Po In Sediment Research Articles

Recognizing the variation of bioavailable organic phosphorus in sediment and its significance between high and low risk periods for algal blooms in Lake Erhai

The sediment-bound organic phosphorus (Po) is increasingly recognized as a critical internal source for the lake eutrophication process due to its potential bioavailability for organisms. However, limited recognition about the bioavailability variations of sediment Po impeded the in-depth understanding upon the biogeochemical process of Po, especially the differences between high and low risk-periods of algal blooms (HRP-ABs and LRP-ABs). Primarily, significant difference between HRP-ABs (July–December) and LRP-ABs (January–June) was discerned by Mann-Kendall tests of TP, Chla and algal biomass. Biochemical and molecular characterizations, e.g., enzymatic hydrolysis with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), were combined to discern the bioavailability variation of sequential extracted sediment Po in HRP-ABs and LRP-ABs. The contents of enzymatically hydrolysable Po decreased in the following order: NaOH-Po > NaHCO3-Po > H2O-Po. The concentrations of bioavailable Po, including labile phosphate monoester (Labile Mono-P) and phosphodiester (Diester-P) were 21.8–58.4 mg/kg (averagely 44.3 mg/kg) and 19.5–35.8 mg/kg (averagely 28.2 mg/kg) in HRP-ABs and LRP-ABs, respectively. Notably, the amounts of bioavailable H2O-Po and NaHCO3-Po in HRP-ABs (13.4–33.3 mg/kg) were nearly 2–3 times of that in LRP-ABs (3.9–14 mg/kg), while no significant NaOH-Po differences were observed. Similarly, contrasting the HRP-ABs with LRP-ABs, more P-containing formulas were assigned in H2O-Po (2526 vs 1884) and NaHCO3-Po (1554 vs 863), with similar abundance in NaOH-Po. Furthermore, the molecular composition of bioavailable Po (Bio-Po, H/C > 1.2 O/C > 0.5), especially Bio-Po containing two P atoms (Bio-2Po) displayed significant variation in H2O-Po (308 vs 391, 217 vs 316) and NaHCO3-Po (114 vs 208, 40 vs 145) between HRP-ABs and LRP-ABs. This was largely attributed to its high bioavailability in Bio-2Po (>50% lipids, proteins and carbohydrates-like). Our findings upon the internally activated accumulation and transformation process interpretation of sediment bioavailable Po are of great significance for lake eutrophication control.

Novel insights into molecular composition of organic phosphorus in lake sediments

Organic phosphorus (Po) plays a key role in eutrophication and ecological equilibrium in lake systems. However, characterizing the composition of Po in lake sediments has been a bottleneck hindering further understanding of the biogeochemical cycle of Po. Here, multiple methods of 31P NMR spectroscopy and molecular weight (MW) ultrafiltration were combined to detect Po composition characteristics from a novel angle in ten lake sediments of China. The results showed that sediment Po mainly consisted of monoester (mono-P, 14±8.8% of the NaOH-EDTA total P on average), diester (di-P, 1.4±1.4%) and phosphonate (phos-P, 0.1±0.1%), while the abundance of Po was largely underestimated by 31P NMR methods. Some specific species of mono-P were successfully determined, and the contents of these species followed a decreasing order: inositol hexakisphosphate (IHP6) > RNA mononucleotides (RNA-mnP) > β-glycerophosphate (β-gly) > D-glucose 6-phosphate (Glu-6) > α-glycerophosphate (α-gly), which was largely dependent upon their bioreactivity. A significant relationship between MW and Po components was observed despite the great differences among sediment samples. For refractory Po components, IHP6 was mainly rich in the MW < 3 kDa while phos-P was almost only detected in the MW > 3 kDa, which largely attributed to their metal binding affinities and characteristics. The abundance of bioreactive Po species (α-gly, β-gly, Glu-6, di-P) in high MW (HMW, > 3 kDa) were all higher than that of low MW (LMW, < 3 kDa) due to microbial degradation and self-assembly. If the HMW organic molecules were biologically and chemically more reactive than its LMW counterparts, the high percentage of α-gly, β-gly, glu-6 and di-P in the HMW portion would highlights their high reactivity from the perspective of MW. These insights revealed the dynamics of the MW distribution of Po components and provide valuable information to better understand the Po composition and bioreactivity in sediments.

