Emily Hoopman. Bayfield High School. December 23, 2012

Transcription

1 A Comparison of Commercial Aeration Systems in Northern Wisconsin Aquaculture Ponds Emily Hoopman Bayfield High School December 23,

2 A Comparison of Commercial Aeration Systems in Northern Wisconsin Aquaculture Ponds Emily L. Hoopman, Star Route Road, Bayfield, WI Bayfield High School, Bayfield, WI Teacher and/or Mentor: Mr. Richard Erickson/ Greg Fischer Aquaculture is the controlled cultivation of aquatic animals and plants. Currently, it's the fastest growing segment of agriculture in the world. The Northern Aquaculture Demonstration Facility (NADF) has a collection of four 0.4-acre ponds designed to research effective aquaculture techniques. An important aspect in ensuring the success of a pond is proper aeration to provide adequate dissolved oxygen (DO). The purpose of this study was to analyze water quality in NADF aquaculture ponds with different aeration systems. The data collected was examined to determine whether each aeration system was able to provide the minimum required DO level of 4 parts per million (ppm). The data was also analyzed to comparatively rate the four different aeration systems. The results indicated there is a statistically significant difference between the aeration systems in each of the ponds (ANOVA, p < 0.05). The windmill aeration system in pond 1 failed to meet the minimum amount of oxygen required. The surface aeration system in pond 2; blower, diffusers, airlifts, and surface aerator in pond 3; and blower, diffusers, and airlifts in pond 4, effectively met the 4 ppm standard. Pond 4 consistently had the highest DO levels, indicating it was the most effective aeration system. 2

3 ACKNOWLEGEMENTS First, I would like to thank the University of Wisconsin Stevens Point Northern Aquaculture Demonstration Facility (UWSP-NADF) for allowing me to conduct my research on their premises and for allowing me to utilize their equipment. I also owe a sincere thank you to facility manager Greg Fischer, along with technicians Kendall Holmes, Lance Bresette, and Nate Martin of UWSP- NADF, Mr. Richard Erickson, my science teacher and advisor, and the Bayfield School District for assistance and support during my research. I extend my thanks to Ellie Hoopman for record taking during data collection. Finally, I would like to recognize and thank Derek Ogle from Northland College in Ashland, WI, for his help with the data analysis. 3

4 TABLE OF CONTENTS List of Tables...5 List of Figures...5 Introduction...6 Hypothesis...9 Materials and Methods...9 Results...12 Discussion...14 Conclusion...16 References

5 LIST OF TABLES Table 1 Pond Aeration Set-Up 9 Table 2 One-Way ANOVA Analysis Dissolved Oxygen (DO, ppm), by week 13 Table 3 Tukey groupings of ponds from highest dissolved oxygen to lowest 14 Table 4 Mean ph (Scale 1-14), analysis 10 weeks 15 LIST OF FIGURES Figure 1 Pond Dimension Map...10 Figure 2 Tukey Test Groupings DO (ppm), analysis week

6 INTRODUCTION Aquaculture is the controlled cultivation of aquatic animals and plants. Currently, it is the fastest growing segment of agriculture in the world (University of Wisconsin Extension, 2009). Wisconsin alone has 2,100 registered fish farms that raise fish for food, stocking, bait, and recreation (Aquaculture demonstration research). The University of Wisconsin- Stevens Point Northern Aquaculture Demonstration Facility (NADF) in Red Cliff, Wisconsin, originated as a result of an Agricultural Development and Diversification Grant offered by the Wisconsin Department of Agriculture, Trade and Consumer Protection that was awarded to the City of Ashland in 1996 (Aquaculture demonstration research). In conjunction with the Wisconsin Aquaculture Association, stakeholders, and citizens, the NADF is now a center for applied research and demonstrations. In 2005, the University of Wisconsin Stevens Point (UWSP), College of Letters and Science, assumed administrative oversight of the facility. Now, the UWSP directs the NADF in collaboration with the Red Cliff Band of Lake Superior Chippewa; the Wisconsin Department of Agriculture, Trade and Consumer Protection; the University of Wisconsin-Extension; and Wisconsin's aquaculture industry (Aquaculture demonstration research). The NADF is equipped with high-tech aquaculture production systems and equipment that allow commercial-scale demonstrations to take place. One of the NADF site resources are a collection of four 0.4-acre complex rearing ponds with a common fish collection basin and 2 settling basins. In 2012, a two-year neural study was initiated at the NADF to compare the performance of two different strains of yellow perch (Perca flavescens). The two strains being utilized in this study were the improved Ohio State yellow perch and a domestic strain of Wisconsin yellow perch. At the end of March, both strains were hatched in the aquatic barn. Fry were reared on 6

