Mercury in Sediments and Sediment Pore Water in the Laurentian Trough

1993 ◽  
Vol 50 (8) ◽  
pp. 1794-1800 ◽  
Author(s):  
Charles Gobeil ◽  
Daniel Cossa
Keyword(s):  
Pore Water ◽  
Drainage Basin ◽  
Sediment Surface ◽  
Vertical Profiles ◽  
Sediment Pore Water ◽  
Overlying Water ◽  
Lawrence Estuary ◽  
Order Of Magnitude ◽  
St Lawrence Estuary ◽  
Dissolved Mercury

The concentration of dissolved mercury in the pore water of Laurentian Trough sediments varies between the detection limit (2.5 pM) and 64 pM, up to an order of magnitude enriched relative to the overlying water. Dissolved mercury is low near the sediment surface, increases with depth to 5 cm, and then decreases with further depth. Redistribution of remobilized mercury within the sediment column is, however, insufficient to explain the observed depth variations in mercury concentration. In the Lower St. Lawrence Estuary, the vertical profiles of mercury in trough sediments tend to be consistent with the chronology of mercury discharges from chlor-alkali plants located in the St. Lawrence drainage basin. The total amount of anthropogenic mercury in sediments deposited below the 200-m isobath in the entire lower St. Lawrence Estuary since the beginning of industrialization is estimated as 170 ± 85 × 103 kg, about six times the amount of natural mercury that has accumulated during the same period. Near the seaward end of the Trough in the Gulf of St. Lawrence, sedimentary mercury concentrations are much lower than in the Estuary, with a significant portion of the anthropogenic mercury deposited in the sediments probably coming from the atmosphere.

Réponses comportementales des polychètes Nereis diversicolor (O.F. Müller) et Nereis virens (Sars) aux stimuli d'ordre alimentaire : utilisation de la matière organique particulaire (algues et halophytes)

1995 ◽  
Vol 73 (12) ◽  
pp. 2307-2317 ◽  
Author(s):  
Marc Olivier ◽  
Gaston Desrosiers ◽  
Alain Caron ◽  
Christian Retière ◽  
Aline Caillou
Keyword(s):  
Potential Role ◽  
Time Budget ◽  
Sediment Surface ◽  
Lawrence Estuary ◽  
Nereis Diversicolor ◽  
Nereis Virens ◽  
Intertidal Ecosystem ◽  
Feeding Area ◽  
St Lawrence Estuary

Plant preference and feeding selectivity were studied in juveniles of Nereis diversicolor O.F. Müller) and Nereis virens (Sars) (Polychaeta: Nereidae) to evaluate the potential role of these species in the integration and transfer of vegetal debris to the littoral ecosystem. Results show that these annelids ingest the main plant species (algae and halophytes) that are abundant in the marshes of the bay of Mont-Saint-Michel (France) and (or) the À l'Orignal Inlet (St. Lawrence Estuary, Canada), independently of their origin or level of decomposition. Juveniles select detritus on the sediment surface (feeding area) and accumulate them in their burrow. Constant irrigation by young individuals (≈35% of time budget) maintains aerobic conditions favouring the decay process of plant debris by stimulating bacterial growth (gardening). Our results suggest that individuals of both N. diversicolor and N. virens play an important role in the transfer and integration processes and the residence time of vegetal detritus of the intertidal ecosystem.

scholarly journals Benthic fluxes of dissolved organic nitrogen in the Lower St. Lawrence Estuary and implications for selective organic matter degradation

2013 ◽  
Vol 10 (5) ◽  
pp. 7917-7952
Author(s):  
M. Alkhatib ◽  
P. A. del Giorgio ◽  
Y. Gelinas ◽  
M. F. Lehmann
Keyword(s):  
Organic Matter ◽  
Pore Water ◽  
Dissolved Organic Nitrogen ◽  
Organic Nitrogen ◽  
Bottom Water ◽  
Estuarine Sediments ◽  
Pore Waters ◽  
Lower Estuary ◽  
Lawrence Estuary ◽  
St Lawrence Estuary

