Watershed runoff can adversely affect the health of coral reefs. Our work will provide coral reef managers with a method to monitor land-based runoff and, in conjunction with other data, to assess runoff mitigation practices.
Why We Care
Coral reef managers are concerned about the impact of land-based runoff on coral reefs. Sediment carried in the runoff can physically bury corals, blocking light needed by symbiotic algae that live in and sustain corals and acting as a vector for land-based contaminants.
For this satellite-based study, we chose three different geographic areas identified by the United States Coral Reef Task Force as priority watersheds for investigation: Guánica Bay, Puerto Rico; West Maui, Hawaii; and Faga’alu Bay, Tutuila, American Samoa. Optical satellite sensors provide a routine means to monitor both the land and ocean portions of the watershed. Ocean color allows these satellite sensors to monitor sediment plumes, which would otherwise require ship- and aircraft-based missions to track, methods that are both expensive and easily hampered by bad weather. Satellite-based monitoring of ocean color provides an effective way to get synoptic and routine (daily) views of sediment plumes.
What We Did
In southwest Puerto Rico, we established a local lead scientist for ocean color–related work, and established satellite-derived sensor product protocols and in situ and laboratory protocols, as well as created suites of products designed to incorporate and increase spatial resolution that is presently evolving. In West Maui, we established a close collaboration with local partners, including the Hawaii Division of Aquatic Resources, the University of Hawaii, the State of Hawaii’s Natural Energy Laboratory of Hawaii Authority (NELHA), and have provided and set up field and laboratory equipment and training for our students and partners. We have also started developing a watershed manager’s graphical information system (GIS)–based tool for both Puerto Rico and West Maui, and will consolidate these systems where appropriate. We have been awarded an ongoing “small business innovative research” project designed to address the lack of in situ data that will automate and supplement our students in situ data measurements.
We have taken water quality measurements (chlorophyll a, total suspended sediments, attenuation coefficients, and some colored dissolved organic matter determinations) and are matching them to Visible Infrared Imaging Radiometer Suite (VIIRS) products. We are investigating re-suspended sediments and near shore micro-currents, along with bottom albedo, to improve products that distinguish land runoff. Working with native Hawaiian students via a local intern program, we have created a GIS data tool and have studied the spatial and temporal resolution of satellite sensors, as well as the number of available in situ measurements for the study in Hawaiian waters. We anticipate the Hawaiian GIS-based system becoming a component of our watershed managers’ tool.
Work in Faga’alu Bay, Tutuila, American Samoa is in the planning stage (waiting for the availability of higher-resolution data).
This project is a collaboration between NCCOS and the NOAA Satellite and Information Service’s (NESDIS) Center for Satellite Applications and Research (STAR). NOAA post-doctoral researcher William J. Hernandez (University of Puerto Rico–Mayaguez) is leading the development of satellite sensor–derived products and in situ water quality and benthic studies for Puerto Rico.
The project received funding from NOAA’s Coral Reef Conservation Program to develop pilot products, which if warranted, will become NOAA operational satellite sensor–derived products that synoptically monitor the runoff plumes in the previously mentioned geographic areas.
What We Found
The sediment plumes in both Guánica Bay and West Maui are more extensive than previously suspected. Our Hawaiian student clearly showed that we need higher spatial resolution imagery that includes morning ascending satellites. The project also requires improved geographic coverage, particularly within the littoral zones.
This watershed monitoring project is ongoing. We are compiling results for Puerto Rico, and ocean color fieldwork is now underway in West Maui. Work in Faga’alu Bay, Tutuila, American Samoa is in the planning stage.
Moving forward, our plan to assist coral reef watershed managers includes:
1) Monitoring plumes as mitigating methods are employed to reduce runoff.
2) Using archived data, where available, to assess which sediment mitigation methods work best for a particular watershed.
3) Determining the distribution of sediments as a function of rainfall amount, plume extent, and surface and subsurface currents.
4) Incorporating models of plume extent and distribution to current monitoring.
5) Determining the source(s) of sediment runoff affecting corals, and generating estimates of the amount of sediment material from watershed runoff that is deposited onto corals.
6) Assessing stressors to coral physiology and ecosystem health, especially sediments, which will tie the monitoring of sediments to coral health.
7) Building a watershed manager’s GIS-based tool for appropriate data sources enabling managers to conduct assessments and research.