Carbon budget of a shallow, lagoonal estuary: Transformations and source-sink dynamics along the river-estuary-ocean continuum

A comprehensive carbon budget was constructed to quantify carbon flows through the freshwater-marine continuum of a temperate, microtidal estuary. We performed coordinated measurements of dissolved inorganic carbon and total organic carbon fluxes to resolve spatial variability between and along the channel and shoals and diel variability across the entire estuary for 2 yr. Net ecosystem metabolism (NEM) was the most significant control on carbon flow within estuary regions. However, metabolic rates were spatially coupled such that counteracting fluxes across the channel-shoal gradient or along the river-ocean gradient resulted in system-wide NEM that was closely in balance (-3.0 +/- 3.3 to 1.1 +/- 4.4 molC m(-2) yr(-1)). Similarly, large diel and seasonal variability in air-water CO2 fluxes were observed during 72 spatial surveys, but these short-term variations generally cancelled out when aggregated to annual budget terms. Although atmospheric exchanges were small (-0.2 +/- 0.1 to 2.0 +/- 0.4 molC m(-2) yr(-1)), they were subject to large errors (+/- 4 molC m(-2) yr(-1)) if diel variability was neglected. Internal mechanisms that maintained balanced carbon flows were strongly impacted by river discharge and were only apparent by separately quantifying channel and shoal fluxes. Notably, metabolic responses of the shoal to river forcing outweighed the responses of the channel, and the net impact was contrary to prior relationships derived from synthesis of lower-resolution carbon budgets. Our budget demonstrates that resolution of carbon fluxes at appropriate scales, including channel-shoal and diel variability, is critical to characterizing ecosystem function and the fate of carbon within the river-ocean continuum

Dynamic variability of the phytoplankton electron requirement for carbon fixation in eastern Australian waters

© 2019 Elsevier B.V. Fast Repetition Rate fluorometry (FRRf) generates high-resolution measures of phytoplankton primary productivity as electron transport rates (ETRs). How ETRs scale to corresponding inorganic carbon (C) uptake rates (the so-called electron requirement for carbon fixation, Φe,C), inherently describes the extent and effectiveness with which absorbed light energy drives C-fixation. However, it remains unclear whether and how Φe,C follows predictable patterns for oceanographic datasets spanning physically dynamic, and complex, environmental gradients. We utilise a unique high-throughput approach, coupling ETRs and 14C-incubations to produce a semi-continuous dataset of Φe,C (n = 80), predominantly from surface waters, along the Australian coast (Brisbane to the Tasman Sea), including the East Australian Current (EAC). Environmental conditions along this transect could be generally grouped into cooler, more nutrient-rich waters dominated by larger size-fractionated Chl-a (>10 μm) versus warmer nutrient-poorer waters dominated by smaller size-fractionated Chl-a (<2 μm). Whilst Φe,C was higher for warmer water samples, environmental conditions alone explained <20% variance of Φe,C, and changes in predominant size-fraction(s) distributions of Chl-a (biomass) failed to explain variance of Φe,C. Instead, normalised Stern-Volmer non-photochemical quenching (NPQNSV = F0′/Fv′) was a better predictor of Φe,C, explaining ~55% of observed variability. NPQNSV is a physiological descriptor that accounts for changes in both long-term driven acclimation in non-radiative decay, and quasi-instantaneous PSII downregulation, and thus may prove a useful predictor of Φe,C across physically-dynamic regimes, provided the slope describing their relationship is predictable. We also consider recent advances in fluorescence-based corrections to evaluate the potential role of baseline fluorescence (Fb) in contributing to overestimation of Φe,C and the correlation between Φe,C and NPQNSV – in doing so, we highlight the need for Fb corrections for future field-based assessments of Φe,C

Two decades of tropical cyclone impacts on North Carolina’s estuarine carbon, nutrient and phytoplankton dynamics: implications for biogeochemical cycling and water quality in a stormier world

Coastal North Carolina (USA) has experienced 35 tropical cyclones over the past 2 decades; the frequency of these events is expected to continue in the foreseeable future. Individual storms had unique and, at times, significant hydrologic, nutrient-, and carbon (C)-loading impacts on biogeochemical cycling and phytoplankton responses in a large estuarine complex, the Pamlico Sound (PS) and Neuse River Estuary (NRE). Major storms caused up to a doubling of annual nitrogen and tripling of phosphorus loading compared to non-storm years; magnitudes of loading depended on storm tracks, forward speed, and precipitation in NRE-PS watersheds. With regard to C cycling, NRE-PS was a sink for atmospheric CO2 during dry, storm-free years and a significant source of CO2 in years with at least one storm, although responses were storm-specific. Hurricane Irene (2011) mobilized large amounts of previously-accumulated terrigenous C in the watershed, mainly as dissolved organic carbon, and extreme winds rapidly released CO2 to the atmosphere. Historic flooding after Hurricanes Joaquin (2015) and Matthew (2016) provided large inputs of C from the watershed, modifying the annual C balance of NRE-PS and leading to sustained CO2 efflux for months. Storm type affected biogeochemical responses as C-enriched floodwaters enhanced air–water CO2 exchange during ‘wet’ storms, while CO2 fluxes during ‘windy’ storms were largely supported by previously-accumulated C. Nutrient loading and flushing jointly influenced spatio-temporal patterns of phytoplankton biomass and composition. These findings suggest the importance of incorporating freshwater discharge and C dynamics in nutrient management strategies for coastal ecosystems likely to experience a stormier future

Estimating seagrass blue carbon and policy implications: The Australian perspective

