Scholarly article on topic 'Degeneration Mechanism Research of Suaeda Heteroptera Wetland of the Shuangtaizi Estuary National Nature Reserve in China'

Degeneration Mechanism Research of Suaeda Heteroptera Wetland of the Shuangtaizi Estuary National Nature Reserve in China Academic research paper on "Biological sciences"

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{"Shuangtaizi River Estuary" / "degeneration mechanism" / " Suaeda heteroptera wetland"}

Abstract of research paper on Biological sciences, author of scientific article — Yan Wang, Ruhai Liu, Huiwang Gao, Jie Bai, Min Ling

Abstract Recently, Suaeda heteroptera wetland of the Shuangtaizi River Estuary national nature reserve in China degenerated seriously, and this has led to a decrease in the Saunders’ Gull population. In this study, the nitrogen, phosphor, organic matter and soluble salt contents in soil were determined, and the biomass(dry weight) and plant height were determined too aiming to explore the mechanism of degeneration of the Suaeda heteroptera population. The nitrogen, phosphor and organic matter contents in four types of wetland were all at D level and fertility degree was lower, It could be inferred that nutrients in soil was not the reason of degeneration of Suaeda heteroptera wetland. However, the soluble salt in mudflat soil reached as high as 2.51% in the spring and was significantly higher than that in other three types of wetland. This might be an important reason that the wetland degenerates into mudflat. We could conclude that the long time of no flooding and strong evaporation caused the increasing of salinity of soil and eventually cause the death of Suaeda heteroptera. In addition to human factors, the natural succession with the enlargement of new mudflat is one of the important reasons that make Suaeda heteroptera wetland disappear somewhere. The restoration measures must conform to the direction of natural evolution, otherwise, this restoration may be not sustainable.

Academic research paper on topic "Degeneration Mechanism Research of Suaeda Heteroptera Wetland of the Shuangtaizi Estuary National Nature Reserve in China"

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Procedía Environmental Sciences 2 (2010) 1157-1162

International Society for Environmental Information Sciences 2010 Annual Conference (ISEIS)

Degeneration Mechanism Research of Suaeda Heteroptera Wetland of the Shuangtaizi Estuary National Nature Reserve in China

Yan WANG, Ruhai LIU *, Huiwang GAO, Jie BAI, Min LING

Key Laboratory on Marine Environment and Ecology of Education Ministry, Ocean University of China, Qingdao 266100

Abstract

Recently, Suaeda heteroptera wetland of the Shuangtaizi River Estuary national nature reserve in China degenerated seriously, and this has led to a decrease in the Saunders' Gull population. In this study, the nitrogen, phosphor, organic matter and soluble salt contents in soil were determined, and the biomass(dry weight) and plant height were determined too aiming to explore the mechanism of degeneration of the Suaeda heteroptera population. The nitrogen, phosphor and organic matter contents in four types of wetland were all at D level and fertility degree was lower, It could be inferred that nutrients in soil was not the reason of degeneration of Suaeda heteroptera wetland. However, the soluble salt in mudflat soil reached as high as 2.51% in the spring and was significantly higher than that in other three types of wetland. This might be an important reason that the wetland degenerates into mudflat. We could conclude that the long time of no flooding and strong evaporation caused the increasing of salinity of soil and eventually cause the death of Suaeda heteroptera. In addition to human factors, the natural succession with the enlargement of new mudflat is one of the important reasons that make Suaeda heteroptera wetland disappear somewhere. The restoration measures must conform to the direction of natural evolution, otherwise, this restoration may be not sustainable.

© 2010 Published by Elsevier Ltd.

Keywords: Shuangtaizi River Estuary; degeneration mechanism;Suaeda heteroptera wetland;

1. Introduction

The natural Suaeda heteroptera community that located in inter-tidal zone of the Shuangtaizi river estuary in Panjin city, Liaoning province of China came into being beautiful red beach landscape, its distribution acreage had once achieved 10 km2. The red beach is the largest breeding habitat for Saunders' Gull (Larus saundersi) in the world and also an important feeding ground and breeding habitat of red-crowned crane that is in severe danger now.

