Biogeochemical Interactions Research Articles

Stoichiometric analyses of soil nutrients and enzymes in a Cambisol soil treated with inorganic fertilizers or manures for 26 years

The biogeochemical interactions between soil nutrients and microbial enzymes in agroecosystems remain poorly understood. The objective of this study was to determine effects of long-term (26 years) application of chemical fertilizers (NPK) or adding manure (M) on the elemental and the enzymatic functional stoichiometric characters in a brown soil. The concentrations of soil elements, i.e. carbon (C), nitrogen (N), phosphorus (P) and sulfur (S) and the activities of soil hydrolases including α (β)‑galactosidase (α-GAL and β-GAL), α (β)‑glucosidase(α-GLU and β-GLU), urease, protease (PR), phosphomonoesterase (PM), Phosphodiesterase (PD) and arylsulfatase (AS) were investigated.Results showed that the NPK additions alone led to a decrease in soil pH and increased the acidification of the soils, while M additions could buffer the acidification. With doubling application rate of M, the concentrations of soil C, N, P and S, and soil enzymes activities increased significantly, but P concentrations increased stronger (doubled) than C and N contents (increased by 30%), leading to shifts in element stoichiometry in response to fertilizer and manure applications. The manure additions led to a relatively constant C:N ratio, a low C:P ratio and a high C:S ratio but lower functional ratios of ln (β-GLU + α-GLU + α-GAL + β-GAL): ln(urease + PR); ln(GLU + GAL): (PM + PD); and ln(GLU + GAL):ln(AS), which implied high availability of P and low availability of S. The comparison of element and enzyme stoichiometry indicated that N and S were limited in the manure plots, and C and P were limited in the NPK and No-NPK fertilizer treatment (WF) plots. The increase in enzyme activities in manure plots was caused primarily by the accumulation of soil nutrients with M treatment and not by a buffering effect on the pH.

Reviews and syntheses: influences of landscape structure and land uses on local to regional climate and air quality

Abstract. The atmosphere and the land surface interact in multiple ways, for instance through the radiative-energy balance, the water cycle or the emission and deposition of natural and anthropogenic compounds. By modifying the land surface, land use and land cover changes (LULCCs) and land management changes (LMCs) alter the physical, chemical, and biological processes of the biosphere and therefore all land–atmosphere interactions, from local to global scales. Through socio-economic drivers and regulatory policies adopted at different levels (local, regional, national, or supranational), human activities strongly interfere in the land–atmosphere interactions, and those activities lead to a patchwork of natural, semi-natural, agricultural, urban, and semi-urban areas. In this context, urban and peri-urban areas, which have a high population density, are of particular attention since land transformation can lead to important environmental impacts and affect the health and life of millions of people. The objectives of this review are to synthesize the existing experimental and modelling works that investigate physical, chemical, and/or biogeochemical interactions between land surfaces and the atmosphere, therefore potentially impacting local/regional climate and air quality, mainly in urban or peri-urban landscapes at regional and local scales. The conclusions we draw from our synthesis are the following. (1) The adequate temporal and spatial description of land use and land management practices (e.g. areas concerned, type of crops, whether or not they are irrigated, quantity of fertilizers used and actual seasonality of application) necessary for including the effects of LMC in global and even more in regional climate models is inexistent (or very poor). Not taking into account these characteristics may bias the regional projections used for impact studies. (2) Land–atmosphere interactions are often specific to the case study analysed; therefore, one can hardly propose general solutions or recommendations. (3) Adaptation strategies, proposed after climatic impacts on the targeted resource have been derived, are often biased as they do not account for feedbacks on local/regional climate. (4) There is space for considering atmospheric chemistry, through land–atmosphere interactions, as a factor for land management, helping to maintain air quality and supporting ecosystem functioning. (5) There is a lack of an integrated tool, which includes the many different processes of importance in an operational model, to test different land use or land management scenarios at the scale of a territory.

