Dissolved Inorganic Phosphate Research Articles

Non-Conventional Metal Ion Cofactor Requirement of Dinoflagellate Alkaline Phosphatase and Translational Regulation by Phosphorus Limitation.

Alkaline phosphatase (AP) enables marine phytoplankton to utilize dissolved organic phosphorus (DOP) when dissolved inorganic phosphate (DIP) is depleted in the ocean. Dinoflagellate AP (Dino-AP) represents a newly classified atypical type of AP, PhoAaty. Despite While being a conventional AP, PhoAEC is known to recruit Zn2+ and Mg2+ in the active center, and the cofactors required by PhoAaty have been contended and remain unclear. In this study, we investigated the metal ion requirement of AP in five dinoflagellate species. After AP activity was eliminated by using EDTA to chelate metal ions, the enzymatic activity could be recovered by the supplementation of Ca2+, Mg2+ and Mn2+ in all cases but not by that of Zn2+. Furthermore, the same analysis conducted on the purified recombinant ACAAP (AP of Amphidinium carterae) verified that the enzyme could be activated by Ca2+, Mg2+, and Mn2+ but not Zn2+. We further developed an antiserum against ACAAP, and a western blot analysis using this antibody showed a remarkable up-regulation of ACAAP under a phosphate limitation, consistent with elevated AP activity. The unconventional metal cofactor requirement of Dino-AP may be an adaptation to trace metal limitations in the ocean, which warrants further research to understand the niche differentiation between dinoflagellates and other phytoplankton that use Zn–Mg AP in utilizing DOP.

Nutrient biogeochemistry in the Cross River estuary system and adjacent Gulf of Guinea, South East Nigeria (West Africa)

The Cross River, Calabar River, and Great Kwa River together form a network of an estuary system otherwise known as the Cross River Estuary system (CRES). Studies of dissolved nutrients and water mass dynamics were conducted mainly in February 2017. Nutrients measured included NO3−, NO2−, NH4+, dissolved inorganic phosphate (DIP), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP) and dissolved silicate (DSi). The rivers were enriched with DSi and depleted of DIP. Dissolved nutrients were more elevated in the Great Kwa River than Cross River and Calabar River. The levels of DSi and DIN were less than average global concentrations, and that of river estuaries affected by anthropogenic activities. DON was the major form of TDN in the Calabar River estuary, and averagely accounted for 68–76% of TDN pool, while DOP accounted for ∼ 54–75% of TDP pool. Similarly, DON was the dominant form of TDN, and represented 75–84% of TDN pool in the Cross River estuary. In contrast, TDN was dominated by DIN, which accounted for 76–84% of TDN pool, while DIP accounted for 56–61% of TDP pool in the Great Kwa River estuary. There was a switch from DOP (67% of TDP) dominated river water to DIP (67% of TDP) dominated estuarine water in the Cross River estuary, due to enrichment of DIP in the lower Cross River estuary. The adjacent shelf was dominated by DON (58% of TDN) and DIP (70% of TDP). Based on nutrient molar ratios, primary production was strongly limited by DIP, especially in the riverine regions, and switched to DIN limitation in the adjacent shelf. Nutrients in the CRES behaved non-conservatively, and were affected by biogeochemical and physical processes. Nutrient budgets were estimated using the classical LOICZ steady−state box model. Atmospheric deposition of dissolved nutrients was very limited compared to riverine supply. The exchange time of water between the CRES and adjacent sea was ∼ 3.5 days, and may have affected biotic processes and nutrient transport. The CRES was an important source of DIP (137 × 103 moL day−1), DOP (92 × 103 moL day−1) and DON (4849 × 103 moL day−1) to the adjacent shelf, which was respectively 7, 4 and 2 times higher than the total riverine input. The ecosystem metabolism of the CRES, inferred from the ΔDIPsystem and ΔDINsystem indicated that respiration of organic matter was higher than primary production with respiration rate of −15.7 × 106 mol C day−1 (−58 mmol C m−2 day−1), while nitrogen metabolism was −3.8 × 106 mol N day−1 (−14 mmol N m−2 d−1), suggesting that the CRES was heterotrophic, and denitrifying more than nitrogen fixation during this study.

Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding dissolved inorganic nitrate uptake in Saccharina latissima and Laminaria digitata (Phaeophyceae).

