Mercury concentrations and associations with dissolved organic matter are modified by water residence time in eastern Canadian lakes along a 30° latitudinal gradient

Abstract Coastal waters have strong gradients in dissolved organic matter (DOM) quantity and characteristics, originating from terrestrial inputs and autochthonous production. Enclosed seas with high freshwater input therefore experience high DOM concentrations and gradients from freshwater sources to more saline waters. The brackish Baltic Sea experiences such salinity gradients from east to west and from river mouths to the open sea. Furthermore, the catchment areas of the Baltic Sea are very diverse and vary from sparsely populated northern areas to densely populated southern zones. Coastal systems vary from enclosed or open bays, estuaries, fjords, archipelagos and lagoons where the residence time of DOM at these sites varies and may control the extent to which organic matter is biologically, chemically or physically modified or simply diluted with transport off-shore. Data of DOM with simultaneous measurements of dissolved organic (DO) nitrogen (N), carbon (C) and phosphorus (P) across a range of contrasting coastal systems are scarce. Here we present data from the Roskilde Fjord, Vistula and Öre estuaries and Curonian Lagoon; four coastal systems with large differences in salinity, nutrient concentrations, freshwater inflow and catchment characteristics. The C:N:P ratios of DOM of our data, despite high variability, show site specific significant differences resulting largely from differences residence time. Microbial processes seemed to have minor effects, and only in spring did uptake of DON in the Vistula and Öre estuaries take place and not at the other sites or seasons. Resuspension from sediments impacts bottom waters and the entire shallow water column in the Curonian Lagoon. Finally, our data combined with published data show that land use in the catchments seems to impact the DOC:DON and DOC:DOP ratios of the tributaries most.

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Water residence time in the Włocławek dam reservoir (the Vistula river, Poland) affects its macrozoobenthos structure

Annales de Limnologie - International Journal of Limnology ◽

10.1051/limn/2018016 ◽

2018 ◽

Vol 54 ◽

pp. 24

Author(s):

Daria Mimier ◽

Elżbieta Żbikowska ◽

Janusz Żbikowski

Keyword(s):

Organic Matter ◽

Residence Time ◽

Organic Matter Content ◽

Matter Content ◽

Bottom Fauna ◽

Water Residence Time ◽

Dam Reservoir ◽

Vistula River ◽

Chironomidae Larvae ◽

Potamothrix Hammoniensis

The aim of our study was to compare the macrozoobenthos structure as well as water and organic matter content of the bottom sediments of two hydrologically different zones of a strongly fluvial the Włocławek Dam Reservoir. Samples were collected from the Włocławek Dam Resevoir at six sites. Three of them were located in the upper, rheolimnic part (URP) of the reservoir and three others in its lower, limnetic part (LLP). Water transparency, sediment water content and organic matter content in the sediments were higher in the LLP. The higher number of taxa and diversity of macrozoobenthos were found in the URP of the reservoir. The density of bottom fauna was slightly higher in the LLP (90,990 ind. m−2) than in the UPR (73,486 ind. m−2), while the significantly higher biomass of macrozoobenthos was found in the URP of the reservoir (2314 g · m−2) than in the LLP (336 g · m−2). The dominant taxa of Oligochaeta and Chironomidae larvae did not show significant differences in the density between both zones. Some taxa were found only in the URP. In this zone, significantly higher densities of other taxa were observed. The only species with greater abundance in the LLP was Potamothrix hammoniensis (Oligochaeta). Due to the very short water residence time, the differences in the parameters under study between the URP and the LLP of the reservoir were smaller as well as the abundance of the macrozoobenthos was distinctly higher than in other reservoirs.

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Widespread variability in overnight patterns of ecosystem respiration linked to gradients in dissolved organic matter, residence time, and productivity in a global set of lakes

Limnology and Oceanography ◽

10.4319/lo.2014.59.5.1666 ◽

2014 ◽

Vol 59 (5) ◽

pp. 1666-1678 ◽

Cited By ~ 17

Author(s):

Steven Sadro ◽

Gordon W. Holtgrieve ◽

Christopher T. Solomon ◽

Gregory R. Koch

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Residence Time ◽

Ecosystem Respiration

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Circulation and oxygenation of the glacial South China Sea

10.5194/cp-2015-167 ◽

2016 ◽

Author(s):

Shuh-Ji Kao ◽

Tzu-Ling Chiang ◽

Da-Wei Li ◽

Yi-Chia Hsin ◽

Li-Wei Zheng ◽

...

