Chemical estimation of phosphorus released from hypersaline pond sediments used for brine shrimp Artemia franciscana production in the Mekong Delta

Artemia production in the Mekong Delta of Vietnam occurs in hypersaline conditions and depends on adequate algal growth. In turn, algal proliferation mostly depends on mineral nutrients derived from pond bottom sediment. This study was carried out to evaluate chemically rapid procedures reliable to estimate the capacity of the sediment in supplying available phosphorous (P) in hypersaline Artemia ponds. To this end, sediments were sampled from Artemia ponds and artificially submerged by Instant Ocean at 70 g L− 1 salinity. The amounts of dissolved reactive P (DRP) and unreactive P (DUP) released from the sediments were analyzed during 4-day submergence. Linear and exponential regression analyses were employed to determine the correlation between the amounts of DRP released over submergence and the concentrations of P extracted by Olsen method and by shaking the soil slurry for 24 h. The results showed that the concentrations of DRP and DUP in hypersaline conditions (EC ≈ 97 dS m− 1) were on average 1.5 to 3 fold higher than those in less saline conditions (EC ≈ 11–23 dS m− 1) (P < 0.001). During the early stage of submergence, the amount of DRP released from sediment after 4 days was linearly correlated with Olsen-P content in the sediment (R2 = 0.64, P < 0.001), while its relationship with DRP present in the saline extracts after a 24-h equilibration followed a logarithmic pattern (R2 = 0.84, P < 0.001). The results from this study revealed that Olsen-P and/or DRP measurements after a 24-h equilibration allow predicting the availability of P in the conditions prevailing in Artemia cultivation.