Abstract. The distribution of dissolved organic nitrogen (DON) and carbon (DOC) in sediment pore waters was determined at nine locations along the St. Lawrence Estuary and in the Gulf of St. Lawrence. The study area is characterized by gradients in the sedimentary particulate organic matter (POM) reactivity, bottom water oxygen concentrations, as well as benthic respiration rates. Based on pore water profiles we estimated the benthic diffusive fluxes of DON and DOC. Our results show that DON fluxed out of the sediments at significant rates (110 to 430 μmol m−2 d−1). DON fluxes were positively correlated with sedimentary POM reactivity and sediment oxygen exposure time (OET), suggesting direct links between POM quality, aerobic remineralization and the release of DON to the water column. DON fluxes were on the order of 30% to 64% of the total benthic inorganic fixed N loss due to denitrification, and often exceeded the diffusive nitrate fluxes into the sediments. Hence they represented a large fraction of the total benthic N exchange. This result is particularly important in light of the fact that DON fluxes are usually not accounted for in estuarine and coastal zone nutrient budgets. The ratio of the DON to nitrate flux increased from 0.6 in the Lower Estuary to 1.5 in the Gulf. In contrast to DON, DOC fluxes did not show any significant spatial variation along the Laurentian Channel (LC) between the Estuary and the Gulf (2100 ± 100μmol m−2 d−1), suggesting that production and consumption of labile DOC components proceed at similar rates, irrespective of the overall benthic characteristics and the reactivity of POM. As a consequence, the molar C/N ratio of dissolved organic matter (DOM) in pore water and the overlying bottom water varied significantly along the transect, with lowest C/N in the Lower Estuary (5–6) and highest C/N (> 10) in the Gulf. We observed large differences between the C/N of pore water DOM with respect to POM, and the degree of the C– versus –N element partitioning seems to be linked to POM reactivity and/or redox conditions in the sediment pore waters. Our results thus highlight the variable effects selective OM degradation and preservation can have on bulk sedimentary C/N ratios, decoupling the primary source C/N signatures from those in sedimentary archives. Our study further underscores that the role of estuarine sediments as efficient sinks of bioavailable nitrogen is strongly influenced by the release of DON during early diagenetic reactions, and that DON fluxes from continental margin sediments represent an important internal source of N to the ocean.

Mercury speciation in the Lower St. Lawrence Estuary

2000 ◽  
Vol 57 (S1) ◽  
pp. 138-147 ◽  
Author(s):  
Daniel Cossa ◽  
Charles Gobeil
Keyword(s):  
Water Column ◽  
Surface Waters ◽  
Feeding Habits ◽  
Mercury Speciation ◽  
Estuarine Sediments ◽  
Sediment Surface ◽  
Pore Waters ◽  
Mass Balance Calculation ◽  
Lawrence Estuary ◽  
St Lawrence Estuary

Mercury speciation was determined in the water column and sediment pore waters of the Lower St. Lawrence Estuary, and total Hg (HgT) was measured in seven biological species, including pelagic and demersal fish and crustaceans. In water, HgT concentrations ranged from 1.8 to 7.8 pM, with the highest levels in surface waters and the lowest in deep waters (1.8-2.9 pM). HgT concentrations in sediment pore waters were 10 times as high, with methyl mercury levels of 5.1-14.4 pM. Reactive Hg (HgR) generally accounted for around 20% of HgT in the water column and <30% in pore waters. The distribution of elemental Hg and HgR suggests that Hg(II) is reduced in surface waters and that inorganic Hg is mobilized during remineralization of organic matter at the sediment surface. In the biota, concentrations ranged between 0.05 and 0.89 nmol·g-1 (wet weight). Feeding habits and habitats account for these observations. Results suggest that the sediment is the main source of Hg contamination for the biota. A mass balance calculation showed that the Hg flux entering the lower estuary from the St. Lawrence River is equivalent to the amount buried in estuarine sediments.

scholarly journals Winter observations alter the seasonal perspectives of the nutrient transport pathways into the lower St. Lawrence Estuary

Ocean Science ◽  
2021 ◽  
Vol 17 (5) ◽  
pp. 1509-1525
Author(s):  
Cynthia Evelyn Bluteau ◽  
Peter S. Galbraith ◽  
Daniel Bourgault ◽  
Vincent Villeneuve ◽  
Jean-Éric Tremblay
Keyword(s):  
Vertical Mixing ◽  
Coast Guard ◽  
Tidal Mixing ◽  
Mixing Processes ◽  
Transport Pathways ◽  
Nutrient Analysis ◽  
Near Surface ◽  
Lawrence Estuary ◽  
Order Of Magnitude ◽  
St Lawrence Estuary

