High Runoff Conditions Research Articles

Weathering in landslide-prone areas: Evidences from hydrochemistry and sulfur isotopic compositions in the Bailong River, northeastern Qinghai-Tibet Plateau

Investigating weathering processes in landslide-prone areas is important for understanding the carbon budget due to weathering during mountain building. Here, we present the monthly hydrochemistry and sulfur isotopic compositions of SO42− (δ34S–SO42−) in the Bailong River which drained landslide-prone areas in the northeastern Qinghai-Tibet Plateau. Ca2+ and HCO3− were dominant in cations and anions respectively, and δ34S–SO42− values varied over a narrow range, from 5.1‰ to 6.7‰. We constrained the sources of major cations and SO42− through an inverse model and the mass balance model of δ34S–SO42−. The results showed that cations in the Bailong River were mainly from carbonate weathering, and sulfide oxidation was an important source of SO42−. Weathering in the Bailong River catchment showed an CO2 source over geologic timescales due to the reaction of H2SO4. The relationship between weathering fluxes and physical erosion rate indicated that high runoff facilitated physical erosion, and in turn accelerated chemical weathering. However, under the conditions of extreme discharge and physical erosion, SO42− fluxes from sulfide oxidation were not as high as expected, which was ascribed to the transport of old landslide deposits where most sulfides had been exhausted. Therefore, in tectonically active areas with massive landslides, the high erosion rate caused by landslides promoted chemical weathering, but sulfide oxidation did not respond sensitively to strong physical erosion under high runoff conditions. This study helped to understand the relationship among landslides, chemical weathering, and geologic carbon cycle.

Dynamics and fluxes of dissolved carbon under short-term climate variabilities in headwaters of the Changjiang River, draining the Qinghai-Tibet Plateau

Carbon-climate feedback is sensitive in the Qinghai-Tibet Plateau. A series of temporal measurements from Jinsha River and Yalong River, in conjunction with flow information, were used to study the carbon dynamics and predict future carbon fluxes under ongoing climate change. DIC and DOC concentrations showed considerable temporal variations, with low DIC and high DOC concentrations in the high-flow season, and vice versa. DIC and DOC concentrations had negative and positive relationships with runoff changes, respectively, showing the hydro-biogeochemical controls on carbon dynamics. With the increase of runoff, the accelerated chemical weathering and the high carbonate buffering capacity should be responsible for the chemostatic behaviors of DIC. Meanwhile, warm weather would enhance organic carbon degradation, and also thicken the active layer of permafrost in the source area, both of which would produce DOC. In addition, organic carbon degradation in the high-flow season would produce DIC with 13C-depleted values. δ13CDIC also had significant temporal variations, synchronous with runoff changes (i.e., light values under high runoff conditions), supporting that biological carbon plays an important role in carbon dynamics during the warm season. Based on the clear positive correlations between carbon fluxes and runoff, we predicted that the sensitivities of DOC fluxes to temperature changes are 12.2%/°C and 8.3%/°C for the Jinsha River and Yalong River, respectively. The sensitivities of DIC fluxes to temperature changes are much lower, which are 5.5%/°C and 6.1%/°C for the Jinsha River and Yalong River, respectively. This study sheds lights on the alpine riverine carbon cycling based on runoff-shifting concentration-isotope (q-C-I) relationships in the Qinghai-Tibet Plateau, which has implications on the understanding of climate forcing on carbon fluxes in alpine areas.

The impact of land use and socio-economic factors on ammonia nitrogen pollution in Weihe River watershed, China.

Rapid socio-economic development has led to a significant deterioration in the water environment, which has limited sustainable regional development. The soil and water assessment tool (SWAT) and statistical regression method were used to model the ammonia nitrogen (NH4+-N) pollution and explore the impacts of land use and socio-economic factors on NH4+-N pollution within the Weihe River watershed in China from 2015 to 2018. The result of SWAT model revealed that the NH4+-N concentrations were usually relatively high under low runoff conditions and relatively low under high runoff conditions. The average NH4+-N concentration in the upper reaches was 0.77 mg/L, whereas it was 0.87 mg/L in the middle and lower reaches of the watershed. Serious NH4+-N pollution mainly occurred in 2015 and 2016, and the V (2.0 mg/L) and V+ (>2.0 mg/L) water quality classes were associated with approximately 6.67% and 28.94% of the total watershed area, respectively. The multiple linear regression indicated that the building land and secondary industry were the significant controlling factors (P < 0.01). According to the scenario analysis, modelled scenarios for interception measures reduced the NH4+-N load to a greater degree than scenarios for source control measures. To improve the surface water quality in the Weihe River, it is recommended to adjust industrial structure, increase sewage treatment, and strengthen the rural management of the watershed.

