Precipitation patterns control the distribution and export of large wood at the catchment scale

Abstract

26Large wood (LW) plays an important role in river ecosystems, but LW-laden floods 27 may cause serious damage to human lives and property. The relationship between 28 precipitation patterns and variations in LW distribution and export at the watershed scale is 29 poorly understood. To explore these linkages, we examined differences in LW distribution as 30 a function of channel morphologies in six watersheds located in southern and northern Japan, 31 and analyzed the impacts of different precipitation patterns on the fluvial export of LW from 32 river catchments. In southern Japan, intense rainfalls caused by typhoons or localized 33 torrential downpours initiate landslides and debris flows that introduce massive amounts of 34 LW into channels. Gravel bars formed by frequent flood events are widely prevalent, and the 35 LW temporarily stored on these bars is frequently moved and/or broken into smaller pieces 36 by floods. In these systems fluvial export of LW is supply-limited, with smaller 37 accumulations and shorter residence times than in northern Japan. Conversely, in northern 38 Japan, where typhoons and torrential downpours rarely occur, LW is mostly recruited by 39 bank erosion, tree mortality and windthrow into channels, rather than by landslides and debris 40 flows. Recruited pieces accumulate in log jams on valley floors, particularly on floodplains 41 supporting mature forests, resulting in larger accumulations and longer residence times. In 42 these watersheds fluvial export of LW is transport-limited, and the pieces gradually 43 decompose during long-term storage as log jams. 44 45

Wood export varies among decadal, annual, seasonal, and daily scale hydrologic regimes in a large, Mediterranean climate, mountain river watershed

“…Across a wide range of reservoirs in Japan, 75 peak annual (Seo et al, 2008) and latitudinal variations in precipitation were significant 76 factors in explaining differences in %&# quantities (Seo et al, 2012), with typhoon-77 generated flooding delivering more %&# into reservoirs even though less stored wood 78 was available for transport in watersheds with higher precipitation totals (Seo et al, 2015). 79…”

Wood export prediction at the watershed scale

“…The broadly defined term of watershed processes used in this study includes hydrologic, geomorphic, hydraulic, ecological, and climatic processes that are known to be present, active, and responsible for variations in wood budgeting components at local and watershed scales (Benda and Sias, ; Gregory et al ., ) and at landscape scales (Seo et al ., ). A companion paper, Senter et al .…”

“…The broadly defined term of watershed processes used in this study includes hydrologic, geomorphic, hydraulic, ecological, and climatic processes that are known to be present, active, and responsible for variations in wood budgeting components at local and watershed scales (Benda and Sias, 2003;Gregory et al, 2003) and at landscape scales (Seo et al, 2015). A companion paper, Senter et al (2017), detailed additional aspects of the work done in the North Yuba River watershed, and introduced a conceptual illustration and functional framework of watershed process wood responses to hydrologic and climatic conditions.…”

Floating matter: a neglected component of the ecological integrity of rivers

“…This cycle is controlled by hydrogeomorphological, biological, and anthropogenic factors (Fig. 2) (Webster and Meyer, 1997;Gurnell et al 2002;Quinn et al, 2007;Tank et al, 2010;Fremier et al 2010;Le Lay et al 2013;Turowski et al 2013;Seo et al 2015;Ruiz-Villanueva et al 2016a,b;Kramer and Wohl 2016;Bunte et al, 2016;Kooi et al 2018, and references therein). The dynamics of FM along rivers are frequently interconnected with those of mineral sediments as demonstated for seeds, vegetative particles of plants, and large wood (e.g.…”