Biogeochemical Conditions Research Articles

Characterization of groundwater and cores in the decommissioned acid in-situ leach uranium mining area: Enlightenment for uranium contaminated groundwater remediation

Acid In-situ Leach (AISL) is predominant technique for uranium mining in sandstone-type deposits in China. However, its impact on the biogeochemical conditions of sandstone uranium deposits remains poorly understood. In this study, we performed detailed physicochemical analyses of groundwater, as well as mineralogical, chemical and biogeochemical analyses of cores collected from the decommissioned AISL uranium mining area in the Yili Basin, northwestern China. After AISL uranium mining, U(IV) minerals and pyrite were oxidized and dissolved. The groundwater in the AISL-mined uranium deposit (AISLMUD) became highly acidic and oxidizing after mining ceased. Pyrite, which significantly influences the migration, transformation and immobilization of uranium, was minimal in all cores. Kaolinite, chlorite, quartz, K-feldspar, albite and muscovite exhibited poor adsorption capacity of U(VI) under strong acid conditions. The AISLMUD demonstrated limited capacity to retain U(VI) under highly acid conditions. Furthermore, high-throughput sequencing analysis revealed a substantial reduction in both microbial diversity and abundance in the cores. Microorganisms associated with U(VI) reduction were detected in the cores, with the exception of sulfate reduction bacteria. However, the results of microbial incubation showed that U(VI) reduction-related bacteria could not be in-situ activated by the addition of electron donors under the environmental stresses induced by prolonged acid in-situ leaching. These findings cast doubt on the feasibility of remediating uranium-contaminated groundwater with a pH below 3 through in-situ activation of U(VI) reduction-related bacteria. This research holds significant implications for evaluating the suitability of existing methods and developing new approaches for the restoration of AISLMUD.

CO2 and CH4 Concentrations in Headwater Wetlands Influenced by Morphology and Changing Hydro-Biogeochemical Conditions

Headwater wetlands are important sites for carbon storage and emissions. While local- and landscape-scale factors are known to influence wetland carbon biogeochemistry, the spatial and temporal heterogeneity of these factors limits our predictive understanding of wetland carbon dynamics. To address this issue, we examined relationships between carbon dioxide (CO2) and methane (CH4) concentrations with wetland hydrogeomorphology, water level, and biogeochemical conditions. We sampled water chemistry and dissolved gases (CO2 and CH4) and monitored continuous water level at 20 wetlands and co-located upland wells in the Delmarva Peninsula, Maryland, every 1–3 months for 2 years. We also obtained wetland hydrogeomorphologic metrics at maximum inundation (area, perimeter, and volume). Wetlands in our study were supersaturated with CO2 (mean = 315 μM) and CH4 (mean = 15 μM), highlighting their potential role as carbon sources to the atmosphere. Spatial and temporal variability in CO2 and CH4 concentrations was high, particularly for CH4, and both gases were more spatially variable than temporally. We found that groundwater is a potential source of CO2 in wetlands and CO2 decreases with increased water level. In contrast, CH4 concentrations appear to be related to substrate and nutrient availability and to drying patterns over a longer temporal scale. At the landscape scale, wetlands with higher perimeter:area ratios and wetlands with higher height above the nearest drainage had higher CO2 and CH4 concentrations. Understanding the variability of CO2 and CH4 in wetlands, and how these might change with changing environmental conditions and across different wetland types, is critical to understanding the current and future role of wetlands in the global carbon cycle.

Functional effects of subsidies and stressors on benthic microbial communities along freshwater to marine gradients.

