This is not a news. The number of plantic species is bigger with depths which is more characteristic for marine to ocean environments, not for continental environment.

Dear Ines Galović,

Both diatoms (pennate and centric)are plankton.

Many thanks

In marine pelagic environments usually centric diatoms dominate, but in continental systems and marine benthic, pennate diatoms are usually the dominants. 

According to my knowledge that the shift from pennate diatoms to centric diatoms may be indicating the change in the aquatic environment (disturb aquatic systems)

I agree with Garcia. Just want to state that in the lentic/lotic ecosystems that you are talking about, the community structure of diatoms shift over the seasons and the degree of disturbance (introduction of pollutants, increase in land drainage after heavy rains etc.) the ecosystem is exposed to. Long term (over decades) studies are needed to confirm if an ecosystem is actually changing in terms of its physicochemical or biological properties!   

This may be of some help:

https://www.researchgate.net/publication/236859113_TEMPORAL_SUCCESSION_OF_PHYTOPLANKTON_ASSEMBLAGES_IN_A_TIDAL_CREEK_SYSTEM_OF_THE_SUNDARBANS_MANGROVES-_AN_INTEGRATED_APPROACH?ev=prf_pub

Article Temporal Succession of Phytoplankton Assemblages in a Tidal ...

Como há muito tempo estou trabalhando com a produção primária do fitoplâncton estuarino (ve artigos em http://www.passavante.pro.br/bibliografica.html) não tenho uma respostas plausível, porém concordo com a resposta da Dra. Dola Bhattacharjee, pois em nossa região ocorre muitas algas penales, tanto no fitoplâncton como a área bêntíca.  

Zanon Passavante

http://www.passavante.pro.br/bibliografica.html

Dear All,

Both lentic and lotic ecosystems recorded predominate, I'd be grateful if have any published papers shows the opposite.

Regards