Transactions of the ASABE

Vol. 56(6): 1357-1363 © 2013 American Society of Agricultural and Biological Engineers ISSN 2151-0032 DOI 10.13031/trans.56.9951 1357

EMERGY EVALUATION OF SEMI-ARID

WATERSHEDS UNDER DIFFERENT

MANAGEMENT STRATEGIES

H. A. Q. Palácio, E. M. Andrade, J. C. N. Santos, J. R. Araújo Neto, P. P. Brasil

ABSTRACT. Due to the environmental impacts generated by economic activities and faced with the challenge of producing food for an increasing population, the sustainability of production methods should be analyzed to determine those with the highest relative yield and the least degradation of the environment. Seeking alternatives for sustainable use of the caatinga biome, this research tested two types of management strategies in watersheds of the semi-arid region in Iguatu, Ceará, Brazil, and compared them to a preserved area of caatinga. To evaluate the performance of the systems, an emergetic methodology, suggested by H. T. Odum, was used. The thinned area showed the best emergy results, with a transformity of 12,975 seJ J-1, while the preserved area and that planted with grass presented transformities of 14,477 and 22,062 seJ J-1, respectively. Through the activity of thinning, where the energy produced was 45% higher, the transformity was lower than that of the unchanged caatinga, showing that the investment in labor for thinning was offset by an increase in energy production. The high transformity of the untouched caatinga indicates that better use could be made of the available resources. This system could be used for beekeeping, ecological tourism, or any other activity that, as with thinning, would not alter the system beyond its capacity for tolerance but that would allow a more efficient use of the natural resources.

Keywords. Brazilian semi-arid region, Caatinga, Emergy, Emergy indicators, Environmental sustainability.

he northeastern region of Brazil has an area of 1,542,257 km2 (MIN, 2005). Within this region is the caatinga, an endemic biome where over 30% of the constituent elements are not present in any

other system on the globe. Their disappearance therefore results in the loss of biodiversity on the Earth. More than 30% of the caatinga biome has been irreversibly changed by human activities that promote erosion and an increase in the water deficit of the soil, contributing to changes in the microclimate and the expansion of desertification, thereby affecting the biodiversity (Araújo et al., 2005). Another relevant fact is that clearing by deforestation and burning are common practices in preparing the land for agriculture in the greater part of this biome, and the use of fire causes changes in present plant communities and their successors (Sheuyange et al., 2005).

Determining the sustainability of production systems is not an easy task. The vast majority of methodologies for system assessment are based on input and output, taking into account those products that have economic value.

Seeking to present a methodology that would assess systems in an integrated fashion, Odum (1996) developed the emergy methodology, which is defined as the available energy of one kind (usually solar) which had previously been required, both directly and indirectly, together with the means of input, in order to make a product or service, and proposes to measure all contributions (money, mass, energy, information) in equivalent terms (emergy). The unit of solar emergy is the solar emergy joule (seJ), to distinguish it from the regular joule (J) and to point out a different type of quality assessment based on a donor point of view (Odum and Odum, 2006; Ortega et al., 2002).

Different indicators, capable of characterizing systems, can be proposed by emergy analysis, allowing different production models, implemented in different places and at different times, to be compared. Among these indicators, transformity (the unit of transformation of energy, which is basic in emergy methodology) measures the quality of energy and its position in the hierarchy of universal energy, being calculated based on strict principles of system organization and energy flow (Li et al., 2010; Odum, 1996; Tilley and Swank, 2003). In general, the higher the transformity, the greater the energy used by the system (Odum, 1996; Li et al., 2010).

Based on these indicators, production models can be assessed to determine which model provides the best environmental, economic, and social performance. In this context, many studies using this methodology have been carried out around the world (Bastianoni et al., 2001; Sheuyange et al., 2005; Rasul and Thapa, 2006; Snyman and Preez, 2005; Zhao et al., 2005; Bonilla et al., 2010; Martin et al., 2006; Lu et al., 2006; Dang and Liu, 2012;

Submitted for review in September 2012 as manuscript number SW

9951; approved for publication by the Soil & Water Division of ASABE inJune 2013.

