the variability of conditions of carbonate allocation on the example of a small flow through łeczna wlodawa lake eastern poland a synthetic index lsi langelier saturation index was calculated to analyze conditions of carbonates allocation the higher lsi value positive or negative the better conditions to deposition or chemical denudation respectively physical chemical research was carried out in the lake catchment system of lake syczynskie located in the border zone of polish lowland and lublin upland the data were collected during the three water years 2007 2009 a hydro chemical state of products of caco3 dissociation in waters was close to the equilibrium for most of the year values of the lsi ranged from 0 08 to 1 44 in the water of the catchment under study the highest lsi values were observed in the lake water the lowest lsi values occurred in waters of the inlet originated from a cretaceous spring allocation conditions were established along inlet lake outlet transect a decrease of carbonates translocation along the transect was typical for the lake syczynskie and it occurred in all seasons a clear seasonality of the carbonate equilibrium state was observed in the lake catchment system under study results showed that inlet of groundwater determined transport of products of calcium and magnesium carbonate dissociation in the catchment lake syczynskie the most stable chemical conditions were observed in winter which resulted from an intense groundwater inflow the least stable conditions occurred in spring in which season conditions of carbonates allocations were modified by precipitation and or surface runoff

enhanced riverine carbon flux from carbonate catchment to the ocean a comparative hydrogeochemical study on ishigaki and iriomote islands southwestern japan 1 riverine carbon transportation is an important carbon flux connecting reservoirs of the atmosphere continents and oceans the flux is strongly related to the important roles of rivers such as regulation of climate change and buffering of ocean acidification here to evaluate the linkage of such functions of rivers and geological characteristics of the watersheds we present the results of a comparative hydrogeochemical study conducted on small subtropical watersheds of aluminosilicate dominated iriomote island and carbonate based ishigaki island southwestern japan rivers on ishigaki island exhibited much higher alkalinity than rivers on iriomote island which was even higher than the mean value of major rivers in the world such as the saint lawrence and the mississippi this high alkalinity was the result of carbonate dissolution enhanced by soil originated co2 as a result of this high inorganic carbon input the ratio of inorganic carbon and nutrients of the river water was higher than that of marine organic matter such as the redfield ratio making the coastal seas a potential source of co2 for the atmosphere

relative weathering intensity of calcite versus dolomite in carbonate bearing temperate zone watersheds carbonate geochemistry and fluxes from catchments within the st lawrence and danube river basins 1 calcite and dolomite solubilities in open weathering environments are proportional to pco2 and inversely proportional to temperature and dolomite solubility is progressively greater than calcite below 25 c the continent scale weathering budget reveals the significance of the northern hemisphere nh to globally integrated riverine fluxes of ca2 mg2 and hco3 the nh contributes 70 of the global hco3 flux while only 54 of the riverine discharge we present results of a comparative hydrogeochemical study of carbonate mineral equilibria and weathering fluxes in two nh carbonate rich river basins surface water geochemistry and discharge were determined for headwater streams in michigan and slovenia within the st lawrence and danube river basins michigan watersheds are established atop carbonate bearing glacial drift deposits derived from erosion of paleozoic strata with thick soil horizons 100 300 cm slovenia watersheds drain mesozoic bedrock carbonates in alpine and dinaric karst environments with thin soil horizons 0 70 cm carbonate weathering intensity is a parameter that normalizes river runoff and hco3 concentration to catchment area meq hco3 km 2 s 1 summing calcite and dolomite contributions and is used to gauge the effects of climate land use and soil thickness on organic inorganic carbon processing rates importantly michigan riverine discharge is one tenth of slovenian rivers providing the opportunity to evaluate the kinetics of carbonate mineral equilibration the study rivers are hco3 ca2 mg2 waters supersaturated for calcite at pco2 values in excess of the atmosphere as discharge varies hco3 concentrations differ by less than 20 for any location and mg2 ca2 remains relatively fixed for michigan 0 5 and slovenia streams 0 4 requiring that dolomite dissolution exceed calcite on a mole basis the ability of calcite and dolomite dissolution to keep pace with increased discharge indicates carbonate weathering is limited only by water flux and temperature dependent solubility in these watersheds carbonate weathering intensity in michigan and slovenia exceeds the world average by factors between 2 and 20 and dolomite weathering intensity estimated from riverine mg2 fluxes exceeds the world average by factors between 2 and 15 thus global fluxes of carbonate related weathering products appear heavily skewed toward carbonate bearing environments at higher latitudes with relatively low mean annual temperatures and high discharge

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

biological and geochemical controls on diel dissolved inorganic carbon cycling in a low order agricultural stream implications for reach scales and beyond abstract movement of dissolved inorganic carbon dic through the hydrologic cycle is an important component of global carbon budgets but there is considerable uncertainty about the controls of dic transmission from landscapes to streams and through river networks to the oceans in this study diel measurements of dic 13c dic dissolved oxygen o2 18o o2 alkalinity ph and other parameters were used to assess the relative magnitudes of biological and geochemical controls on dic cycling and flux in a nutrient rich net autotrophic stream rates of photosynthesis p respiration r groundwater discharge air water exchange of co2 and carbonate precipitation dissolution were quantified through a time stepping chemical isotope 12c and 13c 16o and 18o mass balance model groundwater was the major source of dic to the stream primary production and carbonate precipitation were equally important sinks for dic removed from the water column the stream was always super saturated with respect to carbonate minerals but carbonate precipitation occurred mainly during the day when p increased ph we estimated more than half possibly 90 of the carbonate precipitated during the day was retained in the reach under steady baseflow conditions the amount of dic removed from the overlying water through carbonate precipitation was similar to the amount of dic generated from r air water exchange of co2 was always from the stream to the atmosphere but was the smallest component of the dic budget overall the in stream dic reactions reduced the amount of co2 evasion and the downstream flux of groundwater derived dic by about half relative to a hypothetical scenario with groundwater discharge only other streams with similar characteristics are widely distributed in the major river basins of north america data from usgs water quality monitoring networks from the 1960s to the 1990s indicated that 40 of 652 stream monitoring stations in the contiguous usa were at or above the equilibrium saturation state for calcite and 77 of all stations exhibited apparent increases in saturation state from the 1960 70s to the 1980 90s diel processes including partially irreversible carbonate precipitation may affect net carbon fluxes from many such watersheds

sulfuric acid as an agent of carbonate weathering constrained by δ13cdic examples from southwest china abstract rock weathering by carbonic acid is thought to play an important role in the global carbon cycle because it can geologically sequestrate atmospheric co 2 current model of carbon cycle evolution usually assumes that carbonic acid is the major weathering agent and that other acids are not important here we use carbon isotopic evidence and water chemistry of springs and rivers from the beipanjiang river basin guizhou province southwest china to demonstrate that sulfuric acid is also an important agent of rock weathering the 13 c of dissolved inorganic carbon dic in the water samples ranges from 13 1 to 2 4 and correlates negatively to hco 3 ca 2 mg 2 ratios and positively to so 4 2 ca 2 mg 2 ratios these relationships are interpreted as mixing diagrams between two reactions of carbonate weathering using carbonic acid and sulfuric acid as a proton donor respectively mixing proportions show that around 42 of the divalent cations in the spring water from guizhou are originated from the interaction between carbonate minerals and sulfuric acid it is shown that 40 of this sulfuric acid is derived from the atmosphere and has an anthropogenic origin the remaining 60 are derived from the oxidative weathering of sulfide minerals in sedimentary rocks our results show the positive action of sulfuric acid on the chemical weathering of carbonate particularly we show that sulfuric acid generated by coal combustion has increased by almost 20 the weathering rates of carbonate in southwest china this is a clear evidence that human activities are changing the weathering rates of rocks and demonstrates a negative feedback on the acidification of the ocean by greenhouse gases because of the involvement of sulfuric acid in weathering reactions 63 of the alkalinity exported by rivers is derived from carbonate instead of 50 when atmospheric co 2 is the only acid involved in chemical weathering of carbonate in the guizhou province the weathering of carbonate is thus at least transiently a net source of co 2 to the atmosphere when extrapolated at global scale sulfuric acid induced carbonate weathering could counterbalance a significant part of the co 2 consumed by silicate weathering this paper highlights the competition between silicate weathering by carbonic acid and carbonate weathering by sulfuric acid for the regulation of the atmospheric co 2 level

