Phosphorus Source Identification Along Various Streams in the Minnesota River Basin.

Sediments are a major carrier of phosphorus (P) to rivers and lakes. This study evaluated P properties of channel deposited sediments (DS) and suspended sediments (SS) to identify river reaches that are contributing high P levels in the Greater Blue Earth River Basin (GBERB) and the lower Minnesota River Basin (MRB). Properties analyzed were particle size distribution, total P, and P fractions in bulk and fine sediments. DS analysis showed that (1) isolated Waste Water Treatment Plants and possibly livestock facilities are discharging soluble P to waterways in the MRB, and (2) the P fractionation of fine particles over bulk sediments is helpful to identify river reaches contributing soluble P and particulate P in these basins. SS analysis showed that total P (TP) concentrations in the GBERB (0.84±0.22 mg g^-1) and the lower Minnesota River (0.88±0.12 mg g^-1) were slightly higher and lower than the corresponding concentrations in Lake Pepin sediments in 1400 (0.73±0.06 mg g^-1) and 1996 (1.21±0.24 mg g^-1), respectively. Some of the above differences in TP concentrations between the MRB and Lake Pepin sediments may be due to differences in particle size distribution but it also raises the possibility of legacy P sources between the mouth of the Minnesota River and Lake Pepin. We conclude that P fractionation studies with additional DS and SS be undertaken to (1) confirm the above findings of isolated P sources in the MRB, and (2) assess the existence of legacy/point P sources between the mouth of the Minnesota River and Lake Pepin.