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Title:Holocene guano influences on eutrophication and lacustrine ecology at Kettle Lake, North Dakota
Author(s):Murray, Nicole
Advisor(s):Conroy, Jessica L
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):guano, nitrogen, paleolimnology
stable isotope geochemistry
Northern Great Plains
paleoclimatology, Kettle Lake
Abstract:The grasslands of the Northern Great Plains host a series of migratory birds along the Central Flyway each year. Migratory bird populations have the ability to significantly alter ecosystems along their transit corridors. Coupling this with the sensitivity of grassland lacustrine ecosystems to moisture variability and ecological change, it will be crucial to understand the response of these systems to both future avian influence and climate variability. Here, I examine the influence of climate-forced avian migration on nitrogen cycling at Kettle Lake, North Dakota throughout the Holocene. I investigate this influence using stable nitrogen isotope values (𝛿15N) from lake sediment organic matter, with particular focus on periods of struvite deposition, a magnesium-ammonium-phosphate mineral formed from guano. I find that 𝛿15N is elevated throughout the Holocene in comparison to other lake sediment records in North America of similar temporal length. In particular, 𝛿15N is highest during periods of struvite deposition and in intervals of drought. Additionally, the negatively correlated 𝛿15N-percent Nitrogen abundance (%N) relationship is strongest during struvite-bearing intervals, indicating a depletion of the nitrogen pool. From this I conclude that guano deposition significantly alters nitrogen cycle processes, which are amplified during this time as evidenced by a drop in %N and increase in 𝛿15N beyond estimated guano values. Continuously elevated 𝛿15N in the late Holocene may indicate a “legacy” of bioavailable N from guano deposition, but further indicators are needed to assess this claim. To ensure that my conclusions are based on environmental changes reflected in d15N, I create a model to understand diagenetic changes in the sediment record. I use this “𝛿15N diagenesis model” to assess the degree of diagenetic change from remineralization in the sediment and then correct the original 𝛿15N record accordingly. Generally, trends in the Kettle Lake 𝛿15N are conserved, with the original record showing enrichment of <1‰ on average and greatest disagreement occurring in the Late Pleistocene to early Holocene. These results are valuable as an analog to human-driven eutrophication of surface waters in the Northern Great Plains and indicate that agriculture expansion and intensive animal feeding operations could significantly alter the nitrogen cycle of nearby surface waters.
Issue Date:2020-05-11
Rights Information:Copyright 2020 Nicole Murray
Date Available in IDEALS:2020-08-26
Date Deposited:2020-05

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