Calcium supplementation for trout streams?

[Zach Matthews]

I just had a thought and I wonder if anyone has considered this. This is the DNR’s explanation for Georgia’s relatively poor trout fishing conditions:”

Introduction
Georgia’s approximately 4,000 miles of trout streams are relatively unproductive when compared to streams found in other parts of the country. This is, in part, due to the calcium deficient soils found in north Georgia. Therefore, to meet the demands of over 100,000 trout anglers, stocking and special regulations are used on some streams to maintain acceptable catch rates. The Wildlife Resources Division and the U.S. Fish & Wildlife Service stock streams with rainbow, brown and brook trout from late March through August ( learn about DNR trout hatcheries). The number of trout stocked and the stocking frequency depend on a stream’s fishing pressure, accessibility, and water conditions. In general, streams on public lands are stocked more often and with greater numbers of trout. Trout fishing opportunities vary and include heavily-stocked high-use streams (better for beginners), wilderness streams, streams with special regulations, and small impoundments. Some “special regulation” streams offer trophy or catch and release fishing opportunities (tips on releasing fish).

First of all, I didn’t actually realize we even had a mountain trout closure period. I never fish up there in the winter anyway but it was kind of funny to realize I might have been out of season and never have known it.

But the other thing that this triggered was an idea: if, say, the Hooch above Lanier and below Buford Dam is calcium deficient, isn’t that something TU groups could remedy? For example, when doing stream restoration work, lots of groups will use what we call “rip rap” in Arkansas. That’s typically big white chunks of limestone; could stream restoration emplacements take calcium needs into consideration and use limestone preferentially to raise the PH of the river? As I understand it alkalinity is the key to production of certain river mosses and grasses that end up providing trout habitat, which is why Arkansas is such a fish factory (the Ozark dome is almost solid limestone since it was an ancient sea floor and coral reef bed).

I’m not sure how much calcium would leach out of a mere few hundred yards of rip rap on even a big stream installation, though, so here was my other thought: what if a more active approach was tried? For example, what if there was something like a pressed limestone product (like a really weak concrete for example) that could be made into a slab or tablet form and dropped into the river at a strategic location (like downstream of the generator effluent) where it would take a maximum amount of wear from the water? Such baffles would be designed to erode over time, like a long-release medicine caplet, slowing increasing the PH of the stream by providing the calcium in a dust-like, but non-polluting manner? Has anyone ever tried this or ever even thought of it? It would be like a giant vitamin for the river.

Zach

[Buzz Bryson]

Zach,

There have been several projects over the years, sponsored variously by state/federal agencies, TU, etc., to add supplemental calcium and other minerals to streams to adjust pH, add buffering and the like. Some were on pristine, but mineral-poor streams such as those you mention in GA (and here in NC), some to counteract acidic drainage from mines (e.g, WV), and some to counteract spills (as from tanker wrecks).

The process works. Frequently, the setup involves large, water-driven, rotating drums that grind and dispense the limestone chunks. The problem is that, unless continued indefinitely, the stream will revert to previous conditions. Also, the involved biologists/hydrologists/geologists have to model the stream, and periodically add more as tributaries enter or the minerals are diluted and need supplemented downstream. We’re talking huge quantities in some cases (truckloads), and often, access problems. And low/high water events can be troublesome.

I think one of the issues that has to be overcome is the long-term commitment to such a project. There’s typically a lot of support, but, over time, enthusiasm wanes, and “sponsorship” is lost.

I’ve seen studies that showed significant increases in insect and trout diversity and biomass downstream of “free” (no additional costs) discharges from . . . trout farms and . . . wastewater plants.

Buzz

[Zach Matthews]

Good stuff Buzz!

[Gary Sundin]

There’s a pretty big literature on altering stream acidity with limestone. The effectiveness of limestone as a buffer is directly related to surface area, so tiny grains are more effective than big rocks. I’ve heard of the water-driven grinders that Buzz mentioned, but don’t know how effective they are. Treating pH in streams this way is expensive and most streams will require constant, labor intensive management. In places where it’s done for mitigation of point source pollution the scale of operation involves yellow earth movers, truckloads of material, millions of dollars, to treat a small or medium sized stream. I’m no expert, but it seems pretty well shown that at least salmonids respond positively to buffering treatments.

Many Appalachian streams are unaturally acidic because of acid rain, but they also naturally have low pH and low buffering capacity. The pH of these streams has always dropped after big rain events, and brook trout are better-adapted to these conditions than most other fish.

I think it’s feasible to treat a small stretch of a small stream this way. On a grand public scale it’s arguably too expensive/difficult to justify except to mitigate for pollution. I think something like a 1000-lb. Alka Seltzer tablet that would provide a constant level of buffering for years, and would also not cause any other water quality issues, would be very useful. I’ve never heard of such a thing and I expect the market is wide open.

On the GA closed trout season topic, the DNR is trying to change that right now. There are pubic meetings about a proposal to make all state trout streams year round. Border states have had year round seasons for a long time.

G

[Zach Matthews]

Gary –

Interesting to learn that pH drops when rain events occur. I wonder if that’s part of the trigger that causes rainbows to run upriver to spawn. I know they can “taste” particular sections of water or even tiny feeder streams–I’ve watched that happen.

Zach

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