Dissolved Free Amino Acids Research Articles

Spatial distribution of dissolved free amino acids in three Iberian Atlantic estuaries

Rivers and estuaries are the main link between land and ocean, transferring significant amounts of dissolved organic carbon. These ecosystems receive large amount of dissolved organic matter (DOM) from diverse sources, both allochthonous and autochthonous. Within this pool, dissolved free amino acids (DFAA) represent the most labile fraction, offering valuable insights into DOM composition and diagenetic processes. Our study focused on three Iberian Atlantic estuaries—Guadalquivir, Guadiana, and Tinto-Odiel— that differ in hydrology, land use and DOM sources. We studied the longitudinal distribution of DFAA and their response to tidal cycles across these estuaries. Despite similar DFAA concentrations between estuaries (176.6 nM to 1770 nM) were found, variations in specific amino acids like glutamic acid, taurine, and aspartic acid pointed to a substantial influence of terrestrial inputs in Guadalquivir and Guadiana estuaries and an anthropogenic influence in Tinto-Odiel. Predominant amino acids—serine, glycine, ornithine, and asparagine —comprised more than 50 mol% of the estuarine DFAA pool. The dominance of serine, glycine, and ornithine indicated substantial DOM degradation, possibly associated with the loss of labile DOM during estuarine transport. Concurrently, asparagine prevalence was linked to allochthonous DOM input particularly associated with terrestrial runoff, lateral input, and anthropogenic activities at estuarine margins. Our results underscore the impact of tidal cycles on DFAA distribution and emphasize the potential of DFAA in unraveling estuarine DOM dynamics and their role as indicators of reactivity and composition in estuarine biogeochemistry.

Vertical distribution of dissolved free amino acids and phytoplankton and zooplankton biomasses.

Dissolved Free Amino Acids (DFAA) concentra tions were measured in the water column during a night and day sampling period, following a Lagrangian drogue within Concepción Bay (Chile). For the night-time sampling period no correlations between DFAA and either chlorophyll-fl or zooplankton were observed, although a positive and significant correlation between phytoplankton and zooplankton biomass did exist. During the day chlorophyll-fl and DFAA were correlated throughout the water column, suggesting that excretion, enhanced by photosynthetic activity of primary producers was occurring.

Morphological characteristics of amino acids in wet deposition of Danjiangkou Reservoir in China's South-to-North Water Diversion Project.

Amino acids are an important constituent in organic nitrogen deposition, and changes in the content of their components have a direct impact on the nitrogen input to the ecosystem. From December 2018 to November 2019, 176 precipitation samples were collected at Danjiangkou Reservoir, the source of the middle line of the South-to-North Water Diversion Project, and the variation characteristics of dissolved free amino acids (DFAA) and dissolved combined amino acids (DCAA) were analyzed. The volume-weighted value concentration ranges of DFAA and DCAA were 0.159-1.136μmol/L and 1.603-7.044μmol/L, respectively, and amino acids were dominated by DCAA in wet deposition. Our results showed that glutamic acid (Glu), glycine (Gly), and aspartic acid (Asp) were the dominant amino acids in both DFAA and DCAA. The concentration of DFAA was highest in winter, while the concentration of DCAA was in autumn. Dissolved total amino acids (DTAA) were insignificantly correlated with DFAA, whereas they were linearly correlated with DCAA, indicating a significant influence of agricultural activities on DTAA. The analysis of the backward trajectory of air masses showed that amino acids were mainly influenced by proximity inputs around the reservoir. The bioavailability of organic matter was higher in the southeastern of the reservoir than in the northwestern. The wet deposition flux of TDN was 14.096kgN/ha/year, and the potential ecological impact on water bodies cannot be ignored. This study was conducted to clarify the variation characteristics of amino acids fractions in wet deposition and to provide parameters for regional assessment of amino acids wet deposition. The ecological impact of nitrogen wet deposition on water bodies will be explored to provide a basis for nitrogen pollution control and water quality protection in the middle line of the South-to-North Water Diversion Project.

