Effects of mass wasting on fluvial sediments in Puerto Rico following
Hurricane Maria
Abstract
Mass wasting plays an important role on carbon cycling and sequestration
by exposing fresh, weatherable bedrock and delivering hillslope
sediments to lowlands and fluvial systems. Chemical weathering
signatures of landslide-derived fluvial sediments can be used to
understand linkages between hillslope and fluvial processes, and thus to
characterize spatiotemporal dynamics of sediments. However, chemical
signatures of fluvial sediments derived by landslides are yet to be
fully understood. Here we compare the bulk chemistry, mineralogy, and
grain size of fluvial sediments collected pre- and post-Hurricane Maria
(landfall on Sept. 20, 2017) in the Rio Guayanés and Rio Guayabo River
watersheds in southeastern Puerto Rico to help fill this knowledge gap.
Relative to fluvial muds collected before Hurricane Maria, mud samples
collected after the storm exhibit higher weathering index values, but
coarser grain size modes. We infer that small landslides triggered by
Hurricane Maria transported slope materials from shallow depths,
including weathered topsoil and saprolite, as opposed to previous
deep-seated landslides which likely sampled regolith and bedrock. The
variances in weathering indices observed pre- and post-hurricane do not
reflect climate change, but rather subtle differences in transport
mechanism which produce significant differences in weathering indices
recorded by fluvial sediments. We propose that weathering indices
provide a means to understand sediment dynamics in mountainous regions,
particularly for sediment transported in the immediate aftermath of
landslides triggered by extreme events, such as precipitation and
earthquakes, and also provide important datasets required for mapping
potential carbon sequestration across a landscape.