–by Thanuja Thavarasa
Living organisms need a variety of nutrients in order to grow. For plants, nitrogen is an essential nutrient. Nitrogen, found in the form of nitrate (NO₃ˉ), is taken up through plant roots from the surrounding soil. Thus, we thought it would be interesting to explore the relationships between soil nitrate concentrations and the plant nitrate levels in a riparian area adjacent to the Speed river, right in the middle of the city of Guelph.
On June 12th and 13th, 2019, Aidan and I headed to our site where we measured and created our own 16 m by 30 m sampling grid that extended from the edge of the river to a walking trail. In Figure 1, every interval along the X-coordinate and Y-coordinate axes is two meters, and the apices of the grid correspond to where a soil sample and, when available, a plant sample, were taken. Figure 1 and Table 1 show were we collected 144 soil samples and 131 plant samples.
After collecting all the samples, we returned to the lab to analyze their nitrate concentrations. The soil was passed through a 2 mm sieve and then 5 g of sieved soil was mixed with 25 mL of tap water. Once the mixture set for 5 minutes, a disposable pipette was used to extract liquid from the top of the mixture and then transferred to the Laqua Twin nitrate sensor. Similarly, once sap was extracted from plant samples using a garlic press, the sap was put into the sensor to be analyzed. Figure 2 illustrates plant to soil nitrate ratios with context to their location. Further analysis of the data is in the works. Keep an eye out for Aidan and I at a potential future conference!
Dr. Genevieve Ali is seeking two (2) PhD students to work on the development of models targeting the prediction of water and nutrient connectivity in agro-forested landscapes. The models to be developed will build on traditional hydrologic modelling structures (e.g., grid-based models) as well as ecological models (e.g., agent-based models, graph and circuit theory models), and they will be validated against both ground-based data and remote sensing data.
Home institution: Successful candidates will be based in the School of Environmental Sciences at the University of Guelph (Ontario, Canada), located less than 100 km west of the city of Toronto. Successful candidates will benefit from a highly interdisciplinary environment and work in a new laboratory equipped for high-performance computing. They will also be awarded an annual stipend for three years and have access to guaranteed teaching assistantship positions for three years. Canadian applicants will be eligible for an entrance scholarship on top of their stipend. International students will, rather, be eligible for the International Doctoral Tuition Scholarship that covers the difference between domestic and international tuition fees. Successful applicants will carry research activities leading to participation in national and international conferences, and the publication of peer-reviewed papers. Successful applicants will also have access to a long list of professional development opportunities offered by the School of Environmental Sciences and by the broader University of Guelph community.
Prospective applicants: Successful applicants would be expected to start in January 2020 or May 2020. By the start date, they will be required to have a thesis-based master’s degree in geography, soil science, environmental sciences, ecology or engineering. Previous modelling experience and fluency with MATLAB are required. Knowledge of agent-based modeling principles will be considered an asset.
Selection process: For more information about the PhD positions, or to apply, please contact Genevieve Ali (email@example.com) and provide the following documents:
* A short cover letter or cover email explaining your interest in one of the positions
* Your curriculum vitae
* A copy of your master’s thesis
* Copies of your undergraduate and graduate transcripts
* Contact information for at least 2 references
Closing date: Applications will be reviewed as they are received. The positions will remain open until filled.
— by Aidan Doak
Hydrologists and environmental scientists often look at river flow through time and focus their attention to the minimum, maximum and average values. These values are used to answer questions regarding dry and wet periods, which can lead to hydrological droughts or floods. Less often do we look at the variation of flow over time, which is an indication of how dynamic or “flashy” a given river location is, and how strongly it may be coupled to rainfall inputs. Flow variability is not only important for characterizing hydrological regimes but also for ecological reasons, as some aquatic species require a variety of flow conditions through their different life stages. With that in mind, I did a quick explanatory analysis of flow records from 22 hydrometric stations across the Grand River Watershed.
Ten years (2008-2018) of daily river flow values were analyzed. The coefficient of variation (CV) of flow, which is simply the standard deviation divided by the arithmetic mean, was computed for individual stations over (1) the whole period of record, (2) for individual years, and (3) for individual months grouped across all years. The goal was simply to visualize whether spatial patterns of flow variability change depending on the year or month considered.
Figure 1 shows, for each hydrometric station, CV values (shown as blue circles) calculated using the ten years of daily river flow data. It clearly shows the larger flow variability of headwater locations, compared to downstream locations.
To accompany the set of yearly maps (Figure 2), I calculated the total annual rainfall using the Laurel Creek rain gauge station located in the center of the watershed (Figure 3). A quick, visual assessment of Figures 2 and 3 shows that on a yearly basis, CV values do not increase or decrease monotonically as we move from the headwaters downstream. Also, CV values are not necessarily higher or lower in years with less rainfall.
