Sediment Phosphorus Release Research Articles

Release and transformation of phosphorus in sediment following seasonal freezing-thawing cycles

River ice in the upper Yarlung Zangbo River is characterized by seasonal freezing-thawing cycles (SFTC). It is important to explore the effects of SFTC on phosphorus release and transformation from upstream surface sediments to protect the ecosystem of the Yarlung Zangbo River. The process and mechanism of phosphorus release and transformation in sediments following SFTC were investigated in a laboratory simulation experiment. The results showed that after freezing, sediment particles were broken, the specific surface area was increased by 14%, and the particle size was decreased by 43%, which resulted in weakened adsorption of phosphorus by sediments. Moreover, the destruction of organic matter (OM) on the sediment surface will release more ion adsorption sites and promote the release of phosphorus. The bioavailabilities of exchangeable phosphorus (Ex-P), aluminum phosphorus (Al-P) and iron phosphorus (Fe-P) increased by 60.09%, 86.86% and 31.86%, respectively, after freezing. Organic phosphorus (O-P) is used indirectly by organisms, and O-P content showed a significant correlation with OM content. Water affected the oxygen content in sediments during the freezing period, and continuous hypoxia promoted the release and transformation of Fe-P and Al-P.

How do inundation provoke the release of phosphorus in soil-originated sediment due to nitrogen reduction after reclaiming lake from polder

Different N and P fractions in microcosm incubation experiment was measured using high-resolution in-situ Peeper and DGT techniques combining with sequential extraction procedure. The results showed the synchronous desorption and release of PO43-, S2- and Fe2+ from the solid soil-originated sediment. This trend indicated that the significant reduction of Fe-P and SO42- occurred in the pore water during the inundation. The concentrations of PO43- in the overlying water and pore water increased to more than 0.1 and 0.2 mg/L at the beginning of the incubation experiment. Decreased NO3-concentrations from more than 1.5 mg/L to less than 0.5 mg/L combining with increasing NH4+ concentrations from less than 1 mg/L to more than 5 mg/L suggested the remarkable NO3- reduction via dissimilatory nitrate reduction to ammonia (DNRA) pathway over time. High NH4+ concentrations in the pore water aggravated the release of Fe2+ through reduction of Fe(III)-P as electric acceptors under anaerobic conditions. This process further stimulated the remarkable releasing of labile PO43- from the solid phase to the solution and potential diffusion into overlying water. Additionally, high S2- concentration at deeper layer indicated the reduction and releasing of S2- from oxidation states, which can stimulated the NO3- reduction and the accumulation of NH4+ in the pore water. This process can also provoke the reduction of Fe-P as electric acceptors following the release of labile PO43- into pore water. Generally, inundation potentially facilitate the desorption of labile P and attention should be paid during the reclaiming lake from polder.

Iron-Phosphorus Feedbacks Drive Multidecadal Oscillations in Baltic Sea Hypoxia.

Hypoxia has occurred intermittently in the Baltic Sea since the establishment of brackish‐water conditions at ∼8,000 years B.P., principally as recurrent hypoxic events during the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA). Sedimentary phosphorus release has been implicated as a key driver of these events, but previous paleoenvironmental reconstructions have lacked the sampling resolution to investigate feedbacks in past iron‐phosphorus cycling on short timescales. Here we employ Laser Ablation (LA)‐ICP‐MS scanning of sediment cores to generate ultra‐high resolution geochemical records of past hypoxic events. We show that in‐phase multidecadal oscillations in hypoxia intensity and iron‐phosphorus cycling occurred throughout these events. Using a box model, we demonstrate that such oscillations were likely driven by instabilities in the dynamics of iron‐phosphorus cycling under preindustrial phosphorus loads, and modulated by external climate forcing. Oscillatory behavior could complicate the recovery from hypoxia during future trajectories of external loading reductions.

