A Decision Support Tool for Improved Water Quality
Nearshore ecosystems such as mangrove forests, seagrass beds, and coral reefs are some of the most biologically diverse environments in the world. These ecosystems provide important services that human coastal populations rely upon such as flood and erosion control or water purification. The health of these ecosystems are subject to threats originating both on land and in the ocean, so managing nearshore ecosystems requires a ridge-to-reef approach that accounts for how changes in land use and forest cover affect the near shore environment. Ecosystem and hydrology model–based watershed decision support tools are needed to allow resource managers to make informed decisions on how and where to allocate limited resources to optimize effectiveness of conservation or restoration actions, thereby maximizing the protection of nearshore areas.
The U.S. Forest Service (USFS) has worked with natural resource managers in Palau Forestry, the Coral Reef Research Facility, and the Ministry of the Environment to develop a watershed decision support tool for Babeldaob Island in the Republic of Palau. The USFS team consisted of scientists from the Pacific Northwest and Southwest Research Stations and from the Watershed Professionals Network. The team used the tool to target actions related to forest protection or the restoration of fire degraded savanna back to forest to prevent or reduce sediment delivery to near shore areas, thereby providing detailed information needed to improve decision-making about watershed management that maximizes benefits to nearshore ecosystem health.
Health, which was measured by watershed sediment and water yield, was modeled under three different scenarios: 1) current forest coverage; 2) a hypothetical fully forested Babeldaob Island; and 3) a hypothetical fully deforested Babeldaob Island entirely in grassland-savanna condition. The team integrated these model results into the Ecosystem Management Decision Support System (DSS), a set of software tools that integrates geospatial information to support decision-making via maps and decision scores that prioritize land units for management. Based on these scores of prioritized watershed catchments, managers are able to consider where forest protection or reforestation investments would provide the greatest sediment prevention or reduction-related benefits to coral reef health, while simultaneously meeting terrestrial conservation targets with the lowest amount of funding.
This work yielded key insights: as expected, sediment yield was lowest for catchments with more than 80 percent forest coverage, and highest for those with less than 40 percent forest coverage, the latter being closer to human coastal populations. Catchments’ groundwater recharge also increased in depth with increasing forest cover. Eleven percent of mostly forested catchments were prioritized for protection while 14 percent of catchments were prioritized for reforestation of grassland-savanna.
The decision model suggests that while reforestation of savannas result from easier access, as most identified units are lower elevation and closer to roaded access, cost per acre is relatively high. Conversely, less accessible native forests are less costly to protect per acre, but more difficult to access because they are located primarily in upland areas. The tool not only provides a road map for targeted and efficient sediment prevention or reduction actions but also a visual platform for conceptualizing landscape stewardship including incorporating new layers into decision-making (e.g., culturally important sites, areas of high plant and animal biodiversity).