Dissolved Carbon Research Articles

Application of a novel ball-milled tourmaline-biochar composite materials for remediation of groundwater and bottom mud polluted with heavy metals

A novel composited material of ball-milled tourmaline-biochar (BM-TB) developed have a good adsorption capacity for heavy metal in the wider pH ranges of the aqueous solution. The adsorption capacity of BM-TB for Cd2+ was 142.6 mg/g when the solution pH was 4.0, and when pH was higher than 4.0. When the BM-TB was used to adsorb As, Cd, Cu and Pb from the groundwater, the adsorption percentage obtained 17.4 %, 93.6 %, 64.1 % and 95.9 %, respectively. When the BM-TB was used to remediate the bottom mud, BM-TB can the can significantly reduce the bioavailability of Cu, Cd, Pb, Zn and As and inhibit their enrichment into plant. Additionally, the novel material was remediated the bottom mud, it can amend the bottom mud and enhance the content of dissolved inorganic carbon (DIC), total nitrogen and rapidly available potassium, and significantly reduce the content of dissolved carbon (DC), dissolved organic carbon (DOC) and total dissolved nitrogen (TDN). In addition, the increase of CO2 emission flux was not significant, and gradually decreased with the increase of culture days. The present study provided not only a novel material, but also technology protocol for treatment of acidic wastewater and heavy metals contaminated groundwater and bottom mud.

Dissolved carbon in effluent of wastewater treatment plants and its potential impacts in the receiving karst river

The dissolved carbon cycling in river system fueled by wastewater treatment plant effluent have been a research hotspot. However, the composition of dissolved carbon (DC) in wastewater effluents from karst regions remains poorly understood, resulting in a lack of clarity regarding its impact on the dynamics of dissolved carbon in karst rivers. To address this knowledge gap, this study investigated variations of dissolved inorganic (DIC) and organic C (DOC) components in effluent in karst regions and preliminarily discussed their influence on the DC cycling in karst rivers. The results showed that bicarbonate (HCO3–) in WWTP effluents makes more than 90% of the total dissolved inorganic carbon (DIC). The partial pressure of aqueous CO2 (pCO2) of the effluent reached 14450 ± 10084μtam, and pCO2 level declined with increasing river distance from the effluent discharge, effluent acted as a strong CO2 emitter to the atmosphere. Stable carbon isotope and water chemistry evidence revealed that organic matter degradation made important contributions to the high CO2 concentrations in effluent. PHREEQC mixing simulation together with filed samples data indicated that the DIC species can be changed, and pCO2 increased in receiving karst river water after mixed with effluent. The dissolved organic carbon (DOC) of effluent contained humic-like and protein-tryptophan-like, both of them appeared important and recent autochthonous, which could interfere the distinguish the sources of DOC in receiving karst river water. Thus, these findings highlight that the effluent can be an essential factor for the changes of the karst riverine DC pool, which advance our understanding on karst riverine DC evolution under anthropogenic activities. As more than 30% of the earth surface in China, northern America, and Europe are covered by carbonate rocks, this study has relevant implications for other karst regions as it underscores the influence of WWTP effluents on the carbon cycle in karst rivers. Such information and knowledge are valuable for monitoring and managing effluent-receiving river in other karst regions in the world.

Climatic effect from oyster reef restoration in Spartina alterniflora invaded intertidal mudflat: From the perspective of CH4 and N2O production

Spartina alterniflora is a dominant invasive species along the coast of China. A surprising phenomenon that the oyster reef formation is substituting the S. alterniflora invasion, was recently observed in the west coast of Bohai Bay, North China. As the intertidal mudflat ecosystem is critical for coastal blue carbon, this paper aims to evaluate the climatic effect of the alternation from the perspective of potential CH4 and N2O production. The sediment geochemical properties and potential CH4 and N2O productions were therefore measured in sediments dominated by Spartina alterniflora (SA), oyster reef (OR), mixture of S. alterniflora and oyster reef (SA-OR) and bare mudflat (BM) at an intertidal mudflat. Meanwhile, sediment microbial community structure and function genes were also determined utilizing metagenome high-throughput sequencing technology. Our results indicated that the formation of oyster reef in S. alterniflora invaded intertidal mudflat might slightly reduce the sediment potential CH4 production and enhance the sediment potential N2O production. The oyster reef formation could alter the community composition of methanogens and the abundance of functional genes in methanogenesis, and transform the main pathway from methylotrophic to hydrogenotrophic methanogenesis in surface sediments. Metagenome sequencing revealed that the oyster reef formation may promote nitrification, inhibit dissimilatory nitrate reduction (DNRA) and nitrate assimilation functions, and reduce the abundance of nosZ genes. Mantel analysis showed that pH, soluble salt and dissolved carbon (DC) were the most important factors influencing the composition of microbial community. In general, our results imply that the growth of oyster reef in the S. alterniflora invaded area has opposing effects from the prospective of the potential CH4 and N2O production.