The authors are Helba A. Q. Palácio, Professor, Instituto Federal deEducação, Ciência e Tecnologia do Ceará, Iguatu, Brazil; Eunice M. Andrade, Professor, Julio C. N. Santos, Doctoral Student, and José R. Araújo Neto, Graduate Student, Universidade Federal do Ceará,Fortaleza, Brazil; Paulilo P. Brasil, Undergraduate Student, InstitutoFederal de Educação, Ciência e Tecnologia do Ceará, Iguatu, Ceará,Brazil. Corresponding author: Helba Araújo de Queiroz Palácio, 82 RuaTancredo Neves, Bairro Brasília, Iguatu-CE, Brasil CEP 63500-000; phone: 55-088-3581-3288; e-mail: helbaraujo23@yahoo.com.br.

T

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Campbell and Garmestani, 2012). This study aims to evaluate, based on emergy synthesis indicators, different management strategies applied to watersheds of the semi-arid region in Iguatu, Ceará, Brazil.

MATERIALS AND METHODS The monitored watersheds are located in the basin of the

upper Jaguaribe River, more precisely in the city of Iguatu, between the geographical coordinates 6° 23′ 42″ to 6° 23′ 47″ S and 39° 15′ 24″ to 39° 15′ 29″ W (fig. 1), and are of a small-scale experimental character, i.e., not more than 3 ha.

The soils of the watersheds are classified as typical deep-black, carbonate vertisols with drainage courses of the first and second order with ephemeral drainage. Average soil depth, including unweathered tillage, is approximately 2 m from surface to bedrock. Soils are clay loam with low infiltration rates (table 1). The uppermost 15 cm of the soil profile contains up to 42% clay and 45% loam. As for the form factor, which represents the ratio between the average length of the watershed and its width, the three watersheds fall into the same class. The same behavior is observed for drainage density, which is the ratio between the sum of the watercourses and the area of the watershed. Similar characteristics are observed for the concentration time, which is the time required for the entire area of the basin to contribute to surface runoff at any one control point. As for

the sinuousity of the main watercourse, which represents the relationship between the length of the main channel and the length of the thalweg measured in a straight line, the values are different. The watershed planted with grass has the highest value (2.8), followed by the area with native caatinga (2.06) and the thinned area (1.2).

The climate in the region is of type BSh (semi-arid hot), according to the Köppen climatic classification, with mean temperatures consistently above 18°C in the coldest month. The rainfall presents annual totals of 970 mm, mainly concentrated in the months of January to May, with the

Figure 1. Location of the experimental watersheds, Ceará, Brazil.

Table 1. Morphometric and soil characteristics of the experimental watersheds.

Characteristics Unit

Watershed Native

Caatinga (B2)

Thinned Caatinga

(B1)

Planted with Grass

(B3) Watershed area ha 2.06 1.15 2.80 Main course length m 252.11 147.18 238.20 Watershed slope % 10.59 8.72 5.57 Shape factor - 0.49 0.32 0.43 Drainage density m ha-1 192.59 153.80 146.29 Concentration time h 0.06 0.05 0.07 Main course sinuosity - 2.06 1.20 2.8 Granulometry: Fine sand g kg-1 137 137 315 Loam g kg-1 447 447 425 Clay g kg-1 416 416 260 Saturated conductivity - 0.25 0.25 0.18 Texture class - Clay loam Clay loam Loam

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highest values recorded for the month of March, and evaporation reaches 1988 mm year-1, expressing the high water deficit of the region.

The whole experimental area is fenced to prevent animal entry, and thus in none of the watersheds did grazing occur. The B2 watershed was kept as preserved and presents a caatinga of shrubs and trees, the B1 watershed was thinned to produce natural pasture, a practice often employed by farmers in the Brazilian semi-arid region, and the B3 watershed was cleared, burned, and planted with a grass (Andropogon gayanus Kunt) adapted to the semi-arid region for the production of pasture.

To enable the environmental and economic evaluation of production systems, emergy analysis based on the work of Odum (1996) and Brown and Ulgiati (2004) was applied. As the first step in evaluating the emergy, the system components were identified (i.e., finding the inputs and outputs). Then a systemic diagram of the system was prepared in which all components and energy flows were identified. The emergy flows used 2010 as the base year and had as inputs the energy from the sun and wind (the data were collected at an INIMET weather station 2 km from the survey area), from rain (measured with an automatic weighbridge pluviograph installed within the work area), and the materials and services that were used in the management of the area during the experiment For the internal processes, the increase in biomass of the trees and shrubs was evaluated using the difference between phyto-sociological surveys conducted in the area in 2009 and 2010, with the biomass estimated by allometric equations developed for the caatinga (Silva and Sampaio, 2008) and the herbaceous biomass (monthly direct measurements taken in the area). The principal outputs were surface runoff, soil loss due to erosion (measured with a hydro-sedimentological station installed in each area), evapotranspiration (estimated by the Penman-Monteith model (Allen et al., 1996) based on the data from the INIMET meteorological station), and infiltration (estimated as a function of soil humidity and hydraulic conductivity).

