Slip-off Slope Research Articles

High methane ebullition throughout one year in a regulated central European stream

Ebullition transports large amounts of the potent greenhouse gas methane (CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}) from aquatic sediments to the atmosphere. River beds are a main source of biogenic CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}, but emission estimates and the relative contribution of ebullition as a transport pathway are poorly constrained. This study meets a need for more direct measurements with a whole-year data set on CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document} ebullition from a small stream in southern Germany. Four gas traps were installed in a cross section in a river bend, representing different bed substrates between undercut and slip-off slope. For a comparison, diffusive fluxes were estimated from concentration gradients in the sediment and from measurements of dissolved CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document} in the surface water. The data revealed highest activity with gas fluxes above 1000 ml m-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-2}$$\\end{document} d-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document} in the center of the stream, sustained ebullition during winter, and a larger contribution of ebullitive compared to diffusive CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document} fluxes. Increased gas fluxes from the center of the river may be connected to greater exchange with the surface water, thus increased carbon and nutrient supply, and a higher sediment permeability for gas bubbles. By using stable isotope fractionation, we estimated that 12-44% of the CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document} transported diffusively was oxidized. Predictors like temperature, air pressure drop, discharge, or precipitation could not or only poorly explain temporal variations of ebullitive CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document} fluxes.

Why analysing microplastics in floodplains matters: application in a sedimentary context.

Microplastics in the environment are a relatively new form of anthropogenic contamination. Right now, the research focus is on the detection of microplastic accumulation in different environmental compartments and understanding the processes that have led to its transport. Detailed information on microplastics in floodplain areas and their distribution in depth are still missing to better understand accumulation points. Therefore, this study presents on the one hand microplastic detection in fluvial sediments from nine sampling sites along a river course. Polymers were determined with infrared spectroscopy and additional sedimentary analysis of the grain size and heavy metal concentration was performed. In total, there was less microplastic in the upper than in the lower river course and slip-off slopes were identified as accumulation hotspots also in deeper sediment layers. Mostly, microplastic particles were detected in fine sediment and heavy metal concentrations along the river were similar to those of microplastics. On the other hand, besides the spatial distribution of microplastics and accumulation in floodplain areas, microplastic analysis offered information in a sedimentary context. Sedimentation rates (0.29-4.00 cm a-1) and patterns between temporal deposition and microplastic polymers were identified. The basis for the development of a dating method by detection of MPs in sediments was thus established. Microplastics as a contaminant provide, in addition to the identification of deposition areas, further data in a temporal and sedimentary perspective.

Defining the baseline for river restoration: comparing carabid beetle diversity of natural and human-impacted riparian habitats

Near-natural rivers and riparian ecosystems can represent biodiversity hotspots harbouring many highly specialised, rare and endangered species. During the past centuries, these habitats have been heavily degraded by anthropogenic use, and therefore river restoration is one of the most striking fields of action that is legally defined by the European Union Water Framework Directive. Successful restoration depends on realistic and specified targets that should be defined beforehand and founded on status quo surveys. We present a comparison of carabid beetle communities in riparian habitats of natural and managed river sites of the Mulde River in the Biosphere Reserve Middle Elbe. This endeavour is part of a unique multi-level revitalisation project. Pitfall trapping in 2016 and 2017 yielded 111 carabid species with many species of conservation concern in natural and managed habitats. However, Simpson diversity and functional diversity were lower in the latter. Both habitats harboured specific species assemblages with characteristic indicator species. Additionally, the trap location on slip-off slopes or cut banks was a significant driver of species composition. Our results indicate high ecological development potentials for the Mulde River, but restoration should consider differences between slip-off slopes and cut-off banks. We postulate that future restoration will foster population increases as well as a wider distribution of rare and endangered riparian habitat specialists.

A Study of Co-occurrences of Foraminifera and Mussels in a Polluted Nova Scotian Wetland, Atlantic Canada