Rainfall partitioning and its influence on dissolved carbon and nitrogen fluxes through plant-soil system of a xerophytic shrub in northern China

Dissolved carbon (DC) and dissolved nitrogen (DN) driven by rainfall partitioning are critical components of carbon and nitrogen cycles in terrestrial ecosystems, especially in vegetation restoration areas. However, the variations of DC and DN fluxes in the input (throughfall and stemflow) and output (infiltration and surface runoff) water pathways of shrub ecosystem in drylands were poorly understood. In this study, the rainfall partitioning, dissolved organic and inorganic carbon (DOC and DIC) and DN fluxes in 52 rainfall events affecting a xerophytic shrub ecosystem on the heavily eroded Chinese Loess Plateau were measured over the 2019–2021 rainy seasons. The contributions of plants and topsoil (0–5 cm) to the variations in DC and DN fluxes along water pathways were quantified. We found that the DC and DN fluxes in throughfall accounted for more than 80% of net input flux, and the topsoil infiltration of DC and DN fluxes into soil layer below 5 cm depth were the most important output flux (contribution more than 98%). The mean event plant-derived DC and DN fluxes were 52.2 and 5.3 mg m−2, respectively, accounting for 45.4% and 12.2% of net DC and DN input fluxes (115.2 and 43 mg m−2). The soil-buffered DC and DN fluxes (455.6 and 29.5 mg m−2) were 3.95 and 0.69 times greater than the net input fluxes, respectively. The DC and DN fluxes in infiltration had the best correlation and increased most quickly with rainfall depth in the four different water pathways. Furthermore, the soil carbon content in 0–50 cm depth and soil nitrogen content in 0–10 cm depth in shrub-covered land was significantly higher than those in bare land (p < 0.05). This study highlights the important roles of rainfall partitioning in plant-sourced and soil-buffered DC and DN fluxes, which should be considered in soil carbon and nitrogen accumulation in drylands.

Influence mechanism of groundwater on the carbon cycle in alkaline lakes

The discharge of groundwater to the lake is a mixed process of two different kinds of water, and the hydrochemical action at the contact interface of them may lead to the migration and transformation of carbon. However, the input of carbon from groundwater to surface water is usually measured by the product of dissolved carbon (DC) concentration and water volume at present, and there are few reports on the physicochemical reactions in the mixing process. In this paper, taking Daihai Lake as an example, the principle of mass conservation and hydrogeochemical simulation were used to construct the carbon balance equation of the groundwater and lake water mixing zone, and the mechanism of carbon fixation and emission in the mixing process was analyzed. The results show that the precipitation of calcium carbonate was the main hydrochemical reaction controlling the migration and transformation of dissolved inorganic carbon (DIC) after mixing groundwater with alkaline lake water. A large amount of HCO3– in the lake was transformed into CaCO3 and CO2 under the action of groundwater. The total amount of DIC discharged by groundwater to Daihai Lake was 770 t/a. Due to the water chemical reaction at the interface between groundwater and lake water, the carbon removed by CaCO3 precipitation and CO2 emission was 645 t/a respectively. The mixture of the two kinds of water resulted in a net reduction of 520 t/a of DIC in Daihai Lake. Ca2+ concentration in groundwater was the main factor affecting DIC migration and transformation in the mixing process of the groundwater and lake water. With the increase of Ca2+ concentration in groundwater, more carbon in the form of HCO3– would be separated from lake water. This study has important significance for revealing the impact of groundwater on the lake carbon cycle and the role of groundwater in the global carbon cycle.

