TY - JOUR
T1 - Sustained stoichiometric imbalance and its ecological consequences in a large oligotrophic lake
AU - Elser, James J.
AU - Devlin, Shawn P.
AU - Yu, Jinlei
AU - Baumann, Adam
AU - Church, Matthew J.
AU - Dore, John E.
AU - Hall, Robert O.
AU - Hollar, Melody
AU - Johnson, Tyler
AU - Vick-Majors, Trista
AU - White, Cassidy
N1 - Funding Information:
ACKNOWLEDGMENTS. We thank all of those who contributed to the Flathead Lake long-term monitoring program during the past four decades, including T. Bansak, E. Bilbrey, J. Craft, B. Ellis, J. Nigon, J. Rainieri, J. Stanford, T. Tappenbeck, and many others. M. Trentman provided useful advice on nutrient loading models. D. Whited and B. Bannerman provided information on watershed characteristics. Members of the 2018 and 2019 Field Ecology classes at the FLBS contributed to the bioassay studies. Sampling of Flathead Lake was performed under sampling permits issued by the Confederated Salish and Kootenai Tribe; we are grateful for their partnership. Routine monitoring of Flathead Lake is supported by funds from private philanthropy and from the state of Montana. Early funding for Flathead Lake monitoring came from the McKnight Foundation. Funding for data analysis and manuscript preparation for J.J.E. was provided by the Jessie M. Bierman Professorship, FLBS. We are grateful to R.W. Sterner for early comments on the manuscript. J.Y. was funded by the National Natural Science Foundation of China (41877415) and supported by the Chinese Academy
Funding Information:
of Sciences scholarship for a 1-y visit at the FLBS. Funding from the US National Science Foundation (DEB-1951002 to M.J.C. and S.P.D. and DEB-1950963 to J.E.D.) supported the methane analyses. Members of the FLBS acknowledge that we live and work within the aboriginal territories of the Salish and Kootenai people, whose descendants among the Bitterroot Salish, Upper Pend d’Oreille, and Kootenai tribes continue to act as careful stewards of these watersheds.
Publisher Copyright:
© 2022 National Academy of Sciences. All rights reserved.
PY - 2022/7/26
Y1 - 2022/7/26
N2 - Considerable attention is given to absolute nutrient levels in lakes, rivers, and oceans, but less is paid to their relative concentrations, their nitrogen:phosphorus (N:P) stoichiometry, and the consequences of imbalanced stoichiometry. Here, we report 38 y of nutrient dynamics in Flathead Lake, a large oligotrophic lake in Montana, and its inflows. While nutrient levels were low, the lake had sustained high total N: total P ratios (TN:TP: 60 to 90:1 molar) throughout the observation period. N and P loading to the lake as well as loading N:P ratios varied considerably among years but showed no systematic long-term trend. Surprisingly, TN:TP ratios in river inflows were consistently lower than in the lake, suggesting that forms of P in riverine loading are removed preferentially to N. In-lake processes, such as differential sedimentation of P relative to N or accumulation of fixed N in excess of denitrification, likely also operate to maintain the lake's high TN:TP ratios. Regardless of causes, the lake's stoichiometric imbalance is manifested in P limitation of phytoplankton growth during early and midsummer, resulting in high C:P and N:P ratios in suspended particulate matter that propagate P limitation to zooplankton. Finally, the lake's imbalanced N:P stoichiometry appears to raise the potential for aerobic methane production via metabolism of phosphonate compounds by P-limited microbes. These data highlight the importance of not only absolute N and P levels in aquatic ecosystems, but also their stoichiometric balance, and they call attention to potential management implications of high N:P ratios.
AB - Considerable attention is given to absolute nutrient levels in lakes, rivers, and oceans, but less is paid to their relative concentrations, their nitrogen:phosphorus (N:P) stoichiometry, and the consequences of imbalanced stoichiometry. Here, we report 38 y of nutrient dynamics in Flathead Lake, a large oligotrophic lake in Montana, and its inflows. While nutrient levels were low, the lake had sustained high total N: total P ratios (TN:TP: 60 to 90:1 molar) throughout the observation period. N and P loading to the lake as well as loading N:P ratios varied considerably among years but showed no systematic long-term trend. Surprisingly, TN:TP ratios in river inflows were consistently lower than in the lake, suggesting that forms of P in riverine loading are removed preferentially to N. In-lake processes, such as differential sedimentation of P relative to N or accumulation of fixed N in excess of denitrification, likely also operate to maintain the lake's high TN:TP ratios. Regardless of causes, the lake's stoichiometric imbalance is manifested in P limitation of phytoplankton growth during early and midsummer, resulting in high C:P and N:P ratios in suspended particulate matter that propagate P limitation to zooplankton. Finally, the lake's imbalanced N:P stoichiometry appears to raise the potential for aerobic methane production via metabolism of phosphonate compounds by P-limited microbes. These data highlight the importance of not only absolute N and P levels in aquatic ecosystems, but also their stoichiometric balance, and they call attention to potential management implications of high N:P ratios.
KW - ecosystem
KW - limnology
KW - nitrogen
KW - phosphorus
KW - stoichiometry
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U2 - 10.1073/pnas.2202268119
DO - 10.1073/pnas.2202268119
M3 - Article
C2 - 35858403
AN - SCOPUS:85134508269
SN - 0027-8424
VL - 119
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 30
M1 - e2202268119
ER -