Mitigating eutrophication in shallow lakes necessitates accurate measurement of internal phosphorus loading—a task complicated by intricate sediment–water interactions and insufficient long-term monitoring. This study integrates high-resolution porewater monitoring with machine learning (ML) to quantify internal soluble reactive phosphorus (SRP) release in the large eutrophic Lake Taihu, China. Monitoring across the whole of Taihu Lake throughout 2021–2022 indicated that SRP release fluxes varied from −0.32 to 1.84 mg/(m2·day), with peaks occurring in summer–autumn within algal-dominated zones, where internal SRP release was closely associated with the reductive dissolution of Fe-oxides. Building on these observations, an ML approach using an optimized Ridge model predicted SRP release fluxes over the past two decades. The results showed that internal SRP release contributed an average of 45 % of total phosphorus (TP) increases during critical bloom periods. Structural equation modeling indicated that chlorophyll-a variability was strongly linked to internal SRP release, temperature, and TP, which together accounted for 65 % of the variation, suggesting internal SRP release is a key driver for sustaining algal blooms. Furthermore, two-decade dynamics of internal SRP release revealed that its predominant control factors are shifting from past anthropogenic disturbance pressures to climate-induced processes. The findings highlight the important role of internal SRP release in sustaining eutrophication, and provide scientific guidance for formulating adaptive remediation measures to control its release.

Nickel (Ni) remobilization in eutrophic lake sediments is controlled by interactions between iron-manganese (Fe-Mn) redox processes and dissolved organic matter (DOM), but the mechanisms under different ecological regimes remain unclear. Here, we employed an in situ high-resolution approach integrating HR-Peeper sampling and multi-analytical techniques to simultaneously characterize Ni, Fe, Mn, and DOM in sediment pore water, and applied it to algal- (MLW) and macrophyte-dominated (DTH) zones of Taihu Lake over one year. Dissolved Ni concentrations in overlying water exhibited a sharp, synchronous peak during March-April 2021, exceeding the WHO drinking-water limit (70 μg L-1) by up to 1.4 times. In MLW, this Ni pulse was associated with humic-like DOM-mediated Mn(IV) reduction, evidenced by concurrent increases in Ni, Mn, and humic-like DOM, with Mn identified as the dominant predictor in random forest analysis. Partial least squares path modeling (PLS-PM) further indicated that DOM acted as an electron shuttle, accelerating Mn-oxide reduction (λ = 0.971, p < 0.001) and releasing adsorbed Ni. In contrast, Ni mobilization at the DTH site was primarily governed by DOM complexation. Visual MINTEQ simulations showed that more than 55% of dissolved Ni occurred as Ni-DOM complexes. Consistently, fluorescence titration demonstrated strong coordination between Ni and both protein-like and humic-like DOM components (log Km > 3.682; r > 0.939). Fourier transform infrared spectroscopy combined with two-dimensional correlation analysis further confirmed that Ni primarily interacted with aromatic C-H, alkene CC, aliphatic -COOH, alcoholic C-O, and aliphatic C-H functional groups. These findings provide new mechanistic insight into redox-DOM coupling and its control on Ni cycling in algal- and macrophyte-dominated sediments.

