Transitions in Ancient Inland Freshwater Resource Management in Sri Lanka Affect Biota and Human Populations in and around Coastal Lagoons

Abstract

The increasing anthropogenic pressure on natural environments results in impacts that affect tropical forest areas and their biodiversity. Adverse impacts on terrestrial and oceanic environments often compound in the intertidal area, where mangrove forest ecosystems thrive. In tropical coastal areas of many developing countries where people depend on wood and other mangrove forest products and services, forest degradation leads to socioeconomic problems. At the same time, increasing freshwater needs in these areas are expected to cause additional problems. On the basis of remote sensing and ground truthing complemented by colonial archival material from the Dutch East India Company (1602-1800), we report that changes to the historic system of inland freshwater management have increased dramatically in recent times. Hydrological changes, such as interbasin transfers, have resulted in a qualitative ecological and socioeconomic degradation in three coastal lagoons in southern Sri Lanka. Variations in river hydrology have caused changes in the areas suitable as mangrove habitat and, thus, have resulted in an altered distribution. However, increases in mangrove area can mask the degradation of the site in terms of floristic composition, significance of the species, and biodiversity (this effect is termed "cryptic ecological degradation"). It is important that such changes be carefully monitored to ensure biological and socioeconomic sustainability.

An attempt to recover economic losses from decadal changes in two lagoon systems of Sri Lanka through a newly patented mangrove product

“…Although mangrove ecosystems provide outstanding economic uses and invaluable ecological services, they are still decreasing in surface around the world (Kathiresan & Bingham, 2001) and ranked among the most threatened of coastal habitats, particularly those in developing countries in tropical regions (Saenger et al, 1983). Also in Sri Lanka, mangroves are one of the most misused and threatened coastal eco-systems, and recurrently scientists emphasise the need for mangrove conservation (Dahdouh-Guebas et al, 2002, 2005c and for early detection of its degradation (Dahdouh-Guebas et al, 2005a;Dahdouh-Guebas et al, 2005b). This situation is aggravated by the fact that a considerable portion of the country's mangrove lands are privately owned properties (IUCN, 1996(IUCN, , 2000.…”

“…These two lagoons are in the southern coast of Sri Lanka within a distance of 12 km. The cause of the increase in mangrove cover has been traced to the increased freshwater influx as a result of upstream irrigation works (Dahdouh-Guebas et al, 2005b).…”

“…Studies by Jayatissa et al (2002b), Sooriyaarachchci (2004) and Dahdouh-Guebas et al (2005b) on the changes in cover of different plant species or species assemblages (incl. mangroves) by using remote sensing and geographic information systems (GIS) reveal that the area covered by the low saline mangrove Sonneratia caseolaris (L.) Engler had increased dramatically in both lagoons.…”

“…In Kalametiya, the increase went from 4.5 to 139 ha over a 38 year period. The floristic changes suggested a transition of the mangrove environment from saline to low saline conditions as a result of increased freshwater flow (Dahdouh-Guebas et al, 2005b). The freshwater inflows of these two lagoons have increased since the 1960s, with the commencement of two irrigation projects upstream (Udawalawe irrigation scheme and Muruthawela Wewa), which came into operation in 1967 and 1968 respectively.…”

“…The increased freshwater inflows to these two lagoons altered flora, fauna, and water quality, resulting in a decline of lagoon fishery. In the absence of water quality data for the period prior to 1956, the authors conducted questionnaire surveys and hydrological calculations which proved that the salinity had been higher before the upstream irrigation works started (Dahdouh-Guebas et al, 2005b). The same surveys also revealed a decrease in fisher family demography.…”