Soos Creek multiparameter study

Dissolved oxygen (DO) is vitally important for supporting fish, invertebrates, and other aquatic life. DO levels in a stream can be influenced by:

• Temperature — warm water temperatures can lower DO levels.
• Groundwater — DO is often lower in groundwater.
• Flow — slow-moving water with limited reaeration may have low DO.
• Biological and biochemical processes — this happens at the streambed's sediment layer, often called sediment oxygen demand.
• Aquatic algae and plants — photosynthesis produces oxygen, while decomposition of plants and respiration reduces oxygen levels.
• Wastewater or stormwater — discharges carry nutrient pollution, which can cause the overgrowth of plants and algae. Too much growth can rob the stream of DO.

Our results show:

• No creeks met DO criteria for the full summer of 2023.
• The lowest DO levels were observed from Aug. 15 – 16, 2023, following one of the hottest days of the summer.
• Areas downstream of wetlands, such as upper Big Soos and lake outlets, had lower DO.
• Upper Big Soos had the lowest DO, which may be from multiple natural wetland influences such as:
  • Slow-moving or stagnant water.
  • Greater plant productivity and decomposition.
  • Biological processes in the wetland sediment.
  • Groundwater inputs to the wetlands.
• Many creeks had low DO in the fall and winter, which may be caused by:
  • Discharges of low-DO stormwater and wastewater after rain events.
  • Flush of natural stores of low-DO water from wetlands and lakes after rain events.
  • Greater inputs of low-DO groundwater.

High bacteria levels in streams are a risk to human health and can cause illnesses when people swim and play in the water. Bacteria comes from the digestive tract of warm-blooded animals. Potential sources of bacteria in the Soos Creek watershed include:

• Faulty on-site septic systems.
• Wastewater and stormwater runoff from urban areas.
• Waterfowl, rodents, and other warm-blooded wildlife.
• Pet manure from residential areas.

Our results show:

• Soosette Creek had the highest bacteria levels in the watershed. The Soosette Creek subbasin has the greatest amount of developed land in the watershed.
• A stormwater discharge that flows to Soosette Creek at creek mile 3.6 had the highest bacteria concentrations in this study.
• Jenkins Creek had the highest amount of bacteria flowing to Big Soos. This is determined by using both flow and bacteria concentrations to calculate a bacteria load.
• Jenkins Creek had higher bacteria loads during the summer under low flow conditions. This points to dry-season sources, such as on-site septic systems or wildlife waste, as significant contributors of bacteria.

Excess nutrients can lead to water quality issues such as eutrophication and harmful algal growth. Sources of excess nutrients include:

• Fertilizers.
• Faulty on-site septic system.
• Wastewater and stormwater runoff from urban areas.
• Waterfowl, rodents, and other warm-blooded wildlife.
• Atmospheric deposition of nitrogen.

Our results show:

• A greater amount of nutrients were flowing through the watershed during the fall and winter when streamflows are higher.
• Jenkins Creek had the highest amount of nutrients flowing to Big Soos Creek. This is determined by using both flow levels and nutrient concentrations to calculate a nutrient load.
• The greatest nitrogen and phosphorus concentrations were detected from a stormwater discharge that flows to Soosette Creek near creek mile 3.6.
• Wetlands, such as in upper Big Soos Creek, had higher organic carbon and phosphorus levels.