In the past 20 years, the exploration of deep ocean trenches has led to spectacular new insights. Even in the deepest canyons, an unusual variety of life and unexpectedly high benthic oxygen consumption rates have been detected while microbial processes below the surface of the hadal seafloor remains largely unknown. The information that exist comes from geophysical measurements, especially related to seismic research, and specific component analyses to estimate the carbon export. In contrast, no information is available on metabolic activities in deeper buried sediments of hadal environment. Here we present the first pore water profiles from 15 up to 11 m long sediment cores recovered during three expeditions to two hadal zones, the Japan Trench and the Atacama Trench. Despite low levels of organic debris, our data reveal that rates of microbial carbon turnover along the trench axes can be similar to those encountered in much shallower and more productive oceanic regions. The extreme sedimentation dynamics, characterized by frequent mass wasting of slope sediments into the trenches, result in effective burial of reactive, microbially available, organic material. Our results document the fueling of the deep hadal biosphere with bioavailable material and thus provide important understanding on the function of deep-sea trenches and the hadal carbon cycle.
Warmer and drier climate has contributed to increased occurrence of large, high severity wildfires in the Pacific Northwest, drawing concerns for water quality and ecosystem recovery. While nutrient fluxes generally increase post-fire, the composition of organic matter (OM) transported to streams immediately following a fire is poorly constrained, yet can play an integral role in downstream water quality and biogeochemistry. Here, we quantified spatiotemporal patterns of dissolved OM (DOM) chemistry for five streams burned by wildfires in Oregon, USA in 2020. We sampled over a 24-hour storm event one month after the fire, revealing variable temporal behavior in DOM dynamics. DOM chemistry was directly related with burn severity spatially. Specifically, nitrogen and aromatic character of DOM increased in streams burned at greater severity. Our results suggest a spatial overprinting of DOM dynamics immediately following fire activity and highlight a key gap in our knowledge of post-fire DOM transport to streams.
In both natural and built environments, microbes on occasions manifest in spherical aggregates instead of solid-affixed biofilms. These microbial aggregates are conventionally referred to as granules. Cryoconites are mineral rich granules that appear on glacier surfaces and are linked with expanding surface darkening, thus decreasing albedo, and enhanced melt. The oxygenic photogranules (OPGs) are organic rich granules that grow in wastewater with photosynthetic aeration and present potential for net autotrophic wastewater treatment in a compact system. Despite obvious differences inherent in the two, cryoconite and OPG pose striking resemblance. In both, the order Oscillatoriales in Cyanobacteria envelope inner materials and develop dense spheroidal aggregates. We explore the mechanism of photogranulation on account of high similarity between cryoconites and OPGs. We contend that there is no universal external cause for photogranulation. However, cryoconites and OPGs, as well as their intra variations, which are all are under different stress fields, are the outcome of universal physiological processes of the Oscillatoriales interfacing goldilocks interactions of stresses, which select for their manifestation as granules. Finding the rules of photogranulation may enhance engineering of glacier and wastewater systems to manipulate their ecosystem impacts.
Marine biological activities make substantial influences on aerosol composition and properties. The eastern China seas are highly productive with significant emissions of biogenic substances. Air mass exposure to chlorophyll a (AEC) can be used to indicate the influence of biogenic source on the atmosphere to a certain degree. In this study, the 12-year (2009–2020) daily AEC were calculated over the eastern China seas showing the spatial and seasonal patterns of marine biogenic influence intensity are co-controlled by surface phytoplankton biomass and boundary layer height. The AEC was linearly correlated with aerosol methanesulfonate (MSA) in each of three sub-regions, and the constructed parameterization scheme was applied to simulate the spatiotemporal variation of marine biogenic MSA. This AEC-based approach with observation constraints provides a new insight into the distribution of marine biogenic aerosols which may become increasingly important with the decline of terrestrial input to the studied region.
