Exploring watershed effects on nutrient concentrations in shallow lakes through stable isotope analysis

Thomas A. Langer, Kyle D. Zimmer, Brian R. Herwig, William O. Hobbs, James B. Cotner

Research output: Contribution to journalArticlepeer-review

Abstract

Biogeochemistry patterns in shallow lakes are influenced by both in-lake factors such as ecosystem state as well as watershed-level factors such as land use, but the relative importance of in-lake versus watershed factors is poorly known. This knowledge gap makes it difficult for lake mangers to prioritize efforts on watershed versus in-lake strategies for stabilizing the clear-water state. We studied 48 shallow lakes in Minnesota, USA to assess the relative influence of lake size, land use in watersheds, and ecosystem state (turbid versus clear) on water column total nitrogen (TN) and total phosphorus (TP), as well as δ15N and δ13C in three species of fish. Our land use categories included natural areas, row crop agriculture, and all agriculture (row crops plus alfalfa). A model selection approach revealed different control mechanisms on the behavior of stable isotopes and nutrients. δ13C ratios in fish were most strongly influenced by lake size, while δ15N ratios were influenced by all agriculture in watersheds. In contrast, water column TN and TP concentrations were influenced by the in-lake factor of ecosystem state, with both nutrients lower in the clear state. We detected no effects of land use on TN or TP concentrations, likely due to strong effects of ecosystem state masking watershed effects. However, the strong relationship between agriculture and δ15N in fish indicated that watersheds did influence nutrient processing in shallow lakes, and that effects are not a legacy from past watershed events. Collectively, these observations indicate that lake managers should minimize agricultural intensity in shallow lake watersheds to facilitate the clear-water state, which will, in turn reduce water-column TN and TP relative to the turbid state.

Original languageEnglish (US)
Article number153742
JournalScience of the Total Environment
Volume823
DOIs
StatePublished - Jun 1 2022

Bibliographical note

Funding Information:
Funding was provided by the National Science Foundation (DEB-0919095; DEB-0919070; DEB-0918753), the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR) (Award M.L. 2010, Chap. 362, Sec. 2, Subd. 5 g), and the University of St Thomas. We thank David Staples and Mark Hanson for discussions that improved this manuscript, and the numerous University of St. Thomas undergraduates that assisted with this work.

Funding Information:
Funding was provided by the National Science Foundation ( DEB-0919095 ; DEB-0919070 ; DEB-0918753 ), the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR) (Award M.L. 2010, Chap. 362, Sec. 2, Subd. 5 g), and the University of St Thomas. We thank David Staples and Mark Hanson for discussions that improved this manuscript, and the numerous University of St. Thomas undergraduates that assisted with this work.

Publisher Copyright:
© 2022 Elsevier B.V.

Keywords

  • Alternative stable states
  • Eutrophication
  • Legacy effects
  • Nutrient loading
  • Stable isotopes

PubMed: MeSH publication types

  • Journal Article

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