fishing using bedrock geology: pottsville bedrock

[troutbert]

There is a great deal of very good fishing within the green area shown in the map in the OP.

Here's an extremely common situation. A stream STARTS out in Pottsville, and in that upper end, there are often zero fish of any kind, or a sparse population of brookies. The pH is just too low.

But then as the stream descends, it cuts down through through lower, more fertile layers. So the pH and alkalinity increase, and you often find very good fishing downstream.

It's very similar to the Swift Run example, except that that was in the ridge and valley region, where the infertile layer up on top was Tuscarora. And we are now talking about the Allegheny plateau region, and the infertile layer up on top is Pottsville. But the concept is the same.

 

[k-bob]

yes, look at bedrock changes in streams, where streams are in more than one.

 

[pcray1231]

Agreed,

And in those situations, I doubt it's simply where the stream is located. But % of drainage area above that point in which bedrock type.

A stream itself can flow over decent rock, but there is so little buffering added from the streambed itself. It's just a tiny area. These are freestoners, so we're not talking about massive springs that have flowed underground any great distances. It soaks into the soil and comes out in a large number of small springs.

So what we're really talking about is the buffering capabilities of the surface soil and rock, which are a combination of weathered bedrock and organic material (composting leaves and such).

So, you may have a stream that started in Pottsville, and there are no fish. It may cut into Shenango. But if that start drained a large, high flat area of Pottsville, and then it cuts sharply through a narrow drainage in Shenango, then most of it's water still represents the Pottsville formation and it's still not gonna be very good, even if the bedrock you are on is good. On the other hand, it could flow a long ways on Pottsville, but not pick up much water, then get bigger influxes once it hits a better bedrock type.

So at any given point, what you'd be interested in is the % of the drainage area above that point located in each respective formation.

One take-away would be that if you are in that situation (bad bedrock flowing into good bedrock), go downstream. Fishing may get better due to water chemistry, even if the structure/temperature gets worse. To a point anyway.

Limestoners are different. Water can flow through a poor formation and into a good formation before it ever reaches the surface.

 

[pcray1231]

I've seen that situation with migrating fish, as well. Highish acid concentrations kill eggs well before they kill fish. I'm not even sure that it bothers fish all that much, other than the food base.

In NW PA, I've seen a lot of situations where somewhat acidic headwaters lack much in the way of reproduction. And they lack smaller fish because of it. But in mid-summer, when lower portions with better chemistries are getting borderline warm, fish come upstream. Whether the acid bothers them or not I dunno, but they prefer it to warm water.

It seems weird to have downstream areas loaded with juveniles, where temps are more borderline, but better structure and food exists. But colder upstream areas with less food and cover have the better fish. It seems arse backwards. But it happens. I believe it's due to water chem. The downstream areas are the breeding grounds out of water chem necessity. The upstream areas are holdover grounds due to water temp necessity. The older fish are found upstream.

It may even be a contributing factor to the oft-repeated observation that, along the northern tier, lower trout populations = bigger fish. (the other situation being that a few go downstream to better food bases and even warmer temps, but that one cold spring is capable of oversummering a fish or two, which end up being the king of a rich roost the rest of the year)

These streams usually lack any strong brown trout pops in their brookie dominated reaches, but the real beasts are the rare browns that get up in there from wherever, set up shop in a migration area, and pick off the migrating brookies that must pass through their adopted lair. That's how you grow the odd 20" brown trout in small acidic water with an otherwise poor food base.

 

[FarmerDave]

Pat, yea, PH bothers them. In probably half of those little brookie streams that you fish up in the ANF, if PF&BC stocked rainbows in them in the Spring, they would be belly up in under a half hour. In a quarter of them, browns would be belly up, too. And I am being conservative.

Brook trout can "survive" much lower PH than either Rainbow or Brown trout.

Brook trout can survive down to about 4.0. I know, I did a double take on that, too. One lab study showed even 3.6. If you parked your Subaru in that, after a year all you would have left is the tires and a pile of plastic, with brook trout using it as cover. And even the tires would be no good anymore.

Brown can "survive" down to about 5.0 and Rainbow more liked 5.5.

As far as the eggs go I think the difference in PH is smaller.

That said, Brook trout can migrate or seek out upwellings with higher PH for spawning. That is how you can have some reproduction in some of those streams.

Also browns can migrate up into those streams in the summer for the colder water because the PH is higher then.

So I wasn't arguing with you, just adding to the discussion.

 

[pcray1231]

Agreed that too high a concentration kills them, and I'm not going to deny your numbers as to lethal levels for various species.

But, it kills eggs much sooner (err, umm, meaning it has to be more acidic to kill the fish than the eggs). We're typically talking about acid levels that are non-lethal to fish, but maybe lethal to eggs.

And I have no idea if non-lethal levels "bother" them. We can't just ask one. And they got a brain the size of a pea, if it doesn't kill them, they may pay it no mind.

The best evidence I have of anything is that stocked trout do indeed tend to leave acidic streams soon after being stocked. Not die, just leave. Quite often downstream to whatever that stream runs into. That said, come summer when that other stream warms up, they come right back upstream into the colder acid. So obviously it's preferable to the warmth.

But I also find it quite plausible that presuming non-lethal levels, a fish will get conditioned to it. The stocked trout phenomena is a sudden shock to their systems, after typically being reared in limestone spring fed hatcheries. May be different if the acidity rise is gradual. Like putting a frog into boiling water vs. heating it up slowly (I know, that's a bad analogy, as I've tried it, and the frog cooks either way, lol).

And populations certainly could become resistant. The problem exists that it's lethal to the eggs, but still, assuming a migratory population you could have the eggs in a more basic environment while still selecting for fish that are more tolerant of acid.

 

[FarmerDave]

I'm pretty sure I already agreed with at least most of that in my previous.

Wasn't arguing with you then and am not now. We are just talking two slightly different aspects.

 

[k-bob]

nice summary of some bedrock impacts on water:

“PVA, CCP, and MCG bedrock types, respectively, exhibit low, intermediate, and high bedrock fertility and groundwater pH values.”

(note: PVA = pottsville and alleghany; CCP = catskill, chemung, pocono; MCG = mauch chunk, greenbriar)

Paper: Influence of bedrock geology and tree species composition on stream nitrate concentrations in mid-appalachian forested watersheds