The Correlation Between Plankton Abundance and Water Quality in Donan River

Planktons have ability to live in aquatic ecosystem, including rivers ecosystem, estuary ecosystem, lake ecosystem and ocean ecosystem. The plankton abundance is estimated by correlation with water quality both of salinity, pH, temperature and others. This research aimed to analysis plankton abundance and to analysis correlation between plankton abundance and water quality. This research was conducted in Donan River using random sampling in 10 stations. The plankton are collected using plankton net no 25 and Lackey Drop Mikrotranset Counting (plankton analysis) and APHA (2005) to analysis water quality. The results showed that the plankton abundance ranged between 524 – 6,406 ind L and best correlation with water salinity had index 0.975.


Introduction
Planktons are a micro and macroscopic organisms that plays an important role as the primary producer of an initial chain of food webs (Yan et al., 2012). Planktons are often used as an indicator of water fertility (Umar, 2003). Plankton consists of phytoplankton and zooplankton (Effendi et al., 2016;Su et al., 2015;Abdulwahab and Rabee, 2015) . Phytoplankton are water plants in waters ecosystem, while zooplankton are aquatic organisms characterized as animals (Gharib et al., 2011;Honggang et al., 2012;Khalifa et al., 2015;Pratiwi et al., 2016;Simanjuntak, 2009).
Basically, plankton is food for other animals. The phytoplankton distribution is influenced by the light availability in waters especially in euphotic zone. The ability to create organic substances causing phytoplankton known as primary producers (Li et al., 2012;Masuda et al., 2017).
The Eastern Segara Anakan Lagoon is an aquatic ecosystem take supply of seawater from the Indonesian Ocean and freshwater supply from many rivers including the Donan River, Sapuregel River, Kembang Kuning River, and other rivers (Hilmi et al., 2015(Hilmi et al., , 2019Sari, 2016). Segara Anakan lagoon has several types of ecosystems including estuary and mangrove ecosystem that has a function as a habitat for plankton life. Phytoplankton in Donan River are utilized by nektorn and fish as feed sources. If plankton is not abundant enough, then the growth rate of plankton will not be able to support fish life as handicap of fish growth which give impact for decreasing of fish abundance. Planktons are an organism's group to live in water surface and weak swimmer. The planktons abundance and diversity are influenced by the physical and chemical of water quality like as sedimentation, water level fluctuations, nutrients, heavy metals, temperature, pH, and oxygen content (Heriyanto, 2012;Nagelkerken et al., 2008;Siddiqui et al., 2008) . Whereas zooplanktons are animal organisms that life movements depend on water currents and as a life pillars of marine bio ecosystems because these plankton occupy the basic level of the aquatic food chain (Herbert, 2003;Nagelkerken et al., 2008). Most zooplankton are herbivores and as food for fish. The potential of zooplankton and phytoplankton can be used as an indicator of water fertility.
In general, the potential of plankton consisting of zooplankton and phytoplankton in Segara Anakan Timur is estimated has an abundance of between 500 -6000 ind / L (Kristian, 2019). This research aimed to analysis plankton abundance and to analysis correlation between plankton abundance and water quality.

Study Area
This reseach was conducted in Donan River on 10 stations. The coordinates of site research can be seen on Figure 1.

Research Variables
Research variables are plankton abundance and biodiversity, temperature, water salinity, water pH, nitrate, phosphate, dissolve oxygen, and ammonia.

Sampling Technique
The sampling technique of this research using purposive sampling in Donan river. Purposive sampling using mangrove density as sampling indicator.

Water quality analysis
Water quality analysis in study area using APHA (2005) method will be shown on Table 1.

Plankton Analysis
Water Sampling of 100 liters on the water surface using a 10-liter bucket then filtered using No. plankton net. 25 with a mesh size of 60 μm. Water samples collected in the plankton net container are taken, and transferred into a 50 mL sample bottle. Then add 40% formalin solution to 4% using a dilution formula, and lugol solution as much as 2 drops, then labeled paper, cool in an ice box, then observed in the laboratory. Dilution formula: N1x V1 = N2 x V2 where: N1 = desired formaldehyde concentration (4%) N2 = available formaldehyde concentration (40%) V1 = water volume in the sample bottle (30 mL) V2 = formalin volume in bottles needed (mL) Then water sample was observed by a microscope with a magnification of 10×10 as many as 30 visual fields with 3 repetitions. Previously the sample bottle is homogenized and evenly distributed, after that is taken using a pipette. Then the plankton was identified by (Edmonson, 1966;Sachlan, 1982). Calculation of the number of phytoplankton are calculated using the modified formula from the Lackey Drop Mikrotranset Counting (APHA (American Public Health Association), 1989) that is potential of plankton (individuals L -1 ) = N x F, where: The plankton diversity index is calculated using the Shanon Wiener equation. This calculation illustrates plankton abundance in a community (Krebs, 1989).

