Geochemistry and 14C dating of guano deposits in the Karaftu Cave, Kurdistan, Iran: implication for paleoenvironment.

Karaftu Cave in the northwest of Divandareh includes four floors plus an underground area. The bat hall and its underground area are covered with guano deposits. 14C dating indicates the onset of guano deposition is about 14,260±50 BP years, and its average accumulation rate is about 4.1 mm/yr for depths of 360 to 205 cm. Bacterial and fungal metabolisms decay guano, release acids, and disperse large amounts of microorganisms inside the cave. Interactions between acids and guano caused leaching, dissolution, change in the distribution, and abundance of elements, which leads to the formation of secondary minerals in guano. These variations in minerals and elements also depend on the local climatic conditions. Distribution of elements in the Ce/Ce* versus Pr/Pr* diagram and the correlation coefficient between Ce and Mn display three different paleoclimate conditions (dry, wet, and dry) during the accumulation of the guano. Also, dolomite, phosphate, and iron oxide minerals have been formed during the passage of water through bedrock beneath the guano. This water is unsuitable for drinking and harmful to the organisms in the region. Effect of these acids on the substrate also leads to the collapse of the cave floor, generation of a new underground, fall in the groundwater level, change in the groundwater drainage system, drying of springs around the cave, loss of green cover, and a negative impact on the ecosystem in the region. To keep the cave environment clean and remove these problems, it is better to harvest guano and use it as fertilizer.

210Pb geochronology and metal concentrations in sediment cores recovered in the Alvarado Lagoon system, Veracruz, Mexico.

Three sediment cores recovered from the Alvarado Lagoon System (ALS) in the Gulf of Mexico were used to reconstruct the history of metals and metalloids and their environmental importance. The sedimentary profiles were dated with 210Pb and verified with 137Cs. Maximum ages of 77 and 86 years were estimated. Sediment provenance was described by sedimentological and geochemical proxies. The chemical alteration index (CIA) and weathering index (CIW) revealed moderate to high intensity of weathering in the source area that is controlled tropical climatic conditions, runoff, and precipitation in the basin that feeds sediments to this coastal lagoon. The Al2O3/TiO2 ratios indicated that the sediments were derived from intermediate igneous rocks. The enrichment factor values revealed the lithogenic and anthropic contribution of metals and metalloids. Cd is classified under the category extremely severe enrichment; agricultural activities, fertilizers, herbicides, and pesticides containing Cd are expected to supply this metal to the ecosystem. Factor Analysis and Principal Components provided two main factors, terrigenous and biological origins; ANOVA indicated that there are significant differences between the cores for the parameters analyzed and revealed that there are differences in depositional environments between the recovery zones of the cores. The ALS presented natural variations associated with the climatic conditions, terrigenous input, and its relationship with the hydrological variations of the main rivers. The contribution of this work was to identify the magnitude of the natural component versus the human contribution, mainly of risk metals such as Cd, to support better management of the hydrological basin that affects the ALS.

Abundance and composition of microplastics in Tampico beach sediments, Tamaulipas State, southern Gulf of Mexico.

The abundance and characteristics of microplastics (MPs) in coastal sediments from the Tampico beach, Gulf of Mexico was investigated. The MPs were extracted by a density separation method with saturated solutions of NaCl and ZnCl2, the sediment-solution relationship was 1:3. MPs were classified according to its shape, color, and size under a stereoscopic microscope. Identification of MPs surface was carried out by a Scanning Electron Microscope (SEM). The polymer types were detected by a Fourier-transformed infrared (FTIR) Spectroscopy. Number of MPs in 20 g of sediments varies from 256 to 283 particles. The average abundance of MPs per kg was inferred as ∼13,392 microplastic particles. Fiber was the only MP particle identified in the Tampico beach, its size varied from 1.76 mm to 3.92 mm. Fibers identified were mostly transparent, blue, white, black, multicolor, yellow, pink, and red. Six different polymers were identified, i.e., polyester (PES), polyethylacrylate (PEA), cellophane, polyacrylonitrile (PAN), polystyrene acrylonitrile (SAN), and polyvinyl acetate ethylene (PVAE). PES is the most prevalent polymer in all samples.

Biogeochemical behaviour of cadmium in sediments and potential biological impact on mangroves under anthropogenic influence: A baseline survey from a protected nature reserve.

Cadmium is a toxic element and its effects are well understood for human health, but its biogeochemical behaviour is still poorly studied and understood in natural ecosystems. This work addresses knowledge gaps concerning its presence, biogeochemical behaviour and impacts in mangrove ecosystems. Through geochemical data and multivariate analysis (i.e., factor and cluster analysis) of data from mangroves of Isla del Carmen, one of the largest extents in Mexico we explored the biogeochemical behaviour of Cd, a potentially toxic element, to identify its anthropogenic sources and interactions with sediments. Pollution indices, including enrichment factor (EF), geo-accumulation index (Igeo), sediment quality guidelines (SQG) and toxicological studies were used to assess the biological impacts of Cd and infer the natural levels tolerated by mangrove trees that form the basis of this natural ecosystem. Our results highlighted that Cd accumulation is driven by interactions between organic matter (OM), sulphur and fine particles; whereas enrichment factor showed values of 6.9 (EF) and 3.5 (EF) associated with point sources and ranged between 2 and 2.9 (EF) in relation to non-point sources. Finally, our geochemical approach revealed that Cd enrichment originates from urban activities and from the poor management of urban residuals.

