Inorganic Phosphorus Compounds Research Articles

The effect of natural organic matter (NOM) on the distribution and resources of mobile phosphorus in the bottom sediments of small retention reservoirs

The purpose of the work detailed here was to determine the impact of the distribution of natural organic matter and grain size on the resources and distribution of mobile phosphorus in the bottom sediments of small reservoirs located in catchments subject to different levels of anthropopressure. The research objects were five small reservoirs located in southeast Poland. In small retention reservoirs, it is the anthropogenic impact of the catchment and its geological structure, and to a lesser extent sediment granulation, that determine the distribution of phosphorus fractions (especially in inorganic compounds) and the share of total P they account for. In general, a higher level of contamination of sediments with organic matter (OSION increase) is shown to be associated with a higher content of the organic fraction of phosphorus and easily decomposable organic matter. Within small retention reservoirs under significant anthropogenic influence from the catchment, sandy sediments compared with silty sediments were significantly less loaded with potentially mobile phosphorus as well as with organic forms of phosphorus and (sometimes) nitrogen. The occurrence of humic-metal-phosphate complexes is determined by there being sufficient organic matter, especially humic fractions. Fractions of inorganic phosphorus compounds and organic matter have the terrigenous source of these pollutants in common. The organic sediment index can serve as an adjunctive indicator with which to assess the potential ability of the sediments in small retention reservoirs to internal supply of the water column in nutrients.

Role of Aspergillus niger in Solubilizing P in Togo Rock Phosphate during Composting with Different Organic Wastes

The immobilization and mineralization processes carried out by soil microorganisms have a significant role in controlling the availability of phosphorus in soil. A class of helpful microorganisms known as phosphate solubilizing microbes are able to hydrolyze insoluble organic and insoluble inorganic phosphorus compounds into soluble P (phosphorus) form that is readily taken by plants. The objective of this study was to evaluate the role of different organic waste and Aspergillus niger in solubilizing P in Togo rock phosphate during composting. Composts were prepared using rice straw and citrus waste that had been inoculated with Aspergillus niger and supplemented with rock phosphate. The results showed that co-inoculation system with PSF (i.e. Aspergillus niger) provided optimum condition for P solubilization.

Properties of Microorganisms Isolated from Soils under Conventional and Organic Farming

Оbjective. The article presents the results of research aimed at determining the influence of different methods of tillage on the functional diversity of the soil microbiota. Soil samples containing plant residues from agricultural plots under conventional and organic farming in the Kyiv oblast were used for the study. Methods. Analysis of soil microbiota using differential diagnostic nutrient media by serial dilutions of soil suspension was performed. To quantify the phosphate-mobilizing properties of the isolated microorganisms, the concentration of phosphorus in the solution was measured (grown in NBRIP liquid medium) and detected by the Arenius spectrophotometric method on a Ulab 102UV Spectrophotometer. Results. Th e soil of the plots under organic agrotechnology of cultivation was marked by a greater number of microorganisms of all ecological and trophic groups, except oligonitrophilic and phosphate-solubilizing bacteria. The vast majority of phosphate-transforming bacteria were isolated from the soil of agricultural plots under convection farming. The largest number of cellulose-degrading isolates was isolated from the soil under organic farming plots. Five isolates have the widest range of agronomically useful properties, in particular, the ability to mobilize organic and inorganic phosphates and cellulosolytic activity: 6b, 13b, 18b, 19b, and 8m. After incubation of the isolates on an NBRIP medium at 28°C and 200 rpm for 72 hr, special analyzes for dissolved phosphorus content and pH level in the culture fluid were performed. Isolate 8m selected from chornozem (black soil) under convection agriculture and classified by us as Trichoderma sp. exhibited the highest phosphate-mobilizing activity. The vast majority of bacteria capable of phosphate transformation were isolated from the soil of agricultural areas affected by convection agriculture; and isolates capable of dissolving cellulose — from the soil of organic farming. Conclusions. The initial identification of certain isolates allowed us to classify them as Bacillus and Trichoderma. These isolates are important for further research with the prospect of creating a complex biological preparation with fungicidal properties and the ability to mobilize organic and inorganic phosphorus compounds.

