major and trace element abundances and strontium isotopes in the nyong basin rivers cameroon constraints on chemical weathering processes and elements transport mechanisms in humid tropical environments this paper aims to improve our understanding of chemical weathering processes and element transport mechanisms in the humid tropical environments we studied the nyong river basin 27 800 km2 located on the northwestern part ntem complex of the congo craton central africa the dissolved concentrations i e 0 20 m of major and trace elements dissolved organic carbon doc and the 87sr 86sr ratios have been measured in more than 20 rivers draining watersheds with various surface areas 1 to 28 000 km2 all these rivers exhibit low major cations concentrations i e na mg k ca but high concentrations of some trace elements al fe th zr y ree silica and doc the total dissolved load tds is low 20 mg l 1 and dominated by silica and organic matter the comparison of different watersheds shows us that chemical weathering is more efficient in the small unit watersheds all the sampled rivers exhibit a wide range of 87sr 86sr ratios and high ca na ratio that can be explained by the heterogeneity of the crystalline rock constituting the cratonic basement four selected rivers mengong awout soo and nyong having different drainage areas and hydrological parameters were sampled over a 2 year period collected data show that all these rivers present the same monthly seasonal variations with higher concentrations during rainy season and lower concentrations during dry season this implies that the weathering and transport mechanisms of small watersheds can be extended to the whole nyong basin in the small unit watersheds chemical weathering mainly occurs in swamp zones where mineral dissolution is enhanced by humic substances these swamp zones constitute a pool of organic rich water which can be quickly mobilized during rain seasons in these waters doc and insoluble element concentrations e g al fe and th were strongly correlated which show the key role of organic colloidal matter in the transport of some insoluble elements some other relationships al vs fe ree vs al were also examined in order to get information about chemical weathering or element transport based on these data it has been concluded that the chemical composition of these river waters is controlled by geomorphic and historic factors e g thick cation poor soil in contrast the present day climatic parameters high rainfall and temperature play a minor role in water chemistry regulation even though they are likely to enhance mineral dissolution even if organic matter favors mineral dissolution chemical weathering in this area is low compared to other world regions which suggest on a global scale a relatively small effect of these environments on the co2 consumption

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

sr and 87sr 86sr in rivers draining the deccan traps india implications to weathering sr fluxes and the marine 87sr 86sr record around k t the concentration of dissolved sr and its 87sr 86sr has been measured in the headwaters of the krishna river system and west flowing western ghat rivers all of which have their drainage almost entirely in the deccan traps the sr concentration follows that of ca and mg with sr ca and sr mg ratios similar to that of deccan basalts suggesting that all these alkaline earths are released to waters nearly congruently from the deccan basalts during chemical weathering the 87sr 86sr range from 0 70614 to 0 70986 within that reported for the deccan basalts the dissolved sr flux from the deccan calculated from the measured data is 1 35 108 moles yr 1 0 4 of the global riverine flux which is nearly the same as the proportion of area covered by deccan basalts relative to the global drainage the flux however is a factor of 3 lower than that reported for the narmada tapti wainganga ntw rivers draining the northern deccan this difference in sr flux among rivers draining the various regions of deccan could be natural spatial temporal variations and or due to supply of sr to ntw rivers from nonbasaltic sources model calculations on the role of emplacement and weathering of deccan on marine sr isotope evolution around ktb and late tertiary show that deccan basalts can be an important contributor to the decline in 87sr 86sr during these periods it is shown that to account for the pre ktb dip in 87sr 86sr the flux requirement from deccan at that time would have to be several times the contemporary flux with 87sr 86sr of 0 705 0 708 considering that the area of deccan at ktb was about thrice the present area and that the weathering rate of deccan basalts may have been much higher in early stages following eruption such high fluxes at about ktb seem feasible the disproportionately higher flux requirement for sr is similar to that invoked to explain the pre ktb decrease in 187os 188os the calculations also show that the supply of unradiogenic sr from basalts can have significant control on the long term 66 to 55 ma decline of marine 87sr 86sr

role of microtopography in the formation of sodic soils in the semi arid part of the indo gangetic plains india abstract in the northwestern part of the indo gangetic plains igp india non sodic and moderately sodic soils occur on microhigh mh and highly sodic soils on microlow ml positions under a semi arid climate the main soil forming processes have been clay illuviation deposition of pedogenic calcium carbonate and concomitant development of sodicity the microlows are repeatedly flooded with surface water during brief high intensity showers so the soils are subject to cycles of wetting and drying this provides a steady supply of alkalis by hydrolysis of feldspars leading to precipitation of calcium carbonate at high ph and development of subsoil sodicity this impairs the hydraulic conductivity of soils and eventually leads to the development of natrustalfs with exchangeable sodium percentages increasing rapidly up the profile the semi arid climate and topography interact to facilitate greater penetration of bicarbonate rich water in microlow than microhigh positions thin sections show deformational pedofeatures such as cross and reticulate striation of plasmic fabric disruption of clay pedofeatures and carbonate nodules and elongation of voids as a result of tectonic activity during the holocene in view of the persistent build up of stresses in the igp in general and the study area in particular it seems that the neotectonics have caused the microtopographical variations 0 5 1 m that control the formation of sodic soils

