Seasonal and annual variations in the organic matter contributed by the St Lawrence River to the Gulf of St. Lawrence

The St. Lawrence River discharges a substantial volume of water (405 km³/a) containing suspended (SPM; 3.42 × 10⁶t) and dissolved (68.0 × 10⁶t) materials to the Gulf of St. Lawrence. The total load contains organic carbon in paniculate (POC; 3–14% of SPM), and dissolved (DOC; 3.76 ± 0.63 mg/l) form. The concentration of POC (and particulate organic nitrogen) is positively correlated with discharge (increased during the spring flood and the fall enhancement of flow), but concentration of DOC is not so simply related to discharge. In consequence, the total organic carbon (POC + DOC) load is relatively invariant, and increased annually by only 2–3% despite a progressive increase of 8% in discharge over the years of this study. Seasonal differences in the composition of the particulate organic matter (POM) are interpreted as reflecting dominant contributions from within-river production in summer and from terrestrial sources in spring and fall. In years when the annual discharge was greater than average, a higher proportion of the POM was terrigenous. The organic matter in surface sediments of the estuary to which the river discharges is predominantly of terrestrial provenance.     

The biogeochemical distribution of trace elements in the Indian Ocean

The present review deals with the distributions of dissolved trace metals in the Indian Ocean in relation with biological, chemical and hydrographic processes. The literature data-base is extremely limited and almost no information is available on particle processes and input and output processes of trace metals in the Indian Ocean basin and therefore much research is needed to expand our understanding of the marine chemistries of most trace metals. An area of special interest for future research is the Arabian Sea. The local conditions (upwelling induced productivity, restricted bottom water circulation and suboxic intermediate waters) create a natural laboratory for studying trace metal chemistry.     

Spatial and vertical trends in sediment-phase contaminants in the upper estuary of the St. Lawrence River

The concentration of selected contaminant trace metals and organic contaminants, namely polycyclic aromatic hydrocarbons (PAHs), normal-alkanes, total polychlorinated biphenyls (PCBs), and other organochlorines, was studied in cores from shallow-water fine-grain sediments from both sides of the maximum turbidity zone (MTZ) in the upper estuary of the St. Lawrence. Average trace metal concentrations in the cores were generally lower in downstream sediments, except for Hg and Pb. Hg levels in the cores were very high, exceeding 0.7 μg g^?1 in core C168 (south shore) and 0.19 μg g^?1 in core LE (north shore). Trace metal concentrations in all the cores were highly variable with depth, but after normalization with reference to iron, the trend was remarkably uniform, thus confirming an important inverse relationship with grain size. A similar lack of a well-defined trend was noted in the profiles of the organic components in the modern sediments. Average PAH values for modern sediments at core sites C168 and LO were 1.05 μg g^?1 and 0.44 μg g^?1, respectively (i.e., less than or equal to those in Lake Ontario and upstream in the river). PCB values far exceeded those in upstream sediments (average: 347 ng g^?1 in core LE and 158 ng g^?1 in C168), but were less than in Lake Ontario. Concentrations of chlordane, heachlorobenzene, and mirex were relatively low and uniform in the modern sections of the cores. The vertical uniformity of both the contaminant profiles and those for Cs-137 (C168) suggests that the sediments are relatively young (i.e., definitely less than 35 yr at C168, and probably even less at LE and LO). Therefore no long-term or historical trend is evident.     

Uranium, radon, helium and other trace elements and gases in well waters of parts of the St. Lawrence Lowlands, (Ottawa region) Canada

To test the usefulness of groundwater for U prospecting, 130 domestic wells were sampled from a 22,000 km² rectangular area extending south and west from Ottawa, Ontario. The waters were analyzed for twenty variables including ten gases and five trace elements.The dissolved gases give information on subsurface chemical and geological environments. Carbon dioxide highs occur at the contact of granites and limestones; He highs are along major faults; CH₄ and H₂S reveal strongly reducing environments, and O₂ in wells indicates shallow wells or active water turnover. Rn reveals U mineralization and granitic rocks.The South March U-Cu surface occurrence gives coincident U, Cu, Zn, Pb and Rn highs. A weak U-Rn-Cu high in the Richmond-North Gower area suggests more radioactive subcropping March formation there.A strong regional He anomaly coincident with the outcropping Rockcliffe Formation and controlled by the Hazeldean Fault is believed to be due to deep-seated He, but its coincidence with a weak regional Cu anomaly, a Rn anomaly in the Bells Corners area, its linear northeast trend, the presence of Helikian U-rich source rocks to the southwest, and northeast-dipping Paleozoic sandstones provide both indications of, and the right environment for epigenetic type U-Cu occurrences.     

