scholarly journals Under the surface: what we know about the threats to subterranean fishes in Brazil

2021 ◽  
Vol 19 (3) ◽  
Author(s):  
Maria Elina Bichuette ◽  
Jonas Eduardo Gallão
Keyword(s):  
Water Table ◽  
Food Restriction ◽  
Hyporheic Zone ◽  
Public Awareness ◽  
River Basins ◽  
Physical Change ◽  
Alluvial Sediments ◽  
Base Level ◽  
Threatened Fauna ◽  
Brazilian Biodiversity

Abstract The present work brings information on threats to the subterranean fishes in Brazil. Currently, at least 36 species are known, 22 of which are already formally described. Endemism is the rule for most of them. Regarding their conservation, these fishes are in general considered threatened: and most of the already formally described species are included in national lists of threatened fauna, and only four of them are included in the global list of the IUCN. Regarding habitats, Brazilian subterranean fishes occur in alluvial sediments (part of the hyporheic zone), shallow base-level streams, flooded caves, lakes in the water table, upper vadose tributaries, and epikarst aquifers. We detected 11 main threats, mainly related to agriculture, pasture, and hydroelectric plans, but unmanaged tourism and pollution are also significant threats. Two threats affect a high number of species (physical change of the habitat and food restriction). The river basins with the higher number of identified threats are the upper Tocantins (eight) followed by the upper Paraguaçu (six). Effective proposals to protect this neglected component of the Brazilian biodiversity are still scarce, such as monitoring projects and their function in the subterranean communities, besides education projects aiming to develop public awareness.

‘Looping caves’ versus ‘water table caves’: The role of base-level changes and recharge variations in cave development

Geomorphology ◽  
2014 ◽  
Vol 204 ◽  
pp. 683-691 ◽  
Author(s):  
Franci Gabrovšek ◽  
Philipp Häuselmann ◽  
Philippe Audra
Keyword(s):  
Water Table ◽  
Base Level

scholarly journals The Exact Groundwater Divide on Water Table between Two Rivers: A Fundamental Model Investigation

Water ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 685 ◽  
Author(s):  
Peng-Fei Han ◽  
Xu-Sheng Wang ◽  
Li Wan ◽  
Xiao-Wei Jiang ◽  
Fu-Sheng Hu
Keyword(s):  
Water Level ◽  
Water Table ◽  
Catchment Area ◽  
River Basins ◽  
Two Dimensional ◽  
Local Flow ◽  
Fundamental Model ◽  
Through Flow ◽  
Flow Systems ◽  
Pass Through

The groundwater divide within a plane has long been delineated as a water table ridge composed of the local top points of a water table. This definition has not been examined well for river basins. We developed a fundamental model of a two-dimensional unsaturated–saturated flow in a profile between two rivers. The exact groundwater divide can be identified from the boundary between two local flow systems and compared with the top of a water table. It is closer to the river of a higher water level than the top of a water table. The catchment area would be overestimated (up to ~50%) for a high river and underestimated (up to ~15%) for a low river by using the top of the water table. Furthermore, a pass-through flow from one river to another would be developed below two local flow systems when the groundwater divide is significantly close to a high river.

scholarly journals Grandes capturas fluviais no Brasil: síntese das novas descobertas

2019 ◽  
pp. 23-31
Author(s):  
André Augusto Rodrigues Salgado ◽  
Luís Felipe Soares Cherem ◽  
Michael Vinícius De Sordi
Keyword(s):  
River Basins ◽  
Passive Margin ◽  
South American ◽  
Drainage Network ◽  
The South ◽  
Base Level ◽  
River Capture ◽  
Determining Factors ◽  
Major River