the reflection of oblique incident waves by breakwaters with double layered perforated wall this study examines the reflection of oblique incident waves by breakwaters that consist of a double layered perforated wall and an impermeable back wall the fluid domain is divided into three sub domains and an eigenfunction expansion method is applied in each of the domains in the eigen expansion of the velocity potential evanescent waves are also included numerical results of the present model are compared with experimental data the major factors that affect the reflection coefficient are examined

carbon isotope ratio of dissolved inorganic carbon dic in rivers draining the deccan traps india sources of dic and their magnitudes abstract chemical weathering of silicate and carbonate rocks by carbonic acid is important in the context of atmospheric co 2 sequestration and its delivery to the oceans via rivers as dissolved inorganic carbon dic in this work silicate weathering contribution to dic in the krishna river system draining the deccan basalts in south western india has been determined using a new approach based on 13 c si hco 3 systematics of the waters 13 c in the samples ranges from 8 5 to 20 7 and shows a strong linear inverse trend with si hco 3 r 2 0 80 the si hco 3 ratios in rivers vary from 0 55 to 0 10 the higher value matches the expected ratio for chemical weathering of deccan basalts based on their composition the 13 c si hco 3 trend suggests the mixing of two end members a carbonate derived endmember with low si hco 3 and enriched in 13 c and a silicate derived endmember with higher si hco 3 and depleted in 13 c small rivers of the western ghats are depleted in 13 c 13 c 18 7 2 and have high si hco 3 these properties are interpreted as signatures of basalt silicate weathering with co 2 from c 3 vegetation three samples from the krishna mainstream and two of its larger tributaries the bhima and the ghod are enriched in 13 c 13 c 8 5 to 15 with higher hco 3 and lower si hco 3 ratios indicating that a significant fraction of dic in these samples is derived from carbonate weathering carbonate dispersed in river sediments can be a likely source of dic

strontium isotopes and major ion chemistry in the chambal river system india implications to silicate erosion rates of the ganga article i nfo much higher than the global mean river water a significant fraction of solute abundance in the chambal river is derived from sodium salts unlike the himalayan rivers which exhibit dominance of ca mg salts it is estimated that the chambal river supplies about one third of sodium via the yamuna to the ganga at rajshahi bangladesh with only 6 5 of water discharge the presence of na salts not associated with chloride in the chambal headwaters constraints the application of na na corrected for cl as an index of silicate derived component this finding brings out the need to revisit the estimates of silicate erosion rate ser and associated co2 consumption in the ganga basin downstream allahabad based on na as an index the sr concentration in the chambal tributaries varied from 1 9 m to 5 9 m and 87 sr

sr and nd isotopes in river sediments from the ganga basin sediment provenance and spatial variability in physical erosion 1 sr and nd concentrations and isotope compositions in sediment of the ganga river from gangotri to rajmahal and its tributaries have been measured to determine provenance and the spatial variability in physical erosion among the ganga subbasins sr and nd in silicates range from 37 to 138 and from 10 to 36 g g with 87sr 86sr and nd of 0 7474 0 8428 and 25 5 to 15 5 respectively the results suggest that 65 of ganga mainstream sediments are derived from the higher himalayan crystallines highlighting intense physical erosion in this region the 87sr 86sr values of sediments in the gangetic plain show nearly identical trends during two seasons with a sharp and significant decrease at barauni downstream of gandak confluence this brings out the major impact of the sediment contribution from the gandak to the ganga mainstream model calculation suggests that about half of the ganga sediment at rajmahal is sourced from the gandak the erosion rates in the himalayan subbasins of the ganga range between 0 5 and 6 mm a where a is years with the gandak having the highest erosion rate high relief and intense precipitation over the headwater basins of the gandak appear to drive the rapid and focused erosion of this basin the results of this study and those in literature suggest that the eastern syntaxis brahmaputra the western syntaxis indus and the gandak have much higher physical erosion rates than the other himalayan basins focused erosion in the hot spots of these river basins contributes significantly to the global riverine sediment budget and influence regional tectonics

chemical weathering in the hong red river basin rates of silicate weathering and their controlling factors abstract the hong red river drains the prominent red river fault zone that has experienced various tectonic activities intrusion of magma exhumation of basement rocks and influx of thermal waters associated with the cenozoic collision of india and eurasia we report dissolved major element and sr isotope compositions of 43 samples from its three tributary systems da thao hong main channel and lo encompassing summer and winter seasons carbonic acid ultimately derived from the atmosphere is the main weathering agent and sulfuric acid from pyrite oxidation plays a minor role seasonality is manifested in higher calcite saturation index and mg tz and lower ca mg in summer suggesting calcite precipitation and in higher si na k ratios in summer suggesting more intensive silicate weathering we quantified the input from rain evaporite carbonate and silicate reservoirs using forward and inverse models and examined the robustness of the results carbonate dissolution accounts for a significant fraction of total dissolved cations 55 97 and weathering of silicates makes a minor contribution 1 40 our best estimate of the spatially averaged silicate weathering rate in the hong basin is 170 103 mol km2 yr in summer and 51 103 mol km2 yr in winter we tested for correlations between the rate of co2 consumption by silicate weathering and various climatic air temperature precipitation runoff and potential evapotranspiration and geologic relief elevation slope and lithology parameters calculated using gis clear correlations do not emerge except for co2 and runoff in winter which we attribute to the complex geologic setting of the area the seasonal regime change from physical dominant in summer to chemical dominant in winter and the incoherent timescales involved for the different parameters tested

