scholarly journals Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows

2019 ◽  
Vol 16 (22) ◽  
pp. 4411-4428 ◽  
Author(s):  
Bryce R. Van Dam ◽  
Christian Lopes ◽  
Christopher L. Osburn ◽  
James W. Fourqurean
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Direct Determination ◽  
Florida Bay ◽  
Open Water ◽  
Carbonate Dissolution ◽  
Mixing Processes ◽  
Seagrass Meadows ◽  
Diel Cycles ◽  
Seagrass Ecosystems ◽  
The Impact

Abstract. The net ecosystem productivity (NEP) of two seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles during a short study in the fall of 2018. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air–water gas exchange and contrasting responses to variations in light intensity. We also acknowledge the impact of advective exchange on metabolic calculations of NEP and net ecosystem calcification (NEC) using the “open-water” approach and attempt to quantify this effect. In this first direct determination of NEPDIC in seagrass, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net above-ground primary productivity. NEC was also negative, indicating that both sites were net dissolving carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. However, given the limited spatial (two sites) and temporal (8 d) extent of this study, our results may not be representative of Florida Bay as a whole and may be season-specific. The results of this study highlight the need for better temporal resolution, accurate carbonate chemistry accounting, and an improved understanding of physical mixing processes in future seagrass metabolism studies.

scholarly journals Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows

2019 ◽  
Author(s):  
Bryce R. Van Dam ◽  
Christian Lopes ◽  
Christopher L. Osburn ◽  
James W. Fourqurean
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Direct Determination ◽  
Carbonate Dissolution ◽  
Ph Buffering ◽  
Seagrass Meadows ◽  
Export Ratio ◽  
Diel Cycles ◽  
Budget Analysis ◽  
Seagrass Ecosystems ◽  
Net Heterotrophy

Abstract. The net ecosystem productivity (NEP) of two contrasting seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air-water gas exchange and contrasting responses to variations in light intensity. In this first direct determination of NEPDIC in seagrasses, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net aboveground primary productivity. Net ecosystem calcification (NEC) was also negative, indicating that both sites were net dissolving of carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. Furthermore, a simple budget analysis indicates that these two seagrass meadows have contrasting impacts on pH buffering of adjacent systems, due to variations in the TA : DIC export ratio. The results of this study highlight the need for better temporal resolution, as well as accurate carbonate chemistry accounting in future seagrass metabolism studies.

scholarly journals Anomalies in the Carbonate System of Red Sea Coastal Habitats

2019 ◽  
Author(s):  
Kimberlee Baldry ◽  
Vincent Saderne ◽  
Daniel C. McCorkle ◽  
James H. Churchill ◽  
Susana Agusti ◽  
...  
Keyword(s):  
Red Sea ◽  
Dissolved Inorganic Carbon ◽  
Total Alkalinity ◽  
Carbonate Precipitation ◽  
Mangrove Forests ◽  
Sedimentary Processes ◽  
Carbonate System ◽  
Seagrass Meadows ◽  
Basin Scale ◽  
The Impact

Abstract. We use observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) to assess the impact of ecosystem metabolic processes on coastal waters of the eastern Red Sea. A simple, single-end-member mixing model is used to account for the influence of mixing with offshore waters and evaporation/precipitation, and to model ecosystem-driven perturbations on the carbonate system chemistry of coral reefs, seagrass meadows and mangrove forests. We find that (1) along-shelf changes in TA and DIC exhibit strong linear trends that are consistent with basin-scale net calcium carbonate precipitation; (2) ecosystem-driven changes in TA and DIC are larger than offshore variations in > 85 % of sampled seagrass meadows and mangrove forests, changes which are influenced by a combination of longer water residence times and community metabolic rates; and (3) the sampled mangrove forests show strong and consistent contributions from both organic respiration and other sedimentary processes (carbonate dissolution and secondary redox processes), while seagrass meadows display more variability in the relative contributions of photosynthesis and other sedimentary processes (carbonate precipitation and oxidative processes).

Is carbonate sediment dissolution a significant source of dissolved organic matter to Florida Bay?

