Diatom, macroinvertebrate and Riparian vegetation community structure responses in agriculturally impacted rivers

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dc.contributor.advisor Prof. Victor Wepener en
dc.contributor.author Walsh, Gina
dc.date.accessioned 2010-03-15T06:33:01Z
dc.date.available 2010-03-15T06:33:01Z
dc.date.issued 2010-03-15T06:33:01Z
dc.date.submitted 2008-03
dc.identifier.uri http://hdl.handle.net/10210/3080
dc.description M.Sc. en
dc.description.abstract Pesticides and fertilizers, while allowing increases in food production, also have the ability to find their way into aquatic systems. Irrespective of their route of entry into an aquatic ecosystem, they may affect aquatic biota by influencing survival, growth and reproduction. Secondary effects may occur in which populations of organisms are impacted due to a reduction or elimination of pollution-susceptible species which results in a disturbance of biological processes and interactions due to water quality impacts associated with agricultural practices. Biomonitoring techniques are used to assess the integrity of aquatic ecosystems and provide information on the environmental conditions that have prevailed within a river. Because aquatic organisms are exposed to their environment and all pollutants and toxicants thereof, they will cumulatively reflect the conditions which they are exposed to. This study aims to assess community structure, biotic integrity and feeding traits of aquatic communities at river sites that have varying adjacent land uses. The chosen study area falls within the Crocodile (West) Marico Water Management Area (WMA). Study sites were selected on the Magalies and Crocodile rivers which form Hartbeespoort Dam at their confluence. Agricultural intensity in North West Province is high and irrigation farming tends to be located on the large floodplains associated with the middle Crocodile River. The main economic activity of the WMA occurs in Gauteng, and is generated by the intense urban and industrial activities of northern Johannesburg. These practices ensure that water pollution from agriculture and urban land use is a major problem along segments of the rivers under investigation. Study sites were chosen based on their adjacent land use and consisted of sites related to agricultural, urban and natural activities. Environmental driver components that were assessed included water quality and habitat integrity (IHAS). Biotic response indices were implemented to assess the integrity of diatom (GDI, SPI, BDI, EPI and %PTV), macroinvertebrate (SASS5 and MIRAI) and riparian vegetation (VEGRAI) communities. Principal Component Analysis (PCA) analyses were undertaken on water quality data using Primer version 6 to determine patterns in water quality between sites. Multivariate (CLUSTER, NMDS and RDA) and univariate (Margalef’s index, Shannon-Wiener diversity index and Pielou’s evenness) analyses were performed on macroinvertebrate family data, macroinvertebrate FFG data, diatom species data and riparian vegetation data using Primer version 6 and Canoco version 4.5 in order to elucidate differences in community structure per land use. Results indicated that particular water quality and habitat impacts were present for each land use. Comparison of community structure of diatoms taken from sites with varying land uses showed differences from one another. Relative reference diatom communities comprised of diatom species that had preferences for clean water, whilst community structures of diatoms were modified and showed specific change in relation to agricultural and urban water quality impacts. An increased diversity in air breathing macroinvertebrates was shown at sites with agricultural practices at high flow, where urban sites were differentiated from agricultural sites due to the presence of the Hydropsychidae and Hirudinea families. At low flow macroinvertebrate families making up communities overlapped between land uses. A difference noted at low flow was that the contribution of the Chironomidae was higher at urban sites in comparison to agricultural sites, indicating organic water pollution. The statistical comparison of macroinvertebrate communities, FFGs and riparian vegetation showed that differences between sites with different land uses were not significant. Nonetheless, some differences in refined data were noted for the varying land uses. Considering the macroinvertebrate community make up of the relative reference site, which was comprised of macroinvertebrate families that were more sensitive and showed preferences for higher water quality, community structures of macroinvertebrates were modified and showed change in relation to land use. Macroinvertebrate FFGs indicated that a change in the input of UPOM at agricultural sites, and a change in the presence of FPOM at urban sites were responsible for a shift in the FFG dominance. A difference in riparian integrity was noted between relative reference and test sites, but could not be easily distinguished between test sites with different land uses. Riparian integrity was more predictive of macroinvertebrate FFG structure than actual macroinvertebrate community structure. This indicates that riparian integrity and comparison with biological traits such as FFGs were useful in showing impacts due to organic matter inputs. Overall biotic indices were less useful in distinguishing between urban and agricultural land uses. It appeared that biotic indices masked the changes in the actual taxonomic components, erroneously suggesting that sites with different land uses are similar in terms of ecosystem integrity. It must be noted that integrity indices certainly have an important place in management of aquatic systems, but it appears to be more useful to utilise taxonomic make up and biological traits (in this case of FFGs) to show specific impacts, as these are factors which can be compared across a relatively broad spatial scale. It can be concluded that sites could be separated according to land use based on community structure of diatoms and macroinvertebrates, and biological trait analysis of feeding groups. It was noted that diatom communities were more defined in their response to land use practices in comparison to macroinvertebrate communities. en
dc.language.iso en en
dc.subject Riparian ecology en
dc.subject Water quality biological assessment en
dc.subject Water pollution en
dc.subject Crocodile River (South Africa) en
dc.title Diatom, macroinvertebrate and Riparian vegetation community structure responses in agriculturally impacted rivers en
dc.type Mini-Dissertation en

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