sticky business the influence of streambed periphyton on particle deposition and infiltration strong feedbacks exist between physical and ecological components of aquatic systems aquatic plants can alter flow and sedimentation patterns in turn influencing habitat condition and organism responses in this study i investigate the interactions between streambed periphyton particle deposition and infiltration and flow hydraulics to determine the influence of these organisms on the local environment in a series of flume experiments i measured the effects of two contrasting forms of periphyton at several densities and growth stages on near bed hydraulics particle loss from the water column surface deposition and subsurface infiltration data show that periphyton assemblages altered the rate and quantity of particle deposition via several mechanisms including shear stress modification surface adhesion and bed clogging although trends varied for different size classes within a suspension of fine sediment diatoms and algae had distinctly different effects on hydraulics deposition and infiltration in general diatoms increased the rate of decline in suspended particle concentrations relative to non periphyton surfaces by reducing shear stresses and enhancing surface deposition via adhesion increases in diatom biomass however reduced the quantity and depth of particle infiltration presumably by clogging interstitial pore spaces in turn lowering rates of concentration decline in contrast all algal growth stages had slower or similar rates of concentration decline compared to non periphyton conditions due to partial clogging by high biomass and a lack of adhesion at the bed surface clogging effects were counteracted at later growth stages however as late stage algal structures increased shear stresses and downward advection in turn increasing amounts of infiltration compiled data from several field studies and experiments demonstrate a positive relation between periphyton biomass and inorganic mass but also show a wide range in the relation because of external factors such as discharge and suspended sediment concentration my analysis indicates that the decrease in the concentration of suspended particles under controlled conditions is strongly influenced by periphyton structure through direct mechanisms such as adhesion and clogging as well as indirect changes to hydraulics but that external factors in field settings such as discharge and sediment supply may outweigh the effects of periphyton structure

petrology of serra geral parana continental flood basalts southern brazil crustal contamination source material and south atlantic magmatism the serra geral parana continental flood basalt sg cfb province in brazil is associated with the jurassic cretaceous breakup of gondwanaland and the transition of continental to oceanic magmatism during the opening of the south atlantic ocean a suite of 24 samples representative of the sg cfb in rio grande do sul southern brazil shows a compositional continuum from basalt 50 53 wt sio2 mg 60 45 to basaltic andesite to andesite rhyodacite and rhyolite 73 wt sio2 certain compositional aspects of the mafic rocks e g tio2 k2o cao zr nb zr y ti zr resemble those of basaltic dikes and flows associated with the opening of the north atlantic ocean

double averaging concept for rough bed open channel and overland flows theoretical background the goal of this paper is to discuss the spatial averaging concept in environmental hydraulics and develop it further by considering transport equations for fluid momentum passive substances and suspended sediments the averaging theorems the double averaged in time and in space fluid momentum equation and advection diffusion equations for a passive substance and suspended sediments are introduced and their limitations and applications for modeling rough bed flows experimental design and data interpretation are discussed the suggested equations differ from those considered in terrestrial canopy aerodynamics and porous media hydrodynamics by accounting for roughness mobility change in roughness density in space and time and particle settling effects for the case of suspended sediments we show that the form of the double averaged equations may depend on the type of decomposition of flow variables and that this difference may have important implications for modeling we also show that the suggested methodology offers better definitions for hydraulic characteristics variables and parameters such as flow uniformity flow two dimensionality and bed shear stress

flow adjustment and interior flow associated with a rectangular porous obstruction the flow at the leading edge and in the interior of a rectangular porous obstruction is described through experiments and scaling the porous obstruction consists of an emergent rectangular array of cylinders in shallow flow a configuration that mimics aquatic vegetation the main features of the flow depend upon the non dimensional canopy flow blockage which is a function of the obstruction width and porosity for the ranges of canopy flow blockage tested in this paper the fluid decelerates upstream of the obstruction over a length scale proportional to the array width for high flow blockage the interior adjustment length within the porous obstruction is set by the array width for low flow blockage the array s frontal area per unit volume sets the interior adjustment length downstream of the adjustment regions the interior velocity is governed by a balance between the lateral divergence of the turbulent stress and canopy drag or by a balance between the pressure gradient and canopy drag depending on the lateral penetration into the array of kelvin helmholtz kh vortices which is set by the non dimensional canopy flow blockage for a porous obstruction with two stream parallel edges the kh vortex streets along the two edges are in communication across the width of the array a phenomenon that results in cross array vortex organization which significantly enhances the vortex strength and creates significant lateral transport within the porous obstruction

parana flood basalt volcanism primarily limited to 1 myr beginning at 135 ma new 40 ar 39 ar ages for rocks from rio grande do sul and critical evaluation of published radiometric data abstract 40 ar 39 ar step heating analyses were carried out on seven rocks five basalts an andesite and a rhyolite from the southern parana province 28 s 30 s they yield plateau isochron ages of 135 134 ma in good agreement with published step heating data on rocks from the same area critical review of laser spot isochron ages for rocks from the province ranging from 140 to 130 ma are shown to be unreliable estimates of crystallization ages as the rocks were substantially altered step heating results on three of these rocks thought to yield good plateau ages are shown to be incorrect as a result of a technicality in dating procedures followed u pb ages on zircon and baddeleyite separated from a variety of rock types 30 s 23 s fall in the range 135 to 134 ma all reliable 40 ar 39 ar and u pb ages indicate volcanism was sharply focused initiated at 135 ma and 1 myr in duration no variation of age with either latitude or longitude is noted scrutiny of published 40 ar 39 ar ages on the florianopolis dykes shows they cannot be used as reliable crystallization ages u pb work shows that this dyke swarm was formed coevally with the main part of the parana province most of the published 40 ar 39 ar ages on the ponta grossa dyke swarm are unreliable a few ages appear reliable and suggest the magmatic event in this area may have postdated the main parana pulse by 1 2 myr a single 40 ar 39 ar age from a high nb basalt in the southernmost part 34 s of the parana at 135 ma highlights the need for further radiometric work on other areas of this flood basalt province the parana province postdates the time of the jurassic cretaceous bound ary by 10 myr

