An investigation of the stable isotopes, geochemistry and morphology of major streams in Dominica, Lesser Antilles: 2014 - 2017
Abstract
The island of Dominica is a recently active (<200 ka) volcanic island located in the Lesser Antilles, with nine potentially active centers. Of the volcanic islands of the Lesser Antilles, it is the most rugged and has one the greatest stream densities (350 over 750 km2) and precipitation rates (up to 10,000 mm/yr in the mountainous interior). Sixty-seven meteoric streams across the island have been sampled annually over the last 4 years. Field measurements including pictures, pH and temperature, were recorded and water samples taken and analyzed for alkalinity, major elements (cations and anions), trace elements and stable isotopes (carbon, deuterium, and oxygen). Variations in water chemistry and river morphology were compared to various parameters, including precipitation, landslide locations, and lithology for each of the catchments. Within the study period, on August 27th, 2015, a significant tropical storm, Erika, made landfall in Dominica, depositing more than 500 mm of rainfall in 10 hours. There was little infiltration of the rainwater (over 50-60% run-off), which resulted in significant landslides, flash floods and damage to infrastructure and loss of life. Despite the obvious morphologic changes to the streams and high discharge during the storm event, preliminary analysis has shown little change in major stream geochemistry following the passage of Tropical Storm Erika. The 10-month time gap between the storm and the post-storm field sampling in June 2016 may be a factor of why geochemical changes were not observed. One of the most significant variations of stream composition during the study period was annual shifts in δD between -1.3 to -5.8 ‰ and δ18O between -1.98 to -2.61 ‰. A possible factor influencing the δ18O of surface waters is seasonal variation in rainfall. The dominant control on precipitation δ18O values is the amount effect, whereby rainfall amount and δ18O are inversely correlated. This relationship is a proxy for changes in δ18O values of surface waters. The data also suggest that hydrothermal fluids are not a prominent contributor to Dominican rivers, despite the presence of active volcanism and numerous hydrothermal systems on the island. The exceptions are the White River, which drains the Valley of Desolation and Boiling Lake and the Lamothe River, which drains the Cold Soufrierre.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.H41C1455K
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0470 Nutrients and nutrient cycling;
- BIOGEOSCIENCES;
- 1804 Catchment;
- HYDROLOGY;
- 1836 Hydrological cycles and budgets;
- HYDROLOGY