| Abstrakt: |
Changes in the zooplankton population in shallow, mesotrophic Ubolratana Reservoir were monitored during 2019-2022, years with contrasting environmental conditions of severe drought and flood events. In the six sampling occasions, water storage volume (WSV) was 13 %, 19 %, 58 %, 36 %, 110 %, and 56 % of capacity. Correlations between hydrological and water quality factors and zooplankton densities were analyzed for a better understanding of the drivers of zooplankton production and to enable further development of management approaches. In this study, comparatively low densities of zooplankton were observed during severe drought. The density increased with gradual increases of inflow (INF) and WSV. During mid-rainy season of 2021, the densities of copepods, cladocerans, rotifers and protozoans increased to high levels, with maximums of 13,179 indL-1, 2,883 indL-1, 3,940 indL-1 and 7,401 indL-1, respectively. In contrast, the levels were decreased during high flood conditions (110 % of capacity). In addition, zooplankton density had a highly significant positive relationship (p<0.01) with INF and significant positive relationships (p<0.05) with WSV and density of small-sized protozoans. Copepod and rotifer densities in the lacustrine zone also had significant positive relationships (p<0.05) with total suspended solids (TSS), while they had significant negative relationships (p<0.05) with retention time (RT). Accordingly, it is possible that increases in zooplankton abundance can occur with conditions of comparatively high INF, WSV, and small-size protozoan density. In contrast, habitats with high RT during flood were not as suitable for zooplankton. Overall, the results implied the need to control INF, WSV, and RT for preventing deterioration in the abundance of zooplankton during environmental changes. These findings can be further applied for developing suitable management strategies for conservation of fishery-related resources of the mesotrophic reservoir ecosystem. [ABSTRACT FROM AUTHOR] |
