Showing papers on "Phosphorus published in 2000"

Phosphate depletion in the western North Atlantic Ocean.

Abstract: Surface waters of the subtropical Sargasso Sea contain dissolved inorganic phosphate (DIP) concentrations of 0.2 to 1.0 nanomolar, which are sufficiently low to result in phosphorus control of primary production. The DIP concentrations in this area (which receives high inputs of iron-rich dust from arid regions of North Africa) are one to two orders of magnitude lower than surface levels in the North Pacific (where eolian iron inputs are much lower and water column denitrification is much more substantial). These data indicate a severe relative phosphorus depletion in the Atlantic. We hypothesize that nitrogen versus phosphorus limitation of primary production in the present-day ocean may be closely linked to iron supply through control of dinitrogen (N2) fixation, an iron-intensive metabolic process. Although the oceanic phosphorus inventory may set the upper limit for the total amount of organic matter produced in the ocean over geological time scales, at any instant in geological time, oceanic primary production may fall below this limit because of a persistent insufficient iron supply. By controlling N2 fixation, iron may control not only nitrogen versus phosphorus limitation but also carbon fixation and export stoichiometry and hence biological sequestration of atmospheric carbon dioxide.

Phosphorus management at the watershed scale:a modification of the phosphorus index

Abstract: We considered hydrologic and chemical factors controlling P export from a 39.5-ha mixed land use watershed in east-central Pennsylvania, focusing our evaluation on watershed vulnerability to P loss. The spatial variations of P source factors, soil P, and P inputs from fertilizer and manure were evaluated. Distribution of Mehlich-3 soil P on a 30-m grid over the watershed showed that soil P varied with land use. Soils in wooded areas had low Mehlich-3 P ( 200 mg kg−1. Phosphorus sources and transport controls on P loss were evaluated by examining in-stream P concentrations during storm hydrographs. Phosphorus concentrations decreased 50% downstream from headwaters to watershed outlet, and were more closely related to near-stream (within 60 m) distribution of high-P soils than to that of the whole watershed. This suggests that near-stream surface runoff and soil P are controlling P export from the watershed. Based on these findings, we modified the Phosphorus Index (PI), a user-oriented tool developed by the NRCS-USDA to identify critical source areas controlling P export from agricultural watersheds. The modification separately evaluates P source and transport factors, and incorporates the hydrologic return period to describe contributing areas. The modified PI was applied to the watershed to illustrate interactions between P source and transport processes controlling P export, and approaches for managing P loss.

Phosphate concentrations in lakes

Abstract: Phosphate is an important nutrient that restricts microbial production in many freshwater and marine environments. The actual concentration of phosphate in phosphorus-limited waters is largely unknown because commonly used chemical and radiochemical techniques overestimate the concentration. Here, using a new steady-state radiobioassay to survey a diverse set of lakes, we report phosphate concentrations in lakes that are orders of magnitude lower than estimates made spectrophotometrically or with the frequently used Rigler radiobioassay. Our results, combined with those from the literature, indicate that microbes can achieve rapid turnover rates at picomolar nutrient concentrations. This occurs even though these concentrations are about two orders of magnitude below the level where phosphate uptake is estimated to be half the saturation level for the pico-plankton community. Also, while phosphate concentration increased with the concentration of total phosphorus and soluble reactive phosphorus in the lakes we sampled, the proportion of phosphate in the total phosphorus pool decreased from oligotrophic to eutrophic lakes. Such information, as revealed by the phosphate assay that we use here, should allow us to address hypotheses concerning the concentration of phosphate available to planktonic microorganisms in aquatic systems.

Cyclopentadienylmetal complexes bearing pendant phosphorus, arsenic, and sulfur ligands.

