Fereidoun Rezanezhad

Landfills are one of the largest anthropogenic sources of methane (CH ₄ ), and hot-spots of CH ₄ emissions in landfill cover soils can enrich microbes that oxidize CH ₄ to carbon dioxide (CO ₂ ). CH ₄ oxidation rates are modulated by multiple variables including soil moisture and temperature, although the interactive effects of these factors on CH ₄ oxidation rates have not been well-studied. Here, we conducted closed-headspace batch incubations with cover soil from a former landfill in Ontario, Canada to measure the variations in CH ₄ consumption and CO ₂ efflux rates associated with combined variations in soil moisture and temperature. Soil samples were incubated under a factorial design of 5 soil moisture contents (20%, 40%, 60%, 80%, and 100% water-filled pore space; %WFPS), and 4 temperatures (1, 15, 25, and 35 °C). At each temperature and moisture combination, CH ₄ was spiked into the headspace through multiple consecutive injections, and headspace CH ₄ and CO ₂ concentrations were measured to calculate CH ₄ consumption and CO ₂ efflux rates. The maximum CH ₄ consumption rate was observed at the moderate soil moisture and temperature conditions (330 ± 12.3 nmol h ^-1 g DW ^-1 at 60% WFPS and 25 °C), while the maximum CO ₂ efflux rate was observed at the maximal WFPS and temperature conditions of the experiment (652 ± 85.0 nmol h ^-1 g DW ^-1 at 100% WFPS and 35 °C). A diffusion-reaction model was fit to the observed data to represent the effects of temperature and soil moisture on the CH ₄ consumption and CO ₂ efflux rates. The model predicted similar optimal conditions as those observed for both the CH ₄ consumption and the CO ₂ efflux rates. The modeling and experimental results show that the dominant controls on the optimal soil moisture for CH ₄ consumption are the interactive effects of moisture limitation of microbial activity and of gas (CH ₄ and oxygen) diffusion, whereas for the CO ₂ effluxes, the dominant controls were the interactive effects of moisture limitation of gas (oxygen) diffusion and solute mobility. These results provide insight into how seasonal changes in soil moisture and temperature could impact CH ₄ oxidation rates, and therefore also net CH ₄ emissions, in landfill cover soils and other environments.

Peatlands hold up to one-third of the global organic carbon (C) stock and are considered a critical C sink. Climate models project that the rate of warming in northern peatlands will continue throughout the 21st century, with the greatest warming occurring during the non-growing season (NGS), which is poorly represented in current in-situ measurements. As a result, the contribution of NGS fluxes to annual peatland CO ₂ budgets remains uncertain. Remotely sensed and modeled data products offer a potential means to estimate year-round fluxes, but their performance in peatland ecosystems has not been fully evaluated. In this study, we used the remotely sensed and modeled Soil Moisture Active Passive Level 4 Global Daily EASE-Grid C NEE (SMAP-NEE) data product to acquire 9 years (2015–2023) of SMAP-NEE data for five peatlands. We compared these values to a subset of year-round eddy covariance NEE (EC-NEE) measurements within this time frame at each of the five peatland sites. The analyses showed that the SMAP-NEE data product reports a stronger growing season (GS) sink and a weaker NGS source than the EC-NEE measurements. Using the relationship between SMAP-NEE and EC-NEE, we produced a Corrected-SMAP-NEE dataset, which provided an estimate of seasonal and annual carbon dioxide (CO ₂ ) budgets. Our data analyses of the Corrected-SMAP-NEE dataset showed that NGS CO ₂ emissions represented a highly variable proportion (33%–256%) of the GS CO ₂ uptake, that reduced the annual CO ₂ sink strength proportionally. This work demonstrates the necessity of monitoring during the NGS and highlights the importance of incorporating peatland data into model training to improve CO ₂ flux estimates in these environments.

