Black Water Bodies Research Articles

Fish metacommunity dynamics in the patchy heterogeneous habitats of varzea lakes, turbid river channels and transparent clear and black water bodies in the Amazonian Lowlands of Bolivia

The causes of fish community organization in a system of habitat patches with different environmental conditions were described using a data set of 65 sites sampled during the dry season. Incorporating the patchy heterogeneous structure, variation partitioning allowed us to specifically evaluate the fine-scale neutral processes produced by spatial autocorrelation within habitat patches, and the broad-scale dispersal limitations between patches. Only the second subset of spatial variables was significant; dispersal limitation was relatively low between habitat patches of varzea lakes. An analysis of functional ecology allowed an empirical description of the functional mechanisms of alpha and beta niche differentiation, and an assessment of the phylogenetic signal. The trait-convergence assembly pattern among habitat patches indicated that fish in turbid river channels were better adapted to low light than fish in transparent black and clear water bodies. Also, fish in varzea lakes had a wider ecological range; this association indicated phylogenetic niche conservatism. The trait-divergence assembly pattern was almost expressed by body weight and was prominent in varzea lakes; combined with ecological range and sensory adaptation, this association indicated a marginal phylogenetic signal. These results suggest the radiation of species-rich clades with a high degree of sensory adaptation may have occurred in the seasonal environment of varzea lakes. This resulted in larger ecological distribution and innovative life histories tightly synchronized with periodic flooding. The lineage-specific sensory adaptation and subsequent landscape and evolutional history of habitat specialization were also found to actually contribute to the fish metacommunity dynamic in the Bolivian Amazonian lowland.

Photochemical Dissolved Gaseous Mercury (DGM) formation/consumption in the Negro River Basin, brazilian Amazon

Dissolved gaseous mercury (DGM) formation/consumption was measured during several scientific excursions in the Negro River basin, Amazon, Brazil. Measurements were carried out following diel patterns in both white and black water bodies. In white waters, with pH values around 7 and low dissolved organic carbon (DOC) concentration, mercury saturation prevails during the sunlit period, similar to behavior observed elsewhere. This was attributed to DGM generated by a photoinduced mechanism of Hg2+ reduction. On the other hand, in black waters, with pH around 5 and high DOC values (up to 20 mg L-1), DGM concentration stays below the detection limit during sunlit periods, which was associated to photoinduced Hgº oxidation. Photochemical experiments carried out in situ corroborate the influence of sunlight on DGM formation/consumption. A comparison of diel DGM saturation is presented for both black and white water bodies.

Cladocères de quelques corps d'eaux du bassin moyen de l'Orénoque (Vénézuéla)

The examination of 110 pelagic samples and 16 littoral samples from several water bodies in the middle basin of the Orinoco river (lakes formed by barrage or inundation of the Orinoco and Caroni river systems) revealed 58 taxa of Clado­ cera, of which 24 are new to the Venezuelan launa. Two species, Alona ovata and Bosminopsis macaguensis, are new to science. Alona karelica, a palaearctic species, has never been recorded before on the continent of America. 35 % of the fauna studied are represented by neotropical forms, of which eight are endemic to South America. An illustrated taxonomic section deals with 13 species that are rare or little known. The distribution of species was studied in the environment examined and in the two categories of white and black waters. The richest cladoceran fauna was found in the lakes formed by inundation of the Orinoco, the species diversity being due to littoral forms, chiefly in the Family Chydoridae. In the pelagic environment, white-water bodies were characterised by the species association Moina minuta, Ceriodaphnia cornuta, Bosmina tubicen, and Bosminopsis deitersi, and black-water bodies by the dominance of Bosminidae : Bosmina hagmanni, Bosminopsis macaguensis, Bosminopsis deitersi, Ceriodaphnia cornuta. The case of Daphnia gessneri, generally considered endemic to the Amazon-Orinoco system and present in a single survey, is discussed.