The analyses of sulfate content, δ³⁴S and δ¹⁸O of dissolved sulfate, and δ¹⁸O of water were carried out in a 14 km² crystalline massif located in the Sudety Mountains (SW Poland) to 1) assess the amount of the sulfate delivered to the surface and groundwater systems by modern atmospheric precipitation, 2) determine the effect of altitude on these parameters, and 3) investigate their seasonal variations. In April and November of 2002, August 2003, and March and September of 2005, samples of water were collected from springs and streams of the massif. During these seasons, sulfate contents and δ¹⁸O(SO₄²⁻) values varied from 5.80 to 18.00 mg/l and from 3.96 to 8.23‰, respectively, showing distinctively higher values ofδ¹⁸O(SO₄²⁻) in wet seasons. The δ³⁴S(SO₄²⁻) values had a relatively narrow range from 4.09 to 5.28‰ and were similar to those reported for organic matter in soil and the canopy throughfall in the Sudety Mountains.

Sulfate content, δ³⁴S(SO₄²⁻), δ¹⁸O(SO₄²⁻), and δ¹⁸O(H₂O) values revealed a remarkable dependence on the altitude. The calculated altitude effects for five season averages of these parameters were − 1.00 mg/l/100 m, − 0.18‰/100 m, − 0.27‰/100 m, and − 0.17‰/100 m, respectively. This dependence on the altitude resulted mainly from the mixing of sulfates of different origins such as anthropogenic sulfate, sulfate produced in the soil within the weathered zone of the massif, and that one from the tree canopy. The oxygen isotope mass balance indicates that, in the study area, about one third of the sulfate delivered to the surface and groundwater by modern precipitation comes from anthropogenic pollution. Further interaction of meteoric water within the weathered rocks causes a continuous decrease of δ¹⁸O(SO₄²⁻) values resulting from biological transformation of the sulfate due to plant vegetation and decomposition of organic matter.