Dynamic study on the effect of calcium hydroxide and sodium bicarbonate treatment on the N/P ratio and plankton abundance

The development and growth of plankton in water is influenced by nutrients like nitrogen and phosphorus, which can be determined by the N/P ratio. Excess nutrients in water can lead to Harmful Algae Blooms (HABs). The application of Ca(OH)2 and NaHCO3 in water can control the nutrient elements and plankton abundance. This study was conducted to determine the dynamics of the N/P ratio value and plankton abundance through the application of a (Ca(OH)2) and (NaHCO3) dose of 1 ppm in a fish pond using the descriptive method. Before the application, the pond’s nitrogen range was 1.04 – 1.06mg/l. After application, this increased to 1.07 – 1.39mg/l, while the phosphorus was 0.29 – 0.33mg/l before application. After the administration, the phosphorus increased followed by a decrease ranging from 0.30 to 0.62mg/l and 0.62 to 0.09mg/l respectively. The N/P ratio value before administration was 3.15 – 3.68mg/l and after the application, the N/P ratio decreased to an average value of 1.73 on day 4 followed by a subsequent increase to 14.70 on day 7. The average total plankton density from the three points was 789,583 ind/l before application. After the application, this decreased to 624,166ind/l. In conclusion, the application of Ca(OH)2 and NaHCO3 can stabilize the N/P ratio and decrease the total plankton density.


Introduction
The optimal utilization of resources in an aquatic environment requires the management of the environment itself, including the function of the ecosystem in the water. The interaction between the components of the ecosystem will affect the existence of the nutrients in the water. Plankton are a major component of the food chain in an aquatic environment, hence the presence of nutrients and plankton is an indicator of water fertility. Therefore, plankton abundance in water has an important role [1].
The applied products had a concentration of 1 ppm and the dose used was 815.31 gr. The commercial products consisted of a water-soluble white powder. The application of the products was done by first diluting the products with water, followed by an even distribution throughout the pond.

Water quality measurement
The measurement of the water temperature and dissolved oxygen was done using DO meter YSI 550 A, the pH was measured using a Senz pH pen and the pH paper range was 6.5 -10 Merck KGaA. The nitrite was measured with the use of the spectrophotometric method with a wavelength of 543nm based on SNI06-6989. . Nitrate was measured using spectrophotometry with a wavelength of 410nm based on SNI06-2480-1991, and the phosphate was measured using a spectrophotometer with a wavelength of 880nm based on the 'Standard methods' 20 th edition 1998 test kit was used for ammonium. COD was determined through the closed reflectance method involving a spectrophotometer with a wavelength of 420nm based on SNI 6989.72: 2009. BOD was determined through the Winkler titration method based on SNI6989.2:2009 and the plankton observation was carried out using hemocytometers and plankton identification books.
The water sampling for the testing of nitrite, nitrate, ammonium, phosphate, BOD and COD was carried out using the "closed bottle" principle. The bottle was lowered in water at a certain depth with the state of the bottle being closed. The bottle cap was opened while in the water to allow for the entry of the needed water sample into the bottle. The water quality of the sample was maintained at a temperature of 4 o C since the water quality of the samples may decrease depending on the placement and duration of storage [6].
The temperature measurement, dissolved oxygen, pH and plankton abundance were measured twice a day at 05.00am WIB and 13.00 respectively, since the lowest and highest temperature, pH and dissolved oxygen were recorded in those periods at the ponds. The three parameters fluctuated each day due to several factors such as the weather [7]. The measurement of the nitrites, nitrates, phosphates, ammonium and ammonia and the measurements of COD and BOD were performed every 3 days.

Sampling method and observation of plankton abundance
Plankton sampling was done using a plankton net with a mesh size of 20 microns, since the size of phytoplankton (microplankton) is usually between 20 -200 microns. The use of a plankton net with such a mesh size means that it can be used to filter phytoplankton like diatom and dinoflagellate as well as zooplankton. In addition, with the above mesh size, the water can still go out through the holes of the plankton net [8].
The plankton sampling in shallow waters with a depth of ± 1m was done using a container (bucket) whose volume was known. The volume of the plankton water samples taken can be adjusted to the water conditions in the following order; very fertile waters ± 5 liters, moderate waters ± 30 liters and poor waters ± 100 liters. In this research, 50 liters was used for the water samples [9].
The water samples obtained were filtered using a plankton net and a sample volume of 100ml was obtained. The date, position and depth of the pond samples were labeled. The plankton samples obtained were immediately observed with the use of a binocular microscope with a magnification 100 -1000x.The plankton were then preserved with 4% formalin based on the method that described that plankton samples can be preserved using 4% formalin and that 4% formalin can also be used to stop the plankton from moving, especially zooplankton [8]. The main parameters in this study were the N/P ratio and plankton abundance. The supporting parameter was the water quality data such as pH, DO, temperature, COD and BOD during the research.