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

wave reflection from perforated wall caisson breakwaters abstract analytical models for predicting wave reflection from a perforated wall caisson breakwater have been developed most of the existing models deal with the case in which the waves are normally incident to the caisson lying on a flat sea bottom in the present paper using the galerkin eigenfunction method an analytical model is developed that can predict the reflection coefficient of a perforatedwall caisson mounted on a rubble mound foundation when waves are obliquely incident to the breakwater at an arbitrary angle the developed model is compared with other theoretical results and hydraulic experimental data

petrologic profile of apollo 16 regolith at station 4 the apollo 16 double drive tube core 64001 2 total depth about 60 cm consists of four petrologic units based on the modal abundance of lithic monomineralic and other particles in the 20 500 micron size range of samples from 12 levels variation in the abundance of particles derived directly from bedrocks is low and the core soils probably represent only one set of source rocks the chemical signature of an excessively high mare basalt component at about 42 cm correlates with an excess of regolith breccias which may then be the physical carrier the core soils as a whole show a systematic size composition relationship that may be attributed to a large scale macroscopic reworking and the consequent masking of any or all previous surface process related mixing event however on a much smaller scale about 0 5 cm individual soil layers seem to have evolved more via mixing than via in situ reworking

an experimental study on scale effects in wave reflection of low reflective quay walls with internal rubble mound for regular and random waves abstract physical model tests at small and large scales have been carried out to assess the influence of the model scale on the wave reflection of low reflective quay walls consisting in prefabricated caissons with frontal openings and internal rubble mounds both monochromatic and random waves have been modeled the experiments have been carried out in the small and large scale facilities at laboratori d enginyeria maritima of the universitat politecnica de catalunya in barcelona the approach described in burcharth et al 1999 for the treatment of scale effects for porous flows has been applied to scale down the nominal diameter of the grain material at small scale 1 33 the results with and without correction of scale effects have been compared with large scale ones 1 4 however there is not plenty of literature on wave reflection of such kind of structure matteotti 1991 and faraci et al 2012 carried out physical model tests for configurations similar to the one analyzed in the present work altomare et al 2013a applied an innovative data driven modeling technique to analyze the relationship between wave reflection and hydraulic geometrical parameter for random waves basing the analysis on the results from small scale tests a discussion on similarity or differences with the mentioned studies has been conducted confirming that the approach proposed by burcharth et al 1999 led to more accurate results the main aim of the present work is to provide a reliable description of the behavior of such structure exposed to the wave actions considered remarkable since a similar quay can be implemented as berthing structure inside the harbors the paper underlines the importance of the treatment of the scale effects in such kind of modeling and the choice of a proper model scale finally a new equation to evaluate the reflection coefficient of such kind of structures is proposed

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

detrital sediment fluxes from continents to oceans abstract detrital sediment is carried from land to the sea by three agents rivers glaciers and winds the shoreline is an arbitrary boundary within the detrital sediment transport system which extends from a site of origin across areas of temporary storage to a site of long term deposition the most important of the agents moving sediment across the land is river transport estimated to be in the order of 20 10 12 kg of sediment annually at present analysis of drainage basins indicates that relief and runoff are the most important factors in determining the sediment load of rivers the competence of rivers to transport sediment is governed by the volume flow gradient and the sediment load itself today most large rivers are fed by snowmelt in highland areas runoff from rainfall in the drainage basin and groundwater inflow along the river course water is lost to evaporation and groundwater infiltration river courses can often be divided into two segments a degradational section in which the gradient is relatively steep and little temporary storage of sediment takes place and an aggradational section where the gradient is sharply reduced through meandering and where large scale temporary sediment storage forms a flood plain lakes trap sediment inland and prevent its transport to the sea today many high and mid latitude rivers are interrupted by lakes of glacial origin there are also some large areas of internal drainage that deliver no sediment to the sea the load carried by rivers has been markedly altered by human activity and may have doubled over the past few thousand years only to be reduced in the past century by the widespread construction of dams the ancient use of fire in hunting and its subsequent use in clearing land has increased erosion extensive deforestation and cultivation processes have also increased the sediment supply dam construction is a relatively new factor and affects the sediment transport system by trapping sediment before it can reach the sea the resulting lower sediment supply from rivers is at least in part compensated by increased coastal erosion glacial erosion is difficult to estimate there is an ongoing controversy whether ice sheets are effective erosive agents or not estimates of the present global flux of glacial detritus range from 0 8 50 10 12 kg annually with the lower value most probable the dust flux is in the order of 0 5 to 0 9 10 12 kg annually but may vary greatly with time

