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Phosphate (POOur method comprises (1) POPOWe demonstrated the utility of ZrME for purification of PO

The phosphate oxygen isotope ratio (ZrClOThe adsorption/desorption experiment demonstrated that the ZrIRC resin possessed a sufficient adsorption capacity (153 μmol/resin-mL) and exhibited little isotopic fractionation during the adsorption/desorption processes. Using the PaS-Zir method, we were able to collect sufficient POWe proved that the PaS-Zir method is applicable to oligotrophic freshwater systems and is generally more efficient than the conventional method. In addition, our method is useful for improving the understanding of the P dynamics of oligotrophic ecosystems because of the extremely low concentration of PO

Phosphorus is an essential nutrient for maintaining and increasing crop production. Owing to frequent human activities, phosphorus resources cause serious environmental pollution. Simulating phosphorus transport with a hydrological model could help understand the phosphorus loss processes at catchment scale. However, in previous modeling studies, phosphorus calibration and validation usually run in monthly time steps, it is difficult to correctly simulate the phosphorus transport peak. Additionally, most previous studies have disregarded the form of phosphorus in transported processes and only considered the total phosphorus, which cannot accurately assist in understanding the specific process of phosphorus transport. Rice is an important agricultural product, widely planted in Asia, and the particulate inorganic phosphorus loss in rice paddies is generally high. Previous studies could not fully simulate the transport of different phosphorus forms in rice paddy catchments. We analyzed the impact of climate change on phosphorus transport under different fertilization scenarios using the Soil and Water Assessment Tool. We compared mineral phosphorus flux with the sum of particulate phosphorus and dissolved orthophosphate during the calibration and validation processes. The Nash–Sutcliffe efficiencies of mineral and total phosphorus in both the calibration and validation periods were higher than 0.65. Rice paddies are the major source of phosphorus loss from the catchment, amounting to 5.4 kg/ha, and particulate inorganic phosphorus accounted for 53% of total phosphorus loss. The average annual phosphorus export was 30 tons/yr; the maximum value was nine times higher than the minimum value. Precipitation had a clear impact on phosphorus transport.

The Cimanuk River with a total watershed area of 4010.8 km2 flowing from the Garut Regency to Indramayu Delta is the longest in West Java Province. However, the cumulative effects of climate change, increased population, and fish farming in the coastal area have continuously pressured the availability of water resources in its watershed. This study was, therefore, aimed to analyze the impact of land use and climate change on surface runoff and groundwater using a SWAT model. This is a physically based semi-distributed hydrological model with various applications, particularly to simulate water balance and watershed management. Daily discharge record for 2005–2008, land use data for 2002–2017, and the simulated climate (1979–2003) and projected climate data (2075–2099) retrieved from MRI-AGCM3.2 20-km by the Meteorological Research Institute of Japan Meteorological Agency were used in this research. The result showed that the calibration and validation of SWAT model have exhibited satisfactory criteria for hydrological simulations. The modeled period showed land use changes caused a general increase in runoff and decline in base flow contribution to annual streamflow. The changes between the current and projected climate exhibited increase in Qmax/Qmin ratio in certain years.

This study aims to confirm the effect of a small stream impoundment on phosphorus and nitrogen dynamics in a suburban watershed. The results show that the phosphate concentration in the water body was significantly higher than that in the inflowing water under ordinary flow conditions. The phosphorus promotes algal growth that causes significant diurnal dissolved oxygen variation because of photosynthesis and respiration. The phosphate exchange between the sediment and overlying water was mainly controlled by diffusion flux rather than by advective flux seepage because of large amounts of phosphorus accumulated on the surface of the sediment. When a flood occurs, the phosphorus-enriched water is flushed downstream by rain-swollen currents. In summary, an impoundment affects in-stream phosphorus concentration through organic matter degradation and the release of phosphate in the sediment.

