Bulletin 81 / Minimum Oxygen Levels Survived by Stream Invertebrates
Eugene W. Surber
William E. Bessey Bulletin 81 December 1974
Minimum Oxygen Levels Survived by Stream Invertebrates
Eugene W. Surber Former Research Biologist Virginia Commission of Game and Inland Fisheries
and
William E. Bessey Robert A. Taft Sanitary Engineering Center Cincinnati, Ohio
VPl -WRRC-BULL 81
A publication of Virginia Water Resources Research Center Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061 -r1) "'~DI V-5 ? . > •. ~)I PREFAC.E
In the late spring of 1974 I received two lengthy letters from Gene Surber concerning research he had carried out many years ago but reported for the first time in this Bulletin. Gene was clearly concerned about the fate of this sizable effort, a concern heightened by the fact that he was much weakened by cancer. I felt it was important to ease Gene's mind by immediate publication of the manuscript without either editing or review. Dean Randal M. Robertson of the Research Division, Virginia Polytechnic Institute and State University, agreed after being apprised of the situation. Gene had contemplated some revision of the manuscript and it was in the hands of William T. (Bill) Mason, Jr., Interstate Commission on the Potomac River Basin, when Gene's letters arrived. We felt that the appropriate course of action was immediate publication via the Virginia Water Resources Research Center's Bulletin series. Bill's supportive actions and counsel were exceedingly helpful.
In May of 1974, Gene and I discussed the-manuscript on the telephone. Although his voice was weak and the short conversation clearly tiring, his enthusiasm for and interest in this research were awe-inspiring. Except for the conversion of some figures into a form suitable for publication and for this preface, the manuscript has not been altered. Although I firmly believe in peer review, there are situations where human values should transcend the academic process-and for this I take full responsibility.
My thanks to Dr. Kenneth L. Dickson and Anthony F. Maciorowski for helping with the preparation of the figures for publication.
John Cairns, Jr. University Professor of Zoology and Director, Center for Environmental Studies Virginia Polytechnic Institute and State University
iii TABLE OF CONTENTS
Objective and Procedure
Results 7
Conclusions and Discussion 17
Acknowledgments 19
Literature Cited 20
Figures 21
Tables 39
v LIST OF FIGURES
1. Water bath and glass insect tubes lifted from bath; Insect cells (5) at right ...... 23
2. Diagram of apparatus used for determination of minimum oxygen levels tolerated by stream invertebrates . . . . 24
3. Initial head box, cooling unit (upper left), and Mount Oegasser 25
4. Mount Oegasser 26
5. Fluctuations in oxygen levels in the control and experimental tubes during a 76-hour test (Experiment 8) with four specimens of Orconectes rusticus. Vertical columns show points at which deaths of the individuals occurred in the experimental tube. All control specimens survived. 27
6. Fluctuations in oxygen levels in the control and experimental tubes during a 66-hour test (Experiment 2) with three specimens of Lirceus fontinalis 28
7. Fluctuations in oxygen levels in the control and experimental tubes during an 89-hour test (Experiment 20) with four specimens of Lirceus fontinalis 29
8. Fluctuations in oxygen levels in the control and experimental tubes during a 66-hour test (Experiment 3) with three specimens of Stenonema tripunctatum ...... 30
9. Fluctuations in oxygen levels in the control and experimental tubes during a 69-hour test (Experiment 14) with four specimens of Stenonema heterotarsale 31
10. Fluctuations in oxygen levels in the control and experimental tubes during an 89-hour test (Experiment 20) with four specimens of Stenonema ares 32
11. Fluctuations in oxygen levels in the control and experimental tubes during a 70-hour test (Experiment 7) with three specimens of lsonychia bicolor 33
vi 12. Fluctuations in oxygen levels in the control and experimental tubes during a 91-hour test (Experiment 17) with three specimens of Ephoron leukon 34
13. Fluctuations in oxygen levels in the control and experimental tubes during a 77-hour test (Experiment 8) with two specimens of Acroneuria lycorias 35
14. Fluctuations in oxygen levels in the control and experimental tubes during an 87-hour test (Experiment 16) with four specimens of Psephenus herricki 36
15. Fluctuations in oxygen levels in the control and experimental tubes during a 92-hour test (Experiment 15) with one specimen of Corydalus cornutus 37
vii LIST OF TABLES
1. Number of Experimental Animals Used per Cell in Control and Experimental Cells 41
2. Dissolved Oxygen, Experiment 20 45
3. Summary of Dissolved Oxygen Experiments, Physical and Chemical Data . . . . 46
4. Summary of Results of Oxygen Bioassays 48
5. Minimum Dissolved Oxygen Levels Survived for 12 Hours by Stream Invertebrates 52
viii OBJECTIVE AND PROCEDURE
The objective of this study was to explore, experimentally, the lowest levels of oxygen that could be tolerated by some of the common invertebrate animals of streams in the Cincinnati area. Most of the bottom animals used in the experiments were collected from riffles of the Little Miami River above Milford, Ohio; the East Fork of the Little Miami above Batavia; the Mad River above Urbana, Ohio; and Mt. Carmel Creek near Mt. Carmel, Ohio. The experiments were carried out in a constant temperature bioassay room of the Aquatic Biology Section, Basic and Applied Sciences Branch, Division of Water Supply and Pollution Control, Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio.
Apparatus Two oblong glass tubes were used (Figure 1), each 46.5 centimeters long and 41 millimeters in diameter, with 6 mm bore inlet and outlet stopcocks for regulating the flow-through rate, two 6 mm bore stopcocks for removal of samples (one unneeded), and a 26 mm vertical tube in the top side for diverting the flow temporarily while air bubbles were removed from the apparatus. In normal operation this latter tube was kept closed with a No. 6 rubber stopper, but during the removal of air bubbles, it served as an overflow. The vertical tube was originally designed for the insertion of an oxygen analyzer or an electric stirrer that could aid in the circulation of the water at low flow-through rates, but in these experiments which were run with a flow-through rate of about 600 milliliters per minute, it was found more practical to use the vertical tube for an overflow during insertion of the five insect cells and for removal of air bubbles.
The experimental animals, usually two to four of each species, were placed within each of five clear plexiglass cells that were 51 mm long and 25 mm in diameter (O.D.). Each of the cells had removable plexiglass screw caps at one end while the other end was permanently closed. Short threaded stainless steel rods, 1/8 inch in diameter, were used to joint the five cells together in tandem. A longer stainless steel rod, 115 mm long, extended from the first eel I in the series through a No. 8 rubber stopper which closed the 41 mm opening in the Pyrex glass tube through which all animals were introduced simultaneously at the beginning of a test period. This stopper also served to hold the cells in a straight line within the tube. Each cylindrical plexiglass cell was perforated with 1 /16-inch holes throughout, including both ends, with as many as two dozen perforations to permit adequate circulation of water.
Each of the experimental glass tubes was submersed in a compartment of a stainless steel water bath receiving the same cooling water. The cooling water was pumped with a No. 210 Gorman-Rupp centrifugal electric pump with rubber housing and impellers from a 55-gallon polyethylene tank into the stainless steel tank where it flowed through the two compartments, one containing . the control tube and the other t he experimental, before returning by gravity to the polyethylene tank. A "Blue-M" portable water cooler with thermostat was used to keep the water temperature constant in the water bath system. This arrangement is illustrated in Figure 2.
The glass tubes were held in place in the compartments by means of an adj_ustable horizontal aluminum frame with two arms which could be raised and lowered vertically or tilted to any desired position. A tilted position was used at the beginning of a test period when bubbles were being freed from the apparatus via the vertical t ube or opening through which the test cells were inserted.
Water Supply Regimen for the Experimental Tubes After reducing the pressure by passing through a pressure reduction valve, Cincinnati city water was passed through an activated carbon filter into a stainless steel headbox as illustrated in Figures 2 and 3. Here the temperature was controlled so that a temperature generally not exceeding 22°C was maintained in the control and experimental tubes. To accomplish this, the headbox was provided with a 1900-watt Chromalux heating element connected to a LaPine Electronic Relay, to which t he headbox thermoregulator was also connected.
A small cooling uni t, with stainless steel coils (made in the Air-Conditioning Section of the Robert A. Taft Sanitary Engineering Center) and equipped with a two-stage bulb thermostat (temperature range 10° to 90° F.), was also installed in the headbox for cooling the water when needed. Polyvinyl chloride (PVC) pipe and vinyl tubi ng were used to convey incoming water. into the Mount Degasser (Figure 4), the basic principles of which were described by Mount ( 1961, 1964). The degassing chamber in this apparatus was a 42-gallon pneumatic, galvanized tank (20 by 36 inches) with its interior coated with polyester resin to prevent corrosion and possible contamination by zinc from the galvanized surface. A mercury RGI vacuum control was used for regulating the vacuum. This control utilized a Cartesian Diver type glass float with orifice of a size and type to protect the glass instrument from a sudden release of vacuum. The vacuum control was mounted in a metal frame that could be shifted to a horizontal position during readjustment of vacuu'm. The vacuum range of the control was from 0 - 760 mm (O - 30 inches) of mercury. Coarse adjustments of vacuum were made with vacuum control in a horizontal position when mercury levels inside and outside the glass float were equalized by shaking the mercury in or out of the float's orifice. A bleeder valve was placed in the vacuum line to the left of the gauge (see Figure 2) as indicated in the diagram. A second valve in the vacuum system to the right of the gauge was used during periods when the vacuum in the degassing chamber was being brought
2 down rapidly. This valve was kept closed at other times. During the manipulations of vacuum, the water pressure was maintained at 20 pounds per square inch.
