Event Title

Invertebrate-driven Nutrient Recycling Rrates in a Large River

Presenter Information

Matt Schroer

Location

ECC 216

Event Website

http://water.usu.edu/

Start Date

4-3-2012 5:50 PM

End Date

4-3-2012 5:55 PM

Description

Invertebrate-driven nutrient recycling rates in a large river Matt A. Schroer1, Michelle A. Baker1, Emma J. Rosi-Marshall2, Robert O. Hall3, Jennifer L. Tank4 1Department of Biology, Utah State University, Logan, Utah 2Cary Institute of Ecosystem Studies, Millbrook, New York 3Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 4 Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana Dissolved nutrients from animal excretion can be an important source of limiting elements for primary producers in small streams (Q < 1000 L/s), but little is known about the size and importance of excreted nutrient pools in large river ecosystems. In addition, researchers often assume that excretion rates remain constant throughout the day, but this assumption is untested. Our goal was twofold; first, we evaluated the size of excreted ammonium (NH4+) and phosphate (PO43-) pools from dominant invertebrate taxa, and compared these pools to nutrient uptake rates and phytoplankton nutrient limitation in a 7km reach of the Manistee River, Michigan (Q > 37,000 L/s). Second, we measured diel variation in NH4+ excretion rates from individual stoneflies (Skwala americana). Excretion rates for dominant taxa in the Manistee River ranged from 0.083 to 1.895 µg mgDM-1 hr-1 and from 0.029 to 0.366 µg mgDM-1 hr-1 for NH4+ and PO43-, respectively. At the same time, river-bed nutrient uptake, U, was 120.43 and 13.12 µg m-2 min-1 for NH4+ and PO43-, respectively. Thus invertebrate excretion can potentially account for 10X more P demand than N, which may exacerbate the tendency of river phytoplankton to be more N limited. Averaged diel NH4+ excretion rates in Skwala ranged from 0.287 to 1.477 µg mgDM-1 hr-1. Despite this wide range, most values (6 of 8) fell within a narrow range from 0.403 to 0.519 µgN mgDM-1 hr-1. A large spike in NH4+ excretion rate (1.477 µg mgDM-1 hr-1) occurred at 2:30am, possibly due to Skwala being more active at night. These results suggest that further research is needed to determine whether the assumption of constant excretion rates is valid for stream invertebrates. Our study is the first to consider invertebrate excretion in a large river, and more work is needed to determine the environmental controls on excreted nutrient pools in these ecosystems.

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Apr 3rd, 5:50 PM Apr 3rd, 5:55 PM

Invertebrate-driven Nutrient Recycling Rrates in a Large River

ECC 216

Invertebrate-driven nutrient recycling rates in a large river Matt A. Schroer1, Michelle A. Baker1, Emma J. Rosi-Marshall2, Robert O. Hall3, Jennifer L. Tank4 1Department of Biology, Utah State University, Logan, Utah 2Cary Institute of Ecosystem Studies, Millbrook, New York 3Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 4 Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana Dissolved nutrients from animal excretion can be an important source of limiting elements for primary producers in small streams (Q < 1000 L/s), but little is known about the size and importance of excreted nutrient pools in large river ecosystems. In addition, researchers often assume that excretion rates remain constant throughout the day, but this assumption is untested. Our goal was twofold; first, we evaluated the size of excreted ammonium (NH4+) and phosphate (PO43-) pools from dominant invertebrate taxa, and compared these pools to nutrient uptake rates and phytoplankton nutrient limitation in a 7km reach of the Manistee River, Michigan (Q > 37,000 L/s). Second, we measured diel variation in NH4+ excretion rates from individual stoneflies (Skwala americana). Excretion rates for dominant taxa in the Manistee River ranged from 0.083 to 1.895 µg mgDM-1 hr-1 and from 0.029 to 0.366 µg mgDM-1 hr-1 for NH4+ and PO43-, respectively. At the same time, river-bed nutrient uptake, U, was 120.43 and 13.12 µg m-2 min-1 for NH4+ and PO43-, respectively. Thus invertebrate excretion can potentially account for 10X more P demand than N, which may exacerbate the tendency of river phytoplankton to be more N limited. Averaged diel NH4+ excretion rates in Skwala ranged from 0.287 to 1.477 µg mgDM-1 hr-1. Despite this wide range, most values (6 of 8) fell within a narrow range from 0.403 to 0.519 µgN mgDM-1 hr-1. A large spike in NH4+ excretion rate (1.477 µg mgDM-1 hr-1) occurred at 2:30am, possibly due to Skwala being more active at night. These results suggest that further research is needed to determine whether the assumption of constant excretion rates is valid for stream invertebrates. Our study is the first to consider invertebrate excretion in a large river, and more work is needed to determine the environmental controls on excreted nutrient pools in these ecosystems.

https://digitalcommons.usu.edu/runoff/2012/Posters/2