contrasting compositions and textures of ilmenite in the catoca kimberlite angola and implications in exploration for diamond abstract the catoca group i kimberlite the only currently active diamond producing mine in angola was emplaced in the northeastern part of the lucapa structure we focus here on compositional and textural variations in ilmenite from drill core material in the hope of elucidating events before and during the emplacement of the kimberlitic magma we have characterized four main variants of ilmenite with enrichments in fe 3 mg mn and nearly stoichiometric ilmenite and in seven textural classes and have distinguished crystals of variable size ranging from micro to megacrysts most ilmenite is found to derive through a complex process from replacement of fe 3 rich ilmenite presumably originating by mantle metasomatism at a relatively high f o 2 this fe 3 rich ilmenite reacted with fluids under reducing conditions producing mg rich ilmenite the mn rich ilmenite is produced by interaction with a late co 2 rich fluid the mg rich ilmenite is here clearly a minor phase and a late product of replacement the absence of fresh mg rich ilmenite and the occurrence of fe 3 rich ilmenite do not seem to be convincing arguments to exclude the presence of diamond crystals in a kimberlite compositional attributes must thus be considered with caution and only in light of textural studies in exploration programs

dissolved inorganic carbon in the xijiang river concentration and stable isotopic composition dissolved inorganic carbon dic is one the major products of chemical weathering of the land and it is also one of the most active components in the riverine carbon species concentration and stable isotopic composition of dic in the mainstream of the xijiang river xjr and its two tributaries the guijiang and hejiang rivers were investigated during a hydrological year and a massive flooding dic concentration of most selected sections of the xjr system varied from 750 to 2 400 m with an average of 1 630 390 m dic was significantly diluted in the massive flooding period the stable isotopic composition of dic 13cdic varied from 14 75 to 8 25 with an average of 11 19 1 18 from 17 22 to 10 65 with an average of 13 00 1 86 and from 15 94 to 9 71 with an average of 12 68 1 28 in the mainstream of the xjr the guijiang river and the hejiang river respectively this is jointly determined by the outcrop area of carbonate rocks and the properties of soil organic carbon within the catchments 13cdic is less negative in the dry season because of the increasing contribution from karst groundwater and more negative in the wet season because of the increasing contribution from surface soil water calcite was saturated sometimes at the mainstream sections of the xjr carbonate sourced dic contributes 10 32 43 95 with an average of about 27 69 6 03 of the riverine dic for the xjr the xjr exports about 4 27 1012 g of dic in the surveyed year of which about 83 occurred in the wet season

factors controlling carbon isotope ratios of dissolved inorganic carbon in two major tributaries of the han river korea understanding the carbon cycle of the han river system in korea is of prime interest in managing and preserving this valuable water resource for more than 20 million residents in the area as a part of a comprehensive carbon cycling study for the han river system this report focuses on the carbon isotope compositions of dissolved inorganic carbon dic in its two major tributaries the north and the south han rivers the major difference in carbonate chemistry of the tributaries originates primarily from the lithology of the catchment areas the south han river draining a carbonate dominant terrain has much higher alkalinities and dic concentrations whereas the lower concentrations in the north han river indicate little influence of carbonate weathering likewise 13cdic values in the south han river indicate that the dic input from the carbonate rocks is important in controlling carbon isotope ratios of dic for the north han river the oxidation of organic material influences the amount of riverine dic and 13cdic values to a greater extent overall remarkable seasonal and spatial variations of river chemistry and carbon isotope compositions of dic reflect the variability in geo hydrologic characteristics in the water regime and in metabolic activities in the river water and or the drainage areas copyright 2006 john wiley sons ltd

the role of supergene sulphuric acid during weathering in small river catchments in low mountain ranges of central europe implications for calculating the atmospheric co2 budget abstract the geochemistry of dissolved and suspended loads in river catchments of two low mountain ranges in central europe allows comparison of pertinent chemical weathering rates distinct differences in lithology i e granites prevailing in the black forest compared to palaeozoic sediments in the rhenish massif provide the possibility to examine the influence of lithology on weathering here we determine the origin of river water using the stable isotope ratio 18oh2o and we quantify the geogenic proportions of sulphate from stable isotope ratios 34sso4 and 18oso4 particularly in catchments with abundant pyrite determination of the geogenic amount of sulphate is important since oxidation of pyrite leads to acidity which increases weathering our results show that spatially averaged silicate weathering rates are higher for the river catchments acher and gutach in the black forest 10 12 t km2 yr compared to the river catchments of the mohne dam and the aabach dam in the rhenish massif 2 6 t km2 yr correspondingly the co2 consumption by silicate weathering in the black forest 334 395 103 mol km2 yr is more than twice as high as in the rhenish massif 28 151 103 mol km2 yr these higher rates for watersheds of the black forest are likely due to steeper slopes leading to higher mechanical erosion with respective higher amounts of fresh unweathered rock particulates and due to the fact that the sediments in the rhenish massif have already passed through at least one erosion cycle carbonate weathering rates vary between 12 and 38 t km2 yr in the catchments of the rhenish massif the contribution of sulphuric acid to the silicate weathering is higher in the catchments of the rhenish massif 9 16 than in the catchments of the black forest 5 7 due to abundant pyrite in the sediments of the rhenish massif three times higher long term erosion rates derived from cosmogenic nuclides compared to short term erosion rates derived from river loads in central europe point to three times higher co2 consumption during the past 103 to 104 years

carbon flux and c s isotopic characteristics of river waters from a karstic and a granitic terrain in the yangtze river system abstract we analyzed dissolved major elements 13 c dic and 34 s so4 in river waters from a karstic and a granitic terrain to examine weathering processes and the influence of basin geology on water quality and associated riverine alkalinity transport results show that waters from the karstic terrain have higher total dissolved solids tds major ion concentrations and 13 c dic values but lower k na and si concentration and 34 s so4 values than that from the granitic terrain the compositions of major ions and isotopes indicate that the solutes of the granitic terrain are controlled by processes of silicate and carbonate dissolution by carbonic acid however carbonate dissolution by both carbonic and sulfuric acid are dominant processes in karstic terrain total erosion rates dissolved inorganic carbon dic flux and co 2 uptake were 28 0 t km 2 yr 1 2 9 10 5 mol km 2 yr 1 and 2 3 10 5 mol km 2 yr 1 for the granitic terrain and 70 2 t km 2 yr 1 11 9 10 5 mol km 2 yr 1 and 6 4 10 5 mol km 2 yr 1 for the karstic terrain respectively these results indicated the karstic area plays an important role in uptake of co 2 and dic flux along the yangzte river basin our results also revealed that co 2 uptake due to carbonate chemical weathering in both karstic and granitic terrain is very high and provide as much or more dic flux than that from silicate chemical weathering

