Seasonal methane dynamics in high-elevation lakes in the Sierra Nevada California: the role of elevation, temperature, organic matter, and inorganic nutrients

Abstract

<p>Freshwater lakes are important but poorly constrained sources of methane to the atmosphere due to high, but variable, rates of methane production, as well as limited and inconsistent measurements worldwide. High-elevation lakes have been particularly overlooked—despite their large numbers in mountain ranges around the world, and despite methane dynamics at high elevations may be altered by rapid increases in temperature due to climate change. We examined variations in surface methane concentrations and diffusive fluxes, temperature, dissolved organic matter (DOC), and inorganic nutrients in five montane lakes spanning multiple elevations in the Sierra Nevada of California. Over two years, we found strong and consistent seasonality in methane concentrations in lakes; higher concentrations were typically observed in the warmest months and lower concentrations in fall. Changes in methane concentrations were significantlyrelated to temperature in the majority of the individual lakes (r2 = 0.43-0.81) and related to elevation (r2 = 0.39) and DOC (r2 = 0.30) across lakes. Methane concentrations in lakes at elevations &amp;lt;3000 m were strongly related to temperature, nitrite concentrations and elevation (r2 = 0.90), whereas at elevations &amp;gt;3000 m, methane correlated with dissolved inorganicnitrogen to dissolved inorganic phosphorus ratios and elevation (r2 =0.48). Our results expand on our understanding of temporal variations in methane and demonstrate substantial seasonality in methane concentrations and diffusive fluxes in freshwater lakes—suggesting that temporal variation should be considered in large-scale estimates, and may be a predictable function of elevation, temperature, organic matter, and nutrients.</p>

A novel method for characterising the inter- and intra-lake variability of CH4emissions: validation and application across a latitudinal transect in the Alpine region

“…A stepwise model selection by the Akaike information criterion (AIC) indicated that turbidity (Tur, p < 0.001), dissolved organic carbon (DOC, p < 0.001), dissolved nitrogen (DN, p < 0.001), elevation (Elevation_m, p < 0.01), dried filter carbon (C_filter, p < 0.1) and total phosphorus (TP, p < 1) can predict average lake CH4 fluxes as measured from our EC system (R2 = 0.87). This is consistent with the findings of CH4 concentration of five montane lakes in the Sierra Nevada by (Perez-Coronel et al ., 2020) and, in particular, the dependency of the CH4 fluxes magnitude on the elevation of the lake/catchment as initially hypothesised.…”

Biogeochemical and omic evidence for paradoxical methane production via multiple co-occurring mechanisms in aquatic ecosystems

“…P limitation is common in freshwater lakes, as it is in the open ocean (34, 35, 36). High-elevation lakes in the Sierra Nevada are typically oligotrophic (35, 37), and inorganic phosphate concentrations in the lakes sampled here are consistently near the limits of detection (100 nM) by colorimetric techniques, with the vast majority of measurements <200 nM (38, 39). Under these conditions, organic P compounds— including phosphonates—could serve as important sources of P. Our findings are consistent with this idea, and the presence and expression of phnJ genes indicates that several microbial groups are capable of releasing CH 4 through the cleavage of the C-P bond in MPn (Fig.…”