Waste water disposal

Differences in urbanization and degree of marine influence are reflected in d13C and d15N of producers and consumers in seagrass habitats of Puerto Rico

Olsen, Ylva S., Sophia E. Fox, Erin L. Kinney, Mirta Teichberg, and Ivan Valiela. 2010. Differences in urbanization and degree of marine influence are reflected in delta(13)C and delta(15)N of producers and consumers in seagrass habitats of puerto rico. Marine Environmental Research 69 (3) (APR): 198-206.

Couplings between land use and marine food webs in tropical systems are poorly understood. We compared land–sea coupling in seven sites around Puerto Rico, differing in the degree of precipitation and urbanization, by measuring d13C and d15N in producers and consumers. d15N values were influenced by human activity: the food web from sites near urbanized centers was on average 1‰ heavier in d15N compared to undeveloped sites. This is most likely due to wastewater inputs from septic systems relatively near the shoreline. Changes in d13C were best explained by differences in the degree of marine influence. Where terrestrial inputs from a major river dominated, d13C values were lighter, whereas sites further from land and in locations exposed to oceanic currents had heavier d13C values, characteristic of a marine source of dissolved organic carbon. We found no significant effect of precipitation on connectivity in spite of a twofold difference in annual average rainfall between the north and south coast. The results suggest there is some connectivity between land and sea in Puerto Rico, despite high rates of evaporation relative to precipitation.

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.
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