Firstly, let’s define an ecosystem. An ecosystem is the interaction of abiotic and biotic factors that intersect in a particular environment. The abiotic factors are elements such as substrate, pH value, and temperature, and the biotic factors consist of plants, animals, and microorganisms.
Specific combinations of living organisms and their environment are what shape all ecosystems on the planet. Of these, river ecosystems cover less than 1% of the Earth’s surface, however, they support an incredible plethora of biodiversity and provide the surrounding areas with valuable services.
Follow the Flow of Water
The river ecosystem is one of the most dynamic ecosystems in the world. It is primarily defined by flowing water, with the natural flow regimes being directly linked to the ecological processes. The strength of the water flow varies, often many times from headwater to mouth, but also throughout the year with increased flow following heavy rainfall and snowmelt. The flow of the water shapes the riverbeds, forming many different microhabitats, which are home to a variety of species. Therefore, another defining characteristic of the river ecosystem is a ‘state of continuous physical change’. The chemical properties of the river also change between different rivers and within the same river system, with the substrate sometimes being dominated by inorganic material such as pebbles or organic material such as leaves.
Around 3.5 million miles of river run across the United States. They are typically separated into three distinct types of habitats: riverbeds, riverbanks, and floodplains. They play a fundamental role in connecting habitats, both across the river and by connecting upstream and downstream areas. Due to their everchanging properties, they house many more species than the area they cover hint at, making rivers host to 6% of all described species.
A Service Only Nature Can Provide
In addition to being hotspots for biodiversity, rivers are also hubs of human activity, and the river ecosystems serve us in many ways. Think of things like access to drinking water, transportation, hydropower stations, and recreational activities such as fishing. All these different services are known as ecosystem services; a service that nature provides for us.
The river ecosystem services can be categorized as material, non-material, and regulating. We might tend to first think of rivers as providing us with food, but on a weekend fishing trip, a number of these services could come into play. Material services are food, material goods, and health & genetic resources. Non-material goods are recreational, cultural, and educational services; one might immediately think back to a school fishing trip.
The processes we tend to oversee are the regulating services. However, regulations such as climate regulation can have positive effects on greenhouse emissions. Rivers also provide flood protection, and as the floodplains absorb water, it trickles down through the ground, providing us with an essential water source regulated by river flows that gets filtrated and purified in the process.
The Good With the Bad (and the Ugly)
Throughout history, our lives have been tightly connected to rivers. We have built our towns at their banks, transported our goods on their waters, and slowly but surely altered them to fit our needs. However, some of the alterations can degrade the river system.
Take dams, as an example. While they can provide us with benefits like hydropower, flood control, and water storage, they alter the natural flow of the river and can disrupt the migration patterns of fish. In extreme cases, they completely cut off species from their spawning grounds. In addition, they change the nutrient cycle by altering the amount of water and sediments that flow downstream.
Another significant threat to river ecosystems is pollution from cities or agricultural run-off. Untreated human waste in water systems can also increase the disease risk for wildlife, husbandry animals, and humans alike. Run-off can alter the natural nutrient levels and introduce toxic chemicals that degrade water quality. Frequently, nutrient pollution stimulates primary production, which can lead to ‘dead zones’.
These are areas where a large algae bloom has died down, and now the following decomposition process consumes oxygen to such a degree that marine life cannot survive. The second largest of these dead zones in the world is in the northern Gulf of Mexico, within the U.S.
The Challenges & How We Try to Solve Them
One of the primary challenges concerning the protection and conservation of the river ecosystem is related to the spatial distribution of the river. A river system is the continuum of flowing water from headwater to arrival at sea. Many different factors are likely to affect the river on the chemical and physical level throughout its course. These factors could be the straightening of the river, agricultural runoff or other waste products, dams, or cities. Upstream processes have major effects downstream. Additionally, rivers might also run through different states or countries with different policies on river management.
Historically, rivers have been managed on a more local scale, targeting the direct challenges at hand such as restoration of floodplains and removal of dams. By restoring the natural conditions, local fish populations can prosper and erosion & extreme flooding can be reduced. Recently, this focus has been shifted more towards larger scales of management. One of these management strategies is the implementation of ‘functional flows’. These are managed hydrographs (the water discharge over time) that reproduce the natural water flow while balancing human water needs. The challenge with this sort of management is the construction of the hydrograph to replicate both the temporal variation in water flow and the magnitude.
An area where this management form has recently been implemented is the California Central Valley (CCV) river system. Here, the focus is on retaining the functional key components of water flow, which among other species support the steelhead (Oncorhynchus mykiss), an anadromous member of the Salmonidae family.
The increased temperatures in the CCV and the construction of multiple dams have led to a more than 82% decrease in the historic steelhead habitat. The homogenization of the natural dynamic hydrographs impacts spawning migration for adult steelhead, which is typically carried out during periods of high flow. Monitoring efforts have provided an understanding of the natural movement of the species in relation to water flow, and this knowledge is now applied to construct fall pulse flows and wet-season base flows, which are both important for migration.
What Can We Do?
Large-scale management such as functional flow approaches is unfeasible to undertake for single individuals. However, there are many things you can be aware of on a private level. Always make sure to leave no trace: dispose properly of your trash and make sure to not disturb the natural habitat when visiting your local river. Ensure the proper disposal of chemicals and medicine, limit the use of pesticides and fertilizers, and avoid introducing new species to an ecosystem. Additionally, you can join local initiatives such as river clean-ups and spread awareness of river ecosystems in your community.
Rivers are incredible and intricate systems that we should navigate with care. However, we should not forget to enjoy, have fun with, and utilize the services they provide us.
