Nutrient Sources Within The Upper Mississippi River Basin Minnesota And Wisconsin 1991 93

Author :
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (443 download)

DOWNLOAD NOW!

Download or read book Spatial Distribution of Nutrients in the Mississippi River System (1991-1992) written by and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Concentrations of dissolved nutrients (nitrate, nitrite, ammonium and orthophosphate) were measured on surface-water grab samples collected at ten mile intervals along the entire length of the navigable portion of the Mississippi River during three cruises in June?July 1991, September?October 1991 and March? April 1992. Samples were also collected at the mouths of some of the major tributaries and, at selected points, three-sample cross sections were collected across the river to measure cross-channel variability. Simultaneously with collecting each sample, the discharge of the Mississippi River was estimated, permitting the calculation of the nutrient load in the Mississippi River at each sample point. The large number of samples collected (between 179 and 207 per cruise) give a picture of the instantaneous longitudinal variation of nutrients in the Mississippi River during three different seasons. Both nitrate and orthophosphate loads appear to increase or remain constant downriver for each cruise, indicating that mechanisms for the removal of these compounds are not as rapid as their introduction into the river. In addition, below the confluence of most of the major tributaries, the loads show a?step? increase caused by the nitrate and orthophosphate contributions from the tributaries. From this data, one can identify the possible sources of nitrate and orthophosphate arriving at the Gulf of Mexico from the Mississippi River. During each of the three cruises (at three different seasons), the majority of the nitrate and ortho-phosphate appears to have originated from the Upper Mississippi River Basin, above the con-fluence of the Missouri River. Ammonium and nitrite loads appear to originate as point-sources, but disappear within approximately one hundred miles of their introduction, probably as a result of conversion to nitrate and/or nitrogen gas. Any nitrite or ammonium from the Mississippi River deposited into the Gulf of Mexico therefore probably originated within one hundred miles of the Gulf.