Inflow Of River Water Research Articles

Ra-226 and Rn-222 in saline water compartments of the Aral Sea region

The Aral Sea has been shrinking since 1963 due to extensive irrigation and the corresponding decline in the river water inflow. Understanding of the current hydrological situation demands an improved understanding of the surface water/groundwater dynamics in the region. 222Rn and 226Ra measurements can be used to trace groundwater discharge into surface waters. Data of these radiometric parameters were not previously available for the study region. We determined 222Rn activities after liquid phase extraction using Liquid Scintillation Counting (LSC) with peak-length discrimination and analyzed 226Ra concentrations in different water compartments of the Amu Darya Delta (surface waters, unconfined groundwater, artesian water, and water profiles from the closed Large Aral Sea (western basin).The water samples comprise a salinity range between 1 and 263g/l. The seasonal dynamics of solid/water interaction under an arid climate regime force the hydrochemical evolution of the unconfined groundwater in the Amu Darya Delta to high-salinity Na(Mg)Cl(SO4) water types. The dissolved radium concentrations in the waters were mostly very low due to mineral over-saturation, extensive co-precipitation of radium and adsorption of radium on coexisting solid substrates.The analysis of very low 226Ra concentrations (<10ppq) at remote study sites is a challenge. We used the water samples to test and improve different analytical methods. In particular, we modified a procedure developed for the α-spectrometric determination of 226Ra after solid phase extraction of radium using 3M Empore™ High Performance Extraction Disks (Purkl, 2002) for the analysis of the radionuclide using an ICP sector field mass spectrometer. The 226Ra concentration of 17 unconfined groundwater samples ranged between 0.2 and 5 ppq, and that of 28 artesian waters between <0.2 and 13ppq. The ICP-MS results conformed satisfactorily to analytical results based on γ-measurements of the 222Rn ingrowth after purging and trapping on super-cooled charcoal. The 226Ra concentrations were positively correlated with the salinity and the dissolved NaCl concentrations. The occurrence of unusually high 226Ra activities is explained by radium release from adsorption sites with increasing salinity. The inferred spatial variability of 222Rn in the Aral Sea and of 222Rn and 226Ra in the groundwater of the Amu Darya Delta is discussed in the context of our own previous hydrochemical studies in the study sites. Relatively low 222Rn activities in the unconfined GW (1–9.5Bq/l) indicate the alluvial sediments hosting the GW to be a low-238U(226Ra) substrate. Positive correlations between U and 226Ra, and U and 222Rn are likely related to locally deposited Fe(Mn)OOH precipitates. The 222Rn activity of the GW, however, distinctly exceeds the 222Rn concentration in the Aral Sea (10mBq/l), in principle, making 222Rn a sensitive tracer for the inflow of GW. The high water volume of the Large Aral Sea and wind induced mixing of its water body, however, hamper the detection of local groundwater inflow.

An improved algorithm for remotely sensing marine dissolved organic carbon: Climatology in the northern South China Sea shelf-sea and adjacent waters

By using field in situ observations, data from the NOMAD database, and remotely sensed data from MODIS-Aqua, an improved algorithm has been developed for estimating the surface concentrations of dissolved organic carbon (DOC) in the Northern South China Sea Shelf-sea (NoSoCS) and adjacent waters through a combination of the remotely sensed sea-surface temperature (SST) and the absorption coefficient of colored dissolved organic matter (CDOM). Unlike previously reported algorithms, which were based on only one of these two parameters, this algorithm does not require seasonal tuning and is applicable to both coastal and pelagic waters. The uncertainty in the remotely sensed concentrations of DOC is about ±4–10µM. The climatological distributions of the satellite-derived surface DOC in the NoSoCS and adjacent waters between 2002 and 2012 followed a general trend of increasing concentrations landward, from about 58 and 73μM in the open South China Sea (SCS) in January and July, respectively, to >100μM at the mouth of the Pearl River. The intra-annual changes in the monthly average concentration of DOC in the NoSoCS follow a distinct seasonal cycle, with the lowest and highest concentrations, 56μM and 75μM, in February and July, respectively. The seasonal cycle of DOC was in phase with that of SST but out of phase with that of primary production, suggesting that biological activity was not likely its primary control. Instead, it was consistent with the entrainment of the cold and less DOC-rich sub-surface water in the surface water by enhanced vertical mixing during winter, and the high inflow of organic-rich river water to the NoSoCS in summer. Sub-regionally, lower concentrations of DOC were found in the known upwelling zones in the NoSoCS, where vertical mixing was enhanced. In the inner shelf, the effect of riverine input was indicated by higher concentrations of DOC in the plume of water at the mouth of the Pearl River. This work represents the first attempt to characterize the regional distribution of surface concentration of DOC in the NoSoCS and adjacent waters.

