Differentiation of some Venezuelan blackwater rivers based upon physico-chemical properties of their humic substances

Vegas-Vilarrúbia, Teresa; Paolini, Jorge; Miragaya, Juan Garcia

doi:10.1007/bf00002933

Cited by 13 publications

(5 citation statements)

References 41 publications

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“…Our study also revealed that, for other fish species, the gradient of environmental conditions along the course of the Casiquiare constitutes an ecological barrier for dispersal. The river’s longitudinal fluvial gradient transitions between clearwater conditions having upland hydrological influences, and blackwater conditions associated with the drainage of the sandy, oligotrophic alluvial plains of the Cuchivero geological province (Vegas‐Vilarrúbia et al. , 1988; Fig.…”

Section: Discussionmentioning

confidence: 99%

Fish assemblages of the Casiquiare River, a corridor and zoogeographical filter for dispersal between the Orinoco and Amazon basins

Winemiller

López‐Fernández

Taphorn

et al. 2008

Journal of Biogeography

101

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Aim The aim of this study was to determine whether the Casiquiare River functions as a free dispersal corridor or as a partial barrier (i.e. filter) for the interchange of fish species of the Orinoco and Negro/Amazon basins using species assemblage patterns according to geographical location and environmental features.Location The Casiquiare, Upper Orinoco and Upper Negro rivers in southern Venezuela, South America.Methods Our study was based on an analysis of species presence/absence data and environmental information (11 habitat characteristics) collected by the authors and colleagues between the years 1984 and 1999. The data set consisted of 269 sampled sites and 452 fish species (> 50,000 specimens). A wide range of habitat types was included in the samples, and the collection sites were located at various points along the entire length of the Casiquiare main channel, at multiple sites on its tributary streams, as well as at various nearby sites outside the Casiquiare drainage, within the Upper Orinoco and Upper Rio Negro river systems. Most specimens and field data used in this analysis are archived in the Museo de Ciencias Naturales in Guanare, Venezuela. We performed canonical correspondence analysis (CCA) based on species presence/absence using two versions of the data set: one that eliminated sites having < 5 species and species occurring at < 5 sites; and another that eliminated sites having < 10 species and species occurring at < 10 sites. Cluster analysis was performed on sites based on species assemblage similarity, and a separate analysis was performed on species based on CCA loadings. ResultsThe CCA results for the two versions of the data set were qualitatively the same. The dominant environmental axis contrasted assemblages and sites associated with blackwater vs. clearwater conditions. Longitudinal position on the Casiquiare River was correlated (r 2 = 0.33) with CCA axis-1 scores, reflecting clearwater conditions nearer to its origin (bifurcation of the Orinoco) and blackwater conditions nearer to its mouth (junction with the Rio Negro). The second CCA axis was most strongly associated with habitat size and structural complexity. Species associations derived from the unweighted pair-group average clustering method and pair-wise squared Euclidean distances calculated from species loadings on CCA axes 1 and 2 showed seven ecological groupings. Cluster analysis of species assemblages according to watershed revealed a stronger influence of local environmental conditions than of geographical proximity.Main conclusions Fish assemblage composition is more consistently associated with local environmental conditions than with geographical position within the river drainages. Nonetheless, the results support the hypothesis that the mainstem

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Section: Discussionmentioning

confidence: 99%

Fish assemblages of the Casiquiare River, a corridor and zoogeographical filter for dispersal between the Orinoco and Amazon basins

Winemiller

López‐Fernández

Taphorn

et al. 2008

Journal of Biogeography

101

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“…The mean pH value (7.08) of Lake Kenyir is typical of bicarbonate-type waters, in which the CO 2 -HCO 3 -CO 3 equilibrium system operates (Payne 1986). Low alkalinity and pH values are indicators of low mineralization and high humic substances (Vegas-Villarubia et al 1988). Being in the main basin of Lake Kenyir, the dam sampling site (site 1) has less opportunity for mineralization to occur.…”

Section: Discussionmentioning

confidence: 99%

“…The mean pH value (7.08) of Lake Kenyir is typical of bicarbonate‐type waters, in which the CO 2 ‐HCO 3 ‐CO 3 equilibrium system operates (Payne 1986). Low alkalinity and pH values are indicators of low mineralization and high humic substances (Vegas‐Villarubia et al . 1988).…”

