Responses of Organic Phosphorus Fractionation to Environmental Conditions and Lake Evolution

Tracing sediment sources in a plain river network area by using optimized experimental design and reflectance spectroscopy

Soil erosion in a plain river network area with dense rivers, fertile land, and agricultural development is easily causes river siltation, agricultural non-point source pollution, and water eutrophication. Therefore, the negative impact of the sediment on the environment cannot be underestimated. Most traditional sediment fingerprint tracing studies have focused on mountain basins and lack a scheme suitable for plain river network sediment tracing. Here, a typical plain river network in the Taihu Basin was selected as the study area. The flow structure and characteristics were analysed, and a sampling scheme for the stream segment and a two-step model of sediment tracing in a plain river network were proposed to quantitatively distinguish the types of sediment sources. The results indicated that the traditional discriminant function analysis adequately distinguishes the contribution rate of basin soil and has a good validation accuracy (R2 = 0.96, root mean square error of calibration = 5.91 %), whereas Random Forest obtains better discrimination results by mining non-linear information in the soil spectra of different land types, with R2 values of 0.89, 0.83, and 0.80 for farmland, forest, and grassland, respectively. The average proportion of soil in the sediment in the watershed was 23 %, and the proportion of soil in the watershed increased from upstream to downstream. The sediment sources of the Caoqiao, Yincun, and Shaoxiang Rivers mainly came from grassland (44 %), forest (39 %), and farmland (42 %), respectively. Land-use distribution, water conservation facilities, and soil particle size were the main factors affecting these sources. Each river adopts measures to remove the corresponding pollutants, optimise water and soil conservation measures for riverbank green belts and forest, and regularly clean up silt in water conservancy ditches and rivers, which can reduce the pollution impact caused by sediment.

Spatial dynamics and risk assessment of phosphorus in the river sediment continuum (Qinhuai River basin, China)

This study investigated the concentration and fractionation of phosphorus (P) using sequential P extraction and their influencing factors by introducing the PLS-SEM model (partial least squares structural equation model) along this continuum from the Qinhuai River. The results showed that the average concentrations of inorganic P (IP) occurred in the following order: urban sediment (1499.1 mg/kg) > suburban sediment (846.1-911.9 mg/kg) > rural sediment (661.1 mg/kg) > natural sediment (179.9 mg/kg), and makes up to 53.9-87.1% of total P (TP). The same as the pattern of IP, OP nearly increased dramatically with increasing the urbanization gradient. This spatial heterogenicity of P along a river was attributed mainly to land use patterns and environmental factors (relative contribution affecting the P fractions: sediment nutrients > metals > grain size). In addition, the highest values of TP (2876.5 mg/kg), BAP (biologically active P, avg, 675.7 mg/kg), and PPI (P pollution index, ≥ 2.0) were found in urban sediments among four regions, indicating a higher environmental risk of P release, which may increase the risk of eutrophication in overlying water bodies. Collectively, this work improves the understanding of the spatial dynamics of P in the natural-rural-urban river sediment continuum, highlights the need to control P pollution in urban sediments, and provides a scientific basis for the future usage and disposal of P in sediments.

Microcystis spp. and phosphorus in aquatic environments: A comprehensive review on their physiological and ecological interactions

Cyanobacterial blooms caused by eutrophication have become a major environmental problem in aquatic ecosystems worldwide over the last few decades. Phosphorus is a limiting nutrient that affects the growth of cyanobacteria and plays a role in dynamic changes in algal density and the formation of cyanobacterial blooms. Therefore, identifying the association between phosphorus sources and Microcystis, which is the most representative and harmful cyanobacteria, is essential for building an understanding of the ecological risks of cyanobacterial blooms. However, systematic reviews summarizing the relationships between Microcystis and phosphorus in aquatic environments are rare. Thus, this study provides a comprehensive overview of the physiological and ecological interactions between phosphorus sources and Microcystis in aquatic environments from the following perspectives: (i) the effects of phosphorus source and concentration on Microcystis growth, (ii) the impacts of phosphorus on the environmental behaviors of Microcystis, (iii) mechanisms of phosphorus-related metabolism in Microcystis, and (iv) role of Microcystis in the distribution of phosphorus sources within aquatic environments. In addition, relevant unsolved issues and essential future investigations (e.g., secondary ecological risks) have been highlighted and discussed. This review provides deeper insights into the relationship between phosphorus sources and Microcystis and can serve as a reference for the evaluation, monitoring, and effective control of cyanobacterial blooms.

