Lake Taihu eddy flux mesonet for atmospheric and hydrological research

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1 耶鲁大学 - 南京信息工程大学大气环境中心 Yale-NUIST Center on Atmospheric Environment Lake Taihu eddy flux mesonet for atmospheric and hydrological research Shoudong Liu 1, Wei Xiao 1, Chang Cao 1, Lichen Deng 1, Cheng Hu 1, Ning Hu 1, Hanchao Li 1, Cheng Liu 1, Jing Shen 1, Shiqiang Sun 1, Wei Wang 1, Qitao Xiao 1, Jiaping Xu 1, Dong Yang 1, Mi Zhang 1, Xuhui Lee 1,2* 1 Yale NUIST Center on Atmospheric Environment, Nanjing University of Information Science & Technology, Nanjing, China 2 School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 6511, USA EGU General Assembly 213 Vienna, Austria, April 1, 213

2 Background Lakes play a unique role in global and regional carbon and water cycles. Information on the lake air exchanges of energy, water vapor and CO 2 are important to numerical weather models and climate change study. So far parameterizations of lakes in numerical weather models have been primarily based on oceanic observations and there have been only a few studies on lake air fluxes of greenhouse gases. As a robust flux measurement method, eddy covariance is widely employed in studies on terrestrial ecosystems. However, long term eddy covariance applications are still rare for lake systems.

3 Taihu 太湖 Eddy Flux Project Biogeochemical Biophysical Albedo effect Algae growth & spread CO 2 sink Wind-wave interactions Heat & water fluxes CH 4 /N 2 O source New land surface model Regional weather forecast Pollution reduction Air quality management Climate policy Greenhouse effect Climate model

4 Ecological zones in Lake Taihu Eutrophic area Hypereutrophic area Little photosynthetic activity half of the area covered by macroplant vegetation Submerged macrophytes Macroplant and pen fish culture Transition area between phytoplankton dominance and macroplant dominance (Hu et al. 211)

5 The subarea in Lake Taihu Eutrophic area Hypereutrophic area Little photosynthetic activity half of the area covered by macroplant vegetation Submerged macrophytes Macroplant and pen fish culture Transition area between phytoplankton dominance and macroplant dominance (Qin et al. 21)

6 Taihu Eddy Flux Mesonet Lake Taihu is large (area of 24 km 2 ) and shallow (depth of 2 m) and is situated in the Yangtze River Delta, East China. Five eddy covariance systems were installed on platforms located in the north, east, south, west and middle of the lake, representing different biological zones andwind wind wave wave patterns. One eddycovariance system was installed onthe east shore. (Xiao et al. 213)

7 Meiliangwan site (MLW, 31 o 25 4"N, 12 o 13 8"E) Phytoplankton is abundant and no submerged macrophyte is present. Started on 14 June 21. Water depth: 1.9 m. 35m 3.5 Water temperature and meteorological measurements

8 Dapukou site (DPK, 31 o 15 58"N, 119 o 55 52"E) Phytoplankton is abundant and no submerged macrophyte is present. The measurement started on 18 August 211. Water depth: 2.6 m. Wind speed is ~1% greater than at the rest of the sites ~8.5m ~2.4m ~11.5m

9 Bifenggang site (BFG, 31 o 1 28"N, 12 o 24 1"E) 6 m Submerged macrophytes (mainly Potamogeton malaianus and Hydrilla verticillata) dominate the aquatic ecosystem Started on 15 December 211 Water depth: 1.8 m 8.5 m 2.5 m

10 Xiaoleishan site (XLS, 3 o 59 5"N, 12 o 8 4"E) Transition areabetween phytoplankton dominance and macroplant dominance Started on 24 November 212 Water depth: 1.8 m 6 m 2.5 m 8.5 m

11 Is being built Will be ready in ~1 month

12 Dongshan site (DS, 3 o 2 24"N, 12 o 15 36"E) A companion land site is located in the Dongshan (DS) Peninsular on the southeast shore of the lake.

13 Evaluation of the CLM4 lake model at a large and shallow freshwater lake By reducingk k e to 2% of the value calculated with the parameterization of Henderson Sellers (1985), CLM4 LISSS was able to reproduce the observed vertical thermal stratification and diurnal variations in T s and to improve the T s prediction during frontal disturbances. (Deng et al. 213, in press)

14 (a) ) u * (m s -1 Transfer coefficients of momentum, heat and water vapour in the atmospheric surface layer of a large freshwater lake u 1 (m s -1 ) (b) LE (W m -2 ) (c) ) H (W m -2 ) u 1 (q s - q a ) (kg kg -1 m s -1 ) u 1 ( s - a ) (K m s -1 ) C D1N 1 3 C E1N C H1N BFG DPK MLW Garratt u 1 (m s -1 ) Site 1 3 C D1 1 3 C E1 1 3 C H1 At the MLW and DPK sites (free BFG 1.1 ±.2.95 ± ±.2 of submerged macrophytes), the observed C D1N was higher DPK 1.89 ± ± ±.2 than the prediction according MLW 1.8 ±.2.94 ± ±.2 to the Garratt (1992) model for the marine environment. The effective momentum transfer coefficient was reduced by approximately 4% in the It appears that at the same wind speed, the water surface of the lk lake was rougher than presence of submerged macrophytes. the ocean surface. (Xiao et al. 213, in review)

15 Temporal and spatial variations in radiation and energy balance across a large freshwater lake in China Due to the shallowness of Lake Taihu and high temperature, its annual Bowen ratio was very small (.12.13). Radiation Com mponents (W m -2 ) DPK MLW 6 6 (a) (b) (c) K K R n L L DS The radiation and energy balances showed little spatial variations across this lake at least on the monthly and annual time scale. nergy Fluxes (W m -2 ) E 6 (d) 4 2 DPK R n E H Q Beijing time 6 (e) 4 2 MLW Beijing time 4 (f) DS Beijing time Lk Lake Tih Taihucan be parameterized as one grid cell in climate models. (Wang et al. 213, in review)

16 Ts ( C) Ta ( C) 4 (a) 2 4 (b) DS MLW DPK BFG R n (W m -2 ) Q/G (W m -2 ) 2 (d) 1 5 (e) -5 H (W m -2 ) 4 (c) 2 E (W m -2 ) 2 (f) 1 J A S O N D J F M A M J J A S O N D J F M A M J J A Month The sensible and lt latent theat tfluxes appeared insensitive iti to wind speed, water pollution status and the effect of submerged macrophytes. On the annual time scale, the lake latent heat flux was 37.7 W m 2 or 87% greater than that of the adjacent land site. The commonly used Priestley Taylor coefficient of 1.26 would underestimate the annual evaporation at Lake Taihu by 1%. (Wang et al. 213, in review)

17 Flux gradient measurement of CH 4 /CO 2 /H 2 O and isotopic H 2 O at MLW site p 2 GD EC 2 m GD EC cm 1.1m water surface

18 Poster: EGU GD EC cm 1.1m water surface