Where the Dry Forest Feeds the Sea
THE GULF OF NICOYA ESTUARY
José A. Vargas and Alfonso Mata
THE GULF OF NICOYA (GN) is an estuary located in the northwestern part of the Pacific coast of Costa Rica (10° N, 85° W). The extensive hydrological connection between the GN and watersheds draining into it gives rise to one of the most prominent ecological and geographical systems of Costa Rica (maps 1.1 and 1.2 in chapter 1; chapter 9). Half of this large estuarineterrestrial basin consists of the Tempisque River Basin (TRB), with a variety of ecological, cultural, and socioeconomic resources, some of them conflicting. If the Tárcoles River watershed, which drains the lower sector of the GN, is included, the whole area represents about 25 percent of the country. It has become clear over the past decades that deforestation of the watershed has led to a reduction in average flow of the Tempisque River (TR) in the dry season and to an increase in the magnitude of floods during the rainy season (Lizano 1998). The dry-forestTR-GN system can no longer be considered as composed of separate units because what occurs in the dry-forest watershed has effects on the estuary via the rivers. This chapter focuses on the main physical, chemical, and biological features of the estuary, as well as the main human activities that endanger its sustainable development.
OF THE GN BASIN
The GN receives waters collected by a group of watersheds associated mainly with the TRB in the upper sector of the gulf and the Tárcoles River watershed (from the Western Central Valley), together with other minor areas in the lower sector of the GN (see map 1.1 in chapter 1). Half of the entire drainage system corresponds to the Tempisque Valley, with a total surface area of 5,965 km2. Input from the Caribbean versant through the Arenal reservoir discharges nearly 90 m3/s of fresh water from the ArenalTempisque hydroelectric generating system. Part of this flow is used during the dry season for irri-