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.

Reduced channel morphological response to urbanization in a flood-dominated humid tropical environment

Phillips C.B., Scatena F.N. Reduced channel morphological response to urbanization in a flood-dominated humid tropical environment. Earth Surface Processes and Landforms. 2012. DOI: 10.1002/esp.3345

Urbanization through the addition of impervious cover can alter catchment hydrology, often resulting in increased peak flows during floods. This phenomenon and the resulting impact on stream channel morphology is well documented in temperate climatic regions, but not well documented in the humid tropics where urbanization is rapidly occurring. This study investigates the long-term effects of urbanization on channel morphology in the humid sub-tropical region of Puerto Rico, an area characterized by frequent high-magnitude flows, and steep coarse-grained rivers. Grain size, low-flow channel roughness, and the hydraulic geometry of streams across a land-use gradient that ranges from pristine forest to high density urbanized catchments are compared. In areas that have been urbanized for several decades changes in channel features were measurable, but were smaller than those reported for comparable temperate streams. Decades of development has resulted in increased fine sediment and anthropogenic debris in urbanized catchments. Materials of anthropogenic origin comprise an average of 6% of the bed material in streams with catchments with 15% or greater impervious cover. At-a-station hydraulic geometry shows that velocity makes up a larger component of discharge for rural channels, while depth contributes a larger component of discharge in urban catchments. The average bank-full cross-sectional area of urbanized reaches was 1.5 times larger than comparable forested reaches, and less than the world average increase of 2.5. On average, stream width at bank-full height did not change with urbanization while the world average increase is 1.5 times. Overall, this study indicates that the morphologic changes that occur in response to urban runoff are less in channels that are already subject to frequent large magnitude storms. Furthermore, this study suggests that developing regions in the humid tropics shouldn’t rely on temperate analogues to determine the magnitude of impact of urbanization on stream morphology. Copyright © 2012 John Wiley & Sons, Ltd.

Genotypic Differences in Water Use Efficiency of Common Bean under Drought Stress

Remirez-Builes V.H., Porch T.G., Harmsen E.W. Genotypic Differences in Water Use Efficiency of Common Bean under Drought Stress. Agronomy Journal. Vol 103 Is 4 2011, pp 1206-1215.

Stable isotope ratios of rain and vapor in 1995 hurricanes

Lawrence, JR, SD Gedzelman, XP Zhang, and R. Arnold. 1998. Stable isotope ratios of rain and vapor in 1995 hurricanes. Journal of Geophysical Research-Atmospheres 103 (D10) (MAY 27): 11381-400.

Ge/Si and sr-87/Sr-86 tracers of weathering reactions and hydrologic pathways in a tropical granitoid system

Derry, LA, JC Pett-Ridge, AC Kurtz, and JW Troester. 2006. Ge/Si and sr-87/Sr-86 tracers of weathering reactions and hydrologic pathways in a tropical granitoid system. Journal of Geochemical Exploration 88 (1-3) (JAN-MAR): 271-4.

Ge/Si and 87Sr/86Sr data from primary and secondary minerals, soil waters, and stream waters in a tropical granitoid catchment quantitatively reflect mineral alteration reactions that occur at different levels within the bedrock–saprolite–soil zone. Near the bedrock–saprolite interface, plagioclase to kaolinite reaction yields low Ge/Si and 87Sr/86Sr. Higher in the regolith column, biotite weathering and kaolinite dissolution drive Ge/Si and 87Sr/86Sr to high values. Data from streams at base flow sample the bedrock–saprolite interface zone, while at high discharge solutes are derived from upper saprolite–soil zone. Coupled Ge/Si and 87Sr/86Sr can be effective tools for quantifying the importance of specific weathering reactions, and for geochemical hydrograph separation.

Estimating recharge thresholds in tropical karst island aquifers: Barbados, Puerto Rico and Guam

Jones, IC, and JL Banner. 2003. Estimating recharge thresholds in tropical karst island aquifers: Barbados, puerto rico and guam RID C-8676-2011. Journal of Hydrology 278 (1-4) (JUL 25): 131-43.