Spatial microheterogeneity and selective microbial consumption of dissolved free amino acids in an oligomesotrophic lake

AbstractWe studied the cm to m scale spatial distribution of dissolved free amino acids (DFAA) in the upper epilimnion of oligomesotrophic Lake Zurich in 14 sampling campaigns over > 3 years and at various periods of the growing season. During each campaign, 10 sets of 10 simultaneously drawn samples (10 mL, 2 cm distance) were collected from 5 m depth. DFAA concentrations varied by one to > 3 orders of magnitude within sets, providing field evidence for DFAA release from macroscopic point sources and for substantial variability of the in‐situ growth conditions of bacterioplankton metacommunities. There was a tight relationship between the median DFAA concentration per sampling campaign and the compositional heterogeneity of the 15 most common AA: their composition was similar in samples from campaigns with high median DFAA concentrations, indicating that spatial distribution patterns were mainly a result of physical mixing. By contrast, AA composition was spatially variable in campaigns with low median DFAA concentrations, and serine, aspartate, and glycine were disproportionally high in the 10% samples with highest DFAA concentrations. We hypothesized that pelagic bacteria would preferably target pulses of such locally overrepresented AA. Short‐term incubations with radiolabeled tracers revealed substantially higher microbial uptake of serine and, to a lesser extent, aspartate, than of two amino acids with consistently low in situ concentrations (leucine, isoleucine). This illustrates a “preparedness” of the bacterioplankton to preferably incorporate those AAs that are more available in DFAA hotspots.

Chemically unidentified dissolved organic carbon: A pivotal piece for microbial activity in a productive area of the Northern Patagonian shelf

The biochemical composition and fluorescence properties of DOM were assessed in relation to phytoplankton and major aquatic bacterial clades in a regenerative area of the Argentine Shelf. DOM was mainly of autochthonous biological origin, containing humic- and protein-like substances of medium degree of unsaturation and diagenesis. Biochemical-DOM accounted for 25% of total DOC, being dissolved combined amino acids (DCAA) the dominant fraction followed by free carbohydrates. Phytoplankton was the main source of serine, alanine, and valine, and particulate carbohydrates. Gammaproteobacteria abundance correlated negatively with ammonium and positively with DCAA, suggesting a coupling between ammonium consumption and refractory amino acid production. A preferential utilization of alanine, leucine and threonine as nitrogen source was inferred from the distribution of Cytophaga-Flavobacteria-Bacteroidete in relation with dissolved free amino acids (DFAA). Notably, Alpha- and Betaproteobacteria correlated with the large pool (75%) of chemically unidentified DOC and not with DCAA or dissolved combined carbohydrates. Particularly, Alphaproteobacteria (∼40% of EUB total heterotrophic bacteria) either significantly contribute to the production of the “humic”, refractory fraction of marine DOM, or the latter impairs resource control on their abundance. Spatial heterogeneity inherent to coastal-shelf areas drives important regional variability in the biochemical properties of DOM.

Migratory Zooplankton Excreta and Its Influence on Prokaryotic Communities

Particulate organic matter (POM) (fecal pellets) from zooplankton has been demonstrated to be an important nutrient source for the pelagic prokaryotic community. Significantly less is known about the chemical composition of the dissolved organic matter (DOM) produced by these eukaryotes and its influence on pelagic ecosystem structure. Zooplankton migrators, which daily transport surface-derived compounds to depth, may act as important vectors of limiting nutrients for mesopelagic microbial communities. In this role, zooplankton may increase the DOM remineralization rate by heterotrophic prokaryotes through the creation of nutrient rich “hot spots” that could potentially increase niche diversity. To explore these interactions, we collected the migratory copepodPleuromamma xiphiasfrom the northwestern Sargasso Sea and sampled its excreta after 12–16 h of incubation. We measured bulk dissolved organic carbon (DOC), dissolved free amino acids (DFAA) via high performance liquid chromatography and dissolved targeted metabolites via quantitative mass spectrometry (UPLC-ESI-MSMS) to quantify organic zooplankton excreta production and characterize its composition. We observed production of labile DOM, including amino acids, vitamins, and nucleosides. Additionally, we harvested a portion of the excreta and subsequently used it as the growth medium for mesopelagic (200 m) bacterioplankton dilution cultures. In zooplankton excreta treatments we observed a four-fold increase in bacterioplankton cell densities that reached stationary growth phase after five days of dark incubation. Analyses of 16S rRNA gene amplicons suggested a shift from oligotrophs typical of open ocean and mesopelagic prokaryotic communities to more copiotrophic bacterial lineages in the presence of zooplankton excreta. These results support the hypothesis that zooplankton and prokaryotes are engaged in complex and indirect ecological interactions, broadening our understanding of the microbial loop.

