PARENT SESSION
Wednesday, August 9, 1:30-5:00 pm
COS 64 - Carbon and nitrogen dynamics
Ballroom E, Ballroom Level, Cook Convention Center
Presiders: J Baron and M Santana

Retention and downhill movement of ¹⁵N in an arctic watershed.

Yano, Yuriko^*,1, Shaver, Gaius¹, Giblin, Anne¹, Rastetter, Edward¹, Nadelhoffer, Knute¹, ¹ Ecosystems Center -- MBL, Woods Hole, MA

ABSTRACT- Arctic ecosystems are strongly N limited, although much N exists in soil and a significant amount of N bypasses plant uptake and is lost to streams in dissolved forms. Thus, the long-term N limitation of arctic ecosystems may be driven largely by chemical unavailability of soil N or temporal imbalance between N supply and demand, resulting in losses of plant-available N to streams. Understanding fundamental processes underlying retention and loss is critical for modeling the N budget of arctic watersheds. To better understand N dynamics in arctic ecosystems, we added ¹⁵NH₄ at four different locations (crest, mid-slope, foot-slope, and riparian) along a hillslope in a small arctic watershed in northern Alaska. Soil, vegetation, soil water, and spring-melt water were collected from ¹⁵N-treated plots as well as immediately below the plots to determine the retention and transport of ¹⁵N. After 1 year of the addition, most (>65%) of the ¹⁵N was recovered in the top live-moss/plant layer. ¹⁵N recovery in the top 20 cm of soil was considerable (>5%), especially at the moss-free crest location (36%). Relative mobility of ¹⁵N, expressed as the ¹⁵N value of total dissolved N in the soil water, was compared across seasons. The mobility of ¹⁵N peaked during the snowmelt event at all hillslope locations, but little to no mobility was observed during other seasons. Highest ¹⁵N mobility occurred during snowmelt, coincident with highest water flux, suggesting that most downhill movement of N occurs only during a narrow window of snowmelt.

Key words: Biogeochemistry, N retention and loss, arctic ecosystems