Research at UC Merced--Vernal Pools and Soils

Marilyn and David Araiza, Vernal Pools and Grassland Reserve, 2013

          

 The University of California prides itself on conducting research on an international scale. That said, when I arrived at UC Merced in 2013, the new, small campus had only two other ecologists and very few earth scientists. There were very few high-tech instruments on campus, even in physics and chemistry. While UC Merced lacked the accoutrements I was accustomed to at the Geophysical Laboratory, it was a very upbeat environment and was improving its infrastructure fast.  I built my first isotope lab there in a building that struggled with environmental controls, but we managed to make things work. While pursuing my interests in compound specific isotope analyses of amino acids from various experiments and organisms, the majority of my colleagues were interested in various aspects of soil ecology and biogeochemistry. Adjacent to the campus is the Merced Vernal Pools and Grassland Reserve, a 6,500 acre preserve created in 2013 and available to UC students and faculty for study. My husband served as Director of the Reserve, so we took advantage of his access and its proximity to introduce the students and faculty on campus to stable isotope biogeochemistry.

Reflections in a vernal pool

            Vernal pools are shallow, seasonal wetlands that fill in from late winter to early spring rains on the flanks of the foothills of the Sierras. An impervious layer of sediment located about 1 meter below the surface keeps rainwater from seeping into the ground, thus creating these surface pools. This unique landscape has been decimated by development in California, therefore, it was important when UC Merced built its campus that they avoided plowing over these threatened habitats. Wisely, many acres of vernal pools and grasslands just adjacent to the campus were preserved in 2003 when the campus footprint was established.

            Eastern Merced County grasslands contain the most diverse and abundant vernal pools of any region in California. The UC Merced Reserve vernal pools support many federally-listed endangered plants and aquatic invertebrates (for example, fairy shrimp and tadpole shrimp), and one federally threatened amphibian. The federally endangered San Joaquin Kit Fox (Vulpes macrotis mutica) has been observed in the local area, but has not yet been documented in the Reserve (Toews and Swarth, 2016). The UC Merced Reserve is an outstanding, unique ecosystem and its designation in 2014 by the UC Regents into the UC Natural Reserve System.

            As across much of California over the past 200 years, the grasslands of eastern Merced County have undergone a large-scale replacement of native perennial grasses by a number of European annual grass species. The vast majority of grass species that now cover the Reserve are not native to western North America and includes such species as bromes, wild barley, Italian ryegrass, wild oats (Avena spp.), and annual fescues. Native, annual herbs in the area include the early blooming goldfields, tidytips, Johnny tuck, Frying pan poppy, popcornflowers, Douglas’ meadowfoam, California brodiaea, bluedicks, and clovers.  These native plants, however, make up a very small portion of the total vegetation.

            Cattle grazing takes place mainly during the time of year when these non-native grasses and forbs are growing. Although it might seem contrary to saving native plants, cattle grazing helps maintain the ecological health of the vernal pools by limiting the spread of non-native, European grasses and forbs into and around the vernal pools. The growth of exotic plants into the vernal pools leads to high rates of evapotranspiration, which dries the soil and reduces the number of days that pools are inundated (i.e. hydroperiod).  Adequate grazing also prevents the living and dead undecomposed plant matter (phytomass or “thatch”) from accumulating in pools. Excessive thatch can lead to degradation and eutrophication of the aquatic environment.

Dairy cows grazing on the Reserve

            At the UC Merced Reserve, dairy cows were chosen for grazing. While they are “nice to look at” with their black and white hides, dairy cows are a pain in the neck to work with. They trampled cameras that were deployed in the field, ate plastic pieces off of vehicles, scratched bumpers and fenders, and in general were nosey. Although cattle grazing is considered to be acceptable and necessary for the Reserve, prudent environmental stewardship requires monitoring in order to avoid over-grazing and under-grazing. To accomplish this essential land stewardship, we monitored residual dry matter (RDM) in 2013, 2014, and 2015. This measurement told us whether the land was being effectively grazed or over-grazed.

