Abstract
This study aimed to assess the impact of land use patterns on water quality and benthic diatom community structure and to test the applicability of diatom indices developed in other regions of the world to a small temperate southern African river system. Sampling was conducted at eight study sites along the length of the river on four separate occasions. Multivariate data analyses were performed on the diatom community dataset to specify the main gradients of floristic variation and to detect and visualize similarities in diatom samples in relation to land-use patterns within the catchment. One hundred and twelve (112) diatom species belonging to 36 genera were recorded during the study. Canonical correspondence analysis (CCA) demonstrated that variations in the benthic diatom community structure were best explained by ammonium, nitrate, conductivity, pH, temperature, resistivity and water flow. OMNIDIA was used for calculation of selected diatom water quality indices. A number of the indices, e.g., the trophic diatom index (TDI), eutrophication/pollution index and biological index of water quality (BIWQ), either under- or over-estimated the water quality of the system. With few exceptions, there were no significant correlations (p> 0.05) between the diatom indices’ values and the nutrient variables. The absence of any significant correlations between the diatom indices’ values and selected physico-chemical variables suggests that indices developed in other regions of the world may not be suitable for temperate southern African rivers. Keywords : biomonitoring, diatom indices, diatom community, Kowie River, nitrogen, multivariate analysis, point-source pollution, water quality
Highlights
Rivers, streams, ponds, lakes and reservoirs constitute an estimated 65% of freshwater ecosystems worldwide and are regarded as the most vulnerable water systems globally (Vörösmarty et al, 2010; Schowe and Harding, 2014; Tan et al, 2015)
Significant seasonal differences were observed for dissolved oxygen (H = 7.08, p = 0.001), oxygen reduction potential (H = 39.15, p < 0.001) and water flow (H = 3.72, p = 0.024), while significant site variation was observed for conductivity (H = 20.8, p < 0.001), total dissolved solids (H = 15.94, p < 0.001), salinity (H = 18.73, p < 0.001), water depth (H = 45.47, p < 0.001) and ammonium (H = 13.25, p = 0.001)
We have demonstrated that land-use activities within the Kowie River catchment impacted on the water quality, with ammonium, nitrate and phosphate concentrations closely reflecting the urban and agricultural activities within the catchment
Summary
Streams, ponds, lakes and reservoirs constitute an estimated 65% of freshwater ecosystems worldwide and are regarded as the most vulnerable water systems globally (Vörösmarty et al, 2010; Schowe and Harding, 2014; Tan et al, 2015) Anthropogenic effects, such as increased water consumption, industrial and agricultural activities or urbanisation, and inorganic processes such as erosion, precipitation inputs or weathering of crustal materials, degrade surface waters. This impacts the ecological integrity and functioning of freshwater ecosystems and subsequently impairs their use for domestic, industrial and agricultural purposes (Wu et al, 2012; Venkatachalapathy and Karthikeyan, 2015). Diatoms have been employed as water quality indicators in Europe (Kelly et al 1998; Prygiel et al, 1999), North America (Stevenson and Pan, 1999; Lowe and Pan, 1996; Winter and Duthie, 2000; Lavoie et al, 2006, 2014), South America (Lobo et al, 1996; Bere and Tundisi, 2011), Australia (Chessman et al, 1999; John, 2000), Asia (Lobo et al, 1995; Rothfritz et al, 1997) and, to a lesser extent, Africa (Bellinger et al, 2006; Ndirutu et al, 2006; Taylor et al, 2007a, b; Bere et al, 2014; Mangadze et al, 2015)
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