Antimony (Sb) pollution has become a significant environmental concern in eutrophic lakes, yet the processes governing its migration and transformation in sediments remain poorly understood. Previous studies have primarily focused on static concentration monitoring, with limited attention given to the dynamic behavior and seasonal toxicity variations of Sb. In this study, high-resolution dialysis (HR-Peeper) and multi-spectral techniques simultaneously obtained information on the changes of Sb, Mn, Fe(II), and dissolved organic matter (DOM) in sediment pore water from Meiliang Bay in Taihu Lake throughout the year. We found that soluble Sb concentrations were highest in April, primarily due to the complexation with tryptophan. Random forest, principal component analysis (PCA), redundancy analysis (RDA), partial correlation analysis, variance partitioning analysis (VPA), partial least squares path modeling (PLS-PM) also confirmed that the outbreak of Sb is related to tryptophan. Further analysis with synchronous fluorescence (SF), Fourier transform infrared (FTIR), and two-dimensional correlation spectroscopy (2D-COS) revealed that Sb(V) was more stably bound to aromatic C-H, alcoholic C-O, alkene C = C, and aliphatic -COOH groups in the tryptophan-like. Additionally, the adsorption of algae, the reduction of microorganisms, and the effect of iron and manganese oxides caused the low mobility of Sb in other months. Our study effectively advances the understanding of Sb mobility and bioavailability in lacustrine sediments and highlights the potential for sudden Sb pollution events in eutrophic lakes, which is crucial for the effective prediction and management of Sb pollution.

The comprehensive effects of environmental dredging on heavy metals (HM) are still uncertain. This study comprehensively evaluates the long-term effects of dredging on the environmental risk and bioavailability of HM (Cu, Ni, Zn, Pb, Cd, Cr, and As) in Lake Taihu, China, by comparing simulated dredged treated (D) and undredged (UD) sediment cores under in-situ conditions for one year. Threshold effect level (TEL), geological accumulation index (Igeo), potential ecological risk index (RI), and ratios of secondary phase and primary phase (RSP) methods were used to assess the environmental risk of sediment HM; and the diffusive gradient in thin-films (DGT) technique was applied to assess the bioavailability of sediment HM. The results indicate that Cd was the most polluted metal assessed by the Igeo and RI method, and that dredging significantly reduced the total content of sediment HM, particularly for Cu, Zn, and Cd, and its Igeo and RI index, but caused a slight effect on its fractionation and distinct effect on RSP index. These indices changed independently and seasonally. Porewater analysis suggested higher HM concentrations in summer and winter may cause corresponding deterioration in overlying water. DGT analysis suggested a large proportion of metal-DOM complexes and showed that dredging reduced the bioavailability of Ni, Cd, and As but had a mixed impact (effective and/or ineffective impact varied with seasons) on other metals. These findings highlight the complexity of dredging effects on sediment HM dynamics, underscoring the importance of seasonal monitoring and multi-geoengineering techniques targeted at total and specific metals.

Arsenic (As) is a metalloid that can accumulate in eutrophic lakes and cause adverse health effects to people worldwide. However, the seasonal process and dynamic mechanism for As mobilization in eutrophic lake remains effectively unknown. Here we innovatively used the planar optodes (PO), high-resolution dialysis (HR-Peeper) combined with fluorescence excitation-emission matrix coupled with parallel factor (EEM-PARAFAC) analysis technologies. We synchronously investigate monthly O-2, As, iron (Fe), manganese (Mn), and naturally occurring dissolved organic matter (DOM) changes in sediments of Lake Taihu at high resolution in field conditions. We find high As contamination from sediments with 61.88-327.07 mu g m(-2) d(-1) release As fluxes during the algal bloom seasons from May to October 2021. Our results show that an increase in DOM, mainly for humic-like components, resulting in high electron transfer capacity (ETC), promoted the reductive dissolution of Fe and Mn oxides to release As. Partial least square-path modeling (PLS-PM) and random forest modeling analysis identified that Mn oxide reductive dissolution directly accelerated sediments As contamination, which is the crucial factor. Understanding crucial factor controlling As release is especially essential in areas of eutrophic lakes developing effective strategies to manage As-rich eutrophic lake sediments worldwide.