Responses of coastal sediment phosphorus release to elevated urea loading

Increased urea is one of the common nitrogen forms polluting coastal waters and affecting nutrient dynamics. To investigate the effects of urea on sediment phosphorus (P) release, we carried out a 2-month mesocosm experiment with six targeted loadings of urea (0–0.6 mg N L−1 d−1). Results showed that: i) urea was rapidly transformed into ammonium and then nitrate (NO3−). ii) When nitrogen occurred as urea or ammonium, minor P release was observed. iii) After urea were mostly converted to NO3−, P release became clearer. iv) NO3− had a dual effect by promoting P release through decreasing sediment pH and increasing alkaline phosphatase activity or by inhibiting P release through improving sediment oxidation. v) The overall effects of urea on P release depended on the ultimate NO3− concentrations, being prominent when NO3− ≥ 11 mg N L−1. Our findings are of relevance when determining nitrogen reduction targets needed for combating eutrophication.

Phosphorus internal loading and sediment diagenesis in a large eutrophic lake (Lake Chaohu, China)

Sediment phosphorus (P) release and retention are important in controlling whole-system P dynamics and budget in eutrophic lakes. Here we combine short- (seasonal) and long-term (years to decades) studies to quantify the internal P loading and P release potential in the sediments of Lake Chaohu and explore their controlling mechanisms. In the west region of the lake, short-term P diffusive fluxes ranged from 0.2 mg/m2·d−1 to 6.69 mg/m2·d−1 (averaged 2.76 mg/m2·d−1) and long-term net P release ranged from 2.25 mg/m2·d−1 to 8.94 mg/m2·d−1 (averaged 5.34 mg/m2·d−1); in the east region, short-term P diffusive fluxes varied from 0.73 mg/m2·d−1 to 1.76 mg/m2·d−1 (averaged 1.05 mg/m2·d−1) and long-term P release ranged from 0.13 mg/m2·d−1 to 4.15 mg/m2·d−1 (averaged 1.3 mg/m2·d−1). Both short- and long-term P releases were in the same order of magnitudes as the external P inputs (3.56 mg/m2·d−1). Comparison of the long-term and short-term sediment P release indicates that while the high summer P release in the east might only represent a snapshot value, the sediments in the west contribute to large P release for years or even decades, impeding water quality recovery under lake management. Mobilization of surface sediment legacy P accounted for 81% of short-term P release. The long-term release was dominated by remobilization of iron bond P (BD-P) (average 52.1%) at all sites, while Aluminium-bound P (NaOH-rP) exhibited partly reactive and potentially mobile, releasing P to the water column in most sites in the west. Our study demonstrates the importance of sediments as P sources in lake Chaohu. The combination of short- and long-term P release studies can help understand the roles of sediments in regulating the water quality and eutrophication.

Effects of pH on phosphorus form transformation in lake sediments

Abstract The pH value of lake water varies with the lake environment, which has an effect on the form of phosphorus in sediment, and then the release of sediment phosphorus. The form of phosphorus in sediments was analyzed using field sampling. The environmental conditions with pH values of 4.0, 7.0 and 10.0 were simulated indoors to estimate the effects of pH on phosphorus release from sediments and the content change of various forms of phosphorus was studied. The results showed that in Wuliangsuhai Lake, Ca-P accounted for 54.3%, which was the largest portion of the TP. Phosphorus release was favored under acidic and alkaline conditions, and the alkaline condition was more favorable. The proportion of Fe/Mn-P and Fe/Al-P in the TP decreased with an increase in the pH, while the proportion of Ca-P in the TP increased with an increase in the pH. Under the alkaline condition (pH = 10), Ca-P in the sediment increased significantly, with an increase of 22.5%. However, Fe/Mn-P and Fe/Al-P decreased significantly, with drops of 37.3% and 44.9%, respectively. Under the acidic condition (pH = 4), Fe/Mn-P and Fe/Al-P in the sediment increased significantly, and the increases were 63.1% and 37.1%, respectively. However, Ca-P decreased significantly, with a drop of 39.2%. In general, low pH promoted the release of Ca-P, and a high pH promoted the release of Fe/Mn-P and Fe/Al-P. Wuliangsuhai Lake water is characterized by weak alkaline characteristics throughout the year, and biological available phosphorus accounts for 13.3%–20.9% of the TP, with Fe/Mn-P being the dominant form. This study revealed that the risk of phosphorus release from sediments to the overlying water was greater under alkaline conditions.

