Tides in the area are in the "Diurnal tide" mode with a cycle of about 25 hours, average tides, average amplitude of 150 - 180 cm per day, the largest tide reaches 3.9 m, the smallest is 0.1 m.
Hydrology in the tidal flat area of Giao Thuy district is supplied with water from the Red River. There are two main rivers in the tidal flat area: Vop River and Tra River, in addition to a number of small creeks providing natural water drainage.
Vop River: Flows from Ba Lat estuary to Giao Hai sea, about 12 km long, is the boundary between Con Ngan and Bai Trong. In 1986, the Vop Dam separated the Vop River into two parts: East Vop and Tay Vop. Therefore, without water circulation for many years, the length of the Vop river was filled with silt; In 2002, the Vop Dam was opened, but the current water flow through the Vop River is still very small, fresh water cannot reach the downstream, high salinity in the water has been causing changes in the ecosystem.
Tra River: Flows from Ba Lat estuary south to the sea, meeting Vop River in Giao Hai sea, about 12 km long, and is the boundary between Con Ngan and Con Lu. The Tra River was filled in the middle (from Nut to the end of Con Ngan) because the sea pushed the sand bar across the Ba Mo area (Con Lu) to overflow the floodplain and fill the end of the Tra river.
Thus, the Tra River is only open to traffic when the tide floods the tiger parrot beach. This is also a major limitation to the hydrological conditions in the area, negatively affecting the survival and ineffective development of many plant and animal species in the end areas of Con Ngan and Con Lu.
Hydrological characteristics of the Red River system: The Red River has an average total water volume of 114,109 m3 / year and a sediment flow of 115 million tons/year. This sand and mud flow contributes to accreting the Red River Delta with an average speed of 17 - 83 m/year. In the flood season, the flow accounts for 75 - 90% of the total water volume of the year and carries up to 90% of the sand and mud, causing flooding of the delta, filling up river channels and making the estuary area dry. sweetened. On the contrary, in the dry season, the estuary area is narrowed, the tide rises, bringing salt water deep into the continent along the rivers, increasing the scope of salinity.
The area's seawater salinity varies greatly depending on the hydrological phase and flood regime of the Red River. In winter, the average salinity of sea water
relatively uniform in the range of 28 - 30 o / oo . In summer, the average salinity is lower than in winter, fluctuating between 20 - 27%.
With its geographical location and natural resource conditions with a long history, the Xuan Thuy National Park area has suitable conditions for growing a number of mangrove species to protect the coast, preserve soil, and create Calves are great carbon absorbers. However, climatic factors (cold winters) have significantly affected the distribution, growth and development of mangrove species.
d. Mangrove forest in Xuan Thuy National Park, Nam Dinh
In the study area, there appear 17 species belonging to 11 families, including 6 families of true mangroves such as Mam, Don nem, Duoc, Ban, Aro, Castor and 5 families "joining" mangrove forests including : Beans, Sedge, Rice, Salted Vegetables, Convolvulus, details as follows:
Table 1. 5: Species composition in the study area
The Oro family
Under the dust
Curly fish sauce
Ipomoea pes - caprae
The Don Nem family
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Among the above species, only acanthus, sour crab, fish sauce, mam quan, trang, and tiger are native plants, the remaining species may be species that have moved from other places, they have a large number of species. Small quantity and small size of trees located under the canopy of other tree species.
According to Phan Nguyen Hong (1991), coastal mangrove forests in Vietnam are divided into 4 areas, of which Xuan Thuy National Park is located in area II, an area with conditions such as: Located within the Convergence of the Thai Binh river system, Red river and tributaries, so there is a lot of silt, rich in nutrients, large tidal range of 3 - 4 m, wide mudflats in both the river mouth and coastal areas but are affected by wind. Due to storms, mangrove trees are less developed and the species composition is relatively limited. In this area, the rate at which the dyke is encroaching on the sea is relatively fast, so mangrove trees are only narrowly distributed outside the dyke, along river estuaries. Mangrove forests in Xuan Thuy National Park are currently well protected (there is a national park plan, prepared by Nam Dinh Provincial People's Committee), below is a picture of the study area (Figure 1.5).
Figure 1. 5: Diagram of the research area
Many authors have divided the mangrove flora into two groups: the group of "true" mangrove species and the group of mangrove trees that "join" the mangrove forest. However, many taxonomists often have difficulty distinguishing between these two types (Phan Nguyen Hong, 1999), so the division is only relative.
