karst geology and engineering treatment in the geheyan project on the qingjiang river china abstract the geheyan hydropower project is located in a highly karstified limestone area the shilongdong limestone of the foundation bedrock is strongly karstified over 600 karst caves of different sizes were discovered in the project area with a total volume of more than 60 000 m3 faults parallel to the river are quite developed and karstification is intensified along the faults and their intersections exploration adits following the fault zones show a linear karstification ratio of 50 therefore the potential karst leakage under the dam foundation and around both dam abutments is potentially problematic thanks to a proper investigation program and a large amount of geological investigations and analysis the karst conditions and major karst zones in the dam site had been identified before the construction commenced accordingly the optimum grouting route was chosen and appropriate seepage control measures were adopted during the construction the pre construction investigation results were well confirmed up to now the project has been in good operation for nine years and the engineering treatment are proved to be very effective

granite weathering and the sensitivity of alpine lakes to acid deposition lake chemical data from the national surface water survey nsws were corrected for the effects of regional atmospheric deposition and then used to evaluate the role of weathering in supplying base cations silica sulfate and alkalinity to surface waters in alpine vs subalpine and in glaciated vs unglaciated granitic terrane of the western and southeastern united states thermodynamic models idealized reaction stoichiometry and multivariate regression involving solutes and geographic variables indicate that irreversible weathering can largely account for lake chemistry by contrast relatively minor roles are played by reversible ion exchange in soils and sediments terrestrial bioaccumulation and transformations in lakes the regional patterns in lake acidity components no so4 doc co3 and statistical relationships between acidity and base cations demonstrate that rock weathering is limited by acid inputs in many alpine catchments prior to fall overturn the empirical success of the henriksen alkalinity model depends on a high ca na weathering ratio the latter increases with increasing physical disturbance of the catchment iuvenility hence under natural circumstances attains a maximum as a result of on going or recent glaciation the henriksen model fails in geochemically old terrane where cation losses accompanying silicate weathering attain steady state proportions

geochemical investigations of selected eastern united states watersheds affected by acid deposition the effects of acid deposition on surface waters in eastern united states watersheds having similar size physiography climate and land use are related to the composition of the underlying bedrock watersheds developed on greenstone calcareous shale sandstone granite and schist differ in their ability to neutralize acid deposition surface waters in watersheds developed on greenstone and calcareous shale are not discernably affected by acidification wastersheds developed on sand stone have little capacity to neutralize acid rain consequently stream acidity is similar to that of precipitation watersheds developed on granite and schist are intermediate in their capacity to neutralize acid deposition bedrock composition appears to be the major property controlling surface water chemistry in these systems hydrologic flow paths and the nature of surficial materials and vegetation also influence chemical responses to acid deposition in watersheds

rates and time scales of clay mineral formation by weathering in saprolitic regoliths of the southern appalachians from geochemical mass balance rates of clay formation in three watersheds located at the coweeta hydrologic laboratory western north carolina have been determined from solute flux based mass balance methods a system of mass balance equations with enough equations and unknowns to allow calculation of secondary mineral formation rates as well as the more commonly determined primary mineral dissolution rates was achieved by including rare earth elements ree in the mass balance rates of clay mineral formation determined by mass balance methods have been used to calculate the time needed for a 5 50 g kg 1 change in relative clay abundance in the saprolite at coweeta this corresponds to the response time of the clay mineral to for example a change in climate the 5 change in relative clay abundance is the smallest change that can generally be detected using x ray diffraction xrd response times range from tens of thousands to hundreds of thousands of years extrapolating the coweeta clay formation rates to other southern appalachian regoliths the time required to form measured clay abundances production times in eastern blue ridge and inner piedmont regolith have been calculated the production times of clay mineral assemblages range from 2 k y to 2 m y with mean values ranging from 50 k y to 1 m y the results of this study are consistent with the arguments of thiry 2000 1 that the best resolution of the paleoclimatic record in marine clay rich sediments and mudrocks is 1 or 2 m y 1 ref 107

