Luquillo Experimental Forest: Research History and Opportunities.

Harris, N.L.; Lugo, A.E.; Brown, S.; and Heartsill Scalley, T. (Eds.).
Luquillo Experimental Forest: Research history and opportunities. EFR-1.
Washington, DC: U.S. Department of Agriculture. 152 p.

Long-term dynamics of organic matter and elements exported as coarse particulates from two Caribbean montane watersheds

Heartsill Scalley, T., Scatena, F.N., Moya S., Lugo A.E., 2012 Long-term dynamics of organic matter and elements exported as coarse particulates from two Caribbean montane watersheds. Journal of Tropical Ecology. Vol 28. pp 127-139. doi:10.1017/S0266467411000733

Ciguatera Toxins in the food chain revealed by Stable Isotopes

Winter A., Tosteson T.R. Ciguatera Toxins in the food chain revealed by Stable Isotopes. Bulletin de la Sociatie de Pathologie Exotique, Vol 85, Is 5 Pt 2, 1992 pp. 510-513.


Parrotta J.A., Baker D.D., Fried M. APPLICATION OF N-15-ENRICHMENT METHODOLOGIES TO ESTIMATE NITROGEN-FIXATION IN CASUARINA-EQUISETIFOLIA. Canadian journal of forest research. 1994, Vol 24. pp. 201-207.

Distribution of 137 Cs in soils and vegetation on the island of Puerto Rico

Kline J.R., Colon J.A., Brar S.S. Distribution of 137 Cs in Soils and vegetation on the island of Puerto Rico. Health Physics Pergamon Press 1973. Vol 24, pp. 469-475.

Soils and vegetation of Puerto Rico were collected along five north-south transects of the island and analyzed for 137Cs content. The results showed an apparent gradient of this nuclide with high amounts in the eastern samples and low amounts in the western samples. Activity in samples was strongly related to rainfall patterns on the island; however, high mountain forests were much more highly contaminated than could be accounted for on the basis of rainfall deposition alone. This was attributed to the properties of vegetation itself, rather than alteration of deposition patterns. The vegetation is suggested to have high aerosol interception efficiency and low turnoever rates, which could combine to produce the observed concentations. The data were used to test and reject the hypothesis that observed 137Cs distribution on the island was due to changes in atmospheric aerosol scavenging efficiency. Data from soil samples suggest that the island has intercepted a minimum of 535 Ci of 137Cs from past nuclear weapons tests.

A Simple Model of Strontium and Manganese dynamics in a tropical Rain Forest

Jordan C. F., Kline J.R., Sasscer D.S. A Simple Model of Strontium and Manganese Dynamics in a tropical Rain Forest. Health Physics Pergamon Press 1973. Vol 24 (May) pp. 477-489.

Quantities and fluxes of stable strontium and manganese were measured in a Puerto Rican tropical rain forest. These measurements were used to formulate a mathematical model of the dynamics of these elements. The model was then used to make predictions of the fate of the radioactive analogs of these isotopes after input via atmospheric fallout. The model was partially validated by measuring actual fallout levels in the forest during part of the time span covered by the model's predictions.

Carbon and Oxygen Isotope Time Series From an 18-Year Caribbean Reef Coral

Colonies of Montastrea annularis live near La Parguera, Puerto Rico, and maybe 799 years old. Time series from 1964 to 1982 of delta 13C and delta 18O from a continuous core of these corals are compared to an adjacent environmental record. At the intraannual level, delta 18O correlates well with water temperature. Changes in the amplitude of the delta 18O signal between 1967 and 1976 are attributed to sampling frequency but may be also due to environmental changes such as salinity. Average annual delta 18O, delta 13C and sea surface temperature show similar trends of the period from 1964 to 1982 but expecially from 1969 onwards. Changes in average annual values during this time interval are most likely due to water mass changes brough about by interannual variability of the North Atlantic circulation. Since water temperature at La Parguera are representative of changes occurring in the wider Caribbean, the isotope record from La Parquera corals could be used as a proxy for large-scale environmental changes beyond the historical record through the Little Ice Age.

Vertical Stratification of δ 13C Values in Closed Natural and Plantation Forests in the Luquillo Mountains, Puerto Rico

MEDINA, E., L. STERNBERG, and E. CUEVAS. 1991. Vertical stratification of delta-C-13 values in closed natural and plantation forests in the luquillo mountains, puerto-rico. Oecologia 87 (3): 369-72.

