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Biological Indicators for soil Quality

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What is an indicator?

• An important criterion for an indicator is that it should respond promptly and accurately to perturbation (Holloway e Stork, 1991).

• Any indicator must be “fit for purpose” and therefore able to detect, and resolve, changes brought about by management, land use, pollution or climate change in a known soil at a given location .

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Selection of indicators?• It is unlikely that a sole indicator can be defined with a

single measure.• The basic indicators and the number of estimated

measures are still under discussion.• The national and international programs for monitoring

soil quality presently include biomass and respiration measurements but extended also to nitrogen mineralization, microbial diversity and functional groups of soil fauna

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Biomass Measurements?

• The soil biomass can be measured as microbial biomass and soil faunal biomass.

• The soil microbial mass can be defined as organisms living in soil that are generally smaller than approx 10 µm.

• Most attention is given to fungi and bacteria.• Fumigation-incubation, substrate-induced

respiration, fumigation-extraction and ATP content are widespread indirect methods measuring microbial biomass.

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Nitrogen Mineralization?

• The process of changing free nitrogen from the air into plant useable nitrogen by bacteria is called nitrogen fixation.

• Two types of nitrogen fixing bacteria:– 1) attached to the roots of legumes– 2) live freely in soil (few)

• Bacteria enter the single-celled root hairs where they multiply rapidly due to favorable conditions, the colonies then form into nodules, usually in bunches.

• A reduction in diversity of ammonia oxidisers for tilled soils was found by Bruns et al. (1999) in comparision to the native plots.

• Similarly, Cheneby et al. (2000) investigated denitrifying bacteria in three agricultural soils using classical cultivation techniques and found a good correlation between number and diversity of denitrifies and soil type.

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Microbial bio-indicators?• Brookes (1993) has listed six criteria specific for the

selection of microbiological indicators in soil pollution monitoring. The indicators need to be:– able to be accurately and precisely measured across a

wide range of soil types and soil conditions;– easily and economically measured, as a large number of

analyses usually has to be measured;– of a nature that allows precise determination of the

pollutant effect by comparison with a control or background;

– sensitive enough to indicate pollution but also sufficiently robust not to give false alarms;

– of general scientific validity based on reliable and contemporary scientific knowledge;

– used in sets of two or more to make evaluations more robust.

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The soil fauna as bio-indicators?

• The use of faunal groups as indicators for soil quality needs a choice of organisms, that– Form a dominant group and occurs in all

soil types,– Have a high abundance and high

biodiversity and– Play an important role in soil functioning,

e.g, in food webs.

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Purpose of soil biological measurements

• To develop biological soil quality objectives• To establish trends in soil biological

parameters• To underpin the policies mentioned with

scientific knowledge (to identify and operationalize the “buttons to be pressed”)

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Effects of environmental pollution

Schouten et al. 1997

Life Support Functions

Earthworms, EnchytraeidMites

Protozoans, NematodesSpringtails, Mites

Earthworms,Enchytraeids

Micro-organisms,Soil fauna

Biological Indicator SystemDivS/FG=number of species per functional group, DivF=diversity of

functions, MI=maturity index, PPi=plant parasite index,

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Effects of soil type and land-use More bacteria at higher clay and organic

matter content

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Genetic diversity of bacteria Very low in coniferous forests, high in agricultural soilsError bars indicate SE, n=20 (10 for biological farms)

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Potential N mineralisation:Highest in grassland, lower in arable, lowest in forest

Intensive grassland significantly lower than other categoriesError bars indicate SE, n= 20 (10 for biological)

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Number of nematodes per 100 g soil (1993-1997)

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Soil biota Indicators Grassland on marine-clay (n=20)

Horticulture (n=17).

Bacteria Thymidine assimil. (pmol/g/h) 179.7 108.3 Leucine assimil. (pmol/g/h) 847.9 392.8 Bacterial biomass (µg C/g) 232.4 56.4 CFU (107 CFU/g) 17.1 2.6 Potential. nitrification

(mg NO3-N /kg/week) 93.6 74.0

Biolog LogCFU-50 (activity 50%) 3.73 2.87 H- coefficient (evenness) 0.39 0.6 gg50 (µg soil with 50% funct.) 95 44 Nematodes Abundance (num./100 g) 4629 2069 Number of taxa 26.1 21.8 Maturity Index 1.77 1.47 Trophic diversity index 2.12 1.51 Num. spec. bacterial feeding 11.4 13.3 Num. spec. carnivores 0.4 0.6 Num. spec. hyphal feeding 2.1 2.1 Num. spec. omnivores 1 1.2 Num. spec. plant feeding 11.4 4.5 Num. functional groups 3.9 4.3 Enchytraeidae Abundance (num/m2) 24908 16096 Number of taxa 8.2 5.5 Biomass (g/m2) 5.6 1.10 Number of Friderica (/m2) 8654 1300 Earthworms Abundance (num./m2) 317.9 40.2 Biomass (g/m2) 70.1 3.8 Endogé-species 2.1 0.82 Epigé-species 1.2 0.06 (n=1) (n=1) Mites Abundance (num./m2) 37900 18100 Number of species 23 20 Number of functional groups 8 10 Food web N-mineralization (kg N/ha/y) 335 115 (model- C-mineralisation (kg C/ha/y) 6150 1750 calculations) Stability 0.47 0.61

Summary of indicator values, measured on 20 agricultural grasslands on marine-clay and 17 horticultural farms. n is the number replicates.

