Low Concentrations Of Orthophosphate Research Articles

Impact of orthophosphate on the light-independent production of reactive oxygen species during microbially-mediated Fe redox cycles

Although light-independent production of reactive oxygen species (ROS) in subsurface environments has been increasingly documented, the processes controlling ROS transformations at redox interfaces remain poorly understood. The Fe(III)-reducing facultative anaerobe Shewanella oneidensis promotes light-independent ROS production in the presence of Fe(III) when alternately exposed to oxic and anoxic conditions and represents a good model of microbial processes at redox interfaces. In this study, S. oneidensis was incubated under three different orthophosphate concentrations from low natural conditions to high growth-promoting conditions to identify the processes regulating the light-independent production of ROS during redox oscillations and determine the impact of this important nutrient on ROS generation. Ferryl complexes were not significant intermediates in the redox cycling of Fe in this system. Instead, hydrogen peroxide (H2O2) and hydroxyl radicals (•OH) represented the main ROS produced in a process that is periodic during redox oscillations. Hydroxyl radicals were mainly produced during the aerated phases in concentrations inversely proportional to orthophosphate concentrations as a result of the complexation of Fe(III) and precipitation of oxidation-resistant vivianite. In relatively low orthophosphate concentration compared to the total reactive sites available on the Fe(III) oxides, •OH was produced at the mineral surface. Increased cell metabolic activities in the highest orthophosphate medium may have increased the •OH production efficiency during the aerated phases by enhancing O2•− formation and/or Fe(III) reduction. Unexpectedly, H2O2 was mainly detected under Fe(III) reduction conditions with net production rates that were proportional to orthophosphate concentrations, except when the solubility of vivianite was exceeded. Hydrogen peroxide is proposed to originate from the reduction of dissolved O2 by Fe(II) produced during dissimilatory Fe(III) reduction in microaerobic conditions. Precipitation of vivianite likely affects the availability of Fe(II) for ROS reactions during redox cycles, thus decreasing overall H2O2 production rates. The rise in metabolic activity, outcompetition of Fe(III) hydrolysis by orthophosphate complexation, and potential dimerization of surface generated •OH are proposed to result in the accumulation of H2O2 under suboxic conditions.

SPATIAL DISTRIBUTIONS OF NUTRIENTS AND CHLOROPHYLL-A: A POSSIBLE OCCURRENCE OF PHOSPHORUS AS A EUTROPHICATION DETERMINANT OF THE JAKARTA BAY

Phytoplankton blooms due to nutrient enrichment (eutrophication) have been considered as the primary factor causing several massive fish kills occurred in the Jakarta Bay. This study aims to determine the spatial variation of phytoplankton abundance based on chlorophyll-a concentration and its relationship with nutrient level and composition. A field observation was conducted in July 2015 measuring chlorophyll-a and nutrient concentrations. Chlorophyll-a was measured using fluorometer Trilogy AU-10 while nutrients was using spectrophotometer Shimadzu UV-1800. The result showed that chlorophyll-a concentration was relatively higher in the western compared to the eastern region of the Jakarta Bay. In addition, the western region was high in orthophosphate, nitrate and silicate while the eastern region was high in ammonium and nitrate. Statistical analysis shows that chlorophyll-a had the highest significant correlation against orthophosphate in the western region and chlorophyll-a had no significant correlation with nutrients in the eastern region. It seems that phosphorus was the primary determinant of chlorophyll-a variability with a concentration of orthophosphate of more than 0.028 mg P/L is required to increase chlorophyll-a concentration. In addition, low orthophosphate concentration (0.014 mg P/L) below its minimum requirement for maximum phytoplankton growth was likely the factor causing the absence of chlorophyll-a and nutrients relationship in the eastern region. In summary, phosphorus is seemingly the primary eutrophication determinant in the Jakarta Bay.

Prevalence of chytrid parasitism among diatom populations in the lower Columbia River (2009–2013)