^Corresponding author. Tel.: +86 532 66782356; fax: +86 532 66782810. E-mail address: ruhai@ouc.edu.cn (R. Liu).

1878-0296 © 2010 Published by Elsevier doi:10.1016/j.proenv.2010.10.124

In 1988, the Shuangtaizi River Estuary was included in national nature reserve of China, and in 1993, it was included in protection meshwork of "Chinese and biosphere". It allures a large number of visitors every year and accelerate the economy development of locality. However, recently the massive shrinkage of S.heteroptera vegetation has led to a decrease in the Saunders' Gull population. So the research of degeneration mechanism of Suaeda heteroptera wetland is the most impending thing currently. The four types of Suaeda heteroptera wetland, including flourishing, degenerating, manual resumptive Suaeda heteroptera wetland and mudflat that was Suaeda heteroptera wetland before 2000 were investgated, soil and vegetable samples were collected to analyze the degeneration mechanism of Suaeda heteroptera wetland.

2. Material and Method

2.1. Sampling sites description

The sampling sites are shown in Fig.1. The four types of Suaeda heteroptera wetland, including flourishing, degenerating, manual resumptive Suaeda heteroptera wetland and mudflat were chose as sample point. The soil and plant were collected at June 5, September 15, 2009, and April 5,2010, they represent summer, autumn and spring respectively. The Suaeda heteroptera growth was promising at flourishing Suaeda heteroptera wetland, the mudflat that was Suaeda heteroptera wetland before 2000 has no plant now. The manual resumptive wetland has sparse Suaeda heteroptera plant before 2009, but it restores growth by itself after it was irrigated by water of LaLing river.

2.2. Determination of samples

The nitrogen, phosphor, organic matter and soluble salt contents in soil were determined, and the biomass(dry weight) and plant height were determined too. The soluble salt contents was determined using gravimetric analytical

method, the nitrogen content was determined using kjeldahl determination, the phosphor content was determined using acid melt-molybdenum stibium anti-color method and organic matter content was determined using the method of potassium bichromate-dilution heat colorimetric.

3. Results and Discussion

3.1. The effect of nutrients in soil on the growth of Suaeda heteroptera

The nitrogen and phosphor are necessary nutrients of the growth of plant, and organic matter of soil is the important source of mineral and organic nutrition of plant. If the soil is lack of nutrition, the growth of plant is limited. Spring is the germination season of seed. According to the classification standard of soil fertility of second soil survey of China (table1), the phosphor and organic matter content are all at D level in the spring, the nitrogen content in flourishing and mudflat wetland are at C level, and at D level in degenerating, manual resumptive wetland (fig.2, 3). But the difference is not significant, the nitrogen, phosphor and organic matter content in mudflat is higher than that in other fields. The results showed that the nutrients of soil were not the constraints of the seed germination of Suaeda heteroptera in spring.

Table 1 The classification standard of soil fertility

A level

B level

C level

D level

E level

F level

Range of N(%) Range of P(g/kg) Range of OM(%) Soil fertility degree

>0.2 >1.0 >1.0 very high

0.15-0.2 0.8-1.0 0.8-1.0 high

0.1-0.15 0.6-0.8 0.6-0.8 medium

0.07-0.1 0.4-0.6 0.4-0.6 lower

0.05-0.7 0.2-0.4 0.2-0.4 low

<0.05 <0.2 <0.2 very low

Fig.2 The content of nitrogen and phosphor in soil in spring in four types of Suaeda heteroptera wetland

Fig.3 The content of organic matter in soil in spring in four types of Suaeda heteroptera wetland

At other season, the nitrogen, phosphor and organic matter contents in four types of wetland are all at D level, fertility degree is lower, but the growth status in four type of wetland are different greatly. At flourishing wetland, the dry weight and plant height of Suaeda heteroptera vegetation are all lower than that in degenerating and manual resumptive Suaeda heteroptera wetland (fig.4, 5). It could be inferred that nutrients in soil is not the reason of degenerating of Suaeda heteroptera wetland.

