Northwest Mexico Research Articles

Estructura y diversidad de un matorral dominado por Helietta parvifolia (A. Gray ex Hemsl.) Benth.

Helietta parvifolia es una especie de importancia económica en el norte de México, ya que es una fuente potencial de madera y leña para usos diversos. El objetivo del presente estudio fue evaluar la estructura y diversidad de un matorral maduro de H. parvifolia en el noroeste de México. Se determinó la diversidad de la vegetación mediante el establecimiento de 20 sitios de muestreo de 10 × 10 m cada uno (2 000 m² en total), en donde se registraron las especies, el diámetro normal y de copa de todos los árboles y arbustos con un diámetro ≥ 3 cm. Se calcularon los índices de Margalef, Shannon y Pretzsch para determinar la riqueza, diversidad de especies y estructura vertical, respectivamente. Se registraron 11 especies arbóreas y arbustivas, distribuidas en nueve géneros y seis familias. Fabaceae fue la que registró un mayor número de taxones (cinco); mientras que las familias restantes presentaron solamente un taxón. Tres especies concentraron 82.59 % de los valores de índice de valor de importancia (IVI): Helietta parvifolia, Cordia boissieri y Havardia pallens, con 53 %, 15.44 % y 14.15 %, respectivamente. La mayor abundancia de individuos de clases diamétricas pequeñas sugiere la existencia de un estado de regeneración activo.

Building bridges not walls: the past, present, and future of international collaboration and research in northwest Mexico

Building bridges not walls: the past, present, and future of international collaboration and research in northwest Mexico

Tree Ring‐Based Historic Hydroclimatic Variability of the Baja California Peninsula

AbstractThe Baja California Peninsula is one of the most arid regions in Mexico, receiving an average of only 168 mm of precipitation annually. Climate change scenarios project drier and warmer conditions in the region at the end of this century driven by anthropogenic emissions of greenhouse gases. The growing demand for limited water supplies and the impacts of climate change pose a challenge to manage the already scarce water resources in the Peninsula. Analysis of historical hydroclimatic variability in the Peninsula is limited because most of the early instrumental climate data collection started only in the 1950s. In this study, we reconstruct past precipitation variability for the Peninsula using two tree ring chronologies from northern (Pinus monophylla) and southern (Pinus lagunae) Baja California. Our two reconstructions document multicentury hydroclimatic variability in the Peninsula, including events that turned out to be more extreme than those captured by modern instrumental records. Drought episodes are longer, more frequent, and more intense in the northern peninsula compared to the southern region. Multiyear dry and wet events in our two reconstructions exhibit broad spatial extent, affecting most of northwest Mexico and the western United States, which are mainly caused by broad‐scale atmospheric circulation patterns such as El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). The results of this study allow framing current and projected droughts in a longer‐term context, thus providing a better understanding of past climate variability and a basis for robust water resource management in the region.

Estimation of Solar Resource Based on Meteorological and Geographical Data: Sonora State in Northwestern Territory of Mexico as Case Study

A model developed at the University of Tomsk, Russia, for high latitudes (over 55° N) is proposed and applied to the analysis and observation of the solar resource in the state of Sonora in the northwest of Mexico. This model utilizes satellite data and geographical coordinates as inputs. The objective of this research work is to provide a low-cost and reliable alternative to field meteorological stations and also to obtain a wide illustration of the distribution of solar power in the state to visualize opportunities for sustainable energy production and reduce its carbon footprint. The model is compared against real-time data from meteorological stations and satellite data, using statistical methods to scrutinize its accuracy at local latitudes (26–32° N), where a satisfactory performance was observed. An annual geographical view of available solar radiation against maximum and minimum temperatures for all the state municipalities is provided to identify the photovoltaic electricity generation potential. The outcomes are proof that the model is economically viable and could be employed by local governments to plan solar harvesting strategies. The results are generated from an open source model that allows calculating the available solar radiation over specific land areas, and the application potential for future planning of solar energy projects is evident.

