I think you got your facts wrong so thats why no one answered. Anyway...

Human activities that cause succession of a pond is over use of fertilisers/fertilisers are accidentally poured into a pond. Fertilisers promote growth of plants and in this case, plankton (a type of seaweed that thrives in any body of water). Plankton uses of the oxygen in water can causes submerged plants to die due to lack of oxygen. Plankton also covers the water surface preventing sunlight from reaching the bottom of the pond (plants need sunlight to survive) .After a plant dies bacteria start decomposing the dead plant. Decomposition uses oxygen in the process causing the oxygen content in water to decrease. After all the submerged plants die plankton also dies due to lack of oxygen in water. Therefore after time swampy plants start growing in that area (adaptation via variation) and soil fills up the pond. Afterwards trees start growing and the complete cycle of succession occurs. 

Notes to explain :
-Low oxygen content = high biochemical oxygen demand

-One cycle of succession, one type of plants die to let for another.
 in this case, first cycle is submerged plants then plankton/seaweed (on top of water) then swampy/muddy plants then trees