elemental geochemistry of river sediments from the deccan traps india implications to sources of elements and their mobility during basalt water interaction abstract the abundances of several major na ca mg k al ti fe and minor elements sr ba mn p v cr ni cu and zn have been measured in twenty eight sediment samples from seventeen rivers belonging to the krishna headwaters and west flowing western ghat rivers all of which drain the deccan trap basalts these results particularly those of na ca mg and sr coupled with those reported for these elements in the dissolved phase of the same rivers provide an assessment of their relative mobility and insight into the nature of chemical weathering of deccan basalts the sediments are heavily depleted in na ca mg and sr relative to parent basalts by 60 the abundance ratios of these elements in sediments are roughly the same as those in basalts and in dissolved phases of these rivers das a krishnaswami s sarin m m pande k 2005a chemical weathering in the krishna basin and the western ghats of the deccan traps rates of basalt weathering and their controls geochim cosmochim acta 69 2067 2084 suggesting their near congruent release from basalts to water during chemical weathering both at present and over the residence time of particles in the basin k and ba show limited mobility relative to the above four elements the abundances of k and ba are strongly correlated most likely due to their association in rock forming minerals al fe and ti are generally enriched in the sediments resulting from the loss of more mobile elements from basalts and their association with secondary minerals formed during weathering the data also provide evidence for the fractionation of fe and al during chemical weathering and erosion fe and ti exhibit significant correlation attributable either to their co occurrence in weathering resistant minerals and or due to scavenging of ti by fe oxy hydroxides formed during weathering of basalts the abundance of minor elements mn p v cr ni cu and zn and their ratios with al show significant scatter by and large bracketing the range reported for deccan basalts the wide and overlapping ranges in the concentration of these elements and their ratios relative to al between sediments and basalts place severe constraints in assessing their mobility during weathering and erosion and in judging the role of anthropogenic sources in contributing to their abundances among the minor elements there is a hint that zn concentration may have been influenced by anthropogenic inputs mn v and ni analogous to ti show significant correlation with fe either due to their association with fe ti minerals or their sequestration by fe oxy hydroxides the mobility of elements during weathering and erosion of deccan basalts follows the trend na ca mg sr k ba al fe ti there is considerable spatial variability in the intensity of chemical weathering of deccan basalts the cia chemical index of alteration values for the sediment range between 42 and 92 compared to 37 for the deccan basalts the lower cia values are in sediments richer in caco 3 this may be a result of semi arid climate of the region which facilitate caco 3 precipitation and restrict chemical weathering erosion higher cia values are generally associated with sediments from basins with higher runoff modeling the major element composition of sediment and water yields estimates of particulate abundances in water these estimates agree with the measured values within a factor of 2 for some of the rivers whereas in some others they differ by more than a factor of 3 4 the use of sediment composition instead of that of the suspended matter spatial and temporal variations in sediment flux and non steady state erosion all can contribute to this discrepancy these factors also seem to be contributing to difference in co 2 consumption estimated from sediment composition and that reported based on dissolved phase data

sr and 87sr 86sr in the yamuna river system in the himalaya sources fluxes and controls on sr isotope composition abstract sr and 87 sr 86 sr have been measured in the yamuna river headwaters and many of its tributaries yrs in the himalaya these results with those available for major ions in yrs rivers and in various lithologies of their basin have been used to determine their contributions to riverine sr and its isotopic budget sr in the yrs ranges from 120 to 13 400 nm and 87 sr 86 sr from 0 7142 to 0 7932 streams in the upper reaches draining predominantly silicates have low sr and high 87 sr 86 sr whereas those draining the lower reaches exhibit the opposite resulting from differences in drainage lithology 87 sr 86 sr shows significant co variation with sio 2 tds and na k tz indices of silicate weathering in yrs waters suggesting the dominant role of silicate weathering in contributing to high radiogenic sr this is also consistent with the observation that streams draining largely silicate terrains have the highest 87 sr 86 sr analogous to that reported for the ganga headwaters evaluation of the significance of other sources such as calc silicates and trace calcites in regulating sr budget of these rivers and their high 87 sr 86 sr needs detailed work on their sr and 87 sr 86 sr preliminary calculations however indicate that they can be a significant source to some of the rivers it is estimated that on an average 25 of sr in the yrs is derived from silicate weathering in the lower reaches the streams receive 15 of their sr from carbonate weathering whereas in the upper reaches calc silicates can contribute significantly 50 to the sr budget of rivers these calculations reveal the need for additional sources for rivers in the lower reaches to balance their sr budget evaporites and phosphorites are potential candidates as judged from their occurrence in the drainage basin in general precambrian carbonates evaporites and phosphorites dilute the high 87 sr 86 sr supplied by silicates thus making sr isotope distribution in yrs an overall two end member mixing major constraints in quantifying contributions of sr and 87 sr 86 sr from different sources to yrs rivers are the wide range in sr and 87 sr 86 sr of major lithologies limited data on sr and 87 sr 86 sr in minor phases and on the behavior of sr na and ca during weathering and transport the ganga and the yamuna together transport 0 1 of the global sr flux at the foothills of the himalaya which is in the same proportion as their contribution to global water discharge dissolved sr flux from the yamuna and its mobilization rate in the yrs basin is higher than those in the ganga basin in the himalaya a result consistent with higher physical and chemical erosion rates in the yrs