2020 ◽  
Author(s):  
Mary Zeller ◽  
Bryce Van Dam ◽  
Chris Lopes ◽  
Ashley Smyth ◽  
Christopher Osburn ◽  
...  
Keyword(s):  
Organic Matter ◽  
Surface Water ◽  
Organic Carbon ◽  
Surface Waters ◽  
Florida Bay ◽  
Source Surface ◽  
Carbonate Sediments ◽  
Seagrass Meadows ◽  
Autochthonous Organic Matter ◽  
The Impact

<p>Florida Bay is subtropical embayment characterized by dense Thalassia testudinum seagrass meadows, the prevalence of carbonate-rich sediments, and relatively long residence times (~1 yr). Florida Bay seagrass meadows store appreciable quantities of allochthonous and autochthonous organic matter (OM) as so-called ‘blue carbon’, the fate of which is therefore tied to that of the carbonate minerals it is bound to.  Dissolved organic carbon (DOC) concentrations are also relatively high (~7-12 mg/L), despite potential photo-oxidative loss in this shallow and long residence time system, as well as low internal DOC production due to the ecosystem’s documented oligotrophy.  These carbonate sediments can dissolve through net acid production via sediment heterotrophic processes as well as sulfide oxidation, processes which may be enhanced via O<sub>2</sub> pumping through seagrass roots.  </p><p>This study investigated the impact of carbonate dissolution on the release of sediment-associated OM to surface waters, and the relative contribution of this process to surface water DOC quantity and quality.  We undertook a three-part experimental approach, with analyses including EEMs, δ13C-DOC, and FT-ICR-MS, to better understand the sources and fate of DOC in Florida Bay. 1) We conducted a spatial survey of surface waters, pore waters, and acid-leachable (representing the ‘carbonate-bound’ OM fraction) sedimentary OM.  2)  We conducted a DOM photodegradation study using two potential source surface waters, from a main tributary (Taylor Slough) and a central mangrove island.  3) We conducted benthic flux experiments using intact sediment cores facilitating direct measurements of the quality and quantity of DOC release from sediments. The flux information was placed into the context of sediment dissolution rates, estimated from coinciding determinations of alkalinity and inorganic carbon.</p><p>While analyses are ongoing, our initial results indicate a high degree of similarity between the fluorescence signature (PARAFAC components and fluorescence indices) of acid-leachable sedimentary OM, and that of DOC in pore water and surface water throughout Florida Bay.  Taken together, our study points to sediment dissolution as an important, yet understudied, process affecting organic carbon cycling in carbonate-dominated systems like Florida Bay.</p>

The impact of a benthic filter feeder: limitations imposed by physical transport of algae to the benthos

2005 ◽  
Vol 62 (1) ◽  
pp. 205-214 ◽  
Author(s):  
William J Edwards ◽  
Chris R Rehmann ◽  
Ellen McDonald ◽  
David A Culver
Keyword(s):  
Turbulent Mixing ◽  
Dreissena Polymorpha ◽  
Algal Biomass ◽  
Open Water ◽  
Zebra Mussels ◽  
Mixing Processes ◽  
Filter Feeder ◽  
Western Lake ◽  
Tightly Coupled ◽  
The Impact

We used an acoustic Doppler profiler to investigate the hydrodynamics of a nearshore site in western Lake Erie, and we incorporated the measured parameters in numerical simulations of phytoplankton consumption by benthic zebra mussels (Dreissena polymorpha) to examine the link between pelagic production and benthic filter feeders. Daily-averaged eddy diffusivities varied from 10–5 to 10–4 m2·s–1 at our site. Our simulations demonstrate that diffusivities of this order decrease near-bed algal biomass, while algal biomass in the pelagic remains relatively unaffected. Between 8% and 67% of the algal biomass in the water column could be consumed daily, depending on the shape and magnitude of the diffusivity profile. Correspondingly, in situ vertical biomass profiles showed a near-bed zone of algal depletion, but no impact was observed near the surface. The impact of the zebra mussel in nearshore regions is expected to be stronger than in deeper open water. The flow of algal biomass into the benthos was tightly coupled with turbulent mixing, suggesting that open water algal consumption by zebra mussels is small compared with previously published estimates that ignored vertical turbulent mixing processes.