As the next step, each input stream on the systemic diagram was converted into a line of calculation on the emergy evaluation matrix. On the matrix, all flows of energy, mass, and monetary value that were considered in the process were converted to a common unit basis, solar emjoules (seJ), through emergy transformities taken from the literature and relative to a baseline of 15.83E+24 seJ year-1 (Odum and Odum, 2000). For this step, the item sun was not taken into account, thus avoiding double input. Renewable fractions of the flows were considered, with the percentage of the values of the renewable fractions taken

from Ortega et al. (2002) and Cavalett et al. (2006). The last step of the emergy analysis is the calculation of

the indices for the caatinga biome, with the aim of evaluating the performance of the three management systems under study. The indices used in this study are shown in table 2, with products with high transformity values representing a high cost in energy to the system, and a high value for the energy yield ratio showing that fewer products from the economy were used in its production. However, for the emergy investment ratio, the lower its value the better the efficiency of the system, since less energy originating in the economy is used for each unit of energy produced by the system. The environmental load ratio is a modified indicator that evaluates the environmental load; the more effective a system is, the lower its ELR will be.

RESULTS AND DISCUSSION The systemic diagram (fig. 2) shows the flows for the

different management strategies. For the watershed with natural cover (B2), the flows of seeds, pesticides, and labor were not considered, since B2 depends exclusively on the resources of nature (sun, rain, and wind). Similarly, for the system of thinned caatinga, the flows of inputs originating in the economy (seeds and pesticides) were disregarded. The products or outputs of the system are infiltrated water to replenish the groundwater, runoff water that can be used by other systems, and the increase in biomass that can be used by communities for timber and, for the herbaceous biomass, grazing. Finally, for a better comparison between the emergy flows that support the three management systems, table 3 shows the values for the flows of the three systems.

Based on the values in table 4, a summary of the main flows was prepared. The smallest quantity for the total emergy supporting the system (Y in table 4) is shown by the native caatinga (1.51E+15 seJ ha-1 year-1). Similar values (3.89E+15 seJ ha-1 year-1) for the total emergy of native systems were found by Giannetti et al. (2011). With the changes in natural conditions, the demand for emergy increases: 30% and 115% more emergy for the thinned caatinga and grass, respectively, with far lower values of the total energy for grass (6.02E+06) being found by Dong et al. (2012).

As the degree of interference in the caatinga increased, larger proportions of emergy arising from the economy were used. Other values of the management strategies studied that are worth comparing are the total mass and the total energy produced in each system (table 5).

Table 2. Indices for the emergetic evaluation of caatinga management (source: Odum, 1996; Brown and Ulgiati, 1997, 2004). Indices for Applied Systems Equation Definition

Solar transformity TR = Y/Ep Ratio of the total energy required to sustain a system and the total energy produced.

Emergy yield ratio EYR = Y/F Ratio of the total energy that directs a system and the emergy of the economy.

Emergy investment ratio EIR = F/I Ratio of the energy from the economy and the energy from nature.

Environmental load ratio ELR = (N + MN + SN) / (R + MR + SR) Ratio of the emergy from the economy and the non-renewable emergy from nature, and the renewable emergy from nature.

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Table 3. Calculation table of the flows of emergy synthesis of the native caatinga, thinned caatinga, and area of grass.

Contributions Renewable

Fraction Flow Unit

Emergy Intensity

(seJ unit-1) Reference

Renewable Emergy

(seJ ha-1 year-1)

Non-renewable Emergy

(seJ ha-1 year-1)

Total Emergy

(seJ ha-1 year-1) Native caatinga Renewable 1.51E+15 0 1.51E+15 Sun 1 6.46E+13 J 1 Odum, 1996 6.46E+13 0.00E+00 6.46E+13 Rain 1 4.71E+10 J 30600 Brown and Ulgiati, 2004 1.44E+15 0.00E+00 1.44E+15 Wind 1 8.57E+08 J 2500 Brown and Ulgiati, 2004 2.14E+12 0.00E+00 2.14E+12 Non-renewable Soil losses 0 9.60E+07 J 124000 Brown and Bradi, 2001 0.00E+00 1.19E+13 1.19E+13 Materials - - - - - 0.00E+00 0.00E+00 0.00E+00 Services - - - - - 0.00E+00 0.00E+00 0.00E+00

