Calcium-bound P Research Articles

Soil phosphorus fractionations as affected by cropping systems in the central mid-hills region of Nepal.

Soil plays a critical role as the primary reservoir of phosphorus (P) in terrestrial ecosystems. Sequential fractionation has been extensively utilized to gain insights into the characteristics and dynamics of soil P. However, there is a knowledge gap regarding the different P pools in Nepalese soils. Therefore, this study aimed to investigate the impact of cropping systems on soil P fractions in the central mid-hills of Nepal. The study focused on four cropping systems: vegetable, fruit, rice, and maize-based systems, which exhibited variations in nutrient management, topography, and cropping intensity. A total of 240 soil samples (60 samples from each cropping system) were collected from multiple sites within the central mid-hill region. Standard analytical methods were used to determine the general parameters of the soils, while the sequential fractionation method was employed to assess the organic and inorganic P pools. The results indicated that the effect of cropping systems on soil pH, calcium carbonate (CaCO3) content, and the proportion of sand, silt, and clay was not statistically significant in terms of general parameters. However, significant differences were observed among the different cropping systems in organic matter (OM), electrical conductivity (EC), cation exchange capacity (CEC), and available phosphorus. Similarly, in terms of inorganic phosphorus fractions, loosely bound P (LB-P), aluminum bound P (Al-P), iron bound P (Fe-P), and reductant soluble P (RS-P) were significantly affected, while calcium bound P (Ca-P) did not show a significant difference. Furthermore, in terms of organic phosphorus fractions, labile organic P (L-Po), fluvic acid organic P (FA-Po), and non-labile organic P (NL-Po) exhibited significant differences, whereas moderately labile organic P (ML-Po) and humic acid organic P (HA-Po) did not show a significant difference. Additionally, reductant soluble P showed a significant difference, while total P did not differ significantly. The vegetable-based system exhibited higher levels of the majority of P fractions, followed by the fruit-based, maize-based, and rice-based systems. These findings emphasize the importance of considering cropping systems and their response to different phosphorus pools, as this knowledge can contribute to the development of improved soil phosphorus management strategies and promote sustainable agricultural practices in the region.

Effect of Eighteen Years of Continuous Crop Residue Application on Crop Yields, Soil P Fractions, and Crop P Uptake in Conservation Tillage Under Semi-Arid Tropical Rainfed Conditions

The continuous use of crop residue in soil can enhance the crop yield and potential availability and mobility of P fractions to crops in conservation tillage. A field experiment was conducted to assess the long-term effects of surface crop residue applications on soil P fractions and their relationship with P uptake and crop yields. Field experiment was conducted at ICAR-Central Research Institute for Dryland Agriculture, Hyderabad, India during 2005 to 2022. The experimental treatments applied were: T1 - no crop residue application, T2 - application of crop residue @ 2 t ha-1, T3 - application of crop residue @ 4 t ha-1, and T4 - application of crop residue @ 6 t ha-1 in conservation tillage. The test crops viz. sorghum (Sorghum vulgare) and cowpea (Vigna unguiculata) were grown in a yearly rotation every year in the kharif season in conservation tillage. The results of the long-term study revealed that the per cent increase in sorghum (Sorghum vulgare) grain yield with the application of crop residue at the rate of 2, 4 and 6 t crop residue ha-1was to the tune of 7.9, 16.1 and 26.0%, respectively over no crop residue application. Similarly, the per cent increase in the cowpea (Vigna unguiculata) seed yield was to the extent of 25.2, 43.0 and 64.1% in 2, 4 and 6 t ha-1, respectively over no crop residue application. The sorghum and cowpea stover yield also significantly (p=0.05%) increased with the added levels of the crop residue. Significantly higher P uptake by sorghum and cowpea was recorded in 6 t crop residue ha-1 as compared to the other crop residue treatments. Results of the current study also showed the significant positive response of long-term crop residue application on the P fractions viz., water-soluble phosphorus (WS-P), aluminum bound P (Al-P), iron bound P (Fe-P), calcium bound P (Ca-P) and reductant soluble P (RS-P), and on available P and total P in soil as compared to no crop residue application. The average percent contribution of P fractions toward the sum-total of extracted P was in the order: Fe-P (30.8%)>RS-P (30.7%)>Al-P (24.2%)>Ca-P (9.4%)>WS-P (4.8%). The WS-P and Al-P were found to be the P fractions indicating their specificity by cowpea crop, and WS-P and Ca-P were found to be P fractions indicating their specificity by sorghum crop. The results of the present study will be highly useful in understanding the effect of crop residue application in conservation tillage on the P fractions and their contribution toward P uptake and crop yields.

