California River Research Articles

Stream flow modeling tools inform environmental water policy in California

Management of California's vast water distribution network, involving hundreds of dams and diversions from rivers and streams, provides water to 40 million people and supports a globally prominent agricultural sector, but it has come at a price to local freshwater ecosystems. An essential first step in developing policies that effectively balance human and ecosystem needs is understanding natural stream flow patterns and the role stream flow plays in supporting ecosystem health. We have developed a machine-learning modeling technique that predicts natural stream flows in California's rivers and streams. The technique has been used to assess patterns of stream flow modification, evaluate statewide water rights allocations and establish environmental flow thresholds below which water diversions are prohibited. Our work has informed the statewide Cannabis Cultivation Policy and influenced decision-making in more subtle ways, such as by highlighting shortcomings in the state's water accounting system and building support for needed reforms. Tools and techniques that make use of long-term environmental monitoring data and modern computing power — such as the models described here — can help inform policies seeking to protect the environment while satisfying the demands of California's growing population.

Hydro-morphological parameters generate lifespan maps for stream restoration management

Anthropogenic, eco-morphological degradation of lotic waters necessitates laws, directives, and voluntary actions involving stream restoration and habitat enhancement. Research and engineering efforts are establishing a vast number of stream restoration planning approaches, design testing frameworks, construction techniques, and performance evaluation methods. As the practice of restoration scales up from an individual action at a single site to sequences of actions at many sites in a long river segment, a primary question arises as to the lifespan of such a sequence. This study develops a new framework to identify relevant parameters, design criteria and survival thresholds for ten multidisciplinary restoration techniques, adequate for site-scale to segment-scale application, in a comprehensive review: (1) bar and floodplain grading; (2) berm setback; (3) vegetation plantings; (4) riprap placement; (5) sediment replenishment; (6) side cavities; (7) side channel and anabranches; (8) streambed reshaping; (9) structure removal; and (10) placement of wood in the shape of engineered logjams and rootstocks. Survival thresholds are applied to a sequence of proposed habitat enhancement features for the lower Yuba River in California, USA. Spatially explicit hydraulic and sediment data, together with numerical model predictions of the measures, were vetted against the survival thresholds to produce discharge-dependent lifespan maps. Discharges related to specific flood-return periods enabled probabilistic estimates of the longevity of particular design features. Thus, the lifespan maps indicate the temporal stability of particular stream restoration and habitat enhancement features and techniques. Areas with particularly low or high lifespans help planners optimise the design and positioning of restoration features.

Fishery collapse, recovery, and the cryptic decline of wild salmon on a major California river

Fall-run Chinook salmon (Oncorhynchus tshawytscha) from the Sacramento–San Joaquin River system form the backbone of California’s salmon fishery and are heavily subsidized through hatchery production. Identifying temporal trends in the relative contribution of hatchery- versus wild-spawned salmon is vital for assessing the status and resiliency of wild salmon populations. Here, we reconstructed the proportion of hatchery fish on natural spawning grounds in the Feather River, a major tributary to the Sacramento River, using strontium isotope (87Sr/86Sr) ratios of otoliths collected during carcass surveys from 2002 to 2010. Our results show that prior to the 2007–2008 salmon stock collapse, 55%–67% of in-river spawners were of hatchery origin; however, hatchery contributions increased drastically (89%) in 2010 following the collapse. Data from a recent hatchery marking program corroborate our results, showing that hatchery fish continued to dominate (∼90%) in 2011–2012. Though the rebound in abundance of salmon in the Feather River suggests recovery of the stock postcollapse, our otolith chemistry data document a persistent decline of wild spawners, likely leading to the erosion of locally adapted Feather River salmon populations.

