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National Aquatic Resource Surveys

Northern Plains Ecoregion - National Lakes Assessment 2012 Results

Key Results

A total of 2,740 lakes are represented by the NLA in the Northern Plains ecoregion. Of these lakes, 54% are natural and 46% are man-made.

The NLA uses trophic state as an important indicator of lake condition and assesses the extent of key stressors in the nation’s lakes.

  • In the Northern Plains, 29% of lakes are rated as most disturbed based on trophic state, 43% are eutrophic, 12% are mesotrophic, and 16% are oligotrophic.
  • The most widespread stressors assessed in the Northern Plains are phosphorus (80% of lakes), nitrogen (70%), and lakeshore disturbance (69%).

Trophic State

National Lakes Assessment 2012 Bar Chart of the Trophic State of Lakes in the Northern Plains Ecoregion

Indicator with the Highest Percentage of Lakes in the Most Disturbed Condition: Phosphorus

National Lakes Assessment 2012 Bar Chart of the Condition of Total Phosphorus in the Northern Plains

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National Lakes Assessment 2012 Sampling in the Northern Plains EcoregionNorth Dakota sampling. Photo: Aaron Larsen, NDDOH.

Human Use Condition

Cyanobacteria  is one of three algal toxin related indicators assessed in the NLA (see also chlorophyll a and microcystins).  It serves as a proxy for the presence of algal toxins.  

  • Based on cyanobacteria cell counts, 33% of lakes in the Northern Plains are in the most disturbed condition (i.e., pose a high risk of exposure to algal toxins). 

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    Change from 2007 (for lakes >4 hectares)*

    • For the Northern Plains, the NLA reports a 43% decrease in the proportion of lakes in most disturbed condition between 2007 and 2012 based on the condition of benthic macroinvertebrates.
    • The proportion of lakes in most disturbed condition increased by 22% based on the cyanobacteria risk index.
    • There was also a decrease of 21% in the proportion of lakes in the most disturbed condition based on the lake drawdown exposure indicator.

    To access more indicator graphics please visit the interactive NLA Dashboard.

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    * The change analysis is based on information from two points in time – 2007 and 2012.  The change in condition analysis only considers lakes 4 hectares and larger because smaller lakes were not sampled in 2007.