Anthropogenic inputs from a coastal megacity are linked to greenhouse gas concentrations in the surrounding estuary

Abstract

Coastal megacities deposit significant amounts of carbon (C), nitrogen (N), and pollutants into surrounding waters. In urbanized estuaries, these inputs, including wastewater discharge and surface runoff, can affect biogeochemical cycles, microbial production, and greenhouse gas (GHG) efflux. To better understand estuarine GHG production and its connection to anthropogenic drivers, we quantified carbon dioxide (CO2) and methane (CH4) surface‐water concentrations and efflux in combination with a suite of biogeochemical parameters, including anthropogenic indicators, in the Hudson River Estuary (HRE) and adjacent waters surrounding New York, NY, over a 2‐yr period. The HRE was a source of both CO2 (33 ± 3 mmol CO2 m−2 d−1) and CH4 (177 ± 22 μmol CH4 m−2 d−1) under all measured conditions. Surface‐water salinity, oxygen saturation, fecal indicator bacteria, nitrate concentrations, and temperature best explained the variance in CO2 and CH4 concentrations in multiple regression analyses, producing robust predictive power for both GHGs. Our multifaceted data set demonstrated that CH4 and CO2 surface concentrations are explained in part by enterococci concentrations, a widely used wastewater biological indicator, explicitly linking wastewater inputs to GHG surface concentrations in the HRE. The greatest CO2 and CH4 surface‐water concentrations were found in urban tributaries and embayments, primary wastewater delivery areas throughout the HRE. Estuarine tributaries and embayments have historically received less research attention than midchannel sites, but since these shallow sites may contribute to increased GHG efflux in anthropogenically impacted estuaries, further study is warranted.

Greenhouse gas emissions (CO2 and CH4) and inorganic carbon behavior in an urban highly polluted tropical coastal lagoon (SE, Brazil)

“…Inner and low-salinity estuarine regions have been documented as heterotrophic and large CO2 emitters (Frankignoulle et al 1998;Silvennoinen et al 2008). In several coastal waters worldwide, important CO2 changes have been strongly related to eutrophication (Borges and Gypens 2010;Cai et al 2011;Sunda and Cai 2012;Cotovicz et al 2015;Brigham et al 2019). Overall, when untreated urban wastewater discharges from megacities reach estuarine waters, they enhance the levels of CO2 especially in turbidity coastal waters located at the vicinity of outfalls (Frankignoulle et al 1998;Zhai et al 2007;Sarma et al 2012;Brigham et al 2019).…”

“…For CH4, the eutrophication is related to increasing concentrations in aquatic compartments. Pristine rivers are usually organic matter poor-environments and weak sources of CH4 compared to impacted ecosystems (Richey et al 1988;Purvaja and Ramesh 2000;Brigham et al 2019). The production of CH4 increases with hypoxic and anoxic conditions associated to the increased inputs of organic matter to water and sediments.…”

“…In coastal marine sediments with high salinity, large inputs of organic matter are necessary for methanogenesis to occur and generate CH4 rich gassy-sediments (Martens and Klump 1980;Martens et al 1998). It is particularly relevant the contributions from wastewater treatment plants and direct inputs from untreated domestic effluents that are rich in CO2 and CH4 in disturbed coastal ecosystems (Nirmal-Rajkumar et al 2008;Burgos et al 2015;Cotovicz et al 2016;Brigham et al 2019). This means that regions under influence and/or close to sewage discharge present higher CO2 and CH4 concentrations and emissions.…”

Shifts in methanogenic archaea communities and methane dynamics along a subtropical estuarine land use gradient

“…In other urbanised catchments, the presence of elevated concentrations of DOC coupled with an absence of thermodynamically favourable electron acceptors has been shown to facilitate the proliferation of methanogenic archaea [ 14 , 65 , 66 ]. This implies that increased inputs of organic matter due to catchment urbanisation and modification may lead to an increase in methanogenesis and GHG production [ 11 , 12 ].…”

“…Estuaries contribute between 1 and 7 Tg of CH 4 and 0.1 to 0.25 Gt of CO 2 to the atmosphere each year [9], with the global flux of CO 2 to the atmosphere from estuaries comparable to the uptake of the entire continental shelf, despite estuaries representing only 5% of the continental shelf equivalent surface area [10]. Increasing inputs of anthropogenic pollutants stemming from urban, industrial and agricultural runoff into adjacent estuarine ecosystems have been reported to elevate GHG fluxes [11][12][13]. CH 4 emissions originating from microbial sources have been suggested to contribute about 70% of all global methane emissions [14][15][16].…”