Comparing spatial-temporal characteristics of dissolved nitrogen and phosphorus in water of sea cucumber Apostichopus japonicas culture ponds between sandy and muddy sediments

Abstract

Apostichopus japonicas culture ponds have been invaded by Chaetomorpha valida in recent years in northern China, where the algae may be regionally distribute and the sizes of blooms vary with pond sediments. In this study, the spatial-temporal distribution characteristics of the DIN and SRP in the water of A. japonicas aquaculture ponds with sandy and muddy sediments from March to November 2016 were monitored to analyze whether the overgrowth of C. valida was correlated with the sediments in aquaculture ponds. The surface and bottom water were collected at 6 sampling sites in each aquaculture pond in the field and transported to the laboratory in low temperature incubators for analysis. The results showed that there were no significant differences in the concentrations of the NO3−-N, NH4+-N, NO2−-N and SRP between surface water and bottom water at the same sampling time and site. The relative position of the sampling sites in horizontal direction had no effect on the DIN and SRP concentrations. The variation of the DIN and SRP concentrations over time may be influenced by the biomass of phytoplankton and C. valida. The sediments in the aquaculture ponds had a significant influence on the concentrations of the DIN and SRP in the water. The total DIN concentrations, including all three forms, were slightly higher in muddy ponds than in sandy ponds. Compared with muddy ponds, the SRP concentration in sandy ponds fluctuated greatly with time due to differences in the sediment particle size and adsorption capacity. The biomass of C. valida had the strongest correlation with the NO3−-N concentration in sandy ponds and with the SRP concentration in muddy ponds. Therefore, it is more important to monitor the SRP and NO3−-N concentrations in aquaculture processes. This investigation provided important insight into eutrophication in sea cucumber ponds with different sediments.