Water environment monitoring in shrimp farming

(Baonghean) - To limit water pollution and create conditions for sustainable development in shrimp farming areas, Nghe An Fisheries Industry is applying sustainable aquaculture management methods such as BMP, GAP, VietGAP... However, to effectively implement the above programs, the key issue is good water quality management.

Water quality monitoring activities in commercial shrimp farming areas were conducted in 8 basic shrimp farming areas of the province (6 GAP areas, 2 diversified areas) in the communes of Quynh Xuan, Quynh Loc (Hoang Mai town), Quynh Bang, Quynh Luong, Quynh Thanh (Quynh Luu), Dien Van, Dien Trung (Dien Chau) and Nghi Hop (Nghi Loc). In the above shrimp farming areas, the situation of water pollution is very complicated. This is also the cause of animal diseases causing great damage to households. According to a preliminary survey of water sources in aquaculture areas, 81% of facilities are polluted and only 19% of facilities have good water quality.

Checking shrimp feed consumption. Photo: Hai Yen

There are many causes of water pollution such as: aquaculture activities, wastewater from factories and enterprises, agricultural production activities and wastewater from daily activities in residential areas. In aquaculture areas, 81% of households said that the cause of water pollution is aquaculture. Mr. Nguyen Van An in Quynh Di commune (Quynh Luu district) said: Quynh Di is a commune with a large area of ​​intensive shrimp farming, the water source used for this activity is mainly taken from Hoang Mai river and this is also the place to store wastewater from ponds.

Most of the facilities directly discharge wastewater and sludge into nature after each crop (93% of the opinions). In addition, during the cultivation process, after 30 days of farming, households siphon (suck) sludge from the bottom of the pond into the canal. Thus, households in these areas are very aware of the causes of water pollution, but have not yet found a solution. Currently, the functional agencies of the Department of Agriculture and Rural Development have stepped up propaganda, mobilization and guidance for farming households to apply the VietGAP process. Some households have treated wastewater and collected sludge according to the process, but this rate is very small.

One of the causes of water pollution in intensive shrimp farming is the excess feed in the ponds. In the intensive shrimp farming system, only 15 - 20% of the feed is used for animal tissue development, up to 15% of the total feed is lost due to not being eaten and lost, only 40 - 45% is used in the process of nutritional transformation, maintaining life activities and molting. Overfeeding, unstable water quality, easily soluble feed, difficult to absorb feed and the ability to maintain nitrogen... are discharged into the environment with wastewater. Another problem caused by shrimp farming is the sedimentation of mud in neighboring areas, such as mangrove forests and stagnant water. Most of the excess products in shrimp farming have accumulated at the bottom of the pond. This is a source of danger to shrimp and shrimp farming activities. When the entire pond bottom is dirty, shrimp grow slowly and are susceptible to disease. Through research, it is shown that most shrimp diseases originate from the environment in which they live.

Not only the water environment in the pond is polluted, but the environment outside the shrimp farm also affects the coastal ecosystem. Reusing polluted ponds or discharging into the surrounding environment causes water pollution and impacts coastal activities. Leakage of wastewater as well as pond water also causes salinization of surrounding agricultural land and groundwater (for daily life and drinking). According to the report of the Department of Aquaculture, by October 2014, the whole province had 268.8 hectares of shrimp farming affected by white spot, EMS and environmental diseases. The areas under surveillance have 98.6 hectares of diseased areas, accounting for 37% of the total diseased area, of which the area affected by EMS is 64.3 hectares (accounting for 35% of the area affected by EMS), the area affected by environmental diseases is 23.2 hectares (accounting for 41% of the area affected by environmental diseases), and 11.05 hectares affected by white spot disease (accounting for 40% of the total area affected by white spot disease).

Through the assessment of water quality at Loc Thuy Cooperative, Quynh Bang Commune (Quynh Luu), it shows that: The pH value fluctuates within a narrow range, ensuring veterinary hygiene, environmental protection and food safety, suitable for aquaculture water use. However, the NH3 (Amoniae) index in the water supply and discharge here mostly exceeds the allowable threshold according to QCVN 10-2008 and QCVN 02-19. There are times when it exceeds 10 times, which shows that environmental pollution in sludge discharge from aquaculture is very serious. At the beginning of the farming season (May), this index is within the allowable threshold, then gradually increases in the following months; the H2S value of water is mostly above 0.02 mg/l, exceeding the threshold compared to QCVN 10-2008. From May to October 2014, the entire region had 40 hectares of disease, of which environmental diseases accounted for 32%, white feces disease accounted for 31%. In June 2014, the diseased area was the largest with 4 types of diseases, this was also the time when environmental indicators exceeded the allowable threshold.

In Dien Trung commune (Dien Chau), the pH index is within the allowable threshold, while the NH3 index exceeds the allowable threshold in June, July, August and is higher in wastewater samples. From May to August 2014, a total of 2.5 hectares of diseased area, mainly concentrated in June with 67%, the disease is mainly caused by the environment accounting for 60%. Meanwhile, in Nghi Hop commune (Nghi Loc), the pH index is within the allowable threshold. The NH3 index mostly exceeds the allowable threshold, especially from wastewater sources, in one month it exceeded 20 times (August 2013). The H2S index (gaseous compound at normal temperature, has a foul, toxic odor), BOD5 (dissolved oxygen) are all within the allowable threshold. The alkalinity index is 4 times higher than the allowable threshold in August 2013. In 2013 and 2014, Nghi Hop commune's farming area was affected by environmental diseases such as liver, pancreas, white feces, and white spots. The disease appeared in almost every month of the year.

Assessing the issue of water environment management in aquaculture, Mr. Tran Xuan Quang - Head of Food and Environment Management Department - Aquaculture Sub-Department said: Organizing water quality monitoring to assess water quality and forecast pollution levels is extremely important. On that basis, building effective environmental protection methods and issuing disease warnings, in order to minimize the damage caused by the environment to aquaculture households. In addition to monitoring water quality and proposing activities to control water quality, the relationship between environment and disease is always organically correlated, so it is necessary to simultaneously build water quality monitoring and disease monitoring activities proactively at the same time.

Hoang Thi Ngan

(Department of Aquaculture)