Uptake rates of dissolved inorganic phosphorus and dissolved inorganic nitrogen under unsaturated and saturated conditions were studied in young sporophytes of the seaweeds Saccharina latissima and Laminaria digitata (Phaeophyceae) using a "pulse-and-chase" assay under fully controlled laboratory conditions. In a subsequent second "pulse-and-chase" assay, internal storage capacity (ISC) was calculated based on VM and the parameter for photosynthetic efficiency Fv /Fm . Sporophytes of S.latissima showed a VS of 0.80±0.03μmol·cm-2 ·d-1 and a VM of 0.30±0.09μmol·cm-2 ·d-1 for dissolved inorganic phosphate (DIP), whereas VS for DIN was 11.26± 0.56 μmol·cm-2 ·d-1 and VM was 3.94±0.67μmol·cm-2 ·d-1 . In L.digitata, uptake kinetics for DIP and DIN were substantially lower: VS for DIP did not exceed 0.38±0.03μmol·cm-2 ·d-1 while VM for DIP was 0.22±0.01μmol·cm-2 ·d-1 . VS for DIN was 3.92±0.08μmol·cm-2 ·d-1 and the VM for DIN was 1.81±0.38μmol·cm-2 ·d-1 . Accordingly, S.latissima exhibited a larger ISC for DIP (27μmol·cm-2 ) than L.digitata (10μmol·cm-2 ), and was able to maintain high growth rates for a longer period under limiting DIP conditions. Our standardized data add to the physiological understanding of S.latissima and L.digitata, thus helping to identify potential locations for their cultivation. This could further contribute to the development and modification of applications in a bio-based economy, for example, in evaluating the potential for bioremediation in integrated multitrophic aquacultures that produce biomass simultaneously for use in the food, feed, and energy industries.

Phosphorus Fractionation and Its Bioavailability in Panjang Island Jepara

Panjang Island waters located in Jepara Regency. It has rich diversities of aquatic ecosystems. Panjang Island close to the estuary of Wiso and Sampok River. Nutrient inputs from river to marine waters including phosphorus (P) affect primary productivity. A productive ecosystem is essential for nursery ground and coastal fisheries sustainability. The purposes of this research are to know the value of concentration and distribution of dissolved inorganic phosphate (DIP), the concentration of phosphorus fraction in sediment (Ads-P, Fe-P, Ca-P, TIP, Org-P, Total P) and their bioavailability. The concentration of dissolved inorganic phosphate in the water column shows different patterns where at 0.2 d; 0.6 d; 0.8 d the concentration value ranged between 0.010 μmol/l and 0.022 μmol/l; 0.005 μmol/l and 0.021 μmol/l; 0.010 μmol/l and 0.043 μmol/l. Inorganic phosphate concentrations in the sediment are larger than organic phosphates. The most abundant inorganic phosphate fraction of concentration is Ca-P. The relative abundance for inorganic phosphates follows the order of Ca-P> Fe-P> Ads-P. Concentrations of phosphate fraction in sediment for Ads-P, Fe-P, Ca-P, TIP, Org-P ranged between 0.05 and 0.30 μmol/g; 0.66 and 4.11 μmol/g; 2.9 μmol/g and 7.97 μmol/g; 3.69 and 12.48 μmol/g; 0.49 and 4.55 μmol/g. Total P (TP) has a concentration ranged between 5.13 μmol/g and 13.34 μmol/g. The potential of bioavailability of P (BAP) is 17.5 -53.5% of TP. The concentration and the availability of P in the Panjang Island waters are influenced by various factors such as ocean current and sediment grain size.

