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Erosion and Carbon Dynamics: Conclusions and Perspectives
Published in Eric J. Roose, Rattan Lal, Christian Feller, Bernard Barthès, Bobby A. Stewart, Soil Erosion and Carbon Dynamics, 2005
Eric Roose, Michel Meybeck, Rattan Lal, Christian Feller
Numerous data have been presented about the C losses by various erosion processes at the scale of conventional runoff plots (100 m2) in tropical and Mediterranean areas (Roose and Barthès; Barthès et al.; Blanchart et al.; Morsli et al.; Bilgo et al.; Rodriguez et al.). Compared with biomass production (1 to 20 t ha−1 yr−1), losses of particulate organic carbon (POC) by hydric erosion are moderate: 1 to 50 kg C ha−1 yr−1 when the soil is effectively protected by vegetative cover of residue, 50 to 500 kg C ha−1 yr−1 under clean weeded crops, burned or overgrazed grasslands, and > 1000 kg C ha−1 yr−1 on bare plots under erosion-prone conditions (very steep slopes, intensive and abundant rainstorms). The POC losses mainly depend on the amount of soil eroded and on SOC concentration of the soil surface. Land-use changes cause more drastic changes in soil erosion and SOC stocks than POC erosion because when erosion increases, the C content of sediments decreases, through reduction in interrill erosion and increase in rill erosion.
Ancillary Substances
Published in Robert H. Kadlec, Treatment Marshes for Runoff and Polishing, 2019
A wide spectrum of carbon compounds exists in either dissolved or particulate forms in aquatic systems. The usual dividing line is a 0.45-µm filter. The following distinctions are made as a result of analytical methods: TC = Total Carbon (includes all dissolved and suspended forms)PC = Particulate Carbon (includes organic and inorganic forms)DC = Dissolved Carbon (includes organic and inorganic forms)IC = Inorganic Carbon (includes all dissolved and suspended forms)DIC = Dissolved Inorganic Carbon (usually comprised of CO2, carbonate and bicarbonate)TOC = Total Organic Carbon (includes all dissolved and suspended forms)DOC = Dissolved Organic CarbonPOC = Particulate Organic CarbonNDOC = Non-Dissolved Organic CarbonVOC = Volatile Organic Carbon (Compounds)
Zooplankton response to organic carbon content in a shallow lake covered by macrophytes
Published in Chemistry and Ecology, 2020
Magdalena Bowszys, Bożena Jaworska, Marek Kruk, Anna Goździejewska
Total organic carbon (TOC) occurs in particulate or dissolved forms in water bodies. Dissolved organic carbon (DOC) is a primary regulator of many physical, chemical and biological characteristics of lakes [e.g. 8,9]. DOC content in water can originate from the microbiological degradation of organic matter produced in lakes, but mainly it derives from DOC released by aquatic organisms, i.e. algal exudation and excretion by zooplankton and other aquatic animals [10,11]. Some amounts of DOC are also released into water from zooplankton sloppy feeding or from poorly digested faeces [12]. Phytoplankton DOC sources can be particularly important in eutrophic lakes. During algal blooms, up to 60% of the carbon assimilated during photosynthesis can be released extracellularly into the water as DOC [13,14]. However, in aquatic ecosystems dominated by submerged vascular plants (i.e. macrophytes), phytoplankton can be a less important source of DOC than macrophytes which are known to release substantial amounts of dissolved organic carbon into the environment [15]. Apart from internal organic carbon sources, organic matter can also originate from watersheds, although terrestrial dissolved organic carbon is much less efficiently metabolised in aquatic ecosystem than that produced in lakes [10,11]. Particulate organic carbon (POC) is a heterogeneous mix of living planktonic organisms and organic detritus. In shallow lakes, decreases in POC are expected in habitats covered by plants because of the clear negative correlation between the abundance of phytoplankton and submerged macrophytes [16] and also the increased sedimentation of algae and detritus from reduced turbulence in areas with vegetation [17]. This effect can be enhanced by grazing zooplankton that are usually more abundant in plant-covered areas, since submerged vegetation provides refuge from fish predation to planktonic crustaceans [18].