Abstract: Bidendate ligands have proven important in a variety of complexes and are invaluable in a number of catalytic processes. While ligands of this type usually have two identical ligand fragments (homobidendate ligands), heterobidendate ligands allow for a differentiation of the ligands and therefore are prone to selective reactions. This is especially interesting in cases where the ligands are rather different from one another. Phosphane and cyclopentadienyl ligands are among the most commonly used in organometallic chemistry, and they are quite different in nature: Whereas a phosphane is electroneutral and often subjected to ligand exchange processes, the cyclopentadienyl ligand is normally considered to be negatively charged and rather tightly bound to a metal. Reviewing the literature in the field of cyclopentadienylmetal complexes bearing pendant phosphorus, arsenic, and sulfur ligands is timely given that the number of publications of relevance to this topic is growing exponentially as can easily be seen from the list of references in this review: the number of references since 1993 clearly exceeds that of all years before. The reason for this development may be that cyclopentadienylmetal complexes bearing pendant phosphorus, arsenic, and sulfur ligands are expected to perform chemistry different from that of usual cyclopentadienyl complexes. Indeed this has often been the case. Complexes discussed in this review facilitate the complexation of sensitive ligands, offer new aspects concerning chirality, allow novel reactions, and are beginning to be applied to transition metal catalysis. It is therefore hoped that this review will contribute to these developments by offering state of the art information for those active in the field and, even more important, for those who join in the future. This review covers the chemistry of cyclopentadienylmetal complexes, in which the cyclopentadienyl ligand bears a sidearm which includes a phosphorus, arsenic, or sulfur ligand. The pendant ligand has to be separated from the cyclopentadienyl part, that is, † Dedicated to Professor Günther Wilke on the occasion of his 75th birthday. * To whom correspondence should be addressed. Fax: +49/(0)511/ 762-4616. E-mail: holger.butenschoen@mbox.oci.uni-hannover.de. Holger Butenschön was born and raised in Hamburg, Germany. After his army service he studied chemistry at the University of Hamburg and obtained his Dr. rer. nat. degree in 1983 with Professor Armin de Meijere as a fellow of the Studienstiftung des Deutschen Volkes. From 1983 to 1984 he spent a postdoctoral year with Professor K. Peter C. Vollhardt at the University of California at Berkeley as a NATO fellow. Having returned to Germany, he joined the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr as a Liebig fellow to do preparative organometallic work in the fields of anellated arenechromium complexes and cyclopentadienyl cobalt complexes with pendant phosphane ligands. After his habilitation in 1991 (University of Hamburg), he became a Heisenberg fellow of the DFG at the University of Wuppertal from 1992 to 1993. Since 1993 he has been a professor of organic chemistry at the University of Hannover. In 1999 he was a foreign visiting professor at Kyushu University in Fukuoka, Japan. Holger Butenschön is the editor of the German translation of Peter Vollhardt’s and Neil Schore’s textbook Organic Chemistry as well as a coauthor of the Memofix OC. He currently serves as the chairman of the Hannover district of the German Chemical Society (GDCh). His spare time is occupied by the female part of his family, his wife Bettina and their four daughters Lisa, Nora, Inga, and Lara. 1527 Chem. Rev. 2000, 100, 1527−1564

Aquatic ecology. Phosphorus, the staff of life

Abstract: Studies of lakes in North America reveal that concentrations of phosphate, an essential nutrient for aquatic microorganisms, are 100-1,000 times lower than estimated with conventional techniques. Among the implications are the possible need to rethink nutrient dynamics in both freshwater and marine ecosystems..