inorganic carbon isotope systematics in soil profiles undergoing silicate and carbonate weathering southern michigan usa abstract the upper midwest usa features glacial derived till materials enriched in carbonate minerals but with the uppermost soil layer progressively leached of carbonates in the interval since glaciation groundwaters and groundwater fed surface waters are profoundly influenced by carbonate mineral dissolution stable carbon isotope compositions of soil waters and groundwaters in two southern michigan watersheds huron and kalamazoo were studied as a function of ph 13cco2 types of weathering reactions silicate vs carbonate and degree of isotope equilibration this comprehensive study of carbon isotope biogeochemistry in the vadose zone including soil gas soil water groundwater and soils organic matter carbonate phases elucidates relations between the chemical weathering rates and co2 fluxes in the soil zone such information is important to evaluate responses of terrestrial ecosystems to global climate change in shallow soil zones where only silicate weathering was occurring respiratory co2 was the major source of soil water dic with little addition from the atmospheric co2 isotopic equilibration between 13cdic and 13cco2 occurred in an open system with respect to soil co2 in the deeper soil horizons carbonate dissolution dominated soil water chemistry and saturation with respect to calcite and dolomite was attained rapidly mass balance calculation showed that large amounts of soil co2 were consumed by carbonate dissolution such that the deeper soil zone may not have been an open system with respect to co2 constant 13cdic values 11 were observed in these deep soil waters and also in shallow groundwaters of the huron watershed thus isotopic equilibrium might not be reached between dic and co2 possibly due to a rapid kinetics of carbonate dissolution and limited gas water exchange in the soils if so dic was equally contributed by carbonate minerals 13ccaco3 0 in reaction with soil co2 13cco2 22 soils beneath an agricultural site with a wheat corn soybean rotation the kalamazoo watershed displayed a wide range in 13cco2 values 22 to 12 and the 13cdic of deeper soil waters in contact with carbonate minerals was controlled by seasonal variations of 13cco2 as well as by strong acids produced by nitrification and to a lesser degree by pyrite oxidation both of which could react to dissolve carbonate minerals in addition to carbonic acid dissolution

contributions of c3 c4 organic materials and carbonate rock to dissolved inorganic carbon in a karst groundwater system on miyakojima island southwestern japan summary groundwater 13 c values and chemical compositions were employed to quantitatively evaluate the controlling processes and sources of dissolved inorganic carbon in a karst aquifer system on miyakojima island mi southwestern japan most mi groundwater is ca hco 3 type water but some na cl ca cl or na hco 3 type groundwaters occur formed mainly by seawater intrusion and partly by cation exchange reactions calculations using the wateq4f and phreeqc programs revealed that all mi groundwater not just the ca hco 3 type was strongly influenced by calcite dissolution in a karst aquifer system open with respect to soil co 2 initially derived from organic materials with mainly around 10 50 matm as pco 2 and that most groundwater was saturated with respect to calcite moreover oxidation of ammonium sulfate applied as fertilizer added h to the mi groundwater resulting in surplus calcite dissolution these processes sufficiently explained contents of alkalinity dic and ca 2 in the groundwater and were evaluated by model calculation using the phreeqc program with measured groundwater 13 c and ph values the results showed that the average mass fractions of dissolved inorganic carbon dic initially from calcite dissolution and c3 and c4 organic materials in the groundwater were 46 4 18 5 and 35 1 respectively the model results regarding the origins of dic in the groundwater agreed fairly well with land use distributions on mi in particular with the spatial distribution of forest and sugarcane fields and gave us some constrains of groundwater recharge areas and flowpaths

inorganic carbon dynamics and co2 flux associated with coal mine drainage sites in blythedale pa and lambert wv usa drainage from coal mines where carbonate dissolution is driven by sulfuric acid can result in a net transfer of geologically bound carbon to the atmosphere the flux and downstream evolution of dissolved inorganic carbon dic is presented for two coal mine sites that discharge high concentrations of dic 3 7 4 5 mm c producing a total flux of dic from the mine from 13 to 249 kg c year 18 364 metric tons of co2 year more than 65 of the total dic is lost via co2 evasion with the remaining dic is exported downstream as dissolved species the fate of the dic depends upon the ph of the water which is controlled by evasion of co2 the concentration of pre existing alkalinity carbonate precipitation and dissolution and metal hydrolysis reactions the co2 concentrations and fluxes from the study sites are comparable to those estimated from literature data for other coal mine sites in the appalachian region the total flux estimated from a dataset of 140 coal mines was comparable in magnitude to the co2 emissions from a small coal fired power plant the extent of co2 degassing from mine waters is poorly constrained because 1 flux estimates can be biased low when acid waters are excluded in alkalinity based estimates 2 flux estimates can be biased high if non carbonate alkalinity is present in the mine waters and 3 mine waters react rapidly following discharge hampering the measurement process the study sites presented illustrate the impact of coal mining as an anthropogenic influence on carbon cycling however more data are necessary to fully estimate the importance of this impact on regional scales

geochemistry of the brachiopod hemithiris psittacea from the canadian arctic implications for high latitude palaeoclimate studies abstract fossil shell material from high palaeo latitudes is increasingly studied for environmental forcings specific to these latitudes and as sensitive archives of climate change however more detailed studies of modern analogues are necessary for putting findings into global and high latitude perspectives here we present 13 c and 18 o values as well as mg sr na mn and fe contents for the rhynchonellide brachiopod hemithiris psittacea from friday harbor u s a and twenty five sites from canada ranging in latitude from 48 to 71 n median mn ca ratios are below 0 1 mmol mol and fe ca ratios are below 0 3 mmol mol with no strong correlation between ratios and no apparent geographical relationship mg ca and sr ca ratios vary within relatively narrow limits and yield median ratios of 3 7 mmol mol and 1 13 mmol mol na ca ratios vary widely amongst the sites with median values ranging from 9 to 20 mmol mol relatively uniform median 13 c values of 1 8 0 6 2 sd n 25 are observed for the canadian sites whereas at friday harbor the signature of 13 c depletion in local dic is imprinted in the shell calcite median 18 o values of 0 5 to 2 7 are more variable than carbon isotope signatures and point to precipitation of shell material in seawater diluted by variable amounts of freshwater and affected by seasonal sea ice our results imply that robust elemental patterns and carbon isotope signatures of high latitude brachiopod fossils can be expected for most palaeogeographic situations in contrast 18 o signatures of shell material from high latitude marginal seas particularly during glacial periods would yield unreasonably high seawater temperature estimates unless the oxygen isotopic composition of the ambient water is accurately accounted for in palaeotemperature calculations

isotopic composition of dissolved inorganic carbon in a large polluted river the vistula poland abstract the vistula is a large lowland temperate river receiving high loads of pollutants from a densely populated catchment on the other hand the river is to a relatively small extent affected by channelisation and damming this study is the first attempt to characterise stable isotope aspects of dissolved inorganic carbon in the vistula which is a major source of pollution to the baltic sea isotopic composition of dic and other chemical properties were measured biweekly at the upper reach and monthly at the mouth of the river two longitudinal samplings were performed in hydrological summer and winter conditions short term and short range observations were carried out in an anthropogenically influenced urban reach at cracow most water samples from the vistula and its tributaries analysed in this study had 13 c dic values around the range 12 to 11 typical for european lowland rivers fed by groundwaters on carbonate areas variablity of 13 c dic in this river system is limited except for the impoundments and the specific hydrological conditions the few impoundments that exist on the vistula intensify the photosynthesis respiration cycle as well as the exchange of co 2 with the atmosphere enhanced contribution of biogenic carbon during floods is reflected by lowering of 13 c dic low flows facilitate photosynthetic assimilation and evasion of co 2 into the atmosphere resulting in positive shifts of 13 c dic principal component analysis confirmed that 13 c dic variability at the fixed cross section in cracow reflected releases and withdrawals of co 2 from the riverine dic pool the apparent 13 c dic variability depends to some extent on the spatio temporal context of observations diurnality can be very pronounced in the impounded anthropogenically influenced reaches in warm periods interpretation of the observed riverine 13 c dic patterns can be difficult as the spatial and temporal variabilities combine resulting in convoluted isotopic signals isotopic investigations into the nature of riverine carbon cycling should be supplemented by discharge records and by observations of the parameters influenced by the photosynthesis respiration cycle dissolved oxygen ph p co 2 and of those conservative with respect to biological processes electrical conductivity stable isotope composition of water

