The Interplay between Environmental Conditions and Filamentous Algae Mat Formation in Two Agricultural Influenced South African Rivers |
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| Authors: | P J Oberholster V S Somerset J C Truter A‐M Botha |
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| Affiliation: | 1. CSIR Natural Resources and the Environment, Pretoria, South Africa;2. Department of Botany and Zoology, University of Stellenbosch, Stellenbosch, South Africa;3. cCSIR Natural Resources and the Environment, Stellenbosch, South Africa;4. Department of Genetics, University of Stellenbosch, Stellenbosch, South Africa |
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| Abstract: | The regulation of nutrient inputs into rivers dominated by agriculture land use activities is an important aspect of ecological resilience of aquatic systems and the management of river eutrophication. The overabundance of benthic filamentous algae mats in river systems due to nutrient enrichment can modify the habitats of macroinvertebrate and fish communities as well as clogging irrigation crop sprayers of downstream water users. The current study examined over a period of 2 years (2013–2014) the interplay between physical and chemical river characteristics and epilithic filamentous algae biomass in two South African agricultural influenced rivers. The study area consisted of the Touw and Duiwe Rivers, which run into a proclaimed Ramsar site, namely, the Wilderness Lake System. A strong positive correlation was observed between the maximum filamentous algae biomass (97 chl‐a mg m?2) observed during the dry season and the average water column alkalinity >30 mg l?1. The benthic trophic status of the nine sampling sites during the dry seasons indicated the highest benthic algae biomass with mesotrophic (1.7–21 chl‐a mg m?2) to hypertrophic (>84 chl‐a mg m?2) conditions. During the dry season, only three sampling sites were below the suggested guideline value (35 µg l?1) for total phosphorus (TP), while four sampling sites were below the total nitrogen guideline of 252 µg l?1. In the wet season, two sites were below TP values with five sites below total nitrogen guideline values. From the data gathered, it was evident that water column alkalinity and hardness were the main drivers for the formation or absence of benthic filamentous algae mats in the two river systems and that nitrogen and/or phosphorus concentrations was overshadowed by the physical and chemical characteristics of the river systems at certain sites. Nutrient results for the river bottom sediments revealed that the sediment qualities were variable at the different sampling sites, but more specifically along the longitudinal paths of flow. It was apparent that the high TP concentrations in the water column and bottom sediment, which were lowest during the dry season, were associated with the highest epilithic filamentous algae mat formation. The outcome of the current study shows that a more holistic approach must be followed for the development of future eutrophication guidelines and nutrient thresholds in South African rivers influenced by agriculture land use activities. Copyright © 2016 John Wiley & Sons, Ltd. |
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| Keywords: | benthic trophic status alkalinity hardness nutrient enrichment guidelines |
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