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Groundwater and domestic wastewater are often used in conjunction with surface water to irrigate crops in semiarid areas. A concern associated with this practice is the potential accumulation of arsenic (As) and heavy metals in soil and plants, especially in places where irrigation water contains geogenic As. Studies on arsenic uptake in cereal crops growing under dry and oxidizing conditions are scarce. A one-year field experiment was conducted to evaluate the uptake and translocation of As in barley and oats irrigated with either groundwater (GW) or treated domestic wastewater (TWW) in northern Mexico. The content of As, as well as toxic metals Cd and Pb, were determined in soil and 24 sets each of barley and oat plants. Metal(loid)s accumulated more in the roots and leaves, and less in the stems and grains. Barley grains contained 0.2 mg/kg of As under GW or TWW, whereas oat grains contained twice this amount. Bioconcentration (BCF) and translocation (TF) factors were < 1 for As and Cd in plants irrigated with both GW and TWW indicating that neither barley nor oats are As-accumulators, and their grain and leaves can be safely used for fodder. However, oats irrigated with TWW bioaccumulated Pb in leaves. Conscientious monitoring of As and associated metals in soil and crops irrigated with TWW and GW is recommended.

La presencia de arsénico (As) y flúor (F) en agua subterránea es un problema global que afecta a una gran cantidad de personas en cinco continentes. Estudios al respecto reportan el contenido de As y F en agua, rocas y sedimentos, así como los factores que causan su enriquecimiento. Una cantidad de investigaciones, a la par de extensa, reporta las maneras de maximizar la eficiencia de los diversos tratamientos de agua. La ingesta crónica de agua con niveles altos de As y F causa graves trastornos a la salud. Es entonces necesario encontrar tratamientos efectivos que reduzcan el contenido de estos contaminantes dentro de las condiciones y recursos disponibles. En el presente artículo se hace una síntesis de la información reportada sobre el contenido de As y F en agua subterránea y las condiciones que causan su enriquecimiento. Se compara el caso de Chihuahua con otras zonas que cuentan con geología y clima similares. Se puntualizan tratamientos aplicados para su eliminación del agua de consumo y se discuten procesos de remoción no-convencionales y a escalas de laboratorio que podrían utilizarse con éxito.

The fractured nature of karst terrain makes these areas highly susceptible to contamination. Besides aquifer contamination, impaired karst springs can negatively impact the aquatic habitat of their receiving streams. Five springs of a shallow karst aquifer in southwest Polk County, Missouri, and their receiving stream were selected to construct a baseline of water quality data, using nitrate (NO3) as indicator. The main land use in the study area is cattle farming. Water samples were collected during a 12-month period and analyzed for pH, turbidity, Ca, Mg, HCO3, Cl, SO4, and NO3. Results show that each spring had its own range of values. NO3 and Cl values were below contamination levels and only in a few instances exceeded threshold levels reported for karst areas (NO3-N

Under the current climate crisis, the ecological integrity of forest ecosystems is key to increasing resilience and the sustainability of water and soil resources. Most forests around the world have experienced deforestation and degradation in the past few decades; however, the rate at which these occur varies depending on many factors, including the type of trees, management, and climate. We conducted a review of the deforestation, degradation, and soil erosion of the pine-oak forest within the Rio Conchos basin in northern Mexico. Preference was given to recent studies (last 10 years) conducted within this basin. Out of 27 recent publications on oak forests in Mexico, 19 focused on this forest and half of them were in Spanish. The results show that pine trees are more affected than oak trees, also that the deforestation rate has increased with time and is greater at higher elevations, making this area vulnerable to loss of topsoil during extreme hydrological events. Studies report an annual change in cover rate between 1985 and 2016 of −1.2% for pine, oak and mix vegetation. More recently, between 2000 and 2018, the change in pine cover was calculated as −2.8% concurrent with a +3.4% increase in cover of oak and other secondary vegetation. Proposed conservation strategies vary from runoff control to increased collaboration between landowners, government agencies, and stakeholders.

