The leopold matrix It is a double entry table of cause-effect relationship used in the environmental impact assessment. This matrix systematizes the relationship between the actions to be implemented in the execution of a project and their possible effect on environmental factors..
The Leopold matrix is widely used as a qualitative evaluation method and allows to assign a character to the impact (positive or negative). This matrix method of evaluation was proposed in 1971 by Luna Leopold in collaboration with other North American researchers..
Among its main advantages are being a simple method to implement, low cost and applicable to all types of projects. As the main disadvantage, it exhibits the subjective burden in the researcher's decisions when assigning orders of magnitude and importance.
On the other hand, this method only considers primary impacts of linear interaction, not complex interactions between actions, environmental factors or secondary repercussions..
Since its creation, it has been applied in numerous environmental impact studies in various fields such as mining, construction, aquaculture and agriculture..
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The Leopold matrix is used to assess the potential environmental impact of project execution and was initially developed for mining projects. This method is useful as it is a checklist that uses qualitative information on cause-effect relationships..
In the environmental laws of the world, environmental impact studies are required to approve projects of various kinds, such as the construction of roads, urban planning, industrial plants, mining, oil or any activity likely to affect the environment..
The Leopold matrix is a simple method that allows a first holistic approach to the definition of possible environmental impacts..
When the matrix begins to be elaborated, the actions to be executed in the project to be evaluated are placed in the first row (upper part). At the extreme left (first column) the environmental factors that may be affected by each action are noted..
In the cells formed by the intersection between rows and columns, the magnitude and importance of the impact are noted. The final columns show the totals for the number of positive and negative impacts and the impact for each environmental factor. In the last rows, positive and negative impacts and the impact for each action are noted..
Finally, in the lower right corner the result of the total sum of impacts of actions and that of factors is noted. Both figures must be identical and indicate the level and type of impact (negative or positive).
For Leopold's matrix, 88 environmental factors or components and 100 possible actions to consider are suggested. Therefore, the potential impacts or interactions to be evaluated are 8,800.
Depending on the evaluated project, the researcher selects the environmental factors and actions that he considers and can add some specific ones. When an interaction between an environmental factor and an action is relevant, a diagonal is drawn in that cell.
The values of the magnitude of the impact and the value of its importance have been pre-established in reference tables. From these tables, the researcher takes the values according to his criteria.
In the reference tables, the values of the magnitude of the impact range from + 1 to +10 if the impact is positive. When the impact is evaluated as negative, values between -1 to -10 are assigned.
The assessment of the importance of the impact on the environment always has positive values ranging from 1 to 10.
In the cell of the selected diagonal of the interaction between an environmental factor and relevant action, two values are noted. Above the diagonal the value of the magnitude of the selected impact is noted and below this diagonal the value of the importance.
Subsequently, each cell will have a single positive or negative value, as a result of multiplying the magnitude by the importance. This will be the value and sign of the impact caused by a specific interaction between an action and a given environmental factor..
The total number of negative and positive impacts for each environmental factor is entered in the corresponding columns. In addition, the sum of the total cells for each environmental factor must be recorded..
In the same way, it is done in the corresponding rows for the total negative and positive effects of each action and the total sum.
All the total values of the environmental factors and all the total values for the actions are added, which must match. If the value obtained is negative, it is considered that the overall impact caused by the project negatively affects the environment..
If positive values are obtained, the project is not adversely affecting the environment. In fact, it can be concluded that the project may be favorably increasing environmental factors.
The results obtained in the application of the Leopold matrix can be analyzed using basic statistics or graphically..
For this, the mean and standard deviation are calculated for the sums of the rows and for the columns (aggregation of impacts). Any value in a cell greater than the standard deviation and the mean is considered to affect the environment.
This specific project action must be considered for prevention or mitigation measures..
In this case, the impact values are plotted in Cartesian coordinates, obtaining a point cloud graph. Depending on where the points are concentrated, we will know if the impact of the project is negative or positive..
Among the advantages of the application of the Leopold matrix are:
1.- It presents in a schematic way the actions of a project and their possible effects on environmental factors, being easy to understand.
2.- Includes both the order of magnitude of the impact and the importance assigned to it.
3.- Different matrices elaborated for different alternatives in the project under consideration can be compared.
4.- It is a low-cost application methodology.
5.- It is very useful as an initial application method for a first approximation. Based on its results, more complex studies can be planned.
6.- It is applicable to all types of projects that involve environmental effects.
The following disadvantages of this methodology have been noted:
1.- Subjectivity in the definition of impacts, as well as in the assignment of magnitude and importance. This is the most important disadvantage, since the researcher makes the assignments according to his criteria..
2.- It only considers linear interactions (primary effects), not complex interactions between actions or between environmental factors or secondary effects.
3.- The temporal dimension of the impact is not considered, so there is no difference between short, medium or long-term effects.
4.- The list of actions and environmental factors may leave out elements of specific projects.
5.- It does not consider the probability that the impact actually occurs, since it assumes a 100% probability of occurrence.
6.- It does not allow to highlight specific critical areas of interest.
The Leopold matrix has been widely used in environmental impact assessments since its creation in 1971. During these years, it has undergone some modifications, among which the increase in the number of factors to consider stands out.
The Leopold matrix has been the fundamental basis for many environmental impact assessment methodologies. We have for example the Ecozone II, a decision support system developed during the 1980s of the 20th century.
This system was designed to facilitate environmental impact studies in the agriculture, agribusiness and aquaculture sectors in less developed countries..
An example of the application of the Leopold matrix was the EIA carried out in the marshes of Serbia in 2015.
Marshes are very fragile ecosystems and highly threatened by human activities. In this study, impacts related to urban construction and agriculture were evaluated.
Another case is in Mexico, where there are no official evaluation methods, but it is suggested to apply the Leopold matrix. For example, in this country it has been applied to assess impacts in aquaculture projects.
In the construction of a maritime terminal for the Gas Liquefied Petroleum company in Ecuador, three environmental impact assessments were carried out based on the Leopold matrix method with different modifications. Various environmental factors were taken into account for its application:
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