Razas fisiológicas de Puccinia triticina E. identificadas en el norte de Sinaloa y resistencia de germoplasma

La roya de la hoja causada por Puccinia triticina E. es la enfermedad más importante en el norte y noroeste de México. En el norte de Sinaloa está ampliamente distribuida en las zonas de producción de trigo del Valle del Fuerte y Valle del Carrizo; sin embargo, se desconoce que razas están incidiendo en dicha región. El objetivo fue identificar las razas fisiológicas de roya de la hoja, que se presentan en las principales zonas productoras del norte de Sinaloa e identificar germoplasma con resistencia. Durante el ciclo de cultivo otoño-invierno 2018-2019, se colectaron 50 muestras de roya de la hoja de lotes experimentales y comerciales, dichas muestras se trasladaron al Lanarec. Con la técnica de monopostulares, se realizó la identificación de razas. Posteriormente con las razas más frecuentes se evaluaron bajo condiciones de invernadero y por su resistencia en plántula y planta adulta 35 genotipos de trigo harinero. Se identificaron siete razas fisiológicas de roya de la hoja (CBJ/QQ, MBT/SP, MCT/SP, MGJ/SP, MBJ/SP, MBJ/QQ, MFJ/SP), de las cuales la CBJ/QQ se identificó con mayor frecuencia (29%). De los 35 genotipos evaluados con las razas CBJ/QQ y MCT/SP, se determinó que CONATRIGO F2015 y las líneas CHEWINK #1/MUTUS//MUTUS*2/HARIL#1 y MUTUS*2//ND643/2*WBLL1/3/BORL14 fueron resistentes en plántula y planta adulta a las dos razas, lo que indica que posee al menos un gen de resistencia efectivo a roya de la hoja. La resistencia genética es una de las alternativas de manejo sustentable más viable para el control de las royas del trigo en México.

Knowledge, Attitudes, and Practices Related to Rocky Mountain Spotted Fever in Hermosillo, México.

Rocky Mountain spotted fever (RMSF) is a serious disease in northwest Mexico, particularly in low-income communities. This study aimed to evaluate RMSF-related knowledge, attitudes, and practices in an endemic urban area with a high burden of the disease. A cross-sectional study design using a non-probabilistic household survey was conducted with 400 residents in Hermosillo, Mexico. Primary themes assessed included dog and tick-related exposure, RMSF knowledge, healthcare-seeking behavior, sociodemographic data, and household information. The majority (59%) of those surveyed had heard about RMSF, although only 36% of RMSF-aware respondents knew any RMSF symptoms. Among RMSF-aware respondents, 26% did not know or were unsure of prevention strategies. Individuals in the low socioeconomic status (SES) stratum were less likely to have heard about RMSF (odds ratio [OR]: 0.39; 95% CI: 0.25-0.59), use dog collars or any other product to avoid ticks (OR: 0.40; 95% CI: 0.17-0.99), or check their dogs for ticks (OR: 0.25; 95% CI: 0.09-0.74). The likelihood of observing high numbers of free-roaming dogs in their neighborhood was four times higher in the low SES stratum (OR: 4.19; 95% CI: 2.10-8.38) than in the high SES stratum. These findings emphasize the need for an integrative community approach to improve early recognition of symptoms and knowledge of prevention strategies, particularly in low SES neighborhoods.

Nestosanos en Guadalajara. Triunfo y decadencia de un grupo privilegiado, 1780-1836

Este artículo pretende mostrar cómo los naturales de Lanestosa (Vizcaya) durante el último cuarto del siglo XVIII fueron capaces de crear una importante red de paisanaje en la ciudad novohispana de Guadalajara, hasta convertirse en un grupo privilegiado que alcanzó el éxito económico y social, personificado en la figura de Juan Manuel Caballero. La inestabilidad que conllevó la Insurgencia debilitó su papel protagónico, por lo que muchos nestosanos decidieron regresar a la península con la intención de reemprender sus vidas. Para ello, nos hemos servido de la correspondencia inédita del comerciante asentado en Cádiz Francisco de Carranza, y que además nos ha permitido descubrir aspectos inéditos de la vida de Francisco Martínez Negrete antes de que se convirtiera en uno de los hombres más relevantes del noroccidente mexicano decimonónico.

