In considering material circulation, the connection between forests, rivers, and oceans is essential. It has been pointed out that iron transport of humic substances has an important meaning in marine ecosystems. Studies focusing on the molecular structure of corrosive substances and the vegetation and land use of drainage basins are being conducted. In this study, iron ion elution experiments and iron ion preservation experiments were carried out on humic substances originating from fresh dead leaves of deciduous hardwood and evergreen red pine and evergreen Japanese cedar and Japanese horse mackerel, and then iron ions were measured iron ion and Fe²⁺ concentration together with PH, COD, and DO over time. As a result of the measurement, it was suggested that the obtained measured values showed different characteristics for each origin. It was speculated that fresh dead leaves of deciduous hardwood supply more than twice as much organic matter in the water as the same mass of evergreen cedar leaves and provide many humic substances, and transported iron ions to coastal areas. Humic material originating from Japanese cedar has iron ion transporting ability next to deciduous hardwood in this data. The residual rate of iron ions was 10% at a salt content of 10 mg/L. It showed a tendency to be relatively difficult to remove. Factors other than humic substances were considered to be dominant for Japanese horse mackerel source samples. In the future, detailed research to quantitatively investigate bioavailability, as well as iron ion transport ability, is necessary.

To evaluate changes in the grassland vegetation after grazing of horses, in the grassland which succession progressed, we investigated the vegetation height and the coverage of each plant species in three different management types, namely horse grazing area, burning area, and unmanaged area, during the period between 2015 to 2016, in Appi Kogen, Hachimantai, Iwate Prefecture, Japan. In the horse grazing area, the vegetation height decreased and the coverage decreased in Miscanthus sinensis which is the type of “Dense growth”, whereas increased in Zoysia japonica, Hydrocotyle ramiflora, and Haloragis micrantha which is the type of “Creeping growth”. On the other hand, in the burned area, the coverage increased in Miscanthus sinensis and Carex oxyandra var. oxyandra, whereas it decreased in Hydrocotyle ramiflora and Haloragis micrantha but increased in Zoysia japonica. In the unmanaged area, the coverage of these species did not change, despite it increased in the vegetation height. Differences in the response of these plants in the horse grazing area and the burning area were thought to be due to resistance to eating pressures and preference of horses, and were considered as an effective indicators to judge the status of grasslands for vegetative management by grazing horses.