WATER QUALITY OF PUERTO RICAN STREAMS: A SYNOPSIS OF SOLUTE, NUTRIENT, AND SEDIMENT LOADING

The dissolved load of Puerto Rican streams discharging to the sea is estimated at 3100 tons/day, dominantly bicarbonate waters in the western karst and carbonate rock areas, and less dominantly in the northeast and south. A total suspended solids approximation is 530 tons/day, a figure influenced by numerous reservoirs. All major streams have bacteria problems, indicated by fecal coliform and streptococci concentrations >500 counts/100 ml found during 50-100% of quarterly sampling. Mean nutrient levels are also very high, e.g. total phosphorus exceeds 0.2 mg/L. The highest stream loadings and bacterial concentration are correlated to population concentrations, although density (1100 persons/square mile) is high over the entire island.

The area of the main island is 3435 square miles, with most gages concentrated in more populated (and more humid) areas. Only 640 square miles of non-carbonate areas are concurrently gaged (both flow and quality), with 30-yr mean outflows of ~1120 cfs. Rivers discharging from basins heavily influenced by karst are gaged at ~1180 cfs, but their areas are often described as “indeterminate”-- this region comprises an estimated 900 square miles. The total estimated discharge of Puerto Rican streams is 5400 cfs, a mean areal discharge of 1.6 cfs/ square mile (22 inches/ year), somewhat more than a third of the mean 30-year island precipitation (NOAA, 1961-90) of 63 inches.

A variety of federal and local agencies collect water data. Determination of overall loadings on the island is predominantly impeded by a lack of concurrent discharge and water quality collection sites near the mouths of the streams of the eastern and southern coasts, and uncertainty of the contributory catchment areas of the northwest karst terranes. Discharge totals are also obscured by inter-basinal canal transfers and groundwater pumping, and the unknown extent of offshore karst springs. These current estimates are based on recent delineation of karst catchments and extrapolation of runoff behavior of well-gaged streams.