Characterization and source identification of organic phosphorus in sediments of a hypereutrophic lake

High phosphorus (P) load and consequent algal bloom are critical issues because of their harmful effects to aquatic ecosystems. The organic phosphorus (Po) cycling and hydrolyzation pathway in the sediments of a hypereutrophic lake area with high algae biomass were investigated using stable isotopes (δ13C and δ15N) along with C/N ratios, a sequential extraction procedure, 31P NMR spectrum, and alkaline phosphatase activity (APA) was measured simultaneously. C/N ratios lower than 10 combined with lighter δ13C (−23.5 to −25.2‰) and δ15N values (3.7–9.5‰) indicated that endogenous algal debris contributed to the predominant proportions of P-containing organic matter in the sediments. Sequential extraction results showed that Po fractions decreased as nonlabile Po > moderately labile Po > biomass-Po. Decreasing humic-associated Po (HA-Po) in sediments downward suggested the degradation of high-molecular-weight Po compounds on the geological time scale to low-molecular-weight Po including fulvic-associated Po (FA-Po), which is an important source of labile Po in the sediment. An analysis of the solution 31P NMR spectrum analysis showed that important Po compound groups decreased in the order of orthophosphate monoesters > DNA-Po > phospholipids. The significant correlation indicated that orthophosphate monoesters were the predominant components of HA-Po. Rapid hydrolysis of labile orthophosphate diesters further facilitated the accumulation of orthophosphate monoesters in the sediments. Additionally, the simultaneously upward increasing trend demonstrated that APA accelerated the mineralization of Po into dissolved reactive phosphorus (DRP), which might feed back to eutrophication in algae-dominant lakes. The significantly low half-life time (T1/2) for important Po compound groups indicated faster metabolism processes, including hydrolysis and mineralization, in hypereutrophic lakes with high algae biomass. These findings provided improved insights for better understanding of the origin and cycling processes as well as management of Po in hypereutrophic lakes.

The potential role of sediment organic phosphorus in algal growth in a low nutrient lake

The role of sediment–bound organic phosphorus (Po) as an additional nutrient source is a component of internal P budgets in lake system that is usually neglected. Here we examined the relative importance of sediment Po to internal P load and the role of bioavailable Po in algal growth in Lake Erhai, China. Lake Erhai sediment extractable Po accounted for 11–43% (27% average) of extractable total P, and bioavailable Po accounted for 21–66% (40%) of Po. The massive storage of bioavailable Po represents an important form of available P, essential to internal loads. The bioavailable Po includes mainnly labile monoester P and diester P was identified in the sequential extractions by H2O, NaHCO3, NaOH, and HCl. 40% of H2O−Po, 39% of NaHCO3−Po, 43% of NaOH−Po, and 56% of HCl−Po can be hydrolyzed to labile monoester and diester P, suggesting that the bioavailability of Po fractions was in decreasing order as follows: HCl−Po > NaOH−Po > H2O−Po > NaHCO3−Po. It is implied that traditional sequential fractionation of Po might overestimate the availability of labile Po in sediments. Furthermore, analysis of the environmental processes of bioavailable Po showed that the stabler structure of dissloved organic matter (DOM) alleviated the degradation and release of diester P, abundant alkaline phosphatase due to higher algal biomass promoted the degradation of diester P. The stability of DOM structure and the degradation of diester P might responsible for the spatial differences of labile monoester P. The biogeochemical cycle of bioavailable Po replenishs available P pools in overlying water and further facilitate algal growth during the algal blooms. Therefore, to control the algal blooms in Lake Erhai, an effective action is urgently required to reduce the accumulation of Po in sediments and interrupt the supply cycle of bioavailable Po to algal growth.

