224Ra/228Th disequilibrium in sediments of Lake Taihu: Implications of nitrogen fluxes across the sediment–water interface

2020 ◽  
Author(s):  
Xiaoyan shi ◽  
Xin luo ◽  
Jimmy.Jiu jiao ◽  
Jing huang ◽  
Meiqing lu ◽  
...  
Keyword(s):  
Lake Sediments ◽  
Molecular Diffusion ◽  
Lake Taihu ◽  
Inorganic Nitrogen ◽  
Eastern China ◽  
Water Remediation ◽  
Water Interface ◽  
Benthic Fluxes ◽  
Eutrophic Lakes ◽  
Nitrogen Fluxes

<p>Radium-224 /Thorium-228 (<sup>224</sup>Ra/<sup>228</sup>Th) disequilibrium in sediments is an advanced proxy of benthic processes and has been gradually used to quantify the fluxes and solute transfer across the sediment–water interface (SWI). This study makes the first attempt to explore the nitrogen fluxes across the SWI of Lake Taihu, the third largest and highly eutrophic freshwater lake in eastern China, based on the plumbing of <sup>224</sup>Ra/<sup>228</sup>Th disequilibrium in the lake sediments. The microscopic sediment cores (0-20 cm) were collected in different parts of the lake, and exchangeable <sup>224</sup>Ra and <sup>228</sup>Th in bulk sediments were measured. Dissolved inorganic nitrogen (DIN) in pore water and overlying lake water were also analyzed. Deficits of <sup>224</sup>Ra compared to its parent isotopes <sup>228</sup>Th were observed in the lake sediments, suggesting the influences of mixing processes. The deficits were relatively significant in the western and northern parts, which are consistent with the relative high-eutrophicated areas of the lake. One-dimensional (1D) radium-thorium diagenetic model in the sediment was used to estimate the benthic fluxes based on the <sup>224</sup>Ra deficits. Results show that the benthic fluxes of <sup>224</sup>Ra varied from -0.428 to 1.170 dpm cm<sup>-2</sup> d<sup>-1</sup>, and the bio-irrigation and molecular diffusion are considered to be the major factors. Specifically, in the severely eutrophicated area of the lake, the bio-irrigation predominates in benthic fluxes, reaching up to 97.1% of the deficit of <sup>224</sup>Ra. The DIN benthic fluxes were also quantified, leading to a flux estimation of 3.41 mol m<sup>-2</sup> d<sup>-1</sup>, which exceeds riverine input (2.63 mol m<sup>-2</sup> d<sup>-1</sup>) and the loading derived from lacustrine groundwater discharge (0.02~0.03 mol m<sup>-2</sup> d<sup>-1</sup>). This study reveals that sediment processes could be the vital factors for the lake nutrient loadings, and highly contribute to the lake eutrophication. This study is constructive for the water remediation and ecosystem restoration in Lake Taihu and other large eutrophic lakes elsewhere.</p>

scholarly journals Feedback Regulation between Aquatic Microorganisms and the Bloom-Forming Cyanobacterium Microcystis aeruginosa

2019 ◽  
Vol 85 (21) ◽  
Author(s):  
Meng Zhang ◽  
Tao Lu ◽  
Hans W. Paerl ◽  
Yiling Chen ◽  
Zhenyan Zhang ◽  
...  
Keyword(s):  
Energy Metabolism ◽  
Microcystis Aeruginosa ◽  
Lake Taihu ◽  
Inorganic Nitrogen ◽  
Microbial Community Composition ◽  
Nitrogen And Phosphorus ◽  
Content Type ◽  
Coculture System ◽  
Eukaryotic Microorganisms ◽  
Aquatic Microorganisms