Molecular insight into the release of phosphate from dissolved organic phosphorus photo-mineralization in shallow lakes based on FT-ICR MS analysis

Dissolved organic phosphorus (DOP) is a key factor in the water eutrophication process because of its high potential bioavailability and inorganic phosphate (Pi) compensation ability through bio- and photo-mineralization. However, the research on the characterization and transformation of DOP is insufficient owing to their complex composition. This study investigates the release of dissolved Pi from DOP photo-mineralization in Lake Dong based on Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis. The results showed that the photo-release of dissolved Pi is spatially heterogeneous in Lake Dong and is consistent with the distribution of DOP concentration. The FT-ICR MS results showed that the simulated irradiation decreased the relative abundance (RA) of the DOP molecular formulae with higher molecular weight (MW) and higher double bond equivalence values (DBE), while the RA of DOP molecular formulae with lower MW and lower DBE value increased or remained. Besides, the total RA of lipid-like formulae increased from 49.09% to 55.90%, while the oxy-aromatic-like formulae decreased from 50.91% to 44.10%, suggesting that simulated irradiation would influence the potential bioavailability of DOP. As the main photolysis medium during DOP photo-mineralization, the hydroxyl radicals (∙OH) are mainly derived from dissolved organic matter (DOM) compared to the nitrate (NO₃^-) and iron ion (Fe³⁺) in Lake Dong. These results are important in understanding the ability and mechanism of DOP photo-mineralization and provide suggestions for cycling phosphorus in eutrophic shallow lakes.

Cognizing and characterizing the organic phosphorus in lake sediments: Advances and challenges

Organic phosphorus (OP) is one of the main forms of phosphorus in lake ecosystems. Mounting evidence has shown that sediment OP has become a major but underestimated issue in addressing lake eutrophication and algal bloom. However, a holistic view of sediment OP remains missing. This review aims to provide an overview of progress on the studies of OP in lake sediments, focusing on the contribution of OP to internal P loading, its potential role in algal bloom, and the migration and transformation. In addition, this work systematically summarized current methods for characterizing OP content, chemical fraction, composition, bioavailability, and assessment of OP release in sediment, with the pros and cons of each method being discussed. In the end, this work pointed out following efforts needed to deepen the understanding of sediment OP, namely: (1) In-depth literature review from a global perspective regarding the contribution of sediment OP to internal P loading with further summary about its pattern of distribution, accumulation and historical changes; (2) better mathematical models for describing drivers and the linkages between the biological pump of algal bloom and the replenishment of sediment OP; (3) fully accounting the composition and molecular size of OP for better understanding its transformation process and mechanism; ; (4) developing direct, high-sensitivity and combined techniques to improve the precision for identifying OP in sediments; (5) establishing the response of OP molecular properties and chemical reactivity to OP biodegradability and designing a comprehensive and accurate composite index to deepen the understanding for the bioavailability of OP; and (6) integrating fundamental processes of OP in current models to better describe the release and exchange of P in sediment-water interface (SWI). This work is expected to provide critical information about OP properties and deliver perspectives of novel characterization methods.

Trends and environmental factors of arsenic in sediments from the five lake ecoregions, China

The behavior and risk of arsenic (As) closely relate to its geochemical fractionation and environmental factors in sediments. The soluble (F1), reducible (F2), oxidizable (F3), and residual fraction (F4) of As were extracted in the sediments from Lake Hulun, Wuliangsuhai, and Dalinor of Inner Mongolia Plateau. Coupled with lakes from Eastern and Northeast Plain, Yunnan-Guizhou and Qinghai-Tibetan Plateau, the responses of As fractions to environmental conditions were investigated according to the spatial distribution of As fractionations in five lake ecoregions at a national scale of China. Generally, F1 was more sensitive to environmental changes, and the pH presented significantly negative effects on the amount of soluble As, while water depth played an important role in regulating the distribution of the fraction F2 and F4. The As pools in surface lake sediments presented a latitudinal zonation due to the gradient effects of climate and anthropogenic activities on nutrient decomposition, and their influence on the capacity of sediments holding As. This work indicated that nutrients played a coordinating role in regulating the impacts of climate and environmental factors on As fractionation in aquatic environments.