7 plankton in separate ponds, harvested as small fingerlings (35-40mm), feed trained in separate tanks within the facility, and then returned to the ponds. Then, approximately 9,000 feed trained fingerlings were stocked into each pond with total weights of 40-68Kg. Therefore, a total of four ponds were filled with yellow perch; two containing Ohio State Perch and two containing Wisconsin Perch. The fish remained in the ponds for the duration of the summer, until they grew to an adequate size of 8.5 inches, which is the stocking market for pond-raised fish (Brannan, 2010). In early October, the fish were extracted from the ponds and data was collected based on condition factors (length and weight). Then, the fish were graded and restocked to each pond appropriately. The study is ongoing at this time and has not generated any reportable results to date. The perch will be reared there this winter and next fall until they reach market size, and then will be harvested. An important aspect in ensuring the success of outdoor ponds is proper aeration because dissolved oxygen is one of the key water quality components in the environment of a pond. Dissolved oxygen is gaseous oxygen dissolved in an aqueous solution. In general, it is the amount of oxygen available in the pond water. It is responsible for keeping the inhabitants healthy and the water clean. The baseline level of oxygen required in a pond for yellow perch is approximately 5 ppm (parts per million) (Piavis; Krieger et al., 1983). Biologists from the NADF use an inequality of >4 ppm as the minimum oxygen level required to provide the perch with a suitable environment. The ability of water to hold oxygen decreases as the water temperature increases (Robinson, 2007), so water temperature must stay low enough to avoid a fish kill resulting from low oxygen levels. In some ponds, the lack of aeration can also lead to stratification. This means a layer forms at the bottom of the pond that is unusable by fish because 7

8 it is extremely oxygen deficient. As a result, the living space of the fish decreases and a higher strain is placed on the oxygenated water (NES, 2011). The two main types of pond aeration are surface aeration and bottom based aeration. Surface aerators are generally floating units that pull in water from the surface of a pond and splash it into the air. When the water cascades back down into the pond, an oxygen transfer takes place along with the venting of gases only at the pond's surface. This type of aeration can be classified as vertical. Bottom based aerators, or diffusers, use blowers or compressors to push air to a diffuser on the bottom of the pond, allowing the bubbles to naturally rise to the surface. As the bubbles rise, they destratify the water, eliminating the low oxygen zones at the bottom and mixing it with the oxygen-rich water above (NES, 2011; Tucker, 2005). A good aeration system provides many benefits such as increased production and performance, along with a healthy environment for the fish. Most importantly, fish kills can be prevented. In properly aerated ponds, beneficial pond bacteria are stimulated to efficiently break down waste and reduce the bottom muck layer. This controls odors and hydrogen sulfide that may be present otherwise. Another benefit is the reduction of algae blooms due to the lack of available nutrients for the algae. Aerators facilitate destratification, which improves the overall water quality in the pond. Also, the need for maintenance products is reduced because a pond develops the natural ability to regulate itself. For northern states such as Wisconsin, aeration systems can prevent winter fish kills by keeping the pond s surface from freezing over and allowing it to vent gases (NES, 2011). The purpose of this study was to analyze and compare certain water quality parameters in ponds with different aeration systems. Parameters of dissolved oxygen, ph, temperature, turbidity, and stratification were analyzed to determine which aeration systems could provide the 8

