Water in the World: Interdisciplinary Approaches to Access and Sustainability

Water Quality and Biomonitoring in the Río Lagarto, Costa Rica

DIGS 220

Every odd-year in March, from 2005-2015, the Río Lagarto, Costa Rica has been surveyed by students in Tropical Watersheds and Coastal Ecology. The Río Lagarto originates at approximately 1,500 m in the Monteverde cloudforest region of the Cordillera de Tilarán and steeply descends toward the Pacific coast discharging into the mangrove forests bordering the Gulf of Nicoya. This small Pacific slope river is the western-most of the three rivers, along with their watersheds, that define the Bellbird Biological Corridor. The Bellbird Biological Corridor is a long-term community-based effort to restore natural forest cover to a largely deforested terrain. This reforestation and ecological restoration effort is meant to insure that migratory animals, and the bellbird being used as the symbolic representation for the corridor, have adequate habitat from high-altitude cloud forest to lowland deciduous forest habitat for their sustainable survival. Along the Río Lagarto, water samples were collected from five sites that were characterized by their elevation, canopy coverage, and relation to places of human occupation. Physical, chemical, and nutrient analyses assessed, mainly in situ, were water temperature, dissolved oxygen (DO), pH, conductivity, turbidity, salinity, nitrogen and phosphorus. Total nitrogen and total phosphorus were analyzed upon return in the Winthrop Ecology Laboratory. Lacking local water quality criteria, or standards, for comparison, we used South Carolina water quality criteria (SCDHEC) where possible. Based on SCDHEC criteria, DO was satisfactory except for 2009 and pH levels were normal. Due to variable elevations among the sites, water temperature increased from the upper to lower watershed. Concerning conductivity, it only substantially increased near the mangrove forest due to the influence of saline water from the Gulf of Nicoya. Turbidity was low as expected in the dry season of a typical March without any substantial runoff from the adjacent land. Concerning nutrient analysis, ammonia concentrations did not reveal much information about sewage or agricultural run-off. However, a high phosphate level was observed in 2005 in the upper watershed sampling site; this may be a direct result of runoff from a nearby dairy farm. The highest levels of nitrate were also found at this site based on lab analysis. From year to year, total phosphorous levels were consistently high (above SCDHEC criteria). While an increasing trend was not observed, 2013 had higher total phosphorus levels compared to earlier years. Total nitrogen levels were not excessive except for a value of 8.2 mg/L at the mid-watershed site in 2009. In addition to water quality parameters, biomonitoring was conducted via the collection of macroinvertebrates at the three upper and mid-watershed sites that were accessible on foot. Presence specifically of the aquatic stages of three common insect orders, Mayflies (Ephermeroptera), Stoneflies (Plecoptera) and Caddisflies (Trichoptera) suggest that water quality was satisfactory. In summary, while overall water quality was relatively good and stable over the 10-year period of study, an excess of nutrients, especially phosphorus, was a concern. Although the region is deforested, good water quality may be a result of low population density and the rural setting. In order to maintain water quality and improve the degraded shoreline and embankments, the creation of a wide riparian buffer zone along the Río Lagarto should be considered to reach the goals of the Bellbird Biological Corridor.