We report the first estimates of total surfactant photo-reactivity in the sea-surface microlayer (SML) and in subsurface water (SSW) (Tyne estuary, UK; salinity 0.3-32.0). In addition to temperature, a known driver of surfactant adsorption kinetics, we show that irradiation contributes independently to enhanced interfacial surfactant activity (SA), a notion supported by coincident CDOM photodegradation. We estimate a mean SA production via irradiation of 0.064 ± 0.062 mg l-1 T-X-100 equivalents h-1 in the SML and 0.031 ± 0.025 mg l-1 T-X-100 equivalents h-1 in the SSW. Using these data, we derive first-order estimates of the potential suppression of the gas transfer velocity (kw) by photo-derived surfactants ~12.9-48.9%. Given the ubiquitous distribution of natural surfactants in the oceans, we contend that surfactant photochemistry could be a hitherto unrecognized additional driver of air-sea gas exchange, with potential implications for global trace gas budgets and climate models.
Forests are under major pressures due to contemporary land-use, which creates mosaics of stand-stage development that follow different successional paths, that imply ecosystem complexity. The interplay of carbon and water dynamics across succession involves physical and biological interactions that shape net ecosystem production (NEP) and water use efficiency. Here we present 13 years-site of eddy covariance data (2016-2020) from a seasonally dry tropical forest in Northwestern Mexico to elucidate the environmental controls on ecosystem fluxes and explore the interactions with changes in resource availability. Across a successional gradient, an early (9 years since abandonment) and a mid-successional (about 45 years with natural recruitment and regrowth) sites were net carbon sinks (in the order of 100 to 500 g C m-2 y-1) while an old- growth forest was a chronic net source over the 5 years studied (losing between 100 and 300 g C m-2 y-1). In contrast evapotranspiration was alike at sites and close to the precipitation input. Ecosystem water use efficiency tended to be higher at the old-growth forest site (ca. 3.0 g C m-2 /mm H2O vs. ca. 2.0 g C m-2 / mm H2O at the secondary sites). Water availability and radiation where clearly dominant environmental controls across sites, but notably vapor pressure deficit was not a controlling factor for gas exchange at the old-growth forest. Surface characteristics, canopy structure and species composition may explain differences in NEP across succession in TDF at its northernmost extent.
Since 2007, the global mole fraction of atmospheric methane (CH4) has steadily increased meanwhile the 13C/12C isotopic ratio of CH4 (expressed as δ13C-CH4) has shifted to more negative values. This suggests that CH4 emissions are primarily driven by biogenic sources. However, more in situ isotopic measurements of CH4 are needed at the local scales to identify which biogenic sources dominate CH4 emissions regionally. In California, dairies contribute a substantial amount of CH4 emissions from enteric fermentation and manure management. In this study, we present seasonal atmospheric measurements of δ13C-CH4 from dairy farms in the San Joaquin Valley of California. We used δ13C-CH4 to characterize emissions from enteric fermentation by measuring downwind of cattle housing (e.g., freestall barns, corrals) and from manure management areas (e.g., anaerobic manure lagoons) with a mobile platform equipped with cavity ring-down spectrometers. Across seasons, the δ13C-CH4 from enteric fermentation source areas ranged from -69.7 ± 0.6 per mil (‰) to -51.6 ± 0.1‰ while the δ13C-CH4 from manure lagoons ranged from -49.5 ± 0.1‰ to -40.5 ± 0.2‰. Measurements of δ13C-CH4 of enteric CH4 suggest a greater than 10‰ difference between cattle production groups in accordance with diet. Isotopic signatures of CH4 were used to characterize enteric and manure CH4 from downwind plume sampling of dairies. Our findings show that δ13C-CH4 measurements could improve the attribution of CH4 emissions from dairy sources at scales ranging from individual facilities to regions and help constrain the relative contributions from these different sources of emissions to the CH4 budget.
