PARENT SESSION
Oral Session # 35: Biogeochemistry III: Arctic, Alpine, and Tundra Systems.
Presiding: A Hartley
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Meeting Room 203.

Comparative retention of nitrogen in stream-lake linkages during snowmelt.

Nydick, Koren^*,1, Arp, Chris², Baker, Michelle², Hall, Bob³, Wurtsbaugh, Wayne¹, ¹ Aquatic, Watershed, and Earth Resources Dept., Logan, UT, USA² Biology Dept., Logan, UT, USA³ Biology Dept., Laramie, WY, USA

ABSTRACT- Aquatic ecosystems are important landscape features because of their ability to transform and retain inorganic nutrients such as nitrate. In many landscapes, lakes intersect streams, and this hydrologic connectivity may alter watershed capacity for nutrient uptake. As a part of a study to understand effects of stream-lake interactions on catchment biogeochemistry, we performed a two-week release of ¹⁵N–nitrate and bromide during snowmelt to the inflow stream of Bull Trout Lake, Idaho. After two weeks we accounted for 89% of the ¹⁵N. During this period of high discharge and low temperature, the inflow stream benthos and seston took up only 3% of the ¹⁵N. An additional 29% was removed from the inflow by floodplain exchange. This water, but not ¹⁵N, returned to the stream 1-4 weeks later, suggesting substantial nitrate storage in the floodplain. Lake seston, epiphytes, and zooplankton accounted respectively for 24%, 8%, and <1% of added ¹⁵N. Despite sedimentation of an additional 8% to the benthos, ¹⁵N increments in the lake sediment were too dilute to measure. Lake nitrate accounted for 7% of the ¹⁵N, but no ¹⁵N-nitrate left the outflow and only 6% was transported out of the lake as seston. Thus, the lake and flood plain wetland, but not the stream channel, were effective in retaining nitrate during snowmelt.

Key words: nitrogen cycling, N-15 tracer , stream-lake interactions, mountain ecosystems