Phosphorus And Silicon Along Ecosystems Of East Hainan

Phosphorus and silicon are the necessary nutrients for phytoplankton growth, their distribution and concentrations have impact on primary productivity, phytoplankton composition and biomass. Estuaries are transition zones between rivers and oceans. Studies on phosphorus and silicon cycles in coastal seas have become an important component of mass transport. Five cruises were carried out along coastal ecosystems of Eastern Hainan (such as rivers, estuaries, lagoons and near-shore waters) to understand the levels, distribution and seasonal variations of nutrients, in order to examine biogeochemical processes that influence nutrients variations. Some major conclusions are drawn as follows.1. Concentrations of various forms of phosphorus and silicon in the Wenchang/Wenjiao rivers were quite different, showed wide range of seasonal variations. PIP, POP, BSi and LSi concentrations in the estuaries ranged from 0.01～2.06μmol·L^-1,0.03～2.52μmol·L^-1,0.08～38.6μmol·L^-1 and 0.24～324μmol·L^-1, with similar levels in winter and summer, and both were higher than in spring. Variations of particulate phosphorus with salinity were complicated in low salinity waters in winter and summer, which was affected by the surrounding mangrove ecosystems and aquaculture activities. The concentration of SPM was 0.75 19.7mg/L, BSi/POC ratio was at a low level in the world, which was 0.05. Particulate phosphorus accounted for 63% of total phosphorus in water during winter and summer, which was a major component of total phosphorus; dissolved phosphorus was a major component of total phosphorus in spring. Dissolved silicate was the major component of total silicon in winter, spring and summer. Various forms of phosphorus and silicon significantly correlated with the SPM, influenced by terrestrial input. Runoff was increased during the typhoon, the content of suspended particles increased 3 times, particulate phosphorus and silicon concentrations in water increased significantly. Observations at Gaolongwan indicated that phosphorus and silicon concentrations were less than that in the Wenchang/Wenjiao estuaries and the concentrations were affected by tide.2. In the Wanquanhe estuary, the concentrations of PIP, POP, BSi and LSi were0.06¹.74μmol·L^-1, 0.06¹.83μmol·L^-1, 0.31²0.6μmol·L^-1, 3.30⁶45μmol·L^-1, respectively, with the highest values in spring, and the concentrations of particulate phosphorus and LSi were higher in summer than in winter, which was different from BSi. Compared with other areas in the world, the concentration of LSi was in a higher level, but PIP,POP and BSi were in a lower level. Dissolved phosphorus and silicate were the major components of total phosphorus and silicon, representing 61% and 68% respectively. In addition, all particulate phosphorus and silica were well correlated with suspended particulate matter (SPM), which suggested that the content of particulate phosphorus and silica in the Wanquanhe River estuary were affected by the fluvial input. BSi and POP were related with Chla, indicating that the distribution of POP and BSi were influenced by several reasons such as the biomass of phytoplankton.3. Investigations were carried out in Xiaohai and Laoyehai lagoons in spring and summer. In the Xiaohai lagoon, salinity was low. Concentrations of various forms of phosphorus and silicon in summer were higher than those in spring except for BSi. In spring and summer, the particulate phosphorus represented ca. 70% of total phosphorus, which was a major component of total phosphorus. Dissolved silicate was the major part of total silicon in summer, dissolved and particulate silicon contents werecomparable in spring. Laoyehai lagoon is an enclosed water body with a narrow mouth connected to the South China Sea, and no river input. Affected by aquaculture activities, the concentrations of various forms of phosphorus and silicon were higher. There is no linear relationship between P or Si and salinity, showing a non-conservative changes, dissolved an particulate phosphorus represented 50% of total phosphorus respectively, dissolved phosphorus and silicon were the main component of total P and total Si in summer, and the particulate silicon is the main component of total silicon in spring.4. Various forms of phosphorus and silicon, and SPM in eastern coastal shallow waters of Hainan were higher than those in deep waters influenced by terrestrial input. The horizontal distribution of particulate phosphorus and silicon showed the decreasing trend oceanwards, consistent with the horizontal distribution of SPM. Dissolved phosphorus and silicon were the main component of total phosphorus and silicon in the coastal water.5. Nutrient budgets were constructed and demonstrated that the Wenchang/Wenjiao estuaries and Xiaohai lagoon were the sink of PIP, POP, BSi and LSi in spring. In summer, Xiaohai were the source of POP, and the sink of PIP and particulate silica, the Wenchang/Wenjiao estuaries were the sink of PIP, the source of POP and particulate silicon, meanwhile the Wanquanhe estuary and Laoyehai lagoon were the source of both particulate phosphorus and silicon in both spring and summer, in which the Wanquanhe transport plays a more important role on the coastal ecosystem.