Mercury and selenium concentrations in the crab Callinectes arcuatus from three coastal lagoons of NW Mexico.

Mercury and selenium concentrations and Se:Hg molar ratio in edible muscle and hepatopancreas of the crab Callinectes arcuatus from coastal lagoons of northwest Mexico were determined using atomic absorption spectrophotometry. The three coastal lagoons were Santa María La Reforma (SMLR), Urías (UR), and Huizache-Caimanero (HC); samplings were carried out from December 2016 to October 2017. The mercury ranges in the muscle of C. arcuatus in SMLR, UR, and HC lagoons were 0.31-0.52, 0.15-0.45, and 0.22-0.55 μg g-1, respectively. In hepatopancreas, the values ranged from 0.08 to 0.15, 0.06 to 0.15, and 0.05 to 0.12 μg g-1 in SMLR, UR, and HC lagoons, in that order. For selenium concentrations in C. arcuatus muscle, the ranges 11.64-20.14, 14.88-19.71, and 15.27-29.51 μg g-1 were determined in SMLR, UR, and HC lagoons, respectively. While for hepatopancreas, the ranges were 34.34-44.13, 27.77-40.45, and 15.16-49.80 μg g-1, in that order. No significant relationships (p > 0.05) between mercury and selenium concentrations (in white meat and hepatopancreas) were observed in C. arcuatus carapace width and length. Se:Hg molar ratio values were 98.1 ± 20.8, 171.4 ± 81.6, and 176.8 ± 51.2 for SMLR, UR, and HC lagoons, in that order. This high ratio (> 1) in C. arcuatus edible muscle indicated that selenium concentration was sufficient to neutralize possible mercury toxicity, so it does not represent danger to humans when it is consumed.

Parameterization of the AquaCrop model for simulating table grapes growth and water productivity in an arid region of Mexico

Currently, the AquaCrop model has been widely tested for many fruit/grain crops; root and tuber crops; leafy vegetables, or forage crops, but is restricted to annual herbaceous species, while deciduous crops have received less if no attention. In this context, this study aims to test for the first time the ability of the AquaCrop model to simulate canopy cover (CC), actual evapotranspiration (ETa), total soil water content (TWC), biomass (B) and fruit yield (FY) of table grapes vineyards (Vitis vinifera L., cvs. Perlette and Superior) at the Costa de Hermosillo, Sonora in Northwest Mexico. Observed weather and soil physical parameters, with measured crop parameters from an experiment conducted during 2005 were used to develop climate, soil and crop input files for AquaCrop and for calibrating the model. While collected data during the 2006 growing season were used to validate the model. The model adequately simulated CC, ETa and TWC during 2005 and 2006. The Root Mean Square Error (RMSE) between observed and measured CC, ETa and TWC were 5.18%, 0.46 mm/day and 10.11 mm during 2005, and 8.82%, 0.84 mm/day and 9.1 mm during 2006, respectively. The good accuracy of simulations of CC, ETa and TWC by the model have been confirmed by additional statistical parameters like the coefficient of determination (R2), The Mean Bias Error (MBE), the Willmott’s index of agreement (d) and the Nash–Sutcliffe Efficiency (NSE).For the B and FY simulations, the results showed that the model correctly reproduced the B and FY with NRMSE value of 8.8%. The estimated average value of FY (14.56 t/ha) for both seasons are in the range of the potential yield (14–18 t/ha) of table grapes in the irrigated Costa de Hermosillo in northwest Mexico.After the validation of the AquaCrop model, it was used to evaluate the irrigation scheduling by the farmer as well as to assess the water productivity computed as the ratio of crop production to crop water use. The results showed that, the recommended irrigation by the model was about 547 mm and 509 mm, which it is about half of that applied by the farmer (1006 mm and 929 mm) during 2005 and 2006, respectively. This large difference, which represents approximately 54% and 57% of the irrigation supply, is lost through deep percolation and could be saved without vegetation suffering from water stress while maintaining the same yield. The high loss of water by percolation affects significantly the water productivity (WP), which decreases from 3.22 to 1.74 kg/m3 if we consider the transpiration (WPTr), and the sum of ETa and Percolation (WPETa+Pr) for WP computations, respectively. Consequently, the AquaCrop model can be used as an operational tool by decision makers and growers to improve irrigation management. This is of crucial importance in arid and semi-arid regions where water is becoming increasingly scarce.