Plankton abundance and diversity in the Donnan River
Plankton abundance in Donan river is 524 -6,406 ind L -1 following the treatment and environmental conditions of water ecosystem. The highest abundance is station 9 with abundance 6,406 ind L -1 , while station 8 with the smallest abundance with value is 524 ind L -1 . Plankton abundance in Donan river is relatively low compared to Wiyarsih (2019) research which has abundance 29,888 ind L -1 ( Table 2).
The results of the research showed that Donan river had 15 plankton genera divided into 10 genus of phytoplankton and 5 genera of zooplankton.  Wiyarsih et al., (2019) has argument that the condition of estuary is very influential for plankton abundance especially potential of nitrates and phosphates as main factor to support phytoplankton growth. Sihombing & Aryawati (2013) also notes potential of nutrients such as nitrates and phosphates in the waters have high correlation with abundance of phytoplankton and zooplankton.

Water Quality in Donan River
The physical of water quality were salinity, temperature, pH of water, and the chemical of water quality were DO, water nitrate, aquatic orthophosphate, aquatic ammonia, and also dissolved oxygen can be shown on Table 3. The first factor is water salinity as the total of ion concentration in water (Boyd, 1988). Brackish waters has water salinity between 0.5-30 ppt (Effendi, 2003;Effendi et al., 2016) Salinity can affect oxygen levels in the waters, and has negative correlation with the dissolved oxygen (Karl & Church, 2017;Makmur & Fahrur, 2011;Tsuji & Montani, 2017).
According to (Huang et al., 2003;Xiao et al., 2019) water salinity distribution is influenced by various factors such as the pattern of water circulation, evaporation, rainfall, and river flow. Salinity in Donan river has ranges 18-29 ppt and still available to support the plankton growth because plankton can grow on 10-30 ppt of water salinity (Yuliana, 2017). The second factor is the temperature, the temperature in Donan rivers had range between 26.33-30 °C. This range is in the   optimal range for plankton, because the optimal temperature to support plankton growth and life is 20˚C -30˚C (Yuliana & Ahmad, 2017). The third factor is potential Hydrogen (pH), the water pH in Donan river has ranges between 6.67-7.07 which is optimum standard to support plankton life. Keputusan Menteri Lingkungan Hidup (MENLH), 2004) notes that water pH quality to support marine biota has ranges from 7-8.5. Lamury (1990) give categorizes the levels of water fertility are pH range 5.5-6.5 (unproductive water), pH 6.5-7.5 (productive water), and pH 7.5-8.5 (very productive). Makmur (2011) also notes that most aquatic biota has sensitive to pH changes and has normal ranges between 7-8.5 (Makmur & Fahrur, 2011).
The fourth factor is nitrate as the potential of nitrogen and the main nutrient to support the growth of plants and algae which has characteristic very soluble and stable. The potential of nitrogen in Donan river has ranges between 0.19 to 0.42 mg L -1 . The potential of nitrate is influenced by water current carrying nitrate and abundance of phytoplankton (Shiau et al., 2017;Simanjuntak, 2009). The potential of nitrate levels between 0.3-0.9 mg L -1 was sufficient for the organism's growth and potential of nitrate > 3.5 mg L -1 as critical factors of waters ecosystem. The fifth factor is Orthophosphate as an inorganic phosphate show potential of phosphorus (P) dissolved in water. Orthophosphate can be directly utilized by phytoplankton and aquatic plants (Patty, 2015). Phosphate levels in Donan river has ranges between 0.10 -0.19 mg L -1 . Keputusan Menteri Lingkungan Hidup (MENLH), (2004) notes phosphate standard is 0.015 mg L -1 , then Patty, (2015) and Huang et al., (2003) note 0.087 mg L -1 as the upper limit of uncontaminated water.
The six factor is ammonia as the breakdown of organic nitrogen and inorganic nitrogen which comes from the decomposition of organic matter and biota feces by microbes and fungi. The potential of ammonia in Donan river has ranges between 0.022 to 0.01 mg.L -1 . The low concentration of ammonia in a water is good factor to support biota life. But, the concentration of ammonia can be shown as fertilize the waters with level less than 2 mg L -1 will (Makmur & Fahrur, 2011). The last factor is Dissolved oxygen (DO) as an important factor for the biota or the waters themselves. Dissolved oxygen comes from a process of diffusion from air and organism's photosynthesis in water ecosystem (Heriyanto, 2012). According to Patty, (2015) that the level of dissolved oxygen in a waters will decrease due to the process of decomposition of organic matter, respiration and inhabitation of reaeration. Dissolved oxygen levels in Donan river has ranges between 5.21-5.8 mg L -1 . Keputusan Menteri Lingkungan Hidup (MENLH), (2004) notes that DO is more than 5 mg L -1 (good standard) but less than 3 mg Lwill cause organism death (Hilmi et al., 2019;Kanwilyanti et al., 2013;Pan et al., 2017;Patty, 2015).

The correlation between plankton
abundance and water quality The correlation between water quality with plankton abundance can be seen in Table 4. The correlation showed that water salinity has the highest correlation with score 0.975 and temperature has lowest correlation with score 0.046. While the regression equation model for plankton abundance with water quality factors also can be shown on Table 4.