Phosphorus Fractions In Sediments Research Articles

Nutrients regeneration pathway, release potential, transformation pattern and algal utilization strategies jointly drove cyanobacterial growth and their succession

In order to better understand the contribution of nutrients regeneration pathway, release potential and transformation pattern to cyanobacterial growth and succession, 7 sampling sites in Lake Chaohu with different bloom degree were studied every two months from February to November 2018. The carbon, nitrogen (N) and phosphorus (P) forms or fractions in surface, interstitial water and sediments as well as extracellular enzymatic activities, P sorption, specific microbial abundance and community composition in sediments were analyzed. P regeneration pathway was dominated by iron-bound P desorption and phosphorus-solubilizing bacteria solubilization in severe-bloom and slight-bloom area respectively, which both resulted in high soluble reactive phosphorus (SRP) accumulation in interstitial water. However, in severe-bloom area, higher P release potential caused the strong P release and algal growth, compared to slight-bloom area. In spring, P limitation and N selective assimilation of Dolichospermum facilitated nitrate accumulation in surface water, which provided enough N source for the initiation of Microcystis bloom. In summer, the accumulated organic N in Dolichospermum cells during its bloom was re-mineralized as ammonium to replenish N source for the sustainable development of Microcystis bloom. Furthermore, SRP continuous release led to the replacement of Dolichospermum by Microcystis with the advantage of P quick utilization, transport and storage. Taken together, the succession from Dolichospermum to Microcystis was due to both the different forms of N and P in water column mediated by different regeneration and transformation pathways as well as release potential, and algal N and P utilization strategies.

Spatial Distribution and Environmental Significance of Phosphorus Fractions in River Sediments and Its Influencing Factor from Hongze and Tiaoxi Watersheds, Eastern China.

This study explored the spatial distribution of phosphorus fractions in river sediments and analyzed the relationship between different phosphorus fractions and their environmental influence on the sediments within different watersheds in Eastern China. River sediments from two inflow watersheds (Hongze and Tiaoxi) to Hongze and Taihu Lake in Eastern China were analyzed by the sequential extraction procedure. Five fractions of sedimentary phosphorus, including freely sorbed phosphorus (NH4Cl-P), redox-sensitive phosphorus (BD-P), bound phosphorus metal oxide (NaOH-P), bound phosphorus calcium (HCl-P), and residual phosphorus (Res-P) were all analyzed. The orders of rankings for the P fractions of the rivers Anhe and Suihe were HCl-P > NaOH-P > BD-P > NH4Cl-P and HCl-P > BD-P > NaOH-P > NH4Cl-P, respectively. For the rank order of the Hongze watershed, HCl-P was higher while the NH4Cl-P contents were significantly lower. The rank order for the Dongtiaoxi River was NaOH-P > HCl-P > BD-P > NH4Cl-P, and that of Xitiaoxi River was NaOH-P > BD-P > HCl-P > NH4Cl-P. Compared with the phosphorus forms of the Tiaoxi watershed, NaOH-P contents were significantly higher compared to HCl-P, which was significantly higher in the Hongze watershed. In comparison, NH4Cl-P contents were significantly lower in both. Variations may be attributed to differential discharge of the P form in the watershed due to land-use changes and urban river ambient conditions.

Variability of sedimentary phosphorus fractions in the western and Sandusky basins of Lake Erie

Surface sediments and three sediment cores from the western basin and one sediment core from the Sandusky basin were analyzed to document spatial and temporal changes in five phosphorus fractions and total phosphorus (TP). The areal distributions of the bioavailable fractions NaCl-Pi, NaBD-Pi, and NaOH-Pi and the refractory organic fraction Res-P were broadly consistent and contrasted with those of the detrital fraction HCl-Pi which showed that high concentrations occurred mostly in high-energy littoral zones and low concentrations largely in profundal depositional areas. The contrasting distributions were induced by interactions among tributary inputs, wave action, circulation, and biogeochemical cycling and transfer in the basin. As revealed by the Sandusky basin sediment record, the detrital fraction HCl-Pi was dominant (70% of TP) during European settlement and decreased rapidly by 28.0% in the early 1910s due largely to impoundments of the Maumee and Sandusky Rivers. While HCl-Pi has ever since remained relatively constant, NaCl-Pi, NaBD-Pi, and NaOH-Pi increased significantly between 1950 and 1970 in the two basins. However, the post-regulation sediment records differed considerably among these coring sites. There was a marked increase of TP in two cores, corresponding to recent return of eutrophication and massive harmful algal blooms but contrasting with a relatively constant, low loading into the lake. This signified the role of internal loading as derived partialy from legacy pollution. Furthermore, NaCl-Pi has increased progressively throughout all the records. We conclude that the increased levels of NaCl-Pi in surface sediments may have altered the internal loading and contributed to the resurgences of harmful algal blooms in Lake Erie.

