Deciphering dissolved inorganic carbon dynamics in Xiangshan Bay: isotopic constraints on sources, hydrodynamic controls, and anthropogenic influences

Drainage from coal mines, where carbonate dissolution is driven by sulfuric acid, can result in a net transfer of geologically-bound carbon to the atmosphere. The flux and downstream evolution of dissolved inorganic carbon (DIC) is presented for two coal mine sites that discharge high concentrations of DIC (3.7–4.5 mM C) producing a total flux of DIC from the mine from 13 to 249 kg-C/year (18–364 metric tons of CO2/year). More than 65 % of the total DIC is lost via CO2 evasion with the remaining DIC is exported downstream as dissolved species. The fate of the DIC depends upon the pH of the water which is controlled by evasion of CO2, the concentration of pre-existing alkalinity, carbonate precipitation and dissolution, and metal hydrolysis reactions. The CO2 concentrations and fluxes from the study sites are comparable to those estimated from literature data for other coal mine sites in the Appalachian region. The total flux estimated from a dataset of 140 coal mines was comparable in magnitude to the CO2 emissions from a small coal-fired power plant. The extent of CO2 degassing from mine waters is poorly constrained because (1) flux estimates can be biased low when acid waters are excluded in alkalinity-based estimates; (2) flux estimates can be biased high if non-carbonate alkalinity is present in the mine waters; and (3) mine waters react rapidly following discharge hampering the measurement process. The study sites presented illustrate the impact of coal mining as an anthropogenic influence on carbon cycling; however, more data are necessary to fully estimate the importance of this impact on regional scales.

The biogeochemistry of inorganic carbon and nutrients in the Pearl River estuary and the adjacent Northern South China Sea

The mangrove ecosystem serves as a vital habitat for coastal flora and fauna while playing a crucial role in storing and sequestering carbon as part of global carbon cycles. Therefore, it is imperative to evaluate the carbon dynamics, encompassing storage and sequestration, within mangrove ecosystems and their interconnectedness with natural climate fluctuations and anthropogenic influences, including land-use and land-cover changes (LULCC). Although there has been an increase in monitoring data and literature on mangrove carbon dynamics over the past two decades, there is still limited understanding regarding how climate variability, when combined with anthropogenic drivers, moderates the resilience of carbon storage and sequestration in mangroves. This study aims to build upon and enhance the previous systematic review conducted by Sasmito et al. (2019). Our specific objectives involve collating more recent literature published since 2018 and strengthening the analysis of carbon loss and recovery in tree biomass across different species, as well as its correlation with local and regional climate variations. Additionally, we will explore the impact of various types of land-use and land-cover changes on mangrove forests. Our systematic review will focus on field-based data collected from the Asia Pacific mangrove region, which represents the world’s largest and most diverse mangrove ecosystem and has been extensively studied in comparison to other regions, as indicated by previous systematic reviews. To gather relevant literature, we will conduct comprehensive searches across various databases, including Scopus, Web of Science, and Google Scholar. The structure established by Sasmito et al. (2019) for literature search, screening, and data extraction will be adopted. Data analysis will involve comparing carbon storage and sequestration under locally and regionally varying climatic conditions and anthropogenic influences. Furthermore, we will employ geographical mapping techniques to visualize species distribution and diversity within the Asia Pacific region, while also estimating carbon storage and recovery capacities.

Most transboundary rivers and their wetlands are subject to considerable anthropogenic pressures associated with multiple and often conflicting uses. In the Eastern Mediterranean such systems are also particularly vulnerable to climate change, posing additional challenges for integrated water resources management. Comprehensive measurements of the optical signature of colored dissolved organic matter (CDOM) were combined with measurements of river discharges and water physicochemical and biogeochemical properties, to assess carbon dynamics, water quality, and anthropogenic influences in a major transboundary system of the Eastern Mediterranean, the Evros (or, Марица or, Meriç) river and its Ramsar protected coastal wetland. Measurements were performed over three years, in seasons characterized by different hydrologic conditions and along transects extending more than 70 km from the freshwater end‐member to two kilometers offshore in the Aegean Sea. Changes in precipitation, anthropogenic dissolved organic matter (DOM) inputs from the polluted Ergene tributary, and the irregular operation of a dam were key factors driving water quality, salinity regimes, and biogeochemical properties in the Evros delta and coastal waters. Marsh outwelling affected coastal carbon quality, but the influence of wetlands was often masked by anthropogenic DOM contributions. A distinctive five‐peak CDOM fluorescence signature was characteristic of upstream anthropogenic inputs and clearly tracked the influence of freshwater discharges on water quality. Monitoring of this CDOM fluorescence footprint could have direct applications to programs focusing on water quality and environmental assessment in this and other transboundary rivers where management of water resources remains largely ineffective.