Besides the two plant groups mentioned above, there are also groups of immigrant tree species in the study area. This group includes many species that originally belonged to inland areas and did not participate in mangrove forests, but due to land changes such as road construction, embankment of shrimp ponds, house foundations... high ground is no longer flooded or due to import plant varieties for production.
* Distribution of plant species in the study area:
The presence of a mangrove plant species in a specific area depends on ecological conditions such as temperature, rainfall, soil... Because the research area is located along the coast of region II, so The number of species is poor and the forest structure is quite simple. Among the species with a wide distribution range in this area are species such as Avincennia marina , Aeficeras corniculatum , Kandelia candel , and Acanthus ilicifolus . Derris trifoliata only appears in areas where alluvial soil has stabilized the base with compact clay, flooded at high tide.
Like the distribution of mangrove species over time and space, the distribution of natural communities also follows certain rules and depends closely on the tidal regime and the stability of the ecosystem. background body (Nguyen Boi Quynh, 1997). The main biomes in the area include:
- Avicennia lanata community is a pioneer with Cynodon dactylon and Suaeda maritina species on newly alluvial sandy beaches with average tidal inundation in the Nut beach area of the commune. Giao Xuan, where coastal sand beaches are poor in nutrients.
- Aeficeras corniculatum and Kandelia candel mixed commune on average tidal floodplain, quite stable alluvial soil, located about 0 - 100 m from the river bank towards the mainland.
- The mixed community of Avincennia marina is on the higher layer, followed by tiger and hornbeam on a stable substrate, compact clay, with the participation of acanthus. This group is located in the middle of the forest, they have high density, and the canopy is 100% closed.
- Typical brackish water plant community with Soneratia caseolaris dominant in the upper layer along with other plant species such as holly, sedge, and tiger grass distributed on deep mud flats in estuaries and along the river. In addition, near the dyke, where the terrain is low and muddy, there are also sour crab, holly and black tiger.
From the mouth of the Ba Lat River back along the banks of the Tra River, there are very few natural mangrove trees, but only a few salt-tolerant tree species such as cock grass, sedge, and especially Scirpus kimsonensis (Scirpus kimsonensis) grow strongly . , sometimes covering the entire beach, attracting geese and mallards to feed in flocks.
In the distribution of communities here, we see that there are two types of communities: the mangrove vegetation community with the pioneering role of fish sauce and the community in the brackish coastal water along the Tra River. with the pioneering role of Sour Sourdough.
1.4.2. Social and economic conditions
1.4..2.1. Economic activities
a. Agricultural and aquatic production
In recent years, marine economic development has been identified as a key economic sector in the region's economy. The average annual growth rate reaches 15 - 20%, accounting for 20 - 25% of the agricultural and aquatic products group. All buffer zone communes have had positive changes in the fields of farming, natural exploitation and services. Of which the farming industry accounts for 51.5%, natural exploitation accounts for 48.5%. Many communes have established cooperatives for exploiting and processing aquatic products such as Giao Hai commune and Giao Thien commune.
Mollusk farming in Giao Lac, Giao Xuan and Giao Hai communes is strongly developed, with nearly 500 hectares of sandy beaches in the end area of Con Lu and Con Ngan, generating annual income of tens of billions of dong. (in 2007, it reached nearly 150 billion VND). However, this is still a spontaneous, extensive, and unstable aquaculture profession, so sustainability is not high.
Shrimp farming in the system of shrimp farms in the area has had poor results in recent years because the farming environment is polluted, natural aquatic products have declined due to overexploitation and are gradually drying up. masterpiece of the community. On average, one hectare only yields about 100 kg of shrimp/year, with an average income of less than 15 million VND/ha/year.
Free exploitation of aquatic resources in tidal areas has also brought significant income to local poor and average communities. However, this profession has been concentrating most of the unskilled workers in the area during the off-season, so it has caused many disturbances and complications for the management of aquatic resources and security and order in the region. the outcrop of Xuan Thuy National Park.
b. Services and tourism
Xuan Thuy National Park is a unique tourist destination. This place has both forest and sea; Cool and fresh climate all year round. During the migratory bird season, visitors can directly admire many rare species of birds living in large flocks. Aquatic resources are also quite rich, contributing to creating the highlight of the tour. In recent years, the number of international visitors to Xuan Thuy National Park has been about 30 - 40 groups/year. The number of visitors is about 100 - 200 people/year, with nearly 30 nationalities. The largest nationalities of visitors are British, American, Dutch, and Australian. The majority of visitors are biological scientists (who study birds or mangroves and aquatic life). Some tourists come to see birds during migratory bird season, according to information on the Internet, or through brokers of travel companies such as Saigon Tourist, Dalat Tourist, Sao Mai, Hoan Kiem... Domestic visitors increase every year, about 200 groups/year. The number is about 3,000 - 5,000 people/year. The main subjects are students, visiting officials and local children who travel far to visit their hometowns.
