Westwide

To meet BLM’s national level reporting needs and have an apples to apples comparison of macroinvertebrate conditions across state boundaries, NAMC developed a westwide O/E index in 2018 using a network of interagency reference sites. This index can also be applied for states that lack state specific biocriteria or indices compatible with the BLM’s macroinvertebrate sampling methods. Index precision differs between the Eastern Xeric Plains and all other ecoregions. Therefore, separate benchmarks are used for these two ecoregional areas. To apply this index, samples should be identified to NAMC’s standard taxonomic resolution and collected between May 1st and October 1st.

Index # Reference Sites # Degraded Sites Index Mean Index SD Moderate departure from reference benchmark Major departure from reference benchmark Narative Condition
WestWide- OtherEcoregions 639 NA 1.04 0.16 <= 0.88 <= 0.72 Good, Fair, Poor
WestWide- XericEasternPlains 20 NA 0.98 0.19 <= 0.79 <= 0.6 Good, Fair, Poor

 

Western U.S. with black dots representing MMI reference sites and ecoregions areas in blue with eastern Xeric areas in green
Westwide macroinvertebrate reference sites

Box plots of catch elevation(m) on a scale of 0 to 4000 with a mean of 1750, mean annual precipitation (mm) on a scale of 0 to 4000 with a mean of 1000, temperature (C) on a scale of -1 to 20 with a mean of 5 and log watershed area (km2) on a scale of 0 to 4 with a mean of 1.5
Environmental gradients of references sites used for the westwide index and used for NAMC’s model applicability test

  • Method for accounting for natural environmental gradients: Random forest model predicting group membership
  • Predictors of reference assemblages or metrics: 
    • Mean % of lithological calcium oxide (CaO) content in surface or near surface geology within watershed
    • Latitude of the point
    • Longitude of the point
    • Mean of predicted mean annual stream temperature (Jan-Dec) for years 2008, 2009, 2013, & 2014
    • Mean of predicted mean summer stream temperature (July-Aug) for years 2008, 2009, 2013, & 2014
    • Mean of predicted mean winter stream temperature (Jan-Feb) for years 2008, 2009, 2013, & 2014
    • Mean % of lithological nitrogen (N) content in surface or near surface geology within catchment
    • % of watershed area classified as lithology type: saline like sediment
    • PRISM climate data - 30-year normal mean precipitation (mm): Annual period: 1981-2010 within the watershed
    • Mean runoff (mm) within watershed
    • Mean % of lithological sulfur (S) content in surface or near surface geology within watershed
    • Watershed area (square km) at NHDPlus stream segment outlet, i.e., at the most downstream location of the vector line segment
  • # of Macroinvertebrate groups obtained by hierarchical cluster analysis: 25
  • Fixed count: 300
  • Minimum count: unspecified
  • Operational Taxonomic Unit (OTU) applied: Yes
  • Rare taxa <0.5 probability of capture included: No