In an effort to complete the Deer Creek TMDL study, a sediment load monitoring study began in 2008. Turbidity and Total Suspended Solids data is collected along with other supporting data at several points along the stream and the main tributary (see monitoring locations on map below). The data is collected at vartying flow conditions such as spring snowmelt, storm events, and baseflow in order to understand the sediment load during different hydrologic conditions. Stream flow data is collected at two sites along the stream in order to quantify the amount of water moving through the system. One flow site is located upstream of the mud volcano area and one is located downstream of the mud volcano area. The mud volcanoes are a unique contributor of sediment via groundwater. Data outside the influence of the mud volcanoes (upstream) will be compared to data influenced by the mud volcanoes (donwstream).
Sediment Load Monitoring: Connecting Turbidity, Total Suspended Solids, and Flow Data
Turbidity is the cloudiness of water, and in the case of Deer Creek, the cloudiness is caused by the presence of suspended solids that scatter light in the water column. Units of measurement for turbidity are Nephelometric Turbidity Units (NTU). The state standard of 10 NTU was exceeded for Deer Creek, which led to the impaired water listing. Note the visual difference of a low turbidity reading versus a higher turbidity reading.
TSS (Total Suspended Solids) is the measurement of suspended solids per unit volume of water. TSS is a quantitative measurement while turbidity is a qualitative measurement of the scattering of light particles. In order to complete sediment loading calculations, a quantifiable number needs to be used. A relationship between turbidity and TSS will be established through the pairing of the data.
Stream flow is the quantity of water moving through the channel and is measured in cubic feet per second (cfs). In order to determine the “load” of sediment flowing in the system, data must be collected on stream flow. Stream stage (height of the water) data is being collected on a continuous basis at the two monitoring sites in Deer Creek. Flow measurements are taken periodically to develop a relationship between the stage of the stream and the amount of water flowing at the site.
Once the quantity of water is known in various places in the watershed, the TSS concentrations can be calculated with the flow amount in order to determine the entire load for the system.
20mg/L * 10cfs = ~5,663.3mg/sec or ~1078.74pounds/day
(TSS/sediment concentration) (flow rate) (load)
Sonde; Water Quality Data Collection Unit
Additional water quality information will be collected at the time as turbidity and TSS data in order to understand the relative stream health. A multiparameter sonde (picture below) will be used to collect additional chemistry data in the field. The following gives a brief description of the additional chemistry parameters.
Hydrogen ion concentration (pH) will be measured as an indicator of the solubility and biological availability of chemical nutrients and heavy metals. pH can determine how much and what form of phosphorus is most abundant in what and whether aquatic life can use it. Additionally, metals tend to be more toxic at low pH values because they are more soluble. Diurnal and seasonal changes in pH can also indicate use and production of carbon dioxide for photosynthesis and respiration. As carbon dioxide is removed for photosynthesis, the acidity of water is reduced and pH increases. During respiration, carbon dioxide is produced which dissolved in water as carbonic acid, which lowers the pH. The pH of most natural waters is generally between 6.5 and 8.5.
Dissolved oxygen (DO) will be taken to determine the amount of oxygen available for stream biota. When DO concentrations become low, they can cross a crucial threshold that can negatively affect aquatic life. DO is also related to water temperature. As water temperature rises, its ability to hold DO decreases. Seasonal changes in DO can be affected by seasonal water temperature changes. As water warms in the summer, the DO decreases. A healthy stream generally has a DO saturation above 90 percent.
Temperature measurement will also be taken with the sonde. Similar to oxygen concentration, certain types of biota have temperature thresholds that can be lethal if crossed. The Minnesota DNR Fisheries Division will be monitoring temperature at several sites in the watershed.
Specific conductivity will also be measured with the above parameters. This measurement of the waters ability to carry an electrical current can indicate the presence of inorganic dissolved solids. Conductivity is controlled predominately by the geology of the area. High clay content soils such as those of the Nemadji River Basin tend to have a higher specific conductivity because of the presence of materials that ionize which wash into the water. The case is similar for areas with groundwater influence. See Groundwater Study section for more information on the groundwater study and ion monitoring parameters.