Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system

Abstract

Global change is leading to warming, acidification, and oxygen loss in the ocean. In the Southern California Bight, an eastern boundary upwelling system, these stressors are exacerbated by the localized discharge of anthropogenically enhanced nutrients from a coastal population of 23 million people. Here, we use simulations with a high-resolution, physical–biogeochemical model to quantify the link between terrestrial and atmospheric nutrients, organic matter, and carbon inputs and biogeochemical change in the coastal waters of the Southern California Bight. The model is forced by large-scale climatic drivers and a reconstruction of local inputs via rivers, wastewater outfalls, and atmospheric deposition; it captures the fine scales of ocean circulation along the shelf; and it is validated against a large collection of physical and biogeochemical observations. Local land-based and atmospheric inputs, enhanced by anthropogenic sources, drive a 79% increase in phytoplankton biomass, a 23% increase in primary production, and a nearly 44% increase in subsurface respiration rates along the coast in summer, reshaping the biogeochemistry of the Southern California Bight. Seasonal reductions in subsurface oxygen, pH, and aragonite saturation state, by up to 50 mmol m−3, 0.09, and 0.47, respectively, rival or exceed the global open-ocean oxygen loss and acidification since the preindustrial period. The biological effects of these changes on local fisheries, proliferation of harmful algal blooms, water clarity, and submerged aquatic vegetation have yet to be fully explored.

Preliminary Study on the Dissolved Oxygen Recovery Process in Freshwater Ecosystems under the Coupling Effect of Oxygen-Consuming Pollutants and Temperature

“…Biochemical processes include oxygen consumption and oxygen production processes, which are dominated by the OCP concentrations and hydrobiological activity. − Changes in the DO concentration in water will be affected by combined physical–chemical–biological activities. For example, it has been found that glacial deep ocean deoxygenation is driven by biologically medicated air–sea disequilibrium, ocean circulation accelerates coastal deoxygenation, , and large inputs of anthropogenic contaminants and global warming cause deoxygenation of the water column. ,,,− The data we analyzed indicated that OCPs and temperature are the main factors that affect DO concentrations in freshwater ecosystems.…”

Movement Shapes the Structure of Fish Communities Along a Cross-Shore Section in the California Current

“…A considerable amount of data have been collected in this region, in particular with the California Cooperative Oceanic Fisheries Investigations (CalCOFI) (McClatchie, 2014), or the Newport line (Huyer et al, 2007), which provide a wealth of in-situ observations from hydrography to biology. These observations facilitate the implementation and the validation of physical-biogeochemical models that reproduce ocean currents and primary production in the region, down to resolutions of kilometers or less (Gruber et al, 2006;Capet et al, 2008;Fiechter et al, 2018;Kessouri et al, 2020Kessouri et al, , 2021Deutsch et al, 2021). Combined acoustic-trawl surveys of coastal pelagic species provide fisheries-independent observations of mid-trophic levels for the recent decades (Zwolinski et al, 2014).…”

Recovery in Dissolved Oxygen Levels in Chinese Freshwater Ecosystems in the Past Three Decades

“…The DO levels in water will change if processes become unbalanced when aggravated by, for example, climate warming or environmental pollution. − There is a global consensus that there is widespread deoxygenation in both oceanic and coastal waters. , The situation in freshwater ecosystems is similar. , Analysis of the DO levels in 393 temperate lakes from 1941 to 2017 showed that the decrease in DO levels in freshwater was 2.75 to 9.3 times greater than that observed in oceans worldwide, which could threaten ecosystem services in lakes. , Freshwater is limited and very unevenly distributed in China. It is therefore important to have nationwide information about the levels and concentrations of DO in Chinese freshwater systems.…”