High Water Discharge Research Articles

Non-linear response of the Golo River system, Corsica, France, to Late Quaternary climatic and sea level variations

Disentangling the impact of climatic and sea level variations on fluvio-deltaic stratigraphy is still an outstanding question in sedimentary geology and geomorphology. We used the Golo River system, Corsica, France, as a natural laboratory to investigate the impact of Late Quaternary climate and sea level oscillations on sediment flux from a catchment and on fluvio-deltaic stratigraphy. We applied a numerical model, PaCMod, which calculates catchment sediment production and transport and compared modeling output to the sedimentary record of the Golo alluvial-coastal plain, whose chronology was reinterpreted using new optical stimulated luminescence (OSL) ages on feldspars. Our modeling, OSL ages, and geomorphological results indicate that the two main phases of braidplain development in the Golo alluvial-coastal plain occurred during the cold–dry phases of MIS5 and during the late MIS4-early MIS3, as a consequence of high catchment erosion rates and low water discharge. Incision and sediment reworking occurred during sea level low stand periods (MIS4 and late MIS3-MIS2). High sediment flux pulses from the catchment outlet were generated during the Lateglacial and early Holocene, as a result of the release of sediments previously stored within the catchment and enhanced snowmelt. Our results suggest a non-linear response of the Golo River system to climatic and eustatic changes, caused by sediment storage within the catchment and geomorphological thresholds. This indicates that a direct comparison between palaeo-climate and stratigraphy is not possible without considering catchment sediment storage and sediment transport delays out of the catchment.

Seasonal variation in river water chemistry of the middle reaches of the Yellow River and its controlling factors

In order to reveal the seasonal variations of river water chemistry and its controlling factors in the middle reaches of the Yellow River, river water samples were collected weekly from the Longmen hydrological station over the whole year of 2013. Major cation and anion compositions were measured. The major ionic compositions of the dissolved load exhibited distinct seasonal variability over the one year period, reflecting seasonal differences in relative inputs from various sources and weathering reactions within the catchment. A forward model was used to calculate the apportionments of rain, anthropogenic, silicate, evaporite, and carbonate origins on a seasonal basis. The contributions of both rain and anthropogenic sources to the middle Yellow River were less than ~12% in average, with little seasonal variations in 2013. The calculations showed that silicate sources had a relatively large impact on water chemistry during the pre- and early-monsoon seasons, though both silicate and carbonate weathering increased greatly during the monsoon season. The high silicate input during the pre- and early-monsoon seasons was attributed to the waters potentially derived from plateau headstream, glacial melting, and soil pore. Meanwhile, the dominated contributions of evaporites and carbonates in the late- and post-monsoon seasons were resulted from their rapid dissolution from the loess plateau through physical erosion acceleration along with high water discharge, because widespread loess is characterized by easy denudation and high carbonates and evaporites. Our densely time-series data also highlighted a significant impact of extreme hydrological events on water chemistry in semi-arid area. During the ice melting interval in the springtime, more silicate-origin ions entered the river from melting water, whereas during the stormy event interval in the peak monsoon, more carbonates and evaporites reached the Yellow River from the loess plateau via accelerated physical erosion. Our data shed further light on processes responsible for seasonal variation of river chemistry of the Yellow River and modern loess weathering.

Relationship between water discharge and sulfate sources of the Yangtze River inferred from seasonal variations of sulfur and oxygen isotopic compositions

