Quantifying the effects of submerged aquatic vegetation on internal loading in lake: A modeling study of the largest shallow lake in North China

Elucidating the Composition and Transformation of Dissolved Organic Matter at the Sediment-Water Interface Using High-Resolution Mass Spectrometry

The exchange and transformation of dissolved organic matter (DOM) at the sediment-water interface are crucial factors in regulating watershed biogeochemistry, with the molecular composition of DOM serving as a pivotal determinant in elucidating this process. High-resolution mass spectrometry (HRMS) is an effective tool for resolving the composition of DOM. By analyzing the compositional characteristics of DOM at the sediment-water interface under three different salinities at the same latitude region in northern China, the findings indicate certain variations in component characteristics of DOM between low-salinity inland waters and high-salinity seawaters, with the former exhibiting greater molecular diversity and higher molecular weights, whereas the latter displayed a higher saturation and bioavailability. Notably, the presence of more CHOS substances in the low-salinity inland waters underscores the transformation of the DOM influenced by terrestrial inputs and anthropogenic activities. Conversely, the presence of more CHO and CHNO substances in high-salinity seawater underscores the microbial effects. The chemical transformation process from overlying water to pore water to sediments was characterized by methylation, hydrogenation, decarboxylation, and reduction, as determined by calculating the relations between the H/C and O/C ratios of different compound types. These findings indicate that HRMS can yield more refined results in revealing the process of DOM at the sediment-water interface under different environments, which provides a more reliable basis for a deeper understanding of the source-sink mechanism of sediment organic matter.

Integrated nonstationary and uncertain analysis of coupled relationship of hydrological connectivity and water level in a highly fragmented wetland

Understanding the relationship between hydrological connectivity (HC) and water level (WL) is crucial for effective water resource management and wetland restoration. However, current knowledge regarding this relationship is limited. This study proposed an integrated nonstationary and uncertain analysis framework (INUAF) to investigate the HC-WL relationship with reference to the Baiyangdian wetland, which is a fragmented wetland in North China. With the INUAF, the interannual and intra-annual variations of both HC and WL were examined, together with the wavelet coherence and lag effects between the two variables at multiple scales. The results highlighted marked nonstationarity in HC, WL, and the relationship between them. Scale-dependent lag effects revealed that HC lags WL by 37 days (131 days) at the 1 a scale (4 a scale), and leads WL by 190 days at the 8 a scale, indicating a complex coupled relationship between HC and WL. Additionally, the INUAF was applied to evaluating the uncertainty in the response of lagged HC to varied WL. Results indicated that every 0.2-m increase in WL led to a 2.2%-2.4% higher probability of maintaining high HC for WL between 6.0 and 8.0 m, but a 10%-11% higher probability for WL between 8.0 and 9.0 m. We suggest that a WL of > 8.4 m would produce a probability of > 50% for achieving high HC. These findings provide valuable insights into the HC-WL relationship and could contribute to wetland restoration efforts.

Effect of common ions aging treatment on adsorption of phosphate onto and control of phosphorus release from sediment by lanthanum-modified bentonite

The objective of this work was to explore the influence of combined aging treatment using Na⁺, Ca²⁺, Cl^-, HCO₃^- and SO₄^2- on the adsorption of phosphate (H_iPO₄^i-3) onto and the restraint of internal phosphorus (P) migration into overlying water (OW) by lanthanum modified bentonite (LMB). To achieve this aim, the adsorption characteristics and mechanisms of H_iPO₄^i-3 onto the raw and aged LMBs (named as R-LMB and A-LMB, respectively) were comparatively studied, and the effects of R-LMB and A-LMB treatments (addition and capping) on the migration of P from sediment to OW were comparatively investigated. The results showed that the combined aging treatment of R-LMB with Na⁺, Ca²⁺, Cl^-, HCO₃^- and SO₄^2- inhibited the adsorption of H_iPO₄^i-3. Similar to R-LMB, the precipitation of H_iPO₄^i-3 with La³⁺ to form LaPO₄ and the ligand exchange between CO₃^2- and H_iPO₄^i-3 to form the inner-sphere lanthanum-phosphate complexes are the important mechanisms for the H_iPO₄^i-3 uptake by A-LMB. The R-LMB addition and capping can be effective in the suppression of endogenous P release to OW under hypoxia conditions. The inactivation of diffusive gradient in thin film-unstable P (DGT-UP) and potentially mobile P (PM-P) in sediment acted as a key role in the restraint of internal P release to OW by the R-LMB addition, and the immobilization of DGT-UP and PM-P in the topmost sediment played a key role in the interception of endogenous P migration into OW by the R-LMB capping. Although the Na⁺/Ca²⁺/Cl^-/HCO₃^-/SO₄^2- combined aging treatment had a certain negative effect on the efficiencies of LMB addition and capping to hinder the liberation of P from sediment into OW, the A-LMB addition and capping still can be effective in the control of sediment internal phosphorus pollution to a certain degree. The results of this work indicate that LMB has a high potential to be used as a capping/amendment material to control internal phosphorus pollution.