“The effects of climate change are are really complex,” and “There are a number of changes that are happening together that are going to ultimately affect how ecosystems operate,” Kathy Kelsey, postdoctoral researcher at the University of Alaska Anchorage, told Frontier Scientists.
Kelsey and colleagues are studying changes in the Yukon-Kuskokwim Delta (YKD) of western Alaska, an important place for migratory birds like Pacific black brant geese.
As this goose species grazes on its favorite local plant, a sedge named Carex subspathacea, the species’ behavior and the response of local plant life change local carbon cycling and impact greenhouse gasses. Kelsey stated the research happening in the YKD will help the scientists “Determine overall carbon cycling and changes to the global carbon climate system.”
Cycling greenhouse gasses
Greenhouse gasses like carbon dioxide and methane trap heat in the atmosphere. Human activities like burning fossil fuels, cutting down and burning forests, raising large groups of livestock, manufacturing cement, and producing and transporting oil, coal, and natural gas, manufactured unusually high levels of greenhouse gasses which contribute to global warming.
Those human sources are by far the main driver of excess greenhouse gasses impacting our planet. By talking about geese and greenhouse gasses below, I don’t want to imply the geese are somehow in the wrong. But it’s important to note that greenhouse gasses also cycle due to natural processes, like plants growing, dying and decaying. And those plants are affected by geese. Gaining data about how geese impact greenhouse gasses in the YKD, again, lets scientists “Determine overall carbon cycling and changes to the global carbon climate system,” – Kelsey.
Carbon (C)
Carbon is an essential part of life, and the C of carbon (C) can be spotted in the chemical formulas of carbon dioxide (CO2) and methane (CH4).
During photosynthesis, carbon dioxide helps plants feed themselves and grow. The Carex subspathacea sedge species, like all plants, “Is using energy from sunlight to help it take carbon from the air and incorporate it into its biomass,“ Kelsey explained, “—It is accumulating biomass through photosynthesis.” Plants remove carbon dioxide, an important greenhouse gas, from the atmosphere. The EPA records “Carbon dioxide is removed from the atmosphere (or “sequestered”) when it is absorbed by plants as part of the biological carbon cycle.” (Overview of Greenhouse Gases https://www.epa.gov/ghgemissions/overview-greenhouse-gases).
In plant life, carbon dioxide fluxes are guided by vegetation size, Kelsey said. Larger and more robust plant life has the potential to acquire and store more carbon than smaller plant life. “Anywhere we have taller vegetation, we expect to have a lot more carbon dioxide taken up into vegetation by photosynthesis.” That means the short grazing lawns maintained by geese as they eat Carex subspathacea in the YKD have low carbon storage potential because of their small size.
CO2 and geese
Three years ago when the experiment with Pacific black brant geese began, wire fencing was erected around some areas so that no geese could reach the plants growing there. Kelsey pointed out the plots that were “Excluded from grazing for the last three years.” She noted “In that time the vegetation has grown from really small little Carex grazing lawn into this much much taller Carex,” which stores more carbon dioxide than shorter Carex.
Because of timing mismatch, Carex subspathacea in the YKD might have more time to grow big and tall before migratory geese arrive. Kelsey: “We see an earlier green-up of the vegetation but we don’t necessarily know how the change in the arrival of time of geese is going to keep pace. So if the growing season starts earlier and the geese arrive earlier, then the timing won’t change. But if the growing season starts earlier and the geese arrive at the same time, they are essentially arriving late according to the vegetation.”
“If the geese are hatching later relative to green-up then the vegetation has the opportunity to become established and grow larger,” Kelsey said. “That would definitely have an effect on carbon exchange because you would have more vegetation biomass and be able to uptake more carbon dioxide.”
Locally, more grazing means less potential to store carbon dioxide in vegetation mass and thus more carbon dioxide in the atmosphere.
CH4 and geese
“Methane is a lot harder to predict.” Kelsey told Frontier Scientists. “Methane is produced in soils under anoxic conditions, so either below the water table or in anoxic microsites in the soil. And the thing that makes methane flux tricky to predict or even sometimes to measure is that methane is frequently produced deeper within the soil.” Anoxic conditions are low oxygen conditions (anoxic groundwater has a dissolved oxygen concentration of less than .5 milligrams per litre, according to the U.S. Geological Survey (USGS)).