Resolving sulfate sources in river systems and thus to the global ocean is important for understanding the sulfur biogeochemical cycle. The Yangtze River is one of most important large rivers connecting land and sea, showing a trend of acidification characterized by persistently increasing SO42− concentration. A weekly sampling campaign from the middle Yangtze River in Wuhan was conducted, over a 1-year period in 2011, to systematically examine the effects of seasonality and associated water discharge on the balance of sulfate sources of the Yangtze River. The SO42− concentrations varied from 8.6 to 55.4mg/L with a discharge-weighted average of 30.0mg/L, while the SO42− fluxes varied from 103.2 to 1257.6kg/s with an annual average of 532.5kg/s. The δ34SSO4 values ranged between 6.7‰ and 16.2‰ with a discharge-weighted average of 10.4‰, while the δ18OSO4 values ranged between 1.6‰ and 10.5‰ with a discharge-weighted average of 5.1‰. In comparison to the low water discharge period, the period of high water discharge of the Yangtze River in Wuhan is characterized by 1) a doubling in water discharge with higher water level by 5–10m; 2) a concomitant doubling in SO42− flux without substantial change in SO42− concentration; 3) a systematic increase of δ34SSO4 and δ18OSO4 values; 4) a significant increase of sulfate contribution from evaporites dissolution. From the observed seasonal variation of sulfur and oxygen isotopic composition of sulfate, a relationship between the dynamic water discharge and dominant sulfate sources of the Yangtze River was inferred. During the period of low water discharge in January–mid May, the sulfur and oxygen isotopic compositions of sulfate had averaged values of 8.3±0.4‰ for δ34SSO4 and 4.9±0.7‰ for δ18OSO4, suggesting the riverine SO42− of the Yangtze Riveris derived from sulfide oxidation, atmospheric deposition and evaporite dissolution; whereas during the period of low water discharge in December, the contribution of anthropogenic sulfate could be important, indicated by relatively higher δ34SSO4 (10.5±1.5‰) and δ18OSO4 (9.6±1.0‰) values. In contrast, during the period of high water discharge in June-September, the dual-isotope compositions were characterized by 14.7±0.7‰ for δ34SSO4 and 8.1±0.7‰ for δ18OSO4, indicating sulfate from dissolution of evaporites would be a dominant source. The jump event of dual-isotopic composition between low and high water discharge occurred when a half-year drought suddenly turned into the flood season. Due to the water storage dispatch of the Three Gorge Dam, the Hanjiang River could make a greater impact on the variation of water discharge and thus sulfate sources of the Yangtze River during the transition from high to low water discharge in October–November. However, the relationship between water discharge and sulfate sources of the Yangtze River need s to be confirmed by additional years of observation. Further studies on the mechanisms of water discharge controlling sulfate sources of the Yangtze River is urgently required, as well as a mixing model to calculate the contribution of different sulfate sources.

Modelling the fate of nitrite in an urbanized river using experimentally obtained nitrifier growth parameters

Maintaining low nitrite concentrations in aquatic systems is a major issue for stakeholders due to nitrite's high toxicity for living species. This study reports on a cost-effective and realistic approach to study nitrite dynamics and improve its modelling in human-impacted river systems. The implementation of different nitrifying biomasses to model riverine communities and waste water treatment plant (WWTP)-related communities enabled us to assess the impact of a major WWTP effluent on in-river nitrification dynamics. The optimal kinetic parameters and biomasses of the different nitrifying communities were determined and validated by coupling laboratory experiments and modelling. This approach was carried out in the Seine River, as an example of a large human-impacted river with high nitrite concentrations. The simulation of nitrite fate was performed at a high spatial and temporal resolution (Δt = 10 min, dx¯ = 500 m) including water and sediment layers along a 220 km stretch of the Seine River for a 6-year period (2007–2012). The model outputs were in good agreement with the peak of nitrite downstream the WWTP as well as its slow decrease towards the estuary. Nitrite persistence between the WWTP and the estuary was mostly explained by similar production and consumption rates of nitrite in both water and sediment layers. The sediment layer constituted a significant source of nitrite, especially during high river discharges (0.1–0.4 mgN h−1 m−2). This points out how essential it is to represent the benthic layer in river water quality models, since it can constitute a source of nitrite to the water-column. As a consequence of anthropogenic emissions and in-river processes, nitrite fluxes to the estuary were significant and varied from 4.1 to 5.5 TN d−1 in low and high water discharge conditions, respectively, over the 2007–2012 period. This study provides a methodology that can be applied to any anthropized river to realistically parametrize autochthonous and WWTP-related nitrifier communities and simulate nitrite dynamics. Based on simulation analysis, it is shown that high spatio-temporal resolution hydro-ecological models are efficient to 1) estimate water quality criteria and 2) forecast the effect of future management strategies. Process-based simulations constitute essential tools to complete our understanding of nutrient cycling, and to decrease monitoring costs in the context of water quality and eutrophication management in river ecosystems.

