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HERO ID
4034559
Reference Type
Journal Article
Title
Critical loads of atmospheric N deposition for phytoplankton nutrient limitation shifts in western U.S. mountain lakes
Author(s)
Williams, JJ; Lynch, JA; Saros, JE; Labou, SG
Year
2017
Is Peer Reviewed?
1
Journal
Ecosphere
EISSN:
2150-8925
Volume
8
Issue
10
Page Numbers
e01955
Language
English
DOI
10.1002/ecs2.1955
Web of Science Id
WOS:000414070800003
Relationship(s)
is supplemented by
4034597
: Supplemental materials
Abstract
In many oligotrophic mountain lakes, anthropogenic atmospheric nitrogen (N) deposition has increased concentrations of N, a key limiting nutrient, and thereby shifted phytoplankton biomass growth from N limitation to P limitation. In the western United States, the critical load N deposition rate for these shifts has not been quantified. We synthesized existing mountain lake chemistry, nutrient limitation bioassay, and N deposition data to estimate N critical loads for shifts from N to P limitation of phytoplankton biomass growth. Data from bioassays in 47 mountain lakes were used to define biological (RR-N/RR-P = 1) and chemical (NO3, DIN, DIN:TP) thresholds above which biomass P limitation is more likely than N limitation. Logistic regression was used to calculate critical loads as the total N deposition rate with >50% probability of exceeding biological or chemical thresholds, and thus where P limitation is more likely than N limitation. Logistic regression models were developed with N deposition as the only predictor and with both N deposition and watershed characteristics as predictors. Logistic model performance was evaluated by comparing predicted and observed chemical threshold exceedances in 108 mountain lakes. Across models, estimated critical loads ranged from 2.8 to 5.2 kg total N·ha−1·yr−1. The best-performing model was a univariate logistic model predicting NO3 threshold exceedance, with N deposition as the only predictor. This model yielded a critical load of 4.1 kg total N·ha−1·yr−1 and accurately predicted NO3 threshold exceedance in 69% of lakes. We applied this critical load to an independent sample of 385 mountain lakes with NO3 data to estimate the frequency it would fail to predict a limitation shift—cases where the NO3 threshold for biomass shifts was exceeded, but the critical load was not. The false-negative rate was 13% across the western United States, but was higher (22%) in the Sierras. Performance analyses suggest a 2.0 kg total N·ha−1·yr−1 critical load may avoid false negatives entirely. Critical loads presented here can be used to assess N deposition impacts on western U.S. mountain lakes, and associated performance information can be used to consider if presented critical loads are adequate for specific management applications.
Keywords
critical load; mountain lakes; nitrogen deposition; phytoplankton
Tags
•
ISA NOxSOxPM Ecology (2018)
Cited in the Second Draft
Chapter 1
Appendix 7
Appendix 9
Appendix 16
16.5 Rocky Mountains
•
ISA NOxSOxPM Ecology (2020- Final Project Page)
Cited
Integrated Synthesis
Appendix 7
Appendix 9
Appendix 16
16.5 Rocky Mountains
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