Response of sediment organic phosphorus composition to lake trophic status in China

Organic phosphorus (Po) constitutes the most important fraction of P in lake sediments, and the compositional properties of Po affect its behavior in lake ecosystems. In this study, 31P NMR, FT-IR spectroscopy, and UV–visible absorbance spectroscopy were combined to identify the dynamic composition of sediment Po across two sets of lakes in China ranging from oligotrophic to eutrophic, and their possible effects on lake eutrophication were evaluated. The results showed that sediment Po content (accounting for 24–75% of TP) was positively correlated with trophic status in both Eastern Plain and Yun-Gui Plateau lakes of China, and the linear relationship was more stable compared to total P (TP), implying that sediment Po may be a superior indicator of trophic status than TP. The Po component, phosphonate accounted for only 0.4% or less of Po, while the monoester P and diester P, accounted for 2–24% and 0.5–5% of Po, respectively, and were the main factors causing Po to increase with the increasing trophic status. The factors were closely related to the enhanced organic sewage load and intensification of contemporary sedimentation of phytoplankton. As trophic status increased, sediment Po might integrate into larger amounts of aromatic substances and functional groups, which could enhance the stability of Po in sediments. Furthermore, sediments from lakes with higher trophic status exhibited a higher degree of humification and molecular weights, which impart resistance to biodegradation, and therefore, reduced the risk of sediment Po release. However, the massive accumulation of bioavailable Po (monoester and diester P) allows possible degradation, supporting algal growth and maintains eutrophic status because there is abundant alkaline phosphatase in eutrophic lakes. Thus, to control lake eutrophication more effectively, targeted actions are urgently required to reduce the accumulation and degradation of Po in lake sediment.

Bioavailability and preservation of organic phosphorus in lake sediments: Insights from enzymatic hydrolysis and 31P nuclear magnetic resonance

Bioavailability and preservation of organic P (Po) in the sediment profiles (DC-1 and DC-2) from Lake Dianchi, a eutrophic lake in China, were investigated by a combination of enzymatic hydrolysis and solution 31P nuclear magnetic resonance (NMR) spectroscopy. Results showed that large of Po could be extracted by NaOH-EDTA (NaOH-EDTA Po), with little Po in residues after extraction with NaOH-EDTA. Bioavailability and preservation of NaOH-EDTA Po provide key information for biogeochemical cycling of Po in sediments. The details of P species and their bioavailability in NaOH-EDTA Po showed that 54.8–70.4% in DC-1 and 54.6–100% in DC-2, measured by 31P NMR, could be hydrolyzed by the phosphatase. Whereas, some proportion of NaOH-EDTA Po could not be hydrolyzed by the phosphatase, and decreased with sediment depth. Interaction between Po and other organic matter (e.g., humic acids) is likely an important factor for preservation of these Po in the sediment profiles. Simulation experiments of hydrolysis of model Po compounds adsorbed by minerals, such as goethite and montmorillonite, further indicated that adsorption to minerals protected some Po, especially phytate-like P, from enzymatic hydrolysis, thus preserving these forms of Po in sediments. Interactions of Po with organic matter and minerals in the sediments are two important factors determining biogeochemical cycling of Po in lakes. Intervention to break the cycle of FeP and bioavailable Po (e.g., labile monoester P) in the history of eutrophication is important way to control algal blooming.

Simulated bioavailability of phosphorus from aquatic macrophytes and phytoplankton by aqueous suspension and incubation with alkaline phosphatase

Bioavailability of phosphorus (P) in biomass of aquatic macrophytes and phytoplankton and its possible relationship with eutrophication were explored by evaluation of forms and quantities of P in aqueous extracts of dried macrophytes. Specifically, effects of hydrolysis of organically-bound P by the enzyme alkaline phosphatase were studied by use of solution 31P-nuclear magnetic resonance (NMR) spectroscopy. Laboratory suspensions and incubations with enzymes were used to simulate natural releases of P from plant debris. Three aquatic macrophytes and three phytoplankters were collected from Tai Lake, China, for use in this simulation study. The trend of hydrolysis of organic P (Po) by alkaline phosphatase was similar for aquatic macrophytes and phytoplankton. Most monoester P (15.3% of total dissolved P) and pyrophosphate (1.8%) and polyphosphate (0.4%) and DNA (3.2%) were transformed into orthophosphate (14.3%). The major forms of monoester P were glycerophosphate (8.8%), nucleotide (2.5%), phytate (0.4%) and other monoesters P (3.6%). Proportions of Po including condensed P hydrolyzed in phytoplankton and aquatic macrophytes were different, with the percentage of 22.6% and 6.0%, respectively. Proportion of Po hydrolyzed in debris from phytoplankton was approximately four times greater than that of Po from aquatic macrophytes, and could be approximately twenty-five times greater than that of Po in sediments. Thus, release and hydrolysis of Po, derived from phytoplankton debris would be an important and fast way to provide bioavailable P to support cyanobacterial blooming in eutrophic lakes.

