Patterns in periphyton biomass and community structure in foothill rivers: A comparison between winter and summer rainfall regions

Grainger, Cole Vincent (2017-12)

Thesis (MScConsEcol)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: South Africa has a semi-arid climate with seasonal rainfall whose runoff is jeopardised by high rates of evapotranspiration. These conditions decrease the ability of rivers to dilute point and non-point sources of pollution, which leads to enrichment and the subsequent eutrophication of water bodies. Eutrophication occurs when periphyton communities proliferate through a shift in community structure, accompanied by greater biomass accrual that deteriorates water quality and impairs aquatic ecosystem functioning. The National Eutrophication Monitoring Programme (NEMP) has set water quality guidelines for concentrations of phosphorous and Benthic chlorophyll a, but periphyton are understudied in South African waters, which explains their exclusion from the River Eco-Status Monitoring programme (REMP). To underpin the causes of eutrophication, this study aimed to broaden the knowledge on periphyton-environmental relationships in terms of patterns in peripyton biomass and community structure on a regional scale across seasons in a winter (Western Cape) and summer (KwaZulu-Natal) rainfall region. Periphyton biomass and community structure were observed across flow and enrichment categories and a suite of environmental metrics comprising flow, nutrients, water temperature, sunlight and macroinvertebrates. An in situ tool known as the Benthotorch® was validated to potentially be used in future rapid assessments of trophic status. Periphyton samples from sites representing a range in environmental conditions were collected in autumn and spring which mark the beginning and end of the periphyton growth seasons. Periphyton biomass in the Western Cape was found to be influenced predominantly by the availability of TIN in autumn and WTMAX in spring. In KwaZulu-Natal, periphyton biomass was influenced mostly by flow metrics and WTCV. Periphyton community structure in the Western Cape was influenced mostly by TIN and the length of the growing season in autumn and by EC and the duration of class 1 floods in spring. In KwaZulu-Natal, periphyton community structure was influenced mostly by water temperature and flow metrics in autumn and by the length of the growing season (Since≥2), the duration of class 2 floods and PO4-P in spring. The flow regime is regarded as the primary regulator of flood prone rivers, which was not the case in this study, and calls for future research. Nutrients accounted minimally towards spatial variation in periphyton communities in KwaZulu-Natal possibly due to sites with similar nutrient ranges, or because nutrients are not a key driver of periphyton communities here. The importance of water temperature metrics in both regions stresses the need for water temperature monitoring programmes, that are currently lacking in South Africa. The Benthotorch® estimated periphyton biomass and community structure more accurately at sites that were dominated by diatoms, overestimated cyanobacteria and did not consistently recognize green algae.

AFRIKAANSE OPSOMMING: Suid-Afrika het ‘n half-woestyn klimaat met seisoenale reënval. Die dreinering van hierdie reënval word in gevaar gestel deur hoë evapotranspirasie. Hierdie omstandighede verminder die kapasiteit van riviere om punt- en nie-punt bronbesoedeling te verdun, wat lei tot geweldige eutrofikasie van warm waterbronne. Eutrofikasie kom voor waneer periphyton vermenigvuldig deur verhoogde biomassa en verskuiwings in gemeenskapstruktuur wat waterkwaliteit verswak. Gevolglik word die funksionering van akwatiese ekosisteme benadeel. Die Nasionale Eutrofikasie Monitorprogram (NEMP) het waterkwaliteit riglyne opgestel vir die konsentrasie fosfor en chlorofil a. Daar word egter min klem gelê op periphyton in Suid-Afrikaanse waterbronne, wat die uitsluiting daarvan in die Rivier Ekostatus Monitorprogram (REMP) verduidelik. Dit is nodig om kennis op te doen oor die verhoudings van periphyton in die omgewing om besluite te kan maak wat eutrofikasie geheel en al kan verhoed. Die kern van hierdie studie is om die kennis van periphyton biomassa en gemeenskapstrukture te verbreed op ‘n plaaslike skaal oor seisoene, nl. ‘n winterreënvalseisoen (Weskaap) en ‘n somerreënvalseisoen (Kwazulu Natal). Die relatiewe belang van verryking- en vloeikategorieë is getoets, sowel as ‘n hoeveelheid omgewingsfaktore (vloei, voedingstowwe, water temperatuur, sonlig en algeëtende insekte). Die Benthotorch®, ‘n in situ gereedskapsmodel is beskikbaar gemaak vir toekomstige gebruik vir vinnige assesserings van die trofiese statusse van waterbronne. Periphyton monsters is geneem gedurende herfs- en lenteseisoene, want dit val saam met die groeiseisoene van die periphyton. ‘n Verskeidenheid van areas is gekies vir hierdie studie om ruimtelike variasie en omgewingsfaktore in ag te neem. Daar is gevind dat periphyton biomassas in die Weskaap meestal deur die beskikbaarheid van TIN in die herfsmaande en WTMAX in die lentemaande beïnvloed word. In Kwazulu Natal is dit hoofsaaklik deur vloeifaktore en WTCV beïnvloed. In die Weskaap is periphyton gemeenskapstrukture meestal deur TIN asook die lengte van die groeiseisoen in die herfs beïnvloed, waar dit deur EC en die lengte van klas 1 vloede in die lente beïnvloed is. In Kwazulu Natal is periphyton gemeenskapstrukture in herfsmaande meestal deur watertemperature en vloeifaktore beïnvloed en gedurende lentemaande deur die lengte van die groeiseisoen (sedert≥2), die lengte van klas 2 vloede en PO4-P. Daar is ‘n behoefte aan toekomstige navorsing wanneer daar na die klein bydrae van vloeiings relatief tot voedingstofkonsentrasies en tot ruimtelike variasie in periphyton gemeenskappe gekyk word. Die vloei regime word as die primêre reguleerder, in periphyton gemeenskappe in riviere wat maklik vloed, gesien. Die klein bydrae van voedingstowwe tot die ruimtelike variasie in periphyton gemeenskappe in Kwazulu Natal is waarskynlik die gevolg van die onvoldoende omvang van voedingstowwe in die bestudeerde areas. Die behoefte aan watertemperatuur monitorprogramme word duidelik wanneer daar na die belangrikheid van die watertemperatuurfaktore in albei areas gekyk word. Huidiglik is daar ‘n leemte aan hierdie tipe program in Suid-Afrika. Die Benthotorch® het het goed vergelyk ten opsigte van biomassa skattings, veral in die areas met diatome in groot maat. Dit het egter, in terme van gemeenskapstruktuur-skattings die cyanobacteria oorskat by sekere geleenthede en nie groen alge herken nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102620
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