Keyword(s):

Organic Matter ◽

South China Sea ◽

Residence Time ◽

Primary Productivity ◽

Circulation Pattern ◽

Water Residence Time ◽

Reducing Environment ◽

The Mean ◽

Monsoon Wind ◽

Wind Intensity

Abstract. Degree of oxygenation in intermediate water modulates the downward transferring efficiency of primary productivity (PP) from surface water to deep water for carbon sequestration, consequently, the storage of nutrients versus the delivery and sedimentary burial fluxes of organic matter and associated biomarkers. To better decipher the PP history of the South China Sea (SCS), appreciation about the glacial-interglacial variation of the Luzon Strait (LS) throughflow, which determines the mean residence time and oxygenation of water mass in the SCS interior, is required. Based on a well-established physical model, we conducted a 3-D modeling exercise to quantify the effects of sea level drop and monsoon wind intensity on glacial circulation pattern, thus, to evaluate effects of productivity and circulation-induced oxygenation on the burial of organic matter. Under modern climatology wind conditions, a 135 m sea level drop results in a greater basin closeness and a ~ 23 % of reduction in the LS intermediate westward throughflow, consequently, an increase in the mean water residence time (from 19 to 23 year). However, when the wind intensity was doubled during glacial low, the throughflow restored largely to reach a similar residence time (18.4 years) as today regardless its closeness. Comparing with present day SCS, surface circulation pattern in glacial model exhibits (1) stronger upwellings at the west off Luzon Island and the east off Vietnam, and (2) an intensified southwestward jet current along the western boundary of the SCS basin. Superimposed hypothetically by stronger monsoon wind, the glacial SCS conditions facilitate greater primary productivity. Manganese, a redox sensitive indicator, in IMAGES core MD972142 at southeastern SCS revealed a relatively reducing environment in glacial periods. Considering the similarity in the mean water residence time between modern and glacial cases, the reducing environment of the glacial southeastern SCS was thus ascribed to a productivity-induced rather than ventilation-induced consequence.

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Controls on dissolved organic matter (DOM) degradation in a headwater stream: the influence of photochemical and hydrological conditions in determining light-limitation or substrate-limitation of photo-degradation

Biogeosciences ◽

10.5194/bg-12-6669-2015 ◽

2015 ◽

Vol 12 (22) ◽

pp. 6669-6685 ◽

Cited By ~ 40

Author(s):

R. M. Cory ◽

K. H. Harrold ◽

B.T. Neilson ◽

G. W. Kling

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Residence Time ◽

Thermal Stratification ◽

Bottom Water ◽

Uv Exposure ◽

Low Flow ◽

Flow Conditions ◽

Photo Degradation ◽

High Attenuation

Abstract. We investigated how absorption of sunlight by chromophoric dissolved organic matter (CDOM) controls the degradation and export of DOM from Imnavait Creek, a beaded stream in the Alaskan Arctic. We measured concentrations of dissolved organic carbon (DOC), as well as concentrations and characteristics of CDOM and fluorescent dissolved organic matter (FDOM), during ice-free periods of 2011–2012 in the pools of Imnavait Creek and in soil waters draining to the creek. Spatial and temporal patterns in CDOM and FDOM in Imnavait Creek were analyzed in conjunction with measures of DOM degradation by sunlight and bacteria and assessments of hydrologic residence times and in situ UV exposure. CDOM was the dominant light attenuating constituent in the UV and visible portion of the solar spectrum, with high attenuation coefficients ranging from 86 ± 12 m−1 at 305 nm to 3 ± 1 m−1 in the photosynthetically active region (PAR). High rates of light absorption and thus light attenuation by CDOM contributed to thermal stratification in the majority of pools in Imnavait Creek under low-flow conditions. In turn, thermal stratification increased the residence time of water and DOM, and resulted in a separation of water masses distinguished by contrasting UV exposure (i.e., UV attenuation by CDOM with depth resulted in bottom waters receiving less UV than surface waters). When the pools in Imnavait Creek were stratified, DOM in the pool bottom water closely resembled soil water DOM in character, while the concentration and character of DOM in surface water was reproduced by experimental photo-degradation of bottom water. These results, in combination with water column rates of DOM degradation by sunlight and bacteria, suggest that photo-degradation is the dominant process controlling DOM fate and export in Imnavait Creek. A conceptual model is presented showing how CDOM amount and lability interact with incident UV light and water residence time to determine whether photo-degradation is "light-limited" or "substrate-limited". We suggest that degradation of DOM in CDOM-rich streams or ponds similar to Imnavait is typically light-limited under most flow conditions. Thus, export of DOM from this stream will be less under conditions that increase the light available for DOM photo-degradation (i.e., low flows, sunny days).

