Exploring Alternatives for Sustainable Development in the Tamiahua Wetlands

This article presents a preliminary System Dynamics model developed to analyze the sustainability of a natural reserve in Mexico: the Tamiahua Wetlands. Wetlands are often referred to as nature’s kidneys because they filter contaminants from water. In spite of their importance, wetlands are endangered areas around the world. In order to build the model we take into account the Fishbanks model developed by Meadows (2004) as a starting point. Then, the model considers variables related to changes in total and economically active populations, and contaminants in water. The preliminary model presented in this study implies that fishing activity in the Tamiahua Wetlands, together with contaminants from human activity, have the potential to damage the diversity of species in the ecosystem, endangering its sustainability. Continued work on the model is intended to explore appropriate ways of preserving Tamiahua, providing inhabitants with economic activities that promote the sustainability of the region.


Introduction
This article introduces a preliminary System Dynamics model to analyze sustainability of a natural reserve located in the Northern bound of the State of Veracruz in Mexico: the Tamiahua Wetlands. The model presented in this study is the result of initial conversations among researchers interested in regional development and the preservation of the Tamiahua protected area, and builds upon such System Dynamics models as Fishbanks (Meadows, 2004). One of the authors of this initial study has been involved in extensive field research in Tamiahua, collecting information about water quality. During his fieldwork, he has observed a growth in the fishing industry followed by

Literature review
Wetlands are often referred to as nature's kidneys because they readily filter contaminants from water, there are also famous for their intrinsic beauty and importance as habitat for rare and endangered species as well as their role in carrying out basic ecological functions such as primary productivity, decomposition, nutrient cycling and regulation of fluxes between land and water bodies. These ecosystems can also function to remove and store nutrients and toxic pollutants in runoff from surrounding areas.
Particularly, coastal wetlands play an important role in protecting coastal water quality. They are critical ecosystems that help to regulate and maintain the hydrology by storing and releasing floodwaters. Wetlands are hard to define mainly because they are transition zones. Their hydrology is usually the most important factor determining its character. These regions are considered one of nature's most efficient filters and usually are important nurseries for fish, crabs, shellfish, and an extensive variety of animals.
Despite their importance in the ecosystems, wetlands are endangered zones all around the world. Only in the USA, an annual loss of approximately 1.05 million hectares of wetlands is estimated (Josephson, 1992). Apart from agricultural conversion, wetlands are continuously jeopardized as result of overfishing, burgeoning development, sediment contamination and nutrient pollution, all this is the result of growing population and increasing unplanned development in coastal counties. Such situation in many cases promotes excessive exploitation of fisheries and an increasing number of threatened, endangered and extinct indigenous species.
System Dynamics has been used in exploring the environmental management and sustainability in applications that tackle problems of forestry in Indonesia, irrigated lands in Spain, renewable resource management in Norway, wildlife management in the USA and blue-green algae bloom in the 7 Luis Felipe Luna-Reyes, Jorge A. Durán-Encalada, Erick R. Bandala / coastal waters of Australia (Cavana and Ford, 2004). What these applications have revealed is that modeling dynamically these complex problems with many factors can enlighten the implementation of possible policies to alleviate the problem. System Dynamics has proven to be a useful tool when complex systems need to be re-oriented towards greater sustainability through policies that are quite different from those currently implemented and which should focus on the true driving factors of the system (Martínez Fernández and Esteve Selma, 2004). Our study subscribes to these assumptions and aims.
Particularly, System Dynamics has been used successfully to analyze and study fishing systems in a variety of ways (Morecroft, 2007;Otto and Struben, 2004;Ruth, 1995). Most of these previous efforts were focused on analyzing the problem known as the "Tragedy of the Commons" and policies to control overexploitation of fishing areas. The model presented in this article builds on previous work in System Dynamics and studies the impact of contaminants and of fishing activities on the diversity of species in Tamiahua Wetlands.

