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.

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.

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.