Figure 1: Overview presentation of proposal.

Figure 2: Ontario Benthic Biomonitoring Network Kick and Sweep Training Session, May 2019 (Photo Courtesy of Bryant Serre [per TRCA]).

1.0 Introduction

Benthic macroinvertebrates are bottom dwelling organisms in lotic and lentic ecosystems that have been, and continue to be, surveyed as part of environmental assessment. Benthic organisms refer to the consortia of small aquatic animals and larval starts of insects (e.g., dragonflies or infraorder Anisoptera) that occupy the sediment for a significant duration of their life history (Brinkhurst 1975; Hutchinson 1961) . Benthic macroorganisms confine themselves to river and lake sediment for a series of reasons, such as predation avoidance behaviors and camouflage and providing optimal conditions for initial larval development. However, as they are inhabit aquatic sediment environments, they are in subject to the physical, chemical and biological conditions of streams and lakes. Indeed, as benthos are niche-constrained, populations are concomitantly subject to both short and long term stressors while being easily measured and informative indicators of aquatic health (Read et al. 1983; Reynoldson and Metcalfe-Smith 1992).

Within ecotoxicological assessment of the benthos, individual organism health and state is rarely measured (Fargasova 1999; Bettinetti et al. 2020). Instead, the relative abundance of benthic macroinvertebrates is used to elucidate the biological conditions of aquatic ecosystems. For example, the decreasing relative proportion of Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) (EPT) taxonomic groups, in relation to all other sampled taxa, is used to indicate increasing river or lake stress (United States Environmental Protection Agency (USEPA) 2021). To date, a suite of different metrics have been developed and continually used globally for aquatic monitoring (USEPA 2021).

Under anthropocentric human influence, drainage basins have been urbanized extensively, leading to potentially deleterious effects in aquatic systems. The series of effects on watercourses and waterbodies are diverse; for instance, surface runoff and stormwater collection can mobilize heavy metals (notably mercury, lead, and arsenic), asphaltenes (polycyclic and polynucleic aromatic hydrocarbons or PAHs), macronutrients (e.g., runoff from farm fields promoting excessive algal development), and plastic pollution to cause chronic (i.e., reproductive), lethal (i.e., mortality) and sublethal (i.e., behavioral) biological effects (Muller et al. 2020; Scholz 2015). Moreover, the heightened temperature of urban surfaces (alia the Urban Heat Island Effect, Oke 1982) is often transferred to surface water flows, significantly raises temperatures of receiving watercourses and waterbodies, and concomitantly shifting the range of tolerance for benthic macroinvertebrates and subsequent ecotoxicological impact (Jones et al. 2012). In the context of sustainable development and fighting climate change, the relevance to assessing and continually monitoring of benthic macroinvertebrates is axiomatic.

Currently, benthic health assessments have been limited to individual watersheds and jurisdictions. In Canada, Environment and Climate Change Canada’s (ECCC) Canadian Aquatic Biomonitoring Network (CABIN) has reported on benthic health in individual case areas (e.g., Southwestern Hudson Bay drainage area, Great Slave Lake drainage area): there has not been a comparative analysis of benthic indices across the entire data collection. Moreover, analyses of benthic indices to urbanization across watersheds will elucidate whether benthic macroinvertebrate indices are suitable indicators of aquatic ecosystem health (personal communication, C. Metcalfe (CABIN) 9 March 2022).

1.1 Background of Benthic Macroinvertebrate Monitoring

In North America, there has been use, across several levels of environmental governance, to analyze the relative abundance of benthic macroinvertebrates as a means to discern biological health of lotic (flowing water), lentic (stagnant water), coastal and transitional (e.g., river deltas, mangrove forests) ecosystems. Since 1972, the International Joint Commission (IJC) has used benthic macroinvertebrates, in conjunction with a suite of indicators for monitoring the status of the Laurentian Great Lakes. The use of benthic macroinvertebrate indices was suggested under the the Great Lakes Water Quality Agreement (GLWQA), and they are still used to measure North American's progress towards improving the water quality of watercourses and waterbodies (notably Lake Erie which exhibited severe eutrophication and poor biological quality). In the United States, the United States Environmental Protection Agency’s (USEPA) National Aquatic Resource Surveys (NARS) uses indices of relative benthic populations, in conjunction with measuring river chemical (e.g., conductivity, dissolved oxygen, soil chemistry, macronutrient concentrations), physical (e.g., human disturbance, clarity/turbidity, riparian vegetation condition) and recreational (e.g., presence of filamentous blue-green algae microcystin aeruginosa, enterococci, and faecal coliforms) indicators, to assess the quality and condition of watercourses across the contiguous United States (USEPA 2020). Similarly, Environment and Climate Change Canada’s (ECCC) Canadian Aquatic Biomonitoring Network (CABIN) measures changes in benthic biological communities to assess the state of Canadian lotic systems (ECCC 2018). Regionally, examples can be seen in many watersheds. In Ontario, Canada, the Credit Valley Conservation (CVC) Authority in uses benthic indicators as part of their approach to discern whole watershed health, beyond the confines of the lotic ecosystem itself (CVC 2017). Similarly, the largest Canadian conservation authority, Toronto and Region Conservation (TRCA), collects benthic macroinvertebrate samples frequently as part of their Regional Watershed Monitoring Program (TRCA 2020). While these instances exemplify how there are multiplicitous assessments of water quality using benthos abundance, and across varying continental, federal and provincial extents, benthic indices have not been evaluated wholly across all of Canada as to allow relative comparisons of water quality and potential aquatic ecosystem stress.

1.2 Project Objectives and Questions

Given the foregoing findings, it is the goal of this project to evaluate the health of aquatic ecosystems across Canada, using indices of benthic macroinvertebrate populations. Specifically, it is the objective of this study to test the relationship of the Ephemeroptera, Plecoptera and Trichoptera (EPT) benthic macroinvertebrate index to upstream watershed land cover for each existing sample point. In turn, this will help understand the potential ecotoxicological effects of urbanization on aquatic ecosystem health. This study is guided by the following question: how do benthic population assemblages respond to changes in urbanization within the drainage basin? This objective is accomplished through computing the EPT index for each sample site and the land cover composition of upstream drainage basins for sample sites, and subsequently, testing the statistical relationships between basin land cover and the population EPT index.

Figure 5: Sample points from the CABIN program (in red) with there respective upstream drainage basins (in blue).

3.2 Delineating Drainage Basins

The digital elevation file (Canadian DEM) was imported into ArcGIS, where the Watershed Geoprocessing toolbox was used. Firstly, a depressionless DEM was created by filling surface depressions in the digital elevation file. Secondly, a flow direction raster was computed using the "Flow Direction" tool; a flow direction raster takes into account the eight adjacent cells and assigns a reasonable trajectory of flow for each cell. Typically, the next step is to use the flow direction raster to create a flow accumulation raster, using the "Flow Accumulation" tool; however, as the pour points were already known (i.e., the sample points), this step was avoided. Subsequently, watersheds were delineating using the "Snap Watershed" tool where the flow direction layer and the pour points were used to delineate upstream drainage areas. This process was looped over all points in the dataset to create a total of 1244 watersheds.