Indices to monitor biological soil crust growth rate - lab and field experiments

doi:10.4236/ns.2011.36066

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Vol.3, No.6, 478-483 (2011) Natural Science

http://dx.doi.org/10.4236/ns.2011.36066

Indices to monitor biological soil crust growth rate—lab

and field experiments

Avraham Dody1*, Roni Hakmon1, Boaz Asaf1, Eli Zaady2

1Nuclear Research Center-Negev, Beer Sheva, Israel; *corresponding author: [email protected]

2Department of Natural Resources and Agronomy, Gilat Research Center, Israel.

Received 28 March 2011; revised 23 April 2011; accepted 8 May 2011.

ABSTRACT

The aim of this work was to identify test meth-

ods for accelerating growth of biological soil

crust (BSC). The BSC in the Yamin Plateau in

the north-east of the Negev Desert is composed

of cyanobacteria such as microcoleus spp.

nostoc spp. and others. Cyanobacteria are well

adapted to dry environments, owing to their

ability to survive desiccation, high temperatures

and solar radiation. Since the BSC is a live

component in the ecosystem, it can repair itself

in the event of failures such as environmental

disturbances by living things. In the lab, we

used five different treatments and mediums:

natural BSC, pure sand as reference, pure sand

with spores and propagules, pure sand with

whey, and pure sand with spores and propa-

gules and whey. The spores were collected from

specified collecting areas in the field. Each Petri

dish was irrigated daily with 10 mL of double-

distilled water. The testing period ran for 4.5

months with 10 samples taken from each

treatment at 1.5 month intervals. The analyses

criteria were: NDVI for chlorophyll content by

remote sensing techniques, polysaccharide

content, infiltration rate through the crust, pro-

tein and organic content. The results showed

that NDVI, polysaccharides and infiltration rates

are good indicators for showing growth accel-

eration of the crust; while protein and organic

content were found to be less indicative. The

treatments using whey for preliminary crust

failed in the lab since cracks were observed, but

succeeded in the field experiments. In the field,

we measured only the chlorophyll content with

a time interval of 20 months. The methodology

of how to accelerate the growth of BSC was

found to be effective.

Keywords: Microcoleus Spp; Spores; NDVI;

Infiltration Rate, Polysaccharides Content

1. INTRODUCTION

The main motivation for this study was to identify

how to reduce the migration of contaminants into the

biosphere from waste disposal sites (WDS). According

to International Atomic Energy Agency recommenda-

tions, radioactive (and/or other hazardous materials)

WDS should be under institutional control for a period

of several hundred years after site closure [1]. After that

time, the site should be given back to the public for dif-

fering land uses. We are suggesting the use of a biologi-

cal soil crust (BSC) as a top layer over WDS as soon as

possible after site closure for the following reasons: 1)

BSC has been shown to reduce water infiltration and,

therefore, may reduce the leaching of the contaminants

toward groundwater; 2) The BSC, when grown over

WDS, may reduce the erosion of the topmost layer, and

may also reduce the migration of contaminants into the

biosphere; 3) Since the BSC is composed of live organ-

isms that renew themselves, its longevity and durability

is much longer and greater than any common geo-textile

layer; 4) Since the BSC is composed of live organisms in

the natural, dry ecosystem (with the ability to survive

desiccation, high temperatures and solar radiation) it has

the capability of repairing itself in the case of damage or

disturbance; 5) The BSC can survive climate changes.

It must be stated very clearly that the idea of using the

BSC is not to replace any other engineered barriers, but

as an additional layer that should be applied to the top of

the WDS.