Past, Present and Future Eutrophication Status of the Baltic Sea

We modelled and assessed the past, present and predicted future eutrophication status of the Baltic Sea. The assessment covers a 350-year period from 1850 to 2200 and is based on: (1) modelled concentrations of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorous (DIP), chlorophyll-a, Secchi depth, and oxygen under four different of nutrient input scenarios and (2) the application of a multi-metric indicator-based tool for assessment of eutrophication status: HEAT 3.0. This tool was previously applied using historical observations to determine eutrophication status from 1901 to 2012. Here we apply HEAT 3.0 using results of a biogeochemical model to reveal significant changes in eutrophication status from 1850 to 2200. Under two scenarios where Baltic Sea Action Plan (BSAP) nutrient reduction targets are met, we expect future good status will be achieved in most Baltic Sea basins. Under two scenarios where nutrient loads remain at 1997-2003 levels or increase, good status will not be achieved. The change from a healthy state without eutrophication problems in the open waters took place in the late 1950s and early 1960s. Following introduction of the first nutrient abatement measures, recovery began in some basins in the late 1990s, whilst in others it commenced in the beginning of the 21st century. Based on model results, we expect that the first basin to achieve a status without eutrophication will be Arkona, between 2030 and 2040. By 2060-2070, a status without eutrophication is anticipated for the Kattegat, Bornholm Basin and Gulf of Finland, followed by the Danish straits around 2090. For the Baltic Proper and Bothnian Sea, a good status with regard to eutrophication will not be expected before 2200. Further, we conclude that two basins are not likely to meet the targets agreed upon and to attain a status unaffected by eutrophication, i.e. the Gulf of Riga and Bothnian Bay. These results, especially the prediction that some basins will not achieve a good status, can be used in support of continuous development and implementation of the regional ecosystem-based nutrient management strategy, the HELCOM Baltic Sea Action Plan.

Coastal water quality assessment and groundwater transport in a subtropical mangrove swamp in Daya Bay, China

Coastal water quality assessment is challenging due to the complex hydrological environment in mangrove swamps. Such assessment requires a good understanding of swamp hydrology and potential solute reactions. In this study, we investigated the concentration variations of a suite of major elements (Na+, K+, Ca2+, Mg2+, SO42−, HCO3– and Cl−), nutrients such as dissolved inorganic phosphorous (DIP) and silicate (DSi), and heavy metals (Cu, Zn, As, Hg, Cd, Pb and Cr) along a typical mangrove transect in Daya Bay, China. The transect comprises a tidal creek, a mudflat and two mangrove zones. The major elements exhibited various degrees of dilution and loss, such as losses of K+ due to uptake by mangrove trees and of SO42− due to microbial sulfate reduction. Numerical simulations of groundwater flow showed that the inland fresh groundwater can continuously discharge through the landward mangrove zone, where high concentrations of DIP and DSi occurred. However, the middle mangrove zone served as a sink of DIP and DSi due to the weak hydrodynamic environment. The spatial distribution of heavy metal concentrations showed that only Cu pollution occurred in the creek zone. The Metal Pollution Index (MPI) was developed to compare the enrichment capability of heavy metals at the different sampling sites. Results showed that the intertidal groundwater has the strongest heavy metal enrichment capability, followed by sea water, inland groundwater and river water. Within the intertidal zone, the creek zone has the highest MPI, followed by the mangrove zone and the mudflat zone. The local water circulation occurred around the creek should contribute the high MPI in the creek zone.

Sensitive Determination of the Dissolved Phosphate Pool for an Improved Resolution of Its Vertical Variability in the Surface Layer: New Views in the P-Depleted Mediterranean Sea

An accurate understanding of the biogeochemistry of dissolved phosphate pool in the upper waters of P-depleted oceanic regions is constrained by the low sensitivity of routine phosphate measurements. In this study, by using the sensitive Liquid Waveguide Capillary Cell method, we report the first extensive cross-basin survey of nanomolar dissolved inorganic phosphate (DIP) and dissolved organic phosphate (DOP) concentration in P-depleted surface waters of the Mediterranean Sea during the stratification period. In the north western Mediterranean Sea (NWMS), DIP above the mixed layer depth (MLD) ranged between 4.9 and 26.5 nM. Along an E-W transect crossing Ionian and Tyrrhenian Seas (E-W transect), DIP above the MLD was lower, ranging between 0.9 and 11.4 nM. Contrarily to the traditional view of a depleted and invariant surface dissolved phosphate pool, a significant vertical variability of DIP and DOP was revealed in upper waters. A positive gradient of DIP was observed above the phosphacline, between the MLD and the deep chlorophyll maximum (DCM) depth, suggesting a potential diffusion of new phosphate to near-surface waters, even under stratified conditions. Interestingly, despite this apparent DIP availability, a significant negative gradient of DOP concentration was observed in the same layer. Finally, the positive gradient in DIP coincided with a significant increase in N:P ratio, suggesting a higher rate of increase of N than of P. The results obtained in this study indicate that acquiring nanomolar DIP data is a sine qua non condition for the comprehension and prediction of the biogeochemical functioning of P-depleted oceanic regions, such as the Mediterranean Sea.

