Antibiotics along an alpine river and in the receiving lake with a catchment dominated by grazing husbandry.

The livestock breeding industries face overuse of antibiotics, which has been intensively studied in recent years. However, the occurrence and fate of antibiotics as well as their potential threats to the aquatic environments in alpine and arid regions remain unclear. This study investigated the relationship of the occurrence and concentrations of antibiotics between the Kaidu River and Bosten Lake in a typical alpine basin in China. Hot spots with antibiotic pollution source were explored. The antibiotic concentrations in river water and suspended sediment (SPS) were 2.20-99.4 ng/L and 1.03-176 ng/g. The dominant antibiotics were tetracyclines, sulphacetamide, and ofloxacin in river water and sulfonamides, clarithromycin, roxithromycin, and ofloxacin in SPS. The apparent differences in pollution sources and landscapes in different reaches led to the obvious spatial patterns of antibiotics in the Kaidu River. Higher partition coefficient of antibiotic between SPS and water phases for sulfonamides than tetracyclines was because that tetracyclines strongly responded to clay contents while sulfonamides significantly responded to organic carbon contents in SPS. There were significant differences in detected antibiotic categories between the river and the lake. Fluoroquinolones (especially ciprofloxacin and enrofloxacin) were detected in the lake while sulphacetamide was only detected in the river. Therefore, the surrounding husbandry and aquaculture around the Bosten Lake was an important antibiotic pollution source in addition to inputs from the Kaidu River. This research suggested that alpine lakes could be an important sink of antibiotics in alpine dry regions, and thus impose greater threats to the aquatic ecosystem.

Mismatch between critical and accumulated temperature following river damming impacts fish spawning.

Dam operations considerably influence water temperature regimes in rivers, which affects fish spawning activities. Previous studies have focused on the effects of critical temperature (CT) alterations during the spawning period, and largely ignored the effects of accumulated temperature (AT) alterations on gonadal development. Successful spawning relies on the simultaneous achievement of the two thermal requirements at appropriate times. River damming may cause a mismatch between the times of achieving CT and AT thresholds, and in turn influence fish reproduction. In the present study, spawning events of Coreius heterodon (C. heterodon) from 2009 to 2015 in the upper reaches of the Yangtze River, which are under the influence of cascade dams, were analysed based on the times of achievement of CT and AT thresholds. The CT and AT thresholds for C. heterodon spawning were 18.4 °C and 1324.9 °C·d, respectively. Under pre-impoundment conditions, the time of achievement of the AT threshold was 23 d on average later than that under post-impoundment conditions; however, the time of achievement of the CT threshold was similar under both conditions. The time of achievement of the AT threshold was 10 d earlier than that of achievement of the CT threshold in post-impoundment conditions. Earlier achievement of AT thresholds was followed by reduced spawning. The alteration of temperature rhythm caused by reservoir operations could be the major factor decreasing spawning abundance after river damming. The results of the present study could facilitate sustainable reservoir operations with regards to water temperature management, and thereby improve the conservation of fish resources.