Contemporary changes in sediment yield in an alpine mountain basin due to afforestation (the upper Drôme in France)

The Baurières plain within the upper Drôme River basin was used to reconstruct recent changes in sediment supply in relation to changes in land use within an alpine catchment. A considerable body of archival information is available. Furthermore, the plain acts as a natural sediment trap and the reach–basin interaction has not been disrupted by human activity. Based on archival data, channel geometry measurements, dendrogeomorphological and radionuclide analysis (Cs¹³⁷ and unsupported Pb²¹⁰), the trends in channel change and sediment supply over the past two centuries are assessed and their causes are interpreted.Dendrogeomorphology and radionuclide profiles show that the floodplain is characterised by a decrease in sedimentation rate in the 1960s. The ex-Pb²¹⁰ profiles also suggest a spatial modification of the relative contribution in sediment supply of the catchment. Bedload yields are estimated to be at least 26 m³ km⁻² year⁻¹ between 1928 and 1996 based on an estimate of storage over a channel length of 11.5 km. Archival data concerning bedload removal from traps yields an estimate of 25.6 m³ km⁻² year⁻¹ between 1993 and 2001. These two values are very comparable suggesting no major modification in bedload transport within the reach during the 20th century. If the bedload supply has not strongly decreased in the studied reach during this period, the bedload sources have changed. The volume of sediment stored in the Beaurières area between 1928 and 1996 corresponds to at least 40% of the sediment delivered by channel degradation from an upstream alluvial reach.Both changes in floodplain sedimentation as well as changes in bedload and suspended contributions from catchment sources are interpreted as responses to land use but also flow regime. Hillslope sediment production strongly decreased due to planned hillslope afforestation and torrent regulation at the end of the 19th century, and spontaneous hillslope afforestation resulting from grazing decline, mainly in the two decades following World War II. The observed change in suspended sediment supply which occurred around 1960–1965 has a clear synchronicity with spontaneous catchment afforestation following World War II. After this period, a decrease in sediment supply, a change in source, but also a decrease in peak flow, were observed.Changes in run-off are complex and cannot be caused with only land use change. Flood hydrographs underwent peak decreases and duration increases through the 20th century because of increase in water retention capacity of the forested catchment. In addition flood seasonality has changed, with September and October flood events being much less frequent in the last part of the 20th century.     

Dry Weight Deposition in Polluted Onondaga Lake,New York,U.S.A.

Short and long-term trends in dry weight deposition rates are documented for polluted Onondaga Lake, NY, based on analyses of sediment trap collections made below the epilimnion at a single deep-water location in ten years over the 1980–1992 period using cylindrical traps. Additionally, comparisons of dry weight rates obtained with two different diameter (4.0 and 7.6 cm) traps of the same aspect ratio (6), at four different depths below the epilimnion, and from the lake's two basins, in 1993, are presented to establish the representativeness of the long-term data. The near equivalence of fluxes determined with the different size traps and cumulative deposition rates measured over the range of deployment depths, and the minor differences in flux observed for the two basins, supports the representativeness of long-term data in quantifying deposition rates for the pelagic zone of the lake. Short-term variations in downward flux have been common in the lake over the period of monitoring. The summer-average dry weight deposition rate decreased systematically (by about 45%) following the closure (in 1986) of a soda ash facility that caused enhanced rates of calcium carbonate deposition; from an average of 23.2 to 12.8 g m-² d-¹. These dry weight deposition rates are high compared to values reported in the literature for other lakes, and are responsible for the lake's high rate of net sedimentation.     