Effects of aeration on the suspended matter from a tropical and eutrophic estuary

A comprehensive understanding of the complex biogeochemical interactions between organic matter and persistent contaminants in the suspended matter is vital for eco-efficient estuary recovery. However, little is known regarding aeration effects in suspended particulate aggregates. Therefore, this study aimed to investigate the effects of aeration on the suspended matter from a Tropical and Eutrophic estuarine environment. Anoxic water with 60 g/L of suspended particulate matter (SPM) was collected from Guanabara Bay, Rio de Janeiro, Brazil, transferred to experimental boxes and aerated for 61 days. SPM aggregates monitoring included abiotic variables measurements and, determination of total organic matter (TOM), biopolymers composition, bacterial activity, trace metals, and polycyclic aromatic hydrocarbons (PAHs) concentrations. The aeration enhanced dissolved oxygen (DO) concentration and the redox potential (Eh). However, from days 0 to 61 the predominant bacterial activities were denitrification and fermentation. Electron transport system activity increased after day 10, and aerobic activity was detected after day 19. In summary, aeration increased aerobic bacterial activity, lipids (LIP) and trace metal concentrations, although diminished protein/carbohydrate ratio and PAH concentration. Trace metals concentration (Ni, Pb, Cu, Cr, Mn, and Fe) were the highest on day 19 when the pH was 5.9. Copper presented toxic values (Cu > 20.0 μg/g). The pH showed a strong negative correlation with Eh (r = −0.94; p < 0.001). Acidic environment (pH ≤ 5.9) in marine ecosystems with high loads of toxic trace metals is unsafe for biota. Therefore, managers must be aware of the environmental and biological risks of introducing the aeration technique into a eutrophic marine environment.

Enrichment of Lignin-Derived Carbon in Mineral-Associated Soil Organic Matter.

A modern paradigm of soil organic matter proposes that persistent carbon (C) derives primarily from microbial residues interacting with minerals, challenging older ideas that lignin moieties contribute to soil C because of inherent recalcitrance. We proposed that aspects of these old and new paradigms can be partially reconciled by considering interactions between lignin decomposition products and redox-sensitive iron (Fe) minerals. An Fe-rich tropical soil (with C4 litter and either 13C-labeled or unlabeled lignin) was pretreated with different durations of anaerobiosis (0-12 days) and incubated aerobically for 317 days. Only 5.7 ± 0.2% of lignin 13C was mineralized to CO2 versus 51.2 ± 0.4% of litter C. More added lignin-derived C (48.2 ± 0.9%) than bulk litter-derived C (30.6 ± 0.7%) was retained in mineral-associated organic matter (MAOM; density >1.8 g cm-3), and 12.2 ± 0.3% of lignin-derived C vs 6.4 ± 0.1% of litter C accrued in clay-sized (<2 μm) MAOM. Longer anaerobic pretreatments increased added lignin-derived C associated with Fe, according to extractions and nanoscale secondary ion mass spectrometry (NanoSIMS). Microbial residues are important, but lignin-derived C may also contribute disproportionately to MAOM relative to bulk litter-derived C, especially following redox-sensitive biogeochemical interactions.

Rising bubbles enhance the gelatinous nature of the air–sea interface

AbstractBubbles rising through the water column are known to scavenge organic material and microorganisms, and transport them through the air–sea interface after bursting. This mechanism has important implications for air–sea exchange processes. However, little is known about how bubbles influence the chemical and biological properties of the sea‐surface microlayer (SML), a gelatinous film at the air–sea interface. We used floating mesocosms in the coastal Baltic Sea and a laboratory tank filled with seawater from the North Sea to study the effect of bubbling on the gelatinous nature of the SML. Bubbling was found to always increase concentrations of transparent exopolymer particles (TEP) in the SML. In the field, TEP in the SML already increased after 2 min (53% ± 63%) and 10 min (19% ± 12%) bubbling, respectively. During the tank experiment, TEP enriched in the SML by 312% (± 244%) after &gt; 3 h of bubbling. Therefore, bubbling is a highly efficient mechanism for TEP enrichment in the SML. Bubbling caused enrichment and depletion of microbial abundances (prokaryotes, flagellates, eukaryotes) in the SML. However, the incorporation of 3H‐thymidine (i.e., bacterial carbon production) was consistently stimulated after 10 min of bubbling in the field experiment, indicating a bubble‐induced import of unstressed bacteria and fresh organic substrates into the SML. Overall, our results suggest that the gelatinous matrix of the SML is re‐formed within min after disruption by bursting bubbles, and, thus, highlights the importance of biogeochemical interactions within the air–sea interface.

