Quantifying the Impact of Anthropogenic Atmospheric Nitrogen Deposition on the Generation of Hypoxia under Future Emission Scenarios in Chinese Coastal Waters

Abstract

Atmospheric deposition is an important source of nitrogen to coastal waters. In nitrogen-limited waters, the atmosphere can contribute significantly to eutrophication and hypoxia. This is especially true in China, where nitrogen emissions have increased dramatically and are projected to further increase in the future. Here, we modeled the potential future impact of change in atmospheric nitrogen deposition on hypoxia in Chinese coastal seas. We used changes in nitrogen deposition under two IPCC scenarios that included emission regulation and climate change (representative concentration pathway (RCP) 4.5 and 8.5) to evaluate the impacts of such deposition on hypoxia in the 2030s and 2100s. We found that by 2030 the extent of hypoxic areas would increase up to 5% in China seas under RCP 8.5 due to the projected increase in nitrogen deposition. However, the hypoxia extent was projected to decrease by up to 9% by 2100 once emission regulations included in RCP 4.5 and 8.5 are implemented. The South China Sea was found to be the most sensitive region to changes in nitrogen loads, which indicates that more effort in emissions control is needed to avoid expansion of the hypoxic zones in that specific region.

Impacts and uncertainties of climate-induced changes in watershed inputs on estuarine hypoxia

“…The majority of coastal hypoxia climate impact studies have focused on a select few coastal locations including the Baltic Sea (Meier et al, 2011a,b;Meier et al, 2012;Neumann et al, 2012;Ryabchenko et al, 2016;Saraiva et al, 2019a,b;Wåhlström et al, 2020;Meier et al, 2021;Meier et al, 2022), Chesapeake Bay (Wang et al, 2017;Irby et al, 2018;Ni et al, 2019;Testa et al, 2021;Tian et al, 2021;Cai et al, 2021), and the Gulf of Mexico (Justić et al, 1996;Justić et al, 2007;Lehrter et al, 2017;Laurent et al, 2018). Other projected changes to dissolved oxygen (O2) levels have been documented in nearshore environments including the North Sea (Meire et al, 2013;Wakelin et al, 2020), Arabian Sea (Lachkar et al, 2019), California Current System (Dussin et al, 2019;Siedlecki et al, 2021;Pozo Buil et al, 2021), and coastal waters surrounding China (Hong et al, 2020;Yau et al, 2020;Zhang et al, 2021;. Hypoxia projections in relatively smaller estuaries have also been documented in the Elbe (Hein et al, 2018), Garonne (Lajaunie-Salla et al, 2018), and Long Island Sound (Whitney and Vlahos, 2021).…”

“…Questions of uncertainty due to climate effects in past marine ecosystem impact studies have often been addressed by selecting some combination of ESMs and/or emissions scenarios (Meier et al, 2011a;Ni et al, 2019;Saraiva et al, 2019b;Meier et al, 2019;Meier et al, 2021;Pozo Buil et al, 2021). Additionally, some studies have also sought to account for the importance of managed nutrient runoff from terrestrial (Irby et al, 2018;Saraiva et al, 2019a) and atmospheric (Yau et al, 2020;Meier et al, 2021) sources and their impacts on oxygen levels. Despite some comprehensive efforts to identify sources of uncertainty in coastal oxygen projections (Meier et al, 2019;, few studies have evaluated uncertainties introduced by the choice of specific downscaling method and/or terrestrial model.…”

Regional projection of climate warming effects on coastal seas in east China

“…Precipitation is projected to increase in this region (Li et al 2021), which can also strengthen water column vertical stratification. The areal extent of hypoxia in Chinese coastal waters has also been suggested to be sensitive to atmospheric nitrogen deposition based on a global model of coastal oxygen and nutrient dynamics under future projections (Yau et al 2020).…”