Upper St. Croix Lake Paleoecological Study (1997)
A copy of a 1997 sediment core sample study can be downloaded here.
A sediment core was taken from the lake on 30 April 1997 in the middle of the lake off the State Park. The water depth was 19 feet. The total length of the core was 66 cm (2.2 ft). The core was divided into 1 cm sections and some of these were analyzed for various variables. The information for this study was obtained using the top 27 cm as this covers a time period since 1850.
Paul Garrison, a DNR research scientist, conducted the core sample and its analysis.
Summary
Watershed activities first began to impact the lake around 1940. The resulting increase in soil erosion delivered more sediment and nutrients to the lake increasing algal productivity.
The greatest impact to the lake has occurred since 1970. This resulted in an elevated sedimentation rate and increased nutrients in the lake. The further increased algal productivity and decreased water clarity.
Although the sedimentation rate has declined in the last decade it is still much higher than prior to 1975 and water clarity remains depressed.
The extent of the time of anoxia n the bottom water has increased in recent times. Although these anoxic conditions are not very extensive, they can increase nutrient release from the sediments.
Although the lake has degraded since 1940, it as not been very much compared to many other lakes but is an indication that protection needs to be continued to maintain the lake in good condition.
Click here (requires Adobe reader) for Paul Garrison's September 2004 UW-Extension Lakes Program presentation on Paleolimnology as a Management Tool.