scholarly journals Ecosystem Metabolism Modulates the Dynamics of Hypoxia and Acidification Across Temperate Coastal Habitat Types

2021 ◽  
Vol 8 ◽  
Author(s):  
Ryan B. Wallace ◽  
Bradley J. Peterson ◽  
Christopher J. Gobler
Keyword(s):  
Salt Marsh ◽  
Spatial Variability ◽  
Salt Marshes ◽  
Dissolved Inorganic Carbon ◽  
Open Water ◽  
Ecosystem Metabolism ◽  
Total Alkalinity ◽  
Seagrass Meadows ◽  
Marine Habitats ◽  
Estuarine Site

Changes in photosynthetic and respiration rates in coastal marine habitats cause considerable variability in ecosystem metabolism on timescales ranging from diel to tidal to seasonal. Here, temporal and spatial dynamics of dissolved oxygen (DO), carbonate chemistry, and net ecosystem metabolism (NEM) were quantified from spring through fall in multiple, distinct, temperate estuarine habitats: seagrass meadows, salt marshes, an open water estuary, and a shallow water habitat dominated by benthic macroalgae. DO and pHT (total scale) measurements were made via high frequency sensor arrays coupled with discrete measurements of dissolved inorganic carbon (DIC) and high-resolution spatial mapping was used to document intra-habitat spatial variability. All habitats displayed clear diurnal patterns of pHT and DO that were stronger than tidal signals, with minimums and maximums observed during early morning and afternoon, respectively. Diel ranges in pHT and DO varied by site. In seagrass meadows and the open estuarine site, pHT ranged 7.8–8.4 and 7.5–8.2, respectively, while DO exceeded hypoxic thresholds and aragonite was typically saturated (ΩAr > 1). Conversely, pHT in a shallow macroalgal and salt marsh dominated habitats exhibited strong diel oscillations in pHT (6.9–8.4) with diel acidic (pHT < 7) and hypoxic (DO < 3 mg L–1) conditions often observed during summer along with extended periods of aragonite undersaturation (ΩAr < 1). The partial pressure of carbon dioxide (pCO2) exceeded 3000 and 2000 μatm in the salt marsh and macroalgal bed, respectively, while pCO2 never exceeded 1000 μatm in the seagrass and open estuarine site. Mesoscale (50–100 m) spatial variability was observed across sites with the lowest pHT and DO found within regions of more restricted flow. NEM across habitats ranged from net autotrophic (macroalgae and seagrass) to metabolically balanced (open water) and net heterotrophic (salt marsh). Each habitat exhibited distinct buffering capacities, varying seasonally, and modulated by adjacent biological activity and variations in total alkalinity (TA) and DIC. As future predicted declines in pH and DO are likely to shrink the spatial extent of estuarine refuges from acidification and hypoxia, efforts are required to expand seagrass meadows and the aquaculture of macroalgae to maximize their ecosystem benefits and maintain these estuarine refuges.

scholarly journals Mixing Uncertainties in Low-Metallicity AGB Stars: The Impact on Stellar Structure and Nucleosynthesis

Universe ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 25
Author(s):  
Umberto Battino ◽  
Claudia Lederer-Woods ◽  
Borbála Cseh ◽  
Pavel Denissenkov ◽  
Falk Herwig
Keyword(s):  
Stellar Structure ◽  
Process Efficiency ◽  
Agb Stars ◽  
Mixing Processes ◽  
Data Set ◽  
Convective Envelope ◽  
Capture Process ◽  
Low Metallicity ◽  
Low Mass ◽  
The Impact