Groundwater of northern Mexico contains high concentrations of geogenic fluoride (F−), a contaminant known to affect human health. The origin of F− in groundwater in this region has been related to the weathering of rhyolite and other volcanic rocks present in the alluvium. However, the relationship of F− concentration to water depth has not been established. F− concentrations, pH, and total dissolved solids (TSD) were determined for 18 wells within the Meoqui-Delicias aquifer in 2021. The F concentrations varied between 0.62 mg L−1 and 4.84 mg L−1, and 61% of the wells exceeded the 1.5 mg L−1 guideline. F− concentrations did not correlate to TDS but correlated to well depth (r = −0.52, p < 0.05). Because of the less-than-strong correlation coefficient value obtained, a diagram of F− concentrations vs. well depth was constructed. The diagram showed a distinct enrichment of F− in shallow wells, suggesting that groundwater residence time and evaporation may be important factors in explaining the F− content within the aquifer. This pattern was confirmed after plotting 2003 and 2006 data for the same wells. These findings are important to better understand the distribution of F− in neighboring alluvial aquifers as well as in alluvial aquifers elsewhere.

Implementing sustainable groundwater resources management in coastal areas is challenging due to the negative impacts of anthropogenic stressors and various interactions between groundwater and surface water. This study focuses on nitrate contamination and transport via groundwater-surface water exchange in a Mediterranean coastal area (Guerbes-Senhadja region, Algeria) that is heavily affected by anthropogenic activities. A multi-tracer approach, integrating hydrogeochemical and isotopic tracers (δ

World’s food production relies on crops grown in irrigated land to feed an increasing population. In the long term, irrigation agriculture may cause environmental deterioration to the area (soil degradation, aquifer contamination) and its surroundings (greenhouse gas emission, eutrophication) to compromise crop production. Three irrigated areas in northern Mexico (Yaqui Valley, Delicias, Comarca Lagunera) were examined with respect to the challenges to achieve sustainability using reported values of nitrogen (N) along with the conventional aquifer depletion and water contamination parameters. N2O emissions, measured in only the Yaqui Valley, amounted to up to 4.5% of applied N, and nitrate losses to about 18%. The water tables of these aquifers are dropping at rates of 0.4 m year−1 (Delicias) to 1.5 m year−1 (Comarca Lagunera). High NO3− concentrations in the Comarca Lagunera (66.2% of wells above 10 mg L−1 NO3–N) pose a threat to human health. Although lower than 10 mg L−1 NO3–N in most wells, NO3− levels in Delicias and Yaqui Valley are increasing with time, although more data are needed to confirm the trend. Overall, and although the efforts by farmers still focus on increasing crop yield, awareness of the advantage of implementing measures towards sustainability is on the rise.

Abandoned mines are an abundant and widespread feature [...]

Stream sediments affected by historic mining in Aurora, Missouri, were digested via sequential extraction to determine the amount of Zn, Pb, and Cd bound to each of five geochemical phases: exchangeable, carbonate, Fe-Mn oxides, organic matter, and residual. The metal bound to the exchangeable and carbonate phases represents an approximation of the metal that is bioavailable, and thus a source of toxicity to aquatic biota and a contamination risk to the aquifer underneath. The bioavailable fraction was found to increase with total metal content, comprising an average of 19% of the total Zn, 13% of the Pb, and 14% of the Cd. In general, Pb was preferentially bound to the residual fraction, Zn to the Fe-Mn oxides fraction, and Cd to the organic fraction. As a result of metals binding to different chemical fractions, each of these metals will mobilize differently if/as environmental conditions change and chemical weathering progresses. The most mobile of the three metals was Cd and the least mobile Pb. The concentration pattern for each metal downstream reflects their relative mobility.

La distribución de arsénico (As), bario (Ba), y cobre (Cu) en sedimentos se analizó con el fin de determinar su posible asociación con depósitos minerales en el noreste de Chihuahua. El estudio se basó en 1,016 muestras de sedimento de arroyo y 11 de sedimento de río. Concentraciones enriquecidas y anómalas de cada uno de estos tres elementos se compararon con la ubicación geográfica de depósitos minerales de sulfatos, sulfuros (Pb-Zn-Cu) y óxidos de Cu y Mn utilizando el sistema de información geografica ArcGIS. La concentración natural de fondo para cada elemento correspondió a concentraciones menores al percentil 80 y los valores anómalos a concentraciones mayores que el promedio más dos desviaciones estándar. A las concentraciones intermedias (valores no-anómalos y > percentil 80) se les denominó concentraciones naturales enriquecidas. Las distribuciones de concentraciones naturales, naturales enriquecidas, y anómalas presentaron un patrón de distribución diferente para cada elemento. Un patrón de comportamiento común a los tres elementos fue la relación entre concentraciones anómalas y la presencia de depósitos minerales. Los valores de fondo naturales y enriquecidos se pueden utilizar como base en el monitoreo de cambios en la composición química del área resultantes de actividades mineras y agrícolas, mientras que la identificación de concentraciones anómalas se debe considerar como lugares en donde contaminación está ocurriendo a mayor escala y donde se requiere de algún tratamiento de contención o remediación de contaminantes. DOI: https://doi.org/10.54167/tecnociencia.v2i2.73

