Dissolved Oxygen and the Trout on the Farmington

**AaronJasper** · 10-23-2008, 06:02 PM

Make no mistake fish numbers are down this year based upon electro shocking and catch rates.

I guess our thermometers were right? You can't beat facts and so many "experts" base their opinions on pure speculation. It's also funny that many people claim to be conservationists, when in fact they are only conservationists when it's conveinient to them. Those trout should have been left alone this summer and I am sure those "experts" regret doing some simple research on why we were telling them to do so. Here is my reserch into the reasons why there should have been no angling on that stream this summer.

Please read the following information. You will see the problems that are related to DO level, fishing and trout mortality. I like to base my opinions on facts rather than what I hope to be the fact like some others here. So if you angled with light tippets this summer and were a successful angler, you were also successful at reducing the trout population on the Farmington River.
Why Is Dissolved Oxygen Important?
Like terrestrial animals, fish and other aquatic organisms need oxygen to live. As water moves past their gills (or other breathing apparatus), microscopic bubbles of oxygen gas in the water, called dissolved oxygen (DO), are transferred from the water to their blood. Like any other gas diffusion process, the transfer is efficient only above certain concentrations. In other words, oxygen can be present in the water, but at too low a concentration to sustain aquatic life. Oxygen also is needed by virtually all algae and all macrophytes, and for many chemical reactions that are important to lake functioning.
Dissolved oxygen concentrations may change dramatically with lake depth. Oxygen production occurs in the top portion of a lake, where sunlight drives the engines of photosynthesis. Oxygen consumption is greatest near the bottom of a lake, where sunken organic matter accumulates and decomposes. In deeper, stratified, lakes, this difference may be dramatic - plenty of oxygen near the top but practically none near the bottom. If the lake is shallow and easily mixed by wind, the DO concentration may be fairly consistent throughout the water column as long as it is windy. When calm, a pronounced decline with depth may be observed.
Seasonal changes also affect dissolved oxygen concentrations. Warmer temperatures during summer speed up the rates of photosynthesis and decomposition. When all the plants die at the end of the growing season, their decomposition results in heavy oxygen consumption. Other seasonal events, such as changes in lake water levels, volume of inflows and outflows, and presence of ice cover, also cause natural variation in DO concentrations.
Mid-summer, when strong thermal stratification develops in a lake, may be a very hard time for fish. Water near the surface of the lake - the epilimnion - is too warm for them, while the water near the bottom - the hypolimnion - has too little oxygen. Conditions may become especially serious during a spate of hot, calm weather, resulting in the loss of many fish. You may have heard about summertime fish kills in local lakes that likely results from this problem.

In a nutshell the water on the surface contains all of the oxygen. Where is the water from the lake drawn from?

Reasons for Natural Variation
Oxygen is produced during photosynthesis and consumed during respiration and decomposition. Because it requires light, photosynthesis occurs only during daylight hours. Respiration and decomposition, on the other hand, occur 24 hours a day. This difference alone can account for large daily variations in DO concentrations. During the night, when photosynthesis cannot counterbalance the loss of oxygen through respiration and decomposition, DO concentration may steadily decline. It is lowest just before dawn, when photosynthesis resumes.
Other sources of oxygen include the air and inflowing streams. Oxygen concentrations are much higher in air, which is about 21% oxygen, than in water, which is a tiny fraction of 1 percent oxygen. Where the air and water meet, this tremendous difference in concentration causes oxygen molecules in the air to dissolve into the water. More oxygen dissolves into water when wind stirs the water; as the waves create more surface area, more diffusion can occur. A similar process happens when you add sugar to a cup of coffee - the sugar dissolves. It dissolves more quickly, however, when you stir the coffee.
Another physical process that affects DO concentrations is the relationship between water temperature and gas saturation. Cold water can hold more of any gas, in this case oxygen, than warmer water. Warmer water becomes "saturated" more easily with oxygen. As water becomes warmer it can hold less and less DO. So, during the summer months in the warmer top portion of a lake, the total amount of oxygen present may be limited by temperature. If the water becomes too warm, even if 100% saturated, O2 levels may be suboptimal for many species of trout.
The last sentence is the most important. Even at total possible oxygen saturation, trout can not live in certain water temperatures. However, the water being released into the Farmington is far below adequate because it not only comes from the bottom of the lake AND had a high temperature this summer. These two things combined cause fish to die, especially after being stressed by fishermen.

