Nitrogen occurs abundantly in the Earth's atmosphere in the form of nitrogen molecules. However, nitrogen molecules are stable and few organisms can utilize them directly. Nevertheless, through the artificial production of nitrogen compounds and exhaust gases from production facilities and motor vehicles, large amounts of nitrogen compounds are deposited in forest ecosystems, causing various problems. The responses of forests to deposited nitrogen differ depending on the environment. Those responses are summarized by region (Europe and the US, and Asia (Japan and China)) from previous studies. 1) While indicators of nitrogen saturation are valid in Europe and the United States, attention should be paid to hydrological conditions and other factors when applying them to Japan and other regions. 2) In recent years, high NO3- concentrations have been observed at forested watersheds in Japan due to air pollution near large cities and transboundary air pollution. 3) Significantly high NO3- concentrations have been observed at forested watersheds in China due to nitrogen deposition. 4) Nitrogen loading from rocks is not negligible in some areas. 5) New insights are being obtained into the functions of microbes involved in the nitrogen cycle in soil.

In May 2009, Moriyama Dike was opened in Honjo area, which lies near Lake Nakaumi along the coast of San-in District, Japan, and is isolated by two dikes for land reclamation. This study was conducted to examine the impact of the opening of the dike on water quality as well as fi sh and crustacean life. We carried out a statistical analysis using monthly water-quality observations and a small catch net survey through 2004 to 2014. The analysis results showed that seawater likely flowed into Honjo, and salinity stratification developed. Furthermore, the oxygen deficient layer became thicker and progressed with prolonged duration. From the catch net survey, we found that the number of species of marine fi sh greatly increased; however, no signi fi cant increase in the catch per net was observed. In terms of fi sh and crustacean types, the number of horse mackerel ( Trachurus japonicus ) and Taiwan blue crab ( Portunus pelagicus ) significantly increased. This was considered to be due to the easy access provided by the opening to the Sea of Japan. However, the catch of rock fi sh ( Sebastes schlegeli ) and spiny goby ( Acanthogobius flavimanus ) , decreased after the opening. Because these species prefer benthic life, it was considered to have been a ff ected by oxygen depletion in the lower layer of the Honjo area.

森山堤防の開削が本庄水域の水質に与えた影響を調べるため,2004年から2014年にかけて月1回ずつの調査結果を用いて統計解析を行った。森山堤防開削前後の5年間ずつの塩分のMann-WhitneyのU検定から,森山堤防の開削によって本庄水域下層の塩分濃度が上昇したことが明らかとなった。DOについては開削後の夏季に本庄工区南西部の測点の下層で貧酸素化が進行した。その影響を受け全窒素・全リンが有意に上昇していた。この原因は森山堤防の開削によって測点下層において貧酸素化が進行し,堆積物からの溶出が増加したためと考えられた。

The main objective of this study is to demonstrate the possibility of underwater three-dimensional measurement (underwater SfM) in a coral reef area by structure from motion (SfM). The possibility of underwater SfM using a small submarine (small remotely operated vehicle, sROV) was also investigated. After we conducted underwater SfM and conventional measurements simultaneously for dendritic coral, massive coral, and seaweed Enhalus acoroides in a coral reef area in Amitori Bay of Iriomote Island, we compared and examined the results. Underwater SfM allowed us to measure the heights, major and minor axes, and branch thicknesses of dendritic coral with the accuracy of a maximum and minimum error of 4.5 cm and 0.1 cm, respectively. Consequently, it was verified to be useful for monitoring coral preservation. However, three-dimensional measurements of Enhalus acoroides by SfM were not satisfactory because of swaying of leaves by waves or currents during the taking of sequential photographs. Investigation by sROV provided a clear three-dimensional model, but some technological problems were also revealed.

宍道湖は，湖沼水質保全特別措置法の指定湖沼となっている汽水湖である．宍道湖では湖へ流入する汚濁負荷は減少しているが，湖水の化学的酸素要求量（COD）は増加している．この原因を明らかにするため，我々は COD に影響を与える可能性がある環境因子を用いて重回帰分析を行った．その結果，二枚貝ヤマトシジミ（Corbicula japonica）の漁獲による系外への COD 除去量の減少が宍道湖の水質改善の妨げになっていることが明らかとなった．これまで指定湖沼の水質改善は，栄養塩流入負荷の削減によって達成されると考えられてきた．湖沼水質の効果的な管理・保全を行う上で，生物を通じた物質循環が湖沼水質に与える影響を考慮することが不可欠であることが示された．

The organic carbon concentration of surface sediment influences bottom water hypoxia. To investigate whether the organic carbon concentration of surface sediment can be used to reconstruct temporal changes in organic carbon concentration, surface sediments from Lake Shinji, Shimane Prefecture, Japan were studied. Samples were analyzed using ignition loss. For comparison with earlier studies, the techniques used by these studies were also used herein, and a conversion formula developed to calculate equivalent organic carbon concentrations. The converted organic carbon concentrations at the same locations in 1982, 1997 and 2016 were compared, and found to be significantly lower in 1997. Since the organic carbon concentration decrease in the 1990s was not detected by an earlier study, it was thought that the decrease for around ten years may have been obscured during early diagenesis. In addition, the organic carbon concentration was significantly higher in sediments collected from the western part of Lake Shinji where a halocline exists. When monitoring hypoxia in brackish lakes, attention should be paid to areas with a halocline as well as the deeper areas.