In semiarid and arid regions of the world, when land-

scapes are undisturbed, the soil surface is covered with

BSC. The BSC community varies significantly by pre-

cipitation regime [2-4]. The BSC cover is characterized

by a tightly structured surface and typically varies from

2 mm thick, relatively homogeneous cyanobacterial

crusts, to complex crust composition communities of

mosses, lichens, soil algae, fungi and cyanobacteria of

about 15 mm thickness [5,6]. The primary colonizers of

the crust community, which are composed of cyanobac-

A. Dody et al. / Natural Science 3 (2011) 476-483

479

teria and soil algae, secrete polysaccharide mucilaginous

sheaths on the soil surface that bind together the soil

particles [7-9]. Consequently, they play an important

role in soil surface stabilization for preventing both wind

and water erosion [10,11]. In the Negev desert (Israel),

the combination of relatively high contents of silt and

clay particles and the cyanobacterial exudates change the

soil/water regime by affecting runoff, rain interception,

water-holding capacity and soil moisture content [12-14].

BSC dramatically influences the runoff yield, mainly in

arid and semi arid zones [15].

Field measurements, at several study sites in Israel,

showed that BSC decreased water infiltration [16,17], by

producing a tough cover-layer on the soil surface [4].

The aim of this work was to find the parameters indi-

cating the growth rate of BSC. In nature, the growth rate

of the BSC is very slow (years and more) [18]. For this

study, BSC spores and propagules were collected from

overland runoff in nearby, naturally undisturbed areas

and transferred to the laboratory experiments. The natu-

ral conditions of the field study area are: soil pH around

8, low rainfall amounts (80 mm/y) and high potential

evapotranspiration (2200 mm/y) are the main reasons

that the soil surface is dominated by cyanobacteria

(>80% of the soil cover).

2. METHOD AND MATERIALS

Runoff water containing spores and propagules of the

BSC were collected from a specific collecting system

built in the field at Yamin Plateau, north-east Negev De-

sert, Israel. The dominant cyanobacteria in our study

area are microcoleus spp. and Nostoc spp.

Pure sand (from 0.3 meter below the soil surface) was

collected from the natural, undisturbed nearby area and

used as substrate. Five treatments were considered: 1)

BSC as reference, 2) Pure sand, 3) Pure sand with spores,

4) Pure sand with whey (whey used as coagulating sub-

stance), 5) Pure sand with spores and whey. We worked

with five sets of Petri-dishes, each containing 30 dishes

and totaling 150 samples; each Petri-dish contained 80

grams of pure sand. Runoff water from nearby natural

plots containing BSC spores were used to irrigate treat-

ments 3 to 5 (only once). Then, for the next 4.5 months,

each Petri-dish was irrigated every day with 10 ml of

double-distilled water (DDW). Analysis samples were

taken at intervals of 1.5 months, 3 months and 4.5

months. Similar experiments were run in the field on

fifteen separate 2 × 1 m sand-dune plots where the crust

layer of the soil surface was removed.

Growth rates of the BSC were studied using five dif-

ferent variables: infiltration rate, polysaccharide content,

protein, organic content and Normalized Difference Ve-

getation Index (NDVI) and chlorophyll content. A col-

umn of 100 mm of DDW was placed on each Petri-dish

(with 5 holes in the bottom) and the infiltration rates

were measured. The polysaccharides were measured

with a spectrophotometer (UV-VIS mini-1240 spectro-

photometer, Shimadzu), using Anthron reagent and Sul-

furic acid [19]. Protein content was measured using the

Lowry method [20]. The chlorophyll content was ex-

tracted with acetone and quantified [21]. Organic content

was measured by washing the sample with 0.1 M of HCl

and 5 hours in a 550˚C furnace [22]. Vegetation index

(VI) was developed during recent decades [23], based on

different combinations of the ratio between the R-band

(which corresponds to the region of maximum chloro-

phyll absorption), and the NIR-band (which corresponds

to maximum reflectance of incident light by living ve-

getation). The most widely used index is the NDVI and

is defined as:

NDVI = [NIR – R]/[NIR + R] (1)

where R and NIR are the radiance and reflectance, or at

least “apparent reflectance” in the R and the NIR spec-

tral bands, respectively [24]. The NDVI values lie in the

range –1.0 to +1.0, with denser and/or healthier vegeta-

tion having higher positive values.

