DOI: 10.25338/b8x07h
title: Data for: Mimicking functional elements of the natural flow regime promotes native fish recovery in a regulated river

description: Environmental flows are essential to the conservation of riverine
 biodiversity, and are increasingly designed to protect components of the
 flow regime that support critical ecosystem functions. Yet, few studies
 have quantified biological responses to individual components of
 environmental flows. We used multivariate autoregressive state-space
 (MARSS) models to analyze 25 years of fish assemblage data collected
 before and after court-ratified environmental flows were implemented in
 Putah Creek, a dammed stream in California, USA. We quantified functional
 components of the flow regime that have been identified for Mediterranean
 climate regions of western North America and identified changes in these
 components from before to after the environmental flow regime was
 implemented. Additionally, we compared these values to their predicted
 natural ranges and modeled the probability of native and non-native fish
 assemblages declining by &gt; 80% (quasi-extinction risk) under
 alternative management scenarios spanning the observed range of flow
 conditions. We found that as individual functional flow metrics became
 more similar to the ranges expected under natural, unaltered conditions,
 the quasi-extinction risk for the native fish assemblage decreased. Three
 functional flow metrics that shifted towards natural ranges following
 environmental flow implementation, fall pulse flow magnitude, wet season
 timing, and dry season duration, each corresponded with a 40% or greater
 decrease in native assemblage quasi-extinction risk. However, decreased
 spring recession flows and greater dry season baseflows post-flow
 modification shifted these metrics further from their natural ranges,
 increasing quasi-extinction risk for the native assemblage. Flow
 management scenarios revealed that the non-native fish assemblage
 quasi-extinction risk increased as flow metrics became more natural and
 decreased under more altered flow conditions. Few functional flow metrics
 were restored to their natural ranges following environmental flow
 implementation, yet even the modest changes towards more natural flows
 were found to suppress non-native and benefit native fish assemblages. Our
 findings illustrate that mimicking functional components of the natural
 flow regime is an important tool for designing environmental flows to
 conserve freshwater biodiversity.
description: Fish dataset The fish assemblage of Putah
 Creek was sampled annually by TRPA Fish Biologists and Normandeau
 Associates between 1993 and 2019 (with the exception of 2009 and 2011)
 using single-pass tote barge electrofishing. Fish were sampled at six
 locations downstream of the Putah Creek diversion dam. For these analyses,
 we restricted the sites considered to only the four sites closest to the
 diversion dam. These sites (site codes PDD, I505, STEVE, and PED) were
 approximately 0, 6, 16, and 21 km downstream of the diversion dam
 (respectively). Previous research found that the lower two sites (25 and
 30 km downstream of the dam) were minimally affected by environmental
 flows implementation due to degraded habitat conditions (Kiernan et al.
 2012). Functional flow metric calculations
 Discharge data from the Putah Creek diversion dam were provided
 by the US Bureau of Reclamation for 7/1/1975 – 8/31/202. All functional
 flow metrics were calculated on 40 years of streamflow data, spanning the
 20 years before (pre) or 20 years after (post) environmental flow
 implementation, using the ffcAPIClient package (Santos et al. 2021,
 version 0.9.8.3) in R (R Core Team 2019). However, signal-processing
 algorithms in this version of the ffcAPIClient package do not always
 correctly identify the timing of seasonal transitions in highly modified
 hydrographs (Patterson et al. 2020). To improve the accuracy of flow
 metrics, we developed a ruleset to manually identify seasonal timing
 metrics (Baruch et al., in review). This ruleset was applied to all years,
 and all other metrics were re-calculated following Patterson et al. (2020)
 using the updated timing metrics. Additionally, the fall pulse does not
 occur every year but was an important component of the new environmental
 flow regime. To better understand changes in fall pulse flows, we
 calculated the fall pulse magnitude as the difference between dry season
 median flow magnitude and the maximum magnitude of the first discharge
 event greater than 1.5 times the dry season baseflow that occurred between
 October 1 and December 15th. Years with no fall pulse therefore have a
 magnitude of 0. Predictions of natural, unimpaired streamflow conditions
 were calculated by Grantham et al. ( 2022; additional information
 available at https://rivers.codefornature.org/). Streamflow data for Upper Putah Creek was obtained from the USGS (gauge 11453500) to create a hydrograph of natural streamflow conditions upstream of all major water impoundments and diversions for comparison to the downstream flow conditions. Missing flow data at the Upper Putah Creek gauge were modeled from the nearby Bear Creek gauge (USGS 11451715). The same manual ruleset for functional flow metric calculation was applied to the Upper Putah Creek streamflow data for consistency with the downstream data. References Grantham, T. E., D. M. Carlisle, J. Howard, B. Lane, R. Lusardi, A. Obester, S. Sandoval-Solis, B. Stanford, E. D. Stein, K. T. Taniguchi-Quan, S. M. Yarnell, and J. K. H. Zimmerman. 2022. Modeling functional flows in California’s rivers. Frontiers in Environmental Science 10. Kiernan, J. D., P. B. Moyle, and P. K. Crain. 2012. Restoring native fish assemblages to a regulated California stream using the natural flow regime concept. Ecological Applications 22:1472–1482. Patterson, N. K., B. A. Lane, S. Sandoval-Solis, G. B. Pasternack, S. M. Yarnell, and Y. Qiu. 2020. A hydrologic feature detection algorithm to quantify seasonal components of flow regimes. Journal of Hydrology 585:124787. R Core Team. 2019. R: a language and environment for statistical computing. Vienna, Austria. https://www.r-project.org/. Santos, N., R. Peek, and A. Obester. 2022. ffcAPIClient: Functional Flows Calculator API Client. R package version 0.9.8.3.