9 required minimum dissolved oxygen level of >4 ppm. Furthermore, data from each system were compared to the type of aerator used to oxygenate each pond. This study attempted to identify the positive and negative effects of each aerator on the aquatic ecosystems in northern Wisconsin. The null hypothesis states there will be no statistically significant difference between the dissolved oxygen levels resulting from the different aeration systems used in each of the ponds. MATERIALS AND METHODS The NADF site has a collection of four 0.4-acre ponds (220 ft. x 80 ft. /ea.). Three types of aeration systems were tested by placing one type on each of three ponds. A fourth pond, pond 3, had all electrically powered aerators on it (Table 1). Table 1. Pond aeration equipment for ponds 1-4 Pond 1 Windmill with solar, electric diffuser pump Pond 2 Surface Aerator only Pond 3 Blower, airlifts, diffusers + Surface Aerator Pond 4 Blower, airlifts, diffusers Pond 1 was aerated with two pairs of diffusers placed below the water surface; one pair at approximately 1 m in depth and one pair at 2 m. The aerator was operated by a windmill with solar panel and battery, supported with a linear compressor, and operated 24 hrs/day until warm water temperatures warranted only nightly operation, then operated at night from approximately 9:00 PM-8:00 AM.. Pond 2 was aerated with a single surface aerator placed at a depth of approximately 2 m. The surface aerator was operated 24 hrs/day until warm water temperatures warranted only nightly operation, then operated at night from approximately 9:00 PM-8:00 AM. Pond 3 was aerated with two airlifts and a surface aerator placed approximately 2 m below the surface, with a pair of diffusers placed 1 m below the surface. Airlifts received low-pressure air from the main 5 HP rotary vane blower located in the tractor shed that was piped underground to 9

10 the ponds. This aeration system operated 24 hrs/day until water temperatures warranted only nightly operation, then operated at night from 9:00 PM -8:00 AM. Pond 4 was aerated with two airlifts placed at a depth of approximately 2 m and two diffusers placed at approximately 1 m deep. Airlifts and diffusers received air from the facility rotary vane blower described previously. This system also operated 24 hrs/day until water temperatures warranted only nightly operation, then operated from 9:00 PM-8:00 AM. As a safety precaution, a surface unit was installed in ponds 1 and 4 for use as emergency aeration if the oxygen level dropped below 4 parts per million (ppm). Surface units were from Kasco, Model 2400AF, (Prescott, WI). They are self-contained, lightweight units that float at the surface with a single power cord returning to shore and several mooring lines anchoring the unit. Blowers were from Ametex Rotron, Technical and Industrial Products (Harleysville, PA). The diffuser was a Great Lakes 4- Diffuser Manifold from Aquatic Eco-Systems Inc. (Apopka, FL). Compressors were Easy Pro Linear Air compressors, Model EPW10, from Easy Pro Pond Products (Grant, MI). Testing locations in each pond were marked using metal stakes and green ribbons labeled A through F (Figure 1). 40 ft. F 45 ft. 220 ft. D B A E C 90 ft. 80 ft. Figure 1. Location of data collection points and dimensions for each of Ponds

11 The ponds were prepared with fertilizer and partially filled with water for the perch fry during May 2012 by the NADF facility workers. A YSI Model 550A probe (YSI, Yellow Springs, Ohio) was used to simultaneously collect dissolved oxygen and temperature data from the ponds. The 4 m-long cord on the probe was labeled with alternating widths of blue electrical tape for every half- and full-meter from the recording unit to the probe. A secchi disk was used to measure water turbidity, and the rope on it was also marked in intervals of 10 cm with a black permanent marker. Acidity levels were measured using Eutech Instruments phtestr 10 (Cole- Parmer Instrument Company, Vernon Hills, IL). A 3 m-long floating device was constructed of PVC pipe and foam to serve as an extension to direct the probe away from the edge of the pond. The YSI monitor cord was strung through two metal hooks on the floating device and fastened securely with a wooden clothespin at the end. The foam served as a support to prevent the base of the recording unit from getting wet. Weekly data collection was from 8:00 AM to 9:30 AM for the full set of four ponds. To begin monitoring, the YSI meter was secured to the floating device, turned on, and calibrated for use. Data for points A, B, and C were monitored by wading into the water and dropping the probe below the surface to a depth of 0.5 m. Using the end of the PVC pipe, the probe was gently swirled back and forth, allowing it to take in varying amounts of dissolved oxygen for each location. Data at points D and E were obtained by gliding the floating device outward from the side of the pond and kneeling at the edge to record the data. Data collection at point F involved multiple monitoring steps. Initially, the oxygen percentage, amount (in ppm), and temperature were recorded at the water's surface then at halfmeter intervals down to 1.5 meters. Next, turbidity was measured and recorded using the Secchi disk. Then, the ph was recorded. The values were based on the conventional scale of 0 to 14, 7 11

