# Seasonal Variations of Carbon Dioxide, Water Vapor and Energy Fluxes in Tropical Indian Mangroves
## Materials and Methods
### Eddy Covariance Flux Tower Setup  
On an uninhabited island of about 11 km\({}^{2}\) in Sundarbans, the EC flux tower of 15 m was established at 21\({}^{\circ}\)49\({}^{\prime}\) N latitude and 88\({}^{\circ}\)37\({}^{\prime}\)E longitude on 1 April 2012 (Figure 1) to measure CO\({}_{2}\) and energy fluxes. The tower is surrounded by a continuous mangrove patch with dominant species _viz. Avicennia albu_, _Bruguiera gymnorrhiae_, _Rhizophora_, with a mean canopy height of about 5 m [23].  
A canopy walkway was constructed with cement blocks of 1 m height across the path to the tower in order to reach the EC tower through the marshy land and water-inundated areas (Figure 2). The tower base is established on a 2 m \(\times\) 2 m cement base to prevent it from sinking. The tower of 15 m is composed of triangular aluminum sections. The well-established guy wires hold the tower straight to perform measurements. All the major tower electronics are housed in a water-proof box at a height of 2 m above the ground. The tower is powered by three solar panels (120 W each) with rechargeable batteries.  
Figure 1: Sundarbans flux tower location on the false color composite (FCC) of IRS AWIFS.  
Micrometeorological and trace gas (CO\({}_{2}\)) measurements were made at a height of 10 m. A three-dimensional (3D) sonic anemometer, CSAT-3 (Campbell Scientific Inc., Logan, UT, USA), was used to measure high frequency wind velocity components (_i.e._, 3D orthogonal wind components u\({}_{x}\), u\({}_{y}\), u\({}_{2}\)) and sonic temperature (T). Considering the low power and low maintenance requirement at a remote site location such as Sundarbans (uninhabited and marshy land), an open path infrared gas analyzer system (IRGA), LI-7500A (LI-COR, Lincoln, NE, USA) was installed to measure the densities of carbon dioxide and water vapor. The IRGA was slightly angled to allow surface moisture drainage and prevent direct solar radiation from possibly contaminating readings [26]. The raw measurements from the sonic anemometer and IRGA were recorded using an analyzer interface unit, LI-7550 (LI-COR, Lincoln, USA), at a frequency of 10 Hz. The data is collected from 1 April 2012 to 31 March 2013 on a half-hourly basis with short time gaps (about 6%) due to low solar power (mostly occurring during rainy season due to continuous rains).  
The additional environmental variables were measured above the canopy at 10 s interval, averaged over 10 min and logged on to CR3000 (Campbell Scientific Inc. Logan, UT, USA) data logger. These measurements include net radiation (CNR 4; Kipp and Zonen, Delft, Netherlands) and incoming photosynthetic active radiation (PAR, LI-190 SB; LICOR, Lincoln, USA) at height of 10 m. Measurements also include air temperature and relative humidity (HMP45C-L; Campbell Scientific Logan, UT, USA), wind speed and wind direction (Wind Monitor 5103; RM Young, Traverse, MI, USA) at heights of 2 m, 4 m and 8 m. In addition, soil heat flux (HFT-3; Campbell Scientific, Logan, USA) is measured at two levels (2.5 and 5 cm) and soil temperature (107-B; Campbell Scientific, Logan, UT, USA) at four levels (5, 10, 20 and 40 cm). Precipitation at the study site has been recorded using a tipping bucket TB4-L (Campbell Scientific Inc. Logan, UT, USA).