Check out our video abstract: https://youtu.be/CGzFNU70yUg To date, the perspective of forest ecohydrologists has heavily focused on leaf-water interactions – leaving the ecohydrological roles of bark under-studied, oversimplified, or omitted from the forest water cycle. Of course, the lack of study, oversimplification, or omission of processes is not inherently problematic to advancing ecohydrological theory or operational practice. Thus, this perspective outlines the relevance of bark-water interactions to advancing ecohydrological theory and practice: (i) across scales (by briefly examining the geography of bark); (ii) across ecosystem compartments (i.e., living and dead bark on canopies, stems, and in litter layers); and, thereby, (iii) across all major hydrologic states and fluxes in forests (providing estimates and contexts where available in the scant literature). The relevance of bark-water interactions to biogeochemical aspects of forest ecosystems is also highlighted, like canopy-soil nutrient exchanges and soil properties. We conclude that a broad ecohydrological perspective of bark-water interactions is currently merited.
Abiotic and biotic releases of nitrous acid (HONO) from soils contribute substantially to the missing source of tropospheric HONO and hydroxyl radicals (OH). However, global and regional patterns of soil HONO emissions are rarely quantified, and the contributions of such emissions to atmospheric oxidization capacity are unclear. Here, we present that the best estimate of global soil HONO emissions in 2017 is 9.67 with a range of 7.36-11.99 Tg N yr⁻1, where cropland soils accounted for ~ 79%. The analyses also indicate that regional soil HONO emissions enhanced ground OH concentrations by 10-60% and ozone concentrations by 0.5-1.5 ppb at daytime in the ambient area of Shanghai, China. The impact of soil HONO emissions on OH budgets were more important in rural than urban areas. These findings suggest that the global soil HONO emissions, especially from cropland, could quicken photochemical reactions and aggravate air pollution in rural areas.
The formation of biofilms can increase pathogenic contamination of drinking water, cause biofilm-related diseases, and alter the rate of sediment erosion in rivers and coasts. Meanwhile, some biofilms have been used in moving-bed biofilm reactors (MBBRs) to degrade contaminants in wastewater. Mechanistic understanding of biofilm formation is critical to predict and control biofilm development, yet such understanding is currently incomplete. Here, we reveal the impacts of hydrodynamic conditions and surface roughness on the formation of Pseudomonas putida biofilms through a combination of microfluidic experiments, numerical simulations, and fluid mechanics theories. We demonstrate that biofilm growth is suppressed under high flow conditions and characterize the local critical velocity for P. putida biofilms to develop, which is about 50 μm/s. We further demonstrate that micron-scale surface roughness promotes biofilm formation by increasing the area of low-velocity region. Furthermore, we show that the critical shear stress, above which biofilms cease to form, for biofilms to develop on rough surfaces is 0.9 Pa, over 3 times higher than that for flat surfaces, 0.3 Pa. The results of this study will facilitate future predictions and control of biofilm development on surfaces of drinking water pipelines, blood vessels, sediments, and MBBRs.
Droughts are occurring with increased frequency and duration in tropical rainforests due to climate change, having a significant impact on soil C dynamics. The role of microbes as drivers of changing C flow, particularly in relation to volatile organic compound (VOC) cycling, remains largely unknown. Here, we aimed to characterize microbial responses to drought using an integrative, multiple ‘omics approach, and hypothesized that microbial communities will adapt by altering their C allocation strategies. Specifically, during pre-drought, primary metabolic pathways will be more active with microbes using C towards growth, whereas during drought, microbes will divert C to secondary metabolite (including VOC) production in response to stress. To test this, we conducted an ecosystem-wide 66-day drought experiment in the tropical rainforest biome at Biosphere 2, a glass- and steel-enclosed facility near Tucson, AZ. To track carbon allocation by microbes, we injected C1 or C2 position-specific 13C-pyruvate solution into a 25 cm2 region within a soil flux chamber collar (n=6 locations) and measured C isotope ratios of VOC and CO2 emissions. Soil was collected at 0, 6, and 48 hours after pyruvate addition to examine responses in soil metatranscriptomics, metagenomics, and metabolomics (1H nuclear magnetic resonance [NMR] and Fourier-transform ion cyclotron resonance [FTICR]). Our results indicated that 13CO2 (primarily emitted from C1-13C-pyruvate) fluxes decreased during drought, indicating diminished microbial activity. 13C-VOCs (primarily emitted from C2-13C-pyruvate) fluxes also differed between pre-drought and drought. Furthermore, drought-induced increases in activity of VOC-producing metabolic pathways, including acetate and acetone biosynthesis, were evident, as inferred from volatilome, metabolome, and metatranscriptome data. Overall, these results indicate that integration of multiple ‘omics datasets reveal specific impacts of drought on microbial activity affecting carbon flow in the tropical rainforest soil.
