Table 1 General characteristics of the study reservoirs, water quality data recorded during sampling and sample sizes for R. auricularia and L. stagnalis (ranges followed by means in parentheses).
Baldeneysee | Hengsteysee | Harkortsee | Kemnader See | ||
|---|---|---|---|---|---|
Reservoir data | Construction (year) | 1931 - 1933 | 1927-1929 | 1931 | 1979 |
Length (km) | 7.8 | 4.2 | 3.2 | 3.0 | |
Width (m) | 355 | 300 | 335 | 420 | |
Surface area (ha) | 264 | 136 | 137 | 125 | |
Mean depth (m) | 3.1 | 2.0 | 2.2 | 2.4 | |
Mass development of E. nuttallii | - | + | + | + | |
Water quality data | Dissolved oxygen concentration (mg/L) | 4.45-11.07 (8.09) | 9.1-16.35 (11.07) | 8.08-11.02 (9.56) | 7.24-8.36 (7.87) |
pH | 7.1-7.8 | 7.3-8.7 | 7.5-7.8 | 7.3-7.6 | |
(7.4) | (7.8) | (7.6) | (7.5) | ||
Conductivity (μS/cm) | 390-615 | 341-478 | 438-483 | 415-658 | |
(505) | (406) | (461) | (527) | ||
Temperature (°C) | 9.8-18.2 | 9.3-18.2 | 13-18.6 | 9.9-15.6 | |
(15.0) | (14.2) | (15.8) | (13.9) | ||
Snail data | Radix auricularia | ||||
Total no. of snails (pooled samples) | 169 | 195 | 22 | 44 | |
Mean shell height (mm) | 15.6 ± 3.5 | 19.1 ± 3.5 | 11.9 ± 4.9 | 17.2 ± 5.1 | |
No. of distinct samples used (no. of snails) | 4 (n = 137)a | 4 (n = 166)b | 1 (n = 20)c | ||
Lymnaea stagnalis | |||||
Total no. of snails (pooled samples) | 135 | 11 | 23 | 16 | |
Mean shell height (mm) | 36.3 ± 8.9 | 31.3 ± 8.9 | 38.9 ± 8.7 | 34.3 ± 14.4 | |
No. of distinct samples used (no. of snails) | 3 (n = 110)d | 1 (n = 22)e | |||
Bird data | Fulica atra | > 60/80-100 | > 100 | > 100 | > 50 |
Anas platyrhynchos | 15/20/50 | + | + | + | |
Cygnus olor | 2/6/30 | 40 | 2 | 3 | |
Phalacrocorax carbo | 6 | 5 | + | ||
Larus ridibundus | 10 | + | + | > 40 | |
Branta canadensis | + | 20 | |||
Alopochen aegyptiacus | 2 | ||||
Podiceps cristatus | + | 2 | |||
Tachybaptus ruficollis | 1 | ||||
Ardea cinerea | 1 |