Riverbank Sediments Research Articles

Mobility of trace metals associated with urban particles exposed to natural waters of various salinities from the Gironde Estuary, France

Background, aim and scope Urban systems are hot spots of environmental pollution caused by manifold anthropogenic activities generating traffic-related, industrial and domestic emissions. Besides air, soil and groundwater pollution, pollution of surface water systems is of major concern because they are often (ab)used to export waste of various consistence out of urban areas and become contaminated on varying scales. The Gironde Estuary (southwest France) is affected by various anthropogenic contaminations derived from historic polymetallic pollution mainly due to former mining and ore-treatment and, additionally, from agriculture and urban areas. Although detailed knowledge is available on the impact of mining and anthropogenic activities on the water quality of the Gironde Estuary, almost nothing is known on the urban impact, even though the Garonne Branch which is one tributary of the Gironde system crosses the large urban agglomeration of Bordeaux. The present work links urban geochemistry and estuary research and aims at evaluating the mobility of potentially toxic trace elements (Cd, Cu, Zn, V, Co, Mo, Pb) associated with urban particles under estuarine conditions owing to the particles' role as potential vectors transporting urban pollutants into the estuary. For this, environmentally available fractions of trace elements in representative urban particles (urban dust, road sediment, riverbank sediment, construction materials) from the city of Bordeaux were extracted by natural estuarine waters of varying salinities and compared to commonly applied HNO3 extractions.

Incipient Motion of Riverbank Sediments with Outflow Seepage

Based on a force analysis, an expression is derived to describe the critical Shields number for incipient motion of uniform cohesionless sediment particles on a riverbank slope in terms of flow parameters, outflow seepage, and physical and mechanical properties of sediments. Parametric studies were conducted to investigate quantitatively the effects of hydraulic gradient of seepage, slope angle, and flow direction on the critical Shields number. The results show that the critical Shields number decreases with an increase in the hydraulic gradient. Where bank collapse is concerned, the most dangerous direction of hydraulic gradient of outflow seepage is at an angle equal to the effective internal angle of friction of the sediment mass with respect to slope surface. At a certain value of hydraulic gradient, the critical Shields number decreases with increasing slope angle. Open flow becomes more erosive when the current direction changes from horizontally parallel with the riverbank line to turning downward.

Infrared spectroscopy tracing of sediment sources in a small rural watershed (French Alps)

The present article describes a first attempt to use infrared spectroscopy to trace the origin of suspended river sediments. Fifty samples of the main potential sediment sources within a small catchment area (990 ha) in the French Alps were collected and compared with samples of suspended sediment from the river, collected on various dates during 2006 and 2007 using sediment traps. Two major categories of sediment source were identified: topsoils and river channel sediments. For the qualitative part of the study, each of these two main categories was divided into two sub-categories, that is to say, cultivated and pastureland topsoils, and riverbed and riverbank sediments. Discriminant analysis on the source samples showed that Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy can be used to differentiate between the four potential source materials. To determine whether or not immersion in the river altered the infrared spectra of these source materials, we measured the infrared spectra of samples that had been immersed in the river, in litter bags, for periods of up to 24 days. Immersion did not cause any major changes in the infrared spectra. The contribution of each type of source material to the suspended sediment in the river was quantified using partial least squares (PLS) analyses of DRIFT spectra to compare actual river sediment samples with an experimental model. This model was produced from the DRIFT spectra of a range of calibration samples produced by mixing source material samples in different ratios. The predictions of the model were valid and fell within the confidence interval calculated for the calibration set. Comparisons between suspended sediment samples and the model indicate that the predominant source of the sediment is riverbank erosion, which, in this case, is probably due to trampling by cattle.

