Below are brief descriptions of some individually-led research projects at Angelo. These will be periodically updated.
Current Researchers and Projects
Kelsey Crutchfield-Peters: Plant Available Nitrogen
Across diverse ecosystems worldwide, rhizospheres (composed of plant roots and their associated microbiome) are known to extend beyond soil horizons into weathered bedrock. These deep rhizospheres drive water and carbon cycling meters below the base of soil, supporting forest function. Little is known, however, about how these deep rhizospheres drive nutrient cycling at depth. In her dissertation research, Kelsey combines stable isotope and other biogeochemical techniques to explore how nitrogen (N), the most limiting nutrient to plant growth in terrestrial ecosystems, is cycled throughout deep rooting profiles in the critical zone, asking: (1) how do the chemical forms and concentrations of biologically available N change year round; (2) what is the source and fate of this N; and (3) to what extent do dominant tree species utilize N stored within weathered bedrock?
Kelsey and her colleagues have sampled for plant available nitrogen throughout the entire profile of the unsaturated zone at Rivendell using the VMS for more than two years, including sampling of : dissolved organic N (DON), ammonium (NH4+) and nitrate (NO3-). She has also conducted multi-year monitoring of NH4+ and NO3- standing stock, net mineralization in soil and bulk carbon and nitrogen stable isotopes in soil to generate a baseline of N and C content at our site. Together, these data form the basis for assessing biogeochemical N dynamics throughout the entire unsaturated (i.e. vadose) zone at Rivendell. Kelsey also routinely samples the dominant canopy species for foliar N and C content and stable isotope analysis.
Analyses indicate that the majority of N found in the rock moisture zone is DON, and it is found at ecologically significant concentrations. Total N increases with depth and is dynamic across seasons. The covariation of TN, NH4+, NO3-, and C dynamics also suggest N cycling by plants and/or microbes in the weathered bedrock rhizosphere at Rivendell. Additional analyses are underway to better understand the fate of N in the rock moisture zone, and additional gas sampling and N isotope analysis of dissolved N compounds sampled from the VMS will be performed to take a closer look at nitrogen cycling.
Additionally, to investigate plant uptake of N from rock moisture held in weathered bedrock, in summer 2020 Kelsey conducted an experiment testing N uptake capacity of Douglas fir fine roots growing in soil vs weathered rock. Fine roots from Douglas fir in the soil and saprolite were collected and incubated in 15N-labelled NH4+, NO3- and organic N solutions. Differences in d15N values between the control and 15N treatment roots will be used to calculate N uptake per gram of root. Results from this experiment will inform future research into differential gene expression in roots growing in soil versus weathered bedrock.
Keith Bouma-Gregson: Flow and climate thresholds for algal assemblages in the Eel River: tipping towards toxicity?
Algae are foundational energy sources for food webs in sunlit rivers. Many (like most diatoms) are highly edible and fuel summer growth for fish and macroinvertebrates. Other algal taxa, however, are inedible or even toxic (harmful algae bloom, HAB) degrading aquatic habitats, water quality, and creating public health hazards. Keith Bouma-Gregson is working towards identifying threshold conditions that tip healthy algal assemblages into harmful algal blooms in the Eel, and similar rivers. He has partnered with the Eel River Recovery Project (ERRP, www.eelriverrecovery.org) to develop a citizen science algal monitoring program for the Eel. Keith has also collaborated with Raphael Kudela, UC Santa Cruz, to deploy Prof. Kudela’s cyanotoxin monitoring SPATT samplers throughout
the South Fork and mainstem Eel River during summer base flow. At several sites, they detected the cyanobacterial neurotoxin, anatoxin-a. Starting in since 2002, this toxin has been implicated in the deaths of several dogs after they swam in the Eel River. Keith complements his basin-scale monitoring with local experiments and detailed monitoring of local proliferation and spread of cyanobacterial infestations. As summer flows subside, incipient growths of the potentially toxic cyanobacterium Anabaena spp. start to develop as epiphytes on senescent spires of Cladophora glomerata. Keith monitors and experimentally manipulates light, temperature, nutrients, and flow velocities to understand conditions that allow toxic cyanobacteria to overgrow and dominate the more ‘normal’ edible assemblages of diatoms that cover rocks and surfaces of green macroalgae. Where and when can changing environmental conditions flip edible algal assemblages to assemblages dominated by inedible or harmful algae?
Some climate change scenarios predict larger winter floods and drier summers, which would favor cyanobacteria proliferations. Anthropogenic water withdrawals further depress summertime river discharges, also increasing the likelihood of cyanotoxin production. Knowledge of thermal, solar radiation, and flow regimes that promote cyanobacteria is needed for management to sustain a fish-bearing food web and reduce public health hazard from cyanotoxins. Keith was formerly a PhD student advised by Mary Power in the Integrative Biology department at UC Berkeley, and a postdoc with Jill Banfield in the Earth and Planetary Sciences department at UC Berkeley. He is now the CA Freshwater Harmful Algal Blooms Program Lead at the CA State Water Resources Control Board.
