The aim of this study was to evaluate millimeter-scale deformations in Tallinn, the capital of Estonia, by using repeated leveling data and the synthetic aperture radar (SAR) images of Sentinel-1 satellite mission. The persistent scattered interferometric SAR (PS-InSAR) analysis of images from ascending and descending orbits from June 2016 to November 2021 resulted the line-of-sight (LOS) displacement velocities in the Tallinn city center. Velocity solutions were estimated for the full period of time, but also for shorter periods to monitor deformation changes in yearly basis. The gridded LOS velocity models were used for the decomposition of east-west and vertical velocities. Additionally, the uncertainty of 2D velocity solutions was estimated by following the propagation of uncertainty. The 3D velocity of permanent GNSS station “MUS2” in Tallinn was used to unify the reference of all PS-InSAR velocity solutions. The results of the latest leveling in Tallinn city center in 2007/2008 and 2019 showed rather small subsidence rates which were in agreement with InSAR long-termsolution. However, the short-termInSAR velocity solutions revealed larger subsidence of city center with a rate about –10 mm/yr in 2016–2017, and the uplift around 5 mm/yr in 2018–2019 with relatively stable periods in 2017–2018 and 2019–2021. The inclusion of groundwater level observation data and the geological mapping information into the analysis revealed possible spatiotemporal correlation between the InSAR results and the groundwater level variations over the deep valleys buried under quaternary sediments.

The aim of the study was to assess the P-PO4 and N-NH4 pollution of water in grasslands located on peat soils and to identify the impact of groundwater level on this pollution formation. The research was conducted in 2000– 2010 on grounds of ITP-PIB in Biebrza village (Poland). Within lowland fen a total of 18 monitoring points of groundwater and watercourses were established in 6 separate test stands. The subject of the research was water collected from drainage ditches/channels and groundwater, which was taken from wells installed in organic-soil layer and wells whose bottom was 15–20 cm below this layer. Water samples were collected several times a year, and in the case of groundwater, its level was also measured. It was found that: 1) due to concentration level of P-PO4 and N-NH4, about 46 and 39% of water samples from organic-soil layer and more than 40 and 37% of water samples from mineral- organic-soil layer respectively, were characterized by poor chemical status; 2) due to the exceeding of the limit values of P-PO4 and N-NH4 concentration, water samples from watercourses in over 30 and 27% respectively were not within 1st and 2nd class of surface water quality; 3) P-PO4 and N-NH4 concentrations in each water type were statistically significant and positively correlated with each other; 4) in organic-soil layer the groundwater level changing every 10 cm was a statistically significant factor differentiating the average P-PO4 concentration in groundwater associated with mineral-organic layer of peat soil and average N-NH4 concentration in each type of water.

The presented studies focus on changes in groundwater levels and chemistry, and the identification of important factors influencing these changes on short- and long-term scales in urban areas. The results may be useful for rational and sustainable groundwater planning and management in cities. The studies concerned three aquifers: (1) the shallow Quaternary aquifer, (2) the deep Quaternary aquifer, and (3) the Oligocene aquifer in the capital city of Warsaw (Poland). The spatial variability of groundwater recharge was determined and its changes in time were characterized. The characteristics of groundwater levels were based on long-term monitoring series. The results indicate that urban development has caused overall reduction in infiltration recharge (from 54 to 51 mm/ year), which is particularly clear in the city suburbs and in its centre, where land development has significantly densified during the last 30 years. Studies of groundwater levels indicate variable long-term trends. However, for the shallowest aquifer, the trends indicate a gradual decrease of the groundwater levels. In the case of the much deeper Oligocene aquifer, groundwater table rise is observed since the 1970s (averagely c. 20 m), which is related with excessive pumping. Based on the studied results, the groundwater chemistry in the subsurface aquifer indicates strong anthropogenic influence, which is reflected in multi-ionic hydrogeochemical types and the occurrence of chemical tracers typical of human activity. The Oligocene aquifer is characterized by a chemical composition indicating the influence of geogenic factors.