The hydrological characteristics influence the distribution of phytoplanktons in subtropical reservoirs. However

phytoplanktons also provide feedback to the ambient environment. Taking Lianhe Reservoir as a representative subtropical eutrophication reservoir

the hydrological

chemical

and biological conditions were studied from 2014 to 2015. The results showed that the vertical profiles of pH

dissolved oxygen

and chlorophyll

a

in the water column changed greatly during the thermal stratification period. It was found that the dominant species were from the reservoir itself

not from the shore or receiving rivers

and they were suspected to overcome poor living conditions by entering dormancy in the bottom. The phytoplankton community also had a seasonal variation

with

Cyclotella meneghiniana

as the dominant species during the isothermal mixing period and

Microcystis densa

during the thermal stratification period. The alternative appearance of these species was considered to be influenced mainly by temperature and available light. However

the distribution of phytoplankton could affect the oxygen content in the water column. Furthermore

both phytoplankton and dissolved oxygen determined the vertical profile of total phosphorus. For the one-year budget

it was found that there was a net retention of both nitrogen and phosphorus in the reservoir

and nitrogen input mainly from rainfall and rivers and phosphorus from rivers and sediments.