Caspar Creek macroinvertebrate assemblage responses to forest management and hydrologic disturbance Robert J. Danehy1 and Ivan Arismendi2 1 Catchment Aquatic Ecology, 5335 Saratoga St., Eugene, OR 97405 2 Oregon State University, Department of Fisheries and Wildlife, 104 Nash Hall, Corvallis, OR 97331, USA. Citation: Danehy, R.J. and I. Arismendi. 2018. Caspar Creek macroinvertebrate assemblage responses to forest management and hydrologic disturbance. Unpublished Report prepared for the California Department of Forestry and Fire Protection, contract # 8CA03674. Sacramento, CA. 18 p. Title: Caspar Creek macroinvertebrate assemblage responses to forest management and hydrologic disturbance Danehy1 R.J. and I. Arismendi 2 Abstract: We analyzed data sets from the Caspar Creek Watershed study, with a 55-year comprehensive record of hydrologic regime in two sub-watersheds with different logging treatments, and three separate instream biologic studies conducted since 1990. Long-term data sets of instream biota are rare, and we used them to investigate sediment regime response to forest harvest and extremes in flow regime. Increases in sediment transport after logging were observed in the North Fork during second experiment at Caspar Creek in the 1990’s. Our analysis found turbidities were higher after logging across the range of flows including high magnitude/short duration as well as low magnitude/long duration events. However, few sediment impacts to macroinvertebrate assemblages were observed above and below tributaries with upstream harvest. Specifically, there were no differences in presence/absence of sediment sensitive taxa before and after logging. Moreover, North and South Forks sensitive taxa distributions were similar. With the South Fork, we compared 2016 and 2017 macroinvertebrate assemblages collected in July and May respectively. Statistical classification separated South Fork communities clearly by year and watershed location, reflecting a dynamic community. A six-grouping solution of 81 taxa divided based on relative abundance, watershed distribution, and functional feeding group. Natural disturbance has been high in the watershed recently with discharge regime varying five-fold since 2014, a drought year, and with higher than normal winter flooding in 2017. Sediment sensitive taxa were distributed in two groups of the six and showed no distinguishable patterns. However, overall patterns of the whole macroinvertebrate community structure between years and watershed locations were observed in the classification. Introduction Watershed research at the Caspar Creek Experimental Watersheds is among the most intensive and long- term that has been conducted anywhere in the world. The experimental watersheds consist of two paired basins, the North Fork (NF, 473-ha) and the South Fork (SF, 424-ha). The discharge record at these basins is nearly continuous since 1962 and wet season discharge records from several North Fork tributaries date back to 1985. In addition, water quality measurements, including suspended sediment concentrations (SSC) complement much of these streamflow data. Research is conducted jointly by the US Forest Service Pacific Southwest Research Station and the California Department of Forestry and Fire Protection (CAL FIRE). The watersheds, located on Jackson Demonstration State Forest in coastal northern California, are managed to produce timber in a controlled experimental setting. The old growth coast redwood -- Douglas-fir forest was logged from 1860 to 1904, long before the experimental watersheds were established in 1960. The original harvest included clearcutting, broadcast burning, and log transportation by oxen and splash dam. Following calibration from 1962 to 1967, treatments were initiated in SF (Phase 1) in 1967 and 1971-73. The North Fork served as a control watershed until 1985 when Phase 2 treatments were begun. For the first experiment (Phase 1), 65% of the SF volume was removed by selection harvest and tractor-yarding prior to implementation of the modern California Forest Practice Rules. For the second experiment (Phase 2), 15% of NF was clear-cut in 1985. Road construction and partial clear-cut harvest continued in the remainder of NF from 1989 to 1992 (35% NF harvest) with three tributaries 1. 1. Catchment Aquatic Ecology, Eugene, OR, [email protected] 2. Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 1 gauged as undisturbed controls, five gauged tributaries clear-cut, four nested gauges in partial clear-cuts, and mostly cable yarding (Keppeler, 2012). NF logging occurred using the regulations established by the State Legislature in 1973. Research has focused on logging effects on streamflow and sediment production but has also addressed impacts on water temperature, nutrients, and organic matter regimes (Cafferata and Reid, 2013). Results have been influential both in watershed science and forest management (Cafferata and Reid 2013) and will continue to be a source of relevant information as a third experiment is implemented (Dymond 2016). For example, the Phase 2 experiment in the NF was designed to evaluate cumulative watershed effects by monitoring a network of nested sub-watersheds. The applied research on logging treatments (clear- cut vs selective harvest) and logging methods (tractor vs cable logging) will provide essential information for best management practices (BMP) development. Although the research effort has evolved through time, erosion and sediment transport remain a primary focus. Sediment production has been measured annually at the North and South Fork weir basins since 1962. Suspended sediment concentrations (SSC) were measured initially using fixed stage and manual depth- integrated sampling, and later using flow and turbidity-based automated sampling. The physical measurement of both weir pond deposition and suspended load allows for total sediment export to be estimated (Lewis, 1998) and sources of sediment (Rice et al., 1979) to be identified. Results have been described extensively and numerous papers have consistently reported sediment increases following logging (e.g., Rice et al. 1979; Ziemer, 1981, 1998; Lewis et al., 2001; Keppeler, 2012). How fine sediment regime impacts biology varies, from catastrophic impacts of high flow and elevated SSC that create very poor short-term habitat conditions, to elevated long-term SSC that change conditions less dramatically. High turbidity affects fish behavior (e.g., feeding) and larger grained sediment (coarse sand) can fill pools and clog interstitial spaces for benthic organisms while moving through a basin (Relyea et al., 2011). Comparing the extent of an event, both magnitude and duration, is another physical approach for evaluating sediment regime that will be used here. All these physical methods are robust tools to understand sediment regime in assessing water quality. One shortcoming in their use is that actual biological impacts cannot be directly assessed. Biological assessment approaches have been developed by water quality agencies throughout the world. In California, a well-developed and recognized set of protocols has been created for wadable streams (Ode et al., 2016). These new tools can be used as multiple lines of water quality. In the Caspar Creek Experimental Watersheds, there have been irregular measurements of instream biota, in contrast to the comprehensive efforts in the measurement of physical water quality characteristics. To date, there have been three primary investigations of instream biota (Table 1). From 1986 to 1994, Bottorff and Knight (1996) did a thorough study of instream animals (invertebrates) and plants (algae) in the North Fork during the Phase 2 experiment. In 2008, Cummins and Malkauskas (2008) reported on instream conditions in both basins with a focus on ecological relationships. Most recently the California Aquatic Bioassessment Laboratory has begun annual macroinvertebrate surveys along the South Fork as part of the Phase 3 experiment, beginning in 2016. Combined, these efforts cover 33 years (1986-present). Note that comparisons are complex because the instream invertebrate studies were done at different times, at different locations, and using different approaches to sampling (Table 2). Therefore, interpretations are less thorough than if those factors were more similar. Yet that cannot limit data usage, as biological data is a rare resource. Here, we attempt to carefully explore biological comparisons with multiple tools. In the examination of silvicultural activities and their impacts, instream fish and other biota are a concern. Specific knowledge of activities that may lead to sediment export from uplands to riparian systems has 2 led to well-developed techniques (Best Management Practices - BMPs) that are designed to minimize sediment delivery to streams. There is a considerable body of literature regarding BMPs, with most regions having developed and refined the practices that best fit local needs (Megahan et al., 1972; Ice and Schilling, 2012; Edwards et al., 2016; Cristan et al., 2017). Sediment BMPs are most commonly associated with roads; however, as observed in the Caspar Creek research (Cafferata and Spittler, 1998; Keppeler and Lewis, 2003; Reid and Keppeler, 2012; Reid et al. 2010) there are other sediment sources that require other types of practices as part of a comprehensive BMP plan (e.g., reduction of landslide risks, headward gully expansion). The impacts of changes to fine sediment regime on biota have