COMPARAÇÕES ENTRE MEDIÇÕES EM TEMPO REAL DA pCO2 AQUÁTICA COM ESTIMATIVAS INDIRETAS EM DOIS ESTUÁRIOS TROPICAIS CONTRASTANTES: O ESTUÁRIO EUTROFIZADO DA BAÍA DE GUANABARA (RJ) E O ESTUÁRIO OLIGOTRÓFICO DO RIO SÃO FRANCISCO (AL)

Carbon dioxide (CO2) fluxes from aquatic systems are generally derived from the gradient in the partial pressure of CO2 (pCO2) between air and surface waters. In this study, we compare real-time measurements of water pCO2 using an equilibrator and non-dispersive infrared gas detector, with calculations based on pH and total alkalinity (TA) in two contrasting Brazilian estuaries: Guanabara Bay (Rio de Janeiro) and the São Francisco River Estuary (Alagoas). In Guanabara Bay, the measured and calculated values showed an excellent agreement (R2 = 0.95, p < 0.0001), without significant statistical differences between the two methods. In the São Francisco River Estuary, where the entire gradient from freshwaters to seawater could be sampled, important overestimates were found for the calculated pCO2. The overestimation was on average 71%, and reached up to 737%. This large bias in pCO2 calculation was verified at low pH and TA concentrations in freshwaters (pH < 7.5; TA < 700 µmol kg-1) possibly due to the contribution of organic alkalinity, lowering the buffer capacity of the carbonate system. As such, direct measurements of pCO2 should be considered as a priority for CO2 studies conducted in estuarine systems, particularly tropical systems where physical and biological processes are prone to significant spatial and temporal variability

SPREADING EUTROPHICATION AND CHANGING CO2 FLUXES IN THE TROPICAL COASTAL OCEAN: A FEW LESSONS FROM RIO DE JANEIRO

International audienceIn Brazil and in many other tropical countries, large urban cities and populations are still growing on the coast and coverage in terms of sewage treatments is far from desirable. Cultural eutrophication is not solely a threat for the coastal ocean; it is now acting as one of its major biogeochemical and ecological driver. Along the littoral of the state of Rio de Janeiro, semi-enclosed marine bays and lagoons show clear spatial and temporal pattern of increasing concentrations of chlorophyll a (Chl a), organic carbon, and nutrients in their waters and sediments in urbanized regions. Acting as a buffer, the nearshore ecosystems have turned highly eutrophic and their autotrophic metabolism has been enhanced creating strong carbon dioxide (CO2) sinks. We compile here data of CO2fluxes recently gathered in four coastal marine ecosystems in the state of Rio de Janeiro: the Guanabara Bay and the Araruama, Saquarema and Jacarepagua lagoons. We observed intense CO2 sources in restricted areas at the vicinity of sewage loads, where microbial degradation of organic matter predominates, and large CO2 sinks in confined and nearshore brackish, marine and hypersaline waters, where phytoplankton blooms occur. We also report a correlation across the four ecosystems between the partial pressure of CO2 in waters and the Chl a concentration. Chl a satellite data all along the Brazilian coast suggest that the CO2 sink induced by eutrophication probably occurs in many coastal ecosystems including bays, lagoon and shelf waters, and could contribute to an additional blue carbon. Part of the additional organic carbon is stored in sediments, and part is exported offshore. However, this additional blue carbon has dramatic environment impacts as it would evolve toward the formation of marine dead zones, and could contribute to a production of methane (CH4) a more powerful greenhouse gas. We emphasize an urgent need for multidisciplinary research to promote simultaneously the storage of atmospheric carbon, and the preservation of biodiversity and socio-economic goods in the eutrophic tropical coastal ocean.&#x0D; Keywords: tropical coastal ecosystems, cultural eutrophication, phytoplankton blooms, marine dead zones, blue carbon</jats:p

Inorganic carbon outwelling from mangroves and saltmarshes drives coastal acidification

