Data analysis is critical to nutrient criteria development. Appropriate analysis and data interpretation determines the scientific defensibility and effectiveness of criteria. Therefore, it is important to briefly reevaluate decisions regarding management goals made during previous phases and conceptual linkages between nutrients and assessment endpoints. Analysis can proceed after planning and problem formulation outputs have been reviewed and data sets have been assembled. This section covers important factors to consider in selecting an analytical approach. It also provides detailed instructions on applying three empirical approaches to deriving numeric criteria: reference condition, stressor-response, and mechanistic modeling.

This analysis phase addresses the following topics:

  • Data considerations
  • How to select an analysis approach
  • Analysis approaches
    • Reference Condition
    • Stressor-Response
    • Mechanistic Modeling

Case Studies

St. Louis Bay, MS

  • Develop an approach that can be used regionally
  • Stressor-response and mechanistic modeling approaches were selected

NNC Development for Desert Streams

  • Nutrient dynamics are hard to characterize in streams with high spatial and temporal variability
  • Influencing factors include geology, climate, community structure, N-fixation, and hydrology

Defining Natural Conditions

  • A chlorophyll a rating system was used
  • Chlorophyll a ratings at each location were based on monthly mean photic zone concentrations
  • Other inhibiting factors were considered when there were nutrients but low chlorophyll a

Classification of MN Lakes

  • Developed box-and-whisker plots using data from 90 reference lakes in Minnesota
  • Data included chlorophyll a, TP, TN, and Secchi depth
  • Results supported the use of ecoregions to help develop criteria

Estuarine Criteria in Florida

  • Considered reference condition, stressor-response, and mechanistic modeling approaches
  • Evaluated each approach based on strengths, weaknesses, and applicability
This website is in beta. Information on this website is not final and is subject to change