Emission of nitrous oxide from plain multi-ditch system and its impact factors.

Multi-level ditch area is a major component of the hydrographic net of plain area, China. Given the high concentration of nitrogen (N) in the surface water and vigorous biogeochemical interactions, ditch is likely to be the hot spots of N2O emission. However, N2O emission flux and emission factor (EF5r) of multi-level ditches have not been determined. To address this knowledge gap, a 1-year field work in three ditches with different levels in Chengdu Plain was conducted. It is found that the annual flux of N2O emission and EF5r was higher in the lateral (0.0020 and 83.94μgm-2h-1) and field ditches (0.0019 and 110.75μgm-2h-1) than in the branch ditch (0.0016 and 46.38μgm-2h-1, P < 0.05). It is found that parameters of groundwater level, discharge, precipitation, and NH4+ were the primary factors, and these parameters can model the N2O flux well. Furthermore, the content of NH4+ in the surface water of ditches presented better correlation with the emission of N2O than the content of NO3-. Therefore, controlling NH4+ emission and lessening fertilizer usage in summer may be key solutions for indirect reduction of N2O in Chengdu Plain.

A Review on Managing Agroecosystems for Improved Water Use Efficiency in the Face of Changing Climate in Tanzania

Agroecosystems are important for food production and conservation of biodiversity while continuing to provide several ecosystem services within the landscape. Despite their economic and ecological benefits, most agroecosystems in Tanzania are degraded at alarming rates. Rapid increase of human population and unprecedented impacts of climate change have influenced depletion of natural resource base within agroecosystem in recent decades compared to what communities have experienced before. Increased food demands owing to population increase have increased pressure on exploitation of land resources including water. Cultivation area and irrigation water demands have increased steadily in the last six decades. Nevertheless, approaches used for water supply have not been improved; thus, water use efficiency in most irrigation schemes is quite poor. Conversely, climate smart agricultural practices are practiced less in Tanzania. There is poor adoption of recommended adaptation among smallholder farmers due to several socioeconomic reasons. One of the key objectives of climate smart agriculture is to improve bio-geochemical interactions within landscape and decrease competition of natural resources between humans and other component of agroecosystems. This underscores the assumptions that most cropping systems in Tanzania are not managed sustainably. Moreover, comprehensive assessment of hydrological dynamics within smallholder farming in Tanzania is highly lacking. Therefore, actual causes and extent of water resources depletion are largely unknown among stakeholders. In most tropical landscapes, water resources degradation is influenced by interaction of both anthropogenic and biophysical factors operating at different times and space scales. As the capacity of water-supplying sources continues to decline, Tanzania needs profound changes in agricultural production systems in order to nourish the growing human population. This calls for strategic approaches that have wider adaptability. A literature survey study with the following objectives was conducted (i) to assess current state of agricultural water use and irrigation activities in Tanzania and (ii) to determine major constraints for sustainable water management and identify appropriate adaptation measures for their improvement across diverse cropping systems.

Heterogeneity of water quality signature and feedbacks to carbon sequestration in wetlands across some districts of West Bengal, India

Abstract Water quality measurements can indicate carbon status or algal biomass. Microalgae have an excellent ability to utilize all forms of dissolved inorganic carbon at different pH conditions. Water quality signature (WQS) using three different expressions with (i) pH; (ii) total alkalinity, hardness and total dissolved solids; and (iii) nitrate and conductivity of water was assessed in 32 wetlands distributed across 5 districts of West Bengal, India. Two zones were clearly discernible: coldwater (15–23 °C) high-altitude lakes in Darjeeling, and tropical (31–32 °C) low-altitude wetlands. Multivariate analysis of the Akaike information criterion (ACI) model revealed location-specific variability of agro-climatic and biogeochemical interactions. Dissolved inorganic carbon and inorganic nitrogen appeared to be important in regulating the phytocarbon content of microalgae. The wetlands located in the Gangetic alluvial tropical or semi-coastal areas (Hooghly, 24-Parganas, Nadia, Midnapore) were alkaline (pH = 7.52–7.97) where half-bound carbon dioxide comprised the major component (18–26%) of total inorganic carbon, with moderate to eutrophic (PO4-P− 0.16–0.23 mg/l) states which have a negative feedback to global warming. The heterogeneity of measured water quality signature consolidated the sanative nature of wetlands for their complex functional attributes with agro-climatic, biogeochemical and soil-water-biological interactions.

