Periphytic algal biomass in two distinct regions of a tropical coastal lake Biomassa de algas perifíticas em duas regi es distintas de uma lagoa costeira tropical

AIM: This study assessed the phycoperiphyton biomass in two regions submitted to different human impacts on Juara Lake, a coastal ecosystem with multiple uses, to order to test the hypothesis that the sampling sites that receive domestic sewage shows higher biomass values. METHODS: It was installed three experimental structures with artificial substrate (glass slides) in December 2009 in two sampling sites: ED - near the domestic sewage's release; TR - in the area of intensive fish farming (net cages). Samplings were conducted in each experimental structure, after 21, 26 and 31 days for colonization. We evaluated: transparency, electric conductivity, pH, turbidity, total suspended solids, alkalinity, dissolved oxygen, water temperature, total nitrogen, nitrate, nitrite, ammonia nitrogen, total phosphorus, orthophosphate and silicate. The phycoperiphyton was analyzed regarding biomass: biovolume (total and per class); pigments (chlorophyll-a and b and carotenoids) and phaeophytin; dry weight and ash-free dry weight. RESULTS: TR featured higher values of transparency, water temperature and silicate. ED presented greater values of conductivity, turbidity, total suspended solids, alkalinity, total nitrogen, nitrate, ammonia nitrogen, and orthophosphate. No difference was detected between the sites and the succession of days for the dry weight, ash-free dry weight, chlorophyll-b, carotenoids, phaeopigments, and total biovolume. CONCLUSIONS: Nevertheless, the biovolume of Bacillariophyceae and Chlorophyceae were more representative in ED. Only the higher values of chlorophyll confirmed the hypothesis tested. OBJETIVO: A presente pesquisa visou avaliar a biomassa ficoperifítica em duas regi es submetidas a diferentes impactos antrópicos na lagoa Juara, ecossistema costeiro com múltiplos usos, a fim de testar a hipótese de que a regi o próxima ao lan amento de esgoto apresenta maior biomassa. MéTODOS: Três estruturas experimentais contendo substratos artificiais (lamina de vidro) foram implantadas em dez/2009 em duas esta es amostrais: ED - próxima ao lan amento de efluentes domésticos; TR - na área de piscicultura intensiva (tanques-rede). Foram realizadas coletas, em cada estrutura experimental, após 21, 26 e 31 dias de coloniza o. Foram avaliadas: transparência, condutividade elétrica, pH, turbidez, sólidos totais em suspens o, alcalinidade, oxigênio dissolvido, temperatura da água, nitrogênio total, nitrato, nitrito, nitrogênio amoniacal, fósforo total, ortofosfato e silicato. Três estruturas experimentais contendo substratos artificiais (lamina de vidro)