Modern methane and dissolved organic matter radiocarbon signatures suggest rapid transfer of organic carbon from a tropical forest to the underlying subterranean estuary ecosystem

2020 ◽  
Author(s):  
David Brankovits ◽  
John Pohlman ◽  
Mark Garnett ◽  
Joshua Dean
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Dissolved Organic Matter ◽  
Food Web ◽  
Land Surface ◽  
Dissolved Inorganic Carbon ◽  
Trophic Levels ◽  
Carbon Turnover ◽  
Isotopic Analyses ◽  
Subterranean Estuaries

<p>Biogeochemical processing of dissolved organic matter, including methane, along sharp salinity gradients in subterranean estuaries greatly alters the composition of submarine groundwater discharge into the marine environment. Along the margins of coastal carbonate (karst) platforms, which account for ~25% of all coastlines, subterranean estuaries extend kilometers inland within porous bedrock, flooding extensive cave networks. This environment harbors a poorly understood, but globally dispersed, anchialine fauna (invertebrates with subterranean adaptations) and characteristic microbial communities. In Mexico’s Yucatan Peninsula, microbial processing of methane and dissolved organic carbon (DOC), originating from overlying tropical soils, is the critical link for shuttling organic matter to higher trophic levels of the food web within the coastal aquifer. To better understand carbon turnover during organic matter transformations in this habitat, we collected samples for stable and radiocarbon analyses targeting the biotic and abiotic components of the carbon cycle. In the freshwater, radiocarbon signatures of terrestrially originated DOC (pMC = 105.1; [DOC] = 517 µM; δ<sup>13</sup>C = ˗27.8 ‰) and methane (pMC = 101.6; [CH<sub>4</sub>] = 6460 nM; δ<sup>13</sup>C = ˗71.5 ‰) correspond with modern <sup>14</sup>C ages, suggesting these sources of energy within the habitat are comprised of modern carbon fixed recently by photosynthesizing primary producers at the land surface. By contrast, DOC in the deeper saline groundwater is significantly lower in concentration (21 µM), and substantially older (pMC = 47.3, equates to 6010 ± 95 <sup>14</sup>C yrs). Similarly, dissolved inorganic carbon (DIC) in the freshwater is significantly younger (pMC = 86.5, equates to 1170 ± 15 <sup>14</sup>C yrs) than in the deeper saline water (pMC = 58.4, equates to 4320 ± 25 <sup>14</sup>C yrs). These findings demonstrate that important sources of nutrition for the food web are intimately linked to the overlying subaerial habitat, which suggests these ecosystems are highly vulnerable to nearby land use alterations. Furthermore, this study provides new insights into carbon turnover during the process of methane production/consumption, carbon exchange, and organic matter transformation before the emission of the dissolved constituents into coastal oceans from karst subterranean estuaries. Radiocarbon and stable isotopic analyses of the resident fauna will allow us to evaluate the ecological effects of the rapid top-down transfer mechanism for methane and DOC. Beyond better understanding the sources and fate of these carbon sources, our findings have the potential to support management and conservation efforts aimed at coastal groundwater ecosystems.</p>

scholarly journals Dynamics and Characterization of Refractory Dissolved Organic Matter Produced by a Pure Bacterial Culture in an Experimental Predator-Prey System

2006 ◽  
Vol 72 (6) ◽  
pp. 4184-4191 ◽  
Author(s):  
David F. Gruber ◽  
Jean-Paul Simjouw ◽  
Sybil P. Seitzinger ◽  
Gary L. Taghon
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Dissolved Organic Matter ◽  
Trophic Levels ◽  
Ionization Mass ◽  
Predator Prey ◽  
Doc Concentration ◽  
Pure Bacterial Culture ◽  
New Compounds