Time-scales of sedimentary transfer and weathering processes from U-series nuclides: Clues from the Himalayan rivers

In order to define time-scales of erosion and sedimentary transfer in the Himalaya, 238U– 234U– 230Th disequilibria have been analysed in river bank sediments and in bedloads collected along the Kali Gandaki river, one of the main Nepalese rivers, and in the Ghaghara and Gandak rivers, two major plain tributaries of the Ganges. The Th activity ratios and U/Th ratios in river sediments of the two Ganges tributaries constantly decrease from upstream to downstream. This is related to the maturation of sediments by weathering during their transfer to the plain. The U-series data allow to calculate a transfer time for the sediments in the alluvial Gangetic plain from the chain front to the confluence with the Ganges of about 100 kyr for both rivers. The Kali Gandaki river sediment data highlight a decrease of both the Th isotopic and U/Th ratios which is explained by a mixing between two sources with similar U/Th ratios but having suffered a different U–Th fractionation history. Interpretation of the U-series data in the frame of this scenario gives long time-scales of weathering of several 100's kyr for the Himalayan terranes. The results imply that Himalayan bedrocks are submitted to a long in situ stage of weathering before their erosion and transfer into the rivers. In addition, occurrence of similar U–Sr signatures in dissolved (i.e. < 0.1–0.2 μm) and sediment phases of the Kali Gandaki river suggests that “dissolved” uranium could be carried by colloids constituted by sedimentary microparticles. This precludes the use of U-series disequilibria in this river to calculate weathering budgets and to assess whether the erosion is working at steady-state or not.

Polybrominated diphenyl ethers in fish and sediment from river polluted by electronic waste

The present study investigated contamination of polybrominated diphenyl ethers (PBDEs) in sediment and fish samples collected from rivers in Guiyu, China where electronic waste (e-waste) is recycled and disposed. PBDE congeners with mono-to hepta-brominated and deca-brominated substitutions were detected using (13)C(12) isotope dilution GC/MS/MS and GC/MS methods, respectively. The total PBDE concentrations ranged from 4434 to 16088 ng/g (dry weight) in Nanyang River bank sediment, from 55 to 445 ng/g in Nanyang River bottom sediment and 51.3 to 365 ng/g in Lianjiang River bottom sediment in Guiyu compared with those from 16.1 to 21.4 ng/g in wastewater discharged from a vehicle repairing workshop in Lo Uk Tsuen in Hong Kong. No PBDE congeners were detected in bottom sediment and fish from Mai Po Marshes in Hong Kong. The mean concentrations of total PBDEs in mixed muscles of tilapia (Oreochromis spp) from Lianjiang River were 115 ng/g wet weight (ww) and from wastewater in Hong Kong were 4.1 ng/g ww. Highest mean PBDE concentration was obtained in liver (2687 ng/g ww), followed by abdomen muscle (1088 ng/g ww) of bighead carp (Aristichthys nobilis) collected from Nanyang River. A significant correlation of concentration of each PBDE congener between sediment and muscle from Guiyu was observed. The present results of total PBDEs in sediment and fish were 10 and 1000 times higher than other studies. Open burning and dumping of e-waste are the major causes of PBDE contamination.

Assessment of Coarse Sediment Mobility in the Black Canyon of the Gunnison River, Colorado

The Gunnison River in the Black Canyon of the Gunnison National Park (BCNP) near Montrose, Colorado is a mixed gravel and bedrock river with ephemeral side tributaries. Flow rates are controlled immediately upstream by a diversion tunnel and three reservoirs. The management of the hydraulic control structures has decreased low-frequency, high-stage flows, which are the dominant geomorphic force in bedrock channel systems. We developed a simple model to estimate the extent of sediment mobilization at a given flow in the BCNP and to evaluate changes in the extent and frequency of sediment mobilization for flow regimes before and after flow regulation in 1966. Our methodology provides a screening process for identifying and prioritizing areas in terms of sediment mobility criteria when more precise systematic field data are unavailable. The model uses the ratio between reach-averaged bed shear stress and critical shear stress to estimate when a particular grain size is mobilized for a given reach. We used aerial photography from 1992, digital elevation models, and field surveys to identify individual reaches and estimate reach-averaged hydraulic geometry. Pebble counts of talus and debris fan deposits were used to estimate regional colluvial grain-size distributions. Our results show that the frequency of flows mobilizing river bank sediment along a majority of the Gunnison River in the BCNP has significantly declined since 1966. The model results correspond well to those obtained from more detailed, site-specific field studies carried out by other investigators. Decreases in the frequency of significant sediment-mobilizing flows were more pronounced for regions within the BCNP where the channel gradient is lower. Implications of these results for management include increased risk of encroachment of vegetation on the active channel and long-term channel narrowing by colluvial deposits. It must be recognized that our methodology represents a screening of regional differences in sediment mobility. More precise estimates of hydraulic and sediment parameters would likely be required for dictating quantitative management objectives within the context of sediment mobility and sensitivity to changes in the flow regime.