Wind-splash erosion of bare peat on UK upland moorlands

Peat is a common land surface material in many countries of the world and is particularly important in upland regions of the UK. Peat landscapes represent an important land use for hill farming, water management, and shooting, and are a globally scarce resource. Wind is a fundamental characteristic of upland environments in the UK and has long been recognised as a significant factor in peat erosion. This paper presents the first results of a project that aims to determine the significance of wind action in the erosion of upland peat. Wind erosion monitoring is being undertaken at Moor House in the North Pennines on a 3-ha area of relatively flat, sparsely vegetated peat. Measurements using arrays of passive horizontal mass flux gauges (fixed orientation vertical slot gauges), together with a vertical array of mass flux samplers (directional), provide estimates of sediment flux. A micrometeorological station records local wind speed (four heights), wind direction, rainfall, soil moisture, and temperature conditions. For 1999 and 2000, the annual horizontal net erosion flux is 0.46 and 0.48 t ha⁻¹, respectively. Results of detailed monitoring over a 10-month period demonstrate that the peat sediment flux collected in windward- and leeward-oriented sediment traps on 10 separate occasions is between 3 and 12 times greater in the windward-facing traps. The concentration of peat with height decays rapidly and the majority of the peat is transported close to the ground surface. Above 0.3 m, very little peat is found. Significant horizontal fluxes of peat occur in both wet and dry periods. This is evaluated using the local micrometeorological data to try and predict sediment yields. Correlations among time-averaged friction velocity measurements, surface conditions, and sediment flux are complex. Event-based measurements, as opposed to cumulative sediment yields, are required to resolve this. These results quantify for the first time the significance of wind action in the erosion of peat in a UK upland environment.     

Suspended load and bed load in irrigation furrows

The circulation of water in irrigation furrows is a well-understood physical process. However, theoretical understanding of sediment dynamics is less well established. This study assesses an approach to determine the sediment load in irrigation furrows, involving the use of a suction device for sampling water with suspended sediments at various depths, and a trap for sampling water with sediments moving next to the furrow bed. In addition, an acoustic velocimeter is used to acquire flow velocity profiles, which allow sediment loads to be calculated when combined with the sediment concentration measurements. Use of these devices in irrigation furrows showed that the total sediment load decreases with successive irrigations, and increases as it moves downstream, while the bed load decreases. The bed load represents a small fraction of the total load.Sediment load can be determined with sufficient accuracy for research purposes using simultaneous measurements of the signal-to-noise-ratio of an acoustic velocimeter and the flow velocity. Estimation of the load from point measurements at half the flow depth slightly underestimates the integrated load.     

Sampling soil and sediment depth profiles at a fine resolution with a new device for determining physical,chemical and biological properties: the Fine Increment Soil Collector (FISC)

Purpose

Many environmental investigations (empirical and modelling) and theories are based on reliable information on the depth distribution of physical, chemical and biological properties in soils and sediments. However, such depth profiles are not easy to determine using current approaches, and, consequently, new devices are needed that are able to sample soils and sediments at fine resolutions.

Materials and methods

We have designed an economic, portable, hand-operated surface soil/sediment sampler—the Fine Increment Soil Collector (FISC)—which allows for the close control of incremental soil/sediment sampling and for easy recovery of the material collected by a simple screw-thread extraction system. This innovative sampling system was developed originally for the beryllium-7 (⁷Be) approach in soil and sediment redistribution research. To ensure reliable estimates of soil erosion and sediment deposition from ⁷Be measurements, the depth distribution of this short-lived fallout radionuclide in soil/sediment at the resolution of millimetres is a crucial requirement. This major challenge of the ⁷Be approach can be met by using the FISC.

Results and discussion

We demonstrate the usefulness of the FISC by characterising the depth distribution of ⁷Be at increments of 2.5 mm for a soil reference site in Austria. The activity concentration of ⁷Be at the uppermost increment (0–2.5 mm) was ca. 14 Bq kg^?1 and displayed decreasing activity with depth. Using most conventional sampling devices (i.e. the scraper-plate system), the most accurate depth increment would have been 10 mm, and the activity concentration at the surface would have been considerably lower. Consequently, coarser sampling would have influenced estimates of ⁷Be-derived soil erosion and deposition. The potential application for other soil/sediment properties, such as nutrients (e.g. phosphorus), contaminants and carbon are also discussed.