ABSTRACT We studied the effects of a bacterium (Pseudomonas chlororaphis) and a bactivorous protozoan (Uronema sp.) on transformations of labile dissolved organic carbon (DOC). In 36-day time series experiments, bacteria were grown on glucose both with and without protozoa. We measured bulk organic carbon pools and used electrospray ionization mass spectrometry to characterize dissolved organic matter on a molecular level. Bacteria rapidly utilized glucose, depleting it to nondetectable levels and producing new DOC compounds of higher molecular weight within 2 days. Some of these new compounds, representing 3 to 5% of the initial glucose-C, were refractory and persisted for over a month. Other new compounds were produced and subsequently used by bacteria during the lag and exponential growth phases, pointing to a dynamic cycling of organic compounds. Grazers caused a temporary spike in the DOC concentration consisting of labile compounds subsequently utilized by the bacteria. Grazing did not increase the complexity of the DOC pool already established by the bacteria but did continually decrease the particulate organic carbon pool and expedited the conversion of glucose-C to CO2. After 36 days, 29% of initial glucose-C remained in pure bacteria cultures, while only 6% remained in cultures where a grazer was present. In this study the bacteria were the primary shapers of the complex DOC continuum, suggesting higher trophic levels possibly have less of an impact on the qualitative composition of DOC than previously assumed.

scholarly journals Impact of aquaculture on distribution of dissolved organic matter in coastal Jeju Island, Korea, based on absorption and fluorescence spectroscopy

2021 ◽  
Author(s):  
Jeonghyun Kim ◽  
Yeseul Kim ◽  
Sung Eun Park ◽  
Tae-Hoon Kim ◽  
Bong-Guk Kim ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Fluorescence Spectroscopy ◽  
Dissolved Organic Matter ◽  
Coastal Water ◽  
Coastal Region ◽  
Principal Component ◽  
Distribution Patterns ◽  
Organic Pollution ◽  
Jeju Island

AbstractIn Jeju Island, multiple land-based aquafarms were fully operational along most coastal region. However, the effect of effluent on distribution and behaviours of dissolved organic matter (DOM) in the coastal water are still unknown. To decipher characteristics of organic pollution, we compared physicochemical parameters with spectral optical properties near the coastal aquafarms in Jeju Island. Absorption spectra were measured to calculate the absorption coefficient, spectral slope coefficient, and specific UV absorbance. Fluorescent DOM was analysed using fluorescence spectroscopy coupled with parallel factor analysis. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were measured using high-temperature catalytic oxidation. The DOC concentration near the discharge outlet was twice higher than that in natural groundwater, and the TDN concentration exponentially increased close to the outlet. These distribution patterns indicate that aquafarms are a significant source of DOM. Herein, principal component analysis was applied to categorise the DOM origins. There were two distinct groups, namely, aquaculture activity for TDN with humic-like and high molecular weights DOM (PC1: 48.1%) and natural biological activity in the coastal water for DOC enrichment and protein-like DOM (PC2: 18.8%). We conclude that the aquafarms significantly discharge organic nitrogen pollutants and provoke in situ production of organic carbon. Furthermore, these findings indicate the potential of optical techniques for the efficient monitoring of anthropogenic organic pollutants from aquafarms worldwide.

scholarly journals Distribution of inorganic and organic nutrients in the South Pacific Ocean − evidence for long-term accumulation of organic matter in nitrogen-depleted waters

2008 ◽  
Vol 5 (2) ◽  
pp. 281-298 ◽  
Author(s):  
P. Raimbault ◽  
N. Garcia ◽  
F. Cerutti
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Dissolved Organic Matter ◽  
Dissolved Organic Carbon ◽  
Chlorophyll A ◽  
Organic Phosphorus ◽  
South Pacific ◽  
Nutrient Concentrations ◽  
The South ◽  
Photic Layer