Water entered the vacuum chamber as needed, and the inflow was controlled by a regular water lavatory float valve with a plastic float. The incoming water, as well as the recirculating water, was sprayed into the chamber after being broken up by a piece of folded stainless steel screen. The pump used in this recirculating and pumping system was a Fairbanks Morse and Company Model BR-515 all -iron pump with 1/2 hp motor, which was placed on the bottom shelf of the steel framework supporting the vacuum pump and the degassing chamber (Figure 4). Its capacity was 15.7 gallons per minute at a 60-foot head. A 5-inch diameter circular window in the top of the degassing chamber permitted installation of parts and observation of functioning parts within the tank. The window was made of 0.5-inch thick plexiglass, 6.5 inches in diameter, seated on a 0.75-inch wide metal ring welded to the top of the tank and ground level and smooth. Stopcock grease was used for sealing the cover during operation.
Oxygen was removed from the water by exposure to vacuum created by means of a Precision Scientific Company Model No. 75 vacuum pump that was placed on the second shelf of the steel frame that supported the degassing chamber (Figures 2 and 4).
Degassed water left the bottom of the tank via a 1-inch PVC pipe and was pumped under 20 psi to the experimental insect tubes.
Beyond the pressure gauge was located a stainless steel valve which regulated, in part, the flow of water beyond that point and provided a means of shutting off the water supply to the insect tubes. Pipe size was reduced at this point from 1/2 inch to 1/4 inch. Beyond the valve was located a stainless steel "T" with short nipples connected to two 1/4-inch stainless steel valves for further regulating the flow of water beyond them. Vinyl tubing of 7 /16-inch ID was used to conduct half of the flow of degassed water directly into the inlet of the experimental tube. An approximately equal quantity of degassed water was conducted via vinyl tubing to a second headbox in which the oxygen content was restored to air equilibrium by means of compressed air from ·the building's system. This was led through a diffuser at the bottom of the headbox (see Figure 2). To assure maximum mixing with air and cooled or heated water by elements placed in the headbox, an electric stirrer was provided for thoroughly mixing the water before it passed by gravity to the control insect tube in the control compartment of the water bath below. A Teflon stopcock was used on the 3/8-inch line to the inlet cock of the control insect tube.
3 Water entered each tube at the bottom in the bend or curving section and circulated unobstructed in a clockwise manner down the outside arm of the tube to the second bend where it reached and passed over, under, and through the insect cells, five of which were placed in tandem fashion as indicated in Figure 1. Water left the tubes via a stopcock (maintained in a wide open position) and a short piece of tubing leading into a bottle (into which was inserted a thermometer) suspended from the side of the bath, thence over the side of the water bath by means of 1/4-inch gum rubber tubing to a floor drain. Oxygen determinations and other chemical analyses as well as flow-through rates were made on the outflowing water as it left the two systems, control and experimental.
In the collection of samples for chemical analyses, 125 ml Pyrex ground glass-stoppered bottles were filled from the bottom to overflowing from the 1/4-inch gum rubber outlet tubes which were completely filled with water flowing directly out of the insect tubes. Samples for oxygen determinations were fixed immediately after their collection, and all analyses were made on fresh samples according to "Standard Methods for the Examination of Water, Sewage and Industrial Wastes" (Eleventh edition, 1960). Hydrogen-ion concentrations and specific resistance were determined electrometrically.
Procedure Invertebrates from local streams were placed by species either in several polyethylene trays containing a few algae-covered stones with water strongly aerated with compressed air, or in a stainless steel tank four feet long with channels about six inches wide and six inches deep containing flat, algal-covered (Cladophora) stones and supplied with the same water used in the control experiments. Water was circulated in this simulated stream by means of a paddlewheel, the shaft of which was turned by an electric stirrer with rheostat for controlling speed and water velocity.
Usually three or four specimens of the same size of a given species were placed in each experimental cell along with a small tuft of Cladophora which could be utilized by herbivorous species for food during the experiment. Carnivorous species remained unfed and were usually placed alone in a cell. Five cells were present in the cQntrol tube and five in the experimental tube. The experimental animals were always held in the same position in both tubes. At the conclusion of each experiment, the size of each specimen used was determined and recorded. Table 1 lists the number of animals of each species used in each of the five control and five experimental cells. Their average lengths are given as well as range in size.
Experimental animals were generally placed in their cells and allowed to remain overnight to observe the effects of handling before the vacuum was changed in the 4 degassing chamber and the oxygen content lowered in the water supply of the tubes. One experiment (Table 2) is described in detail here to illustrate the general course of events in an experiment: In Experiment Number 20, four amphipods, Gammarus fasciatus, were placed in each of the first two cells in the series of five cells; three nymphs of Stenonema ares, a common mayfly in local streams, were placed in cell 3; three nymphs of Ephoron leukon, a burrowing mayfly, in cell 4; and one Anax junius, a predacious dragonfly nymph, in cell 5, the last in the series (both in the control and experimental) about 3:00 p.m. on July 23, 1963. None died overnight. The following morning at 8:00 a.m., the vacuum was increased from 152.0 mm to 228.6 mm of mercury. At about 12-hour intervals thereafter, the vacuum was adjusted to bring about a lowering in oxygen content of about 1.0 ppm. The larger changes ranged from 0.6 ppm to 1.2 ppm in the early phases of the progressive reductions, and as higher vacuum was reached, generally smaller reductions in dissolved oxygen occurred. Table 2 also shows at what stage and oxygen level (experimental only) mortality occurred with each species in each cell. In this experiment the temperature remained virtually constant a~ 22.0° C. The flow-through rate in the control varied between 530 ml and 600 ml per minute (average 576 ml) while the flow-through rate in the experimental ranged from 480 ml to 580 ml per minute (average 530 ml).
In Table 3, the ranges in dissolved oxygen and the averages of the results of water analyses made during each experiment are given along with temperatures, flow-through rates, and duration of each experiment.
5 RESULTS
The results of Experiments 1 through 22 are summarized below. A graph (Figure 5) has been prepared to illustrate the type of curve obtained when the amount of oxygen is plotted against per cent mortality. This graph depicts the oxygen curves for the control (upper curve) and the experimental (lower curve). The decline in oxygen content of about 1.0 ppm in the control curve is brought about by the progressive lowering of oxygen in the degassing chamber. In spite of reaeration in the control headbox, the oxygen usually declined somewhat in the control, though it seldom reached levels less than 7.0 ppm. As stated before, the same water source was used in both control and experimental tubes.
There follows by species a summary of the results of several experiments with the same species. Variation between experiments using the same species often occurred, but this can be expected where the animals, few in number, are not reared under controlled conditions. Some variation also might be expected as a result of handling. The statements that follow apply to the animals held in one cell in the experimental tube containing five cells only·.
Results of all experiments are summarized in Table 4. Specimens used in the experiments, elapsed time of each experiment, the experimental dissolved oxygen, and mortality data are presented.
7 Sphaerium striatinum (Sphaeriidae)-Fingernail Clam Experiment 10 - Three specimens shared a cell (third in the series) with a water penny (Psephenus herricki). All sphaeriids lived throughout the experiment in which oxygen was lowered to 0.4 ppm for five hours, and 0.8 ppm for 10 hours prior to that. Experiment 12 - All three of the specimens survived the lowest levels held, 1.1 ppm for 11 hours and 0.6 ppm for 9 hours. Experiment 13 - Three of the four clams survived 0.5 ppm for 12 hours, with one specimen dying at this level. Experiment 17 - All four specimens survived 12 hours at the minimum level (0.5 ppm) reached in this experiment. Experiment 22 - All three specimens survived levels of dissolved oxygen which reached a minimum of 0.15 ppm. Ail Sphaerium striatinum used in the control cells survived each of the above experiments.
Goniobasis livescens (Pleuroceridae)-Snail Experiment 1 - All four specimens survived 16 hours at 0.6 ppm, the minimum level reached. Experiment 2 - All four snails survived when held at 0.8 ppm for two hours and at 1.0 ppm for 16 hours. Experiment 15 - All four specimens I ived throughout the experiment, including a 24-hour ·period in which the dissolved oxygen varied from 0.44 ppm to 0.28 ppm. Experiment 17 - All four snails survived 0.5 ppm for 12 hours. All of the control animals in the above four experiments survived.
Lirceus fontinalis (Asellidae)-Freshwater lsopod Experiment 1 - Two of three specimens survived 2.9 ppm for 12 hours; one lived at 0.8-1.0 ppm for 8 hours, but died when held at 0.6 ppm for 16 hours. Experiment 2 - One of the three specimens died at the 4.8 ppm level and the remaining two died at 2.6 ppm. Handling may have affected the results. Figure 6 shows dissolved oxygen vs. per cent mortality for this experiment. Experiment 5 - Three of the four specimens survived 1.6 ppm for 11 hours and 0.6 ppm for nine hours. Three of four animals in the control cell survived.
Crangonyx setodactylus (Gammaridae)-Amphipod This species was described by Bousfield in 1958 (Canadian Field-Naturalist, Vol. 72, No. 2, pp. 55-113), and this is its first record of occurrence in Ohio (Mt. Carmel, Clermont Co.) and its second in the United States, according to Dr. Thomas E. Bowman, U.S. National Museum (communication of March 23, 1964). Experiment 1 - Of the four specimens in the experimental cell, one perished at 5.2 ppm after nine hours. Another died at the 1.0 ppm level after five hours. The 8 remaining animal died at the 0.6 ppm level. One animal disappeared shortly after the start of the experiment, presumably a victim of cannibalism. Experiment 2 - Three of the four animals used survived 4.8 ppm for nine hours, but one specimen died at the next level, 4.0 ppm, after 15 hours. One other died after 16 hours at 1.0 ppm, and the remaining animal died after two hours at 0.8 ppm. Experiment 3 - Three of four animals survived 0.8 ppm for a 26-hour period. Experiment 5 - All four animals survived 0.6 ppm for a period of 9 hours. No Crangonyx was lost in the control cells.