Distribution and abundance of ichthyoplankton in the Manicouagan River estuary,a tributary of the lower St. Lawrence estuary

The species composition and relative abundance of ichthyoplankton were investigated during summer 1986 at four stations along the salinity gradient in the Manicouagan River estuary, a tributary of the lower St. Lawrence estuary. Physical characteristics of water masses indicated the presence of a strong saline front (>10‰ per km) delineating the freshwater and marine section of the Manicouagan estuary. The estuary supports a depauperate ichthyoplankton community, including four species of pelagic fish eggs and eight species of fish larvae. Species richness increased with salinity. The ichthyoplankton fauna can be divided into two distinct groups: freshwater and marine. These two groups result initially from spawning preferences exhibited by the different species abundance of freshwater larvae was maximal at the head of the estuary and marine larvae were most abundant at the most saline station. The length frequency distribution suggests that marine larvae are not effectively retained within the estuary. The Manicouagan estuary cannot be considered as a major spawning site nor an important nursery zone for any fish found in this area.     

Geochemistry of trace and minor elements in sediments and manganese micronodules from the Angola Basin

Indicator role of trace elements in sedimentation and ore formation is considered for sediments from Station 2182 in the Angola Basin. It is shown that pelagic sediments were formed from two main sources: biogenic calcium carbonate and lithogenic sediment component compositionally similar to the miopelagic clay. Increase of the Mn/Al ratio, Ce anomaly in the REE composition, Co/Ni and Mo/W ratios, and anomalous accumulation of Tl, Pb, Bi and other microelements indicate that sediments from horizons 15–20 and 30–35 cm contain significant amounts of hydrogenic material as Fe-Mn oxyhydroxides. Manganese micronodules (MN) were extracted from different horizons (10–15, 15–20, and 30–35 cm) and analyzed to study the hydrogenic component. Their development is related to retardation of biogenic and lithogenic sedimentation. The studied manganese micronodules are represented by the hydrogenic-diagenetic formations >100 μm in size with Mn/Fe = 2.0–2.8, Co/Ni = 0.2–0.4, Ce an = 4.2–5.7, and Mo/W = 5.2–7.9. The MN content is too low to affect the major and trace element composition of sediments. The main part of Fe and Mn is confined to fraction <10 μm.     

Concentration and association of minor and trace elements in Mukah coal from Sarawak, Malaysia, with emphasis on the potentially hazardous trace elements

The ash yield and concentrations of twenty-four minor and trace elements, including twelve potentially hazardous trace elements were determined in Mukah coal from Sarawak, Malaysia. Comparisons made to the Clarke values show that Mukah coal is depleted in Ag, Ba, Be, Cd, Co, Mn, Ni, Se, U, and V. On the other hand, it is enriched in As, Cr, Cu, Pb, Sb, Th, and Zn. Among the trace elements studied, V and Ba are associated predominantly with the clay minerals. Manganese, Cr, Cu, Th, and Ni are mostly bound within the aluminosilicate, sulphide and/or carbonate minerals in varying proportions, though a portion of these elements are also organically bound. Arsenic, Pb and Sb are mostly organically bound, though some of these elements are also associated with the sulphide minerals. Zinc is associated with both the organic and inorganic contents of the coal. Among the potentially hazardous trace elements, Be, Cd, Co, Mn, Ni, Se, and U may be of little or no health and environmental concerns, whereas As, Cr, Pb, Sb and Th require further examination for their potential health and environmental concerns. Of particular concern are the elements As, Pb and Sb, which are mostly organically bound and hence cannot be removed by physical cleaning technologies. They escape during coal combustion, either released as vapours to the atmosphere or are adsorbed onto the fine fly ash particles.     

