The models cited above assumed that atmospheric hydroxyl radical (OH) sink over the period analysed did not vary. OH reacts with CH4 as the first step toward oxidation to CO2. In global CH4 budgets, the atmospheric OH sink has been difficult to quantify because its short lifetime (about 1 second) and its distribution is controlled by precursor species that have non-linear interactions (Taraborrelli et al., 2012608; Prather et al., 2017609). Understanding of the atmospheric OH sink has evolved recently. The development of credible time series of methyl chloroform (MCF: CH3CCl3) observations offered a way to understand temporal dynamics of OH abundance and applying this to global budgets further weakened the argument for the role of wetlands in determining temporal trends since 1990. Several authors used the MCF approach and concluded that changes in the atmospheric OH sink explained a large portion of the suppression in global CH4 concentrations relative to the pre-1999 trend (Turner et al. 2017610; Rigby et al. 2013611; McNorton et al. 2016612). These studies could not reject the null hypothesis that OH has remained constant in recent decades and they did not suggest a mechanism for the inferred OH concentration changes (Nisbet et al. 2019613). Nicely et al. (2018)614 used a mechanistic approach and demonstrated that variation in atmospheric OH was much lower than what MCF studies claimed that positive trends in OH due to the effects of water vapour, nitrogen oxides (NOx), tropospheric ozone and expansion of the tropical Hadley cells offsets the decrease in OH that is expected from increasing atmospheric CH4 concentrations.
The design and implementation of functional wildlife crossing structures should promote adequate interchange within the populations affected by roads, allow access to important resources, and ultimately enhance the viability of wildlife populations. However, scientifically understanding how much movement within the population is necessary, and what constitutes a barrier to connectivity, are difficult questions, especially for rare, elusive species such as Wolverine, Grizzly Bear or Lynx as captured in Figure 10. Future research using new methods such as non-invasive genetic sampling of hair or scats, satellite technology using global positioning system (GPS) transmitters, and spatially explicit population viability models may help answer some of these elusive management questions regarding roads, habitat fragmentation and population connectivity.
Biology The Dynamics Of Life Answer Key Chapter 2.zip
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