Results and Discussion

Table 2. Chloride levels of each pond compared with the total number of aquatic invertebrate individuals found at their respecive pond.  Values above the CCME's Water Quality Guidelines for the Protection of Aquatic Life chloride threshold are highlighted in yellow. 

The Canadian Council of Ministers of the Environment’s Water Quality Guidelines for the Protection of Aquatic Life states that the threshold for chloride concentration in bodies of freshwater is 120 mg/L. This, compared with the chloride values we obtained for the 5 ponds, shows that concentrations higher than this threshold do not have an impact on the overall abundance of aquatic invertebrates in these ponds (Table 2). It is unclear whether this threshold was created with aquatic invertebrates in mind, or if it focused on larger bodied aquatic organisms such as fish or amphibians. The threshold may have greater applicability depending on the invertebrate Order, however that was not accounted for in the current analysis, but could be applied in the future.

As chloride concentration in mg / L increases, there is usually a decrease in invertebrate abundance, particularly in Orders Ephemeroptera, Diptera, Anomopoda, and Odonata (Figure 10). That being said, the Order Amphipoda was shown to have a positive relationship with chloride concentration, as the number of invertebrates increases as the concentration of chloride increases (Figure 10). P-values for all invertebrates are well above ɑ=0.05, with the closest value being the order Diptera (p=0.262) and the farthest being the order Coleoptera (p=0.789), therefore there is no significant evidence that chloride levels impact invertebrate orders. More research and analysis are needed to determine whether these relationships were due to the effect of chloride itself or a combination of water variables.

Figure 10. Scatterplot representing the number of Amphipoda, Anomopoda, Coleoptera, Diptera, Ephemeroptera, and Odonata individuals found at each pond in relation to the respective pond's chloride concentration in mg / L, respectively. 

While interesting trends and relationships have been discovered, it is clear that more ponds need to be sampled for invertebrates to obtain conclusive results. 

Current invertebrate samples for the rest of the 30 ponds sampled for water chemistry data are continuing to be sorted and identified. When the full dataset is available, (most likely in 2024) these statistics should be run again and compared with the results of this study.

Future sampling efforts should aim to collect their invertebrate and water chemistry samples during the same timeframe as this study, in order to identify and strengthen results and trends. Future studies could also include sampling during different times of year (possibly in the spring, when snowmelt and runoff are highest) to see if there is a difference in water chemistry and invertebrate response. 

Overall further sampling effort and research is needed to determine whether or not water chemistry has a significant effect on the abundance distribution of observed orders of aquatic invertebrates in urban stormwater ponds, and whether these results can be applied to current Canadian Environmental Quality Guidlines to determine if certain aquatic invertebrate Orders could be indicators for these water quality thresholds.