Major River Mouths Research Articles

Holocene transgression of the Rhine river mouth area, The Netherlands/Southern North Sea: palaeogeography and sequence stratigraphy

AbstractThis study presents a detailed reconstruction of the palaeogeography of the Rhine valley (western Netherlands) during the Holocene transgression with systems tracts placed in a precise sea‐level context. This approach permits comparison of actual versus conceptual boundaries of the lowstand, transgressive and highstand systems tracts. The inland position of the highstand Rhine river mouth on a wide, low‐gradient continental shelf meant that base‐level changes were the dominant control on sedimentation for a relatively short period of the last glacial cycle. Systems in such inland positions predominantly record changes in the balance between river discharge and sediment load, and preserve excellent records of climatic changes or other catchment‐induced forcing. It is shown here that the transgressive systems tract‐part of the coastal prism formed in three stages: (i) the millennium before 8·45 ka bp, when the area was dominated by fluvial environments with extensive wetlands; (ii) the millennium after 8·45 ka, characterized by strong erosion, increasing tidal amplitudes and bay‐head delta development; and (iii) the period between 7·5 and 6·3 ka bp when the Rhine avulsed multiple times and the maximum flooding surface formed. The diachroneity of the transgressive surface is strongly suppressed because of a pulse of accelerated sea‐level rise at 8·45 ka bp. That event not only had a strong effect on preservation, but has circum‐oceanic stratigraphical relevance as it divides the early and middle Holocene parts of coastal successions worldwide. The palaeogeographical reconstruction offers a unique full spatial–temporal view on the coastal and fluvial dynamics of a major river mouth under brief rapid forced transgression. This reconstruction is of relevance for Holocene and ancient transgressive systems worldwide, and for next‐century natural coasts that are predicted to experience a 1 m sea‐level rise.

Spatial and Temporal Genetic Variation of Green Mussel, Perna viridis in the Gulf of Thailand and Implication for Aquaculture

The culture of green mussel (Perna viridis) in the Gulf of Thailand depends on natural spat which are believed to come from spawning grounds adjacent to major river mouths. In the present paper, genetic diversity of spatial and temporal populations of green mussel in the Gulf of Thailand was investigated using five microsatellite loci. The results showed moderate genetic variation of all 11 populations (averaged number of alleles per locus, A = 10.4-12.2; effective number of alleles per locus, A(e) = 5.36-6.59; mean allelic richness, A(r) = 10.23-12.06; observed heterozygosity, H(o) = 0.52-0.63, and expected heterozygosity, H(e) = 0.66-0.73) without significant differences among populations. No sign of bottleneck or genetic disequilibrium was observed. Genetic differentiation among spatial populations was low (F (ST) = 0.0046, CI(0.95) = 0.0020-0.0083 for the samples collected in January, 2007, and F (ST) = 0.0088, CI(0.95) = 0.0010-0.0162 for the samples collected in July, 2007) while temporal variation was significant as revealed by the analysis of molecular variance. Multidimensional scaling separated temporal population groups with minor exception. The assignment test revealed that most of the recruits were from other populations.

CHLOROPHYLL SPECIFIC ABSORPTION COEFFICIENTS AND THE IMPACT OF PHYTOPLANKTON TAXONOMIC GROUP OF SURFACE WATERS IN THE NORTHEASTERN GULF OF MEXICO

