The Effects of Road Salt on Stream Water Chemistry in Two Small Forested Watersheds,Catoctin Mountain,Maryland, USA

The Hauver Branch and Hunting Creek watersheds in Catoctin Mountain, Maryland, USA, are small rural watersheds that receive road salt during the winter. Base cation evidence of road salt application in stream water disappears by approximately September for Hauver Branch, but never disappears for Hunting Creek. The fraction of the precipitation-corrected watershed fluxes of both Mg²⁺ and Ca²⁺ attributable to cation exchange associated with road salt Na⁺ inputs are 14 and 19 % for Hauver Branch and Hunting Creek, respectively. The percentage of divalent cations in stream waters resulting from road salt application is calculated using the watershed chemical weathering Na⁺/SiO₂ molar ratio. Calculation of a representative chemical weathering Na⁺/SiO₂ molar ratio may be problematic with spatially variable bedrock, and/or inputs from water softeners, septic systems, and wastewater treatment plants. Therefore, investigations of small forested rural watersheds offer insights into road salt dynamics that may be lost at larger scales and/or with increased urbanization. The quantities of road salt application to the Hauver Branch and Hunting Creek watersheds are 3.3 and 11 t km^?2 year^?1, respectively. The per-lane-length-normalized road salt application rates for the Hauver Branch and Hunting Creek watersheds are 10 and 22 t lane^?1 km^?1 year^?1, respectively. These per-lane-length-normalized road salt application rates are relatively large compared to more urbanized watersheds located north of the study site where the application rates are reported by municipalities. These findings may indicate that road and highway administrations may underestimate their rates of road salt application.     

Rates of Biotite Weathering,and Clay Mineral Transformation and Neoformation,Determined from Watershed Geochemical Mass-Balance Methods for the Coweeta Hydrologic Laboratory,Southern Blue Ridge Mountains,North Carolina,USA

Biotite is a common constituent of silicate bedrock. Its weathering releases plant nutrients and consumes atmospheric CO₂. Because of its stoichiometric relationship with its transformational weathering product and sensitivity to botanical activity, calculating biotite weathering rates using watershed mass-balance methods has proven challenging. At Coweeta Hydrologic Laboratory the coupling of biotite to its transformational weathering product is only valid if the stoichiometric relationship for the two phases is known; this relationship is unlikely layer-for-layer. Rates of biotite weathering and transformation of its secondary weathering product at the Coweeta Hydrological Laboratory are comparable with other Appalachian watersheds. The magnitude and sign of the difference between field- and laboratory-determined biotite weathering rates are similar to those of other silicate minerals. The influence of major-cation proportions in biomass on the rates of biotite weathering and transformational weathering product is greatest for watersheds with high biomass aggradation rates. The watershed with the lowest bedrock reactivity and highest flushing rate yielded the highest gibbsite formation rate of ~500 mol ha^?1 year^?1 and lowest kaolin-group mineral formation rates of 4–78 mol ha^?1 year^?1. The kaolin-group mineral formation rate increases as bedrock reactivity increases and flushing rate decreases to a maximum of ~300 mol ha^?1 year^?1, with a similar minimum gibbsite formation rate. The relative differences in bedrock reactivity and flux of water through Coweeta Hydrological Laboratory watersheds studied appear to be invariant over geologic timescales.     

