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Identifying invertebrate indicators for streamflow duration assessments in forested headwater streams
Citation:
Fritz, K., R. Kashuba, G. Pond, J. Christensen, L. Alexander, B. Washington, B. Johnson, D. Walters, W. Thoeny, AND P. Weaver. Identifying invertebrate indicators for streamflow duration assessments in forested headwater streams. Freshwater Science. The Society for Freshwater Science, Springfield, IL, 42(3):247-267, (2023). https://doi.org/10.1086/726081
Impact/Purpose:
Streamflow duration assessment methods (SDAMs) are rapid, indicator-based tools for classifying streamflow duration at the reach scale. SDAMs use indicators as surrogates because direct measurement of flow duration is too resource intensive for many reaches. Regional SDAMs are used to support the implementation of monitoring, regulatory, assessment and other water-related programs (e.g., CWA jurisdictional determinations, water quality standards, riparian buffer determination). Aquatic invertebrates are among the most common and important indicators used in existing SDAMs. The study used invertebrate data collected from 90 stream reaches distributed across 10 forests and four different regions of the U.S. The primary statistical approach to identify invertebrate taxa using different taxonomic and numeric resolution that can be used as SDAM indicators to distinguish stream reaches with intermittent and perennial flow was a type of machine learning model known as random forest. Random forest models are becoming more prevalent in ecological studies because they are capable of handling complex relationships among parameters used to predict classifications. Another approach, Indicator Species Analysis, was used to validate the selection of invertebrate indicators. Our findings highlight how invertebrate datasets may be used to maximize the information to accurately classify flow duration of stream reaches. Our findings show that there is only modest improvement in classification accuracy by using more resource intensive identification and quantification of invertebrate field data than is typically used for SDAMs. The season (spring vs summer) was a more important factor in predicting flow duration among random forest models than habitat type (riffles vs pools). We recommend invertebrate indicators should be developed regionally based on variable distribution and association with perennial and intermittent reaches across the four forested U.S. regions studied. The anticipated outcome and expected use of the findings from this product are that they inform the development and refinement of SDAMs and other stream assessments that use aquatic invertebrates.
Description:
Streamflow-duration assessment methods (SDAMs) are rapid, indicator-based tools for classifying streamflow duration (e.g., intermittent vs perennial flow) at the reach scale. Indicators are easily assessed stream properties used as surrogates of flow duration, which is too resource intensive to measure directly for many reaches. Invertebrates are commonly used as SDAM indicators because many are not highly mobile, and different species have life stages that require flow for different durations and times of the year. The objectives of this study were to 1) identify invertebrate taxa that can be used as SDAM indicators to distinguish between stream reaches having intermittent and perennial flow, 2) to compare indicator strength across different taxonomic and numeric resolutions, and 3) to assess the relative importance of season and habitat type on the ability of invertebrates to predict streamflow-duration class. We used 2 methods, random forest models and indicator species analysis, to analyze aquatic and terrestrial invertebrate data (presence/absence, density, and biomass) at the family and genus levels from 370 samples collected from both erosional and depositional habitats during both wet and dry seasons. In total, 36 intermittent and 53 perennial reaches were sampled along 31 forested headwater streams in 4 level II ecoregions across the United States. Random forest models for family- and genus-level datasets had stream classification accuracy ranging from 88.9 to 93.2%, with slightly higher accuracy for density than for presence/absence and biomass datasets. Season (wet/dry) tended to be a stronger predictor of streamflow-duration class than habitat (erosional/depositional). Many taxa at the family (58.8%) and genus level (61.6%) were collected from both intermittent and perennial reaches, and most taxa that were exclusive to 1 streamflow-duration class were rarely collected. However, 23 family-level or higher taxa (20 aquatic and 3 terrestrial) and 44 aquatic genera were identified as potential indicators of streamflow-duration class for forested headwater streams. The utility of the potential indicators varied across level II ecoregions in part because of representation of intermittent and perennial reaches in the dataset but also because of variable ecological responses to drying among species. Aquatic invertebrates have been an important field indicator of perennial reaches in existing SDAMs, but our findings highlight how including aquatic and terrestrial invertebrates as indicators of intermittent reaches can further maximize the data collected for streamflow-duration classifications.
URLs/Downloads:
DOI: Identifying invertebrate indicators for streamflow duration assessments in forested headwater streams