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At least 469 records · Page 26Linked to original sources
USGS2007

Impact of hurricanes storm surges on the groundwater resources

Ocean surges onto coastal lowlands caused by tropical and extra tropical storms, tsunamis, and sea level rise affect all coastal lowlands and present a threat to drinking water resources of many coastal residents. In 2005, two such storms, Hurricanes Katrina and Rita struck the Gulf Coast of the US. Since September 2005, water samples have been collected from water wells impacted by the hurricanes' storm surges along the north shore of Lake Pontchartrain in southeastern Louisiana. The private and public water wells tested were submerged by 0.6-4.5 m of surging saltwater for several hours. The wells' casing and/or the associated plumbing were severely damaged. Water samples were collected to determine if storm surge water inundated the well casing and, if so, its effect on water quality within the shallow aquifers of the Southern Hills Aquifer System. In addition, the samples were used to determine if the impact on water quality may have long-term implication for public health. Laboratory testing for several indicator parameters (Ca/Mg, Cl/Si, chloride, boron, specific conductance and bacteria) indicates that surge water entered water wells' casing and the screened aquifer. Analysis of the groundwater shows a decrease in the Ca/Mg ratio right after the storm and then a return toward pre-Katrina values. Chloride concentrations were elevated right after Katrina and Rita, and then decreased downward toward pre-Katrina values. From September 2005 to June 2006, the wells showed improvement in all the saltwater intrusion indicators. ?? 2007 Springer-Verlag.

Environmental Geology↗
USGS2010

Theme section on “Mesophotic coral ecosystems: Characterization, ecology, and management”

Mesophotic coral ecosystems (MCEs) are characterized by the presence of light-dependent corals and associated communities that are typically found at depths ranging from 30 to 40 m and extending to over 150 m in tropical and subtropical regions. The dominant communities providing structural habitat in the mesophotic zone can be comprised of coral, sponge, and algal species. Because working in this depth range is constrained by traditional SCUBA limits, less is known about corals and associated organisms there compared to shallower coral communities. Following the first-ever gathering of international scientists to review and discuss existing knowledge of MCEs, this issue focuses on the ecological characterization, geomorphology, and concept of MCEs as refugia for shallow-water populations. The review and research papers comprising this special issue reflect the current scientific understanding of these ecosystems and the underlying mechanisms that regulate them, as well as potential resource management implications. It is important to understand the value and role of mesophotic coral ecosystems in tropical and subtropical regions as these areas face increasing environmental change and human impacts

Coral Reefs↗
USGS2019

Physical mechanisms influencing localized patterns of temperature variability and coral bleaching within a system of reef atolls

Interactions between oceanic and atmospheric processes within coral reefs can significantly alter local-scale (< km) water temperatures, and consequently drive variations in heat stress and bleaching severity. The Scott Reef atoll system was one of many reefs affected by the 2015–2016 mass coral bleaching event across tropical Australia, and specifically experienced sea surface temperature anomalies of 2 °C that caused severe mass bleaching (> 60%) over most of this system; however, the bleaching patterns were not uniform. Little is known about the processes governing thermodynamic variability within atolls, particularly those that are dominated by large amplitude tides. Here, we identify three mechanisms at Scott Reef that alleviated heat stress during the marine heatwave in 2016: (1) the cool wake of a tropical cyclone that induced temperature drops of 1.3 °C over a period of 8 days; (2) air–sea heat fluxes that interacted with the reef morphology during neap tides at one of the atolls to reduce water temperatures by up to 2.9 °C; (3) internal tidal processes that forced deeper and cooler water (up to 2.7 °C) into some sections of the shallow reefs. The latter two processes created localized areas of reduced temperatures that led to lower incidences of coral bleaching for parts of the reef. We predict these processes are likely to occur in other similar tide-dominated reef environments worldwide. Identifying locations where physical processes reduce heat stress will likely be critical for coral reefs in the future, by maintaining communities that can help facilitate local recovery of reefs following bleaching events that are expected to increase in frequency and severity in the coming decades.

