Grade: 10 | State: Michigan
Grade: 10 | State: Michigan
As I insert yet another sample into the gas chromatograph, I glance at the clock—it’s 3 a.m. I lean back in my chair, tap my foot in an attempt to stay awake in the deserted laboratory and realize I have 535 gas samples to go. Listening to the whirring noise of the running machine, my mind wanders to a scene months earlier. I envision myself standing in a pasture, surrounded by a herd of cattle, as I search desperately for my shovel, which I accidentally left for only a moment. The herd is constantly moving, and my hope of finding the implement is slowly dwindling. I need the shovel to collect dung, a favored food of coprophagous beetles. Finally, I spot the lost shovel and hurry to recover it. Cattle manure surrounds my every step, so I have no trouble amassing the remaining dung needed for my experiment. I am eager to further investigate coprophagous beetles since I learned about their benefits to the pasture ecosystem in previous research. I now wonder how these dung-feeding insects affect levels of methane emissions from cattle dung through their natural activities.
Greenhouse gas emissions contributed by agriculture are a growing worldwide issue, with 10% of all greenhouse gas emissions attributed to farming practices (IPCC 2007). From 1990 to 2009, methane emissions from agriculture grew approximately 14.9% (U.S. Greenhouse Gas Inventory Report 2011). Methane’s global warming potential (GWP) is 21 times that of carbon dioxide by weight and remains in the atmosphere for approximately 12 years (EPA 2010). An estimated 0.7% of methane emissions in the United States come from manure management (Bracmort 2010). In order for methane production to occur from manure pats deposited by cattle in the pasture, anaerobic conditions (absence of oxygen) must be maintained so that the anaerobic microbes can break down the organic matter found in dung (Jun 2002). Moisture promotes anaerobic conditions (Richard 1996) and methane production (Jun 2002).
Coprophagous (dung-feeding) beetles may counteract the process of methane production (methanogenesis) in the pasture by reducing the amount of moisture found in dung (Chiavegato, personal correspondence, 2011). Specifically, coprophagous beetles such as Geotrupidae and Scarabaeidae, known as dung beetles, perform various actions that hasten the drying out of manure. The tunneling (paracoprid) species of dung beetle (i.e., Onthophagus) bury dung beneath the pat in the form of a brood ball to be used for their young. Another group of dung beetle species is the telecoprid, or roller species of dung beetles (i.e., Melanocanthon). These arthropods take the dung and roll it elsewhere, eventually burying it within the soil (Lastro 2006). Dung burial by the telecoprid or paracoprid species of dung beetles takes apart the dung pat, contributing to the breakdown of an anaerobic environment. Dwelling or endocoprid species of dung beetles (i.e., Aphodius) live within the confines of the manure, feeding on its contents in both the larval and adult stage (Floate 2011). Other species of coprophagous beetles, such as those in the family Hydrophilidae, also consume dung (Richardson, personal correspondence, 2010). As this ingestion occurs, liquid is removed from the dung, and air pockets are created within the dung by the movement of the beetles.
In a recent news article, Dr. Shaun Forgie of Landcare Research in Auckland, New Zealand made this statement in regards to the natural activities of dung beetles: “We presume it will have an impact on reducing emissions through the dung burial and improving soil structures, but it has never been scientifically quantified” (Gorman 2011). Studies have been done that analyze the rate of methane emissions from cattle dung (Gupta 2007), but no experimentation has been completed that measures how coprophagous beetles affect the rate of these emissions. Research testing the effect of coprophagous beetles on the emission rates of methane in the pasture would provide a foundational understanding of the role these insects play.
The objective of my study was to answer this question: Would coprophagous beetles’ natural activities result in a reduction of the methane emission rates from cattle dung deposited in the pasture? Treatments were set up in a pasture at the Michigan State University Lake City Research Station in northern Michigan, and emissions were captured in situ using flux chambers. At intervals of 0, 10 and 20 minutes, I removed gas samples from the headspace and then stored the samples in vials for analysis with a gas chromatograph. My hypothesis was that the treatments with beetles added would have the lowest rate of methane emissions, compared to treatments holding dung that was covered to prevent colonization.