Influence of hydropower dams on the composition of the suspended and riverbank sediments in the Danube

Large hydropower dams have major impacts on flow regime, sediment transport and the characteristics of water and sediment in downstream rivers. The Gabcikovo and Iron Gate dams divide the studied Danube transect (rkm 1895–795) into three parts. In the Gabcikovo Reservoir (length of 40 km) only a part of the incoming suspended sediments were deposited. Contrary to this, in the much larger Iron Gate backwater zone and reservoir (length of 310 km) all riverine suspended sediments were deposited within the reservoir. Subsequently, suspended sediments were transported by tributaries into the Iron Gate backwater zone. Here they were modified by fractional sedimentation before they transgressed downstream via the dams. Compared with undammed Danube sections, Iron Gate reservoir sediment and suspended matter showed higher clay contents and different K/Ga and Metal/Ga ratios. These findings emphasize the importance of reservoir–river sediment-fractionation.

Quantifying urban river–aquifer fluid exchange processes: A multi-scale problem

Groundwater–river exchanges in an urban setting have been investigated through long term field monitoring and detailed modelling of a 7 km reach of the Tame river as it traverses the unconfined Triassic Sandstone aquifer that lies beneath the City of Birmingham, UK. Field investigations and numerical modelling have been completed at a range of spatial and temporal scales from the metre to the kilometre scale and from event (hourly) to multi-annual time scales. The objective has been to quantify the spatial and temporal flow distributions governing mixing processes at the aquifer–river interface that can affect the chemical activity in the hyporheic zone of this urbanised river. The hyporheic zone is defined to be the zone of physical mixing of river and aquifer water. The results highlight the multi-scale controls that govern the fluid exchange distributions that influence the thickness of the mixing zone between urban rivers and groundwater and the patterns of groundwater flow through the bed of the river. The morphologies of the urban river bed and the adjacent river bank sediments are found to be particularly influential in developing the mixing zone at the interface between river and groundwater. Pressure transients in the river are also found to exert an influence on velocity distribution in the bed material. Areas of significant mixing do not appear to be related to the areas of greatest groundwater discharge and therefore this relationship requires further investigation to quantify the actual remedial capacity of the physical hyporheic zone.

Uranium and thorium isotopes in the rivers of the Amazonian basin: hydrology and weathering processes

