Control Points in Ecosystems: Moving Beyond the Hot Spot Hot Moment Concept

Landscape analysis of soil methane flux across complex terrain

“…Here, even if the maximum F CH 4 from the riparian area were used to estimate net efflux, it would have to comprise over 25 % of the watershed area to offset the net CH 4 consumption in the uplands. As noted in a recent review by Bernhardt et al (2017), it is critically important to perform these scaling exercises to determine the relative influences of point scale measurements on net watershed balances. These results highlight the importance of accounting for the upland CH 4 sink, which can significantly offset high rates of methane production in riparian areas.…”

“…A spatially explicit understanding of heterogeneity in CH 4 fluxes is necessary for appropriate watershed scale budgets (Ullah and Moore, 2011;Bernhardt et al, 2017), particularly in mountainous regions, where the spatial distribution of resources could have a significant influence on the direction and magnitude of CH 4 fluxes due to the lateral redistribution of water and substrates caused by convergent and divergent areas of the landscape (Davidson and Swank, 1986;Meixner and Eugster, 1999;Wachinger et al, 2000;von Fischer and Hedin, 2002). Although many studies have quantified the magnitude and variability of CH 4 fluxes, they often covered large spatial extents (from transects that are tens of meters to hundreds of kilometers long) which captured significant environmental gradients at those scales, but sampling locations were generally sparse (Del Grosso et al, 2000;Yu et al, 2008;Teh et al, 2014;Tian et al, 2014).…”

Landscape analysis of soil methane flux across complex terrain

“…However, at larger scales these environmental conditions can be heavily influenced by physical processes such as landscape scale (kms) hydrology (Burt and Pinay, 2005;Lohse et al, 2009), and at still larger scales (100 kms; here we will refer to as "ecosystem scale"), parent material and climate create the setting in which these processes occur (Potter et al, 1996;Tang et al, 2006;Tian et al, 2010). 20 A spatially explicit understanding of heterogeneity in CH4 fluxes is necessary for appropriate watershed scale budgets (Ullah and Moore, 2011;Bernhardt et al, 2017), particularly in mountainous regions, where the spatial distribution of resources could have a significant influence on the direction and magnitude of CH4 fluxes due to the lateral redistribution of water and substrates caused by convergent and divergent areas of the landscape (Davidson and Swank, 1986;Meixner and Eugster, 1999;25 Wachinger et al, 2000;von Fischer and Hedin, 2002). Although many studies have quantified the magnitude and variability of CH4 fluxes, they often covered large spatial extents (from transects 10s of meters long to 100s kms) which captured significant environmental gradients at those scales, but sampling locations were generally sparse (Del Grosso et al, 2000;Yu et al, 2008;Teh et al, 2014;Tian et al, 2014).…”

“…Here, even if the maximum FCH4 from the riparian area was used to estimate net efflux, it would have to comprise over 25% of the watershed area to offset the net CH4 consumption in the uplands. As noted in a recent review by Bernhardt et al (2017) it is critically important to perform these 20 scaling exercises to determine the relative influences of point scale measurements on net watershed balances. These results highlight the importance of accounting for the upland CH4 sink which can significantly offset high rates of methane production in riparian areas.…”

On the Relationship Between Flood and Contributing Area

“…The influence of contributing area behaviour is implicitly understood to be very important for solute fluxes. The concepts of 'hot moments' and 'hot spots' (McClain et al, 2003;Bernhardt et al, 2017) capture this idea that there are locations and periods that provide disproportionate sources of chemical 15 loads to streams and lakes. To explain and solve many of today's problems associated with contaminants and excess nutrients in the aquatic ecosystem and human water supply, it is not only necessary to identify the extent and location of contributing areas of solutes, but also the frequency and duration with which these areas are engaged.…”