12 being neutral. These same measurements were then taken at each of the three remaining ponds. Measurements were collected once a week for three months (July-September). The data were analyzed using a one-way ANOVA analysis for each of the ten weeks. The complete analysis contained multiple segments of specialized comparisons such as the Levene's test, Anderson- Darling normality test, and Tukey test. The Levene s test worked by testing the null hypothesis stating the variances of the group are the same. The Anderson-Darling normality test determined if the data set came from a specified distribution (the normal distribution). The Tukey test performed a pairwise comparison of the means. The significance level for this study was 0.05 indicating a 95% confidence level that there was or was not a significant difference. RESULTS During the study period, no supplemental or emergency aeration was required for ponds 2, 3, or 4. The aeration system in pond 1, as designed (windmill with solar panel), was unable to meet the minimum amount of oxygen required and was therefore removed from the study. At that point, the aerator was plugged into a 120V electrical outlet with a timer and used as a normal aeration system. In addition, the emergency surface aerator was used on a few occasions to raise the oxygen levels in pond 1 when they became too low (<4 ppm). An initial one-way ANOVA test was conducted to determine if the oxygen levels in the ponds differed within the first week. The Levene's test for week 1 suggested that the variances were equal among the groups. The Anderson-Darling test suggested that the residuals were normal, p= The assumptions were met for week one. The ANOVA results suggested a strong difference in dissolved oxygen values among the four ponds. Tukey's multiple comparison procedure for week one suggested that ponds 2 and 4 were not statistically different, ponds 1 and 12

13 3 were statistically different, and the three individual groups were statistically different (Figure 2). Pond Figure 2. Tukey test groupings for dissolved oxygen (ppm) for week 1. The primary tests do not support the null hypothesis stating there will be no significant difference between the dissolved oxygen levels resulting from the different aeration systems used in each of the ponds. They imply there is a statistically significant difference between the aeration systems in each of the ponds. Data from each of the ten weeks was analyzed in the same manner as data from week one. Table 2. Dissolved oxygen averages and Tukey groupings for Ponds 1-4 during the ten-week study timeframe. Week Variable P1 P2 P3 P4 1 O₂ Avg Group c a b a 2 O₂ Avg Group c a c b 3 O₂ Avg Group c b bc a 4 O₂ Avg Group c a c b 5 O₂ Avg Group b a b a 6 O₂ Avg Group d b c a 7 O₂ Avg Group c b c a 8 O₂ Avg Group b c c a 9 O₂ Avg

14 Group b ab b a 10 O₂ Avg Group a b b b In the table above, groups with the same letter represent no significant difference between the ponds with different aeration systems, whereas different letters represent a significant difference. The Tukey test, multiple comparisons of means, for weeks one through ten showed no consistent grouping pattern. The standard of 4 ppm was reached in all ponds weekly, except for pond 1 in weeks 1 and 2, and pond 3 in week 2. As a result, it can be concluded that all aeration units were effective according to the standard, except for the windmill/solar aeration unit which was discontinued. DISCUSSION There is a significant difference in the levels of dissolved oxygen in the ponds. In an attempt to classify the most effective aeration system, the Tukey Test results for each week were grouped from highest level of dissolved oxygen to the lowest, with the highest DO level represented by the variable "a" and the lowest by the variable "d" (Table 3). Table 3. Tukey groupings for weeks 1-10 listed from highest dissolved oxygen level (a) to lowest (d). Week a ab b bc c cd d 1 2, , ,3 5 2,4 1, , , , ,3,4 14

