Changes of organic matter in soils irrigated with reclaimed wastewater

Transcription

1 Changes of organic matter in soils irrigated with reclaimed wastewater Bernd Marschner, Elisabeth Jüschke Ruhr-University Bochum Yona Chen, Jorge Tarchitzky Hebrew University Jerusalem (Rehovot) within the GLOWA Research Framework (BMBF & MOST)

2 Background! In many countries, water demand is expected to increase due to population growth and improved standard of living.! Freshwater resources are limited, often overexploited or deteriorated due 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 to rely on marginal waters, such as saline waters or treated wastewater.

3 Water sources and water use in Israel mio m renewable water sources Other Aquifers and surface waters Sea of Galilee Mountain Aquifer Coastal Aquifer

4 Water sources and water use in Israel > 2 fossile water 19% additional sources (35-4 mio m 3 /yr) desalinisation 5% treated wastewater 76% mio m deficit 16 > treated wastewater 2% mio m 3 agricultural sources brackish water 5% fresh water 75% renewable water sources water use Other Aquifers and surface waters Sea of Galilee Mountain Aquifer Coastal Aquifer industry municipal & household agriculture

5 Problems associated with the use of reclaimed 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 groundwater salinisation.! 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.

6 Treated wastewater as irrigation water source (Ramat Hakovesh) parameter unit effluent freshwater EC ds/m Cl mg/l Na meq/l Ca + Mg meq/l ph DOC (Dissolved Organic Carbon) mg/l BOD (Biological Oxygen Demand) mg/l 59.9 * COD (Chemical Oxygen Demand) mg/l 234. ~ 1 ~ 1 * present regulation for BOD in Israel 2 mg/l proposed new regulation 1 mg/l

7 Methodological approach 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

8 Sampling sites for screening Gaaton Yagur Ramat Hakovesh Basra Arad

9 Percolation of soil samples Incubation of soil samples (CO 2, 14 CO 2, 13 CO 2 ) irrigation: 25 mm h duration: 6 h -1, ms Konduktometer Computer Multiplexer 1 96 peristaltic pump Re sp ic o nd 25 ml 1 mm CaCl 2 glass filter plate (pores < 16 µm) - 65 hpa Soil 8 cm 3 Texture, C org, N t, C mic, δ 13 C vacuum pump membrane filtration.45 µm ph, EC, anions, DOC, UV-absorbance, fluorescence, biodegradability, XAD8-fractionation, K DOC, δ 13 C

10 Extractable DOC in the soils from the different study sites 6 freshwater irrigated soil DOC content [mg kg -1 ] effluent irrigated soil Ramat Hakoveshfield Ramat Hakoveshorchard 1 cm Ramat Hakoveshorchard 2 cm Basra Yagur Gaaton

11 Humification Index (HIX) of extractable DOC in the soils from the different study sites 1. freshwater wastewater.8.6 HIX.4.2. RH I RH II 1 cm RH II 2 cm Yagur Basra Gaaton

12 Seasonal differences in DOC properties (Ramat Hakovesh field) 6 5 December hydrophilic DOC hydrophobic DOC June DOC [mg kg -1 ] wastewater irrigated freshwater irrigated wastewater irrigated freshwater irrigated " Consistently more DOC in wastewater irrigated soils " Preferential release or production of hydrophilic DOC compounds during rainy season in both sites

13 Biodegradability and specific UV absorbance (Ramat Hakovesh field) biodegradability [%] fw December ww December fw June ww June specific UV 254 absorbance [l m -1 mg -1 ] " 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?)

14 Soil incubation studies 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 CO 2 -evolution - microbial biomass - microbial cell counts (fluorescence in-situ hybridisation) 2. 4-week incubation of soil samples with substrate additions for the determination of priming effects (glucose, 14 C-fructose, 14 C-alanine) -CO 2, 14 CO 2

15 Soil respiration CO 2 evolution accumulated in a 4 month irrigation experiment fw irrigation ww irrigation Hamra soil Vertisol accumulated CO 2 in mg g accumulated CO2 in mg g freshwater soil wastewater soil freshwater soil wastewater soil " microbial respiratory activity is higher in soils originating from wastewater irrigated sites " Wastewater irrigation in the lab stimulates microbial activity in all soils

16 Bacterial counts after 4 months of irrigation 1.E+9 5 % 5 % 52 % 51 % DAPI EUB338 bacteria per ml soil solution (equivalent to.4 g dry matter) 8.E+8 6.E+8 4.E+8 2.E+8 38 % 51 % 44 % 41 %.E+ fw-fw fw-ww ww-fw ww-ww fw-fw fw-ww ww-fw ww-ww Hamra Vertisol