            After 35 years of having mass spectrometers at my beck and call, during my first 15 months at UC Merced I did not have any isotope instruments. With students David Araiza and Bobby Nakamoto, Chris and I started making RDM measurements using scissors, PVC pipes, sample bags, and a simple balance so that we could start collecting data and figuring out how plants were responding to cattle grazing in the face of a major drought in 2013-2015.

RDM "tool kit"

            We followed standard protocols for RDM sample collection procedures. Sampling sites were selected that represented typical areas where cattle grazed and that spanned the length and width of the Reserve. We traveled by 4WD vehicle to random sampling areas in 2013 and 2014, and to pre-selected sampling sites along transect lines in 2015. We entered the Reserve in the early morning and typically collected samples until about 12:00 pm. At a sampling site, three 1 ft² PVC quadrats were deployed by randomly throwing each one in a different ordinal direction roughly 10 to 15 m apart from one another. After the quadrat was placed on the ground, we did not change its position even if it landed on bare earth. The only time we re-positioned the quadrat was if it landed on a cow patty.

            We found that grazing was uneven across the Reserve as revealed by our sample collection data and data mapping. Uneven grazing is to be expected, but it could mean that some vernal pools are not benefiting from grazing. While uniform grazing is probably not achievable, more attention to cattle dispersion and stocking rates, and regular communication between the grazer and the Reserve director could lead to improvements.  If the University switched to grazing beef cattle, uneven grazing could be significantly reduced. Over the three years cattle removed an average of at least 44%, and up to possibly 79%, of the available, annual forage on the Reserve based on calculations of collected RDM. 

            I learned how to make my time without instrumentation a valuable learning experience. Undergrads accompanied us on RDM sampling days, and we had fun times being in the open air, seeing coyotes, burrowing owls, and eagles appear magically on this vast landscape. When the mass spectrometers arrived, I used the Vernal Pools reserve as a teaching site for students to learn how to conduct field work and understand complex isotope patterns on a landscape.

The grasslands on the Reserve

            Several of my colleagues at UCM, Asmeret Berhe, Stephen Hart, and Teamrat Ghezzehei, were interested in various aspects of soil isotope biogeochemistry. As the director of the isotope facility, I became involved in many of their studies. At first glance, the work did not fully capture my interest, particularly after studying exotic meteorites and amino acids from owls. California is almost exclusively a C₃-plant based ecosystem, so the carbon isotope pattern in soils has a rather small range and matches closely the carbon isotope signals in plants growing on those soils. Soils are one of the major reservoirs of fixed carbon in terrestrial environments. How this carbon is cycled can be important for climate perturbations. Asmeret Berhe and her students are interested in how erosion affects whether a soil holds onto its organic carbon or whether it is released back into the atmosphere as carbon dioxide after the soil moves. This is not an easy question to answer because soil has a complex structure with different parts of soil holding different amounts of organic carbon.

            Berhe and her students developed methods for separating bulk soils into density fractions, which added to the quantitative assessment of how carbon, nitrogen, and even hydrogen is cycled in soils. With carbon isotope measurements, percent total organic carbon, percent total nitrogen, as well as the mass balance of the density fractions, the research became more engaging (e.g., McCorkle et al., 2016; Abney et al., 2017). Together with radiocarbon data to measure the age of the organic carbon in soils, we were able to determine relative reactivities of these different soil fractions.

            Postdoctoral researcher Elizabeth (Liz) Williams pioneered work on hydrogen isotopes in soils based on the work by Ruppenthal et al. (2015). One of the major questions in soil ecology today is whether the organic matter in soil comes from root exudates, litter deposition from the surface, microbial biomass, or a combination of these three sources. Ruppenthal took advantage of the difference in the hydrogen isotopes of leaf water (more positive) relative to those of water in root tissue. He argued that if decomposed leaf litter were the source of soil organic matter, then its isotope composition would be more positive than if it came from root exudates. His conclusion was that soil organic matter in his study site, a grassland ecosystem, was derived primarily from root exudates.   Liz Williams set up a series of experiments using soils from an altitudinal gradient in the nearby Sierra Nevada mountains.  The hydrogen isotope signatures of bulk soil and the heavy, mineral fraction were related to local precipitation. It remains to be seen whether the hydrogen isotopes of deeper soils will carry a palaeoenvironmental signal. Williams’ approach might provide an independent and more holistic assessment than current strategies based on lipid compounds extracted from soils.