Impact of Water-Sediment Regulation on Variations of Amino Acids in the Middle-Lower Yellow River, China

In order to examine the impacts of water-sediment regulation on regional carbon cycling, we collected water, particulate and sediment samples from the middle-lower Yellow River in late June and early July, 2015 and analyzed their specific amino acids (AA), DOC, POC, and bacteria abundance. Summarized by 14 specific AA, the total hydrolysable AA (THAA), particulate AA (PAA), and sediment AA (SAA) varied in ranges of 2.29–9.05 µmol L−1, 5.22–22.96 µmol L−1, and 81.7–137.19 µg g−1 dry weight. After the regulation, dissolved free AA (DFAA) decreased by 29% while DCAA increased by 72%. These variations suggested that DFAA were further degraded, while DCAA molecules were further activated. Meanwhile, PAA increased almost 4 times as many as those before regulation, and SAA increased as well. After regulation, the amounts of bioactive amino acids (Asp, Glu and Gly) increased in THAA but decreased in PAA, with little changes in SAA. The ratios of Asp/Gly in different phases increased after regulation, indicating the AA contributions were promoted by calcareous organisms rather than by siliceous organisms. Multiple correlation analysis showed that PAA was primary representatives of AA and organic carbon, followed by DCAA and POC. Moreover, bacterial reproduction played a key role in shaping the AA compositions and properties, followed by the redox condition and acid-base balance. The results of this study provided a clear evidence for the effects of water-sediment regulation on regional biogeochemistry of organic carbon in the middle-lower Yellow River.

Transformation of amino acid tyrosine in chromophoric organic matter solutions: Generation of peroxide and change of bioavailability.

Studying the photochemical transformation mechanism of dissolved free amino acids (DFAA) in chromophoric dissolved organic matter (CDOM) solution facilitates the understanding of DFAA's environmental fate and bioavailability change upon solar irradiation in natural surface waters. Tyrosine oxidation product (Tyr-OH) was synthesized to quantify the primary transformation product (tyrosine peroxide, Tyr-OOH) in CDOM solution. Both reactions between superoxide radical anion (O2-) and tyrosine radical (Tyr) and between singlet oxygen (1O2) and tyrosine (Tyr) yield Tyr-OOH, which is subsequently transformed into Tyr-OH. The reaction between O2- and Tyr not only generated Tyr-OOH but also caused the regeneration of Tyr. O2- and 1O2 contributed 30-44% to Tyr's transformation in CDOM solutions at pH 8.0, in which 1O2 oxidation accounted for 6-11%. The contribution of O2- to Tyr's phototransformation process was the difference between the total contribution of O2- and 1O2 and the individual contribution of 1O2. Compared with the fast assimilation of Tyr, Tyr-OH was stable in natural water under dark incubation, indicating that phototransformation decreased the bioavailability of Tyr.

Characteristics of Dissolved Organic Nitrogen in Municipal and Biological Nitrogen Removal Wastewater Treatment Plants in Jordan

Abstract The investigation is conducted on the biochemical form and characteristics of wastewater-derived DON in three different WWTPs in Jordan. The main eliminations of DON and biodegradable dissolved organic nitrogen (BDON) noticed along the treatment course are in the Irbid (ITP). Dissolved combined amino acids (DCAA) and dissolved free amino acids (DFAA) in the outlet accounted for less than 4% of the outlet DON of all plants. The DON from the outlet was composed of 90% hydrophilic compounds which stimulate algal growth. The study provided information for future improvement of WWTPs of Jordan and for adjusting the assortment of DON elimination systems to comply with stricter limits.