Phosphorus usage is irreplaceable in agriculture; however, its excessive use leads to wastage of invaluable resources and significant soil surplus. Agronomic soil phosphorus surplus in Asian regions has a much higher level than the global average. And with rapid urbanization and population growth in the recent decades, Asian countries have seen a rise in environmental pollution levels also. This study assessed the detailed phosphorus budget in the Yamato River catchment, an urbanized coastal catchment in Asia, from 1940s to 2010s using Soil and Water Assessment Tool, comprehensively analyzed the effect of anthropogenic factors on long-term phosphorus loading and agronomic soil phosphorus balance. The results showed the peak period of total phosphorus loading and agronomic soil phosphorus surplus occurred in 1970s, at 895 tons/year and 36.6 kg/ha, respectively. The major reasons for increased phosphorus loading and soil surplus during 1940-1970 were rapid population growth and increased fertilizer usage, respectively. Since the 1980s, the construction of wastewater treatment system and reduction in agricultural land contributed to environmental improvement. These anthropogenic factors had a much stronger impact on phosphorus budget than climate change in the study catchment. Soil phosphorus balance is affected by a combination of factors, such as soil properties, fertilizer usage and applied schedule, precipitation event, and crop types. And soil phosphorus surplus may be severely overestimated if the non-point source loss due to precipitation factor is not fully considered.

Groundwater is an extremely valuable resource thus its pollution a call for concern. Amongst the major threats, agricultural leachates often contribute significantly to groundwater pollution. This paper reports an investigation on the effects of citrus agriculture on the groundwater quality aspects of Osakishimojima island. Fifty-one groundwater samples were collected and analyzed for major ions and nutrients. The Gibbs diagram revealed that the overall hydrogeochemical environment of the study area is controlled by rock-water interaction. Two main hydrochemical facies (CaMg-HCO3 and CaMg-SO4) were identified. 48 groundwater samples showed PO43⁻-P content (0.06 - 3.2 mg/L), which exceeds WHO’s recommended maximum permissible limit. High contamination of PO43⁻-P was noticed at depth zones between 3 to 6 m while the highest concentrations were found at depths of 5 m. NO3−-N contamination of groundwater was also observed to decrease with depth. High levels of PO43⁻-P in groundwater may be as a result of heavy fertilizer application by farmers.

To manage and conserve the seagrass bed and ecosystem in tidal flats, this study examined to confirm spatial distribution in groundwater (SGD) on tidal flats with the area of around 100 m square in a small and steep island. Various groundwater and nutrient discharges were observed at the W and E sites. 1) Based on the water budget, the groundwater flux was estimated to be 8.68 m/yr or 23.9 mm/day in E, and 17.75 m/yr or 48.6 mm/day in W, respectively. 2) Spatial distributions of groundwater contribution ratio (%) in pore water at W was around 60% in average, which was 8 times of that in E site. 3) The NO3-N concentration in pore water at W site was about 30 times of that at E because of the low attenuation rate with high groundwater velocity. 4) The temporal variation in groundwater flux with tidal fluctuation indicated 2.5 m/day in maximum and -4.0 m/day in minimum. This huge difference between the average flux and maximum indicated also large seawater recirculation and heterogeneous distribution of SGD. This heterogeneous distribution at this tidal flat would contribute to the activity of seagrass and diversity of ecosystem.

Submarine groundwater discharge (SGD) is an important source of freshwater, nutrients, and other chemicals to the coastal water, and has significant impacts and implications for the coastal environment and ecology. Here, we combined geochemical tracers and hydrologic modeling to investigate the spatial patterns and quantities of SGD and submarine fresh groundwater discharge (SFGD) at a small island of western Japan. The results reveal large spatial variability in SGD and SFGD, significant discharge in areas with steep topography, and much lower discharge from low-lying areas. Topographic influences are likely to be a major driver of spatial variability in SFGD. The 222Rn mass balance model and two-end-member mixing model were used to estimate the SGD and SFGD rates. The values were ranged from 5.43 to 25.4 cm·d−1 with an average value of 16.2 cm·d−1, and 0.39 to 1.98 cm·d−1 with a mean value of 1.17 cm·d−1, for SGD and SFGD, respectively. The total flux of SFGD was calculated to be 8.49 × 106 m3·yr−1, with 4.37 × 106 and 4.12 × 106 m3·yr−1 in the northern and southern regions of the island, respectively. The results were consistent with the values estimated by the topographic-based model. The ratio of the average annual SFGD to average annual precipitation (3.69 × 107 m3 ) reached up to 23%, and the magnitude of annual SFGD was found to be similar to the total discharge from nine large rivers. Since the island faces a risk of water shortage, the results of the study can provide a useful insight into developing appropriate groundwater management strategies in this island's habitats.

