reflections on rivers research and rouse the ways in which rivers adjust their hydraulic roughness to accommodate only loosely correlated changes in their water and sediment discharges are discussed an assessment of the current status of river engineering leads to the conclusion that the major deficiencies of mathematical models of river flow have been their failure to represent the dependence of friction factor on sediment discharge or concentration and to include temperature and channel curvature effects it is argued that the data and computational resources now are at hand to permit development of more inclusive analyses of alluvial channel flow a recently developed computer based predictor for river flow sediment discharge and friction factor and an analytical model of flow in river bends are outlined reflections on rouse s research and writing conclude the paper

early diagenetic processes in deep labrador sea sediments reactive and nonreactive iron and phosphorus a sequential extraction procedure was applied to separate the oxides and lithogenous phases of iron and manganese and the organic and inorganic phosphorus phases in four box cores and one piston core from the slopes and rises of the labrador sea sedimentation rate rather than the location in the basin appears as a master variable of the diagenetic transformations of fe mn and p high sedimentation rate characteristic of two of the box cores led to the creation of zones near the redox boundary of partial reprecipitation of dissolved fe mn and p released in the deeper reducing portions of the sediments in contrast surficial sediments from box cores with 10 times lower sedimentation rate only have sufficient reductive capacity to remobilize mn hydroxides while leaving the fe oxyhydroxides intact under these conditions there is evidence for a redistribution of reactive inorganic p leading to the crystallization of carbonate fluorapatite in the top 30 cm of the cores gradual transformation of bur

early diagenetic processes in recent sediments of the gulf of st lawrence phosphorus carbon and iron burial rates abstract selective extraction procedures were used to quantify different forms of solid phase phosphorus carbon and iron in marine sediments and to evaluate the impact of authigenic formation of mineral forms such as carbonate fluorapatite cfa calcium carbonate caco3 and pyrite fes2 on major elemental cycles during early diagenesis detrital p and fe phases were successfully used as indicators of the constancy or variability of detrital inputs to several sedimentary environments from the deep channels of the gulf of st lawrence in cores characterized by near steady state influx rates solid phase p c and fe data and sediment burial rates indicate that cfa caco3 and probably fes2 are currently forming in the sediments of the gulf however high concentrations and or formation of caco3 in marine sediments appear to inhibit the formation of authigenic cfa on the other hand the formation of fes2 does not influence authigenic cfa precipitation in the deep troughs of the gulf of st lawrence total p burial rates range from 50 to 500 mgp m2 yr truly authigenic precipitation of cfa when observed may represent up to 25 of the total burial rate of p bioturbation of sub surface sediments reduces the potential for authigenic precipitation of cfa and caco3 thus affecting immobilization reactions that have a strong impact on the global oceanic cycles of c and p the spatial heterogeneity of diagenetic reactions precludes the establishment of an accurate quantification of p removal on the scale of a continental shelf such as the gulf of st lawrence

modeling alluvial channels the present state of the art of modeling of flow of water and transport of sediment in alluvial channels is assessed the characteristics of several presently available models are described along with their similarities and differences the general problems in present models are found to be in their choice of sediment transport function assessment of resistance to flow and how it varies with changes in flow and cross section modeling of bed armoring and its effect on sediment transport the allocation of net scour and fill in a stream cross section and the handling of upstream and downstream boundary conditions current work in these areas is described the need for the inclusion of bank scour stream migration and meander development is discussed along with present methods for approaching the assessment of their effects needed areas of research are outlined for the improvement of prediction of scour and fill in alluvial channels

