EGU2020-16637
https://doi.org/10.5194/egusphere-egu2020-16637
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Sedimentary phosphorus speciation dynamics following artificial eutrophication of Lake 227, Experimental Lakes Area, Ontario, Canada

David O'Connell1,2, Nienke Ansems3,4, Ravi Kukkadapu5, Deb jaisi6, Diane orihel7, Barbara Cade-Menun8, Yongfeng Hu9, Johan Wiklund10, Roland Hall10, Hannah Chessell2, Thilo Brehends4, and Philippe Van Cappellen2
David O'Connell et al.
  • 1Trinity College Dublin, Department of Civil, Structural and Environmental Engineering, College Green, Museum Building, Dublin 2, Ireland.
  • 2University of Waterloo, Water Institute, Ecohydrology Research Group, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada.
  • 3Wageningen University, Soil Geography and Landscape Group, P.O. Box 47, 6700AA Wageningen, The Netherlands.
  • 4Utrecht University, Department of Earth Sciences, Faculty of Geosciences, Budapestlaan 4, 3584 CD Utrecht, The Netherlands
  • 5Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA 99354, United States.
  • 6University of Delaware, Department of Plant and Soil Science, Newark, DE 19716 United States.
  • 7Queen’s University, School of Environmental Studies, Kingston, ON K7L 3N6, Canada.
  • 8Agriculture and Agri-Food Canada, SPARC, Box 1030, Swift Current, SK S9H 3X2 Canada.
  • 9Canadian Light Source, Saskatoon, Saskatchewan S7N 2V3 Canada.
  • 10University of Waterloo, Department of Biology, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada.

Stringent environmental policies in many countries have played an extensive role in reducing external phosphorus (P) loading to lakes from agriculture and urban sources. Nonetheless, such reductions in external P loading to many eutrophic lakes have not resulted in the expected concurrent restitution of water quality. Such a delayed recovery of many lakes is blamed both on internal loading of legacy P from lake sediments (i.e., benthic recycling) and the amplification of such internal P loading processes due to the reduction in external P concentrations. Hence, a detailed process understanding of P cycling at the sediment-water interface (SWI) is critical to understand nutrient loading, water quality and associated effects on lake water quality. Much of the work on sedimentary P cycling has traditionally focused on inorganic processes of soluble phosphate, particularly sorption to metals (Fe, Mn, Al) oxyhydroxides and clays. However, there is increasing recognition that organic forms of P, along with interactions between phosphate and humic substances, also play a decisive role in controlling P fluxes between sediments and the overlying water column.

This study focused on gaining further understanding of the such processes through the collection of sediment cores from the oxygenated epilimnion and the mostly anoxic hypolimnion of Lake 227 of the Experimental Lakes Area (ELA) in Ontario, Canada. Since 1969, this unique experimental lake has been fertilized with phosphorus (P), which triggered a relatively rapid trophic transition from oligotrophic to eutrophic conditions. The cores contain a chronological record of changes in sediment burial rates and sediment P speciation across this trophic transition.

Interpretation of such changes was undertaken by coupling results of chemical extractions with 210Pb sediment dating, 31P NMR, XANES and Mössbauer spectroscopy. The major sedimentary P fraction prior to lake enrichment starting in 1969 was organic P (POrg). Fertilization of the lake in 1969 coincided with significant increases in the accumulation rate of sediment, total organic carbon (TOC) and total P (TP), in addition to a marked relative contribution of NaHCO3 extractable P. The combined proportion of PHum and POrg desposited since artificial fertilization in 1969 account for ≥70% of total P burial in the sediments. The anticipated composition of such PHum fractions was hypothesized to be ternary phosphate (PO4) complexes with humic substances. In support of this, the strong linear correlation between P and iron (Fe) extracted by NaHCO3 implies a close association of the two elements in the humic fraction. Furthermore, XANES and Mössbauer spectra indicate that most Fe in the post-1969 sediments is conserved in the +3 oxidation state, which may be ascribed to the stabilization of reducible Fe by organic matter, partially due to the formation of ternary PO4-Fe(III)-humic complexes. Our findings suggest the artificial eutrophication of Lake 227 resulted in the accelerated accumulation of a large sedimentary reservoir of reactive sediment P that may drive continued internal P loading to the water column following the cessation of artificial fertilization. 

 

How to cite: O'Connell, D., Ansems, N., Kukkadapu, R., jaisi, D., orihel, D., Cade-Menun, B., Hu, Y., Wiklund, J., Hall, R., Chessell, H., Brehends, T., and Van Cappellen, P.: Sedimentary phosphorus speciation dynamics following artificial eutrophication of Lake 227, Experimental Lakes Area, Ontario, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16637, https://doi.org/10.5194/egusphere-egu2020-16637, 2020