Field Logs

Our group expected and prepared for 11 wet cold days on the river since the second peak of the hydrograph in the Kobuk River basin comes in August due to summer precipitation events. The basin gets an average of 21 inches (53 cm) per year; yet, as it turned out, our group saw very little of that.

The vegetative communities adjacent to the Kobuk River are comprised of alpine tundra; successional willow/cottonwood forest and climax spruce boreal forest on well-drained soils; and lowland tundra on poorly-drained soils. Soil drainage is determined by slope, soil type, bedrock type and the presence of permafrost.

The spring ice break-up is an important geomorphic driver on many northern rivers, especially on those streams where the break-up is “pre-mature” and capable of generating rapid increases in stage and velocities. (Scrimgeour et. al, 1994) Recent literature identifies several observable features that provide evidence for ice jam flooding, including scars on trees, boulder pavements, ice push marks on channel banks (Burge and Lapointe, 2005), undercut banks, ice-push ridges, island buttresses, and drumlins (Scrimgeour et. al, 1994).

Few folks get to experience the vastness of the Alaskan wilderness. Call it the outback, the bush, or what you will, the wilderness setting of Gates of the Arctic National Park and Preserve is rarely rivaled. Our 11 day wilderness float provided a unique opportunity to put geographic context, and spatial scale, into our collective perspective.

Akpelik Creek demonstrates the significant influence tributaries have on the structure of the Kobuk River and their ability to add complexity and unique habitat to the main channel. Akpelik Creek also contrasts the Kobuk with its presence of large woody debris that plays a role in the structure of its channel compared to the very local influence large woody debris seems to have in the main channel of the Kobuk River.

Excerpts from my field journal:
“The biologists/anglers are still catching grayling mostly, but talk of Sheefish and the hope of a big catch is on the rise…” -August 13, 2008

“I just caught the biggest Sheefish we’ve brought in yet- 29 ½ lbs!

The most recent literature concerning the aquatic benthic macroinvertebrate community of the Kobuk River suggests that the general abundance and diversity of insects are low, due largely impart to extremely harsh and long winters and the subsequent short growing season. Recent data collection on the mainstem of the Kobuk River appears to support this notion; however, side channel and tributary productivity and diversity greatly exceed that of the mainstem Kobuk.

The waters of the Kobuk are often called “gin-clear”, because of the visibility that allows one to see straight to the bottom. This is due to the lack of glaciation at the headwaters. Glaciers grind up rock and sediment and deposit into rivers as fine, powdery sediment, often called “glacial milk”. The low precipitation of the Kobuk watershed has prevented glacier formation; snow melts more or less completely by July. The lack of turbidity in the water allows light to penetrate deeply, and we discovered mats of algae (diatomaceous periphyton, filamentous algae), and patches of aquatic plants and mosses (macrophytic vegetation) everywhere the bottom was protected from scouring during the summer. Other Arctic rivers, which are generally limited by nitrogen or phosphorous, or both, have been shown to have most of their limited production at the interface between moving water and substrate (the epilithos), which allows for a concentration of nutrients at that surface. This appears to be true of the Kobuk, but we were surprised at the consistent quantity of plant growth.

The Kobuk River is surrounded by a shallow active soil horizon with little vegetation that is underlain by permafrost. Because there is limited opportunity for flows to interact with soils and associated solutes, flows from adjacent tributaries, floodplains and seepage are dominated by surface runoff and are “clean” relative to permafrost free systems with deeper active soil horizons. Permafrost effectively traps organic material at various stages of decay and has the potential to be a huge source of sediment and nutrients should it melt under climate warming.

The Kobuk River is influenced by flow contributions from numerous tributaries, lakes and local groundwater and while some of these flows contain high concentrations of nutrients, tannins, and acidity, relatively clean tributaries represent the largest flows and dominate the water quality. At present, these dominant tributaries effectively dilute incoming nutrients, tannins, and other important constituents that contribute to declining water quality.