Nitrate concentration in most aquifers in arid and semi-arid areas has increased in the past several decades as a result of human activities. Under the predominantly oxic conditions of these aquifers, denitrification is inhibited, allowing nitrate, a soluble and stable form of nitrogen (N), to accumulate. Because of its close association with municipal and agricultural wastes, nitrate is commonly used as an indicator of anthropogenic contamination. Aquifers affected by agricultural waste may contain salts from irrigation returns and herbicides in addition to nitrates. Preventing leakage from soil to deeper parts of the aquifer is thus a priority in the sustainable management of aquifers in arid and semiarid areas. Studies report a wide range of nitrate concentrations distributed non-uniformly within the aquifer, with roughly 40% and 20% of sampled wells exceeding 50mg/L nitrate in shallow and deep parts of the aquifer respectively. In aquifers at risk of becoming contaminated, nitrate isotopes (δ15N, δ18O, Δ17O) can be used to identify the source of nitrogen as mineral or organic fertilizer, sewage, or atmospheric deposition. A variety of mathematical models (crop, hydrological, geochemical, or a combination of them) have been successful in identifying best practices that minimize N leakage without negatively affecting crop yield. In addition, field research in crop management, e.g., conservation agriculture, has yielded promising results in determining the adequate dosage and time of application of fertilizers to reduce N losses. Examples of key dryland aquifers impacted by nitrate are discussed, and some of the most pressing challenges to achieve sustainability are presented.

Aquifers in arid and semi-arid areas face great challenges, one of which is implementing a sustainable management instead of mining nearby aquifers. A further challenge is relying on scant and fragmented groundwater information. This study related water quality to land use/land cover (LU/LC) to better understand the response of two aquifers in northern Mexico, Tabalaopa-Aldama (TAB) and Aldama-San Diego (ASD), to human stresses. Fifteen wells were sampled in May, July and October of 2015. The results show a water quality variations with respect to season and to areas where LU/LC has recently changed. Contaminants of concern are As, F, and nitrate. While As and F are natural contaminants, nitrate is anthropogenic, likely a result from wastewater and/or agricultural waste discharges. A relationship between water quality and LU/LC change was observed. Each basin suffered about 46 km2 loss in rangeland between 1993 and 2012; TAB basin to urban and ASD basin to agricultural use. Besides exposing the location of contamination and type of contaminants, water quality data can be used to assess the rate at which aquifers are being degraded (or reclaimed), whereas the combination water quality - LU/LC change offers insights on potential practices that could be implemented towards sustainability.

Determination of spatial and temporal patterns of precipitation and drought remains a challenge in many arid and semi-arid regions. Generally, in these areas, precipitation measurements obtained from field stations are few or unreliable. Reanalysis precipitation data has opened up new large-scale hydrological application in data-sparse or ungauged catchments. This study presents a method based on GIS, statistical tests, and satellite-based precipitation for the analysis of spatial and temporal precipitation and drought trends. As a case study, we used 35 years (1979–2013) of precipitation data from the climate forecast system reanalysis (CFSR) for the Mexican state of Durango. For trend detection, we used the statistical test of Mann–Kendall at 5% standard precipitation index timescale of 12 months (SPI-12) to analyze the spatiotemporal trends of drought, and principal component analysis (PCA) was applied to characterize the spatial patterns. In many of the grid locations analyzed, the precipitation trends were not statistically significant. However, the months within winter and spring, except for June, showed a decreasing trend in precipitation, while the months of July, August, and September showed an increasing trend. This variation in rainfall intensity agrees with the climate pattern reported for this region. The frequency of drought events for each month during the period of analysis was mapped. The incidence of drought events was higher in June and September. Drought events are present all around the state of Durango, but they are more frequent in the northern part, in the Sierra Madre Occidental, Mapimi, and Laguna regions.

