A bloom of cyanobacteria (Cylindrospermopsis raciborskii) in UHE Carlos Botelho (Lobo/Broa) reservoir: a consequence of global change?

Abstract

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.

A Review on the Study of Cyanotoxins in Paleolimnological Research: Current Knowledge and Future Needs

“…As extensively shown, CYN production is highly strain-dependent but geographically extends throughout the globe, encompassing Australia, New Zealand, Antarctica, Asia, South and North America, and Europe [3,81]. A number of its potential producers, such as R. raciborskii and Chrysosporum ovalisporum, are capable of forming blooms at different locations and under favorable conditions, such as eutrophication and increased water temperature [82,83]. As shown, CYN reveals a wide range of cytotoxic activities in vitro and in vivo [84] and was suggested as a causative factor of human poisoning on Palm Island, Australia in 1978 [17]; and, along with MCs, in fatal cases of patients undergoing treatment in a dialysis center in Caruaru, Brazil in 1996 [85].…”

Long-term changes on the structure of fish assemblages in the Lobo-Broa reservoir, Brazil

“…Limnology reports pointed about the damage on its aquatic biodiversity from biotic and abiotic sources (e.g. Pereira et al, 2008;Tundisi & Matsumura-Tundisi, 2014;Rodrigues-Filho et al, 2015;Tundisi et al, 2015). Rodrigues-Filho et al (2015) reported the multiple land uses influence the water bodies and their quality.…”

Effects of global climate change on chlorophyll-a concentrations in a tropical aquatic system during a cyanobacterial bloom: a microcosm study

“…Due to the diversity of phytoplankton species, there are many optimum temperature ranges for growth (Seip and Reynolds, 1995), thus elevated temperatures may not change the size of the community, but rather species composition (Moss et al, 2003Van de Bund et al, 2004. Other studies, however, have found associations between increased temperature and frequency of cyanobacterial bloom phenomena (Reynolds, 2006;Jeppesen et al, 2009;Tundisi et al, 2015;Mowe et al, 2015b) and increased gross primary production (Yvon-Durocher et al, 2015).…”