© Springer International Publishing AG, part of Springer Nature 2018. Blue carbon policy supports carbon sequestration whilst also conserving our remaining seagrass meadows. The complex biogeochemical processes within the sediment of seagrass meadows are responsible for the longevity of the stored carbon. Carbon stock and accumulation rates are controlled by the interaction of hydrodynamic, geochemical and biotic processes unique to each meadow. Carbon content (stock and flux) of a meadow must be quantified for inclusion in carbon accounting, whether for market trading or national greenhouse gas accounting. Management of seagrass blue carbon also requires estimates of additionality, leakage, permanence, conversion and emission factors

An empirical process model to predict microalgal carbon fixation rates in photobioreactors

© 2018 Elsevier B.V. An empirical process model was developed to infer the instantaneous net photosynthesis and carbon fixation rates from continuous pH and dissolved oxygen measurements during microalgal cultivation in photobioreactors. The model is based on the physical and chemical processes that govern the relationship between inorganic carbon supplied to a microalgal culture and the organic carbon fixed into microalgal biomass, with a particular focus on carbonate chemistry and mass transfer. Bayesian statistics were used to estimate the uncertainty in state variables, such as pH, net photosynthesis rate, and bicarbonate ion concentration, based on the constraints imposed by prior knowledge about these variables. The model was verified by batch-culturing the chlorophyte microalga Chlorella vulgaris in a photobioreactor under both bicarbonate-replete and bicarbonate-limiting conditions in order to test its predictive ability under different operational settings. The replicate photobioreactors were set up to simulate a scaled-down vertical cross-section of a typical raceway pond. This model could be used to test the activity and efficiency of carbon concentrating mechanisms in different microalgal species. It also provides a detailed understanding of how the rate of photosynthesis depends on dissolved inorganic carbon concentration, which could lead to better management of carbon supply in large-scale microalgal cultivation facilities

Electricity and biomass production in a bacteria-Chlorella based microbial fuel cell treating wastewater

© 2017 Elsevier B.V. The chlorophyte microalga Chlorella vulgaris has been exploited within bioindustrial settings to treat wastewater and produce oxygen at the cathode of microbial fuel cells (MFCs), thereby accumulating algal biomass and producing electricity. We aimed to couple these capacities by growing C. vulgaris at the cathode of MFCs in wastewater previously treated by anodic bacteria. The bioelectrochemical performance of the MFCs was investigated with different catholytes including phosphate buffer and anode effluent, either in the presence or absence of C. vulgaris. The power output fluctuated diurnally in the presence of the alga. The maximum power when C. vulgaris was present reached 34.2 ± 10.0 mW m−2, double that observed without the alga (15.6 ± 9.7 mW m−2), with a relaxation of 0.19 gL−1 d−1 chemical oxygen demand and 5 mg L−1 d−1 ammonium also removed. The microbial community associated with the algal biofilm included nitrogen-fixing (Rhizobiaceae), denitrifying (Pseudomonas stutzeri and Thauera sp., from Pseudomonadales and Rhodocyclales orders, respectively), and nitrate-reducing bacteria (Rheinheimera sp. from the Alteromonadales), all of which likely contributed to nitrogen cycling processes at the cathode. This paper highlights the importance of coupling microbial community screening to electrochemical and chemical analyses to better understand the processes involved in photo-cathode MFCs

Unlocking the black-box of inorganic carbon-uptake and utilization strategies among coral endosymbionts (Symbiodiniaceae)

© 2020 Association for the Sciences of Limnology and Oceanography Dinoflagellates within the family Symbiodiniaceae are widespread and fuel metabolism of reef-forming corals through photosynthesis. Adaptation in capacity to harvest and utilize light, and “safely” process photosynthetically generated energy is a key factor regulating their broad ecological success. However, whether such adaptive capacity similarly extends to how Symbiodiniaceae species and genotypes assimilate inorganic carbon (Ci) remains unexplored. We build on recent approaches exploring functional diversity of fitness traits to identify whether Ci uptake and incorporation could be reconciled with evolutionary adaptation among Symbiodiniaceae. We examined phylogenetically diverse Symbiodiniaceae cultures (23 isolates, 6 genera) to track how carbon was invested into cellular uptake, excretion, and growth (cell size, division, storage). Gross carbon uptake rates (GPC) over 1 h varied among isolates grown at 26°C (0.63–3.08 pg C [cell h]−1) with no evident pattern with algal phylogeny. Intriguingly, net carbon uptake rates (24 h) were often higher (1.01–5.54 pg C [cell h]−1) than corresponding values of GPC—we discuss how such GPC measurements may reflect highly conserved biological characteristics for cultured cells linked to high metabolic dependency on photorespiration and heterotrophy. Three isolates from different genera (Cladocopium goreaui, Durusdinium trenchii, and Effrenium voratum) were additionally grown at 20°C and 30°C. Here, Ci uptake consistently decreased with temperature-driven declines in growth rate, suggesting environmental regulation outweighs phylogenetic organization of carbon assimilation capacity among Symbiodiniaceae. Together, these data demonstrate environmental regulation and ecological success among Symbiodiniaceae likely rests on plasticity of upstream photosynthetic processes (light harvesting, energy quenching, etc.) to overcome evolutionary-conserved limitations in Ci functioning

Congenital intracranial mesenchymal chondrosarcoma: case report and review of the literature in pediatric patients.

In this paper we report the 1st case of a congenital intracranial mesenchymal chondrosarcoma in a 2-month-old infant, apparently present at birth. A magnetic resonance image showed a large left parietal solid mass, while microscopy revealed a mixture of undifferentiated small cells and mature hyaline cartilage islands, positive for vimentin, S-100, and CD99. A surgical excision was performed but the patient died after a few weeks as a result of a rapid relapse of the tumor. We also review the pediatric cases (in patients less than 20 years old) of extraskeletal (intracranial) mesenchymal chondrosarcomas of the literature, with a focus on the most recent cytogenetic and immunohistochemical studies