The coastal of Lhok Seudu are the coastal that become the place of fishing activity and the cultivation of floating net cages. However, such activity may lead to the entry of nitrate and phosphate elements into the aquatic column because it can increase the chlorophyll-a content in the water and determine trophic status [1-3].

Chlorophyll-a is a pigment in all phytoplankton organisms that can perform photosynthesis and the presence of chlorophyll-a is strongly influenced by the availability of nutrients nitrate and phosphate so as to determine the level of primary productivity of a coastal. The high concentration of chlorophyll-a distribution is strongly related to oceanography condition in a coastal. The content of chlorophyll-a is analyzed by determining the nitrate and phosphate content in the coastal as the macronutrient for phytoplankton [4-6].

Information on the availability of chlorophyll-a in Lhok Seudu coastal is still very limited. This study aims to determine the concentration of nitrate and phosphate to the abundance of chlorophyll-a.

Location

Data collection was conducted in May 2017 in Lhok Seudu coastal, Aceh Province (Latitude: 5°21’4.7”, Longitude: 95°14’14.6”) which is divided into 3 stations with 10 meters distance each station by using purposive sampling method to determine the point of research location (Figure 1).

Figure 1: Map of Lhok Seudu Coastal, Aceh Province.

Material

Materials used are UV-Vis Shimadzhu UV-1700, filterphotometer PF-11, universal bettich centrifuge 320, refractometer, pH meter, and thermometer, GPS, dark bottle, vacuum pump, Whatman filter paper GF/C 42 μm, filtering flask and acetone 90%.

Analysis of chlorophyll-a

1 L water sample was filtered using Whatman 42 GF/C 42 μm filter paper. The filter paper containing chlorophyll-a is folded four times until it becomes a small fold and then inserted into aluminum foil. The chlorophyll-a sample folds are stored in the refrigerator at 4°C for a day.

The filter paper was crushed by adding 5 mL of 90% acetone and kept back in the refrigerator at 4°C for an hour. The extracted sample was fed into a bettich 320 universal centrifuge at 3000 rpm for 30 min [7].

Determination of chlorophyll-a concentration using Shimadzu UV-1700 UV-Vis at the Chemistry Laboratory of the Faculty of Teacher Training and Education, Syiah Kuala University. Nitrate and phosphate concentration were determined using a filterphotometer PF-11 at the Marine Chemistry Laboratory of the Faculty of Marine and Fisheries, Syiah Kuala University. Calculation of the chlorophyll-a concentration is calculated using the equation:

(1)

Information:

Va: Volume of acetone (10 mL);

V: Water volume of filtered sample (mL);

D: Diameter of cuvet (1 mm);

Ca: (11.6 × E₆₆₅)-(1.31 × E₆₄₅)-(0.14 × E₆₃₀);

E: Absorbance where wavelength (corrected with 750 nm wavelength).

The results showed that the concentration of chlorophyll-a in Lhok Seudu coastal ranged from 33 to 22 μmol/L^-1 and total nitrate and total phosphate concentrations ranged from 1310 to 1150 μmol/L^-1 and 86 to 73 μmol/L^-1 (Table 1). The presence of chlorophyll-a is strongly influenced by the supply of nutrients originating from the mainland through the flowing water into the coastal [8-11].

Table 1: Chlorophyll-a concentration.

The highest concentration of chlorophyll-a 33 μmol/L^-1 was found at station 1 whereas the lowest concentration was 22 μmol/L^-1 at stations 3. The chlorophyll-a concentration at station 1 was suspected due to the influence of nutrient supply that settled at the pond cultivation location entering the water column so that the nitrate concentration of 1310 μmol/L^-1 makes the growth of chlorophyll-a to be optimum compared with the growth of chlorophyll-a at stations 2 and 3 [12-14].

Overall, the average concentration of chlorophyll-a at 3 stations is closely related to the presence of nitrate and phosphate elements. A mean concentration of chlorophyll-a indicates that trophic status in Lhok Seudu coastal belongs to the eutrophic category (Table 2) [15-17].

Table 2: Classification of Trophical status.

The presence of nitrate and phosphate elements greatly affects the abundance of chlorophyll-a. Total nitrate concentrations ranging from 1310 to 1150 μmol/L^-1 may be associated with total phosphate concentrations ranging from 86 to 73 μmol/L^-1 (Figure 2). The presence of phosphate nutrients is thought to be originating from land during rain and human activities, especially detergents and wastes coming from the environment so that Lhok Seudu coastal are in very fertile categories [18-21].

Figure 2: Relationship of chlorophyll-a to nitrate and phosphate concentration.

The results showed that the chlorophyll-a concentration at station 1 ranged from 33 to 22 μmol/L^-1, total nitrate and total phosphate concentrations ranged from 1310 to 1150 μmol/L^-1 and 86 to 73 μmol/L^-1. The highest concentration of chlorophyll-a 33 μmol/L^-1 was found at station 1 whereas the lowest concentration was 22 μmol/L^-1 at station 3. Based on chlorophyll-a concentration, total nitrate and total phosphate indicated as eutrophic coastal.

Thanks to the Chemistry Laboratory of the Faculty of Teacher Training and Education, Syiah Kuala University and Laboratory of Marine Chemistry, Department of Marine Science, Faculty of Marine and Fisheries, Syiah Kuala University.