kinetic isotopic fractionation during carbonate dissolution in laboratory experiments implications for detection of microbial co2 signatures using δ13c dic laboratory experiments on reagent grade calcium carbonate and carbonate rich glacial sediments demonstrate previously unreported kinetic fractionation of carbon isotopes during the initial hydrolysis and early stages of carbonate dissolution driven by atmospheric co2 there is preferential dissolution of ca 12 co3 during hydrolysis resulting in 13 c dic values that are significantly lighter isotopically than the bulk carbonate the fractionation factor for this kinetic isotopic effect is defined as carb carb is greater on average for glacial sediments 17 4 than for calcium carbonate 7 8 for the 63 m size fraction a sediment concentration o f5gl 1 and closed system conditions at 5 c this difference is most likely due to the preferential dissolution of highly reactive ultra fine particles with damaged surfaces that are common in subglacial sediments the kinetic isotopic fractionation has a greater impact on 13 c dic at higher caco3 water ratios and is significant during at least the firs t6ho fcarbonate dissolution driven by atmospheric co2 at sediment concentrations o f5gl 1 atmospheric co2 dissolving into solution following carbonate hydrolysis does not exhibit any significant equilibrium isotopic fractionation for at least 6 h after the start of the experiment at 5 c this is considerably longer than previously reported in the literature thus kinetic fractionation processes will likely dominate the 13 c dic signal in natural environments where rock water contact times are short 6 24 h e g glacial systems headwaters in fluvial catchments and there is an excess of carbonate in the sediments it will be difficult apply conventional isotope mass balance techniques in these types of environment to identify microbial co2 signatures in dic from 13 c dic data copyright 2004

recent and historical discharge of a large european river system oxygen isotopic composition of river water and skeletal aragonite of unionidae in the rhine abstract seasonal variations in the oxygen isotopic composition of rhine river water were analyzed in detail and compared with the oxygen isotopic record from recent and historical specimens of freshwater bivalves unionidae the purpose of this study was to investigate the potential use of these aragonitic bivalves as proxy recorders for varying amounts and sources of discharge and thereby infer climate change seasonal variations in the river water 18 o are on the order of 1 2 during summer alpine melt water contributes significantly to the total discharge resulting in average values of 10 to 10 5 whereas the non alpine contribution is higher during winter as indicated by mean 18 o values of 8 5 to 9 the basic pattern of the modern seasonal variation of 18 o of river water can be described by a numerical mass balance approximation of the various contributions from the alpine and non alpine catchments with their average 18 o composition the 18 o of growth increments in the prismatic shell layer of anodonta corresponds perfectly to what is predicted by known fractionation of 18 o between water and aragonite shell growth is restricted to water temperatures above 8 10 c so variations in 18 o and the river water temperature are faithfully recorded by relatively large growth increments during summer the distinctive isotopic signatures of individual flood events during summer and autumn are also recorded in the shells

seasonal changes in the sources and fluxes of dissolved inorganic carbon through the st lawrence river isotopic and chemical constraint the st lawrence river ranks 16 th in the world rivers for its freshwater discharge into the ocean but its particulate fluxes are relatively low due the upstream presence of the great lakes system using notably 13 c measurements in total dissolved inorganic carbon dic at several stations along stream earlier studies provided information on dissolved inorganic carbon dic fluxes through the st lawrence with some constraints on spatial trends with respect to the in situ dic metabolism here we further document annual dic fluxes and seasonal changes in dic supplies and dic metabolism downstream chemical and isotopic measurements were performed in 1998 on a biweekly basis at four different sites these sites represent respectively the great lakes outflow into the st lawrence system supplies from two tributaries one with a silicate rich precambrian bedrock the other with a carbonate rich paleozoic bedrock and the st lawrence outflow into the maritime estuarine system the 1998 survey yielded a total annual dic flux of 6 10 12 to 7 10 12 g of carbon at the quebec city outlet about 40 higher than estimates from earlier studies this represents about 1 5 of the world river dic supplies to the ocean very strong seasonal variations are observed between the summer low water levels when water supplies from the great lakes into the riverine system may represent up to 80 of the total outflow of the st lawrence river and the spring snowmelt period when tributaries may provide up to 80 of this outflow d 13 c dic values respond to this seasonal cycle with near isotopic equilibrium values with atmospheric co2 during summer and strongly depleted values in other seasons notably during the spring high outflow period this seasonal isotopic cycle is more pronounced at the quebec city outlet where the influence of 13 c depleted dic supplies from tributaries is stronger than upstream the low d 13 c dic values observed from fall to spring may be due to a combination of the following factors i enhanced supplies of 13 c depeleted dic from soils and ground waters from watersheds ii higher oxidation rates of dissolved or particulate 13 c depleted organic carbon and iii a reduced incidence of the in situ photosynthetic activity the outflow and isotopic seasonal cycles result notably in a strong negative correlation between d 13 c dic values and discharge rates estimates of dic supplies from tributaries vs those from the great lakes were calculated using either chemical or isotopic approaches dic supplies from tributaries vary between 5 and 60 of total dic examination of pco2 data indicates a negligible seasonal variability at the great lakes outlet with a mean annual value near equilibrium with atmospheric co2 i n contrast strong seasonal changes are observed downstream at quebec city with minimum pco2 values in summer and a mean

the contribution of agricultural and urban activities to inorganic carbon fluxes within temperate watersheds abstract the lateral transport of bicarbonate as dissolved inorganic carbon dic to the oceans is an integral component of the global carbon budget and can represent the sequestration of co 2 from the atmosphere recently studies have implicated land use change in particular agricultural development as an accelerator of bicarbonate export however due to the co variation of land use bedrock and surficial geologies and the relationship between bicarbonate export and climate the impact of anthropogenic activities on dic export remains an important research question in order to examine the land use controls on dic export from small temperate watersheds we sampled 19 streams draining catchments of varying land uses with similar bedrock and surficial geologies in addition to an agricultural effect there was a strong correlation between the percent of watershed in urban development and dic concentrations and dic yields urban watersheds exported 7 8 times more dic than their nearby forested counterparts and 2 0 times more dic than nearby agricultural catchments isotopic data suggest that excess dic export from altered systems results from increased chemical weathering enhanced co 2 production within urban green spaces and as a result of organic matter loading from septic systems and leaky sewer lines furthermore we found that nitrogen additions e g fertilizers and manure are aiding in the dissolution of lime increasing the total export of dic from agricultural watersheds calculated anthropogenic loading rates ranged from 0 43 to 0 86 mol c m 2 yr 1 these loading rates suggest that a significant portion of global dic export might be attributable to human activities although the impacts on co 2 sequestration are difficult to determine

influence of carbonates on the riverine carbon cycle in an anthropogenically dominated catchment basin evidence from major elements and stable carbon isotopes in the lagan river n ireland abstract investigation of anthropogenic versus natural controls of the carbon cycle in the lagan river revealed a strong influence of carbonates this was evident by increasing ph values along the river as well as isotopic compositions of the riverine dissolved inorganic carbon 13cdic that approached expected values for carbonate dissolution this predominant influence of carbonates existed despite their minor abundance of only 5 in this densely populated catchment basin and outlines their capacity of buffering anthropogenic influences and co2 turnover these effects should be even more pronounced in other rivers where carbonates occupy a larger proportion of the catchment basin geology other controls on the riverine carbon cycle were silicate weathering and respiratory turnover of organic material that originated mainly from anthropogenic inputs and increased the dic pool by up to 26 6 predominant natural controls on the lagan river carbon cycle changed to anthropogenic ones closer to the mouth before discharging into belfast lough a recently installed weir caused stagnant seawater to make up between 53 and 92 of the water mass poor vertical mixing caused o2 decreases and anaerobic sedimentary activity that resulted in methane production recently installed aerators at the sediment surface did not prevent ongoing methanogenesis this was documented by decreased pco2 and more 13c enriched dic values at the sediment water interface when compared to those of surface waters from the same sampling sites installations of such weirs in estuaries of other rivers may cause similar anoxic effects that influence their biogeochemistry

