It’s easy to get excited about new science: new discoveries, cool things that have never been seen before, a new solution to an old problem. But sometimes, it’s worth taking a step back to look at what’s been done before, and how history can inform future research.

The U.S. Geological Survey (USGS) has been collecting information on western Lake Erie benthos – the mollusks, snails and worms that live in sediments on the lake bottom – since the 1930s.

Many of these organisms are considered indicators of an ecosystem’s health, so determining changes and trends over time can help management agencies like the Environmental Protection Agency (EPA) evaluate and track the effectiveness of strategies to protect that health.

With data from 1930, 1961, 1982, 1993, 2010 and 2014, USGS researchers like Don Schloesser have a lot to work with, but progression in identification techniques and microscopy means that first the information has to be adjusted to make numbers directly comparable. That means, for example, that if early data only gets as specific as the genus of a mollusk, instead of identifying it down to a specific species, scientists adjust later data accordingly, even if it’s more detailed, to conform to a lowest common denominator.

While the final numbers are still being compiled and standardized as part of the 2014 Cooperative Science and Monitoring Initiative (CSMI) focus on Lake Erie, some general trends in benthos populations have already emerged.

Researchers measure benthos by the number of organisms found in a square meter of sediment, and from 1930 to 1982, those numbers increased dramatically, from 2,000 to almost 146,000 on average. That increase was likely due to the abundance of nutrients found in Lake Erie at the time – those nutrients feed algae, which in turn feed the worms that make up the majority of Great Lakes benthos and tend to indicate poor lake health.

From 1982 to 2003, benthos populations dropped by more than 80 percent, mainly due to pollution reduction efforts that removed nutrients from the environment, as well as increased water clarity caused by zebra and quagga mussels that invaded the lake in the mid-1980s. But by 2014, those numbers had climbed back up, creating a zig zag pattern that closely follows trends in nutrient runoff and algal blooms in the lake and potentially indicates a recurring trend toward excess nutrients. To arrive at those population estimates, researchers took sediment samples at a number of established sampling sites across the western basin to make sure results were directly comparable to previous years’ sampling trips.

They use a ponar grab sampler, which looks a lot like a smaller version of the clamshell grab on an excavator, to pull up sediment from the lake bottom. They then rinse that sample through a fine mesh screen to remove fine silt and clay. Whatever stays on the screen is preserved and taken back to the lab, where it will be further separated into the various benthic sub-groups – mollusks, worms, midges and other benthos – in which the scientists are interested.

Some of that separation can be done by hand, using tweezers and strong lighting. What’s left over is put under a microscope to pick out the smallest organisms. Once everything is separated and preserved in individual vials, those vials are sent off to experts who can identify the collection of mussels or worms more specifically. It’s a long and arduous process, but it provides valuable information to those monitoring and working to preserve the health of the Great Lakes for future generations.

One particular type of benthic organism, the mayfly, has been used as a key indicator of environmental health by agencies like the Ohio EPA to assess how Lake Erie and the other Great Lakes are faring over time. Mayflies require very clean water to breed and begin their life cycle in lake sediments, where they live until the adult mayflies hatch into the swarms many visitors to Lake Erie are familiar with. In western Lake Erie, mayfly populations dropped to essentially zero between 1959 and 1961, and remained extremely low until 1993, when scientists found about twelve mayfly larvae per square meter of sediment. Most recently, those numbers have increased dramatically, to 300-400 mayflies per square meter, a testament to environmental protection efforts and improving water quality.