Stephanie Carlson: Influence of river flow and temperature on O. mykiss
Our work has focused on understanding the influence of river flows (magnitude and timing) as well as its temperature on O. mykiss. O. mykiss are partially migratory, with some individuals migrating to the ocean before returning to the river to breed, and other individuals spending their entire lives in freshwater. Our key recent discoveries include that (1) both geomorphology (knick points) and river flows influence the distribution of migratory adults (high river flows at the right time facilitate upriver passage of migrating adults, Kelson et al. 2020 Molecular Ecology). Moreover, we have found that partial migration in O. mykiss (2) is influenced both by sex (females are more likely to migrate) and genotype (individuals with a migratory-genotype are more likely to migrate, Kelson et al. 2019 Canadian Journal of Fisheries and Aquatic Sciences) and (3) that partial migration has ecological consequences (in stream reaches where migratory genotypes dominated, we’ve found higher densities of young fish and lower densities of older fish, resulting in a simpler size structure, compared to when resident genotypes dominated, Kelson et al. 2020 Ecosphere). Finally, we have explored the importance of cold water plumes in warm mainstem rivers, created by cool tributary in-flows, as thermal refugia for cold-water fishes like salmonid fishes (Wang et al. 2020 River Research and Applications). Stephanie is a professor in Environmental Science, Policy, and Management at UC Berkeley.
Microbes Persist: Systems biology of the soil microbiome
The “Microbes Persist” Soil Microbiome project is a DOE-funded Science Focus Area (SFA) led by Lawrence Livermore National Lab Senior Staff Scientist Jennifer Pett-Ridge.
Microorganisms play key roles in soil carbon turnover and stabilization of persistent organic matter via their metabolic activities, biochemistry, and extracellular products. Microbial residues are the primary ingredients in soil organic matter (SOM), a carbon pool that is critical to Earth’s soil health. The Soil SFA is investigating how microbial cellular-chemistry, functional potential, and ecophysiology fundamentally shape soil carbon persistence. Project members are characterizing this via stable isotope probing (SIP) of genome-resolved metagenomes from soils at three California grassland sites located in Hopland, CA (from Hopland Research and Extension Center) the Angelo Reserve, and Sedgwick Reserve. The SFA focuses on soil moisture as a ‘master controller’ of microbial activity and mortality, since altered precipitation regimes are predicted across the temperate U.S.The ultimate goal of the project is to determine how microbial soil ecophysiology, population dynamics, and microbe-mineral-organic matter interactions regulate the persistence of microbial residues under changing moisture regimes.
David Dralle: Hydrology of seasonally dry ecosystems
David’s research at Angelo focuses on the hydrology of seasonally dry ecosystems. Seasonally dry ecosystems occur in climatic regions that exhibit distinct periods of high water availability followed by extended intervals during which rainfall is negligible and surface water becomes increasingly scarce. Angelo Coast Range Reserve would be considered seasonally dry due to its Mediterranean seasonality, with cool, wet winters and warm, dry summers. However, seasonally dry ecosystems do not only occur in Mediterranean regions, such as coastal California; they are also found throughout the world’s Savanna and Monsoonal climatic regions. All together, seasonally dry ecosystems constitute over 30% of the planet by area and contain over 30% of the world’s population. David’s main focus in these ecosystems is the seasonal streamflow recession – the long, sustained release of groundwater in the form of streamflow over the course of the dry season. He uses a combination of data analytic and mathematical techniques to model streamflow in seasonally dry ecosystems and to infer watershed properties from the character of seasonal recessions. Ultimately, David hopes to use risk-based mathematical frameworks to measure and predict the impact of growing human populations and a changing wet season climate on the important water resources and unique in-stream ecology found in seasonally dry ecosystems. David is former postdoc with the Eel River Critical Zone Observatory at UC Berkeley, as well as a former Assistant Professor at Sacramento State University. He currently works as a Research Hydrologist for the USDA Forest Service.
Sarah Kupferberg: Ecology and Conservation Biology of river-breeding frogs
California’s river breeding foothill yellow legged frog (Rana boylii), is frequently encountered when visitors to the Angelo Reserve walk along the banks of the South Fork Eel River. These sun-loving frogs bask on rocks and jump into the water at the sound of footfall. The population at the Angelo Reserve is robust, but this species is generally in decline, especially in the southern part of its range and where it occurs near large dams. Field observations and experimental manipulations conducted by Sarah Kupferberg at the Angelo Reserve since 1990 have enhanced our knowledge of this species’ adaptations for survival and its vulnerabilities when humans alter rivers by building dams and reservoirs and diverting stream flows.
During the spring breeding season, adult frogs migrate from the narrow shady tributaries like Fox and Elder Creek where they avoid winter floods, to wide shallow cobble bars on the margins of the sunlit South Fork Eel and Tenmile Creek. Because each female lays one clutch of eggs, the total number of egg masses serves as a proxy for the size of the population. Long term monitoring has revealed that several physically-based factors influenced by variation in streamflow may impair the ability of populations to produce new recruits. By studying the population of Angelo Reserve, Sarah and her colleagues have determined that changes to flow velocity and river stage during egg incubation which result in scour or desiccation influence the number of clutches found three years later, when that cohort of tadpoles would have matured into frogs ready to lay eggs for the first time.
Along with colleague Alessandro Catenazzi, Sarah reared tadpoles in enclosures the various streams on the Angelo Reserve, some warm and some cool, to quantify the extent to which water temperature and quality of algal food resources influence tadpole survival, growth and development. The results of these experiments are being used to inform dam management decision making where hypolimnetic releases from upstream reservoirs occur. Cold water released can slow embryonic development and thus extend the period of desiccation / scour risk; cool summer temperatures also decrease survival, decrease size, and increase time to metamorphosis. To reduce these mortality agents, in association with engineer Scott McBain, Sarah has developed a spreadsheet model to predict the hydrologic and thermal mechanics of breeding timing, embryonic and larval development. The model integrates knowledge of individual ecophysiological and behavioral responses to water temperature with channel morphology and stage discharge relationships. When applied to three different regulated rivers in California (Trinity, Tuolumne, and Alameda Creek) the model predicted that the effects of cooler summer temperatures on tadpoles may have more profound impacts than spring flow fluctuation effects on clutches of eggs.