carbon 14 in streams as a tracer of discharging groundwater summary quantification of the volume of groundwater discharge to streams and the source aquifer of that discharge is required to adequately manage the impacts of groundwater use on stream ecosystems this has been achieved through longitudinal surveys of gaseous tracers but their effectiveness can be limited by rapid equilibration between the stream and the atmosphere here we develop the use of carbon 14 in dissolved inorganic carbon dic in a stream as a tracer of groundwater discharge a controlled equilibration experiment was conducted during which groundwater with an initial 14c activity of 5 5 pmc was allowed to equilibrate with the atmosphere over 72 days the effective transfer velocity for 14c was measured as 0 013 m d 1 the method was then tested at an artificial groundwater discharge location where the effective transfer velocity was measured as 0 025 m d 1 in these simple systems the ratio of the effective 14c transfer velocity to the co2 gas transfer velocity is a function of ph and proportional to the fraction of dic present as co2 the method was then applied along a reach of the daly river australia where groundwater discharge is known to occur a decrease of 7 pmc was observed across the major spring discharge zone with subsequent equilibration with the atmosphere occurring over at least tens of kilometres this allowed for the effective transfer velocity to be estimated at between 0 09 and 0 15 m d 1 and for the 14c activity of groundwater discharge to be estimated at between 60 and 66 pmc the equilibration of 14c in stream dic is in the order of 10 times slower than for gas tracers which may allow for the detection of smaller groundwater discharge fluxes than is possible with gas tracers if the total groundwater discharge flux is known measurements of 14c in stream dic can also be used to infer the 14c activity of discharging groundwater this method may be a useful alternative to direct groundwater sampling particularly in remote basins with few groundwater wells

the carbonate system geochemistry of shallow groundwater surface water systems in temperate glaciated watersheds michigan usa significance of open system dolomite weathering we present here a field geochemical study of controls on carbonate weathering within rapidly circulating shallow groundwater surface water systems in the glaciated mid continent region groundwaters and surface waters in three watersheds spanning the upper to lower peninsulas of michigan consist of ca 2 mg 2 hco 3 solutions derived from the open system dissolution of calcite and dolomite in soils developed on mixed mineralogy glacial drift the thermodynamic stabilities of calcite and dolomite both decrease with decreasing temperature with dolomite more strongly affected thus the low mean annual temperature of these temperate weathering environments maximizes the absolute solubility of dolomite as well as its solubility relative to calcite many groundwaters in the study area approach equilibrium with respect to the more soluble dolomite and are moderately supersaturated with respect to calcite groundwaters in each watershed have distinct and relatively narrow ranges of carbon dioxide partial pressure p co 2 values which increase significantly from north to south log p co 2 of 3 0 to 2 2 atm suggesting that there are landscape level differences in carbon transformation rates in soil weathering zones increases in weathering zone p co 2 values produce hco 3 concentrations that vary by a factor of five but the mg 2 ca 2 and mg 2 hco 3 ratios of all groundwaters are similar suggesting relatively constant weathering input ratios of calcite and dolomite although surface waters commonly are between 2 and 10 times supersaturated with respect to calcite the mg 2 hco 3 ratios of surface waters are very close to initial groundwater values suggesting that back precipitation of calcite is not a significant process in these systems the enhanced solubility of dolomite at low temperatures coupled with the landscape level differences in carbon cycling suggest that temperate zone weathering reactions in glaciated terrains are significant contributors to continent scale fluxes of both mg 2 and hco 3

the origins and behaviour of carbon in a major semi arid river the murray river australia as constrained by carbon isotopes and hydrochemistry abstract 13 c values of dissolved inorganic c dic dissolved organic c doc and particulate organic c poc together with 18 o and 2 h values of water 34 s values of dissolved so 4 and major ion concentrations were measured in the murray river and its tributaries between november 2005 and april 2007 to constrain the origins and behaviour of riverine c 13 c dic values in the murray river vary between 9 5 and 4 7 with a range of 13 c dic values of the tributaries are 11 0 to 5 1 dic concentrations of the murray river increase from 25 mg l in the middle and upper reaches of the river to 45 55 mg l in the lower reaches however the mass ratio of dic as a proportion of the total dissolved solids tds decreases from 0 6 0 7 in the headwaters to 0 2 0 3 in the lower reaches of the river with similar downstream changes in dic cl ratios this precludes simple evaporative concentration of dic and is interpreted as the river evading co 2 this interpretation is consistent with p co 2 values that are in the range 550 11 200 ppm volume ppmv which are far higher than those in equilibrium with the atmosphere 360 ppmv the 13 c dic values are similar to those that would be produced by the weathering of marine limestone 13 c 0 however the lack of marine limestones cropping out in the murray darling basin and the relatively uniform 13 c dic values of the murray river even in upland reaches where the dominant rock types are metamorphosed silicates and granites make this unlikely rather the high p co 2 values and 13 c dic values are best explained by a combination of mineralisation of low 13 c organic c and evasion to the atmosphere the rate of these two processes may attain near steady state and control both dic concentrations and 13 c values

unusually heavy stable mo isotope signatures of the ottawa river causes and implications for global riverine mo fluxes abstract the accurate use of mo isotope mass balance modelling of ancient oceans relies on the assumption that the 98mo of modern riverine inputs represents a reasonable estimate of the past a growing number of studies of global rivers have demonstrated significant variation in 98mo from the bedrock sources of mo the ottawa river canada was previously identified as having an anomalously heavy mo isotope composition with a 98mo signature close to seawater 2 3 for a seemingly pristine natural river to further explore this unusual signature we collected and filtered 29 water samples from the ottawa river tributaries and small lakes and analysed them for mo isotopes as well as major and trace elements here we fully document heavy 98mo signatures throughout the ottawa river and its absence in surrounding areas of the wider ottawa river basin orb our results reveal a progressive upstream increase in both mo concentration and 98mo signatures in the ottawa river towards values even heavier than seawater up to 3 13 the heaviest mo isotopic signature of river water measured to date in contrast the tributaries and lakes display far lighter and more consistent 98mo signatures within the range previously found in other rivers weathering of an isotopically heavy bedrock source fractionation during weathering and retention of light isotopes in soils have all been proposed as sources of heavy 98mo in rivers however none of these mechanisms can satisfactorily explain our new observations colloidal and particulate processes that remove elements downstream as inferred from some trace element proxies also cannot explain the decreasing 98mo since the preferential removal of light mo isotopes is predicted from these processes similarly the downstream trends show no apparent relationships with constructed dams or known potential industrial sources therefore our findings from the ottawa river are best explained as the dilution of a yet unidentified point source of heavy mo upstream of sampling or a significant permanent sink for light isotopes existing only in the upper reaches of the catchment in both cases anthropogenic contribution from a large mining district in the headwaters of the river must be considered and should be explored further fractionation of mo in waste rock storage facilities have been previously identified and may provide an unnatural sink for isotopically light mo through the rayleigh type fractionation of dissolved mo on oxyhydr oxide mineral surfaces the implied anthropogenic alteration of the natural mo cycle highlights the significant and wide reaching effects of unnatural point sources of mo on the cumulative 98mo signatures of the catchment and emphasises the necessity for detailed geochemical screening of anomalous river water isotope signatures before natural isotope compositions are inferred

