River Arm Research Articles

Geochemistry of a large impoundment, Part I: solute sources, mixing dynamics, and seasonal anoxia

Lake Texoma is a large impoundment on the border of Texas and Oklahoma, formed from the confluence of two river systems with different salinities, the Red River (total dissolved salt, TDS, of 2700–11 900 mg/l, average of 4862 mg/l) and the Washita River (TDS of 420–915 mg/l, average of 701.4 mg/l). Systematic analyses for major and trace elements were conducted of water samples collected spatially and with depth in the lake in different seasons. Overall, Lake Texoma waters are characterized by Na-Ca-Cl-SO 4 -type waters with spatial distribution shifting from Na-Cl type to Ca-SO 4 type from the Red River arm to the main lake and to the Washita River arm. In addition, vertical and seasonal variations in major and trace elements concentrations indicate major elements in the lake are mainly controlled by different bedrock weathering from the two river systems. Trace elements that exhibit different distribution patterns to the major species are associated with variable sources such as river inflow, summer stratification effects, biological effects and anthropogenic activities. In Lake Texoma, differential inflow volumes and summer stratification are principal factors controlling the variation and geochemistry of lake waters and mixing dynamics. Supplementary material: Summary of major and trace element chemistry in the five zones of Lake Texoma for summer, fall and spring seasons (2003–2004) is available at http://www.geolsoc.org.uk/SUP18771

Mode of hybridogenesis and habitat preferences influence population composition of water frogs (Pelophylax esculentus complex, Anura: Ranidae) in a region of sympatric occurrence (western Slovakia)

Coexistence of sperm-dependent asexual hybrids with their sexual progenitors depends on genetic and ecological interactions between sexual and asexual forms. In this study, we investigate genotypic composition, modes of hybridogenetic gametogenesis and habitat preferences of European water frogs (Pelophylax esculentus complex) in a region of sympatric occurrence. Pelophylax esculentus complex comprises parental species P. ridibundus and P. lessonae, whose primary hybridization leads to hybridogenetic lineages of P. esculentus. Hybrids clonally transmit one parental genome and mate with the other parental species, forming a new generation of hybrids. In the region of western Slovakia, we found syntopic occurrence of diploid and triploid hybrids with P. lessonae, syntopic occurrence of all three taxa as well as the existence of pure P. ridibundus populations. All triploid hybrids were exclusively male possessing one ridibundus and two different lessonae genomes (RLL). Sex ratio in diploid hybrids was substantially female-biased. Irrespective of the population composition, diploid hybrids excluded the lessonae genome from their germ line and produced ridibundus gametes. Contrarily, RLL males unequivocally eliminated the ridibundus genome and produced diploid lessonae sperms. Perpetuation of RLL males in studied populations is most likely achieved by their mating with diploid hybrid females. The composition of water frog populations is also shaped by taxon-specific habitat preferences. While P. ridibundus preferred larger water bodies (gravelpits, fishery ponds, dead river arms), P. lessonae was most frequently found in marshes and smaller sandpits. Pelophylax esculentus occupied predominately similar habitats as its sexual host P. lessonae.

Costs associated with mitigating the impacts on water quality of future development within the Reedy River watershed using various best management practices

This study was initiated to gain a better understanding of how patterns of development within Greenville, SC and its surrounding metro area would affect the Reedy River's water quality and thus costs associated any degradation that may occur. A previously prepared watershed-scale model was modified to yield quantity and quality data that would result from projected growth in Greenville through the year 2030 at three different growth scenarios.The major finding of the study was that water quality and quantity impacts are consistently higher for the 5:1 growth scenario as compared to the 1:1 scenario. As more land is developed in the 5:1 scenario, the amount of stormwater increases while water quality decreases. At Boyd Millpond by 2030, total costs for treatment of total phosphorus and total nitrogen loads resulting from newly developed lands’ stormwater contributions could range from $8 to 1000 million. Results are similar by 2030 for the flow entering Lake Greenwood from the Reedy River Arm. Costs for potential treatment of total phosphorus at this location could range from $10 to 263 million.The cost implications of dealing with water quantity and quality impacts of varying growth scenarios suggest an obvious need for proactive planning and action when it comes to management of nutrients associated with stormwater from future developments within an area.