Compositional Survey of Coprophagous Beetles
Gaining an understanding of the dung beetles’ presence at the Lake City Research Station would provide helpful background information for evaluating the effect of coprophagous beetles on methane emission rates. I designed a study to survey the coprophagous beetle population at the Michigan State University Lake City Research Station. North American dung beetle surveys have been conducted in areas such as Alberta, Canada (Floate 1998), Minnesota (Cervenka 1991), North Carolina (Lastro 2006, Bertone 2005) and Arkansas (Fiene 2010), but no research has been conducted to monitor the seasonal activity and species composition of coprophagous beetles in northern Michigan prior to this study. My goals for this study were to obtain background knowledge regarding the Lake City Research Station’s coprophagous beetle biodiversity, seasonal activity and abundance through the identification and quantification of Scarabaeidae, Hydrophilidae, and Geotrupidae species.
The coprophagous beetle compositional survey was conducted between May and October 2011, with 40 pitfall traps set twice a month, for a total of 12 trapping periods and 480 traps. Traps were set at the Lake City Research Center (44N 18’ 34.68”, -85S 12’ 11.48”), an 850-acre agricultural research farm currently utilizing the method of tall grass grazing (moving 100 head of cattle so they eat roughly half of the vegetation) as well as a traditional grazing method. The station currently holds approximately 180 cattle, and no insecticides are being used to treat these animals (Carmichael, personal correspondence, 2011). I chose two locations for traps and 20 pitfall traps were set at each site. Site A was a pasture that has historically yielded beetles for previous research (see Figure 1). This site does not have cows that reside permanently, and five years prior to this research, this field was a pine forest. My reasoning for beetles being trapped here was due to the fact that pastures were present on both sides of the field for 20 to 30 years before the conversion from a pine forest to a pasture. Traps remained in this location for the duration of the study. Site B at the research station changed with the schedule of the rotational-grazing cattle and was within two kilometers of Site A (see Figure 2). The traps were set in the area adjacent to the pasture in use, approximately three meters from the electric fence to prevent interference from calves. Pitfall traps similar to those used by Floate and Gill (1998) were constructed (see Figure 3), which consisted of an 18.5-oz. plastic cup buried to brim-level in the soil, covered with a 1.27-centimeter-mesh wire screen. Fresh cattle dung was collected in the field and homogenized. Seventy-five grams of this mixed dung was wrapped in a paper towel and placed on top of each screen.
I spaced the traps approximately three meters apart and divided them into two rows of ten. Approximately five ounces of a mixture of dish detergent and water was poured into the traps to prevent the beetles from escaping. After 48 hours, the traps were collected, the water was drained and the beetles were preserved in 80% ethyl alcohol. Preservation jars were labeled with site number and date, and stored for future documentation.
Before identification, I removed the beetles from the alcohol and allowed them to dry to reveal their true colors. I then visited the Albert J. Cook Arthropod Research Collection at Michigan State University to establish key specimens for commonly occurring beetles with the assistance of Gary Parsons, curator of the collection. A second trip to the collection was made after most of the beetles had been identified, using the key specimens to identify the additional species found (see Figure 4). A total of 10,041 individual beetles representing 20 species were collected from May to October, and I identified them to species level with reference to the A.J Arthropod Collection at Michigan State University. Site A yielded 9,103 beetles, while 938 beetles were collected from Site B. Table 1 (in the Appendix) summarizes the total number of beetles of each species collected at each site.
The dominant species for the six-month survey were Onthophagus nuchicornis (3,896 beetles), Chilothorax distinctus (2103 beetles) and Colobopterus erraticus (1613 beetles). Figure 5 provides a visual representation of these three beetle species and their seasonal distribution from May to October. The peak for Colobopterus erraticus was in June, Onthophagus nuchicornis peaked in August and Chilothorax distinctus’ peak began in October. Onthophagus taurus (327 beetles collected),an introduced paracoprid species of dung beetle, was first identified in Michigan through research I conducted in 2010. The specimens I collected this year confirmed the Onthophagus taurus’ continued presence. One telecoprid specimen was collected throughout the survey (Melanocanthon nigricornis). In addition, eight paracoprid and nine endocoprid species were trapped during this study. For the month of September, which was when the methane experiment took place, the three dominant species were Calamosternus granarius (505 beetles), Aphodius fimetarius (504 beetles), and Onthophagus nuchicornis (148 beetles). This study showed overall large populations of coprophagous beetles present at the Lake City Research Center, especially paracoprid and endocoprid species. Both these types of dung beetles, as discussed earlier, could affect the rate of methane emissions from cattle dung through their natural activities.