AbstractTwo expeditions (October 1989 and May 1992) were carried out to two points of the main Amazon River channel and four tributaries. The Solimões and Madeira rivers, taking their origin in the Andes, are whitewater rivers. The Negro River is a typical acid, blackwater river. The Trombetas River flows through bauxite‐rich areas, and is characterized by low concentrations of dissolved humic substances. The 238U, 234U, 232Th and 230Th activities were recorded from dissolved, suspended particulate phases and river bank sediments. The latter were analysed for their 226Ra, 228Ra and 210Pb contents, and also subjected to leaching with 0·2 M hydroxylamine–hydrochloride solution to determine the concentrations of radionuclides bound to amorphous Fe hydroxides and Mn oxides and hydroxides.The dissolved U average concentration in the Amazon system is ten times lower than the mean world river concentration. The uranium concentration observed at Óbidos in the lower Amazon (0·095 µg L−1), where the U content in the river bank sediments and suspended matter is lowest, suggests U release from the solid phase during river transport. About 485 t of U are transported annually to the Amazon delta area in dissolved form, and 1943 t bound to suspended particulate matter.Total U and Th concentrations in the river bank sediments ranged from 1·59 to 7·14 µg g−1 and from 6·74 to 32 µg g−1, respectively. The highest concentrations were observed in the Trombetas River. The proportion extracted by means of the hydroxylamine solution (HL) was relatively high for U in the Trombetas river bank sediment (31%) and for Th in the Solimões sediment (30%).According to the alpha recoil effects, the 234U/238U activity ratios of the Andean river waters and downstream Amazon water (Óbidos) were &gt;1, but were &lt;1 in the Negro River (at Manaus). The activity ratios of dissolved U correlate with pH and also with the U activity ratios in the river bank sediment hydroxylamine extracts. As expected, the 234U/238U activity ratios in river bank sediments were &lt;1 in the Andean rivers and in the downstream Amazon, but they were &gt;1 in the Trombetas and Negro rivers. Such ratios probably result from the binding of dissolved uranium to solid sediment.The 228Th/232Th ratios of river bank sediments were close to unity (except for the Negro River, where it is lower), suggesting no significant Th exchanges between the river water and the sediment. The 226Ra/232Th activity ratios were &lt;1, and the 226Ra/228Ra activity ratios generally were significantly higher than the activity ratios of their respective parents. This perhaps is the result of easier leaching of the 226Ra parent, 230Th, from solid material (owing to the alpha recoil effect) than of the 228Ra parent.Uranium and thorium isotopes were used as tools to evaluate the chemical weathering rate of rocks in the Amazon system, which was estimated to be 2·7 cm 1000 year−1 s−1. Copyright © 2002 John Wiley &amp; Sons, Ltd.

X-Ray analysis of riverbank sediment of the Tisza (Hungary): identification of particles from a mine pollution event

A serious heavy metal pollution of the Tisza River occurred on March 10, 2000, arising from a mine-dumping site in Romania. Sediment samples were taken from the main riverbed at six sites in Hungary, on March 16, 2000. The objective of this work was to distinguish the anthropogenic and crustal erosion particles in the river sediment. The samples were investigated using both bulk X-ray fluorescence (XRF) and thin-window electron probe microanalysis (EPMA). For EPMA, a reverse Monte Carlo method calculated the quantitative elemental composition of each single sediment particle. A high abundance of pyrite type particles was observed in some of the samples, indicating the influence of the mine dumps. Backscattered electron images proved that the size of particles with a high atomic number matrix was in the range of 2 μm. In other words the pyrites and the heavy elements form either small particles or are fragments of larger agglomerates. The latter are formed during the flotation process of the mines or get trapped to the natural crustal erosion particles. The XRF analysis of pyrite-rich samples always showed much higher Cu, Zn and Pb concentrations than the rest of the samples, supporting the conclusions of the single-particle EPMA results. In the polluted samples, the concentration of Cu, Zn and Pb reached 0.1, 0.3 and 0.2 wt.%, respectively. As a new approach, the abundance of particle classes obtained from single-particle EPMA and the elemental concentration obtained by XRF were merged into one data set. The dimension of the common data set was reduced by principal component analysis. The first component was determined by the abundance of pyrite and zinc sulfide particles and the concentration of Cu, Zn and Pb. The polluted samples formed a distinct group in the principal component space. The same result was supported by powder diffraction data. These analytical data combined with Earth Observation Techniques can be further used to estimate the quantity of particles originating from mine tailings on a defined river section.