However, due to outdated and poor facilities, the environment is somewhat affected by the amount of waste left by tourists.
Economic activities of localities in recent times are causing increasing pressure on environmental protection and sustainable economic development in the Xuan Thuy National Park area:
1.4 . .2.2. Social activities
a. Social characteristics
Population and population density: There are five communes in the buffer zone of Xuan Thuy National Park
43,286 people, 12,842 households with a total natural area of 40.18 km 2 . The population density of the communes is relatively uniform, on average 1,077 people/km 2 . The commune with the highest density is Giao Lac with 1,336 people/km 2 , the commune with the lowest density is Giao Thien with 804 people/km 2 .
Population growth rate: The population growth rate of the 5 buffer zone communes is relatively even and average
military over the years is 1.18%; The number of people giving birth to a 3rd or 4th child is still present, often concentrated in communes with many Catholics. The main reason is that people's awareness is still quite heavy on giving birth to children on one side and suffering a lot. the influence of outdated customary laws.
Population growth requires increased living needs and essential needs
while the amount of available resources is limited, especially land resources for agricultural production. The inevitable consequence will be to expand the land area for agricultural production into forest land.
Labor structure: Number of people of working age in Buffer Zone communes is
23,429 people, accounting for 47.40% of the population. Of which, there are 24,501 female workers (accounting for 49.57%). On average, each household has 2 people of working age.
Occupational structure: Human resources in the buffer zone area focus mainly on agricultural and fishery production, accounting for 69.45% of the workforce, the rest are in other occupations.
Table 1. 6: Summary of population and labor in communes in the buffer zone of Xuan Thuy National Park
- Agriculture and fishery labor
- Non-agricultural labor
Source: Giao Thuy district statistical yearbook 2011
With the above labor and population structure, it has put great pressure on environmental resources in the Xuan Thuy National Park area. The reason is partly due to the lack of secondary industries, income from agricultural production does not ensure a living, on the other hand, due to the great attractiveness of the current seafood market, aquaculture and exploitation activities are Exploiting natural resources in the tidal zone of Xuan Thuy National Park has attracted most of the surplus forces of the buffer zone.
b. Life situation of people in communes in the buffer zone
Rich and poor ratio: According to household classification criteria (2002) and results
Directly verifying a number of households in the area (based on two main factors: fixed asset value and average annual income of households). The results show that in recent years, the number of rich and well-off households in buffer zone communes has increased rapidly, and the number of poor households has decreased significantly, to only about 13.4% of poor households (1.4% lower than the district average). ), quite rich 23.2%, average 63.4%.
Income situation: Income in buffer zone communes mainly comes from agriculture and the marine economy, average income is calculated based on the following sources:
- Revenue from food production accounts for: 39.3%
- Income from raising livestock and poultry of all kinds accounts for: 10.0%
- Revenue from marine economy accounts for: 36.1%
- Other industries such as commercial services, industrial and handicraft industries, accounting for 14.6%
Family living conditions: In recent years, the economy in the region has made significant progress, and living conditions in households have also gradually improved. The houses of families in the area are mainly solid and semi-permanent houses, accounting for 63%. Level IV houses account for a small proportion of 37%. Valuable items serving family comfort such as televisions, motorbikes and other valuable items account for a fairly high proportion.
Thus, in the study area there are some characteristics as follows:
Due to not fully understanding the multifaceted value of the mangrove ecosystem, or due to immediate economic benefits, local people who rented land in the area at the beginning of Trong beach and part of Ngan island have cut down the mangrove forests. salinity to convert to aquaculture, or build surrounding banks to retain fresh water and tide water to reduce the salinity of the water and increase the flooding time, so some species of mangrove plants cannot survive (parrot trees), so the area Forest area in this area has decreased significantly. The area at the end of Trong beach and the end of Ngan islet were also extensively cut down to raise wild animals.
Chemicals and potentially toxic substances at the bottom of the lagoon such as CH 4 , H 2 S are transferred by tides to bivalve breeding grounds, reducing the productivity of raising these animals;
Due to the lack of close coordination between sectors, especially fisheries and forestry, not only are forests lost but the ecological balance is reduced.