Flux footprint analysis of a salt marsh ecosystem in the Jiuduansha Shoals of the Changjiang Estuary

doi:10.3969/j.issn.1000-5641.2021.02.005

Abstract

Abstract:

Flux footprint analysis is an important step in studying the carbon, water vapor, and heat flux exchange of land-atmosphere interactions based on the eddy covariance (EC) method. In this research, we used the flux source area model (FSAM) to investigate seasonal flux footprints with different wind directions and atmospheric conditions on the basis of half-hourly EC measurements throughout 2018. The results showed that: ① The flux footprint area changes with the seasons. The largest flux footprint area, ordered highest to lowest, was found in autumn, summer, spring, and winter under stable stratification; meanwhile, under unstable stratification, the flux footprint area did not change significantly between seasons. The daily variation in the footprint, moreover, was obvious and the footprint was found to be larger comparatively at nighttime than that observed during the daytime. ② The flux source area under non-prevailing wind conditions was larger than that under the prevailing wind condition. ③ The flux source area was much larger under stable stratification. The distance between the location of the maximum value of the flux footprint and the station was also found to be much larger under stable stratification.

Key words: Jiuduansha Shoals, eddy covariance technique, FSAM, footprint analysis

CLC Number:

P933

Zihan CHEN, Ying HUANG, Jianwu TANG, Bo TIAN, Fang SHEN, Pengfei WU, Qing YUAN, Cheng ZHOU, Jiangtao WANG. Flux footprint analysis of a salt marsh ecosystem in the Jiuduansha Shoals of the Changjiang Estuary[J]. Journal of East China Normal University(Natural Science), 2021, 2021(2): 42-53.

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	风向/(°)	春季			夏季			秋季			冬季
	风向/(°)	3月	4月	5月	6月	7月	8月	9月	10月	11月	12月	1月	2月
最大风速/(m·s^–1)	22.5 ~ 112.5	9.21	7.99	7.99	6.60	13.55	12.19	7.50	10.10	8.72	9.28	8.52	7.43
	112.5 ~ 202.5	7.72	8.74	7.68	6.88	8.45	12.64	5.67	5.12	4.89	5.33	5.07	8.37
	202.5 ~ 292.5	5.86	7.53	7.51	6.70	9.50	8.15	4.26	3.54	4.62	4.29	3.72	7.11
	292.5 ~ 22.5	9.01	10.39	7.50	5.99	9.63	7.27	6.22	11.17	8.63	8.06	8.76	11.02
最小风速/(m·s^–1)	22.5 ~ 112.5	0.39	0.43	0.38	0.29	0.19	0.37	0.24	0.10	0.20	0.20	0.30	0.69
	112.5 ~ 202.5	0.56	0.41	0.19	0.19	0.071	0.38	0.05	0.27	0.25	0.35	0.28	0.94
	202.5 ~ 292.5	0.92	0.77	0.34	0.44	0.17	0.56	0.28	0.12	0.065	0.33	0.24	0.95
	292.5 ~ 22.5	0.50	0.43	0.08	0.40	0.29	0.19	0.15	0.31	0.29	0.39	0.16	0.27
平均风速/(m·s^–1)	22.5 ~ 112.5	5.45	4.21	3.58	3.31	4.07	4.40	3.47	3.38	3.10	4.46	4.21	3.95
	112.5 ~ 202.5	4.31	4.20	3.59	3.17	4.42	4.77	2.26	2.29	2.29	2.26	2.55	4.12
	202.5 ~ 292.5	3.52	3.69	3.31	2.94	3.93	4.38	2.14	2.07	2.40	2.27	1.86	3.21
	292.5 ~ 22.5	4.94	5.93	3.73	2.93	1.99	4.08	2.71	4.44	3.74	4.62	4.59	4.34
风向频数/%	22.5 ~ 112.5	24.40	18.89	20.95	16.60	12.44	28.02	48.13	62.03	51.23	51.24	56.74	45.61
	112.5 ~ 202.5	50.34	50.28	50.54	59.79	68.93	56.12	22.50	14.65	24.74	16.41	18.75	21.13
	202.5 ~ 292.5	11.02	15.56	18.79	19.38	16.07	11.09	15.63	3.97	6.32	6.73	2.78	12.35
	292.5 ~ 22.5	14.24	15.27	9.72	4.23	2.56	4.77	13.74	19.35	17.71	25.62	21.73	20.91

	Z_m/Z₀	Z_m/L	$ {\sigma }_{y} $ /u*
白天	25.63	– 0.127	2.3532
夜晚	25.63	0.321	2.1667

生态系统	下垫面植被类型	观测高度/m	P水平	最远点距离/m	最大值点距离/m	参考文献
森林生态系统	美洲黑杨	25	0.9	3613.0	317.00	[18]
森林生态系统	橡胶树	25	0.8	1858.0	413.00	[31]
农田生态系统	冬小麦	3.5	0.9	222.0	67.80	[29]
荒漠生态系统	梭梭	11	0.9	670.8	151.06	[32]
湿地生态系统	芦苇	6	0.9	378.2	96.84	[2]
湿地生态系统	芦苇、海三棱藨草	4.8	0.9	438.8	105.20	[28]
湿地生态系统	芦苇	10	0.9	836.0	35.50	本文

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