Response of bacterial extracellular enzymes to inundation of floodplain sediments

1. Bacterial extracellular enzymes provide a measure of microbial response to organic matter supply, pivotal to the recovery of riverine food webs after disturbances such as floods.2. We examined the effects of flood duration on extracellular enzyme response from riverbank and floodplain wetland sediments from the Murrumbidgee River, south‐east Australia.3. There were strong temporal peaks in enzyme activity from both riverbank and billabong sites, peaking between 1 and 5 days following flooding and with a general decline by 21 days. A dominance of non‐glucosidase and xylosidase enzymes resulted in no significant differences between billabong and riverbank sediments. This supports the hypothesis that regulated Australian river systems are driven by autochthonous carbon sources.4. The short response time of the glucosidase after flooding suggests that even short pulses (24 h) in high flows may stimulate bacterial activity, as dissolved organic carbon (DOC) loads also peak at this time. However, a longer wetting time may be needed to drive hydrolysis of the proteins, fatty acids and longer chain polysaccharides, whether in the littoral zone of the river or connection with the floodplain.

Effects of discharge on silver loading and transport in the Quinnipiac River, Connecticut

Silver concentrations were measured in water and sediment samples collected from the Quinnipiac River in Connecticut. This river was chosen for study because of its history of industrialization and high levels of Ag contamination. Sewage treatment plant (STP) effluent accounts for ∼15% of the total river discharge and ∼60% of the dissolved Ag in the water column during baseflow conditions. Erosion of contaminated riverbank sediment is the primary source of particulate Ag in the river. Both dissolved and particulate Ag fractions vary as a function of river discharge. Increased discharge due to rain events decreases the relative importance of STP effluent, and thus dilutes the dissolved Ag concentration in the water column. Conversely, increasing discharge results in higher particulate Ag concentrations from increased erosion. The results of this study clearly indicate that both point and non-point sources contribute significantly to Ag loading in this river system, with the level of river discharge determining the relative importance of each.

Desktop Method for Estimating Vessel-Induced Sediment Suspension

Riverbank erosion involves engineering and environmental concerns. Among several dominant mechanisms of riverbank erosion, navigation effects caused by the passage of vessels are quite important. Field data indicate that large vessels generate large drawdown and small wave heights, whereas small vessels such as pleasure craft generate small drawdown and large wave heights. Passage of both types of vessels may result in bank erosion and a substantial increase in suspended-sediment concentration. Since comprehensive numerical modeling is time-consuming, a desktop computational approach has been offered that helps in providing preliminary answers to several questions related to vessel-induced sediment resuspension. Due to the uncertainties inherent in sediment calculations, order-of-magnitude values are often adequate for decision making. A preliminary assessment of possible impact on vegetation or benthic organisms can then be made based on this information. PC-based FORTRAN programs were developed for (1) computation of time series of vessel-induced waves; (2) erosion and deposition of cohesive sediment under waves and nearshore currents; and (3) computation of noncohesive suspended-sediment concentration caused by river current alone. An application to the Upper Mississippi River Navigation Study is presented. The riverbank sediments were labeled as soft, medium, and hard using their erodibility characteristics. Three water depths (0.5, 1.0, and 1.5 m) were considered. Vessel-induced wave heights ranged from 10 to 60 cm. The maximum concentrations were obtained in 0.5 m water depth with a wave height of 30 cm and in 1.0 m depth with a wave height of 60 cm. The estimated maximum concentrations were 1,463, 56, and 4 mg/L for soft, medium, and hard beds, respectively. Such results will be useful for preliminary assessment of relative impact of increased barge traffic in the river and identification of potential areas along the riverbanks that are likely to be sensitive from the point of view of environmental considerations.