Leaf litter in coastal wetlands lays the foundation for carbon storage, and the creation of coastal wetland soils. As climate change alters the biogeochemical conditions and macrophyte composition of coastal wetlands, a better understanding of the interactions between microbial communities, changing chemistry, and leaf litter is required to understand the dynamics of coastal litter breakdown in changing wetlands. Coastal wetlands are dynamic systems with shifting biogeochemical conditions, with both tidal and seasonal redox fluctuations, and marine subsidies to inland habitats. Here, we investigated gene expression associated with various microbial redox pathways to understand how changing conditions are affecting the benthic microbial communities responsible for litter breakdown in coastal wetlands. We performed a reciprocal transplant of leaf litter from four distinct plant species along freshwater-to-marine gradients in the Florida Coastal Everglades, tracking changes in environmental and litter biogeochemistry, as well as benthic microbial gene expression associated with varying redox conditions, carbon degradation, and phosphorus acquisition. Early litter breakdown varied primarily by species, with highest breakdown in coastal species, regardless of the site they were at during breakdown, while microbial gene expression showed a strong seasonal relationship between sulfate cycling and salinity, and was not correlated with breakdown rates. The effect of salinity is likely a combination of direct effects, and indirect effects from associated marine subsidies. We found a positive correlation between sulfate uptake and salinity during January with higher freshwater inputs to coastal areas. However, we found a peak of dissimilatory sulfate reduction at intermediate salinity during April when freshwater inputs to coastal sites are lower. The combination of these two results suggests that sulfate acquisition is limiting to microbes when freshwater inputs are high, but that when marine influence increases and sulfate becomes more available, dissimilatory sulfate reduction becomes a key microbial process. As marine influence in coastal wetlands increases with climate change, our study suggests that sulfate dynamics will become increasingly important to microbial communities colonizing decomposing leaf litter.

First Insight into the Mobilization and Sequestration of Arsenic in a Karstic Soil during Redox Changes.

Karst terrains provide drinking water for about 25% of the people on our planet, particularly in the southwest of China. Pollutants such as arsenic (As) in the soil can infiltrate groundwater through sinkholes and bedrock fractures in karst terrains. Despite this, the underlying mechanisms responsible for As release from karst soils under redox changes remain largely unexplored. Here, we used multiple synchrotron-based spectroscopic analyses to explore As mobilization and sequestration in As-polluted karstic soil under biogeochemical conditions that mimic field-validated redox conditions. We observed that As in the soil exists primarily as As(V), which is mainly associated with Fe(oxyhydr)oxides. The concentration of the dissolved As was high (294 μM) and As(III) was dominant (∼95%) at low Eh (≤-100 mV), indicating the high risk of As leaching under reducing conditions. This As mobilization was attributed to the fact that the dissolution of ferrihydrite and calcite promoted the release and reduction of associated As(V). The concentration of the dissolved As was low (17.0 μM) and As(V) was dominant (∼68%) at high Eh (≥+100 mV), which might be due to the oxidation and/or sequestration of As(III) by the recrystallized ferric phase. Our results showed that the combined effects of the reductive release of As(V) from both ferric and nonferric phases, along with the recrystallization of the ferric phase, govern the redox-induced mobilization and potential leaching of As in soils within karst environments.

Significant temporal variability leads to estimation bias in greenhouse gas emissions from aquaculture pond systems

Rising demand for aquatic products has expanded aquaculture, significantly elevating greenhouse gas (GHG) emissions from the aquaculture ponds. However, the emission estimation shows huge uncertainty. This study employed a meta-analysis of 1060 datasets of CO2, CH4 and N2O fluxes to examine how temporal variability affects GHG emissions from China's aquaculture ponds and to identify key environmental drivers. The results reveal that China’s aquaculture ponds are significant sources of GHGs to the atmosphere, with fluxes of CO2, CH4, and N2O from coastal pond systems at 5.50, 7.41 mg m² h⁻¹, and 16.72 μg m² h⁻¹ during the farming period, and −8.96, 4.33 mg m² h⁻¹, and 44.98 μg m² h⁻¹ during the non-farming period, respectively. Regarding inland pond systems, the fluxes of CO2, CH4, and N2O were 50.48, 5.19 mg m² h⁻¹, and 36.35 μg m² h⁻¹ during farming period, and 0.90, 1.03 mg m² h⁻¹, and 51.46 μg m² h⁻¹ during non-farming period, respectively. Total GHG annual emissions were 42.17 Tg CO2-eq over a 100-year time scale, predominantly from CH4 at 74.11 %, with CO2 contributing to 9.63 %, and N2O to 6.63 %. Post-cultivation drainage significantly shifts biogeochemical conditions and emission patterns, reducing total GHG emissions. Ignoring the non-farming period leads to overestimated CO2 and CH4 emissions, and underestimated N2O emissions. Our study provides new insights into GHG estimation from aquaculture ponds, highlighting the importance of considering temporal variability in GHG inventories, and supporting the development of management-based mitigation strategies.

