silver creek

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Rothschld, Wisconsin
Some of you may not remember that phosphate detergents were common place until algae blooms began to happen. Then when the algae died in the winter, it consumed the oxygen in the water and there were fish kills. So the EPA and individual states started to ban phosphates first in laundry detergents and then even in dishwasher detergents.

Phosphates in detergent - Wikipedia

Low-Phosphate Dishwasher Detergents That Work

Even farmers got into the act with farming practices that left a buffer zone between the fields they tilled and any adjacent waterways. In Wisconsin, dairy farmers cannot spread manure in the winter in fields near streams because when the snow melts, the manure gets into the streams.

Remember when lawn fertilizer always contained phosphorus. The "NPK" for nitrogen, phosphorus and potassium. Now you CANNOT buy NPK law fertilizer unless is for newly seed lawns. Several states banned NPK fertilizers for lawns. See "these states prohibit phosphorus fertilizer application unless it is for (1) curing a lack of necessary phosphorus, (2) establishing new turf, or (3) repairing turf."


Starter fertilizer below for new lawns 25% Phosphorus.

Notice the "O" in the bag of regular fertilizer below meaning ZERO for the "P" (phosphorus)

These measures serve to reduce the phosphorus that gets into the rivers and low phosphorus causes didymo blooms.

This is my personal theory and I have not read this proposed in any literature but it makes sense to me. I doubt it is the whole story but I think the wholesale banning of phosphates has got to have made an impact on more frequent didymo blooms.


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south of Joplin
That was my theory also, SilverCreek, because the timing was right, but scientists might say that high P detergents and fertilizers didn't keep didymo in check during all those hundreds of years previous to current climate change. They seem to think that because no one wrote about didymo before the mid/late twentieth century that it didn't flare up back in the olden days, my belief is the anglers of the late 19th and early 20th century didn't write about it because it wasn't unusual enough to be remarkable.
Wikipedia says "Phosphorus has a concentration in the Earth's crust of about one gram per kilogram"; so the snow leeching P and melts flowing it into the streams theory is somewhat believable.
However after Bothwell's "Boots" paper I'm reluctant to give that bunch a lot of credit for veracity.
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Annapolis, MD
Exactly! They treated the acid rain problem in Western Maryland with a form of salt. That program started may years ago and I think its still going on.