Abstract Studies of foraminiferal assemblages in intertidal marshes and subtidal creeks usually rely upon sediment samples collected along transects, such that associations with other organisms often go unnoticed. We show that ecologically useful data can be obtained by sampling that is stratified by substrate and microenvironment. The tidal wetland at Lower LaHave, Nova Scotia, Atlantic Canada (44º16′37.39″N, 64º19′46.45″W, area ∼1 km2) comprises mostly sandy sediment occupied largely by the low marsh grass Spartina alterniflora. The wetland is situated next to LaHave Estuary, which is polluted with domestic waste. Microenvironments within the marsh were sampled for total (living + dead) foraminiferal assemblages. The mass of dried sediment examined at each site was used to calculate the foraminiferal number (FN, number of foraminiferal tests per gram of sediment). Sediment samples from the intertidal grass beds reflect a typical low- to high-marsh zonal distribution of benthic foraminifera [FN = 24.7 ± 16.6 g−1 (mean ± standard deviation); n = 716 tests]. Samples from a tidal channel yielded few tests (FN = ∼0.3 ± 0.7 g−1; n = 22). Clutches of the mussel Mytilus edulis occurred in areas of strong current action within the channel and on lower energy slip-off slopes. Mussel clutches from the channel base yielded few tests (FN = ∼0.7 ± 0.7 g−1; n = 25), mostly Miliammina fusca. Clutches from slip-off slopes yielded a significantly richer assemblage (FN = 8.7 ± 4.6 g−1; n = 229) dominated by Elphidium umbilicatulum. We concluded that mussel clutches in low energy areas can be suitable habitat for E. umbilicatulum, either associated with structural complexity of the clutches or with waste products excreted by mussels that may stimulate growth of bacteria or microalgae upon which the foraminifera feed. The results from this study provide a baseline for examining the biotic impact of remediation of the LaHave River on the Lower LaHave wetland.

English

The geomorphic response of a stream to urbanization is a common interruption to the channel geometry equilibrium with dire consequences of sedimentation of reservoirs, mass wasting processes and water quality deterioration. The channel morphology was investigated with respect to deforestation, an increase in built-up surfaces and bank instability within the Motoine/Ngong River sub-catchment of the Nairobi River Basin in Kenya. The study examined the relation between growth of built-up surfaces and channel morphology at four representative sampling points along the course of the River for the period 1976 and 2013 for which there was sufficient record. The findings indicate a steady spatial increase of the built-up surfaces by 50.9% during the period. The impervious surface reduced infiltration capacity, simultaneously increasing surface runoff and stream flow and seasonal flow variability. The increased discharge caused bank erosion in some places and sedimentation in the others, a sinuous channel morphology characterized by river cliffs, river bank cavities, collapsing overhanging banks, tension cracks, slip-off slopes, sand bars and a braided river channel. The changing storage capacity of the Nairobi dam is currently unknown due to lack of instrumentation and hydrological records. Key words: Watershed/catchment, urbanization, built-up surfaces, erosion, sedimentation, channel morphology, Motoine/Ngong River.

The várzea forests in Amazonia: flooding and the highly dynamic geomorphology interact with natural forest succession

Although flooding and the highly dynamic geomorphology influence ecophysiology of trees in Amazonian white-water forests (várzea), information about the extent of these environmental conditions on distribution and richness of tree species is scarce. To better understand dynamic of natural forest succession and the development of different várzea forest types, we inventoried structure and floristic composition of trees ≥10 cm DBH in a total area of 5.24 ha in várzea forests near Tefé and near Manaus, Brazilian Amazon. The forests were of different successional stages and situated on different sites along the flood-level gradient. Topography and average inundation of all inventoried trees was measured with a theodolite. Sedimentation was recorded during the aquatic phase 2000 and the soil texture in each site determined. The low-várzea forests were composed of different successional stages subjected to annual floods between 7 and 3 m. Stand density per hectare averaged 490 individuals in the early successional stage, up to 1000 individuals in the early secondary stage and 434 individuals in the late successional stage, species richness amounted to 4, 45 and 91 tree species, respectively. The high-várzea forests were late successional stages subjected to annual inundations above 3 m. Stand density per hectare averaged 407 individuals and species richness amounted to 68 species in a frequently exploited forest near Manaus and to 172 species in a undisturbed forest near Tefé. Species richness and distribution along the gradients of flooding and sedimentation was well defined. Only 2.6% of 222 recorded tree species occurred over the whole flood-level gradient. Sedimentation was highest in the early successional stages near the slip-off slopes of the main-river channels, and decreased with increasing topographic level of the forested sites and proceeding succession, reaching lowest rates in the high-várzea forests. Simultaneously, soil texture changed from coarse-grained soils in early stages to fine-grained soils in subsequent stages. Thus, natural succession in várzea forests is linked to the biogenical induced silting up of the sites, because dunes and large stems building trees slow down water energy and favour the deposition of fine grained sediment. A special vegetation unit within the low várzea is the ‘chavascal’, a species-poor swamp forest, which establishes in the marginal zone of lakes or in ancient silted up river arms. Since it is located off the direct influence of the main-river channels, it seems to be characterised by longstanding stable environmental conditions, and therefore cannot rank with the successional sequence near the highly dynamic river systems.