15 Pond 4 consistently had the highest dissolved oxygen levels, closely followed by pond 2. For that reason, the combination of blower, airlifts, and diffusers in pond 4 can be classified the most effective aeration system of this study. Throughout the study, the clarity of pond 2 was extremely transparent with an abundant algae bloom. The average Secchi disk reading was 94 cm. All of the ponds yielded ph levels that were consistently basic (>7). The optimum ph range for yellow perch is between 6.5 and 9.2 (Wheldon, 2012). Also, ph values above 9.5 or 10 are generally considered undesirable in aquaculture ponds (Tucker and D'Abramo, 2008). Several instances occurred in which this range was exceeded, and the 10-week average ph for pond 2 was within this range (Table 4). Table 4. Mean ph of ponds 1-4 over the 10-week study. Pond ph Pond 2 was at risk for ph toxicity, which results when certain conditions cause a sudden change in ph, outside the tolerable range (>9.5). Consequently, the animals being cultured could be killed. Phytoplankton in fertile aquaculture ponds often cycles through periods of bloom and collapse. When a mass quantity of algal cells dies, the nutrients released during decomposition promote the growth of a new bloom. When plants are growing quickly, their rapid carbon dioxide uptake may cause high ph until the phytoplankton community comes to a new equilibrium. Extended occurrences of high ph are particularly common in ponds where filamentous algae dominate the plant community. Ponds with filamentous algae usually have clear water, allowing sunlight to penetrate deep into the water column and stimulate intense 15

16 photosynthesis by underwater or floating mats of algae (Tucker and D'Abramo, 2008). This problem was addressed by stirring pond 2 in the later phase of the study. The ph levels decreased minimally over the remainder of the data collection period. Managing high ph in aquaculture ponds varies greatly and no specific management practice is always successful. Note, all ponds produced yellow perch throughout the study and no large die-offs were encountered. CONCLUSION In summary, aeration does positively affect the overall health of northern Wisconsin ponds. The null hypothesis was rejected, indicating a statistically significant difference between aeration systems utilized for this study. Furthermore, pond 4 displayed the most consistent oxygen levels. Pond 1 displayed erratic oxygen levels and did not meet the required standards for the cultivation of yellow perch. The aeration systems used in ponds 2 and 3 are also viable methods because they met the criteria outlined for functional pond rearing of yellow perch. Results of this study may be directly applied to future evolution within the Wisconsin aquaculture industry. This study gives practical information about Wisconsin fish ponds, and could also be used to assist operators with management of their ponds. 16

17 REFERENCES Aquaculture demonstration research outreach. (Brochure ed.). Round Lake Property Owners Association Inc. Retrieved from stocking oct /aquaculture demonstration facility.pdf Brannan, S. (2010, March 01). Faster-growing yellow perch could make aquaculture more viable. Retrieved from Great lakes 4-diffuser manifold. ( ). Retrieved from Krieger, D. A., Terrell, J. W., & Nelson, P. C. National Wetlands Research Center, U.S. Fish and Wildlife Service Habitat suitability information: Yellow perch (FWS/OBS-82/10.55). Retrieved from website: Linear diaphram compressor - epw10. (2011). Retrieved from NES (Natural Environmental Systems, LLC) Pond aeration is critical for a pond's success. Online at Piavis, P. G. Maryland Department of Natural Resources, Fisheries Division. (n.d.). Yellow perch. Retrieved from website: Pond aerators. (2008). Retrieved from Robinson, B Aerate your pond for better water quality. Countryside & Small Stock Journal,

18 Tucker, C Pond aeration. SRAC Publication No U.S. Department of Agriculture, Southern Regional Aquaculture Center, College Station, Texas. Retrieved from website: Tucker, C. S., and D'Abramo, L. R Managing ph in freshwater ponds. SRAC Publication No U.S. Department of Agriculture, Southern Regional Aquaculture Center, College Station, Texas. Retrieved from website: University of Wisconsin Extension Growing wisconsin's aquaculture industry for the global marketplace. Community,Natural Resource and Economic Development Impact Report. University of Wisconsin Extension, Madison, WI. Available online at Weldon, V Yellow perch. University of Arkansas Extension, Pine Bluff, AR. Online at 18