Geology topics

Research about Puerto Rico

Source-linked reports with geographic coverage including Puerto Rico.

At least 181 records · Page 10Linked to original sources

USGS2012

Physiography, geology, and land cover of four watersheds in eastern Puerto Rico: Chapter A in Water quality and landscape processes of four watersheds in eastern Puerto Rico

Four watersheds with differing geology and land cover in eastern Puerto Rico have been studied on a long-term basis by the U.S. Geological Survey to evaluate water, energy, and biogeochemical budgets. These watersheds are typical of tropical, island-arc settings found in many parts of the world. Two watersheds are located on coarse-grained granitic rocks that weather to quartz- and clay-rich, sandy soils, and two are located on fine-grained volcanic rocks and volcaniclastic sedimentary rocks that weather to quartz-poor, fine-grained soils. For each bedrock type, one watershed is covered with mature forest, and the other watershed, like most of Puerto Rico, has transformed from relatively undisturbed pre-European forest to intensive agriculture in the 19th and early 20th centuries, and further to ongoing reforestation that began in the middle of the 20th century. The comparison of water chemistry and hydrology in these watersheds allows an evaluation of the effects of land-use history and geology on hydrologic regimes and erosion rates. This chapter describes the physiography, geology, and land cover of the four watersheds and provides background information for the remaining chapters in this volume.

Professional Paper↗

USGS2012

Land use, population dynamics, and land-cover change in eastern Puerto Rico: Chapter B in Water quality and landscape processes of four watersheds in eastern Puerto Rico

We assessed current and historic land use and land cover in the Luquillo Mountains and surrounding area in eastern Puerto Rico, including four small subwatersheds that are study watersheds of the U.S. Geological Survey's Water, Energy, and Biogeochemical Budgets (WEBB) program. This region occupies an area of 1,616 square kilometers, about 18 percent of the total land in Puerto Rico. Closed forests occupy about 37 percent of the area, woodlands and shrublands 7 percent, nonforest vegetation 43 percent, urban development 10 percent, and water and natural barrens total less than 2 percent. The area has been classified into three main land-use categories by integrating recent census information (population density per barrio in the year 2000) with satellite image analyses (degree of developed area versus natural land cover). Urban land use (in this analysis, land with more than 20 percent developed cover within a 1-square-kilometer area and population density greater than 500 people per square kilometer) covered 16 percent of eastern Puerto Rico. Suburban land use (more than 80 percent natural land cover, more than 500 people per square kilometer, and primarily residential) covers 50 percent of the area. Rural land use (more than 80 percent natural land cover, less than 500 people per square kilometer, and primarily active or abandoned agricultural, wetland, steep slope, or protected conservation areas) covered 34 percent of the area. Our analysis of land-cover change indicates that in the 1990s, forest cover increased at the expense of woodlands and grasslands. Urban development increased by 16 percent during that time. The most pronounced change in the last seven decades has been the shift from a nonforested to a forested landscape and the intensification of the ring of urbanization that surrounds the long-protected Luquillo Experimental Forest.

Professional Paper↗

USGS2012

Hydrology and climate of four watersheds in eastern Puerto Rico: Chapter C in Water quality and landscape processes of four watersheds in eastern Puerto Rico

Puerto Rico lies directly in the path of the easterly trade winds, which deliver steady rainfall to the mountains and steer tropical wave systems toward the island. Hurricanes and tropical storms derived from these tropical waves differ in frequency and intensity, contributing to substantial interannual variation in precipitation and stream discharge. Puerto Rico's steep topography and small water-storage capacity leave the island's water supply and developed flood plains vulnerable to extreme weather events, such as hurricanes, floods, and droughts. This vulnerability may increase in the future owing to ongoing change, both local (such as land-cover shifts, water-supply projects, and construction of roads and other infrastructure) and regional (climate variability and change). Climate change, which could lead to more intense and prolonged droughts as well as an increase in the magnitude and frequency of destructive storms in the Caribbean, may alter temperature and affect the availability of water for human and ecosystem needs. Accurate assessment of hydrologic regimes and water budgets is therefore crucial for effective management of water resources. As part of the U.S. Geological Survey's Water, Energy, and Biogeochemical Budgets program, hydrologic and geomorphologic processes and stream chemistry of four small watersheds in eastern Puerto Rico, which differ in geology and land cover, have been studied since 1991. Spatial and temporal characteristics of precipitation and stream discharge, along with water budgets, were determined for the watersheds for the period 1991 to 2005. The locations of the watersheds relative to the Luquillo Mountains and the range's associated rain shadow dominate hydrological processes, dwarfing influences of land cover. The influence of geology is reflected in recession characteristics of the rivers (recession is faster in soils overlying volcaniclastic bedrock) and in hillslope geomorphic processes (sediment is delivered at higher rates from soils overlying granitic bedrock).