Weathering of the New Albany Shale, Kentucky: II. Redistribution of minor and trace elements

During weathering, elements enriched in black shale are dispersed in the environment by aqueous and mechanical transport. Here a unique evaluation of the differential release, transport, and fate of Fe and 15 trace elements during progressive weathering of the Devonian New Albany Shale in Kentucky is presented. Results of chemical analyses along a weathering profile (unweathered through progressively weathered shale to soil) describe the chemically distinct pathways of the trace elements and the rate that elements are transferred into the broader, local environment. Trace elements enriched in the unweathered shale are in massive or framboidal pyrite, minor sphalerite, CuS and NiS phases, organic matter and clay minerals. These phases are subject to varying degrees and rates of alteration along the profile. Cadmium, Co, Mn, Ni, and Zn are removed from weathered shale during sulfide-mineral oxidation and transported primarily in aqueous solution. The aqueous fluxes for these trace elements range from 0.1 g/ha/a (Cd) to 44 g/ha/a (Mn). When hydrologic and climatic conditions are favorable, solutions seep to surface exposures, evaporate, and form Fe-sulfate efflorescent salts rich in these elements. Elements that remain dissolved in the low pH (<4) streams and groundwater draining New Albany Shale watersheds become fixed by reactions that increase pH. Neutralization of the weathering solution in local streams results in elements being adsorbed and precipitated onto sediment surfaces, resulting in trace element anomalies.Other elements are strongly adsorbed or structurally bound to solid phases during weathering. Copper and U initially are concentrated in weathering solutions, but become fixed to modern plant litter in soil formed on New Albany Shale. Molybdenum, Pb, Sb, and Se are released from sulfide minerals and organic matter by oxidation and accumulate in Fe-oxyhydroxide clay coatings that concentrate in surface soil during illuviation. Chromium, Ti, and V are strongly correlated with clay abundance and considered to be in the structure of illitic clay. Illite undergoes minimal alteration during weathering and is concentrated during illuvial processes. Arsenic concentration increases across the weathering profile and is associated with the succession of secondary Fe(III) minerals that form with progressive weathering. Detrital fluxes of particle-bound trace elements range from 0.1 g/ha/a (Sb) to 8 g/ha/a (Mo). Although many of the elements are concentrated in the stream sediments, changes in pH and redox conditions along the sediment transport path could facilitate their release for aqueous transport.     

Seasonal and spatial dynamics of trace elements in water and sediment from Pearl River Estuary, South China

In this study, spatial and seasonal dynamics of trace elements (Cu, Pb, Zn, Cd, As) in water and sediments were examined in the Pearl River Estuary (PRE), South China. The spatial variations of all the studied trace elements in sediments show the general decrease pattern from northwest to southeast side of the PRE, suggesting that the main sources of these trace elements may originate from terrestrial (rock and soil) weathering and human activities (e.g. agricultural, industrial and municipal wastewaters) via riverine inputs. The dissolved Cu, Pb, Cd, As, and Zn in PRE ranged from 0.34 to 3.26, 0.19 to 4.58, 0.0015 to 0.30, 0.16 to 8.18, 3.74 to 36.10 μg/L, respectively. There are obvious seasonal changes of dissolved trace elements in the PRE aquatic system. The maximum seasonal averages of all the dissolved trace elements excluding Zn were observed in summer, whereas dissolved Zn showed the minimum in this season. The overall spatial pattern of all the dissolved trace elements excluding Zn demonstrates decreasing trends from inshore to offshore, and the highest concentrations of dissolved Cu, Cd, As, and Zn appeared in the western part of PRE or the mouths of Pearl River, suggesting strong riverine and anthropogenic local inputs. PCA and correlation analysis show that the geochemical behavior of dissolved Cu and As are complicated and the dynamics of these two elements are controlled by various physicochemical parameters, whereas physicochemical parameters might play a relatively small role in the distributions of other studied trace elements.     

