Aquatic life at risk from people polluting rivers

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Paris: Rivers, lakes, and wetlands cover only one percent of the earth’s surface, but are home to nearly 10 percent of all species, including fish, mammals, birds, insects, and crustaceans. But these rich, diverse ecosystems are in free fall. Globally, species are declining faster than ever before in human history, and freshwater is losing more species than land or ocean ecosystems.

Today around one in four freshwater creatures is threatened with extinction. Wetlands are disappearing three times faster than forests. Water quality is falling worldwide, polluted by plastic, sewage, mining sludge, industrial and agricultural chemicals and much more. It is challenging to study how these pressures affect aquatic life. There are many different threats and river networks cover wide geographic areas. They often run through remote, almost inaccessible areas. Current techniques for monitoring freshwater species are labor intensive and costly.

In our work as researchers in ecology, we are testing a new method that can enormously expand biomonitoring: the use of environmental DNA or eDNA in rivers to catalog and count species. Federal and local authorities need this data to restore water quality and save dwindling species from extinction.

Traditional methods are slow and expensive

Using traditional biomonitoring methods, scientists only count individual species and their abundance at a few locations. For example, in a recent study of the effects of mining on fish in West Virginia by a team of four researchers, only four sites were sampled.

Collecting and identifying aquatic organisms requires highly skilled ecologists and taxonomists with experience in a wide variety of freshwater species. For every sample of fish or invertebrates collected in the field, it takes hours to weeks to identify all species. Only wealthy nations can afford this costly process.

To conserve threatened and endangered species and keep river ecosystems healthy, large areas must be monitored over time. Sensitive aquatic insects and fish species are the freshwater equivalent of the proverbial canary in a coal mine: the absence of these species is a strong indicator of water quality problems. The cause can be mining, agriculture, urbanization or other sources, as well as dams that block the downward movement of animals.

Free floating genetic evidence

Innovations in genetic engineering have created a powerful, affordable new tool that we’re now testing. The process involves extracting eDNA from genetic material floating in the water – skin, scales, feces, and unicellular organisms such as bacteria.

By analyzing this genetic information, we can identify a wide variety of species. We started considering the use of eDNA for our research in 2018 after several studies showed that they could monitor individual species or groups of organisms in rivers and oceans.

Collecting eDNA is easy: one 4-ounce water sample can collect residual DNA from thousands of water species. Another benefit is that there is no need to kill wildlife for identification.

In the laboratory, we analyze the DNA of different taxonomic groups one after the other: bacteria, algae, fish and macroinvertebrates – organisms that have no backbone and are big enough to see, like snails, worms and beetles. Many researchers only study one group, but we evaluate them all at the same time.

Then we compare our DNA sequences with freshwater species that are already cataloged in existing databases. In this way we can map the distribution and abundance of these organisms within and between rivers.

This process only requires a cheap filter, syringe, and vial, and anyone can do it. Commercial eDNA companies charge less than $ 200 to extract and sequence a sample.

Changed rivers

Using this method, we and a team of four extensively examined 93 rivers in West Virginia in two days – and examined the entire tree of life, from the smallest bacteria to fish.

The Appalachian rivers we are studying are full of life. These are some of the most biologically diverse freshwater ecosystems in the world, home to many species of fish, as well as salamanders, crabs, clams, and aquatic insects. Many cannot be found anywhere else. We counted more than 10,000 different species in these 93 waterways.

The area we have been working in is an intensive coal mining area that has a major impact on the waterways. Liquids draining from mines are acidic, but in this region they react with limestone so the net effect is to make local streams alkaline. Mine drainage also increases the salinity of the streams and levels of sulfate and other contaminants. Our research found that mined watersheds contained 40 percent fewer species than areas without mining operations, and the organisms we discovered were less abundant than in unaffected rivers.

Assessment of river health

We believe this new approach will revolutionize biomonitoring and expand our ability to quantify and study freshwater life. It’s also an important new conservation tool that enables scientists to track changes in populations of endangered or invasive species. Researchers can also use eDNA to monitor biodiversity or discover new species in oceans or soils.

This open science method makes all DNA data generally available, with almost all sequences being stored in public repositories. In the future, we expect it to support many types of research, as well as government and local monitoring and conservation programs. Investing in collecting eDNA and identifying organisms and analyzing their genetic signatures will continue to make it a more effective tool.

Efforts are being made to better control various individual species, with an emphasis on endangered species, invasive species that damage ecosystems and sensitive species that serve as indicators of river health. Scientists freeze eDNA samples at -112 ° F (-80 ° C) in the expectation that advances in technology could provide more information in the future.

Traditional approaches to surveillance remain valuable, but eDNA adds an important new tool to the toolkit. Together, these approaches can answer many questions about food webs, species conservation status, reproduction rates, species interactions, organism health, disease, and more.

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Posted on: Sunday September 19, 2021 12:18 AM IST


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