Textural characteristics and abundance of microplastics in Tecolutla beach sediments, Gulf of Mexico.

Abundance of microplastics in coastal sediments is considered an emerging pollution problem worldwide. In Mexico, studies focused on microplastics in coastal sediments are little. In this study, we analyzed the textural characteristics and investigated the abundance of microplastics in the Tecolutla beach sediments, SW Gulf of Mexico. The extraction of microplastics in sediments was done by density separation. Microplastics were identified by stereomicroscope and scanning electron microscopy, and were classified based on their morphology, color, length, texture, and abundance. Among 181 microplastics, fiber type is predominant (number of microplastics n = 166; 92%) and followed by film (n = 12; 6%) and fragment (n = 3; 2%) types. The most abundant color of microplastics is black (n = 81; 45%) and second dominant color is blue (n = 65; 36%); most of them are fiber type. Based on the textural characteristics of sediments, it was observed that microplastics were derived from the fluvial contribution of the Tecolutla River and were deposited in the coastal environment by ocean currents. This study revealed that the abundance of microplastics was high in fine-grained sediments and was directly proportional to skewness. The results of this study can act as a reference for understanding the abundance of microplastics in the Gulf of Mexico coastal sediments.

Environmental risk of trace elements in mangrove ecosystems: An assessment of natural vs oil and urban inputs.

The petrochemical industry and urban activities are widely recognized worldwide as a source of pollution to mangrove environments. They can supply pollutants such as trace elements that can modify the ecosystem structure and associated services, as well as human populations. Through geochemical data, multivariate statistical analysis and pollution indices such as the enrichment factor (EF), geo-accumulation index (Igeo), adverse effect index (AEI) and the pollution load index (PLI), we evaluated the factors that control trace element distribution, punctual sources and determined the pollution level of sediments and their potential biological impact in the mangrove ecosystem of Isla del Carmen, Mexico. The factor and cluster analysis highlighted that the distribution of trace elements is influenced by the mineralogy, texture as well as urban derived sources. The pollution indices showed values in the punctual sources from the urban area of EF > 10, Igeo > 3, AEI > 3, PLI > 1 by Cu, Zn and Pb. Finally, the results revealed that mangroves from Isla del Carmen has a major influence from urban activities and natural sources rather than oil industry and also indicate a degraded environment as a result of anthropogenic activities that could have knock-on effect for human health if polluted marine organisms derived from the urban mangroves are consumed. CAPSULE ABSTRACT: Surface sediments show the influence of point sources on selected trace element concentrations correlated with human activities within the mangroves of Isla del Carmen, Mexico.

Textural and geochemical characteristics of marine sediments in the SW Gulf of Mexico: implications for source and seasonal change.

Two oceanographic cruises were taken during the winter (SAV I, November and December 2007) and summer (SAV II, July and August 2008) across the mouth of the Papaloapan River in the Gulf of Mexico. Surficial sediment samples were collected from shallow (16-30 m), intermediate (30 to 80 m), and deeper areas (≥300 m). Shallow water sediments are coarser, better-sorted, and primarily composed of sands during the winter, while those found in the summer are finer. At depths greater than 30 m, sediments are primarily fine-grained no matter the season. Major element analysis from shallow areas indicates higher SiO2 concentrations during the windy season with negative correlation against Al2O3 during both seasons, following the respective abundances of sand and muds. High organic carbon content was observed in shallow areas during the summer. Trace metals V, Ni, Cu, Zn, Pb, Li, Cr, Co, and Ba were evaluated. The first six metals showed higher average concentration in the deeper areas, although the highest values at some individual sampling sites for Cr, Co, Cu, and Ba were observed in the coastal area. Factor and cluster analysis were used to explain the sediment distribution pattern and the factors that determine the sediment characteristics within the study area. In shallow areas, four clusters were observed during the winter and five during the summer. The geochemical characteristics of the samples in each cluster suggest association with fluvial sediment input, textural characteristics, heavy minerals, and Cu and Ba concentration. To evaluate the variations in heavy metal concentration, metal enrichment factors (EFs) were calculated. Enrichment in V, Cr, Co, Zn, Ba, and Pb was detected at certain sites, whereas Cu behaved differently. The distribution of Cu enrichment suggests that it may be of natural origin, associated with the lithology of the volcanic continental area. The minor enrichment observed for other elements may be associated with river discharge. According to sediment quality guidelines, trace metal concentrations of Cu, Pb, and Zn present occasional risks to aquatic organisms.