Annual Progress Report Overwintering Results of Ten Aerated Lakes in the Northwest Boreal Region

Transcription

1 Annual Progress Report Overwintering Results of Ten Aerated Lakes in the Northwest Boreal Region By David Jackson Senior Technician August 00 Peace River, Alberta Alberta Conservation Association Northwest Region

2 Table of Contents Page Table of Contents... ii List of Tables... iii List of Figures... iv Abstract... v 1.0 Introduction Study Area Methods Point release system set up and operation Mechanical surface aerator set-up and operation Oxygen sampling methods Results Cecil Thompson Park Pond Moonshine Lake Cummings Lake Spring Lake East Dollar Lake Figure Eight Lake Swan Lake Cutbank Lake Discussion Recommendations Literature Cited ii

3 List of Tables Table 1. Aerated lakes in the Northwest Region Table. Aeration technique and number of aerators at each lake, Table 3. Aerated lakes most recent successive overwintering years Table 4. Remote end of lake oxygen results iii

4 List of Figures Page Figure 1. Northwest Region map of aerated lake locations, Figure. Diagram of a Point Release Pod Figure 3. Diagram of a Mechanical Surface Aerator Figure 4. Oxygen concentrations in Cecil Thompson Park Pond, Figure 5. Oxygen concentrations in Moonshine Lake, Figure 6. Oxygen concentrations in Cummings Lake, Figure 7. Oxygen concentrations in Sulphur Lake, Figure 8. Oxygen concentrations in Spring Lake, Figure 9. Oxygen concentrations in East Dollar Lake, Figure 10. Oxygen concentrations in Figure Eight Lake, Figure 11. Oxygen concentrations in Swan Lake, Figure 1. Oxygen concentrations in Cutbank Lake, iv

5 Abstract Lake aeration is a fishery enhancement technique that is used to maintain dissolved oxygen levels in eutrophic lakes prone to winterkill. Stocked lakes susceptible to winterkill were aerated between October 001 and April 00 included: Cecil Thompson Park Pond, Moonshine Lake, Cummings Lake, Sulphur Lake, Spring Lake, East Dollar Lake, Figure Eight Lake, Swan Lake, Zama Pond and Cutbank Lake. The lakes ranged from to 17 ha and from 3.0 to.0 m in depth. The objective of this project is to sustain dissolved oxygen levels in these lakes at or above 3.0 mg/l to ensure the survival of stocked trout throughout the winter. Mechanical surface aeration was implemented on eight of the ten lakes. At Spring Lake a point release system was operated to destratify the water column in the fall and a 1/3-hp GAST compressor aerated Zama Pond. The aeration program was successful with all ten lakes over wintering as per oxygen concentration collection data. v

6 1.0 Introduction The objective of the aeration program is to overwinter stocked populations of trout in the Northwest Region. Benefits include production of larger fish and year round angling opportunities. Most of these lakes are shallow, productive and subject to prolonged ice and snow cover. Snow depths of >10 cm do not allow sufficient sunlight to penetrate for photosynthetic activity (Miller, T.G and W.C.Mackay draft). The combination of these factors result in anoxic conditions (winterkill). Winterkill occurs when the dissolved oxygen concentrations decline below required levels for fish survival. Decomposition of organic matter, and aquatic life, including fish populations all contribute to the oxygen decline. Aeration introduces oxygen into a lake or pond for the purpose of overwintering fish. Several lake aeration techniques have been used in the Northwest Region. The Alberta Conservation Association uses mechanical surface aeration on eight of the ten lakes. This technique has provided the best results of all the aeration techniques used in the Northwest Region (Miller, T.G and W.C.Mackay draft). On the two other water bodies, Spring Lake and Zama Pond, a point release and a compressor/open ended hose systems were used. Oxygen concentrations, water temperature, ice depths and snow depths were recorded on a monthly schedule. The aeration systems were installed and operated from mid-october to mid-april. This report details each lake s morphometry, prescribed aeration techniques, results and recommendations for the aeration season. Ten stocked lakes susceptible to winterkill were aerated between October 001 and April 00 in the Northwest Region. These lakes were Cecil Thompson Park Pond, Moonshine Lake, Cummings Lake, Sulphur Lake, Spring Lake, East Dollar Lake, Figure Eight Lake, Swan Lake, Zama Pond and Cutbank Lake (Figure 1). The lakes ranged from to 17 ha and 3.0 to.0 m in depth (Table 1). Previous year over wintering results and aeration methods can be found in the Annual Progress Reports, Alberta Conservation Association, Northwest Region ( to ). 1