Source; Schouten et al., 1999.

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Reference values

• Same site at earlier date (longitudinal comparison)

• Similar site elsewhere (transversal comparison)

• Value from the range of observations• Value in natural area on same soil type• ...

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A B C F

A = negative reference D = “good practice”

B = actual quality E = positive reference

C = minimum quality F = optimum quality

0 % 100 %

D E

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Nematode diversity and bacterial growth rate as related to land use intensity (grass

on sand)Nematoden biodiversiteit en bacterie-activiteit

Aantal nematoden taxa

Bacterie-activiteit

0

20

40

60

80

100

1 2 3 4 5 6 7 8 9 10

Grootvee-eenheden (aantal per ha)

Taxa

, Act

ivite

it (%

)

Cattle units (number per ha)

Taxa

, act

ivit

y (%

)

nematode taxa

bacterial activity

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A B C F

A = negative reference D = “good practice”

B = actual quality E = positive reference

C = minimum quality F = optimum quality

Quality deficit0 % 100 %

D E

Distance to target indicator

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thymidine incorp. (90%)

leucine incorp. (92%)

biomass bacteria (312%)

nitrification cap (96%)CFU (85%)

h-bacteria (72%)

div. BFnem (126%)

div. CAnem (20%)

div. HFnem (70%)

div. OMnem (25%)

div.PFnem (63%)

div. Funct. groups (78%)

Maturity Index (81%)

abund. nem (61%)

numb. taxa nem (72%)

Troph. Index nem (95%)

numb. taxa Enchy. (63%)

abund. Enchytraeids (71%) biomass Enchytraeids (44%)

numb. Friderica spec (33%)

abundance earthworms (28%)

biomass earthworms (39%)

endogé worms (70%)

epigé worms (60%)

A, C, D, E, or F

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Soil biological variables in intensive, extensive and biological grassland farms on sand.

Intensive is set to 100% Grass on sand

0

50

100

150

200

250

300Organic matter*

Bacterial biomass

Bacterial growth rate

Bacterial genetic diversity

Bacterial functional diversity*

Bacterivorous nematodes

Fungivorous nematodes*Herbivorous nematodes*

Mites

Enchytraeids*

Earthworms

Potential C mineralisation*

Potential N mineralisation* IntensiveBiologicalExtensive

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A case study• This study was performed within the framework of the Environmental

Monitoring Programme of Castelporziano Estate.• Castelporziano is a natural ecosystem with high environmental

value, and is not concerned with any direct sources of pollution. However it is situated near the city of Rome, some industrial plants, the international airport of Fiumicino, and some highways.

• Soil is mainly plain with sandy materials, and only the inner part is formed of volcanic and alluvial materials with elevation just above the sea level (85m).

• Rainfall total sare 700mm per year, rain pH is 5.5 as average.• The vegetation is typically Mediterranean, mainly oaks, mixed

broadleaf groves, an mediterranean bush along the sea coast.• Areas with reforestation and small agricultural fields are also

present.

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Materials and Methods• Soils were sampled at eight different sites:

(1) wood of Quercus ilex L.; (2) Mediterranean bush (Myrtus communis L., Erica

arborea L., Pistacia lentiscus L., Arbutus unedo L., Juniperus spp., Phyllirea spp., Smilax aspera L., Cistus spp., etc.);

(3) Pinus pinea L. reforestation (60 years old); (4) mixed hydrophilous back-dune wood (Populus alba

L., Quercus cerris L., Fraxinus oxycarpa L.); (5) grazed meadow; (6) undisturbed meadow close to site 5, used as control;(7) arable land;(8) set-aside field, close to site 7, used as control.

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How many samples?

• Five samples of soil from each site were collected (0-20 cm of depth).

• Samples were air-dried and manually sieved (< 2 mm).

• Some soil physical and chemical parameters were measured.

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Result and Discussion1. Comparison of control and disturbed sites

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Result and Discussion2. Cumulated respiration of soils under different wood cover (Quercus ilex, Pinus pinea,Mediterranean bush, mixed back-dune wood)

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Result and Discussion2. Cumulated respiration of soils under different disturbing agents and land use.Set-aside vs. arable land (left), grazed vs. non grazed meadow (right)

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ConclusionsThe study of soil microbial activity showed, as a whole, the existence of marked

differences between adjacent vegetation types and different land uses, despite the similarity of climatic and physical conditions.

Microbial biomass activity and soil organic carbon metabolism could be applied successfully as both soil-state descriptors of natural ecosystems and indicators of disturbance.

The evaluation of soil microbial biomass behaviour and the organic matter storage could be of great help in the understanding and prevention of soil decline mechanisms.

Results showed that biomass C and its ratio to TOC was generally lower if the site was under a stress (e.g. grazing or tillage) or the influence of a pollutant agent, and the metabolic quotient q(CO2) was higher. This would suggest that at least these three indicators could be included in a soil-monitoring program, considering also that their measure can easily be performed in most laboratories without large investments in new or modified equipment.