Assessing hillslope-channel connectivity in an agricultural catchment using rare-earth oxide tracers and random forests models

Soil erosion from agricultural areas is a large problem, because of off-site effects like the rapid filling of reservoirs. To mitigate the problem of sediments from agricultural areas reaching the channel, reservoirs and other surface waters, it is important to understand hillslope-channel connectivity and catchment connectivity. To determine the functioning of hillslope-channel connectivity and the continuation of transport of these sediments in the channel, it is necessary to obtain data on sediment transport from the hillslopes to the channels. Simultaneously, the factors that influence sediment export out of the catchment need to be studied. For measuring hillslope-channel sediment connectivity, Rare-Earth Oxide (REO) tracers were applied to a hillslope in an agricultural catchment in Navarre, Spain, preceding the winter of 2014-2015. The results showed that during the winter no sediment transport from the hillslope to the channel was detected.To test the implication of the REO results at the catchment scale, two contrasting conceptual models for sediment connectivity were assessed using a Random Forest (RF) machine learning method. The RF method was applied using a 15-year period of measured sediment output at the catchment scale. One model proposes that small events provide sediment for large events, while the other proposes that only large events cause sediment detachment and small events subsequently remove these sediments from near and in the channel. For sediment yield prediction of small events, variables related to large preceding events were the most important. The model for large events underperformed and, therefore, we could not draw any immediate conclusions whether small events influence the amount of sediment exported during large events. Both REO tracers and RF method showed that low intensity events do not contribute any sediments from the hillslopes to the channel in the Latxaga catchment. Sediment dynamics are dominated by sediment mobilisation during large (high intensity) events. Sediments are for a large part exported during those events, but the system shows a memory of the occurrence of these large events, suggesting that large amounts of sediments are deposited in and near the channel after these events. These sediments are gradually removed by small events. To better understand the delivery of sediments to the channel and how large and small events influence each other more field data on hillslope-channel connectivity and within-channel sediment dynamics is necessary.

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A model-based sediment connectivity assessment for patchy agricultural catchments

10.5194/egusphere-egu21-562 ◽

2021 ◽

Author(s):

Pedro Velloso Gomes Batista ◽

Peter Fiener ◽

Simon Scheper ◽

Christine Alewell

Keyword(s):

Sensitivity Analysis ◽

Sediment Transport ◽

Surface Waters ◽

Road Network ◽

Input Data ◽

Landscape Patterns ◽

Model Parameters ◽

Agricultural Catchments ◽

Model Based ◽

Sediment Connectivity

<p>Sediment connectivity is highly influenced by landscape patchiness. In particular, linear features such as roads, ditches, and terraces, modify landscape patterns and affect sediment transport from hillslopes to surface waters. Connectivity patterns are commonly assessed by spatially-distributed models, which rely on semi-qualitative indices or numerical simulations of soil erosion and sediment transport. However, model-based connectivity assessments are hindered by the uncertainty in model structure and parameter estimation. Moreover, representing linear landscape features is often limited by the spatial resolution of the model input data. Here we demonstrate how a global sensitivity analysis of the WaTEM/SEDEM model can be used to improve our understanding of sediment connectivity in patchy agricultural catchments of the Swiss Plateau. Specifically, we explored model structural connectivity assumptions regarding road drainage and the presence of edge-of-field buffer strips, as well as the uncertainty in the input data, by means of a Monte Carlo simulation and a high resolution 2 m x 2 m DEM. Our results showed that roads are the main regulators of sediment connectivity in ameliorated Swiss landscapes. That is, our sensitivity analysis revealed that assumptions about how the road network (dis)connects sediment transport from cropland to water courses had a much higher impact on modelled sediment loads than the uncertainty in model parameters. These results illustrate how a high-density road network combined with an effective drainage system increases sediment connectivity from arable land to surface waters in Switzerland. Additionally, our approach underlines the usefulness of sensitivity and uncertainty analysis for identifying relevant processes in model-based sediment connectivity assessments.</p>

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Investigating Sediment Dynamics in a Landslide-Dominated Catchment by Modeling Landslide Area and Fluvial Sediment Export

Water ◽

10.3390/w12102907 ◽

2020 ◽

Vol 12 (10) ◽

pp. 2907

Author(s):

Tse-Yang Teng ◽

Jr-Chuan Huang ◽

Tsung-Yu Lee ◽

Yi-Chin Chen ◽

Ming-Young Jan ◽

...