The variability of 13C values was measured in leaf, stem and root tissues of several tree species growing in closed natural and plantation forests in the Luquillo mountains of Puerto Rico. Results confirm a significant decrease of <513C values from the tree canopy to the forest floor. The values measured in understory plants growing in gaps were not significantly different from the average for plants growing under the forest shade. Seedling leaf values tended to be more positive than those of saplings, probably reflecting the contribution of organic matter from the mother tree. Photosynthetic independence on the forest floor results in a reduction in ?13C value. Stem and root tissue values of seedlings and saplings were less negative than those of the leaves of the same plants. It is suggested that this difference results from the slower change in isotopie composition experienced by the woody tissue, as the seedlings become photosynthetically independent in the forest floor.

Phosphorus and iron cycling in deep saprolite, Luquillo Mountains, Puerto Rico

Buss, Heather L., Ryan Mathur, Arthur F. White, and Susan L. Brantley. 2010. Phosphorus and iron cycling in deep saprolite, luquillo mountains, puerto rico. Chemical Geology 269 (1-2) (JAN 15): 52-61.

Rapid weathering and erosion rates in mountainous tropical watersheds lead to highly variable soil and saprolite thicknesses which in turn impact nutrient fluxes and biological populations. In the Luquillo Mountains of Puerto Rico, a 5-m thick saprolite contains high microorganism densities at the surface and at depth overlying bedrock. We test the hypotheses that the organisms at depth are limited by the availability of two nutrients, P and Fe. Many tropical soils are P-limited, rather than N-limited, and dissolution of apatite is the dominant source of P. We document patterns of apatite weathering and of bioavailable Fe derived from the weathering of primary minerals hornblende and biotite in cores augered to 7.5 m on a ridgetop as compared to spheroidally weathering bedrock sampled in a nearby roadcut. Iron isotopic compositions of 0.5 N HCl extracts of soil and saprolite range from about δ56Fe=0 to −0.1‰ throughout the saprolite except at the surface and at 5 m depth where δ56Fe=−0.26 to −0.64‰. The enrichment of light isotopes in HCl-extractable Fe in the soil and at the saprolite–bedrock interface is consistent with active Fe cycling and consistent with the locations of high cell densities and Fe(II)-oxidizing bacteria, identified previously. To evaluate the potential P-limitation of Fe-cycling bacteria in the profile, solid-state concentrations of P were measured as a function of depth in the soil, saprolite, and weathering bedrock. Weathering apatite crystals were examined in thin sections and an apatite dissolution rate of 6.8×10−14 mol m−2 s−1 was calculated. While surface communities depend on recycled nutrients and atmospheric inputs, deep communities survive primarily on nutrients released by the weathering bedrock and thus are tightly coupled to processes related to saprolite formation including mineral weathering. While low available P may limit microbial activity within the middle saprolite, fluxes of P from apatite weathering should be sufficient to support robust growth of microorganisms in the deep saprolite.

Nitrate isotopic composition between Bermuda and Puerto Rico: Implications for N2 fixation in the Atlantic Ocean

Knapp, A. N., P. J. DiFiore, C. Deutsch, D. M. Sigman, and F. Lipschultz (2008), Nitrate isotopic composition between
Bermuda and Puerto Rico: Implications for N2 fixation in the Atlantic Ocean, Global Biogeochem. Cycles, 22, GB3014,

N and O isotope analyses of water column nitrate between Bermuda and Puerto Rico document a bolus of low-d15N nitrate throughout the Sargasso Sea thermocline, which we attribute primarily to the input of recently fixed N. Although previous work suggests southward increases inN2 fixation and ventilation age, no meridional trend in nitrate d15N is apparent. In the upper 200 m, the algal uptake-driven increase in nitrate d18O is greater than in d15N, because of (1) a higher fraction of nitrate from N2 fixation at shallower depths and/or (2) cycling of N between nitrate assimilation and nitrification. A mean depth profile of newly fixed nitrate estimated from the nitrate isotope data is compared with results from an ocean circulation model forced with different Atlantic fields of N2 fixation. The nitrate from N2 fixation is communicated between the model’s North and South Atlantic and suggests a whole Atlantic N2 fixation rate between 15 and 24 Tg N a1. One important caveat is that fixed N in atmospheric deposition may contribute a significant proportion of the low-d15N N in the Sargasso Sea thermocline, in which case the relatively low rate we estimate for N2 fixation would still be too high.
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