Broken Stream Banks

Failure to maintain buffer zones worsens farm pollution

April 25, 2014

Broken Stream Banks: Perennial Rivers and Streams

The data show that while sizeable numbers of landowners maintain the required 50-foot riparian buffers, many others do not. Buffers are often far narrower than required and in some cases are completely missing. Overall, about 72 percent of the required buffering acres were in place in agricultural areas – an average grade of C (Table 1). But the overall average is misleading, because there are large differences among waterways.

Only 18 percent (87 waterways) earned an A, while 21 percent (101 waterways) got a failing grade. Another 14 percent (66 waterways) earned only a D. Combining the highest and lowest grades, 30 percent earned an A or A- while 35 percent earned a D or F.

Figure 4 paints a compelling picture of just how few waterways were fully buffered. The map shows that perennial streams and rivers with a D or F grade are concentrated in agricultural areas in the southwest, southeast and northwest corners of southern Minnesota and in Watonwan County. In many areas, well-buffered waterways are next door to those with less than 70 percent of the required buffer zones.

In some places, it was obvious that eroding stream banks were cutting into what might once have been an adequate buffer zones. In most cases, however, there was no obvious explanation for the striking differences in the widths of buffer zones of adjacent row crop fields other than variation in practices by the landowners or operators involved. (Figure 5)

EWG’s evaluation revealed other troubling facts. First, we found that row crops often encroached into the 50-foot protected zone, making those buffers far narrower than the required 50-feet. Small perennial streams were particularly hard hit by row crops planted too close to their banks.

In 60 percent of the locations where buffers were too narrow, the buffering vegetation was less than 70 percent of what is required. Less than 60 percent of the required buffer was in place in 30 percent of the locations that were too narrow. Only 3 percent of the narrowed zones had 90-to-100 percent of the required protective buffering.

Most of the too-narrow buffer zones were much narrower than the required 50 feet.

Small Perennial Streams Hard Hit

Figure 6: Small perennial streams account for most of the missing buffer acres adjacent to cropland.

Small streams make up only 31 percent of total miles of perennial waterways.

Pie chart

Small streams account for 45 percent of all missing buffers along perennial waterways.

Pie chart

EWG divided perennial rivers and streams in agricultural areas into three classes based on length. We classed waterways longer than 50 miles as “large,” those 25-to-50 miles long as “medium” and those 1-to-25 miles long as “small.”

Although small perennial streams amount to 31 percent of the miles of waterways EWG evaluated, they account for 45 percent of the total acres of missing buffer. Large rivers and streams make up fully 48 percent of total waterway miles but only 28 percent of the missing acres. (Figure 6)

There was also wide variation among large perennial rivers and streams: Some were hard hit by row crops planted too close to their banks, while others had most or all of the required buffer zones. The Rock River, the south fork of the Watonwan River and the south fork of the Root River – all large waterways – got failing grades because they had less than 60 percent of the required buffer acreage. No large rivers got an A, but the Mississippi, Minnesota and Cedar Rivers rated an A- because they had more than 90 percent of the mandated buffer acres. In many cases, some segments of these largest rivers had far more than 50 feet of buffer along their banks.

Medium-sized waterways that got a failing grade include Pipestone Creek, Beaver Creek in Rock County, Riceford Creek, Mud Creek in Swift County and the north fork of the Watonwan River. No medium streams earned an A, but Florida Creek, the South Branch/Middle Fork of the Zumbro River, Le Sueur Creek, the east branch of the Chippewa River, Lime Creek and Dodge Center Creek all earned an A-.

The grades for small streams were distributed very differently than for large or medium-sized rivers. Thirty-three percent of small streams in agricultural areas earned an A or A-, but 36 percent earned a D or F. (Figure 7) It is striking that the buffer grades for large and medium streams follow the classic bell curve – C was the most common grade, and A’s and F’s were less common. However, failing grades were far more prevalent, accounting for fully 45 percent (459 acres) of all the acreage of missing buffers along small streams.

In fact, small streams account for a dispropor- tionate share of all missing buffer zones along perennial rivers and streams of all sizes, and the buffers tend to be far narrower than the required 50 feet.

This is bad news for southern Minnesota’s water quality. Smaller streams are more intimately connected to agricultural land than larger streams, and buffering them has the largest impact on reducing polluted runoff. Since small streams can account for 90 percent of total stream length in a watershed, their riparian zones can have major effects on water quality throughout the basin.24

Figure 7: Buffers Along Small Perennial Streams Are In Bad Shape

Bar chart showing missing buffers