Downstream Reservoir Research Articles

Productivity and rainfall drive bacterial metabolism in tropical cascading reservoirs

Tropical reservoirs are main carbon sources to the atmosphere, and bacterial metabolism is a key process in these emissions. Here, we explored the drivers of bacterial metabolism in four tropical cascading reservoirs forming a trophic state gradient, and compared them with those found in the literature (mainly from temperate regions). Bacterial production (BP) and growth efficiency (BGE) responded to trophic state-related variables, while bacterial respiration (BR) was weakly and negatively correlated to dissolved organic carbon (DOC). BP and BGE were higher in reservoirs with higher primary production, while BR (high throughout the whole study period) was greater in less productive reservoirs, where planktonic communities were often limited by phosphorus. The high BR and low BGE observed in less productive downstream reservoirs (i.e., less nutrients and organic matter availability) may be explained by increasing nutrient limitation and proportion of recalcitrant DOC along the cascade. Despite the lower productivity, oligotrophic reservoirs may be more important in terms of carbon biogeochemistry, considering that microbes in those systems mineralize more carbon than upstream productive reservoirs. Moreover, the drivers of bacterial metabolism may act differently according to latitude, as seasonality in the tropics is determined mainly by rainfall rather than temperature.

A time-dependent method for the measurement of mass flow rate of gases in microchannels

Accurate measurement methods are required in the analysis of thermodynamic non-equilibrium effects associated with rarefied gas flows. For example, for the specific case of accommodation coefficients measurements, the quantity of interest is often the mass flow rate along the channel. For this purpose, the following paper presents a new time-dependent version of the well-known constant volume method for the accurate measurement of mass flow rates of gases in microchannels. The technique proposed here is an improvement in respect to the classic technique since it can be used for transient experiments. Moreover, it can be applied to configurations with arbitrary upstream and downstream reservoirs dimensions. Particularly, the proposed method relies on the assumption that the flow conductance varies linearly during the experiments and thus the pressure variations in the reservoirs can be fitted by a well-defined exponential function. Then, the instantaneous mass flow rate through the channel can be determined directly from the pressure fitting coefficients. A great advantage of the time-dependent constant volume method is that the measurements can be obtained from a single experiment for a wide range of rarefaction conditions, since the mean pressure between the reservoirs is allowed to change with time. Moreover, this technique represents a convenient manner to provide raw data of pressure variation with time in the reservoirs and transient mass flow rate in the channel by simply providing the fitting coefficients of the theoretically derived functions. A clear geometric criterion is also presented to determine when such mass flow rate measurements can be considered as quasi-steady, corresponding closely to results obtained under steady conditions, when ideally the channel connects two infinite reservoirs at different pressures. Results for flows of nitrogen through a stainless steel microtube (L=92.22±0.01 mm and D=435.5±3.5 µm) were obtained from 118 independent experiments, provided in this work, using two different experimental setups and three different configurations of the system volumes. As expected, no deviation was observed between all experimental campaigns in terms of the reduced mass flow rate. In addition, all results indicate that nitrogen can be considered completely accommodated at the surface of the microtube used, with α=0.986±0.019 when the diffuse-specular gas-surface interaction model is adopted and αt=0.991±0.020 (αn=1) when the Cercignani-Lampis model is adopted.

Pallid sturgeon larvae: The drift dispersion hypothesis

The fate of drifting pallid sturgeon larvae [Scaphirhynchus albus, Forbes and Richardson, 1905] from spawning in the Missouri River below Fort Peck Dam, Montana, USA remains in question. Previous estimates of drift duration used flow modeling and experimental releases of free embryo pallid sturgeon that were recaptured in nets at incremental distances downstream. The recapture studies hypothesized that the released larvae drift along the river bottom in an intact plume that flushes into the downstream reservoir where they die. Results were interpreted that nearly all drifting embryos would reach Sakakawea Reservoir (~375 river km downstream) in just 6 days, suggesting that there is insufficient drift distance for successful reproduction of pallid sturgeon. Those experiments recaptured less than 1% of the released larvae, thus the dispersal fate of the remaining ~99% of drifting larvae remains unknown. We hypothesized that the river is extremely dispersive due to complex channel bathymetry and flow, which spreads the plume of drifting particles bank to bank within a few kilometers downstream of the release location, and that the same would be true for drifting free embryos. This is referred to as the Drift Dispersion Hypothesis. This hypothesis was tested by conducting high-resolution 3D flow and depth mapping, spanning the width of the Missouri River for 338 km in coordination with an embryo release and recapture study conducted in June 2016. Fort Peck Dam discharge was stabilized for the experiment. Hydraulic base maps were used to calculate particle drift paths and estimate drift speeds in (i) the bottom boundary layer (0.5 m) and (ii) the whole water column, as a surrogate for drifting larvae. Drift path patterns indicated wide lateral dispersion across the river, bank to bank. Drift simulations indicated that less than 10% of the fastest drifting embryos could reach Sakakawea Reservoir in just 6.56 days, but only if they remained mid-column and in the channel thalweg the entire distance. However, the fastest drifting particles that remained in the bottom boundary layer would not reach Sakakawea Reservoir for 31 days. Concluded was that most drifting embryos must be swept from the thalweg into low velocity habitats and stall, extending their river residence time. Stall locations were recorded along the entire study reach. The results indicate that drift duration is not the limiting factor for pallid sturgeon recruitment when spawning occurs near the embryo release site downstream of Fort Peck Dam.

Climate Change Impacts on Flow and Suspended Sediment Yield in Headwaters of High-Latitude Regions—A Case Study in China’s Far Northeast

Climate change is expected to have stronger effects on water resources in higher latitude regions. Despite intensive research on possible hydrological responses in those regions to a warmer environment, our knowledge on erosion and sediment yield induced by the climate change in high-latitude headwaters is still limited. In this study, we estimated suspended sediment yields from 2021 to 2050 in a typical headwater area of far Northeast China to elucidate potential impacts of future climate change on surface runoff and erosion in higher latitude regions. We first parameterized the Soil and Water Assessment Tool (SWAT) using historical measurements to estimate runoff from the river basin. The model performed well in both the calibration (2006–2011) and the validation (2012–2014) periods, with an R2 of 0.85 and 0.88 and a Nash-Sutcliffe Efficiency (NSE) of 0.7 and 0.73, respectively. We also utilized historical measurements on sediment yields from the period 2006–2014 to develop a runoff-sediment yield rating curve, and the rating curve obtained an excellent goodness of fit (R2 = 0.91, p < 0.001). We then applied the calibrated SWAT model to two climate change projections, also known as Representative Concentration Pathways (RCP4.5 and RCP8.5), for the period from 2021 to 2050 to obtain future runoff estimates. These runoff estimates were then used to predict future sediment yield by using the developed runoff-sediment yield rating curve. Our study found a significant increase of annual sediment yield (p < 0.05) for both climate change projections (RCP4.5 = 237%; RCP8.5 = 133%) in this, China’s high-latitude region. The increases of sediment yield were prevalent in summer and autumn, varying from 102–299% between the two RCPs scenarios. Precipitation was the dominated factor that determined the variation of runoff and sediment yield. A warming climate could bring more snowmelt-induced spring runoff and longer rainy days in autumn, hence leading to higher erosion. These findings demonstrate that under the changing climate, soils in this high-latitude headwater area would be eroded twice to three times that of the baseline period (1981–2010), indicating a potential risk to the downstream water quality and reservoir management.

Downstream dispersal of zebra mussels (Dreissena polymorpha) under different flow conditions in a coupled lake-stream ecosystem

Dispersal, establishment, and spread of aquatic invasive species such as the zebra mussel (Dreissena polymorpha) can be influenced by riverine velocities and volumetric flows in invaded lake-stream ecosystems. Zebra mussels, which have a planktonic larval form (veliger), disperse rapidly downstream from a source population. Concentrations, dispersal, and body conditions of zebra mussel veligers were studied under different volumetric flow, or discharge, conditions in a coupled lake-stream ecosystem in northern Texas, USA. Veliger densities in lotic environments were strongly related to population dynamics in upstream lentic source populations. A strong exponential decrease in veliger density was observed through a 28-km downstream study reach. Increased water releases from the source reservoir increased veliger flux and dispersal potential, concomitantly increasing veliger flux and decreasing transit time. However, passage through release gates in the dam and increased turbulence in the river during high-discharge events could negatively affect body condition of veligers, and veliger body condition generally decreased from the source population to the farthest downstream site and was lower for veligers during periods of high discharge. Thus increased discharge appears to reduce the proportion of viable veligers because of increased turbulence-induced mortality. Colonization of distant downstream reservoirs can occur if discharge and propagule pressure are sufficient or if interim habitats are suitable for establishment of in-stream populations.