Extracellular Enzyme Activity and Stoichiometry Reveal Nutrient Dynamics during Microbially-Mediated Plant Residue Transformation

Extracellular enzymes are the major mediators of plant residue and organic matter decomposition in soil, frequently associated with microbial metabolic processes and the biochemical cycling of nutrients in soil ecosystems. However, the dynamic trends and driving factors of extracellular enzymes and their stoichiometry during plant residue transformation remain to be further studied. Here, we investigated the dynamics of extracellular enzymes and enzymatic stoichiometry in the “litter-soil” transformation interface soil (TIS) layer, an essential occurrence layer for microbially-mediated C transformation. The results indicated an unbalanced relationship between substrate resource supply and microbial metabolic demand. Microbial metabolism was limited by C (C/N-acquiring enzymes &gt; 1) and P (N/P-acquiring enzymes &lt; 1) throughout the observed stages of plant residue transformation. The initially higher extracellular enzyme activity reflected the availability of the active components (dissolved carbon (DC), nitrogen (DN), microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP)) in the substrate and the higher intensity of microbial metabolism. With the transformation of plant residues, the active fraction ceased to be the predominant microbial C source, forcing the secretion of C-acquiring enzymes and N-acquiring enzymes to obtain C sources and N nutrients from refractory substrates. Moreover, C/N-acquiring enzymes decreased, while C/P-acquiring enzymes and N/P-acquiring enzymes subsequently increased, which suggested that the microbial demand for N gradually increased and for P relatively decreased. Soil microorganisms can be forced into dormancy or intracellular mineralization due to the lack of substrate resources, so microbial biomass and extracellular enzyme activities decreased significantly compared to initial values. In summary, the results indicated that soil nutrients indirectly contribute to extracellular enzymes and their stoichiometry by affecting microbial activities. Furthermore, extracellular enzymes and their stoichiometry were more sensitive to the response of soil microbial biomass carbon.

Dynamics of soluble soil organic matter in Mediterranean maize-based forage system under organic and mineral fertilization

In Nitrate Vulnerable Zones (NVZ), the impact of animal effluent management on soil fertility is essential. A three-year study was carried out in a NVZ (Arborea, Central-western Sardinia, Italy), aiming to analyze the effect of different fertilization systems on soluble and total soil organic matter (SOM) within a silage maize-hay crop cropping system on sandy soil (Oxyaquic Xeropsamment). Four types of fertilization systems were compared: (i) cattle manure; (ii) cattle slurry; (iii) mineral; (iv) slurry + mineral. The water-extractable C and N content (WEC and WEN) from the topsoil (0–20 cm layer, the Ap1 horizon), the dissolved carbon (DC) and the dissolved nitrogen (DN) of the soil solution collected by disk lysimeters placed along the soil profiles, and the C content at the beginning and at the end of the experiment were determined.The seasonal dynamics of WEC in the topsoil seemed mainly associated with the timing of the fertilizer distribution. In the topsoil, WEC was larger under slurry than under mineral treatment. The DC was rather low in the deeper soil layers and did not show any variation due to the fluctuations of fertilizer distribution that were seemingly influenced by the groundwater table. The fertilization systems influenced the soil C inputs and, in turn, the SOM content. Manure promoted a higher C stock in the deeper soil layers among the organic fertilizers. However, the hay crop added with manure and slurry showed lower crop residues and, thus, C input than that added with mineral fertilizer. This result suggests that the management of these organic fertilizers should carefully consider their impact on the overall productivity of the studied cropping system in Mediterranean NVZ to avoid a potential limitation for soil C accumulation in the long term.

Effect of pyrolysis temperature of biochar on Cd, Pb and As bioavailability and bacterial community composition in contaminated paddy soil