The increase in the change of land use in many areas has resulted in an excessive extraction of groundwater, often in volumes that exceed the total recharge in the underlying aquifers. These are expected to be accentuated by climate change. Monitoring and regulating aquifers is a challenging task, especially in developing countries where data are scarce. Over an 11-year interval, the water level (WL) and water quality in wells of three contiguous aquifers in Northern Mexico were measured. An actual average WL drop rate of 2.012 m year−1 rendered unsustainable considering that the area receives 0.35 m year−1 and negligible horizontal flows. Agricultural land use increased fivefold in the last few years at the expense of rangeland, increasing 11.7–76.2% in the three aquifers, and producing a water demand threefold the aquifer recharge. The permanent presence of As and F above guidelines in several wells makes communities vulnerable to ingestion toxicity. The results of this study stress the inability of these aquifers to supply additional water to a large city nearby and the need of immediate corrective actions, e.g., promoting water-efficient irrigation, artificial aquifer recharge, and an efficient and sustained management policy.

The Tri-State Mining District (TSMD) of Kansas, Missouri, and Oklahoma was a world class zinc (Zn) and lead (Pb) producer. Mining ceased in the 1950s, leaving behind a large amount of mine wastes. Although much of the affected areas have been remediated, stream sediments may still contain toxic levels of these metals. The mobility of the metals was determined for sediment samples from Turkey Creek, Missouri. The median values of the metal content were 2700 mg/kg Zn, 161 mg/kg Pb, and 10.8 mg/kg Cd. These concentrations marginally surpass the sediment quality guidelines that differentiate between toxic and nontoxic conditions. Mobility was determined by sequential extraction of two phases&mdash, bioavailable and Fe-oxides. The fraction of the metal available to biota was 7.7% for Zn, 5.0% for Cd, and 0.4% for Pb, whereas the Fe-oxide fraction retained 25% of Zn, 21% of Pb, and 35% Cd. These values roughly agree with the values reported for other areas of the TSMD. Fractionation provides an estimate of the amount of metal available at the present conditions and gives the amount of metal available should the pH and/or Eh vary. The methodology puts an emphasis on ecosystem health and can be applied to other areas where Zn&ndash, Pb concentrations in soils and sediments are a concern.

Lead and zinc (PbZn) mines are a common occurrence worldwide; and while approximately 240 mines are active, the vast majority have been abandoned for decades. Abandoned mining wastes represent a serious environmental hazard, as Pb, Zn and associated metals are continuously released into the environment, threatening the health of humans and affecting ecosystems. Iron sulfide minerals, when present, can form acid mine drainage and increase the toxicity by mobilizing the metals into more bioavailable forms. Remediation of the metal waste is costly and, in the case of abandoned wastes, the responsible party(ies) for the cleanup can be difficult to determine, which makes remediation a complex and lengthy process. In this review, we provide a common ground from a wide variety of investigations about concentrations, chemical associations, and potential mobility of Pb, Zn and cadmium (Cd) near abandoned PbZn mines. Comparing mobility results is a challenging task, as instead of one standard methodology, there are 4-5 different methods reported. Results show that, as a general consensus, the metal content of soils and sediments vary roughly around 1000mg/kg for Zn, 100 for Pb and 10 for Cd, and mobilities of Cd>Zn>Pb. Also, mobility is a function of pH, particle size, and formation of secondary minerals. New and novel remediation techniques continue to be developed in laboratories but have seldom been applied to the field. Remediation at most of the sites has consisted of neutralization (e.g. lime,) for acid mine discharge, and leveling followed by phytostabilization. In the latter, amendments (e.g. biochar, fertilizers) are added to boost the efficiency of the treatment. Any remediation method has to be tested before being implemented as the best treatment is site-specific. Potential treatments are described and compared.

Lead and zinc mining was booming in the early 1900s in and near Joplin, Missouri, a town within the Tri-State Mining District, USA. After the ore became depleted, mining companies moved out, leaving a profoundly disturbed land. Presently, over 90% of the land has been remediated. We collected sediment samples along two creeks flowing through the historically contaminated area that have been identified as major contributors of metals to downstream reservoirs, Center Creek (14 samples) and Turkey Creek (30 samples). Sediment metal content was determined by aqua regia extraction, the potentially bioavailable fraction by 0.11 M acetic acid extraction, and toxicity by &Sigma, PEC-QCd,Pb,Zn. Zinc and lead content in sediments were high in both creeks notwithstanding remediation actions, e.g., median concentrations of 521 mg/kg Pb and 5425 mg/kg Zn in Center Creek, corresponding to 19 and 52 times the background concentration. The metals&rsquo, distribution followed no discernible pattern downstream. The potentially bioavailable fraction varied between 0.36% (Pb, Center Creek) and 4.96% (Zn, Turkey Creek). High toxicity was found in 40% of the samples in Turkey Creek and 78.5% of the samples in Center Creek. While this level of toxicity would likely affect aquatic organisms, its limited mobility under alkaline conditions suggests a lesser threat to humans. On the other hand, this high toxicity will likely persist in sediments for at least a few decades, based on their high metal content and low mobility.