a compositional approach to the reconstruction of geochemical processes involved in the evolution of holocene marine flooded coastal karst basins mljet island croatia abstract geochemical patterns in the environment are always the result of certain processes therefore it is essential to decipher a process to properly evaluate the environmental role and potential of chemical elements compounds this allows the distinction between natural and anthropogenic influence on elemental concentrations however if the compositional nature of geochemical data is neglected erroneous or misleading conclusions regarding the processes involved are probable in this study the reconstruction of depositional environments and processes through the holocene in two sediment cores obtained from submerged sinkholes located on the island of mljet croatia was performed by taking into account the compositional nature of geochemical mineralogical and grainsize data problems involving compositional data are always multivariate for example the concentration of a single element does not carry any interpretative information as only the ratios between elements do this has led to the discovery of a large number of geochemical proxies based on elemental ratios which describe certain environmental conditions and processes involved nevertheless some proxies have been found to be restricted to only some specific environments thus preventing them from being used in general therefore some kind of relation between different proxies is necessary to obtain final conclusions however when using simple elemental ratios those correlations cannot be obtained due to the nature of compositional data with a sequential binary partition of a compositional vector orthonormal log ratio olr coordinates proxies can be constructed when based on expert knowledge those proxies fully acknowledge the geochemical properties of the chosen elements with one major difference that the correlation between newly obtained variables is mathematically well grounded as a result the final conclusion is more accurate in this research geochemical proxies obtained as a representation in olr coordinates of the elements that are enriched compared to the local soil were used to perform principal component analyses it helped to unravel the evolution of sedimentary environments mineralogical xrd and heavy mineral data and grain size analyses supported the conclusions obtained based solely on geochemical data furthermore data analysis suggests that the proxies for redox conditions described in the literature should be used with caution as their use is somewhat limited

mercury contamination of coastal sediments as the result of long term cinnabar mining activity gulf of trieste northern adriatic sea abstract the isonzo river mouth has been the source of hg in the gulf of trieste northern adriatic sea since the sixteenth century making this shallow basin one of the most contaminated marine areas in the length of time and amount of metal accumulated the occurrence and behaviour of total hg range 0 064 30 38 g g 1 average 5 04 g g 1 median 3 10 g g 1 n 80 and related size fractions in sediments of this coastal area were investigated in detail the relationship between total hg and the fine silt clay 210 pb dated core collected in the central part of the gulf was also compared to other heavy metals fe cr cu mn ni and zn a preliminary estimate of hg enrichment shows that the first 50 cm of sediment in the central sector of the gulf of trieste are noticeably contaminated reaching a maximum of up to 25 fold above the proposed natural regional background of 0 17 g g 1 the vertical trend is well correlated to historical data of hg extraction activity at the idrija mine

flow in alluvial river curves uniform flow in curved wide erodible bed channels is formulated on the basis of the conservation of flux of moment of momentum to obtain relations for the vertical distributions of radial plane velocity and radial shear stress the expression for the radial stress exerted on the bed is utilized in a force equilibrium analysis of the moving bed layer to obtain relations for the average transverse slope of the bed and for the radial bed profile the reduction of primary bed shear stress due to the net radial transport of streamwise momentum toward the outer concave bank is then calculated by introducing the derived expressions for the velocity components into the momentum equation for the primary flow direction it is found that the stress reductions in deep narrow channels can exceed 50 bed profiles and velocity distributions measured in natural and laboratory streams are found to be in good conformity with those calculated from this moment based theory

marine geology of the gulf of trieste northern adriatic sedimentological aspects abstract the gulf of trieste the northernmost part of the mediterranean sea is a 20 m deep marine basin influenced by freshwater inflow bottom sediment resuspension and increasing pollution the surficial sediments can be subdivided into seven zones on the basis of grain size and mineral composition the western part of the gulf consists of up to 70 carbonate shells of various organisms molluscs foraminifera and echinoderms in the inner part of the small bays of koper piran muggia and panzano the surficial sediments consist of clayey silt with approximately 30 carbonate a part of the carbonate fraction and all the non carbonate minerals are derived from flysch in the hinterland while the river isonzo is the main contributor of these minerals in the northern part of the gulf of trieste the distribution of suspended sediments shows the highest values in the northern part of the gulf intermediate values in the southeastern part and lowest values in the southwestern sector in the gulf entrance under the influence of the inflow of western istrian waters about one third of the suspended sediment is in the form of organic matter sedimentation rates decrease from about 3 5 mm yr 1 within the small bays to about 1 mm yr 1 in the central part of the gulf gradually increasing to approximately 2 5 mm yr 1 towards the mouth of the river isonzo depth profiles of holocene sediments in the inner part of the bays of koper and piran reveal a change from fluvial to brackish and marine environments