Professional Paper↗

USGS2012

Atmospheric inputs to watersheds of the Luquillo Mountains in eastern Puerto Rico: Chapter D in Water quality and landscape processes of four watersheds in eastern Puerto Rico

Twenty years of precipitation-chemistry data from the National Atmospheric Deposition Program site at El Verde, Puerto Rico, demonstrate that three major sources control the composition of solutes in rain in eastern Puerto Rico. In order of importance, these sources are marine salts, temperate contamination from the Northern Hemisphere, and Sahara Desert dust. Marine salts are a source of roughly 82 percent of the ionic charge in precipitation; marine salt inputs are greatest in January. Evaluation of 15 years of U.S. Geological Survey data for four watersheds in eastern Puerto Rico suggests that large storms, including hurricanes, are associated with exceptionally high chloride concentrations in stream waters. Some of these storms were missed in sampling by the National Atmospheric Deposition Program, and therefore its data on the marine contribution likely underestimate chloride. The marine contribution is a weak source of acidity. Temperate contamination contributes about 10 percent of the ionic charge in precipitation; contaminants are primarily nitrate, ammonia, and sulfate derived from various manmade and natural sources. Peak deposition of temperate contaminants is during January, April, and May, months in which strong weather fronts arrive from the north. Temperate contamination, a strong source of acidity, is the only component that is increasing through time. Sahara Desert dust provides 5 percent of the ionic charge in precipitation; it is strongly seasonal, peaking in June and July during times of maximum dust transport from the Sahara and sub-Saharan regions. This dust contributes, on average, enough alkalinity to neutralize the acidity in June and July rains.

Professional Paper↗

USGS2012

Water quality and mass transport in four watersheds in eastern Puerto Rico: Chapter E in Water quality and landscape processes of four watersheds in eastern Puerto Rico

Water quality of four small watersheds in eastern Puerto Rico has been monitored since 1991 as part of the U.S. Geological Survey's Water, Energy, and Biogeochemical Budgets program. These watersheds represent a montane, humid-tropical environment and differ in geology and land cover. Two watersheds are located on granitic rocks, and two are located on volcaniclastic rock. For each bedrock type, one watershed is covered with mature rainforest in the Luquillo Mountains, and the other watershed is undergoing reforestation after being affected by agricultural practices typical of eastern Puerto Rico. A subwatershed of the Icacos watershed, the Guabá, was also monitored to examine scaling effects. The water quality of the rivers draining forest, in the Icacos and Guabá (granitic watersheds) and Mameyes (a volcaniclastic watershed), show little contamination by human activities. The water is well oxygenated and has a nearly neutral pH, and nutrient concentrations are low. Concentrations of nutrients in the disturbed watersheds, the Cayaguás (granitic rock) and Canóvanas (volcaniclastic rock), are greater than in the forested watersheds, indicating some inputs from human activities. High in-stream productivity in the Canóvanas watershed leads to occasional oxygen and calcite supersaturation and carbon dioxide undersaturation. Suspended sediment concentrations in all watersheds are low, except during major storms. Most dissolved constituents derived from bedrock weathering or atmospheric deposition (including sodium, magnesium, calcium, silica, alkalinity, and chloride) decrease in concentration with increasing runoff, reflecting dilution from increased proportions of overland or near-surface flow. Strongly bioactive constituents (dissolved organic carbon, potassium, nitrate, ammonium ion, and phosphate) commonly display increasing concentration with increasing runoff, regardless of their ultimate origin (bedrock or atmosphere). The concentrations of many of the bioactive constituents eventually decrease at runoff rates greater than 3 to 10 millimeters per hour, presumably reflecting an increased relative contribution from overland flow. Sulfate behaves like the nonbioactive constituents in the Canóvanas, Cayaguás, and Mameyes watersheds but like a bioactive constituent in the Icacos and Guabá watersheds. Storms resulted in several anomalous sample compositions. Runoff waters from a number of storms - mostly hurricanes, but also other storms - have exceptionally high chloride concentrations, presumably resulting from windborne seasalt from the ocean, and low nitrate concentrations, reflecting a dominance of maritime air masses contributing moisture to the storms. High-potassium samples, without high chloride, are also associated with some smaller storms that followed Hurricane Georges in 1998; they are likely related to the breakdown of fallen vegetation. Finally, occasional low-silica events are observed in the Icacos and Guabá watersheds in the years prior to Hurricane Georges, but not after; this difference may be related to a change in hydrologic flow paths.

