Ecological Archives A021-009-A1

Annika W. Walters and David M. Post. 2011. How low can you go? Impacts of a low-flow disturbance on aquatic insect communities. Ecological Applications 20:163–174.

Appendix A (TABLE A1). Habitat and flow characteristics for the control (upper) and low-flow (lower) reaches of diverted streams.1

2005   2006     2007    
       Stream 1 Stream 2 Stream 1 Stream 2 Stream 3 Stream 1 Stream 2 Stream 3
Mean daily flow (m3/s) control 0.0042 0.0040 0.0216 0.0245 0.0366 0.0038 0.0026 0.0046
  low flow 0.0020 0.0020 0.0035 0.0137 0.0183 0.0016 0.0016 0.0015
  % change -52% -50% -84% -44% -50% -58% -38% -67%
  t-test   0.02     0.01     0.04
Coefficient of control 0.28 0.30 0.42 0.47 0.69 0.22 0.52 0.44
variation of flow low flow 0.23 0.57 2.17 0.68 1.11 0.18 0.18 0.64
  % change -15% 91% 411% 45% 61% -20% -65% 45%
  t-test   0.30     0.12     0.36
Average stream width control 1.15 2.05 1.78 3.11 2.57 1.21 2.00 1.45
  low flow 0.89 1.70 1.30 1.87 2.77 0.92 0.91 1.30
  % change -23% -17% -27% -40% 8% -24% -54% -11%
  t-test   0.05     0.17     0.11
Average stream depth control 0.031 0.083 0.085 0.138 0.152 0.035 0.065 0.070
  low flow 0.038 0.054 0.061 0.104 0.101 0.025 0.048 0.054
  % change 23% -36% -28% -25% -34% -27% -26% -23%
  t-test   0.32     0.02     0.01
Pool:riffle ratio control 1.18 2.07 0.31 1.11 0.62 0.41 2.20 1.86
  low flow 1.23 1.02 0.75 0.71 1.45 0.92 4.43 3.34
  % change 5% -51% 137% -36% 136% 126% 102% 79%
  t-test   0.27     0.26     0.05
Water temperature (oC) control 18.5 20.3 19.8 20.4 20.1 18.4 18.8 17.6
  low flow 17.9 19.6 18.3 19.9 19.8 17.3 17.0 17.3
  % change -4% -4% -8% -2% -1% -6% -10% -2%
  t-test   0.02     0.09     0.07
Dissolved oxygen control 7.78 7.25 7.78 7.5 8.27      
(mg/L) low flow 8.21 7.63 7.93 7.99 7.96      
  % change 6% 5% 2% 7% -4%      
  t-test   0.02     0.34      
Conductivity (uS/cm3) control 71 73 55 54 68      
  low flow 79 72 57 55 66      
  % change 11% -1% 4% 2% -3%      
  t-test   0.29     0.40

1August mean daily flow and coefficient of variation of flow is obtained from water logger data. Stream width, depth, and pool:riffle data is the average of ten transects from August/September habitat surveys; surveys were conducted monthly (2005) or biweekly (2006, 2007). Water temperature (all sites 2005 and stream 1 2006), conductivity, and dissolved oxygen data is the average of data collected on two dates at two locations per stream reach. Water temperature data (all sites 2007, and streams 2 and 3 2006) is from water logger data. Significant P values at the 0.05 level from a paired, 1 tailed t test testing differences between control and low flow reaches in diverted streams in each year are denoted in bold.


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