The chlorophyll-specific absorption coefficient at 440 nm (a*ph(440)) of surface water in the Northeastern Gulf of Mexico varied by a factor of 7 (0.02-0.15 m2 mg-1) with the of chlorophyll-a concentration of 0.06-12.25 mg m-3. In general, lower values of a*ph(440) (<0.06 m2 mg-1) were observed in the inshore particularly in the major river mouths. During summer, lower values of a*ph(440) were also observed offshore associated with low-salinity waters of the Mississippi River plume. Higher values of a*ph(440) (>0.1 m2 mg-1) were otherwise observed outside the river plumes in the outershelf and slope, where lower chlorophyll-a concentration occurred. Based on phytoplankton taxonomic groups, the average value of a*ph(440), of microphytoplankton group was significantly lower than that of nanophytoplankton and picophytoplantkon groups, suggesting that an increase in cell optical size (pigment packaging) resulted in decreasing a*ph(440) values. The relationship between a*ph(440) and chlorophyll-a concentration was also not linear, indicating pigment composition played an important role in determining a*ph(440) variability.Keywords: chlorophyll-specific absorption coefficient, microphytoplankton, nanophytoplankton,picophytoplankton, Gulf of Mexico, pigment, packaging effect

CHLOROPHYLL SPECIFIC ABSORPTION COEFFICIENTS AND THE IMPACT OF PHYTOPLANKTON TAXONOMIC GROUP OF SURFACE WATERS IN THE NORTHEASTERN GULF OF MEXICO

<p>The chlorophyll-specific absorption coefficient at 440 nm (a*<br />ph(440)) of surface water in the Northeastern Gulf of Mexico varied by a factor of 7 (0.02-0.15 m2 mg-1) with the of chlorophyll-a concentration of 0.06-12.25 mg m-3. In general, lower values of a*ph(440) (<0.06 m2 mg-1) were observed in the inshore particularly in the major river mouths. During summer, lower values of a*ph(440) were also observed offshore associated with low-salinity waters of the Mississippi River plume. Higher values of a*ph(440) (>0.1 m2 mg-1) were otherwise observed outside the river plumes in the outer<br />shelf and slope, where lower chlorophyll-a concentration occurred. Based on phytoplankton taxonomic groups, the average value of a*ph(440), of microphytoplankton group was significantly lower than that of nanophytoplankton and picophytoplantkon groups, suggesting that an increase in cell optical size (pigment packaging) resulted in decreasing a*<br />ph(440) values. The relationship between a*ph(440) and chlorophyll-a concentration was also not linear, indicating pigment composition played an important role in determining a*ph(440) variability.</p><p>Keywords: chlorophyll-specific absorption coefficient, microphytoplankton, nanophytoplankton,<br />picophytoplankton, Gulf of Mexico, pigment, packaging effect</p>

Characterization of the infralittoral system along the north-east Spanish coast based on sport shore-based fishing tournament catches

Spatial and temporal variations in the structure of fish assemblages were analysed based on the catch data from a total of 2329 shore-based sport fishing tournaments held in north-eastern Spain from 2002 to 2006 with a view to characterizing the infralittoral system along 400 km of coastline and assessing the usefulness of these data as an additional means of monitoring coastal areas. A total of 63 species in 35 families were identified in the catches. Daily catch rates per fisherman varied from 0.1 kg to 0.5 kg according to the fishing area, and maximum catch rates and minimum species richness values were observed in the vicinity of the mouths of major rivers. Cluster analysis yielded six separate major groups. Two groups were characterized by predominantly or entirely rocky bottoms where the main species were Coris julis and Serranus cabrilla and were differentiated by a higher abundance of labrids and serranids and an absence of sparids. A third group encompassed areas under the influence of major rivers, where Chelon labrosus dominated the fish community. The other three groups were dominated by sparids but with differences in the total contribution by the main species, Sparus aurata, Lithognathus mormyrus, and Pagellus acarne, to each fish assemblage, indicating differences in ecological structure. The results suggest that sublittoral fish assemblages can be regarded as ecosystem descriptors and should not be overlooked as indicators of ecosystem changes. The study showed that a structured legislative framework for regulating recreational fishing tournaments can be extremely useful for monitoring littoral fishes at minimal added cost.

Biomarkers of Contaminant Exposure in Chub (Leuciscus cephalus L.) - Biomonitoring of Major Rivers in the Czech Republic.