Laboratory feasibility tests improve decision support for wetland eco-engineering; Lake Bartków Ług (Poland) as test case

Many lakes worldwide are exposed to high anthropogenic impacts including the influx of polluted surface water and groundwater, fish production and nutrient run-off from agriculture in the catchment. We selected the shallow Lake Bartków Ług in Poland, receiving eutrophic River Chodelka water and currently used for fish farming as a case study for decision support with respect to inexpensive ways to improve water quality and facilitate higher biodiversity after fish stock removal. We selected four scenarios: (1) complete isolation from eutrophic water, (2) inflow of P-stripped surface water, (3) temporary water table drawdown, and (4) in-lake P sequestration. For financial reasons, dredging was not an option.The study started with an ecohydrological field survey to investigate the first scenario: isolation from river water inflow and restoration of the discharge of nutrient-poor, Fe-rich groundwater. Although groundwater appeared to be much less eutrophic, it contained low concentrations of Fe and high concentrations of SO42−, which would lead to higher risks of phosphate mobilization from the sediment. Moreover, local hydrology showed almost no discharge of groundwater with the exception of spring.To reduce the risk of failure and avoid high costs without benefits, we pre-tested the other three scenarios using small-scale laboratory experiments. The first experiment, which tested the effects of the influx of water stripped of P (scenario 2), showed that water quality would not improve due to high P-mobilization rates from the sediment to the water layer (internal eutrophication). We therefore investigated two alternative mitigation measures: temporary water table drawdown (scenario 3) and the addition of Fe (scenario 4), both in order to increase P-sorption in the sediment. Temporary lowering of the water table indeed decreased P concentrations in pore water, but not in surface water because sediment Fe concentrations were insufficient. The addition of Fe to the sediment strongly improved water quality by P sequestration leading to almost complete disappearance of P in both pore water and surface water.For the studied lake, successful improvement of the water quality and biodiversity can therefore only be achieved by scenario 4, internal P fixation, after the cessation of fish production. The removal of fish only will not lead to improvement, because of the strong mobilization of P in the sediment. We show that the combination of field research and small-scale laboratory feasibility tests strongly reduces the risks of failure, and avoids less efficient and more costly approaches based on trial and error in the field. We therefore recommend the inclusion of such tests in decision support systems for ecological engineering.

Forecasting changes of hydrological and hydrochemical conditions in the Aral Sea

Abstract: The increase of irretrievable river water withdrawals and regulation of river flow has a negative effect on the natural regime of the Aral Sea. The Amu Darya River and the Syr Darya River Basins are the largest irrigated fanning areas. Their favorable soil and climatic conditions ensure guaranteed yields of various crops on irrigated lands. Since 1961, for the drastic increase of irretrievable river water withdrawal, mainly for irrigation, the inflow of river water into the Aral Sea has started to decrease significantly, accordingly the sea's hydrological and hydrochemical regimes disrupted dramatically. The sea level has continued to drop as evaporation exceeds inflow. This negatively transforms the natural environment and worsens socio-economic conditions in Priaralie as a whole, especially in the lower reaches of Amu Darya and Syr Darya, where natural conditions are largely determined by the sea's impact. At present, this causes desertification of the nonirrigated zone in the deltas, spreading to new areas as the Aral Sea dries out.

Characterization of water pollution in drainage networks using continuous monitoring data in the Citadel area of Hue City, Vietnam.