Isotopic variability (δ18O, δ2H and d-excess) during rainfall events of the north American monsoon across the Sonora River Basin, Mexico

The economic activities of the Sonora strongly depend on groundwater extraction, which is generally of recent meteoric origin. Understanding the hydrological functioning in this semi-arid region, located in northwestern Mexico, is crucial for integrated water management in a changing climate. This study presents a spatio-temporal analysis of the isotopic composition (δ18O, δ2H, d-excess) during the 2018 rainy season in the Sonora River Basin (SRB), a region influenced by the characteristic weather conditions of the North American Monsoon (NAM). The basin is located in the central region of Sonora and covers an area of approximately 27,000 km2. Precipitation was collected using six passive totalizers, distributed spatially from the coast of the Gulf of California up to 1,425 m asl inland. The rainfall isotopic composition is comparable with the Global Meteoric Water Line (GMWL) and with the records of the Global Isotope Network in Precipitation (GNIP) in Chihuahua, Mexico, between 1962 and 1988, and Tucson, Arizona (2018). The temporal variability of rainfall isotope ratios was Δ18O = 7.4‰ and Δ2H = 49.8‰, with a clear depletion pattern (low δ18O) as the monsoon rainy season progressed. The isotopic lapse rate was found to be −1.0‰ in δ18O per km of elevation as a result of the topography relief and rainout effects within the basin. The influence of tropical cyclones such as Hurricane Sergio (October 2018) provided the opportunity to isolate the effects of a tropical storm with respect to the deep convective precipitation, typical of the NAM systems over northwest Mexico.

Molecular Characterization of Norovirus Circulating in Northwest Mexico During 2013-2014.

Norovirus (NoV) is an important etiological agent of diarrhea in children and adults. In Mexico, NoV screening is not routinely performed. NoV is highly infectious and is responsible for massive outbreaks due to the consumption of contaminated food. The study was a cross-sectional design. Samples of diarrheal stools were collected from (62) children and (38) adults with acute gastroenteritis during 2013-2014. The circulating genogroups of NoV were detected by amplifying the RdRp gene fragment, and for the genotyping, the capsid and polymerase fragments were sequenced. Seventy-seven percent of the analyzed samples were positive for NoV. Genotyping was possible for 51 samples; for polymerase GII.P2, GII.P31, GII.P4, GII.P7, GII.P40, and GI.P14 were identified, whereas for capsid, genotypes GI.3, GII.2, GII.4, GII.5, GII.14, and GII.17. In conclusion, there is a high prevalence of gastroenteritis due to NoV in the northwest of Mexico, including genotypes that have not been reported previously in Mexico.

Assessment of heavy metal pollution of drain sediments in the urban area of Mexicali, Mexico

The valley of Mexicali is one of the most important agricultural areas in the northwest of Mexico. Rapid urbanization has meant that parts of the agricultural channels and drains now lie within the urban area. To evaluate the concentrations of heavy metals in urban drain sediments, thirty-one samples were collected in the Mexicali urban area. Mean concentrations of Cd, Cu, Cr, Fe, Ni, Pb and Zn were 0.28, 70.0, 17.0, 4.48 × 10 .4, 13.5, 32.3 and 229 mg kg− 1, respectively. The geoaccumulation index results indicated that most of the drain sediments were from unpolluted to slightly polluted by heavy metals for most of the sites, with the exception of Cu which had seven sites Class 3, two sites Class 4 and two sites Class 5 and 6, respectively. Similarly, the enrichment factors showed that most of the sites had minimum enrichment.