the role of salt marsh erosion in barrier island evolution and deterioration in coastal louisiana abstract barrier shoreline erosion in louisiana reaches over 33 ft yr 10 m yr and island area decreased by 40 between 1880 and 1979 salt marsh erosion is an important factor in evolutionary barrier shoreline development and is presently contributing both directly and indirectly to the deterioration of louisiana s barrier islands the marshes originally developed as fresh marshes associated with regression of mississippi river delta lobes after fluvial abandonment salinity gradually increased and natural habitat change occurred as subsidence of deltaic sediments and transgression of the coastline by marine processes proceeded the marsh surface is subjected to relative sea level rise and unless sufficient sedimentation maintains marsh elevation erosional processes become dominant increased inundation of marsh vegetation stresses even halophytic vegetation and ultimately leads to plant death examination of variations in marsh topography over an area of approximately 2 45 acres 1 hectare revealed marked variations in the frequency and duration of tidal inundation increased flooding of lower areas can be sufficient to cause plant death and the opening of marsh ponds fragmentation of the marsh by these subsidence induced processes is part of the evolution of morphostratigraphic forms in the mississippi deltaic plain from erosional headland with flanking barriers to barrier island arc coastal bays in the mississippi deltaic plain many of which originated as interdistributary bays before transgression are also expanding at the expense of the surrounding salt marshes measurements on the margins of terrebonne timbalier bay approximately 77 mi2 200 km2 in area show that the rate of marginal erosion varies according to the exposure of the bay shoreline to prevailing southeasterly winds and fetch length across the bay in the most exposed areas erosion rates of over 13 ft yr 4 m yr have been monitored and even the north facing bay shorelines of barrier islands experience erosion rates of up to 6 6 ft yr 2 m yr the expansion of coastal bays and the fragmentation of interior marshes by pond formation leads to escalation of marsh erosion and increased threats to barrier islands bay margins disintegrate to a series of small islands which are rapidly eroded by wave attack as islands disappear wave fetch across the bay lengthens and wave attack on these island shorelines as well as back barrier marshes increases erosion of back barrier marshes both deceases island area and reduces the foundation for landward migration of the barrier sand body plans to restore louisiana s barrier islands must address the problem of bay expansion and back barrier marsh erosion in order to maintain a viable barrier beach system

evidence of biogeomorphic patterning in a low relief karst landscape patterned landscapes are often evidence of biotic control on geomorphic processes emerging in response to coupled ecosystem processes acting at different spatial scales self reinforcing processes at local scales expand patches while self inhibiting processes operating at a distance impose limits to expansion in big cypress national preserve bicy in southwest florida isolated forested wetland depressions cypress domes appear to be evenly distributed within a mosaic of short hydroperiod marshes and pine uplands to test the hypothesis that the apparent patterning is regular we characterized frequency distributions and spatial patterns of vegetation communities surface and bedrock elevation and soil properties thickness and phosphorus content nearest neighbor distances indicate strongly significant wetland spatial overdispersion and bedrock elevations exhibited periodic spatial autocorrelation both observations are consistent with regular patterning bedrock elevations and soil p were clearly bimodal suggesting strong positive feedbacks on wetland patch development soil surface elevations exhibited weaker bimodality indicating smoothing of surface morphology by some combination of sediment transport mineral reprecipitation and organic matter production significant negative autocorrelation of bedrock elevations at scales similar to wetland spacing suggest the presence of distal negative feedbacks on patch expansion these findings support the inference of regular patterning and are consistent with the presence of local positive feedbacks among hydroperiod vegetation productivity and bedrock dissolution these processes are ultimately constrained by distal negative feedbacks potentially induced by landscape scale limitations on the water volume required to enable this biogeomorphic mechanism copyright 2014 john wiley sons ltd

the lemniscate loop comparisons with the shapes of streamlined landforms the lemniscate loop is a streamlined geometric form which has a simple algebraic equation containing a parameter whose value governs its overall length to width dimensions the lemniscate has been employed in geomorphology including comparisons with glacial drumlins and erosional streamlined islands in the channeled scabland of eastern washington and within the channels on mars these past comparisons have mainly been visual the present study involves more detailed quantitative comparisons between the lemniscate loop symmetrical airfoils drumlins and various islands formed by water flows the analyses focus primarily on the length to width ratios of these landscape features and their consistency with the analytical lemniscate shape many drumlins are found to be similar to the streamlined lemniscate but an equal number are more closely approximated by an elliptical geometric form the streamlined islands in rivers in the channeled scabland and in the martian channels all have nearly the same ave

evolution of the walvis ridge rio grande rise hot spot system implications for african and south american plate motions over plumes crystallization ages of volcanic rocks dredged or drilled from the walvis ridge ten sites and the rio grande rise one site have been determined by the 40ar 39ar incremental heating technique the fundamentally age progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of tristan da cunha along the walvis ridge and rio grande rise and for the formation of the continental flood basalts located in namibia africa and brazil south america the walvis ridge rio grande rise volcanic system evolved along a section of the south atlantic spreading axis as the african and south american plates migrated apart astride or in close proximity to an upwelling plume reconstructions of the spatial relationship between the spreading axis the tristan hot spot and the evolving walvis ridge rio grande rise volcanic feature show that at about 70 ma the spreading axis began to migrate westward away from the hot spot the resulting transition to intraplate hot spot volcanism along the walvis ridge and associated termination of rio grande rise formation also involved a northward migration of previously formed african seafloor over the hot spot rotation parameters for african motion over fixed hot spots i e absolute motion have been recalculated such that the predicted trail of the tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the walvis ridge african absolute motion has been extended to the south and north american plates by the addition of relative motion reconstruction poles