Fig .4 The biomass (dry weight) of Suaeda heteroptera in different types of wet in summer and autumn

Fig.5 The plant height of Suaeda heteroptera in different types of wetland in summer and autumn

3.2. The effect of soluble salt in soil on the growth of Suaeda heteroptera

According to the research data, we found that the difference of the soluble salt in soil was large (fig.6). The soluble salt in mudflat soil reached as high as 2.51% in the spring and was significantly higher than that in other three types of wetland (fig.6). Some researches had shown that the soluble salt content suitable to the growth of Suaeda heteroptera was 10g kg-1-16g kg-1, and when the soluble salt content was higher than 16g kg-1, the Suaeda heteroptera would grow slowly, or even die, when the soil salt was less than 10g kg-1, the Suaeda heteroptera could grow, but some plants appeared green in spring and summer[1](Zhu et al. 2006). Some researches had shown that although halophytes could resistant salt, but the rate of seed generation is the highest in fresh water, and the generation rate decreases with the salinity increasing outside[2,3] (Baskin et al.,1995; Zhao et al.,1999). The high soluble salt content in soil in spring made the seed of Suaeda heteroptera can not germinate. This may be an important reason that causes Suaeda heteroptera wetland degenerate. At other three types of wetland, the soluble salt content in soil in spring was all suitable to growth.

2. 5 2. 0

1.5 L. 0

0. 5 0. 0

manual degenerating flourishing mudflat resumptive

Fig.6 The content of soluble salt in soil in spring

£ 2.0

O 1.0 w

° 0.5 S I). (I

»manual resumptive

-degenerating

-flourishing

Fig.7 The content of soluble salt in soil in different types of Suaeda heteroptera wetland in different season

In summer, the soluble salt content in soil decreased because of the increasing of participation, quantity of water in river and absorbing salt by plant. In autumn, with strong evaporation, the soluble salt content in soil increases also. At mudflat in autumn, the soluble salt content in soil was lowest, it was because that it happened raining strongly when we collected soil sample at that site. The leaching of rainwater causes the low value of soluble salt content (fig.6). At manual resumptive Suaeda heteroptera wetland, due to fresh water irrigation the soluble salt content in soil in summer was as low as 0.48%, so the plant appeared green. Before 2009, Suaeda heteroptera was sparse at this site.

3.3. The effect of tide on the growth of Suaeda heteroptera

Comparing the flourishing wetland to the manual resumptive and degenerating wetland, we found that the soluble salt content in soil was not the lowest in spring, but it changed smoothly (Fig. 7), this was because that the flourishing wetland was submerged by diurnal tide everyday, the soluble salt content in soil was effected by tide, the salinity in tide changed smoothly too. However, the degenerating wetland is submerged only by spring tide, the manual resumptive wetland is not affected by tide. The results of Cui B.S. shows that the water depth suitable to the growth of Suaeda heteroptera is 0.42m , the interval of ecological threshold is 0.92-0.08m , the most appropriate interval of ecological threshold is 0.67-0.17m[4](Cui et al.,2008). The repeated dipping of tide avoids the salt accumulation in soil because of evaporation. We can conclude that water is another important reason that cause Suaeda heteroptera wetland degenerate.

The height elevation of mudflat increases because of the building of dam on the sea at mudflat, the long time of no flooding (>72h) and strong evaporation cause the increasing of salinity of soil and eventually cause the death of Suaeda heteroptera. At Shuangtaizi River Estuary, the new beach can form every year, the maximum expansion speed is 87 to 683m/a. The mean depositional rate is 0.189m/a. It is filled with sediment in obsolete tidal channel[5] (Zhu et al., 2009). With the increasing of instance to sea, the soluble salt content increases firstly, then decreases, water content decreases too.

3.4. The Succession of Suaeda heteroptera community

The deposit-enlargement of new mudflat drives the succession of natural landscape of Laohe river delta wetland. With the elevating of terrain and desalination of soil, the soil and plant change correspondingly. From the research, we could conclude that the building of dam accelerates the succession from the sea to the land, the order of succession is new mudflat to Suaeda heteroptera wetland to barren mudflat of high salt content to land with sparse

Suaeda heteroptera.