Uptake of inorganic and organic phosphorus compounds by two marine sponges and their associated bacterial communities in aquaria.

Marine sponges are abundant filter-feeders in benthic ecosystems and many host copious microorganisms. Sponges and their symbionts have emerged as major players within marine biogeochemical cycles, facilitating uptake and release of carbon, nitrogen, and sulfur. Sponge holobionts' role in transforming dissolved carbon and nitrogen is well established; however, the same depth of understanding has not yet been extended to phosphorus. In this aquaria-based study, 32 P-labelled orthophosphate and ATP were used to determine that two sponges, Lendenfeldia chondrodes and Hymeniacidon heliophila, both take up ambient dissolved inorganic phosphate (DIP) and dissolved organic phosphorus (DOP). Subsequent genetic analyses and chemical extraction showed that sponge symbionts have the potential to synthesise polyphosphate (poly-P) and that this energy-rich form of stored phosphorus is present in both sponges. L. chondrodes, an oligotrophic sponge with a microbiome dominated by cyanobacteria, stores more phosphorus as poly-P (6%-8% of total phosphorus) than H. heliophila (0.55%), a eutrophic sponge with low cyanobacterial abundance. DIP/DOP uptake, as well as poly-P storage, may be driven by two factors: cyanobacterial abundance and nutrient availability. Considering their prevalence in phosphorus-limited ecosystems and their ability to pump large amounts of seawater, sponge holobionts are likely to be key players within benthic phosphorus cycles.

Functional Metagenomics Approach for the Discovery of Novel Genes Encoding Phosphatase Activity.

Phosphate release from inorganic and organic phosphorus compounds can be enzymatically mediated. Phosphate-releasing enzymes, comprising acid and alkaline phosphatases, are recognized as useful biocatalysts in applications such as plant and animal nutrition, bioremediation, and diagnostic analysis. Here, we describe a functional metagenomics approach enabling rapid identification of genes encoding these enzymes. The target genes are detected based on small- and large-insert metagenomic libraries derived from diverse environments. This approach has the potential to unveil entirely new phosphatase families or subfamilies and members of known enzyme classes that hydrolyze phosphomonoester bonds such as phytases. Additionally, we provide a strategy for efficient heterologous expression of phosphatase genes.

Assessment of inorganic nitrogen and phosphorus compounds removal efficiency from different types of wastewater using microalgae cultures

The efficiency of ammonium nitrogen (N-NH4 +) and phosphate (P-PO4 3-) removal from wastewater with different loads of these nutrients was evaluated using Chlamydomonas reinhardtii (Сhlоrорhуtа) and Oscillatoria neglecta (Суаnорhуtа/Cyanoprokaryota). In addition, functional characteristics of the microalgae under the studied conditions were determined. It was demonstrated that Ch. reinhardtii is resistant to a wide range of concentrations of inorganic nitrogen and phosphorus compounds. Microalgae actively participate in the removal of N-NH4 + from wastewater (removal efficiency of 49–63%, depending on the initial concentration). At the same time, Ch. reinhardtii showed low levels of P-PO4 3- removal (7–18%) from the aquatic environment. O. neglecta, unlike Ch. reinhardtii, is sensitive to excessively high concentrations of N-NH4 + (90–140 mg l−1) and P-PO4 3- (26–90 mg l−1). However, it is characterized by high removal efficiency for both forms of nitrogen (60–61%) and phosphorus (43–55%) at their initial concentrations of 30–50 mg l-1 and 7–14 mg l-1, respectively. Therefore, O. neglecta is best suited for use in wastewater post-treatment.