Changes in Phosphorus Fractions in Soils under Intensive Plant Growth

Abstract: The total quantity of P and plant-available P often differ greatly in soils of the tropics, which typically range in weathering intensity. Assessing available P is fundamental to managing P in many of these soils. Phosphorus availability in some soils has been inferred from the Hedley sequential extraction assuming that each P fraction reflects similar plant availability in different soils. However, experimental measurements of plant P availability were either of short duration or involved multiple P applications, which complicates assessment of the plant availability of P fractions. The objectives of this study were to examine the changes in P fractions under exhaustive cropping on diverse soils and to discern the differences in plant availability among P fractions. Eight soils ranging in weathering from Vertisols and Mollisols to Ultisols and Oxisols were amended with Ca(H 2 PO 4 ).H 2 O to raise soil solution P to 0.2 mg L -1 and planted for 14 crops to remove available P. The results indicated that the Fe-impregnated strip-P and inorganic NaHCO 3 -P (NaHCO 3 -P i ) decreased the most in response to plant P withdrawal in all soils. The inorganic NaOH-P (NaOH-P i ) also declined with plant P uptake in all soils. The HCI-P and residual P seemed to act as a buffer for the strip-P and the NaHCO 3 -P i in the slightly weathered soils, whereas NaOH-P seemed to act as a buffering pool for strip-P and NaHCO 3 -P i in the highly weathered soils. Residual P in the slightly weathered soils was plant-available on a relatively short time scale. In contrast, residual P in the highly weathered soils accumulated in the presence of intensive plant P removal, indicating that it was unavailable to plants. Organic P (NaHCO 3 - and NaOH-P o ) fractions were not significant contributors to available P in these soils that received high levels of inorganic P. Phosphorus fractions separated by the same sequential method were not of equal availability to plants in all soils.

Phosphorus forms and concentrations in leachate under four grassland soil types

Abstract: The transfer of P in water draining from agricultural land can contribute to eutrophication and the growth of toxic algae. Traditionally, research has focused on particulate P transfer in surface pathways, with transfer by subsurface pathways perceived as negligible. We investigated this by monitoring P in leachate draining through large-scale monolith lysimeters (135 cm deep, 80 cm diam.) installed in a field site in southwest England. The lysimeters were taken from four grassland soil types with a range of textures (silty clay-sand) and extractable-P contents (15-75 mg kg -1 NaHCO 3 extractable P) and leachate was sampled over two drainage seasons. Export of total P was 200 μg L -1 were detected from all soil types. Physically, most of the leachate P was dissolved ( 0.45 μm) size fraction, most notably from the sandy-textured soils. Chemically, the leachate was dominated by reactive (inorganic) P from all soil types (62-71%), although a large proportion was in unreactive (organic) P forms (29-38%). Reactive P occurred mainly in the 0.45 fraction. Unreactive P in the 0.45 μm P forms are important in subsurface P transfer.

A metabolic model for biological phosphorus removal by denitrifying organisms.

Abstract: A metabolic model for biological phosphorus removal under denitrifying conditions has been established. The model is based on previous work with aerobic phosphorus removal. The form of the kinetic equations used is the same as for the aerobic model. The main difference is the value of P/NADH(2) ratio in the electron transport phosphorylation with nitrate (delta(N)). This value was determined independently from batch tests with an enriched culture of denitrifying phosphorus-removing bacteria. The measured delta(N) was approximately 1.0 mol ATP/mol NADH(2). This indicates that the energy production efficiency with nitrate compared to oxygen is approximately 40% lower. These batch tests were also used to identify a proper set of kinetic parameters. The obtained model was subsequently applied for the simulation of cyclic behavior in an anaerobic-anoxic sequencing batch reactor at different biomass retention times. The simulation results showed that the metabolic model can be used successfully for the denitrifying dephosphatation process. The obtained kinetic parameters for denitrifying enrichment cultures, however, deviated from those obtained for the aerobic enrichment cultures. (c) 1996 John Wiley & Sons, Inc.

The efficiency of Arabidopsis thaliana (Brassicaceae) root hairs in phosphorus acquisition.

Abstract: Arabidopsis thaliana root hairs grow longer and denser in response to low-phosphorus availability. In addition, plants with the root hair response acquire more phosphorus than mutants that have root hairs that do not respond to phosphorus limiting conditions. The purpose of this experiment was to determine the efficiency of root hairs in phosphorus acquisition at high- and low-phosphorus availability. Root hair growth, root growth, root respiration, plant phosphorus uptake, and plant phosphorus content of 3-wk-old wild-type Arabidopsis (WS) were compared to two root hair mutants (rhd6 and rhd2) under high (54 mmol/m) and low (0.4 mmol/m) phosphorus availability. A cost-benefit analysis was constructed from the measurements to determine root hair efficiency. Under high-phosphorus availability, root hairs did not have an effect on any of the parameters measured. Under low-phosphorus availability, wild-type Arabidopsis had greater total root surface area, shoot biomass, phosphorus per root length, and specific phosphorus uptake. The cost-benefit analysis shows that under low phosphorus, wild-type roots acquire more phosphorus for every unit of carbon respired or unit of phosphorus invested into the roots than the mutants. We conclude that the response of root hairs to low-phosphorus availability is an efficient strategy for phosphorus acquisition.