Summary We documented temporal (2009–2013) and spatial [river kilometre (rkm) 8–rkm 196] patterns of parasitic fungal infections on diatoms in the lower Columbia River, as evidenced by the presence of sporangia attached to diatom frustules. Multiple diatom species were infected by zoosporic fungi (‘chytrids’) throughout the year, with a maximum infection prevalence (Ip) among large diatoms of 36% in spring 2011. At a fixed site at rkm 85, up to 30–45% of the population of Asterionella formosa, the dominant spring diatom, was infected each year during the spring (2010–2013). During this time, high Ip was associated with high host density, low precipitation and low orthophosphate concentrations. Parasite load – the number of sporangia per infected diatom cell, also referred to as the mean intensity of infection, – increased with infection prevalence, but the population average never exceed two parasites per host. Net growth rates of chytrid populations exceeded those of A. formosa host diatoms in the spring under low‐flow conditions. In spring 2013, the prevalence of infection increased from 35 to 78% and the parasite load increased from 1.5 to 2.2 along a downstream transect, suggesting that zoospores were actively infecting hosts in situ and not simply transported allochthonously. The estimated loss of organic carbon associated with diatoms via the parasitic pathway was greatest in spring (averaging c. 10%), with a peak of c. 85 μg carbon L−1 (c. 45% of total large‐diatom carbon) lost from the diatom carbon pool to parasitism in May 2011. Parasites of microalgae may actively shape aquatic food webs within systems like the Columbia River by increasing the availability of large‐diatom carbon to higher trophic levels, thus decreasing downstream export losses to the estuary and coastal ocean.

Proposal of a typology of Spanish mountain lakes and ponds using the composition of functional groups of macrophytes

Before establishing the ecological status of lakes, the Water Framework Directive requires their classification in types. Typically, the development of a typology has been based on abiotic variables. However, for the typology to have validity, the classification of lakes should be corroborated with the biological communities in the bodies of water. In this study, to develop a biologically relevant typology, the natural variability of the macrophyte communities in mountain lakes and ponds was evaluated. The use of functional groups of macrophytes as an alternative to the taxonomic approach was also evaluated. Thirty-one reference mountain lakes and ponds, located in the northwest quadrant of the Iberian Peninsula, were included in the study. The functional groups of macrophytes were based on the inorganic source of carbon used in photosynthesis. The typology developed from the functional groups was more conclusive than the classification derived from the taxonomic data. The primary determinants of the variability in the composition of the functional groups of macrophytes among the different types of lakes were the changes in the pH and in the orthophosphate concentration related to the decomposition of macrophytes. The submerged macrophytes dominated in the lakes with low concentrations of orthophosphate and the highest levels of alkalinity. In the lakes with lower pH values, the floating-leaved macrophytes were the dominant plants when the phosphorus concentration was higher, whereas at intermediate concentrations of phosphorus, the bryophytes and isoetids were more abundant; these two lake types were differentiated because of the dominance of the bryophytes in those lakes with higher acidity.

Shifts in the Gammarid (Amphipoda) Fauna of Brackish Polder Waters in Flanders (Belgium)

The macrocrustacean community of brackish polder waters in Flanders was investigated based on a twenty year survey comprising 430 biological samples taken at 218 different locations. A clear shift in the gammarid community could be observed. After its introduction, the alien Gammarus tigrinus, originating from North America, reached high abundances and became widely spread in the polder waters within a few years. Simultaneously, a decrease in the prevalence of the indigenous brackish water gammarids G. duebeni and G. zaddachi occurred. However, at the same time a decrease in the salinity of the polder waters also was observed. Uni- and multivariate data analysis revealed a clear difference in the environmental preferences of G. tigrinus, G. duebeni, and G. zaddachi. The alien species preferred lower salinities, lower orthophosphate concentrations, and a higher oxygen concentration compared to the two indigenous species. Besides the decrease in prevalence of the native gammarids, a decrease was also observed in prevalence of two other indigenous brackish water crustaceans: Palaemonetes varians and Neomysis integer. It appears that the decrease in salinity is the most important factor causing the decline of the indigenous gammarids and not the introduction of the alien G. tigrinus.

Measuring the benefit of orthophosphate treatment on lead in drinking water

Many water companies are adding low concentrations of orthophosphate to the water supply in order to reduce lead concentrations in drinking water produced from corrosion of lead service pipes. Despite the erratic nature of lead concentrations measured at customer properties it has been possible to quantify the impact of treatment on lead concentrations and thereby quantify the effectiveness of treatment at both a regional and zonal level. This showed that the treatment policy has delivered more than 90 per cent reduction in lead concentrations, and was largely in accordance with theory. Across the region, lead performance and the reduction in lead performance show significant variation. A large part of this variation can be accounted for by variations in the proportion of leaded properties supplied through lead service pipes. Analysis showed that the proportion of particulate lead has also reduced significantly over the last decade. This is attributed to improved mechanical robustness of the corrosion layer caused by changes in its physical structure. This appears to be a very slow process with a natural time-scale of years.

