Streamwatch Project

Water Quality

Benthic macroinvertebrates are a cost-effective, commonly used, and widely accepted tool in water-quality monitoring programs. The Macroinvertebrate Aggregated Index for Streams (MAIS) uses the presence and relative abundances of certain macroinvertebrates, combined with knowledge of their ability to withstand pollution to come up with a water quality "score" for each site. This MAIS score is used to classify streams on a continuum from Good (macroinvertebrate assemblages characteristic of clean, healthy streams) to Fair (experiencing moderate environmental stress) to Poor (experiencing severe environmental stress).Move cursor over graph to see an enlarged view.

Within each reach of the White Clay Creek, sites are in order from upstream to downstream for each branch. Site means are based anywhere from 1-12 years of data taken between 1994-2008.  Site 11 was the only location rated as having Good water quality, 9 sites were Fair (Sites 12, 0, 3, 4, 7, 19, 17, 24, 23) and 8 sites were Poor (Sites 25, 18, 16, 6, 14, 20, 21, 22). All headwater sites (Sites 11, 0, 19) rated higher water quality than downstream locations. All three branches of the Upper White Clay had sites in the Fair and/or Poor category and all sites on the Lower Mainstem were Poor indicating degraded water quality in the White Clay Creek watershed.

The highest MAIS score occurred on the East Branch at Site 11 and the lowest MAIS score was at Site 25, a tributary on the East Branch. A good site is characterized by a dominance of mayflies, stoneflies and caddisflies (a.k.a. EPT) and a bad site has high numbers of pollution tolerant taxa (e.g., worms and midge larvae).

Three Water Quality Indices

There are many variables to consider when monitoring a stream such as collection method (e.g., a defined sample area versus a random collection of many habitats), processing method (e.g., in the field versus a microscope), identification level (e.g., volunteers identifying to a higher level like family versus an expert naming a taxa to species), number of individuals examined (e.g., 100-300), analysis method (what indices are use to evaluate the data), etc.  Because of these factors we wanted to examine using the same data set how different indices compared. We choose three commonly used indices employed by volunteer programs: Macroinvertebrate Aggregated Index for Streams (MAIS), Maryland Indices of Biotic Integrity (MDIBI), and Virginia Save Our Stream (VASOS). MAIS is the primary index we use because we have worked with it for >10 years and feel it represents stream condition well, while MDIBI and VASOS provide perspective.

Table.  Some attributes of three indices used to examine water quality in the White Clay Creek. Learn more about these indices.

Overall, the indices were comparable for most streams.  MAIS and MDIBI gave the same rating for 16 of the 18 streams. Both Indexes rated Poor sites similarly, but MDIBI rated three streams as Good versus only one by MAIS. VASOS rated 14 of the 18 streams the same as the MAIS. In contrast, VASOS rated more sites as Poor compared to MAIS.