Effect of Calcium Peroxide Composite Tablets on Water Remediation and Phosphorus Control in Sediment

Two types of calcium peroxide composite tablets (CPCTs) were prepared, and the inhibition effect on the release of endogenous phosphorus and the influence on the overlying water by mixed-dosing were investigated. The CPCTs were made of calcium peroxide (CaO2), calcined water purification sludge, and hydroxypropyl methylcellulose (HPMC), which were directly pressed into composite tablets, among which Tablet-B (T-B) contained ferrous sulfate (FeSO4) and Tablet-A (T-A) did not. Both the tablets agreed well with the Langmuir and Freundlich isothermal models; the theoretical maximum adsorption capacities of T-A and T-B on phosphorus were 110.908 mg·g-1 and 106.390 mg·g-1, respectively. Compared with the control group, the pH of overlying water was increased, the concentration of Chl-a was decreased by 42.75% and 60.82%, and the DO was increased by 53.73% and 63.30% in group A and B, respectively. The DIP of the overlying water decreased significantly by 54.93% and 25.11% in group A and B, respectively. For the interstitial water in sediment, the DIP in layer Ⅰ (0-2 cm) decreased significantly by 74.81% and 65.66% in group A and B, and the DIP in layer Ⅱ (2-4 cm) decreased significantly by 46.23% in group B, but not obviously in group A. The DIP in layer Ⅲ (4-6 cm) remained unchanged in group A and B. For phosphorus fractions in sediment, the proportion of NH4Cl-P in TP was significantly increased (layer Ⅰ: 16.87% and 13.11%; layer Ⅱ: 12.99% and 11.02%, in group A and B, respectively), and the proportion of Al-P in TP was significantly decreased (layer Ⅰ: 7.58% and 13.91%; layerⅡ: 9.86% and 7.28%, in group A and B, respectively). The other phosphorus fractions did not change significantly. Both T-A and T-B dosing can improve the microbial activity of the surface sediment, though T-A can improve the microbial activity more significantly.

Source identification of phosphorus in the river-lake interconnected system using microbial community fingerprints

Phosphorus, one of the primary limiting factors for eutrophication, plays a crucial role in the ecology health of aquatic ecosystems. However, understanding phosphorus bioavailability and source contributions in contaminated lake sediments which could help develop effective eutrophication management plans is limited largely due to the lack of appropriate methods in large catchments with a complex arrangement of sources. Based on the significant relationships between sediment, phosphorus and microbial community, source-specific microbial community fingerprints formed by machine-learning classification SourceTracker might shed light on determining dominant phosphorus sources in the river-lake systems in the era of high-throughput sequencing. This study was conducted in Dongting Lake that suffered accelerated eutrophication due to considerable phosphorus input from the inflow-rivers. The results of phosphorus fractionation according to the Standards, Measurements and Testing harmonized procedure indicated that sediments in the central lake had a higher concentration of non-apatite inorganic phosphorus (Mann-Whitney U test), which deserves greater attention on the risk of phosphorus release. The significant relationships between phosphorus fractionations, sediment and bacterial community were established with the spearman correlation and network analysis. SourceTracker analysis indicated that the major inflow-rivers of phosphorus sources to Dongting Lake were the Songzi, Miluo, and Xinqiang Rivers. The effects of sediment diffusion distance on phosphorus source apportionment were further confirmed. Taken together, our results contribute to an improved understanding of phosphorus fractionations and source contributions in the river-lake systems and its potential impact to eutrophication management plans.

Concentration, fractionation, and ecological risk assessment of heavy metals and phosphorus in surface sediments from lakes in N. Greece.

