Based on the feedback from two reviewers and my own assessment, I believe the manuscript is worthy of publication. In particular, addressing the concerns of reviewer one about the error in the end member values is important to assessing the uncertainty in the mixing model. However, I have a few additional requests for clarification and editing in the text:

1) While you note that standard errors have been added, please note what those standard errors are in your response so that I can better evaluate the magnitude of uncertainty (given that it's not included in the current online version of the paper).
2) Introduction, line 21: change "actively" to "active"
3) Introduction, line 25: remove "the"
4) Site Description, line 18-19: Please clarify what you mean when you say the max depth was 14 m, but the lake level was 1045 m when sampled (presumable that's relative to sea level?)
5) I would like to see a few sentences that state what the potential implications are for variability in lake surface sediment sources. Does it affect the interpretation of C sources to the lake? Estimates of biological productivity?