Biochemical analysis of organisms to assess exposure to environmental contaminants is of great potential use. Biochemical markers, specifically liver enzymes of the first and the second phase of xenobiotic transformation - cytochrome P450 (CYP 450), ethoxyresorufin-O-deethylase (EROD), glutathione-S-transferase (GST) and tripeptide reduced glutathione (GSH) - were used to assess contamination of the aquatic environment at 12 locations near the mouths of major rivers in the Czech Republic. These rivers were the Lužnice, Otava, Sázava, Berounka, Vltava, Labe, Ohře, Svratka, Dyje, Morava and Odra. The indicator species selected was the Chub (Leuciscus cephalus L.). The highest levels of CYP 450 and EROD catalytic activity were found in livers of fish from the Labe (Obříství) (0.32±0.10 nmol mg-1 protein and 1061.38±545.51 pmol min-1 mg-1 protein, respectively). The highest levels of GST catalytic activity and GSH content were found in fish from the Otava (35.39±13.35 nmol min-1 mg-1 protein and 4.29±2.10 nmol GSH mg-1 protein, respectively). They were compared with levels of specific inductors of these biochemical markers in muscle. The results confirmed contamination of some river locations (Labe Obříství, Svratka).

The Grenvillian and Pan-African orogens: World's largest orogenies through geologic time, and their implications on the origin of superplume

The Neoproterozoic Earth was shaped largely by the Grenvillian and Pan-African orogenies. Out of these, the Grenvillian orogeny has long been regarded to be of minor nature in terms of global-scale orogenic episodes, whereas the Pan-African orogeny has been widely recognized in many continental fragments, although not in major parts of Asia. Based on chronological information in zircons from major river mouths across several important terrains of the globe, we show here that the Grenvillian orogeny contributed significantly to the formation of the continental crust. The time period between 0.6 Ga and 0.8 Ga marked the climax at the dawn of the Pan-African orogeny. Continental crust formed in this period is concentrated in the Pan-African orogenic belts widely across the globe. These regions were widespread over the half hemisphere of the globe, and were subsequently reduced in size after they moved to form Laurasia. The normalized frequency distribution of zircon ages from river-mouth sand over the world clearly demonstrates that Neoproterozoic and (0.9–0.6 Ga) and Grenvillian (1.3–1.0 Ga) peaks define the largest population. This means that extensive subduction, and hence active plate tectonics, might have operated through these periods. The zircon study has also brought to light new regions of the Grenvillian orogenic belts, particularly in the continents which are now covered by thick Phanerozoic sedimentary basins. Based on the new locations of Grenvillian orogens identified in this study, and using the distribution patterns as a marker bed, we propose revised paleogeographic configurations of the Rodinia and Gondwana supercontinents. Our results demonstrate that the Neoproterozoic was the most active period of crust formation in the Earth. The cold basins, formed right after the assembly of Rodinia, exhibit a basin chain fringing the northern periphery of Rodinia, which turned into sites of mantle upwellings and led to the rifting and separation of the supercontinental assembly. The continents then moved northwards after the formation of Gondwana at ca. 540 Ma, and enlarged the northern half of the supercontinent Pangea since 250 Ma. Based on the results, we also evaluate the role of supercontinents in the mechanism of generation of superplumes addressing the enigma that the coldest mantle right above the Core–Mantle Boundary turns to the hottest one over a period of several hundreds of million years. Slab graveyard formed by the Pan-African subduction can be imaged through P-wave tomography. We postulate that the high-velocity anomaly in the D” layer underneath Gondwana has now transformed to the low-V regions to generate the African superplume. The tectonic history of solid Earth in the Phanerozoic seems to be controlled by the slab graveyards formed by the Grenvillian orogeny ca. 1.0 Ga.