the role of vegetation in the formation of anabranching channels in an ephemeral river northern plains arid central australia as the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels riparian vegetation has the potential to influence significantly dryland river form process and behaviour this paper demonstrates how a small indigenous shrub the inland teatree melaleuca glomerata influences the formation and maintenance of anabranching channels in a reach of the ephemeral marshall river northern plains arid central australia here the marshall is characterized by ridge form anabranching where water and sediment are routed through subparallel multiple channels of variable size which occur within a typically straight channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands by providing a substantial element of boundary roughness dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities flow depths and sediment transport resulting in flow diversion bank and floodplain erosion and especially sediment deposition ridges and islands represent a continuum of forms and their formation and development can be divided into a three stage sequence involving teatree growth and alluvial sedimentation 1 teatrees colonize a flat sandy channel bed initiating the formation of ridges by lee side accretion individual ridges grow laterally vertically and longitudinally and maintain a geometrically similar streamlined lemniscate form that presents minimum drag 2 individual ridges grow in size and interact with neighbouring ridges causing the lemniscate forms to become distorted ridges in the lee of other ridges tend to be protected from the erosive effects of floods and survive whereas individual teatrees or small ridges exposed to flow concentrated between larger ridges tend to be removed 3 ridges lengthen and coalesce with downstream ridges eventually subdividing the channel train into well defined anabranches this sequence turns a channel initially obstructed with dense and chaotic stands of teatrees into a well organized system of ridge form anabranches in the moderate to low gradient marshall river which is colonized by an abundance of within channel vegetation and subject to declining downstream discharges this helps to minimize flow resistance thereby maintaining an efficient water and sediment flux copyright 2000 john wiley sons ltd

the effects of seasonal changes to in stream vegetation cover on patterns of flow and accumulation of sediment abstract in stream macrophytes are typically abundant in nutrient rich chalk streams during the spring and summer months and modify the in stream environment by altering river flows and trapping sediments we present results from an inter disciplinary study of two river reaches in the river frome catchment dorset uk the investigation focused on how ranunculus water crowfoot the dominant submerged macrophyte in the study reaches modified patterns of flow and sediment deposition measurements were taken on a monthly basis throughout 2003 to determine seasonal patterns in macrophyte cover associated changes in the distributions of flow velocities and the character and amount of accumulated fine sediment within stands of ranunculus maximum in stream cover of macrophytes exceeded 70 at both sites flow velocities were less than 0 1 m s 1 within the stands of ranunculus and accelerated to 0 8 m s 1 outside the stands during the early stages of the growth of ranunculus fine sediment mostly accumulated within the upstream section of the plant but the area of fine sediment accumulation extended into the downstream trailing section of the plant later in the growing season the fine sediment accumulations were dominated by sand 63 1000 m with silts and clays 0 37 63 m comprising

hydrological connectivity in river deltas the first order importance of channel island exchange deltaic systems are composed of distributary channels and interdistributary islands while previous work has focused either on the channels or on the islands here we study the hydrological exchange between channels and islands and point at its important role in delta morphology and ecology we focus our analysis on wax lake delta in coastal louisiana usa and characterize the surface water component of hydrological connectivity through measurements of water discharge and hydraulic tracer propagation we find that deltaic islands are zones of significant water flux as 23 54 of the incoming distributary channel flux enters the islands a calculation of the travel times through a channel island complex shows travel times through the islands to be at least 3 times their channel counterparts a dye release experiment also indicates that travel times in islands are much longer that those within channels as dye remained in the island for the 3 8 day duration of the experiment additionally islands are more sensitive than channels to environmental forces such as tides which cause flow reversal and thus can increase travel times through the islands our work defines the hydrological network of a river delta to include not only the distributary channel network but also the interdistributary islands quantifies the implications of channel island hydrological connectivity to travel times through the system and discusses the relevance of our findings to channel mouth dynamics at the delta front and the potential for denitrification in coastal systems

petrology of the alkaline rocks of the macau volcanic field ne brazil the macau volcanic field mvf in the borborema province ne brazil contains multiple centres of volcanic activity of early to late cenozoic ages we present element and sr nd pb isotope geochemical data for four of the few most prominent basalt types of this volcanic field serrote preto type serra aguda type pico do cabugi type and serra preta type in order to assess their magmatic history from source to crystallization and the evolution of the mantle beneath the borborema province the basalts are basically sodic nephelinitic basanitic alkali olivine basalts enriched in lile and in nb ta the serra preta cabugi and serra aguda types demonstrate compositions close to primitive characteristics with 10 mgo 15 wt and 200 ppm ni 500 ppm and experienced limited fractional crystallization of olivine clinopyroxene plagioclase oxides with negligible wall rock assimilation rb sr and ba rb constraints support the generation of sio2 undersaturated magmas from mantle melting of amphibole bearing peridotites with minor phlogopite the source for the basanites and alkali basalts is estimated to be a garnet bearing domain around the lithosphere asthenosphere boundary 80 93 km deep while the nephelinites are derived from the adiabatic asthenosphere at 105 km with temperatures of 1480 c their incompatible trace element patterns and sr nd pb isotopic compositions are similar to fozo and em type oib magmas from the comparison of data with those of the ceara mirim dyke swarm we propose that there is a ubiquitous fozo reservoir in the sclm beneath the borborema province this fozo signature characterized the upwelling asthenosphere during the lithospheric extension and thinning at the opening of the equatorial atlantic and is clearly represented in the mesozoic olivine tholeiites of ceara mirim the upwelled asthenosphere cooled as a rigid sclm since the cretaceous and has preserved its fozo signature evident in the macau cenozoic basalts the em signatures in mvf lavas probably represent a deep component derived from metasomatizing fluid melts that have interacted with an originally old oib type mantle to produce metasomatic minerals such as k rich amphibole mica with highly incompatible trace elements contents which enhanced the generation of alkaline magmas through mantle melting

