Freestone vs. Limestone

[afishinado]

To further Midnights point, Big Spring's temp variation is less than one degree F when comparing the August reading to the December reading. Constant 52*.

 

[Chaz]

I won't argue that the limestone springs the feed limestone streams don't vary much. All I'm saying is that the streams themselves do vary a lot more than most anglers think. In other words, many people will write that they have a comstant temperature, nothing could be farther from the truth. Spring Creek will vary from rouhardly a constant temperature.ghly 40 degrees in the winter to 75 degreeis n the summer.

 

[pcray1231]

I'm with Chaz on that one.

Midnight, you are correct, the water temp AT THE SPRING doesn't vary that much throughout the year. But, again, FREESTONERS ALSO COME FROM SPRINGS, and the same is true of those springs, it's essentially the same temp year round.

The temperature thing is purely a function of how far away from the springs you are. Water temps adjust to air temps once the water is on the surface, and the farther away from the spring you are, the more it will vary with the air temps/seasons.

It's just that, because limestoners often have very large springs, it is possible for a sizable stream to be very close to it's source springs, and thus, it is possible for a large stream to stay fairly consistent in its temps. It's also possible to add a new spring downstream, which can be large enough to rejuvinate the temps on its own. Of course, "possible" doesn't mean "is", and limestone streams far from their springs can vary quite a bit in water temps.

Freestoners, on the other hand, because the springs are small and evenly spread out, grow slowly. Once the stream gets sizable the vast majority of its flow is far from it's source springs. So while small freestoners act like limestoners in water temp, it's hard to find larger freestoners which stay consistent in water temps.

 

[ryguyfi]

unforgiven wrote:
Perfect. Thank you Bozeman and Fishidiot.

He called you Bozeman.... I officially hate you more.

 

[jayL]

Don't hate me. It was 16 below this morning.

Save your jealousy for when I am fishing my life away this spring.

 

[midnightangler]

FREESTONERS ALSO COME FROM SPRINGS, and the same is true of those springs, it's essentially the same temp year round.

If you were to compare the fraction of water on a freestone stream (like Slate Run) that comes from springs it would be far less than what you get from springs on a true spring creek like the Letort. Freestoners like slate run depend heavily on precipitation to maintain flows that are suitable for trout. The flow in true spring creeks comes directly out of a limestone aquifer, and they will maintain relatively constant flows even without recent rain. If you go to slate run in the summer after a month without rain, it will look almost like a dry streambed. If you visit the letort at the same time, it will look basically the same as it always does.

It is important to make a distinction between "Limestone streams" and "Limestone-influenced" streams. True spring creeks like the Letort, Big Spring, Falling Spring, and others maintain very constant temperatures. Since the streamflow is primarily derived from subsurface sources, these streams don't tend to get high and muddy after rainfall to the same extent as streams fed by surface water.

Spring Creek is not a true spring creek, although it does have substantial limestone influence. It is fed both by small limestone streams (like Cedar and Thompson runs), limestone springs and small mountain freestones like Galbraith gap run. The same is true for Penns creek, the Little J, and Big Fishing Creek, all of which have varying degrees of limestone influence.

Penns creek is an especially weird case. Even though it is fed by a giant spring, the spring at penns cave must connect directly to surface sources / sinkholes as the flow coming out of the cave can vary significantly. After a heavy rain, the flow coming out of the cave is often muddy. Compare that to say, the flow in the ditch on Big Spring. It would take a pretty extreme rain before that would even begin to get dirty.

Obviously, there is not a clear line between a freestone and a limestone stream. It is a continuum. The point is, if someone is talking about a limestone stream having a constant temperature, they are talking about true spring creeks and not limestone influenced streams and rivers, which are a different animal. Many people have a tendency to refer to all streams with limestone influence as limestone streams. This probably confuses a lot of people, especially those who haven't visited true spring creeks like the Letort.

