Ambientes aquáticos da bacia do rio Iguaçu: aspectos físicos, químicos e cianotoxinas

Abstract

Considered the largest hydric complex in Paraná, the basin Iguaçu has strategic importance, especially regarding the characteristics of the river, by its great extension and the highly exploited hydropower, forming five reservoirs that generate more than 6.000 MW energy. In detriment of its strategic significance, the damming of the Iguassu River modifies the hydraulic characteristics, which may cause some environmental damage, as the incidence of cyanobacterial blooms in reservoirs may submit toxic potential. Are few studies that consider the Iguaçu basin as a whole, evaluating the river and reservoirs forming this important hydrographic complex. Guided by this understanding, this study aims to evaluate the relationship between water quality in the Rio Iguaçu basin and the influence on the occurrence and concentration of microcystin-LR in its reservoirs. For this purpose, three collections of sampling were performed in Iguazu River from its source in the Metropolitan Region of Curitiba to its mouth in Foz do Iguaçu. Samples in four of the five major reservoirs Basin reservoirs were also performed: Foz do Areia, Segredo, Salto and Salto Caxias Santiago and evaluated physical and chemical variables, content and source of organic matter in reservoirs and contamination by microcystin-LR cyanotoxin. Furthermore, in the reservoirs was evaluated the possibility of contamination by cyanotoxin microcystin-LR. The results evaluation enabled the observation of the main influences on the Iguaçu River, such as anthropogenic influences in Curitiba Metropolitan Region, seasonality, and the influence of change promoted by the hydraulic reservoirs. In the studied reservoirs, the main variables are related to hydraulic seasonal retention time, nutrients and primary productivity. The microcystin- LR was detected in the reservoirs of Foz do Areia, Segredo and Salto Santiago, the latter with the highest concentration of intracellular toxin in the center of the lake region, with a concentration of 18.62μg per liter filtered and Foz do Areia, 65μg, on a point margin with a high concentration of chlorophyll-a. The statistical analysis allowed to understand the variables as possibly responsible for increasing phytoplankton biomass, however, it was not possible to obtain significant relations which could explain the production of intracellular microcystin. Front of the observed outcomes, this study points to the need of policies to increase environmental control, aiming to improve in wastewater treatment and the ground use and occupation all along the basin, but more urgently in the Alto Iguaçu.