Purmalis, O. et al. 2019. COMPOSITION AND QUALITY OF FRESHWATER LAKE SEDIMENTS (BALVU AND PĒRKONU LAKES). ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference. 1, (Jun. 2019), 229–235. DOI:https://doi.org/10.17770/etr2019vol1.4129.