Hawai‘i has only 35 square miles of coastal lowland wetlands, but these narrow interfaces between land and ocean are vital. They help control flooding, hold back sediments that can smother downstream reefs, sequester carbon that might otherwise contribute to global warming, and absorb nutrients that can cause algal blooms and harm aquatic animals. Coastal wetlands also offer habitat to endangered waterbirds found nowhere else on earth, such as the Hawaiian stilt, theHawaiian coot, and the Hawaiian gallinule (moorhen).
Given their ecological significance, our coastal lowland wetlands have received little attention from researchers. To remedy this knowledge gap, soil and water conservation professor Greg Bruland and his students have collaborated with scientists from federal agencies and non-governmental organizations as well as land managers across the state to characterize the water, soil, plants, and fish found at 40 semi-natural, restored, and constructed coastal wetlands on five islands. This initial investigation is a key step in developing sound strategies to mitigate harms caused by invasive species and human activity.
The researchers initially sought to identify largely undisturbed coastal wetlands as reference sites on which to model future wetland restoration and creation projects. They discovered that invasive plant and fish species are so pervasive that pristine wetlands can no longer be found. Only 18 of 102 plant species observed were native, and the three most common plants were highly invasive alien species. Likewise, on average more than 80 percent of the fish (as measured by weight) were non-native, and two invasive fish species dominated most of the sites surveyed.
Further monitoring will quantify seasonal changes in wetland water quality, which varies tremendously across the different sites. Preliminary results indicate that the soils of restored and created wetlands are poorer than those of seminatural wetlands: more compacted, more alkaline, and containing less organic matter. These findings suggest that better management of soil conditions and improved invasive species control measures will help ensure the long-term health and function of our coastal wetlands.