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The composition and distribution of semi-labile dissolved organic matter across the southwest Pacific

Biogeosciences ◽

10.5194/bg-16-105-2019 ◽

2019 ◽

Vol 16 (1) ◽

pp. 105-116 ◽

Cited By ~ 2

Author(s):

Christos Panagiotopoulos ◽

Mireille Pujo-Pay ◽

Mar Benavides ◽

France Van Wambeke ◽

Richard Sempéré

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Residence Time ◽

Surface Waters ◽

Euphotic Zone ◽

South Pacific ◽

Bacterial Degradation ◽

The South ◽

Energy Limitation ◽

South Pacific Gyre

Abstract. The distribution and dynamics of dissolved organic carbon (DOC) and dissolved combined neutral sugars (DCNS) were studied across an increasing oligotrophic gradient (18 to 22∘ S latitude) in the tropical South Pacific Ocean, spanning from the Melanesian Archipelago (MA) area to the western part of the South Pacific gyre (WGY), in austral summer as a part of the OUTPACE project. Our results show that DOC and DCNS concentrations exhibited no statistical differences between the MA and WGY areas (0–200 m: 47–81 µM C for DOC and 0.2-4.2 µM C for DCNS). However, due to a deepening of the euphotic zone, a deeper penetration of DOC was noticeable at 150 m of depth at the WGY area. Excess DOC (DOCEX) was determined as the difference between surface and deep-sea DOC values, and euphotic zone integrated stocks of both DOC and DOCEX were higher in the WGY than the MA area. Considering DOCEX as representative of semi-labile DOC (DOCSL), its residence time was calculated as the ratio of DOCSL to bacterial carbon demand (BCD). This residence time was 176±43 days (n=3) in the WGY area, about 3 times longer than in the MA area (Tr=51±13 days, n=8), suggesting an accumulation of semi-labile dissolved organic matter (DOM) in the surface waters of WGY. Average epipelagic (0–200 m) DCNS yields (DCNS × DOC−1) based on volumetric data were roughly similar in both areas, accounting for ∼2.8 % of DOC. DCNS exhibited a longer residence time in WGY (Tr=91±41 days, n=3) than in MA (Tr=31±10 days, n=8), further suggesting that this DCNS pool persists longer in the surface waters of the WGY. The accumulation of DOCEX in the surface waters of WGY is probably due to very slow bacterial degradation due to nutrient and/or energy limitation of heterotrophic prokaryotes, indicating that biologically produced DOC can be stored in the euphotic layer of the South Pacific gyre for a long period.

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Controls on dissolved organic matter (DOM) degradation in a headwater stream: the influence of photochemical and hydrological conditions in determining light-limitation or substrate-limitation of photo-degradation

Biogeosciences Discussions ◽

10.5194/bgd-12-9793-2015 ◽

2015 ◽

Vol 12 (13) ◽

pp. 9793-9838 ◽

Cited By ~ 7

Author(s):

R. M. Cory ◽

K. H. Harrold ◽

B. T. Neilson ◽

G. W. Kling

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Residence Time ◽

Thermal Stratification ◽

Bottom Water ◽

Uv Exposure ◽

Low Flow ◽

Flow Conditions ◽

Photo Degradation ◽

High Attenuation

Abstract. We investigated how absorption of sunlight by chromophoric dissolved organic matter (CDOM) controls the degradation and export of DOM from Imnavait Creek, a beaded stream in the Alaskan Arctic. We measured concentrations of dissolved organic carbon (DOC), as well as concentrations and characteristics of CDOM and fluorescent dissolved organic matter (FDOM), during ice-free periods of 2011–2012 in the pools of Imnavait Creek and in soil waters draining to the creek. Spatial and temporal patterns in CDOM and FDOM in Imnavait Creek were analyzed in conjunction with measures of DOM degradation by sunlight and bacteria and assessments of hydrologic residence times and in situ UV exposure. CDOM was the dominant light attenuating constituent in the UV and visible portion of the solar spectrum, with high attenuation coefficients ranging from 86 ± 12 m−1 at 305 nm to 3 ± 1 m−1 in the photosynthetically active region (PAR). High rates of light absorption and thus light attenuation by CDOM contributed to thermal stratification in the majority of pools in Imnavait Creek under low-flow conditions. In turn, thermal stratification increased the residence time of water and DOM, and resulted in a separation of water masses distinguished by contrasting UV exposure (i.e., UV attenuation by CDOM with depth resulted in bottom waters receiving less UV than surface waters). When the pools in Imnavait Creek were stratified, DOM in the pool bottom water closely resembled soil water DOM in character, while the concentration and character of DOM in surface water was reproduced by experimental photo-degradation of bottom water. These results, in combination with water column rates of DOM degradation by sunlight and bacteria, suggest that photo-degradation is the dominant process controlling DOM fate and export in Imnavait Creek. A conceptual model is presented showing how CDOM amount and lability interact with incident UV light and water residence time to determine whether photo-degradation is "light-limited" or "substrate-limited". We suggest that degradation, and thus export, of DOM in CDOM-rich streams or ponds similar to Imnavait is typically light-limited under most flow conditions.

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