Spatiotemporal variations in phosphorus concentrations in the water and sediment of Jiaozhou Bay and sediment phosphorus release potential

Phosphorus contamination in urbanized bays has been a major concern because the bay restoration is often hindered by complex P sources and behaviors. This study examined the spatiotemporal changes of P species and exchange potential in/between the water and sediment of the Jiaozhou Bay. The results indicated that dissolved P (TDP) and inorganic P (DIP) in the water ranged from 7.8–128.7 and 1.8–14.1 μg/L, respectively; while total P (TP) in the sediment ranged from 213.4–638.7 mg/kg. The TDP and DIP concentrations in the water were high in winter and low in summer, and generally decreased from northeastern or northern areas to southwestern or southern areas mainly due to phytoplankton bloom cycles and riverine and wastewater inputs. TP in the sediment was lower in the northwestern area due to solid dilution effect by the settlement of settled coarser suspended particles. Changes in aquatic geochemical conditions from rivers to bay caused P accumulation in estuarine sediment, with higher P partition in organic fraction (40%). Compared to the estuarine sediment, higher fractions of P were associated with carbonate (34%) and iron oxide (17%) minerals in the bay sediment. Equilibrium P concentrations at zero sorption (EPC0) were 4.1–149.8 μg/L, which was substantially higher than the DIP concentration, demonstrating P release potential from the sediment. In addition, the P release potential was high in the northeastern area while P partition coefficient or buffer intensity (Kd) was high in the northwestern area. EPC0 was significantly positively correlated with soluble and exchangeable P in the sediment while Kd was significantly negatively correlated. These results can provide improved insights into P behaviors in an urbanized bay, particularly the P release potential and spatiotemporal change.

Preparation and application of an innovative integrated agent product for phosphorus control and oxygen release

Abstract In this study, an oxygen-releasing and phosphorus-controlling agent (ORPC) consisting of calcium peroxide (CaO2), bentonite, cement, stearic acid (SA), citric acid (CA) and fine sand was synthesized successfully and used to purify phosphorus-rich river water. The removal of phosphorus using ORPC was studied in actual river water and the results found that over 75.0% phosphorus was removed by adding ORPC at 30 mL h−1 flow rate in initial phosphorus concentrations of 0.76 mg L−1. The ORPC was further used to evaluate the changes of aluminum phosphate (Al-P), ferric phosphate (Fe-P) and calcium phosphate (Ca-P) in sediment. Fe-P, Al-P, and Ca-P in the sediment increased from 0.14, 0.196, and 1.63 mg g−1 to 0.159, 0.372, and 2.74 mg g−1 respectively within 28 days, indicating that the total dissolved phosphorus in the overlying water could be adsorbed by ORPC and further transformed into Al-P, Ca-P, and Fe-P in the sediment, thus inhibiting the release of endogenous phosphorus in sediment to the water. In addition, the performance of ORPC with various contents of SA and CaO2 was investigated. In summary, ORPC can be employed to adsorb phosphorus in water and prevent phosphorus release from sediment, therefore achieving the purpose of controlling phosphorus and maintaining DO at a reasonable level.

Accelerated sediment phosphorus release in Lake Erie's central basin during seasonal anoxia

AbstractEutrophication remains a serious threat to Lake Erie and has accelerated over past decades due to human activity in the watershed. Internal phosphorus (P) loading from lake sediment contributes to eutrophication, but our understanding of this process in Lake Erie is more uncertain than for its riverine P inputs. Past study has focused on incubating sediment cores in oxic or anoxic conditions, meaning we know little about sediment flux during state transitions. We used 56 controlled sediment core incubation experiments to quantify rates and onset of P release in Lake Erie's central basin as a function of depositional environment, season (spring, summer, and fall), temperature, and dissolved oxygen (DO) concentration. P flux under oxic or hypoxic (> 0 to ≤ 2 mg L−1 DO) conditions was slow (0.31–0.50 mg m−2 d−1) compared to anoxic P flux (5.19–30.7 mg m−2 d−1). The transition between slow and fast flux occurred within 24 h of anoxia (0 mg L−1 DO). Oxic or anoxic P flux was generally similar across seasons and incubation temperatures (8°C and 14°C). In 14°C incubated cores anoxic P flux onset was earliest in fall, when sediments had already been exposed to anoxic conditions in the lake. Re‐oxygenation of experimental cores that temporarily developed anoxia reversed the direction of P flux, but P release resumed at similar rates once the water returned to anoxia. Understanding the effects of hypolimnion oxygen conditions on internal P loading allows us to better constrain nutrients sources and implications for P budget management.

