Integrating carbon emission, accumulation and transport in inland waters to understand their role in the global carbon cycle.

Inland waters receive a significant quantity of carbon (C) from land. The fate of this C during transit, whether it is emitted to the atmosphere, accumulated in sediments or transported to the ocean, can considerably reshape the landscape C balance. However, these different fates of terrestrial C are not independent but are instead linked via several catchment and aquatic processes. Thus, according to mass conservation, any environmental change inducing a shift in a particular C fate should come at the expense of at least one other fate. Nonetheless, studies that have investigated C emission, accumulation and transport concertedly are scarce, resulting in fragmented knowledge of the role of inland waters in the global C cycle. Here, we propose a framework to understand how different C fates in aquatic systems are interlinked and covary under environmental changes. First, to explore how C fates are currently distributed in streams, rivers, reservoirs and lakes, we compiled data from the literature and show that 'C fate allocation' varies widely both within and among inland water systems types. Secondly, we developed a framework that integrates C fates in any inland water system by identifying the key processes underlying their linkages. Our framework places the partitioning between the different C forms, and how this is controlled by export from land, internal transformations and hydrology, as central to understanding C fate allocation. We argue that, by focusing on a single fate, studies could risk drawing misleading conclusions regarding how environmental changes will alter the role of inland waters in the global C cycle. Our framework thus allows us to holistically assess the consequences of such changes on coupled C fluxes, setting a foundation for understanding the contemporary and future fate of land-derived C in inland water systems.

Efficiency of crustacean zooplankton in transferring allochthonous carbon in a boreal lake.

Increased incorporation of terrestrial organic matter (t-OM) into consumer biomass (allochthony) is believed to reduce growth capacity. In this study, we examined the relationship between crustacean zooplankton allochthony and production in a boreal lake that displays strong seasonal variability in t-OM inputs. Contrary to our hypotheses, we found no effect of allochthony on production at the community and the species levels. The high-frequency seasonal sampling (time-for-space) allowed for estimating the efficiency of zooplankton in converting this external carbon source to growth. From the daily t-OM inputs in the lake (57-3,027 kg C/d), the zooplankton community transferred 0.2% into biomass (0.01-2.36 kg C/d); this level was of the same magnitude as the carbon transfer efficiency for algal-derived carbon (0.4%). In the context of the boundless carbon cycle, which integrates inland waters as a biologically active component of the terrestrial landscape, the use of the time-for-space approach for the quantifying of t-OM trophic transfer efficiency by zooplankton is a critical step toward a better understanding of the effects of increasing external carbon fluxes on pelagic food webs.

The phantom midge menace: Migratory Chaoborus larvae maintain poor ecosystem state in eutrophic inland waters.

Chaoborus spp. (phantom midge) are prevalent in eutrophic inland waters. In Lake Soppen, Switzerland, C. flavicans larvae diurnally migrate between the methane-rich, oxygen-depleted hypolimnion and sediments, and the methane-poor, oxygen-rich epilimnion. Using a combination of experiments and system modelling, this study demonstrated that the larvae's burrowing activities in and out of the sediment perturbed the sediment and re-introduced sequestered phosphorus into the overlying water at a rate of 0.022 µg P ind-1 d-1, thereby exacerbating internal nutrient loading in the water column. Fluxes of sediment methane and other reduced solutes enhanced by the larval bioturbation would consume oxygen and sustain the hypoxic/anoxic condition below the thermocline. In addition to increasing diffusive fluxes, migrating larvae also directly transported methane in their gas vesicles from the deep water and release it in the surface water at a rate of 0.99 nmol CH4 ind-1 d-1, potentially contributing to methane emission to air. As nutrient pollution and climate warming persist or worsen in the coming decades, proliferation of Chaoborus could intensify this positive feedback loop and delay lake recovery.

Greenhouse Gas Emissions from Freshwater Reservoirs: What Does the Atmosphere See?

Freshwater reservoirs are a known source of greenhouse gas (GHG) to the atmosphere, but their quantitative significance is still only loosely con- strained. Although part of this uncertainty can be attributed to the difficulties in measuring highly variable fluxes, it is also the result of a lack of a clear accounting methodology, particularly about what constitutes new emissions and potential new sinks. In this paper, we review the main processes involved in the generation of GHG in reservoir systems and propose a simple approach to quantify the reservoir GHG footprint in terms of the net changes in GHG fluxes to the atmosphere induced by damming, that is, 'what the atmosphere sees.' The approach takes into account the pre-impoundment GHG balance of the landscape, the temporal evolution of reservoir GHG emission profile as well as the natural emissions that are displaced to or away from the reservoir site resulting from hydrological and other changes. It also clarifies the portion of the reservoir carbon burial that can potentially be considered an offset to GHG emissions.

Ecosystem effects of a tropical cyclone on a network of lakes in northeastern North America.

