Illinois Environmental Protection Agency Lake Oakland and Walnut Point Lake TMDL Development
22 Final Report
4.3.1 Nutrients/Organic Enrichment/Low DO/Excessive Algal Growth
The term nutrients usually refers to the various forms of nitrogen and phosphorus found in a waterbody.
Both nitrogen and phosphorus are necessary for aquatic life, and both elements are needed at some level
in a waterbody to sustain life. The natural amount of nutrients in a waterbody varies depending on the
type of system. A pristine mountain spring might have little to almost no nutrients, whereas a lowland,
mature stream flowing through wetland areas might have naturally high nutrient concentrations. Various
forms of nitrogen and phosphorus can exist at one time in a waterbody, although not all forms can be used
by aquatic life. Common phosphorus sampling parameters are total phosphorus (TP), dissolved
phosphorus, and orthophosphate. Common nitrogen sampling parameters are total nitrogen (TN), nitrite
(NO2), nitrate (NO3), total Kjeldahl nitrogen (TKN), and ammonia (NH3). Concentrations are measured
in the lab and are typically reported in milligrams per liter.
Nutrients generally do not pose a direct threat to the beneficial uses of a waterbody, although high nitrate
concentrations can pose a risk to drinking water supplies. However, excess nutrients can cause an
undesirable abundance of plant and algae growth. This process is called eutrophication or organic
enrichment. Organic enrichment can have many effects on a stream or lake. One possible effect of
eutrophication is low dissolved oxygen concentrations. Aquatic organisms need oxygen to live and they
can experience lowered reproduction rates and mortality with lowered dissolved oxygen concentrations.
Dissolved oxygen concentrations are measured in the field and are typically reported in milligrams per
liter. Ammonia, which is toxic to fish at high concentrations, can be released from decaying organic
matter when eutrophication occurs. Recreational uses can be impaired because of eutrophication.
Nuisance plant and algae growth can interfere with swimming, boating, and fishing. Nutrients generally
do not pose a threat to agricultural uses.
Nitrogen and phosphorus exist in rocks and soils and are naturally weathered and transported into
waterbodies. Organic matter is also a natural source of nutrients. Systems rich with organic matter (e.g.,
wetlands and bogs) can have naturally high nutrient concentrations. Phosphorus and nitrogen are
potentially released into the environment through different anthropogenic sources including septic
systems, wastewater treatment plants, fertilizer application, and animal feeding operations.
4.3.2 Suspended Solids and Sedimentation/Siltation
Excess total suspended solids (TSS) in a stream or lake can pose a threat to aquatic organisms. Turbid
waters created by excess TSS concentrations reduce light penetration, which can adversely affect aquatic
organisms. TSS can also interfere with fish feeding patterns because of the turbidity. Prolonged periods
of very high TSS concentrations can be fatal to aquatic organisms (Newcombe and Jensen, 1996). As
TSS settles to the bottom of a stream, critical habitats such as spawning sites and macroinvertebrate
habitats can be covered in sediment. This is referred to as siltation. Excess sediment in a stream bottom
can reduce dissolved oxygen concentrations in stream bottom substrates, and it can reduce the quality and
quantity of habitats for aquatic organisms. TSS can also pose a threat to recreational uses because of
murky conditions.
Erosion and overland flow contribute some natural TSS to most streams and lakes. In watersheds with
highly erodible soils and steep slopes, natural TSS concentrations can be very high. Excess TSS in
overland flow can occur when poor land use and land cover practices are in place. This potentially
includes grazing, row crops, construction activities, road runoff, and mining. Grazing and other practices
that can degrade stream channels are other possible sources of TSS. Shoreline erosion in lakes can
contribute significant TSS loads due to wave action.