The presence of phosphorus (P) and heavy metals (HMs) in surface sediments originating from lakes Volvi, Kerkini, and Doirani (N. Greece), as well as their fractionation patterns, wereinvestigated. No statistically significant differences in total P content were observed among the studied lakes, but notable differences were observed among sampling periods. HM contents in all lakes presented a consistent trend, i.e., Mn > Cr > Zn > Pb > Ni > Cu > Cd, while the highest concentrations were recorded in Lake Kerkini. Most of the HMs exceeded probable effect level value indicating a probable biological effect, while Ni in many cases even exceeded threshold effects level, suggesting severe toxic effects. P was dominantly bound to metal oxides, while a significant shift toward the labile fractions was observed during the spring period. The sum of potentially bioavailable HM fractions followed a downward trend of Mn > Cr > Pb > Zn > Cu > Ni > Cd for most lakes. The geoaccumulation index Igeo values of Cr, Cu, Mn, Ni, and Zn in all lakes characterized the sediments as "unpolluted," while many sediments in lakes Volvi and Kerkini were characterized as "moderately to heavily polluted" with regard to Cd. The descending order of potential ecological risk [Formula: see text] was Cd > Pb > Cu > Ni > Cr > Zn > Mn for all the studied lakes. Ni and Cr presented the highest toxic risk index values in all lake sediments. Finally, the role of mineralogical divergences among lake sediments on the contamination degree was signified.

Evaluating the effect of dam construction on the phosphorus fractions in sediments in a reservoir of drinking water source, China.

It is widely acknowledged that dams affect sediment transport and water quality. To support water management of reservoirs, it is useful to explore how the fractions of phosphorus (P) in sediments were changed after the dam was built. The aim of this study was to assess the spatial and temporal trends of the P fractions in sediments from the Miyun Reservoir, a pivotal drinking water supply for Beijing City, the capital of China. Nine surface sediment samples, together with a sediment core, were collected. The concentrations of total P (TP) and their fractions were then determined by using a sequential extraction method. The results showed that the reservoir was classified into three areas spatially based on the TP concentrations, i.e., high (Baihe area), medium (transitional area), and low (Chaohe area) concentrations. The concentrations of iron-bound P (BD-P) and metal oxide-bound P (NaOH-P) were higher in the Baihe and Chaohe regions than those in the transitional area and tended to increase with water depth. Dam construction can lead to the concentrations of P increased in sediments and further increase the potential of internal P loadings. This study revealed the effect of dam construction on sedimentary P accumulation. The results will be helpful in better understanding the mobility and bioavailability of P in the aquatic ecosystem, which aim to achieve a more highly targeted environmental management for this important region.

Distribution characteristics of organic phosphorus in the sediments of rivers entering the Lake Hongze and the effects of exogenous substances on their fraction transformation