The development of middle rare earth element enrichments in freshwaters: weathering of phosphate minerals

Many phosphatic minerals of biogenic, authigenic and diagenetic origin are distinguished by rare-earth element (REE) compositions, which have a well-developed middle rare-earth element (MREE) enrichment defined by a gradual increase in the shale-normalized ratios of REE toward the middle of the REE series (La to Lu). Also, the REE composition of dissolved matter in the waters of the Amazon, Fly and Sepik Rivers (as well as other river, lake and ground waters) have well-developed MREE enrichments. The development of MREE enrichments was studied through a series of leaching experiments using river-bank sediments from the Amazon, Fly, Sepik and Mississippi Rivers. A well-characterized phosphate mineral-rich shale with a pronounced MREE enrichment in its bulk composition was also leached in order to better assess the relationship between the weathering of phosphate minerals and the formation of MREE-enriched solutions. The two leaching solutions per sediment consisted of filtered lake water at pH 5 and the same water adjusted to pH 2. Leaching experiments with the four river sediments result in extensive fractionation whereby the REE compositions of the solutions develop MREE enrichments from starting sediments that show no MREE enrichments. The pH 2 leachates have much higher concentrations of the REE and more fully developed MREE enrichments than do the pH 5 leachates. The MREE enrichments at pH 2 usually form within an hour of starting the experiments. The phosphatic shale results show that there is preferential release of large amounts of MREE at pH 5, as well as at pH 2, demonstrating the weather ability of the phosphatic minerals at pHs of natural freshwaters. The Sepik River pH 5 experiment also shows significant MREE enrichment under near-neutral conditions. The development and retention of the MREE enrichments in the leaching solutions is accompanied by an increase in dissolved phosphate concentrations. Although the magnitudes of the MREE enrichment do not directly correlate with the percent of phosphate released, the experimental data suggest that the preferential dissolution of phosphatic minerals during weathering can result in extensive REE fractionation between bulk river sediment and water, leading to freshwaters with MREE enrichments.

ISOTOPIC EVALUATION OF Pb OCCURRENCES IN THE RIVERINE ECOSYSTEMS OF THE KANKAKEE WATERSHED, ILLINOIS‐INDIANA1

ABSTRACT: Environmental background levels of Pb were measured in ponds, river waters, sediments, suspended sediments, rocks, and air particulates within the Kankakee watershed during the period of 1995 to 1999. Stable isotopic Pb distinguished airborne Pb and its incorporation into riverine wetland sediments from geogenic Pb measured in river sediments. The provenance of the naturally‐occurring Pb is from carbonate bedrock and contributes comparable concentrations in riverbank sediments (25.9–30.4 mg kg−1) as Pb found in wetland sediments (18.6–24.8 mg kg−1). Estimates of anthropogenic Pb contributions from airfall into the Kankakee wetlands were found to be near 0.43–0.71 Bq cm−2 yr−1 during 1995 to 1999. While leachable Pb data suggests the uppermost layers of pond sediments were disturbed, 210Pb analyses from undisturbed sedimentation suggests Pb‐bearing sediments accumulate approximately 0.46–0.51 cm yr−1 in the ponds within the riparian zones. Transboundary Pb pollution from aerosols of industrial Pb across the Great Lakes occurs, but Pb isotopy indicates that the Pb concentrations are comparable to natural concentrations of Pb in both waters and sediments within the Kankakee watershed.

Recent mine spill adds to contamination of southern Spain

The retaining wall of a tailings reservoir collapsed at a zinc mine in Spain last spring, releasing into the watershed possibly nearly as much zinc as the mine produces annually. The accident happened April 25,1998, at the Los Frailes mine near Aznalcollar in southern Spain, sending ∼5 x 106m3 of acid sludge into the Guadiamar River. Based on a suite of water and river bank sediment samples collected downstream of the spill on May 1–3, 1998, an estimated 40,000 to 120,000 tons of Zn was added to the watershed. This is comparable to the annual production capacity of the mine of 125,000 tons. While the scale of the accident was certainly very large, an equivalent amount of Zn has been reaching the adjacent Tinto‐Odiel estuary every 1–2 years as a result of mining since the middle of the 19th century. Emergency dikes were built shortly after the accident to prevent contamination of Donana National Park, an important wildlife reserve 40 km to the south of the mine. The composition of samples collected north of the park suggest this diversion was effective.