chemical and strontium oxygen and carbon isotopic compositions of carbonates from the lesser himalaya implications to the strontium isotope composition of the source waters of the ganga ghaghara and the indus rivers samples of precambrian carbonate mostly dolomite outcrops collected across the lesser himalaya have been analysed for their mineralogy chemical composition and isotope ratios of sr o and c to assess the extent of their preservation and their role in contributing to the high radiogenic strontium isotope composition of the source waters of the ganga ghaghara and the indus their sr concentrations range from 20 to 363 ppm 18opdb 1 4 to 12 8 and mn 11 2036 ppm the petrography of the samples their low sr concentrations and wide range of 18o values are suggestive of their postdepositional alteration the 87sr 86sr of the bulk samples and their carbonate fractions are similar to one another with values ranging from 0 7064 to 0 8935 and are generally more radiogenic than that of contemporaneous seawater comparison of the 87sr 86sr and sr ca ratios among the carbonates and silicates from the lesser himalaya and the source waters of the ganga ghaghara and the indus shows that the values for the source waters overlap with those of the silicates but are much higher than those in carbonates an upper limit of carbonate sr in the various source waters is calculated to be between 6 and 43 assuming that all the ca in the rivers is of carbonate origin the results show that on the average weathering of the precambrian carbonates is unlikely to be a major contributor to the highly radiogenic strontium isotope composition of these source waters however they can be a dominant supplier of radiogenic sr to some rivers on a regional scale the silicate sr component in some of the source waters of the ganga bhagirathi bhilangna alaknanda and ganga ghaghara kali and sarju and the indus sutlej was calculated from the ca na sr na ratios and strontium isotope compositions of these rivers and the silicate endmember these calculations suggest that 33 89 of sr in the bhagirathi bhilangna alaknanda ganga and sarju rivers is of silicate origin whereas in the kali and the sutlej it is much lower only 8 the remaining sr to all these waters has to be supplied from other sources such as weathering of carbonates and evaporites this study underscores the importance of weathering of silicates carbonates and evaporites in contributing to the sr mass balance and 87sr 86sr of the source waters of the ganga ghaghara and the indus the present day silicate and carbonate sr contributions to the sr budget of the rivers vary considerably but among the major source waters of the ganga silicate sr exerts a more dominant control on their sr abundance and 87sr 86sr

strontium isotopes and rubidium in the ganga brahmaputra river system weathering in the himalaya fluxes to the bay of bengal and contributions to the evolution of oceanic87sr 86sr the concentrations of rb and sr and87sr 86sr isotopic ratios have been measured in the dissolved load of the ganga brahmaputra g b river system the ganga was sampled extensively from its source at gangotri in the higher himalaya to patna on the alluvial plains the brahmaputra was sampled in its stretch in assam in india the average sr concentration in the ganga at patna is 1 2 mol l and that in the brahmaputra at goalpara is 0 73 mol l the mean87sr 86sr ratios are 0 7239 and 0 7192 respectively the87sr 86sr in the ganga source waters the alaknanda the bhagirathi and their tributaries range between 0 7300 and 0 7986 considerably higher than the global average runoff value of 0 7119 the high87sr 86sr in the ganga source waters result from the intense weathering of precambrian granites and gneisses enriched in radiogenic sr the sr isotope systematics of the ganga waters is dominated by silicate weathering whereas carbonate weathering plays a significant role in their major ion chemistry the g b system transports about 910 million moles of dissolved sr annually to the bay of bengal with an average87sr 86sr of 0 7213 the sr transported by the g b system is about 2 7 of the global dissolved sr flux to the oceans via rivers model calculations reveal that the g b system has contributed significantly to the sr isotope evolution of seawater during the past 20 ma the flux of rb through the g b system is 24 million moles per year this is about 5 of the global river supply of rb to the oceans nearly twice the contribution of water via the g b system to the oceans our study suggests that the marine geochemistries of sr and rb and possibly u may have been influenced considerably by the himalayan orogeny

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

2d numerical simulation of large scale physical model tests of wave interaction with a rubble mound breakwater abstract experimental measurements on a large scale multi layered breakwater model are used to extensively validate a numerical model for wave interaction with permeable coastal structures built in a generic multiphysics cfd code flow 3d a novel contribution to this code is the implementation of the piston type wave maker with active wave absorption the use of active absorption is crucial to maintain an accurate and stable incident wave field in the validation test series with long duration due to the nonbreaking wave conditions the model setup is simplified to two dimensions and single phase laminar flow in the clear fluid region the validation includes a verification of the incident wave field and a detailed study of the hydrodynamics of the flow field within the breakwater the evolution of experimentally measured free surface elevations in and outside the breakwater shows a good agreement with numerical predictions numerical results of pore pressure height throughout the breakwater core are generally corresponding well with experimental values except for a limited zone near the free surface where a clear reduction of the pore pressure is measured due to the effect of air entrainment this validation study using large scale model tests proves that this model and by extension the nowadays standard branch of vof based navier stokes models are a useful tool in predicting wave interaction with permeable coastal structures the study also reveals that it is possible to achieve a level of accuracy that can be considered sufficient for engineering applications even when using some model simplifications in particular those related to the treatment of the aerated turbulent flow on and inside the armor layer

