Treated Wastewater Changes the Export of Dissolved Inorganic Carbon and Its Isotopic Composition and Leads to Acidification in Coastal Oceans

Abstract

Human-induced changes in carbon fluxes across the land-ocean interface can influence the global carbon cycle, yet the impacts of rapid urbanization and establishment of wastewater treatment plants (WWTPs) on coastal ocean carbon cycles are poorly known. This is unacceptable as at present ∼64% of global municipal wastewater is treated before discharge. Here, we report surface water dissolved inorganic carbon (DIC) and sedimentary organic carbon concentrations and their isotopic compositions in the rapidly urbanized Jiaozhou Bay in northeast China as well as carbonate parameters in effluents of three large WWTPs around the bay. Using DIC, δC and total alkalinity (TA) data and a tracer model, we determine the contributions to DIC from wastewater DIC input, net ecosystem production, calcium carbonate precipitation, and CO outgassing. Our study shows that high-DIC and low-pH wastewater effluent represents an important source of DIC and acidification in coastal waters. In contrast to the traditional view of anthropogenic organic carbon export and degradation, we suggest that with the increase of wastewater discharge and treatment rates, wastewater DIC input may play an increasingly more important role in the coastal ocean carbon cycle.

Spatial Variation in Aragonite Saturation State and the Influencing Factors in Jiaozhou Bay, China

“…The total amount of wastewater treated by the three WWTPs located near the northeastern area of JZB is up to~510,000 tons per day ( Figure 1). Therefore, the direct input of treated wastewater was the main reason for the low salinity in this region [11,33]. Additionally, a high-salinity area with a value higher than 30.9 was found in the nearshore area of the western area in summer.…”

“…Terrestrial runoff usually has low pH and [CO 3 2− ] values, which directly lead to a decrease in Ω arag in the receiving water body [21,43]. The rivers entering JZB have no natural runoff, but the daily discharges of the Licun River WWTP, the Lushan River WWTP and the Haibo River WWTP, which are located at the three estuaries in the eastern area of the bay, are up to 250,000, 100,000 and 160,000 tons, respectively [11,44]. The direct input of treated wastewater has become the main form of terrestrial input, and unlike natural rivers affected by seasonal changes, treated wastewater input is a persistent process.…”

“…Coastal waters are the most active areas for fishery production and shellfish farming, and studies related to OA mechanisms are a top priority in the region [5][6][7]. Unlike the open ocean, nearshore acidification is not only affected by global OA caused by increasing atmospheric CO 2 levels but also by the coupled effects of various processes, such as upwelling, organic matter degradation, primary production of phytoplankton and river input, due to the strong interaction between land and ocean, making the acidification mechanism in coastal waters more complicated [8][9][10][11]. In bays, which are highly affected by human disturbance, the mutual enhancement, interference and superimposition of the effects of the above processes are especially prominent.…”

“…Furthermore, JZB is an important shellfish-farming area [31], where scallop, clam and others are vulnerable to low Ω. In recent years, many researchers have conducted extensive studies on the changes in seawater surface dissolved inorganic carbon (DIC), total alkalinity (TA) and CO 2 partial pressure in JZB [11,32,33], but there is little analysis and discussion of Ω arag , especially its controlling processes. Therefore, through two cruise-based investigations in JZB during summer and winter when biological activity is strongest, this study analyses the spatial distribution characteristics of Ω arag in detail and reveals the main processes that cause the spatial distribution difference in Ω arag by qualitative analysis and quantitative calculation.…”

Physical and Biogeochemical Controls on pH Dynamics in the Northern Gulf of Mexico During Summer Hypoxia

“…There are several other processes that may lead to decrease in pH in coastal waters aside from anthropogenic CO 2 invasion. For instance, increases in acidity of coastal waters can also be a result of the input of waters with high carbon loading, that is, river water (Salisbury et al, ), marsh water (Cai et al, ), wastewater (Yang et al, ), submarine groundwater (Wang et al, ), and/or upwelling of anthropogenic CO 2 ‐enriched water (Feely et al, ) as the dissolved inorganic carbon (DIC) to total alkalinity (TA) ratio is often higher in these waters than in seawater. In particular, the sensitivity of estuarine pH and aragonite saturation state is closely related to the carbonate chemistry of river water (Moore‐Maley et al, ).…”