Keyword(s):

Sediment Transport ◽

Transport Model ◽

Sediment Dynamics ◽

Landslide Area ◽

Coupled Models ◽

Sediment Storage ◽

Fluvial Sediment ◽

Sediment Transport Model ◽

Sediment Export ◽

Landslide Model

Few models are capable of simultaneously simulating the sequences of landslide occurrence and sediment export. Quantification of the temporarily stored sediment within the watershed plays a key role to link hillslope landslides with fluvial sediment export. In this study, two coupled models were proposed to simulate time-series total landslide area and the subsequent sediment export on a daily basis with only the inputs of rainfall and runoff. The landslide model considers per-existing and models new landslide, and the sediment transport model incorporates a sediment storage variable. The landslide and sediment transport model were well evaluated with Nash-Sutcliffe efficiency (EC) of 0.89 and logarithmic Nash-Sutcliffe efficiency (EClog) of 0.90, respectively, in the Tsengwen Reservoir watershed in southern Taiwan by using long-term observed data (2005–2015). It is found that reactivated landslides were up to 72% of the pre-landslide area, which contributed sediment comparable to the new landslide. Besides, the landslide model indicates that pre-landslide area controls the total landslide area but when rainfall is large it takes control in turn. With the simulation of sediment storage, the sediment transport model can well simulate the sediment export after the catastrophic event (typhoon Morakot in 2009). During the post-Morakot period, small rainfall and runoff can lead to high sediment export owing to the storage of Morakot-triggered landslide. This model will be a useful tool to diagnose the sediment dynamics in the watershed.

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Groundwater protection and diffuse nitrogen emissions to surface waters – which catchment areas have to be considered?

Water Science & Technology Water Supply ◽

10.2166/ws.2007.072 ◽

2007 ◽

Vol 7 (3) ◽

pp. 103-110

Author(s):

C. Schilling ◽

M. Zessner ◽

A.P. Blaschke ◽

D. Gutknecht ◽

H. Kroiss

Keyword(s):

Surface Water ◽

Total Nitrogen ◽

Surface Waters ◽

Flow Path ◽

Emission Model ◽

Catchment Scale ◽

Danube Basin ◽

Nitrogen Emissions ◽

Nitrogen Levels ◽

Catchment Areas

Two Austrian case study regions within the Danube basin have been selected for detailed investigations of groundwater and surface water quality at the catchment scale. Water balance calculations have been performed using the conceptual continuous time SWAT 2000 model to characterise catchment hydrology and to identify individual runoff components contributing to river discharge. Nitrogen emission calculations have been performed using the empirical emission model MONERIS to relate individual runoff components to specific nitrogen emissions and for the quantification of total nitrogen emissions to surface waters. Calculated total nitrogen emissions to surface waters using the MONERIS model were significantly influenced by hydrological conditions. For both catchments the groundwater could be identified as major emission pathway of nitrogen emissions to the surface waters. Since most of the nitrogen is emitted by groundwater to the surface water, denitrification in groundwater is of considerable importance reducing nitrogen levels in groundwater along the flow path towards the surface water. An approach was adopted for the grid-oriented estimation of diffuse nitrogen emissions based on calculated groundwater residence time distributions. Denitrification in groundwater was considered using a half life time approach. It could be shown that more than 90% of the total diffuse nitrogen emissions were contributed by areas with low groundwater residence times and short distances to the surface water. Thus, managing diffuse nitrogen emissions the location of catchment areas has to be considered as well as hydrological and hydrogeological conditions, which significantly influence denitrification in the groundwater and reduce nitrogen levels in groundwater on the flow path towards the surface water.

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Photonic crystal membrane with single crystalline rare-earth oxide using selective area growth by MBE

2016 Compound Semiconductor Week (CSW) [Includes 28th International Conference on Indium Phosphide & Related Materials (IPRM) & 43rd International Symposium on Compound Semiconductors (ISCS) ◽

10.1109/iciprm.2016.7528793 ◽

2016 ◽

Author(s):

Takehiko Tawara ◽

Hiroo Omi ◽

Thomas McManus ◽

Aleix Llenas ◽

Eiichi Kuramochi ◽

...

Keyword(s):

Rare Earth ◽

Photonic Crystal ◽

Rare Earth Oxide ◽

Selective Area Growth ◽

Single Crystalline ◽

Selective Area ◽

Area Growth ◽

Photonic Crystal Membrane

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Effect of rare earth oxide CeO2 on the anodic bonding performance of PEG-based MEMS encapsulation materials

Advances in Mechanical Engineering ◽

10.1177/16878140211007712 ◽

2021 ◽

Vol 13 (3) ◽

pp. 168781402110077

Author(s):

Chao Du ◽

Cuirong Liu ◽

Xu Yin ◽

Haocheng Zhao

Keyword(s):

Tensile Strength ◽

Rare Earth ◽

Rare Earth Oxide ◽

Solid Polymer Electrolytes ◽

Anodic Bonding ◽

Solid Polymer ◽

Bonding Layer ◽

Scanning Calorimetry ◽

Ion Migration ◽

Bonding Performance

Herein, we synthesized a new polyethylene glycol (PEG)-based solid polymer electrolyte containing a rare earth oxide, CeO2, using mechanical metallurgy to prepare an encapsulation bonding material for MEMS. The effects of CeO2 content (0–15 wt.%) on the anodic bonding properties of the composites were investigated. Samples were analyzed and characterized by alternating current impedance spectroscopy, X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, tensile strength tests, and anodic bonding experiments. CeO2 reduced the crystallinity of the material, promoted ion migration, increased the conductivity, increased the peak current of the bonding process, and increased the tensile strength. The maximum bonding efficiency and optimal bonding layer were obtained at 8 wt% CeO2. This study expands the applications of solid polymer electrolytes as encapsulation bonding materials.

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