Metals in superficial sediments of a cascade multisystem reservoir: contamination and potential ecological risk

Cascade multisystem reservoirs are extremely complex ecosystems that require studies to improve understanding of their dynamics and functioning, including the effects of contamination with metals. In this work, superficial sediments were collected during two sampling campaigns (in the dry and rainy seasons) at 19 sites along a cascade multisystem reservoir in Sao Paulo, Brazil, formed by five reservoirs. The sediments were evaluated considering the following parameters: pseudo-total metals (Cu, Cd, Cr, Ni, Pb, Zn, Mn, Fe, and Al); bioavailable metal (Cu); organic matter; total phosphorus; total nitrogen; and grain size. In the last reservoir of this system, the enrichment factors indicated enrichment of Cu, Pb, Zn, and Mn. Despite this increased metals content, the pollution load index indicated an absence of pollution (PLI < 1), and the ecological risk was low (RI < 150). According to sediment quality guideline criteria, toxicity was unlikely to occur. Principal component analysis (PCA) and one-way ANOVA indicated heterogeneity among the reservoirs (P < 0.01) and between the sampling periods. The PCA results confirmed higher levels of nutrients in the upstream reservoirs, suggesting that nutrients were precipitated in the first reservoirs of the system. On the other hand, metal levels were higher in the downstream reservoirs. The main source of metal contamination in the region was the use of copper sulfate as an algicide. This included contamination by Pb and Zn, due to impurities in the copper sulfate employed. High Mn levels were associated with wastewater discharges and erosion. In addition to helping to improve understanding of the dynamics of metals in cascade multisystem reservoirs, this work could serve as a useful tool for the management of reservoirs with contaminated sediments.

Carbon Emission from Cascade Reservoirs: Spatial Heterogeneity and Mechanisms.

Carbon emission from reservoirs is considered to tarnish the green credentials of hydropower and has been extensively studied in single reservoirs. However, it remains unclear how carbon emission differs in cascade reservoirs and the mechanism behind the differences. In this study, carbon dioxide (CO2) and methane (CH4) emissions from cascade hydropower reservoirs were measured in the Lancang River, the Chinese section of the Mekong River. Our results demonstrate that carbon emissions from the river were increased by dam construction but exhibited spatial heterogeneity among cascade reservoirs. The first, most upstream, reservoir acted as the hotspot of CH4 and CO2 emissions, which were 13.1 and 1.7 times higher than those in downstream reservoirs, respectively. Similarly, the CH4/CO2 ratio of 0.023 in the first reservoir was higher than the others and made a greater contribution to the global warming effects of the cascade reservoirs. The sediment organic carbon in downstream reservoirs was negatively correlated with reservoir age (r2 = 0.993) and decreased at a rate of 0.389 mg g-1 yr-1, suggesting a potential decrease of carbon emission in the future. This study adds to our understanding of carbon emissions from cascade reservoirs and helps to screen effective strategies for future mitigation of the global warming effects from cascade hydropower systems.

Climate, wildfire, and erosion ensemble foretells more sediment in western USA watersheds

AbstractThe area burned annually by wildfires is expected to increase worldwide due to climate change. Burned areas increase soil erosion rates within watersheds, which can increase sedimentation in downstream rivers and reservoirs. However, which watersheds will be impacted by future wildfires is largely unknown. Using an ensemble of climate, fire, and erosion models, we show that postfire sedimentation is projected to increase for nearly nine tenths of watersheds by &gt;10% and for more than one third of watersheds by &gt;100% by the 2041 to 2050 decade in the western USA. The projected increases are statistically significant for more than eight tenths of the watersheds. In the western USA, many human communities rely on water from rivers and reservoirs that originates in watersheds where sedimentation is projected to increase. Increased sedimentation could negatively impact water supply and quality for some communities, in addition to affecting stream channel stability and aquatic ecosystems.