Mesoscale-submesoscale interactions in the Gulf of Mexico: From oil dispersion to climate

In the ocean, forcing acts at planetary scales and dissipation at the microscales. In between are the mesoscales, in a lot of respects akin to nearly two-dimensional, quasi-geostrophically, balanced turbulence. Eddies and fronts, extending from ten to hundred kilometers, represent their best-known dynamical expression. At the ocean boundary layers, near the surface and at the bottom, smaller ageostrophic, coherent flow structures may appear in the form of vorticity filaments, density fronts or coherent vortices, with typical scales of hundreds of meters to few kilometers and a lifespan of few days. These so-called submesoscale circulations provide a pathway for energy transfer towards smaller scales, contribute to the global overturning budget, and impact substantially lateral and diapycnal mixing. They develop in presence of density gradients in the turbulent boundary layers, and their statistics are not well known in a global sense, but are likely to change in the future due to projected changes in near surface stratification.This perspective presents an overview of recent studies illustrating physical and biogeochemical interactions across mesoscale and submesoscale flows focusing on the Gulf of Mexico, where much modeling and observational work has been taking place following the 2010 Deepwater Horizon blow-out. The physical interpretation of several biogeochemical data-sets illustrates how mesoscale and submesoscale circulations impact the dispersion of biologically and climatically relevant tracers, from coral larvae to carbon.The ultimate goal is present the reader with examples of spatial and temporal multiscale interactions in a complex, chaotic system such as the ocean that is key to the future evolution of the climate system with its enormous storage capacity of heat and carbon.

Watershed 'Chemical Cocktails': Forming Novel Elemental Combinations in Anthropocene Fresh Waters.

In the Anthropocene1, watershed chemical transport is increasingly dominated by novel combinations elements, which are hydrologically linked together as 'chemical cocktails.' Chemical cocktails are novel because human activities greatly enhance elemental concentrations and their probability for biogeochemical interactions and shared transport along hydrologic flowpaths. A new chemical cocktail approach advances our ability to: trace contaminant mixtures in watersheds, develop chemical proxies with high-resolution sensor data, and manage multiple water quality problems. We explore the following questions: (1) Can we classify elemental transport in watersheds as chemical cocktails using a new approach? (2) What is the role of climate and land use in enhancing the formation and transport of chemical cocktails in watersheds? To address these questions, we first analyze trends in concentrations of carbon, nutrients, metals, and salts in fresh waters over 100 years. Next, we explore how climate and land use enhance the probability of formation of chemical cocktails of carbon, nutrients, metals, and salts. Ultimately, we classify transport of chemical cocktails based on solubility, mobility, reactivity, and dominant phases: (1) sieved chemical cocktails (e.g., particulate forms of nutrients, metals and organic matter); (2) filtered chemical cocktails (e.g., dissolved organic matter and associated metal complexes); (3) chromatographic chemical cocktails (e.g., ions eluted from soil exchange sites); and (4) reactive chemical cocktails (e.g., limiting nutrients and redox sensitive elements). Typically, contaminants are regulated and managed one element at a time, even though combinations of elements interact to influence many water-quality problems such as toxicity to life, eutrophication, infrastructure and water treatment. A chemical cocktail approach significantly expands evaluations of water-quality signatures and impacts beyond single elements to mixtures. High-frequency sensor data (pH, specific conductance, turbidity, etc.) can serve as proxies for chemical cocktails and improve real-time analyses of water-quality violations, identify regulatory needs, and track water quality recovery following and extreme climate events. Ultimately, a watershed chemical cocktail approach is necessary for effectively co-managing groups of contaminants and provides a more holistic approach for studying, monitoring, and managing water quality in the Anthropocene.