Bioretention cells are a popular type of green stormwater management infrastructure. In urban catchments, they reduce the ‘flashiness’ and volume of surface flow resulting from storms by promoting storage, groundwater infiltration, and evapotranspiration. Although they can also remove pollutants from stormwater runoff, their effectiveness in reducing phosphorus (P) loads is highly variable, in part because of the complex biogeochemical cycling of P in bioretention cell systems. Using time series solid-phase P concentrations measured over a 9-year period on the filter medium from a multi-cell bioretention system in Mississauga, Ontario, Canada, we estimated average total P (TP) accumulation rates of 88 mg P kg⁻¹ y⁻¹ in the top 10 cm and 33 mg P kg⁻¹ y⁻¹ at depths of 25–45 cm. These accumulation rates translate into a net sequestration of TP by the filter medium across the entire system of roughly 4 kg per year. The linear TP concentration versus time trends further imply that the filter medium has yet to reach P saturation. The system can, therefore, be expected to continue reducing stormwater runoff P loads in the foreseeable future. On cores collected in 2019 and 2021 (7 and 9 years post-construction), the depth-dependent solid-phase P chemical speciation was analyzed using an established sequential chemical extraction protocol. The more reactive P fractions and organic P compounds were generally enriched in the upper 10 cm of the filter medium. Accumulation of P associated with organic matter contributed most to the net TP accumulation on the filter medium. Non-metric dimensional scaling (NMDS) further indicated that variations in the concentrations of TP and the P fractions among filter media samples were mainly linked to variations in the concentrations of the redox-sensitive metals iron and manganese and that of organic carbon. Overall, our study highlights that the spatial and temporal distributions and chemical speciation of P can help unravel the mechanisms controlling P abatement of urban stormwater by bioretention systems.

In soils contaminated with petroleum hydrocarbons (PHCs), water table fluctuations (WTFs) affect the kinetics of PHC biodegradation and the generation and transport of carbon dioxide (CO ₂ ) and methane (CH ₄ ). In this study, a 300‐day‐long column experiment was conducted to simulate the effects of WTFs on the aerobic and anaerobic PHC biodegradation pathways. Eight columns were each filled with 45 cm of PHC‐contaminated soil cores. Four columns simulating WTFs were subjected to cycles of drainage and imbibition. The remaining columns remained fully saturated, simulating a static water table. Except for the controls, the columns received injections of ethanol or ethanol plus naphthalene after 111 days of pre‐equilibration. Over the duration of the experiment, soil moisture, surface CO ₂ and CH ₄ effluxes, dissolved concentrations and δ ¹³ C compositions of CO ₂ and CH ₄ , dissolved naphthalene concentrations, and geochemical parameters were monitored. A reactive transport model representing 13 biogeochemical reaction pathways was verified against the acquired data. The experimental and modeling results confirmed that the prevailing pathway generating CH ₄ shifted from hydrogen‐based to acetate‐based methanogenesis in the ethanol and ethanol‐plus‐naphthalene‐spiked columns, while CH ₄ oxidation played a key role in controlling the CH ₄ efflux during the drainage periods. The WTF columns exhibited significantly faster naphthalene attenuation, while the cumulative CO ₂ and CH ₄ effluxes were about twice as high. These observations were attributed to the periodic incursion of air during the WTFs, which increased the porewater‐air interface area for gas transfer while also accelerating the aerobic degradation of soil organic matter and naphthalene.

Accurate stage–area–volume (S-A-V) relationships for lakes with complex bathymetry remain challenging to derive in data‑sparse endorheic basins, where public Digital Elevation Models (DEMs) misrepresent exposed lakebeds and comprehensive bathymetric surveys are cost‑prohibitive. This study presents a geometry‑driven framework that addresses these limitations through three methodological advances: (1) a novel Temporal Stability Ratio (TSR) metric to identify spectrally stable water and land cores enabling the derivation of region‑specific Normalized Difference Water Index (NDWI) thresholds that are resilient to saline‑induced spectral bias; (2) spatiotemporal fusion of multi‑decadal Landsat imagery (1972–2024) with targeted RTK‑GNSS surveys acquired during hydrologic drawdown to reconstruct high‑resolution bathymetry; and (3) analysis of the storage–area sensitivity coefficient ( β = dV / dA ) to delineate hydro‑morphological functional zones with management‑relevant thresholds. The framework is applied to the complex natural laboratory of Iran's Lake Bakhtegan, yielding an optimal NDWI threshold of 0.05 (stability band: 0.03–0.06), robust S-A-V polynomial relationships with R² > 0.96 (up to 0.99), and three β‑defined zones with critical transition thresholds at 268.7, 411.5, and 531.5 km², where, comparing to independent historical estimates, yield Pearson’s correlation coefficient and Cohen’s kappa of r ≈ 0.98 and κ > 0.90 respectively. These thresholds support phased filling strategies that reduce evaporative losses while improving storage reliability. More broadly, the framework provides a reproducible methodology for resolving spectral ambiguities by jointly exploiting sparse geodetic observations and satellite time series, thereby offering a potentially transferable template for environmental flow allocation in complex saline lake systems.

