scholarly journals Aquatic bryophytes play a key role in sediment-stressed boreal headwater streams

Hydrobiologia ◽  
2019 ◽  
Vol 847 (2) ◽  
pp. 605-615 ◽  
Author(s):  
Jarno Turunen ◽  
Timo Muotka ◽  
Jukka Aroviita
Keyword(s):  
Headwater Streams ◽  
Fine Sediment ◽  
Leaf Decomposition ◽  
Ecosystem Functions ◽  
Macroinvertebrate Communities ◽  
Fine Sediments ◽  
Key Factor ◽  
Sediment Cover ◽  
Negative Impacts ◽  
Stream Biodiversity

AbstractForestry-related land use can cause increasing instream sedimentation, burying and eradicating stream bryophytes, with severe ecological consequences. However, there is limited understanding of the relative roles and overall importance of the two frequently co-occurring stressors, increased fine sediments and loss of bryophytes, to stream biodiversity and ecosystem functions. By using random forest modeling and partial dependence functions, we studied the relative importance of stream bryophytes and fine sediments to multiple biological endpoints (leaf-decaying fungi, diatom, bryophyte, and benthic macroinvertebrate communities; leaf decomposition) using field survey data from headwater streams. Stream bryophyte abundance and richness were negatively related to fine sediment cover, highlighting the detrimental effect of sedimentation on bryophytes. However, bryophyte abundance was consistently more important a determinant of variation in community composition than was fine sediment cover. Leaf decomposition was influenced by shredder abundance, water temperature and, to a lesser degree, stream size. Our results suggest that the loss of stream bryophytes due to increasing sedimentation, rather than fine sediments per se, seems to be the key factor affecting multiple biological responses. Enhancing the re-establishment of bryophyte stands could partly compensate for the negative impacts of sedimentation on bryophytes and, consequently, on several other components of boreal stream ecosystems.

Gravel Bed Composition in Oregon Coastal Streams

1980 ◽  
Vol 37 (10) ◽  
pp. 1514-1521 ◽  
Author(s):  
J. N. Adams ◽  
R. L. Beschta
Keyword(s):  
Regression Analysis ◽  
Fine Sediment ◽  
Low Flow ◽  
Coast Range ◽  
Oregon Coast Range ◽  
Oregon Coast ◽  
Gravel Bed ◽  
Fine Sediments ◽  
High Flows ◽  
The Impact

The amount of fine sediments (generally < 1 mm in diameter) in gravel bedded streams is often used as an indicator of habitat quality and also as a measure of the impact from accelerated sedimentation resulting from land disturbance. Five streams in the Oregon Coast Range were studied to evaluate temporal and spatial variability of streambed composition, as well as the factors affecting the amount of fine sediment within the bed. The amount of fine sediments (< 1 mm) contained in frozen streambed cores and expressed as a percentage (by weight) of the total sample proved highly variable in time and space. During a 19-mo sampling period, temporal variability was caused by an occasional flushing of fines from the gravel beds during high flows. Percent fines also varied greatly between streams, between locations in the same stream, and between locations in the same riffle. Streams on 21 Coast Range watersheds were sampled during summer low flow. The amount of fines averaged 19.4% for all watersheds and ranged from 10.6 to 29.4% for streams on undisturbed watersheds. Regression analysis indicated that the watershed slope, area, relief, and land use influenced the amount of fine sediment in the bed. Bed composition varied greatly between locations in the same stream with about 75% of the within-stream comparisons indicating a significant (α = 0.05) difference. Within a single stream, gravel bed composition correlated significantly with channel sinuosity and bank-full stage. Regression analysis and field observations suggested that road construction and logging operations can increase the amount of fines; however, such increases may be temporary if high flows flush the gravelsKey words: bed sediments, forest harvesting, Oregon Coast Range, sedimentation, spawning gravels, stream channels, water quality

Erodibility of fine sediment deposits in gravel bed rivers: investigation of the spatial variability

