As described and discussed in section 1.2, the disposal of river mud has polluted the river water supply to the shrimp ponds. As a result, the aquaculture community of Sidoarjo has become more aware of the importance of the quality of the river water used for their ponds.
Based on participant observation of the daily activities of the aquaculture farmers in managing their ponds and lands during field work between December 2012 and April 2013, the research recorded a good practice of shrimp farmers in filtering river water.
The farmers who were practicing filtering river water were identified as previously being partners of the PT ATINA. This is significant for two reasons: first the degree of success in filtering river water also contributes to providing better water for the
110 shrimp, and second the role of PT ATINA in providing technical assistance also contributes to the farmers’ skill in conducting better aquaculture technique.
5.4.2.1 Biowater filter
Biowater filtration means the use of living vegetation to filter river water. There are at least three species used for filtering the water. The first is Rhizophora spp, which is commonly known as the real mangrove. This type of mangrove has very long roots that penetrate through the mud and elevate the plant above the water. Farmers usually plant this mangrove along the canal that connects the river with the ponds’
water provision (Photo 5.2). The submerged roots absorb pollutants contained in the river water. Several farmers in the control group indicated in informal interviews that they used this type of mangrove as a bio filter of river water. Farmers use the Rhizophora spp for two types of filter methods, the straight and the meandering.
These methods will be discussed in subsection 5.5.
The second species is the Salvinia Molesta; the farmers plant the vegetation in the canal and the water provision area as a water filter. Then the filtered water is distributed to the cultivation pond and discarded water (after use in cultivation pond) goes to the treatment ponds. The Salvinia Molesta has the ability to absorb pollutants such as heavy metals from the river water. On the other hand, there is a disadvantage of using Salvinia Molesta in aquaculture in that it grows rapidly and is able to reach up to 400 tonnes of wet weight per hectare, and can invade the ponds. As a result, many farmers consider it to be a weed in the wetland.
111 Photo 5.2 The Irrigation Canal heading to Shrimp Ponds in Sekardangan
Credit Photo: Author, 2013
The third vegetation used is Eichhornia Crassipes. Eichhornia Crassipes is known as water hyacinth or enceng gondok (Bahasa). Eichhornia Crassipes has the ability to absorb approximately 60-80 percent of nitrogen (Fox, Struik, Appleton, & Rule, 2008) and eliminate approximately 69 percent of potassium from polluted water (Zhou et al., 2007). Eichhornia Crassipes is used as a biological filter for absorbing heavy metals.
Furthermore, Eichhornia Crassipes has other potential commercial benefits as raw material to feed live stock such as cattle, goats, sheep, ducks, and tilapia. It is also used for the production of fibreboard, materials for paper production and, most importantly, water purification (A. Bhattacharya & Kumar, 2010). Interestingly water hyacinth has the potential to be used as a component in producing biogas (A.
Bhattacharya & Kumar, 2010; Gutierrez, Ruiz, Uribe, & Martinez, 2001; Lindsey &
Hirt, 1999).
112 Similar to the Salvinia Molesta, Eichhornia Crassipes has several disadvantages.
This water plant has the ability to grow fast (Jafari, 2010; Parolin, Rudolph, Bartel, Bresch, & Poncet, 2010; Song & Kim, 2013) which causes water blockage due to the density of this plant. In addition, dense concentrations of water hyacinth can hinder the oxygen supply for fish and shrimp. This was present in most of Sidoarjo before the mud volcano.
5.4.2.2 Biological water indicators
Besides using living vegetation, farmers also use aquatic animals such as Green Mussel (Perna Viridis), Mangrove Snail (Telescopium Telescopium L), and Scylla Serrata or Mangrove Crab. These animals are used for filtering or absorbing hazardous material from the water and as a biological indicator of water pollution.
For example, green mussels suck the water for their digestion process. While the green mussels digest, they filter the water. Mussels can filter various contaminants such as heavy metals from pond water.
Mangrove snail or Telescopium Telescopium L has a similar digestion process to green mussel or perna viridis. The shell and soft tissues of Telescopium can be considered as a potential indicator of copper, zinc, and lead (Yap et al., 2009). The shrimp ponds that are equipped with a bio filter system in their water management can increase shrimp survival by up to 25 percent, compared with ponds that do not use a bio filter (Brata Pantjara, Erfan Andi Hendrajat, & Suwoyo, 2010). According to informant 2, this method can be applied in small and large scale shrimp farming.
In an interview, male informant 2 revealed that Sidoarjo shrimp farmers have also used mangrove crab or Scylla Serrata as a biological indicator since 2000. They put crabs in a cage by the water gate, which connects the water reservoir pond with the canal or ditch that flows to the cultivation ponds (see Figure 5.3). The farmers are then able to monitor the water quality through the condition or the health of the crabs.
113 Since suspecting that the mud particles of their pond are similar to the particles of the Porong mud volcano, this method has become widespread since the mud volvano.
The informants explained that the morphology of the species makes it particularly sensitive to the pollutant. Crabs tend to be unusually active or behave abnormally, when the water contains hazardous substances. In the worst situation, when the filter system fails, crabs die. Farmers respond by closing the water gates to isolate the cultivation ponds from suspected pollutants.