Data analysis
To determine the dynamics of the N/P ratio value due to the administration of calcium hydroxide (Ca(OH)2) and sodium bicarbonate (NaHCO3) in the pond, descriptive data was used. An analysis was conducted on the plankton abundance data including plankton identification, the plankton density index, plankton similarity index and plankton dominance index.

Nitrogen dynamics (N)
The results of the nitrogen values on day 0 in the pond before the addition of Ca(OH)2 and NaHCO3 had an average value of 1.05mg/l obtained from points 1, 3 and 5. After the application of Ca(OH)2 and NaHCO3, the average nitrogen value of the three points increased to 1.07mg/l on day 4. On the 7th day, the average nitrogen value increased to 1.39mg/l.
The increased nitrogen value was due to the amount of organic matter in the pond resulting in the binding of Ca 2+ ion to the phosphate ion; deposition occurred to reduce the phosphorus in the water. The decline of phosphorus in water resulted in a decrease in the total plankton density in the pond as an increase in the organic matter can increase the nitrogen in the water. One of the causes of the increased nitrogen in water was because of the increased organic matter in the water [10]. The dynamics of the nitrogen values before and after the administration of Ca(OH)2 and NaHCO3 have been presented in Table 1. 1,09 2 1,1 The results of this research indicate that the nitrogen value in the research fish pond of FMF-Airlangga before and after the administration of Ca(OH)2 and NaHCO3 fell within optimal range for fish farming activities since the range was 1.06-1.38mg/l and the ideal nitrogen range for aquaculture activities ranges from 1 -2 mg/l [11].

Dynamics of phosphorus (P)
The results of phosphorus in the research pond of FMF before application of Ca(OH)2 and NaHCO3 on day 0 was 0.29-0.33mg/l at the three points. After the administration of the two compounds, there was an increase in each point on day 4 which led to an average phosphorus of 0.62mg/l. The increased phosphorus in the pond was caused by the supply of bicarbonate ions through sodium bicarbonate, hence the bicarbonate ions are inorganic carbon sources that can be converted into carbon dioxide by phytoplankton. These ions become a carbon source in the process of photosynthesis which is an important process in the formation of organic matter in water [8].
On the 7th day, the average phosphorus from the three points decreased to 0.09mg/l. This decrease was due to the supply ofCa 2+ ion from calcium hydroxide post-application of calcium hydroxide; this can lower the amount of phosphorus in the water. The above result is in accordance with the statement by Budi [4], stating that the administration of calcium hydroxide can lower the phosphorus in water. The decrease of phosphorus through calcium hydroxide can be explained by a chemical reaction as follows: The results of the dynamics of the phosphorus values before and after the administration of Ca(OH)2 and NaHCO3 have been presented in Table 2. 0.07 0.14 0.07 Based on the results of this research, the value of phosphorus in the studied fish pond before and after the application of Ca(OH)2 and NaHCO3 fell within the optimal range for fish farming as it had an average value of 0.34mg/l. According to [12], the maximal phosphorus value for fish cultivation should be 1mg/l, hence the phosphorus in the FMF pond was within the optimal range for fish farming.

