『Abstract
　We have measured the stable nitrogen isotope values (δ¹⁵N) in two sediment cores sampled 15 years apart (1988 and 2003) from the Eastern Basin of Lake Erie and compared them to the total phosphorus (TP) and biogenic silica (BSi) concentrations in the 2003 core. Changes in the TP, BSi and total nitrogen (TN) accumulations in the 2003 core correspond to three stages in the trophic history of the lake that include the onset (〜1910 to 〜1950), peak (〜1950 to 〜1970), and amelioration (〜1970 to 2003) of eutrophication owing to accelerated nutrient loading. Decreasing BSi:TP atomic ratios (BSi:TPat) from 〜1910 to 〜1970 suggest a gradual Si drawdown in the lake during its progressive eutrophication, which led to Si limitation and reduced diatom settling rates. δ¹⁵N values show pronounced variability in 〜1950 to 〜1970, which corresponds with rapid increases in N from runoffs from the lake catchment. A trend of gradually increasing δ¹⁵N values from 〜1910 to 〜1970 is likely the result of denitrification associated with the development of anoxic bottom waters in the Central Basin of the lake. This study illustrates the complexity of extracting environmental information from δ¹⁵N values in sediments and confirms the need for further studies of the multiple processes and their interactions that contribute to lacustrine δ¹⁵N records.

Keywords: Lake Erie; Sediment; Biological silica; Total phosphorus; Stable nitrogen isotopes; Denitrification』

1. Introduction
2. Descriptions of Lake Erie, core sites, and sampling
3. Methods
　3.1. Core chronology
　3.2. Biogenic silica (BSi)
　3.3. Total phosphorus (TP)
　3.4. Carbon and nitrogen analyses
4. Results
5. Discussion
　5.1. Diatom productivity reported by Si
　5.2. N cycle recorded by sediment δ¹⁵N values
　　5.2.1. Significance of external runoffs on δ¹⁵N variations
　　5.2.2. Significance of within-lake N dynamics on δ¹⁵N variations
6. Summary and conclusions
Acknowledgments
References