Monitoring Mercury in the Loggerhead Sea Turtle, Caretta caretta

The validity of using blood samples and keratinized scutes for nonlethal routine monitoring of mercury (Hg) in loggerhead sea turtles, Caretta caretta, is evaluated in the context of how effectively these matrixes predict internal tissue Hg burdens and the different temporal scales of exposure they represent. Total Hg (THg) was measured in blood and scutes collected from live captures (n = 34) and liver, kidney, muscle, spinal cord, blood, and scutes collected from freshly stranded loggerhead turtles (n = 6) along the coast of the southeastern United States. Linear regressions between monitoring compartments and internal tissues from stranded animals were all statistically significant (r2 > 0.805, p < 0.015) but varied in their utility as a predictive tool depending on which tissues were paired. Blood was an effective predictor of THg in muscle (r2 = 0.988, p < 0.0001) and spinal cord (r2 = 0.988, p < 0.0001), while scute was the most accurate predictor of THg in liver (r2 = 0.948, p = 0.0010). The strength of the relationship between tissues types is believed to reflect the similarity in the temporal scales they represent and the variability in the fraction of methylmercury present. The stability of Hg in the scute matrix makes this tissue preferable for approximating long-term exposure, while blood Hg levels can be affected by recent changes in Hg intake. THg levels in blood and scutes from live captures were highly correlated (linear regression r2 = 0.926, p < 0.0001) and increased significantly with body mass (r2 = 0.173, p = 0.016 and r2 = 0.187, p = 0.012 respectively), further supporting thatthere is a component reflecting long-term accumulation of Hg in these matrixes. We also present a novel technique using the residuals from the blood-scute regression as an index of recent exposure (IRE). The interpretation of this value is derived from the comparison between the most recent Hg intake (which contributes to the Hg measured in the blood) relative to the average past intake (which is recorded in the scute). A stepwise multiple regression revealed a significant positive relationship between the IRE and the proximity of the capture site to the nearest major industrial river mouth (p = 0.0102). This suggests that there is an elevation of bioavailable Hg in nearshore habitats where terrestrial influences and anthropogenic impacts are high. Seasonal foraging site fidelity and the variability in environmental Hg may explain the high intraspecific variability and occasional highly contaminated turtle seen in this and previous studies.

Investigating biotic and abiotic factors affecting the recruitment of an intertidal clam on an exposed sandy beach using a generalized additive model

The existence of biotic interactions among macroinfauna resident on exposed sandy beaches and the potential roles that such interactions might play with respect to structuring these assemblages is currently a controversial topic. To elucidate the relative importance of biotic versus abiotic factors in determining the spatial distribution of beach fauna, we use a generalized additive model, which can account for nonlinear relationships between beach clam recruitment and four explanatory variables: two abiotic (beach gradient and distance from a major river mouth); and two biotic (the abundance of adult clams and the abundance of their juveniles). The study organism, Donax serra Röding, is a fairly typical intertidal filter feeder that dominates the macrofaunal communities on many southern African sandy beaches. Results indicate that a mixture of biotic and abiotic factors mediates recruit abundance, with beach gradient being the most influential, followed by adult and juvenile abundances. Of particular importance was strong evidence of intraspecific interactions between D. serra adults and recruits. Furthermore, despite the existence of a published hypothesis stating that the highest recruitment of this species is found beside river mouths and that the subsequent alongshore distribution of older age classes is determined primarily by distance from a major river mouth, we found the opposite. Lowest recruit abundance was in the vicinity of a river mouth and maximum recruit abundance was near the center of the beach. Distance from the river mouth was also less important in structuring the distribution of recruits than the biotic factors. This emphasizes the complex ecology of organisms inhabiting apparently simple intertidal landscapes, and illustrates how the generalized additive modelling approach can be fruitfully applied to problems in beach ecology.