A successive approximation approach for short-term cascaded hydro scheduling with variable water flow delay

In cascaded hydro systems, water delay time is a very important factor that requires coordination between upstream and downstream reservoirs. Due to the nonlinear characteristics of the water delay time, modeling and solving short-term cascaded hydro scheduling (STCHS) is a very challenging task. This paper proposes a novel STCHS model with continuous variation of water delay time to describe real-world operations in detail. The proposed model includes a nonlinear function related to water delay time. A successive approximation (SA) approach is developed to address the nonlinearity by iterative calculation, making the problem tractable. The proposed model and method are validated with two-reservoir and ten-reservoir systems. Numerical results demonstrate that the proposed method produces more realistic results than existing methods when dealing with STCHS problems.

Significance of wetlands for sediment and nutrient reduction in Lake Tana Sub-Basin, Upper Blue Nile Basin, Ethiopia

Sedimentation from agricultural fields and seasonal eutrophication from non-point source inorganic nutrients (N, P and OM) on the lakes and reservoirs are the main problems in the Tana sub-basin, Ethiopia. The objective of this study was to quantify the amount of suspended sediment concentration and sediment fixed nutrients in the wetland. Two wetlands were selected purposefully to quantify how much sediment and nutrient trapped by the wetlands and 26 runoff events were sampled for each wetland at inlet and outlet points. All runoff samples were filtered by a filter paper and measured after air dried using sensitive balance to determine sediment amount in g/L. Only 10 representative samples were subjected to nutrient analysis in the laboratory. Averagely, 7 g/L (86%) and 3 g/L (80%) suspended sediment was absorbed by wetlands in site 2 and site 1 respectively. Regarding to nutrient loss, 53, 50 and 49% nitrogen, phosphorus and organic matter (OM) was absorbed by wetland in site 2 respectively. Whereas, it was 33, 29 and 31% in site 1. Thus, wetlands have crucial role to catch suspended sediment load and associated nutrients entering into downstream reservoirs and lakes.

Phosphorus fractions and its summer flux from sediments of deep reservoirs located at a phosphate-rock watershed, Central China

Abstract Huangbai River, including four enchained reservoirs, is located in a phosphate-rock watershed in Yichang City, Central China. Previous studies showed that pollution levels due to activities of phosphate mining (PM) were extremely high and the water quality of reservoirs was severely affected by sedimentation. Yet, detailed knowledge of the sediment is lacking at that high phosphorus (P) concentration basin. Therefore, the different P fractions and its diffusion fluxes at the water-sediment interface of four deep reservoirs have been investigated for the first time to understand the internal P loading. The results indicated that the concentrations of total P , ranging from 9,631.5 to 581.6 mg kg−1, exhibited an apparent spatial trend from the upstream to the downstream reservoirs, which corresponded with the activities of P mining in this basin. The P-fraction concentrations obtained from the sites were mainly ranked in this order: P associated with calcium (Ca-Pi) &amp;gt; organic P (Po) &amp;gt; P bound to aluminum (Al), ferrum (Fe) and manganese (Mn) oxides and hydroxides (Fe/Al-Pi). The orthophosphate diffusion fluxes ranged from −0.40 ± 0.09 to 0.95 ± 0.14 mg m−2 d−1 which were positively related to P fraction concentrations while negatively related to oxidation–reduction potential and dissolved oxygen values. These results implied the dynamics role of internal P loading. The principle component analysis suggested that PM activities and internal P loading were the most reactive factors in this river system.