Mercury Sourcing and Sequestration in Weathering Profiles at Six Critical Zone Observatories

AbstractMercury sequestration in regolith (soils + weathered bedrock) is an important ecosystem service of the critical zone. This has largely remained unexplored, due to the difficulty of sample collection and the assumption that Hg is predominantly sequestered within surface soils (here we define as 0–0.3 m). We measured Hg concentrations and inventories in weathering profiles at six Critical Zone Observatories (CZOs): Boulder Creek in the Front Range of Colorado, Calhoun in the South Carolina Piedmont, Eel River in coastal northern California, Luquillo in the tropical montane forest of Puerto Rico, Shale Hills of the valley and ridges of central Pennsylvania, and Southern Sierra in the Sierra Nevada range of California. Surface soils had higher Hg concentrations than the deepest regolith samples, except for Eel River, which had lower Hg concentrations in surface soils compared to regolith. Using Ti normalization, CZOs with <12% rock‐derived Hg (Boulder Creek, Calhoun, and Southern Sierra) had Hg peaks between 1.5 and 8.0 m in depth. At CZOs with >50% rock‐derived Hg, Eel River Hg concentrations and pools were greatest at >4.0 m in the weathering profile, while Luquillo and Shale Hills had peaks at the surface that diminished within 1.0 m of the surface. Hg and total organic C were only significantly correlated in regolith at Luquillo and Shale Hills CZOs, suggesting that Hg sorption to organic matter may be less dominant than clays or Fe(II) sulfides in deeper regolith. Our results demonstrate the importance of Hg sequestration in deep regolith, below typical soil sampling depths.

The impact of persistent dynamics on suspended sediment load estimation

Fluvial suspended sediment concentration and discharge is most commonly estimated by applying rating curves developed over a given base period of sediment monitoring to longer, continuous records of water discharge. This practice invokes the tacit assumption of stationary suspended sediment concentration–water discharge relationships (i.e. suspended sediment behavior). Here the ramifications of this assumption are explored through an investigation into the temporal dependence of suspended sediment concentration–discharge relationships for all hydrologic stations on small rivers draining the west coast of the continental US that have been monitored for suspended sediment over a period of 10 years or more. Persistent suspended sediment behavior was found to be the norm, with 19 of 24 stations expressing apparent monotonic trends over their base periods, and 21 stations with finer scale (subannual to interdecadal) persistent patterns. The identified persistent periods of suspended sediment behavior corresponded to distinct rating curves that differed significantly from other periods in terms of offset, slope, or both. Assuming stationary suspended sediment behavior resulted in 1% to 63% biasing of suspended sediment load. Applying rating curves developed for single persistent periods to broader discharge records resulted in up to 10× potential error in estimated sediment load. The risk of falsely characterizing the long-term (interannual-scale) suspended sediment behavior of a river through a single persistent period of elevated or depressed behavior may be much higher than expected. The average duration of identified persistent periods was 8.6 years, which is longer than the base period of suspended sediment monitoring for most river stations in the US. Peak discharge (high discharge events 20 to 1000 times mean discharge) was usually followed by periods of increased sediment concentration across US Pacific Coast. Seven rivers in Oregon and northern California displayed the same pattern of decadal- to interdecadal-scale elevated suspended sediment concentrations following the Great Christmas Floods of 1964.

Decreased streamflow impacts fish movement and energetics through reductions to invertebrate drift body size and abundance

AbstractStreamflow drives ecological processes across multiple trophic levels making it a “master variable in lotic systems.” In mountain systems, especially those that are regulated, increased frequency of droughts and reductions in snowpack may alter future streamflow regimes and impact ecological processes. We monitored invertebrate drift abundance, size, and diversity as a function of streamflow. We then related these variables to fish movement and energetic efficiencies in the Upper Shasta River in California, above and below a large streamflow diversion. Invertebrate drift biomass was significantly less at impaired flows compared with unimpaired flows, and average body size of invertebrates decreased with decreasing streamflow. Generally, fish movement was greater at the impaired flow site (>50% of the time fish were tracked). Fish movement at the upstream site was negatively related to the size of individual prey items and amount of prey available, and significant drivers were not detected in the flow‐impaired site. Energetic efficiency was reduced by over 70% when search foraging took place, and the net rate of energetic intake was below 0 J/s for low‐flow periods. Our results suggest that fish foraging behaviour may be influenced indirectly by altered streamflow through changes to amount and size of invertebrate drift. A shift to foraging behaviour, coupled with low food availability, results in decreased energetic efficiency. Future prescriptions of flow rates to regulated rivers should account for changes to invertebrate drift, fish behaviour, and fish energetics on seasonal time scales.