Annual River Runoff Variations and Trends for the Andes Cordillera

Abstract We analyzed modeled river runoff variations west of the Andes Cordillera’s continental divide for 1979/80–2013/14 (35 years). Our foci were annual runoff conditions, runoff origins (rain, snowmelt, and glacier ice), and runoff spatiotemporal variability. Low and high runoff conditions were defined as occurrences that fall outside the 10th (low values) and 90th (high values) percentile values of the period of record. SnowModel and HydroFlow modeling tools were used at 4-km horizontal grid increments and 3-h time intervals. NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA) datasets were used as atmospheric forcing. This modeling system includes evaporation and sublimation from snow-covered surfaces, but it does not take into account evapotranspiration from bare and vegetation-covered soils and from river and lake surfaces. In general for the Andes Cordillera, the simulated runoff decreased before 1997 and increased afterward. This could be due to a model precipitation artifact in the MERRA forcing. If so, this artifact would influence the number of years with low runoff values, which decreased over time, while the number of high runoff values increased over time. For latitudes south of ~40°S, both the greatest decrease in the number of low runoff values and the greatest increase in high runoff values occurred. High runoff values averaged 84% and 58% higher than low values for nonglacierized and glacierized catchments, respectively. Furthermore, for glacierized catchments, 61% and 62% of the runoff originated from rain-derived runoff during low and high runoff extreme years, respectively; 28% and 30% from snowmelt-derived runoff; and 11% and 8% from glacier-ice-melt-derived runoff. As the results could be MERRA dependent, more work with other precipitation forcings and/or in situ measurements is needed to assess whether these are real runoff behaviors or artifacts.

Transfer processes of potentially toxic elements (PTE) from rocks to soils and the origin of PTE in soils: A case study on the island of Santiago (Cape Verde)

The understanding of rock-soil geochemical fluxes provides an important tool for evaluating natural environmental risk. In this research we compare the geochemical composition of soils (n=249) collected on Santiago Island (Cape Verde) with their parent rocks (n=96). Basalt and basanites units and overlying soils are relatively rich in Co, Sc, Mg, Ca, Fe, V, Ti, Ni, Cr, and Cu, whilst phonolitic-trachytic units and overlying soils are relatively rich in Zn, P, Sr, Mn, Ba, La, As, Th and Pb. An enrichment of potentially toxic elements (PTE; As, Cd, Co, Cr, Cu, Fe, La, Mn, Ni, Pb, Sc, Th, V) was observed in soils relative to their parent rocks. This enrichment of PTE in Santiago soils results mainly from the removal of mobile elements that are common in primary minerals (e.g., Ca, Na, Mg, K) and coprecipitation and/or adsorption by Fe-oxy-hydroxides and clay minerals (mostly smectite and palygorskyte) under the influence of high pH values. Potentially toxic element contents were found to increase with weathering; oxidation is a major weathering mechanism under a semi-arid climate, and a high correlation between Fe and PTE was found, suggesting that the mobility of PTE is controlled by the iron phases. The level of enrichment of PTE in a specific site does not reflect the bulk concentration and so is not a good indicator of the actual geochemical environmental quality. The extent of contamination is not limited to the vicinity of the source, as contaminated material may be physically remobilized, particularly in high runoff conditions, causing dispersion of geo-pollutants over many kilometres from the source. The geochemical flux clarify the lithological origin of these elements, refuting the hypothesis of an anthropogenic contamination, as the PTE enrichment in Santiago soils is not a local phenomenon, but, on the contrary, occurs over the entire island.