the isotopic composition of authigenic chromium in anoxic marine sediments a case study from the cariaco basin chromium cr isotopes are an emerging proxy for tracking redox processes at the earth s surface however there has been limited exploration of the cr isotope record of modern and recent marine sediments the basic inorganic chemistry of cr suggests that anoxic marine basins should factor prominently in the global cr cycle and that sediments deposited within anoxic basins may offer a valuable cr isotope archive throughout earth s history here we present 53 cr data from sediments of the cariaco basin venezuela a type environment for large perennially anoxic basins with a relatively strong hydrological connection to the global oceans we document a marked positive shift in bulk 53 cr values following the termination of the last glacial maximum followed by relative stasis based on a suite of independent redox proxies this transition marks a switch from oxic to persistently anoxic and sulfidic euxinic depositional conditions within the basin we find good agreement between two independent approaches toward estimating the 53 cr composition of authigenic cr in euxinic cariaco basin sediments and that these estimates are very similar to the 53 cr composition of modern open atlantic ocean seawater these data together with considerations of reaction kinetics and mass balance within the cariaco basin are consistent with the hypothesis that anoxic marine settings can serve as a chemical archive of first order trends in seawater 53 cr composition additionally the cariaco basin data suggest that there has been secular stability in the average 53 cr value of atlantic seawater over the last 15 kyr

lateritic weathering of pyroxenites at niquelandia goias brazil the supergene behavior of nickel two typical lateritic weathering profiles jacuba ahd angiquinho from the niquelandia ni deposits brazil were studied in order to establish the petrological relationship between the supergene ni products and the parental pyroxenes frbm the base to the top of the profiles pyroxenes are replaced by goethite and kaolinite through a series of transitional ni bearing phyllosilicates the mineralogy and the chemical composition especially the ni content of these clay minerals depends on the degree of fracturing and serpentinization of the pyroxenite and the location of the pyroxenite with respect to neighboring dunite within the jacuba profile smectite and pimelite pseudomorphs after pyroxene are especially ni rich and in fact are the most ni enriched clay minerals now known in lateritic weathering profiles

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

influence of mineral weathering and catchment hydrology on drainage water chemistry in three upland sites in england and wales solute budgets and within system variations in water chemistry have been studied at three catchments in western britain the solute budgets showed a net export of calcium and silica from all three sites and of aluminium and magnesium from two hydrogen ion budgets based on bulk precipitation inputs and streamwater outputs underestimated inputs of acidity and fail to take account of within system sources at two sites the aluminium and silica were derived from the soils and the calcium and magnesium from the bedrock compartment there was little if any weathering of the mudstone and slate bedrocks at these two sites calcium and magnesium were derived from carbonate veins and or dolerite intrusions at the third site aluminium and silica were released from the upper soil and calcium and magnesium from the lower soil or underlying calcareous till catchment hydrology was a major factor influencing the pattern and rate of weathering

chemical weathering in two adirondack watersheds past and present day rates rates of chemical weathering in two forested adirondack watersheds were determined from mineral and elemental depletion trends in soil profiles and from input output budgets based on precipitation and surface water chemistry long term rates of weathering have averaged about 500 to 600 eq ha yr for both watersheds since the glaciers retreated from the region about 14 000 yr ago present day denudation rates average 1679 eq ha yr in the panther lake watershed and only 198 eq ha yr in the woods lake watershed mineral weathering reactions in both watersheds involve primarily the dissolution of plagioclase potassium feldspar and hornblende mass balance calculations however indicate that hornblende weathers in disproportionately large amounts in the panther lake watershed relative to its abundance in soils and till cation exchange in the glacial till mantling the panther lake watershed may also play an important role in controlling surface water chemistry in the basin in the panther lake watershed the current rate of weathering which is about a factor of 3 greater than the long term average may reflect a recent adjustment for higher hydrogen ion fluxes brought about by acid deposition the capacity of the thick till deposits in the panther lake watershed to neutralize acidity is ultimately reflected by the circum neutrality of panther lake in the woods lake watershed the soils and thin till deposits cannot effectively neutralize current acid loadings and therefore woods lake is acidic with a ph below 5