This study investigated seasonal variations in spatial distribution, mobilization kinetic and toxicity risk of arsenic (As) in sediments of three representative ecological lakes in Lake Taihu. Results suggested that the bioavailability and mobility of As in sediments depended on the lake ecological types and seasonal changes. At the algal-type zones and macrophyte-type zones, elevated As concentrations were observed in April and July, while these occurred at the transition areas in July and October. The diffusion flux of soluble As ranged from 0.03 to 3.03 ng/ cm2/d, indicating sediments acted as a source of As. Reductive dissolution of As-bearing iron/manganese-oxides was the key driver of sediment As remobilization. However, labile S(-II) caused by the degradations of algae and macrophytes buffered sediment As release at the algal-type and macrophyte-type zones. Furthermore, the resupply ratio was less than 1 at three ecological lakes, indicating the resupply As capacity of sediment solid phase was partially sustained case. The risk quotient values were higher than 1 at the algal-type zones and transition areas in July, thereby, the adverse effects of As should not be ignored. This suggested that it is urgently need to be specifically monitored and managed for As contamination in sediments across multi-ecological lakes.

Rhizoremediation of wetland plants is an environmentally friendly strategy for sediment phosphorous (P) removal, the basic underlying principle of which is the complex interactions between roots and microorganisms. This study investigated the immobilization and mobilization mechanisms of P in the rhizosphere of wetland plants using high-resolution spatial visualization techniques and metagenomic sequencing. Two-dimensional visualization of the spatial distribution of P, iron (Fe) and manganese (Mn) indicated that the sequestration of Fe-oxides rather than Mn-oxides caused the depletion of labile P, resulting in an increase in the Fe-adsorbed P fraction. Plants altered the rhizospheric environments and P-cycling microbial community to mobilize low-availability P from sediments. Mineral P solubilization and organic P mineralization were enhanced by local acidification and increased phosphatase activity, respectively. Microbial P mobilization also increased with increasing relative abundances of P solubilization and mineralization genes (gcd and phnW) and decreasing P transportation genes (ugpA, ugpB, and pit) genes in the rhizosphere. These processes led to the remobilization of 10.04% of inorganic P, and 15.23% of organic P, in the rhizosphere during the incubation period. However, the resupply of P via the above processes did not compensate for the depletion of rhizospheric P via root uptake and mineral sequestration. Our results provide novel insights into the mechanisms of rhizospheric P cycling, which will help to inform future phytoremediation strategies.

Changes in the oxygen and acidic environments of water caused by algal blooms in lakes aggravate the uncertainty of the eutrophication process, profoundly influencing water ecosystems and lake biogeochemical cycles. This study aimed to detail the mechanisms of benthic oxygen and acid processes by determining high-resolution and high-quality chemical gradients and acquiring heterogeneous data for diurnal changes in dissolved oxygen (DO)/pH at the water-sediment interface (SWI) during different stages of algal degradation. Planar optode (PO) systems were used to obtain dynamic two-dimensional (2D) images of DO/pH at a laboratory microcosm interface. The benthic gradient and diurnal variation of DO/pH at the SWI were jointly regulated by the photosynthesis/respiration and migration behaviors of algae, through their influence on the water-carbon chemistry. The DO/pH at the SWI showed unique diurnal variation characteristics at different stages of algal degradation; however, characteristics consistent with the diurnal variation in photosynthesis were limited to the algal growth period. The increase in DO/pH during the daytime resulted from O2-rich and carbonate hydrolysis, to compensate for the reduction in CO2 saturation caused by algal photosynthesis. Nocturnal DO/pH decreased owing to O2 depletion and H+ release, because of increased water CO2 content from algal respiration. When photosynthesis and respiration were inhibited, or not smooth, DO/pH showed a limited increase with uncertainty. The sediment was not completely anaerobic, and DO/pH penetrated to - 20 mm and even to the bottom of the interface (- 40 mm) as a result of algal migration, whereas DO was exhausted and high pH areas transferred to sediments following algal decay. Sediments acted as storage pools in alkaline environments, which posed a potential risk for water eutrophication. The trajectory of algal activity at the SWI was highly consistent with the dynamic variation in DO/pH. Our findings provide new insights for in situ tracking and early prediction of algal blooms, and can be used to formulate a theoretical basis for the mechanism of eutrophication processes and for exploring new algal control technologies.

