Seasonal Changes of Nutrient Concentrations and Phytoplankton Biomass in a Shallow Agricultural Pond

Pond is an ideal study target which can be regarded as an enclosed ecosystem with little external disturbance such as pollution discharge. The aim of the study is to obtain further understandings of freshwater eutrophication mechanism through a one-year´s intensive observation and monitoring program for a shallow pond in Chongming Island, China. The result showed that NO₃-N, PO₄-P and DTP kept in low levels in the pond all through the year with no distinct seasonal variation trends; TN and TP increased with the growth of phytoplankton and the main components of TP was particulate phosphorus. Algae blooms occurred from June to late November and Chl-a concentration peaked from late August to early September. The study also reveals that low TN:TP ratio in the shallow pond is the result of sudden growth and blooming of phytoplankton, not the cause.