What Farm Conservation Does for the Great Lakes: A Model for Alger Creek, Michigan

The Great Lakes face serious threats to water quality, habitat, ecology and coastal health. Excess nutrients from both point and diffuse sources have long fed harmful algal blooms, and since the late 1990s a resurgence of blooms has closed beaches and degraded water across the lakes. Studies increasingly blame phosphorus running off farmland.

The programme

The Great Lakes Restoration Initiative (GLRI), launched in 2010, provides a framework for restoring and protecting the lakes. Within it, a Priority Watersheds Work Group co-chaired by the U.S. Environmental Protection Agency and the USDA Natural Resources Conservation Service (NRCS) targets priority watersheds to cut the phosphorus reaching the lakes. Inside them, NRCS picks small, heavily farmed subbasins for concentrated nutrient-reduction work, extra monitoring and modelling. It gives farmers money and technical help to adopt best management practices (BMPs) that reduce farming's effect on water, and GLRI funds flowing through NRCS aim to saturate these subbasins with them.

This U.S. Geological Survey fact sheet introduces the watershed modelling that will measure how well those practices work, separating the reductions due to GLRI funding from those due to other programmes, and covering practices both already in place and planned.

Figure 1: Priority watersheds (purple) and study subbasins (red) in the Great Lakes area. Base map from the National Park Service's Natural Earth physical map. USGS.

Alger Creek

In Michigan the priority watershed is the Saginaw River watershed in the east-central part of the state, which drains to Saginaw Bay on Lake Huron. The chosen subbasin is Alger Creek, known locally as Kimball Drain: 20 rural square miles entirely in Genesee County, southwest of Flint. About 40 percent of its land is farmed, mainly for corn and soybeans.

Main land uses, from the USDA National Agricultural Statistics Service, 2013.

The practices

Farmers in the subbasin have received substantial funding through the GLRI and the Farm Bill. The practices most often contracted are conservation crop rotation, cover crops, forest stand improvement, nutrient management, and residue management (reduced till and no-till).

• The most common rotation is two years of corn and soybeans. Others are a three-year corn–soybean–winter wheat rotation, and a longer corn–soybean–corn–soybean–hay rotation, with hay grown for 5–6 years after the last soybean harvest.
• Cover crops usually follow winter wheat and soybeans, not corn. Cereal rye is the usual winter cover and can go in as late as November.

Monitoring

Monitoring equipment in the Alger Creek subbasin. Photo by Katherine Merriman, USGS.

The USGS installed an edge-of-field gaging station (0414826544) to measure nutrients in surface runoff from one field, with flow from the subsurface tile drains measured alongside (0414826545). Daily and annual nutrient loads are calculated with the Graphical Constituent Loading Analysis System (GCLAS). A nutrient management plan is to be put in place on the monitored field.

The model

A Soil and Water Assessment Tool (SWAT) model, which simulates hydrology and water quality day by day, is being built to show how much the GLRI practices reduce nutrient loads.

• Practice data: under a memorandum of understanding, NRCS supplied field-by-field records of practices applied from 2004 to 2014 and planned from 2015 to 2018; its field staff add details such as timing of operations, fertiliser or manure type and amount, harvest dates and yields. Fertiliser rates come from local NRCS staff and published recommendations.
• Drainage: the soils are somewhat poorly to poorly drained, and an unknown share of the subbasin is tile-drained to improve yields; the extent is being estimated from land use, soil and slope.
• Calibration: the gage at the subbasin outlet (041482663), installed in April 2012, has too short and too uniform a record to calibrate the model, so the model was extended to the outlet of the Flint River and calibrated against the Flint River near Fosters gage (04149000). Streamflow there stopped in October 2011, and grab samples from August 2000–September 2013 (not in winter) are turned into daily loads with the LOADEST program, so water quality is calibrated for 2004–2011 and validated for 2000–2003.

Figure 2: USGS gaging stations, National Pollutant Discharge Elimination System sites and National Climatic Data Center weather stations in (A) the Alger Creek subbasin and (B) the Flint River watershed, as of September 2014. Base image from the USDA National Agriculture Imagery Program. USGS.

What the model will do

First runs will simulate current practices, separating GLRI-funded from other practices. Later scenarios will test specific practices at different levels of adoption, chosen with local and state NRCS staff. Details for the subbasin, such as fertiliser timing and amounts, cover crop species and typical rotations, were being gathered in 2015. The result will be a tool to judge how far farm practices cut nutrient loads at the scale of a field and a small watershed.

Sources

• Katherine R. Merriman, Development of an assessment tool for agricultural best management practice implementation in the Great Lakes Restoration Initiative priority watersheds—Alger Creek, tributary to Saginaw River, Michigan, U.S. Geological Survey Fact Sheet 2015–3067. https://pubs.usgs.gov/publication/fs20153067