anthropogenic disturbance

Exploration of the Geological Formations of the Luquillo Mountain Range of North Eastern Puerto Rico using X-ray Florescence

Nawal C.. Exploration of the Geological Formations of the Luquillo Mountain Range of North Eastern Puerto Rico using X-ray Florescence. Master's Capstone. University of Pennsylvania 2011.

X-ray Florescence (XRF) is a widely used non-destructive method that measures the elemental composition of materials. This technology was applied to investigate the rocks and sediments in the Luquillo Mountains / El Yunque region of Puerto Rico. Initial testing of wet and dry sediments revealed that the machine records higher elemental concentrations in dry compared to wet sediments as it seems that the water molecules interfere with the X-ray beam on wet samples. The XRF method on dried samples produced reliable results and allowed for the chemical separation of the five basic bedrock types found in the Luquillo Mountains. Of the volcanoclastic the Fajardo Formation can be distinguished from the others by its concentration of Barium (Ba) and Rubidium (Rb). The Unnamed formation was distinguished by Copper (Cu) and the Hato Puerto Formation was distinguished by Nickel (Ni) and Strontium (Sr). The Rio Blanco granodiorite is the youngest rock type of the region and was the only formation whose elemental chemistry was not distinguishable from the othersapparently because it was formed directly from the basic magma that also formed the Luquillo Mountains volcanic rocks. Recent studies have found high levels of Mercury (Hg) in Luquillo stream water. Knowing that the Luquillo region was heavily mined for Gold (Ag) and Silver (Au), the Hg used in historic mining is a possible source of the elevated Hg values. The XRF analysis indicated small quantities of Hg in some rocks but no Hg was found in the sediments and soils surrounding the historic mining sites. Therefore if Hg had been used in historic mining operations it is no longer apparent in the sediments and has presumably been removed by erosion of the site.

Factors Influencing Tropical Island Freshwater Fishes: Species, Status, and Management Implications in Puerto Rico

Neal JW, Lilyestrom CG, Kwak TJ (2009) Factors influencing tropical island freshwater fishes: species, status, and management implications in Puerto Rico. Fisheries 37:546-554

Anthropogenic effects including river regulation, watershed development, contamination, and fish introductions have substantially affected the majority of freshwater habitats in Europe and North America. This pattern of resource development and degradation is widespread in the tropics, and often little is known about the resources before they are lost. This article describes the freshwater resources of Puerto Rico and identifies factors that threaten conservation of native fishes. The fishes found in freshwater habitats of Puerto Rico represent a moderately diverse assemblage composed of 14 orders, 29 families, and 82 species. There are fewer than 10 species of native peripherally-freshwater fish that require a link to marine systems. Introductions of nonindigenous species have greatly expanded fish diversity in freshwater systems, and native estuarine and marine species (18 families) also commonly enter lowland rivers and brackish lagoons. Environmental alterations, including land use and development, stream channelization, pollution, and the impoundment of rivers, combined with nonnative species introductions threaten the health and sustainability of aquatic resources in Puerto Rico. Six principal areas for attention that are important influences on the current and future status of the freshwater fish resources of Puerto Rico are identified and discussed.

Variation in nutrient characteristics of surface soils from the Luquillo Experimental Forest of Puerto Rico: A multivariate perspective

Cox, S. B.; Willig, M. R.; Scatena,F. N.; 2002. Variation in nutrient characteristics of surface soils from the Luquillo Experimental Forest of Puerto Rico: A multivariate perspective.. Plant and Soil 247 : 189-198.

We assessed the effects of landscape features (vegetation type and topography), season, and spatial hierarchy on the nutrient content of surface soils in the Luquillo Experimental Forest (LEF) of Puerto Rico. Considerable spatial variation characterized the soils of the LEF, and differences between replicate sites within each combination of vegetation type (tabonuco vs. palo colorado vs. dwarf vs. pasture) and topographic position (ridge vs valley) accounted for 11–60% of the total variation in soil properties. Nevertheless, mean soil properties differed significantly among vegetation types, between topographic positions, and between seasons (wet vs dry). Differences among vegetation types reflected soil properties (e.g., bulk density, soil moisture, Na, P, C, N, S) that typically are related to biological processes and inputs of water. In forests, differences between topographic positions reflected elements (e.g., Ca, Mg, K, and Al) that typically are associated with geochemical processes; however, the nutrients and elements responsible for topographic differences in dwarf forest were different from those in other forest types. In pastures, differences between topographic positions were associated with the same soil properties responsible for differences among the other vegetation types. Pastures also had reduced N levels and different soil characteristics compared to undisturbed tabonuco forest. The only soil parameter that differed significantly between seasons was soil moisture. Soils of the LEF do not support the contention that N becomes limiting with an increase in elevation, and suggest that absolute pool sizes of N and P are not responsible for the reduction in productivity with elevation.
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