Evolution of particle size and concentration in the Rhône river mixing zone:: influence of salt flocculation

The salt induced flocculation phenomenon is often proposed as a major mechanism influencing the deposition of the suspended matter near the mouth of major rivers. However, depending on the particular mixing conditions between fresh water and marine water and on suspended solids (SS) reactivity, salt induced aggregation may be a minor factor controlling fast deposition of SS. This work combines field studies and laboratory experiments in order to assess the importance of salt induced flocculation in the case of the saltwedge estuary of the Rhône river. Sampling of the mixing zone has been performed in contrasted hydrodynamic conditions from a low water discharge period (500 m 3 s −1) to a small flood event (2400 m 3 s −1) for particle counting and salinity measurements. Through laboratory experiments, it is shown that the Rhône river particulate matter has a poor average reactivity regarding salt induced flocculation. Considering the hydrodynamics of the estuary, we show that the evolution of the concentration of larger particles (>5 μm) can be explained by settling and dilution. In contrast, the smallest measured fraction (2–5 μm) shows a more complex behavior and settling processes alone cannot explain the observed particle concentrations during the field studies. Four hypotheses are discussed for explaining the 2–5 μm particle concentration evolutions.

Human adenoviruses and coliphages in urban runoff-impacted coastal waters of Southern California.

A nested-PCR method was used to detect the occurrence of human adenovirus in coastal waters of Southern California. Twenty- to forty-liter water samples were collected from 12 beach locations from Malibu to the border of Mexico between February and March 1999. All sampling sites were located at mouths of major rivers and creeks. Two ultrafiltration concentration methods, tangential flow filtration (TFF) and vortex flow filtration (VFF), were compared using six environmental samples. Human adenoviruses were detected in 4 of the 12 samples tested after nucleic acid extraction of VFF concentrates. The most probable number of adenoviral genomes ranged from 880 to 7,500 per liter of water. Coliphages were detected at all sites, with the concentration varying from 5.3 to 3332 PFU/liter of water. F-specific coliphages were found at 5 of the 12 sites, with the concentration ranging from 5.5 to 300 PFU/liter. The presence of human adenovirus was not significantly correlated with the concentration of coliphage (r = 0.32) but was significantly correlated (r = 0.99) with F-specific coliphage. The bacterial indicators (total coliforms, fecal coliforms, and enterococci) were found to exceed California recreational water quality daily limits at 5 of the 12 sites. However, this excess of bacterial indicators did not correlate with the presence of human adenoviruses in coastal waters. The results of this study call for both a reevaluation of our current recreational water quality standards to reflect the viral quality of recreational waters and monitoring of recreational waters for human viruses on a regular basis.

A variable velocity flow routing algorithm for GCMs

A global hydrological routing algorithm is developed for use in the coupled general circulation model (GCM) of the Canadian Centre for Climate Modelling and Analysis (CCCMA). Unlike existing schemes that use a constant velocity in surface flow routing calculations, this approach uses a time‐evolving velocity that depends on the amount of runoff generated in the GCM land grid cell. The scheme uses Manning's equation to estimate flow velocities for a river channel with rectangular cross section. The river flow directions at the required GCM resolution are obtained from 1° river flow directions using an algorithm that requires minimal manual intervention. With the use of a suitable roughness coefficient for natural channels in Manning's equation and all other parameters determined from the existing literature, the scheme does not require calibration of parameters and can be used directly in GCMs. Simulated streamflow is compared with observed hydrographs at the mouths of major rivers to show that the scheme performs satisfactorily.

Geochemistry of Surficial and Ice-rafted Sediments from the Laptev Sea (Siberia)