Two steps back, one step forward: reconstructing the dynamic Danube riverscape under human influence in Vienna.

As part of an interdisciplinary project on the environmental history of the Viennese Danube, the past river landscape was reconstructed. This article describes the different types of historical sources used for the GIS-based reconstruction, the underlying methodological approach and its limitations regarding reliability and information value. The reconstruction was based on three cornerstones: (1) the available historical sources; (2) knowledge about morphological processes typical for the Austrian Danube prior to regulation; and (3) the interpretation of past hydraulic measures with respect to their effectiveness and their impact on the river’s behaviour. We compiled ten historical states of the riverscape step-by-step going backwards in time to the early 16th century. After one historical situation had been completed, we evaluated its relevance for the temporally younger situations and whether corrections would have to be made. Such a regressive-iterative approach allows for permanent critical revision of the reconstructed time segments already processed. The resulting maps of the Danube floodplain from 1529 to 2010 provide a solid basis for interpreting the environmental conditions for Vienna’s urban development. They also help to localise certain riverine and urban landmarks (such as river arms or bridges) relevant for the history of Vienna. We conclude that the diversity of approaches and findings of the historical and natural sciences (river morphology, hydrology) provide key synergies.

三峡库区澎溪河鱼类时空分布特征的水声学研究

The Pengxi River has become an important anabranch of the Three Gorges reservoir following construction of the Three Gorges Dam.The river has the largest submersed area and the most extensive riparian zone of all of the tributaries to the reservoir.Changes to the hydrology of the system are expected to affect both the abundance and distribution of fish fauna and environmental conditions in the Pengxi River.We documented the temporal and spatial distribution of fish in the river by conducting acoustic surveys,using a split-beam echo-sounder(Simrad EY60,200 kHz),in autumn(October to November,2009),winter(December 2009 to January 2010),and spring(April to May,2010).During the same period,we also collected samples of the fish assemblage using gill nets and shrimp pots.The acoustic surveys were typically completed during the day,although we also surveyed some sections of the river at night during the winter.We estimated fish density using the echo integral method at three depth strata and in the entire water column several times during each of the three seasons.The depth strata were classified as surface(from transducer to 1/3 total depth),mid-depth(1/3 to 2/3 total depth) and bottom(2/3 total depth to the riverbed).We tested for differences in the distribution of fish throughout the Pengxi River(horizontally,vertically,day and night,and seasonally) using the survey data.Our results suggest there are significant differences in the spatio-temporal distribution of fish in the impounded section of Pengxi River.For example,the horizontal distribution of fish density was not homogeneous,and varied significantly among seasons within the surface(P≤0.01) and mid-depth(P=0.03) water strata,but not among seasons within entire water column(P=0.70).The highest density of fishes was found at the confluence of the Pengxi River arm and the main body of the impoundment.The maximum density was 67.07,19.66,and 17.25 ind./1000 m3 in autumn,winter,and spring,respectively.Within seasons,fish density varied vertically between the surface and bottom strata in winter(P=0.05),but not among other depth strata or seasons(0.15≤P≤0.89).Fish density varied significantly between day and night(P0.05) mainly due to diel vertical migration of the fish.The target strength(TS) of the fish varied significantly among seasons(P0.01),with TS highest in autumn(-57.0±5.6)dB and lowest(-58.6±4.9)dB in spring,possibly due to recruitment of juvenile fish.Catch statistics suggest the assemblage was dominated by small fish in all three seasons,which is consistent with the size estimated from the regression equation between mean target strength and length.Furthermore,a large number of fry(body length: 10—15 cm) were released prior to the survey in the spring,likely contributing to the low TS during the subsequent survey.The distribution of fish was not correlated to the depth of water in autumn and winter(︱r︱0.2),but was moderately and negatively correlated to depth in spring(r=-0.5,P≤0.05).However,the pattern of vertical distribution suggests fish were selecting certain depths.In autumn and winter,the fish were most dense between 22—49 m,and 22—44 m,respectively.In contrast,the majority of fish selected depths between 10—40 m in spring.We hypothesize that a number of ecological factors affect the behavior and distribution of fish in this area.

Spatial variability in the speciation and bioaccumulation of mercury in an arid subtropical reservoir ecosystem

Patterns of spatial variation of mercury and methylmercury (MeHg) were examined in sediments and muscle tissue of largemouth bass (Micropterus salmoides) from Amistad International Reservoir, a large and hydrologically complex subtropical water body in the Rio Grande drainage. The distributions of both Hg and MeHg were compared with environmental and biological factors known to influence production of MeHg. The highest concentrations of total Hg (THg) in sediment were found in the Rio Grande arm of the reservoir, whereas MeHg was highest at sites in the Devils River arm and inundated Pecos River (often more than 3.0 ng/g). Conditions in the sediments of the Devils River arm and Pecos River channel were likely more favorable to the production of MeHg, with higher sediment porewater dissolved organic carbon, and porewater sulfate levels in the optimal range for methylation. Although the detection of different groups of sulfate-reducing bacteria by polymerase chain reaction (PCR) was generally correlated with MeHg concentrations, bacterial counts via fluorescent in situ hybridization (FISH) did not correlate with MeHg. A sample of 156 largemouth bass (<30 cm) showed a spatial pattern similar to that of MeHg in sediments, where fish from the Devils River arm of the reservoir had higher muscle Hg concentrations than those collected in the Rio Grande arm. In 88 bass of legal sport fishing size (>35 cm), 77% exceeded the 0.3 mg/kg U.S. Environmental Protection Agency screening value. This study shows that significant variation in sediment MeHg and biotic Hg concentration can exist within lakes and reservoirs and that it can correspond to variation in environmental conditions and Hg methylation.

The influence of environmental factors on the seasonal dynamics and composition of Rotifera in the Sapucaí River arm of Furnas Reservoir, MG, Brazil

Seasonal fluctuations in the dynamics of the plankton rotifer populations in an oligo-mesotrophic branch of a tropical reservoir were analyzed with respect to the possible influence of environmental conditions (physical, chemical and biological), with emphasis on biological interactions. Samples were taken monthly from August 2006 to July 2007. The well-defined climatic seasons were reflected in variations of the physical and chemical properties of the water. The zooplankton community consisted mainly of Rotifera, Cladocera and Copepoda, with occasional representatives of Chaoborus brasiliensis (Diptera), Ostracoda, Protozoa and Turbellaria. Rotifera was the dominant group in zooplankton community in 5 of the 12 months of the study and were represented by 35 taxa. Redundancy analysis between the rotifer population abundances and the set of environmental variables showed significant (p &lt; 0.05) positive correlations with the chlorophyll a in the rainy season. In the dry period, predation was probably the environmental factor that had the strongest effect on rotifer populations; in particular, the density of the cyclopoid Thermocyclops decipiens showed significant (p &lt; 0.05) negative correlations with many of the rotifer population abundances. In addition, analysis of the co-occurrence of different rotifer species indicated strong competitive interactions between populations, during the rainy period (p &lt; 0.001). Among the biotic environmental factors analyzed, algal biomass had an important role during the rainy period and inter-rotifer competition was also significant in these months. It was probably that predation by the cyclopoid copepod Thermocyclops decipiens determined the structure and dynamics of the rotifer populations in the Sapucaí arm of the Furnas reservoir, during the dry period.