Professional Paper↗

USGS2012

Landslides and sediment budgets in four watersheds in eastern Puerto Rico: Chapter F in Water quality and landscape processes of four watersheds in eastern Puerto Rico

The low-latitude regions of the Earth are undergoing profound, rapid landscape change as forests are converted to agriculture to support growing population. Understanding the effects of these land-use changes requires analysis of watershed-scale geomorphic processes to better inform and manage this usually disorganized process. The investigation of hillslope erosion and the development of sediment budgets provides essential information for resource managers. Four small, montane, humid-tropical watersheds in the Luquillo Experimental Forest and nearby Río Grande de Loíza watershed, Puerto Rico (18° 20' N., 65° 45' W.), were selected to compare and contrast the geomorphic effects of land use and bedrock geology. Two of the watersheds are underlain largely by resistant Cretaceous volcaniclastic rocks but differ in land use and mean annual runoff: the Mameyes watershed, with predominantly primary forest cover and runoff of 2,750 millimeters per year, and the Canóvanas watershed, with mixed secondary forest and pasture and runoff of 970 millimeters per year. The additional two watersheds are underlain by relatively erodible granitic bedrock: the forested Icacos watershed, with runoff of 3,760 millimeters per year and the agriculturally developed Cayaguás watershed, with a mean annual runoff of 1,620 millimeters per year. Annual sediment budgets were estimated for each watershed using landslide, slopewash, soil creep, treethrow, suspended sediment, and streamflow data. The budgets also included estimates of sediment storage in channel beds, bars, floodplains, and in colluvial deposits. In the two watersheds underlain by volcaniclastic rocks, the forested Mameyes and the developed Canóvanas watersheds, landslide frequency (0.21 and 0.04 landslides per square kilometer per year, respectively), slopewash (5 and 30 metric tons per square kilometer per year), and suspended sediment yield (325 and 424 metric tons per square kilometer per year), were lower than in the two watersheds underlain by granitic bedrock. In these granitic watersheds, landslide frequency, slopewash, and suspended sediment yield were 0.43 landslides per square kilometer per year, 20 metric tons per square kilometer per year, and 2,140 metric tons per square kilometer per year, respectively, in the forested Icacos watershed and 0.8 landslides per square kilometer per year, 105 metric tons per square kilometer per year, and 2,110 metric tons per square kilometer per year, respectively, in the agriculturally developed Cayaguás watershed. Comparison of sediment budgets from the forested and developed watersheds indicates that human activities increase landslide frequency by as much as factor of 5 and slopewash by as much as a factor of 6. When the difference in annual runoff is considered, the effect of land use on suspended sediment yields is also notable. Sediment concentration, calculated as sediment yield normalized by runoff, was about 2.3 to 3.7 times as great in the two watersheds in secondary forest and pasture compared with sediment concentration in the watersheds in primary forest. Even in the two watersheds with primary forest cover, the Mameyes and Icacos, located in the Luquillo Experimental Forest, the effects of anthropogenic disturbance were marked: 43 to 63 percent of landslide-related erosion was associated with road construction and maintenance.

