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Past Projects

Ecophysiology

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.

 

Vegetation-induced changes in the stable isotope composition of near surface humidity in a coastal Californian watershed

Kevin Simonin (San Francisco State University) and Todd Dawson (UC Berkeley)

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).

 

Eel River Ecology – Algae

Paleoproductivity of the Eel River as recorded in Eel’s marine canyon diatoms

Jack Blackburn Sculley

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.

 

Eel River Ecology – Wildlife

Impacts of European and native grasses on meadow arthropods

Kirsten Hill

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.

 

Physiology to food webs down river networks

Jonathon Stillman and team

Jonathon, a professor at SFSU 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.

 

Mayfly migrations from mainstems to tributaries can sustain salmonids in warming river networks

Hiromi Uno

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 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.

 

Life history of Mermithid nematode parasites of the migratory mayfly, Ephemerella maculata

Larissa Walder

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.

 

Hydrology & Geomorphology

Origin and spatial extent of wetted channels during summer low flow in the Eel River system

Sky Lovill

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. 

 

Transformation and bioaccumulation of mercury in tributary-mainstem networks of the Eel River

Martin Tsui

 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.