Event Title

Snowmelt Effects on Nitrate Dynamics Along a Stream Network

Location

Eccles Conference Center

Event Website

http://water.usu.edu/

Start Date

4-3-2009 1:40 PM

End Date

4-3-2009 2:00 PM

Description

Snowmelt provides essential nutrients that are transported from the terrestrial landscape through freshwater ecosystems. Microbial and biogeochemical processes can be altered during this pulse of nutrients. We examined the fate of nitrate in a drainage network in the Sawtooth Mountains, Idaho during snowmelt. We conducted a 10 day long 15N-nitrate injection in a headwater stream network above a lake (-5 km stream length) in the Sawtooth Mountains, ID. We sampled 9 locations longitudinally along the stream network before, during and after the injection. At the beginning of snowmelt, stream discharge was lowest in the headwaters and increased by a factor of 10 at the lake inlet (211 to 2,000 l/ s). At the end of the 10 day experiment, discharge had increased to 500 l/s at the headwaters but decreased to 1,070 l/s at the lake inlet. Ambient nitrate concentrations were very low, ranging from 2-10 ?g/l, at all sites along the watershed, with the highest concentration in the headwaters of the network. Nitrate concentrations decreased over the 10 days to below 5 ?g/l at all sites. Stream solute spiraling parameters were used to quantify nitrate uptake dynamics. Uptake length (Sw) was 2,000 m at the beginning of snowmelt and increased to 2,500 m after 10 days. When correcting uptake for discharge (biological uptake only), uptake velocity (Vf) was almost double at the beginning of snowmelt (0.02 cm/s) compared to after 10 days of snowmelt (0.01 cm/s). Some of the nitrate was transformed to NH4 or N gasses, while much of it was immobilized by benthic organic matter pools. From the organic matter data, we estimate N residence time to be greater than 100 days, much longer than the residence time of snowmelt-derived water.

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Apr 3rd, 1:40 PM Apr 3rd, 2:00 PM

Snowmelt Effects on Nitrate Dynamics Along a Stream Network

Eccles Conference Center

Snowmelt provides essential nutrients that are transported from the terrestrial landscape through freshwater ecosystems. Microbial and biogeochemical processes can be altered during this pulse of nutrients. We examined the fate of nitrate in a drainage network in the Sawtooth Mountains, Idaho during snowmelt. We conducted a 10 day long 15N-nitrate injection in a headwater stream network above a lake (-5 km stream length) in the Sawtooth Mountains, ID. We sampled 9 locations longitudinally along the stream network before, during and after the injection. At the beginning of snowmelt, stream discharge was lowest in the headwaters and increased by a factor of 10 at the lake inlet (211 to 2,000 l/ s). At the end of the 10 day experiment, discharge had increased to 500 l/s at the headwaters but decreased to 1,070 l/s at the lake inlet. Ambient nitrate concentrations were very low, ranging from 2-10 ?g/l, at all sites along the watershed, with the highest concentration in the headwaters of the network. Nitrate concentrations decreased over the 10 days to below 5 ?g/l at all sites. Stream solute spiraling parameters were used to quantify nitrate uptake dynamics. Uptake length (Sw) was 2,000 m at the beginning of snowmelt and increased to 2,500 m after 10 days. When correcting uptake for discharge (biological uptake only), uptake velocity (Vf) was almost double at the beginning of snowmelt (0.02 cm/s) compared to after 10 days of snowmelt (0.01 cm/s). Some of the nitrate was transformed to NH4 or N gasses, while much of it was immobilized by benthic organic matter pools. From the organic matter data, we estimate N residence time to be greater than 100 days, much longer than the residence time of snowmelt-derived water.

https://digitalcommons.usu.edu/runoff/2009/AllAbstracts/31