The way rainfall is translated to runoff and streamflow in rivers depends on many complex, interconnected processes in the landscape. Rain falling onto hillslopes, meadows, or forests is either infiltrating into soils or flowing as runoff on the surface of soils. Either way, the moving water is often mobilizing solutes, pollutants, or nutrients along its pathway, which have the potential to contaminate streams and impair water quality. Knowing where these flow pathways occur in the landscape is crucial to prevent pollutants (e.g. excess nitrogen from fertilizer or manure, pesticides, pathogens) from being transported to rivers and lakes, where they can cause algae blooms. Observation of and understanding where and when runoff is occurring in the landscape and how the moving water is transporting pollutants to streams has been at the heart of hydrological research for many decades and has triggered the Clean Water Act in 1972.

For many years, hydrologists (e.g. water scientists) have used hydrologic measurements such as streamflow hydrographs (e.g. graphs of streamflow vs time) to characterize hydrologic- and associated transport-flow pathways, however, these methods do not allow for identifying specific pollutant sources and individual flowpaths of concern in the landscape. In recent years, chemical tracers like bromide or chloride and dyes (blue, red, yellow fluorescent colored dyes) have been used to obtain more information, but the variety of unique tracers available from each type is extremely small, thus limiting the identification of multiple flowpaths at the same time. Additionally, once introduced into the system, it is often problematic to reuse the same tracer because of uncertainty in whether old or new tracers are being detected. 

To overcome the problems that have plagued traditional tracer studies we have developed a new tracer concept that utilizes bio-molecular nanotechnology. We use short, artificially made DNA sequences that are wrapped into a safe, biodegradable polymer composed of polylactic acid (PLA) to protect the DNA from being eaten by microbes during the transport process.  Because DNA is made of the four basic building blocks adenine (A), thymine (T), guanine (G) and cytosine (C) (Fig. 1), which can be combined in any random order, our unique DNA-based tracers allow, in theory, fabrication of an enormous number of unique tracers (approximately 1.61 x 10⁶⁰) with identical transport properties. Because of their unique DNA sequence the tracers have unique IDs, thus, we can use multiple tracers at the same time in the same watershed. The amount of tracer present in a streamwater sample can be estimated with real-time quantitative polymerase chain reaction (qPCR), a method commonly used in molecular biology, which determines the number of DNA copies present in a sample. Finally, during the tracer fabrication process, we can alter the size of the tracer particles to anything from 200 nanometers (size of a virus) to 1 micrometer (size of colloids or bacteria), which helps mimicking the physical transport properties of the pollutant of interest.

In the next two years we will test differently sized DNA tracers in a well-studied, small experimental watershed at SFREC to test their use for identifying hydrologic flow pathways. This study will provide invaluable information for the understanding of processes in hydrologic systems that can be used to improve hydrological and biogeochmical models used to predict transport of pollutants from hillslopes to streams. To achieve this broader goal, we will distribute 5 different DNA tracers at 5 different locations at incrementally increasing distances from a trenched hillslope at SFREC and measure the tracer breakthrough curves in a runoff collection system and the watershed outlet. The injection locations will be chosen to represent a range of specific soil-landscape characteristics such as places with relatively deep soils, shallow soils and areas where flow visually concentrates in the landscape. With the tracer experiments we also hope to quantify preferential flow pathways (e.g. macropore flow) in the watershed. Preferential flow is hypothesized to lead to shorter travel times of water and pollutants through soils and the vadose zone. Because of the variable size of our DNA tracers (0.1-0.4 µm) they could be particularly useful for quantifying macropore and preferential flow because we expect that a small fraction of the tracers will be filtered out in the soil matrix while the majority of the DNA tracers will move along the most rapid flow pathways. The results from these experiments, if successful, will provide improved estimates of the time it takes for water and solutes to travel through the soil to streams, which will allow us to more accurately predict the risk of pollution of streams and surface water bodies during storm events.

Over the last few years Californians have grappled with how to manage lands during times of both drought and plentiful rainfall. At SFREC and on Central Valley rangelands, one question is whether management that promotes high forage in wet years alters ecosystem resilience in dry years. For example, promoting highly productive grasses is a common goal. While drought years can negatively affect productive grasses, less productive species, particularly forbs like filaree, do relatively well in drought years due to decreased competition. Over the last several years the Suding lab and SFREC crew have been building ever-larger drought manipulations to test how different management practices, and associated species mixes, affect forage across good and bad rainfall years.

 

In the first iteration of this project, we looked at how grazing practices and rainfall interact to affect forage over dry and wet years. We hypothesized that grazing practices that maintained a diverse mix of grasses and forbs would promote more stable forage across wet and dry conditions. To test this, we first varied grazing intensity over four years within a pasture to describe how grazing alters grass and forb abundances (Figure 1a). Second, we implemented rainout shelters and irrigation over three years to create “dry” and “wet” plots within areas of different grazing histories (Figure 1b). We found that moderate grazing practices maintained a diverse mix of grass and forb species. This mixture better maintained vegetation cover and biomass across rainfall conditions compared to low-grazed areas dominated only by grasses (Figure 2) (Hallett, Stein, Suding conditionally accepted, Oecologia).

