using bedrock geology info to fish in acidrain areas

[pcray1231]

I've always thought of Indian Run as a freestoner, though I wouldn't be shocked if it does indeed have a little limestone influence just based on where it's located. There are a few brookies in it, but it seems to be dominated by browns.

The area I know best is western PA, though it's been a while for many. Venango/Crawford/Erie County area? A lot of these are 100% browns, but I'm not sure that any remain class A into the true headwaters. Still, they have only browns when they get pretty small. Cherry Run as an example. Another is the whole Pine/Caldwell drainage, which includes the W. Br. which is class A, as well as tribs like Campbell, Golby, Henderson, Porky, Stony Hollow, Middle Branch of the West Branch (lol), Three Bridges Run, Dunderdale. Spring Creek is in the Brokenstraw drainage (although not a true limestoner, it does have a T_Alk of 70 due to a small driftless region). Farther south, you have the infamous Hell Run, fished by many members of this board. It runs into Slimy Pebble in McConnell's Mills. All browns I believe. Pine Creek in Armstrong County fits in the same general criteria, though not as good. All browns to the headwaters.

I think in Berks Cty, Beaver Run is 100% browns? I've always considered it a freestoner like Indian Run, but at a T_Alk of 20 it likely has a touch of limestone influence, I suppose. Even the W. Br. of the Brandywine has a few wild browns up to it's upper reaches. It's not a real strong population but I don't know of any brookies at all up there.

Rambo Run in York Cty is not only class A browns from the headwaters, but it also has an unnamed tributary that is class A browns from the headwaters. T-Alks of 19 and 30, respectively. Could certainly claim some limestone influence, but they're not generally thought of as limestoners. I've never fished these streams and don't know whether they have any brookies, but they are listed as class A browns, not mixed. Un-named tributary from headwaters to mouth is about as "headwaters" as it gets.

One constant does seem to be that in these streams, even if they are freestone by nature, they do tend to have good alkalinity/fertility, which would give credence to the pH argument.

Then you get the Poconos, which are just weird sometimes. Take something like Devil's Hole. There is a SHARP dividing line between 99% browns and 100% brookies. It's a waterfall. I don't think anyone could argue that the water chem, or structure, drastically changes from above to below. This is not a case where anything habitat related makes much sense. But rather, it's clearly a case of opportunity, or as RLeeP states, "access" to an established BT population. I'm quite confident that if the falls were somehow removed, browns would take over areas upstream. How far up? I dunno. But even below the falls the T_Alk is in the 5-6 range, in other words, very low. And the brown trout population is well beyond present, they're quite abundant.

 

[RLeeP]

>>Another is the whole Pine/Caldwell drainage, which includes the W. Br. which is class A, as well as tribs like Campbell, Golby, Henderson, Porky, Stony Hollow, Middle Branch of the West Branch (lol), Three Bridges Run, Dunderdale. >>

At the least, Golby, Henderson, Porky, Three Bridge, the Middle Br. and the West Br. itself all have brook trout populations, as does Pine proper. The others may as well, I don't know about them. All (with the possible/probable exception of Three Bridges where brookies may still comprise the majority) these ST pops are the minority component of the overall population in the stream, but they're there.

 

[sarce]

Pat, you've caught wild browns in the west branch? I've never heard that before. The east branch has a fair amount. And I can also guarantee indian run has zero limestone influence. There is no limestone in that area. Generally, Chester County north of rte. 30 has pretty sucky geology (the lone exception being Valley creek drainage which is right along 30).

darn, I actually have a decent point to make about geology and water temps and brookies vs. browns. If this thread's still going in a few days I'll post my thoughts. gotta run

 

[RLeeP]

When I mentioned that I knew of half a dozen almost certainly all BT streams in Erie and Crawford counties alone, all the streams I had in mind are in the upper French Creek drainage (say, above the borough of Venango...). Well, with one probable exception that is in the Erie County portion of the Brokenstraw drainage. Pretty much everything in the Sugar Creek and Spring Creek (Warren County) watersheds has at least a small brook trout population. Actually, weirdly enough, the massive Spring that sits at the top of the Class A section on Spring Creek actually makes the main stem habitable for ST again after probably being barren of them for the better part of 10 miles. And the upper Spring Creek drainage, up into the branches, always had some of the better brook trout populations anywhere within an hour of where I grew up in central Erie County.

 

[k-bob]

Updated well-water pH numbers below. I sometimes consider two streams that seem about equally attractive (both natural repro, similar drainage and gradient). If one has catskill headwaters geology, while the other is pottsville, these may be interesting. At least when choosing tiny streams from maps with limited experience and info. As TB notes, headwaters geology is another factor to consider, and not a single number that's all you need to know. For example, there are sometimes nearby streams with similar geology, one class A while the other isn't, so other things are going on...