In the Citadel area of Hue City, drainage systems that include canals and ponds are considerable sources of fecal contaminants to inundated water during the rainy season because canals and ponds receive untreated wastewater. It is important to investigate the characteristics of hydraulics and water pollution in canals and ponds. At the canals and ponds, water sampling was conducted during dry and wet weather periods in order to evaluate fecal contamination and to investigate changes in water pollution caused by runoff inflow. Inundated water was also collected from streets during heavy rainfall. At the canals and ponds, concentrations of Escherichia coli and total coliform exceeded the Vietnamese regulation values for surface water in 23 and 24 out of 27 samples (85 and 89%), respectively. The water samples were categorized based on the characteristics of water pollution using cluster analysis. In the rainy season, continuous monitoring was conducted at the canals and ponds using water depth and electrical conductivity (EC) sensors to investigate the dynamic relationship between water level and water pollution. It is suggested that in the canals, high EC meant water stagnation and low EC signified river water inflow. Therefore, EC might be a good indicator of water flow change in canals.

Hydrogeochemical features of groundwater of semi-confined coastal aquifer in Amol–Ghaemshahr plain, Mazandaran Province, Northern Iran

Hydrogeochemical data of groundwater from the semi-confined aquifer of a coastal two-tier aquifer in Amol-Ghaemshahr plain, Mazandaran Province, Northern Iran reveal salinization of the fresh groundwater (FGW). The saline groundwater zone is oriented at an angle to both Caspian Sea coastline and groundwater flow direction and extends inland from the coastline for more than 40 km. Spearman's rank correlation coefficient matrices, factor analysis data, and values of C ratio, chloro-alkaline indices, and Na(+)/Cl(-) molar ratio indicate that the ionic load in the FGW is derived essentially from carbonic acid-aided weathering of carbonates and aluminosilicate minerals, relict connate saline water, and ion exchange reactions. Saline groundwater samples (SGWS) (n = 20) can be classified into two groups. SGWS of group 1 (n = 17) represent the saline groundwater zone below the Caspian Sea level, and salinization is attributed essentially to (1) lateral intrusion of Caspian seawater as a consequence of (a) excessive withdrawal of groundwater from closely spaced bore wells located in the eastern part of the coastal zone and (b) imbalance between recharge and discharge of the two-tier aquifer and (2) upconing of paleobrine (interfaced with FGW) along deep wells. SGWS of this group contain, on average, 7.9% of saltwater, the composition of which is similar to that of Caspian seawater. SGWS of group 2 (n = 3) belong to the saline groundwater zone encountered above the Caspian Sea level, and salinization of the groundwater representing these samples is attributed to irrigation return flow (n = 2) and inflow of saline river water (n = 1).

Hydrochemical water evolution in the Aral Sea Basin. Part I: Unconfined groundwater of the Amu Darya Delta – Interactions with surface waters

Summary The Aral Sea, which has been affected by lake level lowering of approximately 25 m and a salinity increase from 10 to >100 g/l since 1963, represents, along with the Amu Dary Delta a dynamic hydrological system under an arid climate regime. The system receives river water inflow at high seasonal and inter-annual variability from remote alpine source areas. In the Amu Darya Delta, there is a distinct salinity contrast between the low-salinity river water (∼1 g/l) and the salinity of the unconfined GW (GW unconf : 10–95 g/l). The GW unconf levels are predominantly controlled by the seepage of the river water inflow and GW discharge into the shrinking Aral Sea. In June 2009 and August 2009, we sampled water from various sources including surface waters, GW unconf , lake water and soil leachates for chemical analyses. Evaporative enrichment, precipitation/dissolution of gypsum and precipitation of calcite drive the GW unconf to an NaCl(SO 4 ) water type presenting a positive correlation between Na and SO 4 . We model the hydrochemical evolution of the GW unconf in a box model which considers the capillary rise of near-surface GW, the precipitation of minerals in the unsaturated horizon and the seasonal re-flushing of adhesive residual brines and soluble salts. The model documents a rapid increase in salinity over a few annual cycles. Furthermore, the model simulations demonstrate the importance of the aeolian redistribution of soluble salts on the hydrochemical GW evolution. In a lab experiment, halite, hexahydrite and starkeyite are precipitated during the late stages of evaporative enrichment from a representative local brine. Processes specific to different water compartments plausibly explain the variations of selected element ratios. For example, the precipitation of low-Sr calcite in irrigation canals and natural river branches of the delta lowers Ca/Sr. The dissolution of gypsum in soils (Ca/Sr mole ratio ∼ 150) and the possible precipitation of SrSO 4 associated with Sr-depletion in adhesive residual brines increases Ca/Sr in seepage and re-increases Ca/Sr in the unconfined GW. Aral Sea water, which receives high-Ca/Sr surface and groundwater inflow, developed due to continued precipitation of high-Ca/Sr calcite the almost lowest Ca/Sr ratio (∼25) over time. We observed spatial variations in the GW unconf composition: (i) ammonium levels increase strongly due to interaction with lake sediments rich in organic matter and (ii) distinct increases in levels of nitrate, U, Mo and Se locally reflect oxygenation when GW levels decrease. The Amu Darya Delta acts as a sink for boron (uptake via terrestrial vegetation) and a source for bromide (release by degradation of organically-bound Br). Our results concerning the hydrochemical evolution of the GW unconf and additional data from the Aral Sea constrain the parameter ‘GW discharge’ in water budget models of the lake and improve the basis for palaeoclimatic interpretations of sediment records from the Aral Sea.

