Dear Authors,

Your work is a good demonstration of how the isotopic, hydrochemical and hydrological data should be combined to gain insights into the structure and dynamics of groundwater flow, especially that the manuscript addresses also a hot topic in groundwater resources management which are groundwater-surface water interactions. However some aspects of the manuscript require reworking.
Reviewers’ objections to the manuscript, with which I generally agree, run along two lines:
- underutilization of the isotopic and geochemical methods which are used here, except the 14C dating, mostly in a qualitative manner,
- the presented picture of the interactions between the deep, shallow groundwater and surface water is not fully convincing.
Please make sure that your responses to reviewers’ comments are integrated into the revised version of the manuscript. Additionally, I would like to raise the following questions.
1. If the river is gaining than its hydrology and chemical and isotopic signatures should be influenced by the discharging groundwater. Refer to the results presented in the companion paper (Atkinson et al., 2013) which might confirm such influence. Furthermore, can a water budget be set for some river reaches showing fluxes of water coming from deep groundwater, floodplain infiltration, headwaters, etc.? Stable isotopes of water could be helpful here.
2. Grouping the groundwater samples on plots was a good idea. What if the stable isotopic compositions of groundwater averaged for each site were plotted against the MWLs and river water and precipitation signals? In the corrected version of Fig. 4 one can see a trend between sites 1 to 4 towards the more negative values. Is it really there and can this reflect recharge in different climatic conditions? Discuss stable isotopes versus 14C age of groundwater. Finally, the question of the evaporative enrichment is not thoroughly discussed. Could it be hidden in the scatter of data?
Several minor corrections needed:
- change scaling of the vertical axes in figures 3a and 3b to make them correspond to the range of data,
- add information on water sample volumes and handling of samples before analyses,
- add “DIC” subscripts to del13C in Table 1 or explain in the Methods section that carbon isotopic composition is measured for DIC,
- chapter 4.5 should refer to Fig. 5 instead of Fig. 6.

Apparently no information on water sample volumes and handling was added to the Methods section.