The monitoring program in Ashalim stream was established in 2018 to monitor the effect of pollution on the stream’s ecosystems. Fifteen research groups from seven research institutions, specializing in different subjects, are taking part in the monitoring program.

Key findings

The coordinator of the monitoring program in Hamaarag described the key findings: “The monitoring results have shown that there is wide-ranging and ongoing damage to the ecosystem of the Ashalim stream. This damage is evident in both biotic and a-biotic components of the ecosystem, and in the different trophic levels – producers, consumers and predators. The damage to the sandy area located upstream was found to be the most significant, and high concentrations of pollutants were found in the soil in that area. In addition, we found that heavy metals, originating from the pollution incident, accumulated in both plant and animal tissues.

On the other hand, the program coordinator expanded – “certain components of the stream exhibit signs of recovery, due to – among other reasons – an unusual number of rain events and strong floods that impacted the many water pools located in the rocky area of the stream”. This helped the gradual restoration of the invertebrate community that populates the water pools: three years after the pollution incident, lesser crustaceans were found back in the pools, after they were completely absent in earlier surveys. In contrast, the rain events had almost no impact on the sandy area and on the terraces on the banks of the stream, which were damaged by the pollution and still contain high levels of pollutants three years after the event. It was found that the pollution severely affected the soil crusts and bacterial populations, leading, in particular, to the disappearance of the group of bacteria which provides sources of nitrogen to plants.

One significant result indicating the severe effects of the pollution is the damage to the Ashalim stream vegetation – in the incident itself almost half of the shrubs died. During the monitoring efforts in the years following the event it was found that the seed bank in the soil, as well as the richness of plant species in the stream, were relatively low, compared to findings from the control streams, but that the Ashalim stream itself is slowly recovering.

The results of the arthropod monitoring add an important component to the understanding of the impact of the pollution on the stream – seed-eating ants almost completely disappeared from the sandy area, a fact which indicates damage to the plants’ seed bank. In the alluvial area, downstream, a large number of sap-sucking insects, known to be harmful to plants, was observed in the year following the pollution incident, but already one year later their number decreased and returned to normal, compared to the control sites. This is further evidence of the stressed condition of the plants following the incident, as well as evidence of the recovery process in the alluvial area, compared to the sandy area.

What are the plans for the future?

The monitoring program currently focuses on characterizing and understanding the processes in which pollutants accumulate in the food web, and examines whether damage to the populations’ resilience in the long-run is to be expected. Continuing the monitoring and research efforts in the Ashalim stream in the coming years will promote deeper understanding of the damage to the ecosystem, and lead to more informed decision-making regarding the stream’s restoration.

הפוסט Ashalim stream monitoring program הופיע לראשונה ב-Hamaarag.

The coordinator of the monitoring programs in Hamaarag described the program and its findings: “The current pollution event in the Evrona Nature Reserve is not its first. A pollution event in 1975, which occurred in another part of the Reserve, served as a basis for comparison and for the examination of the impact of oil pollution decades after the event. In addition, we compared the polluted areas to a near-by control site which had not suffered oil pollution. Monitoring the pollution and its ecological impacts in the Evrona Nature Reserve is unique on a global level. We have not found documentation of similar cases of the contamination of a desert eco-system with crude oil on such a scale. Our monitoring program had two goals: to characterize the pollution and study the response of the ecosystem response to the pollution. On the physical level, oil pollution caused the formation of a hydrophobic layer in the layer of top-soil, which prevents water from penetrating the soil. Five years after the event, the concentration of pollutants in the soil is still high, and it turns out that the area polluted in 1975 still has a high concentration of pollutants in the ground.”

The effect of the oil soil layer on the ecosystem was examined for the first time on the acacia trees, the keystone species for biodiversity in the nature reserve. The monitoring coordinator expanded: “We did not find damage to the mature acacia trees in the reserve, probably because the pollution did not penetrate the depths at which their root system is located, but we did find considerable damage to the germination of seeds and development of sprouts. The contaminated layer does not allow acacia sprouts to survive. In fact, it limits the capacity of natural regeneration of the population. We have also seen the impacts of pollution in the 1975 polluted site, where the recruitment capacity of young individuals to the acacia population was severely limited. There are hardly any trees in this area that sprouted from 1975 onwards, and it is possible that there has been a similar impact on the germination of other plant species.

The contamination treatments examined so far – cultivation of the the soil, and biological treatment using oil-degrading bacteria – have not yielded satisfactory results, and further possibilities for the treatment and restoration of the nature reserve are currently being considered, as well as a continued monitoring program. According to the program coordinator: “the impact of the contamination on the ecological system of the Evrona Nature Reserve may stay with us for many years to come. The main concern is that in the long term, without extensive remediation of the contaminated soil, the population of acacia trees will decline within several decades, with no natural regeneration of the population thanks to the sprouting of new trees. Damage to this population will lead to a drastic change in the ecosystem and will cause irreversible damage to its other components. At this point, our role is to find the most effective solution for the removal of the contamination, and help remediate the Evrona Nature Reserve ecosystem.”

הפוסט Evrona Reserve monitoring program הופיע לראשונה ב-Hamaarag.