chemical stratigraphy of the parana lavas south america classification of magma types and their spatial distribution a new classification scheme has been developed to assign the lava flows of the parana continental flood basalt province south america into geochemically distinct magma types with six basaltic major and trace element abundances and or ratios by mapping out the spatial distribution of these magma types within the lava sequences it has been possible to determine the internal stratigraphy of the lava pile on a regional scale previous studies on road profiles traversing the well exposed coastal serra geral escarpment of southern brazil are summarised together with results from some new sampled sections more widespread stratigraphical investigations of the parana lavas have been hampered by the lack of sufficient topographic relief and the cover of sedimentary rocks however access to drill core chippings from nine boreholes in the central parana region has provided a unique opportunity to investigate the stratigraphy of the otherwise inaccessible deeper levels of the lava pile and to map out stratigraphic variations in three dimensions the borehole samples have indicated cated a stacking of units of different magma types all overlapping towards the north which suggests that the main locus of magmatism moved northwards with time within the parana basin this migration could be related to the northward propagation of rifting during the initiation of the south atlantic ocean maps of the surface distribution of samples of each magma type show a pattern consistent with the stratigraphy inferred from the boreholes although suggesting that the shift in magmatism may have been towards the northwest on the basis of geochemical similarities between magma types and their inferred stratigraphical relationships it is proposed that the parana can be divided into two principal magmatic centres 1 an older one in the south comprising the gramado esmeralda and urubici magma types and 2 a younger one developed about 750 km to the north formed by the pitanga paranapanema and ribeira magma types

the genesis of the amethyst geodes at artigas uruguay and the paleohydrology of the guarani aquifer structural geochemical oxygen carbon strontium isotope and fluid inclusion study the amethyst bearing geodes found in the flood basalts of the arapey formation at artigas uruguay were formed as protogeodes by bubbles of co2 rich basalt derived fluids the formation of the celadonite rim and the lining of the geodes by agate followed by quartz and amethyst were driven by the artesian water of the guarani aquifer percolating the basalts from below the temperature of the amethyst formation is estimated from fluid inclusion data to be between 50 and 120 c oxygen stable isotope data suggest a crystallization temperature of calcite of about only 24 c the actual wellhead temperature of the water produced from the guarani aquifer in the study area is around 29 c

geochemical and mineralogical evidence for the occurrence of at least three distinct magma types in the famous region bulk rock major and trace element variations in selected basalts from the famous area in conjunction with a detailed study of the chemical compositions of phenocryst minerals and associated melt inclusions are used to place constraints on the genetic relationship among the various lava types the distribution of nio in olivine and cr spinel phenocrysts distinguishes the picritic basalts plagioclase phyric basalts and plagioclase pyroxene basalts from the olivine basalts for a given mg mg fe2 atomic ratio of the mineral the nio content of these phenocrysts in the former three basalt types is low relative to that in the phenocrysts in the olivine basalts the zr nb ratio of the lavas similarly distinguishes the olivine basalts from the plagioclase phyric and plagioclase pyroxene basalts and in addition distinguishes the picritic basalts from the other basalt types these differences indicate that the different magma groups could not have been processed through the same magma chamber and preclude any direct inter relationship via open or closed system fractional crystallization

the loch scridain xenolithic sill complex isle of mull scotland fractional crystallization assimilation magma mixing and crustal anatexis in subvolcanic conduits

petrology and k ar ages of rift related basaltic rocks offshore northern brazil 3 n tholeiitic basaltic rock in three cores from petrobras drill site aps 21 1960 2480 m depths amapa basin offshore brazil is compositionally similar to rift related basaltic rock associated with the opening of both the north and south atlantic oceans sio 2 52 54 wt k 2 o 0 7 1 3 tio 2 1 3 2 whole rock k ar ages are 185 4 183 2 and 126 5 m y if these represent crystallization ages then the older samples correspond to north atlantic tectonism as represented by the liberian dike system and the younger correlates with south atlantic rift related magmatism of which serra geral flood basalts are the best example trace and ree elements identify t type mantle source areas la sm n 2 zr nb 8 11 that feasibly were mixes of n type and p type components metasomatized or veined upper mantle these amapa basin mafic rocks document the southernmost magmatism related to north atlantic rifting as well as early mesozoic mantle source areas and processes beneath gondwanaland such

environmental changes in the pampean area of argentina at the matuyama brunhes c1r c1n chrons boundary abstract the so called pampean sediments are the uppermost sedimentary levels of the chacopampean basin they record the sequence of geologic changes that occurred during the late cenozoic in the pampean area the most important environmental and faunistic changes occurred close to the end of the matuyama chron and beginning of the brunhes chron the relatively wet climate recorded in the region at the end of matuyama chron turned to drier and colder conditions during the beginning of the brunhes chron which also seems to be characterized by an important volcanic activity in the cordillera de los andes an important faunistic turnover between tolypeutes pampaeus and megatherium americanum biozones coincides with lithostratigraphic changes between the ensenada and buenos aires formations the change of polarity matuyama brunhes is observed below this boundary

lip reading recognizing oceanic plateaux in the geological record basaltic oceanic plateaux are important features in the geological record not only do they record ancient mantle plume activity but they also are believed to be important building blocks in the formation of the continental crust in this paper we review the salient features of two cretaceous oceanic plateaux the ontong java and the caribbean colombian thick sequences of predominantly homogeneous basalt the occurrence of high mgo basalt including komatiites and an apparent absence of sheeted dyke complexes in addition pyroclastic deposits may be scarce we then explore ways of distinguishing plateaux from basaltic sequences erupted in different tectonomagmatic settings continental flood basalt provinces island arcs back arc basins ocean islands and mid ocean ridges using these criteria potential archaean and proterozoic oceanic plateaux are reviewed and identified finally we explore how these remnant oceanic plateaux became incorporated into the continents by reviewing the proposed accretion mechanisms for the cretaceous caribbean colombian oceanic plateau on the basis of evidence from south america and the tonalites of the southern caribbean island of aruba

