Martínez-Suárez, Alexander

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    Métodos estadísticos para la detección de umbrales de contaminación en ecosistemas acuáticos de agua dulce
    (2010) Martínez-Suárez, Alexander; Macchiavelli, Raúl E.; College of Arts and Sciences - Sciences; Acuña Fernández, Edgar; Quintana Díaz, Julio; Department of Mathematics; Alston, Dallas
    This paper presents the methodology and results from applying statistical methods to determine the thresholds of contamination of aquatic ecosystems. The objectives are to analyze methods to determine thresholds or turning points for a given variable by using the statistical software program R and to use the methods to determine pollutant thresholds in reservoirs in Puerto Rico. The first part presents these methods, including their theoretical foundations, computational mathematics, and application to streams in the Mid-Atlantic states (USA) during 1993 and 1994. The objective is to compare the predicted results with the published results. The second part applies the methods to real data from Puerto Rico. One of the statistical tools used to develop each of the methods is conditional probability, which requires two variables, Q and X. One variable, Q, represents the known threshold; the other variable X represents the unknown threshold of interest. Given the two variables, the process uses the conditional probability P(q|x) and one of the methods to determine the threshold of interest. In the Mid-Atlantic data, the benthic macroinvertebrate communities (EPT taxa richness) data were used to determine stream impact (the known variable threshold). The percentage of fine substrate (fraction silt/clay< 0.06mm) was used to measure stream sedimentation as the variable of interest. With these two variables, five methods were applied to determine the fine substrate threshold percentage for these streams. With respect to the data in Puerto Rico, chlorophyll a is the variable for which the threshold is known. The variables of interest for which the thresholds were determined were nutrients: total phosphorus and total nitrogen.