The poultry industry is the economic backbone of the south central region of Puerto Rico. However, as in other poultry production regions in the U.S., concern has risen regarding its potentially damaging impact on the environment. Eutrophication of rivers and lakes, induced by excessive nutrient runoff, has forced regulatory agencies to closely evaluate manure disposal practices. Thus, the need is critical for environmentally sound management practices in poultry producing areas. The impact of years of manure applications on the nutritional status of soils was ascertained by evaluating a number of samples from nine poultry farms of Puerto Rico. The farms were selected among those with the highest bird populations. Sixty-seven percent of the samples analyzed contained phosphorus levels (Olsen) in excess of what is considered adequate to support crop growth. Fifty-six percent of these exceeded levels considered by some states as critical for water quality purposes. Measured levels ranged from undetectable values up to 900 mg/kg P. A diagnostic tool known as the P index was used in an effort to identify areas of concern. According to this criterion, all farms studied had zones where nutrient runoff could threaten the quality of the surrounding water bodies.
Elevated phosphorus (P) concentrations in Puerto Rico's surface waters are suspected to be the primary cause of observed eutrophication.This paper summarizes total P concentrations (TP), historical trends, and relationships between biological and chemical parameters at twenty-two surface water monitoring stations of eleven rivers from 1989 through 1997. Four rivers had median TP concentrations in excess of 0.1 mg P/L (which is considered a threshold limit for eutrophication). The remaining seven rivers, excluding Rio Guajataca, had at least 25% of the sampling episodes exceeding 0.1 mg P/L. When all data (n = 539) were considered, TP in the central 50% of the samples (25 to 75 interquartile range) ranged from 0.04 to 0.29, with mean and median values of 0.30 and 0.09 mg P/L, respectively. Pearson correlation coefficients between TP and fecal coliform bacteria, fecal streptococcal bacteria, and total Kjeidhal nitrogen were 0.38, 0.36, and 0.84, respectively, for all the rivers combined. For rivers with the highest TP concentrations differing relationships between TP and biological and chemical parameters were obtained, thus suggesting that diverse sources were contributing to P loads in rivers. Excluding two stations in Rio Grande de Añasco and Rio Grande de Arecibo, the trend was for TP concentrations to decrease or not change from 1989 to 1997. Approximately half of the variation in P loads in all rivers combined was due to instantaneous hydrologic flow discharge, a finding which corroborates our hypothesis that a number of factors (agricultural non-point sources, background non-point sources, point sources) are contributing to the observed TP concentrations.
CARBON SEQUESTRATION IN SOILS OF THE RIO GRANDE DE ARECIBO WATERSHED, WEST-CENTRAL PUERTO RICO
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