Long-term Farming Practices Change Impacts Stream Water Quality

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Long-term Farming Practices Change Impacts Stream Water Quality

In the early 1990s, Acton Lake in southwestern Ohio had a muddy problem. Large amounts of sediment from nearby farms were entering the lake’s watershed. These sediments traveled through streams draining the landscape and were filling up the lake.

By Adityarup “Rup” Chakravorty

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The inside of the automated sampler on Four Mile Creek, with the carousel of bottles used to collect water samples. The PVC pipe to the left houses a pressure transducer connected to a data logger and records the stage (height) of the stream water every ten minutes for a continuous record of stream flow. Photo credit Carrie Ann Sharitt.

 

So, the USDA gave local farmers incentives to change some of their farming practices. One of these practices was conservation tillage, in which the soil is plowed less often. That can reduce sediment runoff.

A new study examines how the switch to conservation tillage has impacted Acton Lake over the past decades. From 1994 to 2014, the researchers measured concentrations of suspended sediment, nitrogen, and phosphorus in streams draining into Acton Lake.

“We find that short-term trends in water quality may not reflect long-term changes,” says study co-author Michael Vanni.

Tracking changes in water quality over the long term is vital, says Vanni, a biologist at Miami University, Ohio. “We don’t have a lot of long-term information on how water quality in a stream or lake responds to agricultural change,” he says.

That might be surprising since many ecologists study agricultural watersheds. But according to Vanni, studies on a given ecosystem are usually short term. “Long-term studies, like ours, can reveal important shifts in water quality,” says Vanni. “Many of the changes we observed can only be seen after studying the streams for 20 plus years.”

Vanni and his colleagues found that water quality responses were different during the first decade of the study (1994-2003) compared to the next (2004-2014). They also discovered that concentrations of suspended sediment, nitrogen, and phosphorus each reacted differently.

Levels of suspended sediment declined throughout the entire study period. However, the decline was much sharper in the first ten years. 

Phosphorus and nitrogen levels had contrasting outcomes. “The concentration of dissolved phosphorus in the streams declined sharply during the first ten years,” says Vanni. “But then, phosphorus levels increased over the next ten years.”

Read the full report on the American Society of Agronomy

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