Hierarchically nested river landform sequences. Part 2: Bankfull channel morphodynamics governed by valley nesting structure

AbstractRiver corridors exhibit landforms nested within landforms repeatedly down spatial scales. In Pasternack et al. (), a new, scale‐independent, hierarchical river classification was developed that uses five landform types to map the domains of a single fluvial process – flow convergence routing – at each of three–five spatial scales. Given those methods, this study investigated the details of how flow convergence routing organizes nested landform sequences. The method involved analyzing landform abundance, sequencing, and hierarchical nesting along the 35 km gravel/cobble lower Yuba River in California. Independent testing of flow convergence routing found that hydraulic patterns at every flow matched the essential predictions from classification, substantiating the process–morphology link. River width and bed elevation sequences exhibit large, nonrandom, and linked oscillations structured to preferentially yield wide bars and constricted pools at base flow and bankfull flow. At a flow of 8.44 times bankfull, there is still an abundance of wide bar and constricted pool landforms, but larger topographic drivers also yield an abundance of nozzle and oversized landforms. The nested structure of flow convergence routing landforms reveals that base flow and bankfull landforms are nested together within specific floodprone valley landform types, and these landform types control channel morphodynamics during moderate to large floods. As a result, this study calls into question the prevailing theory that the bankfull channel of a gravel/cobble river is controlled by in‐channel, bankfull, and/or small flood flows. Such flows may initiate sediment transport, but they are too small to control landform organization in a gravel/cobble river with topographic complexity. Copyright © 2018 John Wiley & Sons, Ltd.

Modeling fine particle dynamics in gravel-bedded streams: Storage and re-suspension of fine particles

Fine particles or sediments have various effects on water quality and aquatic ecosystems. Thus, understanding the dynamics of these fine particles between water body and stream bed is an important issue in sediment research. Previous studies and analysis of empirical data suggest that fine particles are stored in the sediment bed in the low flow regime, where flow rate is smaller than the critical flow rate that mobilizes the sediment bed. These fine particles are re-suspended during flood events when the flow rate becomes larger than the critical flow rate that mobilizes bed material. The transition from pattern recognition to process analysis required incorporation of the dominant processes controlling fine particle dynamics within gravel-bedded streams into a model. The process analysis was performed using continuous flow and turbidity data at two locations on the Russian River in California to test process descriptions and then calibrate a quantitative model to represent those processes. The resulting process model coupled fine particle retention within the sediment bed by filtration and sedimentation with the release of accumulated fine particles in response to flood events. Model parameters, such as the critical flow rate required for initiating sediment bed fluidization, the maximum fine particle storage capacity within the sediment bed, and background particle concentration for the watershed, were estimated from the monitoring data. Model calibration optimized the filtration and the sediment bed fluidization parameters over two or three years of data. Overall, the difference between modeled and observed fine particle mass released from the sediment bed was within 20% of the measured mass.

Effects of Extreme Hydrologic Regimes on Juvenile Chinook Salmon Prey Resources and Diet Composition in a Large River Floodplain