Phosphorus speciation in coastal sediment of Osaka Bay: relation to anthropogenic phosphorus loading

Abstract This study assessed the effect of increased anthropogenic phosphorus (P) loading on P speciation in coastal sediments in Osaka Bay, an urbanized enclosed bay, and one of Japan’s most industrialized regions. The study analyzed Total P (TP) and determined the accumulations of five different P species Exchangeable P (Ex-P), Iron-bound P (Fe-P), Calcium-bound P (Ca-P), Detrital P (Det-P) and Organic P (Org-P)in the sediment using the sequential extraction method. We also estimated the historical P loading into Osaka Bay from major river catchments (the Yodo and Yamato Rivers) using the Soil and Water Assessment Tool. This study identified peak P loading values for the Yodo River in 1965 and the Yamato River in 1968, with the Yodo River being the primary anthropogenic source of P inflow for Osaka Bay. The concentration of TP ranges from 290.5 to 353.1 mg Kg−1 respectively, and the order of concentrations of the different P species is Org-P > Det-P > Ca-P > Fe-P > Ex-P. The results indicate a positive relationship between total P loading and Ca-P during the rapid growth period. We examined two potential mechanisms (adsorption-precipitation process and sink switching) for Ca-P formation and hypothesized that the adsorption-precipitation process is the dominant process, indicating that high anthropogenic P loading causes the accumulation of immobile Ca-P species in coastal sediments and serves as a permanent sink for P, as well as for water quality restoration. This result also suggests the possibility of reconstructing historical human-induced P loadings based on Ca-P in coastal sediments.

Preparation of phosphorus containing products by co-incineration of sludge ash and calcium-based additives: Focusing one-step and multi-step method

Due to the irreplaceable nature of phosphorus (P) in biological growth and the shortage of P rock, it is necessary to recover P from waste, such as sludge ash. P-containing products were prepared using sludge ash and calcium-based additives (CaCO3 and eggshell). In addition, the effects of different incineration methods (one-step method (OSM) and multi-step method (MSM)), additive doses, and incineration temperature on the P content and species in the products were investigated. The results indicated that as the dose of calcium-based additives increased, total P (TP) content in P-containing products reduced, apatite P (AP) content increased, non-apatite P (NAIP) content declined, and P solubility in citric acid content decreased. The amount of AP increased, NAIP reduced, and P solubility in citric acid decreased as the incineration temperature climbed. Although P in P-containing products prepared by OSM and MSM changed in a similar way at different additive doses and temperatures, P-containing products prepared by MSM had at least a 6.1% increase in P solubility in citric acid. Compared with OSM, MSM could save 10% of calcium-based additives when reaching the maximum AP value. Additionally, pure materials were employed to investigate how P species changed during the incineration procedure. The advantage of the MSM-prepared product over the OSM-prepared product may be explained by the high concentration of Ca3(PO4)2 and low concentration of amorphous calcium bound P (Ca-P). Overall, MSM is an effective method to reduce the dose of calcium-based additives and increase the bioavailability of P in P-containing products.

Phosphorus Fractionation in Submerged Black Soil as Influenced by Different Phosphatic Fertilizers

A laboratory incubation experiment was conducted during December, 2017 to March, 2018 in Department of Soil Science and Agricultural Chemistry, College of Agriculture, Raichur, Karnataka, India to study the fractionation of phosphorus (P) in black soil amended with different phosphatic fertilizers under submerged condition. The soil were kept under subemerged condition for 90 days and phophatic fertilizers such as single super phosphate (SSP), diammonium phosphate (DAP) and mussoorie rock phosphate (MRP) alone or in combination with FYM and PSB added through 13 treatment combinations. The soil was analyzed for various inorganic P fractions (saloid P, Al-P, Fe-P, RS-P, occluded P,Ca-P) for 90 days at definite intervals. The results showed that calcium bound P (Ca-P) was the dominant fraction in submerged black soil whereas saloid P recorded as the least dominant fraction. It has seen that application of phosphatic fertilizers significantly increased all the P fractions over control. All the forms of P viz., saloid P, aluminium phosphate (Al-P), iron phosphate (Fe-P),reductant soluble P (RS-P) and occluded P were higher for DAP treatment along with FYM and PSB as compared to SSP and MRP whereas application of MRP along with FYM and PSB recorded significantly higher Ca-P during the incubation period. All the fractions of P were significantly higher at 1st day of incubation after which it decreased with passage of incubation time.