Linking upstream channel instability to downstream degradation: Grenada Lake and the Skuna and Yalobusha River Basins, Mississippi

AbstractUnstable fluvial systems are characterized by actively migrating knickpoints, incising channel beds, failing banks, and recruitment of large woody debris and it would appear that river corridors downstream of these processes would be adversely affected or impaired because of higher fluxes of sediment and other riverine products. In north‐central Mississippi, the Yalobusha River is one such system and the characteristics of two downstream locations are examined to explore this geomorphic linkage between upstream instability and downstream degradation. For the large woody debris plug along the Yalobusha River, it is found that (1) the deposit is composed mostly of sand covered with a veneer of silt and clay, (2) agrichemicals and enriched concentrations of elements are prevalent, and (3) excessive sedimentation and wood accumulation have forced river flow entirely out‐of‐bank. For Grenada Lake, it is found that (1) the impounded sediment is predominantly clay, (2) agrichemicals and elements observed throughout the reservoir show no spatial variation, (3) little difference exists in the amount and quality between the sediments deposited in Skuna and Yalobusha River arms, and (4) only a small fraction of the reservoir's storage capacity has been lost because of sedimentation. While excessive sedimentation and large woody debris recruitment have had a marked affect on stream corridor function in the area of the debris plug, the high sediment loads associated with the unstable portions of the Yalobusha River and their associated products have not been communicated to Grenada Lake. The fish consumption advisories within Grenada Lake and its tributaries due to bioaccumulated trace elements and agrichemicals, appear to be independent of the pervasive river channel instability occurring upstream. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Spatial disconnection of plankton dynamics in an Ozark reservoir

Havel, J.E. and R.G. Rhodes. 2009. Spatial disconnection of plankton dynamics in an Ozark reservoir. Lake Reserv. Manage. 25:28–38. This two-year study examined spatial distribution and seasonal population dynamics of algae and zooplankton in Table Rock Lake (Missouri, USA), a large clear reservoir threatened by increased development in the watershed. Regular samples were collected from a polymictic up-lake site (10 m deep, mean Secchi transparency 1.0 m) and a monomictic down-lake site (37 m deep, 4.0 m Secchi) in the productive James River arm. Average abundance and biovolume of most algae groups showed no statistically-discernable difference between these two sites, and maximum cell densities were similar in magnitude (∼ 105 cells/mL). Exceptional were the chlorophytes, which had their highest abundance up-lake. Based on taxonomic composition, both sites appear to be dominated by pelagic algae, with little evidence of riverine immigrants. Algae and zooplankton showed rapid seasonal changes in total densities and composition, and peak abundances showed no association in time between the two sites. Although no floating or suspended colonies were ever visible in the field, cyanobacteria (particularly Oscillatoria) were common at both study sites, and we found numerous genera linked to nuisance blooms in other lakes. Zooplankton communities differed between sites, with cladocerans common in winter and spring at the down-lake site and rotifers common year round at the up-lake site. Important cladoceran grazers, such as Daphnia, were usually not abundant; however, when they were common, algae abundance was always low.

Mercury concentrations in fish from a Sierra Nevada foothill reservoir located downstream from historic gold-mining operations

This study examined mercury concentrations in whole fish from Camp Far West Reservoir, an 830-ha reservoir in northern California, USA, located downstream from lands mined for gold during and following the Gold Rush of 1848-1864. Total mercury (reported as dry weight concentrations) was highest in spotted bass (mean, 0.93 microg/g; range, 0.16-4.41 microg/g) and lower in bluegill (mean, 0.45 microg/g; range, 0.22-1.96 microg/g) and threadfin shad (0.44 microg/g; range, 0.21-1.34 microg/g). Spatial patterns for mercury in fish indicated high concentrations upstream in the Bear River arm and generally lower concentrations elsewhere, including downstream near the dam. These findings coincided with patterns exhibited by methylmercury in water and sediment, and suggested that mercury-laden inflows from the Bear River were largely responsible for contaminating the reservoir ecosystem. Maximum concentrations of mercury in all three fish species, but especially bass, were high enough to warrant concern about toxic effects in fish and consumers of fish.

