Trophic condition of Madu Ganga Estuary, a Ramsar Wetland in Sri Lanka

Abstract

Madu Ganga Estuary, which extends for 915 ha is a Ramsar wetland in the south-

western coastal region of Sri Lanka. This slow flowing water body is rich in biodiversity with

248 vertebrate species which include 20 endemics and 303 plant species. About 10% of the

111 species of birds are winter migrants. Cinnamon and paddy cultivations form the

dominant land use type in the surrounding area and at present, a nature based tourism

industry is also developing rapidly at the estuary due to its ecological and aesthetic

significance. In addition, resident traditional fishermen are involved in commercial fishing

activities using traditional gear such as Kraals. The present study aimed to figure out the

trophic condition of this important wetland. During the study period from March to

November 2014, the mean values for physicochemical parameters were found to be as

follows; Depth: 1.89 m; Secchi Depth (SD): 0.91 m; Temperature: 30.8 ˚C; Total Dissolved

Solids (TDS): 8.8 g/L; Salinity: 8.29 g/L; pH: 7.2; Dissolved Oxygen (DO): 6.79 mg/L;

Biological Oxygen Demand (BOD 5 ): 1.40 mg/L; Nitrate-N: 0.2 mg/L; Total dissolved

phosphorous: 0.09 mg/L and Total Phosphorous (TP): 0.17 mg/L. The TP values suggest that

the trophic condition of this highly ecologically and economically important wetland is

eutrophic. Excess and indiscriminate use of fertilizer in the watershed area and soil erosion

appear to be the major reasons for this condition, which may be controlled by educating

farmers on repercussions of applying excess amounts of fertilizer and ensuring that only the

recommended levels are applied. Remote Sensing methods can also be used in nearby

agricultural fields to detect the areas where deficiency symptoms are present and fertilizer

can be applied only to those regions. In addition, erosion control methods can also be applied

to retain the fertilizer within the agricultural fields without being washed into the estuary with

storm water.