The impact of human settlement on vegetation and soil stability in Hawke's Bay, New Zealand

Widespread destruction of lowland podocarp/hardwood forests in Hawke's Bay followed permanent Maori settlement of the region. Forests cleared by fires were rapidly replaced with a bracken fern-scrubland which remained the predominant vegetation until European settlers cleared it away for pasture production in the late 1870s. Deforestation began about 500 calendar years B.P., but proceeded faster in the drier lowlands than in the wetter hill country. When the catchments were covered with either forest or fern-scrubland, soil erosion was minimal because the soil structure was maintained by the network of roots and protected from raindrop impact by a dense canopy. The main effect of storms before European settlement was to transport pulses of mostly riverbank sediment into the lakes. However, after European settlement, soil erosion increased markedly. Removal of soil stabilising vegetation and its replacement with pasture has left soft-rock hill country soils vulnerable to erosion and landslides.

A late Holocene history of natural disturbance in lowland podocarp/hardwood forest, Hawke's Bay, New Zealand

Palaeoecological investigations of sediment cores from two lake basins in the Tutira and Putere districts of Hawke's Bay demonstrate the impact of volcanic activity, fires, and storms on the vegetation and soil stability before human settlement and deforestation. A “disturbance curve” derived from the classification and ordination of pollen records, and correlated with charcoal and sediment records, illustrates relative forest disturbance over time. Before anthropogenic forest clearance in Hawke's Bay, forest composition fluctuated frequently as a result of disturbance from fires, droughts, and a major volcanic eruption. Each natural disturbance, indicated by short-term increases of seral taxa, was followed by complete forest redevelopment. Cyclonic storms were not a major cause of disturbance to lowland podocarp/hardwood forests in the region, nor to the bracken-scrubland vegetation that replaced the forest after clearance. However, storms scoured and rapidly transported riverbank sediments into the lake basins. Compared with the preceding natural disturbances, deforestation by early Maori settlers represents a type and magnitude of disturbance previously unrecorded in the cores.

Short exposure to acetylene to distinguish between nitrifier and denitrifier nitrous oxide production in soil and sediment samples

The contribution of nitrifiers and denitrifiers to the nitrous oxide production in slurries of calcareous silt loam and river bank sediment at different oxygen concentrations was determined using acetylene as nitrification inhibitor. The addition of 10 Pa acetylene resulted in inhibition of nitrous oxide production at oxic conditions, but strongly enhanced the nitrous oxide production at oxygen-poor and anoxic conditions. Inhibition of nitrification by short exposure (1 to 24 h) to high concentrations of acetylene (100 Pa to 10 kPa) was tested using the same samples. After the removal of acetylene, nitrification was inhibited almost completely (82% to 89%) for at least 6 days whereas nitrous oxide reduction was restored within a day. It was concluded that the ‘short exposure’ inhibition method resulted in adequate nitrification inhibition without repressing the nitrous oxide reduction in anoxic nitrate-rich microsites and that the method was suitable for assessing the nitrifier contribution to the nitrous oxide emission of intact soil and sediment cores.

Short exposure to acetylene to distinguish between nitrifier and denitrifier nitrous oxide production in soil and sediment samples1

The contribution of nitrifiers and denitrifiers to the nitrous oxide production in slurries of calcareous silt loam and river bank sediment at different oxygen concentrations was determined using acetylene as nitrification inhibitor. The addition of 10 Pa acetylene resulted in inhibition of nitrous oxide production at oxic conditions, but strongly enhanced the nitrous oxide production at oxygen-poor and anoxic conditions. Inhibition of nitrification by short exposure (1 to 24 h) to high concentrations of acetylene (100 Pa to 10 kPa) was tested using the same samples. After the removal of acetylene, nitrification was inhibited almost completely (82% to 89%) for at least 6 days whereas nitrous oxide reduction was restored within a day. It was concluded that the ‘short exposure’ inhibition method resulted in adequate nitrification inhibition without repressing the nitrous oxide reduction in anoxic nitrate-rich microsites and that the method was suitable for assessing the nitrifier contribution to the nitrous oxide emission of intact soil and sediment cores.