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This study investigates the dynamics of riverine DOC concentrations during a series of stream discharge events (3–10 days) following rainstorms of different intensity and duration. We examined six events, when high-frequency (hourly) water samples for DOC (n = 321) were collected in spring (n = 166) and autumn (n = 155). Results identified three distinct water-mediated processes during stream discharges events that linked DOC source supply from agricultural land surfaces with sinks in a receiving river. These were as follows: 1) snowpack drives significant high DOC concentrations in base-flow during spring, 2) abundant organic matter in topsoil from crop residues determines a rapid DOC loading profile in the first flush, and 3) very large hydro-climatic events in snow-melting season over agricultural watersheds could increase the riverine DOC flux by 2.3 folds. These results revealed that ca. 76.5% of annual DOC was exported during a handful of storm-discharge events (78.9% for spring and 74.2% from autumn) over agricultural landscapes. Given the significant amount of riverine DOC exported from agricultural landscapes during severe weather events, our results suggest that changes in climate promote larger precipitation events that would likely enhance the export of terrestrial DOC to receiving water bodies. The study presents a semi-analytical model that is able to extrapolate the riverine DOC dynamics during storm discharge events of varying duration and intensity (R 2 up to 0.9). [ABSTRACT FROM AUTHOR]

Abstract: Understanding the generation mechanisms of lahars is important for improving volcanic hazard assessments. The Taisho lahar (TL) was generated during the 1926 eruption of Tokachidake Volcano, Japan, and was considered a typical snowmelt lahar caused by the runout of hot debris onto a snow-covered slope. A similar mechanism produced a huge mud flow during the 1985 eruption of Nevado del Ruiz, Colombia. However, the origin of water in such lahars remains a controversial topic because the calculated water mass is based on the assumption that all of the snow on the runout area of the TL was melted, although this is much less than the estimated water volume in the TL estimated by previous studies. I have re-examined proximal deposits of the TL and their paleomagnetic characteristics in order to better understand the eruption sequence and formation of the TL. The TL produced two debris avalanche deposits and a surge-like deposit that had relatively high emplacement temperature (~350°C). The deposits are composed of hydrothermally altered andesitic gravel, sand and mud. The high clay content (3–5wt.% clay in the <2mm fraction) and sedimentary characteristics indicate that the flow was a cohesive lahar, most likely induced by collapse of a hydrothermally altered pyroclastic cone (hypocenter). The presence of the surge deposit indicates that the TL was not caused by simple collapse of a cinder cone but by a phreatic explosion that resulted in sector collapse. This suggests that the hydrothermal system was related to the 1926 eruption. The present-day volcano has a large hydrothermal system (1×106 m3 water) beneath the active crater. This study indicates that hydrothermal system explosions can trigger cohesive lahars that contain both snow melt and hydrothermal pore water, and this indicates the need to monitor hydrothermal systems. [Copyright &y& Elsevier]

Abstract: Both Δ14C and δ13C were used to study transport behavior of particulate organic matter (POM) in the Ishikari River in Japan. Water samples were collected once a month from April to September in 2004. Positive correlations were found between Δ14C and particulate organic carbon (POC) content and Δ14C and δ13C values for the POM samples from June to September. However during snow-melt, distinctive minimum values were found for POC content, Δ14C and δ13C. These results indicate the POC was supplied from different sources and by different mechanisms during spring snow-melt and summer because of variations in water level and discharge. [Copyright &y& Elsevier]