This study aimed to evaluate the loading of nutrients of agricultural origin. We investigated monthly nutrient concentrations at 11 stations located in the Hii River, Japan. The nitrogen and oxygen stable isotope ratios in nitrate were applied to distinguish the origin of nitrogen, i.e., from fertilizers applied to paddy fields or from sewage. Although total nitrogen (TN), presumably from transboundary air pollution, was mainly loaded during the cooler season, nitrate originating from fertilizers applied to paddy fields became the main source of nitrogen in the river water during the warmer season. Phosphorus was mainly added in particulate form, and showed increased loading at the upstream stations in the warmer season, but not in the cooler season. Potassium and magnesium—components of fertilizers—showed an increasing trend in the downstream section of the paddy fields. Our results suggest that controlled application of fertilizers is necessary to decrease the nitrogen loads originating from farmlands, particularly from paddy fields. Since the nitrogen isotope of TN in fertilizer showed significantly lower values (mean value −4.6 ‰) than that in river water (mean value 1.8 ‰) or treated water (mean value 21.9 ‰), we could use these values to determine the contribution of TN from fertilizers to river water quality, and can use them to monitor fertilization levels in watersheds.

本研究の目的は,サンゴ礁海域を対象として,SfM(Structure from Motion)による水中3次元計測(水中SfM)の可能性を明らかにすることである.そこで,サンゴ礁海域である西表島網取湾において,枝状サンゴ,塊状サンゴおよび海草であるウミショウブを対象に水中SfMと実施コストが高い従来の測量を同時に行い,これらの結果を比較・検討した. その結果,水中SfMは,サンゴの高さ,長径,短径および枝状サンゴの枝幅を最大誤差4.5 cm,最小誤差0.1 cmの精度で計測でき,サンゴ保全のためのモニタリングなどにおいて有用となることが明らかとなった.一方,ウミショウブは,連続写真撮影中に葉が波や流れによって揺らぐため,SfMによる3次元化が不十分であった.

洪水によってもたらされる栄養塩の負荷が年間の総負荷量に対してどの程度の割合になるのかを調べるため，2010年7月1日から2011年6月30日までの1年間，斐伊川の神立橋において毎日採水を行った。降水量と流量の関係を調べたところ，貯留関数法による1降水と流出高の良い関係式（R2＝0.87）が得られた。調査を行った1年間に200 mmを超える降水が3回あり，これら3回によってもたらされた降水量は年間降水量の41.3％であった。流量は年間流量の34.8％であった。全窒素及び全リンの負荷量は年間の総負荷量の40.7％及び62.2％であった。全リンの負荷量が全窒素のそれよりも大きい理由は全リンの方が流量依存性が高いためであった。

We calculated the changes in the amount of water, total nitrogen ( TN ) , and total phosphorus ( TP ) flowing into Lake Shinji, through a hypothetical flood control channel, using the flow rate data from 1984 to 2013 and L-Q equations developed for the Hii River. Our estimates indicate that in the presence of such a channel, the total water flow into Lake Shinji would be reduced by 1.6%, and TN and TP loads would decrease by 2.8% and 8.9%, respectively. This implies that the concentration of TP has a greater dependence on the flow rate than the concentration of TN. From 2003 to 2014, the ratio of TN to TP at the center of Lake Shinji was 10 to 1. Our results suggest that the operation of a flood control channel would increase this ratio and may cause diatoms to overtake the blue-green algae as the dominant algae in Lake Shinji.

Deposition of atmospheric nutrients is known to alter oligotrophic ecosystems such as the open ocean, but the role of such nutrients in the further deterioration of eutrophic aquatic ecosystems is largely unknown. The Hii River watershed in Japan encompasses lagoons that have been eutrophic since 1980s. This study examined the atmospheric deposition of nitrogen and phosphorus in the Hii River watershed and the nitrogen and phosphorus concentrations in the Hii River over an 11-yr period. Total nitrogen (TN) concentrations of both precipitation and river water were significantly higher in cold months (November-March) than in warm months (April-October). Most of the TN was nitrate, which suggests that the TN source was atmospheric nitrogen from East Asia transported by seasonal winds. In contrast, total phosphorus (TP) concentrations of both precipitation and river water were significantly higher in warm months. Over time, the TN concentration in the river water showed a decreasing trend although the trend was not significant, while the TP concentration increased significantly. This was attributed to an increase in the atmospheric deposition of TP originating from East Asia since 2000. The increase in the deposition of atmospheric phosphorus might also have increased phosphorus leakage from the soils. In this work, the TN : TP ratios for both atmospheric deposition and river water indicate that changes in atmospheric nutrient deposition affect loading rates and N : P ratios. These changes, especially the latter, could have significant ecological effects in eutrophic systems by lowering the N : P ratios, which could induce cyanobacteria blooms.