Seasonal and Spatial Distribution of Phosphorus Fractions in Surface Sediments of the Southern Caspian Sea

This study assesses seasonal fluctuations, spatial distribution and fractions of phosphorus (P) in the surface sediment layer of the southern Caspian Sea. Seasonal fluctuations were insignificant (p-value > 0.05) relative to the mean total P (TP) concentrations. Still, the highest levels were in autumn samples (1555 mg kg−1), followed by winter (1405 mg kg−1), spring (1378 mg kg−1), and summer (1130 mg kg−1). These minor temporal fluctuations in P concentrations are explained by seasonal differences in runoff amount and intensity of rivers discharging into the Caspian sea and thereby their sediment loading and physicochemical characteristics. The large riverine influx has led to TP contamination hotspots in the river deltas of Anzali wetland, Babolrood, and Sefidrud, where high loadings of suspended particles are discharged into the sea. The spatial distribution of TP is thus site-specific and uneven. The main P fraction was calcium-bound P (CaP), reflecting the phosphate (PO43−) strong affinity for, and association with, Ca-bearing minerals. Only a minor fraction of P was determined as loosely bound P (LP). The fraction of the mud size particles was the main explanatory factor for the spatial distribution of overall low levels of non-residual (or bioavailable) P forms (i.e., LP and iron- and aluminum- bound P: FeP and AlP, respectively) during spring and summer, while the sand fraction had strongest explanatory value for the distribution of residual (non-bioavailable) P form (CaP) during autumn and winter. This study demonstrates that P bioavailability in sediments is mainly governed by the physicochemical characteristics of the sediment material, which again is steered by seawater chemistry. A low content of bioavailable P fractions could therefore be explained by the relatively low content of fine-grained (< 63 µm, i.e., mud) particles in sediments of the southern Caspian Sea.

Enrichment of organic carbon increases the flux of phosphorus from sediment in mariculture ponds

Environmental pollution associated with aquaculture activities is one of the major bottlenecks encountered in the sustainable development of fisheries. Accumulating organic carbon (org-C) is an inevitable but undesirable consequence of aquaculture activities, and its degradation influences nutrient flux. However, neither the variations in org-C accumulation nor its impact on phosphorus (P) dynamic has been clearly untangled and reliably quantified so far. Therefore, we carried out a field survey to examine the influences of org-C accumulation on sediment P release in mariculture ponds. The results suggested that org-C contents varied considerably between ponds, being significantly lower in monoculture ponds with bivalve shellfish than in polyculture ponds with bivalve shellfish, shrimp, crab, and fish, likely due to the less-artificial-feeding practice and the function of bivalve shellfish as “environmental cleaners.”Sediment P in mariculture ponds mainly occurred in iron-bound P (44%) and organic-P (hot NaOH-extractable organic + acid-soluble organic P = 56%), while calcium-bound P (CaP) only contributed a tiny proportion of about 1%. The positive correlation between P-flux from sediment and org-C suggested that org-C enrichment can stimulate sediment P release. Further analysis of the linear mixed model combined with piecewise structural equation modeling indicated that the two main forces driving P release - enzymatic hydrolysis release and anoxic desorption - operate with sediment org-C being a significant factor (accounted for 75% of the variation in P-flux). At the same time, other factors such as alkaline phosphatase activity, pH, and CaP may play minor roles in affecting P release. Our findings indicated that org-C accumulated in the aquaculture ponds might trigger sediment P release, posing a potential risk of contaminating the downstream water bodies during tailwater discharge.

Geochemical cycling of phosphorus and iron in a typical reservoir in the area of Xiaoxing’an mountains, northeastern China

Reservoirs have an important impact on riverine material migration and transformation. Taking a drinking water reservoir located in the cold-temperature forest in the Xiaoxing’an mountains as an example, we comprehensively analyzed the fractions and interrelationships of phosphorus (P) and iron (Fe) from soils to riverine and reservoir sediments and discussed the coordinated migration and transformation process of regional P and Fe and the effects of dam interception. The results showed that iron-bound P (Fe-P) and aluminum-bound P (Al-P) were significantly correlated with adsorbed Fe(II), carbonate-bound Fe (Fecarb), low-activity silicate-bound Fe (Feprs), and total contents of Fe (TFe), which indicated that the geochemical cycling of these P fractions and Fe fractions is likely closely related and active in the soils and sediments. Calcium-bound P (Ca-P) was significantly correlated with magnate (Femag) and Feprs, which may be due to the correlation between their background values in this area. The contents of active P including loosely sorbed P (L-P), Al-P, and Fe-P in the reservoir’s sediments were significantly higher than those in the upstream soils and sediments (p &amp;lt; 0.05). However, Ca-P and residual P (Res-P) in soil and sediment samples showed no significant difference between the reservoir and its upstream (p = 0.309 &amp;gt; 0.05 and p = 0.748 &amp;gt; 0.05, respectively). Construction of reservoirs has played a certain role in intercepting P, especially bioavailable P, transferred from upstream soils and riverine sediments. The contents of highly active Fe fractions including easily reducible (amorphous) Fe oxide (Feox1), reducible (crystalline) Fe oxide (Feox2) and Fecarb (p &amp;lt; 0.01), and other Fe fractions (p &amp;lt; 0.05) in the sediments of the reservoir were significantly higher than those in the soil or sediment samples from upstream. This indicated that all Fe fractions migrated in the river were affected by the dam interception. The effects of dam interception would affect the bioavailability of P and Fe and enhance the cycling of nutrients in the region. Finally, this also effects the bioavailability and cycling of P and Fe in the downstream rivers and even the oceans.