Optimizing phenotyping methods to evaluate lodging risk for wheat

• Screening lodging traits for lodging resistance is key for wheat improvement. • Screening seven plants per plot is enough to find genetic variation for lodging traits. • Four key lodging traits can be measured to estimate lodging performance in wheat. Lodging is a complex phenomenon affecting wheat production worldwide and is a consequence of the interaction of wheat plants with abiotic (wind, rain, etc.) and biotic (e. g. plant disease, etc.) factors. Wheat breeders rely heavily on incidences of natural lodging to select lines with resistance; however, the intermittent nature of lodging events means this approach is unreliable. A model of the lodging process has been published to estimate the lodging susceptibility of plants that uses information from 15 stem and root characteristics of field grown plants that influence lodging. This approach estimates lodging susceptibility in the absence of natural lodging. However, the main shortcoming of this methodology for plant breeders is the amount of time required to measure these traits (100–150 min per plot). This study investigated two strategies to optimise the methods of estimating lodging risk in the absence of natural lodging: i) determining the minimum number of plants that must be measured per experimental plot (sample size) to identify genetic differences and ii) minimizing the number of traits required to assess lodging susceptibility increasing the feasibility to apply the methodology in a breeding context. Spring wheat grown under North West Mexico environmental conditions was established during four crop seasons (2010−11, 2011−12, 2012−13 and 2013−14) for this study. Results indicated an optimum sample size of seven plants per plot as the minimum required to identify genetic differences between cultivars with good statistical power and precision (assuming each treatment plot was replicated 3 times). Cultivar ranking and absolute values for trait dimensions were maintained when compared with larger sample sizes. A reduced number of traits can be used to estimate cultivar lodging susceptibility performances and key traits include: plant height, ear number per plant, ear area, natural frequency, breaking strength, length, diameter and wall width of one basal internode, structural rooting depth and root plate spread. Targeting these key traits, this study established that on a daily basis, 10 (47 min per plot) plots can be assessed by measuring seven plants per plot per person. Moreover, if the screening focuses only on the key traits for leverage/stem/root dimensions, then the daily plot assessment capacity would increase to 25.

La Caridad Vieja: Vestiges of a removed HS-epithermal system in the La caridad porphyry Cu–Mo system, northeastern sonora, Mexico, based on XRD, SEM, SWIR spectral analysis and U–Pb zircon dating

The present work contributes with new data to better understand the geology and spatial distribution of the alteration and mineralization events, as well as new U–Pb zircon ages, that allow elucidating the magmatic history of the La Caridad Vieja mineral deposit, which is part of the porphyry Cu–Mo system from La Caridad mine, northwest Mexico. Mineralization is hosted in a sequence of volcanic rocks from the Late Cretaceous-Paleocene Tarahumara Formation and is associated with the emplacement of quartz monzonite stocks, which intruded to volcanic rocks. Detailed studies based on petrography, XRD, SEM and SWIR, indicate that the La Caridad Vieja is characterized by a zone of phyllic alteration dominated by qz-ser in the deepest parts, and it is associated with molybdenite + chalcopyrite + pyrite + galena + sphalerite, with values ranging from 0.1 to 0.9% Cu and <0.02% Mo. Above the phyllic alteration zone, there is an intermediate argillic alteration zone (quartz + kaolinite + halloysite + smectite + illite), mainly with pyrite. In specific areas, advanced argillic alteration is observed (alunite + pyrophyllite + dickite + kaolinite + halloysite) accompanied by pyrite + enargite + famantinite + barite. The new U–Pb radiometric ages in zircons indicate an age of 54.71 ± 0.39 Ma for the upper part of the Tarahumara Formation, while a sample of the mineralizing stock yielded 51.95 ± 0.48 Ma. The results of this investigation suggest that La Caridad Vieja corresponds to a portion of the upper part of the Cu–Mo porphyry of La Caridad, which was downthrown by the La Caridad fault, during the Basin and Range extensional event in the Miocene. The reconstruction of the geological model suggests that La Caridad Vieja corresponds to the transitional zone between the Cu–Mo porphyry and an epithermal high sulfidation mineralization zone, which was eroded. Prior to the dislocation caused by the La Caridad fault, the eroded area was covered by a ferruginous conglomerate overlain by rhyolite flows dated at ~24 Ma. On the other hand, geochronological data suggests that the mineralizing event at La Caridad Vieja, although it is contemporaneous with the porphyry system of the La Caridad mine, it continued in this area at least until ~52 Ma.

Genetic, textual, and archeological evidence of the historical global spread of cowpea (Vigna unguiculata[L.] Walp.)