geochemistry and petrology of the jequie granulitic complex brazil an archean basement complex the jequie granulitic complex is part of the extensive high grade metamorphic terrain located within the sao francisco craton of northeastern brazil some jequie rocks appear to have been formed in the middle archean 3 1 ga from preexisting sialic crust the dominant mineral composition of these rocks is quartz microcline plagioclase hyperstene and occurs over an extensive area 2 000 km2

eroding blanket peat catchments global and local implications of upland organic sediment budgets globally peatlands account for circa 50 of terrestrial carbon storage containing as much carbon as is present in the atmosphere the uplands of the uk have an extensive cover of blanket peat but much of it is actively eroding this paper presents a detailed organic sediment budget for a blanket peat catchment in the north pennines and comparative data from a catchment in the southern pennines the catchments have total sediment yields organic and mineral of 44 and 267 t km 2 a 1 and organic sediment yields 31 and 195 t km 2 a 1 respectively they represent two extremes of a spectrum of eroded peat catchments it is demonstrated that the lower sediment yields in the north pennines are associated with extensive natural revegetation of the catchment and consequent reductions in slope channel linkage construction of a carbon budget for the north pennine catchment demonstrates that particulate carbon losses associated with the fluvial suspended sediment load are the largest single carbon loss from the system the system is currently close to carbon neutral but much higher carbon losses associated with actively eroding systems such as the south pennine site would make these systems a major carbon source the possibility that enhanced summer temperatures and winter storminess will accelerate erosion of upland mires means there is a risk that physical degradation of peatlands could become a significant positive feedback on global warming mitigation of these potential global effects will depend on local management informed by a clear understanding of peatland sediment dynamics the sediment budget data here suggest that in gullied peatlands revegetation of gully floors is an effective control on sediment flux so that techniques such as gully blocking are likely to be effective approaches to erosion control

storm driven groundwater flow in a salt marsh 1 storms can cause significant groundwater flow in coastal settings but prior studies of the effects of storms on groundwater flow and transport have largely focused on very large storms and used salinity as a tracer we have little information about the effects of smaller storms on coastal flow and how storm induced variability affects key tidal wetlands like salt marshes which may remain saline throughout a storm here we show that even the distant passage of a moderate storm can strongly increase groundwater flow and transport in salt marsh ecosystems and adjacent barrier islands groundwater monitoring and radium isotope tracer analyses revealed significant influx of saline creek water into the confined aquifer below the marsh platform driven by storm surge this pulse of fluids reached depths exceeding 5 m and surge enhanced tides propagated through the aquifer to affect flow in the upland 100 m from the creek bank groundwater discharge from the marsh varied significantly prior to the storm doubling during inundating tides compared to a period of noninundating neap tides storm surge then caused groundwater discharge to decline 50 compared to similar inundating tides ra and nutrient poor creek water that entered the confined aquifer below the marsh was quickly enriched in nutrients and carbon even on 12 h tidal cycles so that nutrient discharge was likely proportional to groundwater discharge storm related flow could also drive significant contaminant discharge from developed coastlines the enhanced transport and variability observed here likely affected hundreds of kilometers of the coastline impacted by the storm

hotspots in the southern oceans an absolute frame of reference for motion of the gondwana continents abstract the geometry and geochronology of aseismic ridges and oceanic islands in the southern oceans provide a good test of the proposition that hotspots remain fixed over long periods of time that is motion of an order of magnitude less than the relative motion between plate pairs in most cases it is concluded that inter hotspot movement cannot be discerned for the period 100 m y to present and that widely distributed hotspots in the atlantic and indian oceans provide a frame of reference for plate motions following the disintegration of gondwanaland which is independent of paleomagnetism this frame of reference is absolute in that it gives the motion of the lithosphere with respect to the mantle hotspots the absolute motion model indicates that africa and antarctica are now moving only very slowly that there has been significant relative movement between east and west antarctica since the cretaceous and prescribes the relative motion between the somali and african plates

multiscale flow vegetation sediment feedbacks in low gradient landscapes abstract low gradient fluvial landscapes 1 50 cm km 1 occupy diverse settings inland tidal and deltaic wetlands large river floodplains lowland streams but share many commonalities because of low flow energies these landscapes have abundant vegetation that is submersed or frequently inundated their sediment loads are predominantly fine with large loads transported in suspension the complexities of fluvial vegetation interactions and fine sediment transport have made these landscapes relatively poorly studied in the field of geomorphology yet the importance of understanding their dynamics is paramount these landscapes will be among the first inundated by rising seas and or are presently the focus of the world s largest restoration projects in this synthesis interactions between flow vegetation and sediment documented in inland and tidal marshes chalk and coastal plain streams large river floodplains and deltas are reviewed and classified into feedback processes occurring over a range of five spatiotemporal scales despite different morphologic appearances the feedback processes governing the coevolution of landscapes and vegetation are broadly consistent across settings though modified in their effects by life history traits of vegetation characteristics of the sediment supply external boundary forcing and initial conditions longitudinally elongated patches are common in many settings arising from stress divergence feedbacks however their ultimate morphology is strongly dependent upon the activation of patch or multipatch scale feedbacks which depends on initial densities at the time of colonization generally flow vegetation sediment feedbacks play a dominant role in landscape morphology when the setting is depositional and little initial topographic differentiation is present in that case these feedbacks can explain the apparently paradoxical emergence of high sinuosities or parallel drainage in very low gradients importantly for management flow vegetation sediment interactions may activate a chain of positive feedbacks that engages progressively larger scales resulting in massive destruction of marsh vegetation or topographic homogenization interrupting these feedbacks requires intervention over all scales activated

