.70 M and 1.18 M were found in the surface and bottom water, respectively. The distribution of dissolved inorganic, dissolved organic and particulate phosphate along the bay reflected some peculiar spatial and temporal patterns. A high percentage of dissolved organic phosphate was observed in the Outer Bay while the particulate phosphate peaked in the Middle Bay where an upwelling mechanism was observed. In the bay, the biological production was strongly correlated with the variations in the dissolved inorganic, organic and particulate phosphate. The high phosphate concentration in particles caused the particulate phosphate formed in the Inner Bay to be transported to the outer parts of the bay because of the short water residence time. On the other hand, Principal Component Analysis showed that about 35% of the variation in all variables measured were related to the total phosphate, total dissolved phosphate, dissolved inorganic phosphate and particulate phosphate together with ammonium and reactive-Fe while about 14% of the variation was related to the dissolved organic phosphate and the number of phytoplankton cells, chl-a, pH and O₂.     

Analysis of in situ manganese(II) oxidation in the Columbia River and offshore plume: linking Aurantimonas and the associated microbial community to an active biogeochemical cycle

The Columbia River is a major source of dissolved nutrients and trace metals for the west coast of North America. A large proportion of these nutrients are sourced from the Columbia River Estuary, where coastal and terrestrial waters mix and resuspend particulate matter within the water column. As estuarine water is discharged off the coast, it transports the particulate matter, dissolved nutrients and microorganisms forming nutrient‐rich and metabolically dynamic plumes. In this study, bacterial manganese oxidation within the plume and estuary was investigated during spring and neap tides. The microbial community proteome was fractionated and assayed for Mn oxidation activity. Proteins from the outer membrane and the loosely bound outer membrane fractions were separated using size exclusion chromatography and Mn(II)‐oxidizing eluates were analysed with tandem mass spectrometry to identify potential Mn oxidase protein targets. Multi‐copper oxidase (MCO) and haem‐peroxidase enzymes were identified in active fractions. T‐RFLP profiles and cluster analysis indicates that organisms and bacterial communities capable of oxidizing Mn(II) can be sourced from the Columbia River estuary and nearshore coastal ocean. These organisms are producing up to 10 fM MnO₂ cell^?1 day^?1. Evidence for the presence of Mn(II)‐oxidizing bacterial isolates from the genera Aurantimonas, Rhodobacter, Bacillus and Shewanella was found in T‐RFLP profiles. Specific Q‐PCR probes were designed to target potential homologues of the Aurantimonas manganese oxidizing peroxidase (Mop). By comparing total Mop homologues, Aurantimonas SSU rRNA and total bacterial SSU rRNA gene copies, it appears that Aurantimonas can only account for ～1.7% of the peroxidase genes quantified. Under the broad assumption that at least some of the peroxidase homologues quantified are involved in manganese oxidation, it is possible that other organisms oxidize manganese via peroxidases.     

Uptake of trace metals by sediments and suspended particulates: a review

This review addresses three of the possible mechanisms by which trace metals can be concentrated by sediments and suspended particulate matter. These are physico-chemical adsorption from the water column, biological uptake particularly by bacteria and algae, and the sedimentation and physical entrapment of enriched particulate matter. The relative importance of these three mechanisms will be different, depending upon the aqueous system, but there have been insufficient studies to allow the establishment of even rule-of-thumb guidelines, as yet, about their quantitative importance under different conditions.The importance of natural organic matter in the cycling of trace metals in aquatic systems has been stressed. This organic matter may complex with the trace metals and keep them in solution, or it may enhance the association of the trace metals with particulate matter by becoming adsorbed to the particulate surface and then complexing with the trace metals in the solution phase. Enhanced metal-particulate associations may also arise if the metal-organic complexes are able to adsorb to the surface.The behaviour of natural organic matter may be the single most important influence on trace metal cycling in aquatic systems and should receive considerably more attention in the future.