There are various ways of controlling soil erosion depending on the site or extent of threat, but it all comes down to the protection of the environment — land and marine.
A field guide from the Division of Environmental Quality and Coastal Resources Management illustrates how the sediment-laden runoff ultimately discharges into streams, wetlands and marine resources.
Sediments carry pollutants and nutrients that reduce water quality and impact coastal waters. They end up in the coral ecosystem where they limit photosynthesis, reduce oxygen, clog fish gills, fill spawning grounds, smoth er bottom communities, carry microbes to coral polyps and blur the sight of marine animals so they won’t be able to find food and avoid predators.
In the CNMI, there are over 50 erosion control practices being implemented and most of these, according to Natural Resources Conservation Service district conservationist James T. Eller, fit the job of vetiver grass.
“We use vetiver grass extensively,” Eller said.
This dense and fire tolerant grass is the best way to put up vegetative barrier that can reduce different types of erosion, manage water flow, stabilize steep slopes and trap sediment.
Because of its numerous stems and strong, compact root system the can go down nine to 12 feet in the ground, vetiver grass is well adapted to soil erosion measures.
Used as a barrier, vetiver grass is planted in strips in a single row two to six inches apart from each other. In areas where flow is concentrated, the “thin green line of defense” is planted in double rows.
There are many areas with erodible soil in the CNMI, but coral reef point of contact Fran Castro said the major sites are Laolao Bay on Saipan and Talakhaya on Rota.
To address immediate threats to the coral ecosystems in these two sites, the federal and local governments are working together to come up with the best erosion and sediment control measures.
The CNMI recently received an American Recovery and Reinvestment Act funding through the National Oceanic and Atmospheric Administration for the Laolao Bay Road and Coastal Management Project which aims to reduce water turbidity, improve the coral ecosystem and increase fish abundance in the next five to eight years.
The goal of the project, Eller said, is to prevent sedimentation in Laolao Bay.
Castro said vetiver grass were planted in the bad lands near the Laolao Bay in 1997and 2007.
The other priority project is the Talakhaya Watershed Revegetation Project which aims to reduce the non-point source pollution running off steep slopes of the Talakhaya Watershed into the nearby coral reef ecosystem.
The data gathered by marine monitoring team over the last 10 years revealed that Talahaya reefs have lower coral cover and higher algae cover compared to others in the CNMI.
Although other species of grass have been planted there, Eller said they are also using the robust and very resilient vetiver grass to successfully stabilize the soil surrounding the Talakhaya Watershed.
(To be continue)
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