Cornie van Huyssteen

University of the Free State

Bloemfontein, South Africa

Hydropedology in support of Hydrology and Eco-hydrology

17 November 2013

Farm Inn, Pretoria

What makes wetlands function?

Wetlands saturated in growing season when the plants grow hydrophytic vegetation in the rooting zone impacts soil morphology redox morphology

• grey matrix

• redox accumulations

Introduction

NWA:“Land which is transitional between terrestrial and aquatic systems where the water table is usually at or near the surface, or the land is periodically covered with shallow water, and which land in normal circumstances supports or would support vegetation typically adapted to life in saturated soil.”

Introduction

Land

which is transitional between terrestrial and aquatic systems

where the water table is usually at or near the surface,

or the land is periodically covered with shallow water,

and which land in normal circumstances

supports or would support vegetation typically adapted to life in saturated soil.”

Introduction

soil, terrain, climate

driven by water

may be inundated

exclude extremes / human

plant = indicator

soil = substrate

grading, not modal

Weatherley

Weatherley Laboratory Study

Manguzi Laboratory Study

Florisbad

What is a “saturated soil”

Weatherley

0306191

122152183213243274304335365

gh on gs sp ot re ye ne

Diagnostic horizon group

AD

s>0.

7 (d

ays

ye

ar-1

)

grassland, six years weekly measurements, 28 sites

Weatheley Laboratory Study

y = -4.14x + 10.0y = -15.2x + 17.9

0

1

2

3

4

5

6

7

8

9

0.5 0.6 0.7 0.8 0.9 1.0

Degree of water saturation (S)

pe

y = 22.8x - 11.3

y = 164x - 122

0

5

10

15

20

25

30

35

0.5 0.6 0.7 0.8 0.9 1.0

Degree of water saturation (S)

Fe

(m

g k

g -1

)

59

mVEhpe

Manguzi Laboratory Study

0.65 0.70 0.75 0.80 0.85 0.900

50

100

150

200

250

300

350

400f(x) = NaN x + NaN

Degree of water saturation

Eh

(mv)

Manguzi Laboratory Study

Weatherley free water

rH = 20

Saturation in ot increased with:

ne < ye < ye-gs < gr-gs < sp < gh

depth to impervious layer decreased

Weatherley Topsoils

Weatherley Topsoils

Saturation(months/year)

Chroma Fe mottles Underlying horizon

Depth to impervious layer (mm)

<1 >2 none re, ye, ne >650

1-3 >2 few gs with many Fe mottles

<650

3-6 ≤2 common gs, sp with many Fe mottles, over gh

<550

>6 ≤2 common or many

gh, gs with many Fe mottles

Florisbad

Permanently dry Temporary wet Seasonally wet Permanently wet0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.08 0.53 0.74 0.970.16 0.70 0.79 0.79

Topsoil

Subsoil

Wetland Zone

De

gre

e o

f w

ate

r s

atu

rati

on

(m

3 m

3)

Florisbad

Permanently dry Temporary wet Seasonally wet Permanently wet0

5

10

15

20

25

30

Topsoil

Subsoil

Wetland Zone

rH

rH = 2(Eh/59 + pH)

Ox

Red

“… vegetation...adapted to life in saturated soil.” soil saturated with water

• ADs>0.7

• in growing season– species variation– regional variation

water must be reduced• rH <20

Conclusion