Method
It is clear, from the analysis of the research site, that to achieve a sustainable and holistic understanding of the complexity faced by the Tamiahua Wetlands and its stakeholders, we need to go beyond simply predicting the fishing activity. Economic and social variables interact dynamically with environmental and institutional variables.
To explore the effect of fishing on the interaction of other variables, a System Dynamics model was constructed. System Dynamics, originally known as Industrial Dynamics, is a creation of Jay Forrester in the 1960s at the Massachusetts Institute of Technology (Forrester, 1961). System Dynamics is essentially a methodology which uses the theory of information feedback and control in order to evaluate organizations and problems. The basic idea underpinning this approach is that any complex situation can be described in terms of stocks and flows; flows being main actions increasing or decreasing the stocks. System Dynamics assumes that things are interconnected in complex closed patterns of causality, and that the world is made up of flows, stocks and feedback loops. Other assumptions include that information flows are intrinsically different from physical flows, and that non-linearities and time-delays embedded in the system's structure are important to understand the system behavior (Sterman, 2000). The main focus of the methodology is to capture the structure of complex problems, representing it in terms of stocks, flows and feedback loops, which constitutes a dynamic hypothesis to explain problematic behaviors. The model structure and behavior are then System Theories and Practice, M. Baran, K. Śliwa (Eds.) 8 / Exploring Alternatives for Sustainable Development in the Tamiahua Wetlands compared with known relationships and behaviors in the system in several iterations.
System Dynamics has been used in a variety of contexts, as a problem evaluation on the premises that the structure of a system, that is the way the systems are connected, generates its behavior, aiming to predict the behavior of the system (Richardson and Pugh, 1989, Stave, 2003, Sterman, 2000. While statistical forecasting models rely on equations developed ex post, i.e. following observations, System Dynamics aims first to determine the systems structure consisting of positive and negative relationships between variables, feedback loops, systems archetypes, and delays (Sterman, 2000;Wolstenholme, 1982Wolstenholme, , 2003 followed by ex ante projection where future system states are replicated from the System Dynamics model (Winz and Brierley, 2007).
As already mentioned in this article, the modeling effort is based upon the knowledge and experience of two experts, one on regional development, and the other on water and environment. Although obtaining quantitative data to build the model has proven to be difficult, knowledge from field work on the region has been used to ensure a better understanding of behavior over time and structural hypotheses. The model is still in a preliminary stage, but initial model structure and some key parameters seem reasonable to expert judgment.

The Tamiahua Wetlands
The Tamiahua Lagoon is located in the northern part of the state of Veracruz, Mexico. It is a coastal lagoon and covers an area of 217,500 acres, of 52.2 miles length, 9.6 miles width, and the depth of 2.2-3.3 yards. It has two water mouths, one in the north and another in the south, and is located in between two large rivers, Panuco in the north and Tuxpam in the south (see Figure 1).
There are some valuable natural resources in the area which comprise an important mangrove swamp towards the south of the lagoon and coral reef formations to the east, on the Gulf of Mexico coast. The biodiversity of the place is rich, the area being inhabited by mollusk, crustacean, polychaeta, waterfowl, and a place for turtles laying eggs. Due to its ecology, botany, zoology, limnology, and hydrology richness, the Tamiahua was designated as a protected wetland included in the Ramsar Treaty of November 27th, 2005. The Ramsar Convention provides the framework for national action and international cooperation for the conservation and wise use of wetlands and their resources.
However, in the last ten years, a pollution problem has been affecting fishing activities in the lagoon. Industrial and residential pollutants are brought to the lagoon through 5 main rivers. The main types of pollutants are: hydrocarbon, agro-chemicals, fertilizers, metals and all sort of organic and solid waste (Albert, Bandala, Torres-Nacho, and Villanueva, 2006).

4
There are some valuable natural resources in the area which comprise an important mangrove swamp towards the south of the lagoon and coral reef formations to the east, on the Gulf of Mexico coast. The biodiversity of the place is rich, the area being inhabited by mollusk, crustacean, polychaeta, waterfowl, and a place for turtles laying eggs. Due to its ecology, botany, zoology, limnology, and hydrology richness, the Tamiahua was designated as a protected wetland included in the Ramsar Treaty of November 27 th , 2005. The Ramsar Convention provides the framework for national action and international cooperation for the conservation and wise use of wetlands and their resources.
However, in the last ten years, a pollution problem has been affecting fishing activities in the lagoon. Industrial and residential pollutants are brought to the lagoon through 5 main rivers. The main types of pollutants are: hydrocarbon, agro-chemicals, fertilizers, metals and all sort of organic and solid waste (Albert, Bandala, Torres-Nacho, and Villanueva, 2006).