 

[Chaz]

In the example above of Big Spring, there is approximately 2.5 degree difference at the spring year round. It is a very stable stream in terms of temperature at the spring. However if you go there on a summer day when it's 95 degrees outside the water temperature at Newville will be in the 70's.
I recently saw a study by USGS on their website that compared streams inflow, some of the streams had a base flow of 90% from springs.
So going back to my original statement, yes limestone streams are a more constant temperature, but they are most certainly not a constant temperature.
Anyone arguing that Penns, Spring, and some other big limestone streams aren't "classic" or "true" limestone streams are just saying that to justify their argument.

 

[troutbert]

A limestone stream is a stream that has most of its flow coming out of limestone aquifers.

Limestone streams can be very low gradient, or medium gradient. They can have very fine substrate (silt, sand, gravel) or they may have coarse substrate, commonly cobble, but even boulders and bedrock in some places.

They may have a fairly steady temperature (where they are close to their major springs). Or they may get warm in the summer and cold in the winter, where they are further downstream from their major springs.

They may flow clean most of the time. Or they may flow muddy after a rain, like Penns Creek, Yellow Creek, and Kish Creek.

They may have a low number of species of aquatic invertebrates, or a very high diversity.

None of those things are defining characteristics; they vary a great deal.

The defining characteristic of limestone streams is that the most of their water is coming out of limestone rock formations.

Streams such as Spring Creek, Fishing Creek, Yellow Creek, Kish Creek, Penns Creek are all limestone streams. Most of their water is coming out of the limestone. Some of these have a small amount of flow coming in from freestone tribs, but not enough to change the water chemistry very much.

 

[pcray1231]

If you were to compare the fraction of water on a freestone stream (like Slate Run) that comes from springs it would be far less than what you get from springs on a true spring creek like the Letort. Freestoners like slate run depend heavily on precipitation to maintain flows that are suitable for trout.

This reflects a misunderstanding of freestoners, and I don't think it is true. Aside from right after a rain (which is true of limestoners too), most of the flow in a freestoner also comes from springs. Outside runoff periods, which are short lived, nearly 100% of the water in both types of stream come from springs.

It's just that the nature of the two types of spring are very different. And yes, freestone springs vary much more in flow based on recent (last few weeks) precipitation, while limestone springs vary in flow based on longer term (last few months) precipitation trends. Because precipitation tends to even out over a period of months, limestoners are indeed a more consistent flow rate.

 

[pcray1231]

Easiest to explain in pictures. 🙂 Difference is all in whether or not the bedrock is water permeable.

With the shorter path between being absorbed by the ground and coming out in a spring, yes, the flow rate of a freestone spring varies more based on recent precipitation.

 

[JackM]

pc, interesting pictures. But the top photo does not show an "aquifer." And I think this helps understand your prior statement saying freestones also emenate from springs, just not out of limestone formations.

But, I think there is another subtle difference between freestone springs and limestone springs and that is that in limestoners, the majority of water entering the stream proper is doing so from deep in the aquifer, whereas freestone spring sources are likely to be areas of moisture saturation much closer to the surface of the land, which itself warms and cools considerably depending upon atmospheric conditions. Deeper water sources will not vary that greatly as they are insulated from the earth's internal heat and the sun's warming rays.

Ultimately, alkalinity and pH measures will be your greatest clue to where the majority of the streams source water is coming from.

 

[pcray1231]

whereas freestone spring sources are likely to be areas of moisture saturation much closer to the surface of the land, which itself warms and cools considerably depending upon atmospheric conditions

You're correct up to this point. Even at only a few feet deep, the ground and water doesn't warm or cool significantly throughout the year. Freestone springs are indeed just as constant in temperature as limestone springs. AT THE SPRING itself, that is. Yeah, I've tested it. There might be a degree or two difference, I don't have enough data to prove that one way or the other. But within reason, springs can be considered to be constant in temperature. From freestone springs, I've gotten no lower than 52 degrees in February and no higher than 57 in August. Limestone springs vary similarly, maybe slightly less if at all.

