Changes of organic matter in soils irrigated with reclaimed wastewater

Bernd Marschner, Elisabeth JüschkeRuhr-University Bochum

Yona Chen, Jorge TarchitzkyHebrew University Jerusalem (Rehovot)

within the GLOWA Research Framework (BMBF & MOST)

Background

! In many countries, water demand is expected to increase due topopulation growth and improved standard of living.

! Freshwater resources are limited, often overexploited or deteriorateddue to pollution.

! Global climatic change may aggravate this situation by reducing precipitation and increasing evapotranspiration.

! "Clean" freshwater from ground- and surface waters will be preferentially allocated for use as drinking water and for certain industrial processes.

! For agricultural production, irrigation will therefore increasingly have torely on marginal waters, such as saline waters or treated wastewater.

0

500

1000

1500

2000

renewable watersources

mio

m3

Other Aquifers and surface watersSea of GalileeMountain AquiferCoastal Aquifer

Water sources and water use in Israel

1600

0

500

1000

1500

2000

renewable watersources

mio

m3

Other Aquifers and surface watersSea of GalileeMountain AquiferCoastal Aquifer

0

500

1000

1500

2000

water use

mio

m3

industry

municipal & household

agriculture

1200

600

Water sources and water use in Israel

1600deficit > 400

> 2000agricultural sources

fresh water75%

treated wastewater

20%

brackish water

5%

additional sources (350 - 400 mio m3/yr)

fossile water19%

desalini-sation

5% treated wastewater

76%

Problems associated with the use ofreclaimed wastewater for irrigation

! Microbial pathogens (i.e. coliformes) may contaminate food crops.

! High nutrient loads (esp. N, P) increase the risk of groundwater eutrophication.

! Elevated salt loads can cause soil degradation and groundwatersalinisation.

! Elevated inputs of heavy metals, organic pollutants, hormones and antibiotics may enter food chain or groundwater resources.

! Inputs of particulate and dissolved organic matter can affect mobility of contaminants and physical, chemical or biological soil properties.

Treated wastewater as irrigation water source (Ramat Hakovesh)

* present regulation for BOD in Israel 20 mg/Lproposed new regulation 10 mg/L

parameter unit effluent freshwaterEC dS/m 2.3 1.0Cl mg/L 364.0 201.0Na meq/L 21.4 4.3

Ca + Mg meq/L 6.1 4.1pH 8.3 7.4

DOC (Dissolved Organic Carbon) mg/L 23.5 1.1 BOD (Biological Oxygen Demand) mg/L 59.9 *COD (Chemical Oxygen Demand) mg/L 234.0

~ 1~ 1

1. Site screening (DOM quantity and quality)

2. Repeated sampling (DOM seasonality)

3. Laboratory experiments- soil respiration- substrate induced respiration (Priming)- microbial biomass (CFE)- microbial activities (FISH)

4. Soil organic matter inventories

Methodological approach

Basra

Ramat Hakovesh

Yagur

Gaaton

Sampling sites for screening

Arad

Percolation of soil samples

peristaltic pump

vacuum pump

- 65 hPa

glass filter plate(pores < 16 µm)

250 ml 1 mM CaCl2

irrigation: 25 mm h

duration: 6 h

-1

Soil80 cm3

membrane filtration0.45 µm

Texture, Corg, Nt, Cmic, δ13C

pH, EC, anions, DOC, UV-absorbance, fluorescence,biodegradability, XAD8-fractionation, KDOC, δ13C

MultiplexerKonduktometer

Computer

Respicond

0000,00 mS

1 96

Incubation of soil samples(CO2, 14CO2, 13CO2)

Extractable DOC in the soils from the different study sites

0

10

20

30

40

50

60

RamatHakovesh-

field

RamatHakovesh-orchard 10

cm

RamatHakovesh-orchard 20

cm

Basra Yagur Gaaton

DO

C c

onte

nt [m

g kg

-1]

freshwater irrigated soil

effluent irrigated soil

Humification Index (HIX) of extractable DOC in the soils from the different study sites

0.0

0.2

0.4

0.6

0.8

1.0

RH I RH II 10 cm RH II 20 cm Yagur Basra Gaaton

HIX

freshwater wastewater

0

10

20

30

40

50

60

wastewaterirrigated

freshwaterirrigated

wastewaterirrigated

freshwaterirrigated

DO

C [m

g kg

-1]

hydrophilic DOChydrophobic DOC

December June

Seasonal differences in DOC properties(Ramat Hakovesh field)

" Consistently more DOC in wastewater irrigated soils" Preferential release or production of hydrophilic DOC compounds

during rainy season in both sites

Biodegradability and specific UV absorbance(Ramat Hakovesh field)

0

10

20

30

40

50

60

1.5 2.0 2.5 3.0 3.5 4.0

specific UV254 absorbance [l m-1 mg-1]

biod

egra

dabi

lity

[%]

fw December

ww Decemberfw June

ww June

" Easily degradable DOC compounds with lower SUVA are released during rainy season (Dec – May)

" Wastewater irrigation effects of previous year are more pronounced after rainy season (due to higher microbial activity?)