ABSTRACT The frequency and intensity of cyanobacterial blooms are increasing worldwide. Interactions between toxic cyanobacteria and aquatic microorganisms need to be critically evaluated to understand microbial drivers and modulators of the blooms. In this study, we applied 16S/18S rRNA gene sequencing and metabolomics analyses to measure the microbial community composition and metabolic responses of the cyanobacterium Microcystis aeruginosa in a coculture system receiving dissolved inorganic nitrogen and phosphorus (DIP) close to representative concentrations in Lake Taihu, China. M. aeruginosa secreted alkaline phosphatase using a DIP source produced by moribund and decaying microorganisms when the P source was insufficient. During this process, M. aeruginosa accumulated several intermediates in energy metabolism pathways to provide energy for sustained high growth rates and increased intracellular sugars to enhance its competitive capacity and ability to defend itself against microbial attack. It also produced a variety of toxic substances, including microcystins, to inhibit metabolite formation via energy metabolism pathways of aquatic microorganisms, leading to a negative effect on bacterial and eukaryotic microbial richness and diversity. Overall, compared with the monoculture system, the growth of M. aeruginosa was accelerated in coculture, while the growth of some cooccurring microorganisms was inhibited, with the diversity and richness of eukaryotic microorganisms being more negatively impacted than those of prokaryotic microorganisms. These findings provide valuable information for clarifying how M. aeruginosa can potentially modulate its associations with other microorganisms, with ramifications for its dominance in aquatic ecosystems. IMPORTANCE We measured the microbial community composition and metabolic responses of Microcystis aeruginosa in a microcosm coculture system receiving dissolved inorganic nitrogen and phosphorus (DIP) close to the average concentrations in Lake Taihu. In the coculture system, DIP is depleted and the growth and production of aquatic microorganisms can be stressed by a lack of DIP availability. M. aeruginosa could accelerate its growth via interactions with specific cooccurring microorganisms and the accumulation of several intermediates in energy metabolism-related pathways. Furthermore, M. aeruginosa can decrease the carbohydrate metabolism of cooccurring aquatic microorganisms and thus disrupt microbial activities in the coculture. This also had a negative effect on bacterial and eukaryotic microbial richness and diversity. Microcystin was capable of decreasing the biomass of total phytoplankton in aquatic microcosms. Overall, compared to the monoculture, the growth of total aquatic microorganisms is inhibited, with the diversity and richness of eukaryotic microorganisms being more negatively impacted than those of prokaryotic microorganisms. The only exception is M. aeruginosa in the coculture system, whose growth was accelerated.

Effects of Fe addition on sediment P dynamics in a eutrophic lake

2021 ◽  
Author(s):  
Melanie Münch ◽  
Rianne van Kaam ◽  
Karel As ◽  
Stefan Peiffer ◽  
Gerard ter Heerdt ◽  
...  
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Surface Water ◽  
Water Column ◽  
Sediment Cores ◽  
Surface Water Quality ◽  
Water Interface ◽  
Eutrophic Lakes ◽  
Fe Addition

<p>The decline of surface water quality due to excess phosphorus (P) input is a global problem of increasing urgency. Finding sustainable measures to restore the surface water quality of eutrophic lakes with respect to P, other than by decreasing P inputs, remains a challenge. The addition of iron (Fe) salts has been shown to be effective in removing dissolved phosphate from the water column of eutrophic lakes. However, the resulting changes in biogeochemical processes in sediments as well as the long-term effects of Fe additions on P dynamics in both sediments and the water column are not well understood.</p><p>In this study, we assess the impact of past Fe additions on the sediment P biogeochemistry of Lake Terra Nova, a well-mixed shallow peat lake in the Netherlands. The Fe-treatment in 2010 efficiently reduced P release from the sediments to the surface waters for 6 years. Since then, the internal sediment P source in the lake has been increasing again with a growing trend over the years.</p><p>In 2020, we sampled sediments at three locations in Terra Nova, of which one received two times more Fe during treatment than the other two. Sediment cores from all sites were sectioned under oxygen-free conditions. Both the porewaters and sediments were analysed for their chemical composition, with sequential extractions providing insight into the sediment forms of P and Fe. Additional sediment cores were incubated under oxic and anoxic conditions and the respective fluxes of P and Fe across the sediment water interface were measured.</p><p>The results suggest that Fe and P dynamics in the lake sediments are strongly coupled. We also find that the P dynamics are sensitive to the amount of Fe supplied, even though enhanced burial of P in the sediment was not detected. The results of the sequential extraction procedure for P, which distinguishes P associated with humic acids and Fe oxides, as well as reduced flux of Fe(II) across the sediment water interface in the anoxic incubations, suggest a major role of organic matter in the interaction of Fe and P in these sediments.</p><p>Further research will include investigations of the role of organic matter and sulphur in determining the success of Fe-treatment in sequestering P in lake sediments. Based on these data in combination with reactive transport modelling we aim to constrain conditions for successful lake restoration through Fe addition.</p>

A Numerical Simulation Study of CO2 and N2 as Cushion Gas in an Underground Gas Storage

2021 ◽  
Author(s):  
Kang Tang ◽  
Xinwei Liao ◽  
Xiaoliang Zhao ◽  
Haojie Li ◽  
Xiaoxiao Li ◽  
...  
Keyword(s):  
Capital Investment ◽  
Molecular Diffusion ◽  
Supply And Demand ◽  
Diffusion Mechanism ◽  
Eastern China ◽  
Gas Storage ◽  
Scientific Basis ◽  
Good Choice ◽  
Underground Gas Storage ◽  
Efficient Operation