AbstractClimate and hydrologic variability are defining characteristics of California rivers. Recently, the region experienced an unprecedented drought, and the probability of similarly warm, dry conditions is predicted to increase. In addition to warming air and water temperatures, climate change projections predict increased flooding and sea level rise, likely aggravating the water resource issues that already challenge the western United States. Water managers balance many public interests, including the conservation of native fishes, such as the Chinook Salmon Oncorhynchus tshawytscha. Given projected changes in climate and hydrology, there is an urgent need to understand how salmon respond to these conditions. In this study, we examined how young salmon responded to extreme drought (2012–2015) versus flood (1998–1999) conditions in the Yolo Bypass, a floodplain–tidal slough complex of the Sacramento River, California. We found that the diets of juvenile Chinook Salmon were dominated by aquatic–riparian insects during flooding and were dominated by zooplankton during the drought. Although juvenile salmon that were caught during the drought seemed to have eaten a higher number of prey items on average, they also had higher metabolic costs. Therefore, it is likely that juvenile salmon must augment their foraging behavior to offset higher temperatures and prey shifts. Finally, preferentially consumed, calorically valuable prey (i.e., larger zooplankton and aquatic–riparian insects) have become rare due to habitat degradation and biological invasions, and resource managers must consider re‐establishing productive off‐channel habitats, such as riparian corridors, floodplains, and wetlands.

Storage and export of soil carbon and mineral surface area along an erosional gradient in the Sierra Nevada, California

Steep soil-mantled hillslopes are thought to be important sources of sediments and organic carbon (OC) to rivers. Minerals in these sediments may protect OC from decomposition, yet the significance of such interactions in steep upland soils remains poorly constrained particularly in relation to erosion rates. We examined a tributary basin draining to the Middle Folk Feather River in California, where knickpoint migration has created a series of hillslopes with erosion rates varying over an order of magnitude (35 to 250 mm kyr−1). This setting provides a unique opportunity to study soil OC pools and their erosional exports as a function of changes in erosion rates. Soil OC inventories were 37% lower at rapidly eroding sites relative to slowly eroding sites. This difference was driven by coarse rock contents as rapidly eroding soils had more rock fragments, limiting their capacities to store OC. Although clay contents in soils were negatively correlated with erosion rates, the total mineral specific surface area remained relatively invariant. Based on secondary phyllosilicate minerals present in the studied soils and our field observations of saprocks, we suggest that this discrepancy may have originated from different clay mineralogy (types and abundance) associated with different degrees of deep subsurface chemical weathering. Across the erosion gradient, the radiocarbon age of mineral associated organic matter (MOC) in saprock varied by a factor 2 (from 1045 to 2110 14C years), while soil turnover times estimated from soil thickness and erosion rates varied from 17 to 5.4 kyr. At the site eroding at the fastest rate, the soil turnover time approaches the 14C age of MOC, suggesting erosion can potentially limit the timescale over which MOC is replaced. We found that organic matter generally covered <50% of the total mineral surface. The remaining OC-free mineral surface area, once eroded, may thus have a significant, and to date unquantified, capacity to adsorb additional organic matter, which may act as a long-term atmospheric carbon sink.

Reach specific use of spawning habitat by adult green sturgeon ( Acipenser medirostris ) under different operation schedules at Red Bluff Diversion Dam

Mature green sturgeon, Acipenser medirostris, enter rivers along the western coast of North America in late winter to late spring and migrate upriver to spawning sites. After spawning, they may leave the river or spend the summer and autumn holding in deep pools before departing from the river with the onset of winter rains. Evidence exists that the seasonal Red Bluff Diversion Dam (RBDD) was an obstacle to the upriver migration of green sturgeon in the Sacramento River in Central California. We compared the migratory movements of green sturgeon under three different dam operation schedules, including post-decommissioning, to assess the impact of this management action. The proportion of green sturgeon carrying acoustic transmitters that moved above the RBDD was higher when the gates were closed on June 15, one month later than the historical closure date of May 15, and increased again after the dam was decommissioned. The application of statistical analyses (generalized linear and additive mixed models) to the detection records of green sturgeon highlighted an improvement in connectivity after dam decommissioning. The data also indicate that interannual variation in river condition is an important driver of sturgeon presence on the spawning grounds.

