Land based sources of pollution (LBSP) have the potential to adversely impact coral reef ecosystem, either by directly affecting coral health and reproduction, or by altering the surrounding ecosystem in an deleterious way. Management efforts to reduce LBSP require that we understand the magnitude and extent of pollutants already in the system, and their potential effects on coral reef health.
Why We Care
Faga’alu watershed and Bay, located on the south shore of American Samoa near Pago Pago Harbor, was designated in 2012 by the US Coral Reef Task Force (USCRTF) as a priority watershed for the USCRTF Watershed Partnership Initiative. Significant scientific and management resources are being focused on this system. Part of this management process includes being able to measure ecological change in the system, including potential improvements in coral reef condition and reductions in land based sources of pollution (LBSP).
The watershed has one likely primary source of LBSP stress (a rock quarry generating sediment runoff), but also has several minor potential pollution sources including runoff from roads, poorly functioning septic systems/cesspools, a hospital, a history of piggeries and low intensity agriculture (e.g. bananas), and a now closed bay-side landfill.
In order to measure change, a starting point or “baseline” must be quantified. This study is part of a larger baseline characterization effort, which includes quantification of watershed fluxes of sediments and nutrients, sedimentation rates on corals in the Bay and an assessment of coral reef biological status.
This portion of the study complements these efforts with a quantitative assessment of the pollution present in the Bay.
What We Are Doing
Samples of surface sediments at thirteen sites in Faga’alu Bay and four sites in the watershed streams were collected in January 2014. The standard suite of NOAA National Status and Trends (NS&T) contaminants (metals, PAHs, pesticides, PCBs, organotins) were quantified in these samples. Following data quality assurance, the contaminant data were analyzed statistically and spatially, as well as compared to previously published toxic threshold values.
What We Are Finding
Concentrations of most analytes are below levels of concern. However, a handful of analytes are elevated above sediment quality guidelines and/or are in the 10% of national/historic sediment values (NOAA National Status and Trends dataset). These analytes include: arsenic, chromium, nickel, silver, zinc, various chlorinated pesticides (chlordane, DDT, endosulfan) and PCBs.
The watershed is a clear source of some constituents, such as chlordane, nickel, and zinc.
Some constituents are clearly not coming from the watershed, meaning that there is some other near shore source of pollution. It is possible that the legacy landfill on the north shore is contributing contaminants to the Bay through groundwater.
Nickel and zinc are some of the highest values observed compared to national/historic NOAA values. However, strong relationships between these crustal metals and aluminum, suggests that the source of these metals is crustal erosion, rather than some human use. It is possible that mining activities at the quarry have accelerated erosion, leading to higher than expected metals in the system.
Benefits of Our Work
These data have a two-fold utility. First, this study has identified several potential pollution issues (e.g. elevated concentrations of multiple pollutants near the legacy landfill) which may require additional study, and management actions. Second, this study serves as a baseline of current conditions against which change can be measured, including assessing the efficacy of management activities in the watershed, such as improved erosion control at the quarry.
Two major technical reports will be published in 2015. The first is a comprehensive presentment and analysis of the sediment contaminant information. The second is a shorter report aimed at jurisdictional managers, which summarizes and integrates the sediment contaminant work discussed here, with stream loading (nutrients and sediments) information (San Diego State University) and biological data (NOAA-Coral Reef Ecosystem Division).