Complex sentence: Without stabilising the compacted peat beneath the sludge, the peat loosens and can release phosphorous at a similar rate, so the growth of larger water plants is necessary to complete the transformation.
Split into simpler sentences: Without stabilising the compacted peat beneath the sludge, the peat loosens and can release phosphorous at a similar rate. The growth of larger water plants, which stabilises the floor is therefore necessary to complete the transformation.