Biogeochemical aspects of bottom anoxia in a Mediterranean lagoon (Thau, France)

Physical and chemical characteristics (temperature, salinity, dissolved oxygen), nutrients [dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and silicate], dissolved organic nitrogen (DON) and phosphorus and particulate matter [particulate organic carbon (POC) and nitrogen (PON) and chlorophyll a] were measured at a station located in the deepest part of the Thau lagoon (8.5 m), France, during a 10 d period of bottom anoxia in summer 1994. The upper 8 cm of sediment were also analyzed for ammonium (NH(4)(+)) and SRP concentrations in the porewater. The study period was characterized by mean wind speed under 4 m s(-1) which induced an increase of surface temperature from 18 to 29 degrees C with the formation of a thermocline. The correlation (p < 10(-4)) between the wind speed averaged over the previous day and the difference between bottom and surface temperatures showed that the wind constituted the main vector of vertical mixing. The lack of wind led to dissolved oxygen depletion in the bottom 2 m and to a strong porosity increase in the upper 10 cm of sediment (80 to >95%). Anoxic conditions increased NH(4)(+) and SRP concentrations in porewater from 231 +/- 89 to 1305 +/- 305 (+/- SD) mu M and from 6.6 +/- 0.8 to 108 +/- 43 mu M respectively. The potential increase of NH(4)(+) concentrations in porewater estimated from the mineralization of the microphytobenthos explained 30% of the measured increase in the upper 8 cm of porewater. The study period was characterized by an increase in NH(4)(+) SRP and dissolved Si concentrations in the bottom water column (maxima respectively 24.2, 4.9 and 57 mu M). Linear regressions between nutrient concentrations in the water column and temperature revealed a strong enhancement of bottom fluxes during anoxia. Nitrate + nitrite (NO(3)(-) + NO(2)(-)) were absent in anoxic waters and remained below 0.5 mu M in oxic waters. Monthly concentrations of SRP in the water column of the Thau lagoon from 1970 to 1994 revealed anoxia events by summer peak values corresponding to strong bottom anoxia. Nevertheless, the general trend was a decrease due to the gradual control of eutrophication which should lead to the disappearance of bottom anoxia within the next decade. A fraction of the nutrients of benthic origin was transformed into planktonic particulate matter via primary production which increased the concentrations of chi a from about 1 to 15 mu g l(-1). Concentrations of DON and PON in the water column were significantly correlated, suggesting that DON compounds were released by the pelagic food web but not directly by the sediment. The increase of total nitrogen (DIN + DON + PON), considering the water column as a closed box during 10 d of winds under 5 m s(-1), was estimated at 1.7 mu mol N l(-1) d(-1) and would correspond to a benthic flux of 600 mu mol N m(-1) h(-1) for 10 d

Testing the Waste Based Biorefinery Concept: Pilot Scale Cultivation of Microalgal Species on Spent Anaerobic Digestate Fluids

PurposeA waste based biorefinery approach has been tested.MethodsThis has been investigated by culturing in a 800 L photobioreactor two autotrophic microalgae namely Nannochloropsis oceanica and Scenedesmus quadricauda utilising filtered spent anaerobic digestate fluids of N:P ratio 14.22 as substrate.ResultsSignificant rates of bioremediation simultaneously with biomass and associated end product formation were achieved. Nitrogen and phosphorus of waste based media was decreased up to 90%. The biomass biochemical analysis of the microalgae when grown on the waste based formulated media demonstrated the comparable content of lipids and proteins with the species grown on f/2 media.ConclusionsTheoretical biomethane potential generation, should the algal cultures be placed in an anaerobic digester, was calculated at 0.58 L CH4 g−1 VS for N. oceanica and 0.48 L CH4 g−1 VS for S. quadricauda showing comparable results with other studies of different source of biomass

Estimates of new and total productivity in central Long Island Sound from in situ measurements of nitrate and dissolved oxygen

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Estuaries and Coasts 36 (2013): 74-97, doi:10.1007/s12237-012-9560-5.Biogeochemical cycles in estuaries are regulated by a diverse set of physical and biological variables that operate over a variety of time scales. Using in situ optical sensors, we conducted a high-frequency time-series study of several biogeochemical parameters at a mooring in central Long Island Sound from May to August 2010. During this period, we documented well-defined diel cycles in nitrate concentration that were correlated to dissolved oxygen, wind stress, tidal mixing, and irradiance. By filtering the data to separate the nitrate time series into various signal components, we estimated the amount of variation that could be ascribed to each process. Primary production and surface wind stress explained 59% and 19%, respectively, of the variation in nitrate concentrations. Less frequent physical forcings, including large-magnitude wind events and spring tides, served to decouple the relationship between oxygen, nitrate, and sunlight on about one-quarter of study days. Daytime nitrate minima and dissolved oxygen maxima occurred nearly simultaneously on the majority (> 80%) of days during the study period; both were strongly correlated with the daily peak in irradiance. Nighttime nitrate maxima reflected a pattern in which surface-layer stocks were depleted each afternoon and recharged the following night. Changes in nitrate concentrations were used to generate daily estimates of new primary production (182 ± 37 mg C m-2 d-1) and the f-ratio (0.25), i.e., the ratio of production based on nitrate to total production. These estimates, the first of their kind in Long Island Sound, were compared to values of community respiration, primary productivity, and net ecosystem metabolism, which were derived from in situ measurements of oxygen concentration. Daily averages of the three metabolic parameters were 1660 ± 431, 2080 ± 419, and 429 ± 203 mg C m-2 d-1, respectively. While the system remained weakly autotrophic over the duration of the study period, we observed very large day-to-day differences in the f-ratio and in the various metabolic parameters.This work was supported by the Yale Institute for Biospheric Studies, the Sounds Conservancy of the Quebec-Labrador Foundation, and the Yale School of Forestry and Environmental Studies Carpenter-Sperry Fund.2014-01-0

