Study for investigated the optimum photoperiod from blue LED light for the growth of Chlorella vulgaris in culture tank. Photoperiods from blue LED Light (Light/Dark) were set up at 24:0, 16:8 and 12:12 h. The initial number of C. vulgaris cells was 1.6 x 105 ± 0.12 cells mL-1. Culture medium was using commercially available fertilizers. After 17 days of cultivation, the results showed that the 24:0 h photoperiod had better growth of algae than 16:8 and 12:12 h, with maximum number of cells of 1.64 x 107 ± 0.23 cells mL-1 specific growth rate (SGR) was 0.17 ± 0.05, -0.06 ± 0.11 and -0.19 ± 0.1% day-1 with statistically significant differences (P < 0.05) in day 5 of cultivation. The stationary phase continued up to day 3 of cultivation, between the treatment. The optimum temperature for growth ranged from 35.5–38.5°C. The results showed that blue LED lighting at 24:0 h is the optimum photoperiod for cultivation of C. vulgaris. Keywords: Photobioreactor tank, Photoperiod, Blue LED light, Chlorella vulgaris, Growth rate

Monitoring of aquatic plant biomass in the Petchburi River, a regulated river system in Thailand, was carried out together with the examination of eco-hydrological characters and the sedimentary organic content. The surveys were performed during May, August and November of 2010 and 2011. The results indicated temporal variation in water velocity (0.08-2.51 m/s) and medium to low organic levels (0.58-4.68%) of the benthic substrates. Dominant aquatic plants were Hydrilla verticillata (L.F.) Royle and Potamogeton malaianus Miq. with the highest biomass of 70.84 and 182.72 g/m 2 , respectively. The biomass was substantially decreased during the flood-induced discharge period. This study indicates that Potamogeton has more adaptive potential to high water velocities than Hydrilla, while Hydrilla prefers lower water velocities. Discharge velocities of less than 0.5 m/s could provide positive growth rates of such submerged plants. Approaching the discharge control from this ecological point of view can further contribute to river habitat conservation.

Investigations of dissolved oxygen (DO) levels and related water quality in the Petchburi River, a regulated river system in western Thailand, were conducted at 3-month intervals from May 2010 to February 2012. The results indicated generally good water quality with DO levels >4 mg L(-1). Variations in water quality, particularly the DO and ammonium nitrogen levels along the river, occurred due to discharge regulation and the natural characteristics of the river. The processes which contribute to DO levels include natural saturation (ca 57-78% in the upper river section and ca 44-76% in the lower river section) and aquatic plant DO production (ca 20-36% in the upper river section and ca 24-50% in the lower river section) which is also significant, while re-aeration would be less effective. The DO contribution from pondweed (family Potamogetonaceae) was of interest because of its successional capacity. Future control of river quality will require suitable management of aquatic plant species for conservation purposes.

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