为探究洪泽湖入湖河流沉积物有机磷的空间分布及外源输入对其形态转化的影响，本文利用Ivanoff法开展有机磷形态特征研究，并通过实验室添加常见外源有机质和铁离子，深入探讨外源物质对沉积物有机磷形态变化的长期影响.研究结果表明，洪泽湖入湖河流沉积物有机磷含量范围为34.8~398.6 mg/kg，占总磷的7.7%~36.9%，其中非活性有机磷（NOP） > 中活性有机磷（MLOP） > 活性有机磷（LOP）.濉河沉积物LOP平均占比为19.4%，高于其他河流，而成子河NOP平均占比最高，为56.41%，表明有机磷的空间分布不均匀.总体而言，安河和濉河沉积物中总氮、总磷和有机磷含量显著高于成子河和淮河，显示前两条河流有较高的污染水平.冗余分析表明河流沉积物有机磷形态明显受到其理化性质影响，而不同污染程度沉积物的影响因素有所不同.外源物质添加能够活化沉积物的有机磷，促使NOP向LOP和MLOP转化，有机质输入引起的沉积物有机磷形态变化要大于铁元素输入，而外源物质输入对污染较重河流沉积物的有机磷转化作用更为显著.因此，减少入湖河流周边的外源污染排放是减少湖泊生物可利用磷的有效途径.;In order to explore the spatial distribution of organic phosphorus in the sediments of the rivers entering Lake Hongze and the effects of exogenous inputs on its fraction transformation, we used the Ivanoff method to study the fraction characteristics of organic phosphorus in these sediments. The long-term effects of exogenous substances on the fraction changes of organic phosphorus in sediments were also investigated by adding organic matter and iron ions in the laboratory. The results showed that the contents of organic phosphorus in the sediments of the rivers entering Lake Hongze ranged from 34.8 mg/kg to 398.6 mg/kg, accounting for 7.7% to 36.9% of the total phosphorus, and which showed non-active organic phosphorus (NOP) > middle-active organic phosphorus (MLOP) > active organic phosphorus (LOP). The average proportion of LOP in the sediments of Suihe River was 19.4%, which was higher than that of other rivers. The average proportion of NOP in Chengzi River was 56.41%, which indicated that the spatial distribution of organic phosphorus was uneven. Overall, the contents of total nitrogen, total phosphorus and organic phosphorus in sediments of Anhe and Suihe rivers were significantly higher than those of Chengzi and Huaihe rivers, indicating that the former two rivers had a higher pollution level. Redundancy analysis showed that the fractions of organic phosphorus in river sediments were affected by their physicochemical properties, indicating the different influencing factors for different pollution levels of sediment. The addition of exogenous substances can mineralize organic phosphorus in sediments and promote their transformation from NOP to LOP and MLOP. The change range of organic phosphorus fraction caused by organic matter was greater than that caused by iron, and the transformation effect of exogenous substances on organic phosphorus in heavily polluted sediments was more significant. Therefore, it is an effective way to reduce the bioavailable phosphorus of Lake Hongze by reducing the discharge of exogenous pollutants around rivers.

Environmental Significance of Phosphorus Fractions of Phytoplankton-and Macrophyte-Dominated Zones in Taihu Lake

It is of great importance to study the environmental significance of phosphorus fractions in overlying water and sediments of typical phytoplankton-and macrophyte-dominated zones. It will help to clarify the process of phosphorus migration and transformation in the sediment-water interface, and has practical significance for understanding the eutrophication process and its treatment in different regions of Taihu Lake. The investigation was conducted within typical phytoplankton-and macrophyte-dominated zones of Taihu Lake over four seasons to analyze the spatial and temporal differences between phosphorus fractions in water and sediments, and reveal their environmental significance. The results showed that:① Total phosphorus (TP), total soluble phosphorus (DTP), dissolved inorganic phosphorus (DIP), and particulate phosphorus (PP) in the overlying water of phytoplankton-dominated zones were much higher than those in macrophyte-dominated zones. Most of them showed seasonal characteristics, which were higher in summer and autumn than in winter and spring. PP is the main component of TP, accounting for 71.8% to 89.6%. A similar distribution character was found in the content of chlorophyll (Chl-a) compared with phosphorus concentration in overlying water. ② The concentration of TP in the surface sediments of phytoplankton-dominated zones was 372.38-529.64 mg·kg-1, and that in macrophyte-dominated zones was 304.29-454.27 mg·kg-1. In surface sediments, concentrations of TP in phytoplankton-dominated zones were significantly higher than in phytoplankton-dominated zones. The highest TP concentrations appeared in winter, and the lowest in summer. These were owing to the input of exogenous pollution, and the migration and transformation of internal phosphorus between sediments and overlying water under different environmental conditions. ③ The order of the mass fraction of phosphorus in sediments was:NH4Cl-P < Fe-P < Org-P < Res-P < Al-P < Ca-P. Mobile-P=NH4Cl-P+Fe-P+Org-P, accounting for 9.10%-16.93% of TP in phytoplankton-dominated zones, and slightly higher in macrophyte-dominated zones, where it was 8.11%-13.50%. Res-P accounted for 10.06%-14.97% of TP in phytoplankton-dominated zones, and 11.02%-20.28% in macrophyte-dominated zones. The risk of internal phosphorus release in phytoplankton-dominated zones is high, which is not conducive to the fixation and burial of phosphorus. The eutrophication degree of different regions in Taihu Lake is obviously different, and different characteristics of phosphorus release and burial are showed. The phytoplankton-dominated zones deserve special attention because of their high internal phosphorus load and release potential.

