Bradley Eyre

Southern Cross University · Centre for Coastal Biogeochemistry Research

969 C oral reefs have high biological diversity and provide a myriad of ecosystem services to humans, such as fisheries and tourism 1,2. The CaCO 3 coral reef structure provides habitat for a large number of species. Reef structures are formed through the growth and build up of coral aragonite skeletons, red and green calcareous macroalgae, and oth...

Nitrogen (N) loss from different benthic habitats via net denitrification and burial was quantified, and first-order N budgets were constructed, for three geomorphically distinct shallow warm temperate South-East Australian barrier estuaries. Seagrass communities were the most important benthic habitats for N loss via net denitrification due to a c...

Nitrous oxide is a powerful, long-lived greenhouse gas, but we know little about the role of estuarine areas in the global N2 O budget. This review summarizes 56 studies of N2 O fluxes and associated biogeochemical controlling factors in estuarine open waters, salt marshes, mangroves, and intertidal sediments. The majority of in situ N2 O productio...

Microphytobenthos (MPB) are an important nitrogen (N) sink in coastal systems, but little is known about the fate of this N after it has been assimilated. We used an in situ 15N pulse-chase experiment in subtidal sands to follow the assimilation, trophic transfer, transformation, and flux pathways of MPB-N over 33 d. Throughout the study MPB domina...

Increasing atmospheric CO2 is raising sea surface temperature (SST) and increasing seawater CO2 concentrations, resulting in a lower oceanic pH (ocean acidification; OA), which is expected to reduce the accretion of coral reef ecosystems. Although sediments comprise most of the calcium carbonate (CaCO3) within coral reefs, no in situ studies have l...

This study uses dual‐labeled (¹³C and ¹⁵N) stable isotope applications to examine microbial uptake and short‐term processing of carbon (C) and nitrogen (N) from organic and inorganic compounds in subtropical intertidal sediment. Four treatment applications were applied: (1) algal dissolved organic matter (DOM), (2) amino acid mixture, (3) glucose a...

Estuaries are a globally important source of methane, but little is known about Australia’s contributions to global estuarine methane emissions. Here we present a first-order Australia-wide assessment of estuarine methane emissions, using methane concentrations from 47 estuaries scaled to 971 Australian estuaries based on geomorphic estuary types a...

Estuaries play an important role in connecting the global carbon cycle across the land-to-ocean continuum, but little is known about Australia’s contribution to global CO2 emissions. Here we present an Australia-wide assessment, based on CO2 concentrations for 47 estuaries upscaled to 971 assessed Australian estuaries. We estimate total mean (±SE)...

This study uses dual-labelled ( ¹³ C and ¹⁵ N) stable isotope applications to examine uptake and short-term processing of carbon (C) and nitrogen (N) by microbial communities in intertidal sediment from three subtropical estuarine sites. We examine differences in microbial uptake and retention that arise due to domination of microbial processing by...

Blue carbon is carbon stored long-term in vegetated coastal ecosystems, which constitutes an important sink for atmospheric carbon dioxide (CO 2 ). However, because methane (CH 4 ) and nitrous oxide (N 2 O) have higher global warming potentials (GWP) than CO 2 , their production and release during organic matter diagenesis can affect the climate be...

Fungi are key players in terrestrial organic matter (OM) degradation, but little is known about their role in marine environments. Here we compared the degradation of kelp (Ecklonia radiata) in mesocosms with and without fungicides over 45 days. The aim was to improve our understanding of the vital role of fungal OM degradation and remineralisation...

Coastal ecosystems release or absorb carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), but the net effects of these ecosystems on the radiative balance remain unknown. We compiled a dataset of observations from 738 sites from studies published between 1975 and 2020 to quantify CO2, CH4 and N2O fluxes in estuaries and coastal vegetation i...

Understanding how warming and OA will affect denitrification, and the associated production of N2O, is essential to assess the nitrogen removal capacity of the coastal zone, and the positive warming feedback loop from N2O production in a high-CO2 climate. We estimate that OA may offset the warming increase in estuarine sediment denitrification and...

Attributing nitrogen export to specific land use within heterogeneous catchments remains a challenge due to the spatio‐temporal variability in conditions influencing the mobilization and fate of nitrogen species. This study demonstrates that the measurement of dual stable isotopes of nitrate, taken along with routine tributary measurement of nitrog...