Solar-Induced Chlorophyll Fluorescence (SIF) is a powerful proxy for gross primary productivity (GPP) in Boreal ecosystems. However, SIF and GPP are fundamentally different quantities that describe distinct, but related, physiological processes. Recent work has highlighted non-linearities between SIF and GPP at finer spatial (leaf- to canopy- level) and temporal (half-hourly) scales. Therefore, questions have arisen about when, where, and why SIF is a good proxy for GPP and what the potential sources for divergence between the two are. The goal of this study is to answer two specific questions: 1) At what temporal scale is SIF a good proxy for GPP and 2) What are the predominant physical and ecophysiological drivers of nonlinearity between SIF and GPP in boreal ecosystems? We collected tower-based measurements of SIF (and other common vegetation indices) with PhotoSpec (a custom spectrometer system) and eddy-covariance GPP data at a 30-minute resolution at the Southern Old Black Spruce Site (SOBS) in Saskatchewan, CA. We applied a combination of statistical and machine learning approaches to disentangle the influence of structural/illumination effects and ecophysiological variations on the SIF signal. Our results show that at a high temporal resolution (half-hourly), SIF and GPP are predominantly dependent on photosynthetically active radiation (PAR). Therefore, the non-linear light response of GPP drives non-linearity between SIF and GPP. Additionally, canopy structure and illumination effects become important to the SIF signal at high temporal resolutions. At the seasonal timescale, SIF and GPP exhibit co-varying responses to PAR, even when accounting for changes in canopy structure. We attribute changes in the light responses of SIF and GPP to sustained photoprotection over winter which co-varies with changes in temperature. Finally, we show that the relationship between SIF and GPP has a seasonal dependence caused by small differences between the light use efficiencies of fluorescence and photosynthesis. Accounting for this seasonally variable relationship will improve the use of SIF as a proxy for GPP.
Global change has led to the increased duration and frequency of droughts and may affect the microbial-mediated biochemical processes of intermittent rivers and ephemeral streams (IRES). Effects of flow desiccation on the physical structure and community structure of benthic biofilms of IRES have been addressed, however the dynamic responses of biofilm functions related to ecosystem processes during the dry-wet transition remain poorly understood. Herein, dynamic changes in biofilm metabolic activities were investigated during short-term (25-day) and long-term (90-day) desiccation, both followed by a 20-day rewetting period. Distinct response patterns of biofilm metabolism were observed based on flow conditions. Specifically, biofilms were completely desiccated after 10 days of drying. Biofilm ecosystem metabolism, represented by the ratio of gross primary production (GPP) and community respiration (CR), was significantly inhibited during desiccation and gradually recovered back to autotrophic after rewetting due to the high resilience of GPP. Also, the potential metabolic activities of biofilms were maintained during desiccation and showed a tendency to recover after rewetting. While long-term desiccation caused irreparable damage to the total carbon metabolism of biofilms that could not be recovered to the control level even after 20 days of rewetting. Moreover, the metabolic activities of amine and amino acids showed an inconsistent pattern of recovery with total carbon metabolism, indicating the development of selective carbon metabolism. This research provides direct evidence that the increased non-flow periods affects biofilm-mediated carbon biogeochemical processes, which should be taken into consideration for the decision-making of the ecological and environmental flow of IRES.