Feasibility of using Mg/Al-based layered double hydroxides as an inactivating agent to interrupt phosphorus release from contaminated agricultural drainage ditch sediments

This study aimed to evaluate the feasibility of using Mg/Al-based layered double hydroxides (Mg/Al-LDHs) treatment to prevent phosphorus release from sediments of agricultural drainage ditches. A high-resolution diffusive gradient film technique and a high-resolution peeper technique were used to measure the phosphorus and iron concentrations in the overlying water and sediment profiles at sub-millimeter vertical resolution. Results demonstrated that Mg/Al-LDHs effectively reduced the concentrations of soluble reactive P (SRP) (about 69%) in the overlying water and the concentrations of SRP (about 37.42%) and labile P (about 36.72%) in the pore water. The highly positive correlation (p < 0.01) between SRP and soluble Fe, labile P and labile Fe in the sediment profiles provided high-resolution evidence for the simultaneous release of iron and phosphorus in sediments. Furthermore, Mg/Al-LDHs inactivated mobile P (NH4Cl-P and BD-P) in the uppermost sediment (0–50 mm) and then transformed the mobile P to more stable P (NaOH-rP, HCl-P, and Res-P) (about 81% of total extractable P). An inactivation layer with low phosphorus concentrations was observed in the upper sediment. In brief, the addition of Mg/Al-LDHs to the sediment surface of agricultural drainage ditches was effective in reducing SRP concentrations in the overlying water while effectively hindering the release of sediment internal phosphorus from the pore water to the overlying water.

Spatial Distribution Characteristics of Phosphorus Fractions and Release Risk in Sediments of Honghu International Importance Wetland

According to a spatial distribution analysis of phosphorus in sediments from Honghu Wetland, it was found that TP content in sediments at the mouth of Honghu Lake was 781.31-1955.84 mg·kg-1 and the average value was(1287.21±437.28)mg·kg-1. TP content in sediments in the open water area was 438.33-1554.04 mg·kg-1, with an average value of(718.10±238.15)mg·kg-1. The TP content of sediments in lake inlet was significantly higher than that of sediments in the open water area(P<0.05), and that in the enclosed aquaculture was higher than in the open water area, although no significant difference was observed (P>0.05). The TP content of sediments to the northwest and northeast of Honghu Lake was higher than that to the southwest of Honghu Lake, and the TP content of sediments in The Four-lake main canal was significantly higher than that of Luoshan main canal(P<0.05). The phosphorus input in the Four-lake main canal may be the main source of phosphorus in Honghu Lake sediments. The phosphorus fraction composition in sediments from different sampling sites were significantly different. Fe/Al-P and Ca-P were the main forms of phosphorus in sediments from the lake inlet, while OP and Ca-P were the main forms of phosphorus in sediments from the open water area. The variation in spatial phosphorus form composition was related to the influence of human activity and the distribution of aquatic plants. Fe/Al-P and OP contents were used to estimate the content of biological available phosphorus (BAP) in evaluated sediments, and the proportion of BAP in TP was used to estimate the risk of phosphorus release in Honghu sediments. BAP/TP was 39.8%-69%, with an average of(56.5±7.23)%, indicating a high risk of phosphorus release. OP and BAP were significantly correlated with TP in overlying water(P<0.01), and the correlation between BAP and phosphate in the overlying water was the highest. The results showed that phosphorus concentration in the overlying water may be related to the release of Fe/Al-P and OP into water bodies.

