A recent study led by Smithsonian ecologist Kathy Boomer suggests it is time for a change in at least one area of watershed management. Boomer has been examining the tools scientists and managers use to predict how much sediment runs into the Chesapeake Bay, and by her account, they are way off the mark. The study, co-authored by SERC ecological modeler Donald Weller and ecologist Thomas Jordan, appears in the January/February issue of the Journal of Environmental Quality.
Sediment running into the bay reduces light, suffocates underwater organisms and is a significant source of phosphorous, a nutrient that essentially fertilizes the water promoting algal blooms and many other problems in the bay.
Cities and counties are under increasing pressure to meet total maximum daily loads set by state and federal agencies and to understand where sediments come from, she said. So we tested the tools most widely used now to predict sediment delivery.
Her work has led to a new tactic. Were moving away from focusing on upland erosion and looking more at what happens near streams and in streams during events with high levels of stream sediments.
The new study compared actual measurement of sediments in more than 100 streams in the Chesapeake watershed with predictions from several of the most up-to-date models. All the models failed completely to identify streams with high sediment levels.
There was no correlation at all between the model predictions and the measurements, said Boomer. The study is among the first to directly compare predictions of the widely used models with actual observations of sediments in a large number of streams.
The problem, she said, is that the most widely used models all begin with the same tool, the Universal Sediment Loss Equation. The USLE estimates erosion from five factors: topography, soil erodibility, annual average rainfall amount and intensity, land cover, and land management practi
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