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What factors can we attribute the increase in phosphorus in Lake Erie?

Not all of the factors contributing to the increase in phosphorus in Lake Erie are fully understood.  It is important to note that the increase is with soluable phosphorus rather than total phosphorus.  Soluable phosphorus is phosphorus in solution, unlike total phosphorus which is attached to sediment particles.

There are multiple sources of soluable phosphorus entering Lake Erie.  The Ohio Lake Erie Phosphorus Task Force examined available data for many of these sources.  Point source discharge data for example, have remained relatively constant over the period for which the increases have been documented through stream monitoring data.  Therefore, while a contributing source of phosphorus, point sources are not likely to be a major contributor to the recent increases.

The majority of annual phosphorus loading to Lake Erie has been documented to be from storm-pulsed runoff from the landscape into the streams that drain to Lake Erie.  The Task Force looked at trends in weather patterns since the mid-1990s and observed a decrease in overall snowfall and an increase in higher intensity storms during this period.

The high percentage of agricultural land use in the western basin of Lake Erie (60-80%) led the Task Force to review available information and data regarding agricultural trends.   A key observation of the Task Force was that soil-nutrient interactions are critical to understanding nutrient (phosphorus) movement.  The Task Force looked at a variety of trends in agriculture that may be influencing movement.  While none of these trends can be directly linked to the mid-1990s, the Task Force believes that in the aggregate, they contribute to the change in the annual increases in soluable phosphorus loading. 

Gail Hesse, Ohio EPA

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