Short communicationAlgal community analysis in a waste stabilisation pond
Introduction
Waste stabilisation ponds (WSPs) are often used to purify wastewater because of their high reliability (Kadlec et al., 2010, von Sperling, 2007), simple construction, low operational costs (Hosetti and Frost, 1995, Peña, 2002) and good pathogen removal (Konaté et al., 2013, Sharafi et al., 2012, Rana et al., 2011). Besides the importance of algae in oxygen supply for bacterial oxidation of organic matter, nutrient removal (Fig. S1; Wild et al., 1971), natural disinfection, phosphorus precipitation, ammonia volatilisation (Pearson, 2005) and removal of heavy metals in WSPs (Sekomo et al., 2012, Shpiner et al., 2009, Toumi et al., 2000) it is useful to note that the density and diversity of algae can be used as biological indicators in assessment of WSPs’ water quality (Amengual-Morro et al., 2012, Clesceri et al., 1999). Algae are useful bio-indicators of physical–chemical stress because of their well-documented tolerance (Palmer, 1969). A change in the physical or chemical conditions will result in shifts in community composition (Friedrich et al., 1996). However, the limited knowledge concerning algal diversity, distribution and dynamics in WSPs hampers their use in biomonitoring. Hence, the objective of this work is to assess the spatial distribution of the algal community in facultative and maturation ponds in Cuenca (Ecuador). Through quantitative analysis, the diversity and distribution of the algal community and its relation with the physical–chemical conditions were determined.
Section snippets
The waste stabilisation pond
The WSP is located at Ucubamba Park (2°52′21” S 78°56′30” W) and is designed to treat the domestic effluent from the city of Cuenca (Ecuador). Information on the climatic conditions and operational conditions of the WSP was provided in Fig. S2 and Table S1 (Alvarado et al., 2012). Wastewater entering the WSP first passes through a pretreatment step (screening and grit chamber). After this preliminary treatment, the wastewater is divided into two identical flow lines (Fig. S2). Details on the
Algal species present at the WSP
In total, 30 algal species were recorded belonging to five phyla: Chlorophyta, Chrysophyta, Cryptophyta, Cyanobacteria and Euglenophyta (Table 1). The algal abundance in the WSP was 104–105 cells mL−1, which lies within the range of algal abundance usually found in WSPs, being 104–106 cells mL−1 (Arceivala, 1981).
Spatial distribution of the algae in the WSP
The algal community composition differed between the facultative and maturation ponds. Even within the individual ponds, the composition differed between upstream and downstream sampling
Algal communities and distribution
In the WSP, a large number of algal species were present and five algal phyla were found (Table 1). The BOD surface loading in both ponds was higher than 30 kg BOD ha−1 d−1, according to Pearson et al. (1981) this BOD loading would promote flagellate species and reduce algal diversity. However this is not the case in the system in Ecuador. Although we found an association of BOD concentration with the variation of algal community composition in the WSP in Cuenca (Ecuador), other confounding
Conclusions
We identified the algal community in a waste stabilisation pond in Cuenca (Ecuador) and related the species encountered with the physical–chemical conditions. We found that the diversity distribution of the algal community was associated with the BOD concentration. The algal abundance, species diversity, evenness and richness in the maturation pond were higher than in the facultative pond. The application of Lorenz curves to interpret the algal community in WSPs proved to be a promising
Acknowledgments
The corresponding author received a PhD grant of the Vietnamese government. The research was supported by the VLIR IUC Cuenca and VLIR Ecuador Biodiversity Network projects. We are grateful to ETAPA for allowing us to use their facilities and wastewater treatment pond system to perform this research and Jeroen Van Wichelen for the support regarding the algal community analysis.
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