Geochemical fractionation, potential bioavailability and ecological risk of phosphorus in surface sediments of the Cross River estuary system and adjacent shelf, South East Nigeria (West Africa)

Abstract Phosphorus (P) as an essential macronutrient, plays a crucial role in the regulation of biological productivity and biogeochemical cycling of other biogenic elements in aquatic environments. Different geochemical fractions of sedimentary P were separated and quantified using the sequential extraction (SEDEX) method to evaluate the abundance, sources, distribution, bioavailability and ecological risk of P in surface sediments of the Cross River estuary system (CRES) and adjacent shelf. Sediment grain size composition and bulk organic carbon were also determined. Total P (TP) ranged from 9.21–18.2 μmol/g (average, 13.30 ± 2.08 μmol/g), and comprised mostly of inorganic P (IP) (IP/TP = ~87%). Generally, authigenic P (Ca-P) was the dominant IP fraction (Ca-P/IP = ~37 ± 11.1%), representing an important long-term P reservoir. The range of organic carbon (OC) to organic P (OP) ratio (OC/OP) indicated the predominance of terrestrial OC, and that leachable OP (Le-OP) may be the major OP form in surface sediments of the study area. The partitioning and distribution of different sedimentary P fractions were controlled by the biogeo- and physicochemical conditions favorable for P transformation, sediment grain size composition and sources of sedimentary organic matter. The ratio (Fe/P) of the extractable Fe in citrate-dithionite-bicarbonate solution (FeCDB) to ferric oxide-bound P(Fe-P) revealed the presence of reactive Fe- matrices having strong sorption capacity for P. The contents of potential bioavailable P (BAP) (~34–60% of TP) indicated that P amount in the overlying water column may increase substantially if released from surface sediments. The Fe-P was the major component of BAP, and the relationship between BAP and extractable FeCDB highlighted the significant impact of Fe(III) (oxyhdr)oxides on P mobility and bioavailability. The estimated P enrichment index (PEI) indicated that surface sediment is less impacted by anthropogenic P and poses less ecological risk with respect to sedimentary TP load in the study area.

Response of phosphorus fractionation in lake sediments to anthropogenic activities in China

In this study, geochemical fractionation is used to establish the relationship between sediment phosphorus (P) pools and anthropogenic activities based on the dated sediment from a suite of lakes in China. Our extraction results showed that the inorganic P fractions, including Ca-P (46% of TP) and Fe/Al-P (24%), constitute most of the P in sediments. Soil erosion dynamics and geographic location are the dominant factors controlling the historical distribution and partitioning of Ca-P in sediments, while over the last few decades, industrial and domestic effluents were the leading factor controlling Fe/Al-P. The organic P (Po) fractions, NaHCO3-Po, HCl-Po, and Ful-Po accounted for only 11%, 16% and 12% of Po on average, respectively, whereas Hum-Po and Res-Po made up the dominant Po fraction (59%) and were the main factors controlling Po dynamics due to fertilizer and livestock breeding. Thus, the historical fraction of P in the sediment core can be used as an indicator of anthropogenic activities. Ca-P decreased in the top layers of the cores because of the implementation of the Soil and Water Conservation Law in China since 1991. However, Fe/Al-P and Po continuously increased in the lakes from the economic backward area over the last few decades, which is largely due to enhanced point sources of pollution and an increase in the intensity of agricultural practices. As a potential P source, the massive accumulation of Fe/Al-P and Po would be released into the overlying water to further facilitate eutrophication via increasing pH and alkaline phosphatase and decreasing in the dissolved oxygen concentration. Therefore, in order to control eutrophication more effectively and efficiently, it is essential that the accumulation of sediment Fe/Al-P and Po be decreased immediately and domestic wastewater, poultry excreta, and fertilizer loss must be more carefully controlled, especially in economically backward areas.