Discovering science as a child

Dad, Art Fogel, and Marilyn (2 years old) examining plant specimens, 1954

            As a very young child, I was a wanderer. At the age of only two, I walked about 200 yards through the parking lots of our apartment building to a local grocery store across a fairly busy street. That was in 1955, so there weren’t the zippy cars of today with distracted drivers. I walked myself back home into our apartment without my mother being any wiser. After we moved to our suburban home on Greenvale Road in Moorestown NJ, I lived next door to a gang of adventurous kids—David and Richie Furhman and Albert and Franny Stein. My brother Fred (then called Freddy) was a close partner in all of my adventures as a child as well. Together, we called ourselves the Greenvale Raiders. We roamed the neighborhood before it was built out with other houses. Wandering led me to investigate the natural world.

            Our “home range” was about a mile, a distance that tethered kids these days rarely travel on their own. We especially liked to build bridges with branches and sticks over small streams and creeks. On nice days, we made our way to Moorestown’s Strawbridge Lake where I caught small fish and tadpoles. Without any knowledge of what science was or what a scientist did, I began observations of the natural world here. In 3^rd grade at the age of 9, I started keeping a weather diary noting daily temperatures, cloud types, and precipitation. In summers, I made live insect collections kept in Mason jars on the back patio. By the age of 10, I was creating small mesocosms of plants and animals in jars so I could observe semi-natural habitats.

            The Greenvale Raiders were intensely following NASA’s early astronauts in the Mercury space program listening to the launches and landings on transistor radios. In 1961, we “launched” my hamster, Creampuff, into “space” with a large box kite that we’d built together. When the hamster “touched down” to earth, we had a victory parade around the block with the hamster proudly displayed in a Radio Flyer red wagon. In 6^th grade (11 years old), I wrote an essay my father saved highlighting that when I grew up, I wanted my own chemistry lab, 4 children, and 6 dogs.

Arthur and Florence Fogel, circa 1988

            My parents played supportive roles that aren’t in any way similar to the way that parents have today for encouraging STEM in their kids--enrolling in summer science camps or after school science programs and buying them computers. My father, Arthur Fogel, was raised in a rural community, served as a Lieutenant in the US Navy on a submarine in World War II, and earned a degree in electrical engineering at Penn State. He worked his whole career at RCA (Radio Corporation of America) in Camden NJ as the head of the transformer division, which made important parts for all of the space missions. Our family was the first in the neighborhood to have a color TV, because RCA designed and built them. My dad was an avid hunter, fisherman, and gardener—hobbies he learned growing up in the eastern part of Pennsylvania. Every summer, we headed out to points north or west to visit national parks, fishing spots, and historic sites, in particular battlefields.

            At home, we had the only vegetable garden that I knew of. Every summer my father grew tomatoes, beans, corn, radishes, and lettuces that we ate with relish. He also grew a profusion of different flowers—tulips, irises, dahlias, zinnias, and marigolds. I had my own 3 x 3 foot garden plot, chose my own seeds to plant, and managed my garden from the age of about 7 and older. With him, I was comfortable being in the out of doors, loved working in soil, and liked getting dirty! I also learned to use tools from him. First, gardening tools, then hammers, saws, wrenches, and screwdrivers. We built a dollhouse, a birdhouse, and a rabbit hutch together. When I was about 12 years old, he taught me how to load and fire a rifle and a shotgun. I never hunted, but I was familiar with guns and learned to respect them. Although he was an engineer and not a scientist, he taught me things that were considered “boy’s stuff”, that bolstered me as a female scientist in a largely male world.

My family's "Hunting Cabin" in remote Pennsylvania

            My mother, Florence Fogel, was more of an indoor person and grew up in urban Camden, New Jersey. But she was creative, artistic, and loved to try new things. I learned to sew, clean bathrooms, knit, iron clothing, and make curtains from her. Every year, I chose a different craft project that she helped me figure out. I was provided with coloring books, paints, scrapbook materials, and any sewing supplies I wanted. Together we designed my wardrobe, bought the materials, and constructed the outfits until I was in my early 30s! She took our Girl Scout troop on bike rides, to the racetrack, and camping. I would have been more content to sit in my room and read a book, but she encouraged me to break out of my shell and try new things. Neither parent ever imagined they’d raise a child, a daughter no less, to be a world-renowned scientist.