Interannual changes in summer phytoplankton community composition in relation to water mass variability in the East China Sea

The surface distribution of the phytoplankton community was investigated in July 2009, 2010, 2011, and 2013 on the mid-shelf of the East China Sea (ECS), which is under the influence of Changjiang River Diluted Water (CDW) and the Kuroshio Current. This study, based on a CHEMTAX analysis of phytoplankton pigments, revealed a predominance of cyanobacteria and prochlorophytes in the eastern ECS, which is perennially under the influence of oligotrophic Kuroshio Surface Water. Towards the west, on the mid-shelf of the ECS, the composition of the phytoplankton community varied from year to year. Diatoms dominated in 2009 and 2013, when dissolved inorganic phosphate (DIP) concentrations were higher than during 2010 and 2011. During the latter two years, characterized as high-nitrate years, a mixed population of cyanobacteria, chlorophytes, and other groups was observed. Cluster analysis based on the phytoplankton community composition together with a PCA of shipboard hydrographic and nutrient data for all four years helped to confirm that the summer phytoplankton community structure of the ECS was regulated by the mixing of water masses and the variability of nutrient ratios within the CDW as it moved offshore. Our results show that elevated DIP concentrations in the CDW favor the growth of diatoms and dinoflagellates. The primary pathway for DIP inputs appears to be the upwelling of high-phosphate subsurface waters along the coast of China.

Suitability of various benthic biotic indices in assessing the coastal ecological quality in Fujian Province, China

Three benthic biotic indices, AZTI marine biotic index (AMBI), benthic opportunistic polychaetes amphipods (BOPA), and benthic polychaetes amphipods (BPA), combined with Shannon diversity index (H) were applied in ecological quality status (EQS) assessment, to investigate their suitability at four bays and an estuary in Fujian Province. The results showed that there were substantial differences in the performance of these indices. There were only four sites with the same assessment grades using different indices, accounting for 8.7% of the applied sites. AMBI classified 76.1% of the sites as "Good", while 89.1% of the sites were classified as "High" using BOPA. The assessment results of BPA and H showed obvious gradient changes. For the bay areas, all the BOPA, BPA and AMBI values had no significant correlation with dissolved inorganic phosphate (DIP) and dissolved inorganic nitrogen (DIN) concentrations, suggesting that these indices did not respond to eutrophication pressure. The H value was significantly and negatively correlated with DIN concentration. For the estuarine area, the three indices, i.e . BOPA, BPA and AMBI, had significantly positive correlations with DIN and DIP, and there was no clear spatial variation in the assessment grades of these indices with the distance toward sea. The results suggested that BOPA, BPA and AMBI would overestimate the EQS and would show no response to the eutrophication pressure in estuarine area. Similar to the result from the bay areas,H value in the estuary area was significantly and negatively correlated to DIN. Meanwhile, the assessment grades of the seven sections in the estuary tended to increase with the distance toward the sea. In summary, our results suggested that BOPA, BPA and AMBI would not be suitable for the EQS assessment for Fujian coastal area, while H would be more suitable as it could respond to the main anthropogenic pressures.

Dynamics and controls of heterotrophic prokaryotic production in the western tropical South Pacific Ocean: links with diazotrophic and photosynthetic activity

