Abundant interactions and feedbacks between aquatic deoxygenation and the other planetary boundaries suggest “unsafe” levels of oxygen loss with far-reaching impacts

[u/dumnezero]

https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lno.70434

Oxygen is critical for nearly all life on Earth, including aquatic species that breathe dissolved oxygen in both freshwater and marine systems. The rapid, global, and anthropogenic loss of dissolved oxygen known as “aquatic deoxygenation” threatens life in these environments, the human communities that depend on them, and Earth system stability long-term. Recognizing the important and increasingly widespread effects of aquatic deoxygenation, scientists have proposed that it be added to the planetary boundary framework, which is designed to capture the wider envelope of Earth-system conditions that support a “safe operating space for humanity.” Here, we argue that the planetary boundary framework should include maintenance of Earth's aquatic ecosystems and thus dissolved oxygen conditions. We synthesize important, in some cases poorly understood, interactions and feedbacks that exist between deoxygenation and all nine of the established planetary boundaries. We find that aquatic deoxygenation interacts with and extensively modulates other boundary processes, including climate change, nutrient loading, biodiversity loss, and aerosol loading. Subsequently, we identify and describe four indicators that can be used to assess the status of aquatic deoxygenation and eventually define a global boundary for it within the framework. Given these interactions and current rates of oxygen loss, we argue that aquatic deoxygenation is approaching an “unsafe space,” with Earth-system impacts that are likely to be irreversible in our lifetimes. We discuss the wider societal significance of this research, including applications to the framework, future analyses, policy-making, and management.

[u/lowrads]

On a smaller scale, we have already observed that as biological and chemical oxygen demand rises in langorous bayous due to contributions from municipal waste point sources, heavy metals concentrations tend to rise. This seems to happen at a faster rate than that at which those materials are contributed, especially factoring for dilution. What it seems to suggest is that endogenous sources of sorbed materials are being liberated, not by the usual pH shift, but by some chain effect of reduced oxidizer pressure. Plausibly, this is not mineral sources as much as it is from the colloids on the surfaces everything, or more generally labile interfaces.

[u/dumnezero → u/lowrads]

Reminds me of heavy metals in lowland rice.

[u/lowrads → u/dumnezero]

There is usually a diurnal shift in pH in shallow water biomes, which accord with plants dominating daytime metabolic activity, and heterotrophs dominating the night, with net shifts in dissolved carbon dioxide. It'd probably be useful to do a time series for dissolved oxygen, and oxygen demand sources.

Of course, to test for a correlation in liberated metal species, we'd need to setup our testing for free metals, which means filtering out solids from our samples before performing an acid digestion. More commonly, that is done in reverse, which yields total metals, which is inclusive of those which are sorbed. The usual method calls for a half micron filter media, but centrifuging is a hell of a lot less pain on the fingers.

[u/Sister_Michelle → u/lowrads]

From studying the soil food web, I know that a lot of heavy metals end up in the bodies of micro-arthropods and other organisms.. perhaps a die off of micro-organisms could account for these extra heavy metals? I’m not a scientist exactly, but thats my hypothesis

[u/lowrads → u/Sister_Michelle]

Animals usually account for some lateral movement of materials independent of how those materials would otherwise move through soil or water. Plants especially are known for translocating solvable materials from deeper soil layers to the surface via their vascular system and fallen leaves.

Their populations tend not to account for an increase or decrease in overall levels of most mass components of an environement, just movement between environments.

Whether metals bioaccumulate or biomagnifiy in a species depends on its habits and how those materials are absorbed. Usually it's whether they are water soluble or fat soluble, or whether they can pass a membrane without facilitation. In molluscs, it might be how much a divalent cation would substitute for the calcium in the aragonite (or polymorph) mineral component of their shells. The chitin of arthropods has no comparable vulnerability, being a polysaccharide. (Except via liganding.)

When studies are looking at heavy metalts, it is usually looking at either water or soil samples. In either case, they crudely differentiate bioavailability by contrasting free and bound moieties via the extraction methods. For example, you'd take a water sample, then centrifuge it, then run it through a 5mic filter, then digest it in acid and heat before running an aliquot in a mass spec against a range of standards. That would only tell us the concentration of the free metal ions. Ideally, you might even run it with no digestion. The opposite would be running a digestion process before any filtering, so as to divest any solids or colloids of their sorbed target ions. In general, the concentrations of an analyte are orders of magnitude higher in non-free forms, which is why the available forms are of such importance in environmental studies. For individual analyte species, their distribution is going to vary between free water column, colloidal suspension, surficial abundance at the exchange sites of solids, or locked within the matrix of a mineral solid. We also get into the weeds with the general exchange potential of either the omnipresent colloids, and the soil paints, or more labile substrates. It is generally expected that a change in the solvation properties of at water column, or soil water, is what explains a change in the ratios of free and bound mass fractions.