Gammarus fasciatus (Gammaridae) - Amphipod Experiment 19 - One specimen died at 4.2 ppm when held for six hours. The remaining three specimens survived 1.4 ppm for 12 hours, but died at 0.5 ppm after six hours. Three of four survived in the control cell. Experiment 20 - Cell 1, four specimens survived 1.1 and 1.2 ppm for 11 hours, but none of the four survived 0.4 ppm for 13 hours. Cell 2, three of the four specimens survived 1.1 and 1.2 ppm for 11 hours, but none survived 0.4 ppm for 13 hours. In the control cells, Cell 1, all animals survived, but in Cell 2 only half of the individuals survived. Figure 7 shows dissolved oxygen vs. per cent mortality for this experiment. Experiment 21 - One of the four experimental animals died at 1.6 ppm after six hours. None survived 0.6 ppm or lower after 12 hours at that level.
Cambarus ortmanni (Cambarinae) - Crayfish Experiment 1 - All three specimens survived 0.6 ppm for 16 hours. Experiment 2 - Two of the three animals survived 1.0 ppm for 16 hours and 0.8 ppm for two hours. Experiment 3 - Two of the three animals used survived 0.8 ppm for a 26-hour period. There were no losses of this species in the control cells in any of the above experiments.
Orconectes rusticus(Cambarinae) - Crayfish Experiment 5 - Cell 1, two of the five animals used lived at 0.6 ppm for nine hours. Cell 2, four of the five animals lived at 0.6 ppm for nine hours. In the controls, four of five individuals survived in both Cells 1 and 2. Experiment 8 - All four animals lived for 11 hours at 1.4 ppm, but none survived for 11 hours at 0.8 ppm. All control animals lived. Experiment 12 - One of the three specimens died when held at 2.8 ppm for 12 hours. Another died at 1.6 ppm held for 15 hours. None survived 1.1 ppm or lower. No control animals were lost in this experiment.
9 Stenonema tripunctatum (Heptageniidae) - Mayfly Experiment 1 - One of the three specimens perished at the 5.2 ppm level. Another died at the 2.9 ppm level, and none survived 1.4 ppm for 12 hours. Two of the three control animals survived this experiment. Experiment 2 - Three specimens lived at 2.6 ppm for five hours, but one died after 16 hours at the next level , 1.0 ppm. The remaining two survivors lived for two hours at 0.8 ppm or to the end of the experi ment. Experiment 3 - All three animals survived 2.5 ppm for 10 hours, but died after five hours at 0.8 ppm. Figure 3 shows dissolved oxygen vs. per cent mortality for this experiment. Experiment 4 - One of the two animals died when held at 5.0 ppm. The other animal died at 3. 7 ppm after two hours at that level. Experiment 5 - The one specimen survived 2.0 to 1.6 ppm for 15 hours, but died after nine hours at 0.6 ppm. Experiment 7 - One of two animals died at 2.9 ppm when held for 10 hours. The other animal perished at the 2.3 ppm level when held for eight hours. One of two animals survived in the control. The variability in results in these six experiments may have been due in part to the handling of this large species, but it appears to require about 2.0 ppm to survive.
Stenonema heterotarsale (Heptageniidae) - Mayfly Experiment 7 - Both specimens in the experiment survived 14 hours at 3.1 ppm; after 10 hours at 2.9 ppm, one died. The remaining mayfly lived at 0.8 ppm for 10 hours and was still alive, although in distress, at the close of the experiment. Experiment 8 - Two of the four specimens lived for 11 hours at 1.4 ppm, but none survived 0.8 ppm for 11 hours. Experiment 9 - Two of the three animals survived 2.0 ppm for 14 hours and one survived 1.4 ppm for 10 hours. None survived 0.4 ppm for four hours. In the control cell, two of the three individuals used in this experiment survived. Experiment 12 - All three specimens lived through a 1.6 ppm level for 13 hours. One died at 1.1 ppm after 11 hours, and the last died at 0.6 ppm after 9 hours. Experiment 14 - Two of the four animals survived 1.8 ppm for 14 hours, but none survived 0.8 ppm for 10 hours. Figure 9 shows dissolved oxygen vs. per cent mort Stenonema ares (Heptageniidae) - Mayfly Experiment 3 - Two of the four mayflies used survived 2.5 ppm for 10 hours, and one lived at 0.8 ppm for eight hours. Three of four control individuals survived. 10 Experiment 4 - One of the four specimens survived 1.2 ppm for a 14 hour period and 0.8 ppm for an additional 10 hours. Experiment 16 - Two of the four specimens survived 2.6 ppm for 13 hours. None survived a level of 1.4 ppm. Two of three control animals survived. Experiment 20 - All four animals lived through 1.1 ppm for five hours and three survived 1.2 ppm for an additional six hours. None survived 0.4 ppm for 13 hours. Figure 10 shows dissolved oxygen vs. per cent mortality for this experiment. Experiment 21 - Two of the three experimental animals survived 1.6 ppm for 12 hours. None were living after 12 hours at 0.6 ppm. One of three animals survived in the control cell. Stenonema vicarium (Heptageniidae) - Mayfly Experiment 7 - One of three specimens died at the 2.3 ppm level. The remaining two mayflies died when held at 0.8 ppm for a 10-hour period. Experiment 8 - One specimen perished at 3.6 ppm after 13 hours. The other two specimens died at 0.8 ppm after 11 hours. Two of three control animals survived. Experiment 9 - One mayfly died at 4.0 ppm when held for 14 hours. A second specimen died at 1.4 ppm after 10 hours, and the remaining nymph died at the 0.4 ppm level. Two of three control animals lived. Experiment 11 - One of the two specimens died at the 2.4 ppm level. The other died after being held at 1. 7 ppm for eight hours. None of the control specimens survived. Stenonema femoratum (Heptageniidae) - Mayfly Experiment 10 - Only one test was carried out with this species. Two of three specimens lived through six hours at 2.5 ppm, and one lived for 10 hours at 2.4 ppm. None survived at the 1.3 ppm level. Two of three specimens in the control eel I survived. Heptagenia maculipennis (Heptageniidae) - Mayfly Experiment 10 - Two of the four animals used survived 2.4 ppm for 10 hours. One individual survived all levels and had lived at 0.4 ppm for five hours at the close of the experiment. Three of four survived in the control cell. Experiment 11 - One of three specimens survived 1. 7 ppm for 11 hours, but died at 0.8 ppm. None of the control animals lived. Experiment 15 - Both experimental animals survived 1.9 ppm for 14 hours, although neither survived 0.84 ppm or lower. Three of four control mayflies lived. Heptagenia flavescens (Heptageniidae) - Mayfly Experiment 17 - All survived 2.0 ppm for 12 hours, but none of the four specimens used lived at 1.0 ppm or below. Three of four survived in the control. 