Conclusions

By enabling soil and sediment profiles to be sampled at a depth resolution of millimetres, the FISC has the potential to provide key information when addressing several environmental and geoscientific issues, such as the precise depth distributions of soil/sediment nutrients, contaminants and biological properties.     

Sediment Phosphorus Release at Beaver Reservoir, Northwest Arkansas, USA, 2002–2003: A Preliminary Investigation

Phosphorus (P) release from bottom sediments can be a significant source to the overlying water column, potentially maintaining and enhancing algal growth and eutrophic conditions in lakes and reservoirs. Thus, the objectives of this study were to: (1) measure P flux under aerobic and anaerobic conditions from intact sediment cores collected at Beaver Reservoir, northwest Arkansas, (2) evaluate the spatial variability in measured sediment P flux under aerobic and anaerobic conditions along the reservoir, and (3) compare external and internal P loads to Beaver Reservoir. Six intact sediment cores were collected at three sites representing the lacustrine, transitional, and riverine zones during June 2003, September 2003 and February 2004 and incubated for 21 days in the dark at ～22°C. Three cores from each site were incubated under aerobic conditions and anaerobic conditions. Water samples were collected from the overlying water column in each core daily for the first five days and every other day thereafter and analyzed for soluble reactive phosphorus (SRP). Water removed from the core was replaced with filtered lake water, maintaining a constant overlying water volume of 1 l. Sediment P flux under anaerobic conditions (<0.01–1.77 mg m^?2 day^?1) was generally greater than that measured under aerobic conditions (<0.01–0.89 mg m^?2 day^?1). Some spatial variability existed in sediment P flux where P flux was generally greatest at the sites in the riverine and transitional zones. Maximum sediment P flux was observed under anaerobic conditions in cores collected from the transitional zone during September 2003. Average sediment P flux under aerobic conditions (0.09 mg m^?2 day^?1) and anaerobic conditions (0.31 mg m^?2 day^?1) was greater than the external P flux (0.05 mg m^?2 day^?1) estimated from the Beaver Reservoir tributaries. Results showed that the annual internal P load (7 Mg year^?1) from bottom sediments in Beaver Reservoir was less than 10% of the annual external P load (～81 Mg P year^?1). The internal P load was significant, but it would not currently be cost effective to manage this P source given the large surface area of Beaver Reservoir.     

Sediment and Phosphorous Fluxes Analysis in Aquia Creek,a Sub-watershed of the Chesapeake Bay Basin,VA, USA

Decline in global surface water quality around the world is closely linked to excess sediment and nutrient inputs. This study examined sediment and phosphorus fluxes in Aquia Creek, a fourth-order sub-watershed of the Chesapeake Bay located in Stafford, Virginia. The Revised Universal Soil Loss Equation (RUSLE), sediment delivery ratio (SDR), field sediment traps, bank erosion pins, and LIDAR data, combined with historical aerial images, were used in quantifying rill and inter-rill erosion from the basin, as well as internally generated sediments. Stream water and stream bank soils were analyzed for phosphorus. RUSLE/SDR modeling estimates a basin total sediment flux of 25,247 tons year^?1. The greatest calculated soil losses were in deciduous forests and cropland areas, whereas medium and high-intensity developed areas had the least soil loss. Cut-bank erosion ranged from 0.2 to 27.4 cm year^?1, and annual bank sediment fluxes were estimated at 1444 Mg, with a corresponding annual mass of phosphorous of 13,760 kg year^?1. The highest bank loss estimates were incurred along reaches draining urban areas. Stream water total phosphorous levels ranged from 0.054 μg g^?1 during low flows to 134.94 μg g^?1 during high discharge periods in autumn and spring. These results show that stormwater management practices in urban areas are limiting runoff water and soil contact, reducing surficial soil loss. However, the runoff acceleration due to expansion of impervious surfaces is progressively increasing the significance of intrinsic sediment and phosphorous sources by exacerbating stream bank erosion and resuspension of internally stored sediments.     