Coral Reefs↗
USGS2011

Recent summer precipitation trends in the Greater Horn of Africa and the emerging role of Indian Ocean sea surface temperature

We utilize a variety of climate datasets to examine impacts of two mechanisms on precipitation in the Greater Horn of Africa (GHA) during northern-hemisphere summer. First, surface-pressure gradients draw moist air toward the GHA from the tropical Atlantic Ocean and Congo Basin. Variability of the strength of these gradients strongly influences GHA precipitation totals and accounts for important phenomena such as the 1960s–1980s rainfall decline and devastating 1984 drought. Following the 1980s, precipitation variability became increasingly influenced by the southern tropical Indian Ocean (STIO) region. Within this region, increases in sea-surface temperature, evaporation, and precipitation are linked with increased exports of dry mid-tropospheric air from the STIO region toward the GHA. Convergence of dry air above the GHA reduces local convection and precipitation. It also produces a clockwise circulation response near the ground that reduces moisture transports from the Congo Basin. Because precipitation originating in the Congo Basin has a unique isotopic signature, records of moisture transports from the Congo Basin may be preserved in the isotopic composition of annual tree rings in the Ethiopian Highlands. A negative trend in tree-ring oxygen-18 during the past half century suggests a decline in the proportion of precipitation originating from the Congo Basin. This trend may not be part of a natural cycle that will soon rebound because climate models characterize Indian Ocean warming as a principal signature of greenhouse-gas induced climate change. We therefore expect surface warming in the STIO region to continue to negatively impact GHA precipitation during northern-hemisphere summer.

Greater Horn of Africa↗
USGS2020

Mobility characteristics of landslides triggered by Hurricane Maria in Puerto Rico

Mobility is an important element of landslide hazard and risk assessments yet has been seldom studied for shallow landslides and debris flows in tropical environments. In September 2017, Hurricane Maria triggered > 70,000 landslides across Puerto Rico. Using aerial imagery and a lidar digital elevation model (DEM), we mapped and characterized the mobility of debris slides and flows in four different geologic materials: (1) mudstone, siltstone, and sandstone; (2) submarine basalt and chert; (3) marine volcaniclastics; and (4) granodiorite. We used the ratio of landslide-fall height (H) to travel length (L), H/L, to assess the mobility of landslides in each material. Additionally, we differentiated between landslides with single and multiple source areas and landslides that either did or did not enter drainages. Overall, extreme rainfall contributed to the mobility of landslides during Hurricane Maria, and our results showed that the mobility of debris slides and flows in Puerto Rico increased linearly as a function of the number of source areas that coalesced. Additionally, landslides that entered drainages were more mobile than those that did not. We found that landslides in soils developed on marine volcaniclastics were the most mobile and landslides in soils on submarine basalt and chert were the least mobile. While landslides were generally small (< 100 m 2 ) and displayed a wide range of H/L values (0.1–2), coalescence increased the mobility of landslides that transitioned to debris flows. The high but variable mobility of landslides that occurred during Hurricane Maria and the associated hazards highlight the importance of characterizing and understanding the factors influencing landslide mobility in Puerto Rico and other tropical environments.

Puerto Rico↗
USGS2009

Using indirect methods to constrain symbiotic nitrogen fixation rates: A case study from an Amazonian rain forest