Kayak drifter surface velocity observation for 2D hydraulic model validation

AbstractAdvances in remote sensing, informatics, software, and microprocessors enable meter‐resolution two‐dimensional (2D) hydrodynamic models that produce nearly a census of ecohydraulic conditions over long river segments with 105 to 108 computational elements. It is difficult to test statistical and spatial model performance at such scope using fixed‐point velocity measurements, because field methods are so expensive, laborious, slow, and restricted by safety factors. This study evaluated low‐cost water surface particle tracking by kayak with real‐time kinematic GPS for 2D model validation using 7.2 km of the lower Yuba River in California. Observed flows were between 15 to 140 m3/s, which were in‐channel up to and including bankfull conditions. The coefficients of determination between 5,780 observations and 2D model predictions were 0.79 and 0.80 for velocity magnitude and direction, respectively. When surface speed was downscaled and compared to modelled depth‐averaged velocity, median unsigned difference was 15.5%. Standard hydrological model performance metrics affirmed satisfactory validation. Surface tracking provided the novel benefit of enabling validation of velocity direction, and that testing found satisfactory performance using all metrics. Having 10 to 1,000 times more data enables robust statistical testing and spatial analysis of both speed and direction, which outweighs the loss of depth‐averaged data. Both fixed‐point and kayak particle tracking methods are useful tools to help evaluate 2D model performance.

Synoptic Sampling to Determine Distributed Groundwater‐Surface Water Nitrate Loading and Removal Potential Along a Lowland River

AbstractDelineating pollutant reactive transport pathways that connect local land use patterns to surface water is an important goal. This work illustrates high‐resolution river mapping of salinity or specific conductance (SC) and nitrate ( ) as a potential part of achieving this goal. We observed longitudinal river SC and nitrate distributions using high‐resolution synoptic in situ sensing along the lower Merced River (38 river km) in Central California (USA) from 2010 to 2012. We calibrated a distributed groundwater‐surface water (GW‐SW) discharge model for a conservative solute using 13 synoptic SC sampling events at flows ranging from 1.3 to 31.6 m3 s−1. Nitrogen loads ranged from 0.3 to 1.6 kg N d−1 and were greater following an extended high flow period during a wet winter. Applying the distributed GW‐SW discharge estimates to a simplistic reactive nitrate transport model, the model reproduced observed river nitrate distribution well (RRMSE = 5–21%), with dimensionless watershed‐averaged nitrate removal (kt) ranging from 0 to 0.43. Estimates were uncertain due to GW nitrate data variability, but the resulting range was consistent with prior removal estimates. At the segment scale, estimated GW‐SW nitrate loading ranged from 0 to 17 g s−1 km−1. Local loading peaked near the middle of the study reach, a location that coincides with a shallow clay lens and with confined animal feed operations in close proximity to the river. Overall, the results demonstrate the potential for high‐resolution synoptic monitoring to support GW‐SW modeling efforts aimed at understanding and managing nonpoint source pollution.

Azithromycin sorption and biodegradation in a simulated California river system

Azithromycin (AZ) is a widely-used macrolide antibiotic that is continually deposited into natural waterways by sewage effluent. Though recognized as an emerging contaminant of concern, little is known about its fate and transport in aquatic systems. American River soils and water were used to determine degradation of AZ in microcosms simulating flooded (anaerobic) and non-flooded (aerobic) California watershed conditions. Under aerobic conditions the degradation rate constant (k=0.0084 ± 0.0039 day−1) and DT50 (82.52 ± 56.54 days) were calculated, as AZ disappearance indicated potential degradation. However, based on concurrent product appearance, less than one percent of the parent degraded over 150 days. Throughout the experiment microbial growth was observed by culturing in tryptic soy broth despite antibiotic addition and soil being autoclaved. Sorption likely contributes to AZ recalcitrance, thus the soil-water partition coefficient (log Kd = 2.18 Lkg−1), Freundlich sorption and desorption coefficients (log Kf = 1.90 ± 0.14 and log Kfd = 2.51 ± 0.30, respectively), and organic-carbon-normalized distribution coefficient (log Koc = 4.25 Lkg−1) were also calculated. Based on these results, AZ degradation in aquatic systems will likely be very limited and transport will fluctuate based on the extent of soil-water saturation or bulk movement of sediment.

