The cycling of nutrients is a fundamental process in streams and rivers, and scientists are increasingly recognizing the importance of animal communities to nutrient dynamics in these ecosystems. Despite growing evidence that animal excretion (i.e. urine) can supply limiting nutrients to primary producers in small streams, the importance of excretion is uncertain in large rivers. Accordingly, I used three estimation approaches based on past and new excretion rate data to determine nitrogen (N) and phosphorus (P) excretion inputs from insect communities in four large rivers (discharge > 10 cubic meters per second) in North America, and I compared these rates to both the total demand for nutrients by primary producers and background nutrient levels. Additionally, I compared the ratio of excreted nutrients (N:P) to water nutrient limitation (N-limitation or P-limitation) to understand whether excretion by insects could serve as a potential source of limited nutrients to free-floating primary producers in large river ecosystems. Across all three estimation approaches, total insect community N excretion rates ranged from 18.9 to 1070.1 μg N m-2 hr-1, while community P excretion rates ranged from 16.3 to 378.7 μg P m-2 hr-1. Across all rivers and estimation approaches, community N and P excretion was equal to 0.7 to 32.4% and 0.1 to 6.0% of total N and P demand, respectively. Additionally, excreted N and P was equivalent to 0.5 to 62.3% and 0.2 to 5.5% of background N and P levels, respectively. Excreted N:P ratios suggested that excretion may serve as an important pathway in the alleviation of nutrient limitation for some primary producers in large rivers, although additional research will be required. Compared to smaller stream ecosystems, in which animal excretion can supply >50% of total N demand, and also match > 100% of background N levels, insect excretion appears to play a smaller role in nutrient dynamics of large rivers, although excretion may contribute significantly in rivers with high animal biomass and low background nutrient levels, as for N in the North Platte River in this study.
| Identifer | oai:union.ndltd.org:UTAHS/oai:digitalcommons.usu.edu:etd-4716 |
| Date | 01 May 2014 |
| Creators | Schroer, Matt A. |
| Publisher | DigitalCommons@USU |
| Source Sets | Utah State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | All Graduate Theses and Dissertations |
| Rights | Copyright for this work is held by the author. Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user. For more information contact Andrew Wesolek (andrew.wesolek@usu.edu). |
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