Bio-Physical Impacts of Urbanization on Aquatic Ecosystems

Urbanization has a significant impact on the environment and natural resources, and affects not only the immediate area of urban settlement but a larger peripheral expanse of land and water. A 2008 study published in Frontiers in Ecology and the Environment describes land use, and specifically urbanization, as second only to climate change in its role in altering the structure, function and health of aquatic ecosystems. Urbanization creates water pollution and degrades water quality, and impacts the biophysical structures of aquatic ecosystems in several ways.

Physical Impacts

• Urbanization can alter the physical dimensions of a body of water and thereby alter the aquatic ecosystem. Water resource planning and management for urban areas can include practices such as building dams, rerouting rivers, erecting sea barriers and draining wetlands. Tiffany Garrett of the Environmental Biology Program at Governors State University explains that all of these practices directly affect the balance of life in aquatic ecosystems and can disrupt the complex, interdependent relationships among animals, plants and organisms. Changes to the physical structure of aquatic ecosystems can alter water quality, such as by closing off channels to fresh water sources, and change the composition of subaquatic ground surfaces. These changes directly affect biodiversity and species' viability.

Biological Impacts

• In the textbook Fundamentals of Urban Runoff Management, Richard Horner describes the biological effects of urbanization as including changes in sediment composition and significant decreases in the population of sensitive organisms. Biological alterations affect the health of fish species and plants, and in turn impact the feeding patterns of the species residing in the aquatic habitat. Additionally, changes in sediment, or ground surface cover, or in the distribution of aquatic plant life affects reproductive behavior and the survival of eggs, and thus potentially alters the balance of species.

Pollution

• Although most water pollution is caused by the introduction of chemical compounds into aquatic environments, pollution results in biophysical changes in the ecosystem. Urbanization introduces pollutants into water systems by a variety of means, including dumping, runoff, industrial spillage and acid rain. Pollution alters the pH level, degrades water quality and causes harms that radiate along the food chain. For instance, plant-feeding fish are often more sensitive to certain chemicals, such as mercury, which is commonly found in urban aquatic ecosystems. When fish feed on plants, they consume trace amounts of mercury, which affects their health and population size. If their population diminishes, that loss affects the feeding practices and viability of their predators, who then seek out new sources of prey for food.

Population Pressures

• Urbanization also affects the biophysical composition of aquatic ecosystems by overusing water resources for domestic and industrial purposes. Freshwater ecosystems are particularly affected by population demands for drinking water and agricultural uses. If the size of the population exceeds the limits of the available water resources, urban demands can exhaust water supplies, thereby destroying aquatic ecosystems. Rising population pressures affect not only immediate aquatic ecosystems, but also distant environments, as urban settlements seek out resources to satisfy their growing demands.