Jacques Finlay: Tracing linkages and thresholds of food webs and ecosystems through Eel drainage networks
Dr. Jacques Finlay is a Professor in the College of Biological Sciences at the University of Minnesota. Jacques and his students and colleagues investigate how organisms and environments interact with biogeochemical fluxes, cycles, and transformations. He has used innovative isotope techniques to trace the sources and fateas of solutes transported by rivers, and their exchange between channels and surrounding watersheds. Jacques’ work on how flow and longitudinal changes in photosynthetic demand systematically altered stable 13C enrichment of algae paved the way for better resolution of the importance of algal versus terrestrial carbon sources for consumers in rivers. He has also detected and quantified changes in nitrogen isotopes that correspond to a longitudinal and seasonal increase in cyanobacterial nitrogen fixation in the Eel. He detected an abrupt threshold where watershed areas exceeded 100 km2, where light availability allowed increasing photosynthesis and nitrogen fixation by benthic algal assemblages, which in turn altered stream-water N concentration and N:P ratios and stoichiometry in larger streams and mainstem rivers. Jacques work has also given us glimpses of the spatial dimensions of food web interactions–organisms that co-occur within mm of each other may actually feed from different “resource sheds”. Recently, he has expanded his isotope analysis to use deuterium, and has collaborated with his former student Martin Tsui to use the strange, multiple isotopes of methyl mercury to trace energy exchange between channels and surrounding forests.
Paula Furey: Algal ecology and taxonomy
Dr. Paula Furey is an Associate Professor at the University of St. Catherine in Minneapolis, MN. Paula studies how abundances, health, and taxa of algae change over time and space. Of particular interest to her nitrogen-fixing algal species (cyanobacteria and
diatoms in the family Rhopalodiaceae, which contain cyanobacterial endosymbionts), and how these shift in abundance and species composition seasonally, between different years, and down the drainage network from headwaters in to the main stem of the Eel River. Paula’s research highlights how hydrology, light, temperature, and foodweb interactions can alter species assemblage structure from edible, nutritious diatoms to less nutritious or hard to graze diatoms, or even toxin producing cyanobacteria. Her work on algae-midge interactions demonstrated that shifts in algal species composition caused by midge–algae interactions at small scales (um–m) could affect ecologically significant processes, such as nitrogen fixation and foodweb interactions at larger reach and watershed scales. She is developing a regionally relevant algal identification guide for use by researchers and local water-monitoring groups. Images taken at three scales (environmental context, macroscopic (what we’d see with the naked eye) and microscopic) will provide information key to identification.
Mary Power and ” ‘AFWIT’S” (Algal Food Web Investigation Team)
Our group studies food webs, which in our study areas are primarily fueled by attached algae. We are interested in how attributes and performances of algae and cyanobacteria, their invertebrate and vertebrate grazers, and predators of these grazers affect river, watershed, and coastal ocean ecosystems. We are particularly interested in how key species interactions change under different environmental regimes. To track this, we take advantage of Earth science research in and around our study sites in a “predictive mapping” approach, integrating across space and time to discover:
- Where and when ecological regimes change;
- Which factors cause these changes;
- How local landscape or seasonal controls are altered by changes in climate, land use or biota;
- how local interactions scale up to affect basinwide linkages of river, upland and coastal ecosystems.
The surface area of rivers is small relative to the area of their watersheds; terrestrial plant biomass typically dwarfs that of aquatic primary producers; and gravity pulls material down slopes. For these reasons, it is often assumed that “forests feed their rivers”. Rapid growth and excellent nutritional quality of attached algae like diatoms, however, make them surprisingly important food sources, not only for aquatic consumers, but also for terrestrial biota like spiders, lizards, birds, and bats. We investigate process like insect emergence and algal stranding through which “the river feeds the forest”. We have recently also recently launched studies of linkages of the river to the ocean: examining the potential importance of riverine algal drift for consumers in estuaries; and whether algal-mediated biogeochemistry canaffect primary productivity in the coastal ocean near the river mouth. Mary Power is a Professor in the Department of Integrative Biology at Berkeley, and Faculty Director of the Angelo Coast Range Reserve.
Daniella Rempe: A bottom-up control on fresh-bedrock topography under landscapes
Daniella has been pursuing Zb, the depth to unweathered bedrock, which has been called (by her former advisor, Bill Dietrich) the second most important landscape surface. The depth to unweathered bedrock influences subsurface runoff paths, erosional processes, moisture availability to biota, and water flux to the atmosphere. Daniella formulated a simple model that predicts the vertical depth weathered rock underlying soil-mantled hillslopes. After uplift and erosion bring fresh bedrock near the Earth’s surface, channel incision (e.g. by Elder Creek at Rivendell) causes water that once saturated spaces in the fresh bedrock to drain to the channel. Drainage of the fresh bedrock allows weathering through drying, setting the upper elevational boundary of undrained fresh bedrock, Zb. The slow drainage of fresh bedrock exerts a “bottom up” control on the advance of the weathering front. The thickness of the weathered zone is calculated as the difference between the predicted topographic surface profile (driven by erosion) and the predicted groundwater profile (driven by drainage of fresh bedrock). Together, these factors control how long rock moisture stored beneath hills can sustain runoff to rivers during drought.