The Content of Phosphorus in the Needles of Pinus sylvestris L. Affected by Industrial Air Pollution

A facility for disposal of toxic substances had been functioning in Kirov Oblast between 2006 and 2015. Destruction of phosphorus-containing substances resulted in formation of inorganic phosphorus compounds, which could enter the environment as components of gaseous emissions. The aim of the present work was to study the spatial patterns of accumulation of phosphorus compounds in the needles of Pinus sylvestris L. in the production area. The study was carried out at monitoring sites, which were represented by forest communities (southern taiga subzone) located at different distances from the pollution source (0.96–9.63 km). The total phosphorus in second-year pine needles was determined by the spectrophotometric method. During the research period (2011–2017), total phosphorus in the needles of P. sylvestris varied between 730 and 2229 μg/g. Based on results of cluster analysis, the sites were classified into two groups, which differed in levels of phosphorus accumulation in the needles of Р. sylvestris. The first group included sites with increased accumulation of total phosphorus in pine needles, which were located near the source of pollution in the direction of the prevailing winds. In sites belonging to the second group, the needles contained reduced amounts of phosphorus compounds. During the research period, variations in the amount of phosphorus in pine needles followed a similar pattern. From 2011 to 2016, the accumulation of phosphorus in the needles increased at monitoring sites of both groups. A decrease in total phosphorus in needles in 2017 was caused by a decrease in the release of phosphorus compounds to the environment and the involvement of accumulated phosphorus in the life processes of P. sylvestris. The increased accumulation of phosphorus compounds in needles in the sites near the source of air pollution was not favorable for vital processes of P. sylvestris needles and resulted in a reduction in their lifespan. Thus, the needles of P. sylvestris can be used as an accumulative indicator in areas affected by industrial air pollution by phosphorus compounds

Long-term changes in organic and inorganic phosphorus compounds as affected by long-term synthetic fertilisers and pig manure in arable soils

BackgroundManures and synthetic fertilisers can affect soil pH and plant-microbe processes and thus influence P forms and composition.AimsThe objective of this study was to examine the effects of the 40-year application of synthetic fertilisers or pig manure combined with synthetic fertilisers on the P forms and composition and the response of corn growth and yield to changes in P availability.MethodsA long-term field experiment with unfertilised, urea, urea+superphosphate, pig manure+urea and pig manure+urea+superphosphate fertilised soils was studied. 31P nuclear magnetic resonance spectroscopy was used to quantify P compounds.ResultsThe maximum corn yield was found when adding pig manure+urea, despite Olsen-P was lower than on adding manure+superphosphate. Other monoester P compounds, typically related to microbial biomass and processes were highest on adding pig manure+urea. When adding superphosphate+urea+pig manure a reduction of these P compounds was observed as well as the highest accumulation of inositol hexakisphosphate (IHP). Synthetic fertilisers increased Olsen-P, orthophosphate and other monoester and total IHP and largely decreased soil pH. The addition of pig manure greatly increased the stereoisomers of IHP (myo-IHP, scyllo-IHP, neo-IHP, and D-chiro-IHP) and the concentration of orthophosphate diesters. D-chiro-IHP was not found in unfertilised soils while neo-IHP was not detected in synthetically fertilised soils.ConclusionsP compounds related to microbial processes, such as other monoester, increased when adding pig manure. Additions of superphosphate on top of manures reduced other monoester, while they increased on adding synthetic fertilisers alone. Unfertilised soils were virtually free of P compounds related to microbial processes.

Modification of Glass/Polyester Laminates with Flame Retardants.

This paper presents a review of flame retardants used for glass/polyester laminates. It concerns flame retardants withdrawn from use such as compounds containing halogen atoms and flame retardants currently used in the industry, such as inorganic hydroxides, phosphorus and nitrogen-containing compounds, antimony, and boron compounds, as well as tin–zinc compounds. Attention is also drawn to the use of nanoclays and the production of nanocomposites, intumescent flame retardant systems, and mats, as well as polyhedral oligomeric silsesquioxanes. The paper discusses the action mechanism of particular flame retardants and presents their advantages and disadvantages.