Coastal food web structure, carbon storage, and nitrogen retention regulated by consumer pressure and nutrient loading

Abstract: By factorial field experiments we analyzed the relative effects of increased nutrient (N1P) loading and natural grazing pressure on species composition, carbon storage, and nitrogen retention in the Baltic Sea littoral food web, composed of macroalgae, grazers (snails, isopods, amphipods), and predators (shrimps, crabs, fish). Nitrogen was depleted relative to phosphorus throughout most of the year. Increasing nitrogen (6‐200% over ambient concentrations) enhanced algal productivity and cover of fast-growing annual algae, grazer, and predator densities, suggesting a three-level bottom-up effect. With increasing nitrogen loading, annual algae increasingly blocked perennial algal recruitment (65‐98% decrease) and growth. Grazers counteracted the effects of nutrient enrichment on algal species composition through selective consumption of annual algae. Grazer exclusion had equivalent negative effects on perennial recruitment as a 85% increase in nitrogen loading. Nutrient enrichment increased algal nitrogen content and decreased tissue C : N ratios in spring and summer but not in fall. Carbon storage and nitrogen retention, measured as C and N retained in plant biomass at the end of the growth season, were increased by grazers (C: 39%, N: 24%) but decreased with increasing nitrogen loading (C: 271%, N: 274%). Our results emphasize the important role of grazers in buffering moderate eutrophication effects and illustrate how food web interactions and shifts in species composition are tightly linked to coastal ecosystem function. Currently, humans are more than doubling the rate at which nitrogen and phosphorus enter the global biogeochem

Plant growth and phosphorus accumulation of wild type and two root hair mutants of Arabidopsis thaliana (Brassicaceae)

Abstract: Arabidopsis thaliana root hairs grow longer and denser in response to low-phosphorus availability. We tested the hypothesis that wild-type Arabidopsis would acquire more phosphorus under phosphorus-limiting conditions than mutants that do not have the root hair response. The growth and phosphorus acquisition of wild-type Arabidopsis (WS) were compared to two root hair mutants (rhd6 and rhd2) under eight phosphorus treatments ranging from 0.4 mmol/m 3 to 54 mmol/m3 phosphorus. At the lowest phosphorus treatment, all plants were small and showed severe phosphorus stress symptoms. At 1.5 mmol/m 3 phosphorus, WS plants had greater shoot biomass, absolute growth rate, total phosphorus, and specific phosphorus absorption than the two root hair mutants. At the highest phosphorus treatment, there was no difference between genotypes in any of the parameters measured. We conclude that the response of increased root hair growth under low phosphorus availability in Arabidopsis is important in increasing phosphorus acquisition under phosphorus-limiting conditions.

Ability of restored wetlands to reduce nitrogen and phosphorus concentrations in agricultural drainage water

Abstract: Runoff from artificially drained agricultural lands is a common source of excessive nitrogen and phosphorus to downstream waters. Restored wetlands receiving crop field drainage water are shown to lower concentrations of both nitrogen and phosphorus. Case studies in Maryland, Illinois, and Iowa indicate that wetlands can remove up to 68% of nitrate-nitrogen and 43% of phosphorus from drainage water, although performance varies considerably. Performance comparison across sites indicates that large wetlands relative to the contributing drainage area most effectively improve water quality. Time series data representing periods of both relatively high and low inflow indicate that performance is highly sensitive to retention time, with greatest nutrient removal during flow conditions that facilitate retention times of at least one to two weeks. Where wetlands are incorporated into forested riparian buffer strips, additional water quality benefits are shown.