Abstract. Heterotrophic prokaryotic production (BP) was studied in the western tropical South Pacific (WTSP) using the leucine technique, revealing spatial and temporal variability within the region. Integrated over the euphotic zone, BP ranged from 58 to 120 mg C m−2 d−1 within the Melanesian Archipelago, and from 31 to 50 mg C m−2 d−1 within the western subtropical gyre. The collapse of a bloom was followed during 6 days in the south of Vanuatu using a Lagrangian sampling strategy. During this period, rapid evolution was observed in the three main parameters influencing the metabolic state: BP, primary production (PP) and bacterial growth efficiency. With N2 fixation being one of the most important fluxes fueling new production, we explored relationships between BP, PP and N2 fixation rates over the WTSP. The contribution of N2 fixation rates to bacterial nitrogen demand ranged from 3 to 81 %. BP variability was better explained by the variability of N2 fixation rates than by that of PP in surface waters of the Melanesian Archipelago, which were characterized by N-depleted layers and low DIP turnover times (TDIP < 100 h). This is consistent with the fact that nitrogen was often one of the main factors controlling BP on short timescales, as shown using enrichment experiments, followed by dissolved inorganic phosphate (DIP) near the surface and labile organic carbon deeper in the euphotic zone. However, BP was more significantly correlated with PP, but not with N2 fixation rates where DIP was more available (TDIP > 100 h), deeper in the Melanesian Archipelago, or within the entire euphotic zone in the subtropical gyre. The bacterial carbon demand to gross primary production ratio ranged from 0.75 to 3.1. These values are discussed in the framework of various assumptions and conversion factors used to estimate this ratio, including the methodological errors, the daily variability of BP, the bacterial growth efficiency and one bias so far not considered: the ability for Prochlorococcus to assimilate leucine in the dark.

Nutrients uptake and growth of Ulva lactuca (Linnaeus, 1753) in grey mullet (Mugil cephalus) wastewater versus natural estuarine water

ABSTRACTThis study investigates the capability of Ulva lactuca to grow in an integrated system, aiming to optimise the needing of resources and to decrease the ecological impact of wastewater. The nutrients uptake and the growth of U. lactuca in Mugil cephalus wastewater (WW) were evaluated and compared with U. lactuca cultivated in estuarine water (EW). Fresh thalli of U. lactuca were cultivated for 10 days in 5 L cylindrical tanks, 3 replicates per treatment. The uptake of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP), as well as the biomass yield and specific growth rate of U. lactuca, were assessed every two days. At the end of the experiment, U. lactuca resulted in a higher assimilation of DIN in EW (95.7 ± 0.3%, mean ± SE) than in wastewater (68.7 ± 1.0%) (p < .01). No significant differences were observed in DIP assimilation (>80%), as well as in the biomass yield and specific growth rate. This study demonstrates the efficiency of U. lactuca in the assimilation of DIN and DIP from M. cephalus WW, contributing to reduce the release of dissolved inorganic nutrients in the natural environment.

Benthic cycling of phosphorus in the Eastern Arabian Sea: Evidence of present day phosphogenesis

Abstract Results of a study on phosphorus (P) cycling in the Eastern Arabian Sea provides convincing evidence of present-day phosphogenesis in the study area. This finding contrasts with previous reports of the occurrence of only old phosphorites along the Indian margin. Extensive benthic P regeneration is observed in the sediments that are deposited on topographic highs in the western Indian continental margin , which is impinged by a perennial oxygen minimum zone (OMZ). The phosphate flux from the sediments ranged between 1.1 and 22 mmol m− 2 yr− 1. Among the P reservoirs, biogenic P (Pbio) is the major pool of P within the upper 30 cm of sediment. P released from organic matter decomposition and fish debris dissolution mainly controls benthic P regeneration while the role of redox cycling of iron is weak. The change in authigenic P (Pauth ) with depth in the sediment and concomitant decrease in porewater dissolved inorganic phosphate (DIP), solid phase P bio and organic P (Porg) content collectively indicate the transformation of P from labile phases to an authigenic phase. Molar Corg/Porg and Corg/Preactive ratios also support the notion of ongoing phosphogenesis in the area. The content of carbonate fluroapatite (CFA) is elevated especially in one of the three study sites as a result of in-situ precipitation and a contribution from eolian and water column authigenesis . The estimated burial efficiency of P at the sediment-water interface at two locations is only about 2%, which is much less than in the western Arabian Sea also indicating extensive P regeneration.