Molecular weight driving bioavailability and intrinsic degradation mechanisms of dissolved organic phosphorus in lake sediment

The sediment dissolved organic phosphorus (DOP) for the "internal phosphorus (P) loading" has raised intensive concern, but its bioavailability and intrinsic degradation mechanism have not been fully elucidated. In this work, multi-techniques were combined to construct the response of sediments DOP's bioavailability to molecular weight (MW) based on ten lakes of China, thereby elucidating the intrinsic degradation mechanism of sediment DOP. A high percentage (74.5% on average) and significantly positive correlations with respect to different MWs were observed, highlighting the importance of DOP to dissolved P in sediments. DOP is mainly composed of a low MW (LMW) portion (63.8%) and the substances are primarily derived from microbial sources. Bioavailable DOP species were closely related to MW, with labile monoester P and diester P decreased with decreasing MW. Analysis of environmental processes showed that microbial utilization capacity and the characteristics of dissolved organic matter (DOM) with different MWs were the dominant drivers in determining the bioavailability of DOP. That is, microorganisms exhibit high DOM utilization capacity in LMW portion, promoting the degradation and transformation of bioavailable DOP species. Furthermore, the increased humic and fulvic-like substances by microbial degradation might in turn inhibit the enzymatic hydrolysis of LMW-DOP. This pattern explains why the contents of LMW-DOP are very high, but it contains less bioavailable DOP. By studying the bioavailability of sediment DOPs with different MWs, it is found that, under natural conditions, labile monoester and diester P in LMW-DOP have a high tendency to degrade than those in HMW-DOP. The results further show that, microbial utilization and DOM characteristics, as well as their linkage with DOP's bioavailability and degradability, have important implications for assessing DOP's degradation potential. The insights from this study might shed light on more effective strategies for mitigating the risks of "internal P loading".

Organic P transformations and release from riparian soils responding to water level fluctuation

To manage eutrophication of reservoirs, it is important to consider the potential for unexpected releases of organic phosphorus (OP) from areas around the reservoir where the water level fluctuates. In this study, we investigated the absorption and release of OP from a riparian soil/sediment from the Miyun Reservoir under fluctuating water levels using laboratory simulations. The total organic phosphorus (TOP) content in the soils/sediments ranged from 250.76 to 298.62 mg/kg, which accounted for between 5.6 and 38.5% of the total phosphorus (TP) content. We measured three OP fractions and found that the concentration of moderately labile OP (MLOP) was the highest, followed by labile OP (LOP), and the concentration of non-labile OP (NLOP) was the lowest. As the soils and sediments dried, they adsorbed phosphorus (P). The inorganic phosphorus (IP) contents were significantly and negatively correlated with the LOP and MLOP contents, indicating exchange between IP with these two fractions when the concentrations of bioavailable phosphorus in the soil are low. During flooding, the physicochemical properties varied at the sediment-water interface, inducing the release of Fe/Al-P. Some of the LOP and MLOP in the sediments were mineralized to IP. Our results suggest that when there are external P inputs, P may be released when sediments around a reservoir are subjected to wetting and drying as water levels fluctuate, which may cause P enrichment in reservoirs, especially in areas with poor water exchange.

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 (P_o) fractions, NaHCO₃-P_o, HCl-P_o, and Ful-P_o accounted for only 11%, 16% and 12% of P_o on average, respectively, whereas Hum-P_o and Res-P_o made up the dominant P_o fraction (59%) and were the main factors controlling P_o 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 P_o 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 P_o 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 P_o be decreased immediately and domestic wastewater, poultry excreta, and fertilizer loss must be more carefully controlled, especially in economically backward areas.

Effects of macro metals on alkaline phosphatase activity under conditions of sulfide accumulation

Alkaline phosphatase (AP) is commonly found in aquatic ecosystems as an extracellular enzyme closely related to the biogeochemical cycling of phosphorus. Although the AP activity (APA) is conventionally thought to be a main response to PO₄^3- starvation, significant effects of macro metal elements (Al, Fe, and Ca) and S on the APA were found in this study. The APA was reduced by Al primarily through the adsorption of the enzyme onto AlOOH colloids. Fe²⁺ inhibited the APA via a mechanism involving free radical oxidation. The main mechanism by which Ca²⁺ inhibited the APA was by competing with Mg²⁺ and Zn²⁺ for the active sites of the enzyme. Excessive S^2- could reduce the APA by removing Zn²⁺ from the active sites of the enzyme. The inhibition of APA could be reversed if some metal ions (e.g., Fe²⁺) were precipitated by S^2- under reducing conditions. Therefore, in anaerobic ecosystems, the effects of macro metals on APA under conditions of sulfide accumulation may have innovative implications for phosphorus management.

