The results of preliminary studies on nitrogen, phosphorus, potassium, magnesium and calcium bioaccumulation in the herbaceous plants of mid-forest spring niches are presented in this paper. Studies were conducted in the upper course of the Kamienna Creek, a left bank tributary of the Słupia River located in the area of the Forest Division Leśny Dwór (northern Poland). Groundwater, soil and plant samples were collected from three stands distributed within the headwater bog with Rheic Sapric Histosols covered by age-varied black alder. Based on N, P, K, Ca and Mg contents in the plants, groundwater and soils, bioaccumulation factors of these elements in plants were calculated in relation to groundwater (BF_w) and soil (BF_g). The investigated soils were characterized by strong decomposition of peat mass, acidic pH, high abundance in total nitrogen and low in phosphorus, potassium, magnesium and calcium. The chemical composition of the plants suggests an adequate nutrient supply, especially in the case of potassium, which accumulated in much higher amounts than physiological requirements. The investigated plant species were characterized by varied bioaccumulation factors of the studied elements. The highest bioaccumulation of N and Ca was noticed for Urtica dioica, P for Urtica dioica and Solanum dulcamara, Mg for Caltha palustris and Urtica dioica and K for Geranium robertianum. The shoots of Solanum dulcamara (N, P, K) and Urtica dioica (N, P, K, Ca, Mg) were characterized by a diversity of bioaccumulation factors. Our data confirm strong interactions between water, soil and plants as the main structural and functional components of headwater areas.

Keywords: Bioaccumulation, nutrients, herbaceous plants, headwater areas, Histosols, groundwater.