17 Effects of substrate additions on soil respiration (Ramat Hakovesh orchard, 1-2 cm) 5 feshwater wastewater 4 CO 2 -C [µg g -1 ] % +16% +69% +7% 1 control w/ fructose w/ alanine " Elevated CO 2 -release from wastewater irrigated soil can not be attributed to higher C org content " Microbial activity in the freshwater irrigated soil is limited by the availability of easily degradable substrates

18 Priming effects after substrate additions HaMapil (9-1 cm) 3 freshwater irrigated plot 25 wastewater irrigated plot +157% +186% CO2 [% of SOC] % +238% 5 control w/ alanine w/ fructose " 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

19 Soil respiration after glucose addition (SIR) HaMapil cm freshwater wastewater CO 2 (mg h -1 ) time (d) " Stimulation of microbial respiration by glucose is more rapid and stronger in the wastewater than in the freshwater irrigated soil.

20 Soil organic matter inventories Arad (1 yrs) Basra (3 yrs) SOM (%) SOM (%) soil depth (cm) t/ha freshwater wastewater soil depth (cm) t/ha freshwater wastewater Misra (12 yrs) Yagur (35 yrs) SOM (%) SOM (%) soil depth (cm) t/ha freshwater wastewater soil depth (cm) t/ha freshwater wastewater

21 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-borne OM also contribute to such priming effects.! A depletion of soil OM pools at a rate of >1 t ha -1 annually may have longterm effects on soil fertility and is a source of CO 2 to the atmosphere.

22 Thank you Dankeschön

23 Relevance of the results for the planned research activities Priming effects seem to be ubiquous in soils that receive regular inputs of 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.

24

25 Conclusion 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...

26 Conclusion... direct and indirect methods for determination of activity of the soil bacteria correlate and 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.

27 To slide 5 (priming effects) Priming-Effects are stimulation or inhibition of transformation and utilisation of SOM after addition of organic substrates addition of 14 C-fructose or 14 C-alanine, ms Konduktometer Computer Multiplexer 1 96 Re sp ic o nd 12 CO 2 14 CO 2.6 M KOH freigesetztes CO 2 release of CO 2 12 CO 2 positive 14 CO 2 zusätzliches additional 12 CO 2 12 CO 2 12 CO 2 negative 14 CO 2 12 CO 2 measurement of CO 2 release control without substrate Kontrolle ohne Substrat substrate A Substrat A Substrat B substrate B

28 Effects of substrate additions on the mineralization of SOM (Ramat Hakovesh orchard, 1-2 cm) 8 C org mineralisation [%] control +36% w/ fructose +69% w/ alanine control w/ fructose w/ alanine freshwater irrigated soil wastewater irrigated soil " Priming effects in freshwater irrigated soil correlate with increased C mic " Lack of priming effects in ww soil despite similar substrate utilization indicates that substrates are not limiting microbial activity

29 Results CO 2 evolution per mg microbial biomass C cylinder experiment.6.5 Hamra - freshwater irrigated soil Hamra - effluent irrigated soil Vertisol - freshwater irrigated soil Vertisol - effluent irrigated soil CO 2 in mg h -1 mg C mic before experiment after experiment under fw irrigation after experiment under ww irrigation

30 Field experiment HaMa pil Total and metabolic active bacteria 2.5E+7 83 % DAPI-fw EUB338-fw bacteria per ml soil solution (equivalent to.4 g dry matter) 2.E+7 1.5E+7 1.E+7 5.1E+6 21 % 27 % 52 % 19 % 26 % DAPI-ww EUB338-ww 34 % 9 % 1.E+5-1 cm 1-2 cm 2-3 cm 1 m Tab.: C org in % -1 cm 1-2 cm 2-3 cm 1 m freshwater irrigated soil effluent irrigated soil

31 Increase of active bacterial cells in % during 4 months of effluent irrigation % % after 5 weeks after 1 weeks after 14 weeks after 18 weeks after 5 weeks after 1 weeks after 14 weeks after 18 weeks R²=.96 Hamra freshwater irrigated soil effluent irrigated soil Vertisol

32 Land use: Effects of effluent irrigation Summary Irrigation with treated wastewater influences the amount and properties of organic soil components Shifts in DOC quality during seasons were observed OM level increases in the topsoil of effluent irrigated soils, yet it is depleted from deeper horizons additional DOC as nutrient source in the effluent irrigated soil leads to higher mineralisation of SOM, also in deeper horizons Increased indication of priming effects

33 Priming Effects Mineralisation of SOC [%] Mineralisation of soil organic carbon [%] Ramat Hakovesh orchard 1-2 cm (incubation 31 days) +36% +69% freshwater irrigated soil +16% +7% effluent irrigated soil control fructose alanine in effluent irrigated soil higher mineralisation in the control addition of substrates results in positive priming effects stronger effects in freshwater irrigated soils effluent water contains fresh organic substrates, which enhance the mineralisation 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