DOMINANT FACTORS AFFECTING SEDIMENT OXYGEN CONSUMPTION LEVEL IN INTENSIVE WHITE SHRIMP (Litopenaeus vannamei) POND

Sediment oxygen consumption level is an indicator of mineralization procces intensity and indicator of microorganism activity in the substrate, and also a description of dissolved oxygen consumption or utilization in a water body. This study aimed to evaluate factors of sediment quality which influenced sediment oxygen consumption level. The study was conducted at the experimental pond installation of Research Institute for Coastal Aquaculture (RICA), in Punaga, Takalar Regency, South Sulawesi, using two units of 4000m2 intensive ponds with density of 50ind./m2. Rearing period was approxi-mately in 4months. Pond management was carried out in accordance with standard operating pro-cedures. Homogeneity between experimental units was approached by the uniformity of pond management including pond preparation, shrimp seed management, feed management,and water management. Sediment quality variables measured were redox potential, pH, total organic matter, sediment oxygen consumption, total bacteria, and production aspect. The results showed that the factors which have close relationship with the sediment oxygen consumption were redox potential, organic matter, and total bacteria. The model could be used to predict the sediment oxygen con-sumption on white shrimp pond with the following regression equation Y= 0.0000496 + 0.00025 organic matter + 0.00037 total bacteria - 0.00000948 potential redox with R2 = 0.847.Keywords: sediment oxygen consumption, sediment quality, pond, Litopenaeus vannamei

DOMINANT FACTORS AFFECTING SEDIMENT OXYGEN CONSUMPTION LEVEL IN INTENSIVE WHITE SHRIMP (Litopenaeus vannamei) POND

Sediment oxygen consumption level is an indicator of mineralization procces intensity and indicator of microorganism activity in the substrate, and also a description of dissolved oxygen consumption or utilization in a water body. This study aimed to evaluate factors of sediment quality which influenced sediment oxygen consumption level. The study was conducted at the experimental pond installation of Research Institute for Coastal Aquaculture (RICA), in Punaga, Takalar Regency, South Sulawesi, using two units of 4000m2 intensive ponds with density of 50ind./m2. Rearing period was approxi-mately in 4months. Pond management was carried out in accordance with standard operating pro-cedures. Homogeneity between experimental units was approached by the uniformity of pond management including pond preparation, shrimp seed management, feed management,and water management. Sediment quality variables measured were redox potential, pH, total organic matter, sediment oxygen consumption, total bacteria, and production aspect. The results showed that the factors which have close relationship with the sediment oxygen consumption were redox potential, organic matter, and total bacteria. The model could be used to predict the sediment oxygen con-sumption on white shrimp pond with the following regression equation Y= 0.0000496 + 0.00025 organic matter + 0.00037 total bacteria - 0.00000948 potential redox with R2 = 0.847.<br /><br /><em><strong>Keywords</strong>: sediment oxygen consumption, sediment quality, pond, Litopenaeus vannamei</em>

Numerical analysis of the primary processes controlling oxygen dynamics on the Louisiana shelf

The Louisiana shelf, in the northern Gulf of Mexico, receives large amounts of freshwater and nutrients from the Mississippi–Atchafalaya river system. These river inputs contribute to widespread bottom-water hypoxia every summer. In this study, we use a physical–biogeochemical model that explicitly simulates oxygen sources and sinks on the Louisiana shelf to identify the key mechanisms controlling hypoxia development. First, we validate the model simulation against observed dissolved oxygen concentrations, primary production, water column respiration, and sediment oxygen consumption. In the model simulation, heterotrophy is prevalent in shelf waters throughout the year, except near the mouths of the Mississippi and Atchafalaya rivers, where primary production exceeds respiratory oxygen consumption during June and July. During this time, efflux of oxygen to the atmosphere, driven by photosynthesis and surface warming, becomes a significant oxygen sink. A substantial fraction of primary production occurs below the pycnocline in summer. We investigate whether this primary production below the pycnocline is mitigating the development of hypoxic conditions with the help of a sensitivity experiment where we disable biological processes in the water column (i.e., primary production and water column respiration). With this experiment we show that below-pycnocline primary production reduces the spatial extent of hypoxic bottom waters only slightly. Our results suggest that the combination of physical processes (advection and vertical diffusion) and sediment oxygen consumption largely determine the spatial extent and dynamics of hypoxia on the Louisiana shelf.

Numerical analysis of the primary processes controlling oxygen dynamics on the Louisiana Shelf

The Louisiana shelf in the northern Gulf of Mexico receives large amounts of freshwater and nutrients from the Mississippi/Atchafalaya River system. These river inputs contribute to widespread bottom-water hypoxia every summer. In this study, we use a physical-biogeochemical model that explicitly simulates oxygen sources and sinks on the Louisiana shelf to identify the key mechanisms controlling hypoxia development. First, we validate the model simulation against observed dissolved oxygen concentrations, primary production, water column respiration, and sediment oxygen consumption. In the model simulation, heterotrophy is prevalent in shelf waters throughout the year except near the mouths of the Mississippi and Atchafalaya Rivers where primary production exceeds respiratory oxygen consumption during June and July. During this time, efflux of oxygen to the atmosphere, driven by photosynthesis and surface warming, becomes a significant oxygen sink while the well-developed pycnocline isolates autotrophic surface waters from the heterotrophic and hypoxic waters below. A substantial fraction of primary production occurs below the pycnocline in summer. We investigate whether this primary production below the pycnocline is mitigating the development of hypoxic conditions with the help of a sensitivity experiment where we disable biological processes in the water column (i.e. primary production and water column respiration). In this experiment below-pycnocline primary production reduces the spatial extent of hypoxic bottom waters only slightly. Our results suggest that the combination of physical processes and sediment oxygen consumption largely determine the spatial extent and dynamics of hypoxia on the Louisiana shelf.