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Nutrient concentrations, loading, and N:P stoichiometry (1983 - 2020) and impacts in Flathead Lake (Montana, USA)


Elser, James (2022), Nutrient concentrations, loading, and N:P stoichiometry (1983 - 2020) and impacts in Flathead Lake (Montana, USA), Dryad, Dataset,


Considerable attention is given to absolute nutrient levels in lakes, rivers, and oceans but less is paid to their relative concentrations, their N:P stoichiometry, and to the consequences of imbalanced stoichiometry. Here we report 38 years of nutrient dynamics in Flathead Lake, a large oligotrophic lake in Montana (USA), and its inflows. While nutrient levels were low, the lake had sustained high total N : total P ratios (TN:TP: 60-90:1 molar) throughout the observation period. N and P loading to the lake as well as loading N:P ratio 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 mid-summer, 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 call attention to potential management implications of high N:P ratios.


See methods described in published paper.

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National Science Foundation, Award: DEB-1951002

National Science Foundation, Award: DEB-1950963

National Natural Science Foundation of China, Award: 41877415