Microbial Biomass and Community Composition Involved in Cycling of Organic Phosphorus in Sediments of Lake Dianchi, Southwest China

ABSTRACTOrganic phosphorus (Po) was a major fraction of phosphorus (P) in sediments of lakes, and microbes were involved in most of its relevant biogeochemical cycling. Forms and quantification of Po were investigated by sequential fractionation in 18 sediments of Lake Dianchi, Southwest China. Microbial biomass and community structure in these sediments were determined by phospholipid fatty acids (PLFAs). Distribution of Po fractions were in the rank order that humic Po > nucleic acid and polyphosphate > residual P > Ca-Al-Po > Fe-Po > sugar Po > acid soluble Po > H2O-Po. The recoveries of Po and Pi in these detailed sequential fractions including residual P shows that the total contents of Po in sediments of lakes were overestimated by the Standards, Measurements and Testing (SMT) protocol (ignition method). Microbial biomass including Gram-positive bacteria (14.4–20.0%), Gram-negative bacteria (32.7–38.4%), microeukaryotes (14.9–24.4%), aerobic bacteria (43.6–55.8%), anaerobic bacteria (0–2.9%) and type І methanotrophs (17.6–24.4%) were assigned. Microbial mass and their composition were strongly correlated with H2O-Po, Fe-Po, nucleic acid and polyphosphate, and humic Po, though residual P was likely inert for microbes in sediments. The formation and degradation of Po was closely related with microbial activities in sediments. These findings have implications for understanding the role of microbes on cycling of Po and organic matter in sediments of lakes.

Characteristics of bioavailable organic phosphorus in sediment and its contribution to lake eutrophication in China

This study aims to establish the relative importance of sediment organic phosphorus (Po) to the total P and the major classes of organic molecules that contribute to sediment Po, determined by measuring their susceptibility to enzymatic hydrolysis, across a suite of lakes ranging from oligotrophic to eutrophic status. The results showed that Po accounted for 21–60% of total P, and bioavailable Po accounted for 9–34% of Po in the sediments. The bioavailable Po includes mainly labile (H2O-Po) and moderately labile (NaOH-Po) P forms. For H2O-Po (accounting for only1.4% of Po), 53% (average) was labile monoester P, 28% was diester P and 17% was phytate-like P. For NaOH-Po (accounting for 9–33% of Po), 32% was labile monoester P, 33% was phytate-like P and 18% was diester P. The composition of bioavailable Po, determined by enzyme assays, was related to the lake nutrient levels, which implies that sediment bioavailable Po could act as an effective indicator for lake eutrophic status. With the increase of lake nutrient levels, bioavailable Po content and alkaline phosphatase activity in the sediment all increased, indicating that Po represents an important and bioavailable source of P that increases with eutrophication, and could contribute to internal loading and resistance of eutrophic lakes to remediation. This implies that eutrophic lakes would maintain long-term eutrophic status and algal bloom phenomena even after the external input of P was controlled and the total P concentration of water has declined. Thus, in order to reduce the release risk of sediment P more efficiently and effectively, sediment P control technique should focus not only on reducing the total P and inorganic P, but should also pay close attention to the removal of bioavailable Po.

