This project will facilitate continued data collection on water-carbon linkages between the rainforest and the deeper hydrogeological system by continuing measures and the continuity of a critical data stream begun under previous NSF funding and as the object of planned projects. Routine weekly data will be collected by a local Costa Rican technician (local high school teacher) who has worked with the project since 2000.
This project involved collection of 1 year of data on the amount of water and dissolved carbon leaving two tropical rainforest watersheds via streamflow from the watersheds. The data are being used in a larger ongoing study on the carbon budget of the tropical rainforest and how this budget is influenced by the hydrologic cycle. Working in collaboration with other scientists measuring other large carbon fluxes (for example, respiration and photosynthesis), our data on carbon fluxes in streamwater (and groundwater) are being used to develop the carbon budget (the accounting of carbon inputs and outputs for the ecosystem). The budget will then show whether the ecosystem is a net sink of carbon (more carbon coming in than going out, such that some must be stored in ecosystem soils, sediments, or biomass), or a net source of carbon (more carbon leaving than coming in, so that the ecosystem acts as a net source of carbon to the atmosphere and/or downstream water bodies). Project results on coupled water and carbon fluxes are relevant to ecology and ultimately to understanding the effects of climate change on tropical rainforests. Carbon budgets both affect, and are affected by, climate change, and accurate measurement of carbon budgets clarifies the link between the carbon cycle and climate. For example, is the ecosystem a net source or sink for CO2? The former is a positive feedback on warming (net release of CO2 would promote more warming, which would promote more release of CO2, and so on), while the latter is the opposite (net uptake of CO2 can help to slow warming). There is uncertainty about which applies in general in tropical forests, and concern over the possibility that forest ecosystems may transition from the latter to the former (sink to source) with climate warming. Accurate understanding of the source/sink status of the ecosystem requires accurate accounting of all major carbon fluxes. Data from this project contribute to a longer-term database which is helping clarify the carbon cycle and budget in the lowland rainforest.