Enhanced Rock Weathering (ERW) - the addition of crushed alkaline rocks onto agricultural land - has emerged as a promising approach for atmospheric carbon dioxide removal (CDR). Evaluating the global and UK CDR potential and environmental implications of ERW prior to widespread implementation is essential. Accurate quantification of CDR via ERW requires an understanding of the baseline CO2 flux due to existing natural and anthropogenic influences on weathering. Understanding these baseline weathering fluxes is also important for predicting the capacity of UK rivers to accommodate additional material from ERW, because natural weathering controls river geochemistry.  However, uncertainty exists regarding baseline values and their variability across UK catchments, which have varying lithological, climate, and anthropogenic influences. In this study, we quantify the annual baseline CO2 consumption due to natural weathering in the UK using historical river geochemical data, and a geochemical inversion technique to separate fluxes derived from weathering of silicate and carbonate rocks.Results reveal that baseline silicate and carbonate weathering contributes up to 6.3 Mt CO2 yr-1 as dissolved inorganic carbon (DIC) to UK rivers combined. Within this total, silicate weathering, vital for long- term carbon removal, contributes up to 1.3 Mt CO2 yr-1. Normalising the CDR by catchment area highlights significant variability across the UK, with Midlands and southeastern catchments exhibiting the highest weathering CO2 yields. Increased DIC from baseline weathering in southeastern catchments brings riverine calcite saturation close to saturation thresholds. Consequently, these heightened weathering rates are expected to limit the rivers’ capacity to accommodate additional DIC from ERW. Conversely, our findings suggest that Midlands catchments may offer optimal conditions for ERW implementation- displaying favourable weathering conditions and increased riverine storage capacity to store ERW by-products. Therefore, the suitability of a catchment for ERW application hinges on achieving a balance between favourable weathering conditions and adequate riverine capacity for surplus weathering products. Consequently, a uniform approach to EW implementation may be unsuitable for widespread use in the UK. Instead, we propose a catchment specific approach, involving calculations of the potential river chemistry impacts based on intended spreading rate and arable land area.  Although more demanding, this ensures the safe implementation of ERW without compromising riverine chemical thresholds.The baseline weathering CDR (6.3 MtCO2 yr-1) aligns with the lower end of that proposed achievable through widespread ERW implementation across the UK (6 -30 Mt CO2 yr-1)1. If this anticipated CDR is achieved and evenly distributed within UK rivers as DIC, the background riverine DIC flux would at least double. However, given the heterogenous distribution of arable land, our findings suggest that catchments with extensive arable land may experience a substantial DIC flux from ERW. This flux, especially in regions with high baseline values, could trigger carbonate precipitation, potentially reducing CDR potential by 16- 27%2.References1Kantzas et al (2022) ‘Substantial Carbon Drawdown Potential from Enhanced Rock Weathering in the United Kingdom’, 2Harrington et al (2023), Implications for the Riverine Response to Enhanced Weathering to CO2 Removal in the UK, 

Assessment of carbon flux gradients and dominant processes in a subtropical highly urbanized coastal ecosystem