Organic phosphorus mineralization characteristics in sediments from the coastal salt marshes of a Chinese delta under simulated tidal cycles

Sediment organic phosphorus (OP) mineralization plays an important role in phosphorus cycling in coastal salt marshes. However, information on OP mineralization characteristics in sediments under tidal cycles is limited. Sediment cores were collected from salt marshes which were exposed to tidal cycles. A laboratory manipulation experiment was conducted under simulated tidal flooding cycles. After the completion of each incubation experiment, the inorganic phosphorus (IP) and OP fractions were analyzed and net phosphorus mineralization rates were calculated to investigate the sediment OP mineralization process. Sediment microbial characteristic and chemical properties were determined to identify factors that affect the mineralization of OP in the Yellow River Delta. During the first 2 days of incubation, the tidal cycles significantly increased the microbial biomass in the sediments, which accelerated the assimilation of IP by microorganisms and the transformation of IP into OP in their bodies, thereby causing a significant increase in OP in the sediments. After 2 days of incubation, the mineralization and immobilization of OP entered the adaptation stage and gradually reached the dynamic balance of various phosphorus fractions in sediments. The path analysis showed that microbial biomass phosphorus and carbon (MBP and MBC) and the activity of alkaline phosphatase (AKP) are the direct factors influencing OP mineralization in sediments. The indirect effects of soil organic matter (SOM), water content (WC), exchangeable aluminum (Al0), and exchangeable iron (Fe0) on net phosphorus mineralization rate were relatively high. In the laboratory experiments, we showed that the recovery of tidal cycles caused a fluctuation in OP mineralization and immobilization in sediments, which reached equilibrium over time. The tidal effect was conducive to maintaining the stability of phosphorus in sediments of coastal salt marshes. The findings of this study can contribute to protecting water quality and improving primary productivity in coastal salt marshes by regulating the tidal cycles and the key environmental factors (e.g., SOM, WC, Al0, and Fe0) influencing OP mineralization.

Fate and transport processes of phosphorous fractions in selected surface sediments of Cochin Estuary, Southwest Coast of India

Sediment samples were collected from nine stations located along the Cochin estuary through five seasonal sampling campaigns for evaluating the distribution, accumulation and biogeochemical factors governing the concentration of various phosphorous fractions. Concentrations of sedimentary phosphorus fractions followed the order: iron-bound phosphorus > calcium bound inorganic phosphorous > alkali soluble organic phosphorus > acid soluble organic phosphorous > residual organic phosphorus. The enrichment of calcium bound inorganic phosphorous in the estuarine stations was found to exist in the high alkaline pH. Correlation study revealed that texture of the sediment controlled the distribution of iron bound phosphorous in the sediments. Terrestrial runoff carried huge quantities of humic substances to the riverine sediments that resulted in the peak concentration of alkali bound phosphorous at station S9 during monsoon. Increased levels of acid soluble organic phosphorous was recorded at stations with higher salinity (S5 to S8). Majority of the stations exhibited depleted levels of residual organic phosphorus due to the mineralization process. Meanwhile, total phosphorous ranged between 222.92 ± 3.89 µg/g and 4348.66 ± 15.35 µg/g with significant spatio-temporal variability (p < 0.01). Besides river run off resulted in the transport of organic matter derived from terrigenous, industrial, agricultural and aquaculture sources which brought about large scale accumulation of recalcitrant organic phosphorous in the sediments. Silt and clay exhibited remarkable positive correlations with iron-bound phosphorus, calcium bound inorganic phosphorous and alkali soluble organic phosphorus indicating the role of fine grained sediments in their dispersal mechanism. Multivariate statistical analysis revealed that distribution of phosphorous fractions were mainly controlled by salinity, granulometry, adsorption, desorption, precipitation, redox status, and the microbial processes occurring in the sedimentary environment.

Phosphorus fractions in sediments and their relevance for historical lake eutrophication in the Ponte Tresa basin (Lake Lugano, Switzerland) since 1959