11 Leptophlebia sp. (Baetidae) - Mayfly Experiment 3 - Both specimens survived 2.5 ppm for 10 hours, but neither lived at a 0.8 ppm level. Experiment 4 - One of two nymphs lived for 14 hours at 1.2 ppm and died at the 0.8 ppm level. All mayflies survived in the control cells in these experiments. lsonychia bicolor (Baetidae) - Mayfly Experiment 6 - In this experiment, the single specimen in the cell died after nine hours at 2.6 ppm. Experiment 7 - Two of the three specimens survived 3.1 ppm for 14 hours but died after 10 hours at 2.9 ppm. Figure 11 shows dissolved oxygen vs. per cent mortality for this experiment. Experiment 9 - Of three specimens, one died at 4.0 ppm after 12 hours. None survived 3.4 ppm after 11 hours. In the control, two of three lived. Experiment 10 - One of three specimens survived 10 hours at 2.4 ppm, the others dying at 4.0 ppm and 3.4 ppm. Two of four died in the control cell. Experiment 11 - One specimen survived 11 hours at 1.7 ppm and died at 0.8 ppm. The other three specimens used died at 3.2 ppm. One specimen died in the control cell. Experiment 12 - Neither of the two specimens survived 1.6 ppm for 13 hours. Experiment 15 - All four specimens lived through 3.2 ppm. One died after six hours at 1.9 ppm and two died after six hours at 2.2 ppm. None survived 0.84 ppm for 12 hours. Three of four mayflies survived in the control cell. Experiment 17 - All three specimens survived a level of 2.0 ppm for 12 hours. None survived at a 1.0 ppm level for six hours. Ephoron leukon (Ephemeridae) .:_Mayfly This species was collected from sand and gravel in riffle areas of the East Fork of the Little Miami River above Batavia, Ohio. Experiment 17 - All three specimens survived 2.0 ppm for 12 hours. One specimen died after six hours at 1.0 ppm, and another perished at the same level during the following six hours. The remaining individual survived 12 hours at the same level, but died when 0.5 ppm was held for 12 hours. Figure 12 shows dissolved oxygen vs. per cent mortality for this experiment. Experiment 19 - Cell 1, all three specimens survived 1.4 PP!TI for 12 hours, but none survived 0.5 ppm for the following 12 hours. Cell 5, one specimen died at the 2.4 ppm level and the three animals were all dead after 12 hours at the 1.4 ppm level. In Cell 1, two of three survived in the control cell; in Cell 5, all specimens survived. 12 Experiment 20 - This experiment was inconclusive for this species. Two of three specimens died after six hours at 2.8 ppm. The survivor lived for 15 hours at 1.1 ppm and died when held at 1.2 ppm for an additional six hours. Two of three specimens survived in the control cell. Experiment 22 - Both animals survived 1.4 ppm when held for 12 hours. One died when held at 0.46 ppm for an additional 14 hours, and none lived beyond the 0.25 ppm level. Hexagenia limbata (Ephemeridae) - Mayfly Two sizes (or ages) of nymphs of this widely-distributed burrowing mayfly species were used in these experiments. The larger individuals were near emergence, and in the first experiment (Number 21 ), one emerged as a sub-imago and was drowned in its experimental cell. Both old and young nymphs were able to survive surprisingly low levels of oxygen. Experiment 21 - Cell 1, both nymphs (old) survived all reductions in oxygen level down to 0.2 ppm where they were held for six hours. One emerged at this level and died. Cell 5, one of the nymphs (young) died after 12 hours at 1.6ppm, but the other lived throughout the test in which the minimum level reached 0.2 ppm; the remaining nymph was held at 0.2 ppm for six hours and 0.4 ppm for 24 hours. In Cell 1, one of two survived in the control system; in Cell 5, two of three survived in the control. Experiment 22 - Cell 1, two of three nymphs (young) survived 1.9 ppm for eight hours. One died at 0.25 ppm, and the remaining animal lived throughout the experiment which included 0.15 ppm for three hours. Cell 5, one of the two specimens (old) died when held at 0.25 ppm for 12 hours. The other animal lived to the end of the experiment. In the control, Cell 1, all survived; Cell 5, one of two survived in the control. Acroneuria lycorias (Acroneuriinae) - Stonefly The nymphs of this common species survived well in the controls and may have survived lower levels of dissolved oxygen had it been practical to speed up the current in the tubes. Methods were not altered because one of the objectives of these preliminary tests has been to compare a variety of species under similar conditions. Experiment 4 - Both nymphs survived through 3.7 ppm, but they died when held at 2.4 ppm to 1.2 ppm for 25 hours. All controls lived. Experiment 7 - Both animals survived 2.9 ppm for 10 hours. One died at 2.3 ppm, although the remaining nymph survived 2.3 ppm for eight hours and 1.3 ppm for six hours. No control animals were lost. Experiment 8 - Both animals survived the low level of 1.4 ppm for 11 hours, but died when held at 0.8 ppm. All control animals survived. Figure 13 shows dissolved oxygen vs. per cent mortality for this experiment. 13 Neoperla clymene (Perlidae) - Stonefly Experiment 10 - Both specimens lived at 1.3 ppm and 1.7 ppm for 14 hours, but they failed to survive an exposure to 0.8 ppm for 10 hours. Experiment 11 - One of two nymphs used survived 2.4 ppm for 13 hours and 1. 7 ppm for 11 hours. It died at 0.8 ppm. Experiment 13 - One nymph of the three used survived 2.9 ppm for 12 hours. It died at 1.8 ppm in an unsatisfactory experiment in which two of three control animals were lost. Experiment 15 - Both animals survived at 1.9 ppm for six hours. One died at the next level, 2.2 ppm, but the second nymph survived 0.84 ppm for 12 hours. One control animal was lost. Experiment 16 - Both specimens died at 4.8 ppm. The results were not consistent with other tests in this series. Phasganophora capitata (Perlidae) - Stonefly Experiment 14 - In the only test made with this species, both nymphs survived 4.8 ppm. At 3.9 ppm, one specimen died; the remaining nymph survived . 3.9 ppm for 12 hours, 2.6 ppm for 12 hours, 1.8 ppm for 14 hours, and died at the 0.8 ppm level. All control animals survived. Psephenus herricki (Psephenidae) - Water Penny Experiment 10 - One specimen was carried with three specimens of fingernail clams, Sphaerium, in Cell 3. It survived throughout the run with the minimum level at 0.4 ppm for five hours and 0.8 ppm for 10 hours prior to that. Experiment 12 - All four specimens lived throughout the experimental period, including 1.1 ppm for 11 hours and 0.6 ppm for nine hours. Experiment 13 - All four specimens lived to the end of the experiment, surviving 1.0 ppm for 12 hours and 0.5 ppm for 12 hours. Experiment 16 - One of the four specimens died early in the experiment. The remaining three lived to 0.4 ppm when one died after exposure for nine hours. Figure 14 shows dissolved oxygen vs. per cent mortality for this experiment. All control animals survived all four of the above experiments. Corydalus cornutus (Corydalidae) - Hellgrammite Experiment 14 - The one specimen used survived 1.8 ppm for 14 hours but died at 0.8 ppm. Experiment 15 - The one specimen used lived at 0.84 ppm for 12 hours, 0.28 ppm for six hours, and 0.28 and 0.38 ppm for two hours. It died at 0.44 ppm after 16 hours exposure. Figure 15 shows dissolved oxygen vs. per cent mortality for this experiment. Experiment 16 - The only specimen survived 1.4 ppm for 13 hours and died when held at 0.4 ppm for nine hours. No losses were suffered in the control cells using this species. 