GEOTRACES - An international study of the global marine biogeochemical cycles of trace elements and their isotopes

Trace elements serve important roles as regulators of ocean processes including marine ecosystem dynamics and carbon cycling. The role of iron, for instance, is well known as a limiting micronutrient in the surface ocean. Several other trace elements also play crucial roles in ecosystem function and their supply therefore controls the structure, and possibly the productivity, of marine ecosystems. Understanding the biogeochemical cycling of these micronutrients requires knowledge of their diverse sources and sinks, as well as their transport and chemical form in the ocean.Much of what is known about past ocean conditions, and therefore about the processes driving global climate change, is derived from trace-element and isotope patterns recorded in marine deposits. Reading the geochemical information archived in marine sediments informs us about past changes in fundamental ocean conditions such as temperature, salinity, pH, carbon chemistry, ocean circulation and biological productivity. These records provide our principal source of information about the ocean's role in past climate change. Understanding this role offers unique insights into the future consequences of global change.The cycle of many trace elements and isotopes has been significantly impacted by human activity. Some of these are harmful to the natural and human environment due to their toxicity and/or radioactivity. Understanding the processes that control the transport and fate of these contaminants is an important aspect of protecting the ocean environment. Such understanding requires accurate knowledge of the natural biogeochemical cycling of these elements so that changes due to human activity can be put in context.Despite the recognised importance of understanding the geochemical cycles of trace elements and isotopes, limited knowledge of their sources and sinks in the ocean and the rates and mechanisms governing their internal cycling, constrains their application to illuminating the problems outlined above. Marine geochemists are poised to make significant progress in trace-element biogeochemistry. Advances in clean sampling protocols and analytical techniques provide unprecedented capability for high-density sampling and measurement of a wide range of trace elements and isotopes which can be combined with new modelling strategies that have evolved from the World Ocean Circulation Experiment (WOCE) and Joint Global Ocean Flux Study (JGOFS) programmes. A major new international research programme, GEOTRACES, has now been developed as a result of community input to study the global marine biogeochemical cycles of trace elements and their isotopes. Here, we describe this programme and its rationale.     

Temporal and spatial distribution and production of dissolved gaseous mercury in the Bay St. François wetland, in the St. Lawrence River, Quebec, Canada

Wetlands are valued for their high biodiversity and for their ecosystem services. However, we still do have a poor understanding of their role in the redox transformation of contaminants such as mercury, particularly in fluvial settings. Seasonal and spatial variations in dissolved gaseous mercury (DGM) distribution and production were studied in the Bay St. François, a wetland in the St. Pierre Lake, a fluvial lake of the St. Lawrence River, in Quebec, Canada. A high spatial resolution for DGM, with samples taken every 10-cm depth, was used in field measurements. Through a series of parallel field and incubation experiments, we assessed the main factors determining Hg(0) transformations as a function of depth, seasons, and presence/absence of macrophyte beds. Besides light penetration in the water column and water temperature, iron and dissolved organic carbon likely stimulated Hg(II) reduction. Inversely, chloride favored Hg(0) oxidation. Macrophytes and associated epiphytes appeared to be important sites of adsorption/absorption of Hg(II) and likely of DGM. It seems however that the effects of macrophytes were restricted to immediately adjacent waters. Near the bottom, under anoxic conditions, the reduction of Hg(II) was highly promoted. In addition, sediments and decomposing macrophytes seemed to release DGM and/or reducible Hg to bottom waters. Overall, differences in DGM between surface and bottom waters tended to be more accentuated than observed differences in DGM between macrophyte beds and sites devoid of plant.     

Sedimentation cycle of a freshwater tidal flat in the St. Lawrence estuary

Cap-Tourmente tidal flat is located on the north shore of the St. Lawrence middle estuary, 50 km downstream from Quebec city, Canada. Seasonal variations in sedient accretion were studied during the period without ice from May to December, using horizontal plates in conjunction with vertical stakes. The sedimentological regime which is characterized by very rapid changes, can be divided into four periods. There are two periods of intense erosion in May and October–November; during these months, erosion is initiated by walking and beak probing of very large flocks of snow geese. During the summer, very rapid accretion occurs for approximately 100 days; during this period, the sedimentation rate is 2 mm per day in the lower section of the tidal marsh which is covered with vegetation. Among the numerous factors influencing the sedimentation cycle, the very gradual slope of the upper part of the flat (0.25%) seems to be one of the most important because it results in a very large area (550 m wide) which is protected from strong tidal currents. This latter area is covered with dense and high vegetation which provides an effective protection against erosion unitl the snow geese arrive in October and raze it in a few days. The presence of vegetation reduces the velocities of tidal currents, particularly during ebb and modifies their direction for both flood and ebb, orienting them perpendicularly to the main tidal flow.     