Lake Lugano is one of several deep lakes in Switzerland that have not yet recovered from eutrophication after large reductions of external phosphorus (P) loadings. Persistent eutrophication has been attributed mainly to internal P loadings from sediments. To achieve the restoration goals, it is critically important to evaluate the sediment P availability and release risk in this lake. In this study, we combined sequential P extraction (four fractions) with enzyme hydrolysis to assess distribution characteristics of P forms and potential bioavailability of organic P in an anoxic sediment profile from the Ponte Tresa basin of Lake Lugano, southern Switzerland. Labile P forms, i.e. mostly redox-sensitive iron bound P and metal oxides bound P (Al/Fe-P), comprised ~70% of total P in the sediment profile (1959–2017 CE), suggesting a high potential for P release from the anoxic sediment. Potentially bioavailable organic P forms (determined by addition of substrate specific enzymes) were considerably higher in the surface sediments (top 5 cm), which is very likely to release P in the near future with early diagenesis. The net burial rates (NBR) of redox sensitive Fe-P fraction and total P in sediments both showed significant decreasing trends from 1959 to 2017 CE, when trophic levels of the lake increased from mesotrophic to hypertrophic status. We suggest that, in the Ponte Tresa basin, higher eutrophication conditions led to enhanced sediment P release (mainly from redox sensitive Fe-P fraction), thus reducing P-NBR in sediments. This study highlights the concern that in deep monomictic lakes, eutrophication restoration might be hindered by extensive internal P cycling and reduced capacity of sediment P-trapping.

Sources and Distribution of Phosphorus in Sediments of the Jinpen Reservoir

In order to explore the sources and distribution of phosphorus in sediments of a stratified water source reservoir, the total phosphorus (TP) content and distribution of phosphorus fractions in sedimentation particles and sediments of the Jinpen Reservoir of Xi'an were analyzed from March to November in 2017. The results showed that the TP content in the surface sediments of the Jinpen Reservoir was obviously affected by the deposition of particulate phosphorus (PP), and the correlation coefficient was 0.8775. Besides, this TP pool was also affected by the biogeochemistry of sediments. From June to August, algae in the Jinpen Reservoir propagated intensely, and a large number of dead algae were deposited on the bottom of the water body, which resulted in a type of endogenous pollution dominated by algae. The concentration of PP reached (753.51±17.11) mg·kg-1, and the content of TP increased, with NaOH-nrP as the main component. During the flood season of the Jinpen Reservoir from September to November, the runoff water carried a large amount of sediments with large pollutant loads, which resulted in increases of the concentration of PP in the water body. However, the TP content in the sediment per unit mass was relatively small. As a result, the TP content of surface sediments decreased, with inorganic Ca-P and rest-P as the main forms, which accounted for 55.8%-66.2% of the TP in sediment, and were influenced by particle sedimentation. The SRP, BD-P, and NaOH-srP, the most active fractions, underwent a series of transport and transformation processes under the changing environmental conditions (mainly redox conditions), and these forms were obviously affected by the biochemical processes in sediments and minimally affected by the sedimentation processes of the reservoir.

Spatial variation of phosphorus fractionation in the coral reef sediments of Lakshadweep Archipelago, Indian Ocean

ABSTRACTSurface sediments were collected from the shore and lagoons of Kavaratti, Kadamat and Agatti islands of Lakshadweep Archipelago during May 2015 and analysed for the spatial distribution of the micronutrient element, phosphorus. Phosphorus was separated by sequential extraction procedure into five fractions – exchangeable (Ex-P), iron bound, (Fe-P), calcium bound (Ca-P), organic and residual fractions (OP) and total phosphorus (TP). The average relative contribution of each P species to TP was: OP > Ca –P > Ex – P > Fe – P. The high concentration of organic and residual phosphorus (87–96%) compared to inorganic phosphorus is particularly evident at stations characterised by higher total phosphorus concentrations. Among the three forms of IP in the sediments, Ca-P was dominant at all stations. The OC/OP ratio ranged from 3 to 163 in the sediments, suggesting that the organic matter in sediments had been subjected to degradation. Hence, the major contribution towards organic and residual phosphorus form is from the residual fraction comprising biologically resistant or non-available phosphorus form composed of refractory materials. The concentration of phosphorus reported in the present study is higher than that of the earlier studies in Lakshadweep, indicating a terrestrial and anthropogenic influence on the sediment.