Total emergy 1.51E+15 1.19E+13 1.52E+15 Thinned caatinga Renewable 1.51E+15 0 1.51E+15 Sun 1 6.46E+13 J 1 Odum, 1996 6.46E+13 0 6.46E+13 Rain 1 4.71E+10 J 30600 Brown and Ulgiati, 2004 1.44E+15 0 1.44E+15 Wind 1 8.57E+08 J 2500 Brown and Ulgiati, 2004 2.14E+12 0 2.14E+12 Non-renewable Soil losses 0 1.93E+07 J 124000 Brown and Bradi, 2001 0 2.39E+12 2.39E+12 Materials - - - - - 0 0 0 Services - - - - - 2.07E+14 2.53E+14 4.60E+14 Labor 0.45 4.19E+07 J 11000000 Odum, 1996 2.07E+14 2.53E+14 4.60E+14

Total emergy 1.71E+15 2.56E+14 1.97E+15 Planted with grass Renewable 1.51E+15 0 1.51E+15 Sun 1 6.46E+13 J 1.00E+00 Odum, 1996 6.46E+13 0 6.46E+13 Rain 1 4.71E+10 J 3.06E+04 Brown and Ulgiati, 2004 1.44E+15 0 1.44E+15 Wind 1 7.46E+08 J 2.50E+03 Brown and Ulgiati, 2004 1.86E+12 0 1.86E+12 Non-renewable Soil losses 0 1.67E+09 J 1.24E+05 Brown and Bradi, 2001 0 2.07E+14 2.07E+14 Materials - - - - - 4.23E+11 4.19E+13 4.23E+13 Pesticides 0.01 4.91E+00 kg 2,48E+10 Brown and Ulgiati, 2004 1.22E+09 1.21E+11 1.22E+11 Seeds 0.01 2.85E+01 J 1.48E+12 Ortega, 2002 4.22E+11 4.18E+13 4.22E+13 Services - - - - - 7.48E+14 7.48E+14 1.50E+15 Labor 0.45 1.36E+08 J 1.10E+07 Odum, 1996 7.48E+14 7.48E+14 1.50E+15

Total emergy 2.27E+15 9.97E+14 3.27E+15

Figure 2. Systemic diagram of energy flows in areas of caatinga under different management strategies.

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The system that produced the highest total mass was the system planted with grass (Andropogon gayanus Kunt), representing 265% more total mass when compared to the quantity produced by the native caatinga. The thinned caatinga showed the lowest production of total mass, with 50% of that produced by the native caatinga. Despite this, the thinned caatinga showed the greatest amount of energy produced in relation to the other two systems under study, since this was the system that produced the greatest amount of biomass, and biomass is the product that has the highest added value of energy (Campbell at al., 2005). Thus, the thinned caatinga produced the greatest amount of energy, with 40% more than the native caatinga and 3% more than the system planted with grass.

The transformity calculated for the native caatinga (table 6) was higher than that for the thinned caatinga, which produced 45% more energy than the native caatinga. This result demonstrates that the investment in labor for thinning was offset by an increase in energy production. The high transformity of the native caatinga indicates that better use could be made of the available resources (Bakshi, 2002).

The transformity of the grass area (22,062 seJ J-1) was higher than that of the other two systems, by 53% and 71% for the native caatinga and the thinned caatinga, respectively. A transformity value similar to that of the grass area (24,200 seJ J-1) was found by Bonilla et al. (2010) when evaluating bamboo production in Brazil.

When comparing the grass system with the native caatinga, it can be seen that the energy produced by the grass system is 40% greater (table 4), yet the transformity is 53% higher than that of the native caatinga (table 6). The

predominant factor in the increase in the transformity value of the grass system is its high energy demand (Y), which is 115% greater than the energy required by the native caatinga. The lower transformity of the thinned caatinga system shows that this system was the most efficient in the use of energy. Comparing the transformities found in this study with those found by other authors, it can be seen that the values are compatible; Agostinho et al. (2010) found a value of 16,000 seJ J-1 for an area planted with trees.