Biogeochemical conditions controlling the intensity of paralytic shellfish poisoning (PSP) outbreak caused by Alexandrium blooms: Results from 6-year field observations in Jinhae-Masan Bay, Korea

Previous field observations from 2018 to 2019 revealed that paralytic shellfish poisoning (PSP) caused by the blooms of toxic dinoflagellate Alexandrium species occurred under low concentrations of dissolved inorganic nitrogen (DIN) and high concentrations of dissolved organic nitrogen (DON) and humic-like fluorescent dissolved organic matter (FDOMH) in Jinhae-Masan Bay, Korea. In this study, we obtained more data for DIN, DON, FDOMH, and Alexandrium cell density from 2020 to 2023 to further validate environmental conditions for the PSP outbreak. We also measured total hydrolyzed amino acids (THAA) to determine the bioavailability of DON fueling the PSP outbreak. Over the 6-year observations, there was a consistent pattern of low DIN concentrations and high DON and FDOMH concentrations during the PSP outbreak periods. The Alexandrium cell densities, together with the PSP toxin concentrations, increased rapidly under this environmental condition. The PSP outbreak occurs when a large amount of DIN originating from the stream waters near the upstream sites is transformed into DON by biological production before entering the PSP outbreak area. The produced DON is characterized by high bioavailability based on the various AA-derived indices (enantiomeric ratio, degradation index, non-protein AA mole%, and nitrogen-normalized AA yield). In addition, the intensities of PSP outbreaks are mainly dependent on the conversion stage of DIN to DON and enhanced FDOMH. We found that the strong PSP outbreak occurred consistently under a low level of DIN (<1.0 μM) and high levels of DON (>9.0 μM) and FDOMH (>1.5 R.U.). Thus, our results suggest that the monitoring data of environmental conditions can be used to predict the PSP outbreak in the coastal oceans.

Stability and transformation of jarosite and Al-substituted jarosite in an acid sulfate paddy soil under laboratory and field conditions

Jarosite, a prominent mineral in oxidised acid sulfate soil, is known to sorb and incorporate a variety of elements, including Al. However, to understand the role that jarosite plays in regulating element cycles, it is crucial to understand the stability and transformation pathways of jarosite in an acid sulfate soil under dynamic biogeochemical conditions. In this study, we observed the transformation of unsubstituted jarosite and Al-substituted jarosite, collectively referred to as ‘jarosite’, in an acid-sulfate rice paddy topsoil and subsoil from Thailand. Jarosite was incubated in flooded paddy topsoils and subsoils for up to sixteen weeks, both in laboratory mesocosms and in the field, using bags made of polyethylene terephthalate mesh. One set of mesh bags contained jarosite that was not mixed with any other minerals, and referred to as ‘pure mineral’ incubations. Mineral transformations occurred under the influence of the soil porewater only and were primarily followed by X-ray diffraction analysis. A parallel set of mesh bags contained soil with 57Fe-labelled jarosite enrichment (Fe enriched in soil by a factor of 1.3 but 57Fe enrichment factor of 12.5–13.6), which allowed jarosite transformation to occur in close association with the soil matrix. Mineral transformations in 57Fe-jarosite-enriched soil were followed using 57Fe Mössbauer spectroscopy. In laboratory mesocosms and in the field, jarosite transformed most quickly in topsoil, whereas jarosite underwent limited transformation in subsoils, especially in laboratory mesocosms where Fe reduction was slow. The chemical environment around the jarosite affected the outcome of the transformation processes. Crystalline Fe oxyhydroxides, such as goethite, dominated the products in mesh bags where jarosite was not mixed with soil, whereas short-range-ordered or non-mineral Fe phases, such as Fe(II) sorbed to mineral surfaces or complexed with organic ligands, were dominant transformation products of jarosite when mixed in soil. Furthermore, Al substitution in jarosite caused contrasting effects in mesh bags containing pure minerals or mineral-enriched soil. Aluminium substitution slowed the transformation of jarosite in pure mineral mesh bags, but Al-substituted and unsubstituted jarosite showed similar transformation rates and pathways when incubated as a mixture with soil. The contrasting rate of transformation in topsoil and subsoil, the contrasting products of transformation in pure mineral mesh bags and 57Fe-jarosite-enriched soil, and the contrasting effect of Al substitution in pure mesh bags or jarosite-enriched soil, all demonstrate that the rate and products of jarosite transformation are defined by a balance between competitive transformation pathways that affect the transforming minerals.

