Environmental factors driving the dominance of the harmful bloom-forming cyanobacteria Microcystis and Aphanocapsa in a tropical water supply reservoir.

Harmful cyanobacterial blooms in reservoirs have become a serious global issue for environmental health. However, dominance among different toxic cyanobacteria genera remains poorly understood, especially in tropical areas. We evaluated the influence of environmental factors, including total phosphorus, dissolved aluminum, water level, and precipitation on the change of the dominant genus from Microcystis to Aphanocapsa, in a hypereutrophic tropical reservoir, using 443 water samples over six years of field monitoring by applying generalized linear models (GLM). The results pointed out the prevalence of longer hydrologic retention time leading to enhanced water stability, and nutrients' accumulation into the hypolimnetic zones of the reservoir may have favored the ecophysiological advantages for the picocyanobacteria Aphanocapsa, which reached densities greater than 1 million/ml. In addition, this article also suggests that physical-chemical remediation methods applied for immobilizing phosphorus in the sediments of the reservoir may be low effective in limiting cyanobacterial growth. These findings are not only meaningful to the understanding of the dynamics of cyanobacterial genera but also to improve the management of eutrophic reservoirs in tropical regions. PRACTITIONER POINTS: We assessed cyanobacterial dominance changes based on 6-year field monitoring. First article addressing the dominance of Aphanocapsa spp. in a tropical reservoir. Species of Aphanocapsa responded better to hydrological changes in the reservoir. The use of remediators was accompanied by an increase in cyanobacteria biomass.

Spatial trends in congenital malformations and stream water chemistry in Southern Brazil.

The incidence of variable congenital malformation (CM) among 399 municipalities in the state of Paraná, southern Brazil, suggests the etiological role of environmental factors. This study examined a) environmental concentrations of chlorine anions (Cl-) associated with organochlorines (OCs) and b) associations between these chemicals and agricultural output with CMs using a geographical information system. In one of the three years during the sampling period (2008, 2009 or 2010) Cl-, dichlorodiphenyltrichloroethane (p,p'-DDT), dichlorodiphenyldichloroethylene (p,p'-DDE), dichlorodiphenyldichloroethane (p,p'-DDD), and endosulfan levels were measured in 465 (465/736, 63%) catchment basins. Agricultural outputs for crops during 2006-2010 were also evaluated (t/km2). Further, CM kernel density for the 399 municipalities in Paraná during 2007-2014 was investigated. Cl- levels increased significantly in one of the three years (2008, 2009 or 2010) in western catchment basins, compared to 1996 (p < 0.0001). The municipalities were divided according to the obtained Cl- levels, where sub-region C2 (central-southern) < 1.8 mg/L ≤ sub-regions C1 (northern-western) and C3 (eastern-southern). We identified 8756 cases of CMs among 1,221,287 newborns (NB) in all sub-regions. C1 had higher DDT-DDE-DDD (p,p'-DDT + p,p'-DDE + p,p'-DDD) concentrations, agricultural output, and CM kernel density. C2 and C3 had minor agricultural outputs (per square kilometer) and CM densities. A 2.96 mg/L increase in Cl- between sub-regions C1 and C2 was co-localized with a 45% increase in CM density (spatial relative risk = 1.45, CI 95%: 1.36-1.55). C1 had the highest log likelihood ratios (p = 0.001) identified via SaTScan clustering analyses. Organochlorines and other toxic chlorinated chemicals may contribute to CMs in humans, and these chemicals are ultimately transformed and release Cl- in rivers. Higher Cl- levels were correlated significantly with higher agricultural productivity, DDT-DDE-DDD levels, and CMs in some parts of the northern and western sub-regions (C1).