To further investigate the effect of pyrolysis temperature on bioavailable Cd, Pb and As, as well as the bacterial community structure in multi-metal(loid) contaminated paddy soil, six types of biochar derived from wood sawdust and peanut shell at 300 °C, 500 °C and 700 °C were prepared and incubated with Cd, Pb and As contaminated paddy soil for 45 days. The results showed that adding biochar decreased bioavailable Cd by 31.3%− 42.9%, Pb by 0.61–56.1%, while bioavailable As changed from 9.68 mg kg−1 to 9.55–10.84 mg kg−1. We found that pyrolysis temperature of biochar had no significant effect on Cd bioavailability while Pb bioavailability decreased obviously with pyrolysis temperature raising. Biochar reduced the proportion of soluble and exchangeable Cd from 45.0% to 11.2–15.4% in comparison with the control, while no significant effect on the speciation of Pb and As. Wood sawdust biochar (WSBs) had more potential in decreasing bioavailable Cd and Pb than peanut shell biochar (PSBs). Although high-temperature biochar resulted a larger increase in bacterial species than low-and mid- temperature biochar, feedstock played a more important role in altering soil bacterial diversity and community composition than pyrolysis temperature. PSBs increased the diversity of soil bacteria through elevating soil dissolved carbon (DOC). Biochar altered soil bacterial community structure mainly by altering the level of soil electricity conductivity, DOC and bioavailable Cd. In addition, applying high-temperature PSBs increased the genus of bacteria that relevant to nitrogen cycling, such as Nitrospira, Nitrosotaleaceae and Candidatus_Nitrosotalea.

Dynamics and internal links of dissolved carbon in a karst river system: Implications for composition, origin and fate

Dissolved carbon (DC) deciphers biotic and abiotic processes in aquatic ecosystems, representing a critical component of global carbon cycling. However, underlying drivers of riverine DC dynamics and internal links have yet to be studied. Here, we investigated fluvial physicochemical characteristics, dissolved inorganic carbon (DIC) species, carbon dioxide (CO2) exchange, dissolved organic carbon (DOC) compositions and properties in a karst river system Qijiang, Southwest China. Carbonate dissolution combined with photosynthetic uptake could explain dynamics of DIC species. Carbon sequestration caused low-magnitude of partial pressure of aqueous CO2 (pCO2, 620.3 ± 1028.7 μatm) and water-air CO2 flux (F, 154.3 ± 772.6 mmol/m2/d), yielding an annual CO2 emission of 0.079 Tg CO2/y. Relatively high biological index (BIX, 0.77–0.96 on average) but low humification index (HIX, 0.67–0.78 on average) indicated notable autochthonous processes. Humic-like component was the predominant DOC, accounting for 39.0%-75.2% with a mean of 57.2% ± 6.17%. Meanwhile, tryptophan-like component (5.84% ± 2.31%) was also identified as collective DOC by parallel factor analysis (PARAFAC) across samples. Biological metabolism established internal linkages between DIC and DOC in the karst river system. Our findings highlighted biological process as a determinant for DC cycling in karst aquatic ecosystems.

Dynamics of Dissolved Carbon in Subalpine Forest Streams

Dissolved carbon (DC) in forest streams plays a crucial role in maintaining the structure and productivity of adjoining aquatic ecosystems as well as informing biogeochemical links between mountain forests and adjoining rivers. Nevertheless, the functions of forest stream DC dynamics are rarely incorporated into river management. To better understand the biogeochemical links between subalpine forests and adjoining streams, the seasonal dynamics of DC in 15 representative forest streams were investigated in a geographically fragile subalpine-gorge catchment in the upper reaches of the Yangtze River. Depending on stream characteristics and critical periods, the DC stocks in the streams ranged from 0.22 to 2.35 mg m−2 for total DC, from 0.10 to 1.66 mg m−2 for dissolved inorganic carbon (DIC), and from 0.12 to 1.27 mg m−2 for dissolved organic carbon (DOC). Moreover, the annual stocks of DC, DIC, and DOC were 1.01, 0.56, and 0.45 mg m−2, respectively. Correspondingly, the averaged export rates for DC, DIC, and DOC from the forest streams ranged from 0.27 to 1.98 mg s−1, from 0.24 to 1.48 mg s−1, and from 0.18 to 0.90 mg s−1, respectively, in the subalpine forest catchment. The annual export rates of total DC, DIC, and DOC were 1.06, 0.75, and 0.31 mg C s−1, respectively. In particular, the highest rates of export were 4.67, 3.53, and 1.34 mg s−1 for DC, DIC, and DOC, respectively, in the snowmelt period. The average ratios of DOC to DIC stock in the export water ranged from 0.23–2.41 for the 15 streams, and the average value was 0.85 during this one-year investigation. In addition, the maximum and minimum values of the DC stocks, their exports, and the DIC:DOC ratio were consistently observed during the snowmelt season and the late growing period. In summary, precipitation, temperature, water discharge rate, and sediment depth regulated the stocks and export rates of DC and its components. In general, forest streams are important links between the carbon biogeochemical cycle of subalpine forests and adjoining streams.