Coherence Between Coastal and River Flooding along the California Coast

ABSTRACT Odigie, K.O. and Warrick, J.A., 2018. Coherence between coastal and river flooding along the California coast. Water levels around river mouths are intrinsically determined by sea level and river discharge. If storm-associated coastal water-level anomalies coincide with extreme river discharge, landscapes near river mouths will be flooded by the hydrodynamic interactions of these two water masses. Unfortunately, the temporal relationships between ocean and river water masses are not well understood. The coherence between extreme river discharge and coastal water levels at six California river mouths across different climatic and geographic regions was examined. Data from river gauges, wave buoys, and tide gauges from 2007 to 2014 were integrated to investigate the relationships between extreme river discharge and coastal water levels near the mouths of the Eel, Russian, San Lorenzo, Ventura, Arroyo Trabuco, and San Diego rivers. Results indicate that mean and extreme coastal water levels during e...

30-year response to damming of a Mediterranean river in California, USA

Dry Creek is a major tributary of the Russian River in Northern California (USA) that has experienced hydrologic and morphologic alterations after the closure of Warm Springs Dam in 1983. Our objective is to present a detailed diagnosis of the modification of the creek’s flow and sediment regimes, and interpret the alterations regarding the ecomorphologic evolution previously observed in the creek. Statistical analysis of the river’s flow and sediment series indicates that dam operation has had significant impacts on the magnitude and frequency of occurrence of the highest floods, and the magnitude, variability, and duration of low and very low flows. Similarly, sediment concentration and discharge have also experienced major alterations. Loss of habitat complexity for native flora and fauna (especially endangered salmonids), channel incision, and vegetation encroachment are some of the negative trends found for the creek over the last 30 years, since river regulation began. We discuss the present dynamics of the river and propose, on that basis, the improvement of its hydromorphic functioning as part of future large-scale restoration initiatives.

Derived Observations From Frequently Sampled Microwave Measurements of Precipitation—Part I: Relations to Atmospheric Thermodynamics

This is the first of two papers that quantify the high added value of frequent 3-D radar observations of the atmosphere to capture the dynamics of weather systems. Recent advances in small-satellite and radar technologies, such as the “Radar in Cubesat” developed at the Jet Propulsion Laboratory, are paving the way for the design of convoys of spaceborne radars that can directly observe the evolution of severe weather at very fine temporal scales. The analyses presented here are to establish the relation between such observations to the underlying cloud variables and processes, and to quantify the sensitivity to the different physical and instrument parameters. In this first part, a robust algorithm is proposed to estimate the horizontal advection from successive radar reflectivity measurements, and use it to compute total time derivatives $d_{t} Z$ of the observed radar reflectivity factors $Z$ . As illustrated using Next-Generation Radar measurements in a blizzard coupled with an atmospheric river in California, the maps of $d_{t} Z$ reveal features about locations of sources and sinks of condensed water, which are, otherwise, not visible in the maps of $Z$ alone. Using numerical simulations of the blizzard and a radiative-transfer model to forward calculate the corresponding reflectivity factors $Z$ in the S-band, we show the robust correlation between $d_{t} Z$ and the moistening of the troposphere.

Organic geochemistry of funginite (Miocene, Eel River, Mendocino County, California, USA) and macrinite (Cretaceous, Inner Mongolia, China)

Funginite from the Miocene Sand Bank coal from outcrops along the Middle Fork Eel River in Mendocino County, California, and coprolitic macrinite from the Lower Cretaceous Shengli Formation No. 6 coal, Inner Mongolia, were investigated using optical microscopy, confocal scanning laser microscopy (CLSM), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), Raman micro spectroscopy, and micro-Fourier transform infrared spectroscopy (FTIR). The examinations showed that the Sand Bank funginite has a higher reflectance than the surrounding vitrinite and that the Shengli macrinite has a 0.41–1.13% reflectance range, lower than the reflectance of the adjacent fusinite but higher than the 0.36–0.37% Rr of the vitrinite. CLSM revealed fine structure and morphology of multicellular fungal sclerotia with distinct smooth to granular margins, thick bands enveloping the entire fungal body, and thin- or thick hyphae and hyphae lumens. SEM-EDS indicated that the rootlet interior to the funginite contained Si, Al, S, and Ca; the funginite and macrinite contained S and Ca; and the surrounding matrix contained illite and, perhaps, the phosphates gorceixite-crandallite. The coprolitic macrinite contained quartz and clay. The funginite proved to be more aliphatic than the surrounding vitrinite. The coprolitic macrinite and the macrinite have shorter and more branched aliphatic chains than the associated vitrinite. The obtained results contribute to the assessment of funginite and macrinite in terms of morphology and maceral chemistry, indicating an interaction of plant hosts with mutualistic fungi and decomposers.