Pyrite-stimulated bio-reductive immobilization of perrhenate: Insights from integrated biotic and abiotic perspectives

Microbes possessing electron transfer capabilities hold great promise for remediating subsurface contaminated by redox-active radionuclides such as technetium-99 (99TcO4−) through bio-transformation of soluble contaminants into their sparingly soluble forms. However, the practical application of this concept has been impeded due to the low electron transfer efficiency and long-term product stability under various biogeochemical conditions. Herein, we proposed and tested a pyrite-stimulated bio-immobilization strategy for immobilizing ReO4− (a nonradioactive analogue of 99TcO4−) using sulfate-reducing bacteria (SRB), with a focus on pure-cultured Desulfovibrio vulgaris. Pyrite acted as an effective stimulant for the bio-transformation of ReO4−, boosting the removal rate of ReO4− (50 mg/L) in a solution from 2.8 % (without pyrite) to 100 %. Moreover, the immobilized products showed almost no signs of remobilization during 168 days of monitoring. Dual lines of evidence were presented to elucidate the underlying mechanisms for the pyrite-enhanced bio-activity. Transcriptomic analysis revealed a global upregulation of genes associated with electron conductive cytochromes c network, extracellular tryptophan, and intracellular electron transfer units, leading to enhanced ReO4− bio-reduction. Spectroscopic analysis confirmed the long-term stability of the bio-immobilized products, wherein ReO4− is reduced to stable Re(IV) oxides and Re(IV) sulfides. This work provides a novel green strategy for remediation of radionuclides- or heavy metals-contaminated sites.

Long-Term Dynamics of Major Ion Concentrations in the Water of Lake Teletskoe Tributaries in the Context of Biogeochemical Conditions in Their Drainage Basins

Long-Term Dynamics of Major Ion Concentrations in the Water of Lake Teletskoe Tributaries in the Context of Biogeochemical Conditions in Their Drainage Basins

20th century climate warming and human disturbance triggered high aquatic production and strong water-column mixing in maar Lake Xiaolongwan, northeastern China

Lake ecosystems in northeastern (NE) China are sensitive to global environmental change, and are currently under threats of eutrophication and hypolimnetic anoxia. However, the lack of long-term records of lake production and anoxia in this region makes it difficult to discriminate the impacts of recent anthropogenic activity on lake ecosystems from natural ecosystem variability. This study investigates varved sediments from remote maar Lake Xiaolongwan, NE China and reconstructs high-resolution changes in lake primary production, anoxia, nutrient cycling and catchment processes over the past 1500 years using hyperspectral imaging inferred sedimentary total chlorophyll-a and bacteriopheophytin-a (Bphe-a), combined with sedimentary iron and phosphorus fractions data. Results show that, prior to discernible human impacts in this area from ∼600 CE to 1900 CE, lake primary production was higher during warm periods and reduced during cold periods. Bphe-a records show that hypolimnetic anoxia persisted regardless of temperature variability. Cluster analysis suggests that lake algal communities and biogeochemical conditions in the twentieth-century warm period are unprecedented and significantly different from any other time over the past 1500 years. This phenomenon mostly results from global warming and stronger local catchment disturbance in the early 1900s, combined with atmospheric pollution after the 1950s. Human-driven climate warming has caused stronger seasonal mixing (due to shortened ice-cover duration) and overall better oxygenation in the lake. This study demonstrates clear anthropogenic impacts to lake ecosytems in a relatively pristine region in NE China. We anticipate that our findings will have implications for understanding the status of aquatic ecosystems in NE China under future interacting stressors of anthropogenic climate warming and pollution.

