Rodríguez-Rivera, Paloma

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    Metabolism and trophic status of streams draining basins with different land use in Southwest Puerto Rico
    (2018-12-11) Rodríguez-Rivera, Paloma; Sotomayor-Ramírez, David; College of Agricultural Sciences; Martínez-Rodríguez, Gustavo; Santos-Flores, Carlos; Department of Crops and Agro-Environmental Sciences; Carrero, Katherine
    The eastern part of the Lajas Valley basin has an area of 14,519 ha, a population of about 33,000, and the predominant land use is 9.3% urban or sub-urban, 30% agricultural, and 61% forest / fallow. Quebrada Mondongo and Quebrada Bárbara are two sub-basins with predominant urban and agricultural land use, respectively. Quebrada Mondongo receives processed waters from a secondary sewage treatment plant (WWTP) and WTP and Quebrada Bárbara receives water from a WTP. Previous studies showed that the nutrient levels of streams in these sub-basins had concentrations of total nitrogen (TN) and total phosphorus (TP) in what is considered "enriched" and “impacted”. Assays of benthic metabolism were performed for net primary productivity (NPP) and respiration (R) using in situ recirculating metabolism chambers, and gross primary production (GPP) was computed as GPP = NPP- [-R]. Periphyton biomass, nutrient levels, physical and chemical parameter were also compared between sub-basins and among different points within the sub-basin. Differences between sub-basins were observed and the Quebrada Mondongo had significantly higher periphyton biomass, temperature, DO, specific conductance, flow, pH, TN, dissolved nitrate, TP, and dissolved phosphorus. NPP and R tended to be higher in Quebrada Mondongo, though not significantly. Quebrada Mondongo and the upstream of Quebrada Bárbara had GPP/R <1, suggesting that these benthic ecosystems are predominantly heterotrophic. The WWTP had no apparent effect in the stream ecology, as metabolism rates did not vary significantly from upstream to downstream stations. All sites were classified as either “enriched” or “impacted”, but the urban stream was greatly degraded.