## 5 Discussion  
### Role of the Flora of Buffer Zones in the Bioretention of Environmental Pollutants  
Transitional zones between different types of ecosystems (ecotones) with considerable species diversity and diversity of life forms of plants constitute a perfect biogeochemical barrier for different types of natural and anthropogenic pollutants [15; 23; 27; 29; 30; 31; 59; 60]. In the case of areas with water ecosystems, ecotones are frequently treated as so-called buffer zones that effectively provide physical, chemical and biological protection to water bodies or streams against natural and anthropogenic pollutants from surface and subsurface runoff [31; 61]. Biogenic substances are retained, absorbed, abiotically adsorbed, consumed or biologically transformed by plants and micro-organisms [62]. Plants as bioretention organisms can retain from 10 to 50% of biogas that build their biomass. The rest is physically and chemically bound by other components of a given ecosystem, e.g., through accumulation in the near-surface soil layer [63]. Flora additionally develop an interactive system with soil and the micro-organic edaphon (biofilm) that stimulates many biochemical processes [15; 28; 29; 31; 60]. In the case of shores of water bodies, plant buffer zones additionally stabilise the shoreline, preventing water erosion of the shores. They reduce runoffs and improve the structure of soils [31; 64; 65; 66]. The ability of buffer zones to absorb nutrients also depends on the soil structure, the inclination of the slope and the hydrological and meteorological conditions [67]. The width of the zone is important,  
Figure 9: Mean values with ranges of physical-chemical properties of waters of the pelagial in Lake Piaseczno in the 2015 and 2018 summer seasons. O\({}_{2}\), oxygen concentration (mg O\({}_{2}\)-dm\({}^{-3}\)); temperature (\({}^{\circ}\)C); EC, electrolytic conductivity (uS-cm\({}^{-1}\)); pH, reaction; SD, water transparency (Secchi Disc visibility) (m); TSI SD, Carlson’s Trophic State Index. in accordance with the assumption that with increasing width the effectiveness of bioresorption of nutrients also increases [67; 68]. In the case of the shores of Lake Piaseczno, the mean width of buffer zones related to particular topographic conditions and the recreational infrastructure oscillated at around 10 m. An exceptionally important factor that determines the efficiency of phytogeochemical barriers, however, is their species diversity, which is also related to the diversity of life forms [15; 23; 67]. Buffer zones in lake catchments that constitute a mosaic of trees, shrubs, perennials and grasses show an approximately 6-times higher efficiency in phosphorus bioretention than catchments with a uniform type of vegetation [23]. Depending on species diversity, such zones are capable of bioaccumulation from the catchment area from 1.4 to 344 kg of nitrogen per hectare [26]. An admixture of grasses with an intensive fibrous root system considerably increases the efficiency of biogeochemical barriers, although in the case of the purposeful development of such zones they require moving at the end of the vegetative season [69]. Among grasses, nitrophilic _Phragmites australis_, a common species with low ecological requirements, although indicative of the intensification of eutrophication of ecosystems, substantially contributes to the efficiency of the buffer zones, also capturing considerable amounts of heavy metals, e.g., zinc, or pesticides, e.g., metachlor from the environment [70]. Metachlor is even more effectively assimilated by _Typha latifolia_. Its assimilation from the environment is >88% [71]. A similar higher contribution of plants from the family Fabaceae is determined in phytocoenoses. They are capable of forming dense vegetation patches, are characterised by a long lifecycle, and have the ability to intensively bioassimilate nutrients throughout the vegetative season. They have a fibrous root system that helps to reduce the movement of surface runoff into a lake [61].