Abstract
Global change is reshaping the physical environment and altering nutrient dynamics across the Arctic. These changes can affect the structure and function of biological communities and influence important climate-related feedbacks (for example, carbon (C) sequestration) in biogeochemical processing hot spots such as lakes. To understand how these ecosystems will respond in the future, this study examined recent (< 10 y) and long-term (1000 y) shifts in autotrophic production across paraglacial environmental gradients in SW Greenland. Contemporary lake temperatures and light levels increased with distance from the ice sheet, along with dissolved organic C (DOC) concentrations and total nitrogen:total phosphorus (TN:TP) ratios. Diatom production measured as biogenic silica accumulation rates (BSiARs) and diatom contribution to microbial communities declined across these gradients, while total production estimated using C accumulation rates and δ13C increased, indicating that autochthonous production and C burial are controlled by microbial competition and competitive displacement across physiochemical gradients in the region. Diatom production was generally low across lakes prior to the 1800’s AD but has risen 1.5–3× above background levels starting between 1750 and 1880 AD. These increases predate contemporary regional warming by 115–250 years, and temperature stimulation of primary production was inconsistent with paleorecords for ~ 90% of the last millennium. Instead, primary production appeared to be more strongly related to N and P availability, which differs considerably across the region due to lake landscape position, glacial activity and degree of atmospheric nutrient deposition. These results suggest that biological responses to enhanced nutrient supply could serve as important negative feedbacks to global change.
Highlights
Lakes are prominent features of Arctic landscapes (Paltan and others 2015)
Sediment biogenic silica accumulation rates (BSiARs) decreased with distance from the ice sheet (Figure 2; r = - 0.76, p = 0.030) and were positively correlated with altitude (r = 0.93, p < 0.001) with the highest accumulation rates ‡ 9.5 g m-2 y-1 recorded at the two highest elevation lakes located nearest to the ice sheet
dissolved organic C (DOC) and total nitrogen:total phosphorus (TN) increased with distance from the ice sheet, and these patterns were associated with decreased BSiAR (p < 0.05)
Summary
Lakes are prominent features of Arctic landscapes (Paltan and others 2015). Here, they act as hot spots for nutrient cycling and carbon (C) burial that are highly sensitive to environmental forcing (Anderson and others 2009; Dean and others 2016). Much of this work has focused on shifts in algal (that is, typically diatom) community structure and production allegedly resulting from increased ice-free periods of lakes associated with high-latitude warming (Smol and others 2005; Burpee and Saros 2020). This mechanism undoubtedly plays a role in the rapid contemporary changes observed in many lakes, warming trends are highly asynchronous across the Arctic (Serreze and others 2000; Comiso and Hall 2014), and algal community responses can differ considerably at regional and local scales (Anderson 2000; Fortin and Gajewski 2009). Changes in energy inputs and mass loading into these ecosystems are occurring that could drive shifts in algal communities and confound overly simplistic predictions of the temperature paradigm (Leavitt and others 2009; Saros and Anderson 2015)
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