Quantifying the economic water savings benefit of water hyacinth (<i>Eichhornia crassipes</i>) control in the Vaalharts Irrigation Scheme

Abstract

Global freshwater resources are threatened by an ever-growing population and continued economic development, highlighting the need for sustainable water management. Sustainable management must include the control of any additional factors that may aggravate water scarcity, such as invasive alien plants. Water hyacinth (Eichhornia crassipes), one of the world's most destructive invasive plants, presents a direct threat to economically productive water resources. Through high levels of evapotranspiration, water hyacinth leads to substantial water losses that could otherwise be used more productively, thereby creating an externality on water-dependent industries, such as irrigation-fed agriculture. This study provides an economic valuation of the water-saving benefit of water hyacinth control, using Warrenton Weir on the Vaalharts Irrigation Scheme as a case study. A Residual Value Method was employed to estimate the average production value of irrigation water, based on water's relative proportion of total costs (TC), to serve as a proxy for the value of water lost via evapotranspiration by water hyacinth. Three evapotranspiration to evaporation ratios, derived from the literature, at three levels of invasion (100; 50 and 25% cover), were used to estimate the annual water loss at Warrenton Weir. The average production value of irrigation water was estimated to be R38.71/m 3 , which translated into an annual benefit of between R54 million and R1.18 billion. These results highlight the need for invasive plant control, particularly in economically productive water resources. An alien plant control policy should prioritise invasions of this nature, as they present significant costs to the economy and threaten the sustainability of freshwater resources.

Quantification of the Evaporation Rates from Six Types of Wetland Cover in Palo Verde National Park, Costa Rica

“…This leads to a total contribution of 38% from the total evaporation in marshland ecosystems [75] similar to Palo Verde National Park. Reported values of evaporation for E. crasipes range from 1.02 mm d −1 to 9.8 mm d −1 depending on the ecosystem, season and climatological conditions [35]. Floating plants as N. natans and E. crasipes are influenced mainly by radiation and vapor pressure deficit.…”

“…However, information on evaporation rates are limited for tropical plant species. From the 100 macrophytes reported in Palo Verde National Park [14,15], only T. dominguensis and E. crassipes [28,[34][35][36][37] have published values of evaporation in other regions (e.g., Suriname, South Africa, United States). The effect of invasive plants as T. dominguensis and E. crassipes in wetlands is linked to the increment of evaporation and the subsequent reduction of the water surfaces [38][39][40].…”

Estimation of Water Losses Through Evapotranspiration of Water Hyacinth (Eichhornia crassipes)

“…The surface area of water hyacinth influences the amount of water loss, the low cover of water hyacinth has an impact on the amount of water loss is low, as well as extensive cover conditions have an impact on the amount of greater water loss (Arp et al, 2017;Ali and El-Din Khedr, 2018). The lowest water loss occurred on 21 October 2014, although the average evapotranspiration rate of water hyacinth in October was the highest at 6.16 mm day -1 (Figure 8), however, the cover area of the water hyacinth was recorded as the lowest, which is around 1.29% of the total surface area of the reservoir with an area of 2,969,400 m 2 .…”

“…Water hyacinth has a variety of adverse effects, including creating anoxic conditions on the lake, thus increasing the level of toxicity and disease (Güereña et al, 2015), blocking water canals (Ndimele et al, 2011), interference lake navigation (Tumbare, 2008), ecosystem destruction, increase in mosquito population (Sanmuga Priya and Senthamil Selvan, 2017;Sindhu et al, 2017), threats to the functioning and biodiversity of aquatic ecosystems, fisheries (Attermeyer et al, 2016), interference in irrigation systems (Opande et al, 2004), increased sedimentation (Bordoloi et al, 2015) and leading to increased water loss through evapotranspiration (ET) relative to normal, open water evaporation (Villamagna and Murphy, 2010;Arp et al, 2017).…”

Optimisation of Savannah Land Cover Characterisation with Optical and SAR Data

“…Within the South African part of the study area, 16 different vegetation types are found, mostly belonging to the thornveld, bushveld or savannah grassland categories [37]. In addition, a large part of the study area is arable land (e.g., the Vaalharts Irrigation Scheme [38]), contributing to a significant portion of the country's maize, groundnuts, sunflowers, dry beans and grain sorghum [39]. The area is also a vegetable and citrus fruit producer [40].…”