Assessment of Risk Due to Debris Flow and Its Application to a Marine Environment

The purpose of this study is to evaluate the behavior and mechanism of a debris flow on various slopes through numerical simulation. The numerical simulation consisted of using equations related to mass conservation and momentum conservation in order to consider erosion and deposition, and the Finite Difference Method was applied. As the inflow water discharge in the upstream of the channel increases, the curve of the water discharge exhibits instability and, as time passes, the fluctuation of the high water discharge continues. In regions where the mountain areas and the ocean are connected, it is deduced that the high level of sediment concentration can greatly affect the environment surrounding the ocean. The numerical model of this study was applied in Kangwon Province of South Korea. The results show that when the debris flow reaches downstream, the flow discharge and water flow depth increase. Erosion occurs more than deposition and much of the sediment runs off downstream. The result of the simulation performed at point of sediment discharge runoff is 114,216 m3. This study will provide useful information in predicting disasters caused by debris flow and in planning for various countermeasures to prevent debris-flow-related disasters.

Numerical and Laboratory Approach to the Prediction of Flood Stage in Lowland Tidal River

The revised Malaysian Urban Stormwater Management Manual (MSMA) eludes the importance of tidal backwater analysis in the engineering of lowland river drainage. Tidal gates and flood gates can only be adequately designed if a detailed investigation of the dynamic interactions of tidal high water and storm discharge be conducted. We propose a numerical and laboratory investigation of the lower Klang River in order to better understand the independent and joint effects of these factors to river flood stage.

Climate Change and Land Use Change in the Eastern Coastal Belt of Bangladesh, Elucidated by Analyzing Rice Production Area in the Past and Future

Climate change is an important issue now-a-days. Global warming i.e. climate change causes sea level rise and that affect the coastal agricultural areas of Bangladesh. The net-cropped area of eastern coastal zone in Bangladesh has been decreasing over the years due to various purposes and the most common one is the land inundation and salinity intrusion by tidal water. The main aims of the study is to assess the change in climatic conditions particularly temperature, rainfall and agricultural land use change in the past and future. Past rainfall, temperature and salinity data have been used to assess the climatic and salinity conditions of the area under investigation. Normalized difference vegetation Index (NDVI) and False Color Composite (FCC) of digital Land sat images have been used to identify land use pattern and Boro rice coverage area. During last 31 years (1978 -2009) 31% rice production land has converted to shrimp culture and salt farming. Salinity intrusion is one of the major causes of agricultural land use change. Salinity level has increased dramatically in dry season during last decade due to increase of temperature, low rainfall pattern, high evaporation rate and low water discharge to the river systems. Future landuse has been projected for 2039 by Markov Model. Result shows that rice production area will decrease rapidly due to salinity intrusion as well as climate change which may threat for food security of Bangladesh. Hereafter, the Government of Bangladesh, national and international institutions will have to work together for minimizing the effect of climate change for food security. DOI: http://dx.doi.org/10.3329/jles.v8i0.20151 J. Life Earth Sci., Vol. 8: 83-91, 2013

Diel and seasonal variations in bacterioplankton production in a hypertrophic shallow lagoon

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 72:255-267 (2014) - DOI: https://doi.org/10.3354/ame01701 Diel and seasonal variations in bacterioplankton production in a hypertrophic shallow lagoon Gabriela Onandia*, Maria Rosa Miracle, Cristina Blasco, Eduardo Vicente Department of Microbiology and Ecology, ICBiBE, University of Valencia, Calle Dr. Moliner 50, 46100 Burjassot, Valencia, Spain *Corresponding author: gabriela.onandia@uv.es ABSTRACT: Diel and seasonal variations in bacterial secondary production (BP) were investigated in the hypertrophic Albufera de Valencia (Spain) by measuring 3H-leucine and 3H-thymidine incorporation rates (LIR and TIR). LIR and TIR were positively correlated. Seasonal variations in the LIR:TIR ratio seemed to be related to dissolved organic carbon (DOC) availability, with higher concentrations favoring protein synthesis. The light:dark ratio of the incorporation rates of both radiotracers was close to 1. However, this ratio tended to be >1 when DOC was lower, namely in winter. A clear diel pattern in bacterial activity was found, with an increasing trend during the night hours. The opposite diel pattern was observed for DOC. BP remained similar across seasons but showed a decrease in late winter during a period of high water discharge through the lagoon and concurrent minimum chlorophyll a concentrations. A comparison between hypertrophic systems aiming to explore the upper BP limit indicated that our BP estimates were considerably high but did not surpass previous values in hypertrophic lakes. KEY WORDS: Bacterioplankton production · Carbon flux · Shallow hypertrophic lake Full text in pdf format PreviousNextCite this article as: Onandia G, Miracle MR, Blasco C, Vicente E (2014) Diel and seasonal variations in bacterioplankton production in a hypertrophic shallow lagoon. Aquat Microb Ecol 72:255-267. https://doi.org/10.3354/ame01701 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 72, No. 3. Online publication date: July 10, 2014 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2014 Inter-Research.