Methane gas might be produced underground below the water table then begin to rise through the soil, but it might be consumed by microorganisms in the higher layers of soil (where more oxygen is present) before it ever reaches the atmosphere. Kelsey stated “What we can measure here is going to be the sum of those two processes. So if there is more production than consumption, we’ll see methane coming out of the soil surface. If there is more consumption than production we’ll actually see more methane consumed in the soils.” Things get even trickier because well-grazed areas are likely to have a higher water table “And that probably is a result of the vegetation being much smaller in the grazing lawn and therefore less water is being transpired to the atmosphere,” Kelsey said. She added “We also anticipate that there is higher quality organic matter in the grazing lawns because they have all the fecal additions from the geese. So that might be contributing as well.” These interactions are just some example of how myriad details make understanding and measuring the biological carbon cycle very complex.
After Kelsey and colleagues measured the methane in their study plots, Kelsey reported “We definitely see that there is higher methane production from the grazing lawn areas than from the surrounding areas.”
Locally, more grazing means more methane released to the atmosphere.
Aiming for the tips
Ryan Choi, PhD student at Utah State University, was camp manager of the scientists’ research camp in the Yukon-Kuskokwim Delta (YKD). “Timing is really crucial to maintain the amount of grazing lawn out on the Delta,” Choi described. He said if the geese “Arrive later in the season it gives the plants a lot more time to grow faster, invest more energy into above ground bio mass. It changes the carbon and nitrogen ratios, making [plant tissue] less nutritious for the birds and rendering it less desirable for the birds to feed upon.”
Kelsey described the Pacific black brant eating: “I’m used to seeing them graze on the short vegetation; they lean their head down to pluck it up from near the soil surface,” Kelsey outlined. What happens when geese have to eat tall plants in the Delta? Kelsey described a flock grazing in an unusual way. These geese foraged “In taller grass where they were trying to get at just the tips of the grass. . . at the same level as their heads or above, so they were reaching around trying to snip off the tops of this grass.” Kelsey described “That was actually really comical.”
While they admitted the sights were comical, the scientists also noted the change means less nutrition for the migratory geese and myriad impacts for the environment. When geese arrive late, vegetation has a chance to grow bigger (grow more biomass). Bigger plants with more structure than their freshly-sprouted forms have more carbon storage capacity but also have different carbon to nitrogen ratios, which changes their nutritional quality for herbivores like geese. . . for ideal nutrition the geese need a short well-maintained lawn, not the tips of tall plants. The time when migratory geese reach the YKD changes the status of the Carex subspathacea grazing lawns.
When grazing is hard to predict, so is the carbon cycle. Kelsey: “If the geese arrive later relative to vegetation growth there are all kinds of different changes to biochemical geocycling that could occur.”
Small pieces of a bigger picture
The carbon storage potential of plants in the YKD versus the potential of a rain forest isn’t grand, Kelsey noted. “In terms of carbon exchange we may see a little more carbon uptake and in the scale of global carbon cycling it is quite small, but the way that it is really important and highly influential is because,” Kelsey stated, “This result highlights the fact that not only is climate change an important force that’s going to be altering future carbon cycles but we have to look at these interactions of other factors that may be specific to a location.”
Kelsey said although “Methane is produced and consumed naturally in ecosystems all over the world,” it is also “A fairly powerful greenhouse gas—it’s about 35 times more powerful than CO2 over a 100 year time horizon. So from that perspective, it is important for us to know what ecosystems are producing in terms of methane, so we can have an idea of how much methane is in the atmosphere if we are to predict what we anticipate for warming in the future.”
Detailed and accurate predictions of Earth’s climate future can help our leaders make informed policy decisions. Push us to combat global warming.
Specific information that the scientists gather will be inputted into a supercomputer-driven model (simulation) to help predict future climate conditions. Choi reported Kelsey is “Incorporating a lot of the ecosystem measurements going on out here into this model.” With remote sensing (remote sensing often means using instruments mounted on satellites to gather data) Choi reported “We can make broad generalizations about what’s going on on the landscape, but unless we have on-the-ground measurements for ground truthing— actual data that is being recorded— those models lack a lot…” However, Choi said when data gathered in the field and remote sensing information comes together “A lot of power can be pulled out of those things in combo.”
Kelsey: “The large scale results that we will plot here [aim] to understand: How do these two forces—climate change and herbivory—interact together to affect carbon cycling in certain landscapes,” and “How those two processes together are influencing global carbon cycling.”
Laura Nielsen 2016
(Climate change geese measuring carbon greenhouses gasses Yukon Delta)
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