The slow neutron-capture process (s-process) efficiency in low-mass AGB stars (1.5 < M/M⊙ < 3) critically depends on how mixing processes in stellar interiors are handled, which is still affected by considerable uncertainties. In this work, we compute the evolution and nucleosynthesis of low-mass AGB stars at low metallicities using the MESA stellar evolution code. The combined data set includes models with initial masses Mini/M⊙=2 and 3 for initial metallicities Z=0.001 and 0.002. The nucleosynthesis was calculated for all relevant isotopes by post-processing with the NuGrid mppnp code. Using these models, we show the impact of the uncertainties affecting the main mixing processes on heavy element nucleosynthesis, such as convection and mixing at convective boundaries. We finally compare our theoretical predictions with observed surface abundances on low-metallicity stars. We find that mixing at the interface between the He-intershell and the CO-core has a critical impact on the s-process at low metallicities, and its importance is comparable to convective boundary mixing processes under the convective envelope, which determine the formation and size of the 13C-pocket. Additionally, our results indicate that models with very low to no mixing below the He-intershell during thermal pulses, and with a 13C-pocket size of at least ∼3 × 10−4 M⊙, are strongly favored in reproducing observations. Online access to complete yield data tables is also provided.

Seagrass Ecosystems of Andaman and Nicobar Islands: Status and Future Perspective

2020 ◽  
Vol 7 (4) ◽  
pp. 169-174
Author(s):  
Chatragadda Ramesh ◽  
Raju Mohanraju
Keyword(s):  
Water Quality ◽  
Primary Production ◽  
Environmental Changes ◽  
Future Perspective ◽  
Marine Biodiversity ◽  
Seagrass Beds ◽  
Seagrass Meadows ◽  
Seagrass Ecosystem ◽  
Seagrass Ecosystems ◽  
Nicobar Islands

Seagrasses are unique marine flowering plants that play an important ecological role by yielding primary production and carbon sequestration to the marine environment. Seagrass ecosystems are rich in organic matter, supporting the growth of bio-medically important epi and endophytic microorganisms and harbor rich marine biodiversity. They are an essential food source for endangered Andaman state animal Dugongs. Seagrasses are very sensitive to water quality changes, and therefore they serve as ecological bio-indicators for environmental changes. The benthic components in and around the seagrass beds support a significant food chain for other Micro and organisms apart from fishery resources. The epiphytic bacterial communities of the leaf blades support the sustenance against the diseases. Recent reports have shown that the loss of seagrass beds in tropical and temperate regions emphasizes the depletion of these resources, and proper management of seagrass is urgent. The decline of seagrass will impact primary production, biodiversity, and adjacent ecosystems, such as reefs. Therefore, restoring the seagrass meadows could be possible with effective implementing management programs, including seagrass meadows in marine protected areas, restoration projects, seagrass transplantation, implementation of legislative rules, monitoring coastal water quality and human activities in the coastal zone. Lacunas on the seagrass ecosystem management in Andaman & Nicobar Islands are addressed.

scholarly journals Can land use changes alter carbon, nitrogen and major ion transport in subtropical brazilian streams?

2007 ◽  
Vol 64 (4) ◽  
pp. 317-324 ◽  
Author(s):  
Daniela Mariano Lopes da Silva ◽  
Jean Pierre Henry Balbaud Ometto ◽  
Gré de Araújo Lobo ◽  
Walter de Paula Lima ◽  
Marcos Augusto Scaranello ◽  
...  
Keyword(s):  
Land Use ◽  
Sugar Cane ◽  
Dissolved Inorganic Carbon ◽  
Comprehensive Evaluation ◽  
Land Use Changes ◽  
Agricultural Practices ◽  
Major Ion ◽  
Se Brazil ◽  
Tropical Watersheds ◽  
The Impact

Several studies in tropical watersheds have evaluated the impact of urbanization and agricultural practices on water quality. In Brazil, savannas (known regionally as Cerrados) represent 23% of the country's surface, representing an important share to the national primary growth product, especially due to intense agriculture. The purpose of this study is to present a comprehensive evaluation, on a yearly basis, of carbon, nitrogen and major ion fluxes in streams crossing areas under different land use (natural vegetation, sugar cane and eucalyptus) in a savanna region of SE Brazil. Eucalyptus and sugar cane alter the transport of the investigated elements in small watersheds. The highest concentration of all parameters (abiotic parameters, ions, dissolved organic carbon DOC - and dissolved inorganic carbon - DIC) were found in Sugar Cane Watersheds (SCW). The observed concentrations of major cations in Eucalyptus Watersheds (EW) (Mg, Ca, K, Na), as well as DIN and DOC, were found frequently to be intermediate values between those of Savanna Watersheds (SW) and SCW, suggesting a moderate impact of eucalyptus plantations on the streamwater. Same trends were found in relation to ion and nutrient fluxes, where the higher values corresponded to SCW. It is suggested that sugar cane plantations might be playing an important role in altering the chemistry of water bodies.