The EIR of the native caatinga was not calculated (table 6), since this system does not use resources from the economy. When comparing the EIR for the thinned caatinga system to that for the area planted with grass (Andropogon gayanus Kunt), it can be seen that the thinned caatinga has a value two times greater than that of the grass, showing that thinning has greater potential for exporting local resources and providing a high return on investment. The values of this indicator are also compatible with those found in studies of related activities, where the researchers found values between 1.44 and 4.80 (Odum, 1996; Bastianoni et al., 2001; Souza, 2010; Lu et al., 2006), between 1.90 and 2.42 for a watershed with agricultural activities (Campbell and Garmestani, 2012), and between 1.21 and 1.25 for a basin with a reforestation program (Dang and Liu, 2012). These EIR values can still be improved, reaching between 4.90 and 18.80, if other activities in the area are added (Agostinho et al., 2008), such as the exploitation by organic farming of products of high added value, beekeeping, plant essences, etc.

As the native caatinga system does not use resources from the economy, its EIR was zero (table 6), demonstrating the total independence of this resource. In comparing the EIR of the thinned caatinga system (0.3) with that of the grass system, which presented a value three times higher (0.9), the thinned caatinga is a more accessible system to small producers, having a lower dependence on capital resources.

Similar to the EIR, the native caatinga showed an ELR value of zero, with the grass system presenting the highest value (0.4), four times higher than that of the thinned caatinga system (0.1). These results demonstrate that the strategy of planting grass puts more pressure on the environment than thinned caatinga. The lower environmental pressure of the latter system can be explained by the lower demand for non-renewable energy, as well as a lesser use of resources from the economy. The results of this study confirm the ELR values obtained by Lu et al. (2006), who found values between 0.01 and 0.62 for areas of forest and grass, respectively, which are lower than the values of 4.04 and 5.81 found by Dang and Liu (2012) for a large watershed with different activities and an ecological restoration program.

Table 4. Emergy values that support management strategies appliedto semi-arid watersheds for the year 2010.

Emergy Flows

Emergy (seJ ha-1 year-1) Native

Caatinga Thinned Caatinga

Planted with Grass

Y (total flow supported by system) 1.52E+15 1.97E+15 3.25E+15 I (from nature) 1.52E+15 1.51E+15 1.71E+15 R (renewable from nature) 1.51E+15 1.51E+15 1.51E+15 N (non-renewable from nature) 1.19E+13 2.39E+12 2.07E+14 F (from the economy) 0 4.6E+14 1.54E+15 M (from materials) 0 0 4.23E+13 MR (renewable from materials) 0 0 4.23E+11 MN (non-renewable from materials) 0 0 4.19E+13 S (from services) 0 4.6E+14 1.5E+15 SR (renewable from services) 0 2.07E+14 7.48E+14 SN (non-renewable from services) 0 2.53E+14 7.48E+14

Table 5. Products provided by the management strategies applied tothe semi-arid caatinga for the year 2010.

Products Native

Caatinga Thinned Caatinga

Planted with Grass

Total mass (kg ha-1) 5.33E+5 2.66E+5 1.95E+6 Yield energy (YE, J ha-1) 1.05E+11 1.52E+11 1.47E+11

Table 6. Emergy Indicators for the three management strategies applied to the semi-arid watersheds in 2010.

Indicator Calculation[a] Native

Caatinga Thinned Caatinga

Planted with Grass Unit

Solar transformity TR = Y/Ep 14477.4 12975.0 22062.1 seJ J-1 Emergy yield ratio EYR = Y/F - 4.3 2.1 Dimensionless

Emergy investment ratio EIR = F/I 0.0 0.3 0.9 Dimensionless Environmental loading ratio ELR = (N + MN + SN) / (R + MR + SR) 0.0 0.1 0.4 Dimensionless

[a] Values used for the calculations were taken from tables 3 and 4.

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The emergy analysis indicated that planting grass was a system of low sustainability, a finding confirmed by other research in pasture areas (Snyman and Preez, 2005; Zhao et al., 2005). To this finding should be added the use of fire to clear the area, which leaves the soil uncovered and produces the largest flow coefficient and sediment yield, further compromising the sustainability of this system and confirming the various results showing an increase in degradation for areas where fire is used (Sheuyange et al., 2005; Rasul and Thapa, 2006).

CONCLUSIONS The emergy methodology provided the basis for

evaluating a management strategy applied to caatinga that presented a higher benefit/cost ratio than planting grass. The strategy using thinned caatinga showed lower energy demand and reduced degradation. It can be recommended as a sustainable management strategy for areas of caatinga.

The three strategies considered in this study presented transformities of 14.477, 12.975, and 22.062 seJ J-1 for native caatinga, thinned caatinga, and grass, respectively, showing that planting grass was the least efficient in its use of energy. The low emergy yield of the area planted with grass, associated with high soil and water losses, showed that this strategy causes degradation of areas of caatinga and should be discouraged for systems of agri-food production.

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