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

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

Continuous monitoring of lake dynamics on the Mongolian Plateau using all available Landsat imagery and Google Earth Engine

Lakes are important water resources on the Mongolian Plateau (MP) for human's livelihood and production as well as maintaining ecosystem services. Previous studies, based on the Landsat-based analyses at epoch scale and visual interpretation approach, have reported a significant loss in the lake areas and numbers, especially from the late 1990s to 2010. Given the remarkable inter- and intra-annual variations of lakes in the arid and semi-arid region, a comprehensive picture of annual lake dynamics is needed. Here we took advantages of the power of all the available Landsat images and the cloud computing platform Google Earth Engine (GEE) to map water body for each scene, and then extracted lakes by post-processing including raster-to-vector conversion and separation of lakes and rivers. Continuous dynamics of the lakes over 1 km² was monitored annually on the MP from 1991 to 2017. We found a significant shrinkage in the lake areas and numbers of the MP from 1991 to 2009, then the decreasing lakes on the MP have recovered since circa 2009. Specifically, Inner Mongolia of China experienced more dramatic lake variations than Mongolia. A few administrative regions with huge lakes, including Hulunbuir and Xilin Gol in Inner Mongolia and Ubsa in Mongolia, dominated the lake area variations in the study area, suggesting that the prior treatments on these major lakes would be critical for water management on the MP. The varied drivers of lake variations in different regions showed the complexity of factors impacting lakes. While both natural and anthropogenic factors significantly affected lake dynamics before 2009, precipitation played increasingly important role for the recovery of lakes on the MP after 2009.

Distribution of organic phosphorus species in sediment profiles of shallow lakes and its effect on photo-release of phosphate during sediment resuspension

In this work, the distribution of organic phosphorus (P_o) species in sediment profiles of five shallow lakes was analyzed and its effect on the photo-release of dissolved phosphate (P_i) was investigated during sediment resuspension under simulated sunlight irradiation. The results show that P_o was highly enriched in the surface sediment and gradually decreased as sediment depths increased: 33.10 ± 2.55-96.71 ± 7.60 mg/kg, 33.55 ± 2.34-142.86 ± 5.73 mg/kg, 57.50 ± 3.46-149.68 ± 7.67 mg/kg, 55.18 ± 4.67-168.73 ± 8.31 mg/kg, 98.75 ± 7.56-275.74 ± 10.70 mg/kg for Lake Hou, Lake Tuan, Lake Tangling, Lake Guozheng and Lake Miao, respectively. The photo-release amount of dissolved P_i in the resuspension composed of surface sediments was also higher than that of deep sediment during sediment resuspension under the simulated sunlight irradiation for 9 h. The potential reasons for these results are: (1) difference in morphology and composition of sediments at different depths: the mean particle size of sediment decreased first and then increased as sediment depths increased; (2) difference in composition of P_o species with depths in the sediment profiles: more photolytic P_o species existed in surface sediments confirmed by sequential extraction and ³¹P NMR analysis; and (3) more OH production in the resuspension composed of surface sediment under simulated sunlight irradiation, which directly influence the photo-release of dissolved P_i from photodegradation of organic phosphorus. All of these results indicate that the distribution of organic phosphorus species in the sediment profiles plays an important role in P cycle and its photodegradation during sediment resuspension may be one of the potential pathways for phosphate supplement in shallow lakes.

Taxonomic structure and potential nitrogen metabolism of microbial assemblage in a large hypereutrophic steppe lake

Recent studies have expanded the interests about microbial community and function following the rapid development of high-throughput sequencing techniques in the freshwater ecosystem. In this study, we aimed to attain a deep understanding of microbial community structure and potential nitrogen metabolism in Hulun Lake, a shallow hypereutrophic steppe lake in the Mongolian Plateau in China. The result demonstrated that cyanobacteria were the most dominant phylum. Network analysis showed both intra- and inter-phylum co-occurrence were pervasive, and there were modular structures in the microbial assemblages. The cluster dominated by proteobacteria was mainly negatively connected to the cluster dominated by both proteobacteria and actinobacteria. Cyanobacteria were tightly clustered together and positively connected to these two clusters. The major nitrogen metabolism pathways were glutamine synthetase-glutamate synthase and assimilatory nitrate reduction, indicating the nitrogen was mainly retained in the lake by microbial uptake. Cyanobacteria contributed 43.25% gene reads involved in the overall nitrogen metabolism but mainly contributed to assimilatory nitrate reduction and nitrogen fixation, aggravating the lake eutrophication. This study adds to our knowledge of microbial assemblages and nitrogen metabolism in the shallow hypereutrophic lake and provided an insight understanding for the purposes of lake ecosystem's protection and efficient management in the Mongolian Plateau.

