Pulse flows, or high-flow events such as floods, have a complex and variable relationship with nutrient loading and eutrophication. The timing, intensity, and source of a pulse flow determine whether it mobilizes a large flush of nutrients, causing or worsening eutrophication, or whether it has a more limited impact. A pulse flow can both transport excess nutrients into aquatic systems and alter how those nutrients are processed.
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Nutrient loading is the amount of nitrogen and phosphorus that enters an aquatic system. Pulse flows dramatically impact this process in several ways:
Washes out nutrients from soil: During a flood or heavy rain, high-volume runoff can scour the landscape, eroding nutrient-rich topsoil and carrying it into rivers, lakes, and estuaries.
Transports sediment: Nutrients like phosphorus often bind to soil particles. Fast-moving water can transport this sediment far downstream.
Leaches water-soluble nutrients: Water-soluble nitrates and potassium can be leached out of the soil and flushed into groundwater and surface waters during heavy precipitation.
Mobilizes legacy nutrients: Pulse flows can re-mobilize nutrients that have accumulated in the soil or riverbed sediment over time from agricultural and urban runoff. These are known as "legacy nutrients".
Pulse flows can deliver a massive, concentrated pulse of nutrients, fueling harmful algal blooms and depleting dissolved oxygen as algae die and decompose.
Eutrophication: or more precisely hypertrophication, is the ecosystem's response to the addition of artificial or natural nutrients, mainly phosphates, through detergents, fertilizers, or sewage, to an aquatic system. One example is the "bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Negative environmental effects include hypoxia, the depletion of oxygen in the water, which may cause death to aquatic animals.
You can help reduce negative impacts to our streams. Employ best management practices at home!
The graphs in the left column are recreational sites on the Great Miami (Heritage Park), Whitewater River (Green Acres Kayak), Ohio River (Lawrenceburg), and Dry Fork Creek (Miami Whitewater Forest). The right column contains graphs of precipitation/air temperature (Butler Regional Airport) and Great Miami streamflow at Hamilton dam. In the 2024 examples, increases in rain events close to monitoring days increase streamflow, increase E.coli and nutrient loading. The turbidity chart indicates the amount of disturbance within the waterway from both inflow of tributaries/runoff and the stirring up of sediments within the waterway.
However, something interesting is happening with total phosphorus (P) levels in March. All of the watersheds except the Whitewater have low P while all other parameters in March are in the "fair" to "poor" range. We may infer that, perhaps, this is because there hasn't yet been many fertilizer applications across other areas of the watershed. As you can see by this example, our monthly data collection is a brief snapshot of water quality but it gives us insight into the ways in which our watersheds function.