14 Sialis sp. (Sialidae) - Alderfly Experiment 19 - One of two larvae survived all levels, including 0.3 ppm for six hours. Prior to that it survived 0.5 ppm for 12 hours. The other specimen fell victim to cannibalism. Experiment 22 - Both larvae lived to a 0.24 ppm level. One larva died after 48 hours of 0.26 ppm to 0.24 ppm; the remaining one lived to the end of the experiment, passing through a period when the oxygen level stood at 0.15 ppm for three hours, or 0.27 ppm to 0.15 ppm for a period totalling 97 hours. All animals survived in the control cells. Agrion maculatum (?) (Agrionidae) - Damselfly Experiment 6 - The one nymph used lived at 2.6 ppm for 11 hours, but died at t he 1.6 ppm level. The control animal lived. Argia moesta (?) (Coenagrionidae) - Damselfly Experiment 13 - Both nymphs survived levels to 1.0 ppm when one died. The second nymph survived 1.0 ppm for six hours but expired at the 0.5 ppm level. One of the two control animals died. Boyeria vinosa (Aesch idae) - Dragonfly Experiment 6 - The one nymph used lived to a 1.6 ppm level. Experiment 9 - The one nymph survived 3.4 ppm for 11 hours but died at 2.0 ppm. Anax junius (Aeschnidae) - Dragonfly Experiment 20 - One specimen lived at 2.8 ppm for 12 hours, but it died at 1.8 ppm. The control animal also survived. Plathemis lydia (Libellulidae) - Dragonfly Experiment 4 - The one nymph used lived at all levels including ten hours at 0.8 ppm. The animal in the control cell survived the experiment. Hydropsyche slossonae (Hydropsychidae) - Caddisfly Larva A great deal of difficulty was encountered in keeping Hydropsychidae larvae within their cells and in locating material that could be positively identified, and at the same time large enough to be kept in the cells. Hydropsyche slossonae was collected in the Mad River above Urbana, Ohio. Experiment 6,- Of the five experimental animals present, only one lived through the 3.4 ppm level. All lived in the control. Experiment 8 - None of the four animals survived the 3.6 ppm level. Experiment 11 - All four animals died at 3.6 ppm. 15 Experiment 14 - Three of four specimens lived for 12 hours at 3.9 ppm but none survived 2.6 ppm for 12 hours. Three out of four control animals survived. This is a current-loving species and it is possible that the species would have survived a lower level of oxygen had there been more current. Using a dye, the velocity through the cell section of the experimetal tube (flow-through of 600 ml/min) was 4.4 cm/sec. Tipula abdominalis (Tipulidae) - Cranefly Experiment 9 - The one specimen used lived to the end of the experiment and survived 0.4 ppm for four hours. Experiment 18 - The one specimen used lived throughout the experiment, surviving 0.25 ppm for four hours and 0.28 ppm for seven hours prior to that. The one control animal used died in this experiment. Tabanus sp. (Tabinidae) - Horsefly Experiment 13 - In the only experiment using this animal, it survived 0.5 ppm held for 12 hours, or until the end of the experiment. The animal in the control cell also survived. Hyalella azteca (Gammaridae) - Amphipod Experiment 19 - In an unsatisfactory experiment, Hyalella escaped from the cetl because of the animal's small size. Dineutes sp. (Gyrinidae) - Whirligig Beetle Larva Experiment 18 - In tilis experiment, the only specimen survived 3.0 ppm for 12 hours, but died at the next level, 2.4 ppm. The control animal lived. 16 CONCLUSIONS AND DISCUSSION These biological tests lack the finite endpoints of chemical analyses, as might be expected of living organisms removed from their natural environment and placed for many hours in plexiglass cells. Some mortality undoubtedly occurred as a result of handling, but survival in the controls and the experimentals was more often satisfactory. Several species of organisms survived surprisingly low levels of oxygen. Whether they could survive similar levels under the more complex conditions imposed by the presence of decomposing organic wastes which would reduce oxygen content correspondingly is problematical. The results of experiments such as these might have been very different had different current velocities been used. The work of Jaag and Amb~hl ( 1963) in Switzerland, for example, showed that oxygen is related to the current quite differently for each species and that, in general, the faster the water flows, the lower is the lethal oxygen content. Most of these experiments were conducted at one flow-through rate (600 ml/min) as closely as it could be maintained, and at one velocity, determined with dye to be about 4.4 cm/sec. The program of oxygen reduction amounted to approximately 1 ppm or less per 12-hour period over three days or more. All organisms used in the tests were measured and may reflect age of the organisms to some extent, but more refined studies are needed with individuals of known age in experiments of long enough duration to permit molting when the organisms can be expected to be more sensitive. Perhaps the simplest way to summarize the results of these tests is to designate the approximate lowest oxygen level at which the different species tested were able to survive for 12 hours based on judgment of the results of several tests, the number of which is shown in Table 5. Inspection of a frequency table showing the number of individual specimens that died at different low levels of oxygen in several runs was also a means of arriving at the following figures. Of particular interest were the very low levels of oxygen survived by Sphaerium striatinum, Goniobasis livescens, Sia/is sp., Psephenus herricki, and the burrowing mayflies Ephoron leukon and Hexagenia limbata. When oxygen reached a low level, the above mollusks "clammed up." Sometimes it could be seen that Sphaerium was still alive from the extension of its pink siphons, but both species of mollusks remained inactive and their per cent mortality could only be determined at the end of a run when they were placed in pans of water and allowed to extend their feet. In experiments with Hexagenia limbata, two ages of nymphs were used in the same 17 test. Two large nymphs in Cell 1 survived all reductions in oxygen down through 0.2 ppm held for six hours. One emerged at this level and died. In Cell 5, one of two young nymphs died after 12 hours at 1.6 ppm, but the other lived throughout the test in which it was held at 0.2 ppm for 6 hours and 0.4 ppm for 24 hours! In a second experiment (Experiment 22), the young nymphs were placed in Cell 1 and the large nymphs in Cell 5; as in Experiment 21, both large and small survived levels of 0.26 ppm oxygen or less. 18 ACKNOWLEDGMENTS Specimens of animals were referred to the following specialists for identification to species: Dr. Joseph P. E. Morrison and Dr. Joseph Rosewater, U.S. National Museum, Division of Mollusks {fingernail clams and snails); Dr. Thomas E. Bowman, U.S. National Museum, Division of Marine Invertebrates {Amphipods); Ralph Sinclair, Tennessee Department of Public Health {lsopods); Dr. Jerry Hubschman, U.S. Public Health Service, and Dr. David H. Stansbery, The Ohio State University {Crayfish). Dr. Hubschman contributed reared specimens of Orconectes rusticus and Cambarus ortmanni for these experiments. Speciments of Odonata were identified by Dr. Oliver S. Flint, Jr., U.S. National Museum, Division of Neuropteroids. Dr. Donald I. Mount and Thomas 0. Thatcher made valuable suggestions and helped assemble the Mount vacuum degassing chamber. The Model Shop of the Robert A. Taft Sanitary Engineering Center, through Joe Castelli, made the plexiglass cells for confining individual specimens and the supports for the glass tubes. The Metal Shop, through Charles Howard and Raymond Gebhardt, contributed work on the degassing chamber, the stainless steel insect holding tanks, water baths, and headboxes. Miss Lucy Minogue assisted in the final revision and typing of the manuscript. The writers extend their grateful appreciation to the above persons and to Dr. Clarence M. Tarzwell, Chief of Aquatic Biology Section, for direction in the conduct of this study and for suggestions on the presentation of these data. 19 LITERATURE CITED Jaag, 0. and H. Ambuhl. 