Evaluation of phosphate-uptake mechanisms by Fe(III) (oxyhydr)oxides in Early Proterozoic oceanic conditions

Environmental contextReconstructing the Precambrian oceanic P cycle, in conjunction with the As cycle, is critical for understanding the rise of atmospheric O2 in Earth’s history. Bioavailable phosphorus (P) has been found to regulate photosynthetic activity, whereas dissolved arsenic (As) maxima correlate with photosynthetic minima. New data on empirical adsorption and coprecipitation models with Fe(III) (oxyhydr)oxides suggest coprecipitation is a more efficient method of P sorption than is adsorption in Precambrian surface ocean conditions. AbstractBanded iron formations (BIF) are proxies of global dissolved inorganic phosphate (DIP) content in Precambrian marine waters. Estimates of Precambrian DIP rely on constraining the mechanisms by which Fe(III) (oxyhydr)oxides scavenge DIP in NaCl solutions mimicking elevated Precambrian marine Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are (1) surface attachment on pre-formed Fe(III) (oxyhydr)oxides (adsorption), and (2) incorporation of P into actively growing Fe(III) (oxyhydr)oxides (coprecipitation) during the oxidation of Fe(II) to Fe(III) (oxyhydr)oxides in the presence of DIP. It has been suggested that elevated Si concentrations, such as those suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III) (oxyhydr)oxides; however, recent coprecipitation experiments show that DIP is scavenged by Fe(III) (oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In the present study, we show that the DIP uptake onto Fe(III) (oxyhydr)oxides by adsorption is less than 5 % of DIP uptake by coprecipitation. Differences in surface attachment and the possibility of structural capture within the Fe(III) (oxyhydr)oxides are inferred from the robust influence Si has on DIP binding during adsorption, meanwhile the influence of Si on DIP binding is inhibited during coprecipitation when As(III) and As(V) are present. In the Early Proterozoic open oceans, Fe(III) (oxyhydr)oxides precipitated when deep anoxic Fe(II)-rich waters rose and mixed with the first permanently oxygenated ocean surface waters. Our data imply that, DIP was removed from surface waters through coprecipitation with those Fe(III) (oxyhydr)oxides, rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III) (oxyhydr)oxides, and by the partial release of DIP into the anoxic bottom waters and buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters, both of which would have most likely decreased the productivity of cyanobacteria and O2 production.

Simulating the responses of a low-trophic ecosystem in the East China Sea to decadal changes in nutrient load from the Changjiang (Yangtze) River

Using a three-dimensional coupled biophysical model, we simulated the responses of a lowtrophic ecosystem in the East China Sea (ECS) to long-term changes in nutrient load from the Changjiang (Yangtze) River over the period of 1960–2005. Two major factors affected changes in nutrient load: changes in river discharge and the concentration of nutrients in the river water. Increasing or decreasing Changjiang discharge induced different responses in the concentrations of nutrients, phytoplankton, and detritus in the ECS. Changes in dissolved inorganic nitrogen (DIN), silicate (SIL), phytoplankton, and detritus could be identified over a large area of the ECS shelf, but changes in dissolved inorganic phosphate (DIP) were limited to a small area close to the river mouth. The high DIN:DIP and SIL:DIP ratios in the river water were likely associated with the different responses in DIN, DIP, and SIL. As DIP is a candidate limiting nutrient, perturbations in DIP resulting from changes in the Changjiang discharge are quickly consumed through primary production. It is interesting that an increase in the Changjiang discharge did not always lead to an increase in phytoplankton levels in the ECS. Phytoplankton decreases could be found in some areas close to the river mouth. A likely cause of the reduction in phytoplankton was a change in the hydrodynamic field associated with the river plume, although the present model is not suitable for examining the possibility in detail. Increases in DIN and DIP concentrations in the river water primarily led to increases in DIN, DIP, phytoplankton, and detritus levels in the ECS, whereas decreases in the SIL concentration in river water led to lower SIL concentrations in the ECS, indicating that SIL is not a limiting nutrient for photosynthesis, based on our model results from 1960 to 2005. In both of the above-mentioned cases, the sediment accumulation rate of detritus exhibited a large spatial variation near the river mouth, suggesting that core sample data should be carefully interpreted.

Bioremediation of aquaculture wastewater from Mugil cephalus (Linnaeus, 1758) with different microalgae species

ABSTRACTCurrent aquaculture practices have a detrimental impact on the environment, in particular due to the release of high concentration of nitrogen and phosphorus that can induce eutrophication. This study investigates and compares the capacity of three microalgae species Tetraselmis suecica, Isochrysis galbana and Dunaliella tertiolecta, in the bioremediation of grey mullet Mugil cephalus wastewater. The experiment was conducted in batch conditions for 7 days using completely mixed bubble column photobioreactors. After two days, T. suecica and D. tertiolecta were able to remove more than 90% of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP), whereas I. galbana removed only 32% and 79% of DIN and DIP, respectively. A higher biomass yield resulted for T. suecica (603 ± 34 mg/L, mean ± SE). This study confirms the potential to employ T. suecica in an Integrated Multi-Trophic Aquaculture system for bioremediation of wastewater and identifies D. tertiolecta as another valid candidate species. Moreover, these species can growth in unsterilized culture media, and this reduces energy consumption, costs and efforts.