Ecological diatom guilds are useful but not sensitive enough as indicators of extremely changing water regimes

Classification of taxa into ecological guilds is based on the relation of respective taxa to nutrient enrichment and their resistance to physical disturbance. We hypothesized that ecological guild's proportion and their taxa composition were strongly effected both by extremely changing water regime and nutrient contents. Diatom composition, guild dynam- ics and the diatom-based ecological status assessment index were studied in the Sebes-Koros River (South- East Hungary) in a year with extremely changing water regimes. There were highly pronounced changes in species composition during the whole vegetation period including the formation of running and stand- ing water segments in autumn. While the proportions of ecological guilds showed no significant correlations with the studied environmental parameters, they were more balanced in high water discharge period than in the low water discharge period. Taxa compositions of segments were mainly determined by the preferences and strategies of a respective species and/or genera, regardless to their guild affiliation. These results point out that ecological guild characterisation should be refined using ecological knowledge at the subgenus level. We suggest to establish several subdivisions within the guilds to consider the differences in life strategies (CSR model) and life forms, and to imple- ment the accumulated knowledge of nutrient prefer- ences/indication of a respective taxa.

Impact of artificial water and sediment discharge regulation in the Huanghe (Yellow River) on the transport of particulate heavy metals to the sea

Variations in the concentrations of major particulate heavy metals (PHMs) (Mn, Pb, Zn, V, Cr, and Ni) and fluxes into the sea during the water–sediment regulation scheme (WSRS) in the Huanghe (Yellow River) were examined based on observational and measured data during June and July of 2009. Two stages of variations in the concentrations of PHMs were observed in the WSRS with lower values in the early stage and higher values in the late stage. The early stage corresponded to a high water discharge with coarser sediment that was largely scored from the riverbed, and the late stage corresponded to a low water discharge with much finer sediment that was released from the Xiaolangdi reservoir. The significant increase in PHM concentrations by 2–4 fold from the early to the late stage largely resulted from a decrease in the suspended-sediment grain size and an increase in the quantity of anthropogenic pollutants caused by changes in the sediment sources from riverbed in the lower reaches to the Xiaolangdi reservoir during the WSRS. The concentrations of PHMs, particularly in the late stage of the WSRS, were approximately two times as high as those during the pre-WSRS period as the anthropogenic pollutants have been increasing in recent years. More than 57% of the annual quantity of PHMs was transported to the sea during the WSRS, and over 34% of that from the Xiaolangdi reservoir was delivered to the sea during the late stage of the WSRS over a period of approximately 4–5days. This large quantity of heavy metals, with a high proportion of labile components because of the increasing contribution of anthropogenic pollutants, emptied into the sea over a short period and may thus drastically alter the eco-environment in the river mouth and its adjacent seas.

Pre-vegetation fluvial floodplains and channel-belts in the Late Neoproterozoic–Cambrian Santa Bárbara group (Southern Brazil)

One key element to the understanding of the dynamics of pre-vegetation fluvial systems is the reconstruction of processes operating on their floodplains given that, in modern systems, channel banks and floodplains are the environments most affected by plant colonization. Notwithstanding, few pre-vegetation floodplains have been described, and major questions regarding their most basic characteristics are still unresolved. In order to address these questions, detailed analysis of coeval channel-belt, fluvial floodplain and alluvial-fan deposits from the Santa Bárbara Group (Late Neoproterozoic to Early Cambrian, southern Brazil) was performed. While floodplain facies resemble ephemeral stream deposits, being coarser-grained than modern floodplains and marked by the stacking of flood event cycles, channel-belt deposits show composite bars, which do not present conclusive evidence for high water discharge variation. The floodplain deposits show particular features common to other pre-vegetation fluvial systems, such as better preserved small-scale structures, lack of bioturbation, and abundance of cross-laminated sandstones, while other features differ from previous depositional models, namely abundant mudcracks and evidence of soil formation. The lateral variation of depositional systems recorded in the Santa Bárbara Group shows contrasting signatures of water discharge variation in sand-dominated coeval environments, and offers an example of the relation between different alluvial environments before the evolution of land plants.

