To assess habitat stability of halophyte, we designed three types of experimental systems which were involved seawater tank, Mesocosm and recirculation tank (Figure 1). Nine, 65-L polypropylene tanks were installed indoors. Each Mesocosm engineered with adjustable tidal level. All tanks were flooded simultaneously through

PVC piping system controlled by an electrical solenoid valve with a 24-h interval timer. We adjusted the timer setting daily so that flood/ebb cycles corresponded to 6-h. When the solenoid interrupted seawater flow, mesocosm drained by gravity over the 6-h ebb tide phase to the prescribed depth below the soil surface before the next flood cycle began.

Our experimental design involved flooding all tanks with nature seawater (35 ppt salinity) and then allowing them to drain a prescribed depth below the soil surface on a continuous cycle basis that corresponded with the nature tidal cycle in the same geographic area.

It was constructed the halophyte Mesocosm experimental which was used tidal flat and dredged sediment as a substrate material. With the experimental plot we constructed three Mesocosms of the following conditions: 1) tidal flat sediment with Salicornia herbaria 2) only dredged sediment 3) dredged sediment with Salicornia herbaria.

When ebb-tide, each Mesocosm discharged the seawater to the recirculation tanks. Sampling was performed twice in a week during a month. Seawater temperature and Salinity were measure by using CT (COMPACT CT ACT-HR, ALEC). Chemical Oxygen Demand (COD) was analyzed by Potassium Permanganate test. Total Nitrogen (T-N) was analyzed by Cd-cu reduction method. Total Phosphorus was analyzed by ascorbic acid test.

We monitored the variation of chemical oxygen demand (COD), total nitrogen (T-N) and total phosphorous (T-P) in the sediment of Mesocosm. Samples of 10 cm depth collected at three points in each Mesocosm using core samplers. Sampling performed twice in a week during a month. The samples kept at 4˚C until their arrival at the laboratory.

COD analyzed using the potassium permanganate method [13]. T-N analyzed using the kjeldahl procedure and T-P analyzed using the molybdenum blue method after pretreatment with the ashing method [13].

The emergence of each new aerial shoot was recorded every week throughout the experimental period. When ebb tide drain, we measured the shoot height from the surface of sediment. Actually, it was necessary to analyze biomass but we didn’t analyze. We plotted thirty Salicornia herbeceas in Mesocosm A and C.

The Habitat Suitability Index (HSI) contains nine variables for halophyte (Salicornia herbecea) growth. The Habitat Stability provides an objective quantifiable method of assessing the habitat conditions for Salicornia herbecea within a Mesocosm by measure how well each habitat variable meets the habitat requirements of the species by life stage. The index thus provides an objective basis for predicting impacts, guiding habitat protection, mitigation and enhancement and management decisions.

The task of evaluating the success of coastal marsh restoration has been difficult for lack of scientifically based criteria of habitat suitability for halophyte. An evaluation procedure based on proposed in this study. The following steps are taken to estimate the value of HSI in this mesocosm experiment.

1) Select mesocosm

For the coastal salt marsh in Mesocosm A, Mesocosm C is constructed salt marsh with dredged sediment.

2) Monitor physico-chemical and bio-chemical indicators

Second step in the HSI development process is to measure chemical and biological characteristics to compare the mesocosm A and C. Sea water temperature, salinity, COD, IL, TN and TP were selected as the chemical indicators in Seawater. Then COD, IL, TN, TP were chosen to evaluate the changes of organic matters and nutrients of the sediment in the Mesocosm A and C. Nitrogen and phosphorus are primary macronutrients for plants. Soil organic matters are important for soil quality because they are nutrient sink and source, enhance soil physical and chemical properties, and promote biological activity [14] [15].

The values of COD affect availability of soil nutrients, and solubility of toxic nutrient elements in the soil.

3) Calculate HSI for each qualified indicator

To standardize and non-dimensioned the results of physico-chemical factors results in each Mosocosm, Z-score calculated by Equation (1). Then weight of each factor that influence to plant growth calculated by Equation (2).

4) Do the sum of weight for each physico-chemical factors and Z-score, Habitat Stability Score in Mesocosm A and C calculated by Equation (3).

5) [9] suggest Equation (4), it is a quantifiable method of assessing the habitat conditions for Salicornia herbecea within a Mesocosm by measuring how well each habitat variable meets the habitat requirements of the species by life stage.

