Tag Archives: Nitrate

275 Samples and 276 Mosquito Bites

–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!

URA fieldwork project: nutrient concentrations in select rivers and wetlands in Guelph, ON

— 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.