Pretreatment method for the analysis of phosphate oxygen isotope (δ18OP) of different phosphorus fractions in freshwater sediments

Accurate measurement of the oxygen isotopic composition of dissolved phosphate (δ18OP) of different phosphorus (P) fractions in lacustrine sediments is very difficult because of the influence of large amounts of impurities. In this study, we developed a five-step method for obtaining high purity Ag3PO4 sample for the analysis of δ18OP of different P fractions in freshwater sediments. Sedimentary P was divided into NaHCO3-P, NaOH-P and HCl-P by chemical sequential extraction. Pretreatment procedures for different sedimentary P fractions were improved in the following respects: 1) abandonment of the magnesium-induced coprecipitation method to avoid the introduction of impurity ions, such as Mg2+ and Cl−, and reduce the loss of P; 2) use of a small amount of non-phosphate activated carbon powder to efficiently remove organic matter in extracts of NaHCO3-P and NaOH-P, and reduce the loss of P; 3) adjustment of the HCl-P extract pH to 4 in order to form Fe(OH)3-PO43− coprecipitate, thereby removing most of metals and Cl−. This method reduces the pretreatment steps, simplifies the operation and increases the recovery of phosphate (90.98%–96.69%). The high purity Ag3PO4 sample can be obtained and the repeatability and accuracy of measured δ18OP is better than 0.3‰, demonstrating high reliability and accuracy. This new method was used to analyze the δ18OP of different P fractions in sediments of a eutrophic lake in southwestern China. The preliminary results indicated that the δ18OP in the sediments can be used to identify different P sources, and provide new insights into sedimentary P cycling. The method established in this study provides a powerful tool for investigating the sources and biogeochemical cycle of P in freshwater sediments.

Effects of Exogenous Carbon Addition on Equilibrium Phosphate Concentration and Risk of Phosphorus Release from Sediments in the Shiwuli River, Chaohu Lake Basin

Five surface sediment samples were collected every two months from the Shiwuli River along an urban-rural gradient, Chaohu Lake Basin, from July 2017 to May 2018. Sediment phosphorus fractions were investigated, and equilibrium phosphate concentration (EPC0) and its response to exogenous carbon (sodium acetate) addition were explored. Moreover, the risk of phosphorus release from sediment into water column was also evaluated. Results show that the Shiwuli River was seriously polluted by phosphorus. The average values of total phosphorus content in sediments ranged from 915.04 to 1205.31 mg·kg-1, and it decreased slowly along the urban-rural gradient, while the bio-available phosphorus content remained stable. Exogenous carbon addition not only reduced the EPC0 values of sediments (about 29%), but changed the order of EPC0 values among the five sampling sites as well. In general, the ratio of overlying water SRP (soluble reactive phosphorus) concentration to EPC0 value was 66.7%, and phosphorus adsorption-desorption equilibrium saturation EPCsat<-20% accounted for about 60.0%, indicating that the surface sediments in the Shiwuli River were dominated by phosphorus adsorption, namely, keeping the phosphorus "sink" state. The inputs of exogenous carbon addition increased the proportion of EPCsat<-20% from 60.0% to 73.3%, which lowered the risk of phosphorus release from sediments.

Phosphorus fractionation in surface water and sediments of industrially polluted freshwater reservoir, India

ABSTRACTIndustrial pollutions are responsible for alterations in biogeochemical cycling of phosphorus (P) in freshwater systems. The objectives of the present study were to quantify the major P forms and assess the relationship between P fractions in water and surface sediments of Govind Ballabh Pant Sagar (GBPS) reservoir, India. Surface water samples (n = 48) and surface sediment samples (n = 48) were collected from six regions of GBPS reservoir in December 2014. The results showed that total particulate phosphorus (TPP) and total dissolved phosphorus (TDP) account for 45%–58% and 42%–55% of total phosphorus (TP) in the surface water. The authigenic-P was found to be more than 84% of the total P in surface sediments. The TPP showed a positive statistical relationship with sedimentary P fractions (authigenic-P, exch-P, and organic-P) indicated the impact of industrial pollution load on inorganic and organic P fractions in water and sediments of GBPS reservoir. The discriminant fraction analysis (DFA) revealed that the exch-P, Fe(III)-bound-P, detrital-P, organic-P, and TPP were sensitive indicators of P dynamics in the industrially polluted GBPS reservoir.

Comparative Determination of Phosphorus Fractions in Coastal Surface Sediment (NE Mediterranean Sea) by ICP-OES and UV/VIS Spectrometry

Comparative Determination of Phosphorus Fractions in Coastal Surface Sediment (NE Mediterranean Sea) by ICP-OES and UV/VIS Spectrometry