Stress of urban pollution on largest natural wetland ecosystem in East Kolkata - Causes, consequences and improvement

The impact of sewage pollution on these fish ponds and on the ecosystem is evaluated. Similarly, remedial measures to maintain water quality and to improve resource recovery efficiency are suggested.

Aims:

The aims of the current study are as follows:

1. Environmental behavior of nutrients, solids and organic substances in waste water canals and status of natural  purification
2. Impact of wastewater on fish ponds
3. Barriers and opportunities to maintain fish farming in sustainable manner.

Study area:

This study considers the eastern Kolkata wetlands. In this study six sampling stations along the main canal (SWF) , three sampling stations at the inlets to the ponds; and five ponds (one sampling point for each pond) were selected.

Methodology:

Water samples were collected from the mid stream of waste water canal and midpoint of the ponds either by hand or by the sampler depending on the accessibility to sampling points. The analytical results were processed using various statistical techniques

Results and discussion

Distribution and environmental behaviour of pollutants in waste water canal

The high average values of oxygen demans, nutrients and chloride all suggested that the pollution is leading to deterioration of water quality. The chemical parameters also responded to intermittent discharges from industries through tributaries.

Actual dynamics of pollutants and their influence on waste water canal

The pattern of factor loadings on various pollutants suggest that the combined influences of domestic and industrial discharges contribute to  deterioration of water quality by inhibiting natural purification in waste water canal

Status of natural purification and reduction of pollutants

The samples indicate that intermittent discharges of industrial pollutants to an extent greater than the carrying capacity of the wastewater canal interfere with the natural purification processes. 

Biodegradability of wastewater

The analyses indicate that the rate of biodegradability for organic substances in waste water canal is less than that of typical domestic waste

Influence of wastewater on pond water

Prevailing nitrogen-nitrate levels were not conducive to the rearing of carp. These and other analyses indicate that the increased nitrogen input caused by the waste water threatens fish ponds.

Association of BOD and COD with TSS

Suspended solids enriched with pollutants has adverse impact on fish pond management practice

Barriers to sustainable development

The interruption of natural purification processes is caused largely by poor planning, designing and construction of engineering projects, poor maintenance of waste water canal (siltation), inadequate trained and organized fish farmers’ group to properly maintain fish pond and lack of institutional support. The other major barriers are lack of implementing appropriate legislation to control at source and lack of environment policy specifically framed to restore this wetland in local level.

Possible opportunities to improve ecosystem function

Developing self maintaining pond ecosystem utilizing solar energy and culture of variety of species to cover all the ecological niches is the best option to restore the functionality of the fish pond ecosystem. Various techniques to abet the purification process are detailed in the paper.

Conclusions

The deterioration of water quality in canal and ponds caused irreparable loss of pond ecosystem in terms of poor fish yield, loss of biodiversity and inefficient nutrient recovery.The study suggests that management of waste-fed aquaculture is neglected due to lack of appropriate policies, legislation, institutional frameworks and regulations at the national and local levels. Developing a national policy framework may be necessary to facilitate safe waste-fed aquaculture based on the WHO guidelines.