Professional Paper↗

USGS2012

Effects of earthworms on slopewash, surface runoff, and fine-litter transport on a humid-tropical forested hillslope in eastern Puerto Rico: Chapter G in Water quality and landscape processes of four watersheds in eastern Puerto Rico

Rainfall, slopewash (the erosion of soil particles), surface runoff, and fine-litter transport were measured in tropical wet forest on a hillslope in the Luquillo Experimental Forest, Puerto Rico, from February 1998 until April 2000. Slopewash data were collected using Gerlach troughs at eight plots, each 2 square meters in area. Earthworms were excluded by electroshocking from four randomly selected plots. The other four (control) plots were undisturbed. During the experiment, earthworm population in the electroshocked plots was reduced by 91 percent. At the end of the experiment, the electroshocked plots had 13 percent of earthworms by count and 6 percent by biomass as compared with the control plots. Rainfall during the sampling period (793 days) was 9,143 millimeters. Mean and maximum rainfall by sampling period (mean of 16 days) were 189 and 563 millimeters, respectively. Surface runoff averaged 0.6 millimeters and 1.2 millimeters by sampling period for the control and experimental plots, equal to 0.25 and 0.48 percent of mean rainfall, respectively. Disturbance of the soil environment by removal of earthworms doubled runoff and increased the transport (erosion) of soil and organic material by a factor of 4.4. When earthworms were removed, the erosion of mineral soil (soil mass left after ashing) and the transport of fine litter were increased by a factor of 5.3 and 3.4, respectively. It is assumed that increased runoff is a function of reduced soil porosity, resulting from decreased burrowing and reworking of the soil in the absence of earthworms. The background, or undisturbed, downslope transport of soil, as determined from the control plots, was 51 kilograms per hectare and the "disturbance" rate, determined from the experimental plots, was 261 kilograms per hectare. The background rate for downslope transport of fine litter was 71 kilograms per hectare and the disturbance rate was 246 kilograms per hectare. Data from this study indicate that the reduction in soil macrofauna population, in this case, earthworms, plays a key role in increasing runoff and soil erosion and, therefore, has important implications for forest and water management.

Luquillo Experimental Forest↗

USGS2012

Weathering, landscape equilibrium, and carbon in four watersheds in eastern Puerto Rico: Chapter H in Water quality and landscape processes of four watersheds in eastern Puerto Rico

The U.S. Geological Survey's Water, Energy, and Biogeochemical Budgets (WEBB) program research in eastern Puerto Rico involves a double pair-wise comparison of four montane river basins, two on granitic bedrock and two on fine-grained volcaniclastic bedrock; for each rock type, one is forested and the other is developed. A confounding factor in this comparison is that the developed watersheds are substantially drier than the forested (runoff of 900–1,600 millimeters per year compared with 2,800–3,700 millimeters per year). To reduce the effects of contrasting runoff, the relation between annual runoff and annual constituent yield were used to estimate mean-annual yields at a common, intermediate mean-annual runoff of 1,860 millimeters per year. Upon projection to this intermediate runoff, the ranges of mean-annual yields among all watersheds became more compact or did not substantially change for dissolved bedrock, sodium, silica, chloride, dissolved organic carbon, and calcium. These constituents are the primary indicators of chemical weathering, biological activity on the landscape, and atmospheric inputs; the narrow ranges indicate little preferential influence by either geology or land cover. The projected yields of biologically active constituents (potassium, nitrate, ammonium ion, phosphate), and particulate constituents (suspended bedrock and particulate organic carbon) were considerably greater for developed landscapes compared with forested watersheds, consistent with the known effects of land clearing and human waste inputs. Equilibrium rates of combined chemical and physical weathering were estimated by using a method based on concentrations of silicon and sodium in bedrock, river-borne solids, and river-borne solutes. The observed rates of landscape denudation greatly exceed rates expected for a dynamic equilibrium, except possibly for the forested watershed on volcaniclastic rock. Deforestation and agriculture can explain the accelerated physical erosion in the two developed watersheds. Because there has been no appreciable deforestation, something else, possibly climate or forest-quality change, must explain the accelerated erosion in the forested watersheds on granitic rocks. Particulate organic carbon yields are closely linked to sediment yields. This relation implies that much of the particulate organic carbon transport in the four rivers is being caused by this enhanced erosion aided by landslides and fast carbon recovery. The increase in particulate organic carbon yields over equilibrium is estimated to range from 300 kilomoles per square kilometer per year (6 metric tons carbon per square kilometer per year) to 1,700 kilomoles per square kilometer per year (22 metric tons carbon per square kilometer per year) and is consistent with human-accelerated particulate-organic-carbon erosion and burial observed globally. There is no strong evidence of human perturbation of silicate weathering in the four study watersheds, and differences in dissolved inorganic carbon are consistent with watershed geology. Although dissolved organic carbon is slightly elevated in the developed watersheds, that elevation is not enough to unambiguously demonstrate human causes; more work is needed. Accordingly, the dissolved organic carbon and dissolved inorganic carbon yields of tropical rivers, although large, are of secondary importance in the study of the anthropgenically perturbed carbon cycle.

