Consequences of peatland disturbance for dissolved organic matter and nutrient transport and fate in northern catchments
Creators: Frei, Rebecca J
Publisher: name: University of Alberta Library
Year: 2023

<p>Northern peatlands contain ~415 Pg of carbon (C) in soil organic matter and are significant sources of dissolved organic matter (DOM) in inland waters. DOM includes a range of molecules that are C-rich and may also contain nitrogen (N) and phosphorus (P). The escalating disturbance of peatlands due to climate and land use change disrupts DOM and nutrient composition, transport, and fate in inland waters. Dissolved organic C (DOC; the C component of DOM) plays a pivotal role in the global C cycle, and an overabundance of DOC, as well as excess N and P, can harm aquatic ecosystems and increase water treatment expenses. However, the impact of diverse peatland disturbances on DOM and nutrient export remains uncertain, as does the quality and bioavailability of DOM. Consequently, effectively managing peatland resources amidst changing conditions presents an ongoing challenge. This thesis employs field and lab investigations alongside literature synthesis to unravel the consequences of peatland disturbance on catchment and continental-scale C and nutrient export and fate.<br>
In my first study (Chapter 2), I examined how industrial peat extraction influenced DOC and nutrient export and fate in western Canadian stream networks. Studying 55 nested subcatchments (ranging from &lt;1–180 km2), I analyzed solute concentration, DOM composition, and relative solute attenuation. Peat disturbance increased NH4+ concentration and stream turbidity, while diminishing PO43- sink capacity compared to intact peatlands. Although DOC concentration correlated positively with overall peatland coverage, peatland disturbance had no significant impact. Hydrology, specifically stream flow and flowpaths, primarily governed DOM composition variability, showing minimal response to disturbance. An assessment of mass balance indicated inorganic nutrient attenuation across the stream network, with DOC acting conservatively, similar to base cations. Variable stream flow regulated solute attenuation; dissolved inorganic N (DIN) and DOC experienced greater attenuation during low flows, while PO43- was more attenuated during high flows. Therefore, downstream impact from disturbed peatlands depended on flow conditions.<br>
Chapter 3 explored peatland disturbance&#39;s effect on DOM bioavailability for stream bacteria. Sampling three headwater peatland catchments over 12 months (intact, extracted, and burned), I evaluated DOM composition, biodegradability of DOC, DON, and DOP, and bioavailable C:N:P ratios. Across these catchments, DOM was primarily humic-like, with minimal bioavailability (&lt;1% on average). Extracted peatlands had higher bioavailable DOC, yet bioavailable DON and DOP were rarely detected. Bioavailability of DOC and DON peaked during spring freshet, associated with reduced DOM aromaticity. While DON and DOP remained largely inaccessible to bacteria, inorganic N and P were abundant, particularly DIN in extracted peatlands and PO43- in burned peatlands. Bacterial abundance and C:N:P ratios indicated increased C-limitation due to peatland disturbance.<br>
Chapter 4 delved into northern peatlands&#39; role and the impact of peatland disturbance on continental-scale DOC export and fate. A systematic review of DOC export from northern peatlands, coupled with a random forest model, predicted DOC concentration and yield above 45° N. The review revealed a bias toward wetter climates, overestimating northern peatland DOC export. Key predictors of DOC concentration and yield were peatland coverage, mean annual air temperature, and mean annual precipitation. High-latitude headwater peatland catchments exported ~29 Tg C yr-1 to inland waters and 20 Tg C yr-1 to oceans. While peatland drainage had minor impact on continental-scale DOC export, climate change is projected to increase DOC export by 12%–23% by 2100. This shift stems from higher DOC concentration and yield in present-day discontinuous permafrost regions.<br>
This thesis underscores the impact of peatland disturbance on inorganic nutrient export in western Canada and the global significance of northern peatlands on DOC export to inland waters. By studying catchments in sub-boreal western Canada, my research helps advance the fields of biogeochemistry and ecosystem ecology by linking disturbance patterns to C, N, and P concentration and fate in nested stream networks. Chapter 4 highlights DOC concentration and yield variation across a climatic gradient in northern peatland catchments and underscores the need for research in cooler, drier climates, like those in sub-boreal western Canada. Further studies on novel disturbances and catchment C, N, and P dynamics in these underrepresented regions will help inform global biogeochemical models. This research is poised to guide water managers and policymakers in safeguarding peatlands and freshwater resources amid ongoing climate change and land disturbances.</p>