Tackling Hydrogen Sulphide levels in Serepalem's shrimp farms

By Srirang Kavali - SWP India Program Coordinator

Our India representatives recently undertook a small but crucial study in the village of Serepalem, located within the West Godavari district of the Andhra Pradesh state in India. Farmers in this village suffer a myriad of issues with their culture, including regular mass mortalities, this prompted us to develop a particular interest in the case. The study assessed the levels of Hydrogen Sulphide (H₂S) in shrimp ponds, which is a critical factor that affects the health and productivity of shrimp farms. In all of our samples, we found toxic levels of H₂S.

The Need for the Study

A significant number of Serepalem’s farmers depend on shrimp farming for their livelihood in the village. However, an overlooked aspect of pond management has been the accumulation of sludge over the years. Sludge removal is an essential part of pond preparation, but many farmers have neglected this due to the high costs, in addition to time and logistical constraints. The buildup of sludge often leads to increased levels of H₂S, a potent respiratory toxin for shrimps that affects their uptake and transport of oxygen, which  can significantly compromise their well-being. . H₂S also decreases the pH levels of the water, making the environment acidic.

Methodology and Key Findings 

We initially planned to test samples from 50 shrimp ponds, but stopped at 38 as all of the samples analysed from bottom and surface of the ponds (total 76) showed H₂S levels greater than 0.01 ppm, a concentration deemed highly toxic to shrimps (see testing samples below). The discovery of the H₂S levels not only raised concerns about the health of shrimps in the village of Serepalem, but also raised concerns about the potential that this could be a widespread issue in surrounding areas.

Ponds and H₂S levels

Sludge Removal Intervention

We wanted to assess the impact of sludge removal on H₂S levels, so we chose a pilot pond that had a sludge buildup of 10 years. The process entailed using two motors to  pump out wet sludge over five days. Post-intervention testing showed a significant reduction in H₂S levels from 0.17 ppm to 0.03 ppm on the pond’s surface after a week. However, these levels are still near the toxic threshold for shrimps. Moving forward, our team will test additional sludge removal after a period of pond drying, which we believe will have a greater impact. The farmers involved in this experiment provided positive feedback, noting improvements in the pond conditions.

Installing the sludge pump over floaters

Sludge being pumped out into an adjoining pond

Sludge removal, in either wet or dry form, is an intervention that we plan to undertake in the coming weeks, especially in areas it's been overlooked for years. 

We expect this intervention to reduce bacterial load, lower H₂S levels, restore the depth of the ponds, and improve the overall environment for shrimps (even in subsequent cultures). This focused study underscores both the importance of regular pond maintenance, and a collaborative approach with farmers to implement these practices.

Challenges

While sludge removal at shrimp farms is undoubtedly an effective intervention for maintaining pond health and reducing H₂S levels, it is not without its challenges. One significant challenge is the interconnected nature of input and output canals in many farming areas. For example, the interconnectivity makes it difficult to simply pump the sludge into the canals, as it could contaminate the waterways and disrupt the ecosystem. To address this challenge, farmers must either allocate space for a sedimentation pond or have access to barren land where the removed sludge can be safely deposited. The construction and maintenance of a sedimentation pond or the availability of suitable barren land can be demanding in terms of space and resources, which can pose additional challenges for some shrimp farmers. Despite these challenges, sludge removal remains a vital practice for pond maintenance. Shrimp farmers must find practical solutions to address these challenges while ensuring the long-term health and sustainability of their shrimp farming operations.

Alternatives to Sludge Removal?

Sludge removal in shrimp ponds is a highly effective and sustainable solution compared to costly additives like Ferrous oxide that might not offer long-term efficacy. While additives such as Sodium Molybdate seem to have long-term benefits, they also come at a significant expense: often exceeding 2,000 dollars per treatment.

Sludge removal, on the other hand, offers lasting results by physically eliminating accumulated organic matter and debris from the pond bottom. This not only immediately improves water quality but also prevents further sludge buildup. The benefits are twofold: (1) better water quality for shrimp health and (2) reduced risk of disease. Moreover, sludge removal is a cost-effective option that small-scale farmers can afford, making it a practical and environmentally responsible choice for managing sludge in shrimp ponds.