Page 367 - Soil and water contamination, 2nd edition

354 Soil and Water Contamination

x 1 000 x 100
a 18 b 14
16 6642 6642 6642
12
14
N-Kj (mg kg -1 ) 12 Zn (mg kg -1 ) 10 8
10
6 8 6
4
4
2
2
0 0
0 2000 4000 6000 8000 10000 12000 0 2000 4000 6000 8000 10000 12000
Q (m 3 s -1 ) Discharge (m 3 s -1 )
x 1 000 x 100
c 18 d 14
16 12
14
N-Kj (mg kg -1 ) 12 Zn (mg kg -1 ) 10 8
10
6 8 6
4
4
2
2
0 0
0 5 10 15 20 25 0 5 10 15 20 25
OC (%) OC (%)
e 25
20
OC (%) 15
10

5
0
0 2000 4000 6000 8000 10000 12000
Q (m 3 s -1 )
Figure 18.13 Relationships amongst total Kjehdahl N (N-Kj), Zn , organic carbon (OC) concentrations in
sediment, and discharge (Q) in the river Rhine near Lobith, the Netherlands: a) N-Kj versus Q (1995–2002); b) Zn
versus Q (1988–2002); c) N-Kj versus OC (1995-2002); d) Zn versus OC (1988–2002); e) OC versus Q (1988–
2002) (source: Waterbase, 2013).
enriched in contaminants such as heavy metals , nutrients, and pesticides from industrial and
domestic point discharges and diffuse urban runoff . During hydrological events, soil erosion
on the terrestrial part of the catchment and river bank erosion generate a supply of relatively
uncontaminated, predominantly clastic sediment to the river. This input of fresh sediment
dilutes the contaminated sediment already present in the river system, which is why the
contaminant concentrations in sediment decrease during periods of high discharge.
Despite the decrease in contaminant concentrations in sediment during high discharge,
the sediment concentrations in river water increase so much that total transport or load
(i.e. the product of concentration and discharge; see Section 11.2.2) of sediment-associated
contaminants is almost always greater during high discharge than during low discharge.
18.3.6 Significance of hydrological events for substance transport

The increase in sediment transport during periods of high discharge has significant
implications for the importance of hydrological events for the export of sediment-associated

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