Arsenic and fluoride in drinking water present a significant challenge to public health worldwide. In this study, we analyze the results of one of the largest surveys of drinking water quality in Mexico: 14,058 samples from 3951 sites, collected between January and December 2017. We use these data to identify the distribution and possible origin of arsenic and fluoride in drinking water throughout the country, and to estimate the associated health burden. The highest concentrations appear in alluvial aquifers in arid northern Mexico, where high-silica volcanic rock likely releases both arsenic and fluoride to the groundwater. We find fluoride contamination to be significantly correlated with aridity (Pearson correlation = -0.45, p = 0.0105), and also find a significant difference in fluoride concentrations between arid and humid states (Welch's t-test, p = 0.004). We estimate population exposure by assigning to each town in Mexico the average concentration of any sampling sites within 5 km. Our results show that 56% of the Mexican population lives within 5 km of a sampling site, 3.05 million people are exposed to fluoride above the reference dosage of 0.06 mg/(kg ∗ day), 8.81 million people are exposed to arsenic above the limit of 10 μg/L, and an additional 13,070 lifetime cases of cancer are expected from this arsenic exposure alone. This burden of disease is concentrated in the arid states of north-central Mexico.

Water used for irrigation is a leading source of induced salinity in semiarid areas. Within the Irrigation District 005 in northern Mexico, there are more than 100 dairy farms housing over 72,000 dairy cows, 74% of which are concentrated in approximately 30 intensive-operation farms. Dairy farm effluents (DFE) and manure are collected and stored temporarily until they are applied to the land to fertilize pasture and other crops. DFE vary in salt content, depending on specific farm operations. The risk of soil salinization by DFE was estimated by measuring electrical conductivity (EC) of both well water and DFE, and comparing these values with 2.0 mS cm&minus, 1, a Mexican guideline for wastewater used in agriculture. Half of the effluents exceeded the EC limit, with values as high as 12.4 mS cm&minus, 1, whereas a few exceeded the EC limit in both well and effluent water. The generation of salt and its passing into soils expose a potential for soil salinization, if preventive measures are not taken. A salt load map was created that depicted the areas at higher risk of salinization. The simple technique utilized here can be applied in estimating salinization potential in areas where monitoring of soils, irrigation drains, and shallow groundwater is infrequent.

Purpose Four locations in southwest Missouri, USA, purportedly contaminated with mining wastes, Joplin, Aurora, Springfield, and the James River, were investigated for lead and zinc content using spatial distribution and statistical analyses. Lead (Pb) and zinc (Zn) concentrations in streambed sediment samples were compared spatially against a regional background concentration map to determine both the contamination level and dispersion of these metals.

The salt content of soil and water in endorheic basins within arid areas greatly restrict agricultural activities. Despite this limitation, these lands are increasingly used to accommodate new settlements and/or agricultural practices. This study focuses on the Laguna El Cuervo closed basin of northern Mexico and its underlying aquifer, which has been found to contain high concentrations of arsenic (As) and fluoride (F). The spatial distribution of As and F, their variations with time, and the impact of drought conditions and land-use changes were investigated using well data collected from a total of 27 wells in 2007, 2010, and 2011 (As data also collected in 2005). Four of these wells were used as monitoring wells. Data also included the As content of 140 surface sediments. Results showed that 54.5 % of the wells surpassed the As limit for drinking water of 0.025 mg L(-1) and that 89.0 % surpassed he F limit of 1.5 mg L(-1). Spatial analyses identified the areas in the center of the basin with the highest content of contaminants. Principal component and correlation analyses showed a co-occurrence of As and F with r = 0.55 for the 2011 data and 0.59 for the combined data. In contrast, the relationship of As and F concentrations to droughts and changes in land use were not as clearly shown, possibly because of the short time this area has been monitored. The high As and F concentrations in the groundwater may be limiting the availability of water within this basin, especially considering the greater groundwater demand foreseen for the future. Water-conservation practices, such as drip irrigation and artificial groundwater recharge, should be considered to maintain groundwater levels supportive of agricultural practices.

