. The Canadian field-naturalist. Natural history. 2001 Martin, Brown, Barton, and Power: Stream Invertebrates 71 CO 03 B a u -8 > C o s O ;- 1 4UU â 300- ⢠⢠⢠r2 = p< ⢠200- ⼠⢠⢠100- 0- a ⢠⢠A ⼠⢠5^. Day of winter Figure 1. (a) Regression plot of the number of aquatic invertebrates collected in the drift on days when frazil ice was present from 21 January to 17 March 1998 and from 31 December 1998 to 23 February 1999 (shown as triangles) in the Grand River, Ontario. The regression analysis includes only data from the first winter, (b) Regression plot of the numbe
. The Canadian field-naturalist. Natural history. 2001 Martin, Brown, Barton, and Power: Stream Invertebrates 71 CO 03 B a u -8 > C o s O ;- 1 4UU â 300- ⢠⢠⢠r2 = p< ⢠200- ⼠⢠⢠100- 0- a ⢠⢠A ⼠⢠5^. Day of winter Figure 1. (a) Regression plot of the number of aquatic invertebrates collected in the drift on days when frazil ice was present from 21 January to 17 March 1998 and from 31 December 1998 to 23 February 1999 (shown as triangles) in the Grand River, Ontario. The regression analysis includes only data from the first winter, (b) Regression plot of the number of aquatic invertebrates collected in the drift on days when frazil slush was absent from 16 December, 1998 to 8 March 1999 in the Grand River, Ontario. 16 December was designated as Day 1 of the winter for both seasons. Note that the scale of the y axis varies between panels. atures play important roles in the distribution and survival of aquatic invertebrates (Miller and Stout 1989). Anchor ice and frazil slush were the main focus of this study and appear to be important factors in invertebrate dispersal. Since the greatest abun- dance of immature aquatic insects occurs during the winter season (Maciolek and Needham 1952; Reimers 1957), any conclusions about the dispersal or removal of aquatic invertebrates by anchor ice are 3 3 a o o H z r2 = T p< 0 || o O 8 O *",,,,'''« O 6 â - II o \ (1 4 â â Ice covered period 2 â - ⦠â¦Â«âº ⦠mm ⦠n -- * 20 40 60 Day of winter Figure 2. Regression plot of mean (± SD) number of aquatic invertebrates found on the substrate (organ- isms / cm2) on different days from 16 December 1998 to 8 March 1999 in the Grand River, Ontario. Presence of frazil slush and anchor ice at the sam- pling site (diamonds) and presence of a surface ice cover (a solid line) in the pool upstream of the sam- pling site are also indicated. important in understanding invertebrate and fish ecology. Ancho
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