evidence of magmatic activity related to middle jurassic and lower cretaceous rifting from northeastern brazil ceara mirim k ar age palaeomagnetism petrology and sr 1bnd isotope characteristics the mesozoic magmatic activity in the easternmost part of ne brazil ceara mirim is mainly represented by two pyroxene tholeiitic dykes only few dykes have alkaline character k ar ages and palaeomagnetism data indicate that ceara mirim dykes are of middle jurassic 175 160 ma and early cretaceous 140 130 ma age both middle jurassic and lower cretaceous dykes have high incompatible element concentrations and tio2 with the lower contents generally confined to the middle jurassic dykes rare tholeiitic dykes low in tio2 and incompatible elements are present sr 1bnd isotopic and other chemical data do not support appreciable crustal contamination and in a 87sr86sr vs 143nd144nd diagram almost all the dykes plot in a narrow area of the enriched quadrant of the mantle array tholeiitic and alkaline ceara mirim dykes are related to different parent magmas probably originating by different degrees of melting of garnet peridotite mantle sources characterized by distinct sr 1bnd isotope compositions and small scale chemical heterogeneities ceara mirim tholeiitic dykes show close mineralogical chemical and isotopic similarities with the lower cretaceous high tio2 tholeiites from maranhao sardinha intrusives and parana northern province basins in general chemical and sr 1bnd isotope data for high and low tio2 brazilian mesozoic tholeiites appear to be related to time integrated enriched and depleted mantle components respectively subcontinental mantle heterogeneity is believed to be due to variable enriched components related to metasomatic processes the ceara mirim jurassic dykes correlate well in terms of composition and tectonic setting with the analogue tholeiitic dyke swarms from the benue trough and can be related to the opening of the central atlantic ocean the lower cretaceous ceara mirim magmatic activity corresponds to the coeval one of the benue trough and can be related to the early rifting events responsible for the opening of the equatorial domain of the south atlantic whose oceanic crust formed between 120 and 100 ma

sediment patterns near a model patch of reedy emergent vegetation this laboratory study describes the sediment patterns formed in a sand bed around circular patches of rigid vertical cylinders representing a patch of reedy emergent vegetation the patch diameter was much smaller than the channel width two patch densities solid volume fraction 3 and 10 and two patch diameters 22 and 10 cm were considered for flows above the threshold of sediment motion patterns of sediment erosion and deposition were observed around and within the patch scouring within the patch was positively correlated with turbulent kinetic energy in the patch for sparse patches sediment scoured from within the patch was mostly deposited within one patch diameter downstream of the patch for dense patches which experience greater flow diversion sediment scoured from the patch was carried farther downstream before deposition along the patch centerline differences between the sparse and dense patch patterns of deposition are explained in the context of flow diversion and wake structure which are related to a nondimensional flow blockage parameter while sediment was redistributed near the patch observations suggest that net deposition was not recorded at the reach scale

quantitative evaluation of fractional crystallization in bouvet island lavas abstract bouvet island situated near the southernmost end of the mid atlantic ridge is characterized by lavas ranging in composition from hawaiite through mugearite and benmoreite to rhyolite major and trace elements vary systematically throughout the sequence as do mineral compositions and geochemical modelling indicates that the compositional variations observed in the differentiated lavas can be ascribed to extensive fractional crystallization of a parental hawaiite magma following this scheme the hawaiite parent magma experienced approximately 44 fractional crystallization of plagioclase clinopyroxene olivine opaque oxides and minor apatite to give rise to the mugearite magma which in turn experienced a further 69 fractional crystallization of the same phase assemblage though with more evolved compositions to give rise to the bouvet island rhyolite extensive fractional crystallization 64 possibly separated in time of the parental hawaiite gave rise to the benmoreite magma in the latter scheme the fractionating phases are similar both in composition and proportion to those crystallizing in the passage from hawaiite to mugearite suggesting that the bouvet island hawaiites correspond in composition to a six phase plag of cpx fe ti oxide ap lq saturation surface and that the more differentiated lavas resulted from differing degrees of crystallization on this surface

macrophytes and suspension feeding invertebrates modify flows and fine sediments in the frome and piddle catchments dorset uk summary this research investigated the ecosystem engineering by in stream macrophytes dominated by ranunculus spp and associated suspension feeding blackfly larvae diptera simuliidae for five reaches in the frome and piddle catchments dorset uk over one annual growth cycle 2003 this paper focuses on the modification of flow velocities and the trapping of fine sediment particles in stream macrophyte growth was extensive with maximum percentage cover of 80 recorded in september and october 2003 the macrophyte cover significantly altered flow patterns and flow velocities within and between the macrophyte stands the reduced flow velocities within the plants promoted sediment trapping reaching volumes of 0 085 m3 of fine sediment trapped per metre square of vegetation at one site the effective particle sizes of the sediments trapped within ranunculus stands were dominated by the 250 500 m fraction from march to july 2003 whereas a higher proportion of smaller fractions occurred from october to december faecal pellets were highly abundant in the sediments trapped within ranunculus stands up to 2 2 108 faecal pellets per m2 and their dimensions total size range 25 400 m fall within the dominant size fraction of the trapped sediments our findings demonstrate the need to consider the biogenic component of the fine sediments in chalk streams in future studies of sediment and nutrient dynamics

influence of turbulence on bed load sediment transport this paper summarizes the results of an experimental study on the influence of an external turbulence field on the bed load sediment transport in an open channel the external turbulence was generated by 1 a horizontal pipe placed halfway through the depth ih 2 a series of grids with a clearance of about one third of the depth from the bed and extending over a finite length of the flume and 3 a series of grids with a clearance in the range 0 1 1 0 ih from the bed but extending over the entire length of the flume two kinds of experiments were conducted plane bed experiments and ripple covered bed experiments in the former case the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment transport in the ripple covered bed case the mean and turbulence quantities of the streamwise component of the velocity were measured and the shields parameter due to skin friction was determined the shields parameter together with the rms value of the streamwise velocity fluctuations was correlated with the sediment transport rate the sediment transport increases markedly with increasing turbulence level

