Can the mineralogical signature of suspended sediments inform on the dynamics and resilience of river systems impacted by extreme climate events at Luquillo, Puerto Rico?

Abstract:

Climate change is happening and, in addition to the global rise in temperatures, induces a measurable increase in extreme climate events worldwide. That increase is expected to induce significant modifications in a variety of homeostatic systems, including streams and rivers. In the tropics, intense rainfall and high elevation combine to make tropical rivers the largest sediment source to the oceans. Because streams act as “regulators” of planetary sediment fluxes, an understanding of the effects of extreme events on their dynamic is necessary. Of notable importance, stream resilience and potential feedback aspects need to be assessed and eventually predicted. We captured the impact of a series of post-drought rewetting storms on stream sediment composition and quantities at the outlet of two contrasted rivers of the Luquillo CZO (Puerto Rico). Using quantitative X-Ray diffraction of the collected sediments we aimed at answering two questions: 1) Can the evolution of suspended sediments composition during extreme events inform on stream dynamics, and 2) Are these river systems resilient or destabilized by these events? We observed that, despite differences in watershed geology, the crystalline pool of suspended matter is similar in both rivers and that the amount of crystalline material generally increased with discharge (Figure). However, analysis of the evolution of the distribution of minerals during the sampling campaign, suggests that the activation of discharge-dependent water flowpaths controls the mineralogy of suspended sediments. It also suggests that individual stream settings rather than discharge is the primary control on the nature and quantity of suspended sediments during storm events. Overall, geological setting and pre-storm dynamics controlled sediment transport during storms in these two watersheds. Finally, stabilization of the suspended matter pool during rewetting revealed that both systems were resilient to extreme events with respect to the suspended sediment transport dynamic.