1. 4-month incubation of soil samples from two sites with fresh- and wastewater irrigated field plots, irrigated daily with fresh- or wastewater (factorial design).- monitoring of CO2-evolution- microbial biomass- microbial cell counts (fluorescence in-situ hybridisation)

2. 4-week incubation of soil samples with substrate additions for thedetermination of priming effects(glucose, 14C-fructose, 14C-alanine)- CO2, 14CO2

Soil incubation studies

Soil respiration

Hamra soil

0

2

4

6

8

10

12

14

16

18

freshwater soil wastewater soil

accu

mul

ated

CO

2 in

mg

g-1

Vertisol

0

2

4

6

8

10

12

14

16

18

freshwater soil wastewater soil

accu

mul

ated

CO

2 in

mg

g-1

fw irrigationww irrigation

CO2 evolution accumulated in a 4 month irrigation experiment

"microbial respiratory activity is higher in soils originating from wastewater irrigated sites

"Wastewater irrigation in the lab stimulates microbial activity in all soils

0.0E+00

2.0E+08

4.0E+08

6.0E+08

8.0E+08

1.0E+09

fw-fw fw-ww ww-fw ww-ww fw-fw fw-ww ww-fw ww-ww

Hamra Vertisol

bact

eria

per

mL

soil

solu

tion

(equ

ival

ent t

o 0.

4 g

dry

mat

ter)

DAPIEUB338

38 %

51 %

50 % 50 %

44 %

52 %

41 %

51 %

Bacterial counts after 4 months of irrigation

0

100

200

300

400

500

control w/ fructose w/ alanine

CO

2-C

[µg

g-1]

feshwater wastewater

Effects of substrate additions on soil respiration (Ramat Hakovesh orchard, 10-20 cm)

" Elevated CO2-release from wastewater irrigated soil can not be attributed to higher Corg content

" Microbial activity in the freshwater irrigated soil is limited by theavailability of easily degradable substrates

+36%

+69%+7%+16%

0

5

10

15

20

25

30

control w/ alanine w/ fructose

CO

2 [%

of S

OC

]freshwater irrigated plotwastewater irrigated plot

+170%

+238%

+157%+186%

Priming effects after substrate additionsHaMapil (90-100 cm)

" Microbial activity in the subsoil is highly C-substrate limited" Microbial activity is higher under effluent irrigation, but more

stimulated by substrates under freshwater irrigation

0-10 cm

0.0

0.5

1.0

1.5

2.0

2.5

0 1 2 3 4time (d)

CO

2 (m

g h-1

)

freshwaterwastewater

20-30 cm

0.0

0.5

1.0

1.5

2.0

2.5

0 1 2 3 4time (d)

CO

2 (m

g h-1

)

freshwaterwastewater

90-100 cm

0.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4time (d)

CO

2 (m

g h-1

)

freshwaterwastewater

Soil respiration after glucose addition (SIR)HaMapil

" Stimulation of microbial respiration by glucose is more rapid and stronger in the wastewater than in the freshwater irrigated soil.

-200

-150

-100

-50

00.0 0.5 1.0 1.5 2.0

SOM (%)

soil

dept

h (c

m)

freshwaterwastewater

Yagur (35 yrs)

-200

-150

-100

-50

00.0 0.5 1.0 1.5 2.0

SOM (%)

soil

dept

h (c

m)

freshwaterwastewater

Misra (12 yrs)

-150

-100

-50

00.0 0.5 1.0 1.5

SOM (%)

soil

dept

h (c

m)

freshwaterwastewater

Basra (30 yrs)

-150

-100

-50

00.0 0.5 1.0

SOM (%)so

il de

pth

(cm

)

freshwaterwastewater

Arad (10 yrs)

+8 t/ha

-15 t/ha

-12 t/ha

-40 t/ha

Soil organic matter inventories

Summary and conclusions

! Wastewater irrigation has no consistent effects on the quantity or quality of DOC (or SOC) in topsoils.

! Microbial activity and SOM mineralization are stimulated by the application of wastewater.

! Microorganisms in wastewater irrigated soils are more adapted to the rapid mineralization of easily degradable substrates, but priming effects are more pronounced in soils from freshwater irrigated sites.

! In subsoils, wastewater irrigation can stimulate microbial activity to such an extent, that SOM is mineralized at a higher rate than it is replenished from organic inputs with wastewater.

! This is attributed to the inputs of easily degradable dissolved organic compounds with the wastewater.

! Possibly, leaching of degradation products of particulate wastewater-borneOM also contribute to such priming effects.

! A depletion of soil OM pools at a rate of >1 t ha-1 annually may have long-term effects on soil fertility and is a source of CO2 to the atmosphere.

Thank you

Dankeschön

Relevance of the results for the planned research activities

Priming effects seem to be ubiquous in soils that receive regular inputsof easily degradable organic compounds (such as manures). With our experimental approach, this can be detected at an early stage and thus may help to prevent long-term detrimental changes in soil properties.

Soluble organic compounds have important ecological functions such as substrates for microbial activity or carriers for pollutants.

