Event Title

Invertebrate-driven nutrient recycling in four large rivers

Location

Eccles Conference Center

Event Website

http://water.usu.edu

Start Date

1-4-2014 4:00 PM

End Date

1-4-2014 4:20 PM

Description

The cycling of nutrients is a fundamental ecosystem process in lotic ecosystems, and ecologists are increasingly recognizing the importance of animal communities and consumer-driven nutrient recycling (CNR) to fluvial nutrient dynamics. Despite growing evidence that animal excretion can supply limiting nutrients to primary producers in small streams, the importance of excretion is uncertain in large rivers. Accordingly, I estimated areal macroinvertebrate ammonium (NH4-N) and phosphorus (PO4-P) excretion rates and compared these fluxes to areal ecosystem nutrient demand and background nutrient flux in four large rivers (Q > 10 m3 s-1) in North America. I used three estimation approaches using empirical and literature excretion rates to quantify excreted N and P pools from dominant macroinvertebrate families, and compared these pools to nutrient uptake rates measured using nutrient spiraling methods, as well as the flux of ambient N and P pools. Additionally, I compared the stoichiometric (N:P) ratio of excreted nutrients to water column nutrient limitation to understand whether or not excretion by macroinvertebrates could influence nutrient status of phytoplankton. Across all three estimation approaches, macroinvertebrate assemblage N excretion rates ranged from 18.9 to 1070.1 µg N m-2 hr-1, while assemblage P excretion ranged from 16.3 to 378.7 µg P m-2 hr-1. Across all rivers and estimation approaches, assemblage N and P excretion matched 0.7 to 32.4% and 0.1 to 6.0% of N and P uptake, respectively, and excreted N flux was equivalent to 0.5 to 62.3% of ambient N flux. Excretion N:P ratios did not match pelagic nutrient-limitation, which suggests that excretion does not significantly influence water column nutrient dynamics in rivers. Compared to smaller stream ecosystems, in which animal excretion can not only supply >50% of ecosystem N demand, but also match > 100% of ambient N flux, macroinvertebrate excretion appears to contribute less to ecosystem nutrient dynamics in large rivers, although CNR may contribute significantly in rivers with high animal biomass and low ambient nutrient concentrations.

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Apr 1st, 4:00 PM Apr 1st, 4:20 PM

Invertebrate-driven nutrient recycling in four large rivers

Eccles Conference Center

The cycling of nutrients is a fundamental ecosystem process in lotic ecosystems, and ecologists are increasingly recognizing the importance of animal communities and consumer-driven nutrient recycling (CNR) to fluvial nutrient dynamics. Despite growing evidence that animal excretion can supply limiting nutrients to primary producers in small streams, the importance of excretion is uncertain in large rivers. Accordingly, I estimated areal macroinvertebrate ammonium (NH4-N) and phosphorus (PO4-P) excretion rates and compared these fluxes to areal ecosystem nutrient demand and background nutrient flux in four large rivers (Q > 10 m3 s-1) in North America. I used three estimation approaches using empirical and literature excretion rates to quantify excreted N and P pools from dominant macroinvertebrate families, and compared these pools to nutrient uptake rates measured using nutrient spiraling methods, as well as the flux of ambient N and P pools. Additionally, I compared the stoichiometric (N:P) ratio of excreted nutrients to water column nutrient limitation to understand whether or not excretion by macroinvertebrates could influence nutrient status of phytoplankton. Across all three estimation approaches, macroinvertebrate assemblage N excretion rates ranged from 18.9 to 1070.1 µg N m-2 hr-1, while assemblage P excretion ranged from 16.3 to 378.7 µg P m-2 hr-1. Across all rivers and estimation approaches, assemblage N and P excretion matched 0.7 to 32.4% and 0.1 to 6.0% of N and P uptake, respectively, and excreted N flux was equivalent to 0.5 to 62.3% of ambient N flux. Excretion N:P ratios did not match pelagic nutrient-limitation, which suggests that excretion does not significantly influence water column nutrient dynamics in rivers. Compared to smaller stream ecosystems, in which animal excretion can not only supply >50% of ecosystem N demand, but also match > 100% of ambient N flux, macroinvertebrate excretion appears to contribute less to ecosystem nutrient dynamics in large rivers, although CNR may contribute significantly in rivers with high animal biomass and low ambient nutrient concentrations.

http://digitalcommons.usu.edu/runoff/2014/2014Abstracts/8