Dissolved organic carbon (DOC) is not only a critical component of global and regional carbon budgets, but also an important precursor for carcinogenic disinfection byproducts (DBP) generated during drinking water disinfection process. The lack of process based watershed scale model for carbon cycling has been a limiting factor impeding effective watershed management to control DOC fluxes to source waters. Here, we integrated terrestrial and aquatic carbon processes into the widely tested Soil and Water Assessment Tool (SWAT) watershed model to enable watershed-scale DOC modeling (referred to as SWAT-DOC hereafter). The modifications to SWAT mainly fall into two groups: (1) DOC production in soils and its transport to aquatic environment by different hydrologic processes, and (2) riverine transformation of DOC and their interactions with particular organic carbon (POC), inorganic carbon and algae (floating and bottom). We tested the new SWAT-DOC model in the Cannonsville watershed, which is part of the New York City (NYC) water supply system, using long-term DOC load data (from 1998 to 2012) derived from 1399 DOC samplings. The calibration and verification results indicate that SWAT-DOC achieved satisfactory performance for both streamflow and DOC at daily and monthly temporal scales. The parameter sensitivity analysis indicates that DOC loads in the Cannonsville watershed are controlled by the DOC production in soils and its transport in both terrestrial and aquatic environments. Further model uncertainty analysis indicates high uncertainties associated with peak DOC loads, which are attributed to underestimation of high streamflows. Therefore, future efforts to enhance SWAT-DOC to better represent runoff generation processes hold promise to further improve DOC load simulation. Overall, the wide use of SWAT and the satisfactory performance of SWAT-DOC make it a useful tool for DOC modeling and mitigation at the watershed scale.

Fish farming in coastal areas has become an important source of food to support the world’s increasing population. However, intensive and unregulated mariculture activities have contributed to changing seawater carbonate chemistry through the production of high levels of respiratory CO₂. This additional CO₂, i.e. in addition to atmospheric inputs, intensifies the effects of global ocean acidification resulting in localized extreme low pH levels. Marine calcifying macroalgae are susceptible to such changes due to their CaCO₃ skeleton. Their physiological response to CO₂-driven acidification is dependent on their carbon physiology. In this study, we used the pH drift experiment to determine the capability of 9 calcifying macroalgae to use one or more inorganic carbon (Cᵢ) species. From the 9 species, we selected the rhodolith Sporolithon sp. as a model organism to investigate the long-term effects of extreme low pH on the physiology and biochemistry of calcifying macroalgae. Samples were incubated under two pH treatments (pH 7.9 = ambient and pH 7.5 = extreme acidification) in a temperature-controlled (26 ± 0.02 °C) room provided with saturating light intensity (98.3 ± 2.50 μmol photons m⁻² s⁻¹). After the experimental treatment period (40 d), growth rate, calcification rate, nutrient uptake rate, organic content, skeletal CO₃⁻², pigments, and tissue C, N and P of Sporolithon samples were compared. The pH drift experiment revealed species-specific Cᵢ use mechanisms, even between congenerics, among tropical calcifying macroalgae. Furthermore, long-term extreme low pH significantly reduced the growth rate, calcification rate and skeletal CO₃⁻² content by 79%, 66% and 18%, respectively. On the other hand, nutrient uptake rates, organic matter, pigments and tissue C, N and P were not affected by the low pH treatments. Our results suggest that the rhodolith Sporolithon sp. is susceptible to the negative effects of extreme low pH resulting from intensive mariculture-driven coastal acidification.

Diatom responses to ocean acidification have been documented with variable and controversial results. We grew the coastal diatom Thalassiosira weissflogii under 410 (LC, pH 8.13) vs 1000 μatm (HC, pH 7.83) pCO₂ and at different levels of light (80, 140, 220 μmol photons m⁻² s⁻¹), and found that light level alters physiological responses to OA. CO₂ concentrating mechanisms (CCMs) were down-regulated in the HC-grown cells across all the light levels, as reflected by lowered activity of the periplasmic carbonic anhydrase and decreased photosynthetic affinity for CO₂ or dissolved inorganic carbon. The specific growth rate was, however, enhanced significantly by 9.2% only at the limiting low light level. These results indicate that rather than CO₂ “fertilization”, the energy saved from down-regulation of CCMs promoted the growth rate of the diatom when light availability is low, in parallel with enhanced respiration under OA to cope with the acidic stress by providing extra energy.

Hypoxia (O₂ ≤ 2 mg L⁻¹) can severely threaten the survival of marine life and alter the biogeochemical cycles of coastal ecosystems. Its impacts are dependent on its duration. In the present study, hypoxia was observed in autumn at the end of October 2011. It may be one of the latest recorded annual hypoxic events in the East China Sea (ECS). In the hypoxic regions, a large amount of nutrients and dissolved inorganic carbon were observed to regenerate. Also, acidification (low pH) was observed. On the other hand, hypoxic dissipation may be due to the destratification caused by the upwelling of the hypoxic regions in the ECS. These results suggest that hypoxia may occur for longer periods of time than expected and, accordingly, the effects of hypoxia on the ECS ecosystems should be reconsidered and further evaluated.