Preliminary Assessment of Ecological Status of the Siversky Donets River Basin (Ukraine) Based on Phytoplankton Parameters and Its Verification by Other Biological Data

The river basin of Siversky Donets is of great scientific interest since this river runs through a territory with heavy industry (in particular, coal mining, chemical processing and metal industries). Within the basin, rivers of different sizes were explored (small, medium, large and extra-large) that flow through siliceous and calcareous rocks on the same elevation (lowland—below 200 m a.s.l.). Phytoplankton, as one of the Biological Quality Element, was used to perform the assessment of ecological status of the water bodies within the Siversky Donets river basin in 2019. The state monitoring program based on the updated approaches has been implemented in the river basin for the first time. The composition of phytoplankton species in the basin comprised 167 species (168 intraspecies taxa), mainly Bacillariophyta (63%) and Chlorophyta (22%) with the presence of other species (Cyanobacteria, Charophyta, Chrysophyta, Dinophyta and Euglenophyta). High species diversity and divisions amount are a distinctive property of the smaller rivers, while the bigger rivers show lower number of divisions. The “bloom” events, which are important ecological factors, were not detected in the Siversky Donets river basin. Algal species composition in plankton samples of the basin was identified and series of ecological parameters, such as habitat preferences, temperature, pH, salinity, oxygenation and organic water pollution according to Watanabe and Sládeček’s index of saprobity (S) trophic state and nitrogen uptake metabolism were analyzed. The ecological conclusions were also verified by a canonical correspondence analysis (CCA). The significance of the Canonical Correspondence Analysis (CCA) results was estimated of by a Monte-Carlo permutation test. The high concentrations of inorganic phosphorus compounds (permanganate index (CODMn)) and nitrite ions favored the diversity of Chlorophyta and Cyanobacteria diversity correlated with the levels of bicarbonate and CODMn. High diversity of diatoms was facilitated by the total amount of dissolved solids and chemical oxygen demand (COD). It was found that low water quality could be associated with conditions leading to predominant growth of the mentioned groups of algae. According to the analysis, the highest water quality was characterized by balanced phytoplankton composition and optimal values of the environmental variables. The sites with reference conditions are proposed for future monitoring.

Analysis of the Correlation between the Phytoplankton Development Level, Assessed by Chlorophyll a, and Nutrient Concentrations in Rybinsk Reservoir

A correlation analysis between chlorophyll a, nitrogen, and phosphorus compounds in Rybinsk Reservoir is carried out. During certain periods of the study, a significant correlation between chlorophyll a and inorganic nitrogen and phosphorus compounds is shown. The response of phytoplankton to the total nitrogen and phosphorus concentrations is evaluated.

Intraspecific Variation in Growth and Alkaline Phosphatase Activity of Cylindrospermopsis raciborskii Strains in Response to Different Phosphorus Concentrations and Sources

The cyanobacterial species C. raciborskii are ubiquitous in tropical regions, and its successful invasion into temperate zones has been partially attributed to its ability of survival in low P availability and the existence of multiple ecotypes. To explore the physiological response of different strains to phosphorus fluctuations, four strains of C. raciborskii isolated from the Zhenhai Reservoir were used to investigate their growth and alkaline phosphatase (ALP) activity at different inorganic phosphorus (Pi) concentrations (HP=7.13 mg ·L-1, MP=0.64 mg ·L-1, LP=0.03 mg ·L-1) and different phosphorus forms [dipotassium hydrogen phosphate (K2HPO4), sodium pyrophosphate (K4P2 O7), sodium polyphosphate (K5P3O10), D-glucose-6-phosphate (D-G-6-P), adenosine triphosphate (ATP), cyclic adenosine monophosphate (cAMP)]. Four C. raciborskii strains showed a similar growth response to phosphate changes: their biomass increased with an increase in Pi concentrations, while the ALP activity showed the opposite trend. The ALP activity of C. raciborskii N8 was significantly lower than that of other three strains, regardless of inorganic phosphorus concentrations, suggesting that this strain had a higher adaptability to phosphorus fluctuations. When cultured with different phosphorus forms, the biomass of C. raciborskii N8 and N9 in three dissolved inorganic phosphorus (DIP) compounds were significantly higher than those in three dissolved organic phosphorus (DOP) compounds, with the maximum and minimum specific growth rate in K2HPO4and ATP treatments, respectively. C. raciborskii preferred DIP although they can also utilize DOP to sustain its growth. Under the DOP conditions, the ALP activity of C. raciborskii N8 in the ATP treatment was significantly higher than that in the other two organic phosphorus compounds, while we did not observe similar results in C. raciborskii N9, indicating that strain N8 was more sensitive to DIP deficiency. Our results showed an intraspecific variation within C. raciborskii strains from the same reservoir. Compared with the other strains, strain N8 represented better adaptability to phosphorus fluctuations and DIP deficiency. Variations within C. raciborskii strains may make this species more adaptable to environmental changes and enhance its competitive advantage.

