What causes the geographic variation?
|Back to Top| In addition to land use and nutrient sources, delivery of nutrients to the Gulf by State or sub-basin (as described above) are controlled by hydrology and watershed characteristics. In total, only about 15% of the nitrogen and phosphorus ultimately reach the northern Gulf of Mexico. A major controlling factor is stream size. Delivery of nutrients to the Gulf is highest from watersheds in the central and eastern portions of the Mississippi River Basin that are drained by large, fast flowing rivers with relatively little natural removal of nutrients. These watersheds receive nutrient contributions from agricultural lands and large cities, including those that border large rivers, which enhance nutrient transport to the Gulf. Watersheds in the western Basin contribute relatively small quantities of nutrients to the Gulf, owing to lower precipitation and streamflow and large natural removal of nutrients in streams and rivers. Streams are generally smaller in the western part