Tungsten (W) can be toxic to aquatic organisms. However, the spatiotemporal characteristics and controlling factors of W mobility during harmful algal blooms (HABs) have rarely been investigated. In this study, simultaneous changes in soluble W, iron (Fe), manganese (Mn), and ultraviolet absorbance (UV254) in the sedimentwater interface (SWI) were measured monthly using high-resolution peeper (HR-Peeper) devices. Laboratory experiments were conducted to verify the effects of environmental factors on W release. From May 2021 to October 2021, the concentration and flux of soluble W were higher than in other months. In addition, from May to October, DMAX (the depth at which the maximum concentration occurs on each profile) was 30-50 mm below the SWI, rather than the maximum depth. Principal component analysis (PCA) also divided the year into two periods, designated W-stable (December 2020, January, March, April and November 2021 with low soluble W concentration) and W-active periods (from May 2021 to October 2021 with high soluble W concentration). Laboratory experiments showed that both warming and anoxic conditions caused simultaneous release of soluble W, Fe(II), Mn, and dissolved organic matter (DOM), with strong correlations among soluble W, Fe(II), Mn. Partial least squares path modeling (PLS-PM) and random forest model showed that DOM directly affected W release or indirectly affected W release through promoting ferromanganese (oxyhydr)oxides reduction under warming and anaerobic conditions. The results of the field investigation showed that, in the W-stable period with low T, high DO, and an oxic SWI, the concentrations of soluble W, Fe, Mn, and DOM were low. The redundancy analysis (RDA) showed that these months were mainly affected by water DO. The significant and strong positive correlation among soluble W, Fe and Mn indicated that soluble W was probably scavenged by Fe/Mn (oxyhydr)oxides in the oxic water during the W-stable period. The W-active period corresponded to the cyanobacterial HABs (cyanoHABs) outbreak, with higher T, lower DO, and a more anoxic SWI. During this period, the concentrations of soluble W, Fe, Mn, and DOM were high and their correlations were stronger. RDA showed that these months were mainly affected by T, UV254, soluble Fe and Mn. These results indicated that reductive dissolution of Fe/Mn (oxyhydr)oxides driven by DOM generated in W-active period, especially cyanoHAB-derived DOM, mainly caused soluble W release. These results reveal the coupling relationship between cyanoHABs and W release and emphasize the need for prevention and control of heavy metal release in eutrophic lakes.

Arsenic (As)-contaminated water restoration is extremely challenging because As remobilization from sediments can result in episodic or long-term release of As to the overlying water. In this study, by combining high -resolution imaging techniques with microbial community profiling, we examined the feasibility of utilizing the rhizoremediation of submerged macrophytes (Potamogeton crispus) to decrease As bioavailability and regulate its biotransformation in sediments. Results showed that P. crispus considerably decreased the rhizospheric labile As flux to lower than 4 pg cm-2 s- 1 from larger than 7 pg cm-2 s- 1, suggesting its effectiveness in promoting As retention in sediments. Iron plaques induced by radial oxygen loss from roots decreased the mobility of As by sequestering it. Additionally, Mn-oxides may act as an oxidizer for the oxidation of As(III) to As(V) in the rhizosphere, which can further increase the As adsorption owing to the strong binding affinity between As(V) and Fe-oxides. Furthermore, microbially mediated As oxidation and methylation were intensified in the microoxic rhizosphere, which decreased the mobility and toxicity of As by changing its speciation. Our study demonstrated that root-driven abiotic and biotic transformation contribute to As retention in sediments, which lays a foun-dation for applying macrophytes to the remediation of As-contaminated sediments.