Removal of inorganic and organic phosphorus compounds from aqueous solution by ferrihydrite decoration onto graphene.

Existing research on phosphorus removal from wastewater mostly focused on inorganic phosphorus while ignoring organic phosphorus, which has potential bioavailability. This study aims to provide an innovation for the development of advanced treatment material for both inorganic and organic phosphorus removal in water. In this study, ferrihydrite loaded on the graphene oxide (FeOOH-GO) composite adsorbent was synthesized by surface precipitation method, and its ability to remove both phosphate and diazinon as forms of inorganic and organic phosphorous from water was investigated. Characterization of the loaded composite using X-ray diffraction (XRD), scanning electron microscope (SEM), and Fourier transform-infrared spectroscopy (FTIR) indicated that FeOOH was successfully loaded onto graphene. The results of batch adsorption experiments showed that the adsorbent could remove both inorganic and organic phosphorus compounds simultaneously from water. When FeOOH content is 40%, the equilibrium adsorption amount of FeOOH-GO composite adsorbent for phosphate and diazinon was 5.81 and 23.20mgg-1, respectively. Environmental parameters such as pH and initial concentration have important influence on phosphorus removal by FeOOH-GO composite adsorbent and the removal efficiency of the inorganic and organic phosphorus from water decreases by increasing the initial concentration of phosphate and diazinon and the pH. It was concluded that the FeOOH-GO composite adsorbent has great potential to remove both inorganic and organic phosphate simultaneously from contaminated water.

A Novel Approach for the Quantification of Different Inorganic and Organic Phosphorus Compounds in Environmental Samples by P L2,3-Edge X-ray Absorption Near-Edge Structure (XANES) Spectroscopy.

Phosphorus (P) is an essential element for life on Earth, with an important and oftentimes unaccounted organic biogeochemical component. Current methods for the quantification of different organic P compounds in environmental samples (e.g., soils, sediments) are based on extraction techniques and often associated with incomplete P recovery or sample changes. In this study, we present a protocol for the quantification of different organic and inorganic P species in soils using synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the P L2,3-edge. Its accuracy and precision was evaluated by analyzing 40 standard mixtures composed of seven different inorganic and organic P compounds (with a mean of R2 = 0.85). In addition, we quantified the P species of two soils and two agro-industrial byproducts using P L2,3-edge XANES spectroscopy and the results were compared with those obtained by P K-edge XANES or 31P NMR spectroscopy. Using the P L2,3-edge, we identified different organic Pspecies, including those not identified by the common P K-edge XANES. However, there is a consistent underestimation of organic polyphosphates. Overall, the application of P L2,3-edge XANES provides a higher level of information than by P K-edge XANES, although the ubiquitous use of this novel methodology is still limited to samples with a phosphorus content above 3 mg g-1.

НЕОРГАНІЧНІ ТА ОРГАНІЧНІ РЕЧОВИНИ У ВОДОЙМАХ ДЕНДРОЛОГІЧНОГО ПАРКУ "ОЛЕКСАНДРІЯ" (м. БІЛА ЦЕРКВА)