7 Bistcho Lake Zama Pond 35 High Level Hay-Zama Complex Sulphur Lake Cummings Lake Figure Eight Lake Peace River 88 Moonshine Lake Cecil Thompson Pond Lesser Slave Lake 59 A Spring Lake Cutbank Lake East Dollar Lake 33 Grande Prairie 40 Valleyview Swan Lake Figure 1. Northwest Region map of aerated lake locations,

8 .0 Study Area Table 1. Aerated lakes in the Northwest Region. Lake Location Size Depth (m) *Fish Total Yrs (ha) Max/Mean Stocked Aerated C. Thompson Pond SE W RNTR 8 Moonshine Lake NW W /1.6 RNTR/BNTR 14 Cummings Lake SE W /.0 RNTR/BKTR 16 Sulphur Lake NE W /3.3 RNTR/BKTR 13 Spring Lake NE W6 3.1 /8.6 RNTR/BKTR 4 East Dollar Lake NE W /4.0 RNTR/BNTR 17 Figure Eight Lake SE W /3.0 RNTR/BNTR 16 Zama Pond NE W RNTR 18 Swan Lake SW W /3. RNTR 5 Cutbank Lake NE W /.1 BKTR/RNTR 3 * RNTR - rainbow trout, BNTR - brown trout, BKTR - brook trout 3.0 Methods 3.1 Point release system set up and operation A point release diffuser consists of cm PVC tubing glued together in an "X" shape. The diffuser has four, 1.-m arms with 6.35 mm holes, drilled at 5.4 mm intervals (Figure ). Air is forced, by compression, through the length of hose, 3.8 cm in diameter, lying along the bottom of the lake. The hose was weighed down with bricks and re-bar. A brick was attached to the bottom of the diffuser to prevent it from floating to the surface when in operation. A buoy with a flag attached to the point release keeps the point release level as well as indicates the location of the aeration system below. Each flag / buoy indicates one point release pod. The point release system is exclusively used in Spring Lake (Table ). 3

9 TOP VIEW AT THE END OF EACH ARM IS A SCREW TYPE CAP ALL FOUR ARMS HAVE 1/16 IN HOLES, IN APART IN PVC TUBING AIR HOSE TO COMPRESSOR DIAMETER 3.8 CM POINT RELEASE DIFFUSER ALL JOINTS GLUED (PVC CEMENT) FIGURE. DIAGRAM OF A POINT RELEASE AERATION SYSTEM. Figure. Diagram of a Point Release Pod. 4

10 Table. Aeration technique and number of aerators at each lake, Lake Size (ha) Type and # of aerators Zama Pond 0.5 comp/ 1,1/6 hp Cecil Thompson Pond 0.8 s.a./ 1,1/6th hp East Dollar 5.6 s.a./ 1,1/ hp Cummings 6.9 s.a./ 1,1hp & 1, hp Moonshine 30.8 s.a./ 1,1 hp Spring 3.1 p.r. Figure Eight 38.6 s.a./ 3,1 hp Sulphur 53.4 s.a./ 4,1 hp Swan s.a./ 7,1 hp Cutbank 17.0 s.a./ 10,1 hp s.a. - surface aerator p.r. - point release comp - compressor 3. Mechanical surface aerator set-up and operation The aerator fits into the middle of a square float. The float is anchored at the four corners with small diameter nylon rope and a brick attached at the end of each rope. This keeps the aerator in position and from spinning around. The waterproof electrical cable provides power from the land source to the aerator. The motor is submerged and the prop is approximately 7-10 cm below the surface of the water. When operating, the prop throws water up against the inverted bell, which breaks up the water into small-oxygenated droplets and falls back into the lake. See Figure 3 for a diagram of a mechanical surface aerator. Maintenance is minimal on these aerators. 5