Estuaries play an important role in regulating nitrous oxide (N2O) fluxes to the atmosphere, but little is known about how catchment land‐use changes influence benthic N2O cycling. We measured seasonal benthic N2O fluxes and constructed N2O budgets in three sub‐tropical estuaries draining catchments with contrasting levels of land‐use intensity. Be...

Marine macroalgae are a key primary producer in coastal ecosystems, but are often overlooked in blue carbon inventories. Large quantities of macroalgal detritus deposit on beaches, but the fate of wrack carbon (C) is little understood. If most of the wrack carbon is respired back to CO2, there would be no net carbon sequestration. However, if most...

Earth’s Radiation Budget is partly dictated by the fragile and complex balance between biogenic volatile organic compounds (BVOCs) and greenhouse gases (GHGs), which have the potential to impose cooling or warming once emitted to the atmosphere. Whilst methane (CH4) is strictly associated with global warming due to its solar-radiation absorbing pro...

Estuaries make an important contribution to the global greenhouse gas budget. Yet modeling predictions of carbon dioxide (CO2) and methane (CH4) emissions from estuaries remain highly uncertain due to both simplified assumptions about the underpinning hydrologic and biologic processes and inadequate data availability to uniquely define parameters r...

Globally, coral reefs are threatened by ocean warming and acidification. The degree to which acidification will impact reefs is dependent on the local hydrodynamics, benthic community composition, and biogeochemical processes, all of which vary on different temporal and spatial scales. Characterizing the natural spatiotemporal variability of seawat...

High global uncertainties remain in water‐air CO2, CH4, and N2O fluxes from estuaries due to spatial and temporal variability and the poor predictability of the gas transfer velocity (k600). This is the first study that directly compares k600 of CO2, CH4, and N2O in an estuary with the aim to evaluate the accuracy of using a uniform k600 value for...

Isoprene is an important biogenic volatile organic compound with atmospheric emissions contributing to climate regulation. Because isoprene is predominantly sourced terrestrially, there is limited knowledge on the role it might play in marine systems. Here, we report for the first time isoprene concentrations and tidal fluxes from two subtropical m...

Tropical coastal waters are highly dynamic and amongst the most biogeochemically active zones in the ocean. This review compares nitrogen (N) and phosphorus (P) cycles in temperate and tropical coastal waters. We review the literature to identify major similarities and differences between these two regions, specifically with regards to the impact o...

Estuarine sediments make an important contribution to the global carbon cycle, but we do not know how this will change under a future climate, which is expected to have lower pH oceans and frequent high-temperature days. Six combinations of warming and partial pressures of CO 2 (pCO 2) were chosen to investigate the combined and individual effects...

Atmospheric methane is a potent greenhouse gas that plays a major role in controlling the Earth’s climate. The causes of the renewed increase of methane concentration since 2007 are uncertain given the multiple sources and complex biogeochemistry. Here, we present a metadata analysis of methane fluxes from all major natural, impacted and human-made...

Plain Language Summary Positive rates of net ecosystem calcification and net ecosystem production are regarded as fundamental to the healthy functioning of coral reef ecosystems. In particular, positive ecosystem calcification is required to maintain the structural complexity that sustains many of the ecosystem functions of coral reefs. While most...

Relative to their surface area, estuaries make a disproportionately large contribution of dissolved organic carbon (DOC) to the global carbon cycle, but it is unknown how this will change under a future climate. As such, the response of DOC fluxes from microbially dominated unvegetated sediments to individual and combined future climate stressors o...

Estuaries play a key role in moderating the flow of nitrogen (N) to marine ecosystems. However, the magnitude of this N removal can vary dramatically both within and between estuaries due to the benthic habitats present. Here, we compare denitrification, coupled nitrification–denitrification, anammox, and dissimilatory nitrate reduction to ammonium...

Ocean acidification (OA) and organic matter (OM) enrichment (due to coastal eutrophication) could act in concert to shift coral reef carbonate sediments from a present state of net calcification to a future state of net dissolution, but no studies have examined the combined effect of these stressors on sediment metabolism and dissolution. This stud...

Estuaries make a disproportionately large contribution of dissolved organic carbon (DOC) to the global carbon cycle, but it is unknown how this will change under a future climate. As such, the response of DOC fluxes from microbially dominated unvegetated sediments to individual and combined future climate stressors of warming (from Δ−3 °C to Δ+5 °C...