Possible pathways for mercury methylation in oxic marine waters
Published in Critical Reviews in Environmental Science and Technology, 2022
Kang Wang, Guangliang Liu, Yong Cai
As aforementioned, contradictory results were found in testing the hypotheses of anaerobic microbial Hg methylation in anoxic microniches within oxic waters, thus providing some evidence but not reaching convincing conclusions in verifying this pathway of Hg methylation in oxic seawater. Future research is warranted, especially a combination of incubation experiments determining Hg methylation, occurrence and expression of the hgcAB genes, and measurements of MeHg concentrations in the field, to further elucidate the role of this pathway in marine MeHg production. It is not surprising if anaerobic Hg methylation in anoxic microniches were confirmed, given the molecular evidence of SRB found in the ocean’s three major oxygen minimum zone (OMZs, with DO < 20–45 μmol kg−1 (Gilly et al., 2013)) (Canfield et al., 2010; Carolan et al., 2015; Fuchs et al., 2005) likely in anoxic microenvironments like millimeter scale marine snow (Shanks & Reeder, 1993). Modeling study by Bianchi et al. (2018) suggests that sulfate reduction in large marine particles has a contribution of 0.1% of particulate organic carbon (POC) respiration throughout the tropics, coastal regions and the subarctic North Pacific, and up to ∼1% of POC decomposition in OMZs. If Hg methylation were coupled with the sulfate reduction in anoxic particles, the contribution variation may partly explain the large variability in correlations between Hg methylation and OM remineralization observed across the world oceans (Bowman et al., 2020a; Mason et al., 2012). Meanwhile, the heterogeneity of sulfate reduction contribution also suggests that the to-be-verified methylation pathway may have totally different contributions in forming seawater MeHg in different regions and depths. If this pathway proves true in the future, it is important to quantify its contribution in forming MeHg in marine waters from different regions and depths across the world ocean.
Effect of solar radiation on natural organic matter composition in surface waters and resulting impacts on drinking water treatment
Published in Environmental Technology, 2023
I. Slavik, D. Kostrowski, W. Uhl
Since there was no change in DOC without radiation, it is assumed that the decrease in total DOC is due to a photochemical decomposition of CO2 or due to the formation of particulate organic carbon. This conclusion is supported by the fact that the concentration of viable microorganisms was considerably lower in the irradiated water samples, as shown in Figure 4. To summarise, simulated solar radiation results in the decomposition of humic substances into smaller molecules, that is, building blocks and neutrals, and to a certain degree to CO2. This corresponds with results from the literature where photochemical mineralisation of DOM was observed. Based on their investigation at Lake Skjervatjern in western Norway, Salonen and Vähätalo [37] assumed an epilimnetic light mineralisation of DOM of 25 mg C m–3 d–1 in this region. This is 0.75 mg C L–1 in 30 days, which is lower than the 2 mg C L–1 observed in this study. The lower mineralisation rate in Lake Skjervatjern can probably be attributed to the more northerly position of the study area. Amon and Benner [36] determined an unusually high photochemical DOC consumption of up to 0.05 mg C L–1 h–1 in investigations using water from the Rio Negro. Assuming 10 h of sunlight per day, this rate results in a mineralisation of 15 mg C L–1 in 30 days, which is more than seven times the mineralisation found in our experiments. Once again, the southern location and the associated intensity of solar radiation can be the cause of this effect. In bottle experiments, Molot and Dillon [35] found that up to 50% of DOC can be transferred to inorganic C over 6–11 days of solar radiation. Their experiments were performed using water from headwater streams of Dickie Lake, Ontario, which are characterised by a high DOC concentration of about 18 mgL–1. Unfortunately, the measurement of inorganic C is not described there in a comprehensible manner. Brinkmann et al. [33] observed a decrease in DOC of up to 1 mg L–1 in 24 h, which is about 3 mg L–1 in 72 h, due to simulated solar irradiance in the summer in Germany and assumed that this was primarily caused by mineralisation because the formation of bigger entities or small particles by photocoagulation could not be detected.