Phosphorus / Nitrogen
What about phosphorus and nitrogen?
Stormwater also is the chief mechanism by which nutrients such as phosphorus and nitrogen are flushed from the landscape and carried to Lake Champlain. These elements act as fertilizers for the algal populations in the lake; in the summer months high nutrient levels lead to algal blooms, which have associated health risks.
In addition to flushing out the fertilizer that we put on our lawn, stormwater also flushes out the nutrients which naturally occur in the soil:
"In addition to obvious sources
of nutrients, like cows, unstable streambanks account for a large proportion
of the non-point phosphorus loads. Most phosphorus is bound in the upper soil.
When this soil moves into the water through overland erosion or eroding stream
banks (often caused by the loss of vegetation), the phosphorus comes with it.
Erosion can be amplified by upstream construction projects…"*
Additionally, phosphorus is often transported on or in association with sediment or slightly charged particulate matter found in the suspended solids and sediments. Therefore, by creating higher volumes of stormwater from our impervious surfaces, which leads to more erosion, we increase the potential for phosphorus (typically in the form of phosphate) transport from the land into the lake.
*(Vermont Agency of Natural Resources; Department of Conservation.Winter 2003, Out of the Blue Newsletter.)