This study was carried out to analyze water cycle characteristics and evaluate water retention function in Jeju Gotjawal forest from 2013 to 2017. The average ratio of throughfall, stemflow, interception loss in Seonhul Gotjawal (SH) and Cheongsu Gotjawal (CS) was 43.1%, 15.8%, and 41.1%, respectively. Rainfall-throughfall, rainfall-stemflow, and rainfall-interception loss were expressed as linear regression equation (p<0.001). The comparison results showed that SH was higher than CS (p<0.05), indicating that the canopy area had an important effect on the difference in stand structure. The average water resources retention rate of the Gotjawal region was 41.9%, which is similar to the total water resources retention rate (40.6%) of Jeju Special Self-Governing Province (JSSGP). Currently, the development of Gotjawal is in progress in JSSGP. The development of Gotjawal will lead to a decrease in the water resources retention rate due to changes in the surface environment such as an increase in impervious areas, which will affect the total groundwater content of JSSGP. Therefore, the conservation of the Gotjawal area is judged to be very important from the point of view of water conservation.

The purpose of this study is to investigate the characteristics of water quality in Jeju harbor and to estimate pollutant loadings discharged into Jeju Harbor. To know characteristics of water quality in Jeju harbor and pollutant loadings of Sanzi river, we have investigated from August, 2000 to May, 2001. The results showed that the concentrations of COD, DIN and DIP were in the range of 1.00～4.85㎎/L (mean 2.15㎎/L), 2.14～74.0㎍-at/L(mean 12.20㎍-at/L) and 0.52～4.00㎍-at/L(mean 1.18㎍-at/L), respectively. These values were under Ⅲ class of seawater quality criteria. The ratio of nitrogen to phosphorus was lower than 16 except for Station 1 in Jeju harbor. Therefore, nitrogen was playing an important role in phytoplankton growth as limiting factor in Jeju harbor. The mean values of eutrophication index were exceeding 1, which was the eutrophication criteria. The results of estimating pollutant loadings at Sanzi river are 0.30 ton/day for COD, 300㎏/day for DIN and 18.0㎏/day for DIP, respectively.