ASEPA stream monitoring: results from year 1 and preliminary interpretation

DiDonato, Guy

Tutuila, the largest island of American Samoa, is the location of the majority of American Samoa's perennial stream ecosystems. These systems are poorly understood and currently under threat by the Territory's growing human population. The American Samoa Environmental Protection Agency (ASEPA) monitors local streams using a modified probabilistic design. To select streams for monitoring, all perennial streams on Tutuila are pooled in to four classes, representing levels of anthropogenic disturbance (pristine, minimal, intermediate, extensive) within island watersheds. These classes are determined from watershed population density. In 2003, eight (8) streams, 2 from each watershed class, were selected randomly for monthly monitoring. In addition, a habitat assessment was conducted for each stream during the initial visit. The data show that there is a general gradient of decreasing habitat scores with increasing level of human disturbance as predicted by population density. Furthermore, many of the measured stream variables (temperature, nutrients, etc.) also varied predictably along the watershed disturbance gradient. This monitoring protocol captured in Year 1 the range of variability in these tropical stream ecosystems, and future monitoring will further refine our understanding of these tropical ecosystems and human impacts on them.