Phil Georgakakos studies the distribution of fish and other aquatic vertebrates and their interactions across riverscapes, and how they shift in response to environment conditions, resources, particularly in the context of a changing climate. The historical aquatic vertebrate assemblage of the Eel River has shifted largely in response to overfishing, habitat destruction, and other human-induced activities, and there have been numerous non-native species introductions- notably, the invasive Sacramento Pikeminnow.
As part of his PhD work, Phil conducted repeated snorkel surveys over a five year period at the Eel River in order to investigate patterns of variation in the aquatic vertebrate community through time and space. This study constitutes one of the most extensive survey efforts in space, time, and species of animal counted in a coastal California river. Generally, Phil has found that invasive animals were more abundant in downstream reaches and slower water habitats. Populations of native species tended to be denser upstream, especially in late summer, when invasive numbers are high downstream.
Identifying the drivers that favor native species expansion downstream can help guide restoration efforts hoping to shift assemblages towards more desirable historical states. Phil’s particular observations of the invasive Sacramento Pikeminnow migrating upstream during Spring and early Summer led him and collaborator David Dralle to develop a statistical model to forecast the timing and extent of upstream migration by pikeminnow in response to discharge and air temperature. In years with low flow and high air temperature, the model predicts that pikeminnow will move upstream earlier, overlapping (and competing) with native fishes for a longer period of time. This suggests a potential management technique of decreasing water withdrawals in years of high temperature/low flow in order to keep river temperatures cool, limiting the co-occurrence of pikeminnow and rearing salmonids.
In addition to understanding the negative impacts for native animals that occur in the novel communities created by species introductions , Phil is interested in understanding how altered species interactions, particularly reduced positive interactions influence native species. In Northern California, Pacific Lamprey seasonally enter the coastal rivers in order to spawn. As part of his dissertation, Phil investigated how bioturbation during lamprey redd (spawning nest) construction influences invertebrate drift, juvenile Steelhead foraging behavior and growth potential, and the effects of built lamprey redds on local water velocity.
Phil and his collaborators Gabe Rossi and Sarah Kupferberg have found that drifting invertebrates are more numerous and more concentrated downstream of redd building lamprey, increasing the foraging profitability of juvenile steelhead. He also found that lampreys’ redds can create velocity refugia for aquatic species, as the flow velocity is lower in the bottom of the redd depression. Phil’s observations suggest that this lower flow velocity (as well as other properties of Lamprey redds) may be exploited by foothill yellow-legged frogs who the use the redds as egg mass deposition sites. Overall, Phil’s observations suggest a number of positive interactions that may alter the population dynamics of species interacting with spawning lamprey in the Eel River.
Phil is a former PhD student in the Integrative Biology Department at University of California, Berkeley, and recently started a Postdoc position with Prof. Ted Grantham in the Dept. of Environmental Science, Policy, and Management at UCB.
In his current position, Phil and Ted Grantham are investigating how water withdrawals for cannabis cultivation in the South Fork Eel River influence river flow, temperature, and aquatic organisms. They plan to model the impacts of withdrawals on flow and use these calculations to determine when and where river temperatures might be impacted. Using the results of their modeling work they will also study how changes in these physical characteristics will alter species distributions of aquatic organisms and key ecological interactions. Phil will also continue working with Dr. Mary Power to monitor the movement and distribution of invasive fish and frogs in the upper South Fork Eel River. This monitoring builds on the work he started during his PhD, and aims to determine what factors encourage the spread of native species and inhibit non-natives.
Jesse Hahm: Linkages of geology, topography, and trees
Jesse aspires to better understand process linkages between geology, topography, and life. One striking observation from the Eel River watershed is that the regional forest distribution appears to be controlled to first order by lithologic variation across accreted terranes. For example, coniferous forests are rare in the central mélange belt, but the mechanisms inhibiting conifer forests in the mélange are poorly understood. Jesse also seeks to understand how tectonic forcing, biota, and geomorphic processes produce unique landscape form across the different rock types in the area. For example, hillslopes are steep and convex or planar in the greywackes and argillites of the Eel River Critical Zone Observatory. On neighboring mélange, in contrast, landscapes are gently undulating. Processes responsible for hillslope sediment transport (and ultimately landscape form) are not well understood for either rock type. One way to explore a process inferred from field observation is to cast it in the form of a geomorphic transport law, which can be coupled with continuity (conservation of mass) in a model landscape. Resulting simulations can be compared with high resolution (LiDAR) topography from real landscapes to calibrate and test the validity of the proposed transport law. Jesse Hahm is a former PhD student advised by Bill Dietrich in the Earth and Planetary Science Department, University of California, Berkeley. He is now an Assistant Professor in the Dept. of Geography at Simon Fraser University.