The hydrology and geochemistry of groundwater in tropical island aquifers, such as Barbados, Guam and Puerto Rico, are significantly influenced by tropical climatic conditions. Recharge to these aquifers is the product of regional and local climate patterns that control rainfall. Oxygen isotopes can be used to estimate the amount and timing of recharge on these islands because seasonal fluctuations of rainwater oxygen isotopic compositions are related to the amount of rainfall. The karst aquifers on Barbados, Guam and Puerto Rico have similar rainwater and groundwater oxygen isotopic compositions. Comparison of groundwater and rainwater oxygen isotopic compositions in the three aquifers indicates that: (1) recharge occurs by rapid infiltration with little evaporation prior to recharge; and (2) recharge is associated with similar monthly rainfall thresholds of 190–200 mm. These rainfall thresholds are remarkably similar for three aquifers in different geographic locations. Differences between the spatial variations of groundwater oxygen isotopic compositions on Barbados and Puerto Rico can be attributed to the more complex groundwater flow system on Puerto Rico. The surprising similarities of hydrologic conditions under which recharge will take place can be attributed to similarities in climate and geologic conditions, such as soils and limestone bedrock, that exist on the three islands. We therefore speculate that similar recharge-rainfall thresholds may be observed in other tropical karst aquifers.

Review of Use of Isotopes in Studying the Natural History of Puerto Rico

Evaristo J. Review of Use of Isotopes in Studying the Natural History of Puerto Rico. University of Pennsylvania. 2012.

This review summarizes the earth and environmental science research papers in Puerto Rico that used isotopic techniques between 1965 and 2011. The range of applications in isotope-related research in Puerto Rico has grown steadily, led by the ubiquitous utility of stable isotope ratios in biogeochemical (δ13C, δ15N) and ecological (δ13C, δ15N, δD) research. Moreover, research in climatology has grown in recent years, spanning from the evaluation of the fidelity of isotope records (δ18O, δ13C) as an environmental proxy to the elucidation of multidecadal variability for paleoclimate reconstructions (δ18O and Sr/Ca). On the other hand, in addition to using isotope ratios, hydrological studies in Puerto Rico have also used trace element data to answer flow source (δD, δ18O, 87Sr/86Sr) and solute source (Ge/Si) questions, as well as in examining groundwater/surface flow relationships (222Rn). Finally, various isotope data have been used in trying to understand geomorphological (10Be, δ30Si) and geophysical (Pb, Nd, and Sr) phenomena. It is hoped that this review will be able to contribute to stimulating future interests in isotope-related research as applicable in the LCZO or Puerto Rico, in particular, and/or in comparable humid tropical settings, in general.

Water and energy budgets of rain forests along an elevation gradient under maritime tropical conditions

Holwerda, F., 2005. Water and Energy Budgets of Rain Forests Along an Elevational Gradient Under Maritime Tropical Conditions. PhD Thesis, VU University, Amsterdam, The Netherlands.

From the hydrological point of view, mountains present somewhat of a paradox. Although they provide the bulk of the Earth’s freshwater resources, knowledge of the hydrological functioning of mountainous areas is generally much less extensive, reliable, and precise than that of other, often more easily accessible physiographic regions. Indeed, mountain regions have been referred to as ‘the blackest of black boxes in the hydrological cycle’ (Bandyopadhyay et al., 1997). Data collection networks are more difficult to set up and maintain in complex mountainous terrain, particularly in uninhabited forested headwater areas without road access, and minimum recommended instrumental densities are rarely met (Manley and Askew, 1993). Whilst the hydrological knowledge base on mountains in general has increased considerably in the last few decades, most montane research work has focused on determining catchment water and sediment outputs and their distribution in time and space; snow cover and glacier dynamics; or flood frequencies (Molnar, 1990; Lang and Musy, 1990; Bergmann et al., 1991; Young, 1992; Hofer, 1998), as opposed to the underlying hydrological processes (cf. Bonell, 1993). Until very recently (e.g. Motzer, 2003; Schellekens et al., 2004; Goller et al., 2005), the vast majority of this work dealt with mountains in the temperate zone, with very little pertaining to forested tropical mountains (see summaries of early research by Bruijnzeel and Proctor (1995) and Bruijnzeel (2001)). Knowledge of such processes would serve as a basis for increased understanding of how streamflows emanating from tropical mountains might change as a result of changes in climate, including the lifting condensation level, frequency and density of clouds and, by implication, water inputs and evaporative losses (Bruijnzeel, 2001). The average cloud condensation level on tropical islands can be as low as 600-800 m (Malkus, 1955), although on larger mountains situated further inland this may be closer to 2,000 m (Stadtmüller, 1987). Above this condensation level, the hydrology of the forest changes profoundly because of contributions of cloud water (i.e. fog) deposited to the forest canopy (Bruijnzeel, 2001). There is circumstantial evidence that complete conversion of these ‘tropical montane cloud forests’ (TMCF) to pasture or vegetable cropping may have an adverse effect on dry season flows or even on total water yield because of strongly diminished fog interception after clearing (Ingwersen, 1985; Brown et al., 1996). Similar effects may be expected when the average cloud condensation level is raised because of warming of the atmosphere due to global climate change (Still et al., 1999; Foster, 2001), or clearing of forest at lower elevations (Lawton et al., 2001; Van der Molen, 2002).

