**3. Conclusion**

The chapter contributes to an understanding of the seasonal water balance of lakes located in Antarctic oases. The results and hydrological datasets from the technical reports were critically considered on the consistency of the variables measured as well as for uniforming methods and instruments applied during the measurement campaigns of 2011–2018. It was found that the hydrological observations remain more or less similar year by year for the methods and instruments used. However, the sets of the observed variables vary year by year even for a single lake; thus the multi-year datasets do not provide the similar dataset for the water balance components. The harmonisation of the seasonal hydrological programme is greatly needed to collect suitable datasets and to apply a modelling approach in climate-related and practical studies.

To prepare the uniformed programme of hydrological observations, the location of the temporal hydrological network was suggested for Lake Priyadarshini. The technical reports of the Finnish, Indian and Antarctic research programmes and previous publications allow for the recommendation of optimal solutions for the measurements, including locations of the gauges as well as a set of required instruments for the lakes Kitezh, Stepped, Nella, Progress and Reid.

The water balance is connected to the thermal and chemistry balances. The income and outcome terms of the water balance equation allow for evaluation of a lake retention time, which shows a strong correlation with trace metals like Zn, Cd, Co, Mn and Cu, thus playing an active role in lake water chemistry and primary productivity. The theoretical retention time is defined as a result of the division of a lake volume by inflow or outflow. In specific Antarctic conditions, the inflow/outflow on lakes only occurs during the summer. Thus, the retention time can be evaluated for warm and cold seasons separately and could be the topic of a future study.

#### **Acknowledgements**

We are supported by the Academy of Finland (contract number 304345) and Russian, Indian and Finnish Antarctic Research Program. We also acknowledge ESSO-National Centre for Antarctic and Ocean Research for the funding, logistic and analytical support and UGC for providing the research fellowship.
