This chapter discusses the physical and biological features of five major Mexican rivers-the Río Pánuco, Usumacinta-Grijalva rivers, Río Candelaria, the Yaqui, and the Río Conchos. Five additional rivers-the Chihuahuan Desert's Río Salado; the Río Tamesí, which joins the Río Pánuco near its mouth; the Río Fuerte, which flows through some of the con...
Sixteen trace metals were measured for the first time in cyanobacterial mats and its underlying sediment in eight lakes in the Northern Western desert, Egypt. Al, Ba, Cr, Fe, Pb, Mn, Ni, Cu and Zn concentrations in sediments were many times higher than in cyanobacterial mates. Fe, Al, Mn, Cu were the highest trace metals recorded in the lakes. Geo-...
Presenting the evidence for the relative impact of climate and land use upon landscape dynamics through proxy data and paleoclimate/erosion modeling in Italy, northeast Africa, and Iran.
... In order to obtain southern freshwater inputs, a time series is built based on the composite of temperature, salinity, volume transport and nutrient concentration at the location of the freshwater sources or near it. The information is obtained from values reported in the literature (Milliman and Syvitski, 1992;Herrera-Silveira et al., 2002Yáñez Arancibia and Day, 2004;Hudson et al., 2005;Herrera-Silveira and Morales-Ojeda, 2010;Poot-Delgado et al., 2015;Kemp et al., 2016;Conan et al., 2016) and from observational hydrographic stations near the Yucatán coast (Sect. 2.3). ...
Continental shelves are the most productive areas in the seas with the strongest implications for global nitrogen cycling. The Yucatán shelf (YS) is the largest shelf in the Gulf of Mexico (GoM); however, its nitrogen budget has not been quantified. This is largely due to the lack of significant spatio-temporal in situ measurements and the complexity of the shelf dynamics, including coastal upwelling, coastal-trapped waves (CTWs), and influence of the Yucatán Current (YC) via bottom Ekman transport and dynamic uplift. In this paper, we investigate and quantify the nitrogen budget of dissolved inorganic nitrogen (DIN) and particulate organic nitrogen (PON) in the YS using a 9-year output from a coupled physical–biogeochemical model of the GoM. The sum of DIN and PON is here referred to as total nitrogen (TN). Results indicate that the main entrance of DIN is through its southern (continental) and eastern margins. The TN is then advected to the deep oligotrophic Bay of Campeche and central GoM. It is also shown that the inner shelf (bounded by the 50 m isobath) is “efficient” in terms of TN, since all DIN imported into this shelf is consumed by the phytoplankton. Submarine groundwater discharges (SGDs) contribute 20 % of the TN, while denitrification removes up to 53 % of TN that enters into the inner shelf. The high-frequency variability of the TN fluxes in the southern margin is modulated by fluxes from the YC due to enhanced bottom Ekman transport when the YC leans against the shelf break (250 m isobath) on the eastern margin. This current–topography interaction can help to maintain the upwelling of Cape Catoche, uplifting nutrient-rich water into the euphotic layer. The export of TN at both western and northwestern margins is modulated by CTWs with a mean period of about 10 d in agreement with recent observational and modelling studies.
... Chiapas has a coastline of 270 km and more than 70,000 hectares of estuaries and coastal lagoons (Contreras-Espinosa 2010), which favors the presence of rich fish diversity (Velasco-Colín 1976, Lozano-Vilano and Contreras-Balderas 1987. Much of the state is located in the Usumacinta ichthyographic province/area of endemism (Miller et al. 2005, which means that its continental waters host a high number of endemic species, making Chiapas a freshwater biodiversity hotspot (Hudson et al. 2005. ...
An updated checklist of the distribution of fishes that inhabit the continental waters of the Mexican state of Chiapas is presented. The state was compartmentalized into 12 hydrological regions for the purpose of understanding the distribution of fish fauna across a state with large physiographic variance. The ich-thyofauna of Chiapas is represented by 311 species distributed in two classes, 26 orders, 73 families, and 182 genera, including 12 exotic species. The families with the highest number of species were Cichlidae, Poeciliidae, Sciaenidae, Carangidae, Ariidae, Gobiidae, and Haemulidae. This study attempts to close gaps in knowledge of the distribution of ichthyofauna in the diverse hydrological regions of Chiapas, Mexico.
Globally, nutrient river discharges drive water quality of coastal ecosystems, and excess nutrients can cause eutrophication impacts. The Grijalva-Usumacinta River System (GURS) discharges in the southern Gulf of Mexico (SGoM) and it is the second largest riverine input to the Gulf. To study how contrasting GURS freshwater flow between rainy and dry seasons affects nutrients concentrations in the receiving coastal ecosystem, we evaluated nutrient variability in the water column during both seasons. High inorganic nutrients and total phosphate outline the rivers discharge plumes during rainy season, and were significantly higher than during the dry season throughout the study area, suggesting contrasting seasonal nutrient discharge of the GURS to coastal waters. On average the GURS discharged 141,123 t N yr⁻¹ 6893 t P yr⁻¹ and 928,904 t Si yr⁻¹ to SGoM. These results contribute with a nutrient baseline in the SGoM that could be useful for GURS decision-makers.
