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Rapid erosion in mountain forests results in high rates of biospheric particulate organic carbon (POC) export by rivers, which can contribute to atmospheric carbon dioxide drawdown. However, coarse POC (CPOC) carried by particles >~1 mm is rarely quantified. In a forested pre-Alpine catchment, we measured CPOC transport rates and found that they increase more rapidly with water discharge than fine POC (<1 mm) and dissolved organic carbon (DOC). As a result, decadal estimates of CPOC yield of 12.3 ± 1.9 t C km^yr"1 are higher than for fine POC and DOC, even when excluding 4 extreme flood events. When including these floods, CPOC dominates organic carbon discharge (~80%). Most CPOC (69%) was water logged and denser than water, suggesting that CPOC has the potential to contribute to long-term sedimentary burial. Global fluxes remain poorly constrained, but if the transport behavior of CPOC shown here is common to other mountain streams and rivers, then neglecting CPOC discharge could lead to a large underestimation of the global transfer of biospheric POC from land to ocean. [ABSTRACT FROM AUTHOR]

On geological time scales, the erosion of carbon from the terrestrial biosphere and its burial in sediments can counter CO2 emissions from the solid Earth. Earthquakes may increase the erosion of this biospheric carbon and supply it to mountain rivers by triggering landslides, which rapidly strip hillslopes of vegetation and soil. Over the long term, elevated river sediment loads may promote more efficient carbon burial. However, riverine export of earthquakemobilized carbon has remained poorly constrained. Here we quantify biospheric carbon discharge by the Zagunao River following a large earthquake with a unique set of samples collected before and after the A.D. 2008 Mw 7.9 Wenchuan (China) earthquake. Radioactive and stable carbon isotopes are used to isolate the biospheric carbon, accounting for rock-derived organic carbon inputs. River discharge of biospheric carbon doubled in the downstream reaches, characterized by moderate landslide impact, following the earthquake. The rapid export of carbon from earthquake-triggered landslides appears to outpace its degradation on hillslopes while sediment loads are elevated. This means that enhanced river discharge of biospheric carbon following large earthquakes can link active tectonics to CO2 drawdown. [ABSTRACT FROM AUTHOR]

Large earthquakes in active mountain belts can trigger landslides, which mobilize large volumes of clastic sediment. Delivery of this material to river channels may result in aggradation and flooding, while sediment residing on hillslopes may increase the likelihood of subsequent landslides and debris flows. Despite recognition of these processes, the controls on the residence time of coseismic landslide sediment in river catchments remain poorly understood. Here we assess the residence time of fine-grained (<0.25 mm) landslide sediment mobilized by the C.E. 2008 Mw 7.9 Wenchuan earthquake, China, using daily suspended sediment discharge measured in 16 river catchments from 2006-2012. Following the earthquake, suspended sediment discharge was elevated 3-7x compared to 2006-2007. However, the total 2008-2012 export (92.5 ± 9.3 Mt from 68,719 km²) was much less than estimates of fine-grained sediment input by coseismic landslides (480 +350/-338 Mt) determined by landslide area-volume scaling and deposit grain-size distributions. We estimate the residence time of fine-grained sediment in the affected river catchments using the post-earthquake rate of sediment export, and find that it ranges from one year to over a century. The first-order variability in fine-sediment residence time is proportional to the areal extent of coseismic landsliding, and is inversely proportional to the frequency of intense runoff events (>5 mm day-1). Together with previous observations from the C.E. 1999 Chi-Chi earthquake in Taiwan, our results demonstrate the importance of landslide density and runoff intensity in setting the duration of earthquake-triggered landslide impacts on river systems. [ABSTRACT FROM AUTHOR]

Mineral weathering plays a primary role in the geologic carbon cycle. Silicate weathering by carbonic acid consumes CO² and stabilizes Earth's climate system. However, when sulfuric acid drives weathering, CO² can be released to the atmosphere. Recent work has established that sulfuric acid weathering resulting from sulfide mineral oxidation is globally significant and particularly important in rapidly eroding environments. In contrast, if SO4 ²-produced by sulfide oxidation is reduced during continental transit, then CO² release may be negated. Yet, little is known about how much SO4 ²-reduction takes place in terrestrial environments. We report oxygen and sulfur stable isotope ratios of SO4 ²-in river waters and mass budget calculations, which together suggest that SO4 ²-released from pyrite oxidation in the Peruvian Andes mountains is conservatively exported across ~300 km of the Amazon floodplain. In this system, floodplain SO4 ²-reduction does not counteract the large SO4 ²-flux from Andean pyrite weathering or measurably affect the stable isotope composition of riverine SO4 ²-. These findings support the hypothesis that uplift and erosion of sedimentary rocks drive release of CO² from the rock reservoir to the atmosphere. [ABSTRACT FROM AUTHOR]

Large earthquakes alter physical and chemical processes at Earth's surface, triggering landslides, fracturing rock, changing large-scale permeability, and influencing hydrologic pathways. The resulting effects on global chemical cycles are not fully known. Here we show changes in the dissolved chemistry of the Min Jiang, a river in the Yangtze River (China) headwaters, following the A.D. 2008 Mw 7.9 Wenchuan earthquake. Total solute fluxes transported by the Min Jiang increased after the earthquake, accompanied by an ~4x increase in Na*/Ca ratios (where Na* is Na+ corrected for atmospheric and evaporite contributions) and a 0.000644 ± 0.000146 increase in 87Sr/86Sr isotopic ratios. These changes are consistent with enhanced contribution from silicate sources. We infer that the CO2 consumption rate via silicate-derived alkalinity increased 4.3 ± 0.4 times. If similar changes are associated with other large earthquakes, enhanced solute export could directly link tectonic activity with weathering and alkalinity fluxes that supply nutrients to ecosystems, influence seawater chemistry evolution, and steer Earth's long-term carbon cycle and climate. [ABSTRACT FROM AUTHOR]