 

[duckfoot]

Mmmmm...data...

 

[Chaz]

Perkiomen Watershed is freestone, and has only browns, a lot of them, but it is only browns. PH is fairly high but according to the PFBC it is not a limestone stream if it has under a T/A of over 85? It think that is the threshold Mike quoted.
A stream can have a high PH and not be a limestone stream or limestone influenced.

 

[troutbert]

Geology and streams is a large and complicated topic, and cannot be fully discussed here. But here is one approach to the topic.

Look at the geology maps for streams that you have fished. And start to see the connections and correlations between what you've seen in the landscape, and the what you see on the geology map.

One thing that those of you who love high gradient, gorge streams with lots of rocky habitat will find is that those streams are flowing through infertile rock formations.

And that the fertile streams are much lower in gradient, with wider valley floors, and boulders are rare.

This is because infertile rocks are hard, resistant to erosion. Fertile rocks are soft, and much more easily broken down.

 

[k-bob]

right most steep ravine streams flow through low buffering bedrock... but there are some steep streams with more moderate buffering bedrock types in headwaters or even further down. streams that are small steep and on the acidic side seem ST favorable of course.

 

[PAgeologist]

Troutbert - "This is because infertile rocks are hard, resistant to erosion. Fertile rocks are soft, and much more easily broken down."

This is not really true. Limestone can be extremely hard - I've taken samples that had 15000 to 20000 psi compressive strength. For reference - your average concrete is typically 4000 to 5000 psi.

Limestone dissolves easily due to its chemical composition not due to its softness. Carbonates react readily with acidic water (ie the buffering process) - as part of this process the rock slowly dissolves over time and becomes weaker as its structure is destroyed by the acidic water.

Silica is very inert - it doesnt dissolve or react with water readily. This makes it more resistant to the weathering/erosion processes.

Dont think of it in terms of rock hardness. The rocks resistance to erosion and weathering and its reaction when in contact with acidic water are more important factors.

 

[Chaz]

So here's a question, at what level does Tot. Alc. cause the browns to be the dominant fish? Many of the Class A Streams have long sections of low T/A, lower down they change to brown trout and are dominated by browns, in some cases there is mixed pops. but it seems to change in some streams rather abruptly.

 

[k-bob]

interesting study on a small PA stream that had its pH drop by .92 pH units in an hour in response to 3 in rain/5.5 hours:

http://onlinelibrary.wiley.com/doi/10.1029/WR022i006p00905/pdf

late in article: "Storm 16 from this study may serve to further support this theory of insufficient buffer reaction time in that the stream pH dropped considerably (0 .92 pH unit) within 1 hour of the onset of precipitation, and the resultant influence on the alkalinity was that levels were reduced from 180 #eq/L to 20 #eq/L (CaCO3)."

chaz on your previous point: Not sure, but I think some streams have both a moderate base-rate pH and low alkalinity (alkalinity = buffering capacity in response to an acidic event). If the base-rate pH is not particularly low, BT may thrive even w/ low alkalinity noted on class a list. Lower Devils Hole. think of it as pH slack? someone know more?:

http://www.brodheadwatershed.org/ParadiseCreek/documents/DEHOCR04.pdf

 

[Chaz]

k-bob wrote:
interesting study on a small PA stream that had its pH drop by .92 pH units in an hour in response to 3 in rain/5.5 hours:

http://onlinelibrary.wiley.com/doi/10.1029/WR022i006p00905/pdf

late in article: "Storm 16 from this study may serve to further support this theory of insufficient buffer reaction time in that the stream pH dropped considerably (0 .92 pH unit) within 1 hour of the onset of precipitation, and the resultant influence on the alkalinity was that levels were reduced from 180 #eq/L to 20 #eq/L (CaCO3)."

chaz on your previous point: Not sure, but I think some streams have both a moderate base-rate pH and low alkalinity (alkalinity = buffering capacity in response to an acidic event). If the base-rate pH is not particularly low, BT may thrive even w/ low alkalinity noted on class a list. Lower Devils Hole. think of it as pH slack? someone know more?:

http://www.brodheadwatershed.org/ParadiseCreek/documents/DEHOCR04.pdf

From those numbers I'd say there is some sewerage going into Devils Hole, that may explain why the browns are further up than they used to be.

 

[RLeeP]

>>chaz on your previous point: Not sure, but I think some streams have both a moderate base-rate pH and low alkalinity (alkalinity = buffering capacity in response to an acidic event). If the base-rate pH is not particularly low, BT may thrive even w/ low alkalinity noted on class a list. >.