neutralization of atmospheric acidity by chemical weathering in an alpine drainage basin in the north cascade mountains the most important weathering reaction that neutralizes incoming atmospheric acidity in the south cascade lake basin is weathering of calcite which occurs in trace amounts in veins on joint surfaces and as a subglacial surficial deposit although the basin is underlain by igneous and high grade metamorphic rocks weathering of plagioclase is quantitatively negligible the principal silicate weathering reaction is alteration of biotite to vermiculite these conclusions are based on mass balance calculations involving runoff compositions and on mineralogical observations for predictive modeling of the effects of increased acid deposition it is essential to identify the relevant weathering reactions feldspar weathering is commonly not an important source of solutes in alpine basins underlain by granitic rocks 30 references 2 figures 1 table

meta gabbro weathering in the georgia piedmont usa implications for global silicate weathering rates abstract the mineral assemblages in a vertical weathering profile developed over a meta gabbro terrain were studied for their stoichiometry and relative abundances the site is located in the piedmont province in the southeast portion of the appalachians orogenic belt in a forested residual landscape and a temperate climate the soil is classified as a fine mixed thermic ultic hapludalf and defined by distinct a b and c horizons with thicknesses of 17 62 and 250 cm respectively the primary mineral assemblage consists of 44 wt andesine 40 hornblende 6 quartz 4 biotite 3 ilmenite titanomagntite rutile sphene grains and 3 epidote quantitative xrd detailed xrd clay mineralogy and thin section petrography revealed the incipient breakdown of the primary minerals to vermiculite after biotite oxidation randomly ordered mixed layer mica vermiculite smectite as grain coatings kaolin group minerals after mafic silicate dissolution goethite and hematite vermiculite after biotite expandable clay coatings and all the primary minerals with exception to quartz are dissolved away from the a horizon hydroxy interlayered vermiculite and minor amounts of gibbsite occur as tertiary phases in the a horizon using mineral stoichiometries and average abundances for the parent rock and c b and a horizon estimates of primary mineral mass loss were determined the bicarbonate to silica ratio expected from the mineral loss reactions is 6 times higher than the ratio observed in average groundwater of the georgia piedmont this suggests that although weathering of mafic terrains is important to the long term process of transferring co 2 to the oceans the present day contribution of silicate weathering in temperate climates may be more largely influenced by the weathering of felsic terrain

method of leakage study at the karst dam site a case study khersan 3 dam iran the excellent topographic condition of the limestone canyons for dam construction may be rejected if they are karstified karst features cause the reservoir not to be impermeable enough to permit the water to fill it and leakage occurs and often increases with time moreover karst features may involve the stability of the dam itself a few operated dam sites at the zagros zone encountered a leakage problem furthermore more than 30 dams are presently under study for construction in the zagros zone karst conditions and leakage potential were investigated at an under study site khersan 3 dam for assessing the general methodology for the study of leakage potentials conventional methods for studying karst features geological mapping geomorphology and extensive borings were applied before the dam was constructed these methods are not efficient enough to precisely reveal the karst structure especially hidden and paleokarst nor the hydrological behaviour of the karst structure in different settings of groundwater flow based on the present case study and previous applied approaches by other authors this paper introduces a methodology by means of karst structure and functioning approaches at local and regional scales that cover the conventional methods and overcome their shortages the proposed methodology should be applied before construction of a dam and should include three steps a recognition of geological and hydrogeological settings b delineation and functioning of the karst system related to the future reservoir and c assessment of the leakage potentials following this methodology the most probable leakage zone s and path s at the dam site can be highlighted

interaction between a dam site and karst springs the case of supramonte central east sardinia italy abstract sardinia is one of the italian regions with the greatest number of dams per inhabitants almost 60 for a population of only 1 5 million people many of these dam sites are located on non carbonate rocks along the main rivers of the island and their waters are used for irrigation industrial energy supply drinking and flood regulation purposes the pedra e othoni dam on the cedrino river dorgali central east sardinia is located along the threshold of the palaeozoic basement on the northern border of the supramonte karst area where water is forced to flow out of the system through several resurgences the most famous of which is the su gologone vauclusian spring used for drinking water supply the other main outflows of the system su tippari and san pantaleo springs are at present almost permanently submerged by the high water level of the pedra e othoni dam in the near future water will be supplied also to other communities with a possible increase of water taken from the spring the dam originally meant to regulate the flooding of cedrino river but actually used for all sorts of purposes electricity supply drinking water irrigation of farmlands industrial uses has a maximum regulation altitude of 103 m a s l only slightly less than a meter below the su gologone spring level 103 7 m and 4 and 9 m respectively above the submerged su tippari and san pantaleo springs during floods of the cedrino river occurring on average twice a year also the su gologone spring becomes submerged by the muddy waters of the lake for a time ranging between a couple of hours up to several days making water supply impossible the analysis of the available meteorological and hydrogeological data relative to the december 2004 flood one of the severest of the past 100 years suggests that the reservoir is filled in a few days time several flooding scenarios have been reconstructed using digital terrain models showing that backflooding submerges most of the discharge area of the aquifer having important repercussions also on the inland underground drainage system the upstream flood prone areas prevalently comprise agricultural lands with some sparse houses but also highly frequented tourist facilities fortunately flooding occurs outside the tourist season thus limiting risk to a limited number of local inhabitants massive discharge at the dam site instead determines a more hazardous situation in the cedrino coastal plain where population density in low lying areas is much higher to avoid flooding hazard upstream the water level in the lake should be regulated keeping it low in the flood prone seasons and having it filled from the end of the winter in order to have enough water stocked before the beginning of the summer discharge at the dam site instead should be done cautiously preventing severe flooding of the coastal cedrino plain

geochemical mass balances and weathering rates in forested watersheds of the southern blue ridge ii effects of botanical uptake terms abstract geochemical mass balance methods are commonly used in small watershed studies to estimate rates of primary mineral weathering and soil formation and the contribution of these processes to cation budgets nutrient cycling and landscape susceptibility to acid deposition many researchers employ the balance sheet approach a system of simultaneous linear equations with constant coefficients which represent the steady state behavior of the modelled system most workers also assume that the steady state assumption for the entire system means that botanical factors can be ignored in other words that there is no net elemental transfer between biomass and inorganic compartments of the system however the widely invoked assumption that biomass is at steady state is mathematically a second explicit assumption not a built in mathematical consequence of the assumption of overall steady state the common assumption that the biomass is necessarily at steady state in a steady state system ignores the possibility of uptake of elements into the forest biomass to quantify the implications of the separate mathematical assumptions weathering rates for seven forested watersheds in the southern blue ridge mountains are calculated twice once allowing for net element exchange with biomass and once assuming no net exchange with biomass our calculations show that misunderstanding the mathematical constraints which are built into the most widely used geochemical mass balance equations commonly causes errors underestimates of up to a factor of 4 in the calculated rates of mineral weathering and soil formation this problem is most pronounced for minerals which contain major nutrient elements and for rates calculated from mass balances of those nutrient elements