We analysed nutrients and basic ions (Na, Cl, K, Mg, Si, Ca, and SO 4 ) for a period of 1 year, including every precipitation event, and sampled stream water every 2 weeks from a forest catchment in Shimane Prefecture, Japan. Backward-trajectory analysis revealed that some air masses originated within Japan, but did not affect the precipitation chemistry. Air masses originating from northern China were positively correlated with nutrients and all basic ions. Concentrations of ammonium and dissolved organic nitrogen were much lower in stream water than in precipitation, while those of nitrate and particulate nitrogen were similar in stream water and precipitation. Unlike nitrogen, the dissolved phosphorus concentration was much higher in stream water than in precipitation. Both phosphate and dissolved organic phosphorus (DOP) levels were higher in stream water than in precipitation. Particulate phosphorus (PP) concentrations were very similar in precipitation and stream water. PP showed stronger correlations than potassium with suspended solids (SS) and flow rate, while phosphate and DOP were more strongly correlated with potassium than with SS or flow rate. Stream silica concentrations were not correlated with phosphate but did exhibit a significant negative correlation with DOP. Neither phosphate nor DOP was correlated with calcium. These results suggest that phosphorus is not leaching with silica or calcium as a paired cation, but rather with potassium in this area. Lower nitrogen concentrations in stream water than in precipitation can be attributed to an enhanced uptake of nitrogen by forest soils owing to the increased atmospheric deposition of phosphorus.

We sampled river water from 1 July 2010 to 30 June 2011 in the Hii River. Suspended solids (SS), chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) showed increasing trends during floods. In contrast, dissolved silica (DSi) had a decreasing trend during floods. By comparing estimated loading amounts from a loading-flow (LQ) equation and actual loading amounts from multiplying a given day s chemical species and discharge, TN, nitrate and D-Si showed quantitative agreement between the two estimations. However, loading amounts of SS, COD, TOC, TP and phosphate from a linear LQ equation had lower values than those of actual loadings. The reason for such underestimation is an increased concentration of certain chemical species during flooding or high discharge. Therefore, we applied quadratic or cubic LQ equations. After applying the quadratic LQ equation to certain chemical species that showed low coefficients of determination, values improved. For more accurate loading amounts from an LQ equation, we require observation data from periods of high discharge.

This study characterizes evacuation behavior in Ibaraki Prefecture in the aftermath of the Great East Japan Earthquake and tsunamis based on geographic information, questionnaires, and interview surveys. We identified several factors on which the starting time of evacuation depended, including awareness of evacuation warnings, understanding of anticipated tsunami inundation areas (hazard maps), and distance from anticipated inundation areas. We found that those who were aware of evacuation sites, hazard maps and/or anticipated inundation areas maps, and who lived in inundated areas tended to evacuate earlier. Conversely, many residents delayed their evacuation because they chose to go home and take care of their family first. To improve future responses to likely threats, evacuation behavior and local disaster management plans must be reviewed based on the knowledge gained from this disaster.

A large amount of radiocesium ( 134 Cs and 137 Cs ) was released to the atmosphere from the Fukushima Daiichi Nuclear Power Plant disaster on March 11, 2011. Significant amounts of 134 Cs and 137 Cs were deposited in the drainage basin of Lake Kasumigaura. As might be expected, the concentrations of 134 Cs and 137 Cs varied across the lake basin. We sampled bed sediments from several rivers within the lake basin, and compared the 134+137 Cs concentrations of the silt and clay, sand and gravel sediment fractions. At any given sampling point, the concentrations of 134+137 Cs in silt and clay were always greater than those in sand and gravel, which agrees with previous studies that show increased 137 Cs concentrations with increased specific surface area of sediment. However, the 134 Cs and 137 Cs concentrations of sand were not always greater than gravel, suggesting that the concentration is not always dependent on the specific surface area. The 134+137 Cs concentrations in silt and clay were mostly 1.4 to 4.0 times greater than the concentrations in sand. Overall, the 134+137 Cs concentrations of sediments were correlated with the amounts of 134+137 Cs deposited in the upstream areas.

日本海側を流れる斐伊川において2010年7月1日から2011年6月30日まで毎日採水を行った。期間内の総流量は1.51×109 m3であった。TNの平均値，最小値及び最大値はそれぞれ0.60mg L-1，0.24 mg L-1，1.34 mg L-1であった。NO3-Nはそれぞれ0.50 mg L-1，0.14 mg L-1，1.06 mg L-1であった。河川水中の窒素のほとんどをDINが占めており，そのうちの90％以上がNO3-Nであった。12月から3月にかけてNO3-N濃度の上昇がみられた。 2001-2002年に行った同様の調査と比較したところ，硝酸態窒素の平均値が0.38 mg L-1から0.50 mg L-1に増加していた。斐伊川集水域において人為的汚染の増加は考えられないことから，中国大陸からの越境窒素汚染の影響がさらに大きくなったと考えられた。