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Recharge, discharge and surface water groundwater connectivity
Published in Ian Acworth, Investigating Groundwater, 2019
Aquifer and cave systems where stygofauna (organisms living in groundwater) exist within or associated with the groundwater form a major subdivision of GDE. Karstic systems are clearly the easiest to comprehend here as the secondary porosity (the holes shown in Figure 3.32) in the limestone karst are big enough to allow fish to swim in. This is well demonstrated by Figures 3.33 and 3.32, where unique communities of fish exist at the karst spring and are completely limited to this location, as the stream produced by the spring does not flow very far down the river bed. Fractured rocks may also contain stygofauna of a similar size, but sands and alluvium can only contain microscopic stygofauna. Examples of these are shown in Figures 3.34 and 3.35.
How appropriate are Canadian Water Quality Guidelines for protecting freshwater aquatic life from toxic chemicals in naturally-discharging groundwater?
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2019
James W. Roy, Patricia L. Gillis, Lee Grapentine, Greg Bickerton
Endobenthic organisms (e.g., insect larvae and nymphs, oligochaetes (worms), mollusks, crustaceans, unicellular organisms and resting stages for some key pelagic organisms (e.g., Daphnia ephippia)) are more likely than pelagic and epibenthic fauna to experience high (less-diluted) concentrations of groundwater-associated contaminants (Figure 1). The majority of endobenthic organisms live all or part of their lives in the shallow aerobic zone of sediments (10-20 cm) and therefore they will be most accustomed to groundwater geochemistry (discussed further in point 2 below). There are also deeper-dwelling endobenthic species, such as nematodes, copepods, mites, ostracods, tardigrades and syncarids, which can be found at up to 1 m depth (Williams and Hynes, 1974). Of special note are invertebrates of the groundwater-adapted stygofauna (i.e., fauna residing in caves or aquifers; typically depigmented and blind, often with a small and flattened body-shape), which can reside in aquifers to even greater distances (Humphreys, 2009). Some investigators have recently suggested prioritizing the monitoring of endobenthic fauna to optimize the risk assessment for groundwater-specific contamination (Rasmussen et al., 2016; Roy et al., 2018). This follows the use of the benthic invertebrate community as an in-field biomonitor of groundwater quality by Malard et al. (1996), and the use of sediment-dwelling invertebrates in buried cages as a means of assessing pore water (including upwelling groundwater) quality by Burton et al. (2005). Some efforts at using stygofauna invertebrates in laboratory exposures with groundwater contaminants have also been made, with most focusing on metals (e.g., Canivet et al., 2001; Hose et al., 2016). However, Avramov et al. (2013) employed the groundwater amphipod Niphargus inopinatus in toxicity tests with toluene, a volatile organic compound that is a common groundwater contaminant.