Gobabeb Training and Research Internship Programme 2010
Project 1: The effects of off-road vehicle tracks and their rehabilitation on Hypolithic Cyanobacteria in the gravel plains of the central Namib Desert: Implications for restoration - Atna M Bam
In hyper arid regions such as the Namib Desert, hypolithic cyanobacterial crusts (HLC), which are primarily composed of cyanobacteria and microalgae, are key to ecosystem functioning. These communities stabilize soils against wind and water erosion, enhance nutrient status of vascular plants, and improve soil structure. Hypolithic cyanobacteria have been found to be extremely tolerant of super arid environments but are poorly adapted to compression disturbances like those caused by vehicle tracks. With the recent increase in uranium prospecting, extensive networks of tracks now cover the gravel plains of the central Namib. HLC are easily damaged by off-road driving and raking is the most widely used rehabilitation technique. This study used observational percent cover estimations and chlorophyll a absorbance to compare HLC on the basal surface of quartz stones on year old tracks at Reptile Uranium Namibia and newly raked tracks near Gobabeb.
The year-old tracks near the uranium mine had a higher number of rocks with HLC present compared to the younger tracks at Gobabeb. This suggests that, over time, HLC may be able to re-colonize previously disturbed areas. Comparisons between raked tracks and unraked tracks found that the effects of raking were more harmful than the off-road driving tracks. Raking can flip the quartz stones and expose HLC to harmful radiation in the direct sunlight and should therefore not be used as a rehabilitation technique for off-road tracks. Future studies should monitor the impact of different compression forces and the viability of HLC in different environments near Gobabeb (such as the salt pans or washes) and should extend the sample size.
Project 2: Assessment of gravel plains plant germination in different topsoil treatments in the central Namib Desert - Kaatri Nambandi
Topsoil or the first 20cm of the Earth’s surface is critical to nutrient cycling, seed banks, and maintenance of water infiltration. When this layer is disturbed, by activities such as mining, prospecting, off-road driving, and construction, there is a threat to native seed conservation and proper water drainage. Mining companies in the Namib Desert remove large amounts of topsoil and, understanding it’s role in native seed storage, keep the topsoil in hope to maintain viable seeds for restoring the site after operations. This study observed germination rates of three native plants— Stipagrostis ciliata, Stipagrostis obtusa and Zygophyllum simplex—after planting in three topsoil treatments. The three soil treatments included fertilized topsoil, mixed topsoil (replicating mine disturbance by digging to the calcrete layer and mixing topsoil), and a control with no added soil or practice.
All plots were watered every other day for three weeks but little germination was observed; however, after a 10mm rain event, all plots had significantly higher germination. Final results revealed that the mixed topsoil plots had the lowest germination rates and that there was significantly more germination after the rainfall than after the first three weeks of watering. Rain events, and not just frequent watering, appear to be important for germination in desert ecosystems. Rainfall results in more highly saturated atmospheric water vapour and shade that promotes germination. Similarly, it is clear that the mixed topsoil treatments inhibit successful germination rates. Biological Soil Crust on the surface of topsoil improves nutrient cycling and disruption of this may limit nutrient availability to germinating seedlings. The mines’ practice of storing topsoil for eventual restoration may not actually contribute to seedbank establishment. Future studies should more closely evaluate the species composition and abundance in the gravel plain’s seedbank.
Project 3: Effectiveness of three seed-detritus trap types in the gravel plains of the central Namib Desert - Ndeshipewa V. Shiviya
Natural landforms, small bushes, and even rocky outcroppings protruding from the otherwise flat gravel plains of the Namib Desert help capture nutrient-rich detritus (dead organic matter) and wind dispersed seeds. After large expanses of land are disturbed by mining activities, restoring native vegetation will enhance natural seed capture mechanisms and water infiltration. Placing man-made seed-detritus traps may assist restoration efforts on expired mining lands.
This study observed the effectiveness of three inexpensive and easily constructed seed-detritus seed-detritus trap types: pits, brushpacks, and rockwalls. All three trap types were assembled on both grassy and bare substrates and detritus mass and captured seed numbers were recorded. In this study, pitfall traps were caught significantly more detritus than the other traps in a grassy landscape. Similarly, pitfall traps captured significantly more seeds than the brushpacks or rockwall traps in the grassy landscape. Although the brushpacks did not capture many seeds, there was a similar amount of detritus found in the brushpacks and pitfall traps in the bare landscape. The majority of seeds captured were grasses, likely because grasses dominate the gravel plain ecosystem. These results suggest that pitfall traps are the most effective way to capture seeds and hopefully encourage germination during restoration. Additionally, the brushpacks help capture detritus which decomposes to essential nutrients, holds soil particles together to decrease soil erosion, and may provide habitat for small animals and insects. In order to fully understand the function of seed-detritus traps in restoration activities, future studies should analyse how wind and rainfall events impact the effectiveness of all three trap types.