According to the article 16 of the Basic Environment Law, the government shall establish environmental quality standards, the maintenance of which is desirable for the protection of human health and the conservation of the living environment. Usually, an achievement rate of environmental quality standard is used as pollution control and environmental conservation policies or programs. Since designated categories have different standard values, simple achievement rate (AR) of dividing numbers of achieved points by total monitoring points cannot always explain improvement of environments. In this paper, BOD, one of living environment items in environmental quality standards for water pollution is considered as an example of methodology. This study introduced environmental factors in order to evaluate achievement of higher (or lower) category of standards by giving higher (or lower) scores, which is called a factored achievement rate (fAR). Through efforts of local governments, many monitoring points have satisfied the designated categories and sometimes even higher categories. Upgrading the categories from present designated ones, possible achievement rate can be calculated (pAR).
Similarly, an environmental index (EI), a possible one (pEI) and an adjusted one (aEI) are defined by using environmental factors and designated categories, a corrected one and an adjusted one, respectively.
The calculated results for the 47 prefectures of Japan show that the three achievement rates and present environmental indices could explain present environmental situation and suggest future water environmental policies for each prefecture.
The author met to a pictorial map of Rokugo-Kouya Village in the Tenmei era. This map draws that a “pond” was existed in the center of Rokugo alluvial fan, Akita Prefecture. Ruins of the “pond” is still remain. An analysis on old documents found a couple of findings. Firstly, the “pond” is estimated to have been constructed for paddy rice irrigation in the mid-Edo. Secondly, the “pond” could not store water, because it was located in the part of alluvial gravel layer where infiltration capacity is high. As a result, the “pond” is inferred to have unexpectedly played the same role as groundwater artificial recharge basins.
Water quality in Baiyangdian lake, which is located in North China Plain encountering rapid urbanization, reflects the human activity in the watershed. We define such a lake as an “Environmental Lake”. Human factors in the formation of water quality and ecosystem services as a resilience of the lake, are made clear based on the relationship between characteristics of spatio-temporal distribution of water quality, especially nutritive salt, and land use as an index of human activities.
Land use change maps in the Baiyangdian watershed and surroundings in the laks, are created for different periods. Expanded urban areas and farmland-discharged waste water to the lake cause the deterioration of water quality. Drying up of surface waters by dam construction and leakage of water by ground water extraction also cause the deterioration of water quality.
Long term decrease of annual precipitation leads to decrease of inflow to the lake, and causes the deterioration of water quality. On the other hand, water purification in the lake is recognized along the direction from upper to lower lake-flow, and water quality is improved in September compared to other seasons. In Baiyangdian Lake, the spatio-temporal distribution of water quality is created by both human activities in the watershed and water purification function by ecosystem services of lake water and wetland vegetation.
To determine the mean residence time of spring water in the Kirishima volcanic area, repeated samplings and measurements of CFCs were conducted during the years 2007 to 2013. The observed relationship between CFC-11 and CFC-12 concentrations (tracer plot) and the time series data of the CFC-12 concentration results suggest that most of the springs were recharged through the mixing of groundwater of various ages. Groundwater flow model, which is an essential to estimate the mean residence time, was assumed based on CFCs results and the geological setting of the study site. Through these assumptions, it was determined that the most suitable groundwater flow model to apply in the study area was a combination of exponential mixing flow and piston flow (EMM+PFM). The mean residence time was estimated using a lumped parameter model, taking the above flow model (EMM+PFM) into account. Consequently, the mean residence time was estimated to range from 1 to 58 years. In the areas around the tops of the mountains, most of the springs showed a relatively shorter residence time of less than 10 years. In contrast, relatively longer residence times of 10 to 40 years were distributed around the foot areas of the mountains. Springs located at the foot of the southern mountain of the Kirishima volcanic area showed the longest residence time (50 to 60 years) among all springs studied in the area, and for those with the longest residence time, their dominant groundwater flux type was piston flow. These springs are distributed at the end of the Takachihonomine lava, which is the youngest volcano in the Kirishima area. The longest residence time may have occurred due to a preferential groundwater flow system, which developed from piston flow in the bottom of the youngest volcanic lava.
SPECIAL ISSUE“Project t Research on Reuse of Groundwater and Nitrogen in a Catchment Scale (1)”
In many agricultural areas, nitrogen pollution of groundwater owing to the influence of surplus chemical fertilizer inputs has been reported. In this study, we examine a cultivation system for satsuma mandarin that reuses nitrogen in groundwater to retrench chemical fertilizers and reduce their environmental impact. Specifically, we conducted a field test combining groundwater use and a drip irrigation and liquid fertigation system with year-round plastic mulching, a popular and stable production system for high-quality fruit. We quantitatively evaluated the eutrophication impact using the life cycle assessment method.
Consequently, in a standard cultivation system, the nitrogen emission had a very high impact of approximately 90% of the eutrophication impact. In the drip irrigation and liquid fertigation system, the nitrogen emission was drastically decreased and the eutrophication impact dropped to approximately 15% of that of the standard cultivation system. When the nitrogen balance was evaluated for the basin on the basis of a water source well, the amount of nitrogen in groundwater used by the drip irrigation and liquid fertigation system exceeded the amount of nitrogen emission during the satsuma mandarin production stage. Moreover, according to the estimated eutrophication impact, this cultivation system could be used as a purification system.
The “drip irrigation and liquid fertigation system with year-round plastic mulching (MD system)” is a cultivation method whereby plants are irrigated using a drip tube underneath a plastic mulch sheet. This study investigated how an MD system affected nitrogen (N) leaching by measuring the changes in soil inorganic N levels in a satsuma mandarin orchard.
In the control plot, N, in the form of solid fertilizer, was applied to the surface of the soil according to local fertilization practice. In the MD plot, N, in the form of liquid fertilizer, was applied using the MD system. The amount of N in the MD plot was 60% of the control plot. The total amount of inorganic N in the soil, which was collected at 30–60 cm apart from the tree trunk, was measured in consideration of the distance from the drip tube. As a result, the total amount of inorganic N after cultivation in the MD plot was lower than that in the control plot. The amount of leached N was estimated from the levels of soil inorganic N before and after cultivation, amount of fertilizer N added, and plant absorbed N in the fruit. The estimated amount of leached N from the MD plot was less than that from the control plot. The N applied through irrigation water, which contained nitrate, was similar to the estimated amount of N that leached from the MD plot. Therefore, the results suggest no net N leaching from the MD plot.
In conclusion, the MD system effectively reduced N leaching in the citrus orchard.
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