FLUXES OF CO2 AND CH4 UNDER DIFFERENT TYPES OF COASTAL SALT MARSHES OF THE YELLOW RIVER DELTA: DYNAMIC CHANGES AND DRIVING FACTORS ACROSS DIFFERENT SEASONS - Salt Marshes - page 40

where F is the gas flux. The d c /d t is the slope of the gas concentration curve variation, along
with time. M is the mole mass of each gas. P is the atmospheric pressure in the sampling site.
T is the absolute temperature during the sampling. V 0 , T 0 , P 0 are the gas mole volume, air
absolute temperate and atmospheric pressure under standard conditions, respectively. H is the
height of the chamber during sampling.
During gas sampling, we also measured the air temperature inside and outside the
chambers, atmospheric pressure. Soil temperatures were measured from soil surface to 20cm
depth at 5-cm intervals. Soil volumetric moisture and electrical conductivity (EC) (0, 5, 10
and 15 cm depths) were determined in situ by high-precision moisture measuring instrument
(AZS-2) and soil and solution EC meter (Field Scout), respectively. Soil EC of mudflat was
not determined since the values beyond the pale of the EC meter. At the same time, two soil
samples (0~10cm, 10~20cm) were taken back laboratory for analyzing the soil properties
(TC, TN, NO 3 -N, NH 4 -N).

2.3. Statistical Analysis

The observations were conducted in triplicate with the mean value being analyzed.
Pearson Correlation analyses were used to examine the relationship between fluxes and the
environmental variables by SPSS 20. In all tests, differences were considered significantly
only if p <0.05.

3. R ESULTS

3.1. Variation of CO 2 Flux from Different Vegetations

As Figure1 showed, over all sampling periods, CO 2 fluxes ranged from 2.287 to 331.371
mg/(m 2 ·h) and had obvious seasonal variation (Figure 1), followed the order: winter (9.031
mg/(m 2 ·h)) < autumn (69.730 mg/(m 2 ·h)) < spring (80.010 mg/(m 2 ·h)) < summer (149.631
mg/(m 2 ·h)). The annual average flux of CO 2 was 77.101 mg/(m 2 ·h), indicating that coastal
marsh acted as a CO 2 source.
CO 2 emissions in four sites (the bare land, T. chinensis, S. glauca P. australis ) all
showed single-peak curves and the maximum occurred in April, July, August and September,
respectively. The values among the four marshes were significantly different ( P<0.05 ), and
the CO 2 emission of different ecosystem followed the order: bare land (16.264 mg/(m 2 ·h)) <
S. glauca (64.784 mg/(m 2 ·h)) < P. australis (119.430 mg/(m 2 ·h)) < T. chinensis (167.138
mg/(m 2 ·h)).