Hu Weiping

Temporal-spatial variations of euphotic depth of typical lake regions in Lake Taihu and its ecological environmental significance

By using the data of underwater irradiance measured in the different lake regions of Lake Taihu during 1998–2004 and total suspended solids (TSS), wind speeds of the total 13 stations in typical lake regions during 1993–2003, this paper analyzes the factors of influencing on PAR (photosynthetically available radiation) attenuation, euphotic depth, and presents the temporal and spatial variations of euphotic depth of typical lake regions in Lake Taihu, and the spectral distributions of euphotic depth at station 2. The results show that the concentration of TSS is the most important factor impacting PAR attenuation, followed by chlorophyll a; chromophoric dissolved organic matter (CDOM) has little impact on the PAR euphotic depth. During 1993–2003, the mean yearly PAR euphotic depths of the typical lake regions ranged from 1.04 to 1.95 m with a mean value of 1.35±0.23 m. The PAR euphotic depth fell into 3 spatial zone types: Type I, the lowest, including the lake center and the inflows of rivers; Type II, intermediate, including Meiliang Bay, Wulihu Lake and Gonghu Bay; Type III, the greatest, including the East Lake Taihu; corresponding mean depths were approximately 1.1, 1.4, 2.0 m, respectively. The seasonal variations of euphotic depths were not quite the same in different lake regions. In the lake center, the mean values of PAR euphotic depth in summer and autumn were significantly greater than those in winter and spring; in the Meiliang Bay, winter means were significantly greater than in the other three seasons; in the East Lake Taihu, winter means were significantly less than in the other three seasons. However, no distinct seasonal change was recorded in the Wulihu Lake, Gonghu Bay and the inflows of rivers. The spectral distributions of euphotic depth present a minimal value at the blue light wave band of 400 nm, and a peak at the green light wave band of around 580 nm. In 1998 and 1999, based on the seasonal many-day continuous measurements, the PAR euphotic depths at station 2 were recorded 2.00±0.21, 2.52±0.45, 1.58±0.24, 2.00±0.15 m in spring, summer, autumn and winter, respectively. The peak value of 440 nm absorbed by phytoplankton corresponded to a euphotic depth of only 0.81–1.47 m (mean 1.07±0.29 m), which was much lower than the mean PAR euphotic depth of 1.98±0.41 m.

Migration Mechanism of Biogenic Elements and Their Quantification on the Sediment-water Interface of Lake Taihu: I.Spatial Variation of the Ammonium Release Rates and Its Source and Sink Fluxes

采集柱状芯样，室内静态模拟不同温度下太湖沉积物铵态氮释放．结果表明，经面积加权，5℃、15℃和25℃下氮的交换速率分别为-16．0±17．6mg／(m^2·d)、12．6±6．9mg／(m^2·d)和34．1±20．8mg／(m^2·d)，不同湖区其释放速率差异极大．受外源污染影响较大的水域，氮释放量随温度的升高而增加；受死亡残体沉降和分解影响明显的草藻型湖区，氮的年释放通量较大．全太湖沉积物-水界面NH4^+-N的年净通量为9960．3±4960．0t，其中成汇的通量值约为-911±637．9t／a，大部分泥区在一年中至少经过了一次的源-汇转换过程。The ammonium release of core samplers in Lake Taihu were simulated at different tempera-tures.The results showed that the area-weighed nitrogen exchange rates in the conditions of5℃,15℃,and25℃are-16.0±17.6mg/(m 2 · d),12.6±6.9mg/(m 2 · d),and34.1±20.8mg/(m 2 · d),respectively.But the ammonium fluxes were quite different among the sediments from different lake aveas.In respect of the waters that were greatly influenced by external pollution source,there was a positive correlation be-tween the ammoniumexchange amount and temperature.In the areas where there are more algal gather-ing and macrophyte growth,the annual release fluxes of nitrogen were usually greater because of being impacted with deposition of biological detritus on the surficial sediment.The ammonium exchange amount,on the whole lake,was estimated to be about9960.3±4960.0t/a,of which the sinking flux was about-911±637.9t/a.There appeared source-sink transition at least once in most of the sediment ar-eas.

A Three-Dimensional Numerical Simulation on the Dynamics in Taihu Lake，China(H)： the Typical Wind-driven Current and Its Divergence

本文用垂直谢匀分五层，水平网络蹁为１ｋｍ的压缩σ坐标系下的三维数值模型，计算了太湖典型风场ＳＥ，ＮＷ，ＳＷ风生流，分析了太湖湖流及由各层流场平均得到的整层平均流肪在这三种典型风场作用下随时间的演变特征，探讨了风应力，水面倾斜压强梯度力，湖底摩擦力三者对湖流垂直结构的影响，初步揭示了太湖湖流垂直结构形成的机理。

Reflections on the theory and practice of shallow lake ecosystem restoration

Aquatic ecosystem restoration is a wide-used term at present, and it has gradually aroused the attention of the public and government due to serious environmental problem of lake in China. In fact, as a systematic work, ecosystem restoration makes the ecosystem towards the good state or prestine status. It comes true through the decreasing or amelioration of environmental press combining with single or multi introduced measures of plants and animals. At present, lake ecosystem restoration is usually considered as simple planting grass and cultivating fish etc. or explained as the man-made re-arrangement or incrustation of biocommunity. These bias in cognition result in less successful examples during the long time of the ecosystem restoration practices. Here we put forward an alternative technological way to purify the lake water in part area of Lake Taihu through ecosystem restoration, including three mutual-connected phases, viz,improving the lake condition→restorating aquatic macrophyte→ecosystem transformating from algae-typed to grass-typed lake→improving water quality. Whether this idea directing the restoration of aquatic macrophyte and lake ecosystem is successful will be tested by future practice.

The Study on Natural Restoration of Aquatic Vegetation in the Northern Lakeside, Lake Taihu

It has been observed and studied that the natural restoration process of aquatic vegetation in the experimental enclosure of northern lakeside, Lake Taihu, from 1997 to 1999 years. It is found that the local macrophytes, for example, the Nymphoides peltata, Trapa sp. and Potamogeton malainus Mig, can be naturally restored in the bare lakeside of big shallow eutrophication lakes by an enclosed protection methods. The cover area by species of Nymphoides peltata and Trapa sp. has taken up to 14.3% and 12.7% of the total enclosure area in the summer of 1998, respectively. The companion species of vegetation are Potamogeton malainus Mig, Hydrilla verticillata Royle and Vallisneria spiralis L. The affection to the natural restore of macrophytes by anthropologic readping and fish culture has also been discussed. According to the results of enclosure experiment, it has provided a strategy for control of eutrophication in big shallow lakes, for example, Taihu Lake.

Sediment Re-suspension under Different Hydrodynamic Disturbances in Lake Taihu

Based on the collected wave and current data in July,2002 and April, 2003, Lake Taihu, the wave stress (Tw) and the current stress (Tc) were calculated for better understanding of sediment re suspension mechanism. The results show that Tc is much larger than Tw with the water surface slightly disturbed but no re suspension can be found. Under stronger disturbance, Tw is so much larger than Tc that the current effects can be ignored in the bottom stress calculation. The wave effect is more important than the current effect although Tc is slightly smaller than Tw when the water surface is forced by a moderate wind. In this case, the non linear wave current interaction was favored to be considered for the bottom stress calculation in Lake Taihu. The conclusion can benefit the coming research on nutrients release from sediment and suspended sediment concentration (SSC) response to the surface disturbance.