Abstract Underground gas storage (UGS) is a beneficial economic method of compensating for the imbalance between natural gas supply and demand, which is currently considered an important part of the gas chain. To reduce the capital investment of gas storage, the use of alternative gases as cushion gas is a good choice. However, the mixing of different gases in the UGS challenges the application of alternative gases(N2and CO2) as cushion gas. In this paper, we first conduct the thermodynamic analysis of two alternative gases, namely, N2and CO2. The feasibility of these two gases as cushion gas is discussed. Secondly, a gas storage located in Eastern China is selected. Based on the physical properties of the reservoir, a simulation model with coupled diffusion mechanism is conducted. Finally, the effect of molecular diffusion, gas category and ratio on the dynamic operation of UGS is studied. In addition, the CO2storage capacity under different operating parameters was also analyzed. This study provided a scientific basis for the efficient operation of UGS and the geological storage of CO2.

scholarly journals Sediment-water column fluxes of carbon, oxygen and nutrients in Bedford Basin, Nova Scotia, inferred from <sup>224</sup>Ra measurements

2013 ◽  
Vol 10 (1) ◽  
pp. 53-66 ◽  
Author(s):  
W. J. Burt ◽  
H. Thomas ◽  
K. Fennel ◽  
E. Horne
Keyword(s):  
Organic Matter ◽  
Nova Scotia ◽  
Water Column ◽  
Explicit Knowledge ◽  
Dissolved Inorganic Carbon ◽  
Chemical Constituents ◽  
Water Interface ◽  
Benthic Fluxes ◽  
Pore Waters ◽  
Overlying Water

Abstract. Exchanges between sediment pore waters and the overlying water column play a significant role in the chemical budgets of many important chemical constituents. Direct quantification of such benthic fluxes requires explicit knowledge of the sediment properties and biogeochemistry. Alternatively, changes in water-column properties near the sediment-water interface can be exploited to gain insight into the sediment biogeochemistry and benthic fluxes. Here, we apply a 1-D diffusive mixing model to near-bottom water-column profiles of 224Ra activity in order to yield vertical eddy diffusivities (KZ), based upon which we assess the diffusive exchange of dissolved inorganic carbon (DIC), nutrients and oxygen (O2), across the sediment-water interface in a coastal inlet, Bedford Basin, Nova Scotia, Canada. Numerical model results are consistent with the assumptions regarding a constant, single benthic source of 224Ra, the lack of mixing by advective processes, and a predominantly benthic source and sink of DIC and O2, respectively, with minimal water-column respiration in the deep waters of Bedford Basin. Near-bottom observations of DIC, O2 and nutrients provide flux ratios similar to Redfield values, suggesting that benthic respiration of primarily marine organic matter is the dominant driver. Furthermore, a relative deficit of nitrate in the observed flux ratios indicates that denitrification also plays a role in the oxidation of organic matter, although its occurrence was not strong enough to allow us to detect the corresponding AT fluxes out of the sediment. Finally, comparison with other carbon sources reveal the observed benthic DIC release as a significant contributor to the Bedford Basin carbon system.

Dissolved Inorganic Nitrogen Fluxes at Sediment-Water Interface in Yangtze Estuarine Tidal Flat

2013 ◽  
Vol 726-731 ◽  
pp. 288-295 ◽  
Author(s):  
Huan Guang Deng ◽  
Dong Qi Wang ◽  
Zhen Lou Chen
Keyword(s):  
Tidal Flat ◽  
Environmental Gradients ◽  
Inorganic Nitrogen ◽  
Yangtze Estuary ◽  
Water Interface ◽  
Dissolved Inorganic Nitrogen ◽  
Overlying Water ◽  
Spatial Differences ◽  
Estuary Sediment ◽  
Temporal And Spatial

Yangtze estuary data, collected over three years, indicates that the temporal and spatial distributions of the environmental gradients reflect complicated seasonal changes and spatial differences in the exchange flux of the dissolved inorganic nitrogen (DIN= NH4++ NO3-+ NO2-) across the sediment-water interface. Overall in northern sites of Yangtze estuary, sediment was a source of ammonium (NH4+) (-3.67~10.65 mmol·m-2·d-1) probably because of higher salinities. Sediment was a sink for NH4+ in southern sites (-18.45~3.33 mmol·m-2·d-1) during most years. The exchange behavior of nitrate (NO3-) showed temporal and spatial variation from the upper to lower estuary and ranged from-32.8 mmol·m-2·d-1 to 35.8 mmol·m-2·d-1. The interface exchange direction of ammonium was affected by NH4+ concentration, but the relationship between NO3- concentration and the direction of flux was not obvious. The concentration of nitrite (NO2-) was very low and its interface flux was not related to DIN concentration. Overall, the sediment of Yangtze Estuarine tidal flat was a source of DIN to overlying water in the spring, but a sink for DIN during the other three seasons of the year.

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