The emerging role of drought as a regulator of dissolved organic carbon in boreal landscapes

Abstract

One likely consequence of global climate change is an increased frequency and intensity of droughts at high latitudes. Here we use a 17-year record from 13 nested boreal streams to examine direct and lagged effects of summer drought on the quantity and quality of dissolved organic carbon (DOC) inputs from catchment soils. Protracted periods of drought reduced DOC concentrations in all catchments but also led to large stream DOC pulses upon rewetting. Concurrent changes in DOC optical properties and chemical character suggest that seasonal drying and rewetting trigger soil processes that alter the forms of carbon supplied to streams. Contrary to expectations, clearest drought effects were observed in larger watersheds, whereas responses were most muted in smaller, peatland-dominated catchments. Collectively, our results indicate that summer drought causes a fundamental shift in the seasonal distribution of DOC concentrations and character, which together operate as primary controls over the ecological and biogeochemical functioning of northern aquatic ecosystems.

Small, Coastal Temperate Rainforest Watersheds Dominate Dissolved Organic Carbon Transport to the Northeast Pacific Ocean

“…However, the largest watershed DOC yields occur further south consistent with the idea that temperature is an important control on DOC production within the soil profile (Christ & David, 1996; D’Amore et al., 2010; Ziegler et al., 2017). In addition, the transition from the perhumid rainforest to the seasonal rainforest north of Vancouver Island occurs coincident with the peak in watershed DOC yields suggesting that episodic drying and rewetting of soils may also facilitate DOC production and increase lateral DOC export at the watershed scale (Tiwari et al., 2022; Tunaley et al., 2016). In the southern NPCTR, south of Vancouver Island, watershed DOC yields are limited by relatively lower soil C stocks (Sun et al., 2004) and catchment water yields compared to the northern and central NPCTR.…”

Differential Trends in Iron Concentrations of Boreal Streams Linked to Catchment Characteristics

“…In the present study, these mechanisms could explain the decade‐long increase in DOC and consequently Fe mobilization in the riparian soil and further suggest that severe drought could alter DOC and Fe trends in forested headwater streams long after such events end. Further research will be needed to explore the effects of severe droughts on riparian biogeochemistry and their potential to increase Fe and DOC mobilization (Tiwari et al., 2022).…”

Concentration‐Discharge Patterns Reveal Catchment Controls Over the Stoichiometry of Carbon and Nutrient Supply to Boreal Streams

“…Such observations gain even more importance when considered in the context of general “browning trends” observed across northern aquatic systems (Kritzberg et al., 2020), “wetter autumns/winters” arising from altered precipitation patterns (Teutschbein et al., 2018), and the likelihood of more frequent flood events in the future (Vormoor et al., 2015), all of which may contribute to amplifying the supply of DOC and DON relative to inorganic nutrients across land‐water boundaries. Conversely, an increasing frequency of summer drought in boreal landscapes could drive the opposite trends in streams, with reduced concentrations of DOC (Tiwari et al., 2022) coupled with elevated concentrations of reduced inorganic nutrients (Gómez‐Gener et al., 2020).…”

“…Total annual average precipitation does not show significant trend over the last 40 years, and for our study period there is no evidence of directional changes in annual discharge (Mosquera et al., 2022). However, an extreme drought in the summer of 2018, which was considered the most severe in the last 250 years (Schuldt et al., 2020), had major transient consequences on stream chemistry (Tiwari et al., 2022). Finally, while inorganic N deposition at the KCS has been low historically, these rates have dropped from ca.…”