2021 ◽  
Author(s):  
Hanna Haddad ◽  
Magali Jodeau ◽  
Germain Antoine ◽  
Cédric Legoût
Keyword(s):  
Spatial Variability ◽  
Spatial Organization ◽  
Fine Sediment ◽  
Aquatic Life ◽  
Vegetation Growth ◽  
Gravel Bed ◽  
Fine Sediments ◽  
Sediment Deposits ◽  
Low Altitude ◽  
Gravel Bed Rivers

&lt;p&gt;Fine sediments exhibit various stages of deposition and erosion during their transport from hillslopes to the ocean. In mountainous environments, high fine sediment load during runoff or dam flushing events can lead to important amounts of deposits in gravel bed rivers. Massive deposits may lead to bar elevation, riparian vegetation growth and consequently to bar stabilization, which can increase flood risks. High amount of fine sediment deposits alters also aquatic life and habitat.&lt;/p&gt;&lt;p&gt;In order to better understand the dynamics of re-suspension of these deposits, and to accurately predict it with numerical modelling, field monitoring campaigns were performed to assess both the spatial variability and the controlling factors of the erodibility of fine deposits. The cohesive strength-meter (CSM) device, a pocket penetrometer and a pocket shear vane were used to evaluate the erodibility of fine sediments deposited in two rivers in the French Alps: The Is&amp;#232;re and Galabre.&lt;/p&gt;&lt;p&gt;The results highlight the specificity of gravel bed rivers with an abundance of areas of deposition of fine sediments, which are discontinuous compared to estuaries and lowland rivers. A high spatial variability of the erodibility was observed and related to the spatial organization of the deposits. The location of the deposit and its elevation, the moisture and the grain sizes are inter-related and have important correlations with the erodibility. Measurements show that high altitude dry deposits and low altitude humid deposits are more easily eroded than intermediate deposits with medium moisture. The measured variables explain part of the variability of the erodibility but other processes such as the history or the origin of the deposit might also be important factors to consider.&lt;/p&gt;

Ethnicity, Nationalism, and Migration in Southeast Asia

2018 ◽  
Author(s):  
David Brown
Keyword(s):  
Southeast Asia ◽  
Ethnic Politics ◽  
Domestic Terrorism ◽  
Identity Strategies ◽  
State Legitimacy ◽  
Political Relationships ◽  
Key Factor ◽  
Plural Society ◽  
Negative Impacts ◽  
And Migration

In southeast Asia, ethnic tensions and conflicts stem in large part from economic or power rivalries rather than cultural differences. The political relationships between ethnic identities and nation-state identities in southeast Asia can be analyzed based on three different frameworks, each offering important insights into the region’s complexities and variations. The first is the plural society approach, which points to cultural pluralism as the source of political tensions in southeast Asia. The implication of this view is that ethnic violence will tend to take the form of rioting between people of different cultures as they compete for state resources or power. The second framework is a state legitimacy approach, which argues that the national identity strategies adopted by the state elites are the key factor influencing the structure of ethnic politics. In this context, the strategy of state legitimation is employed to promote the migration of highland ethnic minorities out of their ancestral homeland areas so as to facilitate their economic development, but also their assimilation into the ethnic core. The third framework is a globalized disruption approach, which suggests that globalization has three negative impacts relating to economic disparities, the problematical politics of democratization, and fears of international or domestic terrorism. It can be said that the politics of ethnicity and nationalism in southeast Asia arises from the enhanced appeal of ethnic and national stereotypes for people experiencing diverse insecurities, giving rise to inter-ethnic distrust as well as intra-ethnic factionalism.

scholarly journals Biodiversity breakpoints along stress gradients in estuaries and associated shifts in ecosystem interactions

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Emily J. Douglas ◽  
Andrew M. Lohrer ◽  
Conrad A. Pilditch
Keyword(s):  
Nitrogen Cycling ◽  
Environmental Gradients ◽  
Interaction Network ◽  
Coastal Sediments ◽  
Ecosystem Functions ◽  
Ecological Interactions ◽  
Fine Sediments ◽  
Microbial Nitrogen ◽  
Ecosystem Interactions ◽  
Biodiversity Effects

