Impacts of invasive alien plants on water quality, with particular emphasis on South Africa

Abstract

We review the current state of knowledge of quantified impacts of invasive alien plants on water quality, with a focus on South Africa. In South Africa, over 200 introduced plant species are regarded as invasive. Many of these species are particularly prominent in riparian ecosystems and their spread results in native species loss, increased biomass and fire intensity and consequent erosion, as well as decreased river flows. Research on the impact of invasive alien plants on water resources has historically focused on water quantity. However, although invasive alien plants also affect the quality of water, this aspect has not been well documented. Alien invasive plants increase evaporation rates, and reduce stream flow and dilution capacity. The biomass inputs of alien invasive plants, especially nitrogen fixers such as Acacia spp., alter nutrient cycles and can elevate nutrient concentrations in groundwater. Alien plant invasions alter the fire regimes in invaded areas by changing the size, distribution and plant chemistry of the biomass. More intense fires increase soil erosion and thereby decrease water quality. In contrast to riparian invasions, aquatic invasive plants have been more extensively studied in South Africa and their impacts on water quality have been relatively well monitored. Water quality in South Africa is rapidly deteriorating, and all factors that influence this deterioration need to be taken into account when formulating actions to address the problem. The changes in water quality brought about by alien plant invasions can exacerbate the already serious water quality problems.

Removal of Pb2+ from Water by Synthesized Tannin Resins from Invasive South African Trees

“…South Africa is now considered to be a water-scarce country [4]. Improving water conservation, water quality and water-use efficiency is a key national priority [5]. The availability of water is threatened by the encroachment of a considerable number of non-native species.…”

Linking key environmental stressors with the delivery of provisioning ecosystem services in the freshwaters of southern Africa

“…Aquatic plant invaders include water hyacinth Eichhornia crassipes , water lettuce Pistia stratiotes , Kariba weed Salvinia molesta and red water fern Azolla filiculoides , all of which increase rapidly in biomass resulting in the formation of dense mats in nutrient loaded environments (Chamier et al . ). While this can decrease nutrient loads, the resultant mats reduce light penetration and photosynthesis, reduce water circulation and the diffusion of air into water, and increase organic detritus loads which are broken down by anaerobic processes (Chamier et al .…”

“…While this can decrease nutrient loads, the resultant mats reduce light penetration and photosynthesis, reduce water circulation and the diffusion of air into water, and increase organic detritus loads which are broken down by anaerobic processes (Chamier et al . ). Collectively this often results in anoxic conditions that are uninhabitable by aquatic invertebrates and fishes.…”

Riparian invasion of Lonicera maackii influences throughfall chemistry and rainwater availability

“…Riparian zones are natural buffers along aquatic habitats that help mediate non-point pollution sources entering aquatic systems (Lowrance et al 1984; Barling and Moore 1994), but can also contribute nutrient subsidies to nearby aquatic systems. Riparian function is tightly linked with plant community composition in the riparian zone (Gregory et al 1991); however, in many regions, riparian zones have become degraded due to forest fragmentation, urbanization, and the introduction of invasive plants (Richardson et al 2007;Chamier et al 2012).…”