Jasper Oshun: tracing raindrops through trees and bedrock to streams using stable isotopes
Jasper Oshun studies flow paths of precipitation through a forested hillslope to better understand runoff generation and storm flow, the storage of plant-available water in fractured bedrock beneath the soil surface, and the slow release of rock moisture from a hillslope to the stream. Using measurements of the isotopic composition of water, Jasper can trace a raindrop through the hillslope and identify the depth in the rock beneath from which trees derive their water. Thus far, he has shown that the isotopic composition of water within a hillslope varies as a function of how tightly it is held within the pores of soil and weathered rock. This variability persists throughout the year and is an identifiable ‘blueprint’ from which the above vegetation draws its water. Surprisingly, different species of trees have different water use strategies, which results in adjacent trees partitioning water from the soil, and weathered rock. Species-specific water use by trees on the hillslope may thus affect the amount of water stored in rock, and the slow release of water to our streams. These findings can inform forest management strategies that seek to maximize water yield from our forests. Jasper Oshun is a former Ph.D. student with Bill Dietrich in the Department of Earth and Planetary Science at UCB. He is now an Assistant Professor at Humboldt State University.
Shelley Pneh: Phenology and Photo-documentation of life histories of common aquatic insects in the Eel River, with particular focus on adult emergence
Aquatic insects are some of the most abundant organisms in a freshwater river community. Most aquatic insects live under water as larvae (eating, growing and maturing), then metamorphose as flying adults,whose jobs are to disperse and reproduce. Many aquatic insects emerge synchronously, in large numbers over a short period of time.
Shelley studied emergence patterns of several common mayfly (Ephemeroptera), caddisfly (Trichoptera), moth (Lepidoptera), and true flies (Diptera) found along an eight kilometer reach of the South Fork Eel River at the Angelo Coast Range Reserve (Mendocino Co., CA). Notable synchronous emergence peaks were observed for Gumaga spp. (Sericostomatidae: Trichoptera) and a mayfly, Ephemerella excrucians (Ephemerellidae: Ephemeroptera) with a downstream to upstream emergence pattern. Interspecific temporal segregation was also observed between two mayfly species of Procloeon (Baetidae: Ephemeroptera). Habitat preference was also observed among sampling sites: Petrophila confusalis (Crambidae: Lepidoptera) only emerged over large stones and boulders; Heptageniid mayflies preferred emerging from flowing water and Gumaga and midges (Chironomidae) emerged in highest numbers from slow flowing water. Shelley also compared the efficiency of two different emergence traps.
Blake Suttle: Direct and indirect responses of meadow species and ecosystems to altered rainfall in a California grassland
In a large field experiment that has been running continuously since 2001, Blake Suttle and his students and collaborators have studied direct and indirect effects of altered rainfall regimes in meadow food webs and ecosystems. Blake rigged a clever underground sprinkler system to alter the intensity or duration of the annual rainfall in large, replicated experimental plots. Every year, twelve 70-m2 plots of open grassland are subjected to rainfall changes predicted by the Hadley 2000 climate model for the California North Coast (doubled precipitation during the winter (January-March)). Twelve more plots receive rainfall as predicted under the leading Canadian climate model (double the amount of rain falling later in spring (April-June)). A third group of twelve control plots receive ambient rain. Changes in seasonal water availability had pronounced effects on individual grass, forb, and arthropod species, but as precipitation regimes were sustained across years, feedbacks and species interactions overrode individual physiological responses, and produced patterns opposite to what would have been predicted from the physiological ecology of perennial (native) versus annual (exotic) grasses. Conditions that sharply increased production and diversity through the first 2 years reversed, and caused
simplification of the food web and deep reductions in consumer abundance after 5 years. Changes in these natural grassland communities suggest a prominent role for species interactions in ecosystem response to climate change.
Meredith Thomsen: Long-term research on simulated climate change in meadow ecosystems. A 2005 Berkeley Ph.D., Meredith Thomsen has continued her research at the Angelo as a Professor in the Biology Department at the University of Wisconsin-La Crosse. Since 2006, she has made annual trips with students and UW-L colleague Tim Gerber to help sample the rainfall addition project started by Blake Suttle in 2001. Student participants are a mix of Biology majors and Biology Education majors. All students gain first-hand research experience, and, with Tim’s guidance, the Biology Education majors prepare lesson plans based on the research which align with national science standards. Research experience for future teachers broadens the societal impact of our work, as those students become teachers and share the experience in their K-12 classrooms.
Kirsten Hill: Impacts of European and Native grasses on meadow arthropods
Kirsten Hill studies how invasive annual versus native perennial grasses affect the interactions of spiders and herbivorous insects in meadow food webs. Angelo meadows, which occur along flat river terraces flanking the Eel River, are habitat islands in a sea of forest. These meadows contain vibrant populations of native perennial California grasses and forbs, but are also invaded to various degrees by European annual grasses and weeds. Kirsten hypothesized that the perennial bunch grasses would keep microclimates cool and moist late into the summer, prolonging periods when spiders could grow and feed on grasshoppers, including potential pest species. In contrast, annual grasses die back by mid-summer, leaving hot, barren areas too harsh for spiders, but favorable for warm-adapted grasshoppers. Kirsten has used enclosure experiments, surveys, and meticulous natural history observations to uncover the impacts that dominance of native versus invasive grasses (and grassland restoration) could have on meadow arthropods, and how these arthropods in turn affect meadow flora, including wild flowers. Kirsten Hill is a former Ph.D. from Environmental Science, Policy, and Management at UCB.