AbstractDenitrification in coastal sediments can provide resilience to eutrophication in estuarine ecosystems, but this key ecosystem function is impacted directly and indirectly by increasing stressors. The erosion and loading of fine sediments from land, resulting in sedimentation and elevated sediment muddiness, presents a significant threat to coastal ecosystems worldwide. Impacts on biodiversity with increasing sediment mud content are relatively well understood, but corresponding impacts on denitrification are uncharacterised. Soft sediment ecosystems have a network of interrelated biotic and abiotic ecosystem components that contribute to microbial nitrogen cycling, but these components (especially biodiversity measures) and their relationships with ecosystem functions are sensitive to stress. With a large dataset spanning broad environmental gradients this study uses interaction network analysis to present a mechanistic view of the ecological interactions that contribute to microbial nitrogen cycling, showing significant changes above and below a stressor (mud) threshold. Our models demonstrate that positive biodiversity effects become more critical with a higher level of sedimentation stress, and show that effective ecosystem management for resilience requires different action under different scenarios.

Fine sediment retention in storage chambers: an assessment of time-dependent effects

2002 ◽  
Vol 45 (7) ◽  
pp. 123-131 ◽  
Author(s):  
V.R. Stovin ◽  
J.P. Grimm ◽  
A.J. Saul
Keyword(s):  
Fine Sediment ◽  
Multiphase Model ◽  
Storm Events ◽  
Dimensional Model ◽  
Flow Conditions ◽  
Sediment Retention ◽  
Fine Sediments ◽  
Storage Chamber ◽  
Flow Hydraulics ◽  
The Uk

The optimisation of the design of a storage chamber is generally based upon some measure of the chamber's sedimentation efficiency. In the UK, chambers that minimise the deposition of fine sediments are preferred. Previous laboratory and CFD-based studies to measure efficiency have focused on steady flow conditions. However, both the flow hydraulics within a storage chamber and the pollutant loading in the incoming sewage vary markedly during storm events. This paper outlines a CFD-based approach for determining “overall” chamber efficiency. The approach employs an unsteady volume-of-fluid multiphase model and stochastic particle tracking. Preliminary results from a simplified two-dimensional model are presented.

scholarly journals The Prediction of Fine Sediment Distribution in Gravel-Bed Rivers Using a Combination of DEM and FNN

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1515
Author(s):  
Van Hieu Bui ◽  
Minh Duc Bui ◽  
Peter Rutschmann
Keyword(s):  
Feedforward Neural Networks ◽  
Fine Sediment ◽  
Sediment Distribution ◽  
Gravel Bed ◽  
Fine Sediments ◽  
Porosity Variation ◽  
Sediment Sorting ◽  
Gravel Bed Rivers ◽  
Bed Material ◽  
The Relationship

Large amounts of fine sediment infiltration into void spaces of coarse bed material have the ability to alter the morphodynamics of rivers and their aquatic ecosystems. Modelling the mechanisms of fine sediment infiltration in gravel-bed is therefore of high significance. We proposed a framework for calculating the sediment exchange in two layers. On the basis of the conventional approaches, we derived a two-layer fine sediment sorting, which considers the transportation of fine sediment in the form of infiltration into the void spaces of the gravel-bed. The relationship between the fine sediment exchange and the affected factors was obtained by using the discrete element method (DEM) in combination with feedforward neural networks (FNN). The DEM model was validated and applied for gravel-bed flumes with different sizes of fine sediments. Further, we developed algorithms for extracting information in terms of gravel-bed packing, grain size distribution, and porosity variation. On the basis of the DEM results with this extracted information, we developed an FNN model for fine sediment sorting. Analyzing the calculated results and comparing them with the available measurements showed that our framework can successfully simulate the exchange of fine sediment in gravel-bed rivers.

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