THE ZOOPLANKTON OF THE RÁCKEVE-SOROKSÁR DANUBE: SPATIO-TEMPORAL CHANGES AND SIMILARITY PATTERNS

The Rackeve-Soroksar Danube has a great importance as it is the second largest side arm in the Hungarian section of the river Danube and many demands of exploitation are expected. The aim of this study is to analyse the spatial and temporal changes of the zooplankton (Copepoda, Cladocera) community in this river arm, moreover the similarity patterns of zooplankton communities in different Hungarian water bodies are presented in special consideration of the Rackeve-Soroksar Danube. Basically this study is based on data from literature, however our data are also used for compiling the database for the spatio-temporal changes of the Rackeve-Soroksar Danube. We put emphasis on the three typical sections of the side arm, as these are stressed due to hydromorphological aspects, but creating artificial borders are objectionable as well. The results show that both spatial and temporal changes are evident, what is more, the stagnant water character of the side arm should be underlined.

Drivers of water quality in a large water storage reservoir during a period of extreme drawdown

This study examined the drivers of water quality in a large water storage reservoir (Lake Hume) during a period of extreme drawdown (to less than 3% of capacity). During the period of extreme drawdown, the reservoir can be thought of as consisting of three separate but inter-related parcels of water. The warm surface mixed layer was about 6 m deep. Cold water inflows from the Mitta Mitta River undershot the surface mixed layer in the Mitta Mitta arm of the reservoir and flowed along the bottom of the reservoir to the Dam Wall without substantial interaction with the surface mixed layer. When inflows from the Murray River occurred, the temperature of these inflows was similar to that of the surface mixed layer within the dam and the flows appeared to move within the surface mixed layer towards the Dam Wall. These Murray River inflows were insufficient to promote total mixing of the surface and bottom waters. The Murray River arm of the reservoir became a ‘hot spot’ for nutrient production. Stratification and subsequent anoxic conditions promoted the release of nutrients – ammonium, organic N and total P – from the sediments into the overlying hypolimnion. Because the depth of the lake was relatively shallow due to the extreme drawdown, wind driven events lead to a substantial deepening (turnover) of the thermocline allowing periodic pulses of nutrients into the warm surface layer. These nutrient pulses appeared to stimulate cyanobacterial growth. Warm inflows from the Murray River then served to push the blooms formed in the Murray arm into the main body of the lake.

Zooplankton in a Danube River Arm near Rusovce (Slovakia)

Poor quantity of zooplankton was recorded in a Danube arm situated on the right side of the Danube River in Slovakia (river km 1857) in 2002 and 2003. All over the year the arm is significantly influenced by groundwater by reason of seepage. Because of low mean water temperature (12°C) and poorly developed macrovegetation in particular, the arm reminds gravel pit-like. The annual average of zooplankton biomass was low and ranged from 0.35 g m−3 (2002) to 1.28 g m−3 (2003), because of low crustacean abundance. Total cladoceran abundance was excessively low in both years and ranged from 3.5 N L−1 (2002) to 16.6 N L−1 (2003). Small species, Bosmina longirostris and Chydorus sphaericus were dominant. Only four adult Copepoda — Cyclops vicinus, Thermocyclops crassus, Eurytemora velox and Eudiaptomus gracilis — were recorded in quantitative samples of both years. In the zooplankton assemblage dominated rotifers (Synchaeta pectinata, Synchaeta oblonga, Polyarthra dolichoptera and Keratella cochlearis) which represented 78% and 67% of total abundance respectively. The total of 19 species of rotifers, 34 Cladocera species and 16 taxa of Copepoda were found.