Densidade fitoplanctônica e estado trófico dos rios Canha e Pariquera-Açu, bacia hidrográfica do rio Ribeira de Iguape, SP, Brasil

Regarding the lack of studies about lotic eutrophication, mainly for tropical rivers, this research aimed to assess the density of phytoplanktonic community of two tropical rivers located in Ribeira do Iguape Watershed (Sao Paulo state, Brazil), Canha and Pariquera-Acu Rivers, based on sampling campaigns in January and April, 2007. These results were compared to the mTSI (mean Trophic State Index) values. This index was originally developed for lentic aquatic systems and its calculus depends on total phosphorous, orthophosphate and chlorophyll-a concentrations in water samples. Comparing mTSI values in all sampling stations with the phytoplankton quantitative results, it was possible to verify that mTSI may overestimate the trophic state of lotic ecosystems, since the phosphorus species that integrate its calculus contributed to an improper augmentation on mTSI, which were incompatible with the real associated biological response. Thus, for April sampling, although mTSI values were higher, in general, phytoplankton density were lower (minimum of 83 indmL-1 for Canha River and of 66 indmL-1 for Pariquera-Acu River). In this case, the high total phosphorous concentrations by themselves were not enough to promote proportional phytoplanktonic growth, which was probably limited by other factors, like water temperature, suspended solids concentration, river discharge and zooplanktonic predation. In January, on the other hand, mTSI values were lower, but total phytoplankton density was higher. For this sampling, the lower orthophosphate concentrations in water pointed phytoplankton assimilation of this nutrient.

Spatial and temporal distribution of phytoplankton in a highly stratified estuary (Zrmanja, Adriatic Sea)

The karstic Zrmanja River discharges into the eastern Adriatic Sea, forming a highly stratified estuary with a sharp halocline that divides upper brackish and lower marine layers. Low orthophosphate concentrations and high Redfield ratios indicate that phosphorus limits phytoplankton growth. In addition, high transparency (avg 6.7 m) and oxygen saturation (avg 98.78%) indicate oligotrophy. Maximum phytoplankton abundance reached 3.4 · 10 6 cellsAEl )1 in early spring, a period when the community was composed mainly of diatoms. Dinoflagellates and nanoplanktonic phytoplankton dominated in summer; coccolithophorids and silicoflagellates characterized autumn. Stable conditions in the middle and lower estuary provided a suitable setting for development of microphytoplanktonic diatoms, whereas unstable conditions (frequent salinity variations) at the head of the estuary favored nanophytoplankton. Canonical correspondence analysis identified salinity, temperature, and river inflow as the main factors influencing phytoplankton development. Nutrients strongly limited phytoplankton growth in summer when the river discharge was a

Chemical phosphorus removal model based on equilibrium chemistry

Regulations in many regions of the world require total phosphorus (TP) levels lower than 0.10 mgP/L (100 microgP/L) in effluents, resulting in the need to achieve very low ortho-phosphate (OP) concentrations. Chemical precipitation is a widely used technology for controlling effluent OP discharge, either on its own or supplementing biological methods. The various chemical and physico-chemical mechanisms that result in extremely low residual OP levels are complex and depend on pH. In practice, engineering calculations frequently use an empirical precipitation model. This model requires pH as input and predicts the lowest achievable OP residual of 35 microgP/L at a narrow optimum pH of 6.9-7.0, when an excess of ferric is added. The model has been combined with a biokinetic and weak acid/base chemistry based pH model, to allow accurate prediction of pH, OP residuals and chemical sludge production. Analysis of effluent data from the Blue Plains plant shows that residuals as low as 10 microgP/L OP can be achieved regularly, over a wider pH range. The precipitation model was recalibrated to match the newly available data. Subsequently it was compared with a new, mechanistic precipitation model based on solubility and dissociation constants for actual chemical compounds. The need for more accurate measurement of extremely low OP concentrations and considering the role of organics, adsorption and coagulation in chemical phosphorus removal is demonstrated.

Re-examination of the MAGIC method to determine low orthophosphate concentration in seawater

A new and detailed MAGIC25 procedure is proposed to determine low concentration of orthophosphate in seawater. By preconcentrating phosphate 25 times, the procedure allowed detection of nanomolar concentration in seawater with low concentration of particles (detection limit = 0.8 ± 0.5 nM). The centrifugation step was considerably reduced (from 60 to 10 min) in comparison to previous MAGIC method. The calibration coefficient was determined by performing procedural and extra calibration curves and a previously unknown matrix effect in the MAGIC procedure was revealed. Its omission leads to a 12% underestimation of the phosphate concentration. The necessity of pre-filtration was demonstrated and a turbidity blank was measured to avoid overestimation even in the oligotrophic Mediterranean Sea water. The absence of filter reactivity with phosphate (contamination or retention) was verified. A synthetic reagent blank was proposed to simplify procedure in comparison to previous MAGIC method. The slow down of phosphomolybdenum blue complex was observed in the MAGIC concentrate and this results in a minimum reaction time of 30 min. The sensitivity (ratio of signal/noise) showed a three-fold improvement in comparison to the more recent nanomolar methods. Interferences of arsenate and silicate, commonly observed in the classic phosphomolybdic blue spectrophotometry, were undetectable. The MAGIC25 method appears reliable, sensitive, accurate and relative easy to use during oceanographic cruises. Therefore, MAGIC25 procedure is a useful tool for oceanograph chemists to be used instead of the classic phosphomolybdic blue method when concentration is below 200 nM.