Modelling the impacts of altered management practices, land use and climate changes on the water quality of the Millbrook catchment-reservoir system in South Australia

Sustainable management of drinking water reservoirs requires taking into account the potential effects of their catchments' development. This study is an attempt to estimate the daily patterns of nutrients transport in the catchment – reservoir systems through the application of the ensemble of complementary models SWAT-SALMO. SWAT quantifies flow, nitrate and phosphate loadings originating in catchments before entering downstream reservoirs meanwhile SALMO determines phosphate, nitrate, and chlorophyll-a concentrations within the reservoirs. The study applies to the semi-arid Millbrook catchment-reservoir system that supplies drinking water to north-eastern suburbs of Adelaide, South Australia. The catchment hosts viti- and horticultural land uses. The warm-monomictic, mesotrophic reservoir is artificially aerated in summer. After validating the simulation results for both Millbrook catchment and reservoir, a comprehensive scenario analysis has been conducted to reveal cascading effects of altered management practices, land uses and climate conditions on water quality in the reservoir. Results suggest that the effect on reservoir condition in summer would be severe, most likely resulting in chlorophyll-a concentrations of greater than 40 μg/l if the artificial destratification was not applied from early summer. A 50% curbing of water diversion from an external pipeline to the catchment will slightly limit chlorophyll-a concentrations by 1.22% as an effect of reduced inflow phosphate loads. The simulation of prospective land use scenarios converting 50% of present pasture in the Millbrook catchment into residential and orchards areas indicates an increase of summer chlorophyll-a concentrations by 9.5–107.9%, respectively in the reservoir. Global warming scenarios based on the high emission simulated by SWAT-SALMO did result in earlier growth of chlorophyll-a but overall the effects on water quality in the Millbrook reservoir was not significant. However scenarios combining global warming and land use changes resulted in significant eutrophication effects in the reservoir, especially in the unmanaged condition with stratification in summer. This study has demonstrated that complementary model ensembles like SWAT–SALMO allow to comprehend more realistically cascading effects of distinct catchment processes on internal reservoir's processes, and facilitate integrated management scenarios.

Multi-Stage Dynamic Programming Method for Short-Term Cascade Reservoirs Optimal Operation with Flow Attenuation

In Short-term Cascade Reservoirs Optimal Operation (SCROO), the flow from upstream reservoir to downstream reservoir which propagates in the natural channel can be generalized as not only transposition but also attenuation. In order to get the relative accurate inflow series of downstream reservoir, the paper tries to adopt the Muskingum model to simulate the inflow of the downstream reservoir instead of the easier processing in most papers of SCROO: ignoring the flow attenuation in natural channel. Considering the flow attenuation between the cascade reservoirs, the SCROO problem do not satisfy the “Principe of Optimality” anymore, so the Dynamic Programming(DP) is no longer applicable. The paper proposes a new improved DP named Multi-Stage Dynamic Programming (MSDP) based on DP. In MSDP, multi-stage’s outflow of upstream reservoir is taken into account at the same time and then inflow of downstream reservoir can be calculated by the Muskingum model, which can include much more flow information than the easier processing with DP, and the inflow of downstream reservoir will be closer to the actual one. The paper takes the cascade hydro-power stations consisting of Jindong and Guandi in Yalong river basin as an example to solve the SCROO problem with MSDP. By comparing the operation result of MSDP and DP with the easier processing, the operation strategy of MSDP can gain further benefits than DP’s in actual operation.

Weighting the impacts to stream water quality in small basins devoted to forage crops, dairy and beef cow production

Livestock for beef and milk production are important economic activities worldwide. These require intensive cultures of pastures and forages, with the consequent impacts on water quality in downstream rivers and reservoirs. Monthly temporal variation of nutrients and water quality were assessed along one year at basin scale (basin area <3500 ha). Several indicators of farming intensity (number of dairy cows and beef cows, percentage of area devoted to crops) and management practices (effluent treatment, fertilizer application) were related to the export of nutrients and sediments from the basins and with the water quality of receiving streams using partial least square regression analysis (PLS). According to PLS analysis, the most relevant variables to explain water quality degradation and high export coefficients of nutrients and sediments, were the percentage of basin area dedicated to crop activities and the density of dairy cows without effluent treatment. Beef and dairy cows had an important local impact on stream water without animal access restrictions. We also propose some hypotheses regarding the transport pathways of sediments and nutrients to streams. Our results demonstrate the urgent need to implement best management practices at the farm scale within each basin, focusing on: adequate phosphorus fertilization, implementation of a complete dairy effluent treatment system and animal restriction to fluvial channels.