11 Figure 3. Diagram of a Mechanical Surface Aerator. 6

12 3.3 Oxygen sampling methods During the 001 to 00 aeration season (October to April), an Oxyguard Handy Mark digital meter was used to sample the oxygen levels. The meter displays percent of saturation, oxygen concentration in mg/l and temperature in degrees Celsius. The probe is lowered to the predetermined depth where mg/l and temperature readings are measured, while the probe is moved back and forth. The percent of saturation is used to calibrate the meter before field use. With the exception of Spring Lake and Zama Pond, oxygen sampling was conducted monthly. In past years oxygen sampling occurred bi-monthly. Oxygen values were recorded at Spring Lake in October, December and March while Zama Ponds oxygen sampling was completed once, in February. The number of sampling locations and depths varied proportionally to lake surface area. During the aeration season additional sampling was completed at a point furthest from the aeration site on five of the largest aerated lakes. This sampling was performed in October, December and March to determine area of influence of the aerators. A HACH Kit was used to verify the Oxyguard meter readings on three separate occasions during aeration (October, December, and February). If the readings between the two methods are within one mg/l, then the Oxyguard meter is used exclusively. 4.0 Results Aeration overwintered nine of the ten lakes during the 001 to 00 season. All the aeration systems were installed and operated from October to mid-april, except for Spring Lake, which was operated for 7 days in October. The number and size of mechanical surface aerators varies from lake to lake with lake surface area size. Each 1 hp aerator can successfully aerate 1 to 14 ha. Dangerous ice conditions during the months of November and April disallowed oxygen sampling on some lakes. Table 3 provides details of consecutive overwintering years for each of the aerated lakes. Table 4 shows remote end oxygen concentrations of five of the ten aerated lakes for 001 to 00. Monthly lake oxygen concentrations are graphed in figures 4.1 to 4.9 below. Cecil Thompson Park Pond overwintered using the 1/6 th -hp aerator (Figure 4) Moonshine 7

13 Lake had oxygen levels of 6 mg/l at 1m and 4 mg/l at 3m throughout the aeration season (Figure 5). Table 3. Aerated lakes most recent successive overwintering years. Lake Most Recent Successive Years Overwintering C. Thompson Pond to 01-0 Moonshine Lake to 01-0 Cummings Lake to 01-0 Sulphur Lake 91-9 to 01-0 Spring Lake to 01-0 East Dollar Lake to 01-0 Figure Eight Lake 91-9 to 01-0 Zama Pond to 01-0 Swan Lake to 01-0 Cutbank Lake* to * partial winterkill in Table 4. Remote end of lake oxygen results. Lake Month Depth(m) October December March Cummings Lake 1m n/c n/c n/c n/c n/c n/c Sulphur Lake 1m n/c m n/c Figure Eight Lake 1m n/c 1.75m 4.9 n/c n/c Swan Lake 1m 1.9 n/c 5.7 n/c n/c n/c Cutbank Lake 1m n/c n/c n/c n/c n/c n/c n/c - not completed 8

14 4.1 Cecil Thompson Park Pond Oxygen (mg/l) Depth 1m m Critical 0 Dec Jan Feb Mar Month Figure 4. Oxygen concentrations in Cecil Thompson Park Pond, Moonshine Lake Oxygen (mg/l) Depth 1m 3m Critical 0 Dec Jan Feb Mar Month Figure 5. Oxygen concentrations in Moonshine Lake,

15 Cummings Lake (Figure 6) had two aerators, a 1-hp and a -hp, operating for most of the season. In February, oxygen levels were dropping and an additional aerator (1-hp) was installed. Oxygen levels remained above critical for the duration of the winter. Sulphur Lake overwintered as well (Figure 7). 4.3 Cummings Lake Oxygen (mg/l) Oct Dec Jan Feb Mar Month Depth 1m 3m Critical Figure 6. Oxygen concentrations in Cummings Lake, Sulphur Lake Oxygen (mg/l) Oct Nov Dec Month Depth 1m 3m 5m Critical Figure 7. Oxygen concentrations in Sulphur Lake,

