INTERDISCIPLINARY APPROACHES TO ASSESS THE HYDRO-GEOMORPHOLOGICAL EFFECTS OF LAND USE CHANGE ON MARINE ECOSYSTEMS OF PUERTO RICO AND THE U.S. VIRGIN ISLANDS

Throughout their histories all major islands of the Caribbean have been subjected to the massive removal of their indigenous vegetation cover in favor of agricultural uses, mainly sugar cane. With few exceptions, most islands are currently undergoing a process of reforestation when forest ecosystem services, including those related to water quality, should be in a state of recovery. Therefore, it is puzzling that these reforestation trends are occurring at a time when nearshore marine habitats are at their most deteriorated condition. Given the present-day emphasis of both state and federal agencies on watershed restoration projects focusing on terrestrial sediment loading as a mechanism to improve the current state of marine habitats throughout the US Caribbean, it is of utmost importance to develop a quantitative understanding of the effects of land use change on hydro-geomorphological processes at various spatio-temporal scales. An inclusive definition of land use change is suggested here that not only refers to anthropogenic actions that lead away from pristine conditions (e.g., urbanization), but also encompasses those linked to either active or passive watershed restoration activities.

This presentation will provide an overview of current interdisciplinary approaches to assess both the current and historical effects of land use change in soil erosion and sediment delivery to the marine environment in settings ranging from semi-arid areas of the US Virgin Islands and Southwestern Puerto Rico to the moist climatic zones of northeastern Puerto Rico. A summary of recent empirical studies designed to quantify land use effects in plot- and hillslope-scale erosion rates from foot trails, unpaved roads, and construction sites will accompany discussions on recent efforts to quantify the effectiveness of sediment retention structures and other watershed restoration efforts in contemporary marine sedimentation rates. In addition, this presentation will also include discussions on ongoing projects to assess short and long-term patterns of watershed-scale land use change and associated historical sediment yields, and its temporal association with long-term coral reef growth rates. Examples of currently-used management-oriented applications of our interdisciplinary findings will also be discussed.