Carbon, nitrogen, and phosphorus stoichiometry of cyprinid fishes

Abstract: We investigated the carbon, nitrogen, and phosphorus levels in whole fish and gut samples of several species of cyprinids, relating our findings to nutrient flux models. Some differences in whole-fish nutrient content across species, lakes, and seasons, as well as differences across fish length and mass, were found. N and P contents were highest in fathead minnows and lowest in pearl dace, with northern redbelly dace and finescale dace intermediate. Larger fish had higher percent C and lower percent N and P. However, all differences in whole fish C, N, and P chemistry were small. Cyprinids had the following mean composition: carbon, 46%; nitrogen, 9.7%; and phosphorus, 1.5%. The cyprinid molar C:N:P ratio was 242:16:1. These values make cyprinids relatively low in phosphorus compared to other fish that have been previously studied, especially members of the Percidae and Centrarchidae. Gut contents were lower in N and P than the whole fish, and C:N and C:P ratios were correspondingly higher in gut contents...

Distributions of TOP, TON and TOC in the North Pacific subtropical gyre : Implications for nutrient supply in the surface ocean and remineralization in the upper thermocline

Abstract: We report measurements of total organic phosphorus, nitrogen, and carbon (TOP, TON, and TOC) along a meridional transect in the eastern subtropical North Pacific. In the surface waters, TOP and TON comprise 83% and 98% of the total dissolved phosphorus and nitrogen pools, respectively. Between the equatorial region and the subtropical gyre, there is a distinct gradient in surface TOP of about 0.25 μM, but very little gradient in TON. TOC increases by nearly 30 μM across the same region. Meridional advection of TOP along its gradient via Ekman transport can provide 40-80% of the phosphorus necessary to supply present estimates of particulate phosphorus export from the subtropical gyre. Mass balance requires an additional input of nitrogen to the surface waters to fuel particulate nitrogen export. This input is likely supported by nitrogen fixation. As dissolved organic matter (DOM) is degraded along isopycnals that outcrop within the subtropical gyre, TOP and TOC are consumed more rapidly than TON. TOC and TON contribute 70% and 20% to organic matter remineralization along these isopycnals, respectively, and the C:N ratio for remineralization is 30 ± 10. In contrast, along isopycnals that outcrop to the north of the gyre, both TOC and TON contribute 30% to organic matter remineralization and the C:N ratio is 8 ± 1. Our results suggest that excess TOC, produced within the surface waters of the subtropical gyre during nitrogen fixation, is highly labile and dominates respiration along shallow isopycnals. Preferential remineralization of TOC relative to TON within the gyre results in a negative preformed nitrate signal in the upper thermocline, and may establish a feedback between upper thermocline DOM remineralization and surface ocean DOM production that maintains nitrogen fixation in the surface waters.

Phosphorus Enrichment Affects Litter Decomposition, Immobilization, and Soil Microbial Phosphorus in Wetland Mesocosms

Abstract: affect decomposition, and values less than five can inhibit decomposition of leaf litter (Qualls and Haines, Like many wetland ecosystems, areas of the northern Everglades 1990). While many bogs exhibit very acid conditions of Florida, USA, have been influenced by P eutrophication. Our objective was to determine if P enrichment of water influences the that are potentially inhibitory to decomposition, fens litter decomposition rate and nutrient immobilization by litter and, such as the Everglades often have soil pH values near further, to determine the quantitative relationship of these responses neutrality and near the optimum for decomposition. across a range of P concentrations in surface water. In addition, we High concentrations of dissolved organic acids are a determined whether P additions rapidly elevated microbial biomass common characteristic of many wetlands and can inhibit P in the soil. In order to isolate the effects of P enrichment, we placed decomposition by creating highly acid water. Qualls and bags containing cattail (Typha domengensis Crantz) and sawgrass Haines (1990) showed that this affected decomposition (Cladium jamaicense Pers.) litter into two sets of experimental chan- only by controlling H 1 concentration, not by any other nels into which controlled inputs of five different phosphate concentrainhibitory properties of the organic acid molecules. tions were added continuously. After 1 yr of incubation, litter was The decomposition of plant litter can also be limited analyzed for C, P, N, Cu, Ca, and K content. Loss of C at the end of 1 yr increased linearly with increasing average PO4 content in the by the concentration of inorganic N and P (Alexander, channels with a similar slope for both species of litter. Immobilization 1977) in soil or water surrounding the decomposer micaused an absolute increase in P content of the litter up to approxi- croflora. Suberkropp and Chauvet (1995) found that mately ninefold across the range of water P concentrations, while NO3 concentration was the only variable correlated with immobilization of N, Ca, and K did not vary with water P concentra- differences in litter decomposition among six hardwater tions. During decomposition, litter exhibited a net uptake of Cu (a streams; however, Triska and Sedell (1976) found no nutrient potentially limiting plant growth on peat soils). The microbial decomposition response to NO