Human activities have profoundly altered the global nitrogen (N) cycle. Increases in anthropogenic N have had multiple effects on the atmosphere, on terrestrial, freshwater and marine ecosystems, and even on human health. Unfortunately, methodological limitations challenge our ability to directly measure natural N inputs via biological N fixation (BNF)-the largest natural source of new N to ecosystems. This confounds efforts to quantify the extent of anthropogenic perturbation to the N cycle. To address this gap, we used a pair of indirect methods -analytical modeling and N balance-to generate independent estimates of BNF in a presumed hotspot of N fixation , a tropical rain forest site in central Rondônia in the Brazilian Amazon Basin. Our objectives were to attempt to constrain symbiotic N fixation rates in this site using indirect methods , and to assess strengths and weaknesses of this approach by looking for areas of convergence and disagreement between the estimates. This approach yielded two remarkably similar estimates of N fixation . However, when compared to a previously published bottom-up estimate, our analysis indicated much lower N inputs via symbiotic BNF in the Rondônia site than has been suggested for the tropics as a whole. This discrepancy may reflect errors associated with extrapolating bottom-up fluxes from plot-scale measures, those resulting from the indirect analyses, and/or the relatively low abundance of legumes at the Rondônia site. While indirect methods have some limitations, we suggest that until the technological challenges of directly measuring N fixation are overcome, integrated approaches that employ a combination of model-generated and empirically-derived data offer a promising way of constraining N inputs via BNF in natural ecosystems.

Biogeochemistry↗
USGS2018

Downscaling future climate change projections over Puerto Rico using a non-hydrostatic atmospheric model

We present results from 20-year “high-resolution” regional climate model simulations of precipitation change for the sub-tropical island of Puerto Rico. The Japanese Meteorological Agency Non-Hydrostatic Model (NHM) operating at a 2-km grid resolution is nested inside the Regional Spectral Model (RSM) at 10-km grid resolution, which in turn is forced at the lateral boundaries by the Community Climate System Model (CCSM4). At this resolution, the climate change experiment allows for deep convection in model integrations, which is an important consideration for sub-tropical regions in general, and on islands with steep precipitation gradients in particular that strongly influence local ecological processes and the provision of ecosystem services. Projected precipitation change for this region of the Caribbean is simulated for the mid-twenty-first century (2041–2060) under the RCP8.5 climate-forcing scenario relative to the late twentieth century (1986–2005). The results show that by the mid-twenty-first century, there is an overall rainfall reduction over the island for all seasons compared to the recent climate but with diminished mid-summer drought (MSD) in the northwestern parts of the island. Importantly, extreme rainfall events on sub-daily and daily time scales also become slightly less frequent in the projected mid-twenty-first-century climate over most regions of the island.

Puerto Rico↗
USGS2019

Resolving a paradox—high mercury deposition, but low bioaccumulation in northeastern Puerto Rico

At a “clean air” trade winds site in northeastern Puerto Rico, we found an apparent paradox: atmospheric total mercury (THg) deposition was highest of any site in the USA Mercury Deposition Network, but assimilation into the local food web was quite low. Avian blood THg concentrations (n = 31, from eight species in five foraging guilds) ranged widely from 0.2 to 32 ng g −1 (median of 4.3 ng g −1 ). Within this population, THg was significantly greater at a low-elevation site near a wetland compared to an upland montane site, even when the comparison was limited to a single species. Overall, however, THg concentrations were approximately an order of magnitude lower than comparable populations in the continental U.S. In surface soil and sediment, potential rates of demethylation were 3 to 9-fold greater than those for Hg(II)-methylation (based on six radiotracer amendment incubations), but rates of change of ambient MeHg pools showed a slight net positive Hg(II)-methylation. Thus, the resolution of the paradox is that MeHg degradation approximately keeps pace with MeHg production in this landscape. Further, any net production of MeHg is subject to frequent flushing by high rainfall on chronically wet soils. The interplay of these microbial processes and hydrology appears to shield the local food web from adverse effects of high atmospheric mercury loading. This scenario may play out in other humid tropical ecosystems as well, but it is difficult to evaluate because coordinated studies of Hg deposition, methylation, and trophic uptake have not been conducted at other tropical sites.