Nutrient and carbon dynamics in river ecosystems are shifting, and climate change is likely a driving factor; however, some previous studies indicate anthropogenic modification of natural resources may supersede the effects of climate. To understand temporal changes in river ecosystems, consideration of how these agents act independently and collectively to affect watershed biogeochemistry is necessary. Through the Georgia Coastal Ecosystems Long‐Term Ecological Research Project, we assessed nutrient (phosphorus, nitrogen, silicate) and carbon dynamics, with specific regard to import and export, in the Altamaha River Basin from 2000 to 2012. This is the first study in the region to document the biogeochemical patterns in the Altamaha's four main tributaries, the Little Ocmulgee, Ocmulgee, Oconee, and Ohoopee rivers, and the relationships between biogeochemistry and historical precipitation and discharge patterns as well as agricultural and population census data. As discharge patterns are a primary driver of nutrient loads, we determined that water use was a dominant factor in the shifting ecosystem dynamics. Dissolved inorganic nitrogen loads were primarily driven by population density and dissolved inorganic phosphorus loads were strongly influenced by livestock biomass. Taken together, we conclude that both the transportation and biogeochemical cycling of nutrients within the Altamaha River Watershed were highly impacted by anthropogenic influences, which were then further exacerbated by continued climate change. Furthermore, the N‐ and P‐loads in the Altamaha River and tributaries were dominated by dissolved organic nitrogen and dissolved organic phosphorus, emphasizing a need to further study the bioavailability of these species and the mechanisms driving their potential ecological impacts.

Abstract. Floodplains are important biogeochemical reactors during fluvial transport of carbon and nutrient species towards the oceans. In the tropics and subtropics, pronounced rainfall seasonality results in highly dynamic floodplain biogeochemistry. The massive construction of dams, however, has significantly altered the hydrography and chemical characteristics of many (sub)tropical rivers. In this study, we compare organic-matter and nutrient biogeochemistry of two large, contrasting floodplains in the Zambezi River basin in southern Africa: the Barotse Plains and the Kafue Flats. Both systems are of comparable size but differ in anthropogenic influence: while the Barotse Plains are still in large parts pristine, the Kafue Flats are bordered by two hydropower dams. The two systems exhibit different flooding dynamics, with a larger contribution of floodplain-derived water in the Kafue Flats and a stronger peak flow in the Barotse Plains. Distinct seasonal differences have been observed in carbon and nutrient concentrations, loads, and export and retention behavior in both systems. The simultaneous retention of particulate carbon and nitrogen and the net export of dissolved organic and inorganic carbon and nitrogen suggested that degradation of particulate organic matter was the dominant process influencing the river biogeochemistry during the wet season in the Barotse Plains and during the dry season in the Kafue Flats. Reverse trends during the dry season indicated that primary production was important in the Barotse Plains, whereas the Kafue Flats seemed to have both primary production and respiration occurring during the wet season, potentially occurring spatially separated in the main channel and on the floodplain. Carbon-to-nitrogen ratios of particulate organic matter showed that soil-derived material was dominant year-round in the Barotse Plains, whereas the Kafue Flats transported particulate organic matter that had been produced in the upstream reservoir during the wet season. Stable carbon isotopes suggested that inputs from the inundated floodplain to the particulate organic-matter pool were important during the wet season, whereas permanent vegetation contributed to the material transported during the dry season. This study revealed effects of dam construction on organic-matter and nutrient dynamics on the downstream floodplain that only become visible after longer periods, and it highlights how floodplains act as large biogeochemical reactors that can behave distinctly differently from the entire catchment.

Long-term trends and anthropogenic forcing of surface ocean carbon storage and acidification.

BackgroundFire occurrence is influenced by interactions between human activity, climate, and fuels that are difficult to disentangle but crucial to understand, given fire’s role in carbon dynamics, deforestation, and habitat maintenance, alteration, or loss. To determine the relative balance of climatic and anthropogenic influences on fire activity, we quantified interannual variability in burned area across Ethiopia from 2001 to 2018 and developed a statistical model to assess climate and human factors contributing to patterns of area burned.ResultsAnnual burned area declined nationally and within several regions from 2001 to 2018 and was closely related to climate, particularly antecedent temperature. Of the area that burned at least once, 62% reburned at 1–3-year intervals and the geographic region of frequent-fire areas did not shift over time. Despite increased enforcement of a fire ban over the past 20 years, no strong spatiotemporal shifts in fire occurrence patterns were detected at a national level.ConclusionsOur results suggest that human influence combined with dynamics of vegetation and fuels strongly influenced fire occurrence in Ethiopia, indicating that geographic variation in cultural fire practices was highly influential and relatively unchanging between 2001 and 2018. In contrast, interannual variability in total burned area was strongly related to climate and the influence of climate on fuel abundance. Our results highlight that climate can strongly influence short-term variability in fire activity even as longer-term patterns may depend more strongly on human influence.

