Utah Lake: Shallow Lake Ecology

>   The pristine state for most shallow lakes is a clear water state (top) with a rich array of rooted aquatic plants called macrophytes. Utah Lake's current state is a turbid water state (bottom) driven by single-celled algae (phytoplankton) production.










Utah Lake has always been a shallow lake. Shallow lakes like Utah Lake typically have the potential for two stable ecological conditions. One is a clear water state with a rich array of rooted aquatic plants (macrophytes), and the other is a turbid water state driven by single-celled algae (phytoplankton) production. The pristine state for most shallow lakes is the clear-water state. Disturbance can cause a lake to shift from one state to the other. However, once in a stable ecological state, a lake has a tendency to remain in that state.

Through impacts associated with human population growth, many urban shallow lakes, such as Utah Lake, have been disturbed into a turbid-water state. The progression of clear-water shallow lakes to a turbid state occurs in recognizable patterns. As a result of increased human population growth, nutrient loading to the lake increases, which then triggers an increase in phytoplankton abundance. Aquatic plants become covered with a thin layer of algae that inhibits their ability to phosynthesize. Increased single-celled phytoplankton in the water column reduces light penetration and as shading increases, aquatic vegetation eventually collapses.

With rooted aquatic vegetation gone, the aquatic insects associated with the vegetation disappear along with the animals, fish, and birds that feed on those insects or plants. The refuge that the aquatic plants provided from predation for everything from single-celled aquatic animals (zooplankton) to small fish is also gone, which results in major shifts in predator/prey relationships because of increased vulnerability of prey species.

In the absence of the refuge provided by aquatic plants, large zooplankton disappear as a result of increased predation. The disappearance of the zooplankton, which feed on single-celled plants (phytoplankton), coupled with nutrient increases further elevates phytoplankton biomass. Without aquatic plants, near-shore wave activity is not suppressed and sediments typically anchored by their roots become suspended in the water column and add to already increased turbidity.

The aquatic invertebrate community becomes dominated by bottom dwelling insects like midges (evening midge hatch on Utah Lake is evidence of this). Then, the fish community becomes overrun by bottom feeding species such as carp. The digestive activity of bottom-feeding fish promotes nutrient flux from the sediments into the water column, and their foraging behavior (digging around in the mud in search of food) significantly contributes to re-suspension of sediments, which further contributes to high turbidity.

Reflecting on Utah Lake, disturbances that likely contributed to its existing state include elevated nutrient loading from agricultural runoff and sewage disposal, the introduction and establishment of common carp, and water level fluctuations associated with water management. These three factors affected the survival of rooted aquatic vegetation, which provided the refuge that maintained a stable ecological community.

Large lakes like Utah Lake have the potential for both clear and turbid water states to occur together in the same lake. Large, offshore areas experience wind-driven turbidity; while near-shore areas, embayments, and river deltas are full of diverse aquatic plants maintain clear-water conditions. Vegetated areas provide refuge for prey species including zooplankton, aquatic insects, and young fish. This helps in stabilizing predator/prey interactions and maintaining a more diverse aquatic community.

In order to re-establish a clear-water state, documentation shows that many shallow lakes benefit from the reduction of bottom feeding fish and the decrease of nutrient loading.

The June Sucker Recovery Implementation Program is funding activities to determine the feasibility of reducing and controlling the common carp (bottom feeding fish) population in Utah Lake and is investigating the dynamics of lake level fluctuations. And the Utah Department of Environmental Quality, Division of Water Quality is investigating nutrient loading to Utah Lake and potential mechanisms for its control.

For a detailed explanation of shallow lake ecology please refer to the book Ecology of Shallow Lakes by Marten Schiffer, Kluwer Academic Publishers, 1998, 2001.

Research shows that the decrease in nutrient loading benefits shallow lakes, allowing for an increase in healthy aquatic plant and animal life.

As aquatic vegetation flourishes in shallow lakes, turbidity levels tend to decrease. Such a state allows for more helpful nutrients and aquatic insects to help improve a lakes ecosystem.