In order to evaluate the effect of coprophagous beetles on methane emissions from dung pats, I needed to construct sampling devices. Flux chambers are commonly used to capture greenhouse gas emissions from soil (Leverenz 2010). The static flux chamber design used in this study was based on a similar design used by Chiavegato (personal correspondence, 2011), but were made of different material based on what was available to me. My chambers consisted of an insert pounded into the ground that served as a base, as well as a cap that fit over the insert, capturing gas samples (see Figure 6).
Soil inserts were made from 15.24-centimeter-long sections (diameter = 15.24 cm) of PVC pipe. A mark was made 3.81 cm down the PVC so that the cap could be lowered to the same level for all treatments. Caps placed over the inserts during sampling periods were constructed of white PVC caps (inner diameter = 15.9 cm, height = 6.7 cm). One hole for atmospheric pressure regulation was made on the top, 3 cm from the side (diameter of hole = 2.78 cm). A second hole was drilled for a PVC attachment, which was glued to the cap with a septum attached to the top to be used for extracting samples. I stretched a section of tire rubber around the cap with a pipe clamp. This rubber would flip down and cover the lower section of the cap and part of the insert, ensuring an air-tight seal and minimizing the movement of the cap on the insert.
Prior to experimentation, I tested a flux chamber to ensure that my equipment and methodology would capture gas emissions. I took samples once per day for two days at 0, 10 and 20 minutes within placement of the cap on the insert. These vials were sent to Michigan State University and run through a gas chromatograph in a manner similar to the way the rest of the samples would be analyzed. The results showed that the methane increased over time, so I then used the chambers for the actual experiment.
Based on the abundance of beetles trapped in the beetle survey, I used Site A for this experiment. Treatments were set up for a five-day period, from August 30 to September 3, 2011, and a second five-day sampling period was set up from September 4 to September 8, 2011. The PVC inserts were placed in the ground four meters apart in a circular formation (circumference = 80 meters) to prevent the beetles from favoring a treatment because it was in an outer row. Inserts were pounded halfway into the ground 24 hours before Day 1 of each sampling period to minimize soil disturbance during sampling, as suggested by Parkin and Venterea (2010), and remained in the same location for the entire five-day period (see Figure 7). Twenty-four hours prior to the second sampling period, the inserts were each shifted around the circle two meters, and the dung from the last period was removed. Vegetation inside the inserts was cut to approximately 3 cm.
Live Trapping of Beetles
One hundred-fifty Onthophagus taurus specimens were collected for this experiment on August 27 and 28, 2011, using 34 live pitfall traps that were set for 24 hours, and then re-set. These were similar to the traps used in the beetle survey. Since the specimens needed to be captured alive, I did not mix water with dish detergent and add this to the traps. An inverted cut-off bottle top was placed inside the trap and used as a funnel to keep the specimens inside. Approximately 1 cm of soil was added to the bottom of the trap to allow the beetles to bury within the soil and stay cool in the sunlight. Collections were placed in bins with fresh dung so that the beetles could be used a few days later. Dung for the treatments was acquired fresh and homogenized together for approximately one hour before experiment setup on Day 1 of each sampling period.
All treatments were placed within the inserts, labeled with a flag, and replicated five times. Placement in the circle was randomized (see Figure 12). Once the measured dung was added to the applicable treatments, I calculated the volume within the inserts by measuring across the diameter at 0, 1½, 3, 4½ and 6 inches; measurements were repeated perpendicular to the first at 0, 1½, 4½ and 6 inches. Beetles and screens were then added to the appropriate treatments. Setup procedure was replicated for the second testing period. On days that rain was predicted, I propped a cover in a lean-to style over the inserts so that rainfall would not affect the amount of moisture in the dung (see Figure 13). Temperature, atmospheric pressure and precipitation were recorded daily (see Table 2).
