Ecology of Reservoirs

The physical and chemical variables of the water, and the composition and structure of the zooplankton communities, in Três Marias and Furnas Reservoirs in Minas Gerais, Brazil, were compared to characterize these environments in relation to their trophic state. Higher values of electrical conductivity and chlorophyll-a, total solids, suspended organic matter and total nitrogen concentrations were recorded in Três Marias Reservoir. Higher water transparency and nitrite and nitrate concentrations were observed in Furnas (P < 0.000). Higher zooplankton densities were always obtained in Três Marias Reservoir and, during the rainy period (P < 0.000), with mean values in the dry and rainy periods of 23 721 and 90 872 org m )3 , respectively, in Três Marias Reservoir and 9022 and 40 434 org m )3 , respectively, in Furnas Reservoir. Copepoda was the dominant group in both reservoirs, mainly the younger stages (nauplii and copepodids). Based on the absolute and relative values, the contribution of rotifers was higher in Três Marias Reservoir than in Furnas Reservoir. Although the Trophic State Index, based on water transparency and chlorophyll-a and total phosphorus concentrations, indicated an oligotrophic state for both reservoirs, the higher densities of the zooplankton community in Três Marias Reservoir, as well as the predominance of cyclopoids and smaller-sized species such as bosminids, characterized this environment as mesotrophic. Larger-sized species such as calanoids, daphniids and sidids in Furnas Reservoir characterized the better water quality of this reservoir.

In order to provide guidelines for the management of fish stocks in artificial reservoirs in the Amazon region, the present study analyzed the composition and structure of the fish communities of four sectors (upstream, lake, reservoir, and downstream) of the area affected by the Coaracy Nunes hydroelectric reservoir on the Araguari River in the Brazilian state of Amapá. Variation in ecological parameters was analyzed in the context of the impacts suffered since the damming of the river approximately 40 years ago. Standardized samples of fish were collected in gillnets during eight campaigns in 2009 and 2010. Abundance and biomass were initially evaluated by Analysis of Variance (ANOVA), and lognormal, log-series, geometric series, and broken stick models were then calculated. The K-dominance and Abundance-Biomass (ABC) curves were also analyzed, together with the size-spectrum of the specimens. The results indicated that the sector downstream from the dam had the highest species richness, and was most consistent with the broken stick model. The ABC and K-dominance analyses also confirmed that this sector was the most balanced , in ecological terms. The lake sector had the only community that fitted the geometric series model, and all the analyses indicated a predominance of small individuals , typical of impacted communities. The analyses of the reservoir sector indicated a disturbed environment , whereas the upstream sector was characterized by a more balanced community, reflecting its greater resilience to the impacts caused by the reservoir, and its potential of this area for the conservation of local fish communities. The results also confirmed the applicability of the analytical tools employed for the study of fish communities in reservoir environments.

The physical and chemical variables of the water, and the composition and structure of the zooplankton communities, in Tres  Marias  and  Furnas  Reservoirs  in  Minas  Gerais,  Brazil,  were  compared  to  characterize  these  environments  in  relation to their trophic state. Higher values of electrical conductivity and chlorophyll-a, total solids, suspended organic matter and total nitrogen concentrations were recorded in Tres Marias Reservoir. Higher water transparency and nitrite and nitrate  concentrations  were  observed  in  Furnas  (P< 0.000).  Higher  zooplankton  densities  were  always  obtained  in  Tres Marias  Reservoir  and,  during  the  rainy  period  (P< 0.000),  with  mean  values  in  the  dry  and  rainy  periods  of  23 721  and 90 872 org/ m3,  respectively,  in  Tres  Marias  Reservoir  and  9022  and  40 434 org/ m3,  respectively,  in  Furnas  Reservoir. Copepoda was the dominant group in both reservoirs, mainly the younger stages (nauplii and copepodids). Based on the absolute  and  relative  values,  the  contribution  of  rotifers  was  higher  in  Tres  Marias  Reservoir  than  in  Furnas  Reservoir. Although  the  Trophic  State  Index,  based  on  water  transparency  and  chlorophyll-a and  total  phosphorus  concentrations, indicated  an  oligotrophic  state  for  both  reservoirs,  the  higher  densities  of  the  zooplankton  community  in  Tres  Marias Reservoir,  as  well  as  the  predominance  of  cyclopoids  and  smaller-sized  species  such  as  bosminids,  characterized  this environment as mesotrophic. Larger-sized species such as calanoids, daphniids and sidids in Furnas Reservoir characterized the better water quality of this reservoir.

Aquaculture production in artificial lakes is possible with a proper management of the lake ecosystem. Introduction of fish fingerlings are now a widespread approach in reservoir planning. Dorudzan reservoir is a main source of drinking water for the capital city of Shiraz, which is used for production of several species of cyprinid fishes by the fisheries department. Additionally, few species of native riverine fish are now established in the lake. Every species is supposed to have preferences in selecting different parts of the lake. To investigate possibility of this preference, fishes were sampled twice in winter 2010 and autumn 2011 in three sections of the reservoir, riverine, transitional, and lacustrine. Mesh sizes of 37, 57, and 120 mm were used for sampling. Total number of individuals in each station for all species was counted and their biometry (maximum standard length, fork length, maximum total length, and weight) were measured. Fish populations included Alburnus mossulensis, Capoeta aculeate, Capoeta damascina, Carasobarbus luteus, Carassius gibelio, Cyprinus carpio, and Hypophthalmichthys molitrix. Major parts of the lake showed different compositions of fish assemblages. All 7 species were observed in lacustrine, while 3 species Capoeta aculeate, apoeta damascina, and Cyprinus carpio were present at the transitional section. Riverine section hosted Alburnus mossulensis, Capoeta aculeate and Cyprinus carpio. This habitat preference can help a better utilization of the lake in aquaculture.

The physical and chemical variables of the water, and the composition and structure of the zooplankton communities, in Três Marias and Furnas Reservoirs in Minas Gerais, Brazil, were compared to characterize these environments in relation to their trophic state. Higher values of electrical conductivity and chlorophyll-a, total solids, suspended organic matter and total nitrogen concentrations were recorded in Três Marias Reservoir. Higher water transparency and nitrite and nitrate concentrations were observed in Furnas (P < 0.000). Higher zooplankton densities were always obtained in Três Marias Reservoir and, during the rainy period (P < 0.000), with mean values in the dry and rainy periods of 23 721 and 90 872 org m )3 , respectively, in Três Marias Reservoir and 9022 and 40 434 org m )3 , respectively, in Furnas Reservoir. Copepoda was the dominant group in both reservoirs, mainly the younger stages (nauplii and copepodids). Based on the absolute and relative values, the contribution of rotifers was higher in Três Marias Reservoir than in Furnas Reservoir. Although the Trophic State Index, based on water transparency and chlorophyll-a and total phosphorus concentrations, indicated an oligotrophic state for both reservoirs, the higher densities of the zooplankton community in Três Marias Reservoir, as well as the predominance of cyclopoids and smaller-sized species such as bosminids, characterized this environment as mesotrophic. Larger-sized species such as calanoids, daphniids and sidids in Furnas Reservoir characterized the better water quality of this reservoir.