This paper evaluates environmental conditions responsible for the high concentrations of trace metals in Indonesian coastal groundwater. Indramayu, which has significant potential groundwater resources, but for which limited information is available regarding its vulnerability, is selected as our study area. Results show that Fe2+ and Mn2+ are natural contaminants in the groundwater of the study site. The correlations of trace metals with salinity and redox-sensitive parameters verify that saline water has a significant impact upon the dissolution of Fe and Mn. Furthermore, reductive condition is confirmed to be responsible for Fe and Mn dissolution with a less significant correlation compared to salinity. Moreover, the high concentrations of trace metals are coupled with high dissolved organic carbon (DOC), which indicates that reductive environment may arise because of organic-matter decomposition. Finally, the impact of human activity upon Fe and Mn dissolution is identified at the northern tip of Indramayu, where trace-metal contents are significantly elevated. Further, in the southern part, the groundwater condition is relatively more natural; thus, the impact of human activity upon the presence of Fe and Mn is lesser in this region.

Geochemical evaluation of the species and potential sources of P in groundwater in and around Mataram City, Lombok Island, Indonesia can aid in the initial research on evaluating the fate of P when detailed geological information is unavailable. The results of ion chromatography and inductively coupled plasma-optical emission spectroscopy show that the concentrations of PO43– and total dissolved P (TDP) in groundwater range from approximately 0.1 to 8.5 mg l–1 and from 0.04 to 2.95 mg l–1, respectively. Dissolved inorganic P accounted for 86%, on average, of the TDP concentration, and PO43– represented the predominant P species in this groundwater. The potential sources for most of this dissolved PO43–, according to indices developed based on the PHREEQC software and groundwater quality data, could be the dissolution of hydroxyapatite and/or vivianite minerals. However, the potential sources of dissolved PO43– in groundwater with a TDP concentration of ≥ 1 mg l–1 is likely to be the reduction of Fe(III)–(hydro)oxides, the initial decomposition of organic matter, or the dissolution of carbonate-rich fluorapatite considering the Fe2+, dissolved organic carbon, Ca2+ and F− concentrations measured. In addition, as several groundwater samples had a TDP concentration of ≤ 1 mg l–1 and comparatively high concentration of NO3–, other potential sources of dissolved PO43– in this groundwater could be anthropogenic.

The origin of ammonium-nitrogen in Indonesian coastal groundwater has not been intensively examined, meanwhile the elevated concentration remains a concern. This research aims at tracing the potential sources of ammonium-nitrogen in the groundwater of Indramayu, Indonesia where groundwater is vital for livelihood. From results, a combined examination of nitrogen isotope, coliform bacteria, land-use, and geology confirmed the natural and anthropogenic origins of ammonium-nitrogen in the groundwater. In the brackish-water aquaculture region, groundwater has &delta, 15NNH4 values from +1.8 to +4.8&permil, signifying that ammonium-nitrogen is derived from mineralization of organic nitrogen to ammonium. Furthermore, ammonium has a significantly positive relationship with sodium indicating the exchangeable ammonium is mobilized to groundwater via cation exchange. Meanwhile ammonium-nitrogen from anthropogenic waste was detected in agricultural and residential region. The groundwater has more varied &delta, 15NNH4 values, from &minus, 2.9 to +16.1&permil, which implies attenuation of ammonium-nitrogen from several sources namely manure, mineral fertilizer, sewage, and pit latrines. Also, the presence of E. coli confirms the indication of human and animal waste contamination. However, since ammonium has no relationship with sodium, cation exchange is not feasible and ammonium-nitrogen flows into the groundwater from anthropogenic sources along with liquid wastes.