Effect of microbial growth and electron competition on nitrous oxide source and sink function of hyporheic zones

The hyporheic zones (HZs) are key sites of the production of nitrous oxide (N2O), a potent ozone-depleting greenhouse gas. Denitrification is the primary process of N2O production in HZs, including four reduction steps (NO3−→NO2−→NO→N2O→N2). Electron competition occurs between the four reduction steps and can significantly impact the production of N2O. However, denitrification was typically considered as simplified two step reactions for investigating the release of N2O, neglecting the electron competition among the four-step reactions. Moreover, the N2O production/consumption patterns are regulated by both hydraulic and biogeochemical conditions in HZs. Dynamic microbial growth cannot only mediate the biogeochemical reactions, but also change hydraulic properties spatiotemporally by bioclogging. But microbial growth is rarely considered for investigating N2O dynamics of HZs. To assess these effects on hyporheic N2O dynamics and source-sink function, we establish a novel numerical model of N2O dynamics of HZs, coupling porous flow, reactive transport, electron competition, microbial growth and bioclogging. The results show that the weak electron competitiveness of N2O reductase results in a less allocation of electrons to the N2O reduction process, particularly in situations with limited carbon sources, thus increasing the release of N2O into the rives. Microbial growth significantly influences N2O release from HZs into rivers, increasing by more than two orders of magnitude on average compared to the model neglecting microbial dynamics. In contrast to the classical knowledges that HZs in coarse sediments tending to short residence time cannot act as sources of N2O, dynamic microbial growth obviously increases the potential for N2O release from HZs in coarse sediments to the rivers. The global Monte Carlo regional sensitivity analyses indicate that microbial biomass is the most critical factor determined the hyporheic source-sink function for N2O, followed by carbon oxidation rate and residence time. These are significantly different from previous knowledge that the residence time and oxygen/nitrogen uptake rate are the most sensitive parameters, which may lead to misunderstanding of the key controlling factors of N2O release from HZs. In addition, we propose a new Damköhler number (DaO2∗) of dissolved oxygen by multiplying the classical DaO2 with a dimensionless microbial modification factor for identifying N2O source-sink function of HZs, with DaO2∗ < 1 for N2O sink, while DaO2∗ > 1 for N2O source.

Spatiotemporal investigation of geochemical and hydrological controls on release of soluble reactive phosphorus from the shallow aquifer of a riparian zone.

Phosphorus (P) that accumulates in agricultural riparian zones can be released under certain hydrological and biogeochemical conditions, thereby limiting the effectiveness of these zones in reducing P loads from field to stream. The study objective was to explore factors that may be contributing to, or limiting, high soluble reactive phosphorus (SRP) concentrations in the shallow aquifer of an alluvial upland riparian zone located in a continental climate. Field investigations including porewater sampling from six vertical nests, soil sampling, and continuous soil moisture, groundwater table, and redox measurements were conducted over 19 months. Porewater SRP concentrations were generally low in the aquifer considering all sampling times (median=14.7µg/L; interquartile range [IQR]=11.1µg/L, 287 samples). The overall low SRP may be due to low reducible labile soil P (median=21.1 µgP/g dw, IQR=10.9 µgP/g dw, 21 samples). However, high SRP concentrations(>52µg/L, 95% quartile) did occur intermittently in space and time with no clear spatial or temporal patterns. Analyses indicate that most high concentrations were likely not associated with factors previously reported to influence SRP release in riparian aquifers, including redox conditions, pH, and soil drying and wetting. Further, data indicate that internally released or externally supplied SRP may undergo rapid (re-) sequestration within the aquifer, limiting its vertical or horizontal transport. The study findings highlight the complexity of P behavior in riparian zones and the need for caution when assessing the effectiveness of conservation practices and in interpreting potential impacts of subsurface water quality on stream water quality when monitoring locations are distant from the stream.

