Investigating the effects of intensive agricultural irrigation on tribal resources in Central Minnesota

February 01, 2023

by Philip Margarit and Leslie Ludtke

The 1855 Treaty Territory overlaps partially with the Pineland Sands Aquifer System (Pineland Sands) in Central Minnesota. This region is important culturally, ecologically, and economically, including the headwaters of the Mississippi River and numerous trout streams, recreational lakes, and wild rice water bodies important to the Anishinaabe. The Pineland Sands comprises parts of Becker, Cass, Hubbard, and Wadena counties. Past glaciation in the region deposited a complex system of buried glacial aquifers, with highly transmissive sands layered between lower transmissive tills. The Pineland Sands are highly productive, supporting a rapid expansion of agricultural irrigation in the region with groundwater being pumped at an increasing rate since the 1970’s to support row crop farming in the area. Due to groundwater being an important component of baseflow in the surface water hydrology of the area, the increase of groundwater pumping for irrigation brings up water quantity concerns. With the expansion of modern agriculture in Pineland Sands, comes the expansion of water quality concerns in the region. The high transmissivity of the sands creates a substantial risk for groundwater contamination in the aquifer system. Combined, the water quality and water quantity impacts that come with the explosion of agriculture in the region have concerned local communities, including the Anishinaabe peoples of White Earth Nation, which became the basis of this study. This study aims to investigate how agricultural activity in the region will impact the water resources of the area. The objectives of this study will be accomplished through a combined field campaign with extensive modeling efforts utilizing integrated surface and groundwater models. 

study area

The modeling portion of this study encompasses a telescoping approach to model development, starting with a regional MODFLOW model for the northern Pineland Sands initially developed for the study. Subsequently, a suite of smaller watershed-scale and site-scale MODFLOW models will be developed at finer resolutions. This approach allows the team to investigate impacts and scenarios at several different scales with increasing complexity as the model size decreases. SWAT models will be developed for each field-scale and site-scale MODFLOW model, integrating the recharge and chemical loading fluxes into the model. Once built, these integrated models will allow the team to investigate how changes in parameters such as recharge, land use, groundwater pumping, and chemical loading rates will impact the water quantity and quality of the region. These models will additionally integrate field measurements taken during the study into model calibration and validation. 

A holistic field sampling approach will be implemented to assess possible effects of intensive agricultural water withdrawal on water quality and quantity. Monthly streamflow data will be collected from the three major rivers running through the study area along with water quality data including stable isotopes, pesticides, and major cations and anions. Wild rice within the study area (Fig. 1) will be evaluated along with current mussel populations. A small-scale field study will be conducted to compare soil health of the sandy soil under conventional and regenerative farming practices. Data collected from the field work will aid modeling efforts. This project is being conducted by members from the University of Minnesota – Twin Cities WRS program, the Anishinaabe Agricultural Institute, and the White Earth Nation.

Margarit and Ludtke are advised by John Nieber and Joe Magner.

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