Figure 1
Study area – Drawa catchment area. The examined ditches are shown in the rectangular areas.
Figure 2
Mean + SD values of physicochemical and hydrological variables for the examined ditches divided into six groups according to the current velocity values: 1) <0.05 m s-1, 2) <0.10 m s-1, 3) <0.15 m s-1, 4) <0.20 m s-1, 5) <0.25 m s-1 and 6) >0.25 m s-1. Different letters indicate significant differences p<0.05 in values of variables between groups of ditches.
Figure 3
Mean + SD values of zooplankton abundance (ind. l-1), Shannon’s index and the number of species for the examined ditches divided into six groups according to the current velocity values: 1) <0.05 m s-1, 2) <0.10 m s-1, 3) <0.15 m s-1, 4) <0.20 m s-1, 5) <0.25 m s-1 and 6) >0.25 m s-1. Different letters indicate significant differences p<0.05 in values of variables between groups of ditches.
Figure 4
Relationship between values for zooplankton abundance (ind. l-1), Shannon’s index, the number of species vs. current velocity (m s-1)
Figure 5
Rarefaction curves of Shannon’s index of zooplankton for the examined ditches divided into six groups according to the current velocity values: 1) <0.05 m s-1, 2) <0.10 m s-1, 3) <0.15 m s-1, 4) <0.20 m s-1, 5) <0.25 m s-1 and 6) >0.25 m s-1
Table 1
Significant differences in mean values ± SD of zooplankton abundance (ind. l-1), Shannon’s index and the number of species for the ditches divided into two groups according to the current velocity values: <0.10 m s-1 vs. >0.10 m s-1. ** p<0.01, *** p<0.001
| Taxa | <0.1 m s-1; n = 50 | p | >0.1 m s-1; n = 30 |
|---|---|---|---|
| Bdelloidea | 5.01 ± 4.46 | *** | 1.03 ± 0.90 |
| Keratella sp. | 6.99 ± 21.42 | ** | 1.96 ± 2.25 |
| Polyarthra sp. | 1.28 ± 3.25 | *** | 0.94 ± 0.84 |
| Daphnidae | 7.79 ± 16.00 | *** | 0.05 ± 0.08 |
| Total zooplankton | 41.29 ± 33.71 | *** | 14.31 ± 10.39 |
| Shannon-Wiener index | 1.46 ± 0.40 | *** | 1.87 ± 0.37 |
| Number of species | 7.5 ± 3.5 | ** | 9.9 ± 3.5 |
Table 2
Jaccard’s similarity index values between sites at natural streams and two groups of ditches according to their current velocity value: 1) <0.1 m s-1 and 2) >0.1 m s-1
| < 0.1 m s-1 | > 0.1 m s-1 | ||
|---|---|---|---|
| N2 vs. 11 | 42.1 | N4 vs. 1 | 55.6 |
| N5 vs. 28 | 36.4 | N3 vs. 7 | 66.7 |
| N7 vs. 33 | 21.4 | N1 vs. 5 | 71.4 |
| N16 vs. 46 | 57.1 | N6 vs. 32 | 27.8 |
| N17 vs. 51 | 58.3 | N8 vs. 59 | 46.2 |
| N10 vs. 54 | 33.3 | N9 vs. 63 | 45.5 |
| N11 vs. 61 | 64.3 | ||
| N12 vs. 70 | 37.5 | ||
| N13 vs. 75 | 66.7 | ||
| N14 vs. 76 | 45.5 | ||
| N15 vs. 77 | 46.7 | ||
| Mean | 41.5 | NS p>0.05 | 52.1 |
NS – not significant difference between two groups of sites
Figure 6
nMDS ordination for the total zooplankton abundance at sites in the natural stream (recipient) and ditches (tributary) with different values of current velocity. The grouping in nMDS ordination was based on the Bray-Curtis distances. For symbols, refer to Figure 1.
Table 3
Results of Canonical Correspondence Analysis of zooplankton abundance with the forward selection procedure of environmental variables. Order – Order of integration of variables for analysis
| Order | Variable | Variance | Variance explained (%) | Permutation test | |
|---|---|---|---|---|---|
| F | p | ||||
| 1 | Discharge | 0.20 | 26.0 | 2.72 | 0.005 |
| 2 | Conductivity | 0.10 | 13.0 | 5.32 | 0.005 |
| 3 | Velocity | 0.11 | 14.3 | 2.77 | 0.005 |
| 4 | Dissolved oxygen | 0.09 | 11.7 | 3.69 | 0.005 |
| 5 | Width | 0.08 | 10.4 | 2.72 | 0.005 |
| 6 | Chlorophyll a | 0.06 | 7.80 | 2.35 | 0.005 |
| 7 | Temperature | 0.05 | 6.50 | 1.91 | 0.045 |
| 8 | Depth | 0.04 | 5.20 | 1.94 | 0.055 |
| 9 | pH | 0.04 | 5.20 | 1.72 | 0.075 |
Figure 7
Zooplankton abundance along environmental factors: CCA constrained ordination of samples and taxa from sites with different current velocity in ditches with the forward selection procedure of environmental variables. Numbers indicate the sites. Environmental variables: Veloc – current velocity; Disch – discharge; Temp. – temperature; Cond. – conductivity; Oxy – dissolved oxygen; Chlor a – chlorophyll a. For symbols, refer to Figure 1.