Forest ecosystems are critical for adjusting the dynamic balance of the hydrological cycle. This balance is affected by vegetation community types, phenology, and forest density. Previous long-term catchment-scale model studies have focused on changes in forest areas while ignoring the above factors. Since the 1980s, climate change caused by increases in atmospheric CO2 levels has enhanced forest growth. Moreover, amendments to forest management policies, including intermediate cuttings caused by economic factors, have yielded unprecedented changes in forest ecosystems. In this study, we designed a methodology and created a credible model using the Soil and Water Assessment Tool (SWAT) that can precisely reflect water balance variations caused by different ecosystem situations during long-term changes in forest density. We focused on the Yamato River catchment in Western Japan, which includes three planted forests and one primeval forest, each markedly different with respect to vegetation community composition and management policy. In the process, we examined the ratio of coniferous vegetation and broad-leaved vegetation in different forest areas, used remote sensing methods to quantify the maximum and minimum leaf area index (LAI) of each forest region over 40 years, and calibrated the model by comparing the LAI growth curve, evapotranspiration, and streamflow with observed data. Moreover, we separated the decadal canopy evaporation, transpiration, and soil evaporation from the SWAT output results. We found that (1) forest evapotranspiration has increased in recent decades because of the above reasons; (2) in young or well-managed forests, the forest water balance may have changed significantly with forest growth. For long-term studies, it is necessary to distinguish the growth characteristics of different forests during different periods, and a detailed definition of a mixed forest is required. The forest parameters and growth characteristics are critical for understanding forest ecosystems and cannot be ignored at catchment-scale.

Most semi-enclosed seas have experienced severe eutrophication owing to high nutrient loading from rivers during rapid population growth periods. In Japan, the coastal areas of some megacities (e.g. Tokyo and Osaka) experienced considerable economic growth during the 1960s–1970s. Therefore, determining the amount of nutrient loading during this period is essential to undertake measures for the conservation of coastal environments. However, determining the nutrient loading that occurred several decades ago is generally difficult owing to lacking water quality records. In this study, the nitrogen loading in the Yamato River catchment, an urbanized coastal catchment in Asia, for 80 years from the 1940s to the 2010s is reconstructed using the Soil and Water Assessment Tool. We considered factors such as population growth, wastewater treatment plant (WWTP) construction, and changes in land and fertilizer usage in different urbanization stages. Results show that the total nitrogen loading in the catchment peaked in the 1970s at 6616 tons yr−1 owing to untreated wastewater discharge and rapid increase in population growth. By reducing 57% of the nitrogen loading in the 2010s from the catchment, WWTPs have been instrumental in improving the water environment. The decrease in and integration of agricultural land has reduced nitrogen loading attributed to nonpoint sources; however, this reduction was not obvious because of the high fertilizer usage before the 2000s. Overall, the findings of this study provide a comprehensive understanding of the impact of rapid urbanization in an Asian coastal catchment on nitrogen loading during the high economic growth period in the past. This study will be useful for the long-term assessment of nutrient loading in other.

Submarine groundwater discharge (SGD), the direct discharge of groundwater to the sea, is a ubiquitous phenomenon worldwide. While SGD is defined as “any and all flow of water on continental margins”, this review focuses on the terrestrial fraction, also known as fresh SGD Jakarta Bay, which started from the late 1980s have had greatest impact on mangrove areas and coastal water quality due to the expanding of the city. In such an environment, inputs of nutrients will play an important role in sustaining primary productivity. Atmospheric deposition and riverine runoff have been traditionally considered the main external sources of nutrients to the bay, whereas the role of submarine groundwater discharge has been largely ignored. . In this study, we used radon tracers and salinity to investigate SGD and associated nutrient inputs to Jakarta Bay especially from Citarum Estuary as the main river. The result shows that SGD becomes an important role in understanding the nutrient cycle at Jakarta Bay.

