Written by Baltazar Montemor
Translated by Francisco Chuquela
Saline intrusion and salinization of soils, two phenomena that result more from the action of man than from the nature. It is a reality that affects all the rivers that cross Mozambique, especially those that flow in the Indian Ocean and extensive irrigable areas.
“We have a large part, from the area of Macaneta up to here (Marracuene village, Maputo Province), where nothing is being produced at all. It is not possible to produce because there has been a lot of salinity and the land is severely affected, “said João Palate of the Marracuene Agro Livestock Cooperatives Union.
Palate points as the main cause, the destruction of barriers in the area of the mouth of Incomati River, to give rise to the construction of infrastructures (human action). Incomáti reveals itself to be imposing and gives important space to the sea.
Biologist Carlos Bento defines saline intrusion as being the process of entering the seawater by the river. One of the causes of saline intrusion is the reduction of river flow, which originates from the action of man, who makes different uses upstream.
Irrigation systems, for example, extract large volumes of water, especially if it is a river with large tracts of arable land. The phenomenon can, on the other hand, be caused by hydroelectric exploration of the rivers, or a simple dam.
The dam consists of artificial retention of water, which is released gradually in periods of scarcity. As a consequence, the downstream flow is inevitably reduced. The water force of the river becomes smaller than the force of sea water, which ends up penetrating the river.
The exploration of groundwater also contributes to occurrence of saline intrusion. The serious effect is accentuated by massive exploration of groundwater along the coast. This operation determines a significant reduction of the water table. The pressure that fresh water makes on salt water decreases. As a result, salt water gains ground and penetrates the water table. Most of the time the penetration goes to the point of abstraction, leading to the salinization of the soils.
The salinization of soils begins with the irrigation of the fields with salt water. With evaporation, the salt stays on the surface of the soil. Later, when that amount of salt increases soils begin to become impractical for agriculture.
At first glance the process of penetration of the sea waters into rivers may be considered normal. Normal rivers, without water regularization, during rainy seasons receive a lot of water that drains to wash the ecosystems downstream. In the dry season, the rivers significantly decrease their flow, giving way to the sea.
However, this process does not have many effects, it is a natural phenomenon that allows an almost constant wash of the river. In rivers with regularization this washing is no longer regular, which gives rise to saline intrusion.
The saline intrusion and salinization of the soils translate into serious consequences for the environment. The direct consequence goes to agriculture, since soils lose fitness, or simply become infertile.
Gaza Province, potentially agricultural, is one of the regions of the country affected by both phenomena. “Agriculture is declining in Gaza Province because of saline intrusion and salinization of soils, which destroy organic matter, including the emission of gases,” said Anastácio Mathavele, President of the Forum of Non-Governmental Organizations in Gaza. He summarized that the situation compromised agricultural production and productivity and, above all, major projects and the consumption of water for man and animals. “In cadre, this situation, in fact, compromises the existence of man and all organic matter (crops and everything),” he emphasizes.
All Mozambican rivers that flow into the sea are affected by saline intrusion and salinization of the soils. The Limpopo River, which is born in neighboring South Africa and flows into the sea through Gaza Province, could not be an exception.
Armando Ussivane, Chairman of the Board of Directors of Baixo Limpopo Irrigation System, points out two causes: the first is linked to the soils of that region, which come from marine deposits, being directly responsible for primary salinization from the parent rock. Secondary salinization follows, resulting from poor drainage or poor soil management practices. This happens when the soils are not able to do a natural wash of the salts.
“Normally a flowing process occurs when the washing process is insufficient through the irrigation or rainfall system the salts tend to rise to the surface area of the soils. But when we have this practice of irrigation, with adequate management, accompanied by sufficient rainfall, the tendency of the salt is to precipitate. For this, it is necessary that there be conditions created for that process to be carried out, namely a drainage system operating fully,” explains Armando Ussivane.
Limpopo River area is affected by saline intrusion and salinization. There are areas where the salinity is not yet pronounced, especially upstream and the intermediate zone of the Basin, namely Chókwè, where signs of salinization begin to occur and much more in the downstream zone, Baixo Limpopo, where are extensive areas with serious salinity problems. In the zone further downstream of the Limpopo Basin there is saline intrusion due to rising sea level and progressive penetration of salt wedge into the river.
“This is one of the problems that have been affecting soil productivity, because with poor water quality there is no way to irrigate. I would say that in that area of Xai-Xai from the downstream bridje, there are vast areas that can not be used or irrigated with water from the river, because it is not of good quality (suffered saline intrusion). The current situation is that we have witnessed a progression of the salt wedge, at a distance of 61 kilometers from the river to the mouth,” Armando Ussivane said.
In the irrigable zones of the country there are several manifestations of the direct effects of saline intrusion and salinization: the loss of soil productivity. Farmers do not achieve yields according to the potential, because salt is a major constraint on soil productivity. Salinization, that is, water quality also has a negative influence on productivity. The change in situation involves additional and costly irrigation resources.
Loss of soil productivity as a consequence of saline intrusion and salinization occurs in many regions of the country. Malingapansi, an administrative post in the district of Marromeu in Sofala, is a typical example of this reality. Of great rice producer, only the story remained. It is a village about 60 kilometers from the village of Marromeu, very close to one of the arms of Zambezi River.
In the past, the communities of Malingapansi drew water from one of these arms of Zambezi to irrigate the rice producing areas. These were times when the flow of Zambezi was very strong and there was no saline intrusion. Over time the water underwent salination. Without realizing it, the communities continued to use the same waters to irrigate the agricultural fields and soil salinization was not avoided. Today, Malingapansi’s rice yield is almost zero.
There are cases where even saline resistant mangroves end up dying due to the excessive occurrence of the phenomenon. “In some places, along the coast, we see a massive mortality of mangrove swamps, it seems that there was an atomic bomb in which we see many dead trees, concentrated in the same place. This is nothing more or nothing less than the effects of saline intrusion,” says Carlos Bento. The biologist warns that sites affected by any engineering work, such as the construction of dykes, block the passage of fresh water to do the washing of the soil and with the passage of time the salinity index is increasing.
Mangroves tolerate salinity, but when the threshold of this tolerance is exceeded, as the case seems to be, they begin not to resist and there is no avoiding massive mortality along the coast. (To be continued)