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Basically what would be the long term effect on the health of ecosystem of a lake if tons of powdered silver is mixed into a lake?

This question comes from a hypothetical situation where a lake has been desecrated by evil magics. Water can be purified in flasks by mixing some powered silver into the flask and doing a ritual over it. The clerics of the kingdom know of the ritual and have the resources to do it on this scale. This is the only way they know for purifying the lake of the desecration.

While magic is involved the end result of the magic is a clean lake that just got a lot of powdered silver dumped in it.

What would the damage to the lakes ecosystem be in the months/years following the ritual?

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    $\begingroup$ Poor werewolves, they will die from dehydration. $\endgroup$ – Renan Aug 18 '18 at 4:34
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tl;dr your decomposers, fish, microbes, and clams would all be adversely affected. This will probably be blamed on the curse, though.

https://pubs.acs.org/doi/abs/10.1021/acs.est.6b05508 This is a study on the effect of silver nanoparticles on ecosystems. Here’s my quote:

Minimal variation in the size and surface charge of AgNP indicated that nanoparticles were rather stable during the experiment. Five days of exposure to 0.05 and 0.5 μM AgNP in microcosms shifted bacterial community structure but had no effect on a suite of microbial metabolic activities, despite silver accumulation in the decomposing leaf litter. After 25 days, however, a broad range of microbial endpoints, as well as rates of litter decomposition, were strongly affected. Declines matched with the total silver concentration in the leaves and were accompanied by changes in fungal and bacterial community structure.

Basically, what it is saying is that prolonged exposure to silver nanoparticles causes significant change in decomposing bacteria and fungi, and that silver lasts a long time (minimal variation on size) By 25 days of exposure, metabolism and decomposition rates were affected, and by 5 the structure of colonies had changed. Perhaps after longer term exposure they might die.

Given that silver powder is similar to silver nanoparticles, I would expect similar effects to all that drink from the tainted water. Decomposers would be affected at the very least, and since they are an integral part of an ecosystem, I would expect long term adverse effects.

EDIT:

Even better, I found a Wikipedia page on the impact of Ag0 on environment: https://en.wikipedia.org/wiki/Environmental_impact_of_silver_nanoparticles#Toxicology_in_aquatic_environments

Basically, it says that it is extremely adverse to microbes. The microbes get eaten by bigger things, like fish.

... can accumulate and block the regulation of Na+ and Cl− ion exchange within the gills of fish, leading to blood acidosis which is fatal if left unchecked.

As fish eat phytoplankton, the silver accumulates within their circulatory system, which has been shown to negatively impact embryonic fish, causing spinal cord deformities and cardiac arrhythmia. The other class of organisms heavily affected by silver nanoparticles is bivalves.

Good luck.

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    $\begingroup$ So things wouldn't rot away? That could be seen as purification working too well. $\endgroup$ – Mołot Aug 18 '18 at 10:50
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    $\begingroup$ @Mołot they would rot more slowly, and lots of stuff would die (see answer below) $\endgroup$ – JSCoder says Reinstate Monica Aug 18 '18 at 22:03
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Copper and silver are both toxic to algae and water organisms. Copper is used more often in that role because it is cheaper and bronze is a good structural metal. Bronze urns and flower pots keep the flowers fresh longer by inhibiting bacteria and they discourage mosquito larvae if these vessels collect rain. You can simulate this some by putting a penny in the bottom of your flower vase. When I change the water of the aquarium I have a coil of copper pipe I leave in for a few days, which prevents the water from turning green for months. I have to take the coil out after a day or two because the fish stop eating and get listless.

Silver is chemically similar to copper and has many of the same properties as copper as regards killing algae and microbes. Silver is better tolerated than copper in human tissues. Metallic silver is used in burn creams and the like. Silver metal nanoparticles are used to control algae and microbes. https://www.hindawi.com/journals/bmri/2015/893049/

I think this much silver will increase silver ion concentration in the water. It will be directly toxic to algae, protozoans and animal life. The animals might withstand it but the algae will not and you will crash the base of your food chain; fish that survive the silver will starve.

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