Several cultures in Mexico had a close relationship with wetlands. On the coastal flood plains of southern Veracruz and Tabasco, in the center of the Gulf of Mexico, an area extensively cultivated by the numerous tribes of the Papaloapan, Coatzacoalcos, and Tonala rivers, the Olmecs emerged.
Wetlands have been of great importance to mankind on all continents and today their conservation has become more important. To cite only a few examples of their relevance in human history, the fertile valleys of the Nile, Euphrates and Tigris gave rise to the cultures of the Egyptians and Sumerians.
In the American regions, they also played a predominant role, as in the extensive wetlands of the Amazon, where the population density was 10 to 20 times higher than in the surrounding highlands.
In Mexico, several cultures had a close relationship with wetlands. The Olmecs emerged in the coastal flood plains of southern Veracruz and Tabasco, in the center of the Gulf of Mexico, an area intensely irritated by the many tributaries of the Papaloapan, Coatzacoalcos, and Tonala rivers.
There are reports of the presence of raised fields and channels in several wetlands in the lowlands that were part of Mesoamerica, built to grow a variety of products. The raised fields were located on the banks of the wetlands where there was shallow but frequent flooding, while the channels allowed for navigation, irrigation water, mud for fertilization, and fishing.
During the dry season, the low, wet areas were used for planting, and during the rainy season, the higher fields that were not flooded were used for planting. The Aztecs settled on a lake and a good part of their agriculture was linked to the use of wetlands, using cultivation on chinampas, a more sophisticated system than the elevated fields and still used today.
Wetlands are lands of transition between land and water systems, where the mantle or water table is generally at or near the surface of the land is covered by shallow water. They bring together much of the environmental variability that can be found among the driest ecosystems and form several generally comparable types, differing mainly in their degree of moisture or flooding.
For a wetland to form, several conditions must be combined, each of which gives rise to another. First, there must be enough rain to run off or infiltrate and be greater than the amount that evaporates, so that it can accumulate in a given topography (second factor). Since it accumulates in a depression, in a channel or runs very slowly over a surface, the water (third component) has a hydrological behavior, that is, the quantity, quality, and seasonality of the flood is the main factor that produces a hydromorphic soil and determines the type of wetland.
When water occupies the pores between soil particles and displaces air, hydromorphic soil is formed in which oxygen is scarce. This determines what type of plants can be established to form the wetland. When they are near the coast, salinity is another factor that produces environmental heterogeneity. All of the above results in temporary and permanent herbaceous and arboreal wetlands of freshwater, saline, and hypersaline.
Mexico's wetlands known as marshes and swamps occupy 6.5 percent of the national territory (INEGI, 2005). They include shallow coastal lagoons with their marine grasses, marshes, and oases in the deserts, mangroves and petenes, freshwater herbaceous wetlands (popales, tular), palm groves, and flooded forests. This great variability brings together an enormous amount of flora and fauna species and, therefore, high biodiversity, even though some of them are not very diverse by themselves, such as the mangroves.
Hydrology is the main factor that determines and affects wetlands. Many of the differences between different wetlands are based on hydrological characteristics. This is the seasonal pattern of water level in a wetland and is defined by its duration (time that the flood remains), frequency (the number of times it is flooded in a given time), depth, and time of flooding.
It significantly affects species composition, soil structure, metabolic processes, and often opens the ecosystem to lateral inputs and outputs of materials. Wetlands vary in their hydroperiod and salinity. The marshes and mangroves are periodically flooded by the tides and the former are the most saline. The forests and the popales are flooded with the freshwater of the overflow of rivers and the second ones remain flooded almost all the year.
The environmental services provided by wetlands
Wetlands provide numerous environmental (ecosystem) services to society. These are the ecological processes that natural ecosystems provide to humanity by the mere fact of their existence and functioning, and on which we depend, for example, the oxygen we breathe. They contribute to human well-being and help maintain the biosphere. Wetlands support a rich diversity of plants and animals. This genetic diversity helps maintain the processes inherent in these ecosystems, such as fresh water supply, food production, water filtration and cleaning, sediment retention, and nutrient cyclings such as nitrogen and phosphorus processing.