carbon fluxes pco2 and substrate weathering in a large northern river basin canada carbon isotope perspectives abstract isotopic composition of dissolved inorganic carbon 13 c dic in the ottawa river basin is about 8 and 16 for lowland carbonate and upland silicate tributaries respectively this suggests that 1 the source of dic to the ottawa river is soil respiration and carbonate weathering 2 exchange with the atmosphere is unidirectional or volumetrically unimportant and 3 in river respiration and photosynthesis are not significant influences on the river carbon budget accepting these constraints chemical and isotopic data are used to reconstitute soil pco2 for tributary catchments averages for upland silicate mixed and lowland carbonate basins are calculated to be roughly 2000 5000 and 30 000 ppm respectively these values are used as input to model the pathway of carbon through the watershed rain water to soil water to river water the flux of carbon from the ottawa river as dic is calculated to be 4 3 1010 mol c a utilizing carbon isotopes 75 and 25 of the ca2 mg2 flux is calculated to originate from carbonate and silicate weathering respectively and 61 of the dic is calculated to originate from organic respiration the latter represents some 6 of respired carbon in the basin assuming an average respiration rate of 0 5 mmol c m 2 h 1 based on a diffusion model co2 evasion to the atmosphere from the ottawa river and its tributaries is estimated to be 1 3 1010 mol c a or 30 of the dic flux

chemical dynamics of the st lawrence riverine system δdh2o δ18oh2o δ13cdic δ34ssulfate and dissolved 87sr 86sr chemical and stable isotope analyses of the st clair detroit niagara and st lawrence rivers st lawrence system and their tributaries show that the chemical and isotopic compositions of the waters are strongly controlled by the geology of their drainage basins tributaries draining the canadian shield have very low tds hco3 so42 ca2 mg2 no3 sr2 higher si and fetotal and high 87sr 86sr ratios 0 710 0 713 the grand and thames rivers that drain paleozoic limestones dolostones and evaporites are characterized by opposite attributes the st lawrence and the tributaries draining the canadian appalachians fall between these two endmembers the st clair detroit and niagara rivers do not show any pronounced seasonal variations in major component chemistry due to buffering by the great lakes in contrast pronounced seasonal variations characterize the lower st lawrence mainly because of significant tributary inputs into the overall water budget the d and 18o in the st lawrence range from 60 9 to 44 5 and from 8 5 to 6 1 smow respectively much heavier than the comparative values measured for the tributaries 92 8 to 58 3 and 13 1 to 8 5 this is a consequence of evaporative loss that over the residence time of water of 102 years equals about 7 of the water volume in the great lakes the strontium and sulfur isotopic values for the st lawrence system are relatively uniform with measured values from 0 70927 to 0 71112 for 87sr 86sr and from 4 3 to 5 6 for sulfate 34s their seasonal variations are also minor the strontium and sulfur fluxes of the st lawrence river are calculated to be 7 84 108 and 1 09 1011 mol a respectively the relative contributions of the great lakes tributaries and other sources to these fluxes are 73 16 11 for strontium and 64 13 23 for sulfur isotopic composition of dissolved inorganic carbon 13cdic in the st lawrence system ranges from 4 7 to 0 7 considerably heavier than the values for the tributaries 16 5 to 6 7 the light 13cdic values for the tributaries suggest that co2 from bacterial respiration plays an important role in the isotopic composition of riverine dic however in the main stem river s this bacterial signal is masked by isotopic equilibration with atmospheric co2 due to the long residence time of water in the great lakes seasonally the main stem river s have heavier 13c values in the fall than in the spring a consequence of preferential 12c consumption by photosynthetic plants in the epilimnion of the great lakes during the growth season in the down stream portion of the st lawrence river influx of isotopically light tributary waters causes progressive 13c depletion from 1 3 to 2 0 and 1 4 to 3 0 in the fall and spring respectively the total dic carbon flux of the st lawrence river is calculated to be 3 9 1011 mol a mass balance calculations show that the relative contributions of the great lakes tributaries decay of organic matter exchange with the atmosphere and dissolution of carbonates to this total dic flux are 81 13 2 6 10 in the spring and 83 15 2 4 0 in the fall respectively

the co2 consumption potential during gray shale weathering insights from the evolution of carbon isotopes in the susquehanna shale hills critical zone observatory abstract shale covers about 25 of the land surface and is therefore an important rock type that consumes co 2 during weathering we evaluated the potential of gray shale to take up co 2 from the atmosphere by investigating the evolution of dissolved inorganic carbon dic concentrations and its carbon isotopic ratio 13 c dic along water flow paths in a well characterized critical zone observatory susquehanna shale hills catchment in this catchment chemical weathering in shallow soils is dominated by clay transformation as no carbonates are present and soil pore waters are characterized by low dic and ph in shallow soil porewaters the dic dominated by dissolved co 2 is in chemical and isotopic equilibrium with co 2 in the soil atmosphere where pco 2 varies seasonally to as high as 40 times that of the atmosphere the degradation of ancient organic matter is negligible in contributing to soil co 2 the chemistry of groundwater varies along different flowpaths as soil pore water recharges to the water table and then dissolves ankerite or secondary calcite under the valley floor weathering of carbonate leads to much higher concentrations of dic 2500 mol l and divalent cations ca 2 and mg 2 in groundwaters than soil waters the depth to the ankerite weathering front is hypothesized to be roughly coincident with the water table but it varies due to heterogeneities in the protolith composition groundwater chemistry therefore shows different saturation indices with respect to ankerite depending upon location along the valley the 13 c dic values of these groundwaters document mixing between the ankerite and soil co 2 the major element concentrations dic and 13 c dic in the first order stream incising the valley of the catchment are derived from groundwater and soil waters in proportions that vary both spatially and temporally the co 2 degassed slightly in the stream but little evidence of c isotopic equilibration with the atmosphere is observed due to the short length of the stream and short contact time with air the ankerite reaction front also lies close to the pyrite dissolution front pyrite oxidation in bedrock likely released sulfuric acid and played a minor role in the ankerite dissolution shifting groundwater 13 c dic slightly above the expected mixing values at the catchment scale the stream so 4 2 is also dominantly derived from wet deposition as stream has 34 s so4 values around 3 well within the range of acid deposition a mass balance calculation shows that silicate and ankerite dissolution of the rose hill shale at shale hills consumes co 2 at a rate of 44 and 42 48 mol m 2 ky 1 respectively while degradation of ancient organic matter releases co 2 at a rate of 1 3 mol m 2 ky 1 silicate dissolution at the shallow soils is facilitated by low ph and high soil pco 2 as ankerite dissolution and organic matter oxidation are shown to occur early during shale alteration co 2 consumption by shale weathering is thus limited by initiation of rock disintegration e g fractures and exposure of fresh surface area to infiltrating co 2 and o 2 rich water

what controls the spatial patterns of the riverine carbonate system a case study for north america abstract in this study we analyzed the large scale spatial patterns of river ph alkalinity and co2 partial pressure pco2 in north america and their relation to river catchment properties the goal was to set up empirical equations which can predict these hydrochemical properties for non monitored river stretches from geodata of e g terrain attributes lithology soils land cover and climate for an extensive dataset of 1120 river water sampling locations average values of river water ph alkalinity and pco2 were calculated the catchment boundaries and catchment properties were calculated using gis and different sets of geodata the correlations between the hydrochemical properties and the catchment properties were explored using simple and multiple linear regression analysis for each of the considered hydrochemical parameters a multiple regression equation was fitted for ph with the predictor s mean annual precipitation and areal proportions of carbonate rocks r2 0 60 for alkalinity in addition to these two predictors with subsoil ph and areal proportions agricultural lands r2 0 66 and for ppco2 i e the negative logarithm of pco2 with mean air temperature mean catchment slope gradient and mean annual precipitation r2 0 43 based on these results we argue that spatial patterns in river water ph and alkalinity are governed by catchment processes related to chemical rock weathering for the pco2 on the other hand the spatial patterns are governed by in river processes on which catchment properties can have an indirect effect we conclude that our approach can be used to predict averages of these parameters for non monitored river stretches which in turn allows for a better spatially explicit representation of the rivers carbonate system at the regional to global scale which will be needed for a refined analysis of rivers in the global carbon cycle

controls on the δ13cdic and alkalinity budget of a flashy subtropical stream manoa river hawaii abstract hawaiian streams are flashy in nature because watersheds are small and steep and receive intense and unevenly distributed rainfall as a result stream chemistry is characterized by considerable spatiotemporal variability to examine how rainfall and streamflow affect the solute content of the manoa river in hawaii time series geochemical data collected during 17 sampling campaigns in spring fall of 2010 were evaluated in a coupled 13 c dic major ion inversion model spatially the stream is characterized by a distinct shift from a low hco 3 43 mg l low pco 2 3760 ppmv and heavy 13 c dic 6 5 fingerprint in the upper reaches to a high hco 3 91 mg l high pco 2 8961 ppmv and light 13 c dic 11 7 signature in the lowlands these trends are attributed to 1 progressive weathering of exposed aluminosilicates and 2 downstream enrichment in co 2 from organic matter decay in the soil zone solute i e nitrate yields from nitric acid weathering are generally low 13 c dic and rainfall rates in the mid stream section of the river which is consistent with an atmospheric co 2 dilution effect during high rainfall events this dilution effect needs to be accounted for to reliably describe the role of volcanic island river systems in global assessments of silicate weathering and co 2 degassing

transport of dissolved carbon and co2 degassing from a river system in a mixed silicate and carbonate catchment summary assessing the origin transformation and transport of terrestrially derived carbon in river systems is critical to regional and global carbon cycles particularly in carbonate terrains which represent the largest carbon reservoir on the earth s surface for this reason we evaluated sources cycling and fluxes of dissolved organic and inorganic carbon doc and dic and riverine co 2 degassing to the atmosphere in the santa fe river in north central florida a sub tropical river that flows across two distinct hydrogeological settings of a region dominated by carbonate karst one setting occurs in the upper river catchment where the carbonate floridan aquifer is confined by the siliciclastic hawthorn group while the other setting occurs in the lower catchment where the river flows across the unconfined floridan aquifer the upper catchment is characterized by doc rich and dic poor water and the dic has more variable and lower 13 c values compared to the lower catchment the river in the upper catchment degasses more co 2 to the atmosphere 1156 g c m 2 yr 1 than in the lower catchment 402 g c m 2 yr 1 because soil respired carbon and organic matter decomposition increase dissolved co 2 concentration much of which is consumed during carbonate dissolution reactions in the lower catchment the co 2 flux from the water surface to the atmosphere during a flood event is three times greater than during base flow suggesting that excess precipitation flushes soil organic carbon to the river through interflow and enhances the loss of terrestrial carbon via river water to the atmosphere our values of co 2 fluxes to the atmosphere lie within the range of fluxes from the world s rivers but fluxes from the carbonate dominated region are at the low end while fluxes from the siliciclastic region are at the high end these results indicate that catchment lithologies particularly whether carbonate or siliciclastic as well as flow are critical to carbon budgets in rivers and thus are linked to the global carbon cycle

terrestrial and fluvial carbon fluxes in a tropical watershed nyong basin cameroon abstract the nyong watershed with an area of 27 800 km2 and a mean annual discharge of 390 m3 s 1 is the second largest river in cameroon the nyong watershed serves as an outstanding study area for the examination of carbon fluxes in humid tropical environments because of its limited anthropogenic impact and homogeneous silicate bedrock between april 2005 and april 2007 we sampled water at seven stations from the small watershed of the mengong 0 6 km2 to the nyong at edea 24 500 km2 and monitored temperature ph dissolved inorganic carbon dic and dissolved organic carbon doc contents as well as the isotopic composition of dic 13cdic and doc 13cdoc we estimated terrestrial net ecosystem productivity in the nyong river watershed and measured fluvial fluxes of carbon to the ocean and the atmosphere the nyong river basin sequesters significant amounts of carbon on an annual basis 7 920 000 t c year 1 300 g c m 2 year 1 the combined dissolved organic dissolved inorganic and atmospheric fluxes of carbon from the nyong river only export 3 of this flux from the basin on an annual basis this includes a minimum co2 outgassing of 1487 g c m 2 year 1 comparable to 115 of the annual flux of doc and four times greater than the flux of dic

co2 evasion from the greenland ice sheet a new carbon climate feedback abstract decay of the greenland ice sheet gis figures prominently in climate change predictions but direct carbon cycle feedbacks are poorly constrained here we show that melting of the gis yields a previously unknown flux of co 2 to the atmosphere and we use a reactive transport model to examine if how and to what extent this flux will change as the ice sheet decays in a warmer world water emerges from beneath the isunnguata and russell glaciers in west greenland with co 2 partial pressures pco 2 3 10 supersaturated with respect to atmospheric equilibrium during downstream transport in the akuliarusiarsuup kuua river mineral weathering sequesters 75 of the excess co 2 as hco 3 a carbon sink on human timescales and the remaining 25 evades to the atmosphere scaled to all rivers draining the gis the evasion flux of 0 11 0 03 tg c year compares to fluxes reported for other rivers draining precambrian shield crystalline rocks and having similar dissolved carbonate systematics this flux is insufficient to influence modern day atmospheric co 2 levels and we find that higher meltwater discharge alone will cause only moderate future increases however more substantial increases could occur if meltwaters intersect basal ice known to have elevated pco 2 values worst case model scenarios yield evasion fluxes of 100 20 170 40 tg c year by 2100 these atmospheric co 2 inputs surpass those for arctic lakes and would augment by up to 25 those predicted for permafrost thaw our findings suggest that positive feedbacks linking greenhouse gas emissions arctic climate change and global warming may be stronger than previously realized

the co2 system in rivers of the australian victorian alps co2 evasion in relation to system metabolism and rock weathering on multi annual time scales abstract the patterns of dissolved inorganic c dic and aqueous co2 in rivers and estuaries sampled during summer and winter in the australian victorian alps were examined together with historical 1978 1990 geochemical data this study provides for the first time a multi annual coverage of the linkage between co2 release via wetland evasion and co2 consumption via combined carbonate and aluminosilicate weathering 13c values imply that carbonate weathering contributes 36 of the dic in the rivers although carbonates comprise less than 5 of the study area baseflow interflow flushing of respired c3 plant detritus accounts for 50 and atmospheric precipitation accounts for 14 of the dic the influence of in river respiration and photosynthesis on the dic concentrations is negligible river waters are supersaturated with co2 and evade 27 7 106 mol km2 a to 70 9 106 mol km2 a co2 to the atmosphere with the highest values in the low runoff rivers this is slightly higher than the global average reflecting higher gas transfer velocities due to high wind speeds evaded co2 is not balanced by co2 consumption via combined carbonate and aluminosilicate weathering which implies that chemical weathering does not significantly neutralize respiration derived h2co3 the results of this study have implications for global assessments of chemical weathering yields in river systems draining passive margin terrains as high respiration derived dic concentrations are not directly connected to high carbonate and aluminosilicate weathering rates