Section: Discussionmentioning

confidence: 99%

Temporal changes in the periphytic algal communities in a drowned tropical forest reservoir in Malaysia: Lake Kenyir

et al. 2008

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Periphytic algal assemblages, comprising bacillariophytes, cyanophytes and chlorophytes of standing dead trees in Lake Kenyir, a tropical drowned forest reservoir, were studied during 1995. A total of 317 algal taxa were identified in this study. The monthly floral mean species richness and cell count data demonstrated significant temporal differences between the months, in one-way ANOVA (P < 0.05). Both redundancy analysis and cluster analysis on monthly blue-green abundance and diatom assemblages exhibited conspicuous groupings among the months, with underpinning seasonal differences. The responses were not similar, however, between the upstream and downstream ends of the lake. The grouping or clustering of months can be generalized as: (i) November, December and January as the monsoonal months; (ii) February, March, April and May as the transitional months; and (iii) June to October as the dry months. Based on stepwise multiple regression with forward selection, alkalinity and dissolved oxygen concentration were significant environmental predictors at the downstream dam sampling site, and reactive silica, electrical conductivity, Secchi depth transparency and sunshine hours were significant predicators at the upstream riverine sampling site, based on Monte Carlo tests. Being a ploymictic, mesotrophic lake, the limnology and temporal changes for Lake Kenyir appears to be complex and driven by monsoons, as evidenced from the temporal changes in its periphytic algae communities, particularly the diatom assemblages. The downstream sampling site (site 1) at the dam, in the main basin and deeper zone of the lake, the seasonal amplitude was likely complex because of thermocline formation and stratification processes. In contrast, the upstream sampling site in the Petang River (site 2) exhibited a clearer distinction between the dry and monsoon months, based on its cyanophyte and diatom floral assemblages. These study results are pertinent for lake management, especially for developing biomonitoring programmes or lake productivity studies, as well as for climate change studies, within the context of tropical lake ecology.

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“…The two swamp rivers in our study, however, are natural and undisturbed, with >95% swamp vegetation. They are typical blackwater rivers with low pH, low DO, and variable concentrations of nutrients (Vegas-Vilarrúbia et al, 1988;Küchler et al, 2000;Alkhatib et al, 2007;Horbe and Santos, 2009;Rixen et al, 2010;Ríos-Villamizar et al, 2014). The two focal swamp rivers likely align with "slightly contaminated" NRMN sites because they have DO concentrations approaching hypoxia.…”

Section: Coastal Peat Swamp Riversmentioning

confidence: 99%

Land Use and Land Cover Shape River Water Quality at a Continental Caribbean Land-Ocean Interface

et al. 2022

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Land use and land cover (LULC) can significantly alter river water, which can in turn have important impacts on downstream coastal ecosystems by delivering nutrients that promote marine eutrophication and hypoxia. Well-documented in temperate systems, less is known about the way land cover relates to water quality in low-lying coastal zones in the tropics. Here we evaluate the catchment LULC and the physical and chemical characteristics of six rivers that contribute flow into a seasonally hypoxic tropical bay in Bocas del Toro, Panama. From July 2019 to March 2020, we routinely surveyed eight physical and chemical characteristics (temperature, specific conductivity, salinity, pH, dissolved oxygen (DO), nitrate and nitrite, ammonium, and phosphate). Our goals were to determine how these physical and chemical characteristics of the rivers reflect the LULC, to compare the water quality of the focal rivers to rivers across Panama, and to discuss the potential impacts of river discharge in the Bay. Overall, we found that the six focal rivers have significantly different river water characteristics that can be linked to catchment LULC and that water quality of rivers 10 s of kilometers apart could differ drastically. Two focal catchments dominated by pristine peat swamp vegetation in San San Pond Sak, showed characteristics typical of blackwater rivers, with low pH, dissolved oxygen, and nutrients. The remaining four catchments were largely mountainous with >50% forest cover. In these rivers, variation in nutrient concentrations were associated with percent urbanization. Comparisons across Panamanian rivers covered in a national survey to our focal rivers shows that saltwater intrusions and low DO of coastal swamp rivers may result in their classification by a standardized water quality index as having slightly contaminated water quality, despite this being their natural state. Examination of deforestation over the last 20 years, show that changes were <10% in the focal catchments, were larger in the small mountainous catchments and suggest that in the past 20 years the physical and chemical characteristics of river water that contributes to Almirante Bay may have shifted slightly in response to these moderate land use changes. (See supplementary information for Spanish-language abstract).

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Differentiation of some Venezuelan blackwater rivers based upon physico-chemical properties of their humic substances

Cited by 13 publications

References 41 publications

Fish assemblages of the Casiquiare River, a corridor and zoogeographical filter for dispersal between the Orinoco and Amazon basins

Fish assemblages of the Casiquiare River, a corridor and zoogeographical filter for dispersal between the Orinoco and Amazon basins

Temporal changes in the periphytic algal communities in a drowned tropical forest reservoir in Malaysia: Lake Kenyir

Land Use and Land Cover Shape River Water Quality at a Continental Caribbean Land-Ocean Interface

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