The Laptev Sea, as a part of the world’s widest continental shelves surrounding the Arctic Ocean, is a key area for understanding the land–ocean interaction in high latitude regions. With a yearly freshwater input of 511km3, the Lena River—one of the eight major world rivers—has an influencing control over the environment of this Arctic marginal sea, which is ice-covered during most of the year.In this paper, the first measurements are presented of the major and trace element distribution within the <20μm grain size fraction of surficial sediments and of particulate matter in new and young ice from the Laptev Sea (Siberian Arctic). The concentration and distribution of major and trace elements have been determined in 51 surficial sediment samples covering the whole Laptev Sea shelf south of the 50m isobath. Thirty-one samples of particulate matter in newly formed ice were taken during the freeze-up period in 1995.Median concentration levels of heavy metals in surficial sediments (Ni (46μg g−1), Cu (26μg g−1), Zn (111μg g−1) and Pb (21μg g−1) are within the concentration range of marine unpolluted sediments. Also the sediment-laden ice showed no indication of anthropogenic perturbation of the trace metal inventory. Spatial distribution patterns of heavy metals are mainly determined by variation of mineral composition and different fluvial sediment sources in the eastern and western Laptev Sea.The Laptev Sea shelf is cut by five north–south trending submarine valleys. Enrichment of manganese in the oxic surficial sediment layer within these valleys and the occurrence of small ferromanganese nodules are caused by a high input of dissolved and particulate Mn from the Lena River and a strong diagenetic cycling of Mn on the Laptev Sea shelf. Evidence is given that the content of As in surficial sediments is also strongly affected by diagenetic cycling. This causes surficial sediment As concentrations of more than 100μg g−1. Enrichment of Mn and As was mainly observed in the submarine valleys distant from the major river mouth. The sediment dilution due to higher sedimentation rates near the river outlets and a strong sediment re-working by ice gouging in the shallow areas are the principle causes for the absence of diagenetic accumulation in this region.During the formation of new ice scavenging of riverine suspended matter and resuspension of sediments followed by an incorporation of particles into the ice are important processes for the river–shelf–ocean transport of particulate trace elements. It could be shown that particle-loaded ice posseses the same geochemical signatures as the suspended matter and surficial seafloor sediments in the area of ice origin. This has also strong implications for the contaminant transport on the Arctic shelves and allows to use the geochemical signature of sea ice for the reconstruction of ice drift pattern within the Arctic Ocean.

An assessment of longshore movement in Donax serra Röding (Bivalvia: Donacidae) on an exposed sandy beach

Peak abundances of intertidal populations of a donacid bivalve, Donax serra, occur 10–23 km from major river mouths along exposed sandy beaches of log-spiral bays on the coast of southeast Africa. Postsettlement eastward movement of D. serra from areas of spat settlement by prevailing longshore currents has been suggested as the mechanism which results in the observed population distributions. To estimate the net rates of longshore movement in intertidal D. serra on one of these exposed beaches, we developed and used a novel technique. A metal detector was used to track net change in the positions of intertidal juvenile and adult clams (37–67 mm shell length, 1–3+ years) with aluminum tags glued to the shells over a 3-month period during the austral fall and winter. Estimated net longshore movement of tagged clams ranged from 0.19 to 0.80 m day −1. The net movement of tagged clams was primarily to the east along the beach but the direction of longshore movement varied during the study. Net rates of longshore movement were not correlated with clam size. The burrowing rates and the condition of recaptured tagged individuals were not significantly different from untagged clams after 2 months. The results of this study suggest that average longshore movement rates of intertidal clams, >1 year of age, along the beach are low and the animals are relatively sedentary. The technique developed and used here to estimate net longshore movement rates in D. serra allowed us to successfully recapture and track tagged individuals with very minimal disturbance to the intertidal habitat and associated fauna. Use of this novel technique could potentially enhance investigations of postsettlement movement, growth, zonation, competitive interactions and other aspects of the ecology of mobile soft sediment macrofauna.