Indonesian coastal alluvial plain has a large groundwater storage capacity. However, human perturbation to the groundwater environment has resulted in groundwater contamination. Nitrogen species are parameter those usually detected in Indonesian coastal groundwater. The main objective of this study was to evaluate the possible sources of ammonium (NH4+-N), as one form of nitrogen species, using both chemical properties and geographic information. The study site was Indramayu, a developing rural area located in the northern part of West Java. In August 2017, 20 groundwater and river water samples were collected from sites representative of various types of land-use. The chloride (Cl-) concentration in the samples ranged from 15 mg/L to 12,000 mg/L. Most of the locations represented fresh-brackish to brackish-salt water conditions, indicating the influence of seawater on the groundwater samples. Furthermore, analysis of several nitrogen species identified high NH4+-N concentrations in the samples. Based on the relationship between Cl- and NH4+-N, samples were clustered into three groups. The first and second groups exhibited linear correlations, while in the third group, no relationship between these two parameters was identified. The land-use associated with each group was then evaluated. The main NH4+-N source in the first group was identified as organic sediment, where NH4+-N may be released through ion exchange with sodium, facilitated by the high salinity conditions. The source of NH4+-N in the second group was suggested to be a combination of sediment, fertilizer, and human and animal waste. Finally, it was hypothesized that the source of NH4+ in the third group is mainly human waste.

To estimate the sedimentary environment between the last glacial stage and the Holocene epoch of an enclosed sea in the Okayama Plain, which constitutes a portion of the Seto Inland Sea coast, we collected 4 boring cores at depths of 6 to 19 m, performed radiocarbon dating of the organic matter contained in the clay, identified the volcanic glass from the Aira Caldera eruption, and measured the electrical conductivity of the pore water. Based on these dating analyses, it was evident that the Holocene clay layer that is widely distributed throughout the Okayama Plain had already accumulated prior to 10,000 years ago. In addition, the different hardness and the presence of Aira volcanic ash in the clay layer indicated the sedimentation since Pleistocene. Because the sea level at the time was lower than this clay sedimentation level, those facts suggest freshwater lakes existed in the Okayama Plain which was dammed up by the shallower granite basement in the mouth of Kojima Bay. Based on the long clay core and date for the last 30,000 years, the sedimentation rates were estimated to be 0.18 mm/ year before 8,100 years ago and 1.19 mm/year for the last 8,100 years, respectively. In the sea water rising after 7,000 years ago, the sea level exceeded the dam and the bay became a saline condition.

Land use is a key factor affecting water balance, which in turn affects the water resource availability. Increasing urbanization has altered water balances in river catchments. Although urbanization impacts have been widely investigated, most studies focus on changes in land use area, and the percent imperviousness of urban (PIU) is typically downplayed or ignored. PIU is altered by permeable areas within urban regions being replaced by impervious ones and can influence the spatial flow pattern of water and the hydraulic efficiency of its flows in urban locales. In this study, we consider the increase in urban area PIU due to urbanization, and focus on the PIU’s impact on water balances. We utilize the Soil and Water Assessment Tool to describe the PIU’s impact on long-term (1970s ~ 2010s) water balances in a same catchment with different urbanization levels and quantify these characteristics on spatial and time scales with a combination of remote sensing and numerous hydrological and geographical data. We demonstrate that: (1) Increasing urban PIU has a significant influence on the balance of urban water resources, with an increase to 0.17 causing the urban surface runoff ratio to increase by 0.2; (2) the impact of PIU on surface runoff and baseflows is sometimes more important than area changes in a catchment, especially for those in settings characterized by rapid urbanization. Thus, we note that PIU changes directly affect the water balance and enhance the impacts of area changes. Fundamentally, in the study of water resource management in urban settings or catchments in these, the PIU is a highly important variable to consider.

