Multiple tracers demonstrate distinct sources of dissolved organic matter to lakes of the Mackenzie Delta, western Canadian Arctic

Author Posting. © American Society of Limnology and Oceanography, 2011. This article is posted here by permission of American Society of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 56 (2011): 1297-1309, doi:10.4319/lo.2011.56.4.1297.Lakes of the Mackenzie Delta occur across a gradient that contains three clear end members: those that remain connected to river-water channels throughout the summer; those that receive only brief inputs of river water during an annual spring flood but contain dense macrophyte stands; and those that experience significant permafrost thaw along their margins. We measured dissolved organic carbon (DOC) concentration, dissolved organic matter (DOM) absorption and fluorescence, and stable isotopes of DOM, DOM precursor materials, and bacteria to elucidate the importance of river water, macrophytes, and thermokarst as DOM sources to Mackenzie Delta lakes. Despite standing stocks of macrophyte C that are sevenfold to 12-fold greater than those of total DOC, stable isotopes indicated that autochthonous sources contributed less than 15% to overall DOM in macrophyte-rich lakes. Instead, fluorescence and absorption indicated that the moderate summertime increase in DOC concentration in macrophyte-rich lakes was the result of infrequent flushing, while bacterial δ13C indicated rapid bacterial removal of autochthonous DOC from the water column. In thermokarst lakes, summertime increases in DOC concentration were substantial, and stable isotopes indicated that much of this increase came from C released as a result of thermokarst-related processes. Our results indicate that these distinct sources of DOM to neighboring arctic Delta lakes may drive between-lake differences in C cycling and energy flow. Rapidly assimilated macrophyte DOM should be an important contributor to microbial food webs in our study lakes. In contrast, the accumulation of thermokarst-origin DOM allows for a significant role in physico-chemistry but indicates a lesser contribution of this DOM to higher trophic levels.This study was supported by a Discovery Grant and Northern Research Supplement from the Natural Sciences and Engineering Research Council of Canada (NSERC) to L.F.W.L.; funds from the Science Horizons Youth Internship Program, Northern Scientific Training Program, and NSERC Northern Research Internship. Personal financial support to S.E.T. was provided by a Simon Fraser University CD Nelson Memorial Graduate Scholarship, an NSERC Canada Graduate Scholarship-Doctoral, and a Garfield Weston Award for Northern Research

WETMETH 1.0: A New Wetland Methane Model for Implementation in Earth System Models

Wetlands are the single largest natural source of methane (CH4), a powerful greenhouse gas affecting the global climate. In turn, wetland CH4 emissions are sensitive to changes in climate conditions such as temperature and precipitation shifts. However, biogeochemical processes regulating wetland CH4 emissions (namely microbial production and oxidation of CH4) are not routinely included in fully coupled Earth system models that simulate feedbacks between the physical climate, the carbon cycle, and other biogeochemical cycles. This paper introduces a process-based wetland CH4 model (WETMETH) developed for implementation in Earth system models and currently embedded in an Earth system model of intermediate complexity. Here, we (i) describe the wetland CH4 model, (ii) evaluate the model performance against available datasets and estimates from the literature, and (iii) analyze the model sensitivity to perturbations of poorly constrained parameters. Historical simulations show that WETMETH is capable of reproducing mean annual emissions consistent with present-day estimates across spatial scales. For the 2008–2017 decade, the model simulates global mean wetland emissions of 158.6 Tg CH4 yr−1, of which 33.1 Tg CH4 yr−1 is from wetlands north of 45∘ N. WETMETH is highly sensitive to parameters for the microbial oxidation of CH4, which is the least constrained process in the literature

Changes in Snowfall and Snow on the Ground in the Western Canadian Arctic and Implications to Streamflow

No abstract available

Changes in Snowfall and Snow on the Ground in the Western Canadian Arctic and Implications to Streamflow

No abstract available

Effects of river sediments on coral recruitment, algal abundance benthic community structure on Kenyan coral reefs

