Investigating the potential of floating wetlands in small farm dams in the Western Cape, South Africa

Frenzel, Philip (2018-04)

Thesis (MSc)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The rapid deterioration of surface water quality and habitat quality due to urban sprawl, intensive agricultural practices, land degradation and spread of invasive alien species is an unfortunate reality in many parts of the world. Urgent intervention is necessary to mitigate the negative impacts on riparian and wetland ecosystems to preserve their functioning. Floating wetland studies across the globe have highlighted their potential to successfully purify various wastewater types, attract biodiversity and promote environmental awareness. Selection of appropriate plants to populate these wetlands is key for efficient nutrient removal, surviving herbivory by aquatic birds, excessive wind and fluctuating nutrient levels. I investigated the suitability of floating wetlands to purify agricultural run-off and determined plant survival success on small farm dams in the Western Cape, South Africa. The removal efficiency of nitrogen and phosphorus was investigated in a mesocosm experiment planted with three endemic wetland plant species (Cyperus textilis, Juncus lomatophyllus and Prionium serratum) over one month. In terms of monitoring plant survival success on floating wetlands, it is important to understand the drivers of plant survival and growth as plants are exposed to various threats and pressures in open farm dam settings. Three field visits to existing floating wetlands were conducted over a period of a year in order to better understand the survival success of certain plant species. Plant survival rate was determined by expressing the number of individuals that since the previous field trip as a percentage, whilst growth rate was measured using plant height, and expressed as a percentage of the size of the individual at the time of the first and third field visit. Low nitrate, phosphate and ammonium uptake rates, yet high removal efficiencies were observed across treatments in the mesocosm experiment which suggests that most nutrients that were added into the system were removed successfully. The lack of a significant difference between planted floating wetlands and the control (unplanted) is attributed to insufficient nutrient enrichment in the experiment. Future studies should test more eutrophic conditions. All plants survived and thrived in the simulated conditions and were responsible for the uptake of some nutrients, however, non-significant differences in nutrient storage (roots vs shoots) were observed. Visual observations on plants on floating wetlands implemented on farm dams in South Africa suggest that herbivory by aquatic birds appears to be a major threat to the successful establishment and survival of plants. Changes in water quality (pH, dissolved oxygen, run-off vs effluent storage, water temperature, total dissolved solids and salinity) appear to be significant drivers of plant survival and plant growth. The following species are recommended for use on floating wetlands in the Western Cape of South Africa due to high survival rates: Cyperus dives, Cyperus fastigiatus, C. textilis, Juncus effuses and Schoenoplectus scirpoides. Floating wetlands attracted biodiversity such as aquatic birds, dragonflies and terrapins. Thus floating wetlands appear to be successful in attracting biodiversity to small farm dams. This study provides important baseline information on the potential use of floating wetlands for the dual purpose of nutrient removal and attracting biodiversity.

AFRIKAANSE OPSOMMING: Die vinnige agteruitgang van kwaliteit van oppervlakwater en akwatiese habitatte as gevolg van stedelike verspreiding, intensiewe landboupraktyke, gronddegradasie en verspreiding van indringerspesies is 'n ongelukkige werklikheid in baie dele van die wêreld. Dringende ingryping is benodig om die negatiewe impak op oewer- en vleilandekosisteme te versag om hul funksionering te behou. Studies regoor die wêreld beklemtoon die potensiaal van drywende vleilande om verskeie afvalwatertipes suksesvol te suiwer, biodiversiteit te lok en om omgewingsbewustheid te bevorder. Seleksie van gepaste plante om hierdie vleilande te vul is noodsaaklik vir doeltreffende voedingstofverwydering, oorlewing van herbivorie deur watervoëls, en om oormatige wind en wisselende voedingsvlakke te oorkom. Ek het ‘n ondersoek ingestel op die geskiktheid van drywende vleilande om landbou-afloop te suiwer en die oorlewingsukses van plante op klein plaasdamme in die Wes-Kaap, Suid-Afrika te bepaal. Verwyderingsdoeltreffendheid van stikstof en fosfor is ondersoek in 'n mesokosmeksperiment wat oor een maand met drie endemiese vleilandplantspesies (Cyperus textilis, Juncus lomatophyllus en Prionium serratum) geplant is. Om oorlewingsukses van plante op drywende vleilande te monitor is dit belangrik om die dryfkragte van plantoorlewing en - groei te verstaan, aangesien plante blootgestel word aan verskeie bedreigings en druk in oop plaasdaminstellings. Drie veldbesoeke aan bestaande drywende vleilande is oor 'n tydperk van 'n jaar uitgevoer om die oorlewingsukses van sekere plantspesies beter te verstaan. Die oorlewingsyfer van plante is bereken deur die aantal individue wat sedert die vorige veldbesoek daar was as n persentastie uit te druk, terwyl die groeikoers met planthoogte gemeet is en uitgedruk is as 'n persentasie van die grootte van die individu tydens die eerste en derde veldbesoek.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103923
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