Oxygen isotopes of marine mollusc shells record Eocene elevation change in the Pyrenees

Constraining paleoaltimetry of collisional orogens is critical to understand the dynamics of topographic evolution and climate/tectonics retroactions. Here, we use oxygen stable-isotope record on oyster shells, preserved in marine foreland deposits, to examine the past elevation of the Pyrenees during the Eocene. Our approach is based on the comparison with the Paris basin, an intracratonic basin not influenced by orogenic growth. The finding of a shift of 1.5‰ between 49 and 41Ma, indicating more negative δ18Oc in the south Pyrenean foreland, is interpreted to reflect the inflow of river water sourced from higher elevation in the Pyrenees. To test this and provide paleoelevation estimate, we adopt a morphologic-hydrological model accounting for the hypsometry of drainage basin. Our best fitting model shows that the Pyrenees rose up to 2000m. This indicates that the Pyrenees reached high elevation in the Eocene, thus providing new critical constraints on their long-term orogenic development. δ18O of marine mollusc shells are proved potentially attractive for paleoelevation studies, especially for mountain belts where elevated continental surfaces have not been preserved.

Modern hydrological status estuary of Ili River

This paper addressed problems on the history of the formation and functioning in one of the largest intracontinental estuary in Kazakhstan—the Ili River waterway. Being a natural regulator of the ecological status of the region, Ili River estuary also influences the water regime of Lake Balkash. This paper studied the current state of hydrographic and hydrological networks in a selected area and the distribution of water flow entering the estuary on various ducts. Using a water balance method, in this study, calculated loss of water in the delta also estimated runoff to the peak of delta and the inflow of river water into Lake Balkash for two periods: the natural and disturbed conditions. As a result of work performed, it was possible to trace dynamics of hydraulic parameters for a multiyear period.

Modern hydrological status of the estuary of Ili River

The study addresses the problems and the history of formation and functioning of one of the largest intracontinental estuaries in Kazakhstan—the Ili River waterway. Being a natural regulator of the ecological status of the region, the estuary of Ili River also influences the water regime of Lake Balkhash. This work studied the current state of hydrographic and hydrological networks in a selected area and the distribution of water flow entering the estuary through the various ducts. Using a water balance method, this study calculated the loss of water in the delta, estimated runoff to the peak of delta and the inflow of river water into Lake Balkhash for two periods: the natural-conditioned and disturbed. As a result of the work performed, it was possible to trace the dynamics of hydraulic parameters for a multiyear period.

A 40-year record of carbon-14 and tritium in the Christchurch groundwater system, New Zealand: Dating of young samples with carbon-14

