Contrasts in dissolved, particulate, and sedimentary organic carbon from the Kolyma River to the East Siberian Shelf

Arctic rivers will be increasingly affected by the hydrological and biogeochemical consequences of thawing permafrost. During transport, permafrost-derived organic carbon (OC) can either accumulate in floodplain and shelf sediments or be degraded into greenhouse gases prior to final burial. Thus, the net impact of permafrost OC on climate will ultimately depend on the interplay of complex processes that occur along the source-to-sink system. Here, we focus on the Kolyma River, the largest watershed completely underlain by continuous permafrost, and marine sediments of the East Siberian Sea, as a transect to investigate the fate of permafrost OC along the land–ocean continuum. Three pools of riverine OC were investigated for the Kolyma main stem and five of its tributaries: dissolved OC (DOC), suspended particulate OC (POC), and riverbed sediment OC (SOC). They were compared with earlier findings in marine sediments. Carbon isotopes (δ13C, Δ14C), lignin phenol, and lipid biomarker proxies show a contrasting composition and degradation state of these different carbon pools. Dual C isotope source apportionment calculations imply that old permafrost-OC is mostly associated with sediments (SOC; contribution of 68±10 %), and less dominant in POC (38±8 %), whereas autochthonous primary production contributes around 44±10 % to POC in the main stem and up to 79±11 % in tributaries. Biomarker degradation indices suggest that Kolyma DOC might be relatively degraded, regardless of its generally young age shown by previous studies. In contrast, SOC shows the lowest Δ14C value (oldest OC), yet relatively fresh compositional signatures. Furthermore, decreasing mineral surface area-normalised OC- and biomarker loadings suggest that SOC might be reactive along the land–ocean continuum and almost all parameters were subjected to rapid change when moving from freshwater to the marine environment. This suggests that sedimentary dynamics play a crucial role when targeting permafrost-derived OC in aquatic systems and support earlier studies highlighting the fact that the land–ocean transition zone is an efficient reactor and a dynamic environment. The prevailing inconsistencies between freshwater and marine research (i.e. targeting predominantly DOC and SOC respectively) need to be better aligned in order to determine to what degree thawed permafrost OC may be destined for long-term burial, thereby attenuating further global warming.</p

Seasonal particulate organic carbon dynamics of the Kolyma River tributaries, Siberia

Arctic warming is causing permafrost thaw and release of organic carbon (OC) to fluvial systems. Permafrost-derived OC can be transported downstream and degraded into greenhouse gases that may enhance climate warming. Susceptibility of OC to decomposition depends largely upon its source and composition, which vary throughout the seasonally distinct hydrograph. Most studies on carbon dynamics to date have focused on larger Arctic rivers, yet little is known about carbon cycling in lower-order rivers and streams. Here, we characterize the composition and sources of OC, focusing on less studied particulate OC (POC), in smaller waterways within the Kolyma River watershed. Additionally, we examine how watershed characteristics control carbon concentrations. In lower-order systems, we find rapid initiation of primary production in response to warm water temperatures during spring freshet, shown by decreasing δ13C-POC, in contrast to larger rivers. This results in CO2 uptake by primary producers and microbial degradation of mainly autochthonous OC. However, if terrestrially derived inorganic carbon is assimilated by primary producers, part of it is returned via CO2 emissions if the autochthonous OC pool is simultaneously degraded. As Arctic warming and hydrologic changes may increase OC transfer from smaller waterways to larger river networks, understanding carbon dynamics in smaller waterways is crucial.</p

РОЗРОБКА РЕГІОНАЛЬНОГО ПРОГНОЗУ ЕКОЛОГО-ЕКОНОМІЧНИХ РИЗИКІВ ПРИ ЗАКРИТТІ ШАХТ ЗАХІДНОГО ДОНБАСУ (звіт по темі ГП-412) (заключний)