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

temporal variation in sr and 87sr 86sr of the brahmaputra implications for annual fluxes and tracking flash floods through chemical and isotope composition temporal variations in dissolved sr and its 87sr 86sr in the brahmaputra river were determined for the first time by analyzing biweekly samples collected over a period of about a year at guwahati sr in the brahmaputra range from 0 604 to 1 392 m with 87sr 86sr of 0 71594 to 0 71802 sr concentration decreases in monsoon except for the 15 june 2000 sample which had anomalously high concentrations of sr and major ions compared to the nonmonsoon period the decrease in elemental abundances a factor of 2 is not proportional to the increase in discharge an order of magnitude indicating enhanced weathering during monsoon this can be a cumulative effect of an increase in drainage area and in physical weathering during monsoon 87sr 86sr and other proxies of silicate weathering show a relatively lower contribution from silicate weathering to the major ion and sr budget during monsoon with a concomitant increase in carbonate weathering contribution shorter interaction time between water and minerals during monsoon coupled with the slower weathering kinetics of silicate compared to carbonate can be contributing factors to the seasonal changes in their relative contributions to the major ion budget this study shows that the annual fluxes of various ions catsil and srsil calculated on the basis of measured biweekly concentrations and monthly water discharge data are roughly within 35 of those calculated using either the lowest or the highest concentrations and annual water discharge this implies that a tropical region such as in india where river discharge is governed mostly by monsoon rains the annual elemental fluxes measured during monsoon would be a good approximation for their discharge weighted annual fluxes however an additional sampling during a drier period would be required to understand the weathering processes the geochemistry of the 15 june 2000 sample is anomalous the chemistry of this sample is similar to those from the tibetan region an inference consistent with reports of a flash flood in the brahmaputra due to a natural dam burst in the yigong river of tibet these results highlight the use of the chemical and isotopic composition of water samples to track and quantify the source and discharge of a flash flood

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

sr and 87sr 86sr in waters and sediments of the brahmaputra river system silicate weathering co2 consumption and sr flux abstract the brahmaputra is a major river system draining the himalaya the concentration of sr and its 87 sr 86 sr have been measured in dissolved and particulate phases of the brahmaputra and its tributaries in india to trace the sources of dissolved sr dissolved sr ranges from 250 to 1050 nm with 87 sr 86 sr from 0 71298 to 0 75975 the sr data along with the available concentrations of major ions in the samples show that major contributors of sr in the brahmaputra system are the silicates and carbonates of the himalaya and the transhimalaya and carbonates and evaporites of the tibetan basin silicate sr in the brahmaputra river system ranges from 20 to 80 with an average of 45 the silicate component of sr in the brahmaputra system is similar or marginally higher than that in the ganga system due to contribution from the transhimalayan calc alkaline plutonic rocks which have higher concentration of sr evaporites of the tibetan sub basin and hot springs along the indus tsangpo suture could be the other significant contributors to the dissolved sr budget of the brahmaputra contribution from evaporite dissolution decouples the total dissolved sr flux from the tibetan basin from atmospheric co 2 consumption radiogenic sr of the brahmaputra system is derived from the himalayan silicates whereas other sr sources tend to dilute its radiogenic signature the 87 sr 86 sr of the dissolved phase shows significant correlation with indices of silicate weathering indicating that 87 sr 86 sr can serve as a proxy of silicate weathering at their outflow the brahmaputra is less radiogenic 0 72 compared to the ganga 0 73 however the flux of 87 sr from the brahmaputra is similar to that of the ganga

relative contributions of silicate and carbonate rocks to riverine sr fluxes in the headwaters of the ganges abstract exhumation of the himalayan tibetan orogen is implicated in the marked rise in seawater 87sr 86sr ratios since 40 ma however both silicate and carbonate rocks in the himalaya have elevated 87sr 86sr ratios and there is disagreement as to how much of the 87sr flux is derived from silicate weathering most previous studies have used element ratios from bedrock to constrain the proportions of silicate and carbonate derived sr in river waters here we use arrays of water compositions sampled from the head waters of the ganges in the indian and nepalese himalaya to constrain the end member element ratios the compositions of tributaries draining catchments restricted to a limited range of geological units can be described by two component mixing of silicate and carbonate derived components and lie on a plane in multicomponent composition space key elemental ratios of the carbonate and silicate components are determined by the intersection of the tributary mixing plane with the planes na 0 for carbonate and constant ca na for silicate the fractions of sr derived from silicate and carbonate sources are then calculated by mass balance in sr ca mg na composition space comparison of end member compositions with bedrock implies that secondary calcite deposition may be important in some catchments and that dissolution of low mg trace calcite in silicate rocks may explain discrepancies in sr ca na mg covariation alternatively composition dependent precipitation or incongruent dissolution reactions may rotate mixing trends on cation ratio diagrams however the calculations are not sensitive to transformations of the compositions by incongruent dissolution or precipitation processes provided that the transformed silicate and carbonate component vectors are constrained silicates are calculated to provide 50 of the dissolved sr flux from the head waters of the ganges assuming that discrepancies between ca mg na covariation and the silicate rock compositions arise from addition of trace calcite if the ca mg na mixing plane is rotated by composition dependent secondary calcite deposition this estimate would be increased moreover when 87sr 86sr ratios of the sr inputs are considered silicate sr is responsible for 70 16 1 of the 87sr flux forcing changes in seawater sr isotopic composition since earlier studies predict that silicate weathering generates as little as 20 of the total sr flux in himalayan river systems this study demonstrates that the significance of silicate weathering can be greatly underestimated if the processes that decouple the water cation ratios from those of the source rocks are not properly evaluated