spatial and temporal dynamics of sediment accumulation and exchange along strickland river floodplains papua new guinea over decadal to centennial timescales 1 we investigated the processes of sediment exchange between the strickland river and its lowland floodplain documenting 1 the rates textures and distributions of sediment accumulation 2 temporal variations in these rates 3 the remobilization of sediment by erosive processes and 4 whether net storage is significant over century timescales we used 210pb geochronology of floodplain cores from 11 transects to measure deposition rates over the past 65 years finding a decline from 5 5 cm a 0 10 m distance from the channel to 0 9 cm a 400 m to 0 1 cm a 1 km rates are elevated along curved sections of channel and are stable over time and episodic accumulation is prevalent and may be correlated to floods integrated temporally and spatially the average rate is 1 6 cm a integrating along both sides of 318 river km we studied for the lowland strickland we calculate 12 19 mt of annual sediment accumulation 0 05 mt km or 0 07 of the annual load per km of river length representing 17 27 of the total annual sediment flux we used georeferenced landsat images 1972 2001 to quantify channel migration and the resulting return of sediment to the channel mean lateral migration was 5 1 0 8 m a given the floodplain width of 10 km this implies a waiting time of 1 ka between floodplain formation and subsequent reentrainment of the bank as the channel migrates laterally this raises the possibility that the net return of material from the floodplain due to channel migration could balance the overbank deposition we observed the exchange flux between cut bank erosion and point bar deposition is 20 40 mt highlighting the significance of sediment recycling 50 of the total load such sediment trapping and recycling affects the transport storage and evolution of biogeochemically reactive particles the evolution of the floodplain and the morphodynamics of basin infilling

examining the physical meaning of the bank erosion coefficient used in meander migration modeling widely used models of meander evolution relate migration rate to vertically averaged near bank velocity through the use of a coefficient of bank erosion e in applications to floodplain management problems e is typically determined through calibration to historical planform changes and thus its physical meaning remains unclear this study attempts to clarify the extent to which e depends on measurable physical characteristics of the channel boundary materials using data from the sacramento river california usa bend average values of e were calculated from measured long term migration rates and computed near bank velocities in the field unvegetated bank material resistance to fluvial shear k was measured for four cohesive and noncohesive bank types using a jet test device at a small set of bends for which both e and k were obtained we discovered that variability in k explains much of the variability in e the form of this relationship suggests that when modeling long term meander migration of large rivers e depends largely on bank material properties this finding opens up the possibility that e may be estimated directly from field data enabling prediction of meander migration rates for systems where historical data are unavailable or controlling conditions have changed another implication is that vegetation plays a limited role in affecting long term meander migration rates of large rivers like the sacramento river these hypotheses require further testing with data sets from other large rivers

in channel woody vegetation controls on sedimentary processes and the sedimentary record within alluvial environments a modern example of an anabranch of the river loire france a multidisciplinary approach was used to analyse the role of pioneer trees populus nigra on bar formation in the modern fluvial system of the river loire france data were collected on seven plots located on a secondary channel chosen for their vegetation cover and their sedimentary context physical features of vegetation topographical evolution sediment grain size and flow velocity were investigated during and after floods between 2001 and 2003 woody vegetation responds morphologically to fast flowing waters and sediment deposition these adaptations influence the role played by trees on local sedimentary processes some morphological types of trees exert a strong influence during flood events by deflecting reducing or increasing the flow energy as a consequence the evolution of bedforms distribution of sediment grain size and slopes are controlled by the flood type the morphological context i e high or low energy zones the morphology of the vegetated bar and the characteristics of vegetation conceptual models are proposed to account for local processes and evolution of tree groves the first model which describes the behaviour of groves during a single flood underlines the sediment deposition downstream of the trees and the trapping of bedload sediments during the falling stage of the flood the reorientation of current streams constrained by both local bed topography and woody vegetation induces transverse sediment fluxes for these water levels the control exerted by trees on small scale sedimentary processes becomes significant the second model shows the evolution of vegetation bands over several flood events in particular it describes the influence of vegetation on the fixing and reworking of bedload sediments during the falling limb of the hydrograph the coalescence of vegetation induced bedforms and the resulting morphological changes increase the deflection power of the vegetated bar inducing the deposition of finer sediments

geochemistry and petrogenesis of the mandidarla volcanics northwestern himalayas the proterozoic mandi darla volcanics mdv occur as flows intercalated with the low grade metasediments of the sundarnagar group of the lesser himalayas these volcanics are aphyric and have quenched textures with plagioclase clinopyroxene skeletal microphenocrysts they are of tholeiitic composition and are enriched in feot tio2 incompatible trace and rare earth elements they have relatively high sio2 abundances for their mgo levels which are attributed to high ph2o pertaining during melt generation fractional crystallisation does not appear to have played any major role in the evolution of their bulk chemistry instead they appear to have been generated by different extents of isobaric partial melting of a non pyrolitic and heterogeneous source with enriched and variable fe mg ratios ree modelling suggests that the ree enriched source consisted of variable proportions of at least two end members differing in their mree and hree contents but with similar lree abundances the enrichment of the source is attributed to mantle metasomatism by a melt dominated phase penecontemporaneous with magma generation

vegetative impacts on hydraulics and sediment processes across the fluvial system summary vegetation creates a complicated system of feedbacks and linkages across the fluvial system that is realized through river planform shape interactions occur among flow hydraulics sediment deposition and erosion and plant morphology density and biomechanics interest in the interactions and feedback loops between vegetation and the fluvial system has grown extensively in the past few years this interest is partially driven by the popularity of stream restoration activities worldwide that include re vegetation of stream banks and formation of an ecosystem that is intended to encourage the growth of aquatic macrophytes we present a review of the research into the interactions and dependencies between vegetation and the fluvial system to identify hydraulic and sediment dynamics that are consistent around vegetation located in the channel on channel banks and over the floodplain we illustrate process commonalities operating across spatial locations within the fluvial system and highlight some of the current research opportunities and challenges to encourage research collaborations between those working in areas of the fluvial system traditionally viewed as disparate