The deep water of Eastern Mediterranean Sea is a hotspot for bacterial activity

We investigated the abundance and production of mesopelagic (150–650 m) and bathypelagic (>650 m) bacteria from the poorly-studied Levantine basin (Eastern Mediterranean Sea) during the summers of 2014–2017. We show that the mesopelagic and bathypelagic microbial populations have relatively high cell specific activity, amongst the highest worldwide, likely due to the relatively warm temperatures characterizing these depths in comparison to other oceanic regions. Furthermore, in order to investigate if mesopelagic and bathypelagic microbial populations are limited by the scarce organic carbon substrates in the area, we performed microcosm addition assays of pure glucose (Glu) and/or a mixture of dissolved free amino acids (DFAA). Both the mesopelagic and bathypelagic bacterial populations responded positively to the additions, with bacterial production rapidly increasing within a few hours following the Glu or DFAA amendments. Our results demonstrate that deep-water microbes in the Levantine Basin may be important nutrient recyclers, especially when labile organic carbon is introduced. Our observations may have implications on carbon cycling and sequestration in the oligotrophic Eastern Mediterranean Sea.

Concentration and turnover of dissolved free polyamines on the South Coast of Lake Erie

AbstractDissolved free polyamines (DFPAs) have been suggested as an important source of reduced nitrogen in marine systems, but their importance in the cycling of dissolved organic nitrogen (DON) in freshwater systems has yet to be assessed. This study measured the concentrations, turnover and uptake rates of DFPAs and compared them with those of dissolved free amino acids (DFAAs) in samples from 21 sites along eight coastal transects on the south shore of Lake Erie (LE), a Laurentian Great Lake. DFPA compounds were consistently detected in all samples and their concentrations (16.9–191.5 nmol L−1), turnover (1.6–3.2 d−1), and uptake rates (3.2–192.0 nmol L−1 d−1) were all significantly higher than those reported in marine environments. On the other hand, corresponding DFAA measurements (45.1–822.2 nmol L−1, 3.9–11.4 d−1, and 35–1690 nmol L−1 d−1, respectively) were within the range of reported values in marine environments. The DFPA to DFAA ratios in LE samples ranged between 0.21 and 0.65, which were much higher than what have been reported in marine environments (0.01–0.07). Within the bacterioplankton community, particle‐associated (PAB) and free‐living (FLB) proportions contributed equally to the turnover of DFPAs and DFAAs in LE. PAB and FLB also contributed equally when using requested DFPAs to fulfill their carbon (BCD; 3.1–7.9%) and nitrogen (BND; 13.5–18.5%) demands. Overall, our results suggest that DFPAs is a significant component of labile DON pool in freshwater systems, where they serve more as nitrogen than carbon sources to freshwater bacterioplankton.

Variations in concentrations and sources of bioavailable organic compounds in the Indian estuaries and their fluxes to coastal waters

Estuarine organic matter (EOM) supports heterotrophic carbon demand in the estuaries. However, the fraction of bioavailable organic compounds, which are easily assimilated by biological organisms, in the EOM is unclear. We hypothesize that a significant fraction of dissolved EOM is bioavailable and supports heterotrophic activity in the Indian estuaries. In order to test this hypothesis, 26 major, medium and minor Indian estuaries were sampled during wet and dry periods (2011–2012) for dissolved bioavailable organic compounds and dissolved organic carbon (DOC). The mean concentration of total dissolved carbohydrates (TDCHO) and total dissolved proteins (TDPRO) were higher during wet than dry period in contrary to the observations of dissolved free Amino Acids (DFAA). TDPRO:TDCHO and statistical analysis revealed that terrestrial oganic matter contributed significantly to the EOM in the major and medium estuaries during wet period whereas fresh organic matter derived from in situ production contributed in all estuaries during dry period and minor estuaries during wet period. The lower concentrations of TDCHO and DFAA and their contribution to DOC were observed in the Indian than global estuaries suggesting that either efficient utilization of bioavailable organic compounds or less inputs (autochthonous/allochthonous) in the Indian estuaries. Indian estuaries transported an order of magnitude higher concentration of bioavailable organic compounds to the coastal Bay of Bengal (490 × 109 gC y−1) than to the Arabian Sea (50 × 109 gC y−1). The contribution of bioavailable organic compounds to the DOC export was 25% and 7% in the Bay of Bengal and Arabian Sea respectively. This study suggests that EOM contains a significant fraction of bioavailable organic compounds, as hypothesized, which might support heterotrophic carbon demand in the Indian estuaries as well as adjacent coastal waters.

