The influence of land use on water quality and diatom community structures in urban and agriculturally stressed rivers

Abstract

Epilithic diatom communities offer a holistic and integrated approach for assessing water quality as they remain in one place for a number of months and reflect an ecological memory of water quality over a period of time. The objective of this study is to use diatom assemblages to distinguish between particular land types and associated water quality impacts that are linked to these land-use patterns. Water quality and diatom community data were collected from sites in the Crocodile and Magalies Rivers (Gauteng and North West Province, South Africa) associated with agricultural, urban and natural (reference) adjacent land use respectively. The data collected were subjected to multivariate statistical techniques to analyse spatial and temporal patterns in water quality (principal component analysis) and diatom community structures (non-metric multidimensional scaling) to elucidate hypothesised differences in community structure per land-use type. Five diatom response indices (Generic Diatom Index, Specific Pollution Sensitivity Index, Biological Diatom Index, Eutrophication/Pollution Index and Percentage Pollution Tolerant Valves) incorporated in the OMNIDIA software were implemented to assess the integrity of diatom communities per land-use type. Principle component ordination of water quality describes 56.6% of the variation in data observed, and indicates the separation of reference sites from test sites for low and high flow conditions combined. It was, however, not possible to distinguish between the agricultural and urban land-use sites using PCA based on water quality data. One-way ANOSIM showed a significant difference (p < 0.05) between reference groups, agricultural groups and urban groups, with no significant differences noted ( p > 0.05) between groups made up of sites exhibiting the same land-use patterns. Diatom indices showed that agricultural sites were in a slightly more modified ecological state than urban sites overall. Based on the species similarity (SIMPER analyses), reference sites showed strong associations with Achnanthes minutissima, Gomphonema venusta and Cocconeis placentula var. euglypta, whilst urban sites were associated with Diatoma vulgaris, Navicula tripunctata and Amphora pediculus. Agriculture could be separated into high-and low-intensity practices based on species composition. Sites where high-intensity agriculture took place were dominated by motile species of the genus Nitzschia, and low-intensity agriculture was indicated by motile species of the genus Navicula. Urban sites contained a combination of species that were tolerant of spikes in water quality.

Impacts of land use and population density on seasonal surface water quality using a modified geographically weighted regression

“…In addition, a higher percentage of impervious surfaces in urban areas prevents rainfall from infiltrating into soil resulting in transport of soluble and particulate forms of pollutants to nearby streams through surface runoff. These results are consistent with several previous studies examining pollutant inputs from urban areas (Walsh and Wepener, 2009;Peters, 2009;Tu, 2011;Liu et al, 2013;Mei et al, 2014;Wang et al, 2014).…”

Changes in epilithic diatom communities and periphytic biomass downstream of a reservoir on a Mediterranean river (Calabria region, S Italy)

“…The succession of flow reactivation due to winter rains, flow abatement, and sand accumulation promoted the colonization and persistence of eurivalent taxa with a high colonization rate, tolerating both high and low current velocity as well as temporary burial of coarse substrates. Achnanthidium minutissimum is an early pioneer taxon capable of substrate colonization both at low (Plenkovic-Moraj et al, 2008) and high (Kelly, 2002) current velocity values, tolerating physical disturbance (Walsh and Wepener, 2009), often dominating community in sandy littoral (Cremer, 2006) and able to survive and reproduce in poorly illuminated habitats (Johnson et al, 1997). Cocconeis euglypta is also a pioneer taxon, although colonizing later than Achnanthidium, which shows adaptation to both low (Martina et al, 2013) and high (Battegazzore et al, 2004) current velocities.…”

Assessment of water quality based on diatom indices in a small temperate river system, Kowie River, South Africa

“…Because diatoms are very sensitive to environmental change and/or disturbances such as eutrophication, acidification, land use and pollution, they are considered to be powerful indicators of water quality in freshwater systems (Harding et al, 2005;Taylor et al, 2007a;Walsh and Wepener, 2009;Bere and Tundisi, 2010a;Wu et al, 2012;Rimet et al, 2015). Moreover diatoms have distinct ecological tolerances (Bahls, 1993) and short generation time (Zalack et al, 2010;Tan et al, 2014b), making them suitable indicator organisms for water quality changes over short time scales.…”

“…Diatom indices have been employed in southern African studies, e.g., Bate et al (2004), Bellinger et al (2006), Taylor et al (2007a, b), Walsh and Wepener (2009) and Bere et al (2013), although to a limited extent. The aim of our study was two-fold: (i) to assess the impact of land-use patterns on water quality and benthic diatom community structure in a small temperate South African river in the Eastern Cape Province of South Africa, and (ii) to test whether routinely employed diatom index values are consistent with observed physico-chemical variables along the length of the river.…”