As I recall, this is correct and helps explains for example, why RT (as a species, at least as acid sensitive if not more so than browns) dominate the wild trout fisheries of the southern Appalachians..

 

[k-bob]

guess that's it works... the average pH for DHC in those 15 observations is about 6.75, and the class a list notes its low alkalinity. the pH of DHC may decline from 6.75 to 6 in a snowmelt or heavy rain, still within short-term BT tolerance.

another stream that starts at 6.25 pH and also has low alkalinity may have its pH reduced in snowmelt or rain, so be a ST stream.

places like the east branch fishing creek tribs that start at 5.6 pH may have low trout numbers (page 3-3 below)

http://fcwa.net/wp-content/uploads/eastbranchrestorationplan.pdf

 

[troutbert]

Maybe someone could explain that chemistry for us.

How is it that some streams have low alkalinity and a moderate base-rate pH?

And other streams have low alkalinity and low base-rate pH?

What is going on there?

 

[duckfoot]

troutbert wrote:
Maybe someone could explain that chemistry for us.

How is it that some streams have low alkalinity and a moderate base-rate pH?

And other streams have low alkalinity and low base-rate pH?

What is going on there?

Alkalinity for a trout stream, in chemistry terms, is nothing more than a buffering agent. You use a buffering agent to stabilize the pH of a swimming pool or hot tub so that the bleach doesn't eat away your skin.

Buffering agents don't contribute to the pH scale, but they resist changes.

If I were to dump a bunch of battery acid into two streams, one with a low alkalinity and one with a high alkalinity, the low-Alky stream will have a huge swing in pH, while the higher Alky stream won't change as much.

In other words, pH is how acidic, alkalinity is how much the water can resist change.

I'm sorry if that seems overly simple, but I am doing my best to simplify a very mathematically complicated subject that is a "weed-out" class for freshmen chem majors.

 

[troutbert]

What are the chemicals that create the buffering and what are the chemicals that create the base level pH?

 

[k-bob]

Dwight I dunno but Id look at the bedrock for ph?

duck foot: "pH is how acidic, alkalinity is how much the water can resist change."

OK, so lower devil's hole has a moderate pH, average of about 6.75 (7 is neutral, data in link a few posts above). And low alkalinity (T Alk of 5 on class A list for lower section). Class A BT.

I think lower DHC's combination of moderate pH, low alkalinity, and Class A BT can happen in part because DHC originates in catskill bedrocks. Given low alkalinity, its pH may decline with heavy rain or snowmelt, given near-7 pH starting value, BT can handle a temporary decline?

A low-alkalinity stream whose average pH is closer to 6 may be ST because BT could not handle a snowmelt- or rain-driven pH decline from that base rate. Those EBFC tribs whose average pH is 5.6 may struggle to maintain many ST.

pfbc info on T alk.. influence of soils?:

http://fishandboat.com/images/pages/qa/trout/alkalinity.htm

 

[duckfoot]

troutbert wrote:
What are the chemicals that create the buffering and what are the chemicals that create the base level pH?

The word "alkaline" implies that they are the Earth minerals, AKA Columns I and II on the periodic table. Lithium, sodium, potassium, cesium, magnesium, and calcium are the common ones. Of those I listed, by far calcium carbonate (limestone, sea shells, and coral) is the most effective, followed by feldspar (the most common Earth rock) which carries potassium, sodium, and calcium.

k-bob wrote:
duck foot: "pH is how acidic, alkalinity is how much the water can resist change."

OK, so lower devil's hole has a moderate pH, average of about 6.75 (7 is neutral, data in link a few posts above). And low alkalinity (T Alk of 5 on class A list for lower section). Class A BT.

I think lower DHC's combination of moderate pH, low alkalinity, and Class A BT can happen in part because DHC originates in catskill bedrocks. Given low alkalinity, its pH may decline with heavy rain or snowmelt, given near-7 pH starting value, BT can handle a temporary decline?

A low-alkalinity stream whose average pH is closer to 6 may be ST because BT could not handle a snowmelt- or rain-driven pH decline from that base rate. Those EBFC tribs whose average pH is 5.6 may struggle to maintain many ST.

pfbc info on T alk.. influence of soils?:

http://fishandboat.com/images/pages/qa/trout/alkalinity.htm

Your assumptions are correct. It seems this Lower Devil's Hole has a flow that is either fed by pre-alkalized groundwater, or has the soil chemistry in the watershed to alkalize the naturally (or unnaturally) acidic rainwater. This said, since there is a low alkalinity in the stream, this tells me that a heavy rain and/or snowmelt will readily drop the pH to more acidic conditions.

Soils influence so much of stream chemistry because of rain and snow runoff that goes through a shallow aquifer system, and the high surface area of the soil means the water is more chemical influenced than a slab of rock.