Suspended particulate matter dynamics in coastal turbidity ... · Brussel - RBINS 2/9/2011 Coastal...
14
Human Footprint on the Seafloor Brussel - RBINS 2/9/2011 Suspended particulate matter dynamics in coastal turbidity maximum areas Michael Fettweis Royal Belgian Institute of Natural Sciences Management Unit of the North Sea Mathematical Models Gulledelle 100, B-1200 Brussels, Belgium
Transcript of Suspended particulate matter dynamics in coastal turbidity ... · Brussel - RBINS 2/9/2011 Coastal...
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Suspended particulate matter dynamics in coastal turbidity
maximum areas
Michael FettweisRoyal Belgian Institute of Natural Sciences
Management Unit of the North Sea Mathematical ModelsGulledelle 100, B-1200 Brussels, Belgium
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Coastal turbidity maximum?
Turbidity is a measure of water clarity (optical property of the water) and contains colored dissolved organic matter and Suspended Particulate Matter.
Turbidity maximum occurs in coastal waterways (river plume, estuaries) and is caused by tidal forcingsresulting in trapping and flocculation of SPM at the salt-fresh water wedge (salinity is 2 ppt)
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Coastal turbidity maximum !
Sediment supply (clays, cabonates,..) from English Channel and local erosion.
Trapping due to hydrodynamics & meteoeffects: Residual transport is reduced resulting in a congestions of the SPM in the coastal zone
Strong tidal currents and slack waters stimulate flocculation and thus settling & deposition of SPM
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Aim of Q4D SPM research:SPM dynamics and human impact
1. Natural variability (see mainly next presentation)Near bed processes: high concentrated mud suspensions and fluid mudExtreme events (storms)Meteorological and climatological effects
2. InstrumentationMultiparametric sensors to investigate SPM dynamics: optical and acoustic backscattering, laser diffraction
3. Statistical properties and sampling methodsEvaluation of in situ and remote sensing (MODIS) techniquesSPM concentration as indicator to detect changes in the environment
4. Case study of human impact Disposal of dredged material and SPM concentrationLong term changes in SPM concentration and mud deposits
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Cohesive sediment dynamics
Highly Interdependent Processes : Deposition, Erosion, Sedimentation, Resuspension, Aggregation, Breakup, and so on. (Maggi, 2005)
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
SPM concentration as indicator of anthropogenic impact:long-term data set
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Time series
07
142128
m s
−1
090180270360
°
Wind SpeedWind Direction
5
7
9
11
m
Water Depth
−0.5
0
0.5
m s
−1
Alongshore Subtidal FlowCross−shore Subtidal Flow
0
1
2
3
m
0
80
160
240
µm
Hsd50
1.8
2
2.2
m
Seabed Altimetry
28 30 32 34 36 38 4010
1
102
103
mg
l−1
J Day
OBS 2.0mabOBS 0.2mabADP 2.0mab
Variation in SPM concentration is related to tides, storms and also seasonal changes and human impacts.
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
SPM concentration: log-normal distribution
SPM concentration can be defined as a statistical population. SPM concentration time series are sub-samples of the whole population
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Monitoring the effect of disposal of dredged materialDifferentiating between natural and anthropogenic induced
signal using statistical techniques
experiment conducted by Maritime access division
tripoddisposal site
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Time series of SPM concentration at0.2 m above bed (SPM1) and 2 mab (SPM2)
during after
May – Jun 2008
May – Jun 2009
Nov – Dec 2006
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
Cumulative probability distribution of SPM concentration measured at 2 mab and 0.2 mab
0
0.2
0.4
0.6
0.8
1
0 500 1000 1500
SPM concentration 2 mab (mg/l)
Pro
babi
lity
6a (May 2009)1-5, 6bStand. dev.
6a: during dredging experiment
Significant increase in near bed bottom layer formation of HCMS layers
Median at 0.2 mab is very high during disposal exp. (612 mg/l) this is about 240 mg/l higher than during winter and 330 mg/l higher than during spring 2008)
0
0.2
0.4
0.6
0.8
1
0 1000 2000 3000
SPM concentration 0.2 mab (mg/l)
Pro
babi
lity
6a (May 2009)1-5, 6bStand. dev.
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
HCMS layers
Acoustic detection layer via altimetry of ADV & ADP: the signal is reflected at high SPM concentration decrease in sea level
0 01.8
2
2.2
m
Seabed Altimetry
28 30 32 34 36 38 4010
1
102
103
mg
l−1
J Day
OBS 2.0mabOBS 0.2mabADP 2.0mab
erosion of HCMS
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
13
HCMS layersHCMS layers
Human Footprint on the SeafloorBrussel - RBINS 2/9/2011
SPM concentration distribution can be used as indicator for environmental changes
High concentrated mud suspension have been identified thanks to combination of different instrumentation
SPM dynamics is governed by near-bed processes: New sensors, measuring techniques are needed (see this afternoon)
Take Home Messages