Impact of Long-Term Conservation Agriculture Practices on Phosphorus Dynamics under Maize-Based Cropping Systems in a Sub-Tropical Soil

Over the past decade, scientific studies have increasingly concentrated on the effects of global phosphorus (P) scarcity on food security. A comprehensive strategy that considers demand reduction and recycling possibilities is needed to address the global P scarcity. Reduced tillage along with crop residue retention could decrease fixation of P in soil, improve labile P content and enhance organic-P (Po) buildup and its mineralization by phosphatases; this could be an extra benefit of conservation agriculture (CA) in soils. To study the impact of long-term CA on soil organic and inorganic P fractions and their distribution, a long-term field trial was conducted under a maize-based cropping system with different tillage (zero tillage (ZT), permanent bed (PB) and conventional till (CT) and cropping system (maize–wheat–mungbean (MWMb), maize–chickpea–sesbania (MCS), maize–mustard–mungbean (MMuMb) and maize–maize–sesbania (MMS)). Phosphorus dynamics were studied through sequential fractionation (organic and inorganic P) at 0–5 and 5–15 cm soil depth. The findings showed that a higher amount of soluble and loosely bound P (SL-P) was detected in ZT among the inorganic P fractions, whereas iron-bound P (Fe-P), aluminum-bound P (Al-P), reductant soluble P (RES-P) and calcium-bound P (Ca-P) were found higher in CT in both soil depths. Among Organic-P fractions, moderately labile and non-labile Po was found higher in PB and ZT but, in the case of labile Po, it was found insignificant with respect to tillage operations. Significant synergistic effects of winter legume (chickpea) with summer legumes (sesbania and mungbean) in crop rotation were observed on SL-P, Labile Po, Humic acid-Po, Alkaline phosphatase and MBP at 0–5 and 5–15 cm soil depths. Given the potential relevance of understanding P dynamics for efficient P management in long-term conservation agriculture practices, our findings offers critical new insight for the P management for sustainable development.

Effect of Bacillus megaterium var. phosphaticum applied together with rock phosphate on wheat yield and some soil properties in a calcareous soil

This study aims to determine the effect of Bacillus megaterium var. phosphaticum applied together with rock phosphate on the yield of wheat grown in calcareous soil, some biological properties of soils and phosphorus fractions in the soil under greenhouse conditions. Considering the P fixation capacity of the soil used in the experiments and the amount of P present in the soil, the trial subjects were created based on randomized block designs with 3 replications, depending on whether 0, 25, 50, 75 and 100% of the P required to be given to the wheat plant was met from rock phosphate and whether it was bacterial or not, and finally wheat was grown. In the harvested plants, grain and stem weights were determined, grain and stem P contents were analysed and the amounts removed with grain and stem were calculated. Dehydrogenase (DHA) and phosphatase (PA) enzyme activities were performed in the soil samples taken after harvest. Soluble and loosely bound-P, Calcium-bound-P (Ca-P), Reductant soluble-P (RS-P) fractions and Olsen-P were determined in soil samples taken before planting and after harvest. The percent reduction in the fractions was calculated by using the pre-sowing and post-harvest values of these samples. According to the results, Bacillus megaterium DSM 3228 strain inoculated with rock phosphate increased grain and stem yield, grain and stem P content, and P amount removed by grain and stem of wheat. These parameters were found to be higher at high doses of P applied as rock phosphate. Inoculation increased the DHA and PA values of the soils. A decrease in P fraction forms with low solubility was determined by inoculation, some of this phosphorus was removed by plants and some of it was retained in the soil in different forms.

