Abstract

BARNARD, Sandra; MORGENTHAL, Theunis L.; STOLZ, Michaela  and  VENTER, Arthurita. Impact of land-use and floaw conditions on the phytoplankton of the Sabie River, South Africa. Bothalia (Online) [online]. 2021, vol.51, n.1, pp.1-18. ISSN 2311-9284.  http://dx.doi.org/10.38201/btha.abc.v51.i1.6.

BACKGROUND: The understanding of the impact of land-use on the dynamics of phytoplankton assemblages during varying climate conditions on rivers is limited. OBJECTIVE: To determine the impact of land-use types and flow on phytoplank-ton assemblages in the Sabie River. METHODS: The relationships between land-use patterns, water quality and phy-toplankton assemblages were analysed using canonical correspondence analyses (CCA). RESULTS: Six main land-use types could be distinguished in the eight identified sub-catchments of the river. The CCA results showed that the land-use had a stronger correlation with phytoplankton classes during the higher flow conditions than during low flow conditions. The forestry land-use type had the strongest correlation with nitrate-nitrite concentrations in the Sabie River. Chlorophyll-a concentrations were higher during 2016, and a slightly lower number of genera were observed for the class Chlorophyceae. During 2017 the number of genera of the class Cyanophyceae decreased together with chlorophyll-a and total cell concentrations. CONCLUSION: Low flow conditions favoured filamentous genera that are common to mesotrophic conditions while higher flow conditions favoured single-celled small genera more common to oligotrophic waters with higher disturbance. This study showed that flow has the potential to enhance the impact of land-use on phytoplankton community dynamics in a river system and thereby may have further impacts on the health and activities of surrounding communities.

Keywords : river; water quality; cyanobacteria; drought; phytoplankton biomass.

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