They also provide cultural, recreational, and research services. In particular, the importance of tropical coastal wetlands has been recognized, as they provide nutrients to lagoons and form refuges for juvenile fish and crustaceans, among others; they are important carbon sinks; they store water and help regulate flooding, and they function as protective shields against storms and tides.
Wetland loss and disturbance
Mexico has lost or degraded 62 percent of its wetlands. Not all regions have been equally affected. The greatest losses have occurred in the driest areas of the country, where water has been extracted for irrigation, draining lagoons and wetlands, as well as in the coastal areas of the humid tropics.
The loss and/or degradation is caused by both human actions and natural hazards. Direct actions produced by people's activities include drainage, dredging, and channeling of streams, deposition of fill material, construction of dikes and dams, tillage for agricultural production, logging, pollutants, mining, construction, runoff, the change in nutrient levels (increased nutrient inputs and consequent eutrophication, the release of toxic chemicals, introduction of non-native species which often becomes an invasion of exotics with a strong impact on the ecosystem, grazing by domestic animals, urbanization.
Indirect actions are the clogging and eutrophication in downstream wetlands and are derived from agricultural runoff and erosion, respectively, due to deforestation and upstream cultivation. Natural hazards include erosion, subsidence, sea-level rise, drought, hurricanes, and other storms.
Some of these natural hazards will increase with global climate change (rising air temperatures, changes in precipitation, increased frequency of storms, droughts, and floods, the increased atmospheric concentration of carbon dioxide, and rising sea levels). All of these impacts could affect the species composition and functions of wetlands. On the other hand, these impacts could favor the invasion of exotic species.
Over the past several decades, there have been significant changes in the hydrology of tropical areas. The hydrological changes have occurred due to natural causes and also as a result of people's activities. Wetlands are intimately linked to the basins from which they receive water runoff, suspended solids, and nutrients. This makes wetlands very vulnerable to inadequate basin management and often affects hydrology.
The causes of degradation are described in more detail below. Loss and/or degradation occurs through both human actions and natural threats. They can be both direct and indirect.
Direct actions are of several types:
Actions that modify hydrology and seek to reduce or avoid flooding: drainage of wetlands, dredging and channeling of streams, deposition of fill material to raise the soil level, construction of dikes and dams, construction of infrastructure (e.g. roads) that modify water flows, alterations to runoff from watercourses.
One aspect that is worth highlighting is water damming since a large percentage of the country's water volume (107 billion m3 ) is located in dams, that is, almost a quarter. This has altered the hydrology of the wetlands by modifying the amount of water and the seasonality of flooding in the downstream wetlands.
Another variant of great impact is the extraction of groundwater for cities, industries, and agricultural activities, which leads to hydrological alterations in the wetlands and modifies their functioning (i.e. around Mexico City).
Actions that modify land use: unsustainable logging, for example of mangroves and floodplain forests; farming for agricultural production such as rice cultivation; construction and urbanization on wetlands using geotextiles.
Changes in the chemical composition of water or soil: modification of nutrient levels (increased nutrient inputs and eutrophication of water bodies), pollutants from agricultural, urban, industrial, mining, and petrochemical wastes.
Introduction of non-native species of flora and fauna, either accidentally or deliberately, for example, flood-tolerant fodder species, many of which come from the great flood plains. Some cases that are currently causing strong environmental problems are the water lilies (Eichhornia crassipes), the submerged aquatic Hydrilla verticillata, African forage grasses such as the German grass Echinochloa pyramidalis, the malaria mosquito (Anopheles quadrimaculatus), the Mozambique tilapia (Oreochromis mossambicus), fish of the loricariid family also known as plecos or limpia-peceras.
Among the indirect causes are:
Upstream human activities that cause siltation and eutrophication in downstream wetlands and result from agricultural runoff and erosion, respectively, due to deforestation and upstream land cultivation.