Amount of phosphorus inactivated by alum treatments in Washington lakes

Abstract: The effectiveness of aluminum (Al) at retaining phosphate was investigated in alum-treated Washington lake sediments. Greater than background concentrations of Al and Al-bound phosphorus (Al-P) were detected in three stratified lakes (Lake Ballinger, Phantom Lake, and Medical Lake) and in three unstratified lakes (Lake Erie, Cambell Lake, and Long Lake). The ratio of added Al to P (Al:Al-P) was approximately 11:1 by weight in all six lakes. Added Al ranged from 6 to 83 g Al m-2 , and adsorbed P subsequently ranged from 0.5 to 7.3 g P m-2. P bound to the added Al was apparently removed from the P cycle, as the layers of increased Al-P due to treatment were buried in the sediment at a depth corre-sponding to the approximate time since treatment.

Heterotrophic, Planktonic Bacteria and Cycling of Phosphorus

Abstract: As early as 1956, Rigler reported that heterotrophic bacteria were responsible for a large share of the uptake of inorganic phosphorus (P) in Toussant Lake (Rigler, 1956) Tracer experiments revealed that the bacteria sequestered two thirds of the phosphate, and Rigler stated that if they [bacteria] take up small increments of phosphorus received from inflowing water or from marginal vegetation, [bacteria] may compete with algae for this essential element… If, in this process, they utilize inorganic phosphate, they would reduce the amount of phosphate available to algae and thus reduce the amount of organic matter produced by algae, (p 560)

Phosphite oxidation by sulphate reduction

Abstract: Biological phosphorus occurs almost exclusively as phosphate in the redox state of + V, although a few phosphonic (+ III) and phosphinic (+ I) acids are found as secondary metabolites1 or as constituents of phosphonolipids. Here we show that a culture of a lithoautotrophic bacterium purified from marine sediments in Venice can grow by anaerobic oxidation of phosphite (+ III) to phosphate (+ V) while simultaneously reducing sulphate to hydrogen sulphide. To our knowledge, this is the first description of a redox reaction involving phosphorus in microbial energy metabolism, an activity that might have operated on the early Earth and which could represent an ancient evolutionary trait.