reactant product textures volume relations and implications for major element mobility during natural weathering of hornblende tallulah falls formation georgia blue ridge u s a natural weathering of hornblende from the tallulah falls formation georgia u s a takes place under thoroughly leached oxidizing conditions at the earliest stage of weathering corrosion of hornblende forms denticulated terminations with only minimal porosity apparent within the partially pseudomorphic kaolin group weathering product or between it and the reactant mineral isovolumetric replacement of hornblende by kaolin group clay or precursor products implies inheritance of parent mineral silica tetrahedra by the weathering products and largely immobile behavior of si during early weathering aluminum normally considered immobile or minimally mobile during weathering must be imported into early stage weathering products more advanced weathering of hornblende forms denticulated terminations separated from the earlier formed products by a large continuous peripheral void porosity is much more conspicuous at this stage late stage ferruginous products precipitate from fe mobilized in solution dissolved fe to form the late stage goethite can be entirely derived from the parent hornblende requiring only short transport distances for aqueous fe between the source parent mineral and the location of product precipitation textural and volumetric relationships between naturally weathered hornblende and its partially pseudomorphic weathering products suggest structurally controlled immobility of much parent mineral si and considerable mobilization of al at early stages of weathering but at more advanced stages of weathering the textural and volumetric relationships are consistent with immobility of al and fe and leaching of substantial si and all base cations

natural weathering mechanisms of almandine garnet the weathering of almandine garnet in the oxidized vadose zone of saprolite near otto north carolina begins at grain boundaries and along fractures traversing the garnet grains radially oriented fibrous intergrowths of gibbsite and goethite form layers of uniform thickness which grow by centripetal replacement as weathering proceeds the contact between the garnet surface and the layer of weathering products is sharp and smooth and garnet corners are rounded large well defined etch pits are absent on the underlying garnet surface these observations suggest that diffusion transport of reactants and or products through the gibbsite goethite layer is the rate limiting step in the weathering of almandine garnet in the oxidizing environment of the saprolite in soils overlying the saprolite garnet surfaces are directly exposed to weathering solutions without the intervening surface layer such unprotected grains in soils and stream sediments exhibit numerous large well developed etch pits surface reaction control rather than transport control prevails during weathering of almandine garnet in the absence of protective surface layers of weathering products biochemical or biological processes in the soil apparently prevent the gibbsite goethite layer from forming or persisting soil solutions can therefore react directly with the garnet surface rather than requiring reactants or products to diffuse through the gibbsite goethite coating as in the saprolite the mechanism and rate limiting step of almandine garnet weathering is apparently strongly dependent on the chemical environment in which weathering occurs

direct observation of reactant product interfaces formed in natural weathering of exsolved defective amphibole to smectite evidence for episodic isovolumetric reactions involving structural inheritance abstract high resolution transmission electron microscopy hrtem and energy dispersive x ray microanalysis eds were employed to characterize grain boundary structures in naturally weathered amphibole our observations provide insights into the submicroscopic mineralogic controls on transport of solutions to and from reaction sites finely exsolved amphibole anthophyllite gedrite in outcropping slightly weathered gedrite gneiss transforms isovolumetrically to smectite stacking faults and exsolution lamellar boundaries focus weathering reactions whereas chain width defects decrease the susceptibility of the surrounding amphibole to alteration relatively al poor anthophyllite lamellae alter slightly more readily than those of al rich gedrite large quantites of mg fe si and al are removed from reaction sites however smectite compositions directly reflect

inclusion of the weathering of volcanic rocks in the geocarbsulf model the carbon cycle model geocarbsulf is extended by dividing the weathering of silicates into volcanic and non volcanic rocks the proportion of volcanic weathering is calculated as a function of time from the oceanic record of 87sr 86sr the volcanic proportion is then used to modify the equations for calculating atmospheric co2 by the addition of a new non dimensional volcanic weathering factor the effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales and not sr isotopic data that had been used previously results indicate moderate change from geocarbsulf in the distribution of atmospheric co2 over phanerozoic time this includes an increased minimum in co2 during the late ordovician in agreement with the presence of a continental glaciation at that time and a shift of maximum mesozoic values from the jurassic to the early cretaceous