Deforestation of coastal watersheds is occurring throughout the tropics, altering transport of water, nutrients and sediments to mangrove estuaries and coastal oceans. This occurs because of powerful couplings linking land use changes on upland watersheds to receiving aquatic ecosystems down the topographical gradient. This research uses innovative multidisciplinary ecological, hydrological and biogeochemical approaches along six transects in Panama from watersheds subject to different degrees of deforestation to coastal mangroves. This layout will enable testing of hypotheses relating deforestation to functioning of mangrove ecosystems. Results will provide a fresh view of how coastal zones are organized and how human activities reshuffle natural couplings. The work will be based in the Liquid Jungle Laboratory, a research station that permits doing modern research in a remote setting.
Broader impacts of the work include definition of the connections between land use practices and conditions in adjoining mangroves in tropical coastal areas. Results will furnish information needed for assessing impacts of deforestation on coastal mangrove ecosystems that provide a series of economically valuable ecological services, such as fish and shellfish nurseries, interception of land derived nutrients, export of energy rich materials, stabilization of shorelines, maintenance of biodiversity, and various harvestable yields. An education and outreach program will focus on training U.S. and Latin American postdoctoral, graduate and undergraduate students. Strong collaborations with Panamanian and Argentine colleagues will enable bilingual websites, presentations and new programs to help transfer results to local people, managers, decision-makers, and scientific colleagues by digital, printed and oral means.
This research made intellectual contributions to understanding of the workings of coupled land-estuary-coastal sea regions in the tropics. In addition, the results add knowledge about how tropical subsistence-level conversion of forests to pastures may alter to interactions of coastal zone landscapes and their effects on the sea. In the region of Panama where we carried out the work, subsistence-level land owners cut and burn forests tracts to create pastures that they can ren to absentee livestock owners. Deforested watersheds, surprisingly, discharged less dissolved nutrients than fully forested watersheds. These discharges move down-estuary and are acted upon by the estuarine organisms so that by mid-estuary, the terrestrail imprint has been erased. Nutirents in particulate form are transported downstream, more so from deforested watersheds than forested watersheds. The net result is that there is a large amount of interception of terrestrial materials within estuaries, the estuaries create their own mix of nutirnets, which are then in turn discharged to sea. Thus, the mangrove-lined estuaries both intercept delieveries from land, and the export materials to the coastal waters. In spite of the active interception within mangrovve estuaries, the nutients dischargesd from the estuaries are still enough to subsidize food webs in the coastal seas, owing to the low nutrient status of these tropical coastal surface waters. Human activities therefore can to some degree re-set the role mangrove estuaries play in these coastal seascapes, but are still not enough to thwart the provision of ecological services by mangroves, at least not yet.