Redfield revisited. 2. What regulates the oxygen content of the atmosphere

Abstract: The continuous charcoal record, interpreted with the aid of the results of combustion experiments, indicates that the mixing ratio of atmospheric oxygen has varied remarkably little over the past 350 Myr. We develop a dynamic feedback model of the coupled P, N, C, and O2 cycles and use perturbation analysis and a case study of the past 40 Myr to test various feedback mechanisms that have been proposed to stabilize atmospheric oxygen. These mechanisms involve alterations in nutrient driven productivity and the subsequent burial flux of organic carbon, which provides the main source of atmospheric oxygen. Suppression of the burial of phosphorus sorbed to iron minerals under anoxic conditions in ocean bottom waters tends to increase the ocean nutrient inventory and provide negative feedback against declining oxygen [Holland, 1994]. However, denitrification is enhanced by anoxia, tending to reduce the nutrient inventory and amplify declining oxygen [Lenton and Watson, this issue]. If organic phosphorus removal from the ocean is also suppressed under anoxic conditions, this improves oxygen regulation [Van Cappellen and Ingall, 1994], as does direct enhancement of organic carbon burial due to reduced oxygen concentration in bottom waters [Betts and Holland, 1991]. However, all of the ocean-based feedback mechanisms cease to operate under increases in oxygen that remove anoxia from the ocean. Fire frequency is extremely sensitive to increases in oxygen above 21% of the atmosphere, readily suppressing vegetation on the land surface. This should transfer phosphorus from the land to the ocean, causing less carbon to be buried per unit of phosphorus and providing a weak negative feedback on oxygen [Kump, 1988]. However, a new proposal that increases in oxygen suppress the biological amplification of rock weathering and hence the input of phosphorus to the Earth system provides the most effective oxygen regulation of all the mechanisms considered. A range of proxies suggests that the input of available phosphorus to the ocean may have been significantly reduced 40 Myr ago, suppressing new production and organic carbon burial in the model. With only ocean-based feedback, the atmospheric oxygen reservoir is predicted to have shrunk from ∼26% of the atmosphere 40 Myr ago. However, when land plant mediated negative feedback on phosphorus weathering is added, oxygen is regulated within 19–21% of the atmosphere throughout the past 40 Myr, in a manner more consistent with paleorecords.

Phosphorus Forms and Desorption Patterns in Heavily Fertilized Calcareous and Limed Acid Soils

Abstract: Phosphorus desorption from fertilized soils is significant for agriculture and the environment. This study was aimed at characterizing the forms in which P occurs in calcareous and limed acid soils and their influence on P desorption patterns. The P forms of two limed acid and three calcareous soils of Europe were characterized by chemical extraction, isotopic exchange, and sequential fractionation. Phosphate desorption was studied using resins and goethite as ion sinks. Total P ranged from 705 to 1400 mg kg -1 . Isotopic exchange revealed more surface-adsorbed P in the limed acid than in the calcareous soils. Calcium phosphates predominated in the calcareous and Al and Fe phosphates in the limed acid soils; one limed add soil contained significant amounts of Ca phosphates. The mixed cation and anion exchange resins (ACER) were more effective in desorbing P than the anion exchange resin (AER) and goethite. The desorption curves indicated significant differences in the degree of homogeneity of the P desorption reactions, the greatest and lowest degree of homogeneity corresponding with calcareous soils. The proportion of ACER-extractable P that was plant-available P was >50% for the limed acid and 60% for the limed add and <40% for the calcareous soils. Plant P availability was thus poorer in the calcareous soils than in the limed acid soils.

Production of mucilage by the adriatic epipelic diatom cylindrotheca closterium (bacillariophyceae) under nutrient limitation

Abstract: The carbon partitioning of the epipelic diatom Cylindrotheca closterium (Ehrenberg) Reiman and Lewin isolated from the Adriatic Sea was studied in the laboratory under varying scenarios of nutrient limitation. Total number of cells, photosynthesis measured at 695 μmol photons·m−2·s−1 irradiance (P695-μmol), chlorophyll (a+c) content, respiration, extracellular polymeric substances (EPS), total particulate carbohydrate (TPC), and dissolved carbohydrate were evaluated under nitrogen and phosphorus deficiencies in culture. The highest total number of cells was found in the control, whereas the nitrogen-limited treatment showed the lowest value. During the transition phase of growth, photosynthesis in the nitrogen-limited treatment was 3-fold lower than in the phosphorus-limited treatment and 4-fold lower than in the control. Differences in respiration rates and chlorophyll (a+c) content were even more marked. Dissolved carbohydrate remained the same in all the treatments, whereas during the transition and stationary phase, EPS presented the highest values under phosphorus limitation and the lowest in the control treatment. The production of EPS was closely linked to the periods of carbon assimilation (transition phase) in the nutrient depleted treatments, especially in the phosphorus-limited treatment. These results point out the relevance of the nutrient imbalance (nitrogen or phosphorus) in the production of EPS by the benthic or resuspended diatoms and suggest that these diatoms play an important role in nutrient-unbalanced systems like sediments or marine snow.