Molecular mechanism of glucose-6-phosphate utilization in the dinoflagellate Karenia mikimotoi

Phosphorus (P) is an essential nutrient for marine phytoplankton as for other living organisms, and the preferred form, dissolved inorganic phosphate (DIP), is often quickly depleted in the sunlit layer of the ocean. Phytoplankton have developed mechanisms to utilize organic forms of P (DOP). Hydrolysis of DOP to release DIP by alkaline phosphatase is believed to be the most common mechanism of DOP utilization. Little effort has been made, however, to understand other potential molecular mechanisms of utilizing different types of DOP. This study investigated the bioavailability of glucose-6-phosphate (G6P) and its underlying molecular mechanism in the dinoflagellate Karenia mikimotoi. Suppression Subtraction Hybridization (SSH) was used to identify genes up- and down-regulated during G6P utilization compared to DIP condition. The results showed that G6P supported the growth and yield of K. mikimotoi as efficiently as DIP. Neither DIP release nor AP activity was detected in the cultures grown in G6P medium, however, suggesting direct uptake of G6P. SSH analysis and RT-qPCR results showed evidence of metabolic modifications, particularly that mitochondrial ATP synthase f1gamma subunit and thioredoxin reductase were up-regulated while diphosphatase and pyrophosphatase were down-regulated in the G6P cultures. All the results indicate that K. mikimotoi has developed a mechanism other than alkaline phosphatase to utilize G6P.

Impacts of human activities on nutrient transport in the Yellow River: The role of the Water-Sediment Regulation Scheme

Anthropogenic activities alter the natural states of large rivers and their surrounding environment. The Yellow River is a well-studied case of a large river with heavy human control. An artificial managed water and sediment release system, known as the Water-Sediment Regulation Scheme (WSRS), has been carried out annually in the Yellow River since 2002. Nutrient concentrations and composition display significant time and space variations during the WSRS period. To figure out the anthropogenic impact of nutrient changes and transport in the Yellow River, biogeochemical observations were carried out in both middle reaches and lower reaches of the Yellow River during 2014 WSRS period. WSRS has a direct impact on water oxidation-reduction environment in the middle reaches; concentrations of nitrite (NO2−) and ammonium (NH4+) increased, while nitrate (NO3−) concentration decreased by enhanced denitrification. WSRS changed transport of water and sediment; dissolved silicate (DSi) in the middle reaches was directly controlled by sediments release during the WSRS while in the lower reaches, DSi changed with both sediments and water released from middle reaches. During the WSRS, the differences of nutrient fluxes and concentrations between lower reaches and middle reaches were significant; dissolved inorganic phosphorous (DIP) and dissolved inorganic nitrogen (DIN) were higher in low reaches because of anthropogenic inputs. Human intervention, especially WSRS, can apparently change the natural states of both the mainstream and estuarine environments of the Yellow River within a short time.

Nutrient inputs through submarine groundwater discharge in an embayment: A radon investigation in Daya Bay, China

Daya Bay, a semi-closed bay of the South China Sea, is famous for its aquaculture, agriculture and tourism. Although routine environmental investigations in the bay have been conducted since the early 1980s, evaluations of submarine groundwater discharge (SGD), an important process in exchange between groundwater and coastal seawater, and its environmental impacts have never been reported. In this study, naturally occurring radon isotope (222Rn) was measured continuously at two sites (north-west and middle-east sites) and used as a tracer to estimate SGD and associated nutrient inputs into the bay. The SGD rates estimated based on the 222Rn mass balance model were, on average, 28.2cm/d at north-west site and 30.9cm/d at middle-east site. The large SGD rate at middle-east site may be due to the large tidal amplitude and the sandy component with high permeability in sediments. The SGD-driven nutrient fluxes, which were calculated as the product of SGD flux and the difference of nutrient concentrations between coastal groundwater and seawater, were 3.28×105mol/d for dissolved nitrates (NO3–N), 5.84×103mol/d for dissolved inorganic phosphorous (DIP), and 8.97×105mol/d for reactive silicate (Si). These nutrient inputs are comparable to or even higher than those supplied by local rivers. In addition, these SGD-driven nutrients have a nitrogen-phosphorous ratio as high as ∼43, which may significantly affect the ecology of coastal waters and lead to frequent occurrence of harmful algal blooms.