For soils and sediments, which are complex and heterogeneous, root-triggered processes, bioturbation of benthic communities, and local decomposition of reactive organic materials can greatly increase their biogeochemical heterogeneity. In practice, common monitoring methods can only be used to determine the centimeter- to millimeter-scale heterogeneity from vertical or horizontal one-dimensional profiles. However, significant heterogeneity exists in both soils and sediments on the millimeter to sub-millimeter scales. Therefore, in-situ and high-resolution sampling and imaging methods are essential to capture the spatial and temporal heterogeneity of soils and sediments. This article reviews micro-scale sampling methods in soil and sediments, including diffusive equilibration in thin films (DET), diffusive gradient in thin films (DGT), planar optodes (PO), nanoparticle- and microparticle-based luminescence imaging, and soil zymography. Besides, we introduce their imaging principles and approaches in detail, and discuss some problems and solutions during imaging. Micro-scale sampling and imaging methods have given us many insights into the biogeochemical processes in soils and sediments, but the full potential of these methods has not been exhausted yet. Finally, the potential directions for the development of micro-scale sampling methods in the study of complex biogeochemical processes in heterogeneous soils and sediments are prospected.

The cycling of iron (Fe) and carbon in the rhizosphere of submerged plants and the associated impact on organic carbon (OC) sequestration are poorly understood. We detected the spatiotemporal distribution of CO2 using a planar optode in the rhizosphere of a common submerged plant as an indicator of OC mineralization. We found that the rhizosphere was a hot spot of CO2 and that the CO2 concentration decreased rapidly from the root tip zone (maximum of 19.68 +/- 0.60 matm) to the root base zone (maximum of 12.10 +/- 0.29 matm), with the trend of change being the opposite of that of O2. The Fe plaques in the root tip zone had the highest concentration of amorphous Fe. However, the concentration of Fe-bound OC was not significantly different among the different root parts. Because the relative abundances of ferrobacteria decreased in the order tip (8.45%) > base (4.05%) approximate to bulk sediment (3.05%), the enrichment of CO2 in the rhizosphere was attributed to dissimilatory Fe(III) reduction, O2 induced microbial respiration, and root respiration. Our conclusion was that the root tip of submerged plants is an efficient engine for Fe oxidation-carbon sequestration and Fe reduction-carbon mineralization processes, which may affect the stability of sediment carbon pools.

Capping and oxidation by lanthanum-modified bentonite (LMB) and calcium nitrate (CN) has a dual effect of deep phosphorus (P)/arsenic (As) clearance and surface P/As blockade. However, little information is available on the effect of LMB and CN on heavy metals. In this study, we hypothesize that LMB and CN exerted the same synergistic effect on heavy metals as P and As. We verified this through Rhizon samplers, diffusive gradients in thin films technology (DGT) and planar optode (PO) methods. The results showed that individual and combined LMB and CN treatments temporarily decreased but eventually increased the dissolved oxygen of the sediment-water interface (SWI). DGT-labile sulfide in the surface 110 mm sediment, soluble Fe(II) and DGT-labile Fe(II) in the surface 80 mm sediment were eliminated within 30 days by CN and LMB + CN treatments. A temporary sharp increase in soluble Fe, Mn, Co, and DGT-labile Mn, Co, Cu, and Ni was observed in CN and LMB + CN groups probably due to sulfide oxidation and carbonate dissolution. LMB + CN group showed a less-intense increase in DGT-labile metals and less metal release than the CN group (inferred from the total metal content). This indicates that LMB and CN had a synergistic effect on heavy metals. When using the LMB + CN treatment, LMB partly adsorbed and blocked metal release in sulfide and carbonate bound forms and finally transformed them into Fe and Mn oxides and residual forms. We suggest that CN should be combined with capping agents (at an appropriate pH) to compact sediments and block metal exchange at the SWI.

