STUDY THE EFFECT OF SALINITY AND NUTRIENTS FOR THE GROWTH OF Najas marina AND ITS IMPACT TO AQUATIC BIODIVERSITY IN MADU GANGA RAMSAR WETLAND IN SRI LANKA

Abstract

Madu Ganga is the latest addition to the Ramsar International Convention of Wetlands. Najas marina is an alien aquatic plant and 0.5 m long that are often branched toward the upward portion of the plant. The objective of the study was to study the impact of salinity and nutrients for the growth of Najas marina. Samples were collected for analysed water quality parameters from March, 2006 to January 2007 in the lagoon. Mapping was done using Garmin GPS map 76CS and Arc GIS used to developed maps.Mean nutrient such as, nitrate nitrogen, ammonia nitrogen and orthophosphate concentrations were observed 0.26 ± 0.3 mg/l, 0.057 ± 0.04 mg/l, and 0.354 ± 0.77 mg/l subsequently. Mean salinity variation in bottom and surface are 6.38 ± 6.65 ppt and 4.31 ± 4.68 ppt. Higher bottom salinity was observed in location number 02 (near to sea mouth) and Najas marinawas not present in the area. Najas marina was also not recorded in upper part of the lagoon and fresh water streams studied. High density of Najas marina plants were observed in sampling location 07, 08 and 09, because of the high nutrient concentration flowing through feeding tributaries. More than 25 % of lagoon area was covered by Najas marina.

Environmental factors contributing to the invasion of <em>Najas marina</em> L.in Madu Ganga estuary, a Ramsarwetland in Sri Lanka

“…Similar observations have been made by Amarathunga et al (2010) in studies carried out in 2006-2007 in this wetland. However, present study indicates that the mean values of most of the physicochemical parameters, namely surface water temperature, TDS, Salinity, pH, BOD5, TDP and TP were not significantly different among the 10 sites studied (p>0.05).…”

“…During the present study, higher values than this were reported in 3 sites namely sites 1, 3 and 6. From March to June, the mean nitrate-N content was higher than that reported by Amarathunga et al (2010). During the present study, high mean salinity of 17.5-19.6 g L in July.…”

“…It is well known that the amount of fertilizer used in agricultural activities in many parts of Sri Lanka are very much higher than the required level, so that excess fertilizer are leached into water bodies increasing their nitrate-N and TDP levels (Sangakkara and Wijeyaratne 2015). Amarathunga et al (2010) reported that N. marina was not present in the upper reaches of the estuary where salinity is zero and also near to sea mouth where salinity is very high. It appears that intermediate levels of salinity recorded in the present study favours the growth of this invasive species.…”

“…This was shown by the cluster analysis too as these sites were separated only at a similarity level of 94% (Figure 2). Amarathunga et al (2010) reported that mean nitrate-N content of the estuary to be 0.26 mgL -1 . During the present study, higher values than this were reported in 3 sites namely sites 1, 3 and 6.…”

Lagoons of Sri Lanka: from the origins to the present

“…Being located in the wet zone, draining a small watershed and connecting to the sea through a narrow winding channel 4.6 km long, Madu Ganga also showed a marked zonation in salinity (Table 4). At the marine entrance area salinity ranged from 4.2 to 28 ppt while it was 4-10 ppt for the center of the lagoon and 0-4 ppt towards the freshwater inflow area (Amarathunga et al 2010). Madu Ganga also depicts a typical salinity gradient for a small, seasonally tidal lagoon with a distinct zonation.…”