Urban Floodplains: Fragile and Poorly Protected Ecosystems

Urban floodplains are wetland areas in the city, created when water levels in a nearby river rise, overflow the river’s banks, and temporarily flood local, low-lying areas. This flooding primarily happens during the rainy season. Even if you are a city dweller, you may not have noticed urban floodplains before—but these watery areas are like secret ecosystems right in the middle of the city (Figure 1). Understanding urban floodplains and the benefits they provide can make us feel more connected to these incredible environments and motivate us to protect them!

Urban floodplains are vital areas for a wide variety of species, including fish, amphibians, reptiles, birds, and mammals, in addition to aquatic invertebrates (Figure 2A). These areas provide habitats essential for the reproduction, shelter, and feeding of all these animals. Floodplains are particularly essential ecosystems for fish, as the young forms of many migratory fish species, such as the Curimbatá in South America, develop there. Several species of fish live in urban floodplains during rainy periods when the river level is high, and others live in the floodplains throughout their life cycles (Figure 2B). During the dry season when there is no flooding, fish can live off of fat reserves stored during the rainy season, and they can shelter in the pools of water that do not dry up. They can also move to more suitable areas [1, 2].

One of the fundamental components for the maintenance of urban floodplains is the presence of water plants known as macrophytes. They play important roles in floodplains by providing habitat, adding oxygen to the water, and filtering the water [3]. Additionally, macrophytes serve as food for fish, terrestrial (land-based) invertebrates, aquatic invertebrates, algae, and tiny organisms called phytoplankton and zooplankton.

Urban floodplains act as natural filters, cleaning the water and removing harmful substances like excess sediment, chemicals and nutrients in high concentrations (such as nitrogen and phosphorus), which can cause water to become humid and algae to grow [4]. Despite their biodiversity and environmental services, many people see urban floodplains only as problem areas, prone to flooding, and would rather see them filled in and developed. Understanding and protecting floodplains is crucial to the health of our urban environments. If we can get people involved in this cause, we can help ensure that these incredible places continue to be an important part of our urban landscapes.

Ecosystem Services Offered By Urban Floodplains

Urban floodplains provide four basic types of ecosystem services, which are benefits that nature provides for human beings [5, 6]. First, they provide clean water, food resources (organic matter, insects and other invertebrates, aquatic plants and algae, fish and amphibians, fruits, and seeds), and ecosystem services of economic value. Second, they can help to prevent populated areas from flooding and can reduce erosion (a natural process of soil wear), which contributes to soil protection, riverbank stability, and the preservation of urban and rural infrastructure. Third, they provide cultural benefits—these areas can be beautiful, and they can be spaces for leisure activities, tourism, and environmental education. Finally, urban floodplains provide important homes for biodiverse plants and animals [7, 8].

The Sorocaba River as a Model for Environmental Education

The Sorocaba River is an important river in the State of São Paulo, Brazil. It is a main tributary of the Tietê River [9]. Along this river, one can find hundreds of floodplains in both rural and urban areas. These ecosystems are either permanent or exist only during certain times of the year [10]. The urban floodplains of the Sorocaba River are close to residential neighborhoods and places where they can be easily accessed by the local community.

As part of its efforts to teach individuals about the importance of preserving the Sorocaba River, Brazil’s Department of the Environment established the Sorocaba River Field Trip [11]. This field trip was divided into three schedules according to the age group and the audience involved. Participants’ previous knowledge was also taken into consideration. The first script was aimed at teenagers and adults, the second at schoolchildren, and the third was intended for special groups like elderly or people with disabilities.

Field Trip to the Floodplains: A Strategy for Their Conservation

Considering the previous environmental education actions related to the Sorocaba River, we propose that a similar field trip could be created for urban floodplains, which could be used by any urban area that contains these environments (Figure 3).

To get people interested and select an audience, we first need to create a visit schedule and publicize it to reach as many people as possible. City governments and local universities can help us develop the plan and get the word out. After the field trip is completed, it will be interesting to write up the results and publish them, so that more people have access to the information from the field trip, and so that the municipality can monitor the evolution of the project through the perspective of educators and visitors.

Details of the Sorocaba Field Trip

In the case of Sorcaba, we proposed a field trip route through several nearby urban floodplains, using those existing in the municipality as a model. Five floodplain areas were selected according to the environments that would be most suitable for teaching people about urban floodplains—each of these floodplains presents a different type of environment, so people will have something new to learn in each. At first, we will have one set script for the guide, which can be modified slightly according to the participating audience. Later, the script can be adapted for specific audiences, such as schools, audiences with greater knowledge on the topic, or teenage audiences, among others.

In each floodplain visited, a different and specific aspect will be addressed. In flood plains where fishing is widely practiced by the local people, the field trip guide can discuss the fish and other species present there. In an area that is or was formerly polluted by release of sewage into the river, the guide can address the importance of keeping the water clean, both for public water use and for the health of the floodplains. Furthermore, guides can discuss the environmental impacts that happen when floodplains are healthy and cared for and when they are not, such as the dangerous overgrowth of macrophytes that can happen when the water becomes polluted with domestic waste. Additionally, they can explore how the level of connection between a floodplain and the river influences biodiversity, affecting the abundance and variety of species in the ecosystem.

Final Consideration

Exploring urban floodplains with a focus on the health of the fish population the floodplains’ importance in the survival of the river and local biodiversity teaches people about their connection with the natural landscapes of the urban environment. Through a tour of local floodplains, children can learn about the importance of aquatic ecosystems and how they can contribute to conservation of urban wetlands. Children can share their new knowledge with their parents, siblings, and friends, spreading awareness and helping to ensure the protection of these environments. In this way, children can become true guardians of urban wetlands—areas that are vital both for nature and for people.

The proposed field trip will be an opportunity to publicize the importance of urban floodplains, and hopefully the effort will bring various benefits to the people in those cities. Involving children in this process will help them develop a connection with the environment, increasing their knowledge and environmental awareness and encouraging them to take steps to protect and restore these vital habitats [12, 13].

Glossary

Floodplains: ↑ Areas near rivers that get covered with water during floods.

Invertebrates: ↑ Animals that do not have a backbone, such as insects, mollusks, crustaceans, and worms.

Macrophytes: ↑ Aquatic plants that can be seen without a magnifying glass, important for ecosystems because they provide shelter for other living things and help keep the water clean.

Biodiversity: ↑ The variety of living things on Earth, like different types of plants, animals, and microorganisms.

Ecosystem Services: ↑ Important benefits that nature gives us, like clean air, clean water, and food.

Environmental Education: ↑ Learning about the environment to motivate people to take care of and protect nature.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

The authors would like to thank the Postgraduate Program in Environmental Engineering Sciences at São Carlos School of Engineering - USP for the development of this work and Laboratório de Ecologia Structural e Functional de Ecossistemas - UNIP campus Sorocaba for the logistical support. To Prof. Dr. Francisco Langeani for the identification of the species and deposit in the Fish Collection of the Department of Zoology and Botany of the State University of São Paulo “Júlio de Mesquita Filho” São José do Rio Preto, SP (DZSJRP), to André Luis Minghêti Puga for his assistance in all fieldwork, the CAPES Process 1681410 scholarship granted to the first author, the CNPq Process 130957/2023-2 scholarship granted to the third author and the Vice-Rector of Postgraduate Studies and Research for the scholarship to the fourth author.

AI Tools Statement

The authors would like to acknowledge the use of DALL-E by OpenAI for generating the images in this study, facilitated by the assistance of ChatGPT.