The effects of sediment concentration and season on coral recruitment algal abundance nd benthic community structure were studied in Kenyan coral reef lagoons to determine their potential influence on coral recovery. Nutrient levels and recruit numbers were higher during the southeast monsoon (SEM) than during the northeast monsoon (NEM) season and in sediment-exposed compared to nonsediment exposed reefs. Mean algal biomass also exhibited the same seasonal trend (except at one site), but was higher in the non-sediment exposed reef compared to the other reefs. Corals in the sediment exposed reef exhibited morphological differences relative to the other reefs: fewer corymbose and plate-like but more branching, massive and solitary forms and increased colony and corallite sizes. However, sediments did not suppress coral recruitment rates. These morphological changes coupled with the interaction between biological and physico-chemical characteristics have important ecological and geological implications: by potentially modifying calcium carbonate production and ameliorating the adverse effects of climate induced stress events, this may minimize coral mortality and enhance reef recovery.Key words: Algal biomass, coral recruitment, hydrodynamics, coral morphology, seasonality, sediments

Methane emission dynamics among CO2-absorbing and thermokarst lakes of a great Arctic delta

Lake-rich Arctic deltas differ biogeochemically from tundra lakes, and their role as sources and sinks of greenhouse gases remains poorly understood. Under-ice and open-water changes in methane (CH4) storage (43 lakes, 2014), floating chamber measurements of total and diffusive CH4 evasion to the atmosphere (6 lakes, 2014-2015), and water-column CH4 oxidation (MOX) (6 lakes, 2014-2015) permitted evaluation of how CH4 emissions vary among lakes with differing river-to-lake connection times within the Mackenzie Delta. CH4 emissions during ice-out were considerable, followed by substantial declines as open-water progressed. Water-column MOX rates were highest after ice-out, and declined throughout open-water. After accounting for a strong effect of CH4 substrate levels, MOX rates were inversely related to pH, which can increase to high levels during open-water because of high macrophyte production. Comparisons of water-column CH4 storage versus open-water fluxes (6 lakes) showed that diffusive evasion plus MOX removed most CH4 in the water columns every 1-2 days with only modest changes in storage, suggesting that counter-balancing water-column replenishment is substantial. Lakes with short river-connection times (i.e. most strongly autotrophic and strongly CO2- absorbing in this delta) and thermokarst lakes contribute disproportionately to CH4 flux, relative to lakes with long river-connection times. Thus, this great Arctic delta represents an important system of greenhouse-gas emitting lakes despite prior work showing their net absorption of CO2 during open-water, and having a low landscape area of CO2-saturated thermokarst lakes. Autotrophically absorbed CO2 becomes labile carbon substrate, and is microbially shunted back to the atmosphere as the more potent greenhouse gas CH4

Patterns of hydrogen peroxide among lakes of the Mackenzie Delta, western Canadian Arctic

Dissolved organic carbon (DOC) in Mackenzie Delta lakes varies in composition and concentration, ranging from low concentrations and high colour in frequently flooded lakes to high concentrations in clear lakes that are infrequently flooded. DOC is a precursor to the photochemical production of hydrogen peroxide (H2O2) in lake waters. Here we assessed the patterns of H2O2 using three approaches: (i) H 2O2 levels were tracked in 40 lakes during the open water season from the Arctic summer solstice (24 h sunlight) to late summer; (H) diurnal dynamics of in situ H2O2 were tracked in a pair of lakes with contrasting DOC regimes (coloured vs. noncoloured DOC); and (JH) buildup of H2O2 was tracked in experimental microcosms of lake water exposed to manipulated UV levels. H2O2 levels were highest at the solstice and in intermittently flooded lakes. During 24 h daylight, lakes with contrasting DOC regimes showed cumulative build up of H2O2 during multiple cloudless days. Cumulatively, H 2O2 was highest in the Delta lake with a higher DOC concentration and low in colour. H2O2 buildup in lake water shielded from UVB exposure was not significantly lower from microcosms under full sunlight. UVA was the most important in coloured DOC photobleaching and H2O2 production. © 2006 NRC