1963. "The Effect of Current on the Composition of Biocoenoses in Flowing Water Streams." Int. J. Air Wat. Poll., Pergamon Press (Great Britain) 1963, 7, 317-330. Mount, D. I. 1961. "Development of a System for Controlling Dissolved Oxygen Content of Water." Trans. Am. Fish. Soc., 90(3) :323-327. Mount, Donald I. 1964. "Additional Information on a System for Controlling the Dissolved Oxygen Content of Water." Trans. Am. Fish. Soc., 93(1): 100-123. "Standard Methods for the Examination of Water, Sewage and Industrial Wastes." (11th Ed.) American Public Health Association, New York, 1960. 20 FIGURES 21 ~ +-' ..cro E 0 ...... "'C QJ +-' +-' '.'t: ~ VI · ~ QJ ..c +-' ::J ro or- +-' Q) +-' U1 ... (.) ::J QJ .5?> VI .!:!!. c: QJ u. (.) VI VI +-' ro (.) QJ O> VI "'C c: c: ro ~ +-'ro ..c .... QJ +-' sro 23 l\J .+:>- Figure 2 Diagram of apparatus used for determination of minimum oxygen levels tolerated by stream invertebrates INCOMING COOLING UNIT WATE~~ H~ mun VACUUM CONTIOL SU ..LY LINE noM MEAD aox 55 GAL PLASTIC TANIC .-..~ ,,(/ Figure 3 Initial head box, cooling unit (upper left), and Mount Degasser 25 Figure 4 Mount Degasser 26 Figure 5 Fluctuations in oxygen levels in the control and experimental tubes during a 76-hour test (Experiment 8) with four specimens of Orconectes rusticus. Vertical columns show points at which deaths of the individuals occurred in the experimental tube. All control specimens survived. 10.0 100 9 .0 90 8.0 BO 7.0 70 6 a. a. I 6.0 60 z w >- <9 t:: >- _J x __ ....._ 0 5.0 50 ~ ..,.,.- a: 0 ' ' 0 w ' ..._....- -- - ' ', EXPERIMENTAL :!: >__J 0 ' ' ~ (f) 4.0 ' 40 (f) ' ' 0 ' .... ' ..... , 3.0 ' .... , 30 '•, ' ' ' ', 2 .0 ' 20 ' ,. ' ...... 1.0 ...... 10 0 '--~~-'-~~---'-~~~..1....-.~~_..__~~--'~~~-'--~~~"---'-..._.0 0 10 20 30 40 50 60 70 80 TIME (HOURS) 27 Figure 6 Fluctuations in oxygen levels in the control and experimental tubes during a 66-hour test (Experiment 2) with three specimens of Lirceus fontinalis 10.0 100 9.0 90 8.0 80 70 70 E a. a. I 6.0 60 z >- w --- !:::: (9 ..J >- <( x I- 0 5.0 50 a:: 0 0 w > ~ ..J 0~ 0 4.0 40 (/) (/) 0 3.0 30 ' ' 2 .0 ' ' 20 ' ' ' ' 1.0 ' 10 ' ' • 0 0 0 10 20 30 40 50 60 70 80 TIME (HOURS) 28 Figure 7 Fluctuations in oxygen levels in the control and experimental tubes during an 89-hour test (Experiment 20) with four specimens of Lirceus fontinalis 10.0 100 9.0 90 8.0 80 7.0 70 E a. a. I 6.0 60 z w >- (!) --~ f-- >- ' ..-._ EXPERIMENTAL _J x ' <{ 0 5.0 ...... ' 50 f-- 0 a:: w ' 0 ' ~ >_J ' ' ~ 0 4.0 ' 0 (/) ' ~ 40 (/) \ \ 0 \ \ \ \ 3.0 \ .....__.._ 30 ' ' ' ' 2.0 ' 20 ' ~ \ \ _....._ .... 1.0 ...... 10 ...... 0 0 20 30 40 50 60 70 80 TIME (HOURS) 29 Figure 8 Fluctuations in oxygen levels in the control and experimental tubes during a 66-hour test (Experiment 3) with three specimens of Stenonema tripunctatum '""'~\; \j 10.0 100 9.0 90 8.0 80 ~ 7.0 / \ 70 / \ / \ E / \ a. / a. / \ I / \ 6.0 / \ 60 z / >- w / \ (!) \ !:::: >- \ ...J x \EXPERIMENTAL 0 0 0 10 20 30 40 50 60 70 80 TIME (HOURS) 30 Figure 9 Fluctuations in oxygen levels in the control and experimental tubes during a 69-hour test (Experiment 14) with four specimens of Stenonema heterotarsale i t l'\ 10.0 100 9.0 90 8.0 80 7.0 CONTROL 70 E Q. Q. I 6.0 60 z w >- (!) ~ _J >- <[ x I- 0 5.0 50 a:: 0 0 w \ \ ~ ~ \ ~ 0 \ 0 (/) 4.0 \ 40 (/) 0 3.0 30 2.0 20 1.0 10 0 0 0 10 20 30 40 50 60 70 80 TIME (HOURS) 31 Figure 10 Fluctuations in oxygen levels in the control and experimental tubes during an 89-hour test (Experiment 20) with four specimens of Stenonema ares 10.0 100 9.0 90 8.0 CONTROL D.O. 80 7.0 70 E a. a. I 6.0 60 z >- w ~ (.!) --·" _J >- " '-.-- ...... •, EXPERIMENTAL _J " " ~0 0 4.0 ' "e 40 (/) \ (/) \ \ 0 \ \ \ 3.0 \ 30 ----· ' ' ' ' 2.0 ' ' 20 ' •\ \ \ 1.0 '..-- 10 0 20 30 40 50 60 70 TIME (HOURS) 32 Figure 11 Fluctuations in oxygen levels in the control and experimental tubes during a 70-hour test (Experiment 7) with three specimens of lsonychia bicolor 10.0 100 9.0 90 8.0 80 7.0 70 E a. a. I 6.0 60 z ' >- w ~ <9 _J >- ' 2.0 20 1.0 10 0 ~~~~~~~~~~~~~~~~~~~~~~~~~~~ o 0 10 20 30 40 50 60 70 80 TIME (HOURS) 33 Figure 12 Fluctuations in oxygen levels in the control and experimental tubes during a 91 -hour test (Experiment 17) with three specimens of Ephoron leukon 10.0 100 9.0 90 8.0 80 CONTROL 0.0. 7.0 70 E a. a. .. I 6.0 60 z ' ' >- w ' ... != (.9 \ ...J >- \ x 5.0 \ 50 ~ 0 \ ll: 0 ...... __...._ 0 w ...... EXPERIMENTAL ~ ...... ~ ...... ~ 0 4.0 40 (/) (/) Ci ' 3.0 '""' "' -..., 30 ' ' ' ..... 2.0 ~ 20 \ \ \ \ 1.0 10 0 0 0 20 30 40 50 60 70 80 90 TIME (HOURS) 34 Figure 13 Fluctuations in oxygen levels in the control and experimental tubes during a 77-hour test (Experiment 8) with two specimens of Acroneuria lycorias 10.0 100 9.0 90 8.0 80 7.0 70 E a. a. I 6.0 60 z w >- (!) I- >- ...... :i x __ ~ 0 5.0 50 I- \ a::: 0 '-..------',EXPERIMENTAL w 0 ::i \ ~ 0 ' \ 0~ (f) 4.0 ' 40 (f) ' ' 0 ' ...... , 3.0 ..... 30 ..... --... \ \ ' \ 2.0 \ 20 ' \ ' \ ...... 1.0 ...... 10 0 0 0 10 20 30 40 50 60 70 80 TIME (HOURS) 35 Figure 14 Fluctuations in oxygen levels in the control and experimental tubes during an 87-hour test (Experiment 16) with four specimens of Psephenus herricki 10.0 9.0 90 8.0 CONTROL 80 7.0 70 E a. a. I 6.0 60 z >- w t: (.9 _J >- <[ x I- 0 5.0 50 0::: 0 0 w ~ ~ 0~ 0 (/) 4.0 40 (/) Ci 3.0 30 2.0 20 1.0 10 0 -----.1~~~~~~~~~~~~~~~~~~~~~~~~~~0 0 20 30 40 50 60 70 80 90 TIME (HOURS) 36 Figure 15 Fluctuations in oxygen levels in the control and experimental tubes during a 92-hour test (Experiment 15) with one specimen of Corydalus cornutus 10.0 100 9.0 90 8.0 80 7.0 70 E a. a. I 6.0 60 z >- w I- (.!) >- _J x <{ I- 0 5.0 '--- ..... ------4t, 50 a:: 0 0 w \ EXPERIMENTAL ~ I ::J \ 0~ 0 I Cf) 1.0 \ 40 Cf) \ 1•, 0 \ / ...... \ I '-... I / -.... 3.0 '-'/ '•, 30 ' \ ' \ '\ 2 .0 '..,...... -"", 20 ' ' ' ' ' 1.0 ' 10 ' ' .... , ', '• 0 '--~~_._~~-'-~~~-'---~~-'-~~--'-~~~-'-~~-'-~--"'-'~ 0 0 10 20 30 40 50 60 70 80 TIME (HOURS) 37 TABLES 39 TABLE 1 Number of Experimental Animals Used per Cell in Control and Experimental Cells Experiment Average Range in Number Number Species Length (mm) Length (mm) Used Crangonyx setodactylus 14.0 13.0-15.0 4 Goniobasis livescens 9.0 8.5-12.0 4 Cambarus ortmanni 19.0 18.0-20.0 3 Stenonema tripunctatum 10.5 7.0-16.0 3 1 Lirceus fontinalis 14.4 13.0-16.0 3 2 Stenonema tripunctatum 10.5 7.0-16.0 3 2 Goniobasis livescens 9.6 8.5-12.0 4 2 Crangonyx setodacty/us 14.0 13.0-15.0 4 2 Lirceus fontinalis 14.4 13.0-16.0 3 2 Cambarus ortmanni 19.0 18.0-20.0 3 3 Cambarus ortmanni 22.2 12.0-24.0 3 3 Stenonema tripunctatum 12.8 10.0-15.0 3 3 Crangonyx setodactylus 11.1 7.0-14.0 4 3 Stenonema ares 8.6 8.0-9.5 4 3 Leptophlebia sp. 10.6 9.5-11.0 2 4 Acroneuria /ycorias 17.8 12.0-21.0 2 4 Stenonema tripunctatum 12.0 10.5-13.5 2 4 Leptophlebia sp. 11 .5 9.0-15.0 2 4 Stenonema ares 9.8 9.0-10.0 4 4 Plathemis lydia 22.0 22.0 5 Orconectes rusticus 9.2 8.5-10.0 5 5 Stenonema