hydrogeochemistry and dissolved inorganic carbon isotopic composition on karst groundwater in maolan southwest china the forest ecosystem in the maolan karst forest southwest china is the only concentrated intact and relatively stable karst forest ecosystem which has survived in the area at the same latitude in the world and is a valuable karst forest plant resource as well groundwater samples from maolan karst forest were collected from wells and springs during summer and concentrations of major ions and dissolved inorganic carbon dic isotopic compositions were measured the ph values range from 7 2 to 8 3 results from the dissolution of carbonate hco3 is the dominant species of dic in groundwater calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the groundwaters groundwater samples have 13c values in the range from 8 1 to 16 6 which are lower than that of the other karst city groundwaters in the southwest china combining 13cdic ratios with measurements of hco3 and ph clearly distinguishes the principal processes underlying the geochemical evolution of groundwater in carboniferous carbonate aquifers where processes can be both degradation of organic matters in the soil and the carbonate dissolution

geochemistry of dissolved inorganic carbon and carbonate weathering in a small typical karstic catchment of southwest china isotopic and chemical constraints abstract the sources of dissolved inorganic carbon dic and rock weathering processes were studied in the houzhai catchment a typical karstic catchment in the changjiang river basin southwest china the carbon isotopic compositions 13 c dic of dic in the samples collected from the catchment vary from 13 5 to 6 9 with a mean value of 9 8 the dic in the catchment is thereby considered to be mainly derived from soil co 2 and weathering of carbonate rocks the dic concentrations and the 13 c dic values show pronounced seasonal variations with the lowest values being observed during the high flow season from may to october the logpco 2 values in the waters were positively correlated with the dic contents and negatively correlated to the saturation index of calcite sic and 13 c dic values these observations indicate that co 2 derived from organic matter oxidation plays an important role in the dissolution of carbonate for this typical karstic environment based on a chemical mass balance the weathering rate of carbonate rocks in the houzhai catchment was estimated to be approximately 133 t km 2 year or 584 10 3 mol km 2 year in terms of co 2 consumption rate which is higher than the reported values for other rivers in southwest china

biogeochemical evidence of holocene east asian summer and winter monsoon variability from a tropical maar lake in southern china abstract lake huguangyan 21 9 n 110 17 e a maar lake located near the south china sea can provide valuable sedimentary data regarding past changes of the east asian monsoonal system here we used the proxies of toc 13corg 15n and leaf wax n alkane 13c values 13cwax to reconstruct the lake conditions which in turn revealed patterns in monsoonal changes during the holocene two distinct patterns of proxy changes were identified in the sedimentary profile a marked shift in the 13cwax value at 9 2 ka thousand years ago suggests the abrupt disappearance of c4 plants signaling the enhancement of east asian summer monsoon easm between 9 2 and 1 8 ka a nearly pure c3 terrestrial ecosystem was present with the climax at ca 7 6 ka after ca 3 ka fewer tropical species and a reappearance of c4 plants at 1 8 ka indicate a weakened easm in the late holocene the toc concentration and 15n value proxies appear to be associated with lake aquatic production and upwelled nutrient supply and utilization which are modulated by and thus indicative of the strength of the east asian winter monsoon eawm the two eawm records suggest a weakening trend from the early to late holocene with the most significant transition at 6 ka thus the eawm trend was broadly in phase with that of the easm however the marked easm intensification at 9 2 ka occurred within the period of a strong eawm between 10 5 and 6 ka and lagged the monsoonal enhancement as inferred from the dongge cave 18o values our easm records displays an overall arid wet arid pattern which is in phase with the hydrological variability in tropical australia and anti phase with that in the outer tropical andes these phase relationships might be linked to changes in the thermal state of the tropical pacific during the holocene

petrographic and geochemical characteristics of dolomite types and the origin of ferroan dolomite in the trenton formation ordovician michigan basin u s a three major types of dolomite occur in the trenton formation mid ordovician of the michigan basin these are 1 regional dolomite which is confined to the extreme western edge of the basin 2 cap dolomite which occurs in the upper portion of the trenton and is confined to the basin s southern margin and 3 fracture related dolomite which occurs in association with both large and small scale faults and fractures these three dolomite types can be distinguished from one another by their major element chemistry oxygen isotope ratios and rock texture the regional dolomite is fine grained has 0 34 mol feco3 and mean 18o of 6 8 opbd the cap dolomite is texturally similar to regional dolomite but contains 3 13 0 mol feco3 and has a mean 18o of 7 7 fracture related dolomites are coarse grained low in iron and have the most depleted 18o ratios x 9 0 pdb petrographic relationships imply that the regional dolomite formed prior to the cap dolomite probably during early diagenesis the cap dolomite formed at relatively shallow depths as a result of the interaction of the overlying utica shale and the trenton limestone fracture related dolomites post date the cap dolomite and formed during deeper burial a temperature of precipitation of approximately 80 c was calculated for fracture related dolomites using oxygen isotope data the distribution of the cap dolomite was controlled by the availability of fe2 which was in turn controlled by the availability of s2 in the centre of the basin trenton utica deposition was continuous the upper trenton contained relatively high concentrations of organic matter which was used by sulphate reducing bacteria to produce h2s from seawater sulphate the precipitation of iron sulphides pyrite iron monosulphide followed and used up most of the available fe2 as a result only small amounts of ferroan dolomite formed on the periphery of the basin subaerial exposure resulted in the oxidation of most of the available organic matter sulphate reducing bacteria were therefore limited and produced limited amounts of h2s as a result only a minor amount of iron sulphide iron monosulphide formed the remaining fe2 was then available for the formation of the ferroan cap dolomite this model is supported by the following 1 in the southern margin of the basin the contact between trenton cap dolomite and the overlying utica shale is sharp and probably unconformable in the centre of the basin the contact is gradational 2 in the centre of the basin the total organic carbon content in the upper trenton is an order of magnitude higher than in the cap dolomite 3 the whole rock concentration of iron is high in both the cap dolomite and in slightly dolomitized equivalent beds in the basin centre 4 iron sulphides are abundant in the centre of the basin and mostly in the form of pyrite in the cap dolomite iron sulphide is minor and primarily in the form of iron monosulphide

reconstructing the evolution of the latest pennsylvanian earliest permian lake odernheim based on stable isotope geochemistry and palynofacies a case study from the saar nahe basin germany abstract finely laminated sediments archived the evolution of the latest pennsylvanian earliest permian lake odernheim saar nahe basin germany a succession of evolutionary stages can be distinguished based on variable carbonate carbon 5 to 2 and oxygen 7 to 5 isotopic compositions of dolomite sedimentary organic matter represents primarily a mixture of detrital vascular plant material 13 c around 21 and lake derived photosynthetic algal matter 13 c around 27 this distinction based on organic carbon isotopes is further supported by palynofacies analyses and rock eval data an additional contribution from bacterial biomass is likely bacterial sulphate reduction and thus anaerobic remineralization of sedimentary organic matter is indicated by the presence of sedimentary pyrite observed geochemical changes are attributed to temporal variations in the water balance of lake odernheim including times of stronger evaporation as well as times showing substantial input of freshwater

source parameters of the sierra madre earthquake from regional and local body waves we inverted the three component long period data recorded by the terrascope array for the june 28 1991 sierra madre california event to determine the seismic moment and source orientation of the mainshock ml 5 8 remarkably four of the six stations were located 159 2 0 7 km from the epicenter variations in absolute traveltime were smaller than 2 and 3 for pn and sn whereas the surface waves displayed greater variation similarities in the waveforms and the small variance in traveltime suggest that a common green s function can be used to invert the data we used the whole waveforms excluding the fundamental surface waves at the more distant stations to invert for source parameters the results of the inversion indicated that this event was predominately a thrust type earthquake where the strike rake and dip were determined to be 235 74 and 50 respectively the seismic moment was determined to be 2 5 1024 dyne cm the source duration was found to be about 1 0 seconds by direct measurement of the s wave recorded at the pasadena station located 21 km from the epicenter considering circular rupture we obtain a stress drop of 460 bars