Short-term Effects of Anthropogenic Sediment Additions on Biogeochemical Properties of the Fraser River Estuary (Jan 2025 – Dec 2025)
Abstract
Intertidal mudflats are globally important ecosystems in estuaries. In the Fraser River Estuary in British Columbia, Canada, these habitats host diverse surficial biofilms (microphytobenthos and other microorganisms) that underpin several important functions, including supporting estuarine food webs, biogeochemical cycling, the latter including nutrient provisioning that sustains benthic productivity. However, these habitats are suffering from elevation loss and habitat degradation due to sediment deficit, elevated salinity, relative sea-level rise, and herbivory of migratory birds. Recently, mudflats at Sturgeon Bank, Fraser River Estuary, British Columbia, Canada, have received managed sediment additions as part of the broader Sturgeon Bank Sediment Enhancement Pilot Project at the estuary. The short-term biogeochemical responses of intertidal biofilms can be used as an early signal to assess restoration effectiveness and to predict potential ecological outcomes of restoration interventions. This study compared sediment attributes (organic matter, photosynthetic pigments, and fatty acid composition) at Sturgeon Bank at treatment and control sites under a modified Before-After-Control-Impact (BACI) design, spanning four sampling years in the springs from 2022 to 2024 and from winter to summer in 2025. Linear-mixed effects modelling and analysis of variance revealed that the studied parameters varied annually from 2022 to 2025, with few differences between treatment and control sites, and only a significant treatment-by-year interaction for organic matter in 2025. However, fatty acid analyses indicated potential shifts in the community composition of intertidal biofilm towards greater contributions of dinoflagellates and bacteria at treatment sites. These findings demonstrate that estuarine mudflat ecosystems are highly dynamic and can be resilient to anthropogenic sediment additions. Interannual variability in hydrodynamics and climate were important factors in changes to biofilm biomass, nutritional quality, and phytoplankton taxonomic composition, with mud surface temperature, solar radiation, and freshet-induced salinity fluctuations exerting stronger impacts than the sediment treatment itself. These results highlight the significance of integrating biogeochemical monitoring with traditional physical and meteorological metrics to accurately assess restoration outcomes in dynamic estuaries. This study provides a foundation for adaptive management strategies and informs blue carbon accounting efforts in sediment-deficient coastal ecosystems globally.
Seasonal Methane Dynamics in Small Freshwater Upland Lakes in Southern British Columbia (Apr 2022 – Dec 2024)
My second research project at UBC EEGS examined seasonal methane dynamics in small freshwater upland lakes in southern British Columbia. Freshwater lakes are recognised as important sources of the potent greenhouse gas methane (CH4) in northern latitudes and small temperate lakes have disproportionally higher CH4 fluxes per unit area compared to larger lakes. The Okanagan-Thompson Plateau in southern British Columbia, Canada is home to numerous small upland lakes. However, to date, the understanding of relative magnitudes of internal pathways and processes that lead to CH4 production and emission seasonally from these small remote freshwater lakes remains limited and knowledge of the origin of CH4 excess in their epilimnion is unknown. This study contains two intensive field seasons in the summer and autumn of 2022 and 2023, encompassing nine selected freshwater lakes in the region with a total of over 170 waypoints through water columns, across transects and along shorelines. Using a series of laboratory techniques including Gas Chromatography (GC) for trace gas concentration, Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) for trace elemental abundance and water chemistry analysis, along with various sets of geospatial and statistical analyses and modelling, the CH4 excess was observed in the epilimnion of the study lakes, with higher CH4 nearshore than away from shore and vegetation-rich shoreline being a hotspot of dissolved CH4. The geospatial quantifications have examined four main pathways of CH4 in the epilimnion of five small freshwater lakes in summer, showing the wide range of CH4 storage. These findings suggest that spatial patterns and accumulation of CH4 may be influenced by a combination of lake morphology, the extent of thermal stratification, O2 availability, and the diverse parameters and approaches used for evaluating CH4 mass balance worldwide. Statistical analyses and modelling reveal distinct differences in CH4 dynamics across various lake morphologies, particularly in the relationships between temperature, CH4 and dissolved oxygen levels over depth, indicating that the physical and biochemical characteristics of lakes may explain this variability. It is anticipated that this study will serve as a starting point for further research on the spatio-temporal distribution of CH4 in this region.
The Potential for Abiotic Methane Production associated with Ultramafic Rocks in British Columbia (Sep 2021 – Apr 2022)
My first research project at UBC EEGS focused on the potential for abiotic methane production associated with ultramafic rocks in British Columbia, and possibly be extended to the geological emission of methane from thermal springs in the region to the atmosphere.
Methane (CH4) is the primary component of natural gas and one of the main greenhouse gases apart from carbon dioxide (CO2). It is a powerful yet relatively clean energy source and a major driver of climate change. Methane is often known to be produced from biological or biogenic processes via archaea and thermogenic processes via heat degradation of organic matter. However, it can also be generated by geological means (Judd, 2000). Previous research has found the existence of methane on Mars, and the Mars Science Laboratory (MSL) also detected its temporal patterns where there is no sign of life so far (Webster et al., 2015; Yung et al., 2018). This further indicates that methane can be produced abiotically.
Geological or abiogenic methane generation refers to the absence of organic substances, and large quantities of methane of predominantly abiotic origin have been mainly discovered in mid-ocean ridge hydrothermal systems (e.g., Welhan, 1988; Charlou et al., 1998; Kelley and Fruh-Green, 1999), deep shield rocks (Lollar et al., 1993; 2002), ophiolite seeps (Abrajano et al., 1988; 1990), and continental igneous rocks including ophiolites that are ultramafic rocks obducted on continents where methane is likely produced after serpentinization of peridotite by carbon dioxide hydrogenation following Fischer-Tropsch Type (FTT) reactions (Etiope et al., 2013b; Morrill et al., 2013; Suda et al., 2014). Such reactions have happened at regions of igneous or volcanic activity on land (such as Italy; Yellowstone Park, Wyoming, U.S.A.), and offshore (such as White Island geothermal field, New Zealand; Guaymas Basin, Gulf of California) (Judd, 2000). Recent studies in Greece and mainland Portugal pointed out that methane from serpentinized ultramafic rocks worldwide was only observed in hyperalkaline waters, namely magnesium (Mg)-rich bicarbonate type waters (pH~7-9) due to a shallow open-system weathering of serpentinized rocks, and calcium hydroxide (Ca2+-OH–) waters (pH>10) due to hydration of olivine and pyroxene in a deeper closed-system (Etiope et al., 2013a; 2013b).