tripunctatum 16.0 16.0 5 Crangonyx setodactylus 11.4 9.0-14.0 4 5 Lirceus fontinalis 13.9 12.0-17.0 4 6 Agrion maculatum 14.0 14.0 1 6 Boyeria vinosa 23.0 23.0 6 Stenonema vicarium 11.0 9.0-12.0 4 6 Hydropsyche slossonae 15.0 5 6 lsonychia bico/or 13.4 13.4 1 7 lsonychia bicolor 13.4 12.0-15.0 3 7 Acroneuria lycorias 16.6 15.0-21.0 2 7 Stenonema tripunctatum 10.9 9.0-12.0 2 7 Stenonema vicarium 11.0 9.0-12.0 3 7 Stenonema heterotarsale 10.0 9.0-11.0 2 41 8 Hydropsyche slossonae 15.0 14.0- 16.0 4 8 Acroneuria lycorias 19.0 17.0-21.0 2 8 Stenonema heterotarsale 10.9 9.0-12.0 4 8 Stenonema vicarium 13.8 13.0-15.0 3 8 Orconectes rustlcus 9.7 9.0- 10.0 4 9 lsonychia bicolor 12.2 11.0-13.0 3 9 Boyeria vinosa 23.5 23.0- 24.0 2 9 Stenonema heterotarsale 10.3 8.0-12.0 3 9 Stenonema vicarium 11.0 9.0-12.0 3 9 Tipula abdominalis 61.5 61.5 1 10 Neoper/a clymene 11.5 9.0-12.0 2 10 Stenonema femoratum 11.9 9.0-15.0 2 10 Sphaerium striatinum 6.1 4.0-11.0 3 10 Psephenus herricki 8.7 8.7 10 Heptagenia maculipennis 6.5 6.0-7.0 4 10 lsonychia bicolor 8.5 6.5-11.0 3 11 lsonychia bicolor 9.9 8.0-11.0 4 11 Heptagenia maculipennis 6.3 6.0-7.0 3 11 Hydropsyche slossonae 11.8 15.0-18.0 4 11 Stenonema vicarium 12.8 12.0-14.0 2 11 Ephemerella 8.0 8.0 1 11 Neoper/a clymene 12.5 12.0-13.0 3 12 lsonychia bicolor 2 (measurements misplaced or lost) 12 Stenonema heterotarsale 3 12 Psephenus herricki 4 12 Sphaerium striatinum 3 12 Orconectes rusticus 4 13 Psephenus herricki 8.9 8.5-9.5 4 13 Neoperla clymene 11.5 10.0-13.0 3 13 Eriocera sp. 20.0 20.0 13 Tabanus sp. 30.0 30.0 1 13 Argia moesta 12.5 11.0-14.0 2 13 Sphaerium striatinum 11.3 9.0-12.0 4 14 Hydropsyche slossonae 15.9 14.0-18.0 4 14 Phasganophora capitata 18.0 17.0-20.0 2 14 Stenonema heterotarsale 9.3 6.5-11.0 4 14 Corydalis cornutus 34.5 34.5 1 14 Hydropsyche slossonae 16.5 14.0-17.0 4 15 /sonychia bicolor 9.4 8.0-11.0 4 15 Ephemerella sp. 5.9 5.0-7.0 2 (not successful) 42 15 Goniobasis livescens 15.2 12.0-18.0 4 15 Neoperla clymene 8.0 6.0- 10.0 2 15 Corydalis cornutus 39.0 39.0 16 Stenonema ares 8.0 5.5- 10.0 3 16 Psephenus herrick i 8.4 7.0- 9.0 4 16 Corydalis cornutus 35.5 35.5 1 16 Neoperla clymene 9.2 6.5- 10.5 2 16 Agrion maculatum 24.0 24.0 (no control) 17 Ephoron leukon 16.7 14.0- 20.0 3 17 Hep tagenia flavescens 8.8 6.5-1 1.0 4 17 l sonychia bicolor 9.7 7.0-1 2.0 3 17 A croneuria lycorias 17.0 14.0-1 9.0 17 Sphaerium striatinum 7.6 6.5- 9.0 4 17 Goniobasis livescens 14.3 12.0-1 6. 0 4 18 lsonychia bicolor 7.8 7.0- 9.0 3 18 Sia/is sp. 12.0 12.0 18 Stenonema vicarium 9.1 8.0-10.5 4 18 Tipula sp. 2 18 Dineutes sp. 17.5 10.0-25.0 18 Acroneuria lycorias 7.8 6.0-9.0 2 19 Ephoron leukon 18.2 15.0- 21 .0 3 19 Sia/is sp. 10.5 9.0- 11.0 2 19 Gammarus fasciatus 9.0 7.0-10.0 4 19 Hyalella azteca 4 (escaped from cell) 19 Ephoron leukon 18.2 17.0- 20.0 3 20 Gammarus fasciatus 8.2 5.0-10.0 4 20 Stenonema ares 5.6 4.0-9.5 4 20 Ephoron leukon 15.0 13.0-21.0 3 20 Anax junius 37.0 37.0 21 Hexagenia limbata 20.8 18.0-23.0 2 (large) 21 Stenonema heterotarsale 7.8 7.0-8.0 3 21 Stenonema ares 9.8 7.0-11.0 3 21 Gammarus fasciatus 7.6 4.0- 11.0 4 21 Hexagenia limbata 11.8 10.0-14.0 3 (small) 22 Hexagenia limbata 10.2 8.0- 11.0 3 (small) 43 22 Ephoron leukon 14.8 13.0- 16.0 2 22 Sphaerium striatinum 8.8 6.0- 12.0 3 22 Sia/is sp. 15.3 14.0- 17.0 2 22 Hexagenia limbata 18.4 16.0- 20.0 2 (large) 44 TABLE 2 Dissolved Oxygen, Experiment 20 Vacuum Vacuum Difference Elapsed Flow Rate Date (Inches of (Inches of D. 0 . ppm Change in Time Temp (mm/min.) 1963 Time Mercury) Mercury) Con. I Exp. * Expjlrimental (Hours) ~ Con . I Exp. * 7/ 23 3:00pm 6.5 7.9 5.5 0.0 0.0 21 .0 590 580 7/24 8:00am 6.0 -0.5 7.3 5.6 0.1 17.0 22.0 590 540 7/24 2:00pm 9:0 7.8 5.0 -0.6 23 .0 22 .0 590 520 7/ 24 8:00pm 9.2 3.2 7.7 5.2 0.2 29.0 22.0 590 530 7/25 8:00am 13.7 4.5 7.6 4.0 - 1.2 41 .0 22 .0 560 510 7/ 25 2:00pm 17.5 3.8 7.4 2.8 - 1.2 47.0 22.0 600 510 7/ 25 8:00 pm 17.5 7.6 2.8 0.0 53.0 22 .0 580 580 7/26 8:00am 22.5 5.0 7.4 1.8 -1.0 65.0 22.0 580 530 7/ 26 12:30pm 25.5 3.0 7.4 1.1 -0.7 70.0 22.0 560 530 7/26 7:00pm 25.5 7.4 1.2 0.1 76.0 22.0 570 520 7/ 27 8:00am 28.2 2.7 7.4 0.4 - 0.8 89.0 22.0 530 480 Biological Data Cell Number: Gammarus Gammarus Stenonema Ephoron Anax Elapsed fasciatus fasciatus ares leukon junius time D.O. Con . I Exp.* Con . I Exp.• Con . I Exp.* Con. I Exp.* Con. I Exp.• (Hours) .£E!!!.... L D L D** L D L D** L D L D* * L D l D** .....1..._Q_J,,D* * 0 5.5 4 0 4 0 4 0 4 0 3 0 4 0 3 0 3 0 1 0 1 0 17.0 5.6 4 0 4 0 4 0 4 0 3 0 4 0 3 0 3 0 1 0 1 0 23.0 5.0 4 0 4 0 4 0 4 0 3 0 4 0 3 0 3 0 1 0 1 29.0 5.2 4 0 4 0 4 0 4 0 3 0 4 0 3 0 3 0 1 0 1 41.0 4.0 4 0 4 0 3 1 4 0 3 0 4 0 2 1 3 0 1 0 1 46.0 2.8 4 0 4 0 3 1 4 0 3 0 4 0 2 1 1 2 1 0 1 65.0 1.8 4 0 4 0 3 1 4 0 3 0 4 0 2 1 1 2 1 0 0 1 70.0 1.1 4 0 4 0 3 1 3 1 3 0 4 0 2 1 1 2 1 0 0 1 76.0 1.2 4 0 4 0 3 1 3 1 3 0 3 1 2 1 0 3 1 0 0 1 89.0 0.4 4 0 0 4 2 2 0 4 3 0 0 4 2 1 0 3 1 0 0 1 ~ U1 Con.= Control, Exp. = Experimental L = Living Specimens, D = Dead Specimens TABLE 3 Summary of Dissolved Oxygen Experiments, Physical and Chemical Data Average Average Speci fic Total 0. 0. ppm Average Acidity Alkalinity Average Flow Resis tance Hardness Total 0 3 max·min Temp C ppm ppm pH (mm/min) (ohm/cm ) ppm Hours Con ./Exp.• Con./Exp.• Con ./Exp.• Con./Exp.* Con ./Exp.* Con ./Exp.* Con./Exp.• Con ./Exp. • ~ Experiment 1 (March 23 to March 24, 1963) 8.2-7.0 6.8- 0. 6 17 17 0 0 24 26 8.1 8.4 997 955 4300 4300 76 76 71 Experiment 2 (March 26 to March 29, 1963) 8.2- 6.8 5.8-0.8 21 22 0 0 8.3 8.5 1050 867 66 Experiment 3 (April 1 to April 4, 1963) 8.6-6.2 7.3- 0.8 22 23 0 29 29 8.1 8.5 530 560 3680 3680 78 80 66 Experiment 4 (April 10 to April 13, 1963) 8.2-6.8 5.6-0.8 24 24 0 0 42 42 7.9 8.3 540 468 3150 3125 77 78 77 Experiment 5 (April 23 to April 26, 1963) 9.0-7.6 5.3-0.6 20 20 0 0 26 26 7.9 8.0 674 597 2700 2650 78 78 72 Experiment 6 (April 29 to May 3, 1963) 8.1-7.5 7.4-1.6 20 21 0 7.8 8.1 667 586 2300 2300 99 Experiment 7 (May 6 to May 9, 1963) 8.6-7.7 6.0- 0.8 20 21 0 26 28 8.0 8.2 550 560 3000 3000 98 98 70 Experiment 8 (May 17 to May 20. 1963) 8.2-7.1 5.1- 0.4 21 21 0 52 54 7.9 8.2 510 595 2475 2475 152 1~2 77 Experiment 9 (May 27 to May 29, 1963) 8.4-7.6 5.2-0.4 21 21 0 0 58 58 8.0 8.2 590 565 2330 2330 152 152 51 Experiment 10 (June 4 to June 7, 1963) 8.0-6.6 5.2- 0.4 21 21 0 0 47 47 8.0 8.2 583 654 2290 2250 126 126 75 Experiment 11 (June 10 to June 13, 1963) 8.1-7.1 5.0- 0.8 21 21 0 0 8.0 8.1 600 550 63 Experiment 12 (June 14 to June 17, 1963) 7.5-3.0 5.0-0.6 21 21 0 0 34 30 8.1 8.2 580 550 2525 2525 134 134 80 Experiment 13 (June 18 to June 21 , 1963) 7.6-5.0 5.2-0.5 21 21 0 0 37 38 7.9 8.2 610 540 2600 2575 90 92 72 Experiment 14 (June 21 to June 24, 1963) 7.5- 6.8 4.8-0.8 22 22 0 0 60 67 8.1 8.5 610 525 2650 2600 90 87 69 Experiment 15 (June 24 to June 28, 1963) 7.4- 6.6 5.0- 0.3 22 22 0 0 40 40 8.1 8.4 585 530 2580 2600 97 98 92 46 Experi ment 16 (June 28 to July 2, 1963) 8.0-7.0 5.2- 0.4 22 22 0 36 38 7.9 8.1 590 574 2500 2500 114 122 87 Experiment 17 (July 8 to July 12, 1963) 8.0- 6.8 6.2- 0.5 21 22 0 39 38 7.9 8.1 595 539 2500 2475 119 112 91 Experimen't 18 (July 12 to July 16, 1963) 7.6-7.2 6.0-0.3 20 22 0 0 8.3 8.7 580 570 97 Experiment 19 (July 17 to July 21, 1963) 8.0-7.0 6.2-0.3 22 22 0 0 42 42 8.0 8.2 560 520 2475 2475 122 122 96 Experiment 20 (July 23 to July 27, 1963) 7.9- 7.3 5.6- 0.4 22 22 0 0 46 44 7.9 8.0 576 530 2450 2500 117 115 89 Experiment 21 (July 31 to August 5, 1963) 7.6- 6.8 4.8- 0.2 22 23 0 0 52 52 7.9 8.1 555 610 2300 2250 132 132 119 Experiment 22 (August 6 to August 14, 1963) 7.6-6.2 4.8-0.2 22 23 0 0 47 48 7.9 8.1 560 593 1850 1900 116 112 185 47 ./;::. co TABLE 4 Summary of Results of Oxygen Bioassays Cell Number: 1 2 3 4 5 Elasped D. 0. Time ppm Con. Exp. * Con. Exp. * Con. Exp. * Con . Exp.