Fish diversity in relation to pollution

Note: This project has been designed with schools of Pune in mind. The project can be adapted for schools in other cities that are close to a river.

Hypothesis: Fish species diversity is significantly higher in waters with lower levels of nutrient contents.

Rationale: There are many hypotheses as to what governs the level of diversity of species of some given group of organisms such as plants, fish or reptiles in any locality. More productive and more stable environments are expected to support higher levels of diversity. Similarly environments where the communities have evolved over long periods are also expected to support higher levels of diversity. Any recent drastic change is likely to reduce the levels of diversity because few species would have had a chance to evolve so as to adapt to these conditions. In case of many freshwater bodies, recent decades have witnessed a huge increase in nutrient content, in particular because of discharge of sewage from towns and cities or of fertilizers from tracts of intensive agriculture. This leads to blooms of some algal species and conditions under which few fish species can thrive. As a result one expects lower levels of fish diversity in waters with high levels of nutrients.

Methodology: Many rivers would exhibit much higher levels of nutrients downstream of areas of sewage discharge. Thus Mutha and Mula rivers will have low nutrient levels in stretches closer to their origin near crestline of Western Ghats, and much higher levels in stretches passing through Pune city. One may select several such points for comparison. Throughout its entire extent river fishes are caught by members of Bhoi community. These should be contacted and with their help fish caught in any particular locality documented. This documentation could be in terms of their local names and careful photography by digital camera. If needed specimens may also be purchased from the fishermen. Simultaneously water samples should be collected and analyzed for N and P content and opacity. One may then plot N, P, opacity and number of fish species recorded to test whether the latter declines with increasing N and P content and opacity.

Follow up: It would be interesting to see the extent to which N and P content and opacity are correlated amongst each other and the relative extent to which these variables explain the changes in fish diversity. One may investigate attributes of fish species that are tolerant of high levels of nutrient loading.

Courtesy: Dr Madhav Gadgil