Dissolved Compounds Excreted by Copepods Reshape the Active Marine Bacterioplankton Community Composition

Copepods are important suppliers of bioreactive compounds for marine bacteria through fecal pellet production, sloppy feeding, and the excretion of dissolved compounds. However, the interaction between copepods and bacteria in the marine environment is poorly understood. We determined the nitrogen and phosphorus compounds excreted by copepods fed with two natural size-fractionated diets (<20-µm and 20–150-µm) in the upwelling zone of central/southern Chile in late summer and spring. We then assessed the biogeochemical response of the bacterial community and its structure, in terms of total and active cells, to enrichment by copepod-excreted dissolved compounds. Results revealed that copepods actively excreted nitrogen and phosphorus compounds, mainly in the form of ammonium and dissolved organic phosphorus (DOP), reaching excretion rates of 2.6 and 0.05 µmol L-1 h-1, respectively. In both periods, the maximum excretion rates were associated with the 20–150-µm size fraction, but particularly during spring, when a higher organic matter quality was observed in excretion products compared to late summer. There were higher excretion rates of dissolved free amino acids (DFAAs) from copepods fed with the <20-µm size fraction, mainly histidine (HIS) in late summer and glutamic acid (GLU) in spring. A shift in the composition of the active bacterial community was observed between periods and treatments, which was associated with the response of the common seawater surface phyla Proteobacteria and Bacteroidetes. The specific bacterial activity (16S rRNA: rDNA) suggested a different response to the two size-fractionated diets. In late summer, Betaproteobacteria and Bacteroidetes were stimulated by the treatment enriched with excretion products derived from the 20–150-µm and <20-µm size fractions, respectively. In spring, Alphaproteobacteria were active in the treatment enriched with the excretion products of copepods fed with the <20-µm size fraction, whereas they were inhibited in the treatment enriched with excretion products in the 20–150-µm size fraction. Our findings indicate that different copepod diets can have a significant impact on the quantity and quality of their excretion compounds, which can subsequently generate shifts in the active bacterial composition. The bacterial response is probably associated with common-opportunistic sea surface microbes that are adapted to rapidly reacting to environmental offers.

Linking Compositional and Functional Predictions to Decipher the Biogeochemical Significance in DFAA Turnover of Abundant Bacterioplankton Lineages in the North Sea.

Deciphering the ecological traits of abundant marine bacteria is a major challenge in marine microbial ecology. In the current study, we linked compositional and functional predictions to elucidate such traits for abundant bacterioplankton lineages in the North Sea. For this purpose, we investigated entire and active bacterioplankton composition along a transect ranging from the German Bight to the northern North Sea by pyrotag sequencing of bacterial 16S rRNA genes and transcripts. Functional profiles were inferred from 16S rRNA data using Tax4Fun. Bacterioplankton communities were dominated by well-known marine lineages including clusters/genera that are affiliated with the Roseobacter group and the Flavobacteria. Variations in community composition and function were significantly explained by measured environmental and microbial properties. Turnover of dissolved free amino acids (DFAA) showed the strongest correlation to community composition and function. We applied multinomial models, which enabled us to identify bacterial lineages involved in DFAA turnover. For instance, the genus Planktomarina was more abundant at higher DFAA turnover rates, suggesting its vital role in amino acid degradation. Functional predictions further indicated that Planktomarina is involved in leucine and isoleucine degradation. Overall, our results provide novel insights into the biogeochemical significance of abundant bacterioplankton lineages in the North Sea.

