Roos, J. C.Van Wyk, P. W. J.Venter, Gertruida C.2018-03-192018-03-192000-05http://hdl.handle.net/11660/8047English: The Upper Orange River is defined as the region between the source in the Drakensberg (Lesotho) and the Orange-Vaal confluence. Information on the water quality, phytoplankton composition and the influence of the dams on the Upper Orange River is limited. This study was conducted in order to determine seasonal and spatial patterns in the river system., as well as to determine the influence of the tributaries and the two major dams on the river system. Physical, chemical and biological factors were taken into account. Hypolimnetic water released from the Gariep and Vanderkloof Dams caused a significant decrease in the temperature downstream of the dams. The dams acted as sediment traps and caused the TSS and turbidity in the river system to decrease. A decrease in turbidity resulted in an increase in the light penetration. This created more favourable conditions for primary production and led to algal blooms in the dams. The dams are used for hydro-electric power generation and almost completely diminished seasonal flow patterns. This changed the Upper Orange River into a highly regulated system. The interference with seasonal flow patterns in the river is probably one of the main reasons for outbreaks of the pest blackfly, Simulium chutteri downstream of the dams. The oxygen-depth profile in the Gariep Dam during summer stratification indicated relatively high dissolved oxygen concentrations in the epilimnion (8.2 mg.l-1) and anoxic, near anaerobic, conditions (0.1 mg.l-1) in the hypolimnion. The oxygen decline in the hypolimnion was indirectly the cause of high algal production in the epilimnion during algal blooms. The average pH of the Upper Orange River system was mainly alkaline at 8.1, with an average total alkalinity of 95.2 mg CaC03.rl. This suggested that the Upper Orange River is a wellbuffered system. The average conductivity in the Upper Orange River was relatively low at 19.6 mS.m-1, but increased significantly since 1980. Major ions at Aliwal North occurred in the following proportions, i.e. Ca> Na > Mg > K for cations and CO3 > Cl> SO4 for anions. In the Gariep Dam and at Marksdrift the proportions were: Na > Ca > Mg > K for cations and CO3 > Cl > SO4 for anions. The average P04-P concentration was relatively low at 28.3 µg.l-1 and the average TP concentration was 107 µg.I-1. The average N03-N concentration was high at 312 µg.l-1 and increased in the dams and downstream probably due to agricultural fertilizers and nitrogen fixation by algae. The average chlorophyll a concentration ranged between 0.4 and 1084 µg.I-1, with and average concentration of 10.8 µg.l-1. The very high chlorophyll a concentration was due to a bloom of Microcystis sp. during February in the Gariep Dam. Phytoplankton dynamics manifested themselves in seasonal cycles. Cyanobacteria and Bacillariophyceae dominated during warmer months. The Chlorophyceae replaced cyanobacteria during cooler months. Light penetration in the Gariep Dam and the Vaal River had a major effect on the primary production. The maximum primary production in the Gariep Dam was 14.6 mg C. mg Chla-1 h-1 and in the Vaal River the maximum primary production was 76 mg C. mg Chla-l. h-1. According to the primary production in the Gariep Dam it can be classified as mesotrophic, while the high primary production in the Vaal River indicated eutrophic conditions. The dams exert major influences on the physical, chemical and biological parameters in the river. Low SASS4 scores were obtained and are an indication of poor water quality. This could be ascribed to disturbances by the dams. The serial discontinuity concept (SDC) is applicable in the Upper Orange River. It is likely that agricultural runoff, as well as urban and industrial pollution from the Vaal River catchment would mask the downstream recovery after the Orange- Vaal confluence.Afrikaans: Die Bo-Oranjerivier kan gedefinieer word as die gebied tussen die oorsprong in