缙云山4种林分土壤无机磷与活性铝的含量及分布

PDF HTML阅读 XML下载 导出引用 引用提醒 缙云山4种林分土壤无机磷与活性铝的含量及分布 DOI: 10.5846/stxb202101090092 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 重庆市社会民生类重点研发项目（cstc2018jscx-mszdX0080）；国家自然科学基金项目（31570599） Content and distribution of inorganic phosphorus and labile aluminum in soil of four forest types in Jinyun Mountain Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探索不同林分对土壤中无机磷与活性铝的含量及分布的影响，以及无机磷与活性铝之间的相互关系，以在我国西南地区酸性土壤上的农林经营管理提供理论和实践依据。研究以缙云山广泛分布的4种林分类型：山莓、马尾松、楠竹和柑橘林土壤为对象，采用酸性土壤无机磷分级方法和铝试剂比色法测定了土壤剖面A、B和C层中各形态的无机磷与活性铝的含量，分析了不同林分土壤中无机磷和活性铝的含量和分布特征。结果表明，林分类型显著影响土壤中无机磷与活性铝的含量与分布，且铁磷（Fe-P）、交换态铝（Ex-Al）和羟基铝（Hy-Al）的含量和比例还受到土壤层次的影响。4种林分相比，山莓林能促进闭蓄态磷（O-P）的形成，而马尾松、楠竹和柑橘林则有利于Al-P、Fe-P和Ca-P的形成；柑橘林有利于低活性的腐殖酸铝（Al-AH）形成，而山莓、马尾松和楠竹林促进高活性的Ex-Al或Hy-Al溶出；Ex-Al、Al-P和Fe-P在土层的分布上有表层富集现象，而Hy-Al集中分布于B层。此外，土壤Ex-Al和Al-P与Fe-P之间，Hy-Al和Ca-P之间均呈显著（P<0.05）正相关。因此，林分类型显著影响土壤无机磷与活性铝的含量与分布，高活性铝的溶出显著影响Al-P、Fe-P和Ca-P含量。 Abstract:Phosphorus (P) is an essential element for plant growth, development and metabolism. Soil is a direct donor of phosphorus for plants. Generally, total phosphorus (TP) is plenty in most soils, but its availability to plants is very low. Aluminum (Al) is the most abundant metal element in the earth's crust. When the soil is getting acidified, Al in the forest soil can be activated into Al3+ (exchangeable Al, Ex-Al) or Al (OH)2+, Al (OH)2+ (hydroxyl-Al, Hy-Al), which might precipitate HPO42-, H2PO4-, and PO43- into hard-to-dissolve P and reduce the P availability in consequence. How to prevent the decrease of P availability caused by the dissolution of Al from acidic soil, which is one of the urgent problems to be solved in forest land management. Forest type and soil layer might affect the characteristics and relationships between inorganic phosphorus (IP) and labile Al, which remains poorly understood up to now. The present study aimed to determine the influence of forest type and soil layer on the concentration and distribution of IP and labile Al in soil, in addition to the correlation between labile Al and IP. The soil was collected by digging in three soil layers (A, B and C layer) of four forest types of Rubus corchorifolius, Pinus massoniana, Phyllostachys pubescens and Citrus reticulata forest in Jinyun Mountain, Chongqing, China. Concentrations of IP and labile Al fractions were measured using the traditional method. Results showed that concentrations and proportions of IP and labile Al in soil were significantly affected by forest types and that of iron-bound P (Fe-P), Ex-Al and Hy-Al in soil were significantly different in soil layers. Among the four forest types, Rubus corchorifolius promoted the formation of occluded P (O-P). Whereas, Pinus massoniana, Phyllostachys pubescens and Citrus reticulata were in favor of the formation of aluminum-bound P (Al-P), Fe-P and calcium-bound P (Ca-P). Citrus reticulata was favorable for the formation of low-active Al species (humic acid-Al, Al-AH), while Rubus corchorifolius, Pinus massoniana and Phyllostachys pubescens contributed the dissolution of labile Al from low-active into high-active species (Ex-Al or Hy-Al). In soil layers, Ex-Al, Al-P and Fe-P mainly enriched in the surface among the three soil layers. Hy-Al concentrated in the second soil layer. Meanwhile, the correlations were significantly positive between Ex-Al and Al-P and Fe-P or between Hy-Al and Ca-P in the soil of four forest types. The concentration and distribution of IP and labile Al fractions in soil were significantly affected by forest types. The dissolution of labile Al from low-active into high-active species significantly affected the concentrations of Al-P, Fe-P and Ca-P. This study can provide theoretical and practical basis for the management of agriculture and forestry on acid soils in southwest China. 参考文献 相似文献 引证文献

A conceptual framework and an empirical test of complementarity and facilitation with respect to phosphorus uptake by plant species mixtures

Plant species have different traits for mobilizing sparingly soluble phosphorus (P) resources, which could potentially lead to overyielding in P uptake by plant species mixtures compared to monocultures due to higher P uptake as a result of resource (P) partitioning and facilitation. However, there is circumstantial evidence at best for overyielding as a result of these mechanisms. Overyielding (the outcome) is easily confused with underlying mechanisms because of unclear definitions. We aimed to define a conceptual framework to separate outcome from underlying mechanisms and test it for facilitation and complementarity with respect to P acquisition by three plant species combinations grown on four soils. Our conceptual framework describes both mechanisms of complementarity and facilitation and outcomes (overyielding of mixtures or no overyielding) depending on the competitive ability of the species to uptake the mobilized P. Millet/chickpea mixtures were grown in pots on two calcareous soils mixed with calcium-bound P (CaP) and phytate P (PhyP). Cabbage/faba bean mixtures were grown on both acid and neutral soils mixed with P-coated iron (hydr)oxide (FeP) and PhyP. Wheat/maize mixtures were grown on all four soils. Rhizosphere carboxylate concentration and acid phosphatase activity (mechanisms) as well as plant P uptake and biomass (outcome) were determined for monocultures rhizosphere and species mixtures. Facilitation of P uptake occurred in millet/chickpea mixtures on one calcareous soil. We found no indications for P acquisition from different P sources, neither in millet/chickpea, nor in cabbage/faba bean mixtures. Cabbage and faba bean on the neutral soil differed in rhizosphere acid phosphatase activity and carboxylate concentration, but showed no overyielding. Wheat and maize, with similar root exudates, showed overyielding (the observed P uptake being 22% higher than the expected P uptake) on one calcareous soil. We concluded that although differences in plant physiological traits (root exudates) provide necessary conditions for complementarity and facilitation with respect to P uptake from different P sources, they do not necessarily result in increased P uptake by species mixtures, because of the relative competitive ability of the mixed species.