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

rans vof modelling of the hydraulic performance of the lowreb caisson abstract the lowreb caisson is an innovative multi chambered low reflection structure that incorporates inner weirs at each dissipative chamber to promote wave energy dissipation it was designed to be applied either as external caisson breakwater or as low reflection quay wall in this paper the openfoam cfd numerical package was used to implement a rans vof numerical model of the lowreb caisson concept which was then validated using results from experimental tests in a two step approach qualitatively by comparing the wave structure interaction on both physical and numerical models and quantitatively by comparing the reflection coefficients determined from the results of the numerical model simulations and those from the physical model tests once validated the numerical model was used to carry out a comprehensive study of the hydrodynamic behavior of the lowreb caisson aiming the understanding of the wave energy dissipation mechanisms and the assessment of its hydraulic efficiency with respect to wave reflection under an extended range of hydrodynamic conditions e g water levels wave heights and wave periods the numerical study confirmed the importance of the inner weirs on the wave energy dissipation the hydraulic efficiency of the lowreb caisson was found to be highly influenced by the combined effect of the wave period and water level however the influence of the wave height is not negligible in general energy dissipation increases with the wave height overall the lowreb caisson presents its best performance for the high and mean water level conditions with all the values of the reflection coefficient below 70 and most of them in the range 30 60 the worse results obtained for the lower water level were attributed to the difficulties that waves have to overtop the weirs and enter the dissipative chambers for this water level in addition streamlines velocity and vorticity fields enabled obtaining important insights on the wave energy dissipation processes that take place during the wave structure interaction which results in the development of several vortices not only inside the dissipative chambers but also in front of the structure

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

c o sr and pb isotope systematics of carbonate sequences of the vindhyan supergroup india age diagenesis correlations and implications for global events abstract the vindhyan supergroup of central india records a substantial portion of proterozoic time and contains some of the most disputed precambrian cambrian fossil discoveries despite the significance of these fossil finds many issues including reliable geochronology remained unresolved similarly the geochemical aspects of the sedimentary sequences and their implications to the evolution of proterozoic oceans have been studied only at a reconnaissance level here we report the results of the pb pb dating for the rohtasgarh limestone from the lower vindhyan supergroup giving an age of 1601 130 ma an estimate that is in accord with the recent u pb zircon dating of the lower vindhyan supergroup by rasmussen et al geology 30 2002 103 and ray et al geology 30 2002 131 sr isotope stratigraphy of carbonates from the upper vindhyan supergroup suggests a mid neoproterozoic 750 650 ma age for these formations this in turn argues for a long hiatus between the deposition of the lower and upper vindhyan supergroups our results conflict with the reports of cambrian age small shelly fossils and ediacaran fossils from the upper vindhyan rocks at the same time they suggest that the alleged trace fossils in the lower vindhyan rocks must be of paleoproterozoic age the most common 18 o values for calcitic components from limestone formations of the supergroup range from 10 to 7 similar to paleo neoproterozoic carbonates worldwide the modes of 13 c in the lower and upper vindhyan supergroups are 0 2 and 3 2 respectively again consistent with the worldwide dataset the secular patterns of carbon isotope trends do not support the earlier assumptions that the carbonate sequences at the southern margin correlate with those at the western or northern margins of the vindhyan basin c and sr isotope data provide new calibration points for the seawater evolutionary curves particularly for the paleoproterozoic for strontium isotopes the data from the lower vindhyan supergroup suggest that seawater departed probably less rapidly from mantle values than was previously believed

performance of submerged nearshore sand filled geosystems for coastal protection abstract nearshore submerged structures made of sand filled geosystems are an interesting use for this type of coastal protection technology these systems have an advantage over more traditional materials such as concrete units or rock which is the limited and non permanent impact on natural coastal processes on top of that are also some important research achievements and improvements at the level of the materials however at more exposed hydraulic conditions under high wave energy its application is still hampered by the lack of knowledge about their performance this paper describes research results based on a series of laboratory measurements of the hydrodynamic and morphodynamic change produced in the vicinity of submerged nearshore structures an analysis of the different model outputs produced with respect to sediment transport wave reflection and wave induced pressures has been made and is discussed throughout the paper such a comparative analysis provides insights into the efficiency of each defence scheme in maintaining a beach and in protecting the shoreline the sand filled geosystems as nearshore submerged structures proved to be efficient in retarding the offshore movement of sediments and in maintaining the shoreline even if instabilities due to elements displacement and local scour have been observed

experimental study of the hydraulic efficiency of a novel perforated wall caisson concept the lowreb abstract a novel perforated wall caisson concept the so called low reflection breakwater lowreb based on a three chamber perforated wall and inner weirs is under development in the university of porto faculty of engineering portugal physical model tests carried out in the wave basin of the hydraulics laboratory of the hydraulics water resources and environment division civil engineering department have been used to study the hydraulic processes related to wave reflection the physical model was built to a froude scale of 1 50 test conditions covered two water levels and irregular waves at three significant wave heights 3 0 4 0 and 5 0 m and three peak wave periods 10 14 and 18s three models of varying porosity and vertical slots arrangements were tested under the same hydrodynamic conditions to study how these affect the lowreb performance namely how these affect the wave reflection from the structure as compared to a plain caisson tested under the same conditions the experimental study demonstrates that the lowreb caisson is a valid concept for marine structures namely harbour breakwaters because of its wave energy dissipation capacity for which the inner weirs were found to play a major role results indicate that the hydraulic efficiency of the lowreb caisson increases with wave height for the lower water level and decreases with it for the highest greater efficiency with respect to wave reflection was accomplished with the highest water level