Marine diatoms grown in chemostats under silicate or ammonium limitation. III. Cellular chemical composition and morphology of Chaetoceros debilis, Skeletonema costatum , and Thalassiosira gravida

Three marine diatoms, Skeletonema costatum, Chaetoceros debilis , and Thalassiosira gravida were grown under no limitation and ammonium or silicate limitation or starvation. Changes in cell morphology were documented with photomicrographs of ammonium and silicate-limited and non-limited cells, and correlated with observed changes in chemical composition. Cultures grown under silicate starvation or limitation showed an increase in particulate carbon, nitrogen and phosporus and chlorophyll a per unit cell volume compared to non-limited cells; particulate silica per cell volume decreased. Si-starved cells were different from Si-limited cells in that the former contained more particulate carbon and silica per cell volume. The most sensitive indicator of silicate limitation or starvation was the ratio C:Si, being 3 to 5 times higher than the values for non-limited cells. The ratios Si:chlorophyll a and S:P were lower and N:Si was higher than non-limited cells by a factor of 2 to 3. The other ratios, C:N, C:P, C:chlorophyll a , N:chlorophyll a , P:chlorophyll a and N:P were considered not to be sensitive indicators of silicate limitation or starvation. Chlorophyll a , and particulate nitrogen per unit cell volume decreased under ammonium limitation and starvation. NH 4 -starved cells contained more chlorophyll a , carbon, nitrogen, silica, and phosphorus per cell volume than NH 4 -limited cells. N:Si was the most sensitive ratio to ammonium limitation or starvation, being 2 to 3 times lower than non-limited cells. Si:chlorophyll a , P:chlorophyll a and N:P were less sensitive, while the ratios C:N, C:chlorophyll a , N:chlorophyll a , C:Si, C:P and Si:P were the least sensitive. Limited cells had less of the limiting nutrient per unit cell volume than starved cells and more of the non-limiting nutrients (i.e., silica and phosphorus for NH 4 -limited cells). This suggests that nutrient-limited cells rather than nutrient-starved cells should be used along with non-limited cells to measure the full range of potential change in cellular chemical composition for one species under nutrient limitation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46631/1/227_2004_Article_BF00392568.pd

Quantitative determination of particulate organic N and C in marine phytoplankton samples using mass spectrometer signals from isotope ratio analyses in N-15 tracer and C-13 tracer studies

International audienc

Water flux management and phytoplankton communities in a Mediterranean coastal lagoon. Part 1. How to promote dinoflagellate dominance ?

The Biguglia lagoon is a shallow Mediterranean coastal ecosystem where eutrophication is increasing for years. A channel supplying freshwater was cleared in 2009 to enhance lagoon water circulation and alleviate dystrophic crises. Monthly monitoring was started in 2010 to document the impacts of this action on abiotic characteristics and phytoplankton communities. Three stations were surveyed (by microscopy and HPLC). Evidence suggests that this operation had an unexpected outcome. Salinity footprints indicated the succession of three main hydrological sequences that depended on rainfall and circulation pattern. Diatoms and dinoflagellates dominated the first sequence, characterized by heavy rainfall, while Prorocentrum minimum became progressively the dominant species in the second period (increasing salinities) with extensive bloom over the whole lagoon (5.93*10-(5)cells·L(-1)) during the third period. These phytoplankton successions and community structures underline the risk of pernicious effects arising from remediation efforts, in the present case based on increasing freshwater inputs

Uptake and accumulation of ammonium by Alexandrium catenella during nutrient pulses

Field observations in Thau Lagoon, southern France, indicate that the growth of natural populations of Alexandrium catenella during blooms is limited by nitrogen and exhibits a storage rather than a growth response to an ammonium pulse. Therefore, ammonium uptake and accumulation under transient conditions were investigated in detail in laboratory cultures. Following nitrogen exhaustion from the medium, ammonium pulses of varying magnitudes were induced, and measurements of extra- and intra-cellular ammonium were carried out for 24–72h along with measurements of ammonium incorporation (15N tracer) and inorganic carbon fixation (13C tracer). During vegetative growth, values of intra-cellular ammonium reached 30% (Strain TL01) and 2% (Strain ACT03) of cell nitrogen. When ammonium was available in the culture medium, ammonium uptake estimated by the 15N tracer technique accounted for only 65% of the decrease in external ammonium. This discrepancy is probably due to organic nitrogen excretion. Once external ammonium was exhausted, the observed isotopic dilution of both 13C and 15N cell content indicated uptake of a compound containing both unlabelled carbon and nitrogen atoms