Socio-economic Conditions
Surrounding the Tamiahua Lagoon there are 5 municipalities with a total population of 205,000 inhabitants. The economically active population (EAP) amounts to 40 percent of total population (INEGI, 2005(INEGI, , 2010. The main economic activity in this region is concentrated in the primary sector, mainly agriculture, as 75 per cent of the EAP is located in this sector. Only 2.5 percent operate in the manufacturing sector, and the rest of the EAP work in the service

Socio-economic conditions
Surrounding the Tamiahua Lagoon there are 5 municipalities with a total population of 205,000 inhabitants. The economically active population (EAP) amounts to 40 percent of total population (INEGI, 2005(INEGI, , 2010. The main economic activity in this region is concentrated in the primary sector, mainly agriculture, as 75 per cent of the EAP is located in this sector. Only 2.5 percent operate in the manufacturing sector, and the rest of the EAP work in the service sector (INEGI, 2005(INEGI, , 2010. The net rate of population growth in the region is estimated at 1.8 percent annually. The fishing activity is carried out by approximately 4,000 people (Cooperativa Pesquera, Tamiahua, 2012). They are grouped in 340 business units known as fishing cooperatives, with an average size of 12 people. Out of 4,000 people, 60 percent, that is 2,400, are proprietors of the business units, and the remaining 1,600 fishermen work as employees. It is estimated that the total fleet is composed of 680 fishing boats, which means an average of 2 boats per company.
According to recent data, annual fish catchment is about 12,750 tons. This amounts to an average catchment per boat of 18.75 tons per year, or 37.5 tons per company. The estimated price per ton in the intermediary market is US$1,500.
The market price of a boat is US$10,500, and it has a usable life of 20 years. The operating cost for each boat is estimated to run at US$10,000 per year, including wages.
Cooperatives in Mexico, as the fishing ones in Tamiahua, normally receive financial support by the Federal Government. In particular, the Ministry for Agricultural and Fishing Resources decides on fishing permits and funding for cooperatives after an economic feasibility study.

Model description
The model TAMIAHUA1 consists of four main sectors and was built using Vensim PLE Version 5.8. The first two sectors are similar to the ones used on the Fishbanks model (Meadows, 2004), and include the fish population and the fleet size. The third sector includes population dynamics in the region, and the last sector considers the contamination level in the water of the wetlands. Figure 2 shows the basic structure of fish population and fishing. The red parts in the model are those that are unique to the model presented in this study. The stock of diversity of the species was important to include, given the key role that this diversity plays on the cleaning function of wetlands and its impact on the growth of fish population. As shown in the figure, fishing practices in Tamiahua have been recognized to have an impact on the diversity of the species. Moreover, water contaminants and the diversity of the species have also had an impact on the population of fish in the lagoon.
Figures 3 and 4 represent the growth of the fishing fleet. Figure 3 includes the representation of the attractiveness of the fishing industry compared to other activities in the Tamiahua region. Profit is the difference between income and costs associated to fishing, and the profitability of other economic activities was estimated using the minimum wage in Mexico. As shown in Figure 4, the funding to increase fleet size does not come in this region from profits in the fishing industry, but from subsidies provided by the State government. As described by one of the experts involved in the modeling process, fishing cooperatives' need to increase the fleet or replace the existing boats exerts pressure on State government to provide more public funds to buy new boats. Figure 5 shows the way in which the attractiveness of the fishing industry attracts Tamiahua region inhabitants to join (or leave) fishing cooperatives.   Finally, Figure 6 presents a theory of how contaminants come into the lagoon, and how the lagoon absorbs a fraction of these contaminants before the water reaches the sea. The Tamiahua lagoon has experienced a considerable increase on its pollution levels resulting from the release of chemicals produced in oil-related, industrial and agricultural activities in the zone. During the last fifty years, the system has received oil spills from crude exploitation facilities and oil pipelines. Besides, most of the municipalities settled in the surroundings of the lagoon lack sanitation systems producing domestic wastewater and leachates from solid waste sites are released without any treatment to the lagoon (Albert et al., 2006). As shown in figure 6, contaminants coming from industrial effluents upstream in the rivers and from sewers and human activity may threaten the diversity of the species and have an impact on the absorption capacity of the Tamiahua Lagoon.
Appendix A shows the parameters values and equations that were used for the model.  Figure 7 shows the way in which fishing activity slowly erodes the diversity of the species, eventually impairing the ability of the fish population to reproduce in a healthy way. Figure 8 shows the dynamic behavior of the fleet size, the active fleet and the fleet in harbor. As shown in the figure, the impact on the fish population promoted by contamination and the decrease on the diversity of the species is not yet enough in this model to have an impact on the fishing activities. Given that the actual fleet size is similar to the simulated fleet size, this base scenario suggests that the observed decrease on fishing activity in Tamiahua responds to the contamination of the wetlands or to the impact of the fishing techniques on the diversity of the species.  activities. Given that the actual fleet size is similar to the simulated fleet size, this base scenario suggests that the observed decrease on fishing activity in Tamiahua responds to the contamination of the wetlands or to the impact of the fishing techniques on the diversity of the species.       Figure 9 shows some key behaviors of the ecosystem. During the last years of the simulation, it is possible to observe an important damage in the diversity of the species, which leads to an increase in contaminants in the lake, attributed mostly to the reduction in the capacity of the lagoon to absorb contaminants.

