Evaluation of the environmental and economic aspects of the use of common reed from eutrophic lakes for energy purposes

Spatial expansion of reed communities is one of the most frequently identified causes of biodiversity loss in lake ecosystems. Common reed is an expansive species and at high supply of biogens in the environment, it displaces other species from the rush communities. Common reed is a cosmopolitan species. It habitats wetlands, both dry and submerged, as well as periodically submerged. Increasing the area of reed rushes leads to a reduction in breeding area for many species of avifauna, especially in wetland areas. The effect of eutrophication of water reservoirs is the increase in the area occupied by reed rushes. Removing biomass from water reservoirs is one of the methods of their reclamation; it is done by slowing the eutrophication process. The aim of the study was to evaluate the economic and environmental efficiency of the removal and utilization of common reed from selected lakes of Pojezierze Mazurskie (the Masurian Lake District) for energy purposes. Within the framework of the study objective, in 2016 collected were samples of reeds from 15 selected lakes and the production potential of the studied reed rush communities was estimated. In the collected biomass samples, the calorific value and chemical composition were determined. Based on the calorific value, the potential for using biomass for energy purposes was estimated, and based on the chemical composition, the amount of nutrients removed from the aquatic environment was estimated. The results of the study show that the average biomass collected from the surface of 1 m2 of reed rushes was 1.053 kg DM. Depending on the habitat from which the samples were collected, significant differences in biomass yield were found. The biomass energy value ranged from 16.4 to 18.1 MJ · kg−1, while the ash content ranged from 8.12 to 10.13%. Based on the results of the study, it was estimated that removing reed from 1 ha of rush would remove, on average, approx. 136 kg of nitrogen, approx. 18 kg of phosphorus, 28 kg of sulphur and 155 kg of potassium. The average of over 170 GJ of energy can be obtained from the removed reed biomass. Ash formed during the combustion process can be used as a soil improvement material due to its high macroelement content and a relatively low content of heavy metals. The results show that the removal of common reed can be an effective treatment process resulting in decreasing the lake trophy at an increased supply of nutrients in the catchment area.