Vanadium (V), a hazardous environmental contaminant, can be highly toxic to aquatic or even human life. Nonetheless, knowledge of its redox geochemistry and mobility in sediments, especially those of eutrophic lakes, remains limited. In this study, we combined in situ high-resolution sampling and laboratory simulation experiments for monitoring soluble and labile V to reveal the mobilization mechanism of V in the sediment of Lake Taihu. The results showed that the concentration of soluble V (1.18-5.22 & mu;g L-1) exceeded the long-term ecotoxicology limitation proposed by the government of the Netherlands. The highest value appeared in summer (July to September), with an average concentration of 3.87 & mu;g L-1, which exceeded the short-term exposure limit. The remobilization of V in summer was caused by the combined effect of the reduction of Fe(hydr)oxides and dissolved organic matter (DOM) complexation, which accelerated the release of associated Fe-bound V and increased the solubility of DOM-V. Additionally, V showed high mobility in winter, owing to the species of V(III)/ V(IV) being oxidized to V(V) with higher solubility. It is noteworthy that the elevated remobilization of V in sediments increases the risk of V release from sediments, which poses the threat of water V pollution in Lake Taihu.

Antimony (Sb) is more mobile in lacustrine sediments with seasonal warming. However, the mechanisms of Sb mobility in sediments are still unclear, especially considering the interactions among Sb, iron (Fe), manganese (Mn), and dissolved organic matter (DOM). In this study, high-resolution dialysis (HR-Peeper) and multi-spectral techniques simultaneously investigated changes in Sb, Fe, Mn, and DOM in two different ecological types (algal and grass) sediments with increasing temperature. We found that the dissolved Sb rapidly increased with the increase in temperature. The oxidation of Sb(III) to Sb(V) by Fe/Mn oxides in oxygen (O2) rich overlying water and surface sediment layers was one of the reasons for Sb concentration enhancement in pore water. Further, using excitation-emission matrix and parallel factor analysis (EEM-PARAFAC), synchronous fluorescence (SF) spectroscopy, fourier transform infrared (FTIR) spectroscopy, and two-dimensional correlation spectroscopy (2D-COS) revealed that complexation with DOM was the other reasons for Sb concentration increasing in sediments. This was demonstrated by the similar distribution pattern and significant correlation between Sb and tryptophan-like components. Titration experiments further revealed that Sb was more stably bound to tryptophan-like components in the aromatic C-H (660 cm-1), alcoholic C-O (1115 cm-1), alkene CC (1615 cm-1), and carboxylic acid OH (3390 cm-1) groups. The tryptophan-like components from the algae region had a higher binding force than that from the macrophytes region. Our study effectively promotes an understanding of Sb mobilization in lacustrine sediments.

Internal phosphorus (P) loading can increase the P level in the water column and further sustains cyanobacterial blooms. This study focused on the role of benthic fauna bioturbation in affecting the sediment P release and the P level of water column in a eutrophic lake, Lake Taihu. The macrofauna density decreased from 4766.56 +/- 10541.80 ind/m(2) in 2007 to 345 +/- 447.63 ind/m(2) in 2020 due to the frequent bottom-water hypoxia in Lake Taihu. The reduced macrofauna density majorly resulted from Grandidierella taihuensis, Limnodrilus hoffmeisteri, and Tanypus chinensis larvae, and their total density decreased by approximately 97% in 2020 compared to 2007. G. taihuensis, one of the major benthic faunas, was further used as a representative to investigate the effects of bioturbation on sediment P release using high-resolution sampling and imaging techniques. The results show that G. taihuensis can increase the O-2 penetration depth by more than 20 mm through bio-irrigation, and causes the redox conditions in burrows and surrounding sediments to change dramatically within a few minutes due to the intermittent ventilation. Subsequent oxidation of the soluble Fe(II) led to the formation of Fe-oxide bound P in the surface sediments, thereby increasing the P retention in the sediments. When the G. taihuensis density was 1563 ind/m(2) at the sampling site, approximately 0.12 g m(-2) yr(-1) P can be retained in sediments. As previous studies have shown that L. hoffmeisteri and T. chinensis played a similar role in increasing the P retention in sediments through their bioturbation activities, the sharp decline in benthic fauna density and burrowing ac-tivities in Lake Taihu should be an important reason for maintaining the high P level in the water column by decreasing the P retention in sediments.