Abstract. During the BIOSOPE cruise the RV Atalante was dedicated to study the biogeochemical properties in the South Pacific between the Marquesas Islands (141° W–8° S) and the Chilean upwelling (73° W–34° S). Over the 8000 km covered by the cruise, several different trophic situations were encountered, in particular strong oligotrophic conditions in the South Pacific Gyre (SPG, between 123° W and 101° W). In this isolated region, nitrate was undetectable between the surface and 160–180 m and only trace quantities (<20 nmoles l−1) of regenerated nitrogen (nitrite and ammonium) were detected, even in the subsurface maximum. Integrated nitrate over the photic layer, which reached 165 m, was close to zero. Despite this severe nitrogen-depletion, phosphate was always present in significant concentrations (≈0.1 μmoles l−1), while silicic acid was maintained at low but classical oceanic levels (≈1 μmoles l−1). In contrast, the Marquesas region (MAR) to the west and Chilean upwelling (UPW) to the east were characterized by high nutrient concentrations, one hundred to one thousand fold higher than in the SPG. The distribution of surface chlorophyll reflected the nitrate gradient, the lowest concentrations (0.023 nmoles l−1) being measured at the centre of the SPG, where integrated value throughout the photic layer was very low (≈ 10 mg m−2). However, due to the relatively high concentrations of chlorophyll-a encountered in the DCM (0.2 μg l−1), chlorophyll-a concentrations throughout the photic layer were less variable than nitrate concentrations (by a factor 2 to 5). In contrast to chlorophyll-a, integrated particulate organic matter (POM) remained more or less constant along the study area (500 mmoles m−2, 60 mmoles m−2 and 3.5 mmoles m−2 for particulate organic carbon, particulate organic nitrogen and particulate organic phosphorus, respectively), with the exception of the upwelling, where values were two fold higher. The residence time of particulate carbon in the surface water was only 4–5 days in the upwelling, but up to 30 days in the SPG, where light isotopic δ15N signal noted in the suspended POM suggests that N2-fixation provides a dominant supply of nitrogen to phytoplankton. The most striking feature was the large accumulation of dissolved organic matter (DOM) in the SPG compared to the surrounding waters, in particular dissolved organic carbon (DOC) where concentrations were at levels rarely measured in oceanic waters (>100 μmoles l−1). Due to this large pool of DOM in the SPG photic layer, integrated values followed a converse geographical pattern to that of inorganic nutrients with a large accumulation in the centre of the SPG. Whereas suspended particulate matter in the mixed layer had a C/N ratio largely conforming to the Redfield stochiometry (C/N≈6.6), marked deviations were observed in this excess DOM (C/N≈16 to 23). The marked geographical trend suggests that a net in situ source exists, mainly due to biological processes. Thus, in spite of strong nitrate-depletion leading to low chlorophyll biomass, the closed ecosystem of the SPG can accumulate large amounts of C-rich dissolved organic matter. The implications of this finding are examined, the conclusion being that, due to weak lateral advection, the biologically produced dissolved organic carbon can be accumulated and stored in the photic layer for very long periods. In spite of the lack of seasonal vertical mixing, a significant part of new production (up to 34%), which was mainly supported by dinitrogen fixation, can be exported to deep waters by turbulent diffusion in terms of DOC. The diffusive rate estimated in the SPG (134 μmolesC m−2 d−1), was quite equivalent to the particles flux measured by sediments traps.

scholarly journals Sink or link? The bacterial role in benthic carbon cycling in the Arabian Sea's oxygen minimum zone

2013 ◽  
Vol 10 (11) ◽  
pp. 6879-6891 ◽  
Author(s):  
L. Pozzato ◽  
D. Van Oevelen ◽  
L. Moodley ◽  
K. Soetaert ◽  
J. J. Middelburg
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Particulate Organic Matter ◽  
Experimental Period ◽  
Oxygen Minimum Zone ◽  
Trophic Levels ◽  
Isotope Tracer ◽  
Oxygen Conditions ◽  
Minimum Zone ◽  
Oxygen Minimum