In this study, we investigated the historical variation, source identification, and distribution of heavy metal pollution in sediments of the Pearl River Estuary (PRE) using 210Pb dating. Our results suggest that the heavy metal concentrations were higher in the western part of the estuary. For all heavy metals, Cd was significantly enriched in the sediments. The Pearl River Delta (PRD) has experienced rapid economic development in the past 40 years, a decreasing trend in heavy metal fluxes after 2004 was identified, which suggests a reduction in heavy metal concentrations due to the removal of heavy polluting industries and the effective control of sewage discharge. A binary mixing model reveals that the contributions of anthropogenic Pb ranged from 45.4 to 64%. Based on lead isotopic ratios (206/207Pb and 208/206Pb), it was found that geologic materials and industrial pollution were the main sources of heavy metals in the PRE sediments.

Agricultural land-use has been reduced by mainly urbanization and devastation in Japan. The objective of this study is to evaluate the impact of the decline of agricultural land-use on flood risk and material flux in hilly and mountainous watersheds using Soil Water Assessment Tool. The results indicated that increase of flood risk due to abandonment of agricultural land-use. Furthermore, the abandonment of rice paddy field on steep slope areas may have larger impacts on sediment discharges than cultivated field. Therefore, it is suggested that prevention of expansion of abandonment of rice paddy field is an important factor in the decrease of yields of sediment and nutrients.

Clarifying the variations of groundwater recharge response to a changing non-stationary hydrological process is important for efficiently managing groundwater resources, particularly in regions with limited precipitation that face the risk of water shortage. However, the rate of aquifer recharge is difficult to evaluate in terms of large annual-variations and frequency of flood events. In our research, we attempt to simulate related groundwater recharge processes under variable climate conditions using the SWAT Model, and validate the groundwater recharge using the Hydrus Model. The results show that annual average groundwater recharge comprised approximately 33% of total precipitation, however, larger variation was found for groundwater recharge and surface runoff compared to evapotranspiration, which fluctuated with annual precipitation variations. The annual variation of groundwater resources is shown to be related to precipitation. In spatial variations, the upstream is the main surface water discharge area; the middle and downstream areas are the main groundwater recharge areas. Validation by the Hydrus Model shows that the estimated and simulated groundwater levels are consistent in our research area. The groundwater level shows a quick response to the groundwater recharge rate. The rainfall intensity had a great impact on the changes of the groundwater level. Consequently, it was estimated that large spatial and temporal variation of the groundwater recharge rate would be affected by precipitation uncertainty in future.

Lake Kojima, an artificial lake located in the coastal area of western Japan, is categorized as a hyper eutrophic lake due to the nutrient inputs from the Sasagase River, Kurashiki River and Kamo River. The input nutrient loads from the rivers have never been assessed because there are no observation stations for runoff rate. The objective of this study is to confirm the total nitrogen (T-N) and total phosphorus (T-P) loads into Lake Kojima using the SWAT model for 60 years and considering changes in land use and the amount of domestic wastewater in the watersheds. Estimation results show that more than 90% of the total nutrient load comes from the Sasagase and Kurashiki rivers. The estimated T-N and T-P loads indicated two different trends in the rivers; an increasing trend is found during the period from 1950 to 1980, while a decreasing trend is found during the period from 1980 to 2009. It was suggested that the increasing trend was commonly caused by the combined effects of increase of the amount of domestic wastewater and agricultural wastewater in the watersheds, while the decreasing trend was caused by the expansion of domestic wastewater treatment and decrease of agricultural land use. The contribution ratio of domestic wastewater to the total amount of nutrient load was estimated to be 60% in Sasagase River and 15% in Kurashiki River because the treatment ratio of domestic wastewater in Kurashiki River was higher than in Sasagase River.