does anoxia affect mercury cycling at the sediment water interface in the gulf of trieste northern adriatic sea incubation experiments using benthic flux chambers abstract coastal areas in the northernmost part of the adriatic sea gulf of trieste and the adjacent grado lagoon are characterized by high levels of hg both in sediments and in the water column mainly originating from the suspended material inflowing through the isonzo soca river system draining the idrija nw slovenia mining district into the gulf of trieste hypoxic and anoxic conditions at the sediment water interface swi are frequently observed in the gulf of trieste and in the lagoon due to strong late summer water stratification and high organic matter input mercury mobility at the swi was investigated at three sampling points located in the gulf of trieste aa1 cz and in the grado lagoon bar experiments were conducted under laboratory conditions at in situ temperature using a dark flux chamber simulating an oxic anoxic transition temporal variations of dissolved hg and methylmercury mehg as well as o2 nh 4 no 3 no 2 po 4 3 h2s dissolved fe and mn dissolved inorganic c dic and dissolved organic c doc were monitored simultaneously benthic hg fluxes were higher under anoxic conditions than in the oxic phase of the experiment methyl hg release was less noticeable low or absent in the oxic phase probably due to similar methylation and demethylation rates but high in the anoxic phase of the experiment the mehg flux was linked to so4 reduction and dissolution of fe and mn oxyhydroxides and formation of sulphides re oxygenation was studied at sampling point cz where concentrations of mehg and hg dropped rapidly probably due to re adsorption onto fe mn oxyhydroxides and enhanced demethylation sediments especially during anoxic events should be hence considered as a primary source of mehg for the water column in the northern adriatic coastal areas

characterization and modeling of the cemented sediment surrounding the iulia felix glass abstract about 1800 years ago a roman corbita sunk off the coast of italy carrying a barrel of glass cullet to the floor of the adriatic sea samples of glass cullet and the cemented surrounding sediment have been characterized and the reaction between the glass and the sea water saturated with respect to calcite and dolomite has been modeled results from characterization and modeling show that the phase surrounding and cementing together the sediment grains is a high mg calcite we find that the origin of this cementing phase is likely the reaction between the glass and the sea water to form a mg silicate here modeled as sepiolite mg 4 si 6 o 15 oh 2 6 h 2 o

determination of organic carbon remineralization in near shore marine sediments gulf of trieste northern adriatic using stable carbon isotopes abstract the fate of metabolizable c org was studied and the c org budget was constructed in surficial sediments of the gulf of trieste northern adriatic characterized by high carbonate content bioturbation and benthic microalgal productivity isotopic composition of dic benthic fluxes 13 c j dic values measured in flux chambers over the year was used to differentiate between c org respiration and carbonate dissolution the 13 c j dic values determined at the sediment water interface using laboratory and in situ incubated benthic chambers indicated that dic benthic fluxes originate principally from the degradation of sedimentary organic matter the contribution of carbonate dissolution to dic benthic fluxes was important during the summer period up to 1 4 of dic when the oxidation of sulfides formed strong sulfuric acid summer metabolic dissolution of carbonates in these carbonate supersaturated bottom waters was supported also by benthic ca effluxes in other periods the possible adsorption of hydration species on carbonate surfaces led to ca benthic influxes it was found that the recycling efficiency estimated from dic fluxes and c org burial flux was high 90 comparison between dic benthic fluxes and o 2 consumption revealed similar values considering sulfate reduction and s burial in these sediments about 2 3 of dic production is derived from sulfate reduction and about 2 3 of o 2 consumption could occur in sulfide oxidation to sulfate

phosphorus regeneration and burial in near shore marine sediments the gulf of trieste northern adriatic sea abstract according to bioassay studies and high dissolved nutrient n p ratios in the seawater column phosphorus p is thought to control marine productivity in the northern adriatic sea p in near shore marine sediments of the gulf of trieste the northernmost part of the adriatic sea was investigated using pore water p distributions and benthic p flux studies under oxic and anoxic conditions the data show that p regeneration is up to three fold more extensive in sediments overlain by oxygen depleted waters and proceeds in parallel with fe and mn enhanced benthic fluxes it appears from the incubation experiments that degradation of sedimentary organic matter is the main contribution to the flux of p at the sediment water interface while the release of phosphate adsorbed on the iron oxide surface is of minor importance it appears that about 50 of p in the gulf of trieste is retained within in the sediments probably bonded to clay minerals and carbonate grains or precipitated as fluoroapatite in these sediments total p p tot is preserved preferentially over organic c c org p regenerated from surficial sediments contributes about 1 3 of the p that is assimilated by benthic microalgae the phytoplankton p requirement should be entirely supplied from fresh water sources these results suggest that oxygen depletion in coastal areas caused by eutrophication enhances p regeneration from sediments providing the additional p necessary for increased biological productivity the development of anoxic bottom waters in coastal areas enhances the recycling of p exacerbating the nutrient requirement in the area a geochemical record of p burial in a longer sedimentary sequence revealed an increasing trend of p tot and organic p p org contents occurring approximately 50 years bp after 1950 probably due to increasing use of inorganic fertilizers and detergents in the area

