Long-term study of the drought impact on the phytoplankton concentration and assemblages in two water supply reservoirs in Namibia

IF 1.1 4区 环境科学与生态学 Q3 MARINE & FRESHWATER BIOLOGY African Journal of Aquatic Science Pub Date : 2023-04-03 DOI:10.2989/16085914.2023.2200816
J. Sirunda, P. Oberholster, G. Wolfaardt, Christoff Truter, Sean van der Merwe
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Abstract

Rising temperatures and increased occurrences of droughts, brought on by climate change, are expected to affect reservoir water levels. We hypothesised that the decrease in reservoir volumes in dams with desert climates will favour the growth of phytoplankton biomass, measured as chlorophyll a (Chl a), under drought conditions. Using the threshold levels method of Q50, ten drought years were recorded in the Von Bach Dam (VB) in comparison to seven in the Swakoppoort Dam (SWP). Both dams had significant reduction in percentage volume (vol %). The Chl a in SWP was 81 µg l−1 in drought and 48 µg l−1 in AAR years, compared to VB with 21 µg l−1 in drought and 24 µg l−1 in AAR years. Cyanobacterial cell counts in drought and AAR years in SWP were 129 704 and 77 838 cells ml−1, respectively, while cell counts in drought and AAR years in VB were 5 925 cells ml−1 and 20 070 cells ml−1, respectively. Decreases in phytoplankton biomass and total cyanobacteria were observed in SWP but not in VB. The pattern and magnitude of the statistically significant responses (t-test, p < 0.05) between physico-chemical and biological water quality variables varied among drought and AAR years. We conclude that that there is no clear correlation between drought and phytoplankton biomass from this study and that other anthropogenic–environmental drivers, such as land use impacts, will be needed to further elucidate the response of water quality to droughts.
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干旱对纳米比亚两个供水水库浮游植物浓度和组合影响的长期研究
气候变化导致的气温上升和干旱频发预计将影响水库水位。我们假设,在沙漠气候条件下,水库容量的减少将有利于干旱条件下浮游植物生物量的生长,以叶绿素a (Chl a)来衡量。利用Q50阈值水平法,Von Bach大坝(VB)记录了10年干旱,而Swakoppoort大坝(SWP)记录了7年干旱。两个大坝的体积百分比(vol %)都有显著减少。SWP的Chl a在干旱年份为81µg l−1,在AAR年份为48µg l−1,而VB在干旱年份为21µg l−1,在AAR年份为24µg l−1。SWP干旱年和AAR年蓝藻细胞数分别为129 704个和77 838个细胞ml - 1, VB干旱年和AAR年蓝藻细胞数分别为5 925个细胞ml - 1和20 070个细胞ml - 1。SWP中浮游植物生物量和蓝藻总数减少,而VB中没有。在干旱和AAR年份,理化和生物水质变量之间的响应模式和显著程度(t检验,p < 0.05)有所不同。我们的结论是,干旱与浮游植物生物量之间没有明确的相关性,需要其他人为环境驱动因素,如土地利用影响,来进一步阐明水质对干旱的响应。
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来源期刊
African Journal of Aquatic Science
African Journal of Aquatic Science MARINE & FRESHWATER BIOLOGY-
CiteScore
3.90
自引率
7.10%
发文量
31
审稿时长
>12 weeks
期刊介绍: The African Journal of Aquatic Science is an international journal devoted to the study of the aquatic sciences, covering all African inland and estuarine waters. The Journal publishes peer-reviewed original scientific papers and short articles in all the aquatic science fields including limnology, hydrobiology, ecology, conservation, biomonitoring, management, water quality, ecotoxicology, biological interactions, physical properties and human impacts on African aquatic systems.
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