Limnological studies on a shallow reservoir in western Venezuela (Tulé Reservoir)

Limnological features of Tulé Reservoir, a large and shallow reservoir in western Venezuela were studied from May 1992 to December 1993. This reservoir is polymictic, with a low water transparency. Levels of nitrogen were high and phytoplankton productivity was low. The phytoplankton productivity values may be explained by the low concentrations of orthophosphate during the larger part of the sampling period and the frequent mixing and resuspension of sediments. Heterotrophic bacteria were between 1651.67 and 4365.00 Colony-forming Units/ml. Species composition of the crustacean zooplankton community was similar to other neotropical eutrophic reservoirs.

The effect of rice-seeding rate and fish stocking on the floodwater ecology of the trench of a concurrent, direct-seeded rice-fish system

Concurrent rice-fish systems in the Mekong Delta, Vietnam, are characterized by a rice field surrounded by a trench (on average 1000 m2, covering 15–20% of the field surface). Rice is direct seeded and fish are reared in polyculture. The most common species for polyculture are silver barb Barbodes gonionotus (Bleeker), common carp Cyprinus carpio L. and Nile tilapia Oreochromis niloticus (L.). In a 1996–1997 dry season experiment, the effects of (1) absence or presence of a fish polyculture, and (2) two different rice-seeding rates (100 and 300 kg pre-germinated rice per ha) on the trench floodwater ecology were studied. Fish were stocked in six out of twelve rice-fish plots at the Co Do experimental rice-fish station (10° 10′ N and 105° 20′ E). Silver barb, common carp and Nile tilapia were stocked in polyculture at densities of 3150, 310 and 550 fish/ha, respectively. Several hydrological and biological parameters of the trench floodwater were measured. About 65% of the observed variation in the trench floodwater could be attributed to the fishes stocked and changes in rice-seeding rate. The presence of a fish polyculture increased the water turbidity of the trench floodwater, mainly through suspension of mineral and organic material through fish perturbation. At the lower rice-seeding rate, this resulted in a lower primary production. Photosynthetic activity, dissolved oxygen am and pm showed significant decreases, but only at the lower rice-seeding rate in the presence of fish. Fish polyculture presence resulted in lower ortho-phosphate concentrations, higher phytoplankton communities and higher Protozoa numbers, most probably due to a higher availability of nutrients through fish defecation and perturbation. The rice-seeding rate had a significant impact on pH am, pH pm and temperature pm readings. The survival rate for Nile tilapia and the gross production for Nile tilapia and common carp was higher at the lower rice seeding rate, most probably due to a better aquatic environment of the field. In terms of fish production, the trench floodwater environment was better than the field floodwater. The trench is a very important part of the rice-fish system. It serves as a refuge and supplies reasonable amounts of phytoplankton and zooplankton to the fish.

Point Source Phosphorus Management, a Five Year Southern African Experience

The Vaal River Barrage reservoir is an important source of raw water for the Rand Water Board. Activities in the catchment of this reservoir resulted in enrichment of this water with concomitant eutrophication related water quality problems being experienced by the Rand Water Board. In order to limit enrichment of raw water a standard of 1 mg PO4−P/ℓ for waste water treatment plant effluent was imposed and the effects of this standard on the algal concentrations at the No. 1 intake in the Vaal River Barrage reservoir was investigated. Although only 24 per cent of waste water treatment plants in the catchment of the Vaal River Barrage reservoir complied with the phosphate standard for more than 75 per cent of the time, the amount of phosphate emanating from the treatment plants in general decreased significantly. This resulted in a lower orthophosphate concentration at the Board's No. 1 intake. The associated lower chlorophyll concentrations at No. 1 intake was, however, not only due to the lower orthophosphate concentrations, but also to the residence time and chemical/physical factors. To limit the algal concentrations at No. 1 intake, the 1 mg/ℓ orthophosphate standard will have to be enforced strictly and diffuse source management will have to be implemented.