The content of inorganic nitrogen and phosphorus compounds, chloride, organic matter, and dissolved oxygen was studied in 11 ponds of the “Oleksandriya” Dendrological Park. Samples were taken in summer 2016–2018 in the cascade of ponds located in the Western, Middle, and Eastern ravines of the park. The obtained data suggest that the studied ponds are significantly polluted by inorganic and organic substances, the amount of which remains still very high. The ponds of the Western ravine are characterized by the highest content of inorganic nitrogen compounds and chloride.Thus, in particular, the concentration of ammonium in the Poterchata pond accounted for 103.00–160.00 mg N/L, in the Rusalka pond – 64.00–89.50 mg N/L, in the Vodyanyk pond – 28.00–43.00 mg N/L, whereas in the Skelny pond – 12.00–38.50 mg N/L. The concentration of nitrite in the studied ponds accounted for respectively 1.130–2.213 mg N/L, 1.538–1.950 mg N/L, 0.988–1.388 mg N/L, and 0.730–1.288 mg N/L. The concentration of nitrate was also rather high. Thus, in the Poterchata pond it was 52.00–81.25 mg N/L, in the Rusalka pond – 48.00–73.75 mg N/L, in the Vodyayk pond – 21.50–38.75 mg N/L, whereas in the Skelny pond – 14.50–27.50 mg N/L. The concentration of chloride in the studied ponds accounted for respectively 690.9–795.7 mg/L, 553.8–580.5 mg/L, 283.5–308.4 mg/L, and 274.5–287.1 mg/L. The highest concentration of inorganic phosphorus (0.470 mg/L) was observed in one of the ponds of the Middle ravine. The highest values of dichromate oxidizablity (97.0 and 81.0 mg O/L) were registered in the first two ponds of the Western ravine, which is indicative of their essential contamination by organic matter. The lowest concentration of the dissolved oxygen (3.8 mg/L) was observed in the ponds of the Middle ravine. The complex of measurements aimed at the improvement of the state of the ponds of the “Oleksandriya” Dendrological Park should be elaborated and realized. In particular, it is essential to reveal the main source of the pollution of the ponds of the Western ravine by inorganic nitrogen compounds and chloride, and also to keep them clear of pollutants.

Hydrochemical Regime of the Kiliya Delta of the Danube River in Retrospective and Modern Conditions: I. Main Indicators of Water Chemical Composition

—The article focuses on the changes in the hydrochemical regime of the Kiliya delta of the Danube River, which have occurred during many years of research. It is established that after damming of the Danube River, supersaturation of the river water with dissolved oxygen is observed in the upper and middle river course, which results from an increase in the photosynthetic activity of the algae, a reduction in the content of suspended solids, and pollution of the water with inorganic nitrogen and phosphorus compounds. It is shown that since the 1970s the water mineralization level has increased by approximately 30%. The concentration of Na+, K+, SO42–, and Cl– ions has increased. Cases of saltwater penetration into the waters of the Prorva, the Gneushev, and the Bystryi branches have been observed. In modern conditions, the concentrations of nitrate ions and inorganic phosphorus remain high, whereas the concentration of ammonium nitrogen, on the contrary, has decreased almost thrice. It is found that there is an increase in the concentration of dissolved organic substances, especially in spring and summer, which is due to the intensification of bioproduction processes. Among dissolved organic substances in the water of the Kiliya delta of the Danube River, the dominating position is occupied by humic substances, the relative content of which reaches 54.8–85.6%.

Thermodynamics of Prebiotic Phosphorylation.

The formation of organophosphate molecules by prebiotic processes relies on nonenzymatic synthesis. Given the centrality of phosphorylated biomolecules in metabolic, structural, and replicative processes, it is highly likely that such nonenzymatic synthesis had to occur early in Earth's history. This Review collects and uses thermodynamic data to constrain processes that may have produced organophosphates and evaluates both the plausibility of reactants and the likelihood that environments conducive to phosphorylation were present. The energy required to phosphorylate organics is ∼15 kJ/mol, requiring either very low water activities or reactive inorganic phosphorus compounds. Thermodynamics permits evaluating phosphorylation environments for both plausibility and novelty and shows that several routes would have been available to form these potentially key reagents. Building from phosphate monoesters to diesters may have enabled the synthesis of nucleic acids, perhaps opening a way into the RNA world.

Phosphate Solubilizing Microorganisms: Promising Approach as Biofertilizers

Phosphorus (P) is a macronutrient required for the proper functioning of plants. Because P plays a vital role in every aspect of plant growth and development, deficiencies can reduce plant growth and development. Though soil possesses total P in the form of organic and inorganic compounds, most of them remain inactive and thus unavailable to plants. Since many farmers cannot afford to use P fertilizers to reduce P deficits, alternative techniques to provide P are needed. Phosphate solubilizing microbes (PSMs) are a group of beneficial microorganisms capable of hydrolyzing organic and inorganic insoluble phosphorus compounds to soluble P form that can easily be assimilated by plants. PSM provides an ecofriendly and economically sound approach to overcome the P scarcity and its subsequent uptake by plants. Though PSMs have been a subject of research for decades, manipulation of PSMs for making use of increasing fixed P in the soil and improving crop production at the field level has not yet been adequately commercialized. The purpose of this review is to widen the understanding of the role of PSMs in crop production as biofertilizers.