But freestone springs are much smaller, and freestone streams start small and grow slowly. So at any given point, the % of water in a mature stream that is close to it's source spring is often quite low, and no springs are large enough to "rejuvenate" the stream. Add to that that in dry periods, many of the springs dry up or are reduced to a tiny trickle, and low flows also contribute to warming of the stream.

So yeah, it is accurate to say that some limestoners show a remarkable ability to maintain constant water temps, whereas almost no freestoners do once they get to be a decent size.

And yeah, it's also accurate to say that the best way to tell is with the water chemistry. Limestone is water permeable because it dissolves in water, hence the mineral content. pH is not a super reliable measure. Pretty much all limestoners will be on the basic side, but freestoners can be either basic or acidic, and they can vary greatly from one day to the next. Alkalinity is a very good measure.

 

[troutbert]

Spring water temperatures are constant in freestone areas as well as limestone springs. Springs in the north country in PA flow at 48F, even when the air temperature is over 90F.

Their water temps are actually colder than the limestone springs in central PA (50F), and southcentral PA (52F).

The difference is that the sandstone aquifers in the freestone stream areas in PA simply do not have as much storage capacity as the limestone aquifers.

So they do not have the capacity to soak up water during times when water is abundant (snow melt and rainfall), so they also have less water to release into the streams during dry periods. So, the freestone streams have flashier flow than the limestoners.

In low flow in the summer, the water coming out of springs and groundwater is still the constant temperature. But the difference is that there is little volume of flow.

On a hot day, a trickle of shallow water gets heated up more quickly by the warm air and sun, then a high volume flow. Just as if you put a little water in a saucepan on a stove, you can bring it to boiling temp very quickly. But if you put a big pot of water on the same burner on the stove, it takes much longer to heat up.

 

[pcray1231]

Springs in the north country in PA flow at 48F, even when the air temperature is over 90F.

Their water temps are actually colder than the limestone springs in central PA (50F), and southcentral PA (52F).

Hmm, suspecting my thermometer reads a few degrees warm!!!! But very similar observations.

 

[troutbert]

pcray1231 wrote:

Springs in the north country in PA flow at 48F, even when the air temperature is over 90F.

Their water temps are actually colder than the limestone springs in central PA (50F), and southcentral PA (52F).

Hmm, suspecting my thermometer reads a few degrees warm!!!! But very similar observations.

It may vary a little depending on where you are in the "north country." Spring water temperatures are related to average annual air temperatures. So the further north and higher the elevation, the colder the spring water will be.

 

[midnightangler]

This reflects a misunderstanding of freestoners, and I don't think it is true.

I actually did my doctoral research on flow in porous media, so I have a pretty good grasp of these systems.

I don't necessarily have a problem with saying that "nearly 100%" of the water in a stream like slate run comes from springs. However, it will be true that most of the springs will only contribute to surface flow if there has been significant rainfall within the last 1-2 months. Either way, you have a system that is dependent on recent rainfall to maintain flow. Many seep springs are basically nothing more than runoff from rain events that happens below the surface. They don't store a significant amount of water to put back into the system when it doesn't rain.

Limestone springs are very different. A component of the flows from these springs comes from water stored in limestone aquifers, and the residency times for water stored in these aquifers can be hundreds or even thousands of years. The contribution from the aquifer is essentially independent of rainfall, and these aquifers hold huge volumes of water. The output from most limestone springs also includes components due to conduit flow (ie. water that runs through sinkholes), which do dependent on recent rainfall. Residency times for water in the conduits can be as little as days or weeks.