Knowledge of the sources and flowpaths of water in the Christchurch groundwater system will be vital to future management of the system. To gain such knowledge, oxygen-18 (18O), tritium (3H), carbon-14 (14C), and chemical concentrations have been measured on deep and shallow groundwaters since 1970. 18O measurements show that seepage from the Waimakariri River is the dominant source of the groundwater. Early 3H measurements (in the 1970s) showed non-zero concentrations in the deep groundwaters, but these were discounted at the time as due to “at most a few percent of very young water”. However, reinterpretation in light of the 14C ages in this work has revealed much younger ages for the deep waters than was previously believed, with average ages of 38 years in 1971, 71 years in 1976, 98 years in 1985, greater than 120 years in 1986, and greater than 150 years in 1993–1994. Because the Waimakariri River was identified as the major source of the deep groundwater, the river’s 14C concentration between 1986 and 2006 was modelled by combining the records of its two carbon sources (biogenic carbon and atmospheric CO2). This allowed the initial 14C concentrations of the groundwaters to be unequivocally determined and their mean 14C ages estimated using the same flow model as was applied to the 3H measurements. The resulting mean 14C ages are in the range 5–1500 years. The long sequence of measurements reveals that the mean ages of the deep Christchurch groundwater have changed markedly during the study. The pre-exploitation rate of turnover of water in the system is not known, but was probably quite slow. By the 1970s, ages in the deep system (Aquifers 4 and 5) had become relatively young right across Christchurch (with mean ages of 60–70 years) indicating mainly lateral inflow of young Waimakariri River water because of groundwater abstraction. Mean ages measured since have gradually increased showing increasing upflow of much older water from depth – this water has 10–15% rainfall recharge and is sourced from the inland plains region. There is now (in 2006) a steep gradient in age from west to east across Christchurch (from 300 years to 1400 years) showing that a large body of much older, deeper water is stored on the seaward side of the system where the deep aquifers are blind. This body will yield good quality water for many years, but eventually it is likely to be replaced or bypassed by younger (a few hundred years old), Waimakariri River-dominated but surface recharge-bearing, water from inland.

Major ion chemistry of water and its controlling factors in the Yamzhog Yumco Basin, South Tibet

水化学主离子特征是流域湖泊的一个重要特征,对气候以及河流所经地区的环境具有指示作用.本文对藏南羊卓雍错流域水化学主离子组成特征及其控制因素进行分析,结果显示流域内不同水体(湖水、河水、地下水)之间的主离子组成以及水化学类型差异显著.其中,羊卓雍错的水化学类型为SO₄^2--HCO₃^--Mg²⁺-Na⁺,巴纠错为SO₄^2--Mg²⁺-Na⁺,沉错为SO₄^2--Na⁺-Mg²⁺-Ca²⁺,普莫雍错为HCO₃^--SO₄^2--Mg²⁺-Ca²⁺,空姆错为HCO₃^--SO₄^2--Ca²⁺;流域河水中主要阴离子为HCO₃^-和SO₄^2-,Ca²⁺为绝对优势阳离子;流域地下水化学类型则为HCO₃^--Ca²⁺.究其原因,流域水体化学组成主要受岩石风化作用控制;除此,羊卓雍错、巴纠错和沉错水化学组成亦受自身蒸发-结晶作用的影响.就入湖河水而言,羊卓雍错入湖河水整体受碳酸盐岩石风化的影响较大,蒸发岩溶解的影响次之;沉错和空姆错入湖河流(卡鲁雄曲)的蒸发岩来源则略大于碳酸盐岩来源;而硅酸盐对流域内河水的水化学性质影响较小.与入湖河水相比,羊卓雍错和沉错湖水的Mg²⁺、Na⁺和SO₄^2-含量较高,而Ca²⁺和HCO₃^-含量较低.这应该与湖水蒸发强烈使得湖水中Ca²⁺和HCO₃^-析出并沉积到湖底有关.而空姆错由于湖泊面积小、入湖河水流量大,致使其湖水与入湖河水的主离子组成差异不显著.;Water chemical composition of a lake and its inflow rivers is an important lake characteristic, which can reflect the climatic and environmental background of the basin where the lake is located and the river flows through. Water samples were collected and their major ions were measured from the major lakes (i. e., Yamzhog Yumco, Bajiu Co, Chen Co, Kongmu Co and Pumoyong Co), inflow rivers, and wells in the Yamzhog Yumco Basin. Possible controlling factors on the major ion compositions from different waterbody were analyzed. Results revealed that the major ion compositions (e. g. hydrochemical types) of the water in the basin were significantly different as follows. The major ion compositions of lake water in Yamzhog Yumco, Bajiu Co, Chen Co, Pumoyong Co and Kongmu Co were SO₄^2--HCO₃^--Mg²⁺-Na⁺, SO₄^2--Mg²⁺-Na⁺, SO₄^2--Na⁺-Mg²⁺-Ca²⁺, HCO₃^--SO₄^2--Mg²⁺-Ca²⁺, and HCO₃^--SO₄^2--Ca²⁺, respectively. For the inflow river water, the major anions were HCO₃^- and SO₄^2- and the preponderant cation was Ca²⁺. Comparing with the water chemical compositions of inflow rivers, the contents of Mg²⁺, Na⁺ and SO₄^2- in Yamzhog Yumco and Chen Co were much higher with a relative low contents of Ca²⁺ and HCO₃^-. On the contrary, there was little difference for the Kongmu Co and its inflow rivers. In addition, the major ion compositions of well waters were characterized by HCO₃^--Ca²⁺. Further analysis indicated that the water chemical compositions were mainly controlled by rock weathering in the whole basin, and also by evaporation and crystallization for Yamzhog Yumco, Bajiu Co and Chen Co. For the inflow river waters in the basin, the main controlling factors of chemical compositions were carbonate weathering and evaporite weathering, while the effect of the silicate weathering on the river water chemistry was minor. Thereinto, the dominant controlling processes were carbonate weathering for inflow river waters flowing into Yamzhog Yumco, and the evaporite weathering for the inflow river waters flowing into Chen Co and Kongmu Co. As for the different water chemical characteristics between the inflow river water and lake water of Yamzhog Yumco and Chen Co, the possible reason should own to the strong evaporation of two lakes which may intensify calcium phosphate precipitation. The small lake area of Kongmu Co and the vast amounts of inflowing river water can explain the little difference of water chemical compositions between the lake and its inflow rivers. The study also showed that the controlling processes of water chemical compositions among inflow rivers were different because the different rock-stratigraphic area they flowed was dominated by physical weathering/erosion. With global warming, the style and intensity of rock weathering would be changed. So it is indispensable to further investigate the speed of rock weathering in the basin and its possible response to climate change.