As mentioned above, we sprayed whey on two treat-

ments. Whey is a byproduct of the cheese- and ca-

sein-manufacturing industry [25]. There is continuing

interest in utilizing this byproduct as a fermentation sub-

strate for the production of value-added products. In

order to check its feasibility to create crust in a short

time, we also wanted to study if there was any interrela-

tionship between spores and whey, and how growth rate

may be affected.

Data were processed using analysis of variance with

the ANOVA statistical package. One-way ANOVA, with

Tukey Test’s [26] were used to test the differences be-

tween treatments (crust-control, sand, sand with spores

and sand with spores and whey). The dependent vari-

ables were: infiltration rate, polysaccharide content,

protein, organic content and NDVI for chlorophyll con-

tent. Differences were considered statistically significant

if p < 0.05.

3. RESULTS

The analyses for all treatments were made via the time

sequence sets presented in the following figures.

1) Polysaccharides

In all five treatments, the concentrations of the poly-

saccharides became higher with time (Figure 1).

Changes are almost linear in all treatments, but with

different rate. The highest value of polysaccharides was

found in the whey treatments, and the lowest value in the

sand treatment. The relative highest change was found in

A. Dody et al. / Natural Science 3 (2011) 476-483

480

Figure 1. Polysaccharide content with time. The bars indicate

the ±SE.

the spores’ treatment from 31 to 100 mg/g during 3.5

months. In the ANOVA test, significant differences were

found among the five treatments. On Feb. 06 p < 0.001.

On April 06 p < 0.001. On June 06 p < 0.001.

2) NDVI

The chlorophyll content was measured using remote

sensing techniques—NDVI (Figure 2). The relatively

higher change was found in the medium treated with

spores, even higher than the natural BSC. In the ANOVA

test, significant differences were found among the five

treatments. On Feb. 06 p < 0.005. On April 06 p < 0.005.

On June 06 p < 0.005.

3) Infiltration rates

Infiltration rates were reduced with time in all ex-

periments (Figure 3). The significant change from 9.5 to

4 ml/min occurred during month 3.5, in the medium

treated with spores. In the ANOVA test, significant dif-

ferences were found among the four treatments. On Feb.

06 p < 0.005. On April 06 p < 0.005. On June 06 p <

0.005.

4) Protein content

The changes of the protein content as a function of

time are presented in Figure 4. As seen in April, three

treatments had low concentrations when compared with

February. High concentrations were found in June. Two

weeks between 23.02.06 to 27.4.06 the Petri dishes were

not irrigated due to a technical problem. This might be

explaining the drop in NDVI in some of the treatments.

5) Chlorophyll in the field

We ran limited experiments in the field in order to

gain assumptions about the growth rate in the field

compared to the laboratory experiments. In specific 2 ×

1 m plots (Figure 5), we measured the chlorophyll con-

tent by direct extraction from the top most crust layer of

the soil surface (Figure 6). Twenty months after the be-

ginning of the experiment showed the importance of

sowing spores and propagules on the sandy dunes. As

expected, the crust has the highest chlorophyll content

with the spores’ treatment being significantly higher than

the sand treatments, which is statistically similar to the

Figure 2. Changes in NDVI value with time. The bars indicate

the ± SE.

Figure 3. The rate of infiltration in each of the treatments over

time. The bars indicate the ±SE.

Figure 4. Protein content with time. The bars indicate the ±SE.

whey treatment.

6) Regression line between dependent variables

NDVI was plotted against infiltration rate and poly-

saccharide content (Figures 7(a-b)) and polysaccharides

was plotted versus infiltration rate (Figure 7(c)).

4. DISCUSSIONS

In this study, we examined physical and bio-physio-

logical methods in order to find useful and reliable tech-

niques for monitoring crust development. The findings

showed that NDVI is the favored parameter for assessing

A. Dody et al. / Natural Science 3 (2011) 476-483

481

Figure 5. The experiment plots in the field.