Effect of Myriophyllum verticillatum on controlling phosphorus release from sediment for water environment purification

Eutrophication is one of the most common water pollution problems in the world. In this paper, the effects of Myriophyllum verticillatum on phosphorus content in water and sediment were studied. The results showed that Myriophyllum verticillatum had the strongest purification effect on water sample. Under the condition of sufficient light, suitable temperature and environmental factors not affected by the external environment, the phosphorus content in the overlying water increased first and then decreased. In addition to the external factors, the phosphorus content in the water decreased. The results show that the growth of Myriophyllum verticillatum depends on the change of phosphorus concentration in water. The increase of phosphorus concentration in water will increase the phosphorus concentration in plants and accelerate the growth of Myriophyllum verticillatum. However, the growth of Myriophyllum verticillatum will consume more phosphorus. Myriophyllum verticillatum in sufficient light, suitable temperature, environmental factors are not affected by the outside world. The contents of phosphorus in the sediments showed a downward trend. In addition to the external factors, the phosphorus content in the sediment was reduced by Myriophyllum verticillatum. The relationship between the growth of Myriophyllum verticillatum and the total phosphorus concentration in sediments is interdependent. The release of phosphorus in sediment will increase the phosphorus content in water, which will lead to the enrichment of phosphorus in plants and accelerate the growth of Myriophyllum verticillatum. The growth of Myriophyllum verticillatum will make Myriophyllum verticillatum need more phosphorus, which will accelerate the absorption of phosphorus in water and release more phosphorus from sediment. This is the reaction mechanism of phosphorus removal by Myriophyllum verticillatum; Under the conditions of sufficient light, warm climate and environmental factors not affected by the external environment, the total phosphorus content of Myriophyllum verticillatum was on the rise.

Spatial representation of in-stream sediment phosphorus release combining channel network approaches and in-situ experiments

Impairment of rivers by elevated phosphorus (P) concentration is an issue often studied at outlets of mesoscale catchments. Our objective was to evaluate within-catchment spatio-temporal processes along connected reaches to understand processes of internal P loading associated with sediment input, accumulations in channels and sediment-water column P exchange. Our overall hypothesis was that heterogeneous sediment residence within the channel of a 52 km2 mixed land cover catchment resulted in key zones for sediment-water P exchange. We evaluated the channel network through ground-survey, spatial data methods establishing connectivity and energy gradients. This gave a background to understand sampling of sediments and P release/uptake to the water column using 90 s in-situ resuspension isolating a portion of streambed over five sets of three-location transects in May (spring storms, recent active erosion) and September (summer low flow, longer sediment residence). Simple transect position models (top, mid, bottom) predicted increased sediment resuspension yields and P contents in lower settings. Sediment P release following resuspension were mean (and range) 0.5 (−0.8 to 1.8) and 0.5 (−2.5 to 3.6) mg soluble reactive P/m2 bed in May and September, respectively, strengthening generally down the transects but inconsistently. Relationships (log form) showed a steepening rise in fine sediments, P content, background and disturbance-released dissolved P, with specific stream power < 40 W/m2. In-situ methods showed sediments dominantly (12 cases May, 13 cases Sep) as P sources capable of influencing dissolved P concentrations and with potential explanation that heterogeneous locations of internal P loading influence the systems longer-term observed P trends. Combining channel network, stream power assessment and in-situ sorption studies improved the understanding of influential zones of sediment-water P exchange within this mesoscale catchment. Such methods have potential to inform P model development and management.

High-resolution distribution of internal phosphorus release by the influence of harmful algal blooms (HABs) in Lake Taihu

The Mechanisms driving phosphorus (P) release in sediment of shallow lakes is essential for managing harmful algal blooms (HABs). Accordingly, this study conducted field monitoring of labile P, iron (Fe), sulfur (S), and dissolved manganese (Mn) in different biomass of algae in Lake Taihu. The in-situ technique of ZrO-Chelex-AgI (ZrO-CA) diffusive gradients in thin-films (DGT) and high-resolution dialysis sampler (high resolution-Peeper (HR-Peeper)) were used to measure labile P, Fe, S, and dissolved Mn, as well as their apparent diffusion fluxes at the sediment-water interface (SWI). In addition, the distribution of iron-reducing bacteria (IRB) and sulfate-reducing bacteria (SRB) in sediments was also detected. Results showed that high HABs biomass promoted the reduction of sulfate into labile S, however, IRB is the dominant species. Thus, labile Fe concentrations greatly exceeded labile S concentrations across all sites, indicating that microbial iron reduction (MIR) is the principal pathway for ferric iron reduction. Furthermore, the simple relationship analysis revealed the principal influence P migration and transformation is the Fe–P in high algal biomass sites, while Fe and Mn redox reactions did not significantly influence labile P mobilization in low algal areas.