Elevation of NO3−-N from biochar amendment facilitates mitigating paddy CH4 emission stably over seven years

Biochar application into paddy is an improved strategy for addressing methane (CH4) stimulation of straw biomass incorporation. Whereas, the differentiative patterns and mechanisms on CH4 emission of straw biomass and biochar after long years still need to be disentangled. Considering economic feasibility, a seven-year of field experiment was conducted to explore the long-term CH4 mitigation effect of annual low-rate biochar incorporation (RSC, 2.8 t ha−1), with annual rice straw incorporation (RS, 8 t ha−1) and control (CK, with no biochar or rice straw amendment incorporation) as a comparation. Results showed that RSC mitigated CH4 emission while RS stimulated CH4 significantly (p < 0.05) and stably over 7 experimental years compared with CK. RSC mitigated 14.8–46.7% of CH4 emission compared with CK. In comparison to RSC, RS increased 111–950.5% of CH4 emission during 7 field experimental years. On the 7th field experimental year, pH was significantly increased both in RS and RSC treatment (p < 0.05). RSC significantly (p < 0.05) increased soil nitrate (NO3−-N) compared with RS while RS significantly (p < 0.05) increased dissolved carbon (DOC) compared to RSC. Soil NO3−-N inhibition on methanogens and promotion on methanotrophs activities were verified by laboratory experiment, while soil pH and DOC mainly promoted methanogens abundance. Significantly (p < 0.05) increased DOC and soil pH enhanced methanogens growth and stimulated CH4 emission in RS treatment. Higher soil NO3−-N content in RSC than CK and RS contributed to CH4 mitigation. Soil NO3−-N and DOC were identified as the key factors differentiating CH4 emission patterns of RS and RSC in 2019. Collectively, soil NO3−-N impacts on CH4 flux provide new ideas for prolonged effect of biochar amendment on CH4 mitigation after years.

Bacteriome depiction and the trophic status of the largest Northern highland lake from Andes system: Lago de Tota, Boyacá, Colombia.

Lago de Tota is the largest highland lake in Colombia and one of the most remarkable of Northern Andean Mountain range. This lake is under an anthropogenic-based eutrophication process as a consequence of non-sustainable agriculture practices developing nearby. Notable relationship between the trophic status and Bacteriome loop dynamics has been increasingly disclosed in lakes worldwide. We performed a 16S sequencing analysis to depict the bacterial community present and we inferred its potential gene function in Lago de Tota. Parameters for determining current trophic condition such as total nitrogen (TN), dissolved carbon (DOC), particulate organic matter (POM), and chlorophyll-a (chl-a) were measured. A total of 440 Operational Taxonomic Units (OTUs) arranged into 50 classes were identified based on V3-V4 regions of the 16S rRNA gene, harboring high-frequent likely found environmental classes such as Actinobacteria, Gammaproteobacteria, Bacteroidia, Acidimicrobia, and Verrucomicrobiae. A total of 26 bacterial classes configure most abundant predicted functional processes involved in organic matter decomposition (i.e., carbohydrate metabolism, amino acid metabolism, xenobiotic biodegradation, and energy metabolism). In general, Actinobacteria, Alphaproteobacteria, and Gammaproteobacteria show the highest potential gene functional contributors, although other low-frequent classes OTUs are also relevant in processes of carbohydrate metabolism, xenobiotic biodegradation, and energy metabolism. The Trophic State Index indicates an oligo-mesotrophic status, and additional variables measured (i.e., POM, DOC) suggest the increasing carbon accumulation. Results provide preliminary evidence for several bacteria groups related to eutrophication of Lago de Tota. Under this picture, we suggest that further studies for Bacteriome loop spatial-temporal description are essential to inform local water quality monitoring strategies.