Several million people around the world are currently exposed to excessive amounts of arsenic (As) and fluoride (F) in their drinking water. Although the individual toxic effects of As and F have been analyzed, there are few studies addressing their co-occurrences and water treatment options. Several studies conducted in arid and semi-arid regions of Latin America show that the co-occurrences of As and F in drinking water are linked to the volcaniclastic particles in the loess or alluvium, alkaline pH, and limited recharge. The As and F contamination results from water-rock interactions and may be accelerated by geothermal and mining activities, as well as by aquifer over-exploitation. These types of contamination are particularly pronounced in arid and semi-arid regions, where high As concentrations often show a direct relationship with high F concentrations. Enrichment of F is generally related to fluorite dissolution and it is also associated with high Cl, Br, and V concentrations. The methods of As and F removal, such as chemical precipitation followed by filtration and reverse osmosis, are currently being used at different scales and scenarios in Latin America. Although such technologies are available in Latin America, it is still urgent to develop technologies and methods capable of monitoring and removing both of these contaminants simultaneously from drinking water, with a particular focus towards small-scale rural operations.

Geochemical reactions that may occur on CO2 injection into a sandstone formation in Missouri (MO) were investigated by means of geochemical modeling. Five possible injection sites were considered: two in the northwestern part of the state, two in the northeastearn part, and one in the southwestern part. The Geochemist Workbench software was used to investigate solubility trapping and mineral precipitation. Modeling was performed for two periods: an injection period of 10 yr and a postinjection period where the reactions proceeded to equilibrium. The work presented substantial challenges. Among them are uncertainty in kinetic constants for the dissolution and precipitation of minerals on CO2 injection. Model results include equilibrium values for CO2 stored via solubility trapping ranging from 49-g CO2/kg free formation water in Northeast MO to 78-g CO2/kg free formation water for Southwest MO. Mineral trapping is significantly lower, between 2.6- and 18.4-g CO2/kg free formation water. The model shows siderite and dawsonite as the major carbonate minerals formed, in this order. On a volumetric basis, northwest MO sequestration values were slightly greater than those obtained for northeast MO because of the somewhat greater depth and higher injection pressure at the injection target (Lamotte Sandstone) at the northwestern sites. However, the greater thickness of the aquifer for the northeastern sites provided overall greater sequestration capacity. Greene County was altogether unfit for sequestration because of the low total dissolved solids value of the formation water.

We evaluated the geochemical transformations that would likely occur after injecting CO2 into a sandstone formation using The Geochemist's Workbench, with the intent of simulating CO2 solution and mineral storage mechanisms. We used a hypothetical reservoir intended to closely resemble the Lamotte Sandstone in southwest Missouri, a reservoir rock found at about 600-m (1970-ft) depth, well above the recommended depth for CO2 sequestration of 800 m (2625 ft). In the absence of specific water chemistry and lithology data for this formation at the proposed injection site, the model considered two best estimates of each input parameter. Carbon dioxide (CO2) sequestered in the dissolved phase was found to range between 76.74 and 76.80 g/kg free water, and the pH dropped from 7.7 to 4.8 after a 10-yr injection period. During a 50-yr postinjection interval with no additional CO2(g) added, the model predicted the pH to rise from 4.8 to 5.3 and various minerals to precipitate, among them magnesite, nontronite-Mg, and gibbsite, as well as smaller amounts of siderite and dolomite. Magnesite, siderite, and dolomite contribute to removal of carbon. In general, the model is very flexible, allowing the user to incorporate variations in temperature, pressure, water chemistry, solid-phase mineralogy, and kinetics. Modeling steps are described here as well as the results, which are all based in 1 kg of free water. To determine the total sequestration potential, transport modeling is needed, in addition to the geochemical modeling presented here.

In many remote arid areas the scarce amount of conventional soil salinity data precludes detailed analyses of salinity variations for the purpose of predicting its impact on agricultural production. A tool that is an appropriate surrogate for on-ground testing in determining temporal variations of soil salinity is Landsat satellite data. In this study six Landsat scenes over El Cuervo, a closed basin adjacent to the middle Rio Conchos basin in northern Mexico, were used to show temporal variation of natural salts from 1986 to 2005. Natural salts were inferred from ground reference data and spectral responses. Transformations used were Tasseled Cap, Principal Components and several (band) ratios. Classification of each scene was performed from the development of Regions Of Interest derived from geochemical data collected by SGM, spectral responses derived from ENVI software, and a small amount of field data collected by the authors. The resultant land cover classes showed a relationship between climatic drought and areal coverage of natural salts. When little precipitation occurred three months prior to the capture of the Landsat scene, approximately 15%–20% of the area was classified as salt. This is compared to practically no classified salt in the wetter years of 1992 and 2005 Landsat scenes.