Long-running eddy covariance flux towers provide insights into how the terrestrial carbon cycle operates over multiple time scales. Here, we evaluated variation in net ecosystem exchange (NEE) of carbon dioxide (CO2) across the Chequamegon Ecosystem-Atmosphere Study (ChEAS) Ameriflux core site cluster in the upper Great Lakes region of the USA from 1997-2020. The tower network included two mature hardwood forests with differing management regimes (US-WCr and US-Syv), two fen wetlands with varying exposure and vegetation (US-Los and US-ALQ), and a very tall (400 m) landscape-level tower (US-PFa). Together, they provided over 70 site-years of observations. The 19-tower CHEESEHEAD19 campaign centered around US-PFa provided additional information on the spatial variation of NEE. Decadal variability was present in all long-term sites, but cross-site coherence in interannual NEE in the earlier part of the record became decoupled with time. NEE at the tall tower transitioned from carbon source to sink to a more variable period over 24 years. Respiration had a greater effect than photosynthesis on driving variations in NEE at all sites. A declining snowpack offset potential increases in assimilation from warmer springs, as less-insulated soils delayed start of spring green-up. No direct CO2 fertilization trend was noted in gross primary productivity, but influenced maximum net assimilation. Direct upscaling of stand-scale sites led to a larger net sink than the landscape tower. These results highlight the value of clustered, long-term carbon flux observations for understanding the diverse links between carbon and climate and the challenges of upscaling observations.
The importance of water supplies cannot be overstated, yet contaminant monitoring and management have not seen strong innovation in information and computing technologies (ICT) such as internet-of-things (IoT), big data, arti>cial intelligence (AI) and numerical modelling. As a water risk, regulated contaminated sites are unique in that they have owners with obligation and cost responsibility, creating conditions that traditionally drive technology innovation. As contaminated site management moves toward risk management rather than resource intensive remediation, ICT technologies will be increasingly applied. A high subsurface complexity, varying land and local weather conditions, however, strongly impact contaminant fate and transport to make each site unique. Site uniqueness means that development of innovation is slow to occur due to lack of scale economic bene>ts. For this reason, a key technology suited for early adoption is reactive transport modeling (RTM). Such modelling can be coupled with diverse compute technologies (e.g. Steefel et al. 2021) supporting long term site modeling for climate change. In this presentation, we explore a modeling platform for data-driven RTM. The work draws from extensive research efforts on quantitative, process-based approaches and measurement methods that span multiple disciplines (e.g. Sookhak Lari et al. 2019). Challenges and limitations of such an RTM platform are discussed, considering: 1) complexity levels, modularity, and computational requirements; 2) existing models; 3) adaptiveness to sitespeci> c data and predictive analytics; 4) upscaling of pore-scale processes; 5) platform Rexibility to account for natural depletion processes (e.g. variably saturated media; microbial dynamics; heat transport; contaminant distribution); 6) platform and model operations to handle in situ remedial activities (e.g. point injections; surface cover / solarization; phytoremediation); 7) use of intelligent systems to provide select model parameters from existing big data sets. An RTM platform is an innovation that has many bene>ts, providing a ‘digital twin’ for contaminated site decision making and an ‘innovation playground’ for novel characterization and remediation techniques.