Various biogeochemical processes complicate carbon dioxide (CO₂) behaviour in coastal oceans. Through eight summer surveys, detailed variations in CO₂ mechanisms in the urbanized Jiaozhou Bay, China, were analysed. During the rainless period, respiration and dissolved inorganic carbon input from treated wastewater made the northeastern region a strong CO₂ source, while the western region with cleaner seawater was a weak source because calcium carbonate (CaCO₃) precipitation exceeded primary production. Rainfall events with different intensities and locations caused significantly different effects. When rainfall occurred over the sea, enhanced primary production caused a CO₂ sink; when rainfall induced little terrestrial pollutant input, CaCO₃ precipitation exceeded net primary production, leading to a CO₂ source. When heavy rain caused bulk runoff, the northeastern region was a strong CO₂ source because rivers flowing through downtown regions inputted considerable organic matter, while in the western region, runoff through suburbs and wetlands led to a strong sink.

Microbial communities in subterranean estuaries play important roles in the biogeochemical cycle. However, the microorganisms associated with biogeochemical behaviors in subterranean estuaries have received little attention. Here, the bacterial communities were compared between the fresh and saline groundwater in a subterranean estuary. Correlation analysis between bacterial groups and salinity indicated that different species represented different groundwater types. The key bacterial groups found along the subterranean estuaries have been shown to influence organic pollutant degradation and nitrate utilization. These species may be potential candidates for the in situ bioremediation of subterranean estuaries that are contaminated with pollutants. The utilization of nitrate and organic pollutants by bacteria in subterranean estuaries serves as a nitrate sink and inorganic carbon source. Our results show the role of bacteria in remediating pollutants through submarine groundwater discharge (SGD) to the coastal ocean, and specific species may be helpful in selecting reasonable groundwater end-members and reducing SGD uncertainties.

Copper can be beneficial or harmful to coral at environmentally relevant levels, making environmental monitoring a challenging. Membrane lipids make the cell a dynamic environment according to the circumstances; thus, the lipid profile should be indicative of an environmental/physiological state. To gain more insight into the copper effect on coral health and be a basis of biomonitoring, glycerophosphocholine profiling of coral exposed to microenriched copper levels was conducted in this study. The copper microenrichments resulted in a diacritical effect of decreasing carbonic anhydrase activity, following a supplementation effect, on coral lipid metabolism. Microdifferences in copper levels are critical to determine the coral metabolic state and were therefore included in this study. In addition, an excellent quantitative model correlating the coral lipid variation with the exposed copper levels or the induced physiological effect was obtained to demonstrate its performance for biomonitoring.

The golden tide, caused by the brown algae Sargassum horneri, exerts severe influences on the Pyropia aquaculture of Jiangsu coast, China. To study the outbreak of the golden tide in response to increasing greenhouse gas emissions, S. horneri was cultured under four conditions: ambient condition (10 °C, 400 μatm), elevated temperature condition (14 °C, 400 μatm), elevated CO₂ level (10 °C, 1000 μatm), and potential greenhouse condition (14 °C, 1000 μatm). The growth, photosynthetic performances, and inorganic carbon affinity of S. horneri were studied. The results showed that elevated temperature exerted a more pronounced positive influence on S. horneri growth, photosynthesis, and carbon assimilation than CO₂ enrichment. The growth of S. horneri was significantly improved by moderately elevated temperatures, especially under concurrently elevated CO₂ levels. This suggests that the greenhouse effect will benefit growth and carbon sequestration of S. horneri, which may enhance the frequency and scale of golden tides.

This paper presents the characterization of municipal solid waste (MSW) randomly collected from two material recovery facilities in São Paulo city, before (input — recyclables) and after (output — rejects) the sorting processes. Geo-environmental and geotechnical tests were performed on shredded samples and a digestion method was applied to detect the metals As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn concentrations using an ICP OES. The objective was to assist future activities of integrated solid waste management and soil pollution. Results showed different particle sizes comparing the input (44.6%) and the output MSW (75.1%) passing through the 100-mm sieve. Organic matter and ash contents indicated the influence of inorganic carbon due to the plastics’ presence, with values varying between 6 and 13%. The pH values obtained were neutral and the electrical conductivity of the MSW rejects suggested a higher amount of ions, with values above 1000 µS/cm. Metals analyses show that Cd, Cu, Ni, Pb, and Zn are present in high concentrations, depending on the types of the materials. Standard Proctor compaction curves yielded maximum dry unit weight varying from 6.6 to 10.0 kN/m³ and optimum moisture contents from 20 to 42%. Cohesion ranged from 1.3 to 31.3 kPa and friction angle from 3.2 to 42.9°. The results are comparable with those obtained for other countries using different MSW treatments and contribute to the data basis for MSW from the selective collection, aiming the integrated solid waste management, serving for other countries that adopt MSW sorting and recycling.

Extreme climatic events may be translated into a higher frequency of both dry and wet years. Frequent droughts pose a challenge to water supply in terms of both quantity and quality. In order to cope with this, there has to be a documentation on the concentration of chemicals in water during such events. The southeast region of Brazil experienced a major drought event in 2014 leading to number of social, economic, and environmental impacts. The objective of the present paper is to understand the effect of an extreme drought on dissolved organic and inorganic carbon concentrations of the Piracicabal river, which is under high human pressure. Concentrations of both dissolved organic (DOC) and inorganic carbon (DIC) were monitored daily, for 30 days, during a dry month in 2014. DOC values found here were at least twice those observed in the river in non-extreme conditions. Rain events within this drought led to significant differences in discharge, DOC, and DIC. We built a dilution-concentration model which described an exponential relationship between discharge and both carbon forms. This indicated that drastic changes in concentrations of DOC and DIC are expected during such events. Our results may also apply to a number of regions in the world especially those of the developing countries where rivers are highly subjected to sewage impact.