Fish habitat restoration on the basis of water morphology simulation.

The hydrodynamic conditions of rivers affect fish habitats by influencing parameters such as river bottom topography. Ecological restoration projects change the water morphological characteristics of rivers. Here, water flow characteristics of the upper Yangtze River before and after the construction of a restoration project were analyzed using the computational fluid dynamics simulation method. The longitudinal diversion dam could divide the river into two flow velocity zones, and the outer flow is similar to the original river with a flow velocity of 0.75 m/s. However, flow velocity on the inner side of the river was about 0.25 m/s, forming a larger buffer area. The eddy became more diversified and stable, with a high eddy viscosity coefficient and less fluctuations, at 9 Pa·s; this was conducive to fish aggregation and spawning. At different depths, large gradient differences were observed between the inner and outer sides of the longitudinal diversion dam, and the turbulent current and upward flow of the inner side were obvious; this was more favorable to the aggregation of different fish species. The longitudinal dam body was under a pressure of about 200.2 Pa at the same flow rate; this was significantly lower than the pressure on the transverse dam body. The field flow test and fish survey data showed that the error rate of the simulation using the RNG turbulent model was less than 10% compared with actual mapping. After the restoration of fish habitats by the longitudinal diversion dam, the number of fish species in the area increased from 40 to 49; The density of fish in the water increased from 71.40 fish per 1,000 m2 before the project to 315.70 fish per 1,000 m2 after the project. These results can provide a reference for the rapid assessment of water morphology and fish habitat restoration in the future.

Underwater wireless optical communication system using a 16-QAM modulated 450-nm laser diode based on an FPGA.

An underwater wireless optical communication (UWOC) system with a 450-nm laser diode and a 150-MHz PIN photodiode is presented. The 16-ary quadrature amplitude modulation scheme is employed and realized on a field-programmable gate array (FPGA) to efficiently provide a high data rate. Experimental results show that this system can achieve data rates up to 50 Mbps over a distance of 3 m underwater with a bit error rate (BER) of 7.11×10-4 in artificial seawater at 35‰ salinity, where the attenuation coefficient is 0.481. This BER is below the forward error correction target of 3.8×10-3. Thus, this system can provide reliable high-speed communications over short to moderate distance point-to-point UWOC links.

Effects of portable solar water quality control machines on aquaculture ponds.

The effects of a portable solar water quality control machine (PSWM) on water quality and sediment of aquaculture ponds were studied in bream aquaculture ponds in Shanghai, China. PSWM operation reduced the temperature and dissolved oxygen (DO) differences between upper and lower water levels. Concentrations of NH4+-N, NO2--N, TN, TP, COD and TSS increased rapidly and reached maximums at 12 h. The density and biomass of phytoplankton and levels of chlorophyll a reached maximums after 40 h of PSWM operation. In a 165-day study, the mean concentrations of NH4+-N, NO2--N and the available phosphorous (AP) in the PSWM ponds were significantly lower than in the control ponds, but the TP was significantly greater than the control ponds. Compared with the test began, the thickness of the sediment in PSWM ponds declined by 12.4 ± 4.3 cm, the control ponds increased by 5.0 ± 2.3 cm and the TN and AP levels in sediment significantly declined. PSWM treatment increased the production of bream and silver carp by 30 and 25%, respectively, and the feed coefficient was reduced by 24.2%. Use of PSWM in bream aquaculture ponds improved water quality, reduced sediment, reduced aquaculture pollution emissions and increased production.

Design and Application of a Solar Mobile Pond Aquaculture Water Quality-Regulation Machine Based in Bream Pond Aquaculture.

Bream pond aquaculture plays a very important role in China's aquaculture industry and is the main source of aquatic products. To regulate and control pond water quality and sediment, a movable solar pond aquaculture water quality regulation machine (SMWM) was designed and used. This machine is solar-powered and moves on water, and its primary components are a solar power supply device, a sediment lifting device, a mechanism for walking on the water's surface and a control system. The solar power supply device provides power for the machine, and the water walking mechanism drives the machine's motion on the water. The sediment lifting device orbits the main section of the machine and affects a large area of the pond. Tests of the machine's mechanical properties revealed that the minimum illumination necessary for the SMWM to function is 13,000 Lx and that its stable speed on the water is 0.02-0.03 m/s. For an illumination of 13,000-52,500 Lx, the sediment lifting device runs at 0.13-0.35 m/s, and its water delivery capacity is 110-208 m(3)/h. The sediment lifting device is able to fold away, and the angle of the suction chamber can be adjusted, making the machine work well in ponds at different water depths from 0.5 m to 2 m. The optimal distance from the sediment lifting device to the bottom of the pond is 10-15 cm. In addition, adjusting the length of the connecting rod and the direction of the traction rope allows the SMWM to work in a pond water area greater than 80%. The analysis of water quality in Wuchang bream (Parabramis pekinensis) and silver carp (Hypophthalmichthys molitrix) culture ponds using the SMWM resulted in decreased NH3(+)-N and available phosphorus concentrations and increased TP concentrations. The TN content and the amount of available phosphorus in the sediment were reduced. In addition, the fish production showed that the SMWM enhanced the yields of Wuchang bream and silver carp by more than 30% and 24%, respectively. These results indicate that the SMWM may be suitable for Wuchang bream pond aquaculture in China and that it can be used in pond aquaculture for regulating and controlling water quality.