Temporal variability of dissolved P speciation in a eutrophic reservoir--implications for predicating algal growth

Potential distribution of the invasive freshwater dinoflagellate Ceratium furcoides (Levander) Langhans (Dinophyta) in South America

Dinoflagellates of the genus Ceratium are predominantly found in marine environments, with a few species in inland waters. Over the last decades, the freshwater species Ceratium hirundinella and Ceratium furcoides have colonized and invaded several South American basins. The purpose of this study was to create a distribution model for the invasive dinoflagellate C. furcoides in South America in order to further investigate the basins at potential risk, as well as the environmental conditions that influence its expansion. This species is known to develop blooms due to its mobility, resistance to sedimentation, and optimized use of resources. Although nontoxic, blooms of the species cause many problems to both the natural ecosystems and water users. Potential distribution was predicted by using a maximum entropy algorithm (MaxEnt). Model was run with 101 occurrences obtained from the scientific literature, and climatic, hydrological and topographic variables. The developed model had a very good performance for the study area. The most susceptible areas identified were mainly concentrated in the basins between southeastern Brazil and northeastern Argentina. Besides already affected regions, new potentially suitable areas were identified in temperate regions of South America. The information generated here will be useful for authorities responsible for water and watershed management to monitor the spread of this species and address problems related to its establishment in new environments.

First record of Ceratium furcoides (Dinophyta), an invasive species, in a temporary high-altitude lake in the Iron Quadrangle (MG, Southeast Brazil)

Dinoflagellates of the genus Ceratium are generally marine organisms, but rare occurrences in freshwater have been observed in Brazil. In this paper we are recording for the first time the presence of Ceratium furcoides, an invasive species, in a shallow, natural intermittent pool formed at a high-altitude at the southern end of the Iron Quadrangle, an iron-mining district of Minas Gerais State (Southeast Brazil). Samples were collected in October and November of 2010 (rainy period). The population density of this organism observed in Lagoa Seca ("Dry Pool") was very low, at most 4 ind L-1. Mountain lakes are extremely vulnerable to atmospheric deposition of organisms, making them valuable witnesses both of the many forms of impact arising from human activities and of the extended global connections that facilitate the dispersion and introduction of new species over great distances. Studies on the population dynamics of C. furcoides in natural tropical systems are still rare and very recent to the brazilian scenario and hence the monitoring of its dynamics and the potential impact on aquatic communities of its becoming established are essential to an understanding of the process of bioinvasion by this species.

Drivers of water quality in a large water storage reservoir during a period of extreme drawdown

This study examined the drivers of water quality in a large water storage reservoir (Lake Hume) during a period of extreme drawdown (to less than 3% of capacity). During the period of extreme drawdown, the reservoir can be thought of as consisting of three separate but inter-related parcels of water. The warm surface mixed layer was about 6m deep. Cold water inflows from the Mitta Mitta River undershot the surface mixed layer in the Mitta Mitta arm of the reservoir and flowed along the bottom of the reservoir to the Dam Wall without substantial interaction with the surface mixed layer. When inflows from the Murray River occurred, the temperature of these inflows was similar to that of the surface mixed layer within the dam and the flows appeared to move within the surface mixed layer towards the Dam Wall. These Murray River inflows were insufficient to promote total mixing of the surface and bottom waters. The Murray River arm of the reservoir became a 'hot spot' for nutrient production. Stratification and subsequent anoxic conditions promoted the release of nutrients - ammonium, organic N and total P - from the sediments into the overlying hypolimnion. Because the depth of the lake was relatively shallow due to the extreme drawdown, wind driven events lead to a substantial deepening (turnover) of the thermocline allowing periodic pulses of nutrients into the warm surface layer. These nutrient pulses appeared to stimulate cyanobacterial growth. Warm inflows from the Murray River then served to push the blooms formed in the Murray arm into the main body of the lake.