A Comprehensive Study of Silica Pools and Fluxes in Wadden Sea Salt Marshes

As an essential nutrient for diatoms, silica plays a key role in the estuarine and coastal food web. High concentrations of dissolved silica (DSi) were found in the seepage water of tidal freshwater marshes, which were therefore assumed to contribute to the silica supply to estuarine waters in times of silica limitation. A comprehensive budget calculation for European salt marshes is presented in this study. Earlier, salt marshes were considered to have even higher silica recycling rates than tidal freshwater marshes. Between 2009 and 2011, concentrations, pools and fluxes of silica in two salt marshes at the German Wadden Sea coast were determined (in soil, pore water, aboveground vegetation, freshly deposited sediments and seepage water). Subsequently, a budget was calculated. Special emphasis was placed on the influence of grazing management on silica cycling. Our results show that the two salt marshes were sinks for silica. The average import of biogenic silica (BSi) with freshly deposited sediments (1,334 kmol km^?2 year^?1) largely exceeded the DSi and BSi exports with seepage water (80 kmol km^?2 year^?1). Grazing management can affect silica cycling of salt marshes by influencing hydrology and vegetation structure. Abandoned sites had larger DSi export rates than grazed sites. One third of all BSi imports occurred in only one major flooding, underlining the relevance of rare events in the silica budget of tidal marshes. This aspect has been widely neglected in earlier studies, what might have led to an underestimation of silica import rates to tidal marshes hitherto.     

Isotope Constraints on the Aquatic Carbon Budget: Langat Watershed,Malaysia

Langat River drains a tropical watershed in the southwest of the Malaysian Peninsula. The watershed is heavily urbanized in its downstream portion. Water samples were collected from May 2010 to December 2011, at three localities along the main stem river, 1 location at its Semenyih tributary and from an upstream groundwater source. Concentration and δ¹³C data of riverine DIC and DOC indicate the dominance of C3 plant-derived material as the primary source of carbon, with δ¹³C_DIC values enriched in ¹³C relative to that of the C3 source. This enrichment is likely due to CO₂ outgassing, as calculated concentrations of riverine CO₂ are significantly higher than ambient atmospheric values, with methanogenic activity a theoretically possible contributing factor, particularly at the upstream location. The Langat River therefore acts as a net source of CO₂, with a total sub-basin flux of 19.7 × 10³ t C year^?1. This is comparable to the sum of riverine DOC, DIC and POC loss rates from the sub-basin, calculated as 24.5 × 10³ t C year^?1, and highlights the significance of CO₂ evasion from water bodies to the atmosphere for balancing the budget of the terrestrial carbon cycle. The DIC and DOC concentration and δ¹³C data also suggests that in the more urbanized downriver areas, much of the organic carbon input may be anthropogenicaly derived due to ubiquity of sewage treatment plants and landfill sites. Such human-induced perturbations to riverine carbon cycling should be taken into account in future studies of urbanized watersheds.     

Dolomite Versus Calcite Weathering in Hydrogeochemically Diverse Watersheds Established on Bedded Carbonates (Sava and So?a Rivers, Slovenia)

The relative contributions of dolomite to calcite weathering related to riverine fluxes are investigated on a highly resolved spatial scale in the diverse watersheds of Slovenia, which previous work has shown have some of the highest carbonate-weathering intensities in the world and suggests that dolomite weathering is favored over limestone weathering in mixed carbonate watersheds. The forested Sava and So?a River watersheds of Slovenia with their headwaters in the Julian Alps drain alpine regions with thin soils (<30 cm) and dinaric karst regions with thicker soils (0 to greater than 70 cm) all developed over bedded Mesozoic carbonates (limestone and dolomite), and siliclastic sediments is the ideal location for examining temperate zone carbonate weathering. This study extends previous work, presenting geochemical data on source springs and documenting downstream geochemical fluctuations within tributaries of the Sava and So?a Rivers. More refined sampling strategies of springs and discrete drainages permit directly linking the stream Mg²⁺/Ca²⁺ ratios to the local bedrock lithology and the HCO₃ ^? concentrations to the relative soil depths of the tributary drainages. Due to differences in carbonate source lithologies of springs and tributary streams, calcite and dolomite weathering end members can be identified. The Mg²⁺/Ca²⁺ ratio of the main channel of the Sava River indicates that the HCO₃ ^? concentration can be attributed to nearly equal proportions by mass of dolomite relative to calcite mineral weathering (e.g., Mg²⁺/Ca²⁺ mole ratio of 0.33). The HCO₃ ^? concentration and pCO₂ values increase as soil thickness and alluvium increase for discrete spring samples, which are near equilibrium with respect to calcite. Typically, this results in approximately 1.5 meq/l increase in HCO₃ ^? from the alpine to the dinaric karst regions. Streams in general do not change in HCO₃ ^?, Mg²⁺/Ca²⁺, or Mg²⁺/HCO₃ ^? concentrations down course, but warming and degassing of CO₂ produce high degrees of supersaturation with respect to calcite. Carbonate-weathering intensity (mmol/km²-s) is highest within the alpine regions where stream discharge values range widely to extreme values during spring snowmelt. Overall, the elemental fluxes of HCO₃ ^?, Ca²⁺, and Mg²⁺ from the tributary watersheds are proportional to the total water flux because carbonates dissolve rapidly to near equilibrium. Importantly, dolomite weathers preferentially over calcite except for pure limestone catchments.     

