Bernd Lennartz

Coastal peatlands are increasingly threatened by seawater intrusion and salinity fluctuations under climate change. This study investigated nitrogen dynamics following a storm surge event in a coastal peatland (Hütelmoor) in Northeast Germany, combining surface water monitoring and controlled soil leaching experiments at two locations: a near-natural location (Heiligensee) and a rewetted, historically drained location (Moorhof). Surface water observations revealed pronounced spatial differences in post-flood nitrogen responses. At Heiligensee, ammonium (NH ₄ ⁺ ) concentrations reached up to ~ 179 µmol L ^–1 in early 2019 and remained elevated for several weeks, whereas Moorhof showed lower concentrations with rapid declines following the flood. Soil leaching experiments demonstrated that NH ₄ ⁺ release responded to salinity exposure but was also modulated by location- and depth- specific soil hydro-physical properties. Particularly, subsoils (30–40 cm) at Moorhof, characterized by low porosity and low saturated hydraulic conductivity (Ks), released the highest NH ₄ ⁺ amounts (up to 3.86 mg per sample) under brackish and saline conditions, identifying them as hotspots for nutrient release. Principal component analysis (PCA) showed that the first two components explained 81.5% of the total variance in NH ₄ ⁺ release patterns, separating soils along a structural gradient (PC1: soil organic matter content, bulk density, porosity) and a hydraulic–nutrient gradient (PC2: macroporosity, Ks, NH ₄ ⁺ release). These findings emphasize the need to account for both surface water dynamics and subsurface soil heterogeneity in coastal peatland restoration. Identifying location- and depth-specific nitrogen risks is essential to improve nutrient management and ecosystem resilience under future salinization scenarios. Graphical Abstract

The loss of carbon from peatlands occurs through gaseous emissions and a substantial fraction from aquatic fluxes, specifically dissolved organic carbon (DOC), during mineralisation and degradation processes. Our study hypothesises that DOC production is dependent on pore size, with higher concentrations occurring in finer pores. To investigate this, pore water was extracted at specific pressure heads (-60 and -600 hPa), representing macro- and mid-size pore domains, from degraded peat samples. Soil organic matter content was measured at 34 wt% in the topsoil and 57 wt% in the subsoil. Notably, the more degraded topsoil exhibited significantly higher average DOC concentrations than the subsoil, with levels 1.5 times greater at -60 hPa and 2.4 times higher at -600 hPa. These trends indicate that degraded peat soils are prone to release greater amounts of DOC. Additionally, DOC concentrations in topsoil samples were consistently higher at -600 hPa compared to -60 hPa.The negative correlation between soil organic matter (SOM) and DOC at -600 hPa (r = - 0.53; p < 0.0001) aligns with degradation-driven reductions in SOM and porosity. Degraded topsoil exhibited high DOC variability for SOM < 40 wt%, stabilising below 50 mg/L for SOM ≥ 40 wt%. Through a graphical illustration, we infer that the elevated DOC export is likely due to the higher surface-to-volume ratio observed in mid-sized pores (-60 to -600 hPa), further enhanced by the dual-porosity structure of the degraded topsoil. This structural variation contributes to differences in carbon turnover rates. Additionally, microbial communities and their abundance differ across pore size classes, causing pore size-dependent reactions that influence DOC export.

The hydro-physical properties of peat play a pivotal role in regulating the water, nutrient, and carbon cycles of peatland ecosystems. Despite their importance and complexity, our understanding of peat hydraulic properties remains limited. In this study, we compiled a comprehensive global database of the peat physical, hydraulic, and chemical properties, including bulk density (BD), porosity, macroporosity, saturated hydraulic conductivity (Ks), carbon content, and carbon density, encompassing tropical peatlands, northern fens, northern bogs, and permafrost regions. Our primary objective was to examine how these properties vary along a BD gradient across different climate zones. The results revealed a robust linear relationship between carbon density and BD for peat types with carbon content exceeding 35% (R2> 0.92, p < 0.001), suggesting that these functions can serve as reliable tools for estimating the carbon stock of peatlands. However, the specific functions differed between peat types and climate zones. Total porosity was found to decrease linearly as BD increased, while macroporosity followed a power-law relationship with BD. These trends were consistent across all peat types, underscoring a strong and reliable association between BD and both total porosity and macroporosity. Additionally, Ks exhibited a general decline with increasing BD, with the relationship characterized by log-log functions that varied among peat types and climate zones. This indicates that Ks is significantly influenced by the peat-forming vegetation such as wood, sphagnum, sedge, and the prevailing climatic conditions of the peatland. This study demonstrated that the key peat hydro-physical-chemical parameters—including carbon density, porosity, macroporosity, and Ks can be reliably estimated using the BD, with relatively high coefficients of determination (R2 > 0.4), highlighting the critical importance of determining BD as a proxy for estimating other hydro-physical properties of peat when direct measurements are unavailable.Keywords: peat; physical and hydraulic properties; bulk density; carbon density; saturated hydraulic conductivity, permafrost peatlandsCorresponding author: Haojie Liu (haojie.liu@uni-rostock.de)Phone: +49 (381) 498 3193; Fax: +49 (381) 498 3122

