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Although mangrove forests are great carbon sinks, they also release carbon dioxide (CO2) from soil, plants, and water through respiration. Many studies have focused on CO2 effluxes only from soils, but the role of biogenic structures such as pneumatophore roots has been poorly studied. Hence, CO2 effluxes from pneumatophores were quantified at sediment-air (non-flooded sediment) and water–air (flooded sediment) interfaces along a salinity gradient in three mangrove types (fringe, scrub, and basin) dominated by Avicennia germinans during the dry and rainy seasons in Yucatan, Mexico. Pneumatophore abundance explained up to 91% of CO2 effluxes for scrub, 87% for fringe, and 83% for basin mangrove forests at the water–air interface. Overall, CO2 effluxes were inversely correlated with temperature and salinity. The highest CO2 effluxes were in the fringe and the lowest were in the scrub mangrove forests. Flooding decreased CO2 effluxes from the dry to the rainy season in all mangrove forests. These results highlight the contribution of pneumatophores to mangrove respiration, and the need to include them in our current carbon budgets and models, but considering different exchange interfaces, seasons, and mangrove ecotypes. [ABSTRACT FROM AUTHOR]

Copyright of Ecosistemas y Recursos Agropecuarios is the property of Universidad Juarez Autonoma de Tabasco and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The data set represents the Regional Meteoric Water Line (RMWL) for the Yucatan Peninsula (Mexico), a region with karstic aquifers but little knowledge of the isotopic composition of meteoric water. This data paper comprises the isotopic composition of meteoric water collected from November 2018 to November 2019 as monthly composite samples expressed as weighted monthly mean precipitation from 16 locations across the Yucatan Peninsula. The RMWL was δ2H = 7.803 δ18O + 12.075, with a slope and intercept suggesting precipitation from air that has undergone condensation, air masses with variable moisture or recycled moisture. The average δ18O is −2.57‰ (−12.23 to 1.2‰) and δ2H is −7.94‰ (−83.39 to 18.32‰). This data set was collected by the implementation of an isotopic monitoring network, gathering information useful as a tool for better understanding of the hydrology and hydrogeochemistry of karstic aquifers, and to develop proxies for paleohydrology, ecohydrology, climate change and paleoclimate studies in the Gulf of Mexico and the Great Caribbean Area. [ABSTRACT FROM AUTHOR]

Copyright of Ecosistemas y Recursos Agropecuarios is the property of Universidad Juarez Autonoma de Tabasco and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Tecnología y Ciencias del Agua is the property of Instituto Mexicano de Tecnologia del Agua (IMTA) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Stored carbon varies among wetlands, yet they rank among the highest carbon accumulating ecosystems. Leaf litter production and aboveground carbon storage are frequently used as proxies for estimating primary productivity, which can be affected by flooding, salinity and other environmental factors. The objective of this study was to quantify leaf litter production and soil carbon density in two coastal tropical wetland types, namely mangrove swamps and forested freshwater wetlands. Water and soil physicochemical properties, together with leaf litter production, were measured bimonthly between 2007 and 2009 in wetlands of both types, located on the coast of the Gulf of Mexico. The soils ranged from entirely mineral to entirely organic in the top metre. Mangrove sites had relatively uniform hydroperiods and moderately reductive soils, whereas forested freshwater wetlands had reducing conditions. Electrical conductivity was lower and pH less acidic in forested freshwater wetland soils. Litterfall was around 1000 g m-2 yr-1 and annual production did not differ significantly between wetlands, despite the presence of acidic soils with prolonged flooding and high salinity in the mangrove swamps. Also, there were no consistent differences in soil carbon density between the two wetland types. Some forested freshwater wetlands had low litter production and high soil carbon density, whereas some mangrove swamps had high litter production and low soil carbon density. We present information regarding aboveground biomass turnover and belowground carbon storage in coastal tropical forested wetlands which is greatly needed to support us in understanding, valuing and conserving these neglected ecosystems. [ABSTRACT FROM AUTHOR]

Epilithon is a taxonomically diverse assemblage of aquatic organisms which grow on rocks; this biological compartment is involved in several reactions that contribute to the dynamics of dissolved organic nitrogen in water. Using ceramic tiles colonized in an urban river, this experimental study assessed the relative importance of ammonium uptake by inhibiting nitrification blocking ammonium oxidation with acetylene, as well it tested the hypothesis that epilithon preferentially assimilated ammonium over nitrate. In our experiments, ammonium uptake by epilithon accounted for 46% - 100 % of the ammonium decrease in the water column, whereas nitrate uptake accounted for 0% - 11% of the nitrate decrease. Ammonium uptake rates ranged from 197 to 519 µmol N-NH4 + m-2 h-1, while nitrate uptake rates were from 47 to 85 µmol N-NO3 - m-2 h-1. The rate of preferential assimilation (RPI) was between 1.15 and 1.26, indicating preference for ammonium over nitrate. The results of this research provide valuable information regarding the relative contribution of algal uptake relative to nitrification in epilithon from an urban river. [ABSTRACT FROM AUTHOR]

Highlights • The δ 15N of submerged biomass is correlated to changes in the quality of wastewater treated effluent. • A two sources simple mixing model for NH 4 + and NO 3 − was explored for estimating DIN assimilation. • N isotopic fractionation (α assimilation) in macrophytes was estimated between 1.005 and 1.012. • The δ15N of submerged biomass can be used complementarily to water quality monitoring. Abstract We measured the changes in concentration and isotopic composition of the two major dissolved inorganic nitrogen species (ammonium and nitrate) and the isotopic composition of submerged biomass, in order describe the changes in the nitrogen cycling at a river receiving treated effluent before and after upgrades at a wastewater treatment plant in southwestern Ontario (Canada). We observed that changes in the δ 15N of macrophytes and periphyton are correlated to changes in the quality of treated effluent. We explored two scenarios, differential assimilation of dissolved nitrogen species without isotopic fractionation using a two end-member mixing model, and isotopic fractionation due to assimilation (α assimilation) in macrophytes. The two end-member mixing model suggested different contribution per N specie, and α assimilation was estimated to be around 1.005 and 1.012 before and after upgrades, respectively. Thus, we provided evidence that the δ15N of submerged biomass can be used as a proxy for in-stream nitrogen cycling and complementary to water quality monitoring for evaluating changes in the nitrogen cycling in urban catchments. [ABSTRACT FROM AUTHOR]

