Sarah Davis climbs into a small metal fishing boat at the edge of a one-acre pond near Wilmington, North Carolina. She paddles the boat until the swirling mud is too deep to see and then grabs a small capped vial from her pocket. An N.C. State graduate student in the department of crop science, Davis wants to know if this pond of effluent water—wastewater pumped from the city’s sewage treatment plant—is killing the turf on the golf course surrounding it.
Findings from her research, led by plant physiologist Danesha Seth Carley and published in 2009 in International Turfgrass Society Research Journal, show that the treated water may harm the grass. Those findings also show that what Carley feared the most—salt toxicity—was not a problem. However, nutrients from the effluent water may have an unwelcome effect: attracting pests.
Effluent, or treated water, has traditionally been piped from the sewage treatment plant directly into nearby lakes and streams. To limit the amount being added to freshwater systems, some municipalities are finding other uses for it, such as irrigation.
“When done properly, effluent water is perfect for irrigation,” says Carley, a specialist in turfgrass physiology. “The grass filters the water and keeps excess nutrients from winding up in lakes and streams.”
Because the arid climate and populated cities strain drinking water supplies, municipalities in several western U.S. states have transitioned to landscaping with effluent water. However, scientists in Arizona have found that the water increases the salt content of the soil, creating the potential to kill the turf. Without living plants to absorb the water and filter excess nutrients, water pools on the ground, creating runoff and erosion problems.
So when several North Carolina communities began requiring golf course superintendents to irrigate their turfgrass with effluent water, Carley and a team of plant physiologists and soil scientists from N.C. State University decided to take a closer look at the chemical makeup of the water.
In her lab in the crop science department, Carley takes the liquid contents of the tubes that Davis has brought her and analyzes them with a carbon/nitrogen analyzer. The machine consists of a computer that looks like it’s been salvaged from the 1990s, hooked up to a series of tubes and vials. N.C. State researchers have collected samples from numerous wastewater retention ponds over an 18-month period, from January 2006 to May 2007.
Rows of numbers appear on the monitor screen. The machine has returned data results for sodium, phosphorus, sulfur, nitrogen, magnesium, calcium and carbon. The data give Carley good news—the salinity of the water is at levels tolerable for turfgrass. Only in severe drought would the salt content of the water cause salt toxicity to the turf roots.
However, the high nutrient content, combined with the salts, create a friendlier environment for bacteria and other pests to grow.
“Nutrients increase fungi, bacteria and insect populations in the soil,” Carley says. Some of those insects attract other pests, such as skunks, an unwelcome addition to both the home landscape and the golf course.
Does use of effluent water ultimately mean more skunks in the landscape? Not if soil nutrients are balanced, says Carley. A soil test will indicate how much—if any—fertilizer is necessary.