Extraction of gas samples occurred between 3 p.m. and 7 p.m. once a day. Screens were removed from appropriate treatments immediately prior to the placement of the cap. To ensure correct timing, I placed five caps at a time over the treatments and lowered them to the marked level on the insert. The rubber seal was then flipped over each insert and cap. A 20 mL syringe was inserted into the septum fixed to the cap and pumped two times to guarantee a mixture of air within the headspace (see Figure 14). Gas was extracted at 0, 10 and 20 minutes, and samples were placed in labeled, evacuated vials with metal crimp caps and rubber septa. I took the samples following the randomized-circle order of the treatments; sampling for each group of five was completed before moving on to the next group. Caps were removed after sampling took place each day. Vials were stored for two months until equipment was available and then transported to Michigan State University. I measured the methane emissions from the 600 samples collected using gas chromatography with a Shimadzu GC 2014 equipped with a flame ionization detector (FID) over a period of 95 consecutive hours (see Figure 15). Daily flux (the increase over time) was calculated based on the linear correlation between gas concentration obtained by chromatography and incubation time on chambers. Data was analyzed using a t-test as well as a Mann-Whitney test at the 95% confidence level.
Table 2: Precipitation and Temperature During Experiment
|Period||Day||Atmospheric Pressure||Precipitation||Temperature (°C)||Covers Placed|
Results for Soil Only Treatment
The soil only (SO) treatments showed low to non-detectable methane emissions (x̅ =0.009 µg CH4), while treatments that included dung (BA, DC and DO) had higher methane emissions on all days ( x̅ =5.13 µg CH4). Since the purpose for including the SO treatment was to provide a baseline comparison with the emissions from the dung treatments to verify proper methodology during experimentation, SO emissions were not included in the results.
Results for Beetles Added, Dung Covered, and Dung Open Treatments
The mean fluxes for each treatment on Days 4 and 5 for both sampling periods are shown in Figures 16-19 (n=4-5), since these were the days that showed statistically significant differences between treatments. Compared to dung covered (DC), beetles added (BA) and dung open for beetle colonization (DO) showed significantly lower methane emissions for Days 5 through 5 during both sampling periods. T-tests were performed to compare methane fluxes of beetles added (BA) versus dung covered (DC); dung open for colonization (DO) versus dung covered (DC); and beetles added (BA) versus dung open (DO). In addition, a Mann-Whitney test was performed for each of the comparisons due to possible violations to normality. Before the tests were performed, replicates with negative flux measures were removed.
Beetles Added (BA) compared to Dung Covered (DC): The beetles added treatment showed significantly lower methane emissions compared with the dung covered treatment on Days 4 and 5 of both periods (T-test, p<0.05). The Mann-Whitney test confirmed statistically significant differences at the 5% level on Day 4 of both periods and Day 5 of Period 1.
Dung Open (DO) compared to Dung Covered (DC): The treatments with dung open for colonization showed significantly lower methane emissions compared with the dung covered treatments on Day 4 and Day 5 of both periods (T-test, p<0.05). The Mann-Whitney test confirmed statistically significant differences at the 5% level on the same days.
Beetles Added (BA) compared to Dung Open (DO): The beetles added treatment showed lower methane emissions compared with the dung open for beetle colonization treatment according to the Mann-Whitney test on Day 5 of Period 1. However, this was not shown in the t-test (p<0.10). The dung open treatments showed significantly lower methane emissions compared with the beetles added treatments on Day 5 of Period 2 (T-test, p<0.05).
Discussion and Conclusion
The purpose of this study was to evaluate the effect of coprophagous beetles on methane emission rates from cattle dung deposited in the pasture. My hypothesis was that the treatments with beetles added would have the lowest rate of methane emissions, compared to treatments holding dung covered to prevent colonization. This hypothesis was partially confirmed, as the beetles added treatment did not affect emissions on Days 1 through 3, but did impact emissions on Days 4 through 5 for both periods.