Determination of picomolar dissolved free amino acids along a South Atlantic transect using reversed-phase high-performance liquid chromatography

Abstract Dissolved free amino acids (DFAA) in seawater are a form of nitrogen (N) available for marine microbes. In oligotrophic environments where N-containing nutrients are the limiting factor for microbial growth, N nutrition from DFAA could be crucial, but as yet it is poorly resolved. Measurements of individual DFAA are challenging as concentrations are typically in the low nmol L − 1 range. Here we report modifications to methodology using o-phthaldialdehyde (OPA) derivatization and reversed phase high performance liquid chromatography (HPLC) that provide a 30-fold improvement in sensitivity enabling the detection of 15 amino acids in seawater with a limit of detection as low as 10 pmol L − 1 with accuracy and precision of better than 10%. This analytical methodology is now suitable for the challenging quantitation of DFAA in oligotrophic seawaters. The method was successfully applied to a suite of seawater samples collected on a cruise crossing the South Atlantic Ocean, where concentrations of DFAAs were generally low (sub nmol L − 1 ), revealing basin-scale features in the oceanographic distributions of DFAA. This unique dataset implies that DFAAs are an important component of the N cycle in both near-coastal and open oceans. Further calculations suggest that the proportions of organic N originating from DFAA sources were significant, contributing between 0.2 and 200% that of NH 4 + and up to 77% that of total inorganic nitrogen in the upper 400 m in some regions of the transect.

Coupled Response of Bacterial Production to a Wind-Induced Fall Phytoplankton Bloom and Sediment Resuspension in the Chukchi Sea Shelf, Western Arctic Ocean

Heterotrophic bacterial abundance and production, dissolved free amino acid (DFAA) and dissolved combined amino acid (DCAA) concentrations, and other microbial parameters were determined for seawater samples collected at a fixed station (maximum water depth, 56 m) deployed on the Chukchi Sea Shelf, in the western Arctic Ocean, during a 16-day period in September 2013. During the investigation period, the sampling station experienced strong winds and a subsequent phytoplankton bloom, which was thought to be triggered by enhanced vertical mixing and upward nutrient fluxes. In this study, we investigated whether bacterial and dissolved amino acid parameters changed in response to these physical and biogeochemical events. Bacterial abundance and production in the upper layer increased with increasing chlorophyll a concentration, despite a concomitant decrease in seawater temperature from 3.2°C to 1.5°C. The percentage of bacteria with high nucleic acid content during the bloom was significantly higher than that during the prebloom period. The ratio of the depth-integrated (0–20 m) bacterial production to primary production differed little between the prebloom and bloom period, with an overall average value of 0.14 ± 0.03 (± standard deviation, n = 8). DFAA and DCAA concentrations varied over a limited range throughout the investigation, indicating that the supply and consumption of labile dissolved amino acids were balanced. These results indicate that there was a tightly coupled, large flow of organic carbon from primary producers to heterotrophic bacteria during the fall bloom. Our data also revealed that bacterial production and abundance were high in the bottom nepheloid (low transmittance) layer during strong wind events, which was associated with sediment resuspension due to turbulence near the seafloor. The impacts of fall wind events, which are predicted to become more prominent with the extension of the ice-free period, on bacterial processes and the dynamics of organic matter in the Chukchi Sea Shelf could have far-reaching influences on biogeochemical cycles and ecosystem dynamics in broader regions of the Arctic Ocean.

The behavioural homing response of adult chum salmon Oncorhynchus keta to amino-acid profiles.

Adult chum salmon Oncorhynchus keta homing behaviour in a two-choice test tank (Y-maze) was monitored using a passive integrated transponder (PIT)-tag system in response to river-specific dissolved free amino-acid (DFAA) profiles and revealed that the majority of O. keta showed a preference for artificial natal-stream water and tended to stay in this maze arm for a longer period; natal-stream water was chosen over a nearby tributary's water, but not when the O. keta were presented with a non-tributary water. The results demonstrate the ability of O. keta to discriminate artificial stream waters containing natural levels of DFAA.