Mobilization of trace metals in the rhizosphere of macrophytes is controlled by root-driven chemical changes, especially the steep gradients of O2 and pH from the rhizosphere to bulk sediments. Here, the O2 and pH dynamics, and the distribution of trace metal, in the rhizosphere of Vallisneria spiralis were obtained using planar optodes and diffusive gradients in thin films, respectively. Radial O2 loss (ROL) and acidification occurred on all visible roots of V. spiralis and exhibited highly spatiotemporal dynamics depending on the root growth and various environmental conditions. Trace metals showed different mobilization mechanisms in the rhizosphere. ROL and produced Fe(III) (oxyhydr)oxides decreased the mobility of Fe, As, Co, V and W in the rhizosphere. However, Mn, Ni and Cu exhibited greater mobility in the rhizosphere than bulk sediments as a result of the oxidation of metal sulfide and proton-induced dissolution of minerals. In particular, Co and Ni presented increased activity at the interface between rhizosphere and bulk sediment, which was attributed to the redox dissolution processes of Fe and Mn as a result of ROL and rhizosphere acidification. These results provide new insights into the roles of macrophyte root-induced O2 and pH changes in controlling trace metal mobility in sediments.

Submerged plants and lanthanum-modified bentonite (LMB) have important applications for the remediation of contaminated sediments; however, their combined effect on arsenic (As) removal has not been comprehensively evaluated. In this study, the physicochemical properties and changes in soluble As in sediments treated with LMB, Vallisneria spiralis (V. spiralis), and LMB + V. spiralis were observed at three time points (days 15, 35, and 66), and the changes in microbial and As species in sediments on day 66 were analyzed. LMB + V. spiralis treatment was the most effective for As removal. On day 66, the average concentrations of soluble As at a depth of 0-100 mm decreased by 12.71%, 48.81%, and 59.73% following treatment with LMB, V. spiralis, and LMB + V. spiralis, respectively. Further analysis showed that LMB is more effective at removing As(V) than V. spiralis, while V. spiralis is more effective at removing As(III), and the combination of LMB + V. spiralis is more effective for removing both As(III) and As(V) than individual LMB and V. spiralis treatments. LMB + V. spiralis enhanced the transformation of mobile As to Fe2O3/oxyhydroxide-bound As in sediments and the activity of As-oxidizing microorganisms. LMB promoted the growth of V. spiralis and enhanced the removal of As. This study indicates that this combination is an effective method for removing mobile As from sediments, and could effectively inhibit the release of As from sediments to overlying water.

Abstract For soils and sediments, which are complex and heterogeneous, root-triggered processes, bioturbation of benthic communities, and local decomposition of reactive organic materials can greatly increase their biogeochemical heterogeneity. In practice, common monitoring methods can only be used to determine the centimeter- to millimeter-scale heterogeneity from vertical or horizontal one-dimensional profiles. However, significant heterogeneity exists in both soils and sediments on the millimeter to sub-millimeter scales. Therefore, in-situ and high-resolution sampling and imaging methods are essential to capture the spatial and temporal heterogeneity of soils and sediments. This article reviews micro-scale sampling methods in soil and sediments, including diffusive equilibration in thin films (DET), diffusive gradient in thin films (DGT), planar optodes (PO), nanoparticle- and microparticle-based luminescence imaging, and soil zymography. Besides, we introduce their imaging principles and approaches in detail, and discuss some problems and solutions during imaging. Micro-scale sampling and imaging methods have given us many insights into the biogeochemical processes in soils and sediments, but the full potential of these methods has not been exhausted yet. Finally, the potential directions for the development of micro-scale sampling methods in the study of complex biogeochemical processes in heterogeneous soils and sediments are prospected. Graphical abstract