Sediment Budget Analysis for River Reservoirs

The sediment, budget of a reservoir on the Neckar River, Germany, was investigated by means of experimental and numerical methods. Field measurements of channel bathymetry show that. sedimentation and erosion occur primarily in the lower backwater-influenced section of the reservoir, which stores approximately 350,000 m³ of fine-grained deposits. Sediment load balances for two major storm events in Dec. 1993 and Apr. 1994 showed net erosion of 32,000 ±10,000 tonnes and 24,000 ± 5,000 tonnes of sediment, respectively. A balanced sediment budget, was found for a minor flood in Jan. 1995. In agreement with the field data, numerical simulation of sediment transport. over a period of 45 years demonstrates that the river reservoir served initially as a sediment trap from 1950 to 1978, and since then as a temporary storage basin for sediment.     

A Comparison of Methods for Deriving Solute Flux Rates Using Long-Term Data from Streams in the Mirror Lake Watershed

Calculation of chemical flux rates for streams requires integration of continuous measurements of discharge with discrete measurements of solute concentrations. We compared two commonly used methods for interpolating chemistry data (time-averaging and flow-weighting) to determine whether discrepancies between the two methods were large relative to other sources of error in estimating flux rates. Flux rates of dissolved Si and SO₄ ^2- were calculated from 10 years of data (1981^-1990) for the NW inlet and outlet of Mirror Lake and for a 40-day period (March 22 to April 30, 1993) during which we augmented our routine (weekly) chemical monitoring with collection of daily samples. The time-averaging method yielded higher estimates of solute flux during high-flow periods if no chemistry samples were collected correponding to peak discharge. Concentration-discharge relationships should be used to interpolate stream chemistry during changing flow conditions if chemical changes are large. Caution should be used in choosing the appropriate time-scale over which data are pooled to derive the concentration-discharge regressions because the model parameters (slope and intercept) were found to be sensitive to seasonal and inter-annual variation. Both methods approximated solute flux to within 2^-10% for a range of solutes that were monitored during the intensive sampling period. Our results suggest that errors arising from interpolation of stream chemistry data are small compared with other sources of error in developing watershed mass balances.     

Modelling the Hydro‐Sedimentary Dynamics of a Mediterranean Semiarid Ungauged Watershed Beyond the Instrumental Period

The development of reliable tools to quantify long‐term sediment budgets is critical to establish adequate environmental and management policies in semiarid Mediterranean regions. In this study, we apply a multidisciplinary methodology to estimate water and sediment yields in ungauged Mediterranean watersheds over a period of scarce instrumental data (i.e. second half of 19^th and first half of 20^th centuries). Runoff and precipitation reconstructions have been obtained using an integrative approach involving synoptic reanalysis models, regional climatic datasets, historical archives and palaeoflood proxies from natural archives. The resulting hydrological reconstruction has been implemented on a hydro‐sedimentary distributed model (i.e. TETIS) to understand the hydro‐sedimentary dynamics in the studied watershed. We highlight that, in our study area, regional‐data (instrumental, historical and sedimentary) based models show higher accuracy in the sediment yield and runoff reconstruction than synoptic reanalysis climate models. The modelled sedimentary dynamics for the studied period respond to a complex interplay between human activities and climate variability. During the 19^th century deforestation and grazing activities combined with higher frequency on extreme runoff events resulted in higher runoff and sediment yield in the period 1863–1900. Over the 20^th century, reduced precipitation and land abandonment led to a decrease in erosion rates and sediment yield although increased in 1945–1960 coinciding with a period of higher frequency of heavy rainfalls. This hydrological response to climate and human activities in the study watershed improves our understanding of plausible future trends of environmental degradation in small Mediterranean watersheds under different land use and climate change scenarios. This article includes supporting information which features an explanation of GILMCLIM downscaling model, The precipitation series resulting from the reanalysis data (Figure S1), an analysis of the different precipitation series used (Table S1) and an extensive explanation of how the relation between Puentes and Valdeinfierno reservoirs was considered. Copyright © 2016 John Wiley & Sons, Ltd.     