Variability in Concentrations and Fluxes of Methane in the Indian Estuaries

In order to examine the fluxes of methane (CH₄) from the Indian estuaries, measurements were carried out by collecting samples from 26 estuaries along the Indian coast during high discharge (wet) and low water discharge (dry) periods. The CH₄ concentrations in the estuaries located along the west coast of India were significantly higher (113?±?40 nM) compared to the east coast of India (27?±?6 nM) during wet and dry periods (88?±?15 and 63?±?12 nM, respectively). Supersaturation of CH₄ was observed in the Indian estuaries during both periods ((0.18 to 22.3?×?10³ %). The concentrations of CH₄ showed inverse relation with salinity indicating that freshwater is a significant source. Spatial variations in CH₄ saturation were associated with the organic matter load suggesting that its decomposition may be another source in the Indian estuaries. Fluxes of CH₄ ranged from 0.01 to 298 μmol m^?2 day^?1 (mean 13.4?±?5 μmol m^?2 day^?1) which is ~30 times lower compared to European estuaries (414 μmol m^?2 day^?1). The annual emission from Indian estuaries, including Pulicat and Adyar, amounted to 0.39?×?10¹⁰ g CH₄?year^?1 with the surface area of 0.027?×?10⁶ km² which is significantly lower than that in European estuaries (2.7?±?6.8?×?10¹⁰ g CH₄?year^?1 with the surface area of 0.03?×?10⁶ km²). This study suggests that Indian estuaries are a weak source for atmospheric CH₄ than European estuaries and such low fluxes were attributed to low residence time of water and low decomposition of organic matter within the estuary. The CH₄ fluxes from the Indian estuaries are higher than those from Indian mangroves (0.01?×?10¹⁰ g CH₄?year^?1) but lower than those from Indian inland waters (210?×?10¹⁰ g CH₄?year^?1).     

Stream geochemistry, chemical weathering and CO2 consumption potential of andesitic terrains, Dominica, Lesser Antilles

Recent studies of chemical weathering of andesitic-dacitic material on high-standing islands (HSIs) have shown these terrains have some of the highest observed rates of chemical weathering and associated CO₂ consumption yet reported. However, the paucity of stream gauge data in many of these terrains has limited determination of chemical weathering product fluxes. In July 2006 and March 2008, stream water samples were collected and manual stream gauging was performed in watersheds throughout the volcanic island of Dominica in the Lesser Antilles. Distinct wet and dry season solute concentrations reveal the importance of seasonal variations on the weathering signal. A cluster analysis of the stream geochemical data shows the importance of parent material age on the overall delivery of solutes. Observed Ca:Na, HCO₃:Na and Mg:Na ratios suggest crystallinity of the parent material may also play an important role in determining weathering fluxes. From total dissolved solids concentrations and mean annual discharge calculations we calculate chemical weathering yields of (6-106 t km⁻² a⁻¹), which are similar to those previously determined for basalt terrains. Silicate fluxes (3.1-55.4 t km⁻² a⁻¹) and associated CO₂ consumption (190-1575 × 10³ mol km⁻² a⁻¹) determined from our study are among the highest determined to date. The calculated chemical fluxes from our study confirm the weathering potential of andesitic-dacitic terrains and that additional studies of these terrains are warranted.     