scholarly journals The impact of sedimentary alkalinity release on the water column CO<sub>2</sub> system in the North Sea

2016 ◽  
Vol 13 (3) ◽  
pp. 841-863 ◽  
Author(s):  
H. Brenner ◽  
U. Braeckman ◽  
M. Le Guitton ◽  
F. J. R. Meysman
Keyword(s):  
Coastal Zone ◽  
North Sea ◽  
Dissolved Inorganic Carbon ◽  
Co2 Uptake ◽  
Overlying Water ◽  
Southern North Sea ◽  
The North ◽  
Alkalinity Generation ◽  
The North Sea ◽  
The Impact

Abstract. It has been previously proposed that alkalinity release from sediments can play an important role in the carbonate dynamics on continental shelves, lowering the pCO2 of seawater and hence increasing the CO2 uptake from the atmosphere. To test this hypothesis, sedimentary alkalinity generation was quantified within cohesive and permeable sediments across the North Sea during two cruises in September 2011 (basin-wide) and June 2012 (Dutch coastal zone). Benthic fluxes of oxygen (O2), alkalinity (AT) and dissolved inorganic carbon (DIC) were determined using shipboard closed sediment incubations. Our results show that sediments can form an important source of alkalinity for the overlying water, particularly in the shallow southern North Sea, where high AT and DIC fluxes were recorded in near-shore sediments of the Belgian, Dutch and German coastal zone. In contrast, fluxes of AT and DIC are substantially lower in the deeper, seasonally stratified, northern part of the North Sea. Based on the data collected, we performed a model analysis to constrain the main pathways of alkalinity generation in the sediment, and to quantify how sedimentary alkalinity drives atmospheric CO2 uptake in the southern North Sea. Overall, our results show that sedimentary alkalinity generation should be regarded as a key component in the CO2 dynamics of shallow coastal systems.

Carbon, nitrogen and phosphorus storage in subtropical seagrass meadows: examples from Florida Bay and Shark Bay

2012 ◽  
Vol 63 (11) ◽  
pp. 967 ◽  
Author(s):  
James W. Fourqurean ◽  
Gary A. Kendrick ◽  
Laurel S. Collins ◽  
Randolph M. Chambers ◽  
Mathew A. Vanderklift
Keyword(s):  
Organic Carbon ◽  
Carbon Content ◽  
Primary Productivity ◽  
Florida Bay ◽  
Organic Carbon Content ◽  
Nitrogen And Phosphorus ◽  
Organic C ◽  
Shark Bay ◽  
Seagrass Meadows ◽  
C Storage

Seagrass meadows in Florida Bay and Shark Bay contain substantial stores of both organic carbon and nutrients. Soils from both systems are predominantly calcium carbonate, with an average of 82.1% CaCO3 in Florida Bay compared with 71.3% in Shark Bay. Soils from Shark Bay had, on average, 21% higher organic carbon content and 35% higher phosphorus content than Florida Bay. Further, soils from Shark Bay had lower mean dry bulk density (0.78 ± 0.01 g mL–1) than those from Florida Bay (0.84 ± 0.02 mg mL–1). The most hypersaline regions of both bays had higher organic carbon content in surficial soils. Profiles of organic carbon and phosphorus from Florida Bay indicate that this system has experienced an increase in P delivery and primary productivity over the last century; in contrast, decreasing organic carbon and phosphorus with depth in the soil profiles in Shark Bay point to a decrease in phosphorus delivery and primary productivity over the last 1000 y. The total ecosystem stocks of stored organic C in Florida Bay averages 163.5 MgCorg ha–1, lower than the average of 243.0 MgCorg ha–1 for Shark Bay; but these values place Shark and Florida Bays among the global hotspots for organic C storage in coastal ecosystems.

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