Capturas fluviais foram pouco investigadas no Brasil e apenas recentemente essa situação se alterou e sua ocorrência e feições correlatas foram sistematicamente estudadas para as grandes bacias fluviais não Amazônicas. Esse artigo sintetiza os principais resultados obtidos nos últimos cinco anos e apresenta a diversidade de magnitude e morfológica em seis capturas fluviais ao longo de quatro divisores entre as principais bacias hidrográficas do Brasil. Os resultados indicam que o nível de base, seguido da litoestrutura e da tectônica, constituem os fatores determinantes para ocorrência desses processos. Indicam ainda que as bacias hidrográficas atlânticas estão pirateando áreas das ditas continentais – Paraná e São Francisco – e que essa pirataria acelera o recuo erosivo do escarpamento da margem passiva sul-americana. Por fim, determinaram que as capturas causam a dissecação da rede de drenagem capturada, invertem o fluxo dos canais logo a jusante e, por fim, promovem o rebaixamento geral do relevo pirateado. Large fluvial captures in Brazil: synthesis of new discoveriesRiver captures have barely been studied in Brazil, and only recently the process and correlated features have been systematically studied for non-Amazonian major river basins. This paper synthesizes the main results obtained for the last five years and presents the diversity in magnitude and morphology of six river captures along the four divider of Brazilian-major river basins. The results indicate that the base level, followed by the lithostructure and tectonics, are the determining factors for the occurrence of these processes. They also indicate that the Atlantic basins are pirating areas of the continental ones - Paraná and São Francisco - and that this piracy accelerates the erosive retreat of the South American passive margin escarpment. Finally, they determined that the captures cause the dissection of the drainage network, invert the flow of the channels shortly downstream, and finally, promote the general lowering of the pirated relief. Keywords: River capture, Brazil, Major Basin Dividers, Fluvial Channel.  

Temporal Hyporheic Zone Response to Water Table Fluctuations

Ground Water ◽  
2015 ◽  
Vol 54 (2) ◽  
pp. 274-285 ◽  
Author(s):  
Jonathan M. Malzone ◽  
Sierra K. Anseeuw ◽  
Christopher S. Lowry ◽  
Richelle Allen-King
Keyword(s):  
Water Table ◽  
Hyporheic Zone ◽  
Water Table Fluctuations ◽  
Response To Water

How likely are widespread floods in US river basins? Seeking answers using a stochastic, wavelet-based approach

2020 ◽  
Author(s):  
Manuela Irene Brunner ◽  
Simon Papalexiou ◽  
Eric Gilleland
Keyword(s):  
United States ◽  
River Basin ◽  
Flood Hazard ◽  
Public Awareness ◽  
River Basins ◽  
The United States ◽  
Large River ◽  
Simultaneous Occurrence ◽  
Large Set ◽  
Flood Events

<p>Flooding can affect large regions leading to high economic and societal costs. Estimating regional flood risk is crucial for developing adaptation strategies, public awareness policies, and protection structures. Yet, estimating regional flood hazard is not trivial because of the few large flood events observed. Here, we derive regional flood hazard estimates for large river basins in the United States by using a stochastic streamflow generator. This allows us to increase the number of flood events available for the analysis and to investigate the simultaneous occurrence of flooding in different parts of a river basin. <br>We propose the continuous, stochastic simulation approach (<em>PRSim.wave</em>), which combines a non-parametric spatio-temporal model based on the wavelet transform with the parametric kappa distribution. The model reproduces the temporal and distributional characteristics of streamflow at individual sites and retains the spatial dependencies between sites even for spatial extremes. We use <em>PRSim.wave</em> to generate long and spatially consistent time series of daily discharge for a large set of catchments in the conterminous United States. For each catchment, we extract flood events from the simulated series using a peak-over-threshold approach to derive a spatial dataset of flood occurrences. Using this dataset, we estimate how probable it is that a certain percentage of stations within a specific river basin is jointly flooded. We show that: (1) there are strong regional differences in the likelihood of joint and potentially widespread flooding and (2) there are spatial differences in regional flood hazard estimates which could not be derived from observed data only. We deem our approach a valuable tool for water managers and policy makers to make informed decisions on the risk of widespread flooding.</p>

scholarly journals Diversity of Brazilian Troglobitic Fishes: Models of Colonization and Differentiation in Subterranean Habitats

