An ecological and hydrological evaluation of the effects of restoration on ecosystem services in the Kromme River System, South Africa

Rebelo, Alanna Jane (2012-12)

Thesis (MScConsEcol)--Stellenbosch University, 2012.

Thesis

ENGLISH ABSTRACT: Wetland systems provide vital hydrological ecosystem goods and services to mankind. When wetlands are transformed, through invasion by alien plants or replaced with agriculture, natural capital is lost, and the system is no longer able to provide the same quality of hydrological ecosystem services. Natural capital can be restored, but it involves substantial financial investment, and there is no guarantee that these hydrological ecosystem services will be fully recovered. This thesis aimed to investigate the hydrological impact of the land-cover changes in the Kromme River Catchment over the last 50 years, by using a combination of mapping and hydrological modelling techniques. We hypothesized that wetland loss in the Kromme has resulted in a shift in the flow regime, greater responsiveness to floods as a result of less storage, lower baseflow, and reduced water quality. We also hypothesised that the riparian invasion by Acacia mearnsii has caused flow reductions as a result of increased evaporation relative to the wetlands. Modelling results predict that over the past 50 years, the transformation of the floodplain wetlands in the Kromme River has shifted the flow regime, reducing baseflows and increasing the responsiveness of the catchment to extreme rainfall events. The invasion of A. mearnsii over time has also been predicted to have caused a reduction in river flow. Various restoration scenarios were considered, however if the Kromme were to be restored back to a land-cover state comparable to the 1950’s, 26.9 km2 (65.1%) of A. mearnsii would have to be cleared, and 5.2 km2 (34.2%) of the wetlands would have to be restored. The hydrological benefits would include a predicted increase in riverflow (42 mm/a), baseflow (2.9 mm/a), an increase in flood protection and improved water quality. This restoration strategy could be regarded as a type of insurance plan, and the benefits gained in terms of increased ecosystem service delivery would be the insurance premium. In conclusion it appears that restoration, insuring natural capital in the Kromme River, would provide significant economic returns on investment.

AFRIKAANSE OPSOMMING: Moeraslandstelsels voorsien die mens van noodsaaklike hidrologiese ekosisteemgoedere en -dienste. Wanneer moeraslande verander word, hetsy deur die indringing van uitheemse plante of vervanging met landboubedrywighede, gaan natuurlike kapitaal verlore en kan die stelsel nie meer dieselfde gehalte hidrologiese ekosisteemdienste lewer nie. Hoewel natuurlike kapitaal herwin kan word, behels dit beduidende finansiële belegging, en is daar boonop geen waarborg dat die hidrologiese ekosisteemdienste ten volle sal herstel nie. Hierdie tesis het ten doel gehad om die hidrologiese impak van die grondbedekkingsveranderinge in die Krommerivier-toeloopgebied oor die afgelope 50 jaar met behulp van ’n kombinasie van karterings- en hidrologiese modelleringstegnieke te ondersoek. Die hipotese was dat moeraslandverlies in die Kromme tot ’n verandering in die vloei-regime, hoër responsiwiteit op erge reënval as gevolg van minder bergingsruimte, ’n laer basisvloei en swakker watergehalte gelei het. Daar is voorts gehipoteseer dat die oewerindringing deur Acacia mearnsii ’n verlaging in vloei veroorsaak het weens ’n toename in verdamping uit die moeraslande. Modelleringsresultate dui daarop dat die transformasie van die vloedvlakte-moeraslande in die Krommerivier oor die afgelope 50 jaar die vloei-regime verander het, basisvloei verminder het en die toeloopgebied se responsiwiteit op erge reënval verhoog het. Die indringing van A. mearnsii het ook volgens aanduidings mettertyd ’n vermindering in riviervloei tot gevolg gehad. Verskeie herstelscenario’s is oorweeg. Om die grondbedekking in die Kromme te herstel tot wat dit in die 1950’s was, moet 26,9 km2 (65,1%) van die A. mearnsii verwyder en 5,2 km2 (34,2%) van die moerasland herwin word. Die hidrologiese voordele kan ’n verwagte toename in riviervloei (42 mm/a) en basisvloei (2,9 mm/a), ’n toename in vloedbeskerming sowel as beter watergehalte insluit. Hierdie herstelstrategie kan as ’n soort versekeringspolis beskou word, en die voordele verbonde aan beter ekosisteemdienslewering as die versekeringsuitbetalung. Ten slotte blyk dit dat die herstel van die Kromme, en die gepaardgaande versekering van natuurlike kapitaal, beduidende ekonomiese opbrengste op belegging sal meebring.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/71967
This item appears in the following collections: