Use of sediment elemental and isotopic compositions to record the eutrophication of a polymictic reservoir in central Texas, USA

Christopher T. Filstrup, J. Thad Scott, Joseph D. White, Owen T. Lind

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Paleolimnological studies are rarely performed on reservoirs because of concern that sediments might not accurately chronicle reservoir history. Eutrophication indicators might behave differently in polymictic reservoirs and stratified natural lakes because of system and/or mixing regime differences. Particulate organic carbon (POC), particulate organic nitrogen (PON), and total phosphorus (TP) concentrations, carbon:nitrogen (C:N) and nitrogen:phosphorus (N:P) ratios, and carbon (δ13C) and nitrogen (δ15N) stable isotopes from a sediment core were measured to demonstrate that sufficient information can be derived from sediments to permit a historical reconstruction. The scattered POC data were likely biased by seasonal/annual variability in allochthonous organic matter (OM) loading. The upwardly increasing PON in the sediment core supported historic primary productivity (PP) data, suggesting PON could be a better PP indicator than POC. The upwardly increasing TP documented historic P enrichment. The upwardly decreasing C:N ratio identified an OM source shift from allochthonous to increasingly autochthonous sources with reservoir age. The upwardly increasing N:P ratio implied that N-fixation rates have increased with reservoir age, to compensate for increasing N limitation as the P loading increased. The δ13C decreased as the PP increased with reservoir age producing an atypical relationship compared to stratified natural lakes. The OM source shifts likely biased the δ13C-PP relationship, and might weaken δ13C-inferred PP reconstructions in similar reservoirs. The δ15N increased with reservoir age, likely resulting from dissolved inorganic N (DIN) source changes, rather than nitrate utilization. Watershed urban growth and dairy operation intensification potentially contributed greater loads of isotopically heavy DIN. This study demonstrated that paleolimnology has great potential to assist eutrophication assessment and management efforts in reservoirs.

Original languageEnglish (US)
Pages (from-to)25-39
Number of pages15
JournalLakes and Reservoirs: Research and Management
Volume15
Issue number1
DOIs
StatePublished - Mar 1 2010

Keywords

  • Eutrophication
  • Organic matter
  • Paleolimnology
  • Reservoir
  • Stable isotopes

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