Puerto Rico↗
USGS2012

Ecosystem services from converted land: the importance of tree cover in Amazonian pastures

Deforestation is responsible for a substantial fraction of global carbon emissions and changes in surface energy budgets that affect climate. Deforestation losses include wildlife and human habitat, and myriad forest products on which rural and urban societies depend for food, fiber, fuel, fresh water, medicine, and recreation. Ecosystem services gained in the transition from forests to pasture and croplands, however, are often ignored in assessments of the impact of land cover change. The role of converted lands in tropical areas in terms of carbon uptake and storage is largely unknown. Pastures represent the fastest-growing form of converted land use in the tropics, even in some areas of rapid urban expansion. Tree biomass stored in these areas spans a broad range, depending on tree cover. Trees in pasture increase carbon storage, provide shade for cattle, and increase productivity of forage material. As a result, increasing fractional tree cover can provide benefits land managers as well as important ecosystem services such as reducing conversion pressure on forests adjacent to pastures. This study presents an estimation of fractional tree cover in pasture in a dynamic region on the verge of large-scale land use change. An appropriate sampling interval is established for similar studies, one that balances the need for independent samples of sufficient number to characterize a pasture in terms of fractional tree cover. This information represents a useful policy tool for government organizations and NGOs interested in encouraging ecosystem services on converted lands. Using high spatial resolution remotely sensed imagery, fractional tree cover in pasture is quantified for the municipality of Rio Branco, Brazil. A semivariogram and devolving spatial resolution are employed to determine the coarsest sampling interval that may be used, minimizing effects of spatial autocorrelation. The coarsest sampling interval that minimizes spatial dependence was about 22 m. The area-weighted fractional tree cover for the study area was 1.85 %, corrected for a slight bias associated with the coarser sampling resolution. The pastures sampled for fractional tree cover were divided between ‘high’ and ‘low’ tree cover, which may be the result of intentional incorporation of arboreal species in pasture. Further research involving those ranchers that have a higher fractional tree cover may indicate ways to promote the practice on a broader scale in the region.

Urban Ecosystems↗
USGS2020

Architecture of remnant trees influences native woody plant recruitment in abandoned Hawaiian pastures

Abandoned tropical pastures offer opportunities for passive and active restoration of native forest communities. Tree architecture of remnant canopy trees may be one important factor that can facilitate native plant recruitment in abandoned pastures but has largely been overlooked. Here, we evaluated patterns of native woody plant recruitment under remnant trees in abandoned pastures on Hawai’i Island and how these might be related to both tree architectural features and landscape variables. We measured native woody stems (excluding sprouts of the tree itself) in a 5 m radius around the base of each tree and modeled total basal area of native stems as a function of tree architectural characteristics. Recruitment was positively correlated with tree height as well as horizontal woody area below 1 m (tree structure that occurred below 1 m and was < 45° angle from the ground) around the base of trees. Tall trees likely attract more avian seed dispersers due to their higher visibility on the landscape and increased crown volume. Horizontal woody area likely provides establishment microsites that are above the pasture grass layer, similar to how dead or decaying logs act as nurse substrates. Unlike previous studies, we found little evidence that landscape variables such as distance to the intact forest or nearest canopy neighbor influenced understory recruitment. Tree architectural characteristics can be important predictors of native plant recruitment in abandoned tropical pastures and should be considered in addition to local and landscape-level variables.

Hawaii↗
USGS2023

Rapidly changing range limits in a warming world: Critical data limitations and knowledge gaps for advancing understanding of mangrove range dynamics in the southeastern USA