crustal signatures in the serra geral flood basalt province southern brazil o and sr isotope evidence strontium and oxygen isotopes in igneous rocks from a 35 000 km 2 region of the serra geral parana continental flood basalt province southern brazil indicate that certain mantle derived magmas that formed during the rifting and breakup of gondwana incorporated continental crust sr o and trace element assimilation fractional crystallization models point to variable amounts and types of warm archean granulitic crust 18 o 11 15 and 87 sr 86 sr i 0 735 having contaminated ascending mafic magmas resulting products include evolved rocks basaltic andesite to rhyolite that have 18 o 11 to 15 and 87 sr 86 sr i 0 714 to 0 729 and basaltic rocks that have 18 o 8 to 10 and 87 sr 86 sr i 0 710

morphologic and transport properties of natural organic floc 1 the morphology entrainment and settling of suspended aggregates floc significantly impact fluxes of organic carbon nutrients and contaminants in aquatic environments however transport properties of highly organic floc remain poorly understood in this study detrital floc was collected in the florida everglades from two sites with different abundances of periphyton for use in a settling column and in racetrack flume entrainment experiments although everglades flocs are similar to other organic aggregates in terms of morphology and settling rates they tend to be larger and more porous than typical mineral flocs because of biostabilization processes and relatively low prevailing shear stresses typical of wetlands flume experiments documented that everglades floc was entrained at a low bed shear stress of 1 0 x 10 2 pa which is considerably smaller than the typical entrainment threshold of mineral floc because of similarities between everglades floc and other organic floc populations floc transport characteristics in the everglades typify the behavior of floc in other organic rich shallow water environments highly organic floc is more mobile than less organic floc but because bed shear stresses in wetlands are commonly near the entrainment threshold wetland floc dynamics are often transport limited rather than supply limited organic floc transport in these environments is therefore governed by the balance between entrainment and settling fluxes which has implications for ecosystem metabolism materials cycling and even landscape evolution

velocity profiles in vegetated open channel flows combined effects of multiple mechanisms abstractvertical profile of longitudinal velocity in vegetated channels reflects complex mechanics of flow vegetation interactions and determines the bulk flow velocity and flow rate most available models of velocity profiles in vegetated channels are based on a single physical concept that underpins theoretical considerations and data interpretation however measured velocity profiles suggest that the use of a single concept is not sufficient to cover all possible scenarios of flow vegetation interactions as a result a number of models in which different concepts are applied to different flow regions have been recently developed within this framework the overall velocity profile is represented with a set of linked segments although such segment based models have improved velocity profile description there is a need for more robust approaches and better analytical formulations this paper proposes a new approach where a vertical velocity profile in vegetated channels is modelled as a linear superp

the age origin and tectonics of the grao para group and associated rocks serra dos carajas brazil archean continental volcanism and rifting the grao para group which is host to the large serra dos carajas fe deposits is located in the eastern part of the central brazil shield ssw of belem brazil it is composed of a lower sequence of metavolcanic rocks a middle sequence of iron formation carajas formation and an upper sequence of mixed metavolcanic and metasedimentary rocks the grao para group is overlain by an unnamed sedimentary dominantly sandstone unit and unconformably overlies the older xingu complex the lower metavolcanic sequence of the grao para in the region of the serra norte fe deposits is bimodal with dominant metabasalts metabasaltic andesites and metatrachyandesites and subordinate 10 15 metarhyolitic tuffs and flows most of the metavolcanic rocks are at low to medium metamorphic grade with more intense metamorphism and deformation along the northern contact with the xingu complex the thickness of the metavolcanic section is not known but may be 4 6 km the mafic metavolcanic rocks are enriched in rb ba and k with respect to oceanic basalts and basalts of greenstone belts and are relatively depleted in th sr ta ti and p the mafic rocks also show an enrichment in lrees with flat hree patterns the hrees are correlated with mg number u pb zircon analyses of the metarhyolites from the grao para group yield an age of 2758 39 ma rb sr wholerock analyses of the mafic rocks yield an isochron with an age of 2687 54 ma with an initial ratio of 0 7057 0 0010 the results indicate a late archean age of volcanism in the grao para group much older than previously thought rb sr results from the metarhyolites have been partially reset yielding an age 2497 62 ma sm nd analyses from the grao para metavolcanic rocks were too scattered to yield an isochron but nd values relative to chur at 2758 ma indicate values similar to depleted mantle at this time although with some scatter the trace element data and the sr and nd isotopic results from the mafic rocks are consistent with contamination of mantle derived melts by significant but variable amounts of diverse older continental crust the stratigraphy geochemical and isotopic compositions show that the grao para group originated on extending older continental crust during the archean an age terrane boundary must exist between this archean continental terrane and the apparently ensimatic early proterozoic greenstone belts of the northern amazonian craton similarities to other sequences e g the fortescue group australia suggest that similar tectonic settings were widespread at this time many major iron formations were deposited within these environments indicating significant iron formation development on sialic crust in the late archean u ph zircon analyses from the serra dos carajas granite which intrudes the unnamed sedimentary unit overlying the grao para group yield an age of 1820 49 ma in agreement with previous age determinations this age is similar to the ages for the uatuma supergroup volcanic and shallow plutonic rocks which occur throughout the amazonian craton

geochemistry of early mesozoic tholeiites from morocco abstract mesozoic dolerites from two areas of morocco the high atlas fold belt between marrakech and demnat and the anti atlas belt in the area of foum zquid are most high ti quartz normative tholeiites whichi in many respects resemble mesozoic dolerite dikes from eastern north america the dolerites display a wide range of major and trace element compositions some of which are due to fractional crystallization the doleritic sequences from high atlas also show vertical stratigraphic zonation which is characterized by a progressive depletion of lithophile elements toward the top this trend together with regularities of trace element ratio variations are indicative of a dynamic melting of an initially homogeneous source it is suggested that the continental upper mantle source for dolerites of morocco was enriched in several incompatible elements in comparison with the upper mantle source for ocean floor tholeiites