Nutrient attenuation dynamics in effluent dominated watercourses

In-stream attenuation of dissolved and particulate forms of carbon, nitrogen and phosphorus are a crucial ecosystem service, especially in watercourses downstream of chemical pollution point-sources (i.e. wastewater treatment plants). Most chemical-fate models assume that attenuation is directly proportional to the concentration of available dissolved organic carbon, and inorganic nitrogen and phosphorus compounds in watercourses, but there are multiple evidences of saturation and even inhibition of attenuation at higher concentrations. Our current comprehension of nutrient attenuation kinetics in streams remains a limiting factor for the development and calibration of predictive models of the chemical fate of these compounds in rivers, thus hindering the development and implementation of more effective regulatory strategies. Here, we assessed the in-stream attenuation of dissolved organic carbon, inorganic nitrogen (NH4+, NO2−, NO3−) and phosphorus (PO43-) compounds at increasing concentrations of these compounds, and analyzed the interaction between attenuation kinetics and biofilm structure and function. Specifically, the net balances of these compounds were assessed in artificial streams exposed to eight treatments following the gradient of WWTP contribution to the river flow (0, 14, 29, 43, 58, 72, 86, and 100% of WWTP effluent water). Results indicate that biological in-stream attenuation by a given biofilm of an effluent dominated watercourse might be saturated if exposed for short periods to high nutrient concentrations such as during combined sewer overflow events, but that communities can adapt if exposed long enough to high concentrations, therefore avoiding or at least minimizing saturation. More attention should be therefore given to the management of effluent-dominated watercourses, as reductions in the temporal variability of the discharged wastewater by WWTP might enhance attenuation and thus reduce water quality issues downstream.

Nitrogen and phosphorus recycling mediated by copepods and response of bacterioplankton community from three contrasting areas in the western tropical South Pacific (20° S)

Abstract. Zooplankton play a key role in the regeneration of nitrogen and phosphorus in the ocean through grazing and metabolism. This study investigates the role of the organic and inorganic nitrogen and phosphorus compounds released by copepods on biogeochemical processes and on the microbial community composition during the OUTPACE cruise (18 February–3 April 2015) at three long-duration stations (LD). Two LD stations were located in the Melanesian Archipelago region (MA; LD A and LD B) and one in the South Pacific Gyre (SG; LD C), which represent oligotrophic and ultra-oligotrophic regions respectively. At each station, on-board microcosm experiments were performed with locally sampled organisms, comprising a mix of epipelagic copepods fed with their natural food and then incubated along with wild microbial assemblages. In the presence of copepods, ammonium and dissolved organic nitrogen showed a significant increase compared to a control in two situations: in ammonium concentration (rate: 0.29 µmol L−1 h−1 after 4 h of incubation) in LD C and in dissolved organic nitrogen concentration (rate: 2.13 µmol L−1 h−1 after 0.5 h of incubation) in LD A. In addition, during the three experiments, an enhanced remineralization (ammonification and nitrification) was observed when adding copepods compared to the controls. A shift in the composition of the active bacterial community was observed for the experiments in LD A and LD B, which were mainly characterized by an increase in Alteromonadales and SAR11, respectively, and linked with changes in nutrient concentrations. In the experiment performed in LD C, both groups increased but at different periods of incubation. Alteromonadales increased between 1 and 2 h after the beginning of the experiment, and SAR 11 at the end of incubation. Our results in near in situ conditions show that copepods can be a source of organic and inorganic compounds for bacterial communities, which respond to excretion pulses at different timescales, depending on the initial environmental conditions and on their community composition. These processes can significantly contribute to nutrient recycling and regenerated production in the photic zone of ultra-oligotrophic and oligotrophic oceanic regions.