Climate change is altering species’ range limits and transforming ecosystems. For example, warming temperatures are leading to the range expansion of tropical, cold-sensitive species at the expense of their cold-tolerant counterparts. In some temperate and subtropical coastal wetlands, warming winters are enabling mangrove forest encroachment into salt marsh, which is a major regime shift that has significant ecological and societal ramifications. Here, we synthesized existing data and expert knowledge to assess the distribution of mangroves near rapidly changing range limits in the southeastern USA. We used expert elicitation to identify data limitations and highlight knowledge gaps for advancing understanding of past, current, and future range dynamics. Mangroves near poleward range limits are often shorter, wider, and more shrublike compared to their tropical counterparts that grow as tall forests in freeze-free, resource-rich environments. The northern range limits of mangroves in the southeastern USA are particularly dynamic and climate sensitive due to abundance of suitable coastal wetland habitat and the exposure of mangroves to winter temperature extremes that are much colder than comparable range limits on other continents. Thus, there is need for methodological refinements and improved spatiotemporal data regarding changes in mangrove structure and abundance near northern range limits in the southeastern USA. Advancing understanding of rapidly changing range limits is critical for foundation plant species such as mangroves, as it provides a basis for anticipating and preparing for the cascading effects of climate-induced species redistribution on ecosystems and the human communities that depend on their ecosystem services.

Alabama, Florida, Louisiana, Mississippi, Texas↗
USGS2009

Declining global per capita agricultural production and warming oceans threaten food security

Despite accelerating globalization, most people still eat food that is grown locally. Developing countries with weak purchasing power tend to import as little food as possible from global markets, suffering consumption deficits during times of high prices or production declines. Local agricultural production, therefore, is critical to both food security and economic development among the rural poor. The level of local agricultural production, in turn, will be determined by the amount and quality of arable land, the amount and quality of agricultural inputs (fertilizer, seeds, pesticides, etc.), as well as farm-related technology, practices and policies. This paper discusses several emerging threats to global and regional food security, including declining yield gains that are failing to keep up with population increases, and warming in the tropical Indian Ocean and its impact on rainfall. If yields continue to grow more slowly than per capita harvested area, parts of Africa, Asia and Central and Southern America will experience substantial declines in per capita cereal production. Global per capita cereal production will potentially decline by 14% between 2008 and 2030. Climate change is likely to further affect food production, particularly in regions that have very low yields due to lack of technology. Drought, caused by anthropogenic warming in the Indian and Pacific Oceans, may also reduce 21st century food availability in some countries by disrupting moisture transports and bringing down dry air over crop growing areas. The impacts of these circulation changes over Asia remain uncertain. For Africa, however, Indian Ocean warming appears to have already reduced rainfall during the main growing season along the eastern edge of tropical Africa, from southern Somalia to northern parts of the Republic of South Africa. Through a combination of quantitative modeling of food balances and an examination of climate change, this study presents an analysis of emerging threats to global food security.