This paper examines the nitrogen isotope fractionation factors (α) associated with the volatilisation of ammonia from water under controlled conditions at two pH values (8.5 and 9.2). This experiment assumed the continuous removal of ammonia at a single purge rate of 10 mL air min−1. The fractionation resulting from the removal of total ammonia from the water into an acid trap was named the observed isotope fractionation factor (αobs), and it was measured as 1.019 (±0.0025) at pH 8.5 and 1.030 (±0.0025) at pH 9.2. The observed isotope fractionation factor includes the equilibrium isotope fractionation factor (αeq) and the kinetic isotope fractionation factor (αkin), each one mathematically derived from the experimental data. The equilibrium and kinetic isotope fractionation factors were estimated as αeq = 1.036 (±0.0014) and αkin = 1.050 (±0.003), respectively. Our results are compared to other previously measured and estimated fractionation factors. [ABSTRACT FROM AUTHOR]

Sinkholes are common karst forms were we can access the aquifer. This study describes an 85 m deep sinkhole in north Quintana Roo (Mexico), located at 45 km from the coast, allowing us to explore an open section of the aquifer. The profile of the water column was realized to evaluate the physical chemistry, hydrochemistry and water isotopes (δ2H, δ 18O and 3H) in order to distinguish the stratification. It was identified water-rock interaction (limestone) in the upper section (0–40 m), typical from karst groundwater; a mixing zone approximately 10 m thick, and saline intrusion in the deep section (50–80 m). Salinization of the freshwater was observed, likely due to diffusion of sodium and chloride from the deep water. The hydrochemistry suggests seawater intrusion contributing as much a 60% of the water in the deep section. With the stable isotopes, meteoric water, groundwater and seawater mixing was attested. The tritium measurements suggest that the aquifer has short residence time and fast recharge. Few deep sinkholes in Mexico have been studied, the information obtained in Yumkin contributes to the knowledge and understanding of the Yucatan aquifer system. [Display omitted] • Meteoric water, groundwater and seawater mixing occurs in an 85 m deep sinkhole. • Seawater intrusion is about 60% at 80 m. • Tritium suggest fast groundwater recharge and short residence time. • Data contributes to a better understanding and long-term aquifer management. [ABSTRACT FROM AUTHOR]

The Grand River (Ontario, Canada) is impacted by wastewater treatment plants (WWTPs) that release ammonia (NH3 and NH4 +) into the river. In-river microbial communities help transform this ammonia into more oxidized compounds (e.g., NO3 - or N2), although the spatial distribution and relative abundance of freshwater autotrophic ammonia-oxidizing prokaryotes (AOP) are not well characterized. This study investigated freshwater N cycling within the Grand River, focusing on sediment and water columns, both inside and outside a WWTP effluent plume. The diversity, relative abundance, and nitrification activity of AOP were investigated by denaturing gradient gel electrophoresis (DGGE), quantitative real-time PCR (qPCR), and reverse transcriptase qPCR (RT-qPCR), targeting both 16S rRNA and functional genes, together with activity assays. The analysis of bacterial 16S rRNA gene fingerprints showed that the WWTP effluent strongly affected autochthonous bacterial patterns in the water column but not those associated with sediment nucleic acids. Molecular and activity data demonstrated that ammonia-oxidizing archaea (AOA) were numerically and metabolically dominant in samples taken from outside the WWTP plume, whereas ammonia-oxidizing bacteria (AOB) dominated numerically within the WWTP effluent plume. Potential nitrification rate measurements supported the dominance of AOB activity in downstream sediment. Anaerobic ammonia-oxidizing (anammox) bacteria were detected primarily in sediment nucleic acids. In-river AOA patterns were completely distinct from effluent AOA patterns. This study demonstrates the importance of combined molecular and activity-based studies for disentangling molecular signatures of wastewater effluent from autochthonous prokaryotic communities. [ABSTRACT FROM AUTHOR]

The study of forest hydrology and its relationships with climate requires accurate estimates of water inputs, outputs, and changes in reservoirs. Evapotranspiration is frequently the least studied component when addressing the water cycle; thus, it is important to obtain direct measurements of evaporation and transpiration. This study measured transpiration in a tropical dry deciduous forest in Yucatán (Mexico) using the thermal dissipation method (Granier-type sensors) in representative species of this vegetation type. We estimated stand transpiration and its relationship with allometry, diameter-at-breast-height categories, and previously published equations. We found that transpiration changes over time, being higher in the rainy season. Estimated daily transpiration ranged from 0.562 to 0.690 kg m–2 d–1 in the late dry season (April–May) and from 0.686 to 1.29 kg m–2 d–1 in the late rainy season (September–October), accounting for up to 51% of total evapotranspiration in the rainy season. These daily estimates are consistent with previous reports for tropical dry forests and other vegetation types. We found that transpiration was not species-specific; diameter at breast height (DBH) was a reliable way of estimating transpiration because water use was directly related to allometry. Direct measurement of transpiration would increase our ability to accurately estimate water availability and assess the responses of vegetation to climate change. [ABSTRACT FROM AUTHOR]