Research has shown that human activity is the key factor that causes Suaeda heteroptera wetland degenerate. Such as the building of dam, shrimp pond and road, these activities occupied directly Suaeda heteroptera wetland and made the acreage of Suaeda heteroptera wetland decrease[1] (Zhu et al.,2006). So scientists propose many restoration measures aiming at human factors. For example, digging tidal channel at degenerated mudflat and irrigating by brackish water. But we think the natural succession is one of the important reasons that make Suaeda heteroptera wetland disappear somewhere too. These artificial measures might react on the degenerated wetland in short time, at manual resumptive wetland, Suaeda heteroptera restore growth only by irrigation. But society generally wishes that restoration be made permanent. The ecosystem degradation is reversed and conditions in the future will be improved over their current state. If these artificial measures do not conform to the direction of natural evolution, we must consider whether they can be sustainable.

Wetland restoration is a systematic process[6] (Kirk et al., 2004). The emphasis of wetland restoration is to reestablish the ecological functions and the links between the biotic and abiotic components[7-10] (Loomis et al., 2000; Zedler et al., 2000; Ruiz-Jaen et al., 2005; Gallego Fernandez et al., 2007), and not just restore certain species group. Moreover, restoring aquatic ecosystems is far from an "off-the-shelf' science or technology now[11] (Bernhardt et al., 2005), we should set realistic and dynamic (instead of static) goals for future, instead of past, environment; assume multiple trajectories acknowledging the unpredictable nature of ecological communities and ecosystems; take an ecosystem or landscape approach, instead of ad hoc gardening, for both function and structure; evaluate the restoration progress with explicit criteria, based on quantitative inference; maintain long-term monitoring of restoration outcomes[12] (Choi, 2004). Overall, esteeming natural principles is the important question that we must consider.

4. Conclusions

According to the classification standard of soil fertility of second soil survey of China, fertility degree of soil was lower in four type of wetland, but the growth status in four type of wetland are different greatly, It could be inferred that nutrients in soil was not the reason of degenerating of Suaeda heteroptera wetland. The soluble salt in mudflat

soil reached as high as 2.51% because of the long time of no flooding (>72h) and strong evaporation in the spring, and was significantly higher than that in other three types of wetland, so salinity and water were important reasons that cause Suaeda heteroptera wetland degenerate.

From this research, we could conclude that the order of succession is new mudflat to Suaeda heteroptera wetland to barren mudflat of high salt content to land with sparse Suaeda heteroptera. In addition to human factors, the natural succession with the enlargement of new mudflat was one of the important reasons that made Suaeda heteroptera wetland disappear somewhere. The restoration measures must conform to the direction of natural evolution, otherwise, this restoration may be not sustainable.

Acknowledgements

The authors would like to thank the State Key Projects in the Water Pollution and Control Program (2008ZX07208-009) for supporting this research project. The authors also would like to thank Wang S. for assistance with sample collection.

References

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[2] Baskin CC, Baskin JM. Dormancy types and dormancy-breaking and germination requirements in seeds of halophytes. In: KhanMA, Ungal IA. Biology of salt to lerant plants. Michigan, USA: Chelse; 1995: 23-30.

[3] Zhao KF, Feng LT, Fan H. Characteristics of seed dormancy, dormancy breaking and germination in halophytes. Chinese Bulletin of Botany 1999; 16(6): 677-685.

[4] Cui BS, He Q, Zhao XS. Researches on the ecological thresholds of Suaeda salsa to the environmental gradients of water table depth and soil salinity. Acta Ecologica Sinica 2008; 4(4): 1408-1419.

[5] Zhu LH, Wu JZ, Hu RJ. Geomorphological evolution of the Liaohe river delta in recent 20 Years. Acta Geographica Sinica 2009; 64(3): 357-367.

[6] Kirk JA, Wise WR, Delfino JJ. Water budget and cost-effectiveness analysis of wetland restoration alternatives: a case study of Levy Prairie, Alachua County, Florida. Ecological Engineering 2004; 22: 43-60.

[7] Loomis J, Kent P, Strange L, Fausch K,Covich A. Measuring the total economic value of restoring ecosystem services in an impaired river basin: results from a contingent valuation survey. Ecological Economics 2000; 33:103-117.

[8] Zedler JB. Progress in wetland restoration ecology. Nature 2000; 15: 402-407