Wohl Ellen, Knox Richard L
Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482, USA.
Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482, USA.
Sci Total Environ. 2022 Dec 15;852:158507. doi: 10.1016/j.scitotenv.2022.158507. Epub 2022 Sep 2.
The lack of watershed-scale estimates of floodplain carbon stocks limits recognition of the important role of floodplains and river corridor restoration in efforts to enhance carbon sequestration. We use the South Platte River watershed of Colorado, USA as a case study to illustrate spatial patterns of, and controls on, floodplain carbon stocks at the watershed scale. This case study illustrates the disproportionate importance of floodplains for soil carbon stocks relative to adjacent uplands and provides an example of how spatially explicit data can be used to prioritize floodplain restoration with regard to carbon sequestration. We use the hydrogeomorphic floodplain tool GFPLAIN to delineate the extent of 100-year floodplains in the South Platte River watershed. We distinguish elevation bands for the steppe, montane, subalpine, and alpine zones. We also differentiate bead (floodplain width/channel width ≥ 5) and string (floodplain width/channel width < 5) reaches within the montane and subalpine zones. Drawing on prior, field-based measurements of organic carbon stock in downed, dead wood and soil in these floodplain types, we estimate total floodplain organic carbon stock based on median values of stock in different floodplain types and the spatial extent of these floodplain types. This estimate includes organic carbon stocks in lake and reservoir sediments in the watershed. Soil constitutes the greatest reservoir of floodplain carbon. The total estimated area of floodplain is 2916 km, which is 4.3 % of the total watershed area of the South Platte River. Our preferred estimate is 42.7 Tg C stock (likely range of 39.1-42.7 Tg). This equates to 11.1 % of a previously estimated overall carbon stock (above and belowground biomass and soil organic carbon) in the entire watershed of 384 Tg C. Floodplains are thus disproportionately important, relative to their surface area, in storing organic carbon in this semiarid watershed. Field measurements of floodplain soil organic carbon stocks from across the globe indicate that this finding is not unique to this watershed, with implications for prioritizing floodplain management and restoration as a means of enhancing carbon sequestration.
缺乏对洪泛区碳储量的流域尺度估算，限制了人们对洪泛区和河道走廊恢复在增强碳固存努力中所起重要作用的认识。我们以美国科罗拉多州的南普拉特河流域为例，来说明流域尺度上洪泛区碳储量的空间格局及其控制因素。该案例研究表明，相对于相邻高地，洪泛区对土壤碳储量具有不成比例的重要性，并提供了一个示例，说明如何利用空间明确的数据来确定洪泛区恢复在碳固存方面的优先次序。我们使用水文地貌洪泛区工具GFPLAIN来划定南普拉特河流域百年一遇洪泛区的范围。我们区分了草原、山地、亚高山和高山地带的海拔带。我们还区分了山地和亚高山地带内的辫状（洪泛区宽度/河道宽度≥5）和线状（洪泛区宽度/河道宽度<5）河段。根据此前对这些洪泛区类型中倒下的枯木和土壤中有机碳储量的实地测量，我们基于不同洪泛区类型中储量的中值以及这些洪泛区类型的空间范围，估算了洪泛区有机碳总储量。该估算包括流域内湖泊和水库沉积物中的有机碳储量。土壤是洪泛区碳的最大储存库。估算的洪泛区总面积为2916平方公里，占南普拉特河总流域面积的4.3%。我们的最佳估算值是42.7太克碳储量（可能范围为39.1 - 42.7太克）。这相当于此前估算的整个流域（地上和地下生物量以及土壤有机碳）384太克碳总储量的11.1%。因此，在这个半干旱流域中，相对于其表面积而言，洪泛区在储存有机碳方面具有不成比例的重要性。来自全球各地的洪泛区土壤有机碳储量实地测量表明，这一发现并非该流域所独有，这对将洪泛区管理和恢复作为增强碳固存手段的优先次序具有启示意义。