Biogeochemical fluxes and fate of diazotroph-derived nitrogen in the food web after a phosphate enrichment: modeling of the VAHINE mesocosms experiment

Abstract. The VAHINE mesocosm experiment in the oligotrophic waters of the Nouméa lagoon (New Caledonia), where high N2 fixation rates and abundant diazotroph organisms were observed, aimed to assess the role of the nitrogen input through N2 fixation in carbon production and export and to study the fate of diazotroph-derived nitrogen (DDN) throughout the planktonic food web. A 1-D vertical biogeochemical mechanistic model was used in addition to the in situ experiment to enrich our understanding of the dynamics of the planktonic ecosystem and the main biogeochemical carbon (C), nitrogen (N) and phosphate (P) fluxes. The mesocosms were intentionally enriched with ∼ 0.8 µmol L−1 of inorganic P to trigger the development of diazotrophs and amplify biogeochemical fluxes. Two simulations were run, one with and the other without the phosphate enrichment. In the P-enriched simulation, N2 fixation, primary production (PP) and C export increased by 201, 208 and 87 %, respectively, consistent with the trends observed in the mesocosms (+124, +141 and +261 % for N2 fixation, PP and C export, respectively). In total, 5–10 days were necessary to obtain an increase in primary and export productions after the dissolved inorganic phosphate (DIP) enrichment, thereby suggesting that classical methods (short-term microcosms experiments) used to quantify nutrient limitations of primary production may not be relevant. The model enabled us to monitor the fate of fixed N2 by providing the proportion of DDN in each compartment (inorganic and organic) of the model over time. At the end of the simulation (25 days), 43 % of the DDN was found in the non-diazotroph organisms, 33 % in diazotrophs, 16 % in the dissolved organic nitrogen pool, 3 % in the particulate detrital organic pool and 5 % in traps, indicating that N2 fixation was of benefit to non-diazotrophic organisms and contributed to C export.

Sedimentary BSi and TOC quantifies the degradation of the Changjiang Estuary, China, from river basin alteration and warming SST

Environmental degradation in the Changjiang Estuary has recently become a global topic, given its proximity to Shanghai with a population >23 million. Intensification of human activities affecting the river basin is responsible for this degradation. Dam construction has cut off ca. 2/3 of the sediment flux to the sea, ca. 60% of the dissolved silicate load (DSi) has been retained in the reservoirs, while total phosphorous (TP) and total nitrogen (TN) transport to the sea are many times more than they were a few decades ago. Under such circumstances, details of the estuarine degradation remain poorly understood. This study uses sedimentary biological silicate (BSi) and total organic carbon (TOC) as environmental proxies to reveal the process-response of such degradation since the 1950s. Our results demonstrate the spatial differences of such degradation. The inner zone of the estuary used to be highly turbid, but presently has increasing diatom (BSi) and primary production (TOC), due to lower suspended sediment concentration (SSC) in relation to dam construction. In contrast, increasing riverine dissolved inorganic nitrate (DIN) and dissolved inorganic phosphorous (DIP) input (up to 2–5 times) and decreasing DSi provide a unique setting, with an excess in N and P, which catalyzes non-diatom algae in the less-turbid middle zone of the estuary. These are reflected by decreasing BSi and BSi/TOC since the 1950s, together with an increase of TOC of 20–40%. In the outer zone of the estuary, increasing DIN, DIP, and sea surface temperatures (SSTs), have resulted in the increase of diatom biomass by 15–20% and the growth of primary production by 30–60% since the 1950s. But the drastic decrease in DSi, Si/N, and Si/P depresses the ability of diatoms to develop, resulting in a reduction of 5–10% diatom proportion (BSi/TOC) since the 1930s. This study improves the understanding of the changing estuarine ecosystem in response to global change.