Quantifying the role of agriculture and urbanization in the nitrogen cycle across Texas

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Meyer, Lisa Helper

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Over-enrichment of nutrients in coastal waters has been a growing problem as population growth has enhanced agricultural and industrial processes. Enhanced nitrogen (N) fluxes from land to coast continue to be the result of over fertilization and pollution deposition. This over-enrichment of nutrients has led to eutrophication and hypoxic conditions in coastal environments. This study was conducted along the Gulf of Mexico, through the state of Texas, in order to quantify all agricultural and industrial sources of N in a region which contains a large precipitation gradient, three major metropolitan areas, and one of the top livestock industries in the United States. Nitrogen inputs from fertilizer, livestock, crop fixation, and oxidized deposition from both dry and wet atmospheric processes were quantified and compiled into a Texas Anthropogenic N Budget (TX-ANB). In addition, comparisons and regional enhancements were made to the Net Anthropogenic Nitrogen Input dataset (NANI toolbox), which is a national dataset developed at Cornell University by Hong et al. [2011]. These enhancements ultimately will help understand the full pathways of anthropogenic influences on coastal systems in a regional setting. All three datasets (NANI, NANI Regional, and TX-ANB) indicate agriculture to be the primary contributor to the N cycle in Texas, with TX-ANB showing 38% of inputs from fertilizer, 37% of inputs from livestock, and 2% of inputs from legumes. N input due to atmospheric deposition of oxidized N clearly highlights urban areas, indicating a strong influence of urbanization on the N cycle due to anthropogenic impacts; 23% of N input in Texas is the result of deposition of oxidized N. Quantification of inputs spatially indicates a strong enhancement of N from human influence in the coastal plain where nutrient export is heightened by major storm events. This enhancement of N along a coastal drainage area will likely have a negative impact on downstream environments.



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