N/P ratio dynamics
The average N/P ratio value in the pond before Ca(OH)2 and NaHCO3 administration at points 1, 3 and 5 was 3.49, whereas after the administration of Ca(OH)2 and NaHCO3, on the 4th day there was a decrease in the dynamic of the N/P ratio which resulted in a ratio of 1.74. The next observation was an increase in the N/P ratio which recorded 14.71 as the average ratio from the three study points.
The decrease and increase of the N/P ratio in water is influenced by the phosphorus content in the water. This is in accordance with the opinion of [13], which states that the phosphorus in water is a limiting factor for the N/P ratio. The N/P ratio is derived from the calculated total nitrogen (N) divided by the total phosphorus (P). The greater the N/P ratio value, the smaller the level of phosphate and vice versa. Hence, the higher levels of phosphate in water increases both the diversity and dynamics of plankton abundance in waters.
The dynamics of the N/P ratio value in the research fish pond of FMF before and after the application of Ca(OH)2 and NaHCO3 have been presented in Table 3. It was established that the N/P ratio in the research fish pond of FMF before and after the Ca(OH)2 and NaHCO3 administration was dominated by Blue Green Algae and Green Algae phytoplankton. which were in an N/P ratio that ranged from 6.41 -6.88. According to [13], the N/P ratio in the water influenced the type of plankton that dominated, the water's composition and also that an N/P ratio above 20 will be more dominant in diatomaceous planktons. An N/P ratio of the 10th range will be more dominant in green plankton (chlorella) and an N/P ratio below 10 is a conducive environment for dark green-pigmented plankton (BGA).
The total density of the plankton at 05.00am before the supply of Ca(OH)2 and NaHCO3 at points 1, 3 and 5 were 1,103,125 x 10 4 ind/l, 578.125 x 10 4 ind/l and 678,500 x 10 4 ind/l respectively. The dominant plankton in the pond was phytoplankton such as the Chlorella species, Oocystis species, Polyedrium species, Dinophysis miles and Glocotrichaechinulata. After the addition of Ca(OH)2 and NaHCO3, the total plankton density in the pond at 05.00am each day experienced a change by either an increase or decrease.
The total plankton density at 13:00 before the Ca(OH)2 and NaHCO3 administration at points 1, 3 and 5 was 437,500 x 10 4 ind/l, 206,250 x 10 4 ind/l and 425,000 x 10 4 ind/l respectively. The dominating plankton in the pond was mainly phytoplankton such as the Chlorella species, Gonyanulax polyderm, Calothrix species and Glocotri chaechinulata. The total plankton density also increased and decreased at 13.00 after the Ca(OH)2 and NaHCO3 application.
The decrease in plankton density was due to the Ca(OH)2 compounds, since they can bind the phosphorus compounds in the water [14]. On the 4th day, the phosphorus content increased due to the high intensity of rainfall. This is since rainfall has the ability to stir the pond bottom or sediment. The phosphorus in water can only be found in basic soils, sediments, rocks and organic matter. Even when the phosphorus content in the water increased, the phosphorus content was only used a little by the phytoplankton because the phytoplankton experienced death due to the high rain intensity and phosphorus binding at the start of the study. This is in line with [15].
The increase in the above density occurred due to the dominance of the zooplankton group of plankton. The dominance is caused by the binding of the phosphorus compounds in the water by calcium hydroxide. This was evidenced by the phosphorus content on the 7th day, which declined. The rainy season can also increase the dominance of the zooplankton because the penetration of sunlight in the water was reduced during this period. Therefore, the presence of phytoplankton was replaced by zooplankton because there was less solar energy to be used by the phytoplankton to carry out photosynthesis [16].
The Diversity Index (H) values before the addition of Ca(OH)2 and NaHCO3 at 05.00am at points 1, 3 and 5 were 0.75, 0.29 and 0.57 respectively, while at 13.00, the same points 1, 3 and 5 recorded 0.69, 0.45 and 0.65 respectively. The Diversity Index values after the administration of the two products at 05.00am experienced an increase and a decrease ranging from 0.24-0.66 and the same at 13.00, which also experienced an increase and decrease ranging from 0.35 to 0.66. Since the diversity and community stability of the three observation points was all lower than 2.3062, based on the Shannon-Weaver Diversity Index, they were classified in the low categories with low species counts and with a low distribution of individual numbers for each species.
The Uniformity Index (E) value before the application of Ca(OH)2 and NaHCO3 at 05.00am at points 1, 3 and 5 was 0,38, 0,26 and 0,41 while at 13.00, the uniformity index value of points 1, 3 and 5 were 0,38, 0,41 and 0,4. The Uniformity Index value after the administration of Ca(OH)2 and NaHCO3 at 05.00am also experienced an increase and decrease, ranging from 0.3 -0.42 and at 13.00 also, there was an increase and decrease ranging from 0.32 to 0.42. Based on the Uniformity Index of [6], the spread of the number of individuals per species at all three observation points was close to 0.0 and this spread of individuals can be said to be unequal. There is a tendency for dominance by certain types.
The Dominant Index (C) values before the Ca(OH)2 and NaHCO3 administration at 05.00am at points 1, 3 and 5 were 0.96, 0.98 and 0.96 respectively. Meanwhile at 13.00, points 1, 3 and 5 showed 0,94, 0,98 and 0,96 respectively. The Dominant Index values after the supply of Ca(OH)2 and NaHCO3 at 05.00am increased and later decreased in the range of 0.96 -1; this is the same as the case at 13.00 where it increased and decreased with a range of 0.94 -1. Based on the Simpson Domination Index, there are species that dominate others within the phytoplankton and plankton community structure at all three observation points (close to 1.0) in unstable conditions [6].

Supporting water quality parameters
The water quality parameters measured included temperature, dissolved oxygen, nitrite, nitrate, ammonium, ammonia, phosphate, BOD and COD. The results of the measured water quality parameters have been presented in Table 6 below.  Table 6. Dynamics of the water quality support before and after the application of Ca(OH)2 and NaHCO3.
The temperature dynamics at 05.00am during the study at points 1 and 5 ranged from 26.9 -28.6 o C, while point 3 ranged between 26,9 -28,7 o C. At 13.00, the temperature at points 1 and 5 during the research was said to be around 28,1 -30 o C, and point 3 was between 28,1 -29,7 o C. The above temperature range can be said to be optimal for aquaculture since the optimal temperature range for fish cultivation is 15 -35 o C, according to [17].
The dissolved oxygen content in the pond during the research was equally within the optimal limit for aquaculture activity, especially for the plankton. This is in accordance with the submission of [18], stating that plankton can flourish at oxygen concentrations greater than 3mg/1.
The nitrite and nitrate levels in the research pond during the study also fell within the recommended range for fish cultivation since it was in agreement with [19], who reported that the