Collectively, reservoirs created by dams are thought to be an important source of greenhouse gases (GHGs) to the atmosphere. So far, efforts to quantify, model, and manage these emissions have been limited by data availability and inconsistencies in methodological approach. Here, we synthesize reservoir CH₄, CO₂, and N₂O emission data with three main objectives: (1) to generate a global estimate of GHG emissions from reservoirs, (2) to identify the best predictors of these emissions, and (3) to consider the effect of methodology on emission estimates. We estimate that GHG emissions from reservoir water surfaces account for 0.8 (0.5–1.2) Pg CO₂ equivalents per year, with the majority of this forcing due to CH₄. We then discuss the potential for several alternative pathways such as dam degassing and downstream emissions to contribute significantly to overall emissions. Although prior studies have linked reservoir GHG emissions to reservoir age and latitude, we find that factors related to reservoir productivity are better predictors of emission.

The present study deals with the ecological impacts of the introduction of two alien species of piscivorous fish in several lakes of the Middle Rio Doce lake district in Minas Gerais, Brazil. It was demonstrated that these effects were not restricted only to the fish community. The introduction of the predatory red piranha Pygocentrus nattereri and the tucunaré Cichla cf. ocellaris caused not only a sharp decrease in the number of native fish species, but also major shifts in other trophic levels. Just after the fish were introduced, most lakes began to show conspicuous changes in phytoplankton species composition, in which Cyanophyceae gradually came to dominate. The zooplankton community lost several species, and in some cases, such as Lake Carioca, all the cladoceran species disappeared. On the other hand, invertebrate predators, represented by the dipteran Chaoboridae, boomed in the lake, with higher densities of exotic species, probably as a result of the "ecological release" by reduction of the original fish fauna. There was a general trend of species loss in different trophic levels. All these changes are apparently associated with decreases in water quality. The present situation in these lakes demands new approaches to the management and conservation of these ecosystems.

De Mello NAST, Brighenti LS, Barbosa FAR, Staehr PA, Bezarra Neto JF. 2017. Spatial variability of methane (CH₄) ebullition in a tropical hypereutrophic reservoir: silted areas as a bubble hot spot. Lake Reserv Manage. 35:105—114. The concentration of methane (CH₄) has doubled in the atmosphere over the last 200 yr, raising the need to understand emissions of this potent greenhouse gas from inland waters. CH₄ ebullition is the dominant pathway in shallow aquatic environments and is difficult to quantify due to its episodic nature and heterogeneous spatial distribution. We investigated the temporal and spatial variability of CH₄ ebullition during 2013 in a shallow hypereutrophic urban reservoir, in Belo Horizonte City, Brazil. The average emission measured during summer was 780 mg CH₄/m²/d, ranging from 1 to 3070 (n = 75). During winter, the average emission was 316 mg CH₄/m²/d, ranging from 4 to 1253 (n = 75). A strong spatial variation (P < 0.001) was observed across the reservoir in both seasons. Several folds higher (39—58% of the total) emissions were recorded at the mouth of the main tributaries, which therefore was considered to be a hot spot ebullition zone. This was expected due to its shallow area (mean depth 1.30 m) with low hydrostatic pressure and 2 to 6 C (winter and summer, respectively) higher sediment temperatures, which is aggravated by the intense siltation process resulting from insufficient management of the sewage water entering the reservoir. In this article we demonstrate the consequence of siltation as an enhancing factor for CH₄ emission from the hot spots ebullition zones.

Despite the increasing understanding about differences in carbon cycling between temperate and tropical freshwater systems, our knowledge on the importance of organic matter (OM) pools on light absorption properties in tropical lakes is very scarce. We performed a factorial mesocosm experiment in a tropical lake (Minas Gerais, Brazil) to evaluate the effects of increased concentrations of allochthonous and autochthonous OM, and differences in light availability on the light absorption characteristics of chromophoric dissolved organic matter (CDOM). Autochthonous OM deriving from phytoplankton ( ∼ Chl a) was stimulated by addition of nutrients, while OM from degradation of terrestrial leaves increased allochthonous OM, and neutral shading was used to manipulate light availability. Effects of the additions and shading on DOC, Chl a, nutrients, total suspended solid concentrations (TSM) and spectral CDOM absorption were monitored every 3 days. CDOM quality was characterized by spectral indices (S_250–450, S_275–295, S_350–450, S_R and SUVA₂₅₄). Effects of carbon sources and shading on the spectral CDOM absorption was investigated through principal component (PCA) and redundancy (RDA) analyses. The two different OM sources affected CDOM quality very differently and shading had minor effects on OM levels, but significant effects on OM quality, especially in combination with nutrient additions. Spectral indices (S_250–450 and S_R) were mostly affected by allochthonous OM addition. The PCA showed that enrichment by allochthonous carbon had a strong effect on the CDOM spectra in the range between 300 and 400 nm, while the increase in autochthonous carbon increased absorption at wavelengths below 350 nm. Our study shows that small inputs of allochthonous OM can have large effects on the spectral light absorption compared to large production of autochthonous OM, with important implications for carbon cycling in tropical lakes.