Event Title

Nutrient Fluxes from Sediments in Littoral Zone of an Oligotrophic Mountain Lake in Relation to Wind Activity

Presenter Information

Michelle J. Kang

Location

ECC 216

Event Website

https://water.usu.edu/

Start Date

3-31-2008 6:30 PM

End Date

3-31-2008 6:35 PM

Description

Nutrient fluxes from littoral zone sediments have been suggested as an important factor controlling nutrient levels within lakes. We examined this process in Bull Trout Lake, a 30-ha lake in the Sawtooth Mountains of Idaho. The shallow shelf zone of the lake potentially may contribute significantly to the fluxes of nutrients into the water column. We hypothesized that a major cause of dissolved nutrient release would be wind-induced sediment disruption. The relationships between wind velocity, lake and sediment temperatures, and nutrient levels were studied for five days in August 2007 at two littoral stations─one at a depth of 0.4 m, and another at 1 m. At each station, lake water from 5 cm above the sediments was collected every 1.5 hours with an automated ISCO sampler. Unfortunately, no high-wind events occurred during the sampling period. However, moderate winds showed a strong diel pattern with winds increasing from 09:00 hrs and peaking at 3-6 m/s each afternoon, then declining to zero after 20:00 hrs. This wind pattern was reflected in the temperature profiles where winds mixed the littoral zone water to a depth ≥1 m thereby potentially mixing nutrients from the interstitial waters. After sunset, littoral zone water temperatures cooled from 16°C and reached 6°C before winds commenced in mid-morning. Temperature in the interstitial waters of the sediments were more stable, warming to only 11-12°C and decreasing to 9-10°C by midmorning with a 2-hour lag behind water column temperatures. Ammonia concentrations were extremely low (0-1.8 µg/L) and did not correlate with wind events. However, there was a positive correspondence between total dissolved nitrogen from the 0.4 m depth and winds on some days: When wind velocities exceeded 5 m/s, total dissolved nitrogen increased 42-51 %, and reached 129-135 µg/L 2-3 hours after the highest winds. Additional measurements are needed across a wider range of wind velocities to confirm this result.

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Mar 31st, 6:30 PM Mar 31st, 6:35 PM

Nutrient Fluxes from Sediments in Littoral Zone of an Oligotrophic Mountain Lake in Relation to Wind Activity

ECC 216

Nutrient fluxes from littoral zone sediments have been suggested as an important factor controlling nutrient levels within lakes. We examined this process in Bull Trout Lake, a 30-ha lake in the Sawtooth Mountains of Idaho. The shallow shelf zone of the lake potentially may contribute significantly to the fluxes of nutrients into the water column. We hypothesized that a major cause of dissolved nutrient release would be wind-induced sediment disruption. The relationships between wind velocity, lake and sediment temperatures, and nutrient levels were studied for five days in August 2007 at two littoral stations─one at a depth of 0.4 m, and another at 1 m. At each station, lake water from 5 cm above the sediments was collected every 1.5 hours with an automated ISCO sampler. Unfortunately, no high-wind events occurred during the sampling period. However, moderate winds showed a strong diel pattern with winds increasing from 09:00 hrs and peaking at 3-6 m/s each afternoon, then declining to zero after 20:00 hrs. This wind pattern was reflected in the temperature profiles where winds mixed the littoral zone water to a depth ≥1 m thereby potentially mixing nutrients from the interstitial waters. After sunset, littoral zone water temperatures cooled from 16°C and reached 6°C before winds commenced in mid-morning. Temperature in the interstitial waters of the sediments were more stable, warming to only 11-12°C and decreasing to 9-10°C by midmorning with a 2-hour lag behind water column temperatures. Ammonia concentrations were extremely low (0-1.8 µg/L) and did not correlate with wind events. However, there was a positive correspondence between total dissolved nitrogen from the 0.4 m depth and winds on some days: When wind velocities exceeded 5 m/s, total dissolved nitrogen increased 42-51 %, and reached 129-135 µg/L 2-3 hours after the highest winds. Additional measurements are needed across a wider range of wind velocities to confirm this result.

https://digitalcommons.usu.edu/runoff/2008/Posters/11