Sulfur Redox Cycling Dependent Abiotic Ferrihydrite Reduction by a Desulfitobacterium hafniense

Biogeochemical interactions of iron and sulfur drive their cycles in many environments, which makes understanding the mechanism of sulfur redox cycling dependent abiotic iron(III) reduction by sulfate-reducing bacteria (SRB) particularly important. Here, we present a newly isolated Desulfitobacterium hafniense strain DH with the potential of reducing sulfate, sulfite, thiosulfate, and elemental sulfur from a paddy soil. Strain DH cannot enzymatically reduce ferrihydrite, but it can abiotically reduce ferrihydrite through extracellular electron transfer with biogenic sulfide or other sulfur compounds acting as electron shuttles. Sulfite, elemental sulfur, and thiosulfate, the oxidation products of sulfide, complete the sulfur cycle between ferrihydrite and strain DH. The presence of strain DH at the ferrihydrite surface results in mineral dissolution and secondary mineralization. Proteomic analysis revealed that the expression level of sulfur reduction functional protein DsrC and a thiosulfate reductase in...

The East River, Colorado, Watershed: A Mountainous Community Testbed for Improving Predictive Understanding of Multiscale Hydrological–Biogeochemical Dynamics

Core Ideas Development of a 300‐km2 mountainous headwater testbed began in 2016 in the East River. The testbed can be used to explore how watershed changes impact downgradient water availability and quality. System‐of‐system, scale‐adaptive approaches can potentially improve watershed dynamics simulation. We have new approaches to monitor and simulate water partitioning and system responses. The East River watershed has been developed as a “community” testbed. Extreme weather, fires, and land use and climate change are significantly reshaping interactions within watersheds throughout the world. Although hydrological–biogeochemical interactions within watersheds can impact many services valued by society, uncertainty associated with predicting hydrology‐driven biogeochemical watershed dynamics remains high. With an aim to reduce this uncertainty, an approximately 300‐km2 mountainous headwater observatory has been developed at the East River, CO, watershed of the Upper Colorado River Basin. The site is being used as a testbed for the Department of Energy supported Watershed Function Project and collaborative efforts. Building on insights gained from research at the “sister” Rifle, CO, site, coordinated studies are underway at the East River site to gain a predictive understanding of how the mountainous watershed retains and releases water, nutrients, carbon, and metals. In particular, the project is exploring how early snowmelt, drought, and other disturbances influence hydrological–biogeochemical watershed dynamics at seasonal to decadal timescales. A system‐of‐systems perspective and a scale‐adaptive simulation approach, involving the combined use of archetypal watershed subsystem “intensive sites” are being tested at the site to inform aggregated watershed predictions of downgradient exports. Complementing intensive site hydrological, geochemical, geophysical, microbiological, geological, and vegetation datasets are long‐term, distributed measurement stations and specialized experimental and observational campaigns. Several recent research advances provide insights about the intensive sites as well as aggregated watershed behavior. The East River “community testbed” is currently hosting scientists from more than 30 institutions to advance mountainous watershed methods and understanding.

Experimental Column Setup for Studying Anaerobic Biogeochemical Interactions Between Iron (Oxy)Hydroxides, Trace Elements, and Bacteria.

Fate and speciation of trace elements (TEs), such as arsenic (As) and mercury (Hg), in aquifers are closely related to physio-chemical conditions, such as redox potential (Eh) and pH, but also to microbial activities that can play a direct or indirect role on speciation and/or mobility. Indeed, some bacteria can directly oxidize As(III) to As(V) or reduce As(V) to As(III). Likewise, bacteria are strongly involved in Hg cycling, either through its methylation, forming the neurotoxin monomethyl mercury, or through its reduction to elemental Hg°. The fates of both As and Hg are also strongly linked to soil or aquifer composition; indeed, As and Hg can bind to organic compounds or (oxy)hydroxides, which will influence their mobility. In turn, bacterial activities such as iron (oxy)hydroxide reduction or organic matter mineralization can indirectly influence As and Hg sequestration. The presence of sulfate/sulfide can also strongly impact these particular elements through the formation of complexes such as thio-arsenates with As or metacinnabar with Hg. Consequently, many important questions have been raised on the fate and speciation of As and Hg in the environment and how to limit their toxicity. However, due to their reactivity towards aquifer components, it is difficult to clearly dissociate the biogeochemical processes that occur and their different impacts on the fate of these TE. To do so, we developed an original, experimental, column setup that mimics an aquifer with As- or Hg-iron-oxide rich areas versus iron depleted areas, enabling a better understanding of TE biogeochemistry in anoxic conditions. The following protocol gives step by step instructions for the column set-up either for As or Hg, as well as an example with As under iron and sulfate reducing conditions.

