Cycling and Budgets of Organic and Black Carbon in Coastal Bohai Sea, China: Impacts of Natural and Anthropogenic Perturbations

Abstract

Organic carbon (OC) cycling in coastal seas that connect terrestrial and open oceanic ecosystems is a dynamic and disproportionately important component of oceanic and global carbon cycles. However, OC cycling in coastal seas needs to be better constrained, particularly for geochemically important black carbon (BC). In this study, we conducted multimedium sampling campaigns, including atmospheric deposition, river water, seawater, and sediments in coastal Bohai Sea (BS) in China. We simultaneously quantified particulate OC (POC), particulate BC (PBC), dissolved OC (DOC), and dissolved BC (DBC) and investigated the cycling and budgets of OC and BC. The cycling and budgets of each individual particulate phase (i.e., POC versus PBC) and dissolved phase (i.e., DOC versus DBC) displayed similar patterns, but there were some distinct differences between the particulate and dissolved phases. In the particulate phases, atmospheric and riverine delivery dominated exogenous inputs (>80%), sequestration to sediments dominated removal (~70%), and exchanges in the Bohai Strait resulted in net export. In the dissolved phases, exchanges in the Bohai Strait dominated both import and export and were in a relatively dynamic equilibrium. We found that both natural perturbations, such as spring dust storms, and anthropogenic activity, exerted significant impacts on BS carbon cycling. The integration of regional and global source‐to‐sink process databases made it clear that future BC studies should calculate PBC and DBC fluxes independently. Continuous field observational studies, more details of the biogeochemical processes involved, and consistent BC quantification methods are urgently needed to elucidate coastal OC and BC cycling.

Large-river dominated black carbon flux and budget: A case study of the estuarine-inner shelf of East China Sea, China

“…1), which is also an important part of the East China Marginal Seas, the inputs of BC differed significantly from those in the coastal ECS. Atmospheric deposition and riverine discharge were of equal importance in delivering BC to the coastal Bohai Sea (Fang et al, 2015;Fang et al, 2018). The much higher percentage of BC from riverine discharge in the coastal ECS (~93%) than that in the coastal Bohai Sea (~50%) was primarily due to the overwhelmingly higher BC discharge from the Yangtze River (~485 Gg/yr) than from the Yellow River (~70 Gg/yr).…”

“…The acid-treated sediment residues were diluted with Milli-Q water (18.2 MΩ•cm) and then filtered through pre-combusted (450°C, 4 h) quartz fibre filters (Whatman, 47 mm diameter, nominal pore size 0.7 μm). The filters loaded with sediment residues were airdried and analyzed for BC on a Desert Research Institute (DRI) Thermal/Optical Carbon Analyzer (Model 2001A) following the protocol of Interagency Monitoring of Protected Visual Environment (IMPROVE) (Fang et al, 2015;Fang et al, 2018). A punch of 0.544 cm 2 filter was delivered into an oven for carbon quantification.…”

“…Also, the large uncertainty in the burial flux of BC makes the BC budget poorly constrained. All these sources of uncertainty imply that continuous field observations and consistent BC quantification methods are essential steps for approaching a more reliable BC budget construction (Fang et al, 2018). Regional BC budgets have also been investigated in some other coastal areas, such as the coastal Bohai Sea (Fang et al, 2015), New England continental shelf (Gustafsson and Gschwend, 1998), Gulf of Maine (Flores-Cervantes et al, 2009), and Northern European shelf (Sánchez-García et al, 2012).…”

“…Black carbon (BC) is defined as the aromatic carbonaceous byproduct generated from incomplete biomass burning or fossil fuels combustion (Coppola et al, 2018;Fang et al, 2018). It has recently received substantial attention due to its widely recognized key roles in a variety of biogeochemical processes, including regional and global carbon cycle, climate change, air quality, and public health (Ramanathan and Carmichael, 2008;Anenberg et al, 2012;Bird et al, 2015;Fang et al, 2015).…”

Deoxygenation and Its Controls in a Semienclosed Shelf Ecosystem, Northern Yellow Sea

“…The NYS lies among the Shandong, Liaodong, and the Korean Peninsulas (Figure ), with an area of ~71,000 km 2 and a mean depth of ~38 m. This semienclosed marginal sea is connected to the Bohai Sea (BS) through a narrow strait, whereas it is more open to the SYS (Figure ) (Zhai et al, ). Influenced by the relatively intense land‐ocean interactions (Liu et al, ; Zhang et al, ), the NYS area receives a large amount of nutrients from rivers, including the Yalu and Taedong Rivers (Figure ); the materials from the Yellow River can also be transported to the NYS through the BS strait (Cheng et al, ; Fang et al, ). The hydrographic conditions of the NYS vary by season (Figure ).…”