Nitrogen uptake competition between minute duckweed (LemnaperpusillaTorr) and microalgae under various nutrient composition

Abstract

Implementation of minute duckweed (Lemnaperpusilla) in an integrated aquaculture system for encouraging movement of in-lake floating cage aquaculture to inland base aquaculture has been emphasized as one among various measures for restoring the degraded Lake Maninjau water quality. Unfortunately, in the field, there is a harmful competition between microalgae and duckweed for nutrient uptake. This paper reports an attempt to find out suitable nutrient solution composition for supporting duckweed growth while suppressing the microalgal proliferations. Batch culture of the plant with six varied media treatments (A to L) whichmade from Nitrogen-Phosphorus-Potassium (NPK) fertilizers basis enriched with trace elements, bio-algaecide (Terminalia Cattapa extract), and molasses solutions were examined. The adsorption of TN by duckweed and the assemblage of natural microalgae community was quantified and modelled using mass balance concept approach and non-linear equations. The result showed that among of 12 obtained models, treatment E (a solution which made from NPK fertilizer enriched with molasses and trace element) was the most favourable media composition for promoting duckweed growth and simultaneously suppressed microalgae growth. It is proven from the fact that the TN uptake patterns and the chlorophyll-a content which show chlorophyll-a content werethree magnitudes higher than those were found in treatment A (the most optimum medium for growing microalgae community). The TN uptake rate by minute duckweedin treatment of E was observed as much as 251.54 mg/m2/day while that ofmicroalgae was 208.60 mg/m2/day.