Suzanne Kelson: Eco-evolutionary dynamics of O. mykiss: Causes and Consequences of Alternative Life History Forms
Suzanne studies the alternative life history strategies of Oncorhynchus mykiss. The migratory form (steelhead trout) spends 1-3 years in freshwater, migrates to the ocean to feed and grow, and then returns to freshwater to breed. The resident form (rainbow trout) completes its entire life cycle in freshwater. Each life history is associated with different trade-offs: the migratory steelhead
can reach much larger body sizes and therefore be much more fecund than resident rainbow trout, but steelhead experience higher lifetime mortality rates. Suzanne is interested in the processes that maintain and constrain the life history diversity of O. mykiss at a fine spatial scale – within several replicate streams. Specifically, she is interested in how rainfall and flow patterns (timing and magnitude) influence the ability of migratory adults to ascend cascades, which influences the amount of gene flow between the alternative life histories in a given year. She explored how the presence of life history diversity alters the density and size structure of groups of O. mykiss that occupy these streams during a given year. As the top predator, O. mykiss assemblages of different density and size structure should have different effects on stream food webs. Through mark-and recapture studies, genotyping, and field observations, Suzanne studied the processes that maintain life history diversity and mediate its effects on stream ecology. Suzanne is a former PhD student advised by Stephanie Carlson in the Department of Environmental Science, Policy, and Management at UC Berkeley. She is now a Postdoc in the Global Water Center at the University of Nevada, Reno.
Hyojin Kim: Autonomous Water Sampling for Long-Term Monitoring of Trace Metals in Remote Environments
Hyojin and her colleagues studied the chemical evolution of water as it passed through the critical zone and out into springs or as runoff to Elder Creek. She needed a remotely controlled autonomous method for long-term high-frequency sampling of environmental waters in Rivendell, and designed an apparatus that could sample dissolved trace metals and major ions for month-long periods. Her gravitational filtration system
separated dissolved and particulate phases as samples were collected.
Thus vastly improved her recovery of trace metals (Fe and Mn) and the dissolved major
cation Ca. in some groundwater samples decreased up to 42% without GFS due to CaCO3 precipitation. Hyojin finished her Ph.D. with Jim Bishop in Earth and Planetary Science in 2013.
Percy Link: Different seasonality in transpiration broadleafed trees and conifers in a Mediterranean climate: analysis of multiyear, half-hourly sap flow measurements
In Mediterranean climates, the season of water availability (winter) is out of phase with the season of light availability and atmospheric moisture demand (summer). Percy and her colleagues studied seasonality of tree transpiration in Rivendell, the small (4000 m2), forested, steep (32o) watershed that is the most intensively instrumented site in Angelo. They analyzed 3 years of half-hourly measurements from 39 sap flow sensors in 26 trees, six depth profiles of soil moisture measured by total domain refractometry, and collected micro-meteorological data from five sites. Sap flow measurements showed different seasons of peak transpiration for different tree species that were within several meters of each other. Douglas firs (Pseudotsuga menziesii), were active in the wet Mediterranean winter, with peak transpiration in the spring, followed by a sharp decline in transpiration during the summer dry season. in contrast, Pacific madrones (Arbutus menziesii), and to a lesser extent other broadleaf evergreen species (interior live oaks Quercus wislizeni, tannoaks Notholithocarpus densiflorus, bay Umbellularia californica), transpired maximally in the summer dry season. The difference in transpiration seasonality arises from different sensitivities to atmospheric evaporative demand and root-zone moisture. The greater sensitivity of Douglas fir to water stress appears to suppress their dry season evapotranspiration at the regional scale. Percy Link completed her Ph.D. in Earth and Planetary Science at Berkeley and is now a Software Engineer at Tesla.
Sky Lovill: Exploring the origin and spatial extent of wetted channels during summer low flow in the Eel River system
In seasonally dry environments, wetted channel networks sustain river ecosystems and provide critical surface water for biota during dry summer months. Before entering these channels, however, water must find its way through subsurface pathways–critical links between the hillslope critical zone and the channel.
Sky has surveyed the entire watersheds of Fox (2.7 km2) and and Elder (17.0km2) Creeks in early and late summer of 2012 and 2014. He walked all of both watersheds’ channels, mapping the spatially wetted extent of the drainage network at each occasion. Additionally, Sky traced flow within each sub-drainage area to its’ source in order to obtain water isotope, temperature and flow data.
He has determined that these sources of flow are extremely stable, with less than 5% retraction downslope over the summer months. This suggests that preferential flowpaths and fractures dominate the subsurface hydrology, creating year-round sources of water that fuel biotic life. Sky also has found that these two adjacent watersheds have strikingly similar drainage densities (channel lengths per basin area). This finding advances the theory that watersheds with nearly identical precipitation rates, and lithology should have very similar proportions of wetted flow at any given time of the year. Sky’s data point toward slope aspect (e.g., north- or south facing) as the most influential control on wetted channel flow. He hypothesizes that different tree types cause peak transpiration rates on the north and south facing slopes to be out of phase. This in turn forces the hardwoods on the south facing slopes to extract subsurface water sources with greater force in late summer months than Douglas firs on the north facing slope. This contrasting tree phenology likely plays a large role in north-south differences in flow rates over the summer months.