Food Security↗
USGS1991

U-series ages of solitary corals from the California coast by mass spectrometry

The purpose of this study is to evaluate the feasibility of dating fossil solitary corals from Pleistocene marine strandlines outside tropical latitudes using the recently developed high sensitivity, high-precision U-series technique based on thermal-ionization mass-spectrometry (TIMS). The TIMS technique is much more efficient than conventional a spectrometry and, as a result, multiple samples of an individual coral skeleton, or different specimens from the same bed can be analyzed. Detached and well-rounded fossil specimens of the solitary coral Balanophyllia elegans were collected from relict littoral deposits on emergent marine terraces along the California coast at Cayucos terrace (elevation 8 m, previously dated at 124 and 117 Ky by α counting), Shell Beach terrace (elevation about 25 m, previously undated), Nestor terrace, San Diego (elevation 23 m, previously dated at 131 to 109 Ky ), Bird Rock terrace, San Diego ( elevation 8 m, previously dated at 81 Ky ). Attached living specimens were collected from the intertidal zone on the modern terrace at Moss Beach. Concentrations of 232 Th in both living and fossil specimens are much higher than in reef-building corals (12 to 624 pmol/g vs. 0.1 to 1.6 pmol/g, respectively). However, because 230 Th/ 232 Th in Balanophyllia elegans are very low (2.22 × 10 −3 to 4.33 × 10 −4 ), the high 232 Th concentrations have negligible effect on the 230 Th- 234 U dates. The high 232 Th concentration in the living specimen (33.1 pmol/g) indicates that a significant amount of 232 Th is incorporated in the aragonitic skeleton during growth, or attached to clay-sized silicates trapped in the skeletal material. The calculated initial 234 U activities in the fossil specimens of Balanophyllia elegans are higher than the 234 U activity in modern seawater or in the modern specimen. The higher initial activities could possibly reflect the influx of 234 U-enriched continental water into Pleistocene coastal waters, or it could reflect minor diagenetic alteration, a persistent and fundamental problem in dating all corals. Samples from a compound specimen from the Cayucos terrace were subjected to different preparation procedures. Samples prepared by a standard acid washing procedure yielded 230 Th- 234 U ages of 125, 123, and 122 Ky, whereas samples prepared by an abbreviated procedure without acid washing yield significantly lower ages of 113 and 112 Ky. Two other specimens from the same bed yielded 230 Th- 234 U ages of 118 and 115 Ky. Also, two specimens from a stratigraphically higher bed yielded ages of 120 and 117 Ky, and three specimens from a lower bed yield ages of 115, 113, and 101 Ky. Nine of the twelve ages of the treated samples from the Cayucos terrace range from 125 to 113 Ky. However, the ages do not follow the stratigraphie order. Two possible interpretations are ( 1 ) the age of the terrace deposit is 125 Ky and all younger ages reflect variable diagenetic alteration or (2) the age of the terrace is 125 to 113 Ky and the ages reflect sediment reworking over a period of 12 Ky. Three specimens from a single bed on the Shell Beach terrace yield ages of 126, 122, and 121 Ky, similar to the older ages from Cayucos. The ages of solitary corals from the Cayucos and Shell Beach terraces are similar to ages of reef-building corals from terraces at numerous tropical localities. These are correlated with the last interglacial sea-level highstand, which probably stood 2 to 10 m above present sea level. The youngest ages and present elevations of the Cayucos and Shell Beach terraces yield tectonic uplift rates of 0.01 and 0.15 m/Ky, respectively, assuming the original elevation of each terrace was 7 m. Four specimens from the basal gravel on the Nestor terrace yielded ages of 145, 143, 137, and 133 Ky. The three oldest ages, however, are older than that associated with the last interglacial. The possible explanations for these older ages are ( 1 ) diagenic alteration or ( 2 ) the Nestor terrace deposits reflect in some way a poorly documented early phase of the last interglacial sea level high stand.

Geochimica et Cosmochimica Acta↗
USGS1984

Shoreface translation and the Holocene stratigraphic record: Examples from Nova Scotia, the Mississippi Delta and eastern Australia

Classic descriptive models of barrier sedimentation have been developed with data from the Atlantic and Gulf coasts of the United States. These models are dominated by low to moderate rates of relative sea level (RSL) rise and wave energy. Barriers respond by landward recycling of sediment through the mechanism of shoreface retreat. Sedimentation processes on the central coast of New South Wales (N.S.W.), Australia, consist of rapid RSL rise in early Holocene times followed by a stillstand since 6500 B.P. Wave energy is relatively high year-round and sand sources for barrier formation are only found on the inner shelf. Barrier sedimentation on the central coast of N.S.W. exhibits a thick, composite sequence composed of a basal marine transgressive sand overlain by regressive beach and dune facies. The Louisiana coast surrounding the Mississippi delta is underlain by compacting deltaic muds which generate very rapid rates of RSL rise. The Louisiana coast experiences low wave energy punctuated by high-energy tropical and extra-tropical storm events. Barrier sediments accumulate from the erosion of deltaic headlands and undergo a transformation from subaerial barrier island systems to subaqueous shoals located on the inner shelf. Drumlins experience coastal erosion on the Eastern Shore of Nova Scotia and provide a sediment source for compartmented estuary mouth barriers. An ongoing, moderate rise of RSL results from the passage of a glacial forebulge. Wave energy is intermediate between Louisiana and N.S.W. and displays a seasonal pattern dominated by frequent winter storms. Coastal barrier sedimentation is episodic, consisting of a period of beach ridge progradation followed by barrier destruction and re-establishment further landward. The three contrasting sedimentary sequences found in examples from Louisiana, N.S.W. and Nova Scotia indicate that presently available sedimentation models from locations such as the middle Atlantic or Texas coasts of the United States may only represent well-documented regional case studies. A true generalised coastal sedimentation model is required which can identify the parameters controlling vertical and horizontal translation of the depositional surface and provide relationships between these parameters which quantitatively predict the genesis, distribution and geometry of coastal sedimentary facies.

