Determining the Provenance of Suspended Sediment: Storm Sampling in Northeastern Puerto Rico

Project Description: 

Motivation for study:
1. How does a single precipitation event erode a landscape?
2. Can we determine provenance of suspended sediments during a flood event?
3. Do source areas contributing suspended sediments vary over the course of a hydrograph?

Landscape evolution is largely determined by weathering/erosion rates and subsequent transportation of material. However, it is unclear what controls total denudation, as no strong correlation exists between climate and total denudation. For this project I am interested in identifying possible sediment source regions to better understand weathering and erosion on a short time scale. To do this, we apply multiple isotopic tracers (meteoric 10Be and 7Be) to suspended sediment samples collected from multiple watershed locations at various stages over course of a storm hydrograph.

We are also interested in understanding if sediment sources change over the course of the storm hydrograph due to variations in rainfall magnitude and intensity and changes in flow paths. This isotopic fingerprinting of suspended sediment coupled with proper characterization of source regions will provide a clear and robust understanding of active sediment source regions present throughout the watershed, which could prove key to pinpointing sources of fine sediment pollution, as it is estimated that over 90% of sediment export through river systems in Puerto Rico is through suspended load.

Last summer we collected multiple suspended sediment samples during a high flow event on June 7th, 2011 at three sites; Puente Roto (Mameyes watershed), Bisley I (upper Mameyes watershed), and Rio Icacos (Icacos watershed). This large-scale suspended sediment collection effort was aided by many participants actively conducting research in the Mameyes and Icacos watersheds. In an effort to determine sediment sources and constrains on the amount contributed by each source, we are currently considering a two end-member contribution to suspended sediment during high flow - stable sources, such as ridge top crests and unstable sources, such as landslide scars. Sediments from possible source regions (including ridge top crests and landslide scars) were also collected last summer to compare with the isotopic signals collected in high flow suspended sediment samples (figs. 1 and 2).

Future work will include synthesizing multiple data sets (water stable isotope measurements, Hg analysis, organic matter carbon isotopic composition, etc.) for the same storm event, collecting more high flow suspended sediment collections along with possible source characterization samples in both the Rio Mameyes and Rio Icacos watersheds.

Research Location: 
Core Area(s) and/or Keywords: 

hydrograph, erosion, suspended sediment, isotopic fingerprinting

Source of Funding: 
NSF CZO Program
Contact Information
Person(s) Completing This Form: 
Marcie E. Occhi
Dr. Jane Willenbring, Marcie E. Occhi
Investigator E-mail Addresses: