Assessing aquatic productivity in the housatonic river using the Algal assay:bottle test

Dense algal growth and large diurnal oxygen variations in both free flowing and impounded reaches of the Housatonic River in Connecticut and Massachusetts prompted a concentrated study to assess the need for a comprehensive basin wide phosphorus abatement program and the contribution of point source discharges to eutrophication of the river. Inorganic nutrient levels and bioassay data indicated a predominance of nitrogen limitation below Pittsfield, MA resulting from discharges of phosphorus-rich, municipal and industrial wastewater into the river. N:P ratios suggested that the nutrient status of the river varied, to some extent, even over as short an interval as 2 months and was probably attributable to flow variations in the river. Algal assays of water samples confirmed the nutrient limitation predicted by N:P ratios in 10 out of 13 cases. Additions of varying percentages of untreated, and alum-treated Pittsfield domestic wastewater treatment plant effluent to Housatonic River water, resulted in a linear increase in algal yield that was within 20% of values predicted by inorganic nutrient content. No significant reduction in algal growth response was observed, however, in the alum-treated sewage since its N:P ratio was not sufficiently shifted to phosphorus limitation after 66% phosphorus removal (Al:P equal to 1.3:1). Phosphorus removal at Best Practicable Technology levels would therefore probably not change the nutrient status of the Pittsfield wastewater to phosphorus limitation.     

A long-term view of nutrient transfers through the Seine river continuum

A model (the Riverstrahler model) is used to describe nutrient transfer and transformation at the scale of the whole drainage network of the Seine based on information concerning the basic mechanisms governing N, P and Si inputs to the drainage network and in-stream transformation and retention. It was used to calculate the budget of these nutrients through the whole river continuum from land to sea. With the help of historical documents, the constraints used as forcing function in this model were reconstructed to express the changing conditions of land-use and urban population over the last five hundred years. The corresponding scenarios were run for different hydrological regimes including dry, mean and wet conditions. The results were validated on the long-term series of nutrient measurements spanning more than a century available at some stations on the Seine, upstream and downstream of the city of Paris. The model was also used to explore past and future trends in nutrient loading, retention and delivery to the coastal zone, in response to human management of the terrestrial watershed. Beside the initial pristine state, used as an idealized reference state (with N, P and Si delivered fluxes of about 45-110 kg N km(-2) yr(-1), 2-5 kg P km(-2) yr(-1), 510-1325 kg Si km(-2) yr(-1)), four periods were distinguished. The first one is that of the traditional cottage economy which prevailed, with quite a constant total population, until the end of the 18th century. N, P and Si fluxes were about 235-750 kg N km(-2) yr(-1), 15-60 kg P km(-2) yr(-1) and 425-1280 kg Si km(-2) yr(-1), depending on hydrological conditions. The second period, from the beginning of the 19th century to about the 1950's, corresponded to rapid increase in the total and urban population with a corresponding increase of point sources of N and P. From 1950 onwards, modern farming practices resulted in a dramatic increase in diffuse sources of nitrogen and to a lesser extent phosphorus: riverine N and P export reached 1320-2800 kg N km(-2) yr(-1), and 310-340 kg P km(-2) yr(-1): silica export remained fairly constant at around 410-1260 kg Si km(-2) yr(-1) depending on the hydrological conditions. In the 1990's, the fourth period is represented by a stabilized population and improved wastewater treatment, when the export of phosphorus is reduced to values as low as 40-60 kg P km(-2) yr(-1), but without as effective a reduction of nitrogen export. This represents an unprecedented situation for the marine coastal system, i.e. a shift from nitrogen to phosphorus limitation, as nitrogen is still delivered far in excess of the amount of silica available for diatom blooms.     

Cost assessment and ecological effectiveness of nutrient reduction options for mitigating Phaeocystis colony blooms in the Southern North Sea: an integrated modeling approach

Nutrient reduction measures have been already taken by wealthier countries to decrease nutrient loads to coastal waters, in most cases however, prior to having properly assessed their ecological effectiveness and their economic costs. In this paper we describe an original integrated impact assessment methodology to estimate the direct cost and the ecological performance of realistic nutrient reduction options to be applied in the Southern North Sea watershed to decrease eutrophication, visible as Phaeocystis blooms and foam deposits on the beaches. The mathematical tool couples the idealized biogeochemical GIS-based model of the river system (SENEQUE-RIVERSTRAHLER) implemented in the Eastern Channel/Southern North Sea watershed to the biogeochemical MIRO model describing Phaeocystis blooms in the marine domain. Model simulations explore how nutrient reduction options regarding diffuse and/or point sources in the watershed would affect the Phaeocystis colony spreading in the coastal area. The reference and prospective simulations are performed for the year 2000 characterized by mean meteorological conditions, and nutrient reduction scenarios include and compare upgrading of wastewater treatment plants and changes in agricultural practices including an idealized shift towards organic farming. A direct cost assessment is performed for each realistic nutrient reduction scenario. Further the reduction obtained for Phaeocystis blooms is assessed by comparison with ecological indicators (bloom magnitude and duration) and the cost for reducing foam events on the beaches is estimated. Uncertainty brought by the added effect of meteorological conditions (rainfall) on coastal eutrophication is discussed. It is concluded that the reduction obtained by implementing realistic environmental measures on the short-term is costly and insufficient to restore well-balanced nutrient conditions in the coastal area while the replacement of conventional agriculture by organic farming might be an option to consider in the nearby future.     

Past and future trends in nutrients export by rivers to the coastal waters of China

We analyzed the past and future trends in river export of dissolved and particulate nitrogen (N), phosphorus (P) and carbon (C) to the coastal waters of China, for sixteen rivers, as calculated by the Global NEWS models (Nutrient Export from WaterSheds). Between 1970 and 2000, the dissolved N and P export increased significantly, while export of other nutrients changed less. We analyzed the future trends (2000-2050) for the Millennium Ecosystem Assessment (MEA) scenarios. In general, the largest increases of dissolved nutrients export are projected for the Global Orchestration scenario, assuming a globalized world and a reactive approach toward environmental management. Future trends in river export of nutrients vary largely among basins, nutrient forms and scenarios. We calculate both increasing and decreasing trends between 2000 and 2050. We also identify the sources contributing to the nutrient export. For selected river basins we present results for alternative scenarios, which are based on the Global Orchestration scenario, but assume more environmental management. This illustrates how the NEWS models can be useful in regional analyses for decision making.     

Assessing the effectiveness of actions to mitigate nutrient loss from agriculture: a review of methods

Diffuse nutrient loss from agriculture is degrading surface and groundwater quality throughout Europe, leaving water bodies at risk of not reaching targets set by the Water Framework Directive (WFD). Mitigation methods to reduce diffuse agricultural nutrient loss need to be implemented where water bodies have been identified as at risk of not reaching good status by 2015. Though the effectiveness of individual mitigation methods has usually been assessed in controlled experiments, it is necessary to quantify impact under a wider range of environmental and agricultural conditions and at the catchment scale to ensure that action taken now will be sufficient to meet WFD targets. Due to catchment buffering and long transit times (>50 years), it is unlikely that responses to intervention will be observed by 2015 in many water bodies. In this review, we compare the attributes and usefulness of different approaches (direct measurement, nutrient budgeting, risk assessment and modelling) to assess the efficacy of actions to mitigate sources and transport of nitrogen (N) and phosphorus (P) from agricultural land to water. Modelling and 'measured changes in farm activity' through budgeting avoid the time lags associated with direct measurement and enable rapid evaluations of different options before implementation. Budgeting approaches using on-farm data also provide a simpler, more communicable means of assessment but currently fail to consider the timing and transport aspects of mitigation and assume a direct causal relationship between potential and actual nutrient loss. Risk assessment and modelling applications are potentially more comprehensive and able to better reflect choice of mitigation at a range of scales, but assessments demand increased availability of data, and there is a large degree of uncertainty associated with their spatial and temporal dimensions which is difficult to validate adequately. The failings of individual approaches suggest that these assessment methods should be integrated to maximise their potential usefulness and positive attributes. This will enable nutrient inputs to be utilised most efficiently at broad scales and site specific actions to reduce nutrient transport and delivery can be targeted most cost-effectively at smaller scales. Such an integrated approach will also more effectively engage and involve the farmer in what must be an iterative process.     

Population growth away from the coastal zone: Thirty years of land use change and nutrient export in the Altamaha River, GA

We used more than thirty years of water quality monitoring data collected by the United States Geological Survey at several stations in the Altamaha River and its tributaries to examine the relationship between population density, agricultural land use, and nutrient export from the watershed. Population densities in the Altamaha River watershed increased during the study period, most notably in the upper watershed near metropolitan Atlanta, while agricultural land use declined throughout the watershed. NO_x, TN and P in rivers were related to human population densities, while OC and NH₄⁺ concentrations in rivers were apparently related to agricultural land use. A general pattern of increasing NO_x and TN and decreasing NH₄⁺, P and OC over time throughout the watershed reflected changing population and land use. The overall average load from the Altamaha River to the coastal zone during the study period was 1.1, 5.6, 16.9, 0.9 and 262 kmol km^− 2 yr^− 1, delivering 40, 197, 596, 30, and 9213 · 10⁶ mol yr^− 1 of NH₄⁺, NO_x, TN, P and OC, respectively, to the coastal zone. The nutrient export patterns suggest that N and P loading to rivers in the Altamaha River watershed was greatest in the upper watershed where high population densities were found, and in-stream processing, dilution, and only moderate inputs during transit through the lower watershed resulted in relatively low export from the watershed to coastal waters.     

Dissolved and particulate nutrient export from rural catchments: a case study from Luxembourg

Nutrient enrichment of freshwaters continues to be one of the most serious problems facing the management of surface waters. Effective remediation/conservation measures require accurate qualitative and quantitative knowledge of nutrient sources, transport mechanisms, transformations and annual dynamics of different nitrogen (N) and phosphorus (P) forms. In this paper, nitrate (NO3-N), soluble reactive phosphorus (SRP) and total phosphorus (TP) concentrations and loads are presented for two adjacent rural basins of 306 km2 and 424 km2, and for five sub-basins differing in size (between 1 km2 and 33 km2), land use (extent of forest cover between 20% and 93%) and household pressure (from 0 to 40 people/km2) with the aim of studying the influence of land use and catchment size on nutrient exports. The studied catchments are all situated on Devonian schistous substrates in the Ardennes region (Belgium-Luxembourg), and therefore have similar hydrological regimes. As the study period could not be the same for all basins, annual export coefficients were corrected with the 25 years normalized discharge of the Sure River: two regression analyses (for dry and humid periods) relating monthly nutrient loads to monthly runoff were used to determine correction factors to be applied to each parameter and each basin. This procedure allows for the comparing annual export coefficients from basins sampled in different years. Results show a marked seasonal response and a large variability of NO3-N export loads between forested (4 kg N ha-1 year-1), agricultural (27-33 kg N ha-1 year-1) and mixed catchments (17-22 kg N ha-1 year-1). For SRP and TP, no significant agricultural impact was found. Land and bank erosion control the total P massflow in the studied catchments (0.4-1.3 kg P ha-1 year-1), which is mostly in a particulate form, detached and transported during storm events. Soluble reactive P fluxes ranged between 10% and 30% of the TP mass, depending on the importance of point sources in the basins studied. No relation was found between the size of the basins and the export of nitrate, SRP or TP. Nutrient export, specially for NO3-N and TP, shows significant inter-annual variations, closely linked to inter-annual discharge variations. Flow and load frequency data analysis confirm this association for all the basins on an annual basis. Seasonal or storm specific fluxes strongly deviate from their annual values.     

Identification of nitrogen as a growth-limiting nutrient in wastewaters and coastal marine waters through continuous culture algal assays

Two series of continuous culture algal assays conducted in 1973 and 1974, totalling 63 experiments, were performed on mixtures of seawater and wastewater—both treated and untreated— from five locations along the coasts of MA and RI. The results conclusively show that nitrogen was the growth-limiting nutrient in these wastewaters and in coastal marine environments receiving such wastes. There was a linear relationship between total inorganic nitrogen (ΣN) in the influent and particulate nitrogen (PN) representing algal biomass up to a ΣN concentration of about 10 mg1⁻¹. In addition, the N:P ratios in the test alga. Phaeodactylum tricornutum, varied between 10 and 20 (by atoms), whereas the N:P ratios in the wastewater-seawater mixtures were between 4 and 12, thus providing additional evidence that nitrogen was limiting. Enrichment with nitrogen and/or phosphorus to span a range of N:P ratios from 3.9 to 20 resulted in a linear response in PN concentration to ΣN additions. Additions of P had no effect on algal growth. Removal of detergent-P in communities practicing marine waste disposal will hence have little impact on the control of eutrophication in coastal waters.     

Modeling the contribution of point sources and non-point sources to Thachin River water pollution

Major rivers in developing and emerging countries suffer increasingly of severe degradation of water quality. The current study uses a mathematical Material Flow Analysis (MMFA) as a complementary approach to address the degradation of river water quality due to nutrient pollution in the Thachin River Basin in Central Thailand. This paper gives an overview of the origins and flow paths of the various point- and non-point pollution sources in the Thachin River Basin (in terms of nitrogen and phosphorus) and quantifies their relative importance within the system. The key parameters influencing the main nutrient flows are determined and possible mitigation measures discussed.The results show that aquaculture (as a point source) and rice farming (as a non-point source) are the key nutrient sources in the Thachin River Basin. Other point sources such as pig farms, households and industries, which were previously cited as the most relevant pollution sources in terms of organic pollution, play less significant roles in comparison. This order of importance shifts when considering the model results for the provincial level. Crosschecks with secondary data and field studies confirm the plausibility of our simulations. Specific nutrient loads for the pollution sources are derived; these can be used for a first broad quantification of nutrient pollution in comparable river basins. Based on an identification of the sensitive model parameters, possible mitigation scenarios are determined and their potential to reduce the nutrient load evaluated.A comparison of simulated nutrient loads with measured nutrient concentrations shows that nutrient retention in the river system may be significant. Sedimentation in the slow flowing surface water network as well as nitrogen emission to the air from the warm oxygen deficient waters are certainly partly responsible, but also wetlands along the river banks could play an important role as nutrient sinks.     

Nutrient fluxes in the Po basin.

The nutrient load of the river Po needs to be reduced in order to bring the eutrophication problems in the Northwest Adriatic Sea under lasting control. In this paper we analyse the contribution of the different pollution sources to the nitrogen and phosphorus loads of the river Po (source apportionment). We also estimate the effects of measures that aim to reduce nitrogen and phosphorus pollution in the Po basin (scenario analyses). Using a model (PolFlow) that was previously applied to the Rhine and Elbe basins, we found that more than half of the nitrogen and phosphorus loads in the river Po originates from diffuse sources. The results of the scenario analyses indicate that the measures imposed by the EU Nitrates Directive and the EU Wastewater Treatment Directive may not be stringent enough to achieve a large reduction in the N and P loads in the river Po.     

The effect of primary sedimentation on full-scale WWTP nutrient removal performance

Traditionally, the performance of full-scale wastewater treatment plants (WWTPs) is measured based on influent and/or effluent and waste sludge flows and concentrations. Full-scale WWTP data typically have a high variance which often contains (large) measurement errors. A good process engineering evaluation of the WWTP performance is therefore difficult. This also makes it usually difficult to evaluate effect of process changes in a plant or compare plants to each other. In this paper we used a case study of a full-scale nutrient removing WWTP. The plant normally uses presettled wastewater, as a means to increase the nutrient removal the plant was operated for a period by-passing raw wastewater (27% of the influent flow). The effect of raw wastewater addition has been evaluated by different approaches: (i) influent characteristics, (ii) design retrofit, (iii) effluent quality, (iv) removal efficiencies, (v) activated sludge characteristics, (vi) microbial activity tests and FISH analysis and, (vii) performance assessment based on mass balance evaluation. This paper demonstrates that mass balance evaluation approach helps the WWTP engineers to distinguish and quantify between different strategies, where others could not. In the studied case, by-passing raw wastewater (27% of the influent flow) directly to the biological reactor did not improve the effluent quality and the nutrient removal efficiency of the WWTP. The increase of the influent C/N and C/P ratios was associated to particulate compounds with low COD/VSS ratio and a high non-biodegradable COD fraction.     

