The 5
th
International Symposium on Southeast Asian Water Environment
7 - 9 November, 2007. Chiang Mai, Thailand
================================================================================
============================================================================
ORGANIC MATTER DISTRIBUTION OF THE ROOT ZONE IN A CONSTRUCTED SUBSURFACE
FLOW WETLAND (Le Anh Tuan and Guido Wyseure)
1
ORGANIC MATTER DISTRIBUTION OF THE ROOT ZONE
IN A CONSTRUCTED SUBSURFACE FLOW WETLAND Le Anh Tuan
1,2)
and Guido Wyseure
2)

1) Department of Environmental and Water Resources Engineering, College of Technology
Can Tho University, Campus II, Street 3/2, Can Tho City, Vietnam
E-mail: [email protected]
2) Division for Land and Water Management, Faculty of Bioscience Engineering
Katholieke Universiteit Leuven, B-3001 Heverlee, Belgium
E-mail: [email protected] Abstract

Constructed wetlands are known widely by their characteristic properties like utilization of
natural processes, simple and easy of construction, operation and maintain as well. The
constructed subsurface flow wetland is designed as a tank with an impervious boundary to


The 5
th
International Symposium on Southeast Asian Water Environment
7 - 9 November, 2007. Chiang Mai, Thailand
================================================================================
============================================================================
ORGANIC MATTER DISTRIBUTION OF THE ROOT ZONE IN A CONSTRUCTED SUBSURFACE
FLOW WETLAND (Le Anh Tuan and Guido Wyseure)
2
Soil organic matter (OM) is the organic fraction of soil, including wastewater pollutants, plant
roots, animal and plant residues, and microbial biomass. OM influences the chemical and
physical properties of soils even at the relatively low amount usually found in soils. The
macrophyte plants transport approximately 90% of the oxygen available in the root zone (Lee,
2007). Such the oxygen in the root zone supports the aerobic decomposition process of OM
and the growth of nitrifying bacteria (Reddy et al., 1989; Brix, 1997; Scholz, 2006). However,
Stottmiester et al. (2003) proved that OM in the wastewater is degraded mainly by the
existing of micro-organisms in the wetland system. Composed organic matters synthesize
dark, amorphous, colloidal mass, called humus. Humus is the active component of soil
organic matter and is responsible for water retention, nutrient retention and cohesion. Soil in
CSFW absorbs and stores OM several years. This accumulation potentially leads to a decline
of the filter ability of the constructed wetland.

The objective of this study is to survey the vertical and horizontal distribution of the OM in
sand bed of the experimental constructed subsurface flow wetland in Can Tho University’s
campus, Vietnam. This treatment system are operating since 2003. The hypothesis is the OM
distribution in sand bed descending linearly to the flow direction. 2. Materials and methods

M-)M (M
(%) OM
s
scsc
×
+
=
(1)
The 5
th
International Symposium on Southeast Asian Water Environment
7 - 9 November, 2007. Chiang Mai, Thailand
================================================================================
============================================================================
ORGANIC MATTER DISTRIBUTION OF THE ROOT ZONE IN A CONSTRUCTED SUBSURFACE
FLOW WETLAND (Le Anh Tuan and Guido Wyseure)
3
where
OM - organic matters in present (%);
M
c
- weight of cup (gr);
M
s
- weight of dried sand sample (gr) by drying at 110 °C in 3 hours;
M
sc
- weight of sand and cup after combusting at 550 °C in 3 hours (gr).



4
In analysis, data were compared graphically and by an ANOVA analysis at the significant
level α = 0.05 to test for differences (Neter et al., 1996). The visual appearance of the sand in
CSFW was also observed during the survey.

3. Results and discussion

From the surface to the depth 10 cm, the originally yellow sand is mixed with the OM due to
decomposing plants. From 10 cm to 40 cm, the sand is still yellow and clean with numerous
roots. From 40 cm to 60 cm, the sand color changes from yellow to dark grey and brown.
Lower then 60 cm up to 100 cm, which is the bottom, the sand color returns to the original
yellow. Figure 3 shows the average OM contents in the sand bed are linear reducing to the Ox
direction. In the Oz direction, the average value of OM in each cross-section is highest at the
depth 50 cm and lowest at the depth 80 cm. This result is in line with the visual observation of
the sand color and the root system distribution. The most root density was found at the depth
30 - 50 cm.

50 cm
y = -0.0022x + 3.3117
R
2
= 0.9331
20 cm
y = -0.0021x + 3.1719
R
2
= 0.947 80 cm
y = -0.0021x + 3.2176
R
2

FLOW WETLAND (Le Anh Tuan and Guido Wyseure)
5

The output ANOVA test gives estimated difference of 9 pairs in length statistically significant
differences at the 95.0% confidence level (Table 1). A group of mean (50 cm and 100 cm) is
not statistically significant difference.

Table 1: The multiple range tests for the OM by the length (Ox direction)
Method 95.0 percent least significant (LS) difference
Length Count LS Mean Homogeneous groups
800 15 0.998667 x
400 15 1.374000 x
200 15 1.627300 x
50 15 2.001330 x
100 15 2.038000 x
Contrast Difference +/- Limits
50 - 100 - 0.0366667 0.12887
50 - 200 * 0.374 0.12887
50 - 400 * 0.627333 0.12887
50 - 800 * 1.00267 0.12887
100 - 200 * 0.410667 0.12887
100 - 400 * 0.664 0.12887
100 - 800 * 1.03933 0.12887
200 - 400 * 0.253333 0.12887
200 - 800 * 0.628667 0.12887
400 - 800 * 0.375333 0.12887
* denotes a statistically significant difference.

4. Conclusions



6. References

Brix, H. (1997). Do macrophytes play a role in constructed treatment wetlands? Water Sci.
Technol., 35, 11-17.

Jing, S.R., Y.F. Lin, D.Y. Lee, T.W. Wang. (2001). Using constructed wetland systems to
remove solids from high polluted river water. Wat. Sci. Tech.: Water Supply, 1,89-96.

Kadlec, R.H., R.L. Knight. (1996). Treatment Wetlands. Lewis Publishers, Boca Raton,
Florida, USA. 893 pp.

Lee, B.H., M. Scholz. (2006). What is the role of Phragmites australis in experimental
constructed wetland filters treating urban runoff? Ecol. Eng., 29, 87-95.

Mitsch, W.J., J.G. Gosselink, 2000. Wetlands. John Wiley and Sons, New York. 936p.

Neter, J., M.H. Kutner, C.J. Nachsheim and W. Wasserman. (1996). Applied linear statistical
models. 4th Ed. WCB/McGraw-Hill. 1048p.

Reddy, K.R., W.H. Patrick, C.W. Lindau. (1989). Nitrification-denitrification at the plant
root-sediment interface in wetlands. Limmol. Oceanogr. 34, 1004-1013.

Scholz, M. (2006). Wetland systems to control urban runoff. Elservier, Amsterdam, the
Netherlands.

Stottmeister, U., A. Weisner, P. Kuschl, M. Kappelmeyer, M. Kaster. (2003). Effects of plants
and microorganisms in constructed wetlands for wastewater treatment. Bio-tech. Adv., 22, 93-
177.