 

In the second iteration of this project, we are exploring how rainfall timing alters grassland diversity and forage production. We hypothesized that early-season drought will alter which species recruit that year, with higher forb abundance in dry falls and higher grass abundance in wet years, whereas late-season drought would reduce overall production. To test this, we have implemented large shelters with roofs that are pulled in place to create early-season, late-season and continuous drought as well as a control (Figure 3). We are finding that periodic early-season drought helps to maintain forb diversity in California rangelands. Working with Dr. Whendee Silver, we are also testing the effect of rainfall timing on nutrient cycling and greenhouse gas emissions. We are finding that previous-season rainfall as well as current season alters greenhouse gas emissions, which may be important for managing rangelands for multiple ecosystem services going into the future.

The Sierra Foothill Research and Extension Center in Browns Valley, CA utilizes 130 acres of summer irrigated pasture for cattle grazing. SFREC's irrigation water is supplied by a local water district via pipelines and open ditch distribution sources. The irrigation delivery system applies water through sprinklers, open ditches, and gated pipes. Each irrigated pasture at SFREC is managed for 1) Forage Production, 2) Water Quality, and 3) Soil Quality.

SFREC staff measures forage production in 15 enclosed cages throughout five different irrigated pastures. The treatments within each cage include leaving 4-6 inches of residual grass and measuring Total Forage Production (TFP). Guidelines for general irrigation and pasture management production based on past and current research recommend leaving 4 to 6 inches of residue/grass growth after each grazing period. The basis of this recommendation is to increase forage production (by leaving increased amounts of foliar surface area), improve root development, decrease weeds, cause less stress for forage grasses and increase water infiltration. Total Forage Production is measured by clipping the grass all the way to the ground. This center project is measuring the two treatments (4-6 inches & TFP) on their respective pounds/acre production. Each month (from April through October) forage is clipped from each cage, dried, and weighed (pounds/acre). After the samples are clipped, each enclosed area is leveled to its prescriptive treatment.

During the last two years of field sampling on irrigated pasture at SFREC, there was an increase in forage diversity in the Total Forage Production subplot. Clovers, birdsfoot trefoil, and filaree became increasingly abundant due to the increased sunlight and less crowding from competitive grasses. While the increase in clover and other forbes growth lends to an increase in forage quality, there is an overall decrease in forage production per acre in the TFP treatments when compared to the treatments with 4-6 inches of residual grass.

Numerous other factors can potentially impact irrigated pasture forage growth. Fertilization (rates, composition, timing), irrigation (frequency, amount, duration), grazing (stocking density, class/age of animal), species composition, physical structures (water location, loafing areas, rubbing zones, mineral location), soil properties, aspect,  and slope, are other important components to manage or consider.

Over the past several months, Dr. John Angelos of UC Davis School of Veterinary Medicine has been working on a vaccine for one of the cattle industry's most widespread diseases: infectious bovine keratoconjunctivitis (IBK), commonly known as pinkeye. IBK is caused by an infection of Moraxella bovis in the eye that leads to corneal ulcers, scarring and, in extreme cases, permanent blindness.

According to Dr. Angelos, the disease presents an economic loss for the producer due to the cost of labor to treat the infection, the cost of the antibiotic treatment as well as reduced weight gains. He also notes the disease has certain animal welfare considerations; it can be extremely painful for the infected animal. Currently, there is not an effective vaccine to prevent the painful disease, only a costly treatment.

Dr. Angelos has been working on this vaccine since April, but the vaccine has been developing since the early 2000s. This summer, Dr. Angelos is testing the effectiveness of an intranasal vaccine, rather than the subcutaneous version of previous studies. His hypothesis states “calves vaccinated intranasally with Moraxella bovis cytotoxin (MbxA) will have a significantly reduced cumulative proportion of corneal ulcerations associated with naturally occurring IBK versus control calves.”The team collected blood and tear samples from approximately 180 animals at the UC Sierra Foothill Research and Extension Center and administered either the vaccine or a placebo assigned to the animal. In order to keep the results unbiased, Dr. Angelos did not know which vaccine he was giving to the animals; they were labeled “A” or “B.”

Each week thereafter, he and several students have examined the entire herd, noting those with active cases of pinkeye. If an animal shows signs of pinkeye, an innocuous stain is administered in the eye to see the ulcer, a measurement and a picture are taken to monitor the ulcer from week to week. At the end of the study, animals with active cases of pinkeye will be given antibiotics to cure the pinkeye.

Ultimately, the goal of the research is to create a vaccine that will prevent the disease from occurring. Dr. Angelos explained that although this vaccine has made great advancements, it will need to have subsequent testing and trials to determine if it is viable in the industry. In the video below, Dr. Angelos explains his research and the role of the Sierra Foothill Research and Extension Center in developing a vaccine for infectious bovine keratoconjunctivitis.