Assessment of soil losses and siltation of the K’sob hydrological system (semiarid area—East Algeria)

Soil losses and siltation of the hydrological system (watershed–dam) of K’sob were obtained using direct and indirect methods. The Wadi K’sob watershed of 1,484 km², average slope of 0.14, and average elevation of 1,060 m is located in a semiarid climate. The average annual rainfall is 341 mm and the mean annual water discharge is 0.89 m³/s. Data from the Medjez gauging station located 6 km upstream of the dam, are the daily liquid flow and instantaneous concentrations of suspended sediments. Over a time period from 1973 to 2010, the relationship between water and sediment discharges is quantified by the equation: Q _s?=?5.6 Q ^1.31. Thus, in view of the availability data on a daily scale, the assessment of soil erodibility of the K’sob watershed was used to estimate specific soil losses of 203 t?km^?2?year^?1or 301,000 t eroded annually from the K’sob basin. The bathymetric measurements of the sediment volumes deposited in the K’sob dam, has quantified the annual siltation of 0.8 hm³, corresponding to an average erodibility of the K’sob watershed of 809 t?km^?2?year^?1. However, when adding the volume of sediment removed by the dredging operation and de-silting by the valves during heavy floods, the value of soil losses is 2,780 t?km^?2?year^?1. The indirect assessment of soil erodibility of the basin was obtained by applying two models: the quantitative geomorphological analysis (QGA) and PISA model (prediction of silting in the artificial reservoirs, in Italian: Previsioni dell’Interimento nei Serbatoi Artificiali) using physical and climatic factors in the watershed. The obtained results by QGA method underestimate specific soil losses of 524 t?km^?2?year^?1. The PISA model gives a value of 2,915 t?km^?2?year^?1, which is close to the value obtained by bathymetric measurements. This study concludes that PISA model is most suitable to estimate soil loss and siltation of the K’sob hydrological system.     

The streamflow trend in Tangwang River basin in northeast China and its difference response to climate and land use change in sub-basins

In this study, the hydro-climatic trends (1964–2006) of Tangwang River basin (TRB) were examined using the Kendall’s test. Moreover, the impacts of climate variability and land use change on streamflow in each sub-basin were assessed using the Soil and Water Assessment Tools (SWAT) model. The results indicated that annual mean flow and peak flow showed insignificant decreasing trends (?0.14 m³ s^?1 year^?1, 1 %; ?8.67 m³ s^?1 year^?1, 40 %), while annual low flow exhibited a slightly increasing trend (0.02 m³ s^?1 year^?1, 11 %). Correspondingly, the annual precipitation for the entire basin decreased by 0.02 mm year^?2, while the annual means of daily mean, maximum and minimum temperature increased significantly by 0.07, 0.10 and 0.02 °C year^?1, respectively. On the other hand, with the implementation of “Natural Forest Protection Project” and “Grain for Green Project”, the forests in TRB totally increased by 744.5 km² (4.00 %) from 1980 to 2000. Meanwhile, the grasslands and the farmlands decreased by 378.0 km² (?1.98 %) and 311.9 km² (?1.63 %), respectively. Overall, land use changes played a more important role for the streamflow reduction than climate change for SUB1, SUB2 and SUB3, in which the primary conversions were from grassland, farmland and bare land to forests. Conversely, in SUB4, the influence of climate variability was predominant. The results obtained could be a reference for water resources planning and management under changing environment.     