Cracking the dynamic code of the deep: Unexpected seasonal patterns of active protistan-bacterial microbiomes in the mesopelagic zone of the South China Sea

Disentangling microbial dynamics in the mesopelagic zone is crucial due to its role in processing sinking photic production, affecting carbon export to the deep ocean. The relative importance of photic zone processes versus local biogeochemical conditions in mesopelagic microbial dynamics, especially seasonal dynamics, is largely unknown. We employed rRNA gene transcript-based high-throughput sequencing on 189 samples collected from both the photic and mesopelagic zones, along with seasonal observations, to understand the South China Sea’s protistan-bacterial microbiota diversity, drivers, and mechanisms. Mesopelagic communities displayed unexpectedly greater seasonal but less vertical dynamics than photic counterparts. Temperature, dissolved oxygen, nutrients, and bacterial abundance drove mesopelagic communities vertically. Photic zone processes (using net community production and mixed layer depth as proxies) of past seasons, coinciding with strong monsoon periods, shaped seasonal fluctuations in mesopelagic communities, indicating a time-lag effect. Furthermore, certain microbes were identified as indicators for beta diversity by depth and season. This investigation deepens our understanding of how and why mesopelagic communities vary with season and depth. Recognizing the time-lagged effect of photic zone processes on mesopelagic communities is crucial for understanding the current and future configurations of the ocean microbiome, especially in the context of climate change and its effect on carbon export and ocean storage.

Fungal diversity in sediments of the eastern tropical Pacific oxygen minimum zone revealed by metabarcoding.

Oxygen minimum zones (OMZ) represent ~8% of the ocean, with the Pacific as the largest and top expanding area. These regions influence marine ecosystems, promoting anaerobic microbial communities. Nevertheless, only a fraction of microbial diversity has been studied, with fungi being the less explored component. So, herein we analyzed fungal diversity patterns in surface and subsurface sediments along a bathymetric transect using metabarcoding of the ITS1 region in the OMZ of the Mexican Pacific off Mazatlán. We identified 353 amplicon sequence variants (ASV), within the Ascomycota, Basidiomycota, and Rozellomycota. Spatial patterns evidenced higher alpha diversity in nearshore and subsurface subsamples, probably due to temporal fluctuations in organic matter inputs. Small-scale heterogeneity characterized the community with the majority of ASV (269 ASV) occurring in a single subsample, hinting at the influence of local biogeochemical conditions. This baseline data evidenced a remarkable fungal diversity presenting high variation along a bathymetric and vertical transects.

Marine Phosphate Level During the Archean Constrained by the Global Redox Budget

AbstractUnderstanding the oceanic phosphate concentration is critical for understanding marine productivity and oxygen evolution throughout Earth history. During the Archean, estimates of marine phosphate levels range from scarce to enriched conditions. However, biogeochemical conditions required for sustaining high phosphate concentrations while retaining an anoxic atmosphere during the Archean remain ambiguous. Here, we employ a biogeochemical model of the marine phosphate cycle to determine the conditions under which oceanic phosphate levels could have been higher than present‐day values during the Archean after the emergence of oxygenic photoautotrophs (OP). We show that, under the presence of OP, phosphate‐rich oceans require the limitation by factors other than phosphate, or a high outgassing rate of reducing gases. If these conditions were not met, the occurrence of oceanic phosphate levels higher than present‐day values during the Archean would require the absence of OP.