Environmental filters predict the trait composition of fish communities in reservoir cascades

Dam construction alters flow regimes and can change the composition of aquatic communities. Using data from three Brazilian hydrographic basins, we tested the hypothesis that reservoir cascades act as environmental filters for fish traits. This dataset included information on different environmental variables and fish traits (diet, migration, fecundation, parental care, position in the water column, and body size), and we used multivariate analysis (partial RLQ) to quantify the relationships between environmental variables, species abundance and traits. We found that the abundance of migratory species declined towards downstream reservoirs, which tend to be smaller and less turbid with a shorter water residence time than upstream reservoirs. We also found evidence of an association between reservoir age and the domination of fish communities by small-sized species with parental care, external fecundation, and benthic habits. Our findings suggest that particular fish traits are selected for across reservoir cascades.

Optimal crop plans for a multi-reservoir system having intra-basin water transfer using multi-objective evolutionary algorithms coupled with chaos

Optimizing a multi-reservoir system is complicated, since the operation of one reservoir depends on other reservoir and may also have conflicting multiple objectives. The conflicting purposes of a multi-reservoir system requires a systematic multi-objective study. Recently, multi-objective evolutionary algorithms (MOEAs) have been widely used for the multi-objective analysis of the reservoir systems. However, the simple MOEAs result in premature convergence and local optimal solution for complex non-linear multi-objective optimization problems. To improve the performance and maintain the diversity in the population, chaos is being combined with the evolutionary algorithms for optimizing complex problems. In the present study, the chaos algorithm is coupled with MOEAs such as non-dominated genetic algorithm-II (CNSGA-II) and multi-objective differential evolution algorithm (CMODE) to derive an optimal crop planning for a multi-reservoir system having intra-basin water transfer. The model is developed with the objective of maximizing the net benefits and maximizing the crop production, subject to various physical, land and water availability constraints. The resulted optimal policy is further assessed using a simulation model and its performance is evaluated using various statistical indices. It is found that CMODE has resulted in slightly higher net benefits of Rs. 1921.77 Million and 1201.55 thousand tons of crop production with an irrigation intensity of 106.29% compared to other techniques used in this study. It has also resulted in an optimal spatial and temporal intra-basin water transfer from the upstream reservoirs to the downstream reservoir. The simulation of optimal results showed that the optimal policies obtained from CMODE performed well for longer period with less irrigation deficits. All the reservoirs in the system achieved more than 95% reliability in meeting the irrigation demands and intra-basin water transfer.

Application of Polyurethane Abrasion Resistance Paint on the Arch Gate of Tunnel Spillway in Xiaolangdi

Seventeen consecutive concerned water-sediment regulation has been carried out in Yellow River Xiaolangdi reservoir since 2002, in order to reduce the downstream river channel and reservoir sediment deposition. The water flow went through the arc working gate place will reach 33 m/s during the flood and sand, combined with open/close state under dynamic water in the daily operation, there are some serious erosion pit appeared on the arc facade panels. The gate was thinned, and the service life got shorter, which threated the safe operation of the gate. Therefore, it is necessary to use new type high abrasion resistance and high corrosion double function of paint to repair the gate panel. High elastic polyurethane resistant paint was developed, whose polyurethane was the main basic material, adding antirust pigment and scales the water-blocking material of stainless steel. The abrasive wear performance of two kinds of paint was tested by using rotary machine in the conditions of four different flow velocity and 50 kg/m3 sediment concentration, the results showed that the wear resistance of polyurethane abrasion resistance paint is 50 to 80 times of stainless steel flake epoxy paint. The drawing method is adopted to test the paint and substrate of peel strength, the results showed that the bonding performance of polyurethane abrasion resistance paint is equal to the stainless steel flake epoxy paint. The self-developed paint was carried out on the arc working gate place after a flood test, compared with the traditional protection plan, the results showed that the paint on arc gate had played a very good effect of corrosion and abrasion protection, and had very good practicability and value of popularization and application, which provided reference for other tunnel gate abrasion protection.