* Con. Exp.* o** o ** ~ (Exp) L D L L D L o ** L D L D** L D L o** L D L Experiment 1 (March 23 to March 26, 1963) Crangonyx Cambarus Stenonema Lirceus Goniobasis setodacty/us ortmanni tripunctatum fontinalis livescens 0 6.8 4 0 4 0 3 0 3 0 3 0 3 0 3 0 3 0 4 0 4 0 71 0.6 4 0 0 4 3 0 3 0 2 1 0 3 3 0 0 3 4 0 4 0 Experiment 2 (March 26 to March 29, 1963) Stenonema Goniobasis Crangonyx Lirceus Cambarus tripunctatum /ivescens setodacty/us fontinalis ortmanni 0 5.4 3 0 3 0 4 0 4 0 4 0 4 0 3 0 3 0 3 0 3 0 66 0.8 3 0 2 1 4 0 4 0 4 0 0 4 3 0 0 3 3 0 2 0 Experiment 3 (April 1 to April 4, 1963) Cambarus Stenonema Crangonyx Stenonema Leptophlebia ortmanni tripunctatum setodactylus ares sp. 0 5.4 3 0 3 0 3 0 3 0 4 0 4 0 4 0 4 0 2 0 2 0 66 0.8 3 0 2 1 3 0 0 3 4 0 3 1 3 1 0 4 2 0 0 2 Experiment 4 (April 10 to April 13, 1963) Acroneuria Stenonema Leptophlebia Stenonema P/athemis lycorias tripunctatum sp. ares lydia 0 2 0 2 0 2 0 2 0 2 0 2 0 4 0 4 0 1 0 1 0 77 0.8 2 0 0 2 2 0 0 2 2 0 0 2 4 0 1 3 1 0 1 0 Experiment 5 (April 23 to April 26, 1963) Orconectes Orconectes Sten onema Crangonyx Lirceus rusticus rusticus tripunctatum setodactylus fontinalis 0 5.0 5 0 5 0 5 0 5 0 1 0 1 0 4 0 4 0 4 0 4 0 72 0.6 4 1 2 3 4 1 4 1 1 0 0 1 4 0 4 0 3 1 1 3 Experiment 6 (April 29 to May 3, 1963) A gr ion Boyeria Stenonema Hydropsyche /sonychia maculatum vinosa vicarium slossonae bicolor 0 7.4 1 0 1 0 1 0 1 0 4 0 4 0 5 0 5 0 1 0 1 0 99 1.7 1 0 0 1 1 0 0 1 4 0 1 3 5 0 0 5 1 0 0 Experiment 7 (May 6 to May 9, 1963) lsonychia Acroneuria Stenonema Stenonema Stenonema bicolor lycorias tripunctatum vicarium heterotarsale 0 6.0 3 0 3 0 2 0 2 0 2 0 2 0 3 0 3 0 2 0 2 0 70 0.8 3 0 0 3 2 0 0 2 1 1 0 2 3 0 0 3 2 0 Experiment 8 (May 17 to May 20, 1963) Hydropsycht. Acroneuria Stenonema Stenonema Orconectes slossonae lycorias heterotarsale vicarium rusticus 0 5.0 4 0 4 0 2 0 2 0 4 0 4 0 3 0 3 0 4 0 4 0 77 0.4 1 3 0 4 2 0 0 2 4 0 0 4 2 1 0 3 4 0 0 4 Experiment 9 (May 27 to May 29, 1963) lsonychia Boyeria Stenonema Stenonema Tipula bicolor vinosa heterotarsale vicarium abdominalis 0 5.2 3 0 3 0 1 0 1 0 3 0 3 0 3 0 3 0 1 0 1 0 51 0.4 2 1 0 3 1 0 0 1 2 1 0 3 2 1 0 3 1 0 1 0 Experiment 10 (June 4 to June 7, 1963) (A) Sphaerium striatinum Neoperla Stenonema (B) Psephenus Heptagenia lsonychia clymene femoratum herricki macu/ipennis bicolor 0 5.4 2 0 2 0 3 0 3 0 (A) 3 0 3 0 4 0 4 0 3 0 3 0 ~ (B) 2 0 1 0 c.o 75 0.4 2 0 0 2 2 1 0 3 (A) 4 0 3 0 3 1 1 3 3 0 0 3 (B) 2 0 1 0 Experiment 11 (June 10 to June 13, 1963) CJ1 0 lsonvchia Heptagenia Hydropsyche Stenonema Neoperla bicolor maculipennis slossonae vicarium clymene 0 4.3 4 0 4 0 3 0 3 0 4 0 4 0 2 0 2 0 3 0 3 0 63 0.8 2 2 0 4 0 3 0 3 3 1 0 4 0 2 0 2 3 0 0 3 Experiment 12 (June 14 to June 17, 1963) lsonychia Sten onema Psephenus Sphaerium Orconectes bicolor heterotarsale herricki striatinum rusticus 0 4.9 2 0 2 0 3 0 3 0 4 0 4 0 3 0 3 0 3 0 4 0 80 0.6 1 1 0 2 3 0 0 3 4 0 4 0 3 0 3 0 3 0 3 Experiment 13 (June 18 to June 21, 1963) Psephenus Neoperla Tabanus Argia Sphaerium herricki clymene sp . moesta striatinum 0 5.2 4 0 4 0 3 0 3 0 1 0 1 0 2 0 2 0 4 0 4 0 72 0.5 4 0 4 0 1 0 0 3 1 0 1 0 1 0 0, 2 4 0 3 Experiment 14 (June 21 to June 24, 1963) Hydropsyche Phasganophora Stenonema Corydalis Hydropsyche slossonae capita ta hetero tarsale cornutus slossonae 0 4.8 4 0 4 0 2 0 2 0 4 0 4 0 1 0 1 0 4 0 4 0 69 0.8 3 1 0 4 2 0 0 2 4 0 0 4 1 0 0 1 3 1 0 4 Experiment 15 (June 24 to June 28, 1963) lsonychia Heptagenia Goniobasis Neoperla Corydalis bicolor maculipennis livescens clymene cornutus 4 5.0 4 0 4 0 4 0 2 2 4 0 4 0 2 0 2 0 1 0 1 0 92 0.4 3 1 0 4 3 1 0 4 4 0 4 0 3 1 0 2 1 0 0 Experiment 16 (June 28 to July 6, 1963) Stenonema Psephenus Corydalis Neoperla A gr ion ares herricki cornutus clymene maculatum 0 5.2 3 0 4 0 4 0 4 0 1 0 ,1 0 2 0 2 0 1 0 87 0.4 2 1 0 4 4 0 0 4 1 0 0 1 2 0 0 2 0 Ephoron Heptagenia lsonychia (B) Sphaerium Goniobasis leukon flavescens bicolor striatinum livescens 0 6.2 3 0 3 0 4 0 4 0 3 0 3 0 (A) 1 L) 1 0 4 0 4 0 (B) 4 0 4 0 91 0.5 3 0 0 3 3 1 0 4 3 0 0 3 (A) 1 0 0 1 4 0 4 0 (B) 4 0 4 0 Experiment 18 (July 12 to July 16, 1963) lsonychia Stenonema Tipula Dineutes Acroneuria bicolor vicarium sp . sp. lycorias 0 5.5 3 0 3 0 4 0 4 0 2 0 2 0 1 0 1 0 2 0 2 0 97 0.3 3 0 0 3 0 4 0 4 1 1 1 0 1 0 0 1 2 0 0 2 Experiment 19 (July 17 to July 21, 1963) Ephoron Sia/is Gammarus Hya/el/a Ephoron /eukon sp. fasciatus azteca leukon 0 6.2 3 0 3 0 2 0 2 0 4 0 4 0 4 0 4 0 3 0 3 0 96 0.3 2 1 0 3 1 0 2 0 3 0 0 4 3 0 0 3 Experiment 20 (July 23 to July 27, 1963) Gammarus Gammarus Stenonema Ephoron Anax fasciatus fasciatus ares /eukon junius 0 5.5 4 0 4 0 4 0 4 0 3 0 4 0 3 0 3 0 1 0 1 0 89 0.4 4 0 0 4 2 2 0 4 3 0 0 4 2 1 0 3 1 0 0 Experiment 21 (July 31 to August 5, 1963) Hexagenia Stenonema Stenonema Gammarus Hexagenia limbata hetero tarsale ares fasciatus limbata 0 4.8 2 0 2 0 3 0 3 0 3 0 3 0 4 0 4 0 3 0 3 0 119 0.2 1 0 2 0 3 0 0 3 1 2 0 3 4 0 0 4 2 Experiment 22 (August 6 to August 14, 1963) Hexagenia Ephoron Sphaerium Sia/is Hexagenia limbata /eukon striatinum sp . limbata CJ1 0 4.8 3 0 3 0 2 0, 2 0 3 0 3 0 1 0 2 0 2 0 2 0 ...... 185 0.3 3 0 1 2 2 0 0 2 3 0 3 0 1 0 *Con.= Control, Exp.= Experimental ** L = Living Specimens, D = Dead Specimens TABLE 5 Minimum Dissolved Oxygen Levels Survived for 12 Hours by Stream Invertebrates Minimum Name of Common Number of Oxygen Organism Name Family Experiments Level ppm Sphaerium striatinum Fingernail Sphaeriidae 5 0.5 clam Goniobasis livescens Snail Pleuroceridae 4 0.5 Lirceus fontinalis lsopod Asellidae 2 1.5 Crangonyx setodactylus Amphipod Gammaridae 4 0.8 Gammarus fasciatus Amphipod Gammaridae 4 1.0 Cambarus ortmanni Crayfish Cambarinae 2 0.6 Orconectes rusticus Crayfish Cambarinae 3 1.0 lsonychia bicolor Mayfly Bactidae 9 3.0 Leptophlebia sp. Mayfly Bactidae 2 1.2 Stenonema tripunctatum Mayfly Heptageniidae 3 2.0 Stenonema heterotarsale Mayfly Heptageniidae 6 1.5 Stenonema vicarium Mayfly Heptageniidae 3 2.0 Stenonema ares Mayfly Heptageniidae 6 1.0 Stenonema femoratum Mayfly Heptageniidae 2.5 Heptagenia flavescens Mayfly Heptageniidae 2.5 Heptagenia maculipennis Mayfly Heptageniidae 3 2.0 Ephoron leukon Burrowing Ephemeridae 4 1.0 mayfly Hexagenia limbata Burrowing Ephemeridae 2 0.5 mayfly Acroneuria lycorias Stonefly Acroneuriinae 3 1.4 Neoperla clymene Stonefly Perlidae 5 2.5 Phasganophora capitata Stonefly Perlidae 1.8 Psephenus herricki Water penny Psephenidae 4 0.5 Corydalis cornutus Hellgrammite Corydalidae 3 1.0 Sia/is sp. Alderfly Sialididae 2 0.3 Agrion maculatum Damselfly Agrionidae 2 1.6 Argia moesta Damselfly Coenagrionidae 1 1.6 Anax junius Dragonfly Aeschidae 2 2.5 Boyeria vinosa Dragonfly Aeschidae 2 2.5 Plathemis lydia Dragonfly Libellulidae 0.8 Hydropsyche slossonae Caddisfly Hydropsychidae 4 3.5 Tipula sp. Cranefly Tipulidae 3.5 larva 52 VIRGINIA WATER RESOURCES RESEARCH CENTER BLACKSBURG, VIRGINIA 24061