Experimental Column Setup for Studying Anaerobic Biogeochemical Interactions Between Iron (Oxy)Hydroxides, Trace Elements, and Bacteria

Experimental Column Setup for Studying Anaerobic Biogeochemical Interactions Between Iron (Oxy)Hydroxides, Trace Elements, and Bacteria

Measurements of windblown dust characteristics and ocean fertilization potential: The ephemeral river valleys of Namibia

Abstract Delivery of nutrients to the ocean by mineral aerosol deposition involves complex biogeochemical interactions that include atmospheric processing, dissolution and biotic uptake of available nutrients in the surface waters. Research into the fertilization potential of aeolian dust is currently constrained by a lack of understanding of the nutrient composition and bioavailability in dust source areas. Further, research into hot-spots of dust emission has largely focused on paleo-lacustrine sources and pans, to the detriment of other potential sources such as ephemeral river valleys in desert regions. Here, we investigate the sediment characteristics and nutrient content of windblown and surface sediments of a largely overlooked southern African dust source, Namibia’s ephemeral river valleys. We deployed monitoring equipment in three river valleys to capture deflated sediments and monitor airborne dust concentration and meteorological conditions throughout an annual dust season. Our results show that windblown dust within the river valleys is easily transportable offshore from Namibia over the Benguela Upwelling System, an intensely productive region of the South Atlantic Ocean. We demonstrate that the windblown dust contains iron, phosphorus and nitrogen nutrients, each of which may positively impact primary production rates when deposited in the complex upwelling system. The river valley dust has a significantly higher content of nutrients than either of southern Africa’s major dry lake bed dust sources, Etosha and Makgadikgadi Pans. This aeolian work builds on previous source sediment findings proposing the ephemeral river valleys of Namibia as regionally important sources of dust with enhanced ocean fertilisation potential.

Ecological Stoichiometry of Ocean Plankton.

Marine plankton elemental stoichiometric ratios can deviate from the Redfield ratio (106C:16N:1P); here, we examine physiological and biogeochemical mechanisms that lead to the observed variation across lineages, regions, and seasons. Many models of ecological stoichiometry blend together acclimative and adaptive responses to environmental conditions. These two pathways can have unique molecular mechanisms and stoichiometric outcomes, and we attempt to disentangle the two processes. We find that interactions between environmental conditions and cellular growth are key to understanding stoichiometric regulation, but the growth rates of most marine plankton populations are poorly constrained. We propose that specific physiological mechanisms have a strong impact on plankton and community stoichiometry in nutrient-rich environments, whereas biogeochemical interactions are important for the stoichiometry of the oligotrophic gyres. Finally, we outline key areas with missing information that is needed to advance understanding of the present and future ecological stoichiometry of ocean plankton.

Predicting organic matter, nitrogen, and phosphorus concentrations in runoff from peat extraction sites using partial least squares regression

AbstractOrganic matter and nutrient export from drained peatlands is affected by complex hydrological and biogeochemical interactions. Here partial least squares regression (PLSR) was used to relate various soil and catchment characteristics to variations in chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations in runoff. Peat core samples and water quality data were collected from 15 peat extraction sites in Finland. PLSR models constructed by cross‐validation and variable selection routines predicted 92, 88, and 95% of the variation in mean COD, TN, and TP concentration in runoff, respectively. The results showed that variations in COD were mainly related to net production (temperature and water‐extractable dissolved organic carbon (DOC)), hydrology (topographical relief), and solubility of dissolved organic matter (peat sulfur (S) and calcium (Ca) concentrations). Negative correlations for peat S and runoff COD indicated that acidity from oxidation of organic S stored in peat may be an important mechanism suppressing organic matter leaching. Moreover, runoff COD was associated with peat aluminum (Al), P, and sodium (Na) concentrations. Hydrological controls on TN and COD were similar (i.e., related to topography), whereas degree of humification, bulk density, and water‐extractable COD and Al provided additional explanations for TN concentration. Variations in runoff TP concentration were attributed to erosion of particulate P, as indicated by a positive correlation with suspended sediment concentration (SSC), and factors associated with metal‐humic complexation and P adsorption (peat Al, water‐extractable P, and water‐extractable iron (Fe)).

