Martínez-Martínez, Edwin

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    Predicting sediment and nutrient loads in tropical watersheds in Puerto Rico
    (2006) Martínez-Martínez, Edwin; Pérez-Alegría, Luis R.; College of Agricultural Sciences; Martínez-Rodríguez, Gustavo A.; Sotomayor-Ramírez, David; Department of Crops and Agro-Environmental Sciences; Harmsen, Eric W.
    High and resilient sediment and nutrient concentrations in streams are precursors or indicators of stream impairment. According to recent estimates by USEPA (2001), about 40% of the monitored national water supplies do not meet quality standards to support designated uses. A similar situation is observed in Puerto Rico. The 2002 water quality inventory of Puerto Rico reports that 67% of the monitored river miles were impaired (JCA, 2002). In this study water quality parameters were sampled during the 2004-2005 water year in four sub watersheds of the Río Grande de Arecibo watershed, located in the central part of Puerto Rico. The objective of this thesis research was to determine sediment and nutrient loads and to propose mathematical relationships to relate sediment and nutrient loads to physiographic and hydrologic properties of the sub watersheds. Sampled variables included pH, temperature, conductivity, salinity, water velocity, total suspended sediment, chlorophyll-a, total Kjeldahl nitrogen (TKN), total phosphorus (TP) and dissolved phosphorus (DP) loads. Sediment loads and yields from storm events ranged from 3,041 metric tons/event, 32.45 metric tons/km2 (Río Limón) to 29.99 metric tons/event, 1.69 metric tons/km2 (Río Jauca). Nutrient concentrations range, from 6.49 to 1.11 mg/L of TKN, 1.82 to 0.05 mg/L of TP and 0.24 to 0.05 mg/L of DP. A method for developing predictive equations of nutrient and sediment loads for tropical sub watersheds is presented in this thesis research. TSS, TKN, TP and DP annual load predictive equations were generated and calibrated using the Partial Least Square regression method in the statistical software MINITAB version 14. The predicted R2 values for the TSS, TKN, TP and DP annual loads using a 2-component model are 0.74, 0.95, 0.97 and 0.99.