Acid deposition strongly influenced element fluxes in a forested karst watershed in the upper Yangtze River region, China

The hydrological fluxes and associated element input–output budgets were investigated from July 2007 to August 2008 in a forested karst watershed in Guizhou, southwest China. Banning logging in the watershed (mountain closure) has been in practice as an effort to reduce soil erosion and its impact to Yangtze River. The watershed lies in an area heavily affected by acid deposition. Therefore, specific objective of this study was to investigate the impact of acid deposition on elemental fluxes in the forested karst watershed. Weekly bulk precipitation, throughfall, and stemflow samples were collected from two forest plots. Volume and chemistry of streamflow out of the watershed were continuously monitored to determine the concentration and fluxes of elements. The bulk precipitation had low pH value of 4.8 as annual volume-weighted mean and high SO42--S and Ca2+ concentrations. Concentrations of elements were higher in throughfall or stemflow than the bulk precipitation. Forested karst watershed had low streamflow but high water discharge through deep seepage, occupying 4.0% and 40.4% of the annual bulk precipitation, representatively. Streamflow had high and constant pH value of 8.3 as annual mean, and was dominated by Ca2+ and Mg2+. The annual net input of SO42--S into the watershed was greater than 40kgSha−1year−1. The strikingly high rate of output of Ca2+ and Mg2+, greater than 250kgha−1year−1 and 150kgha−1year−1, representatively, reflected the fast weathering of carbonaceous rocks, and the strong neutralizing capacity of weathering to acid deposition in the karst watershed. This research indicates that acid deposition strongly influenced the export of nutrients out of the karst watershed and can accelerate transformation of the local land form.

Fluvial sediment supply, mud banks, cheniers and the morphodynamics of the coast of South America between the Amazon and Orinoco river mouths

Abstract The overarching morphosedimentary control on the coast of South America between the Amazon and Orinoco rivers is the massive muddy discharge of the Amazon (from c. 754×10 6 to 1000×10 6 t a −1 ). This mud supply by the world’s largest river reflects sediment sourcing from the Andes, weathering in a tropical–equatorial climate and the extremely high water discharge ( ca 173 000 m 3 s −1 ). Amazon mud forms an estuarine mega-turbidity maximum on the shelf that feeds the growth of a subaqueous delta. About 15–20% of this mud forms coastal banks that migrate towards the mouth of the Orinoco, which has constructed a large subaerial delta. This muddy coast exhibits interspersed beaches and cheniers constructed from sand supplied by the smaller rivers and by the Orinoco, and is characterized by extremely large spatio-temporal geomorphic variability resulting from intense wave-reworking of the migrating banks, mangrove colonization and destruction, and erosion in interbank areas. These dynamic processes also drive important biogeochemical recycling, enhancing coastal productivity while efficiently remineralizing organic matter and promoting authigenic mineral formation. This muddy coast is being impacted by human-induced changes, in Guyana in particular. The Amazon–Orinoco coast provides an analogue for muddy, wave-dominated shorefaces in the geological record.

Maternal and environmental influences on egg size and juvenile life‐history traits in Pacific salmon

Life-history traits such as fecundity and offspring size are shaped by investment trade-offs faced by mothers and mediated by environmental conditions. We use a 21-year time series for three populations of wild sockeye salmon (Oncorhynchus nerka) to test predictions for such trade-offs and responses to conditions faced by females during migration, and offspring during incubation. In years when their 1100 km upstream migration was challenged by high water discharges, females that reached spawning streams had invested less in gonads by producing smaller but not fewer eggs. These smaller eggs produced lighter juveniles, and this effect was further amplified in years when the incubation water was warm. This latter result suggests that there should be selection for larger eggs to compensate in populations that consistently experience warm incubation temperatures. A comparison among 16 populations, with matching migration and rearing environments but different incubation environments (i.e., separate spawning streams), confirmed this prediction; smaller females produced larger eggs for their size in warmer creeks. Taken together, these results reveal how maternal phenotype and environmental conditions can shape patterns of reproductive investment and consequently juvenile fitness-related traits within and among populations.