Distribution of the primary production and chlorophyll a in the Kara Sea in September of 2007

The studies were performed from September 10 to 29 of 2007 in the Kara Sea in transects westward of the Yamal Peninsula, near the St. Anna Trough, in the Ob River’s estuary, and on the adjacent shelf. The concentration of chlorophyll a in the euphotic layer changed from 0.02 to 4.37 mg/m3, amounting on the average to 0.76 mg/m3. The primary production in the water column varied from 10.9 to 148.0 mg C/m2 per day (the mean was 56.9 mg C/m2 per day). It was shown that frontal zones divided the Kara Sea into distinct areas with different productivities. The maximum levels of the primary production were measured in the deep part of the Yamal transect (132.4 mg C/m2 per day) and the shallow Kara Sea shelf near the Ob River’s estuary (74.9 mg C/m2 per day). The characteristics of these regions were the low salinity of the surface water layer (19–25 psu) and the elevated silicon content (12.8–28.1 μg-atom Si/l), which is explainable by the river water inflow. The frontal zones of the Yamal Current in the Yamal and Ob transects displayed high values of the assimilation numbers, amounting to 2.32 and 1.49 mg C/mg of chlorophyll per h, respectively (the maximal for the studied regions).

Secondary production and biomass of Cladocera in marginal lakes after the recovery of their hydrologic connectivity in a river–reservoir transition zone

Secondary production and biomass of Cladoceran populations were studied in two marginal lakes whose connections to a tropical river were re-established after a prolonged drought period. This study investigates the process of the recovery of the cladoceran populations after the hydrologic reconnection with the river was established. It also compares the energetic dynamic of Cladoceran populations in two lakes, one with a wide and another with a narrow connection to the river. Samples were collected every 48 h for 1 month, immediately after the river water inflow to the lakes, and 7 months after the reconnection with the river during a period of hydrologic stability of the lakes. Secondary production and biomass were compared between lakes and periods, to identify the main controlling factors for the observed variations in Cladoceran productivity. Cladocerans were more productive during the rainy period, immediately after the increased water volume, when high water temperatures were recorded in the two lacustrine systems. Secondary production and biomass values were higher in the more eutrophic lake, wherein the water chemical and physical characteristics presented slow alterations during the rainy period. Although the lake with large spatial heterogeneity and linkages with the river exhibited high Cladoceran richness, the secondary production and biomass were low. Variations in water volumes and temperatures and changes in trophic status affected the secondary production and biomass of the main Cladoceran species in the two studied lakes.

