| Summary: | Salmon netpen culture operation is going to grow in the next 5 years in British Columbia, and this culture generates nutrient loading. Kelp could utilize this nutrient to grow. To investigate the feasibility of an integrated culture of kelp and salmon, 3 consecutive experiments (each lasted 9 days) using kelp (Laminaria saccharina) (length 15 cm) were conducted at Marine Ecosystem Programme (West Vancouver) during April-September, 1990. The objectives were to test the effect of flow and kelp density on nitrogen removal, nitrogen uptake, growth, biomass and dissolved oxygen production of kelp. The flow treatment consisted of 3 levels (8.1-24, 25-44.1, 65.2-83.51 h⁻¹), and the density treatment consisted of 4 levels (0, 10, 15, 20 plants/tank or 0, 370, 555, 740 kelp/m³, respectively). The kelp were grown in 12 Plexiglas tanks (45x45x20 cm⁻³). Water samples of NH₄⁺ and NO₃⁻ (morning, afternoon), growth measurement and biomass harvesting were conducted every 3 days.
Luxurious uptake of nitrogen was not evident because C/N ratio (10-11) was stable in all experiments. The treatments with kelp demonstrated higher total nitrogen removal than the controls (no kelp). The removal rate ranged 32.9-339 μmol l⁻¹ h⁻¹ (30-40%).
The total nitrogen uptake rate ranged 6.1-22.5 μmol g⁻¹ dry mass h⁻¹. The high-flow, low-density tank had the highest total nitrogen uptake. The mean uptake based on 3 days growth for all flow-density combinations were similar. The range of mean uptake based on 3 days growth was 5.4-8.3 μmol g⁻¹ dry mass h⁻¹. The kelp utilized NH₄⁺ and NO₃⁻ equally. No differences of total nitrogen (NH₄⁺ and NO₃⁻), NH₄⁺ and NO₃⁻ uptake values were evident between morning and afternoon sampling time for all flow-density combinations.
The growth ranged between 6.5-9 % d⁻¹. The biomass production ranged from 1.3-2.1 g per sampling. The highest growth rate and biomass production was performed by kelp in the high-flow, low-density tank. The biomass production appeared to increase as nitrogen uptake increased. Intraspecific competition to light appeared to occur in the medium and high kelp density tanks.
Tanks with kelp contained higher dissolved O₂ than control (no kelp) tanks. No difference of dissolved O₂ was evident in the morning and afternoon periods in all flow-density combinations. The range of dissolved O₂ in the kelp tanks was 7.1-9.5 mg 1-1, and the highest value was found in the low-flow, high-density tank.
The low-density and high-flow combination would be applicable in an integrated culture of kelp and salmon. Depending on the current and the desired N removal efficiency, the suggested kelp raft will consist of a number of kelp units, which are between 120 to 480 m long and 0.15 m² in cross sectional area.
The result of high growth and biomass production would serve the purpose of maximum nitrogen purification of salmon culture effluent. In addition, the cultured kelp would provide oxygen through photosynthetic activity.
A model for predicting total nitrogen uptake was presented. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate
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