1. Suspended Particulate Matter concentration and HACH/OBS Turbidity
In the Southern North Sea, the Scheldt & the Gironde Rivers and Río de la Plata Estuary
B. Nechad, A. Dogliotti, D. Doxaran, E. Knaeps, Q. Vanhellemont, D. van der Zande, K. Ruddick
BELCOLOUR-2
PROJECT

2. Overview SPM & Turbidity (T) Variability Conclusions Instruments
Measurement methods
Sites
Variability
Through sites
SPM vs T relationship
Conclusions

3. Instruments SPM filters: Portable HACH 2100P OBS500
GF/F pre-ashed at 450°C for 1h
washed in 500mL MilliQ, dried at 75°C for 1h
pre-weighted (Sartorius, precision: 0.1mg)
stored in desiccator/50 mm Petri dish
Portable HACH 2100P
Light emitted at 860 nm, scattered at 90° T in Formazin Nephelometric Units (FNU)
OBS500
Side-scattered: T (FNU)
Back-scattered light, 850 nm  Tb in Formazin Backscatter Units (FBU)

4. Methods 1/2 – T
Mix the sample (tumble container gently), take subsample in a turbidity vial / Rinse the vial with the sampled water / Fill the vial/ Clean outside of vial with milliQ & dry / Wipe with oiled then dry cloth / Visually inspect for dust / Tumble gently 3 times up-down/ Set to automatic range scaling and signal averaging / Record 3 times with same sample (tumble gently 3 times up-down in between records)
[For Remote Sensing algo. developpement and products validation: in-water in situ measurements at depth <3m]
OBS500 just below the water surface / Continuous measurements (1 scan per second, record 1 average/std/min/max T and Tb per minute) / Remove first&last 2 records (bubbles effect)

5. Methods 2/2 - SPM Sample below the surface (0.5m depth, <3m)
Mix the sample: 2 full rotations tumbling the container, gently
Take a subsample for turbidity measurement
Determine filtration volume based on turbidity (Neukermans et al., 2012)
Wet the GF/F filters with MQ and filter the sample / Rinse the measuring cylinder with 3x50ml / Filter 250ml of MQ / Rinse each funnel with 3x50ml
After filtering: remove the funnel, rinse the rim with MQ
Put in freezer, GF/F to be dried at 75°C for 24 hours, weighted
Measure turbidity after all filtrations
Rinse filter holders and bottom of funnel with MQ

6. Sites Southern North Sea (SNS) Scheldt (SC) Gironde (GIR)
Mediterranean Sea (MS)
French Guyana (FG)
Río de la Plata (RdP)
Dogliotti et al., 2015

7. Variability: SPM & T time series
Different sampling periods and frequencies
Various ranges at the 6 sites
Similar variations of SPM and T at each site
Though some differences between SPM and T

8. Variability: SPM/T ratio (1/2)
Low wind: small-sized particles in suspension/water surface
Moderate wind: both fine/coarse particles in re-suspension
High wind: larger muddy flocs to break

9. Variability: SPM/T ratio (2/2)
SPM/T generally in [ mg/l/FNU]
All sites show SPM/T~1 mg/l/FNU
Need of more simultaneous pigments, PIM/POM, wind & current data esp. for “outliers”

10. Conclusions Summary+ Is T a good surrogate for SPM?
SPM vs T is highly affected by particles size distr. [e.g. Landers and Sturm 2013]
In low wind conditions (and clearer waters) SPM vs T is highly affected by pigments
During re-suspension, SPM vs T may be hugely affected by heterogeneous types of particles (depends on sampling rate?)
In highly mixed waters the relationship -> stabilize
Is T a good surrogate for SPM?
YES in well mixed waters
Network for Marine Optics Measurements in Turbid Waters (TurbiNET)
Testing: OBS300, OBS500, OBS501
Validating with HACH and SPM measurements
Future: continuous measurements (<2m depth below surface)