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

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

Synergistic removal effect of P in sediment of all fractions by combining the modified bentonite granules and submerged macrophyte

The removal efficiency of sediment phosphorus (P) with the in-situ synergistic effect of modified bentonite granules (MBG) and Vallisneria spiralis (V. spiralis) in West Lake, Hangzhou, China was investigated for the first time in the study. CMBG-Na10-450 (nitrification (10% Na₂CO₃)-calcination (450 °C) combined modification) was prepared and characterized, and the removal effects of sediment P of all fractions with CMBG-Na10-450 and V. spiralis in combination and separately were evaluated in batch experiments. Results showed that CMBG-Na10-450 could promote the growth of V. spiralis, and the residual P of the sediment not adsorbed on CMBG-Na10-450 was changed through root oxygenation and nutrition allocation, and then enhanced the extra P adsorption on CMBG-Na10-450. The combination of MBG and V. spiralis exhibited a synergistic removal effect higher than the summation of MBG and V. spiralis applied separately. The results of microcosm experiments showed that the combination of CMBG-Na10-450 and V. spiralis enhanced the function of P metabolism by increasing the special genus that belongs to the family Erysipelotrichaceae.

Spatial and historical distribution of organic phosphorus driven by environment conditions in lake sediments

The chemistry of sedimentary organic phosphorus (OP) and its fraction distribution in sediments are greatly influenced by environmental conditions such as terrestrial inputs and runoffs. The linkage of OP with environmental conditions was analyzed on the basis of OP spatial and historical distributions in lake sediments. The redundancy analysis and OP spatial distribution results suggested that both NaOH-OP (OP extracted by NaOH) and Re-OP (residual OP) in surface sediments from the selected 13 lakes reflected the gradient effects of environmental conditions and the autochthonous and/or allochthonous inputs driven by latitude zonality in China. The lake level and salinity of Lake Hulun and the runoff and precipitation of its drainage basin were reconstructed on the basis of the geochemistry index. This work showed that a gradient in weather conditions presented by the latitude zonality in China impacts the OP accumulation through multiple drivers and in many ways. The drivers are mainly precipitation and temperature, governing organic matter (OM) production, degradation rate and transportation in the watershed. Over a long temporal dimension (4000years), the vertical distributions of Re-OP and NaOH-OP based on a dated sediment profile from HLH were largely regulated by the autochthonous and/or allochthonous inputs, which depended on the environmental and climate conditions and anthropogenic activities in the drainage basin. This work provides useful environmental geochemistry information to understand the inherent linkage of OP fractionation with environmental conditions and lake evolution.

Imaging Organophosphate and Pyrophosphate Sequestration on Brucite by in Situ Atomic Force Microscopy

In order to evaluate the organic phosphorus (OP) and pyrophosphate (PyroP) cycle and their fate in the environment, it is critical to understand the effects of mineral interfaces on the reactivity of adsorption and precipitation of OP and PyroP. Here, in situ atomic force microscopy (AFM) is used to directly observe the kinetics of coupled dissolution-precipitation on cleaved (001) surfaces of brucite [Mg(OH)₂] in the presence of phytate, glucose-6-phosphate (G6P) and pyrophosphate, respectively. AFM results show that the relative order of contribution to mineral surface adsorption and precipitation is phytate > pyrophosphate > G6P under the same solution conditions and can be quantified by the induction time of OP/PyroP-Mg nucleation in a boundary layer at the brucite-water interface. Calculations of solution speciation during brucite dissolution in the presence of phytate or pyrophosphate at acidic pH conditions show that the solutions may reach supersaturation with respect to Mg₅H₂Phytate.6H₂O as a Mg-phytate phase or Mg₂P₂O₇ as a Mg-pyrophosphate phase that becomes thermodynamically stable before equilibrium with brucite is reached. This is consistent with AFM dynamic observations for the new phase formations on brucite. Direct nanoscale observations of the transformation of adsorption/complexation-surface precipitation, combined with spectroscopic characterizations and species simulations may improve the mechanistic understanding of organophosphate and pyrophosphate sequestration by mineral replacement reactions through a mechanism of coupled dissolution-precipitation occurring at mineral-solution interfaces in the environment.