Physical processes controlling bacterial distribution and variability in the upper St. Lawrence estuary

The vertical structure of the water column and the spatial distribution and semidiurnal variability of bacteria were investigated at six stations in the upper St. Lawrence estuary. The σ₁ profiles indicate that the upper St. Lawrence is a partially mixed estuary. Stratification results from buoyancy input from the freshwater outflow of the St. Lawrence River, and its variability is controlled by tidal and, to a lesser extent, wind mixing. Calculations show that tidal mixing largely exceeds mixing caused by wind. Free and attached bacteria presented different patterns of spatial distribution and temporal variability. Free bacteria exhibited highest mean concentrations at the freshwater station (3.5–4.4 10⁶ml^?1) and lowest concentrations at the downstream stations (0.3–0.5 10⁶ml^?1); their numbers declined exponentially relative to salinity. Attached bacteria had highest mean concentrations (3.2–5.5 10⁶ml^?1) at salinities between 0.5 and 5 and were virtually absent at downseam stations (<0.05 10⁶ml^?1). The importance of semidiurnal variability was demonstrated Over the idal cycle, variability of attached bacteria was always greater than that of free bacteria. The analysis of causal models between salinity and free and attached bacteria, showed that the two types of bacteria are uncoupled and that both types have a strong relationship with salimity. Physical processes are thus important controlling factors of the distribution and variability of bacteria. Results suggest that large-scale processes, such as freshwater outflow and residual circulation, largely control free bacteria, whereas short-term and more local processes (e.g., sediment resuspension caused by wind) may also be important in the control of attached bacteria.     

Distribution of arsenic and other minor trace elements in the groundwater of Ischia Island (southern Italy)

The island of Ischia belongs to the active volcanic area of Naples. It is formed from Quaternary volcanic rocks and exhibits intense hydrothermal activity, which is manifested through numerous springs, fumaroles and sporadic geysers. The content of minor and trace elements in groundwater has been analyzed, including some elements that are considered toxic for humans. Mean concentrations of As, B, Fe, Mn, Sb, and Se in samples from 43 aquifer points exceed the WHO recommended values and the limits set by European and Italian legislation (98/83/CE and DM 471, respectively). In general, the spatial distribution of the elements follows a common pattern: it is governed by a marked structural control, which favors hydrochemical processes that liberate the elements into the water.     

Partition coefficients of trace elements: Application to volcanic rocks of St. Vincent,West Indies

Island arc basaltic rocks (basalts and basic andesites with SiO₂ < 56.5%) from the Soufrière volcano. St. Vincent, West Indies (prehistoric lavas and 1902 and 1979 eruptions) underwent extensive fractional crystallization at various levels during the ascent of the magma. Although the precipitation of minerals occurring in coarse-grained cumulate inclusions dominated the derivation of basic andesites from basaltic magma, the distribution of the trace elements is not consistent with a simple fractional crystallization process. The lavas have a partially cumulate character and were probably generated from similar but separate parental magmas. The partition coefficients of transition and large ion lithophile elements are given for clinopyroxene, amphibole. olivine, plagioclase and titanomagnetite in basaltic liquid which crystallized under well-defined P-T conditions. The temperatures obtained from the geothermometers based upon the distribution of the major elements are in good agreement with the data from trace element geothermometers.     

Distribution of major, minor and trace elements in Hat Creek Deposit No. 2, British Columbia, Canada

The major-, minor- and trace-element contents of coals from Hat Creek No. 2 deposit, British Columbia, are determined using INAA and inductively coupled plasma emission spectrometry (boron only).

Al, Cr, Fe, Mn and Na were found to be inorganically bound in the coal while As, B and S are associated with the organic fraction of the coal. The rare-earth element concentrations in the coal are variable, however, the LREE/HREE ratio decreases from base to the top of the deposits. Many elements show little variation in concentration with depth; however, the gradual increase of As and S with depth appears to be rank related and indicative of progressive decrease in porosity with increasing rank.

