Stable Isotopic Evaluation of Recharge into a Karst Aquifer in a Glaciated Agricultural Region of Northeastern Wisconsin, USA
Round 1
Reviewer 1 Report
Groundwater contamination from septic systems and the application of dairy cattle manure has been a long-standing problem in rural area. To address the issue, it is important to evaluate aquifer recharge processes. Based on the viability of time-series stable isotope data, the authors checked the isotopic response of groundwater to rainfall and snowmelt events. Although the many samples are collected and the sampling wells show reasonable representation in casing depths and depth to bedrock, major flaws still exist which makes the explanation and results are unconvincing. My concerns with the manuscript are included as following:
(1) Precipitation samples are less representative due to rain gauge sites far from the wells, which results in the mismatch of isotopic compositions at event scale. Although the authors inferred the isotopic compositions for some events, uncertainty is significant. I recommend checking the isotopic responses in a larger time scale given that the same annual variation pattern is feasible. Moreover, at the event scale, the isotopic response could be insignificant when the isotopic composition of the events is similar with that of groundwater in pre-event periods. That means not all response can be detected based on isotopic signals. The shortage of the analysis should be mentioned and discussed.
(2) The isotopic results indicate different water sources between A, B and C, D. It is unusual that deeper groundwater present heavier-isotope enriched composition, which is of great scientific interest and need to be explained in detail. Different recharge regimes might be also play an important role. I recommend the authors to compare the annual average of isotopic composition in precipitation with the averages of groundwater from wells. At the same time, make clear the isotopic composition of the Lake. I guess the deep groundwater might be influenced by the lake water, while the shallow groundwater is mainly influenced by local precipitation.
(3) The linear regression relation is only confirmed in precipitation. There is usually no the similar linear regression for groundwater probably due to various mixing of precipitation fuzzing the relation. The relative strong linear isotopic relation for Well A could be the result of weak mixing.
Author Response
Thank you for your careful review. Please see our combined file with responses to all 3 reviewer comments.
Author Response File: 
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Reviewer 2 Report
(1) more quantitative data is suggested to add to the conclusions part.
(2) the data or evidence should be used to evaluate the results from the stable isotopic.
(3) it is suggested to describe the pollution source and how to move into the Karst aquifer, and analyze the influence of soil and karst development on the contaminant transport.
Author Response
Thank you for your careful review. Please see our combined file with responses to all 3 reviewer comments.
Author Response File: Author Response.docx
Reviewer 3 Report
Thanks for this interesting and well written manuscript. I had few suggestions directly in the annotated manuscript.
Comments for author File: 
Comments.pdf
Author Response
Thank you for your careful review. Please see our combined file with responses to all 3 reviewer comments.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Line 416, the second "than", a typographic error?
