BBEST practices: Intentional efforts to identify elusive flow-ecology thresholds

• Hydrologic alteration thresholds are critical for river management but elusive. • Literature review compared traditional scientific studies with consensus approaches. • Consensus approach found thousands of thresholds, far more than scientific literature. • Re-analysis of trend data from literature detected previously undetected thresholds. • Intentional interdisciplinary approaches may be needed to identify elusive thresholds. Developing and discerning flow-ecology relationships, particularly identifying the limits of hydrologic alterations on aquatic ecosystems, is critical for effective water resource management. In the absence of clear, empirically derived hydrologic alteration thresholds, alternative methods such as consensus and knowledge co-production, have been employed. One example is the BBEST (Basin and Bay Area Expert Science Team) program in Texas established with the explicit goal of identifying thresholds for river systems. In this study, we conducted a comprehensive review and meta -analysis of the standing scientific literature on flow-ecology relationships in Texas and neighboring geographies and compared that literature with reports from BBEST and the Texas Instream Flow Program (TIFP). We extracted all available flow-ecology values, including trend data, thresholds, before/after comparisons, and qualitative responses, yielding a total of ∼27,000 observations. Despite three times as many scientific literature sources, 85 % of flow-ecology observations were obtained from BBEST and TIFP reports. Of these observations, 83 % (∼19,000) were thresholds, whereas these types of observations were virtually absent in the scientific literature (< 100; ∼2 %). By reanalyzing flow-ecology trend observations from literature, we found repeated evidence of the presence of thresholds, all of which were from studies originally failing to report any such values. With the exception of high flow pulses, magnitude-related thresholds from BBEST and TIFP were not significantly different from hydrologic values in scientific literature where thresholds were undetected. These observations support the position that lack of thresholds could be due to elusivity rather than absence, and intentional interdisciplinary efforts may be a step forward in identifying flow thresholds.