the Drakensberge (Lesotho) en die Oranje-Vaal samevloei. Beperkte inligting is beskikbaar oor die waterkwaliteit en die invloed van die damme op die Bo-Oranjerivier. Die doel van die studie was om seisoenale and ruimtelike veranderinge in die rivierstelstel te bepaal, sowel as om te kyk na die invloed van die sytakke en die twee groot damme op die rivierstelstel. Fisiese, chemiese en biologiese faktore is ondersoek. Water wat vrygestel is vanuit die hipolimnion in die Gariep en Vanderkloof damme het gelei tot betekenisvolle verlaging in die watertemperatuur in die rivierstelsel onder die damme. Die damme het sediment teruggehou en dit het gelei tot verlaagde totale gesuspendeerde materiaal (TSS) en dus ook verlaagde troebelheid. Verlaagde troebelheid het verbeterde ligindringing tot gevolg gehad, wat gunstige toestande geskep het vir algopbloeie. Die damme, wat gebruik word vir hidro-elektriese kragopwekking, het seisoenale vloeipatrone feitlik heeltemal uitgewis en dus die Bo-Oranjerivier verander in 'n hoogs gereguleerde stelsel. Die verandering in seisoenale vloei patrone is moontlik een van die hoof oorsake van die probleme wat onder die damme ondervind word met die swartvliegie, Simulium chutteri. Die suurstof-diepte profiel in die Gariep dam gedurende somer stratifikasie het relatief hoë konsentrasies opgeloste suurstof getoon in die epilimnion (8.2 mg.l-1) en feitlik anoksiese toestande in die hipolimnion (0.1 mg.I-1). Die lae suurstof konsentrasies in die hipolimnion was die indirekte gevolg van die hoë alg produksie in die epilimnion gedurende 'n opbloei. Die gemiddelde pH (8.1) was hoofsaaklik alkalies, met 'n gemiddelde totale alkaliniteit van 95.2 mg CaC03.l-1 . Dit dui daarop dat die Bo-Oranjerivier stelstel goed gebuffer is. Die geleiding in die Bo-Oranjerivier was relatief laag met 'n gemiddeld van 19.6 mS.m-1. Die samestelling van makro ione by Aliwal Noord was soos volg: . Ca > Na > Mg > K vir katione en CO3 > Cl > SO4 vir anione. Die samestelling in die Gariep dam en by Marksdrift was soos volg: Na> Ca > Mg > K vir katione en CO3 > Cl > SO4 vir anione. Die gemiddelde konsentrasie PO4-P was relatief laag teen 28.3 µg.l-1 en die gemiddelde konsentrasie TP was 107 µg.l-1. The gemiddelde konsentrasie N03-N was hoog teen 312 µg.l-1 en het vermeerder stroom-af moontlik a.g.v. bemestingstowwe en stikstof-vaslegging deur alge. Die chlorofil α konsentrasie het gewissel tussen 0.4 en 1 084 µg.l-1 met gemiddeld 10.8 µg.l-1. Die hoë konsentratsie was as gevolg van 'n Microcystis opbloei in die Gariep dam gedurende Februarie. Fitoplankton dinamika het seisoenale patrone gevolg. Cyanobakterieë en Bacillariophyceae het gedomineer gedurende die warmer maande en Chlorophyceae het cyanobakterieë vervang gedurende die koeler maande. Primêre produksie in die Gariep dam en in die Vaalrivier is hoofsaaklik bepaal deur ligindringing. Maksimum produktiwiteit in die Gariep dam was 14.6 mg C. mg Chla-1 . h-1 en in die Vaalrivier was dit 76 mg C. mg Chla-1 . h-1 . Na aanleiding van die primêre produksie kan die Gariep dam geklassifiseer word as mesotrofies, terwyl die hoë produksie in die Vaalrivier dui op eutrofiese toestande. Die damme beïnvloed die fisiese, chemiese en biologiese toestande in die rivier. Lae SASS4 waardes is gevind, wat op swak waterkwaliteit dui. Die lae waardes kan toegeskryf word aan die versteuring van die rivierstelsel deur die damme. Die SDC (serial discontinuity concept) is van toepassing op die Bo-Oranjerivier. Dit is moontlik dat die herstel van die rivier stroomaf verskans kan word deur afloop vanaf landbou bemestingstowwe, sowel as deur stedelike en industriële besoedeling vanaf die Vaalrivier opvangsgebied, na die Oranje-Vaal samevloei.enUpper Orange RiverWater qualityPhytoplanktonTrophic statusChlorophyll aNitratePhosphatePrimary productivitySASS4Water quality management -- South Africa -- Orange RiverFreshwater quality -- South Africa -- Orange RiverDissertation (M.Sc. (Botany and Genetics))--University of the Free State, 2000DissertationUniversity of the Free State