Biochar Mitigated Paddy CH &lt;sub&gt;4&lt;/sub&gt; Emission Stably Over Seven Years with NO &lt;sub&gt;3&lt;/sub&gt; &lt;sup&gt;-&lt;/sup&gt;-N Elevation the Decisive Factor the Last Year

Biochar application into paddy is an improved strategy for addressing methane (CH4) stimulation of straw biomass incorporation. Whereas, the differentiative patterns and mechanisms on CH4 emission of straw biomass and biochar after long years are still blur. Considering economic feasibility, a seven-year of field experiment was conducted to explore the long-term CH4 mitigation effect of annual low-rate biochar incorporation (RSC, 2.8 t ha-1), with annual rice straw incorporation (RS, 8 t ha-1) and control (CK, with no biochar or rice straw amendment incorporation) as a comparation. Results showed that RSC mitigated CH4 emission while RS stimulated CH4 significantly (p < 0.05) and stably over 7 experimental years compared with CK. RSC mitigated 14.8 ~ 46.7% of CH4 emission compared with CK. In comparison to RSC, RS increased 111 ~ 950.5% of CH4 emission during 7 field experimental years. On the 7th field experimental year, pH was significantly increased both in RS and RSC treatment (p < 0.05). RSC significantly (p < 0.05) increased soil nitrate (NO3--N) while RS significantly (p < 0.05) increased dissolved carbon (DOC) when compared to each other. Soil NO3--N inhibitory on methanogens and promotion on methanotrophs was verified by laboratory experiment, while soil pH and DOC mainly promoted methanogens abundance. Significantly (p < 0.05) increased DOC and soil pH enhanced methanogens growth and stimulated CH4 emission in RS treatment. Higher soil NO3--N in RSC than CK and RS contributed to CH4 mitigation. Soil NO3--N and DOC were identified as the key factors differentiating CH4 emission patterns of RS and RSC in 2019. Collectively, soil NO3--N impacts on CH4 flux provide new ideas for prolonged effect of biochar on CH4 mitigation after years.

Vertical Distribution of Soil Dissolved Carbon and Its Influencing Factors in the Artificial Shelterbelt Irrigated with Saline Water in an Extreme Drought Desert

Dissolved carbon (DC) is the most active carbon fraction in soils. Vegetation restoration and reconstruction accelerate the carbon cycle in arid desert regions. Studying the DC distribution in soil profiles of artificial shelterbelt under saline irrigation can provide theoretical support and decision-making basis for artificial shelterbelt management, development, and utilization in arid desert areas. In this study, we took the artificial shelterbelts drip-irrigated with five different mineralization and one shifting sandy land (CK) along the Taklimakan Desert Highway as sampling plots, analyzed and discussed the vertical distribution characteristics of soil dissolved organic carbon (SDOC) and dissolved inorganic carbon (SDIC) in the 0-1 m profiles, and further analyzed their relationships among different factors. The results showed that SDOC and SDIC of CK and shelterbelts under 2.82 g·L-1 irrigation showed an "I" type distribution with a linear function relationship. The SDOC and SDIC of four other treatments showed a "Γ" type distribution with power function relationships. The fluctuation ability and contribution degree of SDOC and SDIC of different treatments in the surface layer were higher than those in the lower layers, and the fluctuation and contribution intensity of SDOC were higher than those of SDIC. Except for 2.82 g·L-1 treatment, the average SDOC contents of other treatments were 2-4 times those of SDIC. The average SDOC content of 2.82 g·L-1 treatment was lower than CK; other treatments were 3-5 times that of CK; and the average SDIC content of all treatments increased 15.0%-57.9% than CK. For the 0-5 cm layer, SDOC content increased with the irrigation water mineralization except the 2.82 g·L-1 treatment, but SDIC content firstly increased and then decreased with increasing mineralization, and that for the 4.82 g·L-1 treatment was highest. The SDOC and SDIC were positively correlated with EC, SOC, irrigation water mineralization, SIC, and soil moisture, for which they both showed a weak positive correlation with soil moisture; they were negatively correlated with soil depth. The SDOC and SDIC showed a weak negative correlation and a weak positive correlation with pH, respectively. In summary, the mineralization of irrigation water has an important impact on the vertical distribution of SDOC and SDIC, and their distribution also has close relationships with EC, SOC, SIC, soil moisture, and soil depth, which is of great significance for plantations in extremely drought deserts.