Temporal changes in suspended sediment transport during the past five decades in a mountainous catchment,eastern China

Purpose

Analysis of sediment transport is an effective approach for identifying sediment sources and for catchment management. However, a long-term analysis of sediment variability at multiple time scales is less available, especially in mountainous catchments. This study aims to determine sediment sources and to identify sediment transport dynamics, as well as the influencing factors, through analyzing long-term sediment fluxes at different time scales.

Materials and methods

In this paper, 32 years of sediment flux in an instrumented mountainous catchment in eastern Zhenjiang Province, China, was investigated at multiple time scales (i.e., monthly, seasonal, annual, and event). Sediment yields (SYs) during three time periods (i.e., 1964–1977, 1978–1989, and 2010–2015) were first classified by the Mann-Kendall and cumulative anomaly tests, and then sediment fluxes for each period were investigated and compared at multiple time scales.

Results and discussion

Annual SYs ranged from 29 to 308 t year^?1 during the recording period and were significantly influenced by several high magnitude flood events. The mean annual SYs decreased from 153.82 t year^?1 in 1964–1977, to 97.79 t year^?1 in 1978–1989, and to 91.08 t year^?1 in 2010–2015 due to improved soil conservation measures and increased reservoirs. At the seasonal scale, over 92% of the sediment was transported in spring and summer over the recording period. Heterogeneous sediment sources, partial areal distribution of rainfalls, and other factors led to complex suspended sediment concentration versus water discharge hysteresis loop patterns at the event and monthly scales.

Conclusions

The improved soil conservation measures and increased reservoirs over the recent decades decreased sediment availability, and the number and the magnitude of flood events from 1964 onward. However, the flood sediment fluxes in a few months were still high due to extreme precipitation events in recent years. The work can provide guidance for addressing sediment problems in this and/or other similar catchments.

     

Polluted precipitation and the geochronology of mercury deposition in lake sediment of northern Minnesota

Elevated Hg levels in game fish from wilderness lakes in northern Minnesota led to the present study of sediment cores from two lakes to ascertain the source and history of Hg deposition. Natural background levels of Hg were found to range from 0.03 to 0.06 μg g^?1, with cultural levels as high as 0.16 μg g^?1. Reconstructed geochronologies reveal a dramatic two-fold increase in Hg flux, from 0.008 to 0.017 μg cm^?2 yr^?1, occuring after the year 1880, suggesting an anthropogenic influence. No industrial or geologic source of Hg is found in the study watersheds. The entire historical increase in Hg flux can be accounted for by atmospheric loading provided that 1/5 of all the Hg presently supplied to the watershed via precipitation is ultimately deposited in lake sediment. Hg levels in fish are not correlated with Hg levels in lake sediment, although there is a link to acid-sensitivity of lake water, amount of acid-neutralizing geologic material exposed in the watershed, and watershed area/lake volume ratio. Thermal stratification of lake water and a complexation-adsorption mechanism are proposed to account for variations in Hg levels observed in sediment collected from different sites.     

Earthworm contributions to soil nitrogen supply in corn-soybean agroecosystems in Quebec, Canada

Accurately quantifying the soil nitrogen(N) supply in crop fields is essential for enabling environmentally sustainable and economically profitable crop production. It requires using field-based methods to account for the contribution of soil biota, including earthworms, to N mineralization in temperate agroecosystems. The direct contribution of earthworms to the soil N cycle is the N they release throughout their life and after death, and it can be estimated using the secondary production method. This study was conducted in 2014 and 2015 in two adjacent fields with annual corn-soybean rotation in Ste-Anne-de-Bellevue, Quebec, Canada. The cumulative biomass of Aporrectodea spp. in two no-till corn-soybean agroecosystems was determined, and the direct N flux from these earthworms was estimated during the corn and soybean phases of the rotation. Secondary production was estimated by sampling earthworms biweekly during April–June and September–November and inferring the change in earthworm biomass between sampling dates using a size frequency calculation. The N flux was calculated as the sum of the N released through excretion, during periods when earthworms were active, and from mortality. The secondary production of the Aporrectodea population was estimated to be 8–43 g ash-free dry weight m~(-2) year~(-1), and the N flux was 22–105 kg N ha~(-1) year~(-1). The N flux was higher at the early vegetative growth stage, which is a period of high N demand for corn. These findings suggest that refining the N fertilization recommendation by accounting for soil N supplied by earthworms could potentially reduce fertilizer costs and environmental N losses.     