When I say a "true spring creek", I mean a spring creek where a significant fraction of the water is coming directly from the aquifer as opposed to from other limestone conduits. These streams have very stable flows and temperatures, like the chalk streams of England or the cumberland valley limestones streams. The base output of the spring at Penns cave is 1-2 cfs. A big reason that Penns creek tends to get low without rain is that the springs that feed it are heavily dependent on conduits (and therefore rainfall) to maintain a high flow. The aquifer provides relatively little water directly to the stream. While this doesn't have a significant impact on the temperature or chemistry of the water leaving the spring, it has a big difference on the minimum flows in penns creek. This in turn has a big effect on the stream temperatures downstream because whenever the wide streambed isn't covered by water it warms up the creek a lot. Stable flows result in more stable temperatures because the surface to volume ratio is smaller at minimum flow.

We have a number of very large springs in Centre county. However, conduit flow and runoff play a very significant role in determining the flows of the central PA limestone creeks. I argue that this differentiates them from what I would call the "true spring creeks" of the cumberland valley or the chalkstreams in england. A higher fraction of the water in those streams is coming directly out of the aquifer, which is why they don't get as low as the streams in Central PA. The character of Penns creek is very different from a stream like the Letort or the Test. This isn't a knock on Penns creek, its just an explanation of why some limestone streams behave differently.

 

[pcray1231]

Sounds reasonable, and more in depth than my explanation. Makes you kinda have to explain the various types of water and groundwater. Play with names if you want, just trying to understand/explain the concepts.

Runoff - Comes off of the surface after precipitation events, never enters the ground. Plays a part in both freestoner and limestoner alike, though, the longer the watershed, the longer this will take to exit the system. Temperature varies with the seasons and the surface it runs over (higher on pavement, etc.). Flows highly dependent on recent precipitation on the order of hours or days.

Freestone springwater - enters soil and loose rock, but not bedrock, as in my "freestoner" drawing. Comes out of springs, however, they are generally small springs. Temperature is consistent year round. Flow rate is dependent on precipitation trends on the order of weeks up to a month or so.

Conduit water - Like my "limestoner" drawing. Absorbs into soil, and penetrates bedrock, forming underground streams which emerge at limestone springs. Constant temperature year round, limestone chemistry. Flow rate varies on precipitation trends (several months).

Aquifer - Water that was absorbed by rock and released slowly. Various rock types absorb various amounts of water. Comes out in larger, generally limestone springs. Constant temperature year round, limestone chemistry. Flow rate highly independent of recent precipitation trends (maybe somewhat dependent on the order of decades or more).

 

[troutbert]

"Spring Creek is more classic and has a less diverse assortment of water types and critters. (Some of the lack of critter diversity is also due to pollution, but even in perfect health, it still would not display the diversity of Penn's and Fishing.)"

That statement is false. It's well known, and documented by Penn State reserachers, that Spring Creek had a great diversity of insect life, and pollution has wiped many of the species out.

There are still many people around who remember fishing the Green Drake hatch on Spring Creek. They were eliminated in the 1950s.

Spring Creek has a medium-gradient, and the substrate is cobble dominated. So it is very different than streams such as the Letort, Big Spring, and Falling Spring, which have a lower gradient, and finer substrate (gravel).

Limestone streams have a great variety of conditions. If you want to break them into two broad categories, you can use this break down.

I. Low gradient, fine substrate (typically gravel dominated)

II. Medium gradient, coarse substrate (typically cobble dominated)

But some streams have both types of waters, on different parts of the stream.

And both of these stream types are "normal", "typical" and "true."

In PA the mileage of the second category of limestone stream is probably greater than the first.

 

[Chaz]

There is a very direct connection between the flow in a freestone stream to the last rain event. That's one reason why they are as flashy as they are.. The base flow of freestone streams is very low because the sandstone aquafiers they eminate from hold only a fraction of the water a limestone aquafier holds.
Flows from limestone springs are well documented and have a fairly constant flow, but they DO vary in flow depending on rainfall, but rainfall has much less impact on the base flow inpart because the limestone itself is very pourous and holds much of the water that falls on the ground releasing it at the large springs.
Because sandstone ls hard and not pourous, most of the rainfall runs off. What water that is held in the aquafier is released slowly over a long period and the flow is very low.