Charles Post: foraging and food-web impacts of American dippers (Cinclus mexicanus) under different flow regimes
Charles Post studied the foraging and food-web impacts of American dippers (Cinclus mexicanus) under different flow regimes. Dippers are voracious predators on aquatic insects and small fish, but their impacts as predators in river food webs are not yet well documented. With intensive field observations of marked individuals, Charles has evaluated dipper impacts on a dominant algae grazer, Dicosmoecus gilvipes, whose heavy armor protects it from gape-limited predators like fish. Dicosmoecus populations are usually knocked back by scouring winter floods in the Eel, but when these floods don’t occur during drought, large numbers survive to graze down algae, with cascading consequences for other web members including salmonids who derive much of their energy from algal-based food webs. Charles is also investigating how flow depth, flow velocity, and substrate affect the foraging rates and choices by dippers in open and experimentally arranged river habitats. He will document their habitat use and foraging patterns over reach scales, where locations of favorite emergent boulders, nest locations, and riparian forest offset from channels all
algae, with cascading consequences for other web members including salmonids who derive much of their energy from algal-based food webs. Charles is also investigating how flow depth, flow velocity, and substrate affect the foraging rates and choices by dippers in open and experimentally arranged river habitats. He will document their habitat use and foraging patterns over reach scales, where locations of favorite emergent boulders, nest locations, and riparian forest offset from channels all influence foraging patterns of dippers over larger spatial scales. His aim is to understand (1) How American dippers change their habitat use and foraging choices under different flow regimes, which vary seasonally and with year-to-year variation in rainfall. (2) How dipper impacts on dominant grazers and primary producers will differ across hydrologic regimes. These insights will inform efforts to forecast how these amazing birds and their impacts will respond to changes in climate or land cover that rivers along the North Coast will confront over the years ahead. Charles Post is a former Master’s student with Mary Power in the Department of Integrative Biology at UCB.
Jack’s research interests centered on how food webs or ecosystems respond to climate change and to changes in disturbance regimes over decadal to century-long time-scales. Using cores sampled by Chuck Nittrouer and Tina Drexler at the University of Washington, he quantified diatom frustule (glass shells that encase cells) abundances from in a marine canyon carved at low sea stand off the mouth of the Eel River. These cores record almost 100 years of sediment deposition, with annual resolution. During 13 years when Mary Power surveyed algal abundance upstream in the modern Eel, the abundances of freshwater diatoms in core laminae correlate reasonably well with magnitudes of summer algal blooms, which tend to be larger following scouring winter floods. Jack used this marine record of freshwater diatoms, as well as marine diatoms, to evaluate how changes in river discharge and marine upwelling over annual and multi-year time scales have affected recent paleo-productivity in the linked river-coastal ocean ecosystem. Jack completed his Ph.D. in 2014 in Integrative Biology at UC Berkeley.
Kevin Simonin (San Francisco State University) and Todd Dawson (UC Berkeley): Vegetation induced changes in the stable isotope composition of near surface humidity in a coastal Californian watershed
At the Rivendell watershed on the Angelo Reserve we’ve used the oxygen and hydrogen stable isotope composition of meteoric waters as well as the derived d-excess parameter from these data to reconstruct changes in atmospheric water pools (e,g. sources, origins and overall balance) and the climatic conditions that prevail during surface evaporation. The d-excess parameter in particular was valuable in helping us evaluate the influence of forest canopies on atmospheric humidity within the mixed evergreen forest that inhabits the site. We found that during the day, when tree transpiration was at a maximum, the d-excess of atmospheric water vapor suggested the predominance of transpired water (from the trees) within the background atmosphere over this ecosystem while at night when transpiration was minor, the d-excess of atmospheric water vapor suggest the predominance of an ocean derived water vapor source. Observed diurnal fluctuations around the d-excess of background water vapor provided strong evidence that during the day as the land surface warms and the boundary layer above the ecosystem grows, the plants alter the isotope composition of atmospheric humidity but in a non-steady state, non- equilibrium manner. In contrast, at night equilibrium among the water pools in the ecosystem dominate as the atmosphere stabilizes. These daytime and nighttime fluctuations around the d-excess of ocean derived water vapor highlight the importance of plant transpiration for the isotope hydrology of near surface humidity and subsequently for the isotope composition of condensate like dew, an important water input to this ecosystem. (see Simonin et al., Ecohydrology, 2013, DOI: 10.1002/eco.1420).
Jonathon Stillman and team: Physiology to food webs down river networks
Jonathon, a professor at UCSF and in Integrative Biology at UCB, links the physiology of invertebrates to their performances in a changing world, led a BIGCB (Berkeley Initiative Global Change Biology) team that investigated how the thermal performance of aquatic insect larvae will affect the trophic ecology of warming rivers. Larvae of insect grazers vs. predators may also differ in the efficiency with which they use energy under various thermal regimes. Metabolic energy efficiency is maximized at optimal temperatures and declines at higher temperatures due to an increase in fermentative metabolism and an induction of stress
responses to cope with thermal or oxidative damage. Jonathon and his team compared thermal effects on gene expression of four aquatic insects (Pteronarcys californica, Calinueria californica, Hesperoperla pacifica and Dicosmoecus gilvipes) across temperatures of the spring-summer range during late larval instar phase (~12-30°C). Illumina RNA-seq, de novo transcriptome assembly using Trinity, and analysis using Bowtie2/eXpress and EdgeR were used to identify differentially expressed genes within
each species. Heat sensitive predator taxa exhibited a reduced induction of cellular stress response genes. Biomarkers of thermal acclimation from the dominant predator-resistant grazer in the Eel River, Dicosmoecus gilvipes, were used to compare across a fine-scale range of temperatures, and across populations from sites with differing thermal characteristics. These data allow a fine-scale analysis of local physiological adaptation to temperature and shifts in metabolic ecology of streams across much of the central to northern California landscape.