Functions of extracellular polymeric substances in partitioning suspended and sinking particles in the upper oceans of two open ocean systems

AbstractMarine particle dynamics and carbon export, involving extracellular polymeric substances (EPS) like transparent exopolymer particles (TEP) and Coomassie Brilliant Blue‐stained particles (CSP), are poorly understood. Although TEP adhesive properties may enhance carbon export by facilitating aggregate formation, their low density can also enhance particle suspension. Factors influencing TEP regulation of particle dynamics remain unclear. To investigate EPS contributions to particle dynamics, we investigated ratios of TEP to particulate organic carbon (POC) and of CSP to POC in suspended and sinking particles collected with marine snow catchers. Samples were collected in a subarctic region near Hokkaido during a spring phytoplankton bloom and in the oligotrophic, subtropical Kuroshio region. At Hokkaido, the mean TEP : POC ratio of sinking particles (0.075 μg Xeq. : μg C) was &gt; 30× lower than in suspended particles (2.3), consistent with a model prediction of selective retention of buoyant TEP‐rich particles in the upper water column. In the Kuroshio region, sinking particles also contained fewer TEP than suspended particles; however, the TEP : POC ratio of sinking particles (1.0) was &gt; 10× higher than at Hokkaido, suggesting that TEP constitute a significant carbon component of sinking particles. These findings indicate that TEP facilitate aggregation of high‐density particles and particle sinking in the Kuroshio region. Distributions of CSP : POC ratios between suspended and sinking particles resembled TEP : POC ratios in both regions, implying a significant contribution of CSP to particle dynamics. We propose that EPS have divergent effects on suspension and sinking of marine particles, which vary with particle composition and biogeochemical conditions.

Seasonally varying biogeochemical regime around the coral habitats off central west coast of India

The Western Indian Continental Shelf (WICS) experiences upwelling during the Southwest Monsoon (SWM), leading to deoxygenation and acidification of subsurface waters. The region has patchy growth of corals, e.g. in the Grande Island and Angria Bank. Measurements made during the late SWM of 2022 reveal that the shelf waters around the Grande Island were subject to varying environmental conditions, viz. lower temperature (21.3–26.1°C), oxygen (0–4.9 mL L−1) and pHT (7.506–7.927). Complete anoxia was associated with sulphide build-up to a maximum of 5.9 μmol L−1 at 17 m depth. An additional episodic condition (high temperature, low oxygen and pH) also occurred associated presumably with a plankton bloom in April 2017. Hence, unlike the offshore coral site Angria Bank, waters around the Grande Island experiences extreme changes in physico-chemical conditions (e.g. Ωarg ∼1.2–1.8 during October 2022) seasonally as reported here. The biogeochemical conditions are however not as intense (Ωarg = 0.6) as observed along the eastern boundary upwelling system of the Pacific Ocean.

Metal-oxide precipitation influences microbiome structure in hyporheic zones receiving acid rock drainage.

In streams receiving acid-rock and mine drainage, the abundant precipitation of iron minerals can alter how groundwater and surface water mix along streams (in what is known as the "hyporheic zone") and may shape the distribution of microbial communities. The findings presented here suggest that neutral pH streams with large, well-mixed hyporheic zones may harbor and transport diverse microorganisms attached to particles/colloids through hyporheic pore spaces. In acidic streams where metal oxides clog pore spaces and limit hyporheic exchange, iron-oxidizing bacteria may dominate and phylogenetic diversity becomes low. The abundance of iron-oxidizing bacteria in acid mine drainage streams has the potential to contribute to additional clogging of hyporheic pore spaces and the accumulation of toxic metals in the hyporheic zone. This research highlights the dynamic interplay between hydrology, geochemistry, and microbiology at the groundwater-surface water interface of acid mine drainage streams.

A decade-long cruise time series (2008–2018) of physical and biogeochemical conditions in the southern Salish Sea, North America

