Preliminary studies on the productivities of the two most abundant macrophytes in Subang lake.
Both plants, although found in similar habitats, occupied very distinct ecological niches. Ipomoea aquatica had emergent shoots with submerged stoloniferous components. Salvinia molesta occupied the space between the I. aquatica plants, sheltered by them. I. aquatica seemed the more aggressive of the two, colonising new areas before S. molesta. Fluctuations in water levels affect significantly the productivity of both macrophytes, directly for I. aquatica and indirectly, in the form of increased light intensity, for S. molesta. The submerged components of I. aquatica showed some resistance to adverse conditions, ensuring perpetuation of the species when favourable conditions returned. Nitrogen and phosphorus are important growth factors in both macrophytes. Ipomoea, especially, showed a high absorption capacity for ammonium-nitrogen. Potassium and calcium are relatively high while magnesium and sodium are low in these habitats. Chloride and sulphate show negative and positive relationships with productivity of the macrophytes respectively. From summary.