Urbanization significantly impacts phosphorus (P) cycling and transport from terrestrial to aquatic ecosystems, hence, contributing to the eutrophication of receiving water bodies. Global urban growth projections underscore the need for a better understanding of the P sources, pathways, and eutrophication potential of urban stormwater runoff, as well as the effectiveness of current stormwater best management practices (BMPs) in mitigating urban P export. Traditional and low-impact development BMPs, including stormwater ponds and bioretention cells, while primarily intended to decrease peak flows, have the potential to attenuate P loads across urban areas. Here, we consolidate current knowledge on urban stormwater P, in the literature and through analysis of the International Stormwater BMP Database (ISBD), focusing on P concentrations, yields, loads, and chemical speciation. Moreover, we assess the P reduction or enrichment effects of urban stormwater BMPs and identify key knowledge gaps and research priorities. In particular, we propose that future research should comprise more detailed studies on the diversion of P to the subsurface by BMPs, the P biogeochemical transformation processes within BMPs, the interactions of P with other urban pollutants, the current and future impacts of climate change on urban P speciation and export loads, and expanding data collection across geographies.

Impacts of nutrient enrichment on soil carbon cycling have been extensively studied in temperate and tropical regions where intensive agriculture and land development has led to large increases in anthropogenic inputs of nitrogen (N) and phosphorous (P). However, how soil carbon sequestration and soil–atmosphere gas exchanges in cold regions respond to greater inputs of N and P remains poorly known despite recent observations showing significant increases in porewater N and P in burned subarctic peatlands and downstream waters. Wildfires and enhanced hydrological connectivity due to permafrost thaw therefore have the potential to change carbon turnover and gas emissions in the soils of northern peatlands. To start exploring the sensitivity of peatland soil biogeochemistry to variations in N and P availability, we measured the carbon dioxide (CO₂) and methane (CH₄) production rates during a month-long incubation experiment with soils from a bog and fen collected at the long-term Scotty Creek research station in the Northwest Territories, Canada. Sub-samples of the peatland soils were divided into containers to which artificial porewater solutions were added. These solutions were amended with either dissolved inorganic N, dissolved inorganic P, or dissolved N and P together. Unamended controls were run in parallel. The containers were cycled through pre-set temperature steps of 1, 5, 15, and 25 °C. Overall, the fen soil yielded higher CO₂ and CH₄ production rates than the bog soil. The amendment of N in the bog soil produced more CO₂ compared to its control, while the amendment of P increased CO₂ production in the fen soil. The amendment of N and P together reduced CO₂ production but increased that of CH₄ in both the fen and bog soil incubations. Porewater chemistry at the end of the 30 d experiment showed aqueous C, N, and P stoichiometric ratios that trended toward those of the soil microbial biomasses, hence implying that the initial microbial nutrient status played a crucial role in determining the responses to the different nutrient amendments. Our results demonstrate that porewater nutrient availability and soil carbon cycling interact in complex ways to change CO₂ and CH₄ production rates in peatland soils, with potentially far-reaching implications for the impacts of wildfires and permafrost thaw on peatland–atmosphere carbon exchanges.

Flooding events following periods of drought can export large quantities of sulfate (SO42-) from headwater wetlands to surface waters, however the source and mechanism of SO42- release have rarely been studied. Due to the projected increases in severity and frequency of summer droughts and episodic flooding events as a result of climate change, there is a need to better understand the nature of episodic pulses of sulfate from wetlands and their downstream impacts on water quality. In this study, we monitored the evolution of the concentration and isotopic composition of surface and groundwater SO42- in Beverly Swamp, a peat marsh area in southern Ontario, Canada, during a controlled field-scale flooding event. The event was created by the rapid drawdown of the upstream located Valens Reservoir at the end of a drought period. Up to seven-fold increases in SO42- concentrations, relative to the pre-flood background levels, were observed during the flooding of the marsh. Stable S and O isotope ratios were analysed in stream and groundwaters to investigate the sources of SO42-.Following the flooding event, SO42- concentrations in the outflow from the marsh increased significantly, while δ34S-SO42- values decreased. The latter is interpreted as indicative of SO42- generated by sulphide oxidation (Schiff et al. 2005). Sulphide is likely produced by dissimilatory SO42- reduction occurring during wet conditions, with storage of the resulting sulfide minerals in the upper peat layers. During the dry summer, the sulfides are re-oxidised to SO42- and flushed from the wetland during flooding. Stable 18O-H2O isotope signatures identified water released from Valens Reservoir as the initial driver of the SO42- export across the wetland, followed by groundwater seepage from the deeper peat layers. Acidity increased shortly after the SO42- pulse, but quickly dropped down to background levels due to buffering capacity of the wetland.