Effects of sea-level rise and climatic changes on mangroves from southwestern littoral of Puerto Rico during the middle and late Holocene

We evaluated the response to sea level rise and climatic changes of the northeastern Caribbean by establishing a palaeoenvironmental reconstruction of the Flamenco Lagoon, located in the coastal side of the Guanica Dry Forest, a MAB/UNESCO reserve in the semi-arid southwestern coast of Puerto Rico (17°57′10.31″N, 66°50′39.30″W). The reconstruction was based on pollen records, sediments analysis, δ13C, δ15N, C/N data and AMS 14C dating of one sediment core. The geology of the area is rocky calcareous karst with rocky outcrops and canyons, with intermittent streams that move water during periods of high run-off conditions. The present lagoon is surrounded by rocky outcrops where dry forest vegetation is present on the terrestrial sides, and sand dunes on the coastal side. We propose that the studied lagoon developed after the stabilization of sea level rise in the region following three main stages: (1) before ~5400calyr BP, sediments were accumulated according to small channels dynamics and trees, shrubs and herbs were present. The sedimentary organic matter was mainly sourced from terrestrial C3 and C4 plants. (2) Between ~5400 and ~4400calyr BP, tidal flats were established and mangroves, mainly represented by Rhizophora trees, migrated landward with sea level rise and established in the area, and the sedimentary organic matter was sourced from terrestrial C3 plants. (3) Around 4400calyr BP, sea level was near the stabilization, the endorheic minibasin was closed when a coastal sand dune was established as a result of drier climatic conditions. Mangroves were eliminated from the system as a result of the closure of the area by sand dunes and increased salinity in water due to high evaporative demand of the climate. The pollen dominance of herbaceous and shrubby vegetation prevails until present. Throughout the lagoon development, sedimentary organic matter was sourced from C3 and C4 plants, as well as phytoplankton organic matter. The closure of the lagoon and the drier conditions prevalent in the region during the late Holocene, which lasts until the present day, and increased the contribution of salinity tolerant phytoplankton that characterizes the current conditions of the Flamenco Lagoon.

Formation and structure of the turbidity maximum in the macrotidal Charente estuary (France): Influence of fluvial and tidal forcing

Understanding estuarine sediment dynamics and particularly turbidity maximum dynamics is crucial for the management of these coastal systems. Various processes impact the formation, movement and structure of the turbidity maximum. Several studies have shown that tidal asymmetry and density gradients are responsible for the presence of this suspended sedimentary mass.The Charente estuary is a highly turbid system (with suspended sediment concentrations often in excess of 5 g/L) that remains poorly understood despite its strong impact on local activities. In this study, a three-dimensional hydrosedimentary model is developed to represent the sediment dynamics of this estuary. Model validation demonstrates good accuracy, especially on reproducing semi-diurnal and spring-neap variability. Several simulations are performed to evaluate the influence of tides and river discharge on the turbidity maximum. Mean and maximum suspended sediment concentrations (SSC) and sediment stratification are calculated. SSC transects are also used to visualize the suspended sediment distribution along the estuary.The turbidity maximum generally oscillates between the river mouth and the Rochefort area (20–30 km upstream). The model shows strong variations at different time scales, and demonstrates that SSC is mainly driven by deposition/resuspension processes. Spring-neap comparisons show that the turbidity maximum is not well-defined during neap tides for low and mean runoff conditions. Simulations of spring tides and/or high runoff conditions all result in a compact suspended sedimentary mass.Performing simulations without taking density gradients into account demonstrates that tidal asymmetry is the main mechanism leading to the formation of the turbidity maximum. However, density gradients contribute to maintaining the stability of the turbidity maximum. Vertical stratification traps sediments at the bottom. Longitudinal stratification ensures a sharper edge at the downstream limit of the suspended sedimentary mass, preventing a massive export of sediments.

Infragravity currents in a small ría: Estuary-amplified coastal edge waves?