Concentrations of alkalinity (TA) and dissolved inorganic carbon (DIC) in porewater as well as in surface water measured during timeseries (fixed location) and spatial surveys (fixed time period) were compiled from 38 mangrove- and 8 saltmarsh-dominated creeks and estuaries. We used data from creeks that were predominantly surrounded by mangrove or saltmarsh vegetation and with minimal confounding factors such as mixed vegetation or large catchments. These creeks were located in either pristine or anthropologically impacted estuaries or coastal areas. Anthropologically impacted areas were defined as areas that were affected by nearby urban or agricultural activities, potentially delivering pollutants, e.g., sewage or fertilizers, to creeks. We also included pristine mangrove- and saltmarsh dominated estuaries. When available, environmental parameters were also recorded, i.e., season, salinity, temperature, pH, dissolved oxygen (DO), water level, porewater tracer radon (222Rn), partial pressure of carbon dioxide (pCO2), dissolved organic carbon (DOC), particulate organic carbon (POC), nitrate and nitrite (NOx), ammonium (NH4), total nitrogen (TN), phosphate (PO4), and total phosphorus (TP). Methods used to determine parameters are explained in each corresponding reference

A global database of dissolved organic matter (DOM) measurements in coastal waters (CoastDOM v1)

International audienceAbstract. The measurements of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) are used to characterize the dissolved organic matter (DOM) pool and are important components of biogeochemical cycling in the coastal ocean. Here, we present the first edition of a global database (CoastDOM v1; available at https://figshare.com/s/512289eb43c4f8e8eaef) compiling previously published and unpublished measurements of DOC, DON, and DOP collected in coastal waters. These data are complemented by hydrographic data such as temperature and salinity and, to the extent possible, other biogeochemical variables (e.g., Chlorophyll-a, inorganic nutrients) and the inorganic carbon system (e.g., dissolved inorganic carbon and total alkalinity). Overall, CoastDOM v1 includes observations from all continents however, most data were collected in the Northern Hemisphere, with a clear gap in coastal water DOM measurements from the Southern Hemisphere. The data included were collected from 1978 to 2022 and consist of 62339 data points for DOC, 20360 for DON and 13440 for DOP. The number of measurements decreases progressively in the sequence DOC > DON > DOP, reflecting both differences in the maturity of the analytical methods and the greater focus on carbon cycling by the aquatic science community. The global database shows that the average DOC concentration in coastal waters (average (standard deviation; SD): 182 (314) µmol C L−1; median: 103 µmol C L−1), is 13-fold greater than the average coastal DON concentrations (average (SD): 13.6 (30.4) µmol N L−1; median: 8.0 µmol N L−1), which was itself 39-fold greater than the average coastal DOP concentrations (average (SD): 0.34 ± 1.11 µmol P L−1; median: 0.18 µmol P L−1). This dataset will be useful to identify global spatial and temporal patterns in DOM and to facilitate reuse of DOC, DON and DOP data in studies aimed at better characterising local biogeochemical processes, closing nutrient budgets, estimating carbon, nitrogen and phosphorous pools, as well as identifying a baseline for modelling future changes in coastal waters

A global database of dissolved organic matter (DOM) concentration measurements in coastal waters (CoastDOM v1)

Measurements of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) concentrations are used to characterize the dissolved organic matter (DOM) pool and are important components of biogeochemical cycling in the coastal ocean. Here, we present the first edition of a global database (CoastDOM v1; available at https://doi.org/10.1594/PANGAEA.964012, Lønborg et al., 2023) compiling previously published and unpublished measurements of DOC, DON, and DOP in coastal waters. These data are complemented by hydrographic data such as temperature and salinity and, to the extent possible, other biogeochemical variables (e.g. chlorophyll a, inorganic nutrients) and the inorganic carbon system (e.g. dissolved inorganic carbon and total alkalinity). Overall, CoastDOM v1 includes observations of concentrations from all continents. However, most data were collected in the Northern Hemisphere, with a clear gap in DOM measurements from the Southern Hemisphere. The data included were collected from 1978 to 2022 and consist of 62 338 data points for DOC, 20 356 for DON, and 13 533 for DOP. The number of measurements decreases progressively in the sequence DOC > DON > DOP, reflecting both differences in the maturity of the analytical methods and the greater focus on carbon cycling by the aquatic science community. The global database shows that the average DOC concentration in coastal waters (average ± standard deviation (SD): 182±314 µmol C L−1; median: 103 µmol C L−1) is 13-fold higher than the average coastal DON concentration (13.6±30.4 µmol N L−1; median: 8.0 µmol N L−1), which is itself 39-fold higher than the average coastal DOP concentration (0.34±1.11 µmol P L−1; median: 0.18 µmol P L−1). This dataset will be useful for identifying global spatial and temporal patterns in DOM and will help facilitate the reuse of DOC, DON, and DOP data in studies aimed at better characterizing local biogeochemical processes; closing nutrient budgets; estimating carbon, nitrogen, and phosphorous pools; and establishing a baseline for modelling future changes in coastal waters