Aquatic System - Toronto and Region Conservation Authority

order coldwater tributaries that appear to have local groundwater sources (KatabokokonkCreek and unnamed tributary that both flow into the main branch of the Little Rouge).The groundwater model suggests that approximately 2/3 of groundwater discharge enters thesystem via small, low order streams (see Chapter 4 Groundwater). When integrated with thefisheries data, it is in these small streams that healthy populations of brook trout and redsidedace are predominately found. Challenges to maintaining existing groundwater flow regimesmay increase for streams reliant on local recharge/discharge as these areas are within theurbanizing boundary. Unless mitigated, the change in impervious cover during development inthis area of recharge may result in flow loss to these streams. Two figures illustrate thewatershed areas that are predicted to have high groundwater discharge (>2.5 L/s) based ongeology (Figure 8-1) and whether that groundwater is sourced locally (short tracks) orregionally (long tracks) (Figure 8-2). It is noted that the fisheries data and field knowledge oflocal stream habitat supports the groundwater model results.8.3 Measuring and Evaluating the Aquatic SystemThere are two types of measurements taken to evaluate the aquatic system: biotic and abiotic.biotic measures refer to living organisms, both plant and animal. Species numbers, distributionand community structure can provide a good measure of environmental condition at the localsite level and, in some cases, over a larger region. Abiotic measures refer to physical orchemical factors that respond to environmental change. For example, other chapters havediscussed how human land use change has altered watersheds by modifying channelstructure, altering baseflows, increasing the volume and frequency of runoff and peak flows,chemical contamination of ground and surface water, erosion and sediment loading andaltering water temperature.Having identified the two categories of measures, the decision around which of the many bioticand abiotic metrics are chosen for an evaluation is fundamental to a meaningful analysis. Withthat, pinpointing thresholds at which ecological integrity is put at risk due to landscape changeis a difficult procedure owing to the synergistic effects of changes to water quality, quantity,riparian vegetation, temperature, human use, and a host of other factors. By convention,knowledge of the natural physiographic setting coupled with indices that examine speciessensitivity to physical in-stream parameters (e.g. Fish and Invertebrate Indices of Biotic Integrityor other measures (e.g. stream thermal stability, baseflow and surface flows) have been usedto assess the aquatic system. While useful, there is still interpretation associated with thesetechniques and growing evidence that the current application (as a metric) of these commonlyused indices/measures may not be appropriate at large spatial scales or within the context ofan urbanized watershed. That is, the context and/or purpose for which some indices wereoriginally developed may not transfer well to measuring the impacts of change to thelandscape. Metrics that arguably have interpretive limitations will be identified and discussed inthe following section.8-3