Professional Paper↗

USGS2012

Weathering processes in the Rio Icacos and Rio Mameyes watersheds in Eastern Puerto Rico: Chapter I in Water quality and landscape processes of four watersheds in eastern Puerto Rico

Streams draining watersheds of the two dominant lithologies (quartz diorite and volcaniclastic rock) in the Luquillo Experimental Forest of eastern Puerto Rico have very high fluxes of bedrock weathering products. The Río Blanco quartz diorite in the Icacos watershed and the Fajardo volcaniclastic rocks in the Mameyes watershed have some of the fastest documented rates of chemical weathering of siliceous rocks in the world. Rapid weathering produces thick, highly leached saprolites in both watersheds that lie just below the soil and largely isolate subsurface biogeochemical and hydrologic processes from those in the soil. The quartz diorite bedrock in the Icacos watershed weathers spheroidally, leaving large, relatively unweathered corestones that are enveloped by slightly weathered rock layers called rindlets. The rindlets wrap around the corestones like an onionskin. Within the corestones, biotite oxidation is thought to induce the spheroidal fracturing that leads to development of rindlets; plagioclase in the rindlets dissolves, creating additional pore spaces. Near the rindlet-saprolite interface, the remaining plagioclase dissolves, hornblende dissolves to completion, and precipitation of kaolinite, gibbsite, and goethite becomes pervasive. In the saprolite, biotite weathers to kaolinite and quartz begins to dissolve. In the soil layer, both quartz and kaolinite dissolve. The volcaniclastic bedrock of the Mameyes watershed weathers even faster than the quartz diorite bedrock of the Icacos watershed, leaving thicker saprolites that are devoid of all primary minerals except quartz. The quartz content of volcaniclastic bedrock may help to control watershed geomorphology; high-quartz rocks form thick saprolites that blanket ridges. Hydrologic flow paths within the weathering profiles vary with total fluid flux, and they influence the chemistry of streams. Under low-flow conditions, the Río Icacos and its tributaries are fed by rainfall and by groundwater from the fracture zones; during storm events, intense rainfall rapidly raises stream levels and water is flushed through the soil as shallow flow. As a result, weathering constituents that shed into streamwaters are dominated by rindlet-zone weathering processes during base flow and by soil weathering processes during stormflow. The upper reaches of the Mameyes watershed are characterized by regolith more than 35 meters thick in places that contains highly fractured rock embedded in its matrix. Weathering contributions to stream chemistry at base flow are predicted to be more spatially variable in the Mameyes watershed than in the Icacos watershed owing to the more complex subsurface weathering profile of the volcaniclastic bedrocks of the Mameyes watershed.

