The dairy effluent management systems has an effect on the nutrient composition of the effluent applied to the land due to losses or changes in pathways associated with different effluent management systems that are included in the model.
For example, N losses due to denitrification and volatilisation are higher when effluent is stored in a Holding pond than when direct application occurs with Spray from sump. A proportion of the nutrient stored in ponds settles to the sludge, with the proportion varying with nutrient and storage time. This can result in N:P and N:K ratios of the applied effluent changing when different management systems are selected.
Holding ponds can also be significant sources of methane CH₄ emissions.