SELECTED HYDROLOGIC, WATER-QUALITY, BIOLOGICAL, AND SEDIMENTATION CHARACTERISTICS OF LAGUNA GRANDE

摘要

Selected hydrologic, water-quality and biological data were collected at Laguna Grande to determine the ecosystem's health based on regulatory standards. A bathymetric survey showed that the lagoon had a mean depth of 3 meters and contained about 662,000 cubic meters at mean sea level. Water-quality properties such as temperature, pH, dissolved oxygen, and salinity varied temporally not areally. Total nitrogen and phosphorus concentrations averaged 0.28 and 0.022 milligrams per liter respectively, which is in compliance with regulatory standards set by the Puerto Rico Environmental Quality Board. Laguna Grande produced about 507 metric tons of organic carbon per year with 86 percent of the community primary productivity generated by periphyton and macrophytes, and 14 percent by phytoplankton. Dissolved oxygen, nutrients, and productivity data indicate that Laguna Grande is a mesotrophic water body. Fecal indicator bacteria concentrations ranged from 160 to 60,000 colonies per 100 milliliters with higher concentrations in areas near residential and commercial establishments, exceeding standards of the Puerto Rico Environmental Quality Board. Bottom sediment accumulation determined a depositional rate of about 0.44 centimeters per year potentially converting the lagoon into a marshland in about 700 to 900 years. A water budget revealed that during a typical year the lagoon flushed about 13 percent of its volume every day, equal to once every 7.7 days or 47 times per year.