Ortiz-Zayas J.R.

Urban influences on the nitrogen cycle in Puerto Rico

Ortiz-Zayas, J. R., E. Cuevas, O. L. Mayol-Bracero, L.
Donoso, I. Trebs, D. Figueroa-Nieves, and W. H. Mcdowell.
2006. Urban influences on the nitrogen cycle in Puerto Rico.
Biogeochemistry 79:109–133.

Anthropogenic actions are altering fluxes of nitrogen (N) in the biosphere at unprecedented rates. Efforts to study these impacts have concentrated in the Northern hemisphere, where experimental data are available. In tropical developing countries, however, experimental studies are lacking. This paper summarizes available data and assesses the impacts of human activities on N fluxes in Puerto Rico, a densely populated Caribbean island that has experienced drastic landscape transformations over the last century associated with rapid socioeconomic changes. N yield calculations conducted in several watersheds of different anthropogenic influences revealed that disturbed watersheds export more N per unit area than undisturbed forested watersheds. Export of N from urban watersheds ranged from 4.8 kg ha)1 year)1 in the Rı´o Bayamo´ n watershed to 32.9 kg ha)1 year)1 in the highly urbanized Rı´o Piedras watershed and 33.3 kg ha)1 year)1 in the rural-agricultural Rı´o Grande de An˜ asco watershed. Along with land use, mean annual runoff explained most of the variance in fluvial N yield. Wastewater generated in the San Juan Metropolitan Area receives primary treatment before it is discharged into the Atlantic Ocean. These discharges are N-rich and export large amounts of N to the ocean at a rate of about 140 kg ha)1 year)1. Data on wet deposition of inorganic N (NHþ4 þ NO 3 ) suggest that rates of atmospheric N deposition are increasing in the pristine forests of Puerto Rico. Stationary and mobile sources of NOx (NO+NO2) and N2O generated in the large urban centers may be responsible for this trend. Comprehensive measurements are required in Puerto Rico to quantitatively characterize the local N cycle. More research is required to assess rates of atmospheric N deposition, N fixation in natural and human-dominated landscapes, N-balance associated with food and feed trade, and denitrification.

Integrated Water Resources Management in the Luquillo Mountains, Puerto Rico: An Evolving Process

Ortiz-Zayas, J.R. and F.N. Scatena. 2004. Integrated Water Resources Management in the
Luquillo Mountains, Puerto Rico: An Evolving Process. Water Resources Development. 20 (3): 387-398.

The ecologically unique forest ecosystems of the Luquillo Mountains in Eastern Puerto Rico and the scenic value of its forests, rivers and surrounding beaches have promoted population growth, tourism and light industry, thus increasing regional water demands. In light of further increases in future water demand, integrated water resources management (IWRM) initiatives are rapidly evolving in this area. In an effort to seek international collaboration and information exchange on IWRM, the Luquillo Mountains joined the Hydrology for the Environment, Life, and Policy (HELP) Programme of the United Nations Educational, Scientific, and Cultural Organization (UNESCO)/International Hydrological Programme (IHP) in 1999. The paper was prepared to document existing IWRM efforts and to promote internal discussion for further IWRM development in the region.

Helping HELP with limited resources: the Luquillo experience

Scatena, F.N.; Ortiz-Zayas, JR; Blanco-Libreros, J.F. 2008. Helping HELP with limited resources: the Luquillo experience. Water SA. 34(4 special HELP edition): 497-508.

By definition the HELP approach involves the active participation of individuals from a wide range of disciplines and backgrounds, including representatives of industry, academics, natural resource managers, and local officials and community leaders. While there is considerable enthusiasm and support for the integrated HELP approach, a central problem for all HELP basins is how to effectively engage individuals and groups with few, if any financial resources. In the Luquillo HELP project we have managed this issue by focusing our efforts on holding small, public meetings and workshops with technocrats and managers who are engaged in local water resource management. To date several forums have been organised, including: technical meetings with the directors of natural resource agencies; presentations and panel discussions at the meetings of local professional societies, including the societies of Civil Engineers and Architects, the Commonwealth Association of Tourism, the Association of Builders and Developers, and the Puerto Rican Association of Lawyers. During these forums HELP specialists gave presentations and led discussions on how integrated watershed management can help resolve local problems. Because the audience are directly involved with these issues, they are quite responsive to these discussions and have often provided unique solutions to common problems. Technical workshops are co-sponsored by local municipalities – these day-long workshops are hosted by a municipality and include managers from other municipalities, the local water authority, and local community leaders. Additional activities include: technical advice on water infrastructure projects is given; there are educational exchanges between local and international students, scientists, natural resource managers, and community leaders; and synthesis publications relevant to integrated water resource management are produced. Other activities have included compiling oral environmental histories and organising watershed restoration activities. This paper describes these activities and discusses the benefits and costs of each approach.

Metabolism of a tropical rainforest stream

Ortiz-Zayas, J.R. et al. Metabolism of a tropical rainforest stream. Journal of the North American Benthological Society, Volume 24, No. 4, pages 769–783.

Gradients in photosynthesis (P) and respiration (R) were measured on an unperturbed portion of the Rio Mameyes, a tropical stream in the Luquillo Experimental Forest, northeastern Puerto Rico. Rates of P, which were similar to those of streams in temperate-deciduous forests, were low in the heavily canopied headwaters (<70 g O2 m−2 y−1) and were higher (453–634 g O2 m−2 y−1) in middle and lower reaches. Periphyton biomass did not show the expected increase as the canopy opened downstream, probably because of increasing herbivory in downstream reaches. Rates of R, which were much higher than in most temperate streams, also were lower in the headwaters (767 g O2 m−2 y−1) than in the middle and lower reaches (1550–1660 g O2 m−2 y−1). High rates of R and suppressed periphyton abundance caused annual P/R to be <<1 from headwaters to lower reaches. Results for the Rio Mameyes suggest that intense herbivory, which is favored by the presence of large herbivores and consistently high temperatures, may be more typical of tropical than temperate streams. Results also show that the tropical rainforest provides the stream with sufficient amounts of labile organic C to support high rates of respiration over long distances across the basin.
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