Suspended Solids: What is it?
- Suspended solids are the fine particles of sediment in the water. Examples: soil, biological solids, decaying organic matter, and particles discharged in wastewater.
- Pollutants can attach to suspended solids.
Image 1: Photo credit, Great Lakes Inform (April, 2012). Sediment, nutrients, and pollutants from the Fox River flowing into southern Green Bay.
Total Suspend Solids (TSS):
- Total suspended solids (TSS), turbidity, and water clarity are all methods of measuring the amount of sediment in waterbody.
- The Lower Fox River TMDL calculates sediment concentrations by estimating and measuring TSS.
- TSS is the unit of measurement for the TMDL.
Why should we care about TSS?
- Sediment enters our waterways through a wide range of methods; however, it is most often attributed to urbanization and agriculture. By removing trees and other natural vegetation, the soil structure is disturbed, which leads to increased erosion and sedimentation.
- Suspended solids enter Green Bay primarily through the Fox River and the smaller streams within the Fox River Basin.
- The suspended solids load at the mouth of the Fox River is approximately 151,915 tons/year (Total Maximum Daily Load and Watershed Management Plan for the lower Fox River Basin and Lower Green Bay, 2012 and State of the Bay, 2013), which is equivalent to 416 tons or roughly 27 standard dump trucks (carrying approximately 15.5 tons, Figure 1) of sediment per day. However, almost 70 percent of the sediment is delivered within a short window (13-15 days) during the spring (Grayczyk et al. 2012).
Figure 1: Annual sediment load into Green Bay from the three major river basins (Lower Fox River, Upper Fox River, and Wolf River) 151,915 tons, which is equivalent to 416 tons per day or approximately 27 standard dump trucks (carrying 15.5 tons) per day (TMDL and Watershed Management Plan for the lower Fox River Basin and Lower Green Bay, 2012 and State of the Bay, 2013).
Impacts of Suspended Solids:
- Dead Zones: Increased sediment reduces water clarity and therefore, less light is able to penetrate the waters’ surface and reach plants underwater. Reduced sunlight, reduces photosynthesis activity and oxygen production, which can create hypoxic (low-oxygen) conditions and can contribute to dead zones.
- Biological: Increased sedimentation can have several negative impacts on the biology of an aquatic system.
- Reduced water clarity decreases visibility for fish and diving birds.
- Suspended solids can clog fish gills and cause increased levels of stress, which is often already amplified due to hypoxic conditions.
- Suspended solids that settle at the bottom of a river or lake can bury fish eggs, fish nursery areas, and invertebrate habitat, which can negatively impact the food chain.
- Economics: Suspended solids settle at the bottom of a waterbody, creating a shallow waterway. Due to the shipping industry, which navigates through Green Bay and the Fox River, increased sedimentation has had significant financial ramifications. Maintaining shipping channels by dredging the sediment is a costly and continuous project.