The coefficients for all of these sources and factors were highly significant ( p < 0.01), indicating that each of the sources, land-to-water factors, and instream/reservoir factors are important in describing the distribution in measured loads.
In the tributaries that contribute the largest loads to each of these three lakes, there was a decreasing trend in TP loads from 1970 to 2007 (including the Saginaw River, which contributes ∼60% of the total load to Lake Huron; the Maumee River, which contributes ∼50% of the total load to Lake Erie; and St.