Assessing Decadal-Scale Change at the Shingobee Headwaters, North-Central Minnesota

Research and monitoring at the Shingobee Headwaters Aquatic Ecosystems Project advances understanding of physical, chemical, and biological processes at the air-water, air-land, and land-water interfaces on a small-watershed scale. The 28 km² watershed, located near the headwaters of the Mississippi River, consists of two lakes and associated streams and wetlands and is typical of much of the landscape in the northern-lakes region of Minnesota. During a severe drought in 1976-77, some lake levels decreased a large amount while others were little changed. This led to the hypothesis that groundwater might be a large component of the water budget of some lakes and might be serving to stabilize their lake levels. In 1978, study of the water budget, and the groundwater component in particular, was begun at a lake that had no stream inputs or losses. In 1989, the scope expanded to a second lake nearby that did have a stream flowing to and from it, and included study of limnology, biogeochemical processes, and carbon budgets. Over the decades, the study has grown in scope and in value because of its long-term record. Durations of wintertime ice cover have increased for both lakes. Lake temperatures at the surface have both warmed and cooled, depending on the season, but lake temperatures near the deepest parts of both lakes have warmed during all months when the lakes are ice-free. Phenology data now consists of more than 800 parameters measured, and trends are mixed. First sightings of some species are trending earlier while others are trending later. Nearly all trends have small statistical significance and would be difficult or impossible to detect without a long-term record. The broad range of limnological, biological, chemical, hydrological, and climatological data collected at Shingobee, combined with the long duration of the study, demonstrates the value of this and other similar studies for documenting changes and trends, whether driven by climate or other processes. Without these long-term watershed-scale studies, many subtle changes, along with associated implications, would be unknown.