Professional Paper↗

USGS2012

Storage capacity and sedimentation trends of Lago Garzas, Puerto Rico, 1996-2007

Lago Garzas is located in west-central Puerto Rico, about 3.5 kilometers southwest of the town of Adjuntas, in the confluence of the Río Vacas and three other unnamed tributaries (fig. 1). The dam is owned and operated by the Puerto Rico Electric Power Authority (PREPA), and was constructed in 1943 for hydroelectric power generation and municipal water use along the southern coast. The dam is a semi-hydraulic earthfill embankment lined with boulders, and has a height of 61.57 meters, a top width of 9.14 meters, a base width of 365.76 meters, and a crest length of 227.37 meters; State Road PR-518 crosses the top of the dam. A morning-glory-type spillway is located near the west abutment of the dam at an elevation of 736.12 meters above mean sea level (Puerto Rico Water Resources Authority, 1969). Figure 2 shows an aerial photograph of the Lago Garzas earthfill dam and the morning-glory spillway section. Additional information and operational procedures are provided in Soler-López and others (1999). During July 17-18, 2007, the U.S. Geological Survey (USGS) Caribbean Water Science Center, in cooperation with the Puerto Rico Aqueduct and Sewer Authority, conducted a bathymetric survey of Lago Garzas to update the reservoir storage capacity and update the reservoir sedimentation rate by comparing the 2007 data with the previous 1996 bathymetric survey results. The purpose of this report is to describe and document the USGS sedimentation survey conducted at Lago Garzas during July 2007, including the methods used to update the reservoir storage capacity, sedimentation rates, and areas of substantial sediment accumulation since 1996.

Lago Garzas Basin Area↗

USGS2012

Disseminated toxoplasmosis in Antillean manatees Trichechus manatus manatus from Puerto Rico

Necropsies were conducted on 4 Antillean manatees Trichechus manatus manatus that were stranded in single events on the coastal beaches of Puerto Rico from August 2010 to August 2011. Three manatees were emaciated and the gastrointestinal tracts were devoid of digesta. Microscopically, all manatees had severe widespread inflammatory lesions of the gastrointestinal tract and heart with intralesional tachyzoites consistent with Toxoplasma gondii identified by histological, ultrastructural and immunohistochemical techniques. The gastrointestinal lesions included severe, multifocal to diffuse, chronic-active enteritis, colitis and/or gastritis often with associated ulceration, necrosis and hemorrhage. Enteric leiomyositis was severe and locally extensive in all cases and associated with the most frequently observed intralesional protozoans. Moderate to severe, multifocal, chronic to chronic-active, necrotizing myocarditis was also present in all cases. Additionally, less consistent inflammatory lesions occurred in the liver, lung and a mesenteric lymph node and were associated with fewer tachyzoites. Sera (n = 30) collected from free-ranging and captive Puerto Rican manatees and a rehabilitated/released Puerto Rican manatee from 2003 to 2012 were tested for antibodies for T. gondii . A positive T. gondii antibody titer was found in 2004 in 1 (3%) of the free-ranging cases tested. Disease caused by T. gondii is rare in manatees. This is the first report of toxoplasmosis in Antillean manatees from Puerto Rico. Additionally, these are the first reported cases of disseminated toxoplasmosis in any sirenian. The documentation of 4 cases of toxoplasmosis within one year and the extremely low seroprevalence to T. gondii suggest that toxoplasmosis may be an emerging disease in Antillean manatees from Puerto Rico.

Diseases of Aquatic Organisms↗

USGS2011

Long-term patterns and short-term dynamics of stream solutes and suspended sediment in a rapidly weathering tropical watershed

The 326 ha Río Icacos watershed in the tropical wet forest of the Luquillo Mountains, northeastern Puerto Rico, is underlain by granodiorite bedrock with weathering rates among the highest in the world. We pooled stream chemistry and total suspended sediment (TSS) data sets from three discrete periods: 1983–1987, 1991–1997, and 2000–2008. During this period three major hurricanes crossed the site: Hugo in 1989, Hortense in 1996, and Georges in 1998. Stream chemistry reflects sea salt inputs (Na, Cl, and SO 4 ), and high weathering rates of the granodiorite (Ca, Mg, Si, and alkalinity). During rainfall, stream composition shifts toward that of precipitation, diluting 90% or more in the largest storms, but maintains a biogeochemical watershed signal marked by elevated K and dissolved organic carbon (DOC) concentration. DOC exhibits an unusual “boomerang” pattern, initially increasing with flow but then decreasing at the highest flows as it becomes depleted and/or vigorous overland flow minimizes contact with watershed surfaces. TSS increased markedly with discharge (power function slope 1.54), reflecting the erosive power of large storms in a landslide-prone landscape. The relations of TSS and most solute concentrations with stream discharge were stable through time, suggesting minimal long-term effects from repeated hurricane disturbance. Nitrate concentration, however, increased about threefold in response to hurricanes then returned to baseline over several years following a pseudo first-order decay pattern. The combined data sets provide insight about important hydrologic pathways, a long-term perspective to assess response to hurricanes, and a framework to evaluate future climate change in tropical ecosystems.