Abstract. The St. Lawrence Estuary connects the Great Lakes with the Atlantic Ocean. The accepted view, based on summer conditions, is that the estuary's surface layer receives its nutrient supply from vertical mixing processes. This mixing is caused by the estuarine circulation and tides interacting with the topography at the head of the Laurentian Channel. During winter when ice forms, historical process-based studies have been limited in scope. Winter monitoring has been typically confined to vertical profiles of salinity and temperature as well as near-surface water samples collected from a helicopter for nutrient analysis. In 2018, however, the Canadian Coast Guard approved a science team to sample in tandem with its ice-breaking and ship escorting operations. This opportunistic sampling provided the first winter turbulence observations, which covered the largest spatial extent ever measured during any season within the St. Lawrence Estuary and the Gulf of St. Lawrence. The nitrate enrichment from tidal mixing resulted in an upward nitrate flux of about 30 nmol m−2 s−1, comparable to summer values obtained at the same tidal phase. Further downstream, deep nutrient-rich water from the gulf was mixed into the subsurface nutrient-poor layer at a rate more than an order of magnitude smaller than at the head. These fluxes were compared to the nutrient load of the upstream St. Lawrence River. Contrary to previous assumptions, fluvial nitrate inputs are the most significant source of nitrate in the estuary. Nitrate loads from vertical mixing processes would only exceed those from fluvial sources at the end of summer when fluvial inputs reach their annual minimum.

scholarly journals Nutrient transport pathways in the Lower St. Lawrence Estuary: seasonal perspectives from winter observations

2021 ◽  
Author(s):  
Cynthia Evelyn Bluteau ◽  
Peter S. Galbraith ◽  
Daniel Bourgault ◽  
Vincent Villeneuve ◽  
Jean-Éric Tremblay
Keyword(s):  
Vertical Mixing ◽  
Coast Guard ◽  
Tidal Mixing ◽  
Mixing Processes ◽  
Transport Pathways ◽  
Nutrient Analysis ◽  
Near Surface ◽  
Lawrence Estuary ◽  
Order Of Magnitude ◽  
St Lawrence Estuary

Abstract. The St. Lawrence Estuary connects the Great Lakes with the Atlantic Ocean. The accepted view, based on summer conditions, is that the Estuary's surface layer receives its nutrient supply from vertical mixing processes. This mixing is caused by the estuarine circulation and tidal-upwelling at the Head of the Laurentian Channel (HLC). During winter when ice forms, historical process-based studies have been limited in scope. Winter monitoring has been typically confined to vertical profiles of salinity and temperature and near-surface water samples collected from a helicopter for nutrient analysis. In 2018, however, the Canadian Coast Guard approved a science team to sample in tandem with its icebreaking and ship escorting operations. This opportunistic sampling provided the first winter turbulence observations, which covered the largest spatial extent ever measured during any season within the St. Lawrence Estuary and Gulf. The nitrate enrichment from tidal mixing resulted in an upward nitrate flux of about 30 nmol m−2 s−1, comparable to summer values obtained at the same tidal phase. Further downstream, deep nutrient-rich water from the Gulf was mixed into the subsurface nutrient-poor layer at a rate more than an order of magnitude smaller than at the HLC. These fluxes were compared to the nutrient load of the upstream St. Lawrence River. Contrary to previous assumptions, fluvial nitrate inputs are the most significant source of nitrate in the Estuary. Nitrate loads from vertical mixing processes would only exceed those from fluvial sources at the end of summer when fluvial inputs reach their annual minimum.

Trace metal cycling in the Whau Estuary, Auckland, New Zealand

2008 ◽  
Vol 5 (4) ◽  
pp. 289 ◽  
Author(s):  
Michael J. Ellwood ◽  
Peter Wilson ◽  
Kay Vopel ◽  
Malcolm Green
Keyword(s):  
New Zealand ◽  
Water Column ◽  
Pore Water ◽  
Chemical Speciation ◽  
Particulate Material ◽  
Particulate Phase ◽  
Sediment Pore Water ◽  
Overlying Water ◽  
Metal Concentrations ◽  
Dissolved Phase

