What's your question? Ask

It sounds like a sulfur reducing bacteria has taken over your lawn. This is going to be a tedious process to bring it back to a usable state. I would have that same university test for what bacteria is causing the issue. You may need to kill this off before the sulfur can be flushed out of the soil. Likely, after killing the bacteria, you can use citric acid to remove excess mineral content from the soil, as well as flushing with large amounts of water, after.

Well, I am all the way in Texas so you may have a tree that does not grow on this side of the pond but last month in the park, a Cottonwood Tree was causing similar trouble. The light white fluffy fibers can accumulate in yards, get into homes, block drains and gutters, and clog up filters. These poplar trees shed cotton during June and July.

I have read that a high-concentration vinegar directly onto the soil could last longer than a month but note that many organic diluted vinegar solutions are sprayed on the plant leaves. Small amounts/drops that fall while spraying may last just a few days. There are sometimes plants/weeds that may require additional counter measures to fully remove.

It sounds like this spot is diseased with something that covers a broad range of plants. This happens when soil remains too wet, typically.

You may need fungicides, or biofungicides to clean up the area. Here are some articles that will help:

https://www.gardeningknowhow.com/special/organic/biofungicide-information.htm

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

https://www.gardeningknowhow.com/garden-how-to/info/what-is-copper-fungicide.htm

If you can let it dry out for an entire year, then it will be safe to plant by this time next year. You can, also, attempt to bake the soil on the lowest setting for 3 hours. Generally, you want to aim for a temperature of about 150, but this is not possible with most ovens. This is what I would do, but both methods work, equally, as well.

There are many ways to go about this. Here are some articles that will help:

https://www.gardeningknowhow.com/garden-how-to/projects/how-to-solarize-garden-beds-to-eliminate-garden-pests-in-the-soil.htm

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

https://www.gardeningknowhow.com/garden-how-to/info/what-is-copper-fungicide.htm

https://www.gardeningknowhow.com/special/organic/biofungicide-information.htm

If all attempts at killing the disease fail, you can try your local extension service:

https://www.gardeningknowhow.com/extension-search