Response of phosphorus in estuaries to soil erosion – A new insight into sediment phosphorus fractions and sources

Phosphorus (P) is a chemical element that can cause lake eutrophication, tracing the source of P in lake sediments is crucial in the management and control of nutrient discharges in a watershed. To combine watersheds with lakes and provide watershed surface feature support for the traceability of sediment P fractions, the estuary was used as the key location collecting sediments. The Revised Universal Soil Loss Equation was used to simulate the spatiotemporal distribution characteristics of soil erosion, the relationship between sediment P fractions to soil erosion was analyzed for different watersheds and buffer zones, thus revealing the mechanism of this relationship. The proportion of P fractions first respond to the manner of P loss in a watershed, then the factors affecting the sediment P fractions are determined. When calcium-bound P (Ca-P) accounted for more than 40% total P (TP), forest land soil erosion plays an important role in increasing the proportion of Ca-P in sediment, the correlation coefficient can reach 0.66 when the soil erosion in mountainous area is large. When P bound by iron oxides or hydroxides (Fe-P) and aluminum-bound P (Al-P) were the main components of TP in sediment, the P fractions in the sediment is affected complexly. The phosphate fertilizer application and arable land soil erosion increased the Fe-P and Al-P contents in sediments. As the buffer distance increased, the correlation coefficient between soil erosion modulus and Fe-P showed a decreasing trend. The adsorption capacity of the sediments for P was influenced by water quality, which led to changes in Fe-P and Al-P contents of sediments over time. Main findingsSoil erosion has an influence on the P fractions of sediments. Ca-P comes from forest land, while Fe/Al-P are active P, which are affected by phosphate fertilizer, land use, buffer distance and human activities.

Submerged macrophytes successfully restored a subtropical aquacultural lake by controlling its internal phosphorus loading.

Intensive aquaculture has largely changed the global phosphorus (P) flow and become one of the main reasons for the eutrophication of global aquatic ecosystem. Artificial planting submerged macrophytes has attracted enormous interest regarding the restoration of eutrophic lakes. However, few large-scale (>80km2) studies have focused on the restoration of aquatic vegetation in the subtropical lakes, and the mechanism underlying the restrain of sediment P release by macrophytes remains unknown. In this study, field surveys and the diffusive gradients in thin films (DGT) technique were used to elucidate the effects of macrophytes on internal P loading control in a typical eutrophic aquacultural lake. Results showed that half of the P content in overlying water and sediments, particularly dissolved P in overlying water and calcium bound P (Ca-P) in sediment, were removed after restoration. Temperature, as well as dissolved oxygen (DO) and P concentration gradients near the sediment-water interface (SWI) jointly controlled the release of labile P from surface sediments. Submerged macrophytes can effectively inhibit the release of sediment P into the overlying water, which depended on DO concentration in the bottom water. Future restoration projects should focus on the temperature response of submerged macrophytes of different growth forms (especially canopy-forming species) to avoid undesirable restoration effects. Our results complement existing knowledge about submerged macrophytes repairing subtropical P-contaminated lakes and have positive significance for lake restoration by in situ phytoremediation.

A Dual Source of Phosphorus to Lake Sediments Indicated by Distribution, Content, and Speciation: Inle Lake (Southern Shan State, Myanmar)

In this study, grab and core sediments from Inle lake were collected and analysed for their water and organic matter (O.M.) contents. Total phosphorus (TPSMT) and P fractions, namely inorganic-P (IP), organic-P (OP), P bound to Al, Fe and Mn oxy-hydroxides (Fe-P), and calcium-bound P (Ca-P) were determined by a sequential extraction procedure. TPSMT varied considerably (152–1980 mg/kg), with minimum concentrations detected at sites away from the main inflow rivers and maximum concentrations in the floating gardens area. In core sediments, TPSMT concentrations tended to decrease with depth, reaching values of &lt;100 mg/kg. Concerning P forms, the overall abundance sequence in grab sediments was IP &gt;&gt; OP and Ca-P ≥ OP &gt; Fe-P, whereas in core sediments it showed marked differences with depth and between sites. The relative abundance of the inorganic species (Ca-P, Fe-P) was controlled by the mineralogy of the sediments. While the TPSMT distribution pointed to an increased anthropogenic input, the relative abundance of P species provided information on the P origin, incorporation processes, and evolution over time. This information, combined with chemical and mineralogical data, permitted to identify two different P sources: the agricultural input in the floating gardens area and the detrital input related to soil erosion.

