Abstract
This study examined conservation easements and their
effectiveness at reducing phosphorus and solids transport
to streams. The U.S. Geological Survey cooperated with
the Minnesota Board of Water and Soil Resources and
worked collaboratively with the Hawk Creek Watershed
Project to examine the West Fork Beaver Creek Basin in
Renville County, which has the largest number of Reinvest
In Minnesota land retirement contracts in the State (as of
2013). Among all conservation easement programs, a total
of 24,218 acres of agricultural land were retired throughout
Renville County, and 2,718 acres were retired in the West
Fork Beaver Creek Basin from 1987 through 2012. Total land
retirement increased steadily from 1987 until 2000. In 2000,
land retirement increased sharply because of the Minnesota
River Conservation Reserve Enhancement Program, then
leveled off when the program ended in 2002.
Streamflow data were collected during 1999 through
2011, and total phosphorus and total suspended solids data
were collected during 1999 through 2012. During this period,
the highest peak streamflow of 1,320 cubic feet per second
was in March 2010. Total phosphorus and total suspended
solids are constituents that tend to increase with increases in
streamflow. Annual flow-weighted mean total-phosphorus
concentrations ranged from 0.140 to 0.759 milligrams per
liter, and annual flow-weighted mean total suspended solids
concentrations ranged from 21.3 to 217 milligrams per liter.
Annual flow-weighted mean total phosphorus and total
suspended solids concentrations decreased steadily during the
first 4 years of water-quality sample collection. A downward
trend in flow-weighted mean total-phosphorus concentrations
was significant from 1999 through 2008; however, flow-weighted
total-phosphorus concentrations increased
substantially in 2009, and the total phosphorus trend was
no longer significant. The high annual flow-weighted mean
concentrations for total phosphorus and total suspended solids
in 2009 were affected by outlier concentrations documented in
March 2009.
Agricultural land-retirement data only were available
through 2008; therefore, it was not possible to compare total
phosphorus and total suspended solids concentrations to
agricultural land-retirement data for 2009–11. A downward
trend in annual flow-weighted mean total-phosphorus
concentrations was related significantly to annual land
retirement for 1999–2008. The relation between annual
flow-weighted mean total suspended solids concentration
and annual land retirement was not statistically significant
for 1999–2008. If land-retirement data had been available
for 2009–11, it is possible that the relation between total
phosphorus and land retirement would no longer be
evident because of the marked increase in flow-weighted
concentrations during 2009. Alternatively, the increase in
annual flow-weighted mean total-phosphorus concentrations
during 2009–11 may be because of other factors, including
industrial discharges, increases in drain tile installation,
changes in land use including decreases in agricultural
land retirement after 2008, increases in erosion, increases
in phosphorus applications to fields, or unknown causes.
Inclusion of land-retirement effects in agency planning along
with other factors adds perspective with regard to the broader
picture of interdependent systems and allows agencies to make
informed decisions on the benefits of perpetual easements
compared to limited duration easements.
|
First posted February 8, 2014
Part or all of this report is presented in Portable Document Format (PDF). For best results viewing and printing PDF documents, it is recommended that you download the documents to your computer and open them with Adobe Reader. PDF documents opened from your browser may not display or print as intended. Download the latest version of Adobe Reader, free of charge.
|