COMPARISON OF WATER AND SEDIMENT QUALITY PARAMETERS INFLUENCING MANGROVE ECOSYSTEM
Population increase coupled with the destruction of mangrove forest through human activities such as deforestation, conversion of mangroves to agricultural land, sewage discharge and effluent from industries has negatively impacted the environment and led changes in the water (Hauff et al., 2006; Smith, 1992; Lugo and Snedaker, 1974) and sediment quality of mangrove ecosystem. Mangaluru (12.87°N 74.88°E) is one of the urban coastal cities in Dakshina Kannada district of Karnataka. It has a population of 5,55,244 (as per 2011 estimated) and area of 132.45 km2. The major rivers Netravati and Gurupura forms an estuary and drain into the Arabian Sea. Destruction of the mangroves on the river banks and in the estuarine area had led to decrease in mangrove area. Water and sediment quality parameters were monitored from two sites in Gurupura river a degraded ecosystem in which mangroves were planted and another a non-mangrove area. In addition to this a natural mangrove area in less disturbed habitat with better diversity of mangroves in Hegemadi situated on the banks of Shambhavi river was selected. Principal Component Analysis (PCA) was carried out to ascertain the most important parameters influencing the stations selected in combination as well as separately in mangroves planted area (St-1), a non-mangrove habitat (St-2) and a natural mangrove ecosystem (St-3). Water and sediment quality data were collected for a period of 6 years (2011-2016) on monthly basis from the stations. Fig. 1 depicts the PCA biplot of all parameters estimated for the three stations under study.
It was seen that the influence of salinity was the highest in the system and diagonally opposite to that of nutrient silicate, indicating that rainfall and consequent river discharge contributed to the growth of mangroves. Moreover, rainfall, silicate, nitrate and phosphate were correlated. In the natural mangrove ecosystem (St-3) the major contributors were in the order Salinity (24.9%) >Rainfall (16.7%)>Silicate (12.1%)>pH (8.7%)> Chlorophyll c(7.3%)> Nitrate (6.3%)> Chlorophyll a (5.3%)> water temperature(3.9%)> Chlorophyll b (3.3%). In St 1 and St 2 the contribution of Chlorophyll was not observed indicating lesser productivity due to disturbed ecosystem. It was seen that pH was observed to be diagonally opposite to rainfall, silicate, nitrate and phosphate in all the three stations indicating that lesser river discharge could negatively influence the ecosystem. The Sand % and Silt % was also observed to be diagonally opposite in all the three stations. A diversity rich mangrove ecosystem had more silt as the roots help retain the turbid water during monsoon. June, July and August were the months observed contributing to the growth of mangroves.