Phosphorus dynamics in the North Pacific subtropical gyre

Abstract: Phosphorus (P) dynamics were studied during several research cruises to Stn ALOHA and in the 'Climax region' of the North Pacific subtropical gyre (NPSG) in 1996-1997. The aim of this study was to: (1) investigate the coupled uptake and regeneration of inorganic phosphate (Pi) and the production of dissolved organic phosphorus (DOP), (2) quantify the size of the biologically available P (BAP) pool, and (3) estimate the relative bioavailability of select organic P compounds to the natural microbial assemblages. At all stations, the microbial community was dominated by prokaryotes (> 99.5% of total cell numbers); Prochlorococcus spp. was the dominant pigmented group (>97% by numbers), comprising 20 to 30% of the total prokaryotic population. Phosphate uptake rates were 3.0 to 8.2 nM d -1 (median = 3.5 nM d -1 ) and P pool turnover times ranged from 2 to 40 d (median = 9 d). The BAP pool generally exceeded the Pi pool, suggesting rapid turnover of at least a portion of the much larger DOP pool. The net production of DOP was approximately 10 to 40% of the net P uptake. Both the dissolved and the particulate organic matter pools were enriched in carbon (C) and nitrogen (N) relative to P, compared to the Redfield molar stoichiometry of 106C:16N:1P. The half-saturation constant, Km, values for Pi uptake were higher than the ambient Pi pool concentrations, and uptake rates were positively correlated with exogenous Pi additions over the range tested (Pi = 25 to 250 nM). The bioavailabilities of exogenous adenine and guanine nucleotides were generally higher than other organic P compounds we tested. The net Pi regeneration rate from nucleotides was up to 50 times higher than the net Pi uptake rates, indicating a large potential for the regeneration of Pi from specific organic compounds. These P pool dynamics observed in the NPSG are consistent with a microbial community currently under P control.

Quantitative phosphorus measurement: A field test procedure for archaeological site analysis at Piedras Negras, Guatemala

Abstract: Currently there is a wide interest in the use of chemical analyses for the evaluation of anthropogenically altered soils and other archaeological deposits. Because soil phosphorus levels increase in areas of human habitation, and leave a permanent signature that can only be removed by erosion of the soil itself, phosphorus mapping has become a popular field procedure to indicate areas of habitation where overt evidence of ancient occupance is absent. We have developed a methodology to obtain accurate acid-extractable phosphorus concentrations (mg/kg) in calcareous soils under the primitive field conditions of Piedras Negras, Guatemala. Predicated on Mehlich-II acid extractant and colorimetric methods, this procedure processed 36 samples per hour at very low cost per sample. Based on eight replicate measurements of a group of samples, the coefficient of variation of the procedure was 8.3%. Subsequent analysis of 35 soil samples in a controlled laboratory revealed a moderate correlation of 0.44 between the Mehlich-extractable phosphorus and total phosphorus. The correlation was 0.91 between the Mehlich procedure and Olsen bicarbonate extractable phosphorus, indicating that Mehlich-based results are similar to those obtainable using a traditional extractable phosphorus method on soils of neutral to alkaline pH. There was a moderate correlation between Mehlich P and ring-test rating (r = 0.42). The wider dynamic range of the Mehlich extraction, coupled with the use of a battery-operated colorimeter, facilitated the finding of a refuse midden within an area of phosphate enriched soils. Further tests indicated that phosphorus concentrations measured in the field deviated by only 7% from those made under controlled laboratory conditions. © 2000 John Wiley & Sons, Inc.

Seasonality in phosphorus release rates from the sediments of a hypereutrophic lake under a matrix of pH and redox conditions

Abstract: Phosphorus release rates were measured on intact sediment cores collected from the major depositional basin of Onondaga Lake, a dimictic, calcareous, hypereutrophic system in Syracuse, N.Y., U.S.A....