Where x_i: raw data, μ: mean value, σ: S.D., Z_i: Standing value of environmental factors in mesocosm, γ_i: weight value of environmental factors, D_i: measured value of environmental factors, n: number of environmental factors in mesocosm (n = 9), V_Ri: initial value of HSS in mesocosm, V_Ci: measured value of HSS in mesocosm at each time.

To analyze the variation of HSI according to the time, it base on initial HSI value. If HSI value is close to one, it is possible to judge the more proper habitat for halophytes.

Initial temperature of inflow seawater is 16.1˚C. After one month, temperatures in each Mesocosm are 16.2˚C, 16.3˚C, 16.0˚C. There is no significant variance in Mesocosm (Figure 2(a) and Figure (b)). Seawater temperature shows rapidly variance between 15 and 27 days which is effected indoors laboratory experiments, it is easily effected by indoors temperature. Salinity reduced until 12 days and then stabilized after 21 days.

Inflows seawater of COD concentration is 3.25 mg/l. After one month, outflow seawater of COD concentrations ranged from 2.99 to 3.38 mg/l in Mesocsom (Figure 2(c)). The lowest COD concentration was observed at Mesocsom A, whereas the highest concentrations was recorded at Mesocosm B. Mesocosm A only reduced COD concentration, however, Mesocosm B and C were little increased. Reduction ratios of COD of the influent seawater in Mesocosm A and C that planted vegetation are higher than mesocosm B. When organic matter in seawater flowing into the Mesocosm tanks, it can settle to the sediment or absorbed by vegetation so that the removal of organic matter in decomposition process is carried out by microorganisms in the Mesocosm A and C. While Mesocosm B does not have any vegetation, COD removal rate is lower than other Mesocosms.

Inflows seawater of T-N concentration is 1.08 mg/l. After a month, outflows seawater concentrations ranged from 1.026 to 1.037 mg/l in Mesocosm (Figure 2(d) and Figure 2(e)). Nitrogen release can stimulate primary production in both the emergent marsh [16] and in downstream receiving waters [17]. T-N may be removed from the salt marsh completely via denitrification, which occurs under anaerobic conditions and are more likely to be found in water-logged sediments [18]-[21].

In case of T-P concentration, after a month 68.2%, 48%, 57% were reduced in Mesocosm A, B, C. The high productivity of natural salt marsh is largely dependent on the abundance and availability of primary plant nutrients, N and P, within the sediment. Phosphorus release can also stimulate production under conditions of high N or low salinity [22].

The availability of these nutrients, despite almost constant anaerobiosis, has been attributed to an energy subsidy provided by tidal fluctuations.

Figure 3(a) represents the variance of COD in Mesocosm with time. COD concentration in sediment is reduced 44%, 28%, 8% in Mesocosm A, B, C in a month. Generally, COD concentration is reduced with time. Reduced rates of COD concentration in Mesocosm B and C are lower than that in Mesocosm A.

Initial T-N concentration is the lowest in Mesocosm A, the concentration in Mesocosm B and C are similar. Generally, T-N concentration is reduced compare with initial concentration except Mesocosm B (Figure 3(b)). In case of T-P concentration reduced generally but there was no significant variance (Figure 3(c)). Denitrification rates can be limited by carbon availability and in this way, vegetation can influence denitrification rates in directly [23] [24]. Vegetation may also influence nitrification and denitrification by influencing the oxygen concentration of the salt marsh substrate within the rhizosphere [25] or by providing bacteria which can fix N in root nodules. There is evidence that N removal efficiency is not affected by the length of time the salt marsh has received N pollution, while, in contrast, the ability of a salt marsh to remove P is known to decline with time [26]. As a result, salt marsh have been associated primarily with a reduction in N loading, rather than functioning to reduce P loading to water bodies.

Shoot height of Salicornia herbecea was recorded about every week in a month. Average shoot height in Mesocosm A is changed from 7.3 cm to 7.9 cm, Mesocosm C is changed from 6.8 cm to 7.1 cm (Table 1). Generally, variance of shoot height is smaller than natural salt marsh, it seems that Mesocosm system is an enclosed system.

Habitat Stability Index is calculated by using the results of indicators in Mesocosms. Compare with Mesocosm A and C, average HSI value is 0.89 in Mesocosm A and 0.91 in Mesocosm C (Table 2). Average HSI value in Mesocosm C is higher than that in Mesocosm A.