The two treatments with beetles (BA and DO) did not show a significant difference in methane emissions compared to the treatment without beetles (DC) on Days 1 through 3 for either sampling period. The insignificant differences in methane emissions between treatments on the first three days may have been due to the fact that the dung was so wet initially that it may have counteracted the beetles’ impact. On Days 4 and 5 of both periods, the emissions were significantly lower in the DO and BA treatments compared to DC treatments. This could be due to the fact that the beetles created tunnels within the pat (see Figure 20), which hastened the drying out of the dung. Since methanogenesis requires anaerobic conditions, the removal of moisture, along with the creation of air pockets, may explain the decline in methane production.
During the experiment, I observed beetles landing on dung covered treatments, attempting to get to the dung (see Figure 21). Beetles also seemed to be highly attracted to dung open for colonization, and many tunnels and insects were seen within the manure. When the DO treatment dung pats were visually compared after the experiment to the BA treatments, the dung open for colonization seemed to have a higher population of beetles and tunneling (see Figures 22–23). Although this observation was made in the field, when the BA and DO treatments were compared statistically, both treatments seemed to have a similar effect on the methane emission rates. On Day 5 of Period 1, BA treatments had lower methane emissions than DO, while on Day 5 of Period 2, DO treatments had lower emissions compared to BA. On Day 4 of both periods, the difference between BA and DO treatments was not statistically significant.
During this research, certain factors may have affected the outcome of the experiment. Minor changes in timing when I was sampling or operating the gas chromatograph may have occurred during experimentation. Also, environmental factors such as ambient temperature, precipitation and pressure fluctuations could have affected the results. Since the effect of coprophagous beetles on methane emissions from cattle dung has not been previously quantified, the results could not be compared to other studies; more studies need to be done in this area. This study provides a baseline for comparison. Future experimentation could be done in a laboratory setting in which environmental factors were controlled. Also, adding multiple species of beetles to a dung pat and beginning gas sampling on the third day and continuing for a greater length could benefit this research. In the future, I would like to investigate how coprophagous beetles affect other greenhouse gas emission rates, such as nitrous oxide and carbon dioxide.
Coprophagous beetles provide many benefits for the pasture ecosystem. Research has shown they have an advantageous effect on plant growth (Borghesio 1999), decrease the fly population (Nichols 2008), assist with bioturbation (Mittal 1993), and cycle nutrients into the soil (Gillard 1967). My quest to investigate how coprophagous beetles impact methane emissions led me from collecting dung in a cattle pasture to identifying beetles at my kitchen counter, and finally, running samples through a gas chromatograph in a laboratory. Although I did not solve the problem of global warming, I learned that these small beetles that have been the focus of my research have their place in the search for a way to reduce methane emissions from agriculture. As a better understanding is gained of coprophagous beetles’ role in reducing methane emissions from cattle dung, protecting these beetles’ biodiversity and abundance becomes even more imperative.
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I would like to extend my appreciation to Dr. Kevin Floate of the Lethbridge Research Centre for his invaluable assistance with the aspects of my research concerning coprophagous beetles. I thank my parents, who provided aid with transportation, paper edits and encouragement. Additionally, I thank my mother, who ran the gas chromatograph for a few hours each night during sample running so that I could sleep. I am grateful to Dr. Wendy Powers of Michigan State University for allowing me to access the gas chromatograph. I also appreciate Marilia Chiavegato, a Ph.D. student at Michigan State University, for her advice about setting up a methane experiment and the equation to calculate methane fluxes. Gary Parsons, the curator of the A.J. Arthropod Collection at MSU, helped with identification of the key species I had collected. Access to the Lake City Research Center was given by Doug Carmichael, the station manager. Assistant professor of statistics Holly Schalk, at Ferris State University, helped me to run a statistical analysis on the data collected from the greenhouse-gas methane experiment.
Table1.Species of coprophagous beetles recovered from dung-baited pitfall traps at the LakeCity Research
Center in Michigan from May through October 2011.
This winning entry in the museum's Young Naturalist Awards 2012 is from a Michigan tenth grader. Rachel investigated whether dung-feeding beetles could lower methane production in the pasture. Her essay discusses:
Supplement a study of ecology with an activity drawn from this winning student essay.