Johnson County Wastewater officials are attributing a large kill off of fish in area creeks northeast Johnson County to a natural phenomenon known as “turnover.”
Residents and city officials first began noticing small dead fish popping up in the creek May 11. The problem was especially apparent in the creek outside the entrance to Kansas City Country Club on Mission Lane in Mission Hills, where a sewer main causes water to slow, catching debris and dead fish in the process. Mission Hills City Administrator Courtney Christensen said that officials from Johnson County’s Environmental Division, Johnson County Stormwater, Kansas Fish and Wildlife, Kansas Water Resources and the Environmental Protection Agency were all involved in the investigation into what caused the kill. She said that the city was informed that water tests revealed no chemicals that could have cause the problem. Instead, the researchers say the fish died due to lack of oxygen in the water.
Tony Holt, Directof of Johnson County Wastewater’s Water Quality Laboratory, provided this explantation of “turnover,” and how it strips oxygen out of the water:
Turnover is a natural spring and fall phenomenon that occurs in response to temperature changes – particularly rapid shifts of temperature and wind. Over the winter, the water in deeper pools stratifies into cold top and warmer bottom layers. The bottom layers collect organic debris and become anoxic, or almost anaerobic. Bacteria that thrive in anaerobic conditions live in and under the debris, producing waste products that include hydrogen sulfide and other bad smelling gasses. The bottom layers are very dark colored. Since the bottom layer is warmer and somewhat less dense than the top, the stratification is unstable – that bottom water layer wants to rise.
When the weather conditions are right, the top and bottom layers mix. All the nasty looking and smelling material, bacterial waste products and gasses from the bottom layer of water come up to the surface. These materials rapidly absorb the oxygen in the stream so that the fish have nothing to breath. If the fish can’t escape, they will die. This condition lasts for a few days in small streams and longer in lakes. Once the water layers mix, wind and air from the atmosphere supply oxygen (replace it). The black material from the bottom settles again and the shallower water becomes high enough in oxygen to support fish again.