Abstract. Coastal and estuarine waters of the northern California Current system and southern Salish Sea host an observational network capable of characterizing biogeochemical dynamics related to ocean acidification, hypoxia, and marine heatwaves. Here, we compiled data sets from a set of cruises conducted in estuarine waters of Puget Sound (southern Salish Sea) and its boundary waters (Strait of Juan de Fuca and Washington coast). This data product provides data from a decade of cruises with consistent formatting, extended data quality control, and multiple units for parameters such as oxygen with different end use needs and conventions. All cruises obtained high-quality temperature, salinity, inorganic carbon, nutrient, and oxygen observations to provide insight into the dynamic distribution of physical and biogeochemical conditions in this large urban estuary complex on the west coast of North America. At all sampling stations, conductivity–temperature–depth (CTD) casts included sensors for measuring temperature, conductivity, pressure, and oxygen concentrations. Laboratory analyses of discrete water samples collected at all stations throughout the water column in Niskin bottles provided measurements of dissolved inorganic carbon (DIC), dissolved oxygen, nutrient (nitrate, nitrite, ammonium, phosphate, and silicate), and total alkalinity (TA) content. This data product includes observations from 35 research cruises, including 715 oceanographic profiles, with &gt;7490 sensor measurements of temperature, salinity, and oxygen; ≥6070 measurements of discrete oxygen and nutrient samples; and ≥4462 measurements of inorganic carbon variables (i.e., DIC and TA). The observations comprising this cruise compilation collectively characterize the spatial and temporal variability in a region with large dynamic ranges of the physical (temperature = 6.0–21.8 ∘C, salinity = 15.6–34.0) and biogeochemical (oxygen = 12–481 µmol kg−1, dissolved inorganic carbon = 1074–2362 µmol kg−1, total alkalinity = 1274–2296 µmol kg−1) parameters central to understanding ocean acidification and hypoxia in this productive estuary system with numerous interacting human impacts on its ecosystems. All observations conform to the climate-quality observing guidelines of the Global Ocean Acidification Observing Network, the US National Oceanic and Atmospheric Administration's Ocean Acidification Program, and ocean carbon community best practices. This ongoing cruise time series supports the estuarine and coastal monitoring and research objectives of the Washington Ocean Acidification Center and US National Oceanic and Atmospheric Administration (NOAA) Ocean and Atmospheric Research programs, and it provides diverse end users with the information needed to frame biological impacts research, validate numerical models, inform state and tribal water quality and fisheries management, and support decision-makers. All 2008–2018 cruise time-series measurements used in this publication are available at https://doi.org/10.25921/zgk5-ep63 (Alin et al., 2022).

Precipitation fuels dissolved greenhouse gas (CO2, CH4, N2O) dynamics in a peatland-dominated headwater stream: results from a continuous monitoring setup

Stream ecosystems are actively involved in the biogeochemical cycling of carbon (C) and nitrogen (N) from terrestrial and aquatic sources. Streams hydrologically connected to peatland soils are suggested to receive significant quantities of particulate, dissolved, and gaseous C and N species, which directly enhance losses of greenhouse gases (GHGs), i.e., carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), and fuel in-stream GHG production. However, riverine GHG concentrations and emissions are highly dynamic due to temporally and spatially variable hydrological, meteorological, and biogeochemical conditions. In this study, we present a complete GHG monitoring system in a peatland stream, which can continuously measure dissolved GHG concentrations and allows to infer gaseous fluxes between the stream and the atmosphere and discuss the results from March 31 to August 25 at variable hydrological conditions during a cool spring and warm summer period. Stream water was continuously pumped into a water-air equilibration chamber, with the equilibrated and actively dried gas phase being measured with two GHG analyzers for CO2 and N2O and CH4 based on Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS) and Non-Dispersive Infra-Red (NDIR) spectroscopy, respectively. GHG measurements were performed continuously with only shorter measurement interruptions, mostly following a regular maintenance program. The results showed strong dynamics of GHGs with hourly mean concentrations up to 9959.1, 1478.6, and 9.9 parts per million (ppm) and emissions up to 313.89, 1.17, and 0.40 mg C or N m−2h−1 for CO2, CH4, and N2O, respectively. Significantly higher GHG concentrations and emissions were observed shortly after intense precipitation events at increasing stream water levels, contributing 59% to the total GHG budget of 762.2 g m−2 CO2-equivalents (CO2-eq). The GHG data indicated a constantly strong terrestrial signal from peatland pore waters, with high concentrations of dissolved GHGs being flushed into the stream water after precipitation. During drier periods, CO2 and CH4 dynamics were strongly influenced by in-stream metabolism. Continuous and high-frequency GHG data are needed to assess short- and long-term dynamics in stream ecosystems and for improved source partitioning between in-situ and ex-situ production.