Effects of Sediment Microenvironment on Sedimentary Phosphorus Release Under Capping

The sediment microenvironment has an important effect on the release of endogenous phosphorus. In this study, the influence of two different in-situ covering materials on the sediment microenvironment were compared, and the controlling effect of endogenous phosphorus release were studied. The sediment microenvironment was represented by the concentration of NH4+-N, Fe2+ in interstitial water, and microbial activity. The results showed that the concentrations of NH4+-N and Fe2+ were lower under ACPM coverage than those of the Phoslock® group, and the microbial activity was higher, indicating that the redox potential of ACPM coverage was higher than that of Phoslock®. Furthermore, the bottom sediment microenvironment was in an aerobic state. Compared with the Phoslock® group, the DIP concentrations in both the overcover water and porewater in the ACPM group were higher, indicating that Phoslock® was superior to ACPM with respect to the phosphate adsorption capacity, suggesting that the sediment microenvironment was not the only criterion for phosphorus adsorption. In the fixation process of endogenous phosphorus, both of the covering materials were conducive to the fixation of inter phosphorus, and Ca-P increased significantly. On the other hand, oxidizing ACPM led to an increase in NH4Cl-P and a significant decrease in Fe/Al-P. This promotes the release of active phosphorus, which is conducive to the cleaning of the sediment and phosphorus release.

Deep-water inflow event increases sedimentary phosphorus release on a multi-year scale

Abstract. Phosphorus fertilisation (eutrophication) is expanding oxygen depletion in coastal systems worldwide. Under low-oxygen bottom water conditions, phosphorus release from the sediment is elevated, which further stimulates primary production. It is commonly assumed that re-oxygenation could break this “vicious cycle” by increasing the sedimentary phosphorus retention. Recently, a deep-water inflow into the Baltic Sea created a natural in situ experiment that allowed us to investigate if temporary re-oxygenation stimulates sedimentary retention of dissolved inorganic phosphorus (DIP). Surprisingly, during this 3-year study, we observed a transient but considerable increase, rather than a decrease, in the sediment efflux of DIP and other dissolved biogenic compounds. This suggested that the oxygenated inflow elevated the organic matter degradation in the sediment, likely due to an increase in organic matter supply to the deeper basins, potentially combined with a transient stimulation of the mineralisation efficiency. As a result, the net sedimentary DIP release per m2 was 56 %–112 % higher over the years following the re-oxygenation than before. In contrast to previous assumptions, our results show that inflows of oxygenated water to anoxic bottom waters can increase the sedimentary phosphorus release.

Key drivers structuring rotifer communities in ponds: insights into an agricultural landscape.

Understanding the influence of environmental and spatial factors on the structure of aquatic communities remains a major challenge in community ecology. This study aims to identify main drivers of rotifer abundance and diversity in ponds embedded in an intensive agricultural landscape in Northeast Germany. We studied 42 ponds of glacial origin (kettle holes) covering a wide range of environmental parameters. The predominant factors structuring the rotifer metacommunity shifted from abiotic environmental filtering in spring to unstudied factors in autumn, while spatial factors remained less important. Fertilizer-driven salinization, internal nutrient recycling, primary productivity and sediment phosphorus release were the prevalent biogeochemical processes in the ponds. Both fertilizer-driven salinization and primary productivity negatively affected rotifer alpha diversity, and positively affected beta diversity. This impact was lower in forest ponds than in those surrounded by arable fields or grassland. However, rotifer diversity did not significantly differ among land-use categories. Our results indicate that the long-term impact of intensive agriculture in the region and the associated widespread eutrophication overrides the direct influence of land use on rotifer diversity but point to an indirect effect via fertilizer-driven salinization. Furthermore, this study highlights the role of ponds in enhancing regional biodiversity in agricultural landscapes.