Marine Geology↗
USGS1990

Thrust-ridge paleodepositional model for the Upper Freeport coal bed and associated clastic facies, Upper Potomac coal field, Appalachian Basin, U.S.A.

A blind-thrust-ridge model is proposed to explain the lack of coarse clastic material in the vast minable Upper Freeport coal bed (UF). This coal bed contains only fine elastic partings and is overlain by regionally extensive, closely spaced channel-belt deposits in the Upper Potomac coal field of the Appalachian basin. A blind-thrust ridge may have formed a sediment trap and prevented c coarse fluvial sediments from entering the swamp during a period (Westphalian D) when the thick Upper Freeport peat accumulated. Anticlinal thrust ridges and associated depressions may have existed uninterrupted for about 40 km parallel to the Appalachian orogen. Sediment shed from the breached anticlinal ridges accumulated in the sediment trap and was carried out of the ends of the trap by streams that occupied the shear zone at the ends of the blind-thrust ridge. The extent, parallel to the orogen, of thick, areally extensive UF is related to the length of the blind-thrust ridge that, in turn, controlled the spacing of the river-derived coarse clastic sediments that entered the main basin from the east. The thrust plane eventually emerged to the surface of the blind-thrust ridge and peat accumulation was terminated when the ridge became eroded and the sediment trapped behind it was released. The peat was buried by abundant coarse clastic sediment, which formed closely spaced channel belts and intervening flood basins. This model has implications for widespread peat deposits (now coal) that developed in tropical regions a few hundred kilometers from the sea in a tectonically active foreland basin.

International Journal of Coal Geology↗
USGS1990

Studies of angiospermous woods in Australian brown coal by nuclear magnetic resonance and analytical pyrolysis: new insight into early coalification

Many Tertiary coals contain abundant fossilized remains of angiosperms, which commonly dominated the ancient peat-swamp environments; modern analogs of such swamps can be found in tropical and subtropical regions of the world. Comparisons of angiospermous wood from Australian brown coal with similar wood buried in modern peat swamps of Indonesia have provided some new insights into coalification reactions. These comparisons were made by using solid-state 13 C nuclear magnetic resonance (NMR) techniques and pyrolsis-gas chromatography-mass spectrometry (py-gc-ms). These two modern techniques are especially suited for detailed structural evaluation of the complex macromolecules in coal. The earliest transformation (peatification) of organic matter in angiospermous wood is the degradation and removal of cellulosic components and the concomitant selective preservation of lignin-derived components. The angiospermous lignin that becomes enriched in wood as a result of cellulose degradation also is modified by coalification reactions; this modification, however, does not involve degradation and removal of the lignin. Rather, the early coalification process transforms the lignin phenols (guiacyl and syringyl) to eventually yield the aromatic structures typically found in brown coal. One such transformation, which is determined from NMR data, involves the cleavage of aryl-ether bonds that link guaiacyl and syringyl units in lignin, and this transformation leads to the formation of free lignin phenols. Another transformation, which is also determined from the NMR data, involves the loss of methoxyl groups, probably via demethylation, to produce catechol-like structures. Coincident with ether-cleavage and demethylation, the aromatic rings derived from lignin phenols become more carbon-substituted and cross linked, as determined by dipolar-dephasing NMR studies. This cross linking is probably responsible for preventing the lignin phenols, which are freed from the lignin macromolecule by ether cleavage, from being removed from the coal by dissolution. Pyrolysis data suggest that the syringyl units are altered more readily than are guaiacyl units, and this difference in resistance leads to an enrichment of the guaiacyl units in fossil angiospermous woods. Many of the coalification reactions noted above occur to some degree in all angiospermous fossil wood examined; however, some significant differences are observed in the degree of coalification of the fossil wood samples from the same burial depth in the brown coal. These differences indicate that the depth and duration of burial are probably not entirely responsible for the variations in degree of coalification. Different rates of degradation in peat may have contributed to the variations in the apparent degree of coalification; some woods may have been altered more rapidly at the peat stage than others. Although preliminary, this systematic study of botanically related wood in peat and coal results in a more detailed differentiation of coalification reactions than have previous investigations. The combined use of solid-state 13 C NMR and py-gc-ms has facilitated this detailed insight into the coalification of angiospermous wood.

