PARENT SESSION
OOS 2: Anthropogenic Disturbances to Western Alpine Lakes: Past, Present, and Future .
Organized by: JE Saros and CE Williamson
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room E 143.
Nitrogen cycling in stream-lake linkages: An example of a mountain watershed with low atmospheric N deposition.
Nydick, Koren*,1, Wurtsbaugh, Wayne1, Baker, Michelle2, Hall, Robert3, Arp, Chris2, Marcarelli, Amy1, 1 Aquatic, Watershed, and Earth Resources Department, Logan, UT, USA2 Biology Department, Logan, UT, USA3 Zoology Department, Laramie, WY, USA
ABSTRACT- How is nitrate retained, transformed, and transported downstream by stream-lake linkages in mountain watersheds with relatively low nitrate inputs? The answer is important for understanding the effects of elevated N deposition on lakes and streams in impacted regions. We addressed this question with two-week releases of 15N-nitrate to the inflow stream of Bull Trout Lake (Sawtooth Range, Idaho) during both snowmelt and baseflow, when stream nitrate concentrations were near 10 and 4 microg N/L, respectively. The inflow stream took up 30% and 74% of the N15-nitrate addition during the snowmelt and baseflow experiments, respectively. Most of this 15N uptake was via hydrologic loss to the floodplain and not via biological processes. For both additions, the lake took up the remaining 15N-nitrate and none was detected in the outflow. Only about 2-8% of the 15N left the lake as seston (algae, bacteria, and detritus) and very little (<1%) was exported as DON. In the lake, most of the N15 was taken up by seston and retained as sedimented material. Comparison of short-term and long-term 15N sedimentation rates and also loss rates of seston 15N in the water column suggests that about half of the sedimentation was mineralized and recycled back into seston. 15N uptake by benthic algae (epiphytes and epipelon) was less than the pelagic. Microcosm experiments, however, suggest that benthic nitrate uptake could be substantial for shallower lakes. The picture that emerges is a linked aquatic ecosystem which is extremely efficient at taking up, retaining, and recycling nitrate-N through both hydrologic stream processes and biological lake processes.
Key words: lake, hydrology, nitrate, stream