Otolith chemistry indicates walleye movement and entrainment in a large serial reservoir system

AbstractUnderstanding fish movement in impounded river systems is important for fisheries management. Otolith chemistry was used to examine walleye Sander vitreus (Mitchill) intra‐ and inter‐reservoir movement in four Missouri River impoundments. Age‐0 individuals were reclassified with 75%–93% accuracy to known natal sites, allowing for reliable evaluation of movement patterns of age‐1 and older fish. Nearly half of walleye occupied the same location annually (i.e. site residency) between 2009 and 2010. In 2011, during the largest flood on record since 1898, downstream movement (49% of age‐1 and older fish) exceeded upstream movement (7%) and site residency (33%) across the study area. After the flood, most walleye moved downstream within reservoirs (45%) or were site residents (37%). Entrainment occurred most frequently during the flood year and was proportionally greatest in downstream reservoirs. Otolith chemistry is useful for understanding walleye movement and entrainment and is a tool for fisheries management with applications such as informing reservoir water releases, harvest regulations and habitat protection and rehabilitation within and outside the Missouri River reservoir system.

Comparison between steady state method and pulse transient method for coal permeability measurement

Coal permeability measurement is significant for research on reservoir characteristics and development of coalbed methane. In order to find a favourable method to obtain exact data of coal permeability, two different methods are operated to investigate coal permeability evolution. Steady state method is applied with constant upstream gas pressure and downstream pressure to keep constant pressure difference. Permeability is measured when velocity of gas flow is constant. Pulse transient method is applied with a pulse upstream pressure increment to discharge gas through coal sample to downstream gas reservoir. Permeability is calculated when the upstream reservoir and downstream reservoir reach a new equilibrium pressure. Experiments by different methods are both conducted on 2.5 cm diameter, 2.5–5 cm long cylindrical samples at same constant confining pressure and axial pressure, using both non-adsorbing (helium (He)) and strongly adsorbing (carbon dioxide (CO2)) gases. Every single coal sample is measured by both methods, while all samples are collected from Southeast Ordos Basin in China. The results are compared to investigate the advantages and disadvantages of the two methods. Permeability measured by steady state method is slightly larger than that measured by pulse transient method, which indicates that pulse transient method is preferable for measuring low permeability measurement. Factors that may influence the results of measurement are analyzed. Steady state method may destroy the structure of coal and slightly enlarge the pore fracture, with constant pore pressure, which results in higher permeability. On the contrary, pulse transient method keeps samples close to in situ condition, which obtains more exact data. However, several improvements are needed to minimize the error of the pulse transient methods. Temperature has important influence on permeability measurement.

Air-water CO2 and CH4 fluxes along a river-reservoir continuum: Case study in the Pengxi River, a tributary of the Yangtze River in the Three Gorges Reservoir, China.

Water surface greenhouse gas (GHG) emissions in freshwater reservoirs are closely related to limnological processes in the water column. Affected by both reservoir operation and seasonal changes, variations in the hydro-morphological conditions in the river-reservoir continuum will create distinctive patterns in water surface GHG emissions. A one-year field survey was carried out in the Pengxi River-reservoir continuum, a part of the Three Gorges Reservoir (TGR) immediately after the TGR reached its maximum water level. The annual average water surface CO2 and CH4 emissions at the riverine background sampling sites were 6.23±0.93 and 0.025±0.006mmolh-1m-2, respectively. The CO2 emissions were higher than those in the downstream reservoirs. The development of phytoplankton controlled the downstream decrease in water surface CO2 emissions. The presence of thermal stratification in the permanent backwater area supported extensive phytoplankton blooms, resulting in a carbon sink during several months of the year. The CH4 emissions were mainly impacted by water temperature and dissolved organic carbon. The greatest water surface CH4 emission was detected in the fluctuating backwater area, likely due to a shallower water column and abundant organic matter. The Pengxi River backwater area did not show significant increase in water surface GHG emissions reported in tropical reservoirs. In evaluating the net GHG emissions by the impoundment of TGR, the net change in the carbon budget and the contribution of nitrogen and phosphorus should be taken into consideration in this eutrophic river-reservoir continuum.