Diversity ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 106
Author(s):  
Eleonora Trajano
Keyword(s):  
Phylogenetic Diversity ◽  
Hyporheic Zone ◽  
Genetic Isolation ◽  
Phenotypic Differentiation ◽  
Base Level ◽  
Over Time ◽  
Lentic Waters

The Brazilian subterranean ichthyofauna is distinguished worldwide by high taxonomic and phylogenetic diversity, involving at least 30 exclusively subterranean (troglobitic) lineages. This may be explained by high native epigean diversty, allied to opportunities for colonization and genetic isolation in the subterranean biotope, thence originating troglobites. An updated list of Brazilian troglobitic lineages and a review of previous hypotheses on modes of colonization and differentiation in subterranean habitats are presented with fresh data and models. Colonization of and isolation in the subterranean biotope are independent processes, usually separate over time. Access to subterranean habitats varies from the (sub)horizontal through sinkholes and resurgences of base-level streams and vadose tributaries to the vertical by shallow and deep phreatic waters through the hyporheic zone. Phenotypic differentiation of subterranean populations originating troglobites may be achieved by various, non-mutually exclusive modes of genetic isolation, e.g., directly in base-level streams and upper tributaries through the extinction of epigean populations, due to drainage discontinuation in dry paleoclimatic phases (or by other causes), by topographic isolation due to a lowering of the regional base level and karst catchments or by parapatric differentiation. Differentiation may also be a consequence of transition from lotic to lentic waters in flooded caves, and from shallow to deep phreatic habitats.

scholarly journals Contrasted Chemical Weathering Rates in Cratonic Basins: The Ogooué and Mbei Rivers, Western Central Africa

2021 ◽  
Vol 2 ◽  
Author(s):  
Jean-Sébastien Moquet ◽  
Julien Bouchez ◽  
Jean-Jacques Braun ◽  
Sakaros Bogning ◽  
Auguste Paulin Mbonda ◽  
...  
Keyword(s):  
Chemical Weathering ◽  
Natural Waters ◽  
Isotope Composition ◽  
Central Africa ◽  
River Basins ◽  
Tectonic Activity ◽  
Weathering Rates ◽  
Base Level ◽  
Solute Fluxes ◽  
Dissolved Load

Despite the absence of tectonic activity, cratonic environments are characterized by strongly variable, and in places significant, rock weathering rates. This is shown here through an exploration of the weathering rates in two inter-tropical river basins from the Atlantic Central Africa: the Ogooué and Mbei River basins, Gabon. We analyzed the elemental and strontium isotope composition of 24 water samples collected throughout these basins. Based on the determination of the major element sources we estimate that the Ogooué and Mbei rivers total dissolved solids (TDS) mainly derive from silicate chemical weathering. The chemical composition of the dissolved load and the area-normalized solute fluxes at the outlet of the Ogooué are similar to those of other West African rivers (e.g., Niger, Nyong, or Congo). However, chemical weathering rates (TZsil+ rate expressed as the release rate of the sum of cations by silicate chemical weathering) span the entire range of chemical weathering intensities hitherto recorded in worldwide cratonic environments. In the Ogooué-Mbei systems, three regions can be distinguished: (i) the Eastern sub-basins draining the Plateaux Batéké underlain by quartz-rich sandstones exhibit the lowest TZsil+ rates, (ii) the Northern sub-basins and the Mbei sub-basins, which drain the southern edge of the tectonically quiescent South Cameroon Plateau, show intermediate TZsil+ rates and (iii) the Southern sub-basins characterized by steeper slopes record the highest TZsil+ rates. In region (ii), higher DOC concentrations are associated with enrichment of elements expected to form insoluble hydrolysates in natural waters (e.g., Fe, Al, Th, REEs) suggesting enhanced transport of these elements in the colloidal phase. In region (iii), we suggest that a combination of mantle-induced dynamic uplift and lithospheric destabilization affecting the rim of the Congo Cuvette induces slow base level lowering thereby enhancing soil erosion, exhumation of fresh primary minerals, and thus weathering rates. The study points out that erosion of lateritic covers in cratonic areas can significantly enhance chemical weathering rates by bringing fresh minerals in contact with meteoric water. The heterogeneity of weathering rates amongst cratonic regions thus need to be considered for reconstructing the global, long-term carbon cycle and its control on Earth climate.

