Emerging dominance of summer rainfall driving High Arctic terrestrial-aquatic connectivity

Abstract

Hydrological transformations induced by climate warming are causing Arctic annual fluvial energy to shift from skewed (snowmelt-dominated) to multimodal (snowmelt- and rainfall-dominated) distributions. We integrated decade-long hydrometeorological and biogeochemical data from the High Arctic to show that shifts in the timing and magnitude of annual discharge patterns and stream power budgets are causing Arctic material transfer regimes to undergo fundamental changes. Increased late summer rainfall enhanced terrestrial-aquatic connectivity for dissolved and particulate material fluxes. Permafrost disturbances (<3% of the watersheds’ areal extent) reduced watershed-scale dissolved organic carbon export, offsetting concurrent increased export in undisturbed watersheds. To overcome the watersheds’ buffering capacity for transferring particulate material (30 ± 9 Watt), rainfall events had to increase by an order of magnitude, indicating the landscape is primed for accelerated geomorphological change when future rainfall magnitudes and consequent pluvial responses exceed the current buffering capacity of the terrestrial-aquatic continuum.

Complex Vulnerabilities of the Water and Aquatic Carbon Cycles to Permafrost Thaw

“…Permafrost and seasonally frozen ground are barriers to vertical and horizontal subsurface water flow, so subsurface decomposition and transport diminish, and storage prevails when soil organic carbon is frozen. When surface runoff occurs, organic carbon export commonly derives from current vegetation sources with limited permafrost contributions (Dean et al, 2020;Beel et al, 2021). Dissolved inorganic carbon, the largest component of aquatic carbon exported to oceans, derives from mineralization of modern and permafrost organic carbon, exchange of CO 2 with the atmosphere, and dissolution (weathering) of carbonate minerals.…”

Assessment of the sediment and associated nutrient/contaminant continuum, from permafrost thaw slump scars to tundra lakes in the western Canadian Arctic

“…It is notable that the frequency of rainfall and extreme events is expected to increase under climate change. [3][4][5]21…”

“…This is particularly true given that the sediments delivered to the lakes are of a geochemically relevant (due to particle-bound nutrients/contaminants) fine-grained fraction regardless of RTSS (d 50 of <5 μm -Figure 3), and the knowledge that Arctic contaminant transport is strongly tied to increasing suspended sediment yields from increasingly denudated landscapes. 21 Further, with the projected increase in the magnitude and frequency of precipitation, [3][4][5] and a temporal shift to increasing late summer storms, 21 rainfall-generated washoff will couple RTSSs with surrounding lakes with greater frequency, thus resulting in future increased sediment delivery and ecological effects. For example, the fine sediment loading can influence light attenuation, which may affect photochemical processing and changes in nutrient and contaminant concentration with time.…”

“…Furthermore, modeling suggests that there will be an increase in late summer rainfall which will further enhance the connectivity of sediments from terrestrial to aquatic system. 21 However, little information is available on the terrestrial and aquatic hydrological and sedimentological processes between RTS events and as the RTSS slowly stabilizes with age.…”

Seasonal Changes in Hydrology and Permafrost Degradation Control Mineral Element‐Bound DOC Transport From Permafrost Soils to Streams

“…Spring thaw and late‐summer rain events (referred as peak events in the following) are two key periods for lateral transport of soil constituents to Arctic rivers (Beel et al., 2021). According to the pulse‐shunt model (Raymond et al., 2016), the spring snowmelt and summer rain events are the periods when DOC can be flushed directly from soils into Arctic rivers (Finlay et al., 2006; Koch et al., 2013; Kutscher et al., 2017; Mann et al., 2012; Raymond et al., 2007; Rember & Trefry, 2004; Spencer et al., 2009; Wickland et al., 2012) accompanied by high riverine concentrations of mineral elements (Bagard et al., 2011; Krickov et al., 2019; Pokrovsky, 2016; Pokrovsky et al., 2010; Vorobyev et al., 2019).…”