Environmental context. The accumulation of trace metals from urban runoff is a serious environmental concern. In the present paper we show that, in the case of the Whau Estuary, Auckland, New Zealand, there is a significant particulate Zn input, of which a significant amount of Zn is lost from the particulate phase into the dissolved phase within the water column, and via molecular diffusion across the water–sediment interface. The present study shows that changes in the chemical speciation of Zn, associated with changes in salinity, play a major role in regulating the recycling of this metal between the particulate and dissolved phases. Abstract. Dissolved Zn, Cd, Cu, Fe, and Pb concentrations were measured along a salinity gradient in the Whau Estuary, Auckland, New Zealand. We found a mid-salinity maximum in dissolved Zn and Cd concentrations, consistent with significant loss of these metals from the particulate phase into the dissolved phase. Changes in the chemical speciation of these two metals were coupled to changes in salinity and this was the major driver for Zn and Cd loss from particulate material. Contrastingly, Cu concentrations were conservative with salinity, whereas there was significant scavenging of Fe and Pb from the dissolved phase into the particulate phase. Analysis of sediment pore-water metal concentrations indicated a peak in Zn concentration within the suboxic layer. The peak occurred at a shallower depth than those for Mn and Fe. The concentration gradient across the sediment–water interface suggests that diffusional loss of Zn from the sediment pore water into the overlying water column was occurring. Conversely, the diffusion of Cu from the water column into the sediment pore water was likely to occur because pore-water Cu concentrations were lower than the overlying water column concentrations. The results from the present study show the importance of chemical speciation and the lability of metals attached to particulate material as potentially being a critical determinant on sediment metal concentrations.

scholarly journals Spatio-temporal Variation in Nutrient Profiles and Exchange Fluxes at the Sediment-Water Interface in Yuqiao Reservoir, China

2019 ◽  
Vol 16 (17) ◽  
pp. 3071 ◽  
Author(s):  
Wen ◽  
Wu ◽  
Yang ◽  
Jiang ◽  
Zhong
Keyword(s):  
Pore Water ◽  
Water Source ◽  
Water Soluble ◽  
Drinking Water Source ◽  
Eutrophic Lakes ◽  
Overlying Water ◽  
Total N ◽  
Yuqiao Reservoir ◽  
Nutrient Profiles ◽  
Main Component

Nutrients released from sediments have a significant influence on the water quality in eutrophic lakes and reservoirs. To clarify the internal nutrient load and provide reference for eutrophication control in Yuqiao Reservoir, a drinking water source reservoir in China, pore water profiles and sediment core incubation experiments were conducted. The nutrients in the water (soluble reactive P (SRP), nitrate-N (NO3−-N), nitrite-N (NO2−-N), and ammonium-N (NH4+-N)) and in the sediments (total N (TN), total P (TP) and total organic carbon (TOC)) were quantified. The results show that NH4+-N was the main component of inorganic N in the pore water. NH4+-N and SRP were higher in the pore water than in the overlying water, and the concentration gradient indicated a diffusion potential from the sediment to the overlying water. The NH4+-N, NO3−-N, and SRP fluxes showed significant differences amongst the seasons. The NH4+-N and SRP fluxes were significantly higher in the summer than in other seasons, while NO3−-N was higher in the autumn. The sediment generally acted as a source of NH4+-N and SRP and as a sink for NO3−-N and NO2−-N. The sediments release 1133.15 and 92.46 tons of N and P, respectively, to the overlying water each year.

scholarly journals Hydrochemistry of sediment pore water in the Bratsk reservoir (Baikal region, Russia)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
V. I. Poletaeva ◽  
E. N. Tirskikh ◽  
M. V. Pastukhov
Keyword(s):  
Pore Water ◽  
Ionic Composition ◽  
Water System ◽  
Water Reservoir ◽  
Environmental Parameters ◽  
Water Area ◽  
Pore Waters ◽  
Overlying Water ◽  
Major Ion ◽  
Bratsk Reservoir

AbstractThis study aimed to identify the factors responsible for the major ion composition of pore water from the bottom sediments of the Bratsk water reservoir, which is part of the largest freshwater Baikal-Angara water system. In the Bratsk reservoir, the overlying water was characterized as HCO3–Ca–Mg type with the mineralization ranging between 101.2 and 127.7 mg L−1 and pore water was characterized as HCO3–SO4–Ca, SO4–Cl–Ca–Mg and mixed water types, which had mineralization varying from 165.9 to 4608.1 mg L−1. The ionic composition of pore waters varied both along the sediment depth profile and across the water area. In pore water, the difference between the highest and lowest values was remarkably large: 5.1 times for K+, 13 times for Mg2+, 16 times for HCO3−, 20 times for Ca2+, 23 times for Na+, 80 times for SO42−, 105 times for Cl−. Such variability at different sites of the reservoir was due to the interrelation between major ion concentrations in the pore water and environmental parameters. The major factor responsible for pore water chemistry was the dissolution of sediment-forming material coming from various geochemical provinces. In the south part of the reservoir, Cl−, Na+ and SO42− concentrations may significantly increase in pore water due to the effect of subaqueous flow of highly mineralized groundwater.

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