Improved Management of Water Resources

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Water scarcity in semi-arid and arid regions is the hallmark of desert formation and the basis of dryland vulnerability to land degradation. Thus, creative and effective management of water resources is critical to reversing desertification and restoring the health of degraded drylands. At the Zuckerberg Institute for Water Research, part of the Jacob Blaustein Institutes for Desert Research at Ben-Gurion University of the Negev, active projects are under way in Israel, Africa and Asia.

Israel’s Jezreel Valley, a formerly marshy ecosystem with limited agricultural potential, underwent considerable drainage work in the 1980s to turn the semi-arid Valley into a fertile basin for farming. Crop irrigation to improve yields was introduced by constructing a series of artificial reservoirs that stored recycled urban wastes. However, farmers found that land adjoining the reservoirs became saline and unusable, an entirely unexpected development.

Zuckerberg Institute researchers used studies of underground water movement to explain this problem. Applying hydrochemical and isotope tracing studies, they found that the reservoirs partially blocked the normal outflow of the low-lying salt-rich groundwater. Therefore, low-salt irrigation water mixed with the saline ground water, which built up close to the soil surface. Evaporation of this water by solar heat left the salts behind, producing a saline topsoil unfit for farming.

Uncovering the mechanism of salineation enabled an approach for reversing the soil degradation. Combined horizontal drains with deep vertical shafts were introduced into the partially confined, shallow saline aquifer, releasing the groundwater pressure buildup. This allowed washing, drying and aeration of the topsoil for reintroduction of sustainable, intensive agriculture in the abandoned fields.

Researchers of the Zuckerberg Institute investigated the agriculture and hydrology of the Ily River delta, a region negatively affected by the diversion scheme. Field data were collected and combined with numerical and management strategies. By quantitatively characterizing the complex hydrological features of the region, the scientists devised cost-effective recommendations to mediate the damaging effects of human activities on the region’s agriculture.

Scientists at the Blaustein Institute for Desert Research have designed a novel approach to conserving runoff in the “takyr.” By setting up an infiltration basin at an appropriate location in the local watershed and digging special “submerging wells,” precipitation can be funneled into the ground to create a layer of fresh water over the saline water table. This so-called “artificial lens of fresh groundwater” floats like oil above the high-density, salt-rich groundwater.

The group has carried out a long-term study determining the quantity of water that can be stored in the “lens” and how this changes with weather conditions and soil and water-table properties. They found that a long period of drought causes the “lens” water to spread out and change its shape, making retrieval much more difficult. The researchers are now carrying out both experimental and modeling studies to better understand the physical chemical process taking place in the artificial lens to achieve longer-term stability. At any rate, in Turkmenistan deserts, these “lenses” are often the only source of fresh water available for small farms and livestock husbanders.

In order to increase vegetative coverage in arid regions, it is essential to increase the effective supply of water to the degraded land. One approach widely used since ancient times is water harvesting. Here naturally generated runoff from a largewatershed area is trapped by ground modifications that bring the flow into a much smaller expanse. Thus the quantity of precipitation concentrated in the receiving area will greatly exceed meteorologically measured rainfall.

Researchers at the Blaustein Institute for Desert Research have adapted this approach for the simultaneous production of firewood and fodder in a system known as runoff agroforestry. Productivity is further increased by planting an “intercrop” between rows of trees. This highly effective technique is extremely suitable for arid environments, and allows farmers to increase their yields of various agricultural products.

The BIDR investigators established a runoff agroforestry system in the dry Turkana district of Northern Kenya. Growing shallow-rooting annuals and deep-rooting perennials, the system takes advantage of blue leaf wattle (Acacia saligna) as the tree component, due to its drought resistance, and sorghum (Sorghum bicolor) and cowpea (Vigna unguiculata) as intercrops. Studies showed that trees grew particularly well, and when the soil was deep enough, large volumes of runoff water could be stored underground, producing high yields of intercrops.

In order to advance use of blue leaf wattle in reversing desertification, the effects of different growing conditions on tree performance were evaluated in Israel’s Negev desert. Flood scheduling, supplemental drip irrigation timing, and irrigation water qualities on tree growth were measured. Appropriate conditions for strengthening tree survival were determined. In addition, pollarding of the wattle (cutting low-lying branches down to the trunk) was investigated to increase sunlight entering the forest floor and improving intercrop growth. This procedure was found not to affect root numbers, and after a year of re-growth the development of roots, trunk, branches and the plant’s unusual variety of leaves (phyllodes) was satisfactory, independent of the watering treatment applied. These studies further strengthened the value of blue leaf wattle for runoff agroforestry and fighting desertification.

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