Influence of natural organic matter on the bioavailability and preservation of organic phosphorus in lake sediments

Information about the bioavailability and sequestration of organic phosphorus (Po) in sediments is fundamental to understanding biogeochemical cycling of phosphorus (P) in eutrophic lakes. However, the processes governing preservation of Po in sediments are still poorly understood. Sequential extraction of Po by H2O (H2O-Po) and NaOH–EDTA (NaOH–EDTA Po), in combination with enzymatic hydrolysis/31P NMR, was applied to estimate the bioavailability of Po in sediments of Lake Tai (Ch: Taihu), China. Of H2O-Po and NaOH–EDTA Po, 45.5–89.4% and 30.4–71.3% respectively were hydrolyzed by phosphatase, and therefore considered to be biologically available. Of NaOH–EDTA Po, 28.7–69.6% could not be hydrolyzed by phosphatase; this portion was characterized by 31P NMR as monoester P and/or diester P. Simulation experiments of hydrolysis of model Po compounds in the presence of humic acids (HA), which were used as a model for natural organic matter (NOM), and metals, including Al, Ca, and Fe, have demonstrated that enzymatic hydrolysis of labile monoester P was weakly reduced by HA or metal ions. Condensed phosphate (e.g., pyrophosphate) and phytate-like P (e.g., inositol phosphates) were resistant to enzymatic hydrolysis in the presence of HA and/or metal ions, which indicated that they may be possibly preserved in sediments. These observations suggest that NOM in sediments can be a significant factor determining the bioavailability and preservation of Po in sediments. The presence of metals would enhance the effect of NOM on preservation of Po in sediments. Formation of Po–metal–HA or Po–metal complexes might be mechanisms responsible for these processes.

Characteristics of Phosphorus Compounds and Their Effects in Sediments of an Eutrophic Chaohu Lake, China

Surface sediments and sediment cores in a shallow eutrophic lake, Chaohu Lake, were analyzed by 31P‐NMR to reveal the phosphorus (P) species and their effects on upper water quality. Total P (TP) in the NaOH‐EDTA extracts was dominated by inorganic phosphate (Pi), with higher levels being observed in the heavily eutrophic western lake (79.1 ± 1.7%) than in the eastern lake (68.1 ± 2.4%). These findings were opposite to those for organic phosphorus (Po). Pi (ortho‐phosphate and pyrophosphate) and Po (phosphonates, ortho‐phosphate monoesters and phospholipids, DNA) were detected in the NaOH‐EDTA extracts of the sediments by 31P‐NMR. The majority of Po consisted of ortho‐phosphate monoesters (80.2 ± 2.7%). For sediment cores, the contents of phospholipids and DNA declined more rapidly than that of ortho‐phosphate monoesters and pyrophosphate as sediment depth increased, with these compounds primarily occurring in the top 10 cm of sediment. The positive relationship between Po in sediment and TP in the water showed that Po compounds in the sediment would be released to the water. These compounds of Po will be mineralized to Pi and potentially bioavailable for recycling to surface water, supporting further growth of aquatic organisms and leading to algal blooms.

Characterization of Organic Phosphorus in Lake Sediments by Sequential Fractionation and Enzymatic Hydrolysis

The role of sediment-bound organic phosphorus (Po) on lake eutrophication was studied using sequential extraction and enzymatic hydrolysis by collecting sediments from Dianchi Lake, China. Bioavailable Po species including labile monoester P, diester P, and phytate-like P were identified in the sequential extractions by H2O, NaHCO3, and NaOH. For the H2O-Po, 36.7% (average) was labile monoester P, 14.8% was diester P, and 69.9% was phytate-like P. In NaHCO3-Po, 19.9% was labile monoester P, 17.5% was diester P, and 58.8% was phytate-like P. For NaOH-Po, 25.6% was labile monoester P, 7.9% was diester P, and 35.9% was phytate-like P. Labile monoester P was active to support growth of algae to form blooms. Diester P mainly distributed in labile H2O and NaHCO3 fractions was readily available to cyanobacteria. Phytate-like P represents a major portion of the Po in the NaOH fractions, also in the more labile H2O and NaHCO3 fractions. Based on results of sequential extraction of Po and enzymatic hydrolysis, lability and bioavailability was in decreasing order as follows: H2O-Po > NaHCO3-Po > NaOH-Po, and bioavailable Po accounted for only 12.1-27.2% of total Po in sediments. These results suggest that the biogeochemical cycle of bioavailable Po might play an important role in maintaining the eutrophic status of lakes.