A national-scale data set for dissolved carbon and its spatial pattern in lakes and reservoirs across China

A dissolved carbon (DC) data set, including dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), from 224 lakes (513 stations) and 141 large reservoirs (337 stations) across China is presented in this study. In addition to DC, the data set also includes results for electrical conductivity (EC), total phosphorus (TP), chlorophyll-a and transparency. The impact of trophic status and EC gradient on DC concentration in water bodies are discussed. Results from our investigation indicate that DC in saline (EC > 1000 μS cm−1) water bodies (mean ± S.D, 297.13 ± 356.14 mg L−1, n = 186) are much higher than those in fresh water bodies (79.55 ± 199.34 mg L−1, n = 669). Similarly, eutrophic water bodies (n = 552) exhibited higher DC concentrations than mesotrophic (n = 215) and oligotrophic water bodies (n = 85); DC in lakes (158.445 ± 286.52 mg L−1, n = 513) was significantly higher than DC in reservoirs (37.83 ± 37.53 mg L−1, n = 337). All data used in this investigation is accessible online.

Determining nitrogen and carbon footprints to reveal regional gross primary productivity and differentiation characteristics in karst and non-karst watersheds, China

This study revealed the difference of regional gross primary productivity (GPP) in two different geomorphic provinces. We used δ13C, δ15N, and δ18O to trace carbon (C) and nitrogen (N) footprints in two different watersheds in China and analyzed differences in regional economic development. The total dissolved total nitrogen (DTN) and dissolved carbon (DC) deposition fluxes were 16.93 kg N·hm−2·yr−1 and 27.67 kg C·hm−2·yr−1 in the Chenqi watershed (karst) and 43.88 kg N·hm−2·yr−1 and 49.15 kgC·hm−2·yr−1 in the Xiangxi watershed (non-karst), respectively. Rainwater was more enriched in δ13C in the Xiangxi watershed (−14.4‰±1.89‰) than in the Chenqi watershed (−8.54 ± 3.87‰). In addition, DTN efflux was 244.22 and 941.61 kg N·hm−2·yr−1 and efflux of DC was 4157.86 and 9129.22 kg C·hm−2·yr−1 in surface water and groundwater in Chenqi watershed. And DTN efflux was 413.68 kg N·hm−2·yr−1 and DC was 2846.05 kg C·hm−2·yr−1 in Xiangxi watershed. Nitrate nitrogen (NO3−-N) and dissolved inorganic carbon (DIC) were the main forms of DTN and DC, respectively in both watersheds (both >84%). Carbonate reaction and groundwater were the main sources in the Chenqi watershed (contribution rates >30%), while atmospheric deposition and soil water were the main sources in the Xiangxi watershed (contribution rates are >22% and >28%, respectively). Using C and N footprints, we speculated that the direct causes of economic disparity in the two watersheds were nutrients lost with soil erosion which limited vegetation growth. Therefore, it is necessary to plant the suitable vegetation rationally. This study also provides a scientific basis for economic development and ecological environment coordinated sustainable development.

The prevalence of nonlinearity and detection of ecological breakpoints across a land use gradient in streams

Human activities can alter aquatic ecosystems through the input of nutrients and carbon, but there is increasing evidence that these pressures induce nonlinear ecological responses. Nonlinear relationships can contain breakpoints where there is an unexpected change in an ecological response to an environmental driver, which may result in ecological regime shifts. We investigated the occurrence of nonlinearity and breakpoints in relationships between total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and total dissolved carbon (DOC) concentrations and ecological responses in streams with varying land uses. We calculated breakpoints using piecewise regression, two dimensional Kolmogorov-Smirnov (2DKS), and significant zero crossings (SiZer) methods. We found nonlinearity was common, occurring in half of all analyses, with some evidence of multiple breakpoints. Linearity, by contrast, occurred in less than 14% of cases, on average. Breakpoints were related to land use gradients, with 34–43% agricultural cover associated with DOC and TDN breakpoints, and 15% wetland and 9.5% urban land associated with DOC and nutrient breakpoints, respectively. While these breakpoints are likely specific to our study area, our study contributes to the growing literature of the prevalence and location of ecological breakpoints in streams, providing watershed managers potential criteria for catchment land use thresholds.