Response of microcrustacean communities from the surface—groundwater interface to water contamination in urban river system of the Jarama basin (central Spain)

In order to evaluate the water quality at the surface/groundwater interface (hyporheic zone), the pattern of microcrustacean assemblages in response to environmental stress caused by urban industrial contamination was studied in the Jarama River basin (central Spain) during high water discharges (March and April 2011). The clustering of biological variables and the concentration of urban contaminants in hyporheic waters showed that pristine hyporheic waters have moderate species diversity (two to seven species) and dominance of k strategist stygobites, whereas excessively contaminated sites are devoid by crustaceans. An intermediate level of disturbance in hyporheic waters is associated with a peak of species taxonomic diversity (four to nine species) and proliferation of r strategist more tolerant species. Typical species found in hyporheic zone, e.g., Paracyclops imminutus (Copepoda, Cyclopoida), Cryptocandona vavrai (Ostracoda) and Herpetocypris chevreuxi (Ostracoda), were good indicators of high concentrations of Cr, Mn, Ni, Cd, Pb and VOCs; whereas the stygobites do not show any significant correlation. The effectiveness of hyporheic crustaceans as efficient bioindicators for assessing the current ecological status of river ecosystems is emphasised.

Trace Metal Budgets for Forested Catchments in Europe—Pb, Cd, Hg, Cu and Zn

Input/output budgets for cadmium (Cd), lead (Pb) and mercury (Hg) in the years 1997–2011 were monitored and determined for 14 small forest-covered catchments across Europe as part of the Integrated Monitoring program on the effects of long-range pollutants on ecosystems. Metal inputs were considered to derive from bulk deposition, throughfall and litterfall. Outputs were estimated from run-off values. Litterfall plus throughfall was taken as a measure of the total deposition of Pb and Hg (wet + dry) on the basis of evidence suggesting that, for these metals, internal circulation is negligible. The same is not true for Cd. Excluding a few sites with high discharge, between 74 and 94 % of the input Pb was retained within the catchments; significant Cd retention was also observed. High losses of Pb (>1.4 mg m−2 year−1) and Cd (>0.15 mg m−2 year−1) were observed in two mountainous Central European sites with high water discharge. All other sites had outputs below or equal to 0.36 and 0.06 mg m−2 year−1, respectively, for the two metals. Almost complete retention of Hg, 86–99 % of input, was reported in the Swedish sites. These high levels of metal retention were maintained even in the face of recent dramatic reductions in pollutant loads.

Manila water's experience in the provision of sewerage service in the east zone of Metro Manila

In 1997, major improvements were needed in the provision of water and sewerage services in Metro Manila. Only 26% of the population served had 24-hour access to potable water and a mere 3% were connected to adequate wastewater treatment facilities. Coupled with these conditions were issues of high non-revenue water and indiscriminate discharge of untreated wastewater to all major water bodies of the metropolis. As a result, the Metropolitan Waterworks and Sewerage System (MWSS), the government agency mandated to provide water and sewerage services in Metro Manila, privatized its operation via a public-private partnership. Manila Water Company obtained the exclusive right of providing these services for the East Zone of Metro Manila. This paper identifies the challenges encountered in providing sewerage services during Manila Water's first 15 years of operation. Poor data availability, lack of available land, fragmented infrastructure planning, and low customer acceptance were among the key challenges that threatened the efficient delivery of service. Consequently, this paper also highlights the resultant strategies employed by Manila Water to address the aforementioned challenges. Implementation of inventive technical solutions, combined with the harnessing of human resources and increased stakeholder awareness, were among the strategies utilized to provide sewerage and sanitation services in the most efficient manner possible. As of 2012, Manila Water now operates 38 wastewater facilities with a total capacity of 135 million liters per day (MLD) corresponding to 100% septage coverage and 23% sewerage coverage of the East Zone of Metro Manila.