Change in carbon flux (1960–2015) of the Red River (Vietnam)

Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 1960–2015. The results show that total carbon flux of the Red River averaged 2555?±?639 kton C year^?1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year^?1 during the 1960s to 1372 kton C year^?1 during the 2010s and showed clear seasonal and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone.     

Understanding the Cyclicity of Chemical Weathering and Associated CO<Subscript>2</Subscript> Consumption in the Brahmaputra River Basin (India): The Role of Major Rivers in Climate Change Mitigation Perspective

Weathering of rocks that regulate the water chemistry of the river has been used to evaluate the CO₂ consumption rate which exerts a strong influence on the global climate. The foremost objective of the present research is to estimate the chemical weathering rate (CWR) of the continental water in the entire stretch of Brahmaputra River from upstream to downstream and their associated CO₂ consumption rate. To establish the link between the rapid chemical weathering and thereby enhance CO₂ drawdown from the atmosphere, the major ion composition of the Brahmaputra River that drains the Himalaya has been obtained. Major ion chemistry of the Brahmaputra River was resolved on samples collected from nine locations in pre-monsoon, monsoon and post-monsoon seasons for two cycles: cycle I (2011–2012) and cycle II (2013–2014). The physico-chemical parameters of water samples were analysed by employing standard methods. The Brahmaputra River was characterized by alkalinity, high concentration of Ca²⁺ and HCO₃ ^? along with significant temporal variation in major ion composition. In general, it was found that water chemistry of the river was mainly controlled by rock weathering with minor contributions from atmospheric and anthropogenic sources. The effective CO₂ pressure (log\({{\text{P}}_{{\text{C}}{{\text{O}}_{\text{2}}}}}\)) for pre-monsoon, monsoon and post-monsoon has been estimated. The question of rates of chemical weathering (carbonate and silicate) was addressed by using TDS and run-off (mm year^?1). It has been found that the extent of CWR is directly dependent on the CO₂ consumption rate which may be further evaluated from the perspective of climate change mitigation The average annual CO₂ consumption rate of the Brahmaputra River due to silicate and carbonate weathering was found to be 0.52 (×10⁶ mol Km^?2 year^?1) and 0.55 (×10⁶ mol Km^?2 year^?1) for cycle I and 0.49 (×10⁶ mol Km^?2 year^?1) and 0.52 (×10⁶ mol Km^?2 year^?1) for cycle II, respectively, which were significantly higher than that of other Himalayan rivers. Estimation of CWR of the Brahmaputra River indicates that carbonate weathering largely dominates the water chemistry of the Brahmaputra River.     

Weathering fluxes of arsenic from a small catchment in Slovak Republic

Inputs of As to a small catchment due to chemical weathering of bedrock, mechanical weathering of bedrock, and atmospheric precipitation were 71.53, 23.98 and 0.02 g ha⁻¹ year⁻¹, respectively. The output fluxes of As due to mechanical erosion of soil, biological uptake, stream discharge, and groundwater flow were 6.32, 4.77, 0.37 and 0.02 g ha⁻¹ year⁻¹, respectively. The results indicate that arsenic accumulates in soil and regolith with a very high rate. This is attributed to the selective weathering and erosion with respect to arsenic and fixation of arsenic in the secondary solids produced by weathering. The output fluxes of As in stream and groundwater in Vydrica catchment in Slovak Republic (0.39 g ha⁻¹ year⁻¹) based on muscovite–biotite granites and granodiorites were much lower compared to catchments in a gold district in the Czech Republic. These results may be ascribed to the low levels of arsenic pollution measured in Vydrica catchment. The arsenic fluxes were estimated by calculation of mechanical and chemical weathering rates of the bedrocks in Vydrica catchment from mass balance data on sodium and silica. The justification of the steady state of Na and Si is that neither of the elements is appreciably accumulated in plants and in exchangeable pool of ions in soil.     