Climate: natural hazards such as erosion, subsidence, sea-level rise, drought, hurricanes, and other storms.
Trends of change and threats
Changes in wetlands have been documented primarily for mangroves, but much remains to be done for the other wetland types. In this section, the main demographic, economic, agricultural and pollution trends will be analyzed, and the threat they represent if they are not adequately addressed, that is, with a vision of sustainability.
A large part of Mexico's wetlands are coastal. In this sense, demographic changes and coastal zone development are having a significant impact on Mexican wetlands and the trend is upwards, as is the case on the coast of Quintana Roo and Jalisco. Mexico has had a high population growth rate, which has produced strong pressures on natural resources, both land, and water.
In recent years, population settlements on the Mexican coast have been changing, and in some regions in a very important way, with significant repercussions on the conservation and transformation of wetlands. In 1987 there were 126 coastal municipalities and 20 years later, 161. This speaks of an increase in the number of inhabitants and densification, as well as economic development in the coastal area. There are states where a high percentage of the population lives in coastal municipalities (especially those linked to tourism and services).
The increase in population in the coastal zone constitutes a threat to the wetlands since a good part of the urban and agricultural growth is occurring and will occur in these ecosystems through changes in land use. In addition, their loss puts the coastal population and the tourist developments themselves at risk, reducing the environmental services of protection of the coastline, containment of the salinization of the phreatic mantles, and disappearance of the zones of percolation and storage of the great water avenues produced by storms and hurricanes.
Mexico is a developing country that needs to diversify its activities, generate jobs, and raise the standard of living of its people. This has led to the promotion of important programs for the economic development of the coastal zone, which include energy generation, port development and growth, the establishment of new tourist enclaves, and corridors, such as Cancun-Tulum.
Many politicians and a good part of society consider that environmental protection impedes development. However, it has been seen that poverty is partly a consequence of environmental degradation. Today, powerful economic development often leads to a major transformation of nature. A relatively stable economy and politics are fundamental triggers for economic development, leading to the existence of large projects and funding for them.
The planning and implementation of these large projects are often based on inadequate environmental impact studies, with strong consequences for the environment, and Mexico is no exception. Environmental impacts are seen as a cumbersome procedure and not as a contribution to the environmental improvement of the project. Large development projects have produced direct and indirect alterations and this can be seen in coastal wetlands.
For example, in regions with strong pressure to develop tourist projects, such as the coast of Quintana Roo and more specific areas such as the Bays of Huatulco and Puerto Vallarta, many of the wetlands have disappeared and have been replaced by urban and infrastructure constructions. The damage produced by the hurricanes in Cancun has had strong economic costs, not only environmental. The expansion of the Port of Veracruz and the Port of Tuxpan are being financed on a strong impact on the Veracruzano Reef System and the mangroves of Tuxpan.
For Mexico, oil is the most valuable resource in the coastal area and the one that produces the most foreign currency. Since the eighties to date, more than 90 percent of oil and gas production comes from coastal states, from oil fields either in the coastal plain or in the continental platform of the Gulf of Mexico. This has brought the construction of road infrastructure, industrial plants, and urban developments to house incoming workers and a huge network of transportation pipelines. Much of this occurs over extensive flood plains, such as those in southern Veracruz and Tabasco. There is no assessment of the changes this has brought to the functioning of the wetlands and the various Mexican Official Standards of Pemex do not contemplate the mitigation of environmental impacts to these ecosystems.
Agricultural and aquaculture activities
The most widespread transformation has been due to the growth of the agricultural frontier, which has been slow but extensive. This has brought the slashing and burning of vegetation, the drainage and filling of wetlands to turn them into "fields suitable for productive activity". The consequences have been modifications in the composition of species, loss of biodiversity, and alterations in functioning. They often involve wetland drainage works permanently altering the hydrology. The low price of milk and meat for producers and extensive cattle management practices exert constant pressure on wetlands to incorporate them into productive cattle lands.
