Event Title

Nutrient limitation in Cutler Reservoir: Will Phosphorus Reduction Affect Eutrophication?

Presenter Information

Benjamin Abbott

Location

Eccles Conference Center

Event Website

http://water.usu.edu/

Start Date

4-3-2009 10:00 AM

End Date

4-3-2009 10:20 AM

Description

Cutler Reservoir in Cache Valley Utah is currently the focus of a Utah Department of Environmental Quality Total Maximum Daily Load (TMDL) assessment concerning phosphorus. It isn't, however indisputably established that phosphorus is the nutrient responsible for the eutrophication and resulting low oxygen levels. The identification of the limiting nutrient in Cutler could change management options in the quest to reduce eutrophication. In September 2008 we measured total nitrogen (TN) and total phosphorus (TP) in Cutler and a less impacted reference wetland, Dingle Marsh in the Bear Lake National Wildlife Refuge in Idaho. For Cutler we measured an average TP level of 0.67 mg L-1, TN of 1.72 mg L-1, and a low TN:TP ratio of 3.8. Mean nutrient concentrations in Dingle Marsh were much lower: 0.04 mg L-1 for TP, 0.46 mg L-1 for TN, and 14.5 for the TN:TP ratio. We also conducted a 12-day nutrient addition bioassay to determine nutrient limitation of P and N and shifts in relative algal species abundance using a 2X2 factorial experimental design. Our results indicate that algal growth in Cutler Reservoir was primarily N limited. With both the N and N+P treatments cyanobacteria in the natural culture media were replaced with green algae. Dingle Marsh exhibited co-limitation with relatively low chlorophyll a levels. With the Dingle Marsh inocula, all treatments showed an increase in the relative abundance of cyanobacteria with the most marked augmentation in the control and P treatments. Our results suggest that a reduction of phosphorus would not cause any reduction in eutrophication and oxygen depletion in Cutler Reservoir until reduced to below 0.11 mg L-1, at which level it would become the nutrient limiting algal growth.

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Apr 3rd, 10:00 AM Apr 3rd, 10:20 AM

Nutrient limitation in Cutler Reservoir: Will Phosphorus Reduction Affect Eutrophication?

Eccles Conference Center

Cutler Reservoir in Cache Valley Utah is currently the focus of a Utah Department of Environmental Quality Total Maximum Daily Load (TMDL) assessment concerning phosphorus. It isn't, however indisputably established that phosphorus is the nutrient responsible for the eutrophication and resulting low oxygen levels. The identification of the limiting nutrient in Cutler could change management options in the quest to reduce eutrophication. In September 2008 we measured total nitrogen (TN) and total phosphorus (TP) in Cutler and a less impacted reference wetland, Dingle Marsh in the Bear Lake National Wildlife Refuge in Idaho. For Cutler we measured an average TP level of 0.67 mg L-1, TN of 1.72 mg L-1, and a low TN:TP ratio of 3.8. Mean nutrient concentrations in Dingle Marsh were much lower: 0.04 mg L-1 for TP, 0.46 mg L-1 for TN, and 14.5 for the TN:TP ratio. We also conducted a 12-day nutrient addition bioassay to determine nutrient limitation of P and N and shifts in relative algal species abundance using a 2X2 factorial experimental design. Our results indicate that algal growth in Cutler Reservoir was primarily N limited. With both the N and N+P treatments cyanobacteria in the natural culture media were replaced with green algae. Dingle Marsh exhibited co-limitation with relatively low chlorophyll a levels. With the Dingle Marsh inocula, all treatments showed an increase in the relative abundance of cyanobacteria with the most marked augmentation in the control and P treatments. Our results suggest that a reduction of phosphorus would not cause any reduction in eutrophication and oxygen depletion in Cutler Reservoir until reduced to below 0.11 mg L-1, at which level it would become the nutrient limiting algal growth.

https://digitalcommons.usu.edu/runoff/2009/AllAbstracts/39