Martin Tsui: Transformation and bioaccumulation of mercury, a global pollutant, in tributary-mainstem networks of the Eel River
Atmospheric deposition dominates mercury in this semi-remote ecosystem. Martin is interested in using Angelo Reserve as a model to examine factors such as canopy cover and stream productivity affect mercury cycling. Over the last 6-7 years, Martin and his colleagues have found substantial transformation of mercury in the stream network especially the downstream sections, including methylation of mercury and photo-breakdown of methylmercury, due to the high abundance of microbial communities to methylate mercury and sunlight availability to break down methylmercury, respectively. Lately, Martin has measured stable isotope compositions of mercury in food webs throughout the stream network and demonstrated that some fish (steelhead trout) and stream invertebrates (water strider) had mercury burden partially or solely from terrestrial sources in some headwater streams, implying that stable mercury isotopes can also be used as a powerful tracer for energy sources besides commonly used carbon and hydrogen stable isotopes. Right now, Martin and his group are examining the stable mercury isotope compositions in different forests across the United States and one of them is within Angelo Coast Range Reserve, and the goal is to elucidate the sources of methylmercury in forest food webs by using this novel isotope tool, and research is on-going at the moment. Martin Tsui is an Associate Professor at the University of North Carolina at Greensboro.
Hiromi Uno: Mayfly migrations from mainstems to tributaries can sustain salmonids in warming river networks
Hiromi Uno has discovered an unusual mayfly, Ephemerella maculata (Ephemerellidae), whose life cycle migration may help sustain steelhead populations in the warming rivers of California. Every summer for twenty years, Angelo researchers puzzled over a mysterious phenomenon. For about a month, the pools of cool, large areas of pools in Fox Creek, a dark tributary stream near the researcher cabins, would become encrusted with dead insects. Hiromi looked more closely, and noticed that 1) they were almost all female mayflies, and 2) they were all a species, Ephemerella maculata, whose nymphs do not occur in these dark tributaries. After consulting an expert taxonomist, she was able to identify E.maculata nymphs, which are very different from the adults. She found that these nymphs only reared in the warm mainstem South Fork Eel, where they fed on abundant algae. Nymphs emerge in early summer, adult winged females mate, then swarm up dark, cool tributaries, where they plunge into white-water riffles, shed their eggs, and die. As spent mayflies drift into pools, juvenile steelhead and giant Pacific salamanders gorge themselves on their dead or moribund bodies. The egg masses, however, are not eaten, even when offered to predators experimentally. Egg masses look like small, translucent pieces of brown popcorn. They sink, stick to the stream bed, and go into a resting period (diapause) for many months, until the first winter rains, when they hatch and tiny, new nymphs are washed down into the mainstem.
Hiromi Uno at Jane’s Riffle, where only nymphs of E. maculata are found. photo by Charles Post.
Hiromi has captured the hatching and recently hatched egg cases of E. maculata as the first winter flood of swept them down the tributary into the mainstem South Fork Eel River. This mainstem habitat warms over the spring and summer to become a productive habitat for mayfly nymphs, but stressful for cold-water steelhead trout (Oncorhyncus mykiss), which typically rear in rivers for one and half years before they migrate to the ocean. In warming rivers of Northern California, rearing juvenile steelhead are increasingly restricted to cool tributaries, where little food is produced. Hiromi’s experiments have shown that the migration of E. maculata helps sustain summer rearing by juvenile salmonids in cool tributary refuges where they would otherwise be food-limited. By transferring energy subsidies from productive mainstems to food-limited tributaries, this mayfly appears to enhance the resilience of steelhead populations in the warming rivers of northern California. Hiromi was a Ph.D. student with Mary Power in the Dept. of Integrative Biology at UCB. She is currently a JSPS Postdoctoral Fellow at Hokkaido University.
Larissa Walder: Life history of Mermithid nematode parasites of the migratory mayfly, Ephemerella maculata
Larissa Walder has worked with graduate student Hiromi Uno and invertebrate taxonomist George Poinar (Oregon State Univ.), allowing George taxonomically identify the first mermithid nematode species known to science. Mermithids are parasites of mayflies, including the migratory mayfly discovered by Hiromi Uno. Larissa and Hiromi studied the life cycle of the Mermithid nematode parasite relative to that of their migratory aquatic host, the mayfly, Ephemerella maculata. Eggs of E. maculata hatch in tributaries, then the aquatic nymphs drift downstream to mature and rear in the mainstem. In early summer, aerial adult mayflies emerge synchronously from the mainstem and return to the tributaries to lay eggs. Nematodes exit from adult mayflies after the mayflies have oviposited and drowned in the tributary. Larissa, Hiromi, and helpers collected 304 adult mayflies to measure the infection rate and the reduction in host fecundity. They also surveyed the spatial distribution and interaction of E. maculata and Mermithid nematodes across seasons. Almost half of the 304 mayflies they sampled were infected, and no infected female mayflies produced eggs, indicating the nematodes sterilize the host mayflies. Larissa sampled monthly, and found that immature nematodes emerged from host
mayflies in summer when the adult mayflies oviposited. These juvenile nematodes matured outside of the host, mated, and oviposited in tributary sediments near host egg masses. E. maculata eggs hatched and the nymph mayflies drifted downstream in December/January before the nematode eggs hatched. Nematode egg masses probably wash into mainstems when winter storms flush tributaries. These ecological detectives (Larissa et al.) are still trying to figure out how, when, and where juvenile nematodes infect their nymphal mayfly hosts. Larissa graduated in 2014 with a BS from Berkeley, and is teaching high school in Oakland CA.