Longitudinal Patterns in Stream Channel Geomorphology and Aquitic Habitat in the Luquillo Mountains of Puerto Rico

The hydrologic, geomorphic, and ecological dynamics of tropical montane streams are poorly understood in comparison to many temperate and/or alluvial rivers. Yet as the threat to tropical freshwater environments increases, information on the dynamics of relatively pristine streams is important for understanding landscape evolution, managing and conserving natural resources, and implementing stream restoration. This dissertation characterizes the geomorphology and hydrology of five adjacent watersheds draining the Luquillo Experimental Forest (LEF) in northeastern Puerto Rico, and discusses implications on aquatic habitat. I performed several interrelated studies, including: 1) formulating a geographic information systems (GIS) framework to estimate hydrologic parameters from topographic information and hydrologic records, 2) developing a method to determine active stream channel boundaries (“bankfull” stage) that allows for comparison of channel geometry on the basis of flow-frequency, 3) decoupling the relative influences of lithologic and hydraulic controls on channel morphology using an extensive field-based stream survey and analysis of stream profiles, channel geometry, and sediment dynamics, 4) linking network- and pool-scale geofluvial dynamics to the abundance of migratory fish and shrimp through a collaborative analysis combining geomorphic surveys and aquatic faunal sampling. This research indicates that these streams have some properties resembling both temperate montane and alluvial rivers. Similar to low-gradient rivers where floodplains mark channel boundaries, the active channel stage in these streams is defined by the incipient presence of woody vegetation and soil development. Systematic basin-scale geomorphic patterns are well-developed despite apparent non-fluvial and lithologic control on local channel morphology. This implies that strong fluvial forces are sufficient to override channel boundary resistance; a feature common in self-forming “threshold” alluvial channels. Migratory aquatic fauna abundances are influenced by a variety of geomorphic factors such as barrier waterfalls and suitable headwater habitat, and are consequently highly variable and patchy. These results stand in contrast to the notion that aquatic communities mirror systematic geomorphic gradients, but rather acknowledges the influences of multiscale geomorphic processes. Ultimately, this research provides baseline information on physical and biological processes in relatively unaltered tropical streams and can be used to inform further studies that document human interactions with stream networks.

Integrated Water Plan for Puerto Rico, December 2006

"Plan Integral de Agua" December, 2006.

Water is a natural resource important for life, growth and development of cities and towns. It's "Not just the most basic of necessities it's also the basis of sustainable development." The spatial and temporal distributions varies in such a way that its in abudnant in some regions and times while is is vary limited in others. While it is considers a renewable resource it is no less correct that improper management can lead to a reduced quantity and quality of available water. It's also the case that contamination can also render the resource unusable. For these reasons the availability, quality, and management of water resources represents a grand challenge for Puerto Rico and most of the world. El agua es un recurso natural de vital importancia para la vida, crecimiento y desarrollo de los pueblos. Es “[n]o sólo la más básica de las necesidades, sino también el núcleo del desarrollo sostenible”1. Su distribución espacial y temporal varía de forma que, mientras es abundante en unas regiones o épocas, en otras es muy limitado. A pesar de que se considera un recurso renovable no es menos cierto que su manejo inapropiado, puede tener el efecto de reducir la cantidad disponible y utilizable del recurso. De igual forma, la contaminación irreversible del recurso puede convertirlo en uno agotable. Es por ello que la disponibilidad, calidad y manejo adecuado del recurso representa un gran desafío para Puerto Rico y la mayor parte del mundo.
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