Controls on seasonal variations of silicate weathering and CO2 consumption in two river catchments on the NE Tibetan Plateau

Water samples from the Buha and Shaliu Rivers, located on the semi-arid northeastern Tibetan Plateau, were collected weekly over a one year period. The major ionic compositions of water samples were measured and the daily contents of suspended particulate material (SPM) were monitored in both rivers in order to investigate the influence of lithology, climate and physical erosion on seasonal silicate weathering. In the Shaliu River, weathering of trace amounts of calcite contributes more than 50% of the Ca2+ and HCO3- to the river water. Through high-resolution variations of Ca2+ concentrations and elemental ratios, the signal of carbonate precipitation is captured at the end of monsoon in this river. The measured physical erosion rate is only 8.7–16.0mm/kyr in this semi-arid region, which is 2–3 orders of magnitude lower than that in the Himalaya and nearby regions.In contrast with several orders of magnitude in seasonal variations of silicate weathering rates in both catchments, the distinct lithology between the catchments only leads to a 15 times difference of annual net CO2 consumption. The correlation analysis shows that seasonal silicate weathering is strongly dependent on water discharge in the semi-arid area. The most important observation is that, unrecognized by the previous studies, both physical erosion rate and air temperature exhibit two distinct trends with silicate weathering rates (and net CO2 consumption) during the years. The two trends might suggest that temperature plays a more important role on the CO2 consumption rate before the mid-monsoon under a condition of low water discharge than that after the monsoon with a high water discharge. During the period before the mid-monsoon, the relationship between temperature and silicate weathering rate exhibits higher activation energy than after the mid-monsoon, suggesting a greater dissolution of uneasily weatherable minerals from groundwater, frozen soil, and/or dust input. The relationship between erosion and weathering during the period before the mid-monsoon indicates a faster increase of silicate weathering rate, because freezing erosion produces large amount of high surface area minerals.

A Late Pleistocene–Holocene wetland megafan in the Brazilian Amazonia

Despite the growing interest in megafans, definitions provided for this type of environmental setting have not yet been widely agreed upon. A record of sedimentary facies distribution in both space and time including a larger number of analogs is particularly needed for improving megafan facies models. This work focuses on a large fan-like feature from an Amazonian wetland in northern Brazil. Morphological data based on remote sensing, as well as sedimentary facies and radiocarbon analyses, were integrated to propose that this feature is related to a megafan system active during the Late Pleistocene to Holocene. The megafan displays a divergent drainage network, gently-dipping slope, and concave-up and convex-up longitudinal and transverse profiles, respectively. Near surface deposits correspond to fining and coarsening upward sands related to active channels and overbank sand sheets/terminal fan lobes. Sediments are interbedded with abandoned channel/floodplain and lake/pond muds. Morphostructural analyses and drainage anomalies revealed a geological setting affected by reactivation of pre-existing faults contemporaneous with sediment accumulation. Establishment of a megafan system in this wetland most likely occurred within a slightly tectonically subsiding basin under favorable climatic conditions. During wet seasons, high water discharge would have favored sediment transport from highlands into this depositional site. High summer temperatures and drought under a monsoonal regime kept the water levels low. The described megafan could serve as an analog for contemporary tropical wetland megafans formed under a monsoonal climate regime.

Phytoplankton functional and morpho-functional approach in large floodplain rivers

Influence of hydrological characteristics and nutrient concentrations on phytoplankton was investigated in four large rivers (Mura, Drava, Danube and Sava) in the Pannonian ecoregion in Croatia to understand how phytoplankton of rivers can be explained by the “different functional group approach”. To gain a clearer understanding of the factors that affect river phytoplankton, the present study examined phytoplankton biomass and composition in relationship with physical and chemical parameters assessed in detail by preparing self-organising maps using functional groups and morpho-functional groups. Total nitrogen along with water residence time showed to be the best predictor to determine phytoplankton biomass and chlorophyll a. Phytoplankton diversity increased with higher water discharge, but it had the consequence of diluting algae and decreasing biomass. Bacillariophyceae and Chlorophyceae species dominated the phytoplankton assemblages in all rivers. Diatoms predominated in rivers with shorter residence time. Dominant diatom codons of functional groups were C, D and TB while morpho-functional groups were represented by only diatom group VI. As residence time increased, the proportion of chlorococcalean green algae, represented by functional group codon T and morpho-functional group IV grew in summer. Since potamoplankton is dominated by diatoms, functional groups with its fine partition of diatom codons proved to be excellent descriptor of the potamoplankton. Application of morpho-functional groups originally developed from the lake data, showed to be limiting because of the predominating presence of only one diatom group.