As fall arrives in central Illinois, the trees' leaves will change in color. Ponds undergo changes too. In the fall, ponds experience something referred to as the fall turnover.

The fall turnover in ponds is caused by a mixing of the water from the surface to the bottom of the pond. Throughout the year, the density of the water in a pond changes as the temperature changes. Water reaches its maximum density when it is 39 degrees Fahrenheit. As temperatures either drop below or rise above this temperature, the density of the water lessens.

Therefore layers of water develop in the pond during the summer, each with a different density caused by temperature. The top layer of water in the pond is the warmest and least dense layer. The bottom layer of water in the pond is the coolest and denser than the other layers. In between these two layers is somewhat of a confining layer which doesn't allow the top and bottom layers to mix during the summer.

In the fall the water in the top layer cools and when the water is approximately the same temperature throughout the pond, mixing occurs and is referred to as the fall turnover. Water temperature is just one change that occurs in a fall turnover. Oxygen holding capacity increases too, because high temperatures reduce the capacity for holding dissolved oxygen.

However, the change that pond owners notice is the color of the water during a fall turnover. Typically the water suddenly turns brown and somewhat murky. Some people describe the water as being stained. The color is related to organic material that has been in the bottom layer of the pond throughout the summer and is now distributed throughout the pond from top to bottom.

Generally, after several days the water clears up because of the settling of the organic material. The fall turnover is usually not harmful to aquatic life in the pond because even though it appears suddenly, it is a gradual change within the pond, but the color sometimes alarms pond owners. An understanding of seasonal changes and natural interactions that occur in your pond can help you better understand how management inputs, such as vegetation management affects the pond.

The University of Illinois Champaign Extension Unit will host a Twilight Pond Walk to help you better understand your aquatic resource on September 2^nd, from 5:00 to 7:00 pm. The workshop is a result of a collaborative effort between the Champaign County Soil and Water Conservation District, Illinois Department of Natural Resources, Champaign Park District and the University of Illinois Champaign Extension Unit.

The workshop will begin at the University of Illinois Champaign Extension Unit in the auditorium at 5:00 pm. The Champaign Extension Unit is located at 801 North Country Fair Drive in Champaign. The educational presentations will be conducted at two nearby ponds through a walking tour to the pond locations. Mike Garthaus, IDNR Fisheries Biologist and Dave Shiley, U of I Extension, will present information on fisheries management, vegetation management, nuisance wildlife issues, tree selection and best management practices around ponds. Bruce Stikkers, Champaign County Soil and Water Conservation District will be on hand to discuss erosion and sediment control.

There is a $10 per person fee for this workshop which can be paid at the door or your can register online. Please dress appropriately, as we will be standing and walking the majority of the seminar. For more information contact the University of Illinois Champaign Extension Unit at 217-333-7672.