Sediment microbial communities are an important sink for both organic and inorganic nitrogen (N), with microphytobenthos (MPB) biomass making the largest contribution to short-term N-assimilation and retention. Coastal waters are increasingly subject to anthropogenic nutrient enrichment, but the effect of nutrient enrichment on microbial assimilati...

Isoprene is the most abundant biogenic volatile organic compound (BVOC) on the planet, with annual emissions accounting for up to half of all BVOC emissions. Isoprene has been measured extensively in terrestrial habitats where it is highly abundant; however, there is limited knowledge on marine systems where it is found at lower concentrations. Her...

Southeast Asian peatland-draining rivers have attracted much attention due to their high dissolved organic carbon (DOC) yield and high CO2 emissions under anthropogenic influences. In August 2016, we carried out a field investigation of the Rajang River and its estuary, a tropical system located in Sarawak, Malaysia. The Rajang has peatland in its...

Microphytobenthos (MPB) are an important nitrogen (N) sink in coastal systems, but little is known about the fate of N assimilated by MPB. We used an in situ 15N pulse‐chase experiment in intertidal, nonpermeable, sandy mud to trace the assimilation, transformation, and loss from the sediment of MPB‐N over 31 d. Following assimilation, 15N was tigh...

Isoprene is a biogenic volatile organic compound (BVOC), which is predominantly emitted by terrestrial plants but also from marine systems. However, the marine contribution to isoprene emissions is less understood due to the difficulty of measuring trace concentrations in seawater. Previous methods using “purge and trap” coupled with flame ionizati...

Coastal waters are known to emit globally significant quantities of CH 4 , a potent greenhouse gas, but the potential of the rapid and ongoing human alterations to coastal areas to alter these emissions remains undefined. Here we addressed this gap by quantifying water-to-air CH 4 fluxes and δ 13 C-CH 4 values in subtropical estuaries at Low (n = 3...

Due to decreases in seawater pH resulting from ocean acidification, permeable calcium carbonate reef sands are predicted to be net dissolving by 2050. However, the rate of dissolution and factors that control this rate remain poorly understood. Experiments performed in benthic chambers predict that reefs will become net dissolving when the aragonit...

Benthic O2 fluxes are often used as proxy for C turnover by assuming reduced equivalents formed during anaerobic mineralization are fully reoxidized. Coastal settings, particularly seagrass meadows, periodically experience resuspension events, which can challenge this assumption. This study evaluates the effect of resuspension on the benthic O2 flu...

Bottom trawling and eutrophication are large stressors that are critically coupled. Here we show, using a before‐after control‐effect design, the significant reduction in denitrification as a result of experimental bottom trawling in a shallow coastal system. Trawl disturbance destroys the complex three‐dimensional redox structures in surface sedim...

Coral reefs are facing intensifying stressors, largely due to global increases in seawater temperature and decreases in pH. However, there is extensive environmental variability within coral reef ecosystems, which can impact how organisms respond to global trends. We deployed spatial arrays of autonomous sensors across distinct shallow coral reef h...

Shallow, permeable calcium carbonate (CaCO3) sediments make up a large proportion of the benthic cover on coral reefs and account for a large fraction of the standing stock of CaCO3. There have been a number of laboratory, mesocosm, and in situ studies examining shallow sediment metabolism and dissolution, but none of these have considered seasonal...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Policies aiming to preserve vegetated coastal ecosystems (VCE; tidal marshes, mangroves and seagrasses) to mitigate greenhouse gas emissions require national assessments of blue carbon resources. Here, we present organic carbon (C) storage in VCE across Australian climate regions and estimate potential annual CO2 emission benefits of VCE conservati...

Combined pressures from inland agricultural intensification and coastal development are dramatically altering estuaries’ structure and function. Despite the established global significance of estuarine carbon (C) cycling, the impact of growing anthropogenic stress on coastal C inputs and exports is unclear. To address this gap, we evaluated the mag...

The term Blue Carbon (BC) was first coined a decade ago to describe the disproportionately large contribution of coastal vegetated ecosystems to global carbon sequestration. The role of BC in climate change mitigation and adaptation has now reached international prominence. To help prioritise future research, we assembled leading experts in the fie...

South-east Asian peatland-draining rivers have attracted much attention due to their high dissolved organic carbon (DOC) yield and high CO2 emissions under anthropogenic activities. In August 2016, we carried out a field investigation of the Rajang river and estuary, a tropical system located in Sarawak, Malaysia. The Rajang has peatland in its est...