Abstract. The bacterial loop, the consumption of dissolved organic matter (DOM) by bacteria and subsequent transfer of bacterial carbon to higher trophic levels, plays a prominent role in pelagic food webs. However, its role in sedimentary ecosystems is not well documented. Here we present the results of isotope tracer experiments performed under in situ oxygen conditions in sediments from inside and outside the Arabian Sea's oxygen minimum zone (OMZ) to study the importance of the microbial loop in this setting. Particulate organic matter, added as phytodetritus, was processed by bacteria, protozoa and metazoans, while dissolved organic matter was processed only by bacteria and there was very little, if any, transfer to higher trophic levels within the 7 day experimental period. This lack of significant transfer of bacterial-derived carbon to metazoan consumers indicates that the bacterial loop is rather inefficient, in sediments both inside and outside the OMZ. Moreover, metazoans directly consumed labile particulate organic matter resources and thus competed with bacteria for phytodetritus.

scholarly journals Origin and fate of particulate and dissolved organic matter in a naturally iron-fertilized region of the Southern Ocean

2014 ◽  
Vol 11 (10) ◽  
pp. 14097-14132 ◽  
Author(s):  
L. Tremblay ◽  
J. Caparros ◽  
K. Leblanc ◽  
I. Obernosterer
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Dissolved Organic Matter ◽  
Southern Ocean ◽  
Surface Waters ◽  
Bacterial Degradation ◽  
Natural Iron ◽  
Average Proportion ◽  
Carbon Pump ◽  
Microbial Carbon

Abstract. Natural iron fertilization of high-nutrient low-chlorophyll (HNLC) waters induces annually occurring spring phytoplankton blooms off Kerguelen Islands (Southern Ocean). To examine the origin and fate of particulate and dissolved organic matter (POM and DOM), D- and L-amino acids (AA) were quantified at bloom and HNLC stations. Total hydrolysable AA accounted for 21–25% of surface particulate organic carbon (%POCAA) at the bloom sites, but for 10% at the HNLC site. A marked decrease in %POCAA with depth was observed at the most productive stations leading to values between 3 and 5% below 300 m depth. AA contributed to only 0.9–4.4% of dissolved organic carbon (%DOCAA) at all stations. The only consistent vertical trend was observed at the most productive station (A3-2) where %DOCAA decreased from ∼2% in the surface waters to 0.9% near 300 m. These AA yields and other markers revealed that POM and DOM were more rapidly altered or mineralized at the bloom sites compared to the HNLC site. Different molecular markers indicated that POM mostly originated from diatoms and bacteria. The estimated average proportion of POM from intact phytoplankton cells in surface waters was 45% at the bloom station A3-2, but 14% at the HNLC site. Estimates based on D-AA yields indicated that ∼15% of POM and ∼30% of DOM was of bacterial origin (cells and cell fragments) at all stations. Surprisingly, the DOM in HNLC waters appeared less altered than the DOM from the bloom, had slightly higher dissolved AA concentrations, and showed no sign of alteration within the water column. Unfavorable conditions for bacterial degradation in HNLC regions can explain these findings. In contrast, large inputs of labile organic molecules and iron, likely stimulate the degradation of organic matter (priming effect) and the production of more recalcitrant DOM (microbial carbon pump) during iron-fertilized blooms.

USE OF DISSOLVED ORGANIC MATTER BY MICROORGANISMS: FORMATION OF WATER QUALITY IN A POND OF A HIGH TROPHIC LEVEL

Fisheries ◽  
2020 ◽  
Vol 2020 (5) ◽  
pp. 25-29
Author(s):  
Anatoliy Sadchikov ◽  
Sergey Ostroumov
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Organic Carbon ◽  
Dissolved Organic Matter ◽  
Trophic Level ◽  
Aquatic Ecosystem ◽  
High Trophic Level ◽  
Bacterioplankton Community ◽  
Algae And Bacteria

The role of algae and bacteria in the consumption and mineralization of dissolved organic matter (DOM) in a highly trophic aquatic ecosystem was studied. The phytoplankton and bacterioplankton community consumed 60% of added DOM in August and 56% of DOM in September. Of the uptaken DOM, a significant amount of organic carbon was mineralized. In August 42.7% and in September 29% of organic carbon (of the consumed organic matter) were used for respiration.

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