C:N:P stoichiometry in Lake Superior: freshwater sea as end member

New and synthesized information about linked carbon (C), nitrogen (N), and phosphorus (P) cycles in Lake Superior indicate the ways that Earth's largest lake by area can be considered extreme, unusual, or an end member among lakes. Lake Superior is characterized by low P concentration but excess nitrate and high TN:TP and NO3-:PO43- ratios. Nitrate levels continue to rise in Lake Superior. Rates of primary productivity are modest, but due to spatial structuring as well as long food chain lengths, only small fractions of that organic carbon are likely usable by top trophic levels. Similarly, due to great depth and consequent efficient C cycling, low organic C concentrations are present at the redox boundary in the lake sediments. In this study, changes in biomass C, N, and P as a function of season and depth are presented for Lake Superior in more detail than previous studies. Linkages between biomass and P were weak at best, which was unexpected given the N: P imbalance in the lake. Both seston C and chlorophyll showed distinct mid-depth maxima, but these relatively large biomass pools were spatially removed from the main stratum involved in primary productivity. Seston P also was most concentrated within the mid-depth biomass maximum. Lake Superior is unusual among lakes in terms of N:P balance, and the limited availability of organic C to promote denitrification is a plausible mechanism to explain this.