Variation in thermal niche of a declining river‐breeding frog: From counter‐gradient responses to population distribution patterns

Abstract When dams or climate change alter the thermal regimes of rivers, conditions can shift outside optimal ranges for aquatic poikilothermic vertebrates. Plasticity in thermal performance and preference, however, may allow temperature‐vulnerable fauna to persist under challenging conditions. To determine the effects of thermal regime on Rana boylii (Ranidae), a threatened frog species endemic to rivers of California and Oregon, we quantified tadpole thermal preferences and performance in relation to thermal conditions. We monitored temperature and censused populations across a coastal to inland cline in six catchments where dams have altered thermal environments in close proximity to river reaches with natural conditions. We found geographic variation in population distribution and abundance based on river size combined with water temperature. The large inland rivers that supported breeding frogs, although cooler in spring due to snowmelt, became warmer during the summer than occupied coastal sites. Inland populations were constrained to reaches where the average temperature over the warmest 30 days ranged from 17.6 to 24.2°C, higher than coastal rainfall‐driven systems where averages ranged from 15.7 to 22.0°C. Frogs in rivers with hypolimnetic‐release dams bred in colder waters than they did in free‐flowing rivers. Common‐garden and field translocation experiments revealed local adaptations in larval growth and phenotypically plastic thermoregulatory behaviour. Tadpoles from all rivers had a positive linear growth response to temperature, but individuals from inland rivers displayed intrinsically higher growth rates. Consistent with a counter‐gradient model of selection in which the response to temperature change is in the opposite direction of the change, individuals from cooler rivers selected warmer temperatures. When reared under common conditions, however, tadpoles showed similar temperature preferences regardless of source river. Our results suggest a role for local growth rate adaptation in structuring the distribution of Rana boylii. Plastic thermoregulatory behaviour by tadpoles may explain how small populations are able to persist where dams release cold water. Management of edgewater habitats to increase the availability of warm micro‐sites may ameliorate this impact.

Inland Geographic Response Plan (GRP) for Complex, Variable, Limited Access River Settings

ABSTRACT 2017-427 Geographic Response Plans (GRPs) are a key tool in response preparedness, but are limited in inland settings, especially in remote areas. Development of a GRP for 200 miles of the Feather River in California required consideration of highly variable seasonal flow conditions, extremely limited access, and numerous sensitive ecological and cultural resources. This setting required adjustments to the typical prioritization of GRP response strategies based on the sensitivity of potentially exposed resources at risk, and instead increased focus on access and infrastructure locations in relation to natural and man-made collection areas. With a highway on one side of the steep-walled canyon, and a state-designated “high-hazard area” for the railroad line on the other, the GRP also needed to consider a wide variety of potentially released material types and source points. The scoping and GRP development was led by a steering committee including the Union Pacific Railroad and BNSF Railway, the U.S. EPA (Region 9), CA Department of Fish and Wildlife Office of Oil Spill Prevention and Response (OSPR), ARCADIS, and numerous regional and local organizations as well as response contractors. The resulting GRP is a pragmatic document that provides critical response information to optimize the efficiency and effectiveness of the first 24 – 48 hours of incident response in this challenging environment. This paper discusses the challenges faced and the resultant strategic measures addressing limited access, fast-water booming, resource mapping, and other critical planning parameters to develop a pragmatic and effective GRP.