Land-Based Pollution

Impacts of Land‐Based Sources of Pollution on Coral Reefs

Land‐Based Sources of Pollution are a significant threat to the integrity of nearshore coral ecosystems in the USVI. Rates of silt accumulation, often associated with terrestrial sediment‐laden runoff, increase dramatically from offshore to nearshore waters of the USVI (Smith et al. 2008). Terrestrial silt and clay particles less than 0.75μM diameter have strong negative effects on economically important stony corals, including bleaching, disease, and mortality (Weber et al. 2006). Data from the TCRMP shows that nearshore sites the highest levels of silt input are sicker than other reefs. This indicates that USVI corals are suffering from sediment impacts that are degrading nearshore coral reef systems and limiting the benefits they provide to our community.

Less is known about other land‐based sources of pollution and their impacts on coral reef ecosystems. These include toxins carried with run‐off or leached from domestic and industrial activities, such as the central waste dumpsters that are often sited on roadways adjacent to ghuts. Nutrients carried or leached from sediments can also have indirect effects on corals by stimulating benthic macroalgae and nuisance algal blooms. Nutrients can also reduce water clarity and block light to corals through the stimulation of microscopic algae in the water column (phytoplankton).

The good news is that the effects of land‐based sources of pollution are very amenable to management actions. Many problems can be tackled through simple solutions intended to keep sediments out of coastal waters, which do not require expensive restoration or inhibit economic development.

Recommendations

Strategy #1 Implement standards, certifications, and educational programs for contractors and heavy machinery operators that offer guidance for earth moving. This guidance could include months where earth work is not advised due to the potential of soil loss through runoff, such as during tropical storm periods (Jul.‐Nov.).

Strategy #2 Unpaved roads are the largest artificial producers of terrestrial sediment in the USVI (Ramos‐Scharrón and MacDonald 2007b). Identify the worst roads and target these for publically supported restoration. Offer tax rebates to homeowners for road paving or implementation of sediment reduction techniques. Strengthen requirements for private and commercial road construction that reduce sediment production (e.g., slope restrictions, re‐grading requirements, special restrictions near drainages).

Strategy #3 Protect salt ponds as they are very effective natural sediment retention structures. Restore salt ponds that have been compromised by berm opening or infilling and create artificial sediment retention ponds along problematic ghuts.

Strategy #4 Invest in research to understand how terrestrial sediment levels affect coral reefs, what thresholds of sediment most impact corals and what could be tolerated, and identify coastal areas where sediment mitigation is most likely to protect coral reefs, particularly those within marine protected areas.