AbstractCowpea (Vigna unguiculata[L.] Walp.) was originally domesticated in sub‐Saharan Africa but is now cultivated on every continent except Antarctica. Utilizing archeological, textual, and genetic resources, the spread of cultivated cowpea has been reconstructed. Cowpea was domesticated in Africa, likely in both West and East Africa, before 2500 BCE and by 400 BCE was long established in all the modern major production regions of the Old World, including sub‐Saharan Africa, the Mediterranean Basin, India, and Southeast Asia. Further spread occurred as part of the Columbian Exchange, which brought African germplasm to the Caribbean, the southeastern United States, and South America and Mediterranean germplasm to Cuba, the southwestern United States, and Northwest Mexico.

Spatial distribution of soil carbon storage in desert shrubland ecosystems of northwest Mexico

The scarce information about soil carbon (C) storage in water-stressed ecosystems limits our understanding on soil contribution to the C cycle in arid zones. This study, performed in arid NW México: (i) estimated soil capacity to store organic C (SOC) and inorganic C (SIC) linked to topography; (ii) determined the spatial distribution of regional SOC stocks; and (iii) analysed if different land-uses affect the C:N ratio. Contents of SOC from different landforms and land uses varied from <0.2 to ~45 Mg ha−1; shallow mountain soils and alluvial plains showed the minimum and maximum values, respectively, underlying the topography relevance to soil depth. The SIC varied from <0.05 to ~32 Mg ha−1, highlighting inorganic C storage. With SOC content data and environmental databases, this study achieved the regional spatial distribution of SOC stocks (0–30 cm) by predicting modelling. The average SOC stock (0–30 cm) was estimated in 25 ± 9.9 Mg ha−1 for the region. Changes in land-use from natural conditions apparently reduced N content, varying C:N ratio from 7.90 to 13.68 and reflecting the importance of land management. The results confirmed the value of arid soils to store C and their contribution to global C and N cycles.

A Multicriteria Assessment of Vulnerability to Extreme Rainfall Events on the Pacific Coast of Mexico

The likely increase in extreme rainfall events (ERE) due to climate change, particularly associated with tropical storms and hurricanes, threatens coastal communities worldwide. A model based on socioeconomic and environmental indicators was used to assess and categorize vulnerability to ERE at the municipal level, in Sinaloa, a coastal state of northwest Mexico. Coastal vulnerability was assessed based on a system of indicators, integrated into five criteria within two higher categories: response capacity (Economic conditions, Social development, and Living standards), and severity (Geographic exposure and Risk intensifiers). From a preliminary set of 25 indicators, three of them were selected by criterion using the Delphi method, and their values were later standardized from 0 (low) to 1 (high) on a vulnerability scale. Both criteria and indicators were weighted following an analytical hierarchical process (AHP), resulting in the main determinants of vulnerability being Geographic exposure (0.43) and Economic conditions (0.34). This first approach to a vulnerability assessment using standardized values showed that Guasave (to the north) and Escuinapa (to the south) are the most vulnerable municipalities, scoring >9.0 (with 15 being the maximum score). In contrast, Culiacán and San Ignacio, both central municipalities, ranked as the least vulnerable (<5.5). A further analysis using the integral vulnerability index (IVI) corroborated Guasave (3.73) and Escuinapa (3.15) as the most vulnerable, discarding latitudinal changes as a possible promotor of vulnerability. Although the coastal population was the main determinant of vulnerability (median = 0.57), other indicators associated with severity as well as response capacity were responsible for the increase in IVI scores. This study highlights the need for an integrated vulnerability analysis to support public policies and the decision-making process to protect coastal communities from environmental climate change.