Fishing and consumption patterns of anglers adjacent to the Oak Ridge Reservation, Tennessee: higher income anglers ate more fish and are more at risk

The risks from consuming self‐caught fish are receiving international attention because of high levels of contaminants in some species. The ethnic, income, and educational differences in fishing and fish consumption patterns of 202 anglers fishing along the Clinch River arm of Watts Bar Reservoir adjacent to the US Department of Energy's Oak Ridge Reservation (ORR) or along Poplar Creek within ORR boundaries were analyzed to understand how to design a risk communication strategy. Because of elevated PCB concentrations in striped bass (Morone saxatilis), catfish (Ictalurus spp.), and sauger (Stizostedion canadense) due partly from contaminants released from the ORR in East Tennessee, the Clinch River arm of Watts Bar Reservoir is under a fish consumption advisory, while portions of Poplar Creek are under advisories because of mercury. Most studies find that a high proportion of anglers eat their catch, and people with lower incomes and less education generally eat more self‐caught fish than others fishing in the same region. Calculating fish consumption individually for each person indicated that a considerable number of people ate more fish from the study area than the amount used to calculate risks when developing fish consumption advisories, and people who ate fish more often usually ate larger portions. Unlike previous studies of fish consumption, this study indicated that a smaller proportion of anglers ate their fish, and those that ate the most were the high income anglers for this fishing population, rather than those with lower incomes. This suggests that risk communication strategies must include site‐specific information on the population at risk from fish consumption, and that targeting only low income, low education anglers will miss some people who are most at risk.

Changes in Diet and Food Consumption of Largemouth Bass Following Large-scale Hydrilla Reduction in Lake Seminole, Georgia

Largemouth bass Micropterus salmoides Lacepede growth (in length) increased an average of 14% and bioenergetics modeling predicted a 38% increase in total annual food consumption following a large-scale reduction of hydrilla Hydrilla verticillata L.f. Royle in Spring Creek, a 2,343-ha embayment of Lake Seminole, Georgia. Coverage of submersed aquatic vegetation (SAV) declined from 76% to 22% in 1 year due to a drip-delivery fluridone treatment. In contrast, largemouth bass growth only increased an average of 4% and bioenegetics modeling predicted a 13% increase in total food consumption over the same time period in the Chattahoochee River embyament, where SAV coverage naturally declined from 26% to 15%. Diets were collected from a total of 4,409 largemouth bass over a 2.5-year period in the two embayments; the primary diet item (by weight) for largemouth bass in both embayments was sunfish (mostly Lepomis spp.). Diets before and after SAV reduction were generally similar for fish greater than stock-size (≥203 mm) in the Spring Creek arm; however, fewer invertebrates were consumed after SAV reduction. Low diet similarity was observed in smaller fish, caused by a decline in consumption of grass shrimp and sunfishes and an increase in use of damselflies, shiners Notropis spp., and topminnows Fundulus spp. after SAV reduction. Diets were similar between the same time periods for all sizes of fish in the Chattahoochee River arm. These results agreed with many laboratory results describing the effects of aquatic plant density on largemouth bass food consumption and growth, and demonstrated that increased predation efficiency resulting from decreased plant abundance was likely a stronger factor determining growth rates than any potential diet shift that may occur as a result in vegetation decline.

A Crisis in Confederate Command: Edmund Kirby Smith, Richard Taylor, and the Army of the Trans-Mississippi (review)