Observations are presented of estuarine infragravity oscillations in a very small estuary, the Ría de Santiuste, northern Spain, that discharges into a bay. Time-scale calculations and measurements indicate that the most likely source of amplified infragravity waves within the estuary are coastal edge waves, which appear to be resonating between the headlands of the bay, and onshore-offshore seiching of waters that may be resonating between the beach and the bay's seaward limit. Infragravity waves in the estuary have a narrow, power-dominant periodicity range of 4.3–4.8 min. Generally, only very weak waves, and at other periodicities, occur within the tidal river when it is unaffected by the tide. Although infragravity water-level amplitudes are small in the tidal river, typically ∼0.01 m during high water, the corresponding velocity amplitudes are significant, typically ∼0.1 m s−1, despite the occurrence of high runoff conditions during these measurements. Within the estuary and close to the mouth, near-bed salinity shows considerable variability that is a consequence of salt wedge oscillations with periodicities that are within the range of 4.3–4.8 min. Model results for simulated neap to spring high-water water levels show that wave periodicities in the range 3.5–4.5 min correspond approximately to 3λ/4 resonances. The model also indicates that an effect of low runoff is to greatly enhance resonant behaviour within the estuary, such that water level amplitudes of 0.02 m at the mouth can produce wave currents as fast as 0.4 m s−1 within the estuary, compared with ∼0.1 m s−1 during high runoff.

Mobility of aqueous contaminants at abandoned mining sites: insights from case studies in Sardinia with implications for remediation

Public awareness of environmental health issues has increased significantly in recent years, creating the need for detailed scientific studies that can identify potential environmental problems. This paper reports the results of hydrogeochemical surveys carried out in Sardinia, an Italian region with a long mining history. When mining operations in Sardinia ceased, actions for limiting the potential adverse effects of mine closure on the water system were not undertaken. Drainages from flooded mines and seeps from mining residues left on the ground are the main mining-related sources of contamination in Sardinia. Due to the proximity of mining sites to water resources and land that is within reach of animals and humans, the major risks to human health are associated with the direct discharge of contaminated waters into the streams and soils located down-gradient of the abandoned mines. Results of hydrogeochemical surveys carried out under different seasonal conditions showed that the dispersion of toxic and harmful elements (As, Cd, Ni, Pb, Sb and Zn) increases during the rainy season, especially under high runoff conditions. These results should help regional and national authorities to address present environmental regulations, particularly those regarding the quality of water resources. Furthermore, the results might be useful elsewhere for planning remediation actions at abandoned mining sites. Lessons learned by past mining in Sardinia indicate that correct disposal and management of mining residues should be mandatory from the beginning of exploitation and processing at each active mine. This would allow reduction of the environmental risks as well as the cost of remediation.

Drainage morphometry and its influence on landform characteristics in a basaltic terrain, Central India – a remote sensing and GIS approach

An attempt has been made to study drainage morphometry and its influence on landform processes, soil physical and land erosion characteristics in Vena river basin of basaltic terrain (Deccan traps), Nagpur district, Maharashtra, Central India. High Spatial Resolution Indian Remote Sensing Satellite (IRS)-ID Linear Image Self Scanning (LISS)-III sensor data of 7 March 2000 in conjunction with Survey Of India (SOI) topographical sheets (1:50,000 scale) were used for systematic analysis of various morphometric, lithological and landform characteristics of the river basin. Morphometric analysis was carried out at sub basin level using Spatial Analysis System (SPANS ver. 7.0) GIS system to analyze the influence of drainage morphometry on landforms, soil depth, drainage, available water holding capacity (AWC) and land erosion characteristics. Ten distinct landforms were identified in the basin based on visual interpretation of satellite sensor data. These are dissected ridges, isolated mounds, linear ridges, escarpments, plateau spurs, subdued plateau, rolling plains, foot slopes, narrow valleys and main valley floor. Very shallow soils exists on dissected ridges, isolated mounds, linear ridges, escarpments and plateau spurs covering the sub basins nos. 1, 5–7, 9, 15 and 16 and are associated with high drainage density (Dd), impermeable geology and high runoff conditions. High drainage density, high bifurcation ratio (Rb) and steep slopes are the main causative factors for the development of well-drained soils. The AWC is low in the soils of higher elevations covering the sub basins 1, 2, 3, 4, 7 and 9 whereas, it is very high at lower elevation in the sub basins nos. 12, 13 and 19. Sub basins nos. 1, 2, 5, 15 and 16, associated with high drainage density, stream frequency (Fu) and texture ratio (T) showed very severe to severe erosion. The analysis reveals that the influence of drainage morphometry is very significant in understanding the landform processes, soil physical properties and erosional characteristics. The study demonstrates that remotely sensed data and GIS based approach is found to be more appropriate than the conventional methods in evaluation and analysis of drainage morphometry, landforms and land resources and to understand their inter-relationships for planning and management at river basin level.