Figure 9. Contaminants and ecosystem diversity
The initial explorations with the model involved 5 parameter changes producing also 5 basic scenarios. In the first scenario, we increased the damage on the ecosystem produced by the fishing activity. The second scenario consists of an increase in incoming contaminants to the lagoon. The third and fourth scenarios involve changes in the attractiveness of alternative economic activities, making fishing more or less attractive. The last scenario explores the impacts of increased resources from government to the fishing industry.
As shown in Figures 10 to 13, attractiveness of alternative economic activities have a very limited impact on model behavior. The main reason is that the main source of economic resources to increase the fleet size is government funds. An increase in government funds, on the other hand, does have an impact on the sustainability of the ecosystem because it allows for the fleet size growth, accelerating damage to the ecosystem, and collapse of the fishing industry. Increasing contaminants from rivers and changes in fishing practices for ones with higher environment impacts have an important impact on fish population. Increased contaminants have a more continuous impact,  Figure 9 shows some key behaviors of the ecosystem. During the last years of the simulation, it is possible to observe an important damage in the diversity of the species, which leads to an increase in contaminants in the lake, attributed mostly to the reduction in the capacity of the lagoon to absorb contaminants.

Notes: Pppm: Parts per million. Dmnl: Dimensionless, as it refers to Diversity of Species/Normal Diversity of Species. FIGURE 9. Contaminants and Ecosystem Diversity
The initial explorations with the model involved 5 parameter changes producing also 5 basic scenarios. In the first scenario, we increased the damage on the ecosystem produced by the fishing activity. The second scenario consists of an increase in incoming contaminants to the lagoon. The third and fourth scenarios involve changes in the attractiveness of alternative economic activities, making fishing more or less attractive. The last scenario explores the impacts of increased resources from government to the fishing industry.
As shown in Figures 10 to 13, attractiveness of alternative economic activities have a very limited impact on model behavior. The main reason is that the main source of economic resources to increase the fleet size is government funds. An increase in government funds, on the other hand, does have an impact on the sustainability of the ecosystem because it allows for the fleet size growth, accelerating damage to the ecosystem, and collapse of the fishing industry. Increasing contaminants from rivers and changes in fishing practices for ones with higher environment impacts have an important impact on fish population. Increased contaminants have a more continuous impact, and increased impact from fishing practices contributes to a faster decline in fish population. Luis Felipe Luna-Reyes, Jorge A. Durán-Encalada, Erick R. Bandala / and increased impact from fishing practices contributes to a faster decline in fish population.

Conclusion
In this short article, we presented a preliminary model to study the sustainability of the Tamiahua Lagoon considering the fishing activity and the impact this activity makes on the diversity of species in the lagoon. Additionally, the model includes the impact of contamination of the wetlands. Preliminary experiments suggest that fishing practices and contamination have the potential to create a significant imbalance in the system, apparently in a more important way that the actual fishing intensity. Fishing activity is considerably limited by the availability of government funds. In this way, government decisions on funding the fishing activity affect the stability of the system.
Although the model presented in this study has a reasonable structure, it still needs to be refined in terms of parameter values, mostly those associated to the ecosystem. We will continue our experiments with the model to create a series of policy recommendations to the State Government of Veracruz in Mexico.

/ Exploring Alternatives for Sustainable Development in the Tamiahua Wetlands
This rate represents the cleaning process that happens in the Wetlands (010) Contaminants in rivers = 5000 Units: ppm These are contaminants coming from rivers, regularly they are fertilizers that accumulate in the river because of agricultural activities (011) Contaminants in sewers = 12000 Units: ppm These are contaminants coming from sewers, regularly these contaminants are city residuals that accumulate in the river because of urban activities, both residential and industrial (012