Cladophora as ecological engineer:A new test from the largest lake of Qinghai-Tibet plateau with filamentous algal blooms

Filamentous algae blooms(FABs)have been increasing globally in recent years,and their presence can have both harmful and beneficial effects on aquatic ecosystems.As one of the most common FABs,Cladophora blooms have been reported in the lakes of the Qinghai-Tibet Plateau during the past few years.However,there have been few studies focused on how FABs impact other aquatic organisms,especially in alpine lakes since these are at the forefront of responding to global climate change.In this study,the phytoplankton communities in different regions of Qinghai Lake were profiled in different seasons using meta-barcode sequencing.The phytoplankton assemblages in areas with Cladophora blooms were compared to those without Cladophora.The phytoplankton community structure correlated with physicochemical properties including water temperature,electrical conductivity,nitrate,and the presence or absence of Cladophora blooms.The relative abundance of Bacillariophytes was found to be higher in zones with Cladophora blooms than in other regions.Significant seasonal changes in phytoplankton biomass andβdiversity were observed in zones with Cladophora blooms.Growth and microbial degradation of Cladophora can change the pH,dissolved oxygen,secchi depth,and nitrate.Together with seasonal temperature and electrical conductivity changes,Cladophora growth can significantly impact the phytoplankton biomass,community dissimilarity and assembly process.These results showed that Cladophora plays a key role in littoral aquatic ecosystem ecology.

Experimental study on discharge coefficient of a gear-shaped weir

This study focused on hydraulic characteristics around a gear-shaped weir in a straight channel. Systematic experiments were carried out for weirs with two different gear heights and eight groups of geometrical parameters. The impacts of various geometrical parameters of gear-shaped weirs on the discharge capacity were investigated. The following conclusions are drawn from the experimental study:(1) The discharge coefficient(m_c) was influenced by the size of the gear: at a constant discharge, the weir with larger values of a/b(a is the width of the gear, and b is the width between the two neighboring gears) and a/c(c is the height of the gear) had a smaller value of m_c. The discharge capacity of the gear-shaped weir was influenced by the water depth in the weir.(2) For type C1 with a gear height of 0.01 m, when the discharge was less than 60m^3/h and H_1=P < 1.0(H_1 is the water depth at the low weir crest, and P is the weir height), m_c significantly increased with the discharge and H_1=P; with further increases of the discharge and H_1=P, m_cshowed insignificant decreases and fluctuated within small ranges. For type C2 with a gear height of 0.02 m, when the discharge was less than 60m^3/h and H_1=P < 1.0, m_csignificantly increased with the discharge and H_1=P; when the discharge was larger than 60m^3/h and H_1=P > 1.0, m_c slowly decreased with the increases of the discharge and H_1=P for a=b 1.0 and a=c 1.0, and slowly increased with the discharge and H_1=P for a=b > 1.0 and a=c > 1.0.(3) A formula of m_cfor gear-shaped weirs was established based on the principle of weir flow, with consideration of the water depth in the weir, the weir height and width, and the height of the gear.

Clear-water local scouring around three piers in a tandem arrangement

Experiments of local scouring around three piers were carried out under steady clear-water conditions. We investigated the role of pier spacing and flow rate in scour depth and progression. The scour-hole depth around the upstream pier was the same as that for single piers and independent of pier spacing. The scour behavior of the middle and downstream piers progressed through a synchronous scouring region, a transition region, and a radical deviation region as the fluid velocity increased. The critical velocity from the synchronous scouring region to the transition region for the middle and downstream piers was the same, which linearly increased with pier spacing. The degree of deviation in the radical deviation region for the middle and downstream piers was dependent on the pier spacing. The critical velocity from the transition region to the radical deviation region for the middle pier increased with the pier spacing. When the spacing was larger than 11 times the diameter of a pier, the scour depths of the three-pier configuration were the same as for the single piers, which indicates the limit of inter-pier fluid–structure interaction. Finally, the data from this study are used to derive adjustment factors to predict the local scour depth around three piers.

Critical velocities for local scour around twin piers in tandem

Experiments of the local scour around twin piers are carried out under steady clear-water conditions, including 95 tests to observe the influence of the pier spacing and the flow velocity on the local scour characteristics of the twin piers. It is shown that the start of the transition region is synchronous with the sediment transport from the upstream scour hole to the downstream one. The equations for the critical velocities are derived to quantify the velocity range of each of four different scour regions. Finally, a prediction formula of the downstream pier scour depth in the radical-deviation region is established.