Distribution and Fate of Organochlorine Pollutants in the Pearl River Estuary

Samples of surface sediment and suspended particulate matter (SPM) were collected from the Pearl River estuary, China, and the distribution and concentration of hexachlorocyclohexanes (HCHs), DDTs and polychlorinated biphenyls (PCBs) were extensively studied. The concentration ranges of HCHs, DDTs and PCBs in the sediments were 0.28–1.23 ng g −1, 1.36–8.99 ng g −1 and 0.18–1.82 ng g −1, respectively. The concentrations of HCHs, DDTs and PCBs in the SPM varied both with the sampling locations and the season of collection. Higher concentrations were recorded in the SPM as compared with sediments. The distribution pattern of such organochlorine compounds (OCs), in the Pearl River estuary, showed that sources were some major river mouths and input from Shenzhen Bay. The concentrations of OCs were, however, low as compared with other estuaries and seas. The environmental fate of the OCs during estuarine mixing was determined, in part, by physicochemical and biochemical properties. The absorption and sedimentation of SPM were also considered important factors. Marine sediments may, therefore, be regarded as an important reservoir of hydrophobic and persistent OCs.

Reproductive segregation among the Barbus intermedius complex of Lake Tana, Ethiopia. An example of intralacustrine speciation?

Reproductive segregation among the large barbs Barbus intermedius complex, Cyprinidae, of Lake Tana, Ethiopia, was investigated in the mouths and upstream reaches of rivers tributary to the lake, during the spawning seasons of 1993 and 1994. The percentage of running fish of four Barbus morphotypes [Acute (Ac), Bigmouth big‐eye (Be), Intermedius (In), and Shorthead (Sh)] peaks with the highest water level of the lake. Large differences are apparent in the minimum fork length of running fish among morphotypes [c. 12 cm for male Sh and 28 cm for male Bigmouth small‐eye (Se)]. Significant differences occur in temporal, but especially in spatial patterns of the relative abundance of running morphotypes, when the lake is compared with the four major river mouths and their upstream reaches. These different relative abundances are clearest among Ac, Be, In, Sh and Troutlike (Tr). Also, the absence from the rivers of some morphotypes that are usually abundant in the lake itself [Barbel (Ba), Dark (Da), Lip (Li), and Zurki (Zu)], and the abundant presence in the rivers of Tr, rare in the lake, strengthen the hypothesis that spatial and/or temporal spawning segregation is present among the morphotypes. There are indications that Bighead (Bh) and Zu spawn in the lake itself, while other morphotypes were only found running in or near rivers. Combined with the morphological, ecological, and genetic differences, these data suggest the existence of several Barbus species, forming a unique species flock, which probably evolved within the lake. The presence of several, instead of one Barbus species complicates management of sustainable fisheries and protection of the lake's biodiversity. Present results show the importance of the rivers for Barbus reproduction and stress the urgent need for careful management of fishing activities in spawning times and areas.

HISTORICAL BIOGEOGRAPHY OF WEST INDIAN VERTEBRATES

▪ Abstract The vertebrate fauna of the West Indies (1262 species) exhibits high levels of endemism and has a taxonomic composition characteristic of more isolated oceanic islands. Many groups that are widespread on the mainland are absent in the islands, and some of those present are characterized by large adaptive radiations. The growing fossil record of West Indian vertebrates, including mid-Tertiary amber fossils (considered here to be 20–30 million years old), indicates that this pattern of reduced higher-taxon diversity has persisted for a long period of time. Phylogenetic relationships of nonvolant groups display a strong South American influence, whereas volant groups (birds and bats) and freshwater fish show closer ties with Central and North America. Molecular estimates of divergence times between island taxa and their mainland counterparts indicate a Cenozoic origin (within the last 65 million years) for nearly all groups examined. Together, data from different sources point to an origin by overwater dispersal for a large majority of the vertebrate fauna. The prevailing current direction, from southeast to northwest, and the wide scattering of estimated times of origin suggest that much of the nonvolant fauna arrived by flotsam carried from the mouths of major rivers in northeastern South America. Spatial relationships, especially considering low sea levels during the Pleistocene, appear to better explain the routes of colonization taken by the volant fauna and freshwater fish. Caribbean geologic history does not preclude an origin by late Mesozoic vicariance for several possibly ancient groups, although an early Cenozoic arrival by dispersal also cannot be discounted. An integrative approach to historical biogeography is shown to be more insightful than the current trend in the field, cladistic biogeography, which places prime emphasis only on phylogenetic relationships.