Puerto Rico↗

USGS2011

New seafloor map of the Puerto Rico Trench helps assess earthquake and tsunami hazards

The Puerto Rico Trench, the deepest part of the Atlantic Ocean, is located where the North American (NOAM) plate is subducting under the Caribbean plate (Figure l). The trench region may pose significant seismic and tsunami hazards to Puerto Rico and the U.S.Virgin Islands, where 4 million U.S. citizens reside. Widespread damage in Puerto Rico and Hispaniola from an earthquake in 1787 was estimated to be the result of a magnitude 8 earthquake north of the islands [McCann et al., 2004]. A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918 [Mercado and McCann, 1998]. Large landslide escarpments have been mapped on the seafloor north of Puerto Rico [Mercado et al., 2002; Schwab et al., 1991],although their ages are unknown.

Puerto Rico Trench↗

USGS2011

Coral skeletal carbon isotopes (δ 13 C and Δ 14 C) record the delivery of terrestrial carbon to the coastal waters of Puerto Rico

Tropical small mountainous rivers deliver a poorly quantified, but potentially significant, amount of carbon to the world’s oceans. However, few historical records of land–ocean carbon transfer exist for any region on Earth. Corals have the potential to provide such records, because they draw on dissolved inorganic carbon (DIC) for calcification. In temperate systems, the stable- (δ 13 C) and radiocarbon (Δ 14 C) isotopes of coastal DIC are influenced by the δ 13 C and Δ 14 C of the DIC transported from adjacent rivers. A similar pattern should exist in tropical coastal DIC and hence coral skeletons. Here, δ 13 C and Δ 14 C measurements were made in a 56-year-old Montastraea faveolata coral growing ~1 km from the mouth of the Rio Fajardo in eastern Puerto Rico. Additionally, the δ 13 C and Δ 14 C values of the DIC of the Rio Fajardo and its adjacent coastal waters were measured during two wet and dry seasons. Three major findings were observed: (1) synchronous depletions of both δ 13 C and Δ 14 C in the coral skeleton are annually coherent with the timing of peak river discharge, (2) riverine DIC was always more depleted in δ 13 C and Δ 14 C than seawater DIC, and (3) the correlation of δ 13 C and Δ 14 C was the same in both coral skeleton and the DIC of the river and coastal waters. These results indicate that coral skeletal δ 13 C and Δ 14 C are recording the delivery of riverine DIC to the coastal ocean. Thus, coral records could be used to develop proxies of historical land–ocean carbon flux for many tropical regions. Such information could be invaluable for understanding the role of tropical land–ocean carbon flux in the context of land-use change and global climate change.

Puerto Rico↗

USGS2011

Productivity of a coral reef using boundary layer and enclosure methods

The metabolism of Cayo Enrique Reef, Puerto Rico, was studied using in situ methods during March 2009. Benthic O 2 fluxes were used to calculate net community production using both the boundary layer gradient and enclosure techniques. The boundary layer O 2 gradient and the drag coefficients were used to calculate productivity ranging from −12.3 to 13.7 mmol O 2 m −2 h −1 . Productivity measurements from the enclosure method ranged from −11.0 to 12.9 mmol O 2 m −2 h −1 . During the study, the mean hourly difference between the methods was 0.65 mmol O 2 m −2 h −1 (r 2 = 0.92), resulting in well‐reconciled estimates of net community production between the boundary layer (−33.1 mmol m −2 d −1 ) and enclosure (−46.3 mmol m −2 d −1 ) techniques. The results of these independent approaches corroborate quantified rates of metabolism at Cayo Enrique Reef. Close agreement between methods demonstrates that boundary layer measurements can provide near real‐time assessments of coral reef health.