Turbidity is a good indicator to determine the quality of the water; it is a measure of the number of particles in suspension in the water. Using ocean color data, we analyzed the seasonal variability of turbidity in front of the Campeche Bank and part of the confluence zone of the coastal currents coming from the Tamaulipas-Veracruz and Campeche platforms [94°W-87.6°W and 18°N-24°N]. The extended platform has several river discharges that are strongly influenced by winds and the loop current coming from the Strait of Yucatan. 2003-2020 was analyzed using satellite images (reflectance, Chlorophyll, sea surface temperature, and altimetry), reanalyzed winds and discharges from the grijalva-usumacinta river system. We used seasonal climatologies, Hovmoller diagrams, and Orthogonal and Complex Empirical Functions to describe the data. In addition, through the “Coastal and Regional Ocean Community model-CROCO) the surface fields of Salinity and velocity were incorporated into the analysis. The results indicated that the seasonal turbidity and its intensification in autumn and winter on the western side of the Campeche platform are due mainly to the contribution of intense flows from the Grijalva-Usumacinta which is further dynamically mix in autumn by the southwest winds, the cyclonic gyres, and the return currents. In spring-summer, the same forcing persists; however, the turbidity decreases due to the ineffectiveness of the intense zonal winds to produce Ekman transport.
Species distribution models (SDMs) are an increasingly important tool for conservation particularly for difficult-to-study locations and with understudied fauna. Our aims were to (1) use SDMs and ensemble SDMs to predict the distribution of freshwater mussels in the Pánuco River Basin in Central México; (2) determine habitat factors shaping freshwater mussel occurrence; and (3) use predicted occupancy across a range of taxa to identify freshwater mussel biodiversity hotspots to guide conservation and management. In the Pánuco River Basin, we modeled the distributions of 11 freshwater mussel species using an ensemble approach, wherein multiple SDM meth-odologies were combined to create a single ensemble map of predicted occupancy. A total of 621 species-specific observations at 87 sites were used to create species-specific ensembles. These predictive species ensembles were then combined to create local diversity hotspot maps. Precipitation during the warmest quarter, elevation, and mean temperature were consistently the most important discriminatory environmental variables among species, whereas land use had limited influence across all taxa. To the best of our knowledge, our study is the first freshwater mussel-focused research to use an ensemble approach to determine species distribution and predict biodiversity hotspots. Our study can be used to guide not only current conservation efforts but also prioritize areas for future conservation and study. K E Y W O R D S climate, conservation, habitat, maxent, mycetopodidae, random forest, species distribution model, unionidae
Tropical Usumacinta River is the tenth largest in North America and Mexico's principal river. Diverse and increasing anthropogenic activities (e.g., land-use change, agriculture, urban development) occur along the river and most likely alter its water quality. We used inverse geochemical models (PHREEQC code) and chemical diagrams to determine the water chemistry in the mainstream and principal tributaries, the principal geological and anthropic causal factors, and the effects of tropical seasonality. The dominant chemical water type in the river is CaMgSO4HCO3 in the dry season, while CaMgHCO3SO4 in the rainy season. The water-rock interaction processes in the dry season are: gypsum, halite, and sylvite precipitation, and Mg2+ to Na + ion exchange in the middle basin; calcite, kaolinite, and SiO2(a) precipitation, CO2, dolomite, gypsum, halite, sylvite, and K-feldspar dissolution, nitrification, and Ca2+ to Na + ion exchange in the lower basin. In the rainy season, the processes are: plagioclase and sylvite precipitation, calcite, dolomite, gypsum, halite, kaolinite, and K-feldspar dissolution in the middle basin; kaolinite precipitation, dolomite, gypsum, halite, K-feldspar, and sylvite dissolution, and nitrification, in the lower basin. The model outcome reveals the water-rock interactions that control the chemical composition in the river are mainly the carbonate and secondly the silicate weathering in the dry season. In contrast, in the rainy season, the weathering of carbonate and silicate rocks have the same weathering proportion. At the same time. The model of the dry season reveals the influence of a saline water intrusion in the lower basin. The effects caused by agricultural activities as nitrification are evident in the lower basin of the dry season. In contrast, it is not present in the rainy season most likely associated to the river flow dilutes the nitrates. The results of this research are slightly different from other tropical rivers with similar geology, with a predominance of Ca2+ and Mg2+ cations, and HCO3- and SO42- anions. This investigation is the first to present the major ions composition, chemical water types, and water-rock interactions in the tropical Usumacinta River. The methodology herein used proved to be useful to understand the chemical changes in rivers with various geological materials that could be applied in other tropical and temperate rivers.
