Mangroves discovered near Thatta

Karachi: Experts have discovered and are trying to preserve the presence of mangroves in a site located some 120-kilometres inshore in the Thatta district — adjacent to the south-eastern lower part of Keenjhar Lake. What is unique about this patch of vegetation, according to experts, is that is it far from the shore, and is also not connected to the River Indus or the sea.

In a recent study titled ‘A Unique Basin: Mangrove Stand of the Indus Delta’ by Syed Mohammad Saifullah and Fayyaz Rasool and sponsored by Mangrove Ecosystem Lab, Department of Botany, University of Karachi, it was found that locals who use Avicenna marina for feeding their cattle may have introduced propagules in the area. The basin forest flourishes well for long periods without seawater intrusion elsewhere. Experts believe that there may have been a connection between these plants and the Indus River in the past. The propagules of Avicenna marina drifted into an area where they were trapped, thus germinating and eventually becoming full-fledged trees.

The mangroves were discovered in a low-lying area of about 12 acres, isolated from Keenjhar Lake by a narrow embankment as high as four metres on the western side and from the Indus River at a distance of three kilometres on the eastern side. It is located in close vicinity of an old graveyard with 16th-century Chawkandi style graves, and is isolated by a stony embankment with a concrete road on top without any opening. The Indus River flows some three kilometres west of the site. The lake is 20 miles long, 34 feet deep and covers an area of about 50 square miles and has a storage capacity of 0.524MAF. The lake receiving water from the River Indus through the Kotri Baghar Upper Feeder, supplies about 1,000 cusecs of water per day to Karachi. The study pointed out that big trees have been chopped off for wood by locals and the remaining shrubs are subjected to grazing.

Mangroves are terrestrial plants that have inhabited coastal areas to avoid competition from other such plants. They have adopted several physiological and morphological mechanisms to overcome salt stress, including salt exclusion. In fact, mangroves grow happily along rivers and can also grow in fresh water.

In 1974, researchers described five different types of mangrove forests or environmental settings — fringe forest, dwarf forest, over-wash forest, riverine forest and basin forest. Fringe forests are the most common type, inhabiting coastal margins and inshore protected areas. The first three types are tide-dominated, the fourth river-dominated while the last one does not fall into either of the two categories because it is isolated from the river and seashore. Basin forests are located in depressions inside the land, far away from the sea and hardly receive any seawater except at extraordinarily high tides. They have also been considered as a closed mangrove ecosystem, they said.

The present mangrove stand may be classified into this category. However, it is a little different because it is not connected to the sea through any channel or water course. It is about 120 kilometres inland from the nearest seashore, which is perhaps the first ever record of the inland limit of mangrove occurrence. Earlier reports of black mangroves were found 100 kilometres inland from the shore.

The recent construction and expansion of a pucca road on the embankments separating the site from the lake has affected vegetation in the area. It is also expected that the area may be reclaimed as a tourist spot in future, thereby eliminating the remaining mangroves. Researchers have urged the Environmental Protection Agency (EPA) and Sindh Forest Department to (SFA) to declare the area as protected.

The area of study was within the dense mangrove stand, and contained shallow water which was pale yellow in colour. The water was actually from underground seepage because there was no open connection between the area and the lake or the Indus River. Its salinity was as low as three to four per cent but in exposed sites, the salinity of the water present in small depressions was as high as 10 to 15 per cent. The chemical analysis of the mangrove mud revealed that the soil was rich in organic matter as compared to that of the fringe forest and other marine types. The basin forests are known to be rich in this because of the absence of diurnal tidal mixing and low flushing. In this case, there is no tidal mixing at all and no export of organic matter. The litter is accumulated along with other decomposing parts of the plant, resulting in peat formation.

Basin mangrove forests are characterised by fully grown trees of mangroves that act as nutrient sinks which allow maximum growth. Although the mangroves were spread all over, the thickest mangrove cover occupied an area of about four acres in the middle. The mangroves belonged to only one species, Avicenna marina, growing as bushes as tall as 1.5m. Earlier large trees, as high as 10m or more, would grow in the area but were all cut by locals. Now, only their stumps remain. By Jan Khaskheli, Source The News International