Puerto Rico↗

USGS2011

Testing coral-based tropical cyclone reconstructions: An example from Puerto Rico

Complimenting modern records of tropical cyclone activity with longer historical and paleoclimatological records would increase our understanding of natural tropical cyclone variability on decadal to centennial time scales. Tropical cyclones produce large amounts of precipitation with significantly lower δ 18 O values than normal precipitation, and hence may be geochemically identifiable as negative δ 18 O anomalies in marine carbonate δ 18 O records. This study investigates the usefulness of coral skeletal δ 18 O as a means of reconstructing past tropical cyclone events. Isotopic modeling of rainfall mixing with seawater shows that detecting an isotopic signal from a tropical cyclone in a coral requires a salinity of ~ 33 psu at the time of coral growth, but this threshold is dependent on the isotopic composition of both fresh and saline end-members. A comparison between coral δ 18 O and historical records of tropical cyclone activity, river discharge, and precipitation from multiple sites in Puerto Rico shows that tropical cyclones are not distinguishable in the coral record from normal rainfall using this approach at these sites.

Puerto Rico↗

USGS2011

Halloysite nanotubes and bacteria at the saprolite-bedrock interface, Rio Icacos watershed, Puerto Rico

Quartz diorite bedrock underlying the Luquillo Mountains of eastern Puerto Rico undergoes weathering at one of the fastest documented rates for granitic rocks in the world. Although tropical temperatures and precipitation promote rapid weathering in this location, increased bacterial densities in the regolith immediately above the bedrock suggest that microorganisms contribute to mineral weathering as well. Deep saprolite and saprock samples were obtained at the bedrock interface in an upland location (Guaba Ridge) in the Rio Icacos watershed for examination by environmental scanning electron microscopy (ESEM). In ESEM images, mineral nanotubes were observed to occur frequently in association with coccus- and rod-shaped structures resembling bacteria. These nanotubes (50–140-nm width and 150–2700-nm length) were identified as halloysite using transmission electron microscopy. Observations of multiple nanotubes on the surfaces of an individual cell are consistent with the cell's exterior functional groups interacting with Si in pore water to facilitate halloysite nucleation. We propose that one mechanism by which bacteria contribute to the rapid weathering of quartz diorite minerals in this regolith is by lowering the free energy for secondary mineral formation. The presence of bacterial surfaces may result in more rapid removal of Si from solution, thereby increasing the dissolution rates of primary minerals.

Puerto Rico↗

USGS2011

Sedimentation survey of Lago Cerrillos, Ponce, Puerto Rico, April-May 2008

Lago Cerrillos dam, located in the municipality of Ponce in southern Puerto Rico, was constructed in 1991 as part of the multipurpose Rio Portugues and Bucana Project. This project provides flood protection, water supply, and recreation facilities for the municipio of Ponce. The reservoir had an original storage capacity of 38.03 million cubic meters at maximum conservation pool elevation of 174.65 meters above mean sea level and a drainage area of 45.32 square kilometers. Sedimentation in Lago Cerrillos reservoir has reduced the storage capacity from 38.03 million cubic meters in 1991 to 37.26 million cubic meters in 2008, which represents a total storage loss of about 2 percent. During July 29 to August 23, 2002, 8,492 cubic meters of sediment were removed from the Rio Cerrillos mouth of the reservoir. Taking into account this removed material, the total water-storage loss as of 2008 is 778,492 cubic meters, and the long-term annual water-storage capacity loss rate is about 45,794 cubic meters per year or about 0.12 percent per year. The Lago Cerrillos net sediment-contributing drainage area has an average sediment yield of about 1,069 cubic meters per square kilometer per year. Sediment accumulation in Lago Cerrillos is not uniformly distributed and averages about 3 meters in thickness. This represents a sediment deposition rate of about 18 centimeters per year. On the basis of the 2008 reservoir storage capacity of 37.26 million cubic meters per year and a long-term sedimentation rate of 45,794 cubic meters per year, Lago Cerrillos is estimated to have a useful life of about 814 years or until the year 2822.

Lago Cerrillos↗