Below is a chart showing DO levels and their effect on salmonid populations. On tailwaters like the Little Red, Norfork, and White Rivers in Arkansas the D.O. levels are between 2 and 6 ppm with COLD water there are many fish kills within 8 miles of the dams on these streams. The exception would be the Norfork where low D.O. levels cause fish kills throughout the entire stream due to the fact that it is only slightly more than 4 miles long.

In-stream Dissolved Oxygen (mg/L)
A. Embryo and larval stages
No production impairment 11
Slight production impairment 9
Moderate production impairment 8
Severe production impairment 7
Limit to avoid acute mortality 6
B. Other life stages
No production impairment 8
Slight production impairment 6
Moderate production impairment 5
Severe production impairment 4
Limit to avoid acute mortality 3

REFERENCES
Michaud, J.P. 1991. A citizen's guide to understanding and monitoring lakes and streams. Publ. #94-149. Washington State Dept. of Ecology, Publications Office, Olympia, WA, USA (360) 407-7472. Moore, M.L. 1989.
NALMS management guide for lakes and reservoirs. North American Lake Management Society, P.O. Box 5443, Madison, WI, 53705-5443, USA (http://www.nalms.org).

Recommended oxygen levels for all spawning salmonids is a minimum of 80 percent saturation with temporary levels no lower than 5mg/l. While maximum sustained swimming speeds of adult coho were adversely affected when dissolved oxygen was reduced below saturation at temperatures from 10°C (50°F) to 20°C (68°F) (Reiser and Bjornn 1979). Though different from steelhead, adult rainbow trout show negative effects at concentrations less than about 5 mg/l or 50% saturation, including elevated breathing amplitude, reduced heart rate, and reduced swimming speeds (Vinson and Levesque 1994).

Reiser and Bjornn (1979) report that low dissolved oxygen concentrations during egg incubation may delay hatching, increase anomalous development, stimulate premature hatching, and ultimately lead to weaker, smaller fry. They further state that coho salmon and steelhead survival drops off dramatically when intragravel dissolved oxygen concentration falls below an average of about 8 mg/l. Although dissolved oxygen requirements for successful incubation are species and developmental stage dependent, they suggest minimum concentrations at or near saturation with temporary reductions no lower than 5 mg/l for anadromous salmonids. Similar to adult dissolved oxygen criteria, Davis (1975) categorizes dissolved oxygen criteria for salmonid larvae and mature eggs based on oxygen tension gradient and metabolic requirements, both in mg/l and as percent saturation. The results are presented in Table 3.7. As with Table 3.6, the percent saturation values account for required oxygen tension gradient and sufficient oxygen.
Maximum growth for juvenile coho occurs at about 8.3 mg/l (Colt et al 1979). Herrmann et al (1962) reported that the growth of juvenile coho salmon maintained at 20°C declined slightly when concentrations were reduced from 8 mg/l to 5 mg/l, while growth declined more rapidly at lower concentrations. Mortality was high at levels averaging 2.1 to 2.3 mg/l, and those surviving showed a reduced consumption and weight loss (Colt et al 1979).
References
Colt, J., S. Mitchell, G. Tchobanoglous, and A. Knight. 1979. The use and potential for aquatic species for wastewater treatment: Appendix B, the environmental requirements of fish. Publication No. 65, California State Water Resources Control Board, Sacramento, CA.
Davis, J.C. 1975. Minimal dissolved oxygen requirements of aquatic life with emphasis on Canadian species: a review. Journal of Fisheries Research Board Canada. 32(12), 2295-2332.
Deas, M.L. and G.T. Orlob. 1999. Klamath River Modeling Project. Project #96-HP-01. Assessment of Alternatives for Flow and Water Quality Control in the Klamath River below Iron Gate Dam. University of California Davis Center for Environmental and Water Resources Engineering. Report No. 99-04. Report 236 pp.
Krenkel, P.A. and V. Novotney. 1980. Water Quality Management. Academic Press, New York.
North Coast Regional Water Quality Control Board. 2001. Water Quality Control Plan for the North Coast Region. Staff report adopted by the North Coast Regional Water Quality Control Board on June 28, 2001. Santa Rosa, CA. 124 p. Appendix.
United States Environmental Protection Agency (EPA). 1973. Development of Dissolved Oxygen Criteria for Freshwater Fish. Ecological Research Series EPA-R3-73-019. February.
Water Quality Assessments. 1996. Water Quality assessments: A guide to the use of biota, sediments and water in environmental modeling. Ed. D. Chapman. Published on behalf of UNESCO United Nations Education, Scientific, and Cultural Organization; WHO World Health Organization; UNEP United Nations Environmental Program. Chapman & Hall, London.