impact of anthropogenic combustion emissions on the fractional solubility of aerosol iron evidence from the sargasso sea we report empirical estimates of the fractional solubility of aerosol iron over the sargasso sea during periods characterized by high concentrations of saharan dust summer 2003 and by low concentrations of aerosols in north american maritime north atlantic air masses spring 2004 and early summer 2004 we observed a strong inverse relationship between the operational solubility of aerosol iron defined using a flow through deionized water leaching protocol and the total concentration of aerosol iron whereby the operational solubility of aerosol iron was elevated when total aerosol iron loadings were low this relationship is consistent with source dependent differences in the solubility characteristics of our aerosol samples and can be described by a simple mixing model wherein bulk aerosols represent a conservative mixture of two air mass end members that carry different aerosol types saharan air which contains a relatively high loading of aerosol iron 27 8 nmol fe m 3 that has a low fractional solubility 0 44 and north american air which contains a relatively low concentration of aerosol iron 0 5 nmol fe m 3 that has a high fractional solubility 19 historical data for aerosols collected on bermuda indicate that the low iron loadings associated with north american air masses are typically accompanied by elevated v al fe al and v mn mass ratios in the bulk aerosol relative to saharan dust which are indicative of anthropogenic fuel combustion products the identification of similar compositional trends in our sargasso sea aerosol samples leads us to suggest that the elevated solubility of iron in the aerosols associated with north american air masses reflects the presence of anthropogenic combustion products which contain iron that is readily soluble relative to iron in saharan soil dust we thus propose that the source dependent composition of aerosol particles specifically the relative proportion of anthropogenic combustion products is a primary determinant for the fractional solubility of aerosol iron over the sargasso sea this hypothesis implies that anthropogenic combustion emissions could play a significant role in determining the atmospheric input of soluble iron to the surface ocean

pore waters of the central pacific ocean nutrient results interstitial waters from the manop siliceous and calcareous ooze sites in the central pacific ocean were recovered by shipboard squeezing and centrifuging techniques and an in situ harpoon sampler the pore waters were analyzed for nutrients carbonate system species mn 2 ca 2 total alkaline earth metals and dissolved oxygen siliceous ooze site only in calcareous sediments the co 2 alkalinity po 4 3 and ca 2 results obtained from shipboard techniques are significantly different than those recovered in situ the other species measured as well as all of the data from the siliceous ooze site reveal no significant dependence on the method used to sample the pore water the relative changes in o 2 no 3 mn 2 alkalinity and co 2 indicate that respiration using o 2 no 3 and mno 2 as electron acceptors is the dominant reaction affecting the pore water species we develop a model which simulates the fate of pore water oxygen and nitrate and particulate organic carbon in sediments this model includes the effects of pore water diffusion oxygen and nitrate respiration sediment accumulation sediment mixing and changes in sediment porosity we observe that factor of 2 variations in the rates of sediment mixing and accumulation have only a minor effect on the pore water profiles the major factor controlling the pore water profiles is the flux of organic carbon across the sediment water interface we conclude that the large intra site variability observed in the interstitial water nitrate profiles is probably caused by small scale variations in the flux of organic material

