Katherine Lininger and Micah Nelson are investigating how much carbon is stored in floodplains in the central Yukon River basin in interior Alaska. They and their colleagues just got back from spending five weeks in the field on two different river trips.
By Katherine Lininger and Micah Nelson
Understanding the global carbon cycle, or how carbon moves through the land, ocean, and atmosphere and where it is stored, is important for fully understanding climate change and how humans are affecting our climate. One aspect of the carbon cycle that isn’t well understood is how much carbon is stored in river floodplains. There may be more carbon in rivers and floodplains than we previously thought, which is important for determining the movement of carbon between the land, ocean, and atmosphere.
As rivers transport sediment and organic matter, they can deposit those materials in their floodplains, storing carbon. We are quantifying that storage in the boreal (subarctic) zone through our research on floodplains in the Yukon Flats National Wildlife Refuge in interior Alaska, a refuge of over 11-million acres with wetlands, river floodplains, and boreal forests accessible only by boat, plane or helicopter.
We successfully completed floats in inflatable kayaks down two rivers in the refuge, the Dall River and Preacher Creek. Our main goals were to collect sediment samples from different points along the floodplains to quantify how much organic carbon is stored in the floodplains and to look at wood accumulations and logjams in rivers to see what effect that wood is having on the physical character of the rivers and their floodplains.
Our first trip on the Dall River started with an hour and a half float plane flight over the White Mountains and Yukon River and down into the Yukon Flats, where we were dropped off on a lake near the river.
We floated about 60 miles down to the confluence of the Dall River and the Yukon River, stopping along the way to get sediment samples with a soil auger, measure wood accumulations on the floodplain and in the river, and take tree cores to date trees and have some idea of how old the floodplain is. Since trees add one ring each year, we will count the rings in a tree core to get its age, which will give us a minimum age for when that floodplain surface was created.
Fallen trees and dead wood in rivers, also called instream wood, can change the way the water flows and the river looks, providing diverse habitat for aquatic animals and helping enhance the accessibility of floodplain habitats. The logjams we encountered also made for some challenging portages (carrying and dragging our gear) through the floodplain vegetation.
Our Dall River trip ended with some sampling on the Yukon River mainstem and a 28-mile float down the Yukon River to the Dalton Highway bridge, where we were picked up.
On our second trip, we accessed Preacher Creek by four-wheeling on a rustic trail through the White Mountains. When we arrived at Preacher Creek, we packed up our gear and ended up running some small rapids on Preacher Creek for our first few days due to the high water from recent precipitation. During this trip, we had to take care to avoid dead wood and overhanging trees while navigating the meander bends.
We sampled in the same way that we did on the first trip, stopping along the river to get sediment and measure wood accumulations.
We were picked up by a floatplane after portaging our boats, gear, and sediment to a floodplain lake.
In total, we shipped over 500 pounds of sediment to Colorado State University, where we will analyze it to see how much carbon is stored in these floodplains. Despite some difficulties with nearly constant swarms of mosquitos and lots of precipitation (it was the wettest June and second wettest July in recorded history), our sampling and fieldwork were extremely successful, and we are excited to get the results back from our sediment analyses. It was incredible to be in a place without any signs of human habitation, spending a month on our own with only the non-human environment as our companion. We’re looking forward to more fieldwork next summer, when we will continue to investigate carbon storage and instream wood along more rivers in the central Yukon basin.