Prehispanic societies transformed large areas of tropical forest in Mexico and Central America, a region now known as the Maya lowlands, into highly engineered urban and agricultural landscapes, over a period of more than two millennia. This chapter provides an overview of the impacts of the ancient Maya on their environment, with a focus on the history of Maya modification of local and regional geomorphic systems during the late Holocene. An overview of the geomorphology of the Maya lowlands is provided, with key examples of Maya interactions with and modifications of the landscape. The Maya converted natural ecosystems into vast urban and rural infrastructure with locally attuned water management systems that included reservoirs, wetland fields and canals, terraces, field ridges and water temples. Evidence for increasing Maya deforestation, carried out for urbanization and agriculture, is preserved in the form of deep sequences of anthropogenic sediments that cascaded through catchments, buried Maya infrastructure and paleosols, silted in reservoirs, waterways, floodplains and wetlands, and accumulated on lake bottoms. The use of proxies for ancient Maya land-use intensity, such as inorganic and organic geochemistry and stable carbon isotopes, soil organic matter and mineral magnetism, are briefly reviewed. The Maya geomorphic impacts were sufficiently severe that centuries of erosion left a region-wide anthropogenic chronostratigraphic marker known as the ‘Maya Clay’ across much of the southern Maya lowlands. The greatest geomorphic impacts of the Maya in the region began to diminish by c. 1000 BP, in response to social and political upheavals that have been referred to as the ‘Maya Collapse.’ Geomorphological, geoarcheological, and paleoenvironmental investigations have provided data that can be used to quantify Maya-mediated environmental impacts and test hypotheses about climate and environmental drivers of societal ‘Collapse.’
Multiple factors control the flow distribution in a river bifurcation. However, one factor that requires further analysis is the effect of upstream reservoirs. Such is the case of the bifurcation of the Mezcalapa River into the Samaria and Carrizal rivers located in the lowlands of the Grijalva River basin, Mexico. Four dams were commissioned in the upper basin, the first in 1967 and the last in 1987. Since the late 1960s the distribution of the flow at the bifurcation has varied considerably. The flow captured by the Carrizal River between the late 1960s and mid 1980s gradually decreased from 40% to 10%, and later, between the mid 1980s and early 2000s, it increased up to 75%. During the same period, the Samaria River had a reversed pattern. Here, using a 2D hydro‐morphodynamical model, the impact of an upstream reservoir (that causes homogenization of the flow hydrograph and sediment retention) on bed morphology and flow distribution in a river bifurcation is analyzed. The results indicate that the sediment retention is the factor of largest impact on the flow distribution. The upstream channel incises, and the process propagates to the diffluent with the larger energy gradient developing positive feedback were the erosion increases the hydraulic capacity to capture more flow, resulting in more erosion. The flow homogenization has also an impact. The suppression of peak flows reduces the sediment load capacity in the diffluent with lower energy gradient, generating sedimentation at its entrance and diminishing its hydraulic capacity.
Particulate organic carbon (POC) derived from inland water plays an important role in the global carbon (C) cycle; however, the POC dynamic in tropical rivers is poorly known. We assessed the POC concentration, flux, and sources in the Usumacinta, the largest tropical river in North America, to determine the controls on POC export to the Gulf of Mexico. We examined the Mexican middle and lower Usumacinta Basin during the 2017 dry (DS) and rainy (RS) seasons. The POC concentration ranged from 0.48 to 4.7 mg L−1 and was higher in the RS, though only in the middle basin, while remaining similar in both seasons in the lower basin. The POC was predominantly allochthonous (54.7 to 99.6%). However, autochthonous POC (phytoplankton) increased in the DS (from 5.1 to 17.7%) in both basins. The POC mass inflow–outflow balance suggested that floodplains supply (C source) autochthonous POC during the DS while retaining (C sink) allochthonous POC in the RS. Ranging between 109.1 (DS) and 926.1 t POC d−1 (RS), the Usumacinta River POC export to the Gulf of Mexico was similar to that of other tropical rivers with a comparable water discharge. The extensive floodplains and the “Pantanos de Centla” wetlands in the lowlands largely influenced the POC dynamics and export to the southern Gulf of Mexico.
Yaqui Catfish Ictalurus pricei is an understudied species with limited information of its ecology, distribution, and local habitat use. Native to the southwest United States and northwest Mexico, Yaqui Catfish populations are declining which has prompted the species to be listed as threatened in the United States and a species of concern in Mexico. Water over-allocation, habitat degradation, invasive species introductions, and hybridization with non-native Channel Catfish I. punctatus have caused the populations in Mexico to decline. The United States population collapsed after years of low recruitment. To better focus conservation efforts, as well as define habitat associated with Yaqui Catfish occurrences, we assessed the distribution in the Yaqui River Basin of Mexico using historical data at a landscape scale. Yaqui Catfish were historically found across the watershed among a diversity of environments, but most frequently associated with small, intermittent streams. Basin landcover was dominated by forest, shrubland, and grassland and Yaqui Catfish generally occurred in stream segments in similar proportions. However, a small number of Yaqui Catfish occurrences were associated with urban and cropland landcover types greater than that which was present on the landscape. With the species facing declines in the region, this work will help inform future conservation efforts aimed at securing this species, protecting suitable habitat and better defining its current status in Mexico.