Studies on development and environmental effects of halophyte communities in Saemangeum reclaimed land

Abstract

The two objectives of the present dissertation are to clarify development of halophyte communities constructed in Saemangeum reclaimed land and to quantify the environmental effects of halophyte communities. Through halophyte community development using 11,652 kg of eight halophytic species in 2,866 ha of the land from 2006 to 2008, halophytic area confined to autogenous 689 ha in 2005 increased to 4,364 ha by 6.3 times. The number of halophytic species increased from 4 in 2006 to 25 in 2008 and both average and maximum population densities rapidly increased. Besides, the number of plant species increased in 79% of the common quadrats for three years and halophyte community growth classified into five classes (from Class 1 to Class 5 with smaller numbers indicating better growth) was improved as the proportion of quadrats belonging to Class 1 or Class 2 increased from 38% to 86.8%. In salt response and flooding experiments, halophytic species with ever-increasing emergence percentage as soil electrical conductivity (EC) dropped to 0.88 dS m-1 through four-time desaltings were Suaeda asparagoides, Suaeda japonica, Limonium tetragonum, and Atriplex gmelini. S. asparagoides and S. japonica had an advantage for growing in the intermittently-flooded condition. Annual halophytes of S. asparagoides, S. japonica, and S. europaea were categorized into the upper EC group. Halophyte communities always located above high water level during the growing seasons and did not emerge in the seawater-flooded areas. In 2006, magnesium, potassium and sodium as well as soil EC had a significantly negative relationship with halophyte community growth. The negative relationship between plant species and soil EC persisted until 2008. Plant height was found to have a significantly negative relationship (R2=0.95) with soil EC. The electrical conductivity of a saturated soil extract (ECe) according to halophyte community growth from seven ECe maps made by electromagnetic measurement system was 24 to 27(±9) dS m-1 for Class 1, 31 to 36(±8) dS m-1 for Class 2, 33 to 37(±10) dS m-1 for Class 3, and 29 to 33(±13) dS m-1 for Class 4 respectively. Sixty eight % of quadrats in rake-plowing area showed growth better than Class 4, whereas 53% of quadrats in non-plowing area did. In the experiments on wind reduction by halophyte communities, the wind was blocked at a height of 20 cm within a halophyte community beginning to be clearly reduced from the starting point of halophytes and stabilized through halophytes. The maximum wind reduction was 82 to 38% at a height of 20 cm within a halophyte community. Wind velocity was reduced through halophytes largely at heights of below 60 cm, which are lower than halophytes. Wind reduction percentage by a halophyte community was maximally 76% at a height of 20 cm. Total suspended particulate (TSP) decreased by 60.7% passing through a group of transplanted halophytes and the reduction effect continued almost the same to 50 m behind the community. Dust reduction behind halophyte communities amounted to 43.8 ug m-3 for TSP and 14.7 ug m-3 for PM10 (Particlulates <10 μm). TSP collected within halophyte communities averaged 37.0 ug m-3 with differenences among four halophyte communities of S. asparagoides, Phragmites communis, Atriplex subulatus, and S. europaea. Nitrogen (total nitrogen), phosphorus (P2O5), and sodium (Na+) contents absorbed by halophytes in 2005 before halophyte community development were 2.60, 0.14, and 4.98 g m-2 respectively. Nitrogen, phosphorus, and sodium contents in S. asparagoides, S. japonica, and S. europaea were 1.24 to 2.20 g m-2, 0.07 to 0.13 g m-2, and 2.91 to 4.59 g m-2. However, in 2010 after halophyte community development, they were 0.45 g m-2, 0.04 g m-2, and 0.08 g m-2 respectively. On the basis of halophyte community area developed in 2006 (1,236 ha), the amount of total nitrogen (T-N), P2O5 and Na+ absorbed by only a major halophytic species of S. asparagoides amounted up to 439, 78, and 914 ton respectively. In conclusion, it was most critical to select halophytic species with superior qualities against the harsh environment of reclaimed land such as salinity and flooding for halophyte community development. The annual halophytes mainly used in sowing not only held high germination capacity and velocity but also displayed broad salt-adaptability and tolerance to flooding. Sowing in the area at higher elevation than high level of seawater was important for halophyte communities to emerge. EC among soil properties had a significantly negative relationship with halophyte community until 2008. It was found that halophyte communities were capable of collecting significant dust as well as definitely reducing and stabilizing wind velocity. A great deal of nitrogen, phosphorus, and sodium absorbed into halophytic species in the reclaimed land can consequently contribute for lowering the levels of soil nitrogen and phosphorus leading to freshwater lake eutrophication or improving salt-affected soils.