Concentrations of B and Cr are sensitive to the environment of coal deposition, with coal deposited in a freshwater environment (Hat Creek No. 2 deposit), having low B and high Cr compared with more brackish coals.     

Source and mobility of minor and trace elements in a volcanic aquifer system: Mt. Vulture (southern Italy)

In this paper we provide a geochemical investigation on 34 groundwater samples in the Mt. Vulture volcanic aquifer representing one of the most important groundwater resources of the southern Italy pumped for drinking and irrigation supply. The present study includes the first data on the abundance and mobility of minor and trace elements and the thermodynamic considerations on water–rock interaction processes in order to evaluate the conditions of alkali basalt weathering by waters enriched in magma-derived CO₂. The results highlight the occurrence of two hydrofacies: bicarbonate alkaline-earth and alkaline waters deriving from low-temperature leaching of volcanic rocks of Mt. Vulture, and bicarbonate-sulfate-alkaline waters (high-salinity waters) related to prolonged water circulation in alkali and feldspathoids-rich pyroclastic layers interbedded with clay deposits. The Al-normalized relative mobility (RM) of metals in Vulture's aquifer varies over a wide range (10^− 1 < RM < 10⁴), confirming that the basalt weathering is not a congruent and isochemical process. Chemical equilibrium studies show that the bicarbonate alkaline-earth and alkaline waters, having a short interaction with silicate minerals, plot very close to the kaolinite–smectite stability boundary, whereas the high-salinity waters fall in the stability field of smectite and muscovite because of prolonged interaction with alkali and feldspathoids-rich pyroclastic layers. Overall, for the bicarbonate alkaline-earth and alkaline waters, the release of toxic metals in solutions is related to the spatial variation of host-rock geochemistry, the high-salinity waters, collected near urban areas, show values higher than legal limits for Ni and As, likely as a consequence of anthropogenic contribution.     

January snow accumulation in the St. Lawrence Valley (1961-1990)

Located in Eastern Canada, the St. Lawrence Valley (between Montreal and Quebec City; ±350 km) is known as one of the snowiest populated valleys in the world. Usually more than 250 cm of snow falls every winter. Snowstorms are frequent, as more than 10 major snowstorms are registered every year [1] interfering greatly with human activities. Numerical analyses (univariate analysis, discriminant analysis and stepwise multiple regression) for the 1961-1990 period on total snow depth for the month of January reveals three winter-regional climates along this valley: A-) the southern part of Montreal; slightly warmer with less snow and less rainfall, B-) the area around Quebec City; colder with more snow and C-) an intermediate corridor in-between those two cities. Two major variables were identified as responsible for explaining these three winter regional climates: maximum temperature and rainfall.     

Sources,sinks and distribution of organic carbon in the St. Lawrence Estuary,Canada

Carbon isotope ratio analysis of particulate, planktonic, and sedimentary organic carbon and dissolved inorganic carbon has been used to study the sources and sinks of the organic carbon in the St. Lawrence Estuary and Gulf of St. Lawrence, Canada. Particulate organic carbon (POC) isotope ratios in the upper St. Lawrence Estuary are uniform and indistinguishable from those of POC in the St. Lawrence River and of planktonic organic carbon in both areas. The abundance of freshwater diatoms in the upper Estuary suggests that upper Estuary POC is predominantly “fresh” organic matter of riverborne origin. Upper Estuary POC is isotopically different from POC in the lower St. Lawrence Estuary and Gaspé regions, but is not different from POC from the surface waters of the open Gulf of St. Lawrence. The isotopic composition of planktonic organic carbon mirrors that of the POC, indicating that the POC in the lower Estuary and Gulf is also “fresh” organic matter. Since the lower Estuary POC forms an isotopic barrier between the upper Estuary POC and the Gulf of St. Lawrence POC, there appears to be little mixing of POC between these three reservoirs. Therefore POC in the lower Estuary and Gulf is most likely both produced and deposited (or degraded) in situ.An examination of carbon isotope ratio differences between the planktonic and dissolved inorganic carbon reservoirs shows that this difference varies significantly and somewhat unpredictably between sectors of the study area. Interpretation of environmental carbon isotope data on the basis of an assumed, constant fractionation factor may be subject to large errors. Direct measurement of both reservoirs is obviously preferable.