chemical weathering in the krishna basin and western ghats of the deccan traps india rates of basalt weathering and their controls rates of chemical and silicate weathering of the deccan trap basalts india have been determined through major ion measurements in the headwaters of the krishna and the bhima rivers their tributaries and the west flowing streams of the western ghats all of which flow almost entirely through the deccan basalts samples n 63 for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002 the total dissolved solid tds in the samples range from 27 to 640 mg l 1 the rivers draining the western ghats that flow through patches of cation deficient lateritic soils have lower tds average 74 mg l 1 whereas the bhima except at origin and its tributaries that seem to receive na cl and so4 from saline soils and anthropogenic inputs have values in excess of 170 mg l 1 many of the rivers sampled are supersaturated with respect to calcite the chemical weathering rates cwr of selected basins which exclude rivers supersaturated in calcite and which have high cl and so4 are in range of 3 to 60 t km 2 y 1 this yields an area weighted average cwr of 16 t km 2 y 1 for the deccan traps this is a factor of 2 lower than that reported for the narmada tapti wainganga ntw systems draining the more northern regions of the deccan the difference can be because of i natural variations in cwr among the different basins of the deccan ii selection of river basin for cwr calculation in this study and iii possible contribution of major ions from sources in addition to basalts to rivers of the northern deccan traps silicate weathering rates swr in the selected basins calculated using dissolved mg as an index varies between 3 to 60 t km 2 y 1 nearly identical to their cwr the ca mg and na mg in these rivers after correcting for rain input are quite similar to those in average basalts of the region suggesting near congruent release of ca mg and na from basalts to rivers comparison of calculated and measured silicate ca in these rivers indicates that at most 30 of ca can be of nonsilicate origin a likely source being carbonates in basalts and sediments the chemical and silicate weathering rates of the west flowing rivers of the deccan are 4 times higher than the east flowing rivers this difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates the silicon weathering rate swr in the krishna basin is 15 t km 2 y 1 within a factor of 2 to those in the yamuna bhagirathi and alaknanda basins of the himalaya suggesting that under favourable conditions intense physical weathering high runoff granites and the other silicates in the himalaya weather at rates similar to those of deccan basalts the co2 consumption rate for the deccan is deduced to be 3 6 105 moles km 2 y 1 based on the swr the rate though is two to three times lower than reported for the ntw rivers system it still reinforces the earlier findings that in general basalts weather more rapidly than other silicates and that they significantly influence the atmospheric co2 budget on long term scales

reconciling the elemental and sr isotope composition of himalayan weathering fluxes insights from the carbonate geochemistry of stream waters determining the relative proportions of silicate vs carbonate weathering in the himalaya is important for understanding atmospheric co2 consumption rates and the temporal evolution of seawater sr however recent studies have shown that major element mass balance equations attribute less co2 consumption to silicate weathering than methods utilizing ca sr and 87sr 86sr mixing equations to investigate this problem we compiled literature data providing elemental and 87sr 86sr analyses for stream waters and bedrock from tributary watersheds throughout the himalaya mountains in addition carbonate system parameters pco2 mineral saturation states were evaluated for a selected suite of stream waters the apparent discrepancy between the dominant weathering source of dissolved major elements vs sr can be reconciled in terms of carbonate mineral equilibria himalayan streams are predominantly ca2 mg2 hco3 waters derived from calcite and dolomite dissolution and mass balance calculations demonstrate that carbonate weathering contributes 87 and 76 of the dissolved ca2 and sr2 respectively however calculated ca sr ratios for the carbonate weathering flux are much lower than values observed in carbonate bedrock suggesting that these divalent cations do not behave conservatively during stream mixing over large temperature and pco2 gradients in the himalaya the state of calcite and dolomite saturation was evaluated across these gradients and the data show that upon descending through the himalaya 50 of the streams evaluated become highly supersaturated with respect to calcite as waters warm and degas co2 stream water ca mg and ca sr ratios decrease as the degree of supersaturation with respect to calcite increases and mg2 ca2 and hco3 mass balances support interpretations of preferential ca2 removal by calcite precipitation on the basis of patterns of saturation state and pco2 changes calcite precipitation was estimated to remove up to 70 of the ca2 originally derived from carbonate weathering accounting for the nonconservative behavior of ca2 during riverine transport brings the ca sr and 87sr 86sr composition of the carbonate weathering flux into agreement with the composition of carbonate bedrock thereby permitting consistency between elemental and sr isotope approaches to partitioning stream water solute sources these results resolve the dissolved sr2 budget and suggest that the conventional application of two component ca sr and 87sr 86sr mixing equations has overestimated silicate derived sr2 and hco3 fluxes from the himalaya in addition these findings demonstrate that integrating stream water carbonate mineral equilibria divalent cation compositional trends and sr isotope inventories provides a powerful approach for examining weathering fluxes