Stakeholder diversity correlates with governance network performance in two artisanal fisheries in Northwest Mexico

The sustainability of fisheries depends not only on the condition of the fish stock but also on the complex interrelationships of stakeholders. In this study, we employed network analysis to study the social structure of governance in two fisheries in Northwest Mexico. We selected two artisanal fisheries that are well-known to serve as examples of successful and less effective governance: the red spiny lobster fishery (RLF) and the swimming crab fishery (SCF), respectively. We built two networks that represent the relationships between stakeholders in each fishery. We found that stakeholders with higher levels of centrality are more diverse in the RLF compared with the SCF. We also found that the RLF has characteristics of a more collaborative network with subgroups with a high diversity of stakeholders, which is in contrast with the SCF. Additionally, given the similarity of stakeholders' roles in the RLF, more stakeholders are able to play roles currently played by other stakeholders, which is in contrast to the SCF, where the roles are more divided. These results helped to elucidate the structure of governance networks and the stakeholder's roles, highlighting that the different levels of governance efficiency are related to stakeholder diversity.

Abundance and harvest strategy of three species of clam (Bivalvia: Veneridae) located in new fishing banks in the Gulf of California

Clams of the family Veneridae in northwest Mexico have traditionally been exploited by small-scale fisheries. Despite their socioeconomic importance for coastal communities in the region, most catch zones are currently in decline due to a lack of harvest control regulations that would impede the depletion of local fishing banks. In Puerto Libertad, in the northern reaches of the Gulf of California, banks of commercially unexploited clam species, including Megapitaria aurantiaca, M. squalida and Dosinia ponderosa, were discovered. The adequate management and exploitation of these banks requires developing basic knowledge regarding the abundance of the species and establishing reference points to determine clear, simple harvest regulations. The goal of this study was to identify population abundance in these banks and ascertain the parameters of the life history of the species found there in order to propose a harvest strategy that will allow the sustainable exploitation of this resource. A total of 288 transects were conducted in the two clam banks to identify species density. Abundance was determined using a geostatistical method. The relative cohort biomass-at-length was estimated to evaluate the effect of different lengths of first capture on the remaining biomass. Based on these data, two harvest control regulations were proposed: a maximum catch (Cmax) of 10% of the total estimated biomass, and a minimum optimal catch size (Lc). The abundance estimates were M. squalida (266,293–381,881 individuals); D. ponderosa (2,779,100–3,455,597); and M. aurantiaca (408,783–447,391). The harvest control regulations proposed are: M. squalida, Cmax = 2.98 t and Lc = 50.33 mm; D. ponderosa, Cmax = 49.67 t and Lc = 103.44 mm; and M. aurantiaca, Cmax = 15.87 t and Lc = 80.85 mm. These results are important as reference information for implementing harvest strategies in clam-fishing banks, and as a contribution to the management and sustainable exploitation of fisheries in the region.

Precipitation of secondary phases of iron and its role in controlling the mobility of potentially toxic elements in soils in a semiarid river basin in Northwest Mexico

Soils have the ability to retain potentially toxic elements (PTEs) through different chemical processes that promote low mobility of these elements, such as the precipitation of secondary phases of Fe, which facilitate the adsorption/co-precipitation of PTEs. The main objective of this study was to evaluate the mobility of PTEs present in an acid solution in two soils with different concentrations of calcite, understanding the role of secondary iron phases in the retention of these elements. To evaluate this phenomenon, intact soil columns of two different types of soils from the Sonora River in Northwest Mexico were exposed to an acid solution with high concentration of dissolved PTEs (mainly Fe, Al, and Cu). The Tinajas soil was free of carbonates while the Bacanuchi soil had more carbonate content than the Tinajas soil. Secondary precipitates corresponding to secondary phases of iron (mainly ferrihydrite and jarosite) were identified by X-ray diffraction. Using scanning electron microscopy, the PTEs retained in the soils were identified. The presence of calcite favored the neutral pH values in the collected leachates in the Bacanuchi soil; consequently, the mobility of the PTEs present in the acid solution was nullified. Furthermore, this process facilitated the retention of the toxic elements in the Bacanuchi soil. The retention of PTEs was 100% in the Bacanuchi soil where the natural acid-neutralizing capacity in this soil was associated with calcite. The formation of secondary phases of Fe, among them ferrihydrite, jarosite, and schwertmannite, mainly in Bacanuchi soil, promoted the retention of Al, As, Cd, Cu, Fe, Mn, and Pb (elements analyzed in this work). Results of this work can provide key insights to improve cleanup and conservation strategies in mining sites.