Al-PHOSLOCK thin-layer capping to control phosphorus release from sediment: effect of hydraulic retention time and phosphorus migration/transformation mechanism

This work aimed to (i) investigate the effect of hydraulic retention time (HRT) on controlling the release of phosphorus from sediment and (ii) interpret the phosphorus migration and transformation mechanism in the Al-PHOSLOCK thin-layer capping system. A 35-day laboratory dynamic simulation experiment was conducted by applying the Al-PHOSLOCK thin-layer capping to evaluate the effect of HRT on interrupting the release of phosphorus from contaminated sediments. The total phosphorus (TP), inorganic phosphorus (IP), organic phosphorus (OP), non-apatite inorganic phosphorus (NAIP), and apatite phosphorus (AP) were identified as different phosphorus species and analyzed during the experiment to further elucidate the migration and transformation of phosphorus. The release of phosphorus from contaminated sediment was successfully suppressed by the Al-PHOSLOCK capping layer with an efficiency of higher than 90%. The HRT exerted a dual role on phosphorus controlling: at low HRT, slight water flow facilitated phosphorus migrating out from sediment and diffusing to the overlying water; at high HRT, the migration of phosphorus from overlying water back to sediment was strengthened. It was demonstrated that the phosphorus release was effectively controlled by the Al-PHOSLOCK thin-layer capping under different HRT conditions (static, 0.5 d, 1.0 d, and 3.0 d). The mechanism of phosphorus migration and transformation in the Al-PHOSLOCK thin-layer capping system was elucidated, including three significant stages of physical interception, adsorption, and capture/hold/transform process. This study verified the good capacity of the Al-PHOSLOCK capping system for controlling the release of sediment phosphorus under different HRT. Therefore, it was expected to be a promising approach in the handling of water eutrophication.

Iron filings application to reduce lake sediment phosphorus release

Natarajan P, Gulliver JS, Arnold WA. 2021. Iron filings application to reduce lake sediment phosphorus release. Lake Reserv Manage. 27:143–159. Surface water impairments due to excess phosphorus loading from the watershed and internal recycling from sediments have been reported worldwide. This study investigated the application of iron metal filings to lake sediments as a method to control sediment phosphorus release. Using batch studies, a zero-valent iron filings material was selected for laboratory dosing experiments with lake sediment cores. Iron filings doses of 0 (control), 0.01, 0.1, and 1 g/cm2 were added to sediment cores collected from a eutrophic lake in Minnesota, United States, to determine the impacts of iron addition on the oxic and anoxic phosphate (PO4-P) flux at 20 C and 10 C in the laboratory. Under oxic conditions, PO4-P release did not occur from the sediments, and low water column PO4-P concentrations were maintained in the iron-dosed and control cores. After switching to anoxic conditions, the 0.1 and 1 g/cm2 iron doses continued to reduce or fully prevent sediment PO4-P flux. The enhanced supply of iron in the sediments was found to reduce the porewater PO4-P, resulting in no apparent PO4-P diffusion across the sediment–water interface and low PO4-P in the overlying water under oxic and anoxic conditions. Further evaluation using in situ experiments is needed to assess the effectiveness of iron filings addition in sequestering sediment phosphorus under natural conditions.

Influence of sulfate reduction on fraction and regeneration of phosphorus at sediment-water interface of urban malodorous river.

The effective control of the release of endogenous phosphorus is an urgent problem in the management of urban malodorous rivers. This research explored the fraction and regeneration of phosphorus of urban malodorous river in the context of sulfate reduction. It was found that sulfate reduction could promote sediment phosphorus release. The contents of total phosphorus (TP) and soluble reactive phosphorus (SRP) in the overlying water presented a decreasing trend after the initial increase during the operation of 120days. The phosphorus release was positively related to the input of sulfate, and the maximum values of TP and SRP (14.01mg/L and 12.27mg/L, respectively) in the overlying water were observed when 8mM Na2SO4 was added. Moreover, the addition of sulfate could significantly affect the distribution of phosphorus fraction in the sediment and promote the transformation of moderately active phosphorus (NaOH-P, D. HCI-P) to more active phosphorus Resin-P), which resulted in more release of phosphorus to the overlying water. In addition, it was observed that sulfate input could increase the relative abundance of phosphate solubilizing bacteria (PSB) and sulfate-reducing bacteria (SRB) from 0.69 to 1.1% and 4.92 to 9.03%, respectively.