The authors introduced polar science in a fourthgrade classroom by means of 3 hands-on activities that addressed (1) the melting of glaciers and ice, (2) the differences between the North and the South Pole, and (3) the geography and landforms of Antarctica. An assessment 4 months after the original activity showed that students remembered the concepts well. The material also applies to places other than the poles and has applications in physics, meteorology, and geography.

An area near the city of Chihuahua has been traditionally irrigated with wastewater to grow forage crops. It has been hypothesized that metal levels could be found in these soils high enough to cause potential health problems to the population. The objective of this study was to determine heavy metal concentrations in different soils due to irrigation practices. Four soil types were evaluated; a soil with a past and present history of wastewater irrigation (S1), a soil with a history of wastewater irrigation until 2003 (S2), a soil with no irrigation history (S3), and a soil similar to S1 and adjacent to the river where the wastewater is transported (S11). Three soil depths were evaluated; 0-15, 15-30 and 30-50 cm. Consequently, a total of 150 soil samples were analyzed evaluating pH, EC, OM and the following elements; Na, K, Cd, Pb, Ni, Cr, Cu and Fe. The pH (P=0.000) and EC (P=0.000) were different for each soil type but no differences were noted for soil depth and the interaction. Maximum pH levels were noted in S3 with a value of 8.74 while maximum EC was observed in S1 with a value of 0.850 dSm-1. The OM level was different for soil type (P=0.000), soil depth (P=0.005) and the interaction (P=0.014). S1 and S11 obtained maximum levels of OM while minimum levels were noted in S3. Maximum OM levels were observed at the 0-15 cm depth followed by the 15-30 cm depth and finally at the 30-50 cm depth. The highest concentration of metals was as follows: K in S1 (359.3 mg kg-1); Cd in S1 (4.48 mg kg-1); Pb in S11 (155.83 mg kg-1); Ni in S1 (10.74 mg kg-1); Cu in S1 (51.36 mg kg-1); B in S3 (41.5 mg kg-1); Fe in S3 (20,313.0 mg kg-1), Cr in S3 (44.26 mg kg-1) and Na in S3 (203.0 mg kg-1). The conclusion is that some metals are present in the soils due to anthropogenic activities but others are present in natural forms.

The objective of this study was to determine the seasonal and downstream water quality variations of the San Pedro River in Chihuahua, Mexico. Water samples were collected monthly from October 2005 to August 2006 in triplicate, totaling 165 water samples. The five sampling locations were: below the Francisco I. Madero dam (LP); between Rosales and Delicias (RD); Meoqui (M); El Torreon (ET), and Julimes (LJ). The levels of As, Be, Ca, Cd, Co, Cu, Cr, Fe, Li, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sr, Ti, Ta, V and Zn were measured using an Inductively Coupled Plasma- Optical Emission Spectrometry (ICP-OES) Perkin Elmer 2100. In addition, temperature, pH, electrical conductivity and total and fecal coliformes were determined. The statistical analysis considered a factorial treatment design; where factor A was the location point and factor B was sampling date. In addition, a multivariate technique looking for principal components was performed. The results indicated that some samples exceeded Mexican standards for As, Be, Ca, Cd, Co, Cr, Fe, Mn, Ni, Pb, Sb, Se, Sr and Zn. The As level must be considered for a red flag to the communities along the Rio San Pedro because both the monthly average level (0.10 mg L-1) and location (0.10 mg L-1) exceeded the Mexican and International norms. The multivariate analysis showed a predominant aggregation at the LP location, meaning that there was a predominance of As, Sr, Fe and Li. At the rest of the locations the elements did not present a tendency for aggregation. Statistics applied to sampling month showed that December, January, March and April were aggregated in a negative quadrant of component 1 indicating a predominance of V, Ni, Be, Fe and As. Overall, the results confirmed that this stretch of the San Pedro River is contaminated with heavy metals and other contaminants that might affect human health as well as the health of the ecosystem.