Here we document the regional effects of Tropical Cyclone Irene on thermal structure and ecosystem metabolism in nine lakes and reservoirs in northeastern North America using a network of high-frequency, in situ, automated sensors. Thermal stability declined within hours in all systems following passage of Irene, and the magnitude of change was related to the volume of water falling on the lake and catchment relative to lake volume. Across systems, temperature change predicted the change in primary production, but changes in mixed-layer thickness did not affect metabolism. Instead, respiration became a driver of ecosystem metabolism that was decoupled from in-lake primary production, likely due to addition of terrestrially derived carbon. Regionally, energetic disturbance of thermal structure was shorter-lived than disturbance from inflows of terrestrial materials. Given predicted regional increases in intense rain events with climate change, the magnitude and longevity of ecological impacts of these storms will be greater in systems with large catchments relative to lake volume, particularly when significant material is available for transport from the catchment. This case illustrates the power of automated sensor networks and associated human networks in assessing both system response and the characteristics that mediate physical and ecological responses to extreme events.

Assessment of self-efficacy for caregiving: the critical role of self-care in caregiver stress and burden.

OBJECTIVE: Little attention has been given to assessing the importance of self-care and communication in the caregiving setting, especially caregiving for those who are terminally ill. The Caregiver Inventory (CGI), a measure of self-efficacy for caregiving that includes these two dimensions, was subjected to psychometric analyses. METHOD: One hundred and thirty-three primary caregivers completed the CGI; of those, 81 also completed the Perceived Stress Scale (PSS), Caregiver Burden Inventory (CBI), and a measure of caregiver tasks (ADLR-CG). Based on home visits, social workers also rated the caregiver tasks required (ADLR-SW). Exploratory Factor Analysis, as well as reliability and validity analyses were conducted. RESULTS: Fit indices in M + I (V. 5.1) indicated a four factors solution: Managing Medical Information (α = 0.64), Caring for Care Recipient (α = 0.78), Caring for Oneself (α = 0.88), and Managing Difficult Interactions/Emotions (α = 0.76). The CGI was highly negatively related to stress (PSS, r = -0.54, p = 0.001) and burden (CBI, p = -0.37, p = 0.001); ADLR-CG was related to burden (r = 0.43, p = 0.001) but not stress. In regression and relative importance analyses, Care of Oneself and Managing Difficult Interactions/Emotions emerged as equal in terms of having the strongest and most robust negative relationships with stress and burden. SIGNIFICANCE OF RESULTS: Results suggest that the CGI is a reliable and valid measure of self-efficacy for caregiving, and indicate the importance of self-efficacy for self-care and for managing difficult communication in successfully navigating the demands of caregiving for terminally ill persons.

Clinical inquiries: How should you manage a depressed patient unresponsive to an SSRI?

The best approach among studied alternatives to manage a patient with treatment-resistant depression is not clear from the evidence. All of the options reviewed seem to have about a 25% to 30% success rate. Switching to other antidepressants or augmenting with non-antidepressant drugs has the best supporting evidence (strength of recommendation [SOR]: B).1 Adding additional antidepressants (SOR: B), using psychotherapy (SOR: B), and initiating electroconvulsive therapy (ECT) (SOR: C) are options. Various antidepressants are used as add-on therapy. Psychotherapy is often recommended, though the evidence of benefit after a failed course of initial therapy is sparse. The evidence supporting use of ECT in treatment-resistant depression is weak. Comparison among the options is based on expert opinion (SOR: C). Additional reports from the STAR*D trial may improve the quality of the evidence in the near future.

Differential allele-specific accumulation of bovine kappa-casein mRNA throughout lactation.

A differential allele-specific accumulation of kappa-casein mRNA that is not linked to the kappa-casein protein variants is described in Holstein cows. Actually, cows genotyped kappa-casein AB were a mixed population. For the first group of kappa-casein AB cows, allele A-specific kappa-casein mRNA contents within mammary epithelial cells were lower than the allele B-specific ones (cows LH), suggesting that the allele A-specific kappa-casein gene was expressed with lower efficiency in mRNA. For the other group of kappa-casein AB cows, allele A- and B-specific kappa-casein mRNA accumulated to a similar level within mammary epithelial cells (cows HH). The objective of this study was to determine whether the accumulation of allele-specific kappa-casein mRNA remained constant throughout lactation for the two groups of cows. Quantitative RT-PCR was used to monitor Holstein cows kappa-casein AB genotyped HH and LH throughout lactation for the proportion of allele B-specific mRNA accumulation relative to the total kappa-casein encoded mRNA within mammary epithelial cells: RNA was extracted from milk somatic cells known to contain a small proportion of mammary epithelial cells. Mean values of allele B-specific mRNA content were 50.6+/-0.5 and 54.0+/-0.9%, for cows HH and cows LH, respectively, and did not vary during lactation (P> 0.10). This suggests that the phenotypic expression of the genetic mutation that causes the differential allele-specific accumulation of kappa-casein mRNA was not affected by physiological and environmental factors, which tend to vary considerably throughout lactation.