Global use of reactive nitrogen (N) has increased over the past century to meet growing food and biofuel demand, while contributing to substantial environmental impacts. To project future N inputs for crop production, many studies assumed that Nitrogen Use Efficiency (NUE) remains the same as the current level under a Business-As-Usual (BAU) scenario. This assumption ignores potential NUE changes caused by shifting crop mixes and the diminishing return of yield increase to N inputs at a given level of technology and management practices (TMP). To evaluate the impacts of these two factors on the projection of future N inputs, we developed and tested three approaches, namely “Same NUE”, “Same TMP”, and “Improving TMP”. We found that the approach considering the diminishing returns in yield response (“Same TMP”) resulted in 268 Tg N yr-1 of N inputs which were 61 and 48 Tg N yr-1 higher when keeping NUE at the current level with and without considering crop mix, respectively. If TMP is assumed to continue to evolve at the pace of past five decades, the projected N inputs reduce to 204 Tg N yr-1, but still 59 Tg N yr-1 higher than the inputs in the baseline year 2006. Overall, our results suggest that the BAU approach that assumes constant NUE may be too optimistic in projecting N inputs, and the full range of projection assumptions need to be carefully explored when investigating future N budgets.
Coastal tropical waters are experiencing rapid increases in anthropogenic pressures, yet coastal biogeochemical dynamics in the tropics are poorly studied. We present a multi-year biogeochemical time series from the Singapore Strait in Southeast Asia’s Sunda Shelf Sea. Despite being highly urbanised and a major shipping port, the strait harbours numerous biologically diverse habitats, and is a valuable system for understanding how tropical marine ecosystems respond to anthropogenic pressures. Our results show strong seasonality driven by the semi-annual reversal of ocean currents: dissolved inorganic nitrogen (DIN) and phosphorus varied from ≤0.05 µmol l-1 during the intermonsoons to ≥4 µmol l-1 and ≥0.25 µmol l-1, respectively, during the southwest monsoon. Si(OH)4 exceeded DIN year-round. Based on nutrient concentrations, their relationships to salinity and coloured dissolved organic matter, and the isotopic composition of NOx-, we infer that terrestrial input from peatlands is the main nutrient source. This input delivered dissolved organic carbon (DOC) and nitrogen, but was notably depleted in dissolved organic phosphorus. In contrast, particulate organic matter showed little seasonality, and the δ13C of particulate organic carbon (-21.0 ± 1.5‰) is consistent with a primarily autochthonous origin. Diel changes in dissolved O2 varied seasonally with a pattern that suggests that light availability controls primary productivity more than nutrient concentrations. However, diel changes in pH were greater during the southwest monsoon, when remineralisation of terrestrial DOC lowers the seawater buffer capacity. We conclude that terrestrial input results in mesotrophic conditions, and that the strait might be vulnerable to further eutrophication if nutrient inputs increase during seasons when light availability is high. Moreover, the seasonality of diel pH variation suggests that coral reefs exposed to terrestrial organic matter in the Sunda Shelf may be at significant risk from future ocean acidification.
We conducted microcosm incubation experiments in contrasting biogeochemical areas of the South Indian Ocean and Indian sector of the Southern Ocean to determine the phytoplankton response to aerosol related nutrient release. Dry depositions of 2 mg.L-1 of dust from Patagonia or 25 mg.L-1 of ash from the Icelandic stratovolcano Eyjafjallajökull were added to trace metal clean incubations of surface seawater, along with nutrients (Si, Fe, N or P) at five stations. We interpreted the biological response based on abiotic experiments of aerosols nutrient release. We showed that both types of aerosols increased significantly the primary production by resolving some main local nutrient limitations of the Southern Ocean, at least for iron and to a lesser extend for silicon. Phytoplanktonic communities reacted differently to the additions; however added nutrients/aerosols were mostly beneficial for diatom growth, responsible for 40 to 100 % of the algal biomass increase, depending on the region and aerosols. Nonetheless, the aerosols did not relieve main N limitation of the LNLC area, as neither dust nor ash released significant amounts of NOx. According to these findings, characteristic localized high deposition of volcanic eruptions be of equal or higher importance to phytoplankton compared to desert dust, despite ashes’ lower nutrient solubility to the ocean.