Reef-building corals thrive within hot-acidified and deoxygenated waters

Coral reefs are deteriorating under climate change as oceans continue to warm and acidify and thermal anomalies grow in frequency and intensity. In vitro experiments are widely used to forecast reef-building coral health into the future, but often fail to account for the complex ecological and biogeochemical interactions that govern reefs. Consequently, observations from coral communities under naturally occurring extremes have become central for improved predictions of future reef form and function. Here, we present a semi-enclosed lagoon system in New Caledonia characterised by diel fluctuations of hot-deoxygenated water coupled with tidally driven persistently low pH, relative to neighbouring reefs. Coral communities within the lagoon system exhibited high richness (number of species = 20) and cover (24–35% across lagoon sites). Calcification rates for key species (Acropora formosa, Acropora pulchra, Coelastrea aspera and Porites lutea) for populations from the lagoon were equivalent to, or reduced by ca. 30–40% compared to those from the reef. Enhanced coral respiration, alongside high particulate organic content of the lagoon sediment, suggests acclimatisation to this trio of temperature, oxygen and pH changes through heterotrophic plasticity. This semi-enclosed lagoon therefore provides a novel system to understand coral acclimatisation to complex climatic scenarios and may serve as a reservoir of coral populations already resistant to extreme environmental conditions.

Mean hydrography on the continental shelf from 26 repeat glider deployments along Southeastern Australia.

Since 2008, 26 glider missions have been undertaken along the continental shelf of southeastern Australia. Typically these missions have spanned the continental shelf on the inshore edge of the East Australian Current from 29.5–33.5°S. This comprehensive dataset of over 33,600 CTD profiles from the surface to within 10 m of the bottom in water depths ranging 25–200 m provides new and unprecedented high resolution observations of the properties of the continental shelf waters adjacent to a western boundary current, straddling the region where it separates from the coast. The region is both physically and biologically significant, and is also in a hotspot of ocean warming. We present gridded mean fields for temperature, salinity and density, but also dissolved oxygen and chlorophyll-a fluorescence indicative of phytoplankton biomass. This data will be invaluable for understanding shelf stratification, circulation, biophysical and bio-geochemical interactions, as well as for the validation of high-resolution ocean models or serving as teaching material.

Iron and Sulfur Porewater and Surface Water Biogeochemical Interactions in Subtropical Peatlands

Core Ideas Surface water sulfate has been implicated in influencing Hg cycling and methylation, this relationship is tenuous at best therefore other variables and biogeochemical cycles could be involved with Hg methylation dynamics. While thought of as a minor biogeochemical constituent, Fe is involved several biogeochemical interactions including the regulation of surface water sulfate concentrations by producing iron minerals. The results of this study suggest that dissolved organic C supply has the ability to regulate dissimilatory sulfate reduction, rather than sulfate supply within the Everglades marsh. Elevated sulfate (SO42−) concentrations have been implicated in affecting Hg cycling and methylation within the Everglades, leading to environmental concerns regarding methyl‐Hg (MeHg) accumulation in wildlife. The interaction of S and Hg cycles is not fully understood in freshwater wetlands, and factors regulating these elemental cycles are warranted. Iron has been demonstrated to influence S cycling patterns, which in turn could influence Hg cycling. Therefore, this study explores Fe and S interactions across three distinct Everglades freshwater marshes in South Florida. Surface water SO42− was positively correlated with porewater sulfide (S2−) concentrations (r = 0.57) due to reducing conditions favoring conversion of SO42− to S2−. Dissolved Fe concentrations were lower in surface water than in porewater presumably due to geologic or biogeochemical reactions that precipitate Fe, essentially removing it from the water column. Both porewater S2− and surface water SO42− were negatively related with Fe porewater concentrations (r = −0.64 and r = −0.72, respectively). Sulfate reduction estimates were highly variable between sampling locations with high S2− to SO42− ratios occurring at relatively low porewater Fe concentrations, while low S2− to SO42− ratios occurred at high Fe concentrations. Porewater dissolved organic carbon (DOC) significantly influenced porewater S2− concentrations (R2 = 0.55 and slope = 0.74), suggesting that organic substrate supply could in part be regulating SO42− reduction. Iron was a major control of SO42− reduction and S cycling and thus has the potential to indirectly affect Hg cycling by altering patterns of SO42− reduction and mitigating SO42− reduction‐induced Hg methylation.