Climatic and geomorphic controls on the erosion of terrestrial biomass from subtropical mountain forest

Abstract

[1] Erosion of particulate organic carbon (POC) occurs at very high rates in mountain river catchments, yet the proportion derived recently from atmospheric CO 2 in the terrestrial biosphere (POC non-fossil ) remains poorly constrained. Here we examine the transport of POC non-fossil in mountain rivers of Taiwan and its climatic and geomorphic controls. In 11 catchments we have combined previous geochemical quantification of POC source (accounting for fossil POC from bedrock), with measurements of water discharge (Q w ) and suspended sediment concentration over 2 years. In these catchments, POC non-fossil concentration (mg L À1 ) was positively correlated with Q w , with enhanced loads at high flow attributed to rainfall driven supply of POC non-fossil from forested hillslopes. This climatic control on POC non-fossil transport was moderated by catchment geomorphology: the gradient of a linear relation of POC non-fossil concentration and Q w increased as the proportion of steep hillslopes (>35 ) in the catchment increased. The data suggest enhanced supply of POC non-fossil by erosion processes which act most efficiently on the steepest sections of forest. Across Taiwan, POC non-fossil yield was correlated with suspended sediment yield, with a mean of 21 AE 10 tC km À2 yr À1 . At this rate, export of POC non-fossil imparts an upper bound on the time available for biospheric growth, of $800 yr. Over longer time periods, POC non-fossil transferred with large amounts of clastic sediment can contribute to sequestration of atmospheric CO 2 if buried in marine sediments. Our results show that this carbon transfer should be enhanced in a wetter and stormier climate, and the rates moderated on geological timescales by the regional tectonic setting.

Variability in runoff fluxes of dissolved and particulate carbon and nitrogen from two watersheds of different tree species during intense storm events

“…Higher annual POC fluxes than DOC fluxes were observed in some mountainous forested watersheds (Kao and Liu, 1997;Kim et al, 2010;Lloret et al, 2013), which does not agree with our finding and some other studies Inamdar et al, 2011;Jeong et al, 2012). The differences in findings may be related to the topography of forested watershed because steeper slopes induce higher fluxes of POC (Hilton et al, 2012;Janeau et al, 2014;Jung et al, 2012).…”

Understanding terrestrial organic carbon export : a time-series approach

“…While similar within uncertainty, our estimates are slightly lower than catchment-specific rhenium-based values, and may suggest additional OC petro oxidation in locations not captured by our soil samples such as landslide colluvium (Emberson et al, 2016) and/or during fluvial transit (Galy et al, 2008a). This flux is on the same order of magnitude as CO 2 drawdown due to OC bio export from rivers combined with subsequent burial in marine sediments [Taiwan average: (21 ± 10) t C km −2 yr −1 ; Figure 6.S2C; Hilton et al, 2012] as well as that due to weathering of silicate minerals (LiWu River: 7.04 t C km −2 yr −1 ; Figure 6.S2D;Calmels et al, 2011). OC petro oxidation in thin mountain soils is therefore a quantitatively important process in setting the net role of these systems within the global carbon cycle.…”

“…Well-characterized OC petro and OC bio yields by these rivers (Hilton et al, , 2012 as well as previous estimates of catchment-wide OC petro oxidation rates using the trace element rhenium , provide a framework in which to interpret our results. Soil samples span a range of lithologies (Tananao schist, Lushan and Pilushan sedimentary formations), depths (0.0 m to 0.9 m), slope angles (1°to 50°), and elevations (122 m to 3192 m) that are representative of the mountain belt .…”

“…For example, recent studies (e.g. Hilton et al, , 2012 highlight the importance of erosive processes and sediment yield in determining both OC bio and OC petro export fluxes, suggesting that increased storm-driven erosion due to elevated pCO 2 could provide a negative feedback by increasing OC bio burial in marine sediments.…”

Spatial and temporal dynamics of biogeochemical processes in the Fraser River, Canada : a coupled organic-inorganic perspective

“…The amount of riverine particulate organic carbon (POC) derived from recent terrestrial photosynthesis versus aquatic productivity and weathering of petrogenic organic carbon is controlled by a range of tectonic, climatic, geomorphologic, and biogeochemical processes (Blair et al, 2004;Leithold et al, 2006;Longworth et al, 2007;Hilton et al, 2010;Hovius et al, 2011;Hilton et al, 2012;Bouchez et al, 2014), which differ significantly across river basins.…”