Initial development of a benthic macroinvertebrate multimetric index for monitoring the ecological integrity of northern Mongolian streams

The quality and quantity of Mongolia’s water resources are being degraded by ineffective water-management. There is no widely accepted biomonitoring system for Mongolia, only hydrological and chemical monitoring, with limited relevance for living organisms. Therefore, this study has aimed to develop a Mongolian-specific multimetric index and biocriteria applicable to the biological assessment of Mongolian streams. A total of 66 stream sites in northern Mongolia were selected representing different gradients of land use. In total, 30 candidate metrics representing the following four categories of ecological condition were used: diversity/richness, composition/abundance, trophic status, and tolerance/sensitivity. The resulting candidate metrics were evaluated using a stepwise procedure for metric variability, redundancy, sensitivity, and responsiveness to environmental gradients. According to the Mann-Whitney U test, 21 metrics showed statistically significant differences between the reference and impaired groups (P < 0.05). A metric showed interquartile overlap and thirteen metrics were redundant based on Spearman’s correlation analysis (r > 0.8). Finally, five metrics were retained and included in the multimetric index system and all clearly distinguished reference and impaired sites. Then the range of the multimetric index score (numerical value 0–1) was subdivided into five categories (reference/excellent ≥ 0.8, good < 0.8 to ≥ 0.6, moderate < 0.6 to ≥ 0.4, poor < 0.4 to ≥ 0.2, severe < 0.2) related to level of impairment. Thus, this multimetric index successfully distinguished reference from impaired conditions, demonstrating its applicability for northern Mongolian stream assessment. Hence, the Mongolian-specific Macroinvertebrate Multimetric Index (MMI-MON) can be used as a principal assessment tool for assessing waterways in northern Mongolia and possibly throughout the country, detecting future changes and providing valuable information for land-use management and conservation of aquatic ecosystems of Mongolia.