Event Title

Nitrogen Cycling in the Littoral Zone of a Subalpine Oligothophic Lake–Nutrient Processing and Fluxes Quantified using a Mesocosm 15N-nitrate Addition

Presenter Information

R. S. Lockwood

Location

ECC 216

Event Website

http://water.usu.edu/htm/conference/past-spring-runoff-conferences

Start Date

5-4-2007 6:15 PM

End Date

5-4-2007 6:20 PM

Description

Numerous studies suggest the importance of benthic processes in the littoral zones of lakes for nitrogen cycling. This mesocosm experiment used 15N-nitrogen to test and quantify the hypothesis of “nutrient spiraling” – that littoral zone processes convert available inorganic forms of nitrogen (nitrate) into refractile dissolved organic nitrogen (DON) that may be transported down the watershed. The movement and transformation of 15N-nitrate from the water column into the sediments and seston was measured for a week during midsummer in replicate 1.5-m long mesocosms in Bull Trout Lake (Sawtooth Mountains, Idaho, USA). Seston assimilated a small fraction of the tracer while over 70% moved into the benthos. These fluxes are consistent with the amount of biomass in each zone (Chl a: 0.150 ug/cm2 sestonic; 56.4 ug/cm2 benthic). The columns were then flushed and the fluxes of various forms of 15N (NO3, NH4, DON) from the sediments into the pelagic zone and the subsequent uptake by seston was measured for an additional week. The results of this experiment can be incorporated into landscape scale models of watershed nitrogen retention and processing.

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Apr 5th, 6:15 PM Apr 5th, 6:20 PM

Nitrogen Cycling in the Littoral Zone of a Subalpine Oligothophic Lake–Nutrient Processing and Fluxes Quantified using a Mesocosm 15N-nitrate Addition

ECC 216

Numerous studies suggest the importance of benthic processes in the littoral zones of lakes for nitrogen cycling. This mesocosm experiment used 15N-nitrogen to test and quantify the hypothesis of “nutrient spiraling” – that littoral zone processes convert available inorganic forms of nitrogen (nitrate) into refractile dissolved organic nitrogen (DON) that may be transported down the watershed. The movement and transformation of 15N-nitrate from the water column into the sediments and seston was measured for a week during midsummer in replicate 1.5-m long mesocosms in Bull Trout Lake (Sawtooth Mountains, Idaho, USA). Seston assimilated a small fraction of the tracer while over 70% moved into the benthos. These fluxes are consistent with the amount of biomass in each zone (Chl a: 0.150 ug/cm2 sestonic; 56.4 ug/cm2 benthic). The columns were then flushed and the fluxes of various forms of 15N (NO3, NH4, DON) from the sediments into the pelagic zone and the subsequent uptake by seston was measured for an additional week. The results of this experiment can be incorporated into landscape scale models of watershed nitrogen retention and processing.

http://digitalcommons.usu.edu/runoff/2007/AllPosters/10