Protozoan communities serve as a strong indicator of water quality in the Nile River

Abstract

The relationship between the protozoan communities and environmental variables was studied in the Nile River to evaluate their potential as water quality indicators. Protozoans were sampled monthly at six sampling sites in the Nile's Damietta Branch across a spatial gradient of environmental conditions during a 1-year cycle (February 2016-January 2017). The Protozoa community was comprised of 54 species belonging to six main heterotrophic Protozoa phyla. The abundance (average, 1089 ± 576.18 individuals L^-1) and biomass (average, 86.60 ± 106.13 μg L^-1) were comparable between sites. Ciliates comprised the majority of protozoan species richness (30 species), abundance (79.72%), and biomass (82.90%). Cluster analysis resulted in the distribution of protozoan species into three groups, with the most dominant species being the omnivorous ciliate Paradileptus elephantinus. Aluminium, fluoride, and turbidity negatively affected abundance and biomass, while dissolved oxygen and potassium positively impacted biomass. Of the dominant species recorded over the study area, the amoebozoa Centropyxis aculeata was associated with runoff variables, while the bacterivorous ciliates Colpidium colpoda, Glaucoma scintillans, and Vorticella convallaria were related to the abundance of heterotrophic bacteria, phytoplankton biomass, and total organic carbon. Total dissolved salts, PO₄, NH_3, NO₂, dissolved oxygen, and total organic carbon were the strongest causative factors for protozoa distribution. The α-Mesosaprobic environment at site VI confirmed a high load of agricultural runoffs compared to other sites. This study demonstrates that protozoans can be a potential bioindicator of water quality status in this subtropical freshwater river system.

Keywords: Bioindicator; Nile River Damietta branch; Protozoa; Water quality.

Figure 1

Map of the study area showing the sampling locations. This figure was generated using Esri ArcMap v. 10.4.1.

Figure 2

Potential geometric shapes of the Protozoa species in the study area.

Figure 3

Ordination diagram by PCA of the 72 sampling units classified spatially (A) and seasonally (B), based on the correlation matrix of the most important environmental parameters. As shown in Table 2, variables with a correlation <  ± 0.5 were eliminated from the ordination plot.

Figure 4

Cluster analysis of Protozoa taxa based on species abundance at the 72 sampling units, formed by Ward's method as linkage rule and Euclidean distances as similarity measure.

Figure 5

Spearman correlations between water quality parameters and Protozoa community dynamics. Only parameters with significant correlations are included in the diagram. T (temperature), Tu (turbidity), Alk (alkalinity), Am (ammonia), nit (nitrite), Pho (phosphate), Sil (silicate), TOC (total organic carbon), Ab (Protozoa abundance), B (biomass), S (species number), and H (Shannon index).

Figure 6

Spatial variations in abundance(A), biomass (B), relative abundance (C) and relative biomass (D) of protozoans from the six sites in the Nile River's Damietta region. The letters indicate significant differences based on one-way ANOVA with the Tuckey's test. Error bars represent the standard error of the mean.

Figure 7

(A) Ordination diagram by CCA analysis of protozoa species as a function of environmental variables, (B) Systematic classification of species as a function of environmental variables. (C) Distribution of sampling units along the gradients of environmental variables. For abbreviations of environmental factors, see Table 2.

Figure 8

Mean saprobic index values at the six sampling sites.