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Headwater gas exchange quantified from O2 mass balances at the reach scale.

ABSTRACT: Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon-relevant gases. Thus, we characterized variability in the gas exchange coefficient (k 2) and dissolved oxygen (O2) gas transfer velocity (k) in two lowland headwaters of the River Avon (UK). The traditional one-station open-water method was complemented by in situ quantification of riverine sources and sinks of O2 (i.e., groundwater inflow, photosynthesis, and respiration in both the water column and benthic compartment) enabling direct hourly estimates of k 2 at the reach-scale (~ 150?m) without relying on the nighttime regression method. Obtained k 2 values ranged from 0.001 h-1 to 0.600?h-1. Average daytime k 2 were a factor two higher than values at night, likely due to diel changes in water temperature and wind. Temperature contributed up to 46% of the variability in k on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that k variability is aligned with dominant temperature trends rather than with short-term changes. Similarly, wind correlation with k increased when clustering wind speeds in increments correspondent with dominant variations (1 m?s-1). Time scale is thus an important consideration when resolving physical drivers of gas exchange. Mean estimates of k 600 from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O2 budget assessment (within < 10%), adding further support to the validity of upscaling efforts aiming at quantifying large-scale riverine gas emissions.

SUBMITTER: Rovelli L

PROVIDER: S-EPMC6220971 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Headwater gas exchange quantified from O2 mass balances at the reach scale.

Rovelli L L Attard K M KM Heppell C M CM Binley A A Trimmer M M Glud R N RN

Limnology and oceanography, methods 20180928 10

Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon-relevant gases. Thus, we characterized variability in the gas exchange coefficient (k 2) and dissolved oxygen (O2) gas transfer velocity (k) in two lowland headwaters of the River Avon (UK). The traditional one-station open-water method was complemented by in situ quantification of riverine sources and sinks of O2 (i.e., grou ...[more]

PMID: 30450019

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Project description:Background: HIV infection is associated with impaired gas transfer in the lung as indicated by a low diffusing capacity (DLCO). Mechanisms for reduced DLCO in the setting of HIV infection are not well understood. We hypothesized that HIV-associated gas exchange impairment is indicative of system-wide perturbations that could be reflected by alterations in peripheral blood gene expression. Methods: A total of 40 HIV-infected (HIV+) and uninfected (HIV-) men with preserved versus reduced DLCO were selected from a larger cohort study of lung function. All subjects were current smokers and those with acute illness, lung diseases other than COPD or asthma were excluded. Total RNA was extracted from peripheral blood leukocytes (PBLs) and hybridized to whole-genome microarrays. Gene set enrichment analysis (GSEA) was performed between HIV+ vs. HIV- subjects with preserved DLCO and those with impaired DLCO to identify differentially activated pathways. Results: Using pathway-based analyses we found that in subjects with preserved DLCO, HIV infection is associated with activation of processes involved in immunity, cell cycle, and apoptosis. When we applied a similar analysis to subjects with low DLCO, we identified a much broader repertoire of inflammatory and immune-related pathways in HIV+ patients relative to HIV- subjects, with up-regulation of multiple interleukin pathways, interferon signaling, Toll-like receptor signaling, and T cell/B cell receptor signaling. We confirmed elevated circulating levels of IL-6 in HIV+ patients with reduced DLCO relative to the other groups. Conclusions: Our findings reveal that PBLs of subjects with HIV infection and low DLCO are distinguished by widespread enrichment of immuno-inflammatory programs. Activation of these pathways may alter the biology of circulating leukocytes and play a role in the pathogenesis of HIV-associated pulmonary gas exchange impairment. Total RNA was isolated from peripheral blood leukocytes in four subject groups: 1. HIV-, low DLCO (N = 11); 2. HIV+, low DLCO (N = 10); 3. HIV-, preserved DLCO (N = 9); 4. HIV+, preserved DLCO (N = 9). Each sample was hybridized to an Affymetrix PrimeView Human Gene Expression microarray for a total of 39 experiments.

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Headwater gas exchange quantified from O2 mass balances at the reach scale.

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Headwater gas exchange quantified from O<sub>2</sub> mass balances at the reach scale.

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