Geochemical fluxes and weathering of volcanic terrains on high standing islands: Taranaki and Manawatu-Wanganui regions of New Zealand

Sediment fluxes from high standing oceanic islands (HSIs) such as New Zealand are some of the highest known [Milliman J. D. and Syvitski J. P. M. (1992) Geomorphic/tectonic control of sediment discharge to the ocean: the importance of small mountainous rivers. J. Geol.100, 525-544]. Recent geochemical work has suggested that along with their extremely high physical weathering yields, many New Zealand watersheds also have very high chemical weathering yields. In New Zealand, the magnitude of both the physical and chemical weathering yields is related to the lithology of the watershed. Most of the previous work on this topic has been undertaken in Southern Alps watersheds of schist and greywacke and in East Cape watersheds of semi-consolidated marine sediments and greywacke. We recently sampled North Island watersheds in the Taranaki and Manawatu-Wanganui regions which have been subjected to volcanism since the Miocene. We sampled watersheds that contain both volcanic and sedimentary rocks. A series of water and sediment samples was collected and analyzed for major, minor and trace elements. This was done to quantify the weathering intensities in the watersheds and to establish the relationship between physical and chemical weathering yields in volcanic lithologies. Our results reveal distinct chemical signatures for the different regions. Waters draining the Taranaki region volcanics are significantly enriched in K⁺, and depleted in Ca²⁺ and Sr²⁺ compared to waters draining the Manawatu-Wanganui region volcanics, which also traverse expanses of sedimentary siltstones and mudstones. The Ca²⁺ and Sr²⁺ depletions may reflect the relative absence of CaCO₃ in the Taranaki region watersheds. In addition, sediment samples from the Taranaki region show significant enrichment in Ti, Al, Ca, Fe, Mn, Mg, Ca, and P and depletion in Si and Rb compared to those of the Manawatu-Wanganui region. From total dissolved solids concentrations and mean annual water discharge, we calculate chemical weathering yields of 60-240 tons km⁻² a⁻¹. These weathering yields fall within the middle to upper range of those previously documented for the Southern Alps (93-480 tons km⁻² a⁻¹) and East Cape (62-400 tons km⁻² a⁻¹). Calculated silicate weathering yields of 12-33.6 tons km⁻² a⁻¹ and CO₂ consumption of 852-2390 × 10³ mol km⁻² a⁻¹ for the rivers draining the Taranaki volcanic region are higher than those previously reported for watersheds hosted in sedimentary and metamorphosed rock terrains on HSIs. CO₂ consumption is found to be within the range previously measured for the basaltic terrains of the Deccan Traps (580-2450 × 10³ mol km⁻² a⁻¹) and Réunion Island(1300-4400 × 10³ mol km⁻² a⁻¹). Our calculated chemical weathering yields demonstrate the importance of HSIs, particularly those with volcanic terrains, when considering global geochemical fluxes.     

Submarine Groundwater Discharge as a Source of Dissolved Inorganic Nitrogen and Phosphorus to Coastal Ponds of Southern Rhode Island