Some of this research might show us why wild trout are not so prevalent in the Farmington River. They need 8 ppm of D.O. to survive. However, stocked trout can survive with levels of 3 ppm, which would be lethal to eggs and fry.

To conclude, the Farmington River does not come from a source where 100 percent oxygen saturation is possible. Because of this the oxygen content of the water IS SUFFICIENT FOR THE TROUT TO SURVIVE WITHOUT ANGLING PRESSURE WHEN THE WATER WAS ABOVE 68. THIS SUMMER, HOWEVER, GIVEN THAT THERE WERE PEOPLE FISHING FOR THEM AND GIVING THEM UNDUE STRESS THERE WAS ENGOUGH TRAUMA ON THE FISH TO CAUSE A FISH KILL, WHICH WAS THE RESULT OF ANGLING MORTALITY.

The Main reason to stop angling in streams when the water temps are above 70 degrees F has to do mostly with oxygen levels. Water at a high temp can only hold so much oxygen. The Farmington due to it’s source does not hold enough oxygen even at lower water temperatures.

**Magnet** · 10-24-2008, 03:30 AM

The evidence from the fall shocking is substantial and irrefutable. Your research regarding angling / fish mortality should be considered in the future by the DEP. When heavy early season dam releases are necessary, and water temperatures reach a critical level, it would make sense that the fishery be shut down for the summer months. Will it happen? Of course not! At the very least your dialogue on this topic can get some of us to think about a self imposed shut down next year if these conditions arise again.

**Davyfly** · 10-24-2008, 10:24 PM

The issue of DO levels that by and large are problematical for tail water systems can be dealt with.
If the agencies concerned are forced to comply with State requirements.

Here in Arkansas the State min requirement is 6 ppm, which for given periods of the year is not met for the main reason that the COE are not forced to comply.

The problem arises due to the situation that exists in the lakes above the dams. Each year will differ, and the reason why it will is due to the level of water contained.
This year we saw serious rain fall which rose the lakes way above flood stage, the consequence of that was flooded timber and agricultural land. This resulted in a abnormal level of contaminants entering the lake systems.

Given the lake levels and the depth that water is drawn from, where the process of aerobic breakdown cannot take place, the consequence is water released that is below 6ppm, with a average temperature in the low 40s.

As of now we see a very different situation. Water temperature is in the high 50s to 60s, but the Do levels are between 3 and 5.
Trout can tolerate 5 much less than that problems may arise.
Fish will not feed, even if they do they are not able to digest food intake.
low DO levels increase dramatically bacterial and parasitic infections in the gills, which will cause mortality. Fish will become stressed and lose weight.

We do not stock our rivers when DO levels fall below 5ppm, or until a given point downstream shows the DO levels acceptable.

High water temperature will have the same adverse effects to Trout.

The two ways the situations can be dealt with are.
The introduction of a 4bay liquid oxygen system in the main body of the lake, which will create the balance of oxygen needed to breakdown matter and maintain a higher level of DO.
The second is be able to draw off water of adequate temperature from given levels during the seasonal changes that take place at given levels.

I find it a ridiculous situation that the powers that be do not close your rivers down to fishing when fish are subject to stress and mortality.
If the system is one that does not enable any carry over of fish, that might be a different matter.

The only reason l would suggest that they do not do it is due to loss of economic value to both State and local business activty.

Davy.

**Nymphmeister** · 10-28-2008, 02:37 PM

I would love to see specific data for the Farmington & Housatonic Rivers, showing daily high & low DO readings for the entire year- averages or what the range of high to low is don't tell you much useful info. I suspect that the Housy has higher DO levels when water temps are in the 65-75 range and Farmington trout almost shut off and Housy trout are still actively feeding & seem in great shape. Of course it all gets way too complicated for my little pea brain to process when you add in stuff like saturation, distance from the dam, time of day, water level in the reservoir, Fall "turnover", etc.