Temporal and spatial variations of particulate and dissolved amino acids in the East China Sea

Concentrations of amino acids in dissolved and particulate pools in the East China Sea (ECS) were determined during two cruises (October–November 2013 and May–June 2014). The spatial distributions of total hydrolyzed amino acids (THAA), dissolved combined amino acids (DCAA), dissolved free amino acids (DFAA), and particulate amino acids (PAA) in the study area were considerably influenced by phytoplankton biomass and circulations. In addition, in situ phytoplankton production and terrestrial input are the major sources of amino acids in the ECS. The %C-PAA and %N-PAA positively correlated with chlorophyll a (Chl-a), thus reflecting their phytoplankton sources. The concentrations of amino acids were higher in coastal waters than in open sea, revealing the effects of terrestrial input on amino acid concentrations. Moreover, the vertical distributions of THAA, DCAA, DFAA, and PAA exhibited similar patterns, i.e., decreasing trends from the surface water to the bottom water. Our study indicated that the deposition of phytoplankton biodetritus may affect the vertical distributions of amino acids. The major constituents of THAA were glycine, serine, and glutamic acid, whereas the major constituents of PAA are glycine, glutamic acid, and alanine. The diel variation of THAA presented a certain hysteresis, following the variation of Chl-a. Particle sorption had a contribution in describing the particulate pool and dissolved pool in the Changjiang River.

Quantitative PCR analysis of the spatiotemporal dynamics of Aureococcus anophagefferens and Minutocellus polymorphus and the relationship between brown tides and nutrients in the coastal waters of Qinhuangdao, China

Brown tides caused by the excessive growth of the pelagophyte Aureococcus anophagefferens have occurred frequently in Qinhuangdao, China, since 2009. In this study, the temporal and spatial variations of A. anophagefferens and Minutocellus polymorphus were analyzed using real-time fluorescent quantitative PCR. The relationship between nutrient contents and brown tide events as well as the impacts of the brown tides on the composition of phytoplankton is discussed. The results showed that A. anophagefferens reached peak densities in July. Brown tides occurred in the coastal waters of Funing and Changli, and the main affected areas shifted from south to north throughout the experiment. The A. anophagefferens brown tide event was not monospecific, as M. polymorphus and Prorocentrum minimum were also observed. A redundancy analysis (RDA) indicated that decreasing concentrations of dissolved inorganic nitrogen (DIN) and increasing concentrations of the available organic nitrogen compounds (urea, dissolved free amino acids (DFAA), and dissolved combined amino acids (DCAA)) from March to June may have resulted in the outbreak of the brown bloom of A. anophagefferens, coinciding with a reduction in the community diversity of phytoplankton in the coastal waters of Qinhuangdao.

Spatiotemporal variation of dissolved carbohydrates and amino acids in Jiaozhou Bay, China

Surface seawater samples were collected from Jiaozhou Bay, China, during six cruises (March–May 2010, September–November 2010) to study the distribution of dissolved organic matter including dissolved organic carbon (DOC), total dissolved carbohydrates, namely monosaccharides (MCHO) and polysaccharides (PCHO) and total hydrolysable amino acids. These included dissolved free amino acids (DFAA) and combined amino acids (DCAA). The goal was to investigate possible relationships between these dissolved organic compounds and environmental parameters. During spring, the concentrations of MCHO and PCHO were 9.6 (2.8−22.6) and 11.0 (2.9−42.5) μmol C/L, respectively. In autumn, MCHO and PCHO were 9.1 (2.6−27.0) and 10.8 (2.4−25.6) μmol C/L, respectively. The spring concentrations of DFAA and DCAA were 1.7 (1.1−4.1) and 7.6 (1.1−31.0) μmol C/L, respectively, while in autumn, DFAA and DCAA were 2.3 (1.1−8.0) and 3.3 (0.6−7.2) μmol C/L, respectively. Among these compounds, the concentrations of PCHO were the highest, accounting for nearly a quarter of the DOC, followed by MCHO, DCAA and DFAA. The concentrations of the organic compounds exhibited a decreasing trend from the coastal to the central regions of the bay. A negative correlation between concentrations of DOC and salinity in each cruise suggested that riverine inputs around the bay have an important impact on the distribution of DOC in the surface water. A significant positive correlation was found between DOC and total bacteria count in spring and autumn, suggesting bacteria play an important role in the marine carbon cycle.