Measurements of groundwater-dissolved inorganic nitrogen (nitrate?+?nitrite?+?ammonia) and phosphate concentrations were combined with recent, radium-based, submarine groundwater discharge (SGD) fluxes and prior estimates of SGD determined from Darcy’s Law, a hydrologic model, and total recharge to yield corresponding SGD nutrient fluxes to Ninigret, Point Judith, Quonochontaug, and Winnapaug ponds, located in southern Rhode Island. Results range from 80 to279 mmol N m^?2 year^?1 and 4 to 15 mmol P m^?2 year^?1 for Ninigret, 48 to 265 mmol N m^?2 year^?1 and 4 to 23 mmol P m^?2 year^?1 for Point Judith, 31 to 62 mmol N m^?2 year^?1 and 1 to 2 mmol P m^?2 y^?1 for Quonochontaug, and 668 to 1,586 mmol N m^?2 year^?1 and 29 to 70 mmol P m^?2 year^?1 for Winnapaug ponds, respectively. On a daily basis, the SGD supply of dissolved inorganic nitrogen and phosphorus is estimated to represent ～1–6 % of the total amount of these nutrients in surface waters of Ninigret, Point Judith, and Quonochontaug ponds and up to 84 and 17 % for Winnapaug, respectively, which may reflect a greater SGD nutrient supply to this pond because of the proximity of fertilized golf courses. With regard to the total external input of these essential nutrients, SGD represents 29–45 % of dissolved inorganic nitrogen input to Ninigret, Point Judith, and Quonochontaug ponds and as much as 93 % for Winnapaug pond. For phosphorus, the contribution from SGD represents 59–85 % of the total external input for Ninigret, Point Judith, and Quonochontaug ponds and essentially all of the phosphorus input to Winnapaug pond. Estimated rates of primary productivity potentially supported by the average supply of dissolved inorganic nitrogen from SGD range from 10 g C m^?2 year^?1 for Ninigret, 13 g C m^?2 year^?1 for Point Judith, 4 g C m^?2 year^?1 for Quonochontaug, and as high as 84 g C m^?2 y^?1 for Winnapaug pond. The imputed SGD-derived rates of primary productivity represent 4–9 % of water column primary production for Ninigret, Point Judith, and Quonochontaug ponds, and 74 % for Winnapaug pond, a result that is reasonably comparable to several other coastal environments where estimates of SGD nutrient supply have been reported. The implication is that SGD represents an ecologically significant source of dissolved nutrients to the coastal salt ponds of southern Rhode Island and, by inference, other coastal systems.     

The formation and development of debris flows in large watersheds after the 2008 Wenchuan Earthquake

The Wenchuan earthquake has caused abundance of loose materials supplies for debris flows. Many debris flows have occurred in watersheds in area beyond 20 km², presenting characteristics differing from those in small watersheds. The debris flows yearly frequency decreases exponentially, and the average debris flow magnitude increases linearly with watershed size. The rainfall thresholds for debris flows in large watersheds were expressed as I?=?14.7 D ^?0.79 (2 h?<?D?<?56 h), which is considerably higher than those in small watersheds as I?=?4.4 D ^?0.70 (2 h?<?D?<?37 h). A case study is conducted in Ergou, 39.4 km² in area, to illustrate the formation and development processes of debris flows in large watersheds. A debris flow develops in a large watershed only when the rainfall was high enough to trigger the wide-spread failures and erosions on slope and realize the confluence in the watershed. The debris flow was supplied by the widely distributed failures dominated by rill erosions (14 in 22 sources in this case). The intermittent supplying increased the size and duration of debris flow. While the landslide dam failures provided most amounts for debris flows (57 % of the total amount), and amplified the discharge suddenly. During these processes, the debris flow velocity and density increased as well. The similar processes were observed in other large watersheds, indicating this case is representative.     

Integration of geospatial technologies with RUSLE for analysis of land use/cover change impact on soil erosion: case study in Rib watershed,north-western highland Ethiopia

In recent times, soil erosion interlocked with land use and land cover (LULC) changes has become one of the most important environmental issues in developing countries. Evaluation of this complex interaction between LULC change and soil erosion is indispensable in land use planning and conservation works. This paper analysed the impact of LULC change on soil erosion in the north-western highland Ethiopia over the period 1986–2016. Rib watershed, the area with dynamic LULC change and severe soil erosion problem, was selected as a case study site. Integrated approach that combined geospatial technologies with revised universal soil loss equation model was utilized to evaluate the spatio-temporal dynamics of soil loss over the study period. Pixel-based overlay of soil erosion intensity maps with LULC maps was carried out to understand the change in soil loss due to LULC change. Results showed that the annual soil loss in the study area varied from 0 to 236.5 t ha^?1 year^?1 (tons per hectare per year) in 1986 and 0–807 t ha^?1 year^?1 in 2016. The average annual soil loss for the entire watershed was estimated about 40 t ha^?1 year^?1 in 1986 comparing with 68 t ha^?1 year^?1 in 2016, a formidable increase. Soil erosion potential that was estimated to exceed the average soil loss tolerance level increased from 34.5% in 1986 to 66.8% in 2016. Expansion of agricultural land at the expense of grassland and shrubland was the most detrimental factor for severe soil erosion in the watershed. The most noticeable change in soil erosion intensity was observed from cropland with mean annual soil loss amount increased to 41.38 t ha^?1 year^?1 in 2016 from 26.60 in 1986. Moreover, the most successive erosion problems were detected in eastern, south-eastern and northern parts of the watershed. Therefore, the results of this study can help identify the soil erosion hot spots and conservation priority areas at local and regional levels.     