Influence of calcrete on the geometry of arroyos near Buckeye, Arizona

The geometry of arroyos on alluvial fans of the Buckeye, Arizona, area is influenced by an impervious, indurated calcic soil (calcrete) at or near the surface of the fans. Channel width-depth ratio, cross-sectional area, gradient, and location of erosion and deposition in the channel are related to calcrete in the bed and banks of the channels. Calcrete causes three or four sequential types of channel reach: (1) In the headward part of the channel, the bed is on calcrete and banks are in alluvium. The cross-sectional area is small and the width-depth ratio is high. (2) Bed and banks are developed completely in calcrete in reach 2. Cross-sectional area is high and width-depth ratio is low. Gradual incision into the calcrete results in gradient steepening and nickpoints. Reach 2 is not present if incision through the calcrete occurs as one nick-point, thus resulting in sequential reaches of one, three, and four. (3) In reach 3, bed and lower banks are developed in alluvium, and calcrete caps the banks. Here the cross-sectional area is high and width-depth ratio is moderate to high. (4) Lateral undercutting of the calcrete and deposition of topographically lower inner terrace deposits, or berms, on the slip-off slope mark the beginning of the fourth type of reach. The consequence of calcrete destruction and berm formation in the banks of reach 4 is an increase in width-depth ratio and a marked decrease in channel cross-sectional area, resulting in a change from confined to over-bank flow.

Chlorite and mica as indicators of depositional environment and provenance

The nature and distribution of clay minerals in three distinct penecontemporaneous facies of Upper Devonian alluvial-plain sedimentary deposits have yielded information on contrasting drainage conditions and the petrology of the source rocks. Slip-off slope deposits characteristically have (1) chlorite of relatively high magnesium content and (2) a low proportion of chlorite to mica. In contrast, the chlorite in oxbow-lake and overbank flood-plain deposits is more abundant and is of an iron-rich variety. The source rocks appear to have consisted predominantly of pelitic schist of the greenschist facies.

Microclimatic Influences on Ground Temperatures and Permafrost Distribution, Mackenzie Delta, Northwest Territories

Variations in ground thermal regime were studied over a small area in the east-central part of the Mackenzie Delta, Northwest Territories, about 50 km northwest of Inuvik. Vegetation shows a successional sequence related to river migration and there is a complex interaction between vegetation, topography, and microclimate.Measurements from five sites show that significant differences in thermal regime exist beneath various types of vegetation. There is a general decrease in mean annual ground temperatures with increasing vegetation. The mean annual air temperature in this area is −9 °to −10 °C, but microclimatic factors lead to mean surface temperatures of between 0 °C and −4.2 °C.In summer, variations in net radiation account for the differences in ground thermal regime at the three sites on the slip-off slope. At the other two sites a surface layer of moss and peat leads to small values in ground heat flux and is instrumental in maintaining lower temperatures there. Removal of 10 cm of organic material at one site led to an increase of 3 °C in the mean daily 10 cm temperature.In winter, on the slip-off slope, variations in snow accumulation lead to ground temperature variations greater than those due to vegetation per se. Spatial variation of about 20 °C in ground surface temperature was measured in March 1970; during July and August 1970 the maximum spatial variation observed was only 10 °C. Differences of up to 6 °C in 1 m temperatures were measured over a distance of only 12 m. Snow cover is a permafrost-controlling factor in this area; where accumulations are greatest a talik has formed due to the insulating effect of deep snow.

Reel Sediments in the Valley of the River Hei, Iwate Prefecture

The River Hei flows to the east across the central part of Kitakami Mountains and debouches in its lower course into the embayed Miyako Lowland. In the middle course, the river makes incised meandering. A section cut into a slip-off slope of a meander shows a sequence of down-stream migration of the bending and accompanying deposition of fluviatile and subaerial sediments (see illustration). The fluviatile sediments are red; such materials are found in residual form both in the mountains and on the terraces along Sanriku coast.Such paleopedological data are useful for the study of the chronological relation of the incised meandering in the mountains with the coastal terrace formation and the evolution of the mountain landscape.

Neotectonics in Geomorphology

Neotectonics in Geomorphology

Lateral Activity in a River of Northwestern Canada

The work reported has a background in several principles of fluvial hydraulics: the tendency to flow in channels, the concentration of fluvial force against concave banks, the mechanism of interdependence, the importance of approximate grade and its result, non-vertical corrasion. An example of breaching by lateral corrasion of a bedrock meander neck is described, and evidence from maps is brought forward to demonstrate horizontal bedrock erosion at a rate of 1 foot a year. A rate of upstream knickpoint migration of 100 feet a year is established from observation. A topographic form consisting of a slip-off slope with a prominence at its lower end is given the name pembina-the origin of which is traced to non-vertical corrasion. The theoretical search for this origin is dependent on the hypothesis of unequal activity.