Liu Shoudong

Spatial distribution and temporal variability of stable water isotopes in a large and shallow lake

ABSTRACT Stable isotopic compositions of lake water provide additional information on hydrological, meteorological and paleoclimate processes. In this study, lake water isotopic compositions were measured for more than three years in Lake Taihu, a large and shallow lake in southern China, to investigate the isotopic spatial and seasonal variations. The results indicated that (1) the whole-lake mean δ2H and δ18O values of the lake water varied seasonally from −48.4u2009±u20095.8 to −25.1u2009±u20093.2u2005‰ and from −6.5u2009±u20090.9 to −3.5u2009±u20090.8u2005‰, respectively, (2) the spatial pattern of the lake water isotopic compositions was controlled by the direction of water flow and not by local evaporation rate, and (3) using a one-site isotopic measurement to represent the whole-lake mean may result in unreasonable estimates of the isotopic composition of lake evaporation and the lake water residence time in poorly mixed lakes. The original data, documented here as an online supplement, provides a good reference for testing sensitivity of lake water budget to various isotopic sampling strategies. We propose that detailed spatial measurement of lake water isotopic compositions provides a good proxy for water movement and pollutant and alga transports, especially over big lakes.

Transfer coefficients of momentum,heat and water vapour in the atmospheric surface layer of a large shallow freshwater lake: A case study of Lake Taihu

In studies of lake-atmosphere interactions,the fluxes of momentum,water vapor and heat(latent and sensible heat) are parameterized as being proportional to the differences in wind,humidity and air temperature between the water surface and a reference height above the surface.The proportionality or transfer coefficients are often assumed to follow the gradient observation above lake surface or the parameterizations established for the marine atmospheric surface layer.Optimization against the eddy covariance and micrometeorology measurements made over a large shallow freshwater lake(Lake Taihu) shows that the transfer coefficients of momentum(CD10N),water(CE10N) and heat(CH10N) were CD10N=1.52×10-3,CE10N=0.82×10-3 and CH10N=1.02×10-3,respectively.These values are in good agreement with the values derived from the eddy covariance measurement in other inland lakes.Comparison with oceanographic parameterizations suggests that lake surfaces were aerodynamically rougher than open oceans under similar wind conditions,which may due to the shallow depth of the lake,and that these parameterizations can bias the annual lake evaporation estimate by as much as 40% higher.Our results also suggest that these coefficients can be regarded as constants independent of stability and wind speed.Sensitivity analysis indicated that the mean error between calculation and observation of latent heat flux(LE) decreased 0.5 W/m2,that of sensible heat flux(H) decreased 0.4 W/m2,and no difference between friction velocity(u*) calculation and observation if stability correction was considered since around 83% of data were in neutral condition.If the effect of wind was considered,the mean error between calculation and observation decreased 0.004 m/s for u*,increased 1.3 W/m2 for LE,and negligible for H.This study can provide reference for the research on lake-atmosphere interaction.

Estimating evaporation over a large and shallow lake using stable isotopic method: A case study of Lake Taihu

Accurate estimation on lake evaporation was vital to hydrology, meteorology and limnology. Based on the data of water budgets, meteorological and stable isotopic observation over Lake Taihu from 2013 to 2015, the evaporation of Lake Taihu was esti⁃ mated using the isotopic mass balance model, the water mass balance method and the Priestley⁃Taylor model. The seasonal and in⁃ ter⁃annual variabilities of lake evaporation were analyzed, and the performance of the water balance method and the stable isotopic water balance model were evaluated with the Priestley⁃Taylor model result as reference. The results indicated: Evaporation of Lake Taihu was higher from May to September and less in winter. Annual evaporation in 2013, 2014 and 2015 was 1069, 894 and 935 mm, and the inter⁃annual variation was controlled by weather condition. Lake evaporation during the period from December 2013 to November 2014 calculated using the Priestley⁃Taylor model was 885 mm, and the result of the isotopic mass balance model was similar with a value of 893 mm. Whereas it was overestimated significantly by the water balance method with a value of 1247 mm.

Estimate of gas transfer velocity between water-air interface in a large lake based on different models: A case study of Lake Taihu

Gas transfer velocity ( k) is a factor driving Greenhouse gases exchange between water-air interface. But the estimate of k showed great uncertainly. To explore the control factors and variation of k,and select suitable k estimate model in large lake,three different parameterized equations were chosen for estimating k in Lake Taihu. Results indicated that velocity scales for wind shear and convection ( u* and w* ,respectively) showed diurnal cycle with high values during nighttime and low values during day, which were two important parameters in k estimate. As a result,k showed similar variation. In the large lake,the k was mainly dominated by wind shear,and wind speed was useful for estimating k. The annual mean value of k ranged from 1.27 to 1.46 m /d in Lake Taihu. Because of the spatial heterogeneity,the parameterized models in single site maybe not suitable for estimating k in other lakes. However,the lake area may be useful predictor for k.

Characteristics of modelling hourly water surface evaporation in Lake Taihu and comparison of simulation results by three models

Water surface evaporation on hourly timescale can affect the thermal and dynamic structure of the aloft atmospheric boundary layers. Understanding the main drivers of hourly evaporation and accurate evaporation model can improve weather forecast and air quality prediction in catchment. Based on half⁃hour flux, radiation and micrometeorological observations at the Bifenggang site in Lake Taihu in 2012 and 2013, the main drivers of Lake Taihu hourly evaporation were investigated. Then the performance of three models ( traditional mass transfer model, Granger and Hedstrom model and DYRESM model) was evaluated against latent heat flux measured by eddy covariance. The results showed that the main driver for Taihu hourly evaporation was the product of the water vapor pressure difference at water⁃atmosphere interface and wind speed, rather than the expected net radiation. The Willmott