scholarly journals Time response of the water table and saltwater transition zone to a base level drop

2008 ◽  
Vol 44 (12) ◽  
Author(s):  
Y. Kiro ◽  
Y. Yechieli ◽  
V. Lyakhovsky ◽  
E. Shalev ◽  
A. Starinsky
Keyword(s):  
Transition Zone ◽  
Water Table ◽  
Time Response ◽  
Base Level

Modeling effects of physical and chemical heterogeneity of alluvial sediments on hyporheic exchange

2020 ◽  
Author(s):  
Fulvio Boano ◽  
Eugenio Pescimoro ◽  
Audrey Sawyer ◽  
Mohamad Reza Soltanian
Keyword(s):  
Hydraulic Conductivity ◽  
Organic Carbon ◽  
Hyporheic Zone ◽  
River Sediments ◽  
Hyporheic Exchange ◽  
Biogeochemical Model ◽  
Chemical Heterogeneity ◽  
Organic Carbon Content ◽  
Alluvial Sediments ◽  
Physical And Chemical

<p>Exchange of water and nutrients between a river and the surrounding hyporheic zone is controlled by multiple factors, including river morphology, streamflow variability, connection with groundwater, and sediment properties. Among these factors, the heterogeneity of river sediments is known to strongly affect the fate of nutrients exchanged with the hyporheic zone, but this influence has received relatively little attention compared to other factors. Moreover, sediments are heterogeneous in terms of both physical properties (i.e., hydraulic conductivity) and chemical composition (e.g., organic carbon content), but studies about heterogeneity have mostly focused on variations of hydraulic conductivity compared to the variations of chemical properties of sediments.</p><p>This contribution presents a modeling analysis of the influence of physical and chemical heterogeneity of alluvial sediments on lateral hyporheic exchange in meandering rivers. Sediments are treated as a binary mixture of mineral sand and organic silt, and a coupled hydraulic and biogeochemical model is employed to simulate the effect of different silt/sand ratios on exchange and reaction of organic carbon, oxygen, nitrate, and ammonium. Model results show that sediments with higher content of silt are characterized by lower exchange fluxes, but their higher carbon availability fosters higher rates of biochemical reactions and hence leads to higher nitrogen removal by net denitrification. These results indicate the importance of improving the description of sediment heterogeneity in modeling studies of hyporheic exchange.</p>

scholarly journals Occurrence of alien spirlin (Alburnoidessp.) in the Neretva river basin

2019 ◽  
pp. 15 ◽  
Author(s):  
Jasna Vukić ◽  
Kristýna Eliášová ◽  
Dario Marić ◽  
Radek Šanda
Keyword(s):  
River Basin ◽  
Bosnia And Herzegovina ◽  
Fish Species ◽  
Native Species ◽  
Public Awareness ◽  
River Basins ◽  
Freshwater Ecosystems ◽  
Danube River ◽  
Alien Fish ◽  
Alien Fish Species

Northern Mediterranean region is characterised by an exceptional richness of the freshwater ichthyofauna. Many fish species of this region are endemic to a single or a few river basins. This is also the case of the Neretva river basin (Adriatic Sea slope), where 17 out of 34 native species are endemic solely to this river basin. However, these unique Mediterranean freshwater ecosystems are fragile and are susceptible to human-induced changes, including introduction of alien fish species. We report here a finding of the 32ndalien fish species in the Neretva river basin, spirlinAlburnoidessp., which was found at two localities in Bosnia and Herzegovina. The spirlin species was identified by molecular means as so far unnamed species with the native range in the Sava river basin (Danube river basin, Black Sea slope). Based on the comparison ofcytochrome bsequences, the introduced population originated most probably from nearby rivers of the Danube basin in Bosnia and Herzegovina (Vrbas and Bosna river basins). Such a high number of alien fish species reported in a single river basin is alarming and pointing to a necessity of raising public awareness, especially among local fishermen.

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