Chemical weathering in granitic environments

Factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature. Based on a transition state theory model, we evaluated the effects on chemical weathering of runoff, temperature and pH. The dependence between temperature and runoff, and chemical weathering is complicated by other factors such as the presence/depth of soil cover. Soil cover favors chemical weathering when it is thin and rich in weatherable minerals. In contrast, it reduces chemical weathering when is thick and poor in primary minerals. Processes that increase the contact time and the surface of the water–rock interactions such as physical denudation, increase chemical weathering rates in granitic environments. The effect of temperature can be quantified assuming an apparent activation energy value of 48.7 kJ/mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions.

Seepage scald in southeastern Australia

This study addresses the problem of seepage scald in southeastern New South Wales. Limited information was available on soil and hydrological properties of these areas and a case study of the Yarralaw seepage scald was undertaken to answer questions concerning the scald's origin, the threat of scald expansion and possible offsite effects. The results have application to a number of similar sites in southeastern New South Wales. Scald formation was not related to any particular soil property inherent to the scalded area. Grassland and scald soil profiles were similar, with the major difference being the surface horizon. The grassland surface was relatively permeable but the scald surface was sodic, highly dispersive and compacted. As a result, it had lower permeability than the grassland. Soil salt loads were high only in the surface horizons of the scald. The water table in the lower catchment, even at its lowest level, was within 2 m of the ground surface. Upward capillary water movement is causing the salinity, but the salinity is confined to the scald because downward leaching in the grassland keeps the surface of these areas relatively salt-free. The areal extent of the Yarralaw seepage scald has been stable since 1962. High runoff conditions in the future may cause further scald expansion and it is important that reasonable measures be taken to prevent this. However, scald growth appears to be catastrophic in nature, with the majority of the damage occurring in a relatively short period of time in the early stage of formation. On the scald surface, the degradation is a progressive process but scald expansion appears to be catastrophic. This type of formation has important implications for management and emphasizes the need for seepage scald prevention.

Observed fluxes of water, salt and suspended sediment in a partly mixed estuary

Observations of the residual fluxes of water, salt and suspended sediment are presented for seven stations along the Tamar Estuary. The data include measurements over single spring and neap tidal cycles, and are generally applicable to medium or high run-off conditions. Surface to bed differences in salinity are typically of the order of several parts per thousand. Gravitational circulation is an important component of residual flow in the deep, lower reaches of the estuary. Here, Stokes drift is insignificant. In the shallow upper reaches, the major residual currents are generated by Stokes drift and freshwater inputs. Data are compared with predictions from Hansen and Rattray's (1966) model of estuarine circulation. Salt fluxes due to tidal pumping and vertical shear are directed up-estuary at spring tides, tidal pumping being dominant. Tidal pumping of salt is also directed up-estuary at neap tides, although it is insignificant in the lower reaches, where vertical shear dominates. Tidal pumping of suspended sediment is directed up-estuary near the head at spring tides, and probably contributes to the formation of the turbidity maximum. The existence of the turbidity maximum is predicted using a simplified model of the transport of water and sediment. The model shows that an additional mechanism for the existence of the turbidity maximum is an up-estuary maximum in the tidal current speeds (and thus resuspension). In the lower reaches, transport of suspended sediment is directed down-estuary at both spring and neap tides, and sediment is essentially flushed to sea with the fresh water.

Chlorinated Hydrocarbon Insecticide Residues in Winter Flounder, Pseudopleuronectes americanus, from the Weweantic River Estuary, Massachusetts

Residues of DDT, heptachlor, and dieldrin were found in tissues of winter flounder, Pseudopleuronectes americanus (Walbaum), from the Weweantic River estuary, Massachusetts during 1966–67. In nonmigratory juveniles, seasonal accumulation patterns were demonstrated for DDT, heptachlor, and two related breakdown products, DDE and heptachlor epoxide. Peak concentrations of the parent compounds were more closely associated with high runoff conditions than any specific application in the estuarine drainage. Dieldrin was present uniformly throughout the year.Migratory adult flounder, present only between October and May, contained heptachlor and heptachlor epoxide levels similar to juveniles, but significantly less DDE. Adult female flounder sequentially concentrated DDT, DDE, and heptachlor epoxide in their ripening ovaries as the spawning season approached.