In the area of aquaculture, the main crop that has become widespread in the country is tilapia, a very aggressive species introduced from Africa and present in a large number of water bodies. It has been an economic benefit, but the cost has been the disappearance of many of the native species that could be important alternatives as well. Another one that has become generalized in states like Sinaloa, Sonora, and Chiapas is the cultivation of shrimp, using mangrove areas. Ecuador and the Philippines followed this path and had a short boom and then heavy economic losses in the shrimp industry, due to the loss of environmental services such as water cleaning and filtration, among others.
The trend towards urbanization is producing a greater generation of polluted water in human settlements, which is often collected in drainage systems and discharged at one or a few points. Sometimes there are treatment plants to receive them, but in most cases, they are dumped into water bodies and wetlands. The capacity of these systems to clean water, a service they have provided to humanity for hundreds of years, has been exceeded. At the municipal level, a considerable part of the funds are used to build infrastructure, including treatment plants (usually primary treatment only), but these are rarely in working order. Therefore, in the coming years, the trend is to increase pollution levels in wetlands, water bodies, and even groundwater.
The enrichment of the water by the nutrients carried overproduces changes in the composition and structure of the communities. Eutrophication leads to a change in algae populations and the explosion of populations of some phanerogams has also been related to this increased availability of nutrients (i.e. Pistia stratiotes, Typha domingensis, Eichhornea crassipes).
Increased vulnerability to climate change
The deterioration of wetlands from the above causes makes them more vulnerable to other types of impacts such as those of climate change. Both droughts and the increase in the quantity and timing of water are effects on the hydrology of the wetland, which produce alterations in its functioning. A degraded wetland has less capacity to respond to modifications in its hydrology. This results in a greater vulnerability of coastal populations to impacts such as storms and hurricanes. The modification of the hydrology has made the wetlands lose their capacity to function as sponges that retain and release excess water.
The future. Opportunities
The economic development of the country is fundamental, but it must be aimed at increasing and maintaining the well-being of the majority of society and never at increasing poverty or deteriorating quality of life. Therefore, the challenge today is to achieve growth that provides well-being and wealth, and that guarantees these same conditions for the next generations of Mexicans. The use of goods and services provided by wetlands to society is of great importance, so it is necessary to seek alternatives that allow economic development but also the maintenance of their functions.
This means the conservation of the ecological integrity of these ecosystems, defined as the capacity to support or maintain a natural and balanced biological system. It is necessary to work on options and strategies, such as sustainable development, to ensure that under the scenario of growth and development of the coastal zone, the biodiversity of the wetlands, their functioning, and the water source from which they feed, is preserved. There are various alternatives in several areas to move towards sustainable development, which can be used and focused on the use and conservation of wetlands and their environmental services, although it is necessary to strengthen them.
Planned socio-economic development
This legal instrument contemplated in the Mexican environmental legislation can generate planning at the municipal level of land use that puts limits to the changes that are produced for agricultural and urban purposes and that is accompanied by strategies and economic packages that encourage good management practices. This would guarantee that no infrastructure development takes place in wetlands and that conservation areas and buffer zones are established around the main wetlands.
Socio-economic development and projects to attract investment, as well as population migration to the coastal zone, should only be carried out based on territorial planning, which also lays the foundations for integrated management of the coastal zone. One of the main forms of mitigation for the impact of climate change on wetlands is adequate planning, through the creation of scenarios that allow the population's safety to be put before infrastructure development.
Alternatives for sustainable development
The National Development Plan proposes sustainable development as one of its objectives. As in the previous case, this is an important step. However, not all current environmental policies reflect this vision. It is necessary, on the existing legal basis, to work on mechanisms and strategies to implement sustainable development programs as true economic alternatives and to give weight to environmental issues, including the water cycle and wetlands. Likewise, the use of biotechnology should be encouraged to conserve and restore wetlands (water cleaning, erosion control, edge retention), as well as sustainable practices in aquaculture, agriculture, ecotourism, etc.