USE OF RESERVOIR DEPOSITS AND CAESIUM-137 MEASUREMENTS TO INVESTIGATE THE EROSIONAL RESPONSE OF A SMALL DRAINAGE BASIN IN THE ROLLING LOESS PLATEAU REGION OF CHINA

This paper reports the results of an investigation of the erosional response of the 3·86 km² Zhaojia Gully catchment in the rolling loess plateau region of Zichan County, Shaanxi Province, China. In the absence of direct measurements, information derived from reservoir deposits and from caesium-137 measurements on both the catchment soils and reservoir deposits was used to obtain a retrospective assessment of the longer-term (ca. 30 year) erosional response of the catchment and of the relative contributions of the rolling plateau surface and the gully areas to the sediment output from the basin. Net erosion rates on cultivated land occupying the gentle crest slopes and steeper lower slopes of the rolling plateau and the steep gully slopes were estimated to be 4500 t km⁻² year⁻¹, 8584 t km⁻² year⁻¹ and 15851 t km⁻² year⁻¹, respectively. Estimates of annual sediment yield from the study catchment based on analysis of sediment deposits in the two sediment-trap reservoirs ranged between 4627 and 32472 t km⁻² year⁻¹. Almost all the sediment transported from the catchment was contributed by 2–4 large floods each year. Measurements of the caesium-137 content of recent sediment deposits in a sediment-trap reservoir allowed the relative contributions of the total sediment yield derived from the rolling plateau and gully areas of the catchment to be estimated at 23 and 77 per cent, respectively. Analysis of the sediment deposits dating from 1973–1977 in another sediment trap reservoir allowed individual flood event couplets to be identified and indicated that the sediment associated with the first one or two floods in a season, when the soils of the plateau area were relatively dry, was derived primarily from the gully areas. The cultivated soils of the rolling plateau contributed an increased proportion of the total sediment yield during the latter stages of the flood season when the soils were wetter, and surface runoff and erosion were more widespread. Based on analysis of the caesium-137 content of the sediment deposited in this sediment-trap reservoir, the relative contributions of sediment from the rolling plateau and gully areas over the period 1973–1977 were estimated to be 21 and 79 per cent, respectively. The results obtained demonstrate the potential for using caesium-137 measurements and analysis of reservoir deposits to document the erosional response of a drainage basin. © 1997 John Wiley & Sons, Ltd.     

Establishing a Holocene sediment budget for the river Dijle

A Holocene sediment budget was constructed for the 758 km² Dijle catchment in the Belgian loess belt, in order to understand long-term sediment dynamics. Hillslope sediment redistribution was calculated using soil profile information from 809 soil augerings, which was extrapolated to the entire catchment using morphometric classes. As large parts of the forests within the catchment prove to have undergone little or no erosion since medieval times, a correction was applied for the presence of forests. Total Holocene erosion amounts 817 ± 66 Mt for the catchment, of which 327 ± 34 Mt was deposited as colluvium. This corresponds with a net Holocene soil erosion rate of 10.8 ± 0.8 × 10³ Mg ha^− 1 for the entire Dijle catchment. Alluvial deposits were studied through 187 augerings spread over 17 cross-valley transects. The total alluvial sediment deposition equals 352 ± 11 Mt or 42% of total eroded sediment mass. Results indicate that at the scale of a medium-sized catchment the colluvial sediment sink is as important as the alluvial sediment sink and should not be neglected. As a result the estimation of erosion through alluvial storage and sediment export would yield large errors. Dating of sediment units show an important increase in alluvial deposition from medieval times onwards, indicating the important influence of agricultural activities that developed from that period. Mean sediment export rates from the catchment for the last 1000–1200 years range between 0.8 and 1.3 Mg ha^− 1 a^− 1 and are consistent with present suspended sediment measurements in the Dijle. Erosion for agricultural land for this period is 9.2 ± 2.2 Mg ha^− 1 a^− 1. Sediment budgets for the various tributary catchments provide an insight in the sources and sinks of sediment at different scales within the catchment.     

