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 scientist, a family, a community do if nation states are so irresponsible for everything we hold dear? Of course, we can decrease emissions and overconsumption as much as possible by moving to renewable energy, better diets, and become climate activists. These are global priorities for every citizen and family. Our community of aquatic scientists has additional scientific responsibilities to understand as much as possible and propose innovative actions to assist in the recovery of aquatic ecosystems from accelerated anthropogenic damage. Actions go beyond a need to understand IPCC projections of climate impacts from carbon emissions.
Ocean acidification is a terrifying concept; but the most urgent 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 control the Earth’s coastal and freshwater N, P cycles. The Millennium Ecosystem Assessment predicted an increase in global sewage emissions of 12.0–15.5 Tg N and 2.4–3.1 TgP/year by 2050, and these may have already been exceeded. Lu et al. (2024) found that as a city grows energy use becomes more efficient and greenhouse gas emissions (GHG) 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.
GHG emissions from unsustainable burning must decrease; but we are in a major nearshore, coastal/freshwater acidification crisis due to the accelerating quantities of nutrients (N to estuarine/coastal ecosystems, P to freshwaters) being discharged causing severe hyper-eutrophication and a cascade of adverse impacts to ecosystem functions and critical habitats. Coastal/freshwater acidification is due to the intensity of nutrient loading rates as there are clear links between acidification, hypoxia, intense algal blooms, and eutrophication. pCO2 conditions being experienced now 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 CO2 increases.
Nutrient discharges are the main cause of coastal/freshwater acidification, not GHG CO2 dissolving into water. Many (most?) freshwater and coastal ecosystems are net heterotrophic (Duarte and Prairie 2005); they are “sewage-fuelled” marine ecosystems discharging CO2 to the atmosphere. Jamaica Bay off New York City is a hypereutrophic estuary that receives ~90% of its N from four wastewater treatment plants that discharge ~ 1 billion liters of effluent daily. pCO2 concentrations in bottom waters in summer exceed 2000 μatm (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 CO2/d to the atmosphere; CO2 emissions from the Scheldt estuary, Belgium/Netherlands were 2/3 due to heterotrophy and 1/3 due to ventilation. Bastviken et al. (2024) found that, given recent global freshwater CO2 emissions of ~1.4 PgC (CO2 eq)/year, freshwaters were a very important component of the global GHG balance comprising ~79% of the terrestrial GHG sink. They 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 proposals by policy-makers, regulators, sanitary engineers and scientists for the massive expansion of capital-intensive sewer systems, the requiring installations of “alternative septic systems, or dilution “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.
An alternative community-based, integrated restorative aquaculture with UD nutrient diversion model is underway in a coastal area of New England, US. It illustrates the potential of nature-based, solutions which can accelerate the development of low trophic level aquaculture and help ameliorate the nutrient/carbon crisis of aquatic ecosystems. Efforts combined applied science from Europe and North America in shellfish aquaculture with urine diversion (UD). UD is the concept of separating and collecting urine from wastewater at the source for reuse as fertilizers (struvite). Approximately 80% of the N and ~60% of P in wastewaters are from urine; but urine is only ~1% of wastewater volume (Wald 2022). The Green Center developed low-cost UD and the community approved zoning and guidelines for shellfish aquaculture as public-private partnerships. The community provided shellfish farmers with floating gear and seed. Farmers paid a $20,000 access fee to the community and were obligated to grow a preset minimum biomass on all leases. In 2023, shellfish farmers harvested 1.43 million oysters from 0.6 ha. The community used a peer-reviewed science finding that each oyster harvested removed ~0.28 gN. Thus, in 2023, a total of ~400 kgN was removed from ~0.6 ha of oysters. N removal by oysters offset ~$4.5 million in costs for new sewer infrastructure and harvests produced ~$350,000 in revenue.
Restorative shellfish aquaculture removes nutrients in situ already present, while UD prevents new nutrients from entering aquatic systems. Citing 2023 data scientists calculated that some N-impaired estuaries from septic leachates would not require expensive sewering or alternative septic systems at all. Although UD alone could meet nutrient reduction goals, restorative shellfish aquaculture improved water quality and would help reduce capital investments. Restorative shellfish aquaculture and UD would be much more rapidly implemented and would improve aquatic ecosystems sooner than the decades-to-implement sewers and septic systems.
Alternative, integrated ecological approaches to aquatic ecosystem restoration are nature-based solutions that create new community revenues, jobs, produce nutritious, tasty foods, and recover valuable fertilizers. They use fewer natural resources, are more environmentally beneficial and sustainable than conventional solutions, less expensive, and would avoid future, very large GHG emissions. A nature-based solution incorporating shellfish aquaculture and UD demonstrates how homeowners and coastal communities can work together to better accomplish environmental restoration and provide an alternative to investments in capital intensive sewer/septic systems being promoted worldwide as the sole solution to our aquatic/coastal crisis.
References
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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
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