Bacterial 5'‐nucleotidase activity in estuarine and coastal marine waters: Characterization of enzyme activity

We measured 5′‐nucleotidase by following the hydrolysis of ATP and measured alkaline phosphatase by conventional fluorometric techniques. 5′‐Nucleotidase (5PN) was found in all estuarine and coastal marine waters where measurements were made, regardless of the degree of eutrophication or phosphate concentrations. Its activity was usually concentrated in the bacterial size fraction. 5PN was competitively inhibited only by 5′‐nucleotides and was distinguishable from alkaline phosphatase by both this substrate specificity and the lack of inhibition by low concentrations of orthophosphate. The percent of uptake of orthophosphate regenerated by 5PN was inversely related to the ambient phosphate concentration.

Alkaline Phosphatase Activity in the Red‐Tide Dinoflagellate, Ptychodiscus brevis

Abstract. Alkaline phosphatase activity (APA) was found in a nearshore, natural population of the red‐tide dinoflagellate Ptychodiscus brevis. Initial hydrolysis rates were enhanced by two orders of magnitude within 24 h upon addition of ammonium. Other nutrient (additions) or no additions also lead to a higher, although less pronounced increase in activity. Enhanced growth after nutrient additions combined with specific APA indicated that the bloom was both N and P limited. Since the natural population was a mixture of diatoms and the dinoflagellate, APA was also measured in unialgal cultures of P. brevis. APA was not reduced but enhanced by the addition of low concentrations of orthophosphate (0.5 and 1 μM). Higher orthophosphate concentrations (5 to 20 μM) reduced APA, although activity returned to control levels within 2 to 6h. Repression occurred within 30 sec after a 20 μM orthophosphate addition. Cells which had APA repressed by an orthophosphate addition regained their initial activity within 2 h after washing with phosphate‐free media. Phosphorus‐deficient cells of P. brevis possess an alkaline phosphatase system which is capable of continued activity at low in situ orthophosphate levels.

Processing of willow leaves in two Alberta Rocky Mountain streams

Nylon bags of 3.5 mm and 0.25 mm mesh were used lo investigate the processing of Salix drummondiana Barratt leaves in two second order Alberta Rocky Mountain Creeks, Twin Creek and Cabin Creek. Micro‐organism processing and macroinvertebrate shredding of the leaves were significantly greater in Twin Creek where it was estimated that macroinvertebrate shredding was responsible for 45% of the weight loss. The decay coefficient (k = 0.0209) for the leaves in Twin Creek, the more typical Rocky Mountain stream, was similar to that reported for the fastest decaying leaves in warmer streams. The predominant shredder among the leaves in the mesh bags, Zapada columbiana (Classen) (Plecoptera, Nemouridae) was also the most abundant macroinvertebrate in the benthos of Twin Creek. In Cabin Creek the predominant organism in the benthos, Oreogeton sp. was poorly represented in the leaves. Low orthophosphate concentration of the water and precipitation of calcium carbonate onto the leaves may have inhibited the biotic processing of leaves in Cabin Creek.

Photosynthesis in Isolated Chloroplasts of the Crassulacean Acid Metabolism Plant Sedum praealtum

Intact chloroplasts were isolated from protoplasts of the Crassulacean acid metabolism plant Sedum praealtum D.C. Typical rates of CO(2) fixation or CO(2)-dependent O(2) evolution ranged from 20 to 30 micromoles per milligram chlorophyll per hour and could be stimulated 30 to 50% by several Calvin cycle intermediates. The pH optimum for CO(2) fixation was 7.0 to 7.6 with considerable activity as low as pH 6.4. Low concentrations of orthophosphate (Pi) (optimum 0.4 millimolar) stimulated photosynthesis while high concentrations (5 millimolar) caused some inhibition. Both CO(2) fixation and CO(2)-dependent O(2) evolution exhibited a relatively long lag phase (4 to 6 minutes) which remained constant between 0.4 to 5 millimolar Pi. The lag phase could be decreased by addition of dihydroxyacetone-phosphate or ribose 5-phosphate. Further results are presented which suggest these chloroplasts have a functional phosphate translocator.A long lag period at optimum Pi concentration, no effect of high Pi levels on the lag phase, lack of severe inhibition of photosynthesis by high Pi concentrations, and the relatively low pH optimum for photosynthesis are characteristics unlike those previously reported with chloroplasts of C(3) plants.

Determination of Orthophosphate in Fresh and Saline Waters

This article discusses experimental studies on extending the concentration range of orthophosphate beyond that stated by Murphy and Riley, and intensifying the color formed so as to make the method more sensitive at low orthophosphate concentrations.