Florence Fogel with dress designed for Marilyn circa 1970

            I was always an avid reader and finished all of our libraries’ books about dogs and horses, which I loved. At home, I had a set of the Golden Nature Guides on birds, flowers, trees, rocks and minerals, and weather. I kept these close by my bed and consulted them frequently when I observed something new in the neighborhood. I marked the pages with check marks when I identified a new species. It was a matter of personal pride that I knew all of the mammals from all of the continents. I kept scrapbooks with pictures of animals. As a child, I had no recognition that everyone didn’t have the same interest in the natural world as I did.

            In 6^th grade (11 years old), I wrote the following, dated Sept. 5, 1963, after a spectacular summer vacation to the Wild West. Having an opportunity at a young age to see such spectacular places surely influenced me.

This summer we went to Wyoming and Montana. We saw some moose, bear, and marmits (sic) in Yellowstone National Park. We stayed at Cooke City in Montana. One day we went fishing. You had to hike back about 3 miles over mountains. The flys (sic) and mosquitos were bad that day and it was hot. When we got there we had drank all the water we brought. So we found a fresh stream and filled up the thermos jug. I caught 2. Altogether we had 14 fish. We got firecrackers in Wyoming and set them off on the Fourth of July. We went to two rodeos. I nearly froze at one of them. We met our friends that we had a barbecue with four years ago. I went horse back riding there and you could gallop all you wanted. Also I saw a square dance on horses. There was a creek in front of our cabin. You couldn’t swim in it because the current was to swift. I took a raft down it and over the rapids. There were cows on the other side of the creek. One had one horn. At night they had a roundup. I couldn’t sleep because of the mooing. We got home in 3 ½ days. We drove from five in the morning to seven at night. One motel stopped had an indoor swimming pol. We got home on July 16.

            I returned to Yellowstone almost 20 years later as a scientist and spent three years studying its natural environments.

Brother Fred Fogel, Mom Florence Fogel, and Marilyn, Beartooth Mtn. Pass, Montana, 1963

            My interest in meteorology, biology, entomology, and space studies didn’t register as necessarily important to me as a child, but the science gene was there. In junior high school (12-14 years old), I had two male science teachers who I thought were rock stars. Mr. Parks supposedly taught us earth science and biology, but I recall him taking us out to the parking lot and teaching us the names of all the parts of a car and how automobiles worked. He also brought in chicken embryos, clams, and worms for us to dissect. Somehow he knew someone in the medical field who had a human brain in a bowl that he brought in to show us. We got to touch it! I thought that was so cool. Mr. Barnosky taught chemistry, in particular he taught us about isotopes—something I’ve centered my career on. While I enjoyed other subjects like Geography and Math, the science classes were the most fun.

            In high school, my favorite classes were Chemistry and Biology. At the time, I thought the interest was due to the fact that I had good teachers, a factor that surely influenced me. Mr. Boehmler, my Chemistry teacher, had a droll way of explaining with simple precision the nature of chemical bonds, reaction mechanisms, and physical properties of various compounds. A trim man with horn-rimmed glasses, always wearing a white shirt and tie, he presided over chemistry labs with patience and calmness. When students dropped glassware, he looked sternly towards the careless student and asked, “Did it break?” Amidst the hormonal ups and downs of high school, I managed to learn enough chemistry to place out of the first college class at Penn State.

            In the 1960s, we didn’t have science fairs. My parents weren’t scientists. When I look back at my interests, I can clearly see the start of the pathway forming my long scientific career. The early interest in dogs and horses—something many girls are taken with—seemed fairly normal. But, being comfortable in the natural world and being allowed to roam, enjoy touching bugs, going fishing, and being at home in the out of doors was not readily associated with being a girl at this time. I was fortunate that my parents never pushed me to more girly pursuits and away from informal science. I was lucky to be able to recognize that feeling of “fit” and “fun” when I started my academic career at Penn State as a biology major. I have never looked back.