A tracer budget quantifying soil redistribution on hillslopes after forest harvesting

Managing the impacts of erosion after forest harvesting requires knowledge of erosion sources; rates of sediment transport and storage; as well as losses from the system. We construct a tracer-based (¹³⁷Cs) sediment budget to quantify these parameters. The budget shows significant redistribution, storage and transport of sediment between landscape elements and identifies the snig tracks and log landings as the major impact sites in the catchment. Annual sediment losses from them were estimated to be 25±11 and 101±15 t ha⁻¹ year⁻¹, respectively, however, it is probable that most of this is due to mechanical displacement of soil at the time of harvesting. The budget showed greatest net transport of material occurring from snig tracks; representing some 11±4% of the ¹³⁷Cs budget. Of the latter amount, 18%, 28% and 43% was accounted for within the cross banks, filter strip and General Harvest Area (GHA), respectively. The ¹³⁷Cs budget also showed the GHA to be a significant sediment trap. The filter strip played a fundamental role in the trapping of material generated from the snig tracks, the mass delivery to them from this source was calculated to be 1.7±0.6 kg m² year⁻¹. Careful management of these remains critical. Overall we could account for 97±10% of ¹³⁷Cs. This retention suggests that (within errors) the overall runoff management system of dispersing flow (and sediment) from the highly compacted snig tracks, by cross banks, into the less compacted (and larger area) GHA and filter strips has effectively retained surface soil and sediment mobilised as a result of harvesting at this site.     

Improving precision in sediment source and erosion process distinction in an upland catchment,south-eastern Australia

Analysis of sediment sources is an important component in the development of catchment sediment budgets and in determining links between erosion from sources and sediment delivery to catchment outlets. In this study ¹³⁷Cs and ²¹⁰Pb_ex were used to determine surface and sub-surface source contributions of fine sediment in a small upland headwater catchment (1.6 km²) in south-eastern Australia. The findings from this analysis are employed in an adjustment procedure to better differentiate sediment source erosion processes by utilising channel survey and erosion pin data. This improved the precision of estimates of sediment-source erosion-process contributions from hillslopes and channel/gully walls. A mean of 74% of in-channel deposits and suspended sediment exiting the study catchment was derived from sub-surface sources and when adjusted for erosion process this increased to 81%, which may be attributed to channel and gully wall erosion alone. Net erosion of the channel floor was low and constitutes only a small part of the total channel source input to sediment flux. Variability in sediment source contributions within the catchment was high, with rapid transition from hillslope to channel source dominance of sediment flux with distance downstream in the study catchment.     

Fingerprinting Sediment Sources After an Extreme Rainstorm Event in a Small Catchment on the Loess Plateau,PR China

Soil erosion is a severe problem on China's Loess Plateau due to its fine‐grained soils and the increasing frequency of extreme rainfall events. Accordingly, this study used a 100‐year frequency rainstorm dataset to analyse sediment deposition and sources in a 27‐km² catchment with a dam field area of 0·14 km² based on the hypothesis that sediments were intercepted by the dam (before collapse) during the rainstorm event and deposited in the dam field. This study applied composite fingerprinting, which revealed the sediment source contributions and estimated sediment deposition. Sediment deposition (626·4 kg m⁻²) decreased linearly or exponentially with increasing distance from the dam. Composite fingerprints based on the optimal parameters revealed relative sediment contributions of 44·1% ± 25·5%, 37·7% ± 35·0%, 9·0% ± 11·4% and 9·2% ± 11·5% by bare ground, croplands, grassland and forests, respectively. The 5‐year cumulative sediment deposition from normal rainfall was 2·3 × 10⁴ t less than the extreme rainstorm. Bare grounds and croplands were the dominant sediment sources following both the extreme rainstorm and normal erosive rainfall events but varied at different areas of the check‐dam. Erosion patterns and start times depended on land use type, thereby affecting sediment profiles in the dam field. Furthermore, severe erosion from bare ground that were all gully slopes and gully walls occurred throughout the rainfall, whereas grasslands and forest erosion occurred earlier and croplands later. Finally, extreme rainfall promoted mass wasting on slopes, gully slopes and gully walls, which are important in determining extreme rainstorm erosion pattern variation. This study aimed to reveal erosion pattern variation under extreme rainstorm events. Copyright © 2017 John Wiley & Sons, Ltd.     