Effects of Invasive Spartina alterniflora Loisel. and Subsequent Ecological Replacement by Sonneratia apetala Buch.-Ham. on Soil Organic Carbon Fractions and Stock

Background and Objectives: The rapid spread of invasive Spartina alterniflora Loisel. in the mangrove ecosystems of China was reduced using Sonneratia apetala Buch.-Ham. as an ecological replacement. Here, we studied the effects of invasion and ecological replacement using S. apetala on soil organic carbon fractions and stock on Qi’ao Island. Materials and Methods: Seven sites, including unvegetated mudflat and S. alterniflora, rehabilitated mangroves with different ages (one, six, and 10 years) and mature native Kandelia obovata Sheue, Liu, and Yong areas were selected in this study. Samples in the top 50 cm of soil were collected and then different fractions of organic carbon, including the total organic carbon (TOC), particulate organic carbon (POC), soil water dissolved carbon (DOC) and microbial biomass carbon (MBC), and the total carbon stock were measured and calculated. Results: The growth of S. alterniflora and mangroves significantly increased the soil TOC, POC, and MBC levels when compared to the mudflat. S. alterniflora had the highest soil DOC contents at 0–10 cm and 20–30 cm and the one-year restored mangroves had the highest MBC content. S. alterniflora and mangroves both had higher soil total carbon pools than the mudflat. Conclusions: The invasive S. alterniflora and young S. apetala forests had significantly lower soil TOC and POC contents and total organic carbon than the mature K. obovata on Qi’ao Island. These results indicate that ecological replacement methods can enhance long term carbon storage in Spartina-invaded ecosystems and native mangrove species are recommended.

Dissolved carbon fluxes in a vegetation restoration area of an eroding landscape

Dissolved carbon (DC) is a critical component of the global carbon (C) cycle. DC transport occurs through water-driven erosion and infiltration during rain storms. To explore the specific role of DC flux in topsoil C pool dynamics during rainfall events and predict the trend of ratios of lateral versus vertical DC efflux from topsoil in a vegetation restoration area, we measured the major DC fluxes at four runoff plots, during rainfall events in an eroding soil landscape on the Chinese Loess Plateau. The results show that topsoil vertical DC efflux into deep soil layers accounted for approximately 98.7 (±1.0) % of the total dissolved carbon efflux in plots with vegetation versus 95.3% in a plot without vegetation. The carbon sequestration capacity of the top soil would be underestimated by up to 38 (±5) % if the vertical DC efflux was omitted. The ratios of lateral versus vertical DC efflux tended to increase with rainfall intensity. The results of this study improve understanding of the carbon cycle processes during rainfall events in general and estimation of carbon sequestration rates in vegetation restoration regions such as the Chinese Loess Plateau in particular.

Migration and transformation of dissolved carbon during accumulated cyanobacteria decomposition in shallow eutrophic lakes: a simulated microcosm study.

The decomposition processes of accumulated cyanobacteria can release large amounts of organic carbon and affect the carbon cycling in shallow eutrophic lakes. However, the migration and transformation mechanisms of dissolved carbon (DC) require further study and discussion. In this study, a 73-day laboratory microcosm experiment using suction samplers (Rhizon and syringe) was conducted to understand the migration and transformation of DC during the cyanobacteria decomposition. The decomposition of cyanobacteria biomass caused anoxic and reduction conditions, and changed the acid-base environment in the water column. During the early incubation (days 0–18), a large amount of cyanobacteria-derived particulate organic matter (POM) was decomposed into dissolved organic carbon (DOC) in the overlying water, reaching the highest peak value of 1.82 g L−1 in the treatment added the high cyanobacteria biomass (470 g). After 18 days of incubation, the mineralization of increased DOC to dissolved inorganic carbon (DIC) maintained a high DIC level of overlying water in treatments added cyanobacteria biomass. The treatment added the medium cyanobacteria biomass (235 g) presented the lower DOC/total dissolved carbon ratio than the high cyanobacteria biomass associated with the lower mineralization from DOC to DIC. Due to the concentration differences of DIC at water-sediment interface, the main migration of DIC from pore water to overlying water occurred in the treatment without added cyanobacteria biomass. However, the treatments added the cyanobacteria biomass presented the obvious diffusion of DOC and the low migration of DIC at the water-sediment interface. The diffusive fluxes of DOC at the water-sediment interface increased with the cyanobacteria biomass added, reaching the maximum value of 411.01 mg/(m2·d) in the treatment added the high cyanobacteria biomass. In the overlying water, the group added the sediment and medium cyanobacteria biomass presented a faster degradation of cyanobacteria-derived POM to DOC and a higher mineralization level of DOC to DIC than added the medium cyanobacteria biomass without sediment. Therefore, during accumulated cyanobacteria decomposition, the biomass of accumulated cyanobacteria and sediment property can influence the migration and transformation of DC, playing an important role in carbon cycling in shallow eutrophic lakes.