Seasonality of flow variation is evident when the data is displayed monthly (Figure 4), but this time again the location with the highest variability are located in the headwaters. While those results are not surprising, they do highlight the critical importance of headwaters for the hydrological and ecological integrity of watersheds.
— by Aidan Doak, on behalf of myself and Thanuja Thavarasa
On May 8th, 2019, Thanuja and I kicked off our summer undergraduate research assistant (URA) positions at the University of Guelph. There were many potential projects planned for the months to come and a water chemistry analysis project was at the top of our list. The goal was to observe and compare any relationships between nitrate and phosphate concentrations in different water systems within the Grand River Watershed. The city of Guelph, located right in our backyard, became our primary focus. We collected water samples from six sites after significant rainfall events. We have provided a map showing our six site locations below (Figure 1) and a table displaying sampling dates and precipitation totals since the previous outing (Table 1).
Samples were tested for electrical conductivity and oxygen reduction potential in the field. Afterwards, they were brought back to the lab for turbidity measurements, filtration and analysis of nitrate and phosphate concentrations. We have compiled our data and graphed some of our results below. The straight blue line in each figure highlights the 0.03 mg/L provincial water quality standard for phosphate.
The Eramosa River and the Speed River were our two river sites, with relatively wide channels (Figure 2A and 2B). Both sites demonstrate a similar nutrient behavior; consistently higher concentrations of nitrates compared to the wetland sites (Figure 3), and phosphate concentrations that vary over time more compared to wetland sites. Phosphate concentrations fluctuate within 0.03 mg/L of the provincial water quality standard. The known, higher mobility of nitrate compared to phosphate could explain this behavior. The high levels of nitrate are potentially a product of recent rainfall events, washing nitrates downstream.
A riparian wetland located next to the Speed River was sampled at two locations; the first was closest to the river and the second was adjacent to a walking trail (Figure 3A and 3B). The wetland experienced many expansions and contractions throughout the two-month sampling period. On May 21st, there was no surface water at the Speed River Wetland Trail location so we could not take a sample. The Speed River Wetland Trail location experienced phosphate concentrations three times larger than the provincial standard, while the adjacent Speed River Wetland location had a phosphate concentration that was ten-fold the same standard. The ability of soils to retain phosphate, paired with the expansion and contraction characteristics of the wetland adjacent to the Speed River, may explain those dynamics. Wetlands are nutrient sinks as they prevent nutrients from reaching rivers and streams, which is an environmental benefit.
The Solstice Wetland (Figure 3D) exhibited a different relationship between phosphate and nitrate concentrations compared to the other river and wetland sites. The Solstice Wetland behaved as a perennial wetland as it always had surface water in the depression during the two-month sampling period. On the other hand, the Speed River Wetland is intermittent: it expanded and contracted to the extent that no surface water was present on multiple sampling days. At the Solstice Wetland site, nitrate and phosphate concentrations were strongly correlated, as indicted by their synchronous increasing and decreasing behaviors.
— by Thanuja Thavarasa, on behalf of myself, Aidan Doak and Jamie Bain
Water flow through soil is quite complex. It can move either vertically or horizontally dependent on a variety of factors like soil texture and different types of rainfall events. It can be valuable to know these water flow patterns since they can be used, for instance, to track and regulate the movement of harmful nutrients (like phosphate) to rivers and lakes.
Here is a quick video that shows our work in the field from our own perspective.
At the University of Guelph, the Dairy Bush is divided into two adjacent sectors: a forested area and a grassland area. After scouting the location, we thought it would be interesting to compare and contrast water flow patterns between these two land covers. Thus, on June 3rd, 2019, Genevieve, Aidan, Jamie and I set out to prepare two 1 m by 1 m plots. The idea behind this project was to evenly spread 30 L of water across the plot. The water was dyed with an environmentally friendly blue dye prior to the experiment. After a couple of days, the goal was to excavate these plots and visualize soil water flow patterns via the blue soil stains left behind by the blue water. We ran into a water application problem on the grassland plot due to tall shoots and strong winds. Fortunately, we were still able to successfully saturate the plot with the 30 L of water.
Drs. Madhur Anand and Genevieve Ali are looking for a motivated graduate student to take on a new project on hydrological, chemical and ecological connectivity. Additional details about the project and the position requirements can be found in the PDF ad.
MSc or PhD position available – Environmental sciences, University of Guelph
Are you an undergraduate student interested in both hydrology and ecology? If so, you may be a perfect fit for one of two summer research assistant positions. More details in the advert: Summer URA advert for 2019 (Ecohydrology)