Published research emphasizes rapid downstream export of terrestrial carbon from mountainous headwater rivers, but little work focuses on mechanisms that create carbon storage along these rivers, or on the volume of carbon storage. Here we estimate organic carbon stored in diverse valley types of headwater rivers in Rocky Mountain National Park, CO, USA. We show that low-gradient, broad valley bottoms with old-growth forest or active beaver colonies store the great majority of above-and below-ground carbon. These laterally unconfined valley segments constitute o25% of total river length, but store B75% of the carbon. Floodplain sediment and coarse wood dominate carbon storage. Our estimates of riverine carbon storage represent a previously undocumented but important carbon sink. Our results indicate that: not all mountainous rivers rapidly export carbon; not all valley segments are equally important in carbon storage; and historical changes in riverine complexity have likely reduced carbon storage.

In this paper we describe hillslope‐scale, rainfall‐simulation experiments on karst shrublands dominated by Ashe juniper. These simulations, designed to mimic flood‐producing rainfall events, were carried out at two sites separated by 206 km within the Edwards Plateau of Central Texas. Five hillslope plots were instrumented—two shrub‐covered (canopy) plots and three intercanopy plots measuring 12–14 m in length. We repeated the experiments on the canopy plots after removing the shrubs. For the canopy plots, both before and after shrub removal, 50% or more of the water applied exited the plots as subsurface stormflow and no overland flow occurred. For the intercanopy plots, subsurface stormflow amounted to less than 10% of the water applied and overland flow was between 10 and 50%. These experiments demonstrate the importance of subsurface stormflow in semiarid karst shrublands during flood events, and more generally highlight the fact that subsurface stormflow is important in some semiarid landscapes.

In drylands across the globe, grasslands and savannas have succumbed to encroachment by woody plants. There is a concern that, in some cases, these changes may lead to lower groundwater recharge and streamflow. In karst landscapes, the effect of woody plants on recharge is difficult to determine because of the shallow and rocky soils. In our study, we estimated the amount of water entering a shallow cave (3–5 m deep) as a surrogate measurement for groundwater recharge, to evaluate whether the removal of Ashe juniper (Juniperus ashei) above the cave would affect recharge. Three sets of large‐scale rainfall simulations were conducted in 2005, before removal of the overstory juniper; seven were conducted in 2008, soon after the juniper were removed; and two were conducted in 2009, one year after juniper removal. We found that recharge occurred mainly via conduits or macropores and, as such, was extremely dynamic and responsive to rainfall. The amount of recharge ranged from 3% to 17% of the water applied, the higher percentages being measured when antecedent soil conditions were wet. At least in this case of recharge taking place via conduit flow, removal of the juniper had little if any effect. Copyright © 2012 John Wiley & Sons, Ltd.

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