Fate and Transport of Copper Applied in Channel Catfish Ponds

A pilot-scale study and field measurements at commercial ponds were conducted to investigate the environmental fate of copper (Cu) applied as an algaecide in commercial catfish ponds. In the pilot study, a total of 774 g Cu(II) was applied to an experimental catfish pond over a period of 16 summer weeks. More than 90% of Cu applied became associated with suspended sediment particles within a few minutes of addition, and then nearly all Cu applied was transferred to the sediment phase within about 2 days. At the end of the study, the peak Cu content in the sediment increased from an initial concentration of 25～35 mg kg^?1 to about 200 mg kg^?1, and the applied Cu was able to reach a sediment depth of about 16 cm. Meanwhile, Cu concentration in the catfish body decreased from 12.7 ± 2.81 mg kg^?1 to 6.15 ± 2.54 mg kg^?1. Copper mass balance indicated that virtually all Cu applied was retained in the sediment. Only 0.01% of the total Cu applied was taken up by fish and 0.1% remained in pond water. Data from 3 commercial fishponds of different ages (1–25 years) and with different sediment types (acidic, neutral and calcareous) supported the pilot-scale observation. Both pilot-testing results and field measurements revealed that Cu is predominantly accumulated within the top sediment layer and barely reached the bottom soil regardless of the pond age and the type of the sediments. Field monitoring of groundwater quality suggested that the copper leaching into the groundwater surrounding the ponds was insignificant.     

Distinguishing regional and local sources of pollution by trace metals and magnetic particles in fluvial sediments of the Morava River, Czech Republic

Purpose

Regional contamination of southern Moravia (SE part of the Czech Republic) by trace metals and magnetic particles during the twentieth century was quantified in fluvial sediments of the Morava River. The influence of local pollution sources on regional contamination of the river sediments and the effect of sampling site heterogeneity were studied in sediment profiles with different lithologies.

Materials and methods

Hundreds of sediment samples were obtained from regulated channel banks and naturally inundated floodplains and proxy elemental analyses were carried out by energy dispersive X-ray fluorescence spectroscopy (ED XRF) and further calibrated by inductively coupled plasma mass spectrometry (ICP MS). Magnetic susceptibility was determined as a proxy for industrial contamination. The age model for the floodplain sediments was established from ¹³⁷Cs and ²¹⁰Pb dating. Trace metal contamination was assessed by establishing the lithological background values from floodplain profiles and calculating enrichment factors (EF) of trace metals (i.e. Pb, Zn, Cu) and magnetic susceptibility for the entire study area.

Results and discussion

Channel sediments are unsuitable for the reconstruction of historical regional contamination due to their lithological heterogeneity and the “chaotic” influence of local sources of contamination, as well as the possibility of geochemical mobility of pollutants. On the other hand, sediments from regulated river banks qualitatively reflected the actual, local contamination of the river system.

Conclusions

This approach allowed us to distinguish the influence of local sources of contamination by comparison with more spatially averaged contamination signals from distal floodplain profiles. The studied area is weakly contaminated (EF ～1–2), while individual sediment strata from regulated channel banks reflect local sources of contamination and contain up to several times higher concentrations of trace metals.