Рукопис закінчено 5 грудня 2010 р. Результати роботи розглянуто науково-технічною радою, протокол № 4 від 09.12.2010 р.РЕФЕРАТ Звіт про НДР: 98 c, 27 рис., 9 табл., 29 джерело, 3 додатки. Об’єкт дослідження – процес аналізу та прогнозування еколого-економічних ризиків, які викликані гірничовидобувними роботами. Мета проекту – розробка методики регіонального прогнозу еколого-економічних ризиків, можливість виникнення яких зумовлена техногенним впливом вугільних шахт, що функціонують або закриваються. Мета етапу – апробація розробленої методики регіонального прогнозу еколого-економічних ризиків з урахуванням взаємного впливу шахтних ком-плексів Західного Донбасу, що працюють та закриваються. На основі результатів проведення експериментального моделювання еколого-економічного ризику для шахт родовища Західного Донбасу та аналізу розроблених моделей еколого-економічних ризиків отримано якісні й кількісні показники, які дали можливість розробити набор керуючих заходів для мінімізації наслідків функціонування або закриття шахтних комплексів

Seasonal variability in particulate organic carbon degradation in the Kolyma River, Siberia

Major Arctic rivers are undergoing changes due to climate warming with higher discharge and increased amounts of solutes and organic carbon (OC) draining into rivers and coastal seas. Permafrost thaw mobilizes previously frozen OC to the fluvial network where it can be degraded into greenhouse gases and emitted to the atmosphere. Degradation of OC during downstream transport, especially of the particulate OC (POC), is however poorly characterized. Here, we quantified POC degradation in the Kolyma River, the largest river system underlain with continuous permafrost, during 9-15 day whole-water incubations (containing POC and dissolved OC - DOC) during two seasons: spring freshet (early June) and late summer (end of July). Furthermore, we examined interactions between dissolved and particulate phases using parallel incubations of filtered water (only DOC). We measured OC concentrations and carbon isotopes (δ13 C, Δ14 C) to define carbon losses and to characterize OC composition, respectively. We found that both POC composition and biodegradability differs greatly between seasons. During summer, POC was predominantly autochthonous (47-95 %) and degraded rapidly (~33 %) whereas freshet POC was largely of allochthonous origin (77-96 %) and less degradable. Gains in POC concentrations (up to 31 %) were observed in freshet waters that could be attributed to flocculation and adsorption of DOC to particles. The demonstrated DOC flocculation and adsorption to POC indicates that the fate and dynamics of the substantially-sized DOC pool may shift from degradation to settling, depending on season and POC concentrations - the latter potentially acting to attenuate greenhouse gas emissions from fluvial systems. We finally note that DOC incubations without POC present may yield degradation estimates that do not reflect degradation in the in situ river conditions, and that interaction between dissolved and particulate phases may be important to consider when determining fluvial carbon dynamics and feedbacks under a changing climate

Cognitive function is associated with risk aversion in community-based older persons

<p>Abstract</p> <p>Background</p> <p>Emerging data from younger and middle-aged persons suggest that cognitive ability is negatively associated with risk aversion, but this association has not been studied among older persons who are at high risk of experiencing loss of cognitive function.</p> <p>Methods</p> <p>Using data from 369 community-dwelling older persons without dementia from the Rush Memory and Aging Project, an ongoing longitudinal epidemiologic study of aging, we examined the correlates of risk aversion and tested the hypothesis that cognition is negatively associated with risk aversion. Global cognition and five specific cognitive abilities were measured via detailed cognitive testing, and risk aversion was measured using standard behavioral economics questions in which participants were asked to choose between a certain monetary payment ($15) versus a gamble in which they could gain more than$15 or gain nothing; potential gamble gains ranged from $21.79 to$151.19 with the gain amounts varied randomly over questions. We first examined the bivariate associations of age, education, sex, income and cognition with risk aversion. Next, we examined the associations between cognition and risk aversion via mixed models adjusted for age, sex, education, and income. Finally, we conducted sensitivity analyses to ensure that our results were not driven by persons with preclinical cognitive impairment.</p> <p>Results</p> <p>In bivariate analyses, sex, education, income and global cognition were associated with risk aversion. However, in a mixed effect model, only sex (estimate = -1.49, standard error (SE) = 0.39, p < 0.001) and global cognitive function (estimate = -1.05, standard error (SE) = 0.34, p < 0.003) were significantly inversely associated with risk aversion. Thus, a lower level of global cognitive function and female sex were associated with greater risk aversion. Moreover, performance on four out of the five cognitive domains was negatively related to risk aversion (<it>i.e</it>., semantic memory, episodic memory, working memory, and perceptual speed); performance on visuospatial abilities was not.</p> <p>Conclusion</p> <p>A lower level of cognitive ability and female sex are associated with greater risk aversion in advanced age.</p