Human impact on N, P, and Si cycle: an aquatic perspective Didier Baho Tarikul Islam Mohammad Ashraful Haque Mollah Lorenz Meire Applied ecosystem ecology

Introduction Nitrogen Phosphorus Silica

Nutrient balance Low deposit of N N limiting High deposit of N P limiting

Nutrient balance 60 % reduction in dissolved silica transport DSi

Ecological Consequences Eutrophication: Source: RMB Environmental Laboratories, 2007 Increase in level of N and P

Consequences of Eutrophication Increase in Cyanobacteria bloom causing a decline in the effective light regime. Depletion of O 2 due to enhanced decomposition of organic matter Source: Bellingham 2008 Cyanobacteria bloom Overwinter fish death caused by decrease O 2 depletion

Depletion of oxygen can increase the release of phosphorus sequested in the sediments Source:

Shift in Phytoplankton communities P limitation cause a shift towards nutrient poor phytoplankton Shift due to DSi reduction Diatoms Dinoflagellates and Coccolithophore. DSi

Biological Pump Biological pump is primarily limited by the availability of light and nutrients, and not by carbon.

Impact on biological pump Decrease in DSi shifts diatoms communities which affect carbon sequestration, consequently soft pump rate decreased DSi demand is met up by two process –In open ocean>by upwelling –In coastal water> by river input

a. Preventive process: Reduction of N and P flux before water discharge (eg. ↓ P in detergent) Environment friendly agricultural methods Treatment of Sewage before discharge in catchement Management options

b. Curative process: Biomanipulation: Introduction of Piscivores and improvement the trophic cascades ＋

Conclusion N:P:Si Ratio

Thank you for your attention!

References