Monitoring of groundwater quality changes trend in four plains of Gilan province during a 12-year period

Drought and water shortage in recent years caused rice farmers to use maximum groundwater as a secure source. However, the rice is affected not only by the quantity but also by the quality of water. The purpose of this study was to evaluate trend of quality parameters of groundwater in wet and dry periods in 4 plains including Astaneh, Talesh, Lahijan and Foumanat, which are all located in Gilan province.
In this investigation, data was collected for quality parameters from 15 groundwater of the 4 plains of Gilan province from 2003 to 2014. The data was collected from 15 piezometer wells of Astaneh, 41 piezometer wells in Talesh, 24 piezometer wells in Lahijan and 44 piezometer wells in Foumanat. For each well, two time series of 15 quality parameters in wet and dry periods were created in SPSS software. The trend was evaluated by Mann- Kendall test that is a nonparametric method.
The results showed that in both periods, the trend of most quality parameters was declined, However, the quality decline in wet period was more severe. In both periods, the pH and Na % were increasing. Additionally, in dry period, the increasing trend of SAR and SO4 was observed. Overall, the water quality of wells in Talesh plain for cultivation of rice was better than the other plains.
Consumption of groundwater of all the plains in both wet and dry periods for agricultural purposes and especially rice cultivation was without limitation. According to the decreased concentration of the measured parameters during the studied period, it can be expected that groundwater quality of Gilan province plains has been improved.