Reviewed by: A Crisis in Confederate Command: Edmund Kirby Smith, Richard Taylor, and the Army of the Trans-Mississippi Richard M. McMurry A Crisis in Confederate Command: Edmund Kirby Smith, Richard Taylor, and the Army of the Trans-Mississippi. By Jeffrey S. Prushankin. Baton Rouge: Louisiana State University Press, 2005. ISBN 0-8071-3088-5. Maps. Illustrations. Notes. Bibliography. Index. Pp. xx, 308. $39.95. In the spring of 1864 Union forces launched a double offensive against the Confederates in the "Trans-Mississippi." One arm of this effort advanced up the Red River into northwestern Louisiana; the other came overland across southern Arkansas. The Yankee objective was Shreveport, near the Louisiana-Texas border and the center of Confederate power, authority, and industry west of the Mississippi River. On 8 April at Mansfield southeast of Shreveport the Confederates turned back the Red River arm of the Yankee campaign. They then shifted their main effort northward to meet the other Federal column. That force, learning [End Page 514] of the result at Mansfield, soon turned back, and the danger to the Rebel position came to an end. Both Union columns were able to retreat without suffering serious damage. Jeffrey Prushankin uses this campaign as the focus of his fine study of Confederate command in the Trans-Mississippi. The leading Rebels—General Edmund Kirby Smith, commander of the department, and Major General Richard Taylor, in charge of Rebel forces defending Louisiana—are the central figures. The two had long disagreed about the overall policy that the Secessionists should follow west of the Mississippi. Smith favored efforts to regain Arkansas and to establish Rebel rule over Missouri (he owed his command to Arkansas and Missouri politicians). Taylor, who lived near New Orleans, believed that the Confederates should devote their main attention to Louisiana, with the ultimate objective of retaking New Orleans (captured by Federal forces in April 1862). This difference greatly hampered Rebel operations in the department, especially in 1864 when the Trans-Mississippi Confederates faced their most serious challenge. The dispute came down to what the Rebels should attempt to do in the aftermath of their victory at Mansfield. Should they concentrate on exploiting that success by mounting a full-scale effort to pursue the beaten Federals as they fled back down the Red River, as Taylor advocated, or should they shift troops northward to meet the enemy force in Arkansas, as Smith preferred? The former course might produce a great victory, perhaps even including the capture or destruction of the powerful fleet of gunboats that accompanied the Red River column. The second strategy would ensure the safety of the department. Taylor favored the former strategy; Smith preferred the latter. Since Smith commanded the department, many of the troops who had helped Taylor triumph at Mansfield went north to Arkansas. Taylor, left with a weakened force, could not trap the Unionists he had beaten at Mansfield, and they eventually escaped from the Red River Valley. Smith was able to do little more than follow and skirmish with the retreating column in Arkansas. Soon after the campaign ended the Smith-Taylor differences broke into the open and quickly turned very personal and very bitter. The whole sorry episode furnishes an excellent example of how military operations should and should not be conducted and of how good or bad personal chemistry can affect a nation's military fortunes. Readers wanting tactical lessons can skip this book. Those who wish to ponder the larger aspects of warfare can learn much from studying how Smith and Taylor defended the Trans-Mississippi in 1864. Richard M. McMurry Roanoke, Virginia Copyright © 2006 Society for Military History

Mineralogical and geochemical investigation of sediment in the Snake River arm of the Dillon Reservoir, Summit County, Colorado, USA

AbstractMineralogical and chemical analyses of sediment in the Snake River arm of the Dillon Reservoir provided insight into the transport and fate of trace metals in this system, which provides potable water to the city of Denver in Colorado. The sediments contain metal hydroxide precipitates and sorbed trace metals that formed upstream in the Snake River and in Deer Creek, Peru Creek and other tributaries. Iron and trace metal concentrations in the sediments reach a maximum about halfway down the 3.3 km arm, with their distribution probably controlled by physical processes acting on the settling of precipitates entering the arm from the mouth of the Snake River. The concentration of molybdenum is at background concentration near the mouth of the Snake River, increasing towards the centre of the reservoir, where values are 10 times greater, owing to contamination from the Ten Mile Creek and Blue River arms of the reservoir. The results of a sediment‐leaching experiment demonstrated that the relative ease of extraction with a decreasing pH value in the sediments is zinc &gt; cobalt &gt; copper &gt; nickel &gt; lead. Although most of the trace metals are low in concentration, or are strongly sorbed in the sediments, the relatively high concentration of zinc and its relatively high mobility make it a metal of potential concern in the reservoir.

