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Streams and rivers are major sources of greenhouse gases (GHGs) to the atmosphere, as carbon and nitrogen are converted and outgassed during transport. Although our understanding of drivers of individual GHG fluxes has improved with numerous site‐specific studies and global‐scale compilations, our ability to parse out interrelated physical and biogeochemical drivers of gas concentrations is limited by a lack of consistently collected, temporally continuous samples of GHGs and their associated drivers. We present a first analysis of such a dataset collected by the National Ecological Observatory Network across 27 streams and rivers across ecoclimatic domains of the United States. Average concentrations of CO2 ranged from 36.9 ± 0.88 to 404 ± 33 μmol L−1, CH4 from 0.003 ± 0.0003 to 4.99 ± 0.72 μmol L−1, and N2O from 0.015 to 0.04 μmol L−1 and spanned ranges of previous global compilations. Both CO2 and CH4 were strongly affected by physical drivers including mean air temperature and stream slope, as well as by dissolved oxygen and total nitrogen concentrations. N2O was exclusively correlated with total nitrogen concentrations. Results suggested that potential for gas exchange dominated patterns in gas concentrations at the site level, but contributions of in‐stream aerobic and anaerobic metabolism, and groundwater also likely varied across sites. The highest gas concentrations as well as highest variability occurred in low‐gradient, warmer, and nonperennial systems. These results are a first step in providing unprecedented, continuous estimates of GHG flux constrained by temporally variable physical and biogeochemical drivers of GHG production. [ABSTRACT FROM AUTHOR]

Investigates the mechanical properties of alternating poly(propylene carbonate) (PPC) copolymer in the U.S. Method used to determine the thermal stability of PPC; Molecular weight of PPC; Percentage rate used to purify propylene oxide and carbon dioxide.

Summary • Understanding and predicting the impacts of elevated atmospheric CO2 , elevated nitrogen deposition, and decreases in plant diversity require better understanding of the way in which plant species influence soil CO2 flux. • In experimental grassland plots where atmospheric CO2 , nitrogen supply, and species composition and diversity were manipulated, species effects on soil CO2 flux during 19 sampling periods over 2 yr were determined for 16 grassland species. • The average effect of a species on soil CO2 flux was correlated with biomass of the species grown in monoculture, suggesting that effects of species on soil CO2 flux are related to the potential productivity of a species and total belowground C allocation. During dry, warm conditions there is a greater effect of elevated atmospheric CO2 on soil CO2 flux and during these times deeper-rooted species contribute to soil CO2 flux more than average. • Although differences in responses to elevated CO2 and nitrogen among species were not great, decreases in diversity can affect belowground carbon allocation depending on the plant traits of the species that are lost from ecosystems. [ABSTRACT FROM AUTHOR]