Estuarine N 2 O emissions contribute to the atmospheric N 2 O budget, but little is known about estuary N 2 O fluxes under low dissolved inorganic nitrogen (DIN) conditions. We present high-resolution spatial surveys of N 2 O concentrations and water-air fluxes in three low-DIN (NO 3⁻ < 30 μmol L ⁻¹ ) tropical estuaries in Queensland, Australia (Jo...

Blue carbon refers to the carbon accumulation capacity of vegetated coastal habitats, including salt marshes, mangroves forests and seagrass meadows. Here we present estimates of organic carbon (Corg) and calcium carbonate (CaCO3) burial rates from 4 seagrass species (Halophila ovalis, Posidonia australis, Ruppia megacarpa, Zostera muelleri) in 3 t...

A dimethyl sulfide (DMS) vertical concentration profile and DMS surface emission flux were quantified in undisturbed acid sulfate soils (ASS) at Cudgen Lake on the north coast of New South Wales, Australia. A deuterated internal standard was used to account for soil adsorption characteristics. The DMS vertical concentration profile increased expone...

Coccolithophores are unicellular marine phytoplankton and important contributors to global carbon cycling. Most work on coccolithophore sensitivity to climate change has been on the small, abundant bloom-forming species Emiliania huxleyi and Gephyrocapsa oceanica. However, large coccolithophore species can be major contributors to coccolithophore c...

Global warming (and the consequent increase in sea surface temperature) is expected to modify rates of gross primary production (GPP), respiration (R), and net calcium carbonate (CaCO3) dissolution in permeable coral reef carbonate sediments. Previous simulations of seawater warming on coral reef sediments found a decline in the GPP/R ratio and an...

Seagrass morphology varies greatly between species and can impact their nitrogen (N) cycling capacity, including dinitrogen (N2) fixation. We used a 15N—N2 stable isotope technique to measure N2 fixation rates in different zones of two morphologically diverse seagrass communities, Zostera muelleri and Halophila ovalis in Moreton Bay, Australia. Iso...

Tropical peat-draining rivers are known as potentially large sources of carbon dioxide (CO2) to the atmosphere due to the high loads of carbon they receive from surrounding soils. However, not many seasonally resolved data are available, limiting our understanding of these systems. We report the first measurements of carbon dioxide partial pressure...

Ongoing alterations to estuaries by inland agricultural intensification and coastal development could affect their capacity to regulate the flux of excess terrestrial nitrogen (N) to the coastal ocean. Here, a new multiform δ15N metric was developed to measure how “pristine,” moderately impacted, and highly degraded estuaries recycle (assimilation,...

Mangrove forests can be a source or a sink of nitrous oxide (N2O) to the atmosphere, but seasonal mangrove N2O dynamics are not well understood. We used continuous high-resolution N2O concentration data to construct seasonal budgets of N2O in two tropical mangrove-lined creeks for both the wet and dry seasons. Furthermore we used N stable isotope a...

Organic matter burial in mangrove forests results in the removal and long-term storage of atmospheric CO2, so- called “blue carbon.” However, some of this organic matter is metabolized and returned to the atmosphere as CH4. Because CH4 has a higher global warming potential than the CO2 fixed in the organic matter, it can offset the CO2 removed via...

Shallow coastal waters in many regions are subject to nutrient enrichment. Microphytobenthos (MPB) can account for much of the carbon (C) fixation in these environments, depending on the depth of the water column, but the effect of enhanced nutrient availability on the processing and fate of MPB-derived C (MPB-C) is relatively unknown. In this stud...

Intensifying agricultural production and coastal urbanization are increasing nitrogen (N) loads to estuaries, potentially increasing emissions of the greenhouse gas nitrous oxide (N2O). Here we present a first assessment of how changes in land use intensity affect estuarine N2O fluxes. We measured N2O concentrations over marine-freshwater transects...

The treatment of organic wastes remains one of the key sustainability challenges facing the growing global aquaculture industry. Bioremediation systems based on coupled bioturbation–microbial processing offer a promising route for waste management. We present, for the first time, a combined biogeochemical–molecular analysis of the short-term perfor...

Acid reef-flux The uptake of anthropogenic carbon dioxide from the atmosphere is reducing the pH of the oceans. Ocean acidification means that calcium carbonate—the material with which coral reefs are built—will be more difficult for organisms to generate and will dissolve more quickly. Eyre et al. report that some reefs are already experiencing ne...