Responses in the James River Arm of Table Rock Lake, Missouri (USA) to point-source phosphorus reduction

Click to increase image sizeClick to decrease image sizeKey words: Point-source loadingphosphoruschlorophyllreservoir

The várzea forests in Amazonia: flooding and the highly dynamic geomorphology interact with natural forest succession

Although flooding and the highly dynamic geomorphology influence ecophysiology of trees in Amazonian white-water forests (várzea), information about the extent of these environmental conditions on distribution and richness of tree species is scarce. To better understand dynamic of natural forest succession and the development of different várzea forest types, we inventoried structure and floristic composition of trees ≥10 cm DBH in a total area of 5.24 ha in várzea forests near Tefé and near Manaus, Brazilian Amazon. The forests were of different successional stages and situated on different sites along the flood-level gradient. Topography and average inundation of all inventoried trees was measured with a theodolite. Sedimentation was recorded during the aquatic phase 2000 and the soil texture in each site determined. The low-várzea forests were composed of different successional stages subjected to annual floods between 7 and 3 m. Stand density per hectare averaged 490 individuals in the early successional stage, up to 1000 individuals in the early secondary stage and 434 individuals in the late successional stage, species richness amounted to 4, 45 and 91 tree species, respectively. The high-várzea forests were late successional stages subjected to annual inundations above 3 m. Stand density per hectare averaged 407 individuals and species richness amounted to 68 species in a frequently exploited forest near Manaus and to 172 species in a undisturbed forest near Tefé. Species richness and distribution along the gradients of flooding and sedimentation was well defined. Only 2.6% of 222 recorded tree species occurred over the whole flood-level gradient. Sedimentation was highest in the early successional stages near the slip-off slopes of the main-river channels, and decreased with increasing topographic level of the forested sites and proceeding succession, reaching lowest rates in the high-várzea forests. Simultaneously, soil texture changed from coarse-grained soils in early stages to fine-grained soils in subsequent stages. Thus, natural succession in várzea forests is linked to the biogenical induced silting up of the sites, because dunes and large stems building trees slow down water energy and favour the deposition of fine grained sediment. A special vegetation unit within the low várzea is the ‘chavascal’, a species-poor swamp forest, which establishes in the marginal zone of lakes or in ancient silted up river arms. Since it is located off the direct influence of the main-river channels, it seems to be characterised by longstanding stable environmental conditions, and therefore cannot rank with the successional sequence near the highly dynamic river systems.

Predation on Juvenile Salmonids by Smallmouth Bass in the Lower Granite Reservoir System, Snake River

AbstractWe estimated the consumption of juvenile salmon Oncorhynchus spp. and steelhead O. mykiss by smallmouth bass Micropterus dolomieu in the tailrace and forebay of the Lower Granite Dam and compared this consumption with that in the two major river arms of the upper Lower Granite Reservoir, Snake River, Idaho–Washington. We examined over 9,700 smallmouth bass stomachs from April through August during 1996 and 1997. Juvenile salmonids were not a major component of smallmouth bass diets by weight and number at any location in either 1996 or 1997. Of the approximately 8,600 stomach samples containing food items, only 67 had juvenile salmonid remains. Juvenile salmonids accounted for approximately 11% of smallmouth bass diets by weight in the forebay in 1996 and 5% in the Snake and Clearwater river arms in 1997, with smaller proportions at other locations. Crustaceans and nonsalmonid fishes were the dominant prey items by weight at all locations in 1996 and 1997 except for the Snake River arm in 1996, where macroinvertebrates were dominant. Monthly consumption rates (smolts/bass/d) of juvenile salmonids by smallmouth bass were highest in the forebay (0.02) in April 1996 and in the restricted zone of the forebay (0.05) in July 1997. We estimated that approximately 17,500 (1996: 6,728; 1997: 10,809) juvenile salmonids were consumed by smallmouth bass from April through August in 1996 and 1997. High flows and resulting lower water temperatures and higher turbidity in the Lower Granite Reservoir during our study probably affected salmonid predation rates by smallmouth bass. Management efforts directed at enhancing migratory conditions for juvenile salmonids (e.g., higher flows, lower water temperatures, and higher turbidity) will probably also reduce predation from smallmouth bass.