Lake Superior Phosphorus Loading


Lake Superior Phosphorus Loading Study is designed to study Phosphorus loads to Lake Superior from major tributaries. Three tributaries will be monitored for nutrients and total suspended solids. These tributaries represent various land uses and a portion of Wisconsin’s drainage areas in the Lake Superior basin. DNR staff will collect up to 25 water samples annually from locations towards the mouth of each tributary for analysis of at the Wisconsin State Lab of Hygiene (WSLH). Samples will be collected at least monthly with more frequent sampling in spring months for runoff events. Additional event based samples can be collected at the discretion of the biologist at other times of the year. This sampling will continue for five years. The need for continued monitoring and frequency of monitoring will be reassessed after the 2017 sampling season. Discharge data is needed to calculate mass and make annual load estimates. Discharge values will be obtained from existing USGS gauging stations located on these tributaries. Assistance from USGS will be sought for load calculations under a future project. Two of the stations, the Bois Brule River at Brule and Bad River at Odanah, are well established long-term trend (LTT) monitoring locations. This project expands the frequency of sample collection at these two LTT sites.


The objective is to obtain long term information about trends in phosphorus loading to Lake Superior from the tributary rivers in Wisconsin. Where discharge data is available it has been used to establish a combination of monthly sampling with flow proportional sampling protocol. More frequent sampling is scheduled for months with largest mean monthly discharge rates. A sampling schedule has been established based on best professional judgment after reviewing monthly stream flow statistics. It is expected that winter conditions may occasionally prohibit sample collection at some or all stations which will lower the number of samples collected per year. Samples from the LTT sites on the Brule and Bad Rivers are currently collected quarterly and four samples per year will continue to be funded through Tier 1 monitoring funds. The National Estuary Research Reserve (NERR) for the St Louis River is setting up its monitoring program and has been consulted as a potential partner for sampling and analysis. The sample location on the Bad River is located within the reservation boundaries of the Bad River Band of the Lake Superior Tribe of Chippewa Indians. The Bad River Band has also been contacted as a potential partner and to avoid duplication of effort.


Data collection began in 2012. We are working with the USGS to calculate initial phosphorus load calculations for the tributaries included in the study.

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