Consequences of Increasing Hypoxic Disturbance on Benthic Communities and Ecosystem Functioning

Disturbance-mediated species loss has prompted research considering how ecosystem functions are changed when biota is impaired. However, there is still limited empirical evidence from natural environments evaluating the direct and indirect (i.e. via biota) effects of disturbance on ecosystem functioning. Oxygen deficiency is a widespread threat to coastal and estuarine communities. While the negative impacts of hypoxia on benthic communities are well known, few studies have assessed in situ how benthic communities subjected to different degrees of hypoxic stress alter their contribution to ecosystem functioning. We studied changes in sediment ecosystem function (i.e. oxygen and nutrient fluxes across the sediment water-interface) by artificially inducing hypoxia of different durations (0, 3, 7 and 48 days) in a subtidal sandy habitat. Benthic chamber incubations were used for measuring responses in sediment oxygen and nutrient fluxes. Changes in benthic species richness, structure and traits were quantified, while stress-induced behavioral changes were documented by observing bivalve reburial rates. The initial change in faunal behavior was followed by non-linear degradation in benthic parameters (abundance, biomass, bioturbation potential), gradually impairing the structural and functional composition of the benthic community. In terms of ecosystem function, the increasing duration of hypoxia altered sediment oxygen consumption and enhanced sediment effluxes of NH4 + and dissolved Si. Although effluxes of PO4 3− were not altered significantly, changes were observed in sediment PO4 3− sorption capability. The duration of hypoxia (i.e. number of days of stress) explained a minor part of the changes in ecosystem function. Instead, the benthic community and disturbance-driven changes within the benthos explained a larger proportion of the variability in sediment oxygen- and nutrient fluxes. Our results emphasize that the level of stress to the benthic habitat matters, and that the link between biodiversity and ecosystem function is likely to be affected by a range of factors in complex, natural environments.

In situ O2 dynamics in submerged Isoetes australis: varied leaf gas permeability influences underwater photosynthesis and internal O2

A unique type of vernal pool are those formed on granite outcrops, as the substrate prevents percolation so that water accumulates in depressions when precipitation exceeds evaporation. The O2 dynamics of small, shallow vernal pools with dense populations of Isoetes australis were studied in situ, and the potential importance of the achlorophyllous leaf bases to underwater net photosynthesis (PN) and radial O2 loss to sediments is highlighted. O2 microelectrodes were used in situ to monitor pO2 in leaves, shallow sediments, and water in four vernal pools. The role of the achlorophyllous leaf bases in gas exchange was evaluated in laboratory studies of underwater PN, loss of tissue water, radial O2 loss, and light microscopy. Tissue and sediment pO2 showed large diurnal amplitudes and internal O2 was more similar to sediment pO2 than water pO2. In early afternoon, sediment pO2 was often higher than tissue pO2 and although sediment O2 declined substantially during the night, it did not become anoxic. The achlorophyllous leaf bases were 34% of the surface area of the shoots, and enhanced by 2.5-fold rates of underwater PN by the green portions, presumably by increasing the surface area for CO2 entry. In addition, these leaf bases would contribute to loss of O2 to the surrounding sediments. Numerous species of isoetids, seagrasses, and rosette-forming wetland plants have a large proportion of the leaf buried in sediments and this study indicates that the white achlorophyllous leaf bases may act as an important area of entry for CO2, or exit for O2, with the surrounding sediment.

Uranium and its decay products in samples contaminated with uranium mine and mill waste

The routine determination of the activity concentrations of uranium isotopes ( 238 U, 235 U and 234 U), thorium isotopes ( 232 Th, 230 Th and 228 Th), 231 Pa, 226 Ra, 210 Pb and 210 Po in the environment is one of the most important tasks in uranium mining areas. Natural radionuclides contribute negligibly to the external radiation dose, but in the case of ingestion or inhalation can represent a very serious hazard. The objective of this study was to determine the activities of uranium and its decay products 230 Th, 231 Pa, 226 Ra, 210 Pb and 210 Po in sediments and water below sources of contamination (uranium mine, disposal sites and individual inflows) using gamma and alpha spectrometry, beta counting, the liquid scintillation technique and radiochemical neutron activation analysis.