Human impacts on streams and rivers
Watercourses vary in size from tiny streams you can straddle, to large rivers that are visible from the moon. On a regional scale, streams and rivers connect landscape types and provide corridors for migration of animals and humans, and dispersal of energy and organisms. On a local scale, streams and rivers provide ecosystem services such as habitat, temperature regulation, nutrient retention, water and food for many organisms, including humans. Human activities during the last few centuries have led to worldwide ecological degradation of the valuable freshwater ecosystems. Below, we give examples of six impact types, many of which interact:
A. Alteration of flow and water level regimes
Damming and regulation of flows and water levels can provide renewable energy, but modification of flow and water level regimes reduces biodiversity levels and affects important ecosystem processes, such as nutrient cycling and sediment dynamics. In addition, dams fragment the streams and rivers, disrupting natural corridors, for example the pathways for fish migration and plant dispersal.
B. Habitat loss
In addition to damming, many streams and rivers are facing increasing pressures from other physical impacts, such as channelization, urbanization, forestry and agriculture. These activities have substantially decreased the available habitats for many types of organisms, and are reducing the biodiversity of freshwater ecosystems.
Fish is an excellent source of protein, and fishing is the principal livelihood for millions of people around the world. Overfishing occurs when fishermen catch more fish than the population can replace through natural reproduction. Overfishing threatens the existence of some species and affects the food chains of entire ecosystems.
D. Exotic invasion
Humans introduce many exotic species that can spread to water bodies and their riparian zones and become invasive. Their development constitutes a big threat to local, native communities and ecosystem dynamics.
Pollutants in streams and rivers come from point sources, such as industrial and sewage treatment plants, and non-point sources, such as land runoff, atmospheric deposition and seepage. Pollutants in streams and rivers affect water quality, spread diseases, destroy ecosystems, disrupt food-chains and kill or injure organisms.
F. Climate change
Climate change affects streams and rivers in many ways. Rising temperatures increase evapotranspiration, modify water quality and threaten biota. Normally ice-covered streams and rivers will face a shorter and more variable ice season, and more precipitation will fall as rain instead of snow. Changing precipitation and runoff patterns modify flow and water-level regimes, with consequences for fluvio-geomorphological processes, water quality and biota. For example, non-native species will be able to expand their ranges, in many cases to the detriment of the native species.