Comparisons between the chemical compositions of lake water, inflowing river water, and lake sediment in Nam Co, central Tibetan Plateau, China and their controlling mechanisms

The chemical composition of lake water and inflowing river water was investigated in Nam Co (lake), Tibetan Plateau, in September 2005. Lake water samples (n=76) were collected at different depths along a south–north transect of the eastern part of the lake while water samples were collected from 69 rivers flowing into the lake; a sediment core was collected at 64m midway along the water survey transect to investigate salt precipitation. Na+ and Ca2+ were the dominant cations, accounting for 76.2% and 60.6% of the lake and river water cations, respectively while HCO3− was the dominant anion accounting for 70.8% and 93.4% of lake and river anions, respectively. CaCO3 precipitation from the water column decreased Ca2+ in the lake water, with the relative proportion of other ions increasing significantly. Evaporation–crystallization processes largely control Nam Co lake-water chemistry, while rock weathering is the dominant processes influencing the chemistry of river water; carbonate and silicate weathering are the major sources of ions in these rivers.

Off‐channel temporary pools contribute to native riparian plant species diversity in a regulated river floodplain

AbstractOff‐channel temporary pools on riverbanks have characteristic seasonal wet–dry cycles resulting from direct inflow of river water or hyporheic flow seepage. This study addressed two questions regarding the role of temporary pools in supporting diversity of riparian vegetation in a regulated river in Japan: (1) do temporary pools maintain high native riparian plant species diversity? And, (2) how do physical environmental factors affect the pattern of plant species distribution? The study was conducted on a 1‐km section of the Hayade River alluvial fan in Niigata Prefecture, central Japan. Two to five transect belts consisting of 20 contiguous plots (1 m × 1 m) were laid out in two off‐channel temporary pools and six other sites classified by physiognomy. Vascular plant presence, relative elevation, and substratum type were recorded in all plots. Species richness, Simpson's reciprocal index (1/D), and Shannon–Wiener function (H′) were calculated by life form to estimate plant species diversity. Two conclusions could be drawn from the results. First, the temporary pools maintained high native riparian plant species diversity in this regulated river floodplain. Second, several environmental factors (seasonal wet–dry cycle, low elevation, complex micro‐topography, and fine substrata) created spatial and seasonal heterogeneity of moisture conditions in the temporary pools, supporting plant species diversity. For sustainable maintenance of riparian plant species diversity, progressive river‐management should restore original riverine dynamics to generate a shifting mosaic of diverse geomorphology.

Elution Behavior of Nutrient Salts from Sediment and its Impact on Water Bodies

This paper describes the influence of nutrient salts eluted from the bottom of a closed water area where polluted sediment has been deposited by inflowing river water. The elution pattern was monitored at our experimental facility. Both the sediment pore water and water above the bottom were sampled using a dialyzer sampler (peeper). The pore water of the eutrophicated sediment contained a large amount of nutrient salts, and the effect of elution was confined to a limited area of the bottom surface. The nutrient concentration of the sediment pore water was closely related to both the water temperature and dissolved oxygen (DO) concentration. The eluted nutrients from the sediment provided a source for phytoplankton and algae growth. This experimental data indicated that the water quality of the surface was not directly connected to the eluted nutrient salts, while it was indirectly affected by the total ecosystem, including all the organisms within an area and their environment.

