Regulation of the nitrogen biogeochemistry of mountain lakes by subsidies of terrestrial dissolved organic matter and the implications for climate studies

Abstract

Stable isotopes of nitrogen (N) were analyzed in modern sediments of mountain lakes, dissolved organic matter (DOM), and sediment cores spanning the past 12,000 yr to test the hypothesis that spatial and temporal (100-1000 yr) variation in the N content of mountain lakes is regulated by influx of allochthonous DOM. Analysis of spatial patterns in an elevation gradient of 75 mountain lakes revealed that most N was associated with DOM rather than inorganic N, particularly in subalpine lakes (, 1700 m above sea level). Similarly, analysis of N isotope ratios (d 15 N) from 22 lakes showed that whole sediments of subalpine sites were significantly more depleted (0.74% 6 1.58%) than were those of alpine lakes above 2200 m (3.04% 6 1.21%), consistent with the depleted d 15 N of isolated DOM (, 1.3%). Sedimentary d 15 N values of Crowfoot Lake, presently near tree line, also varied greatly during the past 12,000 yr, with enriched values (, 4%) during the alpine phases of the lake's history and depleted values (, 1%) during the intervening subalpine phase (ca. 10,050-4160 14 C yr before present) when DOM was abundant. In contrast, sedimentary d 15 N values remained constant (, 2.5%) at Snowflake Lake, an alpine reference site that never experienced a DOM-rich subalpine phase. These analyses suggest that climate regulates N influx and lake biogeochemistry by changing the subsidies of terrestrial DOM, and warn that future climate change may initially reduce N influx on a decadal scale by reducing hydrologic transfer before increasing N subsidies on a centennial scale by increasing terrestrial production of DOM.

Magnitudes and controls of organic and inorganic carbon flux through a chain of hard‐water lakes on the northern Great Plains

“…Implications for climate effects on lakes-Modest extrapolation of the findings of the whole-lake C budgets suggests that future climate variability will affect C flux through prairie lakes mainly by altering influx of water and solutes, as suggested elsewhere for studies of nitrogen influx Bunting et al 2010). Although E influx during summer (irradiance, atmospheric heat) causes synchronous seasonal changes in lake chemistry (evaporative concentration) that can alter CO 2 fluxes over large spatial extents Finlay et al 2009), massbalance studies suggest that atmospheric CO 2 exchange represents only a small component of total C flux in hardwater lakes (Fig.…”

“…For example, while reduced water influx should decrease DIC content and the intensity of CO 2 evasion, nutrient input to lakes should also decline (Schindler and Donahue 2006;Leavitt et al 2009;Bunting et al 2010), constraining autotrophic production and consumption of CO 2 , while evaporative concentration of lakes may partly offset reduced subsidies of allochthonous IC . On the other hand, declining winter runoff should also reduce influx of allochthonous OC and its processing by heterotrophic bacteria.…”

Interactive effects of higher temperature and dissolved organic carbon on planktonic communities in fishless mountain lakes

“…See Fig. Thus, our findings suggest that climate-induced increased inputs of terrestrial DOC, due to development of soil and vegetation (Bunting et al, 2010;Sadro et al, 2012), may lead to an increased C : P ratio in the dissolved and particulate nutrient pool in alpine lakes. dissolved organic matter due to greater terrestrial inputs (Kopacek et al, 2011).…”

“…Firstly, warming alone or increased DOC alone may decrease production of autotrophic phytoplankton (Blomqvist et al, 2001). Secondly, warming combined with increased DOC inputs, due to increased soil and vegetation cover of alpine catchments (Bunting et al, 2010), can increase C : P of the particulate nutrient pool in alpine lakes (Kopacek et al, 2011). Secondly, warming combined with increased DOC inputs, due to increased soil and vegetation cover of alpine catchments (Bunting et al, 2010), can increase C : P of the particulate nutrient pool in alpine lakes (Kopacek et al, 2011).…”

Assessing the sensitivity of alpine lakes and ponds to nitrogen deposition in the Canadian Rocky Mountains

“…However, moderately elevated levels of nitrogen deposition are considered relatively recent phenomena in the less developed Canadian Rockies , and paleolimnological evidence suggests that nitrogen levels in several of the non-glaciated alpine lakes have remained stable over the past century (R.D. Vinebrooke, unpublished data;Bunting et al, 2010). Therefore, widespread phosphorus limitation of these and other large alpine lake ecosystems in the region likely reflects their natural trophic status.…”