16 Spring Lake overwintered with oxygen levels above 3 mg/l down to approximately 7 m (Figure 8). East Dollar Lake overwintered with operation of the ½ hp aerator (Figure 9). 4.5 Spring Lake Oxygen (mg/l) Oct Dec Mar Month Depth 1m 5m 10m Critical Figure 8. Oxygen concentrations in Spring Lake, East Dollar Lake 8 Oxygen (mg/l) 6 4 Depth 1m 4m 7m Critical 0 Dec Jan Feb Mar Apr Month Figure 9. Oxygen concentrations in East Dollar Lake,

17 Figure Eight Lake was aerated with 3, 1-hp surface aerators (Figure 10). The lake went into freeze up with lower oxygen than normal but steadily increased throughout the aeration season. Swan Lake continues to over winter successfully (Figure 11). Oxygen concentrations dropped rapidly throughout the aeration season then began to stabilize in March. 4.7 Figure Eight Lake 8 Oxygen (mg/l) 6 4 Depth 1m 4m Critical 0 Oct Dec Jan Feb Mar Month Figure 10. Oxygen concentrations in Figure Eight Lake, Swan Lake Oxygen (mg/l) Oct Dec Jan Feb Mar Month Depth 1m 4m Critical Figure 11. Oxygen concentrations in Swan Lake,

18 Cutbank Lake experienced a substantial winterkill by January 00 and had only five of the ten aerators operating in February. A three-hour test netting was completed and compared to the previous fall (001) test netting confirming the oxygen sampling data. Figure 1 shows the rapid oxygen decline at the mid-lake sampling location ending well below critical levels. The low oxygen levels were caused by a combination of several factors large amounts of snow cover (>10 cm) early on and throughout the winter, low water in the lake which in turn allowed super cooling of aeration site freezing in several of the aerators, and high productivity. The oxygen levels dropped at 3 mg/l per month from ice up on. By January 00, oxygen concentrations at two of the three oxygen-sampling sites were at or below the minimum for trout survival. However, a cell of oxygen (> 3 mg/l) approximately 100 m wide and approximately 500 m long, with a max depth of 1.75 m, was created along the shoreline, southwest of the aeration site over wintering an unknown number of trout. 4.9 Cutbank Lake Oxygen (mg/l) Depth 1m 3m Critical 0 Dec Jan Feb Month Figure 1. Oxygen concentrations in Cutbank Lake,

19 At Zama Pond oxygen data was not recorded this year. The Zama City Society operates the aeration unit and contact ASRD (Alberta Sustainable Resource Development) if fish have died. 5.0 Discussion Cutbank Lake, the largest of the aerated lakes at 17 ha, recorded a partial winterkill during the season. Low water levels, large amounts of snow cover, and super cooling of the aeration site contributed to the partial winterkill. Cutbank Lake had over wintered for the previous two years. Cummings Lake had a third aerator installed, in January, due to oxygen values dropping rapidly. Low water levels and large amounts of aquatic vegetative growth during the summer contributed to low oxygen levels. The lake should be able to overwinter with one 1- hp aerator. Several different aquatic vegetation controls have been discussed but thus far none have been implemented. If a fourth aerator is needed in the future, serious decisions will need to be made as to the continuing of this project. Figure Eight Lake overwintered although oxygen values were not as high entering into ice up as in most other years. A late season algae die-off and subsequent oxygen reduction due to the decay process caused the lower oxygen values. 6.0 Recommendations 1. At Cutbank Lake to alleviate the super cooling and freezing over of the aeration site, moving the aeration system out 150 m further will be implemented in the fall (November) pending funding. The repositioning of aeration system would almost double the water depth, of the aeration site, from 1.75 m to >3 m. This would allow all 10 of the aeration systems to function in extreme cold periods and providing a larger area of oxygenated water for fish to overwinter. 7.0 Literature Cited 14

20 Miller, T.G and W.C.Mackay, 1996 draft. A comparison of mechanical surface aeration and point release air injection used to prevent winterkill in Alberta. Second annual progress report on winter lake aeration. Department of Biological Sciences, University of Alberta. 64pgs. 15