Prediction of Density Flow Plunging Depth in Dam Reservoirs: An Artificial Neural Network Approach

AbstractExperimental findings and observations indicate that plunging flow is related to the formation of bed load deposition in dam reservoirs. The sediment delta begins to form in the plunging region where the inflow river water meets the ambient reservoir water. Correct estimation of dam reservoir flow, plunging point, and plunging depth is crucial for dam reservoir sedimentation and water quality issues. In this study, artificial neural network (ANN), multi‐linear regression (MLR), and two‐dimensional hydrodynamic model approaches are used for modeling the plunging point and depth. A multi layer perceptron (MLP) is used as the ANN structure. A two‐dimensional model is adapted to simulate density plunging flow through a reservoir with a sloping bottom. In the model, nonlinear and unsteady continuity, momentum, energy, and k–ε turbulence equations are formulated in the Cartesian coordinates. Density flow parameters such as velocity, plunging points, and plunging depths are determined from the simulation and model results, and these are compared with previous experimental and model works. The results show that the ANN model forecasts are much closer to the experimental data than the MLR and mathematical model forecasts.

Limited Recovery of the KelpEisenia bicyclisAfter Population Reduction of the Sea UrchinsHemicentrotus pulcherrimusandAnthocidaris crassispinaon Kii Peninsula, Southwestern Japan

We gauged the effect of the sea urchins Hemicentrotus pulcherrimus and Anthocidaris crassispina on an Eisenia bicyclis kelp bed on the Kii Peninsula in southwestern Japan. We monitored sea urchin density, size, and vertical algal distribution every 2 months from September 2000 to March 2002 and in September 2002 in a 40-m2 plot that stretched from the intertidal (reef) zone to the subtidal zone at depth of up to 2 m. The sea urchin densities were more than 40 individuals/m2 (H. pulcherrimus) and more than 5 individuals/m2 (A. crassispina) during September 2000 to May 2001. These densities decreased abruptly to less than 20 and less than 1 individual/m2 in October 2001, respectively, coincident with low salinities of less than 23 practical salinity unit (PSU) in late June because of river water inflow. Until May 2001, adult E. bicyclis grew only on the intertidal reef, and articulated coralline turf was predominant in the subtidal zone. From January 2002, the kelp bed expanded slightly to the upper subtidal zone, but most young kelp growing at a depth of more than 1.5 m disappeared, despite the low sea urchin density. It is likely that abiotic factors resulting from the river water inflow inhibited the growth of E. bicyclis.

Geo-chemical Behavior of Uranium in the Sambhar Salt Lake, Rajasthan (India): Implications to "Source" of Salt and Uranium "Sink"

Among several salt lakes in the Thar Desert of western India, the Sambhar is the largest lake producing about 2 × 105 tons of salt (NaCl) annually. The “lake system” (lake waters, inflowing river waters, and sub-surface brines) provides a unique setting to study the geo-chemical behavior of uranium isotopes (238U, 234U) in conjunction with the evolution of brines over the annual wetting and evaporation cycles. The concentration of 238U and the total dissolved solids (TDS) in lake water increase from ~8 μg L−1 and ~8 g L−1 in monsoon to ~1,400 μg L−1 and 370 g L−1, respectively, during summer time. The U/TDS ratio (~1 μg g−1 salt) and the 234U/238U activity ratio (1.65 ± 0.05), however, remain almost unchanged throughout the year, except when U/TDS ratio approaches to 3.8 at/or beyond halite crystallization. These observations suggest that uranium behaves conservatively in the lake waters during the annual cycle of evaporation. Also, uranium and salt content (TDS) are intimately coupled, which has been used to infer the origin and source of salt in the lake basin. Furthermore, near uniform ratios in evaporating lake waters, when compared to the ratio in seawater (~0.1 μg g−1 salt and 1.14 ± 0.02, respectively), imply that aeolian transport of marine salts is unlikely to be significant source of salt to the lake in the present-day hydrologic conditions. This inference is further consistent with the chemical composition of wet-precipitation occurring in and around the Sambhar lake. The seasonal streams feeding the lake and groundwaters (within the lake’s periphery) have distinctly different ratios of U/TDS (2–69 μg g−1 salt) and 234U/238U (1.15–2.26) compared to those in the lake. The average U/TDS ratio of ~1 μg g−1 salt in lake waters and ~19 μg g−1 salt in river waters suggest dilution of the uranium content by the recycled salt and/or removal processes presently operating in the lake during the extraction of salt for commercial use. Based on mass-balance calculations, a conservative estimate of "uranium sink" (in the form of bittern crust) accounts for ~5 tons year−1 from the lake basin, an estimate similar to its input flux from rivers, i.e., 4.4 tons year−1.