SGEM SGEM 2019. 19th international multidisciplinary scientific geoconference. Vol. 19. Ecology, economics,education and legislation Issue: 5.4 28.6.-7.7.2019, Albena / rec. Valeriy Bondur, Raimonds Ersteins. -- 1.vyd. -- Sofia SGEM world science 2019. -- 420 s. -- ISBN : 978-619-408-87-4. -- ISSN : 1314-2704. -- 10.5593/sgem2019/5.4. Bondur, Valeriy. Ersteins, Raimonds