International Journal of Coal Geology↗
USGS1990

A quantitative micropaleontologic method for shallow marine peleoclimatology: Application to Pliocene deposits of the western North Atlantic Ocean

A transfer function was developed to estimate summer and winter paleotemperatures for arctic to tropical regions of the western North Atlantic Ocean using fossil ostracode assemblages. Q-mode factor analysis was run on ostracode assemblages from 100 modern bottom sediment samples from continental shelves of North America, Greenland and the Caribbean using 59 ostracode taxa. Seven factors accounting for 80% of the variance define assemblages that correspond to frigid, subfrigid, cold temperate, mild temperate, warm temperate, subtropical and tropical climatic zones. Multiple regression of the factor matrix against observed February and August bottom temperatures yielded an astracode transfer function with an accuracy of about ??2??C. The transfer function was used to reconstruct middle Pliocene (3.5-3.0 Ma) shallow marine climates of the western North Atlantic during the marine transgression that deposited the Yorktown Formation (Virginia and North Carolina), the Duplin Formation (South and North Carolina) and the Pinecrest beds (Florida). Middle Pliocene paleowater temperatures in Virginia averaged 19??C in August and 13.5??C in February, about 5??C to 8??C warmer than at comparable depths off Virginia today. August and February water temperatures in North Carolina were 23??C and 13.4??C, in South Carolina about 23??C and 13.5??C and in southern Florida about 24.6??C and 15.4??C. Marine climates north of 35??N were warmer than today; south of 35??N, they were about the same or slightly cooler. Thermal gradients along the coast were generally not as steep as they are today. The North Atlantic transfer function can be applied to other shallow marine Pliocene and Pleistocene deposits of eastern North America. ?? 1990 Elsevier Science Publishers B.V.

Marine Micropaleontology↗
USGS2020

Agricultural land-use change alters the structure and diversity of Amazon riparian forests

Riparian forests play key roles in protecting biodiversity and water resources , making them priorities for conservation in human-dominated landscapes, but fragmentation associated with expanding tropical croplands threatens their ecological integrity. We compared the structure of tropical riparian forests within intact and cropland catchments in a region of intensive soybean production in the southeastern Brazilian Amazon. We studied forest plots (varying from 120 to 210 m long) that bisected riparian zone forests and headwater streams in ten catchments. Four plots were within large areas of intact primary forest and six were in bands of protected riparian forest along streams within croplands as required by the Brazilian Forest Code. We found that riparian forests in croplands harbored fewer species of trees and seedlings/saplings, and had higher proportions of opportunistic, pioneer tree species. We also found greater variation in tree species composition, and higher internal dissimilarity in croplands compared with forests. The observed patterns in tree species composition were driven mainly by differences between riparian forest-cropland edges and those bordering intact upland forests. Forests nearest to streams in cropland and forested catchments were more similar to one another. Results suggest that wider buffers are needed at the edges of croplands to maintain riparian forest structure. The minimum 30-m riparian buffers now required by the Brazilian Forest Code may thus be insufficient to prevent long-term shifts in riparian forest species composition and structure.

Biological Conservation↗