The primary objectives of peatland restoration are to reduce greenhouse gas emissions and maintain water quality. However, the effects of human activities, such as drainage and rewetting, on pore water quality remain insufficiently understood. In this study, we synthesized pore water quality data from 197 northern peatlands, encompassing natural, drained, and rewetted systems. Our analysis revealed that drainage significantly increases the concentrations of dissolved organic carbon (DOC), ammonium, and phosphate in pore water compared to natural peatlands. While rewetting reduced these concentrations, they remained elevated relative to natural systems. Notably, pore water concentrations in rewetted peatlands were closely linked to water table levels, with peak concentrations observed under inundated conditions, particularly in fen peatlands. Over an approximately 30-year observation period, no consistent temporal trends in pore water quality following rewetting were identified. These findings highlight the complexity of pore water quality responses to rewetting and the importance of long-term monitoring for optimizing peatland restoration practices.

Coastal peatlands are vulnerable to environmental changes, including salinity fluctuations caused by storm surge-induced seawater intrusion. This study investigates ammonium (NH₄⁺) release patterns during simulated sea flooding event in two locations of a coastal peatland in Northeast Germany (Hütelmoor): a near-natural location and a historically drained and rewetted location. Undisturbed soil samples (N=18) were collected from two depths (0–10 cm and 30–40 cm) at each location. A leaching experiment was conducted using three salinity treatments (N=3): groundwater (control,

Pollution from industrial wastewater containing dyes poses a significant health concern in many countries, necessitating advanced remediation techniques. This study explores using a magnetized Kaolin filter cake (KFC)-Fe3O4 composite, synthesized through a co-precipitation method, as an adsorbent for removing Reactive Black 5 (RB5) from aqueous solutions. This method enables quick and easy separation of the adsorbent, resulting in no secondary pollution. The synthesized adsorbent was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) techniques to analyze its crystalline nature, microstructures, functional group, and surface area respectively. The efficiency of the adsorbent for dye removal in a batch system was examined by studying various parameters, including pH, contact time, adsorbent dosage, and initial dye concentration. To optimize the RB5 removal procedure, a Box-Behnken design (BBD) was employed under response surface methodology (RSM). The pseudo-second-order model best described the adsorption kinetics, while the Langmuir equation accurately described the isotherm. The maximum adsorption capacity was determined to be 92.84 mg/g. Thermodynamic studies revealed that the adsorption of RB5 onto the Kaolin filter cake-Fe3O4 composite is spontaneous and endothermic. Notably, the adsorption activity of RB5 by KFC-Fe3O4 composite remained effective even after five successive cycles. Overall, the Kaolin filter cake-Fe3O4 composite is a highly efficient adsorbent for treating aqueous solutions containing dyes, with easy separation from the solution using a magnet after the reaction.

The discharge of textile effluents containing dyes poses severe environmental risks. This study aimed to develop a Fe_3 O_4–HTM (magnetite–heat-activated termite mound) composite via the coprecipitation method for the adsorption of Basic Blue 41 (BB41) dye from textile wastewater under batch conditions. The Fe_3 O_4–HTM composite was characterized using BET (surface area), XRD (crystalline structure), FTIR (functional groups), and SEM (microstructure) analyses, confirming the successful synthesis of Fe_3 O_4–HTM. Comprising 80% HTM by mass, the composite demonstrates economic viability. Using batch experiments and a Box-Behnken design, the adsorption performance of Fe_3 O_4–HTM for BB41 dye removal from aqueous solutions was evaluated. Optimization of the sorption process revealed that a dosage of 2.6 g/L, a contact time of 47.5 minutes, a temperature of 60°C, and an initial dye concentration of 100 mg/L resulted in a BB41 dye removal efficiency of 98%. Additionally, Fe_3 O_4–HTM effectively removed BB41 dye from real wastewater samples, achieving a removal efficiency exceeding 80%, highlighting the improved sorption properties of the modified termite mound. The spent Fe_3 O_4–HTM was easily separated from the treated solution using an external magnet and successfully recovered. Its reusability demonstrated a dye removal efficiency of 78% after four cycles, without compromising its magnetic properties. Overall, the magnetically separable Fe_3 O_4–HTM composite shows significant potential for the treatment of textile wastewater.