Erosion balance in the watersheds of the western Paris Basin by high-frequency monitoring of discharge and suspended sediment in surface water

An accurate quantification of erosion, based on high-frequency monitoring of river discharge and suspended sediment fluxes is proposed for two watersheds in the western Paris Basin, a sensitive area with respect to erosion phenomena. This continuous monitoring makes it possible to include flood events of short duration, but significant erosion potential. The obtained erosion rate (16 and 21 t?km^?2?yr^?1) is among the weakest of the planet (3.5 to 18?000 t?km^?2?yr^?1). However, this annual balance does not reflect the behaviour of these rivers which can be torrential in certain cases. To cite this article: B. Laignel et al., C. R. Geoscience 338 (2006).     

Geoarchaeological insights gained from surficial geologic mapping,middle Moche Valley,Peru

We present the results of detailed surficial geologic mapping for a 10 km² area of alluvial (quebrada) deposits located in the middle Moche Valley of Peru, where archaeological features and deposits provide cross‐cutting relationships and numerical age control for late Holocene erosion and deposition associated with El Niño. Despite surfaces containing clasts that are heavily pitted and cracked due to salt weathering, archaeological and ¹⁴C dates indicate that most quebrada landforms in the study area are late Holocene in age and may reflect enhanced alluviation associated with increased El Niño activity beginning ca. 6000 cal yr B.P. Our study provides criteria for correlative dating of other Holocene landforms in the Moche Valley area but urges caution in long‐distance (>100 km) correlation because of geographic variability in surface weathering. Surficial geologic mapping aided by archaeological age control allows improved understanding of the rates of landscape change important to the development of complex irrigation‐based societies in the Peruvian Desert. © 2003 Wiley Periodicals, Inc.     

Stream chloride concentrations as a function of land use: a comparison of an agricultural watershed to an urban agricultural watershed

The concentration of chloride (Cl^?) in streams in northern regions has increased as a result of applications of deicers. This study focused on quantifying the relationship between land use and stream Cl^? concentrations. The study area comprises two adjacent watersheds in central Illinois, with similar geology and climate but different land uses (agricultural and urban). GIS analysis delineated watershed land use and calculated road surface areas. Stream water samples were collected and analyzed for anionic composition. During the winter months, streams dominated with urban land use experienced a 20-fold increase in Cl^? concentrations (range between 36 and 1350 mg L^?1); Cl^? concentrations in agricultural dominated streams also increased, but the increase was smaller (3X) and concentrations remained low (between 11 and 58 mg L^?1). As road salts are not the sole source of Cl^? in a stream, Cl^? and bromide (Br^?) mass ratios (Cl/Br) and Cl^? and sodium (Na) molar ratios ([Cl]/[Na]) were used to identify potential sources of Cl^?. The ratios indicate urbanized watersheds were impacted by road salts; agricultural watersheds ratios indicate other anthropogenic sources. A nonlinear relationship between urban land use and stream Cl^? concentrations indicates urban land use as low as 23% results in elevated Cl^? concentrations (greater than 150 mg L^?1) in stream waters.