The Impact of Land Use Practices on Nutrients in Freshwater Streams, Guanacaste, Costa Rica

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The Impact of Land Use Practices on Nutrients in Freshwater Streams, Guanacaste, Costa Rica
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Hagamen, Lindsay
Brown University
Place of Publication:
Providence, RI
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Agricultural intensification, specifically the applications of nitrogen (N) fertilizer to crop fields in temperate climates, has dramatically increased yields and helped to feed a growing global population. At the same time, however, N additions have had cascading and deleterious effects on downstream aquatic ecosystems, where nutrient loading drives eutrophication. Intensive, high nitrogen agriculture is now rapidly expanding in the tropics, but its effects on tropical streams have not been nearly as well documented as in temperate zones. In this study, I sampled streams from 12 subwatersheds in the Tempisque River Basin, in northwestern Costa Rica, that drain markedly different land use types (> 50% agriculture, forest, or pasture). There was no significant difference between N concentrations in pasture and forest streams. Ammonia (NH4 + -N), nitrate (NO3 -_ N), and dissolved organic nitrogen (DON) all increased linearly as the fraction of agriculture within the watershed increased, and land use within 1km upstream from the sampling site best described the variation in nitrogen concentrations (R 2 =0.49, 0.52, 0.59 respectively), compared to land use within 500m, 2000m, 5000m upstream or within the entire watershed. High rates of N fertilization (rice 140-180 kg N/ha-yr; sugarcane 100-150 kg N/hayr) may be increasing the N availability in streams draining agricultural fields throughout the Tempisque River Basin, potentially driving eutrophication. More research is necessary to establish annual nutrient fluxes and to understand the impacts of changing nutrient availability on stream ecology and downstream aquatic ecosystems.

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Source Institution:
University of Florida
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University of Florida
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Applicable rights reserved.
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