DOC amounts and properties are easily determined and together with data on soil microbial activity are sensitive parameters and powerful tools for the detection of soil quality changes.

Both soil types are effected differently by effluent irrigation

Bacterial activity is increased through effluent irrigation

Hamra: increase of activity with irrigation duration in effluent irrigated soil

Vertisol: irrigation duration has no obvious effect on the activity of bacteria in effluent irrigated soil

The strongest increase in activity could be determined in effluent irrigated soil under effluent irrigation

Microorganisms are already adapted to the compounds of the effluent water as substrate and develop better after irrigation break during winter

...

Conclusion

direct and indirect methods for determination of activity of the soil bacteria correlateand a shift to an increase of activity can be seen

effluent irrigated soil in the field experiment appeared to have clearly higher activity and the activity declined with depth

freshwater irrigated soil showed no higher bacterial activity and no effects in depth

Treated wastewater used as irrigation water causes a lasting change of bacterial activity in soils. This depends

on the soil type as well as on the irrigation duration.

...

Conclusion

... stimulation or inhibition of transformation and utilisation of SOM after addition of organic substrates

Priming-Effects are ...

Kontrolle ohneSubstrat

Substrat A Substrat B

positiv

negativ

12CO2frei

gese

tzte

s C

O2

12CO2

12CO2

14CO2

14CO2

zusätzliches12CO2

Kontrolle ohneSubstrat

Kontrolle ohneSubstrat

Substrat A Substrat B

positiv

negativ

12CO2frei

gese

tzte

s C

O2

12CO2

12CO2

14CO2

14CO2

zusätzliches12CO2

positive

control without

substrate

substrate A

substrate B

rele

ase

of C

O2

additional 12CO2

negative

0.6 M KOHMultiplexerKonduktometer

Computer

Respicond

0000,00 mS

1 96

12CO214CO2

measurement of CO2 release

addition of 14C-fructose or 14C-alanine

To slide 5 (priming effects)

" Priming effects in freshwater irrigated soil correlate with increased Cmic

" Lack of priming effects in ww soil despite similar substrate utilization indicates that substrates are not limiting microbial activity

Effects of substrate additions on the mineralization of SOM (Ramat Hakovesh orchard, 10-20 cm)

cont

rol

cont

rol

+36%

+69%

0

2

4

6

8

freshwater irrigated soil wastewater irrigated soil

Cor

g min

eral

isat

ion

[%]

w/ f

ruct

ose

w/ f

ruct

ose

w/ a

lani

ne

w/ a

lani

ne

Results

CO2 evolution per mg microbial biomass Ccylinder experiment

0.00

0.01

0.02

0.03

0.04

0.05

0.06

before experiment after experiment under fw irrigation

after experiment under ww irrigation

CO

2in

mg

h- 1m

g C

mic

-1

Hamra - freshwater irrigated soilHamra - effluent irrigated soilVertisol - freshwater irrigated soilVertisol - effluent irrigated soil

Field experiment HaMa´pil

Total and metabolic active bacteria

1.0E+05

5.1E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

0-10 cm 10-20 cm 20-30 cm 1 m

bact

eria

per

mL

soil

solu

tion

(equ

ival

ent t

o 0.

4 g

dry

mat

ter)

DAPI-fwEUB338-fwDAPI-wwEUB338-ww

0.100.921.172.03effluent irrigated soil

0.150.300.492.23freshwater irrigated soil

1 m 20-30 cm10-20 cm0-10 cmTab.: Corg in %

21 %

27 %19 %

34 %

83 %

52 %

26 %

9 %

freshwater irrigated soileffluent irrigated soil

Increase of active bacterial cells in % during 4 months of effluent irrigation

-2

42

-28

-11

8

2214

46

-40-30-20-10

0102030405060

after 5 weeks after 10 weeks after 14 weeks after 18 weeks

%

Hamra

Vertisol19 20 20

46

1518

-31

17

-40-30-20-10

0102030405060

after 5 weeks after 10 weeks after 14 weeks after 18 weeks

%

R²=0.96

Land use: Effects of effluent irrigationLand use: Effects of effluent irrigation

Summary

• Irrigation with treated wastewater influences the amount and properties of organic soil components

• OM level increases in the topsoil of effluent irrigated soils, yet it is depleted from deeper horizons

• Shifts in DOC quality during seasons were observed

Increased indication of priming effects

leads to higher mineralisation of SOM, also in deeper horizons

additional DOC as nutrient source in the effluent irrigated soil

Mineralisation of soil organic carbon [%]Ramat Hakovesh orchard 10-20 cm

(incubation 31 days)

+36%+16%

+69%+7%

0.0

2.0

4.0

6.0

8.0

freshwater irrigated soil effluent irrigated soil

Min

eral

isat

ion

of S

OC

[%]

controlfructose

alanine

• in effluent irrigated soilhigher mineralisationin the control

• addition of substrates results in positive priming effects

• stronger effects infreshwater irrigated soils

effluent water contains fresh organic substrates, which enhance themineralisation of SOM already in the field

in these soils priming may occur directly after addition of effluent water,easy available pool in the soil is used all the time

Priming Effects