BENSON -- Late season rains brought more than met the eye to the Chippewa River in 2005.
As water flows increased, so did the pollutants washing into the stream. Pollutant levels in the 120-mile river nearly doubled last year, monitoring by the Chippewa River Watershed Project staff and volunteers shows. Of particular concern was the rising load of sediment being carried by the river.
"We still have some work to do,'' said Paul Wymar, watershed scientist, while outlining the monitoring results for suspended sediments with members of the Chippewa River Watershed Project on Friday in Benson. Wymar will be giving a detailed analysis of the 2005 monitoring at the watershed project's annual meeting on March 3 in Glenwood.
What he revealed on Friday suggests that progress toward cleaning up the river has stalled in some areas.
There's no doubt that last year's higher-than-average rainfall is partly to blame. Wymar said that in most years, rainfall amounts decrease through the summer months and pollutant levels begin falling accordingly.
ADVERTISEMENT
Last year brought a different picture. Heavy rains in late spring and early summer washed through fields before crops had developed the full canopies that can reduce erosion.
And surprisingly, late rains in August and September also served to transport more pollutants into the water. Rain events varied, but Wymar said there was as much as eight to 10 inches of rain recorded in the Swift Falls area in late August.
By the end of the monitoring season, measurements made at the Minnesota Highway 40 bridge indicate that the Chippewa River had carried more than 50,000 tons of sediments in 2005, according to the data. That's the highest level in eight years of monitoring by the watershed project. It's more than double the average of 22,000 tons per year.
More work is needed to identify all the causes, but Wymar said it is apparent that both in-stream erosion of riverbanks and runoff from farm fields, construction sites and other overland sources are to blame. The greatest source of bank erosion occurs in the lower portion of the river, from the confluence of Shakopee Creek to the Highway 40 bridge.
The hydrology of the basin has changed to the point that monitoring has shown a four-fold increase in the volume of water carried by the river after rain events, according to Wymar. The result of moving that much more water all the faster contributes to the bank erosion or sloughing so evident along this portion of the river.
Along with concerns about sediment, the monitoring for 2005 showed that there remains higher-than-desired fecal coliform levels in the river and its tributaries.
Because of the monitoring, more than two dozen reaches of waterways within the basin were added this year to the "impaired waters" list maintained by the Minnesota Pollution Control Agency, according to Kylene Olson, watershed director. She said fecal coliform and turbidity problems are responsible for most of the impaired water listings in the basin.
The basin did not see the progress it would like in controlling nitrogen and phosphorus runoff into the river, either. Wymar said that monitoring for 2005 suggests that a slow trend toward reducing the concentrations of phosphorus in the river has reached a plateau. The river carried more than 100 tons of phosphorus to the Minnesota River in 2005.
ADVERTISEMENT
Nitrogen levels increased. Last year the Chippewa River poured more than 1,400 tons of nitrogen into the Minnesota River.
Pollution problems vary throughout the 1.3 million-acre basin, depending both on urban concentrations, land use practices and geology. In general, the greater pollutant sources come from the subbasins that flow through Shakopee Creek, the East Branch and the Chippewa River at Clontarf.
Wymar said the last year's data also showed that cleaning up the Chippewa River will go a long way toward helping clean up the upper Minnesota River. The Chippewa River and Pomme de Terre River contributed about 80 percent of the water flow into the upper portion of the Minnesota River, far surpassing the Lac qui Parle River and Big Stone Lake basins as sources.