Continental-Scale River Flow in Climate Models

The hydrologic cycle is a major part of the global climate system. There is an atmospheric flux of water from the ocean surface to the continents. The cycle is closed by return flow in rivers. In this paper a river routing model is developed to use with grid box climate models for the whole earth. The routing model needs an algorithm for the river mass flow and a river direction file, which has been compiled for 4 deg x 5 deg and 2 deg x 2.5 deg resolutions. River basins are defined by the direction files. The river flow leaving each grid box depends on river and lake mass, downstream distance, and an effective flow speed that depends on topography. As input the routing model uses monthly land source runoff from a 5-yr simulation of the NASA/GISS atmospheric climate model (Hansen et al.). The land source runoff from the 4 deg x 5 deg resolution model is quartered onto a 2 deg x 2.5 deg grid, and the effect of grid resolution is examined. Monthly flow at the mouth of the world's major rivers is compared with observations, and a global error function for river flow is used to evaluate the routing model and its sensitivity to physical parameters. Three basinwide parameters are introduced: the river length weighted by source runoff, the turnover rate, and the basinwide speed. Although the values of these parameters depend on the resolution at which the rivers are defined, the values should converge as the grid resolution becomes finer. When the routing scheme described here is coupled with a climate model's source runoff, it provides the basis for closing the hydrologic cycle in coupled atmosphere-ocean models by realistically allowing water to return to the ocean at the correct location and with the proper magnitude and timing.

Geochemistry of hydroxy acids in sediments—II. Estuarine and coastal marine environments

Homologous series of α/β, (ω-1) and ω-hydroxy fatty acids (FAOHs) were analyzed in relation to their geochemical implication in estuarine and coastal marine environments. Mineral digestion with hydrofluoric/hydrochloric acid followed by alkaline saponification was used for determination of both “acid-labile” and saponifiable FAOHs in modern sediments. Sediment samples examined in the present work were collected from the shallow Tokyo Bay and deep Sagami Bay areas in Japan. A short sediment core, major river mouth sediments and suspended particles in the region were also examined. The most remarkable variation observed was the iso/anteiso abundance ratios of branced C 15 and C 17 β(α)-FAOH, which were high in the river mouth sediments, suspended particles and surface layers of the core sediment. The ratios decreased with increasing burial depth and with the distance from the river mouths or from the shore line. This fact suggested that the ratios might indicate the extent of short term early diagenetic alteration of bacteria-derived organic matter. Another point inferred was the abundances of C 22–C 26 α(β)-FAOH and C 16–C 28 ω-FAOH, both of which were elevated considerably in the river mouth sediments. The abundance of these long-chain α(β) and ω-FAOH was thought to indicate eventually the deposition and/or active microbial reworking of the terrigenous higher plant debris at the freshwater/seawater interface.

Status and Trends of the Lake Ontario Macrobenthos

The benthic macroinvertebrate community of Lake Ontario was examined relative to communities found in the other Great Lakes and also relative to trends over time. In the nearshore, populations are heavily influenced by municipal and industrial inputs. For example, oligochaete abundances in the nearshore are higher than in any of the other Great Lakes (excluding shallow Lake Erie), communities have been altered even to relatively deep depths near the major river mouths, and the pollution-sensitive Pontoporeia hoyi is scarce along the southern shoreline east of the Niagara River mouth. In the profundal, benthic composition is similar to that found in the other Great Lakes, but biomass is less than might be expected given the amount of organic material settling to the bottom. Benthic standing stocks in this region have apparently declined almost threefold since the 1960s. Reasons for this decline do not appear to be related to trends in water column productivity or to predation pressure, but may be related to the accumulation of contaminants. Research needs include studies to assess benthic trends over a much broader area of the lake and studies to examine the impact of sublethal levels of contaminants.