Coupling characteristics and environmental significance of nitrogen, phosphorus and organic carbon in the sediments of Erhai Lake.

The contents and forms of nitrogen (N), phosphorus (P), and organic carbon (C) were determined with 40cm (approximately 1600s) core sediments from Erhai Lake on the Yungui Plateau of China as the sample. The vertical distribution characteristics, coupling relationships and ecological indicator significance of C-N-P were studied and identified. The results showed that the total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) contents were in the ranges of 1436-8255mg·kg-1, 1287-5462mg·kg-1, and 870.26-1507.74mg·kg-1, respectively. In the Erhai Lake sediments, the main forms of TOC, organic nitrogen (ON) and organic phosphorus (OP) were humus, TN, and TP, respectively. The deposition of C, N, and P in the Erhai Lake sediments was divided into four periods. In the initial development period (from 40 to 23cm), C, N and P were deposited and released synchronously; the main form of N was nontransferable total nitrogen (NTN), and that of P was inorganic phosphorus (IP). In the ecological recovery period (from 22 to 14cm), C and N were deposited synchronously, and their deposition amounts were more than that of P. C, N and P were released synchronously. The main form of N was transferable total nitrogen (TTN), and that of P was IP. In the rapid economic growth period (from 13 to 0cm), C, N, and P were deposited and released synchronously; the main form of N was NTN, and that of P was OP. In comparison to the other periods, this period was a period of higher active soil organic carbon (ASOC). In the integrated management period (surface sediment), C and N were deposited and released synchronously, and their deposition amounts were greater than that of P. The main form of N was NTN, that of P was OP, and the ASOC content was high. When exogenous inputs were the main sources of C, N, and P, the deposition forms of P and N were mainly OP and NTN, respectively, and those of IP and TTN were calcium-bound P (Ca-P) and ion-exchange form N (IEF-N), respectively. When endogenous inputs were the main sources of C, N and P, the deposition forms of P and N were mainly IP and TTN, respectively, and those of IP and TTN were Fe/Al-P and weak acid extractable form (WAEF-N), respectively. The content ratio of Ca-P and Fe/Al-P, as well as that of IEF-N and WAEF-N, could reflect the changes in the contribution of endogenous and exogenous sources to the Erhai Lake sediments.

Influence of hypoxia on phosphorus cycling in Alappuzha mud banks, southwest coast of India

The southwest coast of India is known to experience two concurrent processes during the southwest monsoon, namely coastal upwelling and mud banks at selected stretches such as that off Alappuzha. The mud bank sediments were found to contain very high concentrations of phosphorus (ave. 2255 ± 278 μg/g), and the present study measured changes in concentration of elements such as carbon, phosphorus, iron, and manganese within the Alappuzha mud banks, to understand the influence of upwelling on the cycling of these elements. The results showed that coastal upwelling led to hypoxic conditions within the mud bank region during the peak southwest monsoon, which induced significant changes in the phosphorus fractions in the sediments. There was an enrichment of iron, caused by the efflux of reactive Fe from the subsurface sediment layers and depletion of manganese, due to reductive dissolution of Mn oxides and subsequent release of Mn. The low molar ratios of total organic carbon to total nitrogen (9 ± 1) and total organic carbon to organic phosphorus (118 ± 57) generally indicated that the organic matter was relatively fresh and derived from marine plankton. Sedimentary phosphorus also exhibited wide fluctuations in its geochemical forms during hypoxia. Five geochemical forms of P such as exchangeable P (Ex-P), Fe and Mn bound P (Fe-P), P from Al oxides, non-reducible Fe bound P and organic P (Non Red-P), calcium bound P (Ca-P) and refractory organic P (ROP) were extracted, adopting sequential extraction procedure. The percentage contribution of various P forms were 2%–11% Ex-P, 4%–25% Fe-P, 4%–10% Non Red-P, 60%–78% Ca-P and 4%–12% ROP. The fractionation study revealed that precipitation of apatite and vivianite are the significant pathways of phosphorus enrichment in mud bank sediments. The study indicates that the enrichment of labile P fractions could be mediating the enhancement in biological production in the Alappuzha mud banks during the southwest monsoon.