Figure 6. The changes in chlorophyll a+b in the field from

January 2006 to August 2007.

biological soil-crust growth rate. It is a reliable method

for showing the increase of crust development in time,

good correlations were found between the variables; in-

filtration rates and polysaccharide content (as presented

in Figure 7). This result concurs with other studies which

found that NDVI is well correlated with various vegeta-

tion parameters such as green biomass [27] and photo-

synthetic activity [28]. It has also been found to be useful

for various image analyses like crop classification, green

coverage and change detection. The reflectance spectra of

BSC in semi-arid regions of Australia was studied on a

variety of soils [29]. Noticeable differences upon wetting

of the BSC were observed using her method. Conse-

quently, it is assumed that a vegetation index, such as

NDVI, can serve as a second indicator for recovery of

BSC. In [30,31] the authors tested whether the high

NDVI values may be caused by the photosynthetic activ-

ity of BSCs, which cover most of the soil surfaces in the

semi-arid regions of the Negev Desert. They found that

the spectral reflectance curves of lower plants can be

similar to those of higher ones and their derived NDVI

values can be as high as 0.30 units. A high correlation (r

= 0.79) was reported between NDVI values and chloro-

phyll content of a wet BSC [6,32].

A similar reliable method was found with infiltration

rate measurements. Decreases of the infiltration rate

(a)

(b)

(c)

Figure 7. (a) The correlation between the dependent variables:

NDVI vs. infiltration rate. (b) The correlation between the

dependent variables: NDVI vs. polysaccharides. (c) The corre-

lation between the dependent variables: polysaccharides vs.

infiltration rate.

were shown with crust development over time. Both of

the last two analyses used NDVI and infiltration rate

measurements, and were nondestructive techniques for

the soil surface in the Petri-dishes.

During the growth and the laboratory experiments we

used double distilled water (DDW) in order to eliminate

any side effect of the photoautotrophic organisms and

their exudates that may dissolve within the water and

affect the results. For this reason we did not use sterile

runoff water. It was reported in the literature that runoff

water contain nutrients and organic matter other than

propagules [33]. Polysaccharide content in the soil as an

indicator of the presence of cyanobacteria microcoleus

A. Dody et al. / Natural Science 3 (2011) 476-483

482

spp. was found to be a good parameter to present the

development of the crust (although only 1 gram of soil

surface was taken for each replicate). Because protein

and organic content are related to two other variables,

the standard deviations were relatively too high, in order

to identify clear trends in the development of the crusts.

The sandy soil used for the experiments was taken

from a depth of 30 cm, under the assumption that no

spores and propagules existed at that level. The fact that

there were changes in all the parameters in the pure sand

treatment used as reference proves that our assumption

was wrong.

The next stage of our study focuses on the develop-

ment of a bio-reactor to grow BSC spores and propa-

gules, as well as to figure out optimum conditions (bio-

logical and cost-beneficial). The spores and propagules

will be seeded on the target areas in order to shorten the

coverage time of the area with BSC (compared to natural

growth).

More field experiments are needed to study the appli-

cations under field conditions, but our preliminary re-

sults showed fast establishment of the spores on sand

dune soil at the north-eastern Negev Desert (Yamin pla-

teau). Again, for the point of view of WDS, it must be

stated very clearly that the idea of using the BSC is not

to replace any other engineered barriers, but to add an

additional top layer that increases the soil surface stabil-

ity by using natural components of the ecosystem in the

arid landscape.

5. CONCLUSIONS

 NDVI, polysaccharides and infiltration rates are good

indicators for showing growth acceleration of the

crust;

 Protein and organic content were found to be less

indicative.

 The treatments using whey for preliminary crust

failed in the lab since cracks were observed, but suc-

ceeded in the field experiments.

 In the field, we measured only the chlorophyll con-

tent with a time interval of 20 months.

 The methodology of how to accelerate the growth of

BSC was found to be effective.

6. ACKNOWLEDGEMENTS

The authors wish to thank Faina Tziperman from Gilat-ARO for her

assistance in the laboratory work and Catherine Kelly for reviewing the

English.

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