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjus

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

phosphorus distribution c n p ratios and δ13coc in arctic temperate and tropical coastal sediments tools for characterizing bulk sedimentary organic matter abstract onshore offshore trends in phosphorus p organic carbon oc and total nitrogen tn concentration p distribution elemental organic c n p ratios and stable carbon isotopic composition of oc 13 c oc of surficial sediments are presented from three river dominated coastal regimes the mackenzie river beaufort shelf in the canadian arctic the mississippi delta and louisiana shelf in the temperate gulf of mexico and the tropical amazon shelf these parameters measured in surficial sediments from the three sites are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge trends in elemental ratio data from the arctic transect and a portion of the gulf of mexico transects can be explained in terms of a two end member mixture of terrestrial and marine phytodetritus in the arctic transect covariation of organic c p ratios with 13 c oc is consistent with a two end member mixture of terrestrial and marine organic matter a similar relationship between c p ratios and 13 c oc is not evident in gulf of mexico or amazon shelf sediments at these sites the two end member model fails to explain the data adequately the most striking feature of the onshore offshore trends in elemental oc op and oc tn ratios is the occurrence of low ratios in sediments from deep water stations in the gulf of mexico and all stations on the amazon shelf resulting from p and n enrichments exceeding the redfield ratio for marine plankton three explanations are discussed to account for these low ratios 1 the dominance of refractory op and on compounds in the residuum of degraded organic matter 2 differential sorption of op and n compounds regardless of lability on the surfaces of the fine grained sediments characteristic of these sites and 3 a dominance of bacterial biomass or components derived from bacterial biomass elemental ratios and 13 c oc signatures indicate that differential sorption may be most important in the deep water gulf of mexico sites in contrast elemental ratios and 13 c oc on the amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass or derivative substances

method for computing bed profiles during floods the purpose of this paper is to present the results of studies that were made to develop a new methodology for computing transverse river bed profiles by using aerial photographs taken during floods a newly developed and simplified analytical model for computing transverse river bed profiles is tested with data of aerial photographs in this model required data for computing the transverse river bed profiles are only observed data on water surface velocity distributions water surface gradient water discharge and transverse sediment size distributions to evaluate the transverse water surface velocity distributions and longitudinal water surface gradients a series of aerial photographs were analyzed by using a precision analytical plotter this analytical model gives good agreement between observed and computed transverse riverbed profiles

processes controlling phosphate adsorption by iron hydroxides in estuaries abstract phosphate adsorption by iron hydroxides is studied in the laboratory on p depleted and p saturated seston and on post glacial clays all samples from the saint lawrence estuary levels of adsorption and desorption are distinguished on the basis of significantly different ratios of the particulate iron hydroxides fecdb to inorganic non detrital phosphorus pcdb adsorption equilibrium is quickly reached for the desorbed and the sediment samples when agitated with po4 p enriched seawater this level is characterized by a mean fe p cdb value of 14 identical to the dominant one in the st lawrence p adsorption on p saturated particulate matter is found to be reversible under low reducing conditions because of the narrow ph range in the st lawrence estuary ph does not seem to influence the reaction rate the partial phosphate desorption corresponds to values of the fe p cdb ratio of 18 without any fe release these conditions are similar to those at the surface of estuarine marsh sediments the stirring experiments in the laboratory are adequately reproducing the natural behaviour of the particulate matter but the kinetics of the re adsorption reaction are much faster than in the estuary

influence of water column anoxia on the elemental fractionation of carbon and phosphorus during sediment diagenesis abstract organic carbon oxidation and benthic total phosphorus flux measurements from sites covering a range of bottom water oxygen concentrations have been compiled the data show that p regeneration relative to carbon oxidation is much more extensive in sediments overlain by oxygen depleted waters these results are consistent with studies showing that low oxygen bottom water concentrations correlate with reduced total phosphorus burial efficiencies and enhanced organic carbon burial efficiencies based on these observations a positive feedback is proposed between water column anoxia enhanced benthic phosphorus regeneration and marine productivity this feedback may help explain the widespread accumulation of organic rich marine sediments from anoxic waters observed in the geologic record

phosphorus forms related to sediment grain size and geochemical characteristics in french coastal areas abstract phosphorus forms with respect to sediment characteristics such as grain size and major chemical elements were studied in french coastal marine areas the bay of seine and the loire and gironde estuaries in the three areas fe al bound phosphate fe al p and exchangeable phosphate exch p were significantly related to the proportion of fine fraction calcium bound phosphate ca p was found in all grain size classes with comparable concentrations in the bay of seine where there was no correlation between ca p and ca this corresponded to the calcium s marine origin shells in the bay of seine in contrast the correlation of ca p with ca and the fine fraction of the sediment in the loire and gironde estuaries was characteristic of the predominant metamorphic origin of ca p in these areas useful information for interpretation of p forms can be obtained from major sediment characteristics thus for areas where specific relationships have previously been established good estimates of p forms could be predicted from sediment properties