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The UHE Carlos Botelho (Lobo/Broa reservoir) was selected in 1971 for a program of ecological research, and in the last 44 years continuous sampling and studies, characterized very well this artificial ecosystem and its watershed (Tundisi and Matsumura Tundisi, 2013). The mechanisms of functioning of the reservoir were well known and the maintenance of good water quality (low conductivity -average (10-20uSxcm -1 ; periodic turbulence with re-oxygenation of the whole water column, and high saturation of oxygen (80-100%); low retention time (< 20 days) and a extensive macrophyte grow in the headwaters that prevent high nutrient load. This is the picture for the last 44 years. The phytoplankton composition was consistent with the oligomesotrophic characteristic of the reservoir: predominance of diatoms and chlorophyceae with a maximum of 10µg/l chlorophyll. However in the winter of (july) 2014 the following changes were observed: a heavy bloom of cyanobacteria occurred for the first time in the reservoir. This cyanobacteria Cylindrospermopsis raciborskii, is a invasive species. Very high chlorophyll levels (up to 100µg/l) were measured and high concentration and input of phosphorus was also detected (Tundisi and Matsumura-Tundisi, 2014).The explanation for this sudden appearance of blooms, can be attributed to the following factors: increase of up to 2°C above the average water temperature during the winter; lower rainfall during summer (30% less of the yearly average of 1.500 mm). Increase in the retention time (from <20 days up to 60 days) in order to maintain volumes for hydroelectricity production.This cyanobacteria bloom can be attributed to changes in the regional climate and the hydrological regime, with consequences for the dam operation.As described by Paerl and Huisman (2008), global warming affects patterns of precipitation and drought. The changes in the hydrological cycle enhanced cyanobacterial dominance. Heavy rains after extensive drought periods, increase nutrient input promoting phytoplankton growth. During periods of drought ,residence time, increase, thus promoting blooms.As a further consequence of this process,extensive periods of drought prevent silica discharge into the reservoir reducing diatom growth; the Lobo/Broa reservoir had a predominance of Aulacoseira italica during many years due to silica concentrations of up to 5mg/l. This effect of silica reduction was described by Schindler (2006) in his review of eutrophication.As a result, today, Lobo/Broa reservoir is eutrophic. To our understanding this is a clear evidence of an effect of global changes at a local and regional freshwater ecosystem. Impacts of the cyanobacteria blooms were immediate mainly on recreation, sport fisheries ,aquatic sport activities due to the danger of toxicity. Also fish mortality was detected during periods of intense blooms.

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Friction spot welding (FSpW)

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The feasibility of dissimilar friction stir welding between Ti-6Al-4V alloy and AISI 304 austenitic stainless steels was investigated. Sound joints were achieved when placing titanium as the upper workpiece of the lap configuration. Joints were successfully produced by employing a welding speed of 1 mm/s and rotational speeds of 300 and 500 rpm. A lamellar microstructure was formed in the stir zone of Ti-6Al-4V, where grain size was found to increase with increasing rotational speed, and austenitic equiaxed grains were obtained near the interface of 304 stainless steels coupon. SEM-EDS analysis of the interface revealed a thin intermixed region and suggested intermetallic compound formation. Microhardness data in the titanium weld zone for both rotational speeds exhibited slightly lower values than the base material, with the lowest values in the heat affected zone, whereas the microhardness values in the stainless steel side around the weld center were found to be higher than those obtained for the base material.