The total P estimation with hyper-spectrum – A novel insight into different P fractions

Phosphorus (P) is one of the main characterization parameters of soil fertility and an important element affecting vegetation growth. This paper used the multivariate stepwise regression to estimate the soil P concentration through multiple mathematical transformation of the original spectrum, evaluate the accuracy of different models, and determine the optimal modeling method. The total P (TP) is classified as loosely adsorbed P (Ad-P), P bound by iron oxides or hydroxides (Fe-P), aluminum-bound P (Al-P), calcium-bound P (Ca-P) and residual P (Re-P). Then the relationship between various P fractions and soil properties and their spectral characteristics were analyzed. The effects of different P fractions on total P (TP) estimation were discussed from the aspects of selected bands, corresponding forms and spectral transformation forms, the direct and indirect estimation models are constructed respectively, which provided a new idea for soil spectrum estimation of soil properties. The results show that (1) Al-P is the main component of TP, and its spectral characteristics are not obvious, and the correlation coefficient between Al-P and TP is 0.437, which is the main reason for the stability of TP estimation model. (2) Soil organic matter and Ca-P have the greatest influence on TP estimation. When the band is less than 1200 nm, soil organic matter concentration is the main factor affecting TP estimation. When the wavelength is greater than 1200 nm, Ca-P is the main factor affecting TP estimation. (3) An indirect estimation model of TP was developed by using Ca-P, the R2 of the calibration reached 0.78, and the R2 of the validation reached 0.66, the model is stable and can be used to estimate TP content. It is proved that it is a feasible method to estimate the TP content through the spectral characteristics of P fractions, the relationship between organic matter and TP is not the only key reason for the successful estimation of TP.

Fine-scale remobilization of phosphorus by rooted macrophytes (Phragmites australis) growth in lake sediments: evidence from a holistic growth period simulation study

Aquatic vegetation serves an important structuring function in shallow freshwater ecosystems. Although increasing evidence indicates that sediment-associated phosphorus (P) is mobilized by aquatic macrophytes under P-deficient conditions, the influence of the holistic growth period of rooted macrophytes on transfer mechanism and bioavailability of sediment P around rhizosphere at millimeter scale remains unclear. In this present study, a 120-day batch intact sediment microcosm simulation was implemented to explore the effect of the whole Phragmites australis growth period on the stability and exchange of sediment P across critical micro-interfaces in lacustrine ecosystems. High-resolution dialysis peeper (HR-Peeper) was used to investigate the variations of pore water P in sediments around the P. australis rhizosphere and Zr-oxide diffusive gradients in thin-film (DGT) sampler was used to capture changes in the two-dimensional (2D) images of labile P over the whole growth period. Phosphorus fractionation showed a general decrease of total phosphorus (TP) and calcium-bound P (Ca-P), whereas an increase in iron-adsorbed P (Fe-P), loosely bound P (LS-P), and organic P (Org-P) was observed on day 120 compared to the values on day 0. Notably, the Ca-P content decreased by approximately 77%, while the Fe-P content increased by approximately 400%. Highly synchronous rises in P release flux and in the morphological characteristics of P. australis were the exponential function of incubation time. High-resolution data demonstrated that concentrations of soluble reactive P (SRP) and labile P concentrations in pore water were prominently enhanced by P. australis growth. Meanwhile, a top-down root-shaped patchy distribution pattern of labile P in the pore water was obviously stimulated over time. The reason for this phenomenon could be ascribed to remobilization of sediment mineral P by root organic exudates, as well as Fe-coupled accumulation of labile P due to oxygenation of Fe2+ followed by the formation of Fe plaques on the root surface within the more oxic rhizosphere. The annual growth period of P. australis could persistently enhance the mobility of sediment P, converting it from a more inert status to a redox-sensitive species. Our findings highlight that remobilization of sediment-associated P by P. australis accounts for a significant portion of the P cycle in eutrophic lake ecosystems.

Remobilization mechanism and release characteristics of phosphorus in saline sediments from the Pearl River Estuary (PRE), South China, based on high-resolution measurements

The internal loading of phosphorus (P) is commonly considered an essential factor contributing to eutrophication in freshwater bodies. However, investigation of the lability and remobilization characteristics of P in estuarine saline sediments has been limited. In this study, a sequential chemical extraction procedure and high-resolution measurement using the diffusive gradients in thin film (DGT) technique were employed to explore the lability, potential remobilization mechanism and release characteristics of sediment P in the Pearl River Estuary (PRE), South China. The P accumulated significantly in sediments along the west coast of the PRE due to the combined effects of terrestrial P inputs and specific hydrological conditions. The geochemical fractions of sediment P followed the order of organic P (Org-P) (mean: 58.6%) > iron-bound P (Fe-P) (23.4%) > calcium-bound P (Ca-P) (17.4%) > loosely bound P (LS-P) (0.63%). Synchronous vertical variations in DGT-labile Fe and P in the upper and middle parts of the sediment profiles confirmed that Fe-coupled P mobilization occurred in saline sediments. In contrast, sulfate reduction in bottom sediments supposed to decouple the Fe-P cycling relationship. Additionally, the formation of an “iron curtain” (Fe oxyhydroxides) in the oxic surface sediments efficiently prevented upward diffusion of P, leading to relatively low effluxes of P (0.098–6.59 ng cm−2 d−1) across the sediment-water interface.