Reduction in riverine freshwater supply due to climate change as well as anthropogenic activities are documented throughout the globe. How river discontinuity in upstream reaches and the subsequent reduction in freshwater influx alter inorganic and organic carbon dynamics in downstream estuaries adjacent to mangroves has been rarely reported. We investigated the dynamics of the inorganic carbon system and organic matter (OM) in two Indian estuaries near mangroves; riverine freshwater supply to the Matla Estuary was reduced and that to the Dhamra Estuary was uninterrupted. Seasonal sampling was conducted over an annual cycle. We used elemental and stable isotope signatures to delineate the sources of OM and dissolved inorganic carbon (DIC). We found that compared to the Dhamra, the reduced riverine freshwater supply to the Matla increased the marine influence in the estuary on the OM degradation pathways and decreased CO2 emissions to the atmosphere. In the Dhamra, higher seasonal variability in biogeochemical pathways, facilitated high internal carbonate buffering capacity; in contrast in the Matla, the greater marine influence increased the carbonate buffering capacity, resulting in retention of higher DIC concentrations and low CO2 emissions. Dissolved and particulate organic carbon concentrations were higher in the Dhamra than the Matla, indicating higher riverine supply of these. The present study can contribute an overlooked effect of long‐term changes in riverine freshwater supply on the carbon dynamics of mangrove‐dominated estuaries, which might help to improve the understanding of coastal carbon budgets in a changing world.

Carbon and Nitrogen Spatial Segregation and Stoichiometry in the Surface Sediments of Southern Chilean Inlets (41°–56°S)

Fluxes of dissolved inorganic carbon in three estuarine systems of the Cantabrian Sea (north of Spain)

Fluxes of dissolved inorganic carbon in three estuarine systems of the Cantabrian Sea (north of Spain)

Catchments draining urban agglomerations are particularly exposed to significant anthropogenic pressure. Along watercourses, various types of wastewater are discharged, including both area pollution sources (e.g., parking lots, streets) and point sources, such as the discharge of treated wastewater from large municipal sewage treatment plants.Field studies were conducted in Radom, along the Mleczna River, using the hydrochemical mapping method. Sixteen points and hydrological nodes were identified along the river's longitudinal profile, at locations where wastewater or other watercourses discharge. The studies were carried out twice (November 8-9, 2024), and 66 water samples were collected. During the fieldwork, selected physicochemical parameters (electrical conductivity, pH, dissolved oxygen content, and water temperature) were measured in two series, and water samples were taken for further laboratory analysis. In the laboratory, the chemical composition of 14 major ions (Ca, Mg, Na, K, NH4, Li, HCO3, SO4, Cl, NO3, NO2, PO4, F, Br) was analyzed using ion chromatography (DIONEX ICS 2000). The Elementar Vario TOC Cube analyzer was also used to determine the content of organic carbon (TOC), inorganic carbon (TIC), total carbon (TC), and total nitrogen (TNb).Spatial variation analysis of physicochemical properties and ion concentrations indicates that anthropogenic influence is noticeable across all parameters along the longitudinal profile of the Mleczna River. It is worth noting that along the hydrochemical profile, there is primarily an increase in the concentrations of chloride and sodium. These ions are associated with the water and wastewater management of the city of Radom. This is especially evident at hydrological-chemical node number 9, where stormwater from the city’s drainage system is discharged. Anthropogenic pressure is reflected in a change in the hydrochemical type – particularly noticeable in the suburban area, where treated wastewater is discharged from the sewage treatment plant into the Pacynka River, a tributary of the Mleczna River (node 15). The natural hydrochemical type, related to the geological structure, changes from a typical, simple HCO3-Ca type to a four-ion, complex HCO3-Cl-Ca-Na type.