The global climate crisis caused by unsustainable hydrocarbon emissions has placed Humanity and our Earth into a new, sorrowful era of biosystems collapses and community catastrophes. The global scientific consensus used to urge nation states to make significant, credible emission reductions has not been enough, as wars, political malfeasance and malaise by arrogant, corrupt leaders are in ascendance.What can an individual, a family, a community do if nation states are so irresponsible? Of course, we can decrease emissions and overconsumption as much as possible by moving to renewable energy, choosing better diets, and becoming climate activists. These are global priorities for every citizen and family.
Our community of aquatic scientists have additional responsibilities. We must understand and communicate as much as possible the root causes and propose innovative actions to assist in the recovery of aquatic ecosystems from accelerated anthropogenic damage.
Actions that go beyond a need to understand IPCC projections of climate impacts - in addition to a better understanding of the impacts of accelerating carbon dioxide emissions due to unsustainable fossil fuel combustion.
Ocean acidification is a terrifying concept; but the most urgent aquatic priority is coastal/freshwater ecosystem acidification from nutrients, especially nitrogen (N), which has been called “the forgotten element of climate change”.
Wastewater discharges to aquatic ecosystems from coastal urbanization and unsustainable agriculture now control the Earth’s coastal and freshwater nutrient (N, P) cycles, not geochemistry.
The Millennium Ecosystem Assessment predicted an increase in global sewage emissions of 12.0–15.5 Tg (12-15.5 million metric tons (MMT)) of nitrogen and 2.4–3.1 Tg (2.4-3.1 MMT) of phosphorus per year by 2050. These magnitudes may have already been exceeded.
Lu et al. (2024) found that as a city grows, energy use becomes more efficient and greenhouse gas emissions decrease, but that water use increases exponentially. Thus, wastewater discharges grow at a faster rate than a growing urban population.
Tuholske et al. (2021) showed that 58% of coral reefs and 88% of seagrass beds of the 135,000 watersheds mapped globally were exposed to wastewater N inputs.
Greenhouse gas emissions from unsustainable burning/fossil fuel combustion must decrease; however, they are not the major cause of our nearshore, coastal/freshwater acidification crisis. This is due to the vast (and accelerating) quantities of nutrients being discharged from wastewaters and agriculture, which are causing severe hyper-eutrophication and a cascade of adverse impacts to ecosystem functions, critical habitats, and biodiversity.
There are clear links between coastal/freshwater ecosystems' acidification, anoxia and hypoxia due to the increasing global spread and number of intense algal blooms leading to eutrophication.
Acid conditions in aquatic systems are due to the microbial degradation of these algal blooms. Microbes respire carbon dioxide leading to incredibly high concentrations of dissolved carbon dioxide in aquatic systems, especially in bottom waters.
The acid conditions now being experienced in coastal/freshwater ecosystems are not expected to occur in the open ocean within the next hundred years - if ever - given IPCC projections of anthropogenic atmospheric carbon dioxide increases.
Thus, the real alarm bell ringing in my head now is COASTAL/FRESHWATER ACIDIFICATION - not ocean acidification - due to accelerated nutrient discharges. Nutrients are the main cause of coastal/freshwater acidification, not emissions of carbon dioxide to the atmosphere that slowly dissolve into water.
Many (most?) freshwater and coastal ecosystems are net heterotrophic (Duarte and Prairie 2005); and many are “sewage-fueled” aquatic ecosystems that emit carbon dioxide to the atmosphere!
There are examples everywhere, worldwide. One is Jamaica Bay, a hypereutrophic estuary in New York, USA. This bay receives ~90% of its nitrogen from four wastewater treatment plants that discharge ~ 1 billion liters of wastewater effluents every day. Dissolved carbon dioxide (pCO2) concentrations in the bottom waters of the bay in summer exceed 2000 μatm (the CO2 concentration in the atmosphere is ~437 ppm now) (Wallace et al. 2014).
Almost 30 years ago, Frankignoulle et al. (1998) found an area of European estuaries emitted ~3000 MT of carbon dioxide per day to the atmosphere. Carbon dioxide emissions from the Scheldt estuary (Belgium/Netherlands) were 2/3 due to heterotrophy (microbial respiration of carbon dioxide) and 1/3 due to ventilation.
Carbon dioxide emissions from freshwaters are similarly alarming.
Tranvik et al. (2009) estimated that freshwater systems globally emit ~1.4 PgC (1400 MMT as carbon dioxide equivalents) per year. That magnitude of carbon dioxide emissions is equivalent to ALL fossil fuel emissions! Bastviken et al. (2024) added to the alarm and estimated global methane emissions from freshwaters, which are increasing rapidly due to dam construction and reservoir creation.
Quantification of the very high carbon dioxide emissions from freshwater systems has put into question how well scientists know the global greenhouse gas (GHG) balances between the ocean and terrestrial sinks. Bastviken et al. (2024) stated that, “the terrestrial GHG sink may be smaller than currently believed, and data on GHG release from inland waters are needed in future revision of net continental GHG fluxes.”
“Solutions” to accelerating urban wastewater discharges to coastal/freshwater systems are dominated by sanitary engineers and scientists who are trying to convince policy-makers and regulators that the world needs a massive expansion of capital-intensive sewer systems, or installations of expensive “alternative" septic systems, or pipes to take our wastes “offshore” in the hope of restoring the water quality of valuable aquatic ecosystems. Such calls require large and unprecedented government expenditures and residential tax increases.
There are alternative community-based models that challenge these "solutions". See the integrated restorative aquaculture with UD nutrient diversion model developed by The Green Center in a coastal area of New England, USA (described on our EAI website in the “Projects” section).
References
Bastviken, D. et al. 2010. Freshwater methane emissions offset the continental carbon sink. Science 331, https://doi.org/10.1126/science.119680
Duarte, C.M. and Y.T. Prairie. 2005. Prevalence of heterotrophy and atmospheric CO2 emissions from aquatic ecosystems. Ecosystems 8: 862–870, https://doi.org/10.1007/s10021-005-0177-4
Frankignoulle, M. et al. 1998. Carbon dioxide emission from European estuaries. Science 282,
https://doi.org/10.1126/science.282.5388.434
Green Center, Two-Month Urine Diversion Project Final Report MASSTC County of Barnstable MA. https://newalchemists.files.wordpress.com/2024/03/green-center-ud-project-final-report-2024-03-13.pdf
Lu, M. et al. 2024. Worldwide scaling of waste generation in urban systems. Nature Cities, 1, https://doi.org/10.1038/s44284-023-00021-5
Rich Earth Institute, https://richearthinstitute.org/
Tranvik et al. 2009. Lakes and reservoirs as regulators of carbon cycling and climate. Limnology & Oceanography 54(6, part 2): 2298-2314.
Tuholske, C. et al. 2021. Mapping global inputs and impacts from human sewage in coastal ecosystems. PLoS ONE 16(11): e0258898. https://doi.org/10.1371/journal. pone.0258898
Wald, C. 2022. The urine revolution: how recycling pee could help to save the world. Nature 6502, 202. https://doi.org/10.1038/d41586-022-00338-6
Wallace, R. et al. 2014. Coastal ocean acidification: The other eutrophication problem. Estuarine, Coastal and Shelf Science 148 (2014) 1e13