The agricultural frontier and good production practices
It is necessary to harmonize production practices with the conservation and sustainable management of wetlands. The introduction of exotic species should be done following justified monitoring and evaluation plans. It is essential to create a cross-section of environmental topics among the environmental, social, agricultural, forestry, and fisheries agencies.
Transversality in government institutions
A great weakness is that both in the various government departments and among the investors themselves, the idea that the project rules over the environment still prevails, and the latter has to be adapted to the needs. As long as there is no real recognition and acceptance that nature and ecosystems impose limits on development and growth and that projects must adapt to the environment, sustainable development cannot take place. It is necessary to work on mechanisms and strategies for mainstreaming environmental issues among the various secretariats and the three levels of government, and this is one of the main approaches to integrated management of the coastal zone.
Protection and conservation of wetlands
Biosphere reserves and natural protected areas. The increase in the number of federal and state-protected natural areas in the last 10 years has been very important. The category that has been most consolidated is that of Biosphere Reserves since most already have management plans, personnel, and budget. Further progress is needed for the other state and federal categories, in addition to establishing new protected areas in those regions that lack them.
One of the problems in natural protected areas is that the source of water that maintains the wetlands and the various links they have with other ecosystems are often not considered. Rivers, runoffs, or water infiltration areas that subsequently flow into wetlands are outside of protected natural areas. This makes these ecosystems vulnerable and somehow management plans must take into account this situation.
Incorporation of new wetland conservation and management concepts
Mexico has had great growth in the number of Ramsar sites. It is worth mentioning that more than a third of Ramsar sites also have another protection category, such as National Park or Biosphere Reserve. The category of Ramsar priority wetlands doesn't imply the need to buy or expropriate land, which allows, in a country with Mexico's population, the creation of areas with sustainable management that guarantees their conservation.
One of Mexico's commitments for each Ramsar site is to have a management plan, which must have a strong participatory component from the government and society (www.ramsar.org). This provides an important alternative for developing sustainable management plans for wetlands in all regions of the country.
Ad hoc legislation
Mexico requires specific legislation for wetlands, which guarantees the conservation of environmental goods and services provided by these ecosystems.
The lack of knowledge about these ecosystems in tropical areas, both at the scientific level and at the level of society, makes them one of the most threatened environments in our country. It is important to generate lines of work on various wetland issues, from hydrology to ecology and ecophysiology, and link them with multidisciplinary research schemes involving other areas of knowledge, i.e. anthropology, sociology, etc.
Evaluation and valuation of environmental services and inclusion in national policies
Wetlands provide many valuable environmental services to society, yet they are largely ignored by society and politicians, and negative externalities continue to increase. It is necessary to generate local information on these environmental services that integrate the views of the people and help to conserve the environment that gives them work, home, and food today.
Governance and conflict resolution among stakeholders
Social participation is fundamental in the conservation and management of resources and the environment. Wetlands are generally areas of conflict between sectors with different visions, i.e., drainage for livestock and urbanization versus water conservation and fisheries. It is important to create work forums (for example, for the development of management plans for Ramsar sites) and in a second stage to constitute networks of communication, relationship, and interaction, which gives sustainability to the processes.
Social awareness and environmental education
Nowadays, nature conservation cannot be conceived without the participation of society. It is necessary to bring the information closer to the different social sectors to have a participatory and responsible population for the relationship of society with nature.
Finally, the large number of stakeholders with interests in wetlands requires established national wetland policies, mechanisms for interaction, joint work and consultation, and structures for their implementation. This vision has not yet been implemented in Mexico, but it is a task in which we must all participate.
Integral planning that ensures the maintenance of environmental services in wetlands with the above-mentioned strategies, among others, constitutes an opportunity for our society. The instruments and actors exist; all that is required is the capacity and political will to turn them into an engine of opportunities and well-being.
Research and texts: Patricia Moreno-Casasola Barceló