美国路易斯安那州可持续海岸带总体规划研究

可持续海岸总体规划的提出对降低滨海城市灾害损失具有重大作用。路易斯安那州通过总结长期沿海减灾和恢复工作,提出通过制定可持续海岸总体规划降低沿海地区脆弱性,维持沿海工业和企业长期稳定可持续发展。该规划针对灾害的严重程度提出不同应对场景,通过土地开发与工程营建、降低洪水风险和减灾资金分配等措施,促进规划实施。规划中设计的适应性管理、建立动态资源数据库、海岸信息管理系统等减灾工具和方法,对我国综合防灾减灾规划有启示作用。     

Changes in a temperate estuary during the filling of the biggest European dam

This study aimed to determine whether and how the disruption of river flow, during the filling of the Alqueva dam, influenced the variability of abiotic and biotic factors in the Guadiana estuary, particularly the abundance and distribution of anchovy eggs. River inflow was found to be the most important factor in determining abiotic and biotic variability in the Guadiana estuary. Seasonal patterns were obscured by long periods of low inflow (mid April to early December 2002), which caused marked changes in the estuary. The estuarine turbidity maximum zone was displaced towards the upper estuary, to at least 38 km from the river mouth, 8 to 16 km upstream from previous records. The dynamics of nutrient stoichiometry was also affected. In the upper and middle estuary, P was more potential limiting than N and potential Si limitation was only frequent on the coast, with direct and/or indirect influence in changing phytoplankton dynamics and composition. Previously, the upper estuary alternated between potential P limitation during winter, Si limitation during spring and mid summer and N limitation during mid summer and autumn. The flooding of vast areas in the catchment of the dam probably caused the increase of DSi concentrations, as well as maximal N and P loadings. The abundance of larval stages of anchovy decreased, putatively because estuarine productivity has also decreased. In April 2002 there was an uncontrolled discharge from the Alqueva dam, which reduced the abundance of anchovy eggs by 99.99%. It is suggested that dam managers should mimic, as much as possible, the natural river flow, in order to minimize the impact on downstream ecosystems. Management efforts should not be restricted to the areas upstream of the dam, but should also encompass the estuary and adjacent coastal area.     

Landscape planning to reduce coastal eutrophication: agricultural practices and constructed wetlands

Southern Sweden suffers from coastal eutrophication and one reason is the high nitrogen load through rivers. The major part of this load originates from diffuse land-based sources, e.g. arable soil leaching. Effective reduction of load from such sources demand careful landscape analysis, combined with changed behaviour of the stakeholders. This study describes a chain of methods to achieve trustworthy management plans that are based on numerical modelling and stakeholders participation and acceptance. The effect of some measures was unexpected when modelling their impact on the catchment scale.Management scenarios to reduce riverine nitrogen load were constructed in an actor game (i.e. role-play) for the Genevadsån catchment in southern Sweden. The game included stakeholders for implementation of a loading standard for maximum nitrogen transport at the river mouth. Scenarios were defined after negotiation among involved actors and included changes in agricultural practices, improved wastewater treatment, and establishment of wetlands. Numerical models were used to calculate the nitrogen reduction for different measures in each scenario. An index model (STANK) calculated the root zone leaching of nitrogen from crops at four type farms. This generated input to a catchment scale model (HBV-N) and farm economics. The economic impact of different sets of remedial measures was evaluated for each type farm and then extrapolated to the catchment.The results from scenario modelling show that possible changes in agricultural practices (such as tuning, timing of fertilisation and ploughing, changed crop cultivation) could reduce the nitrogen load to the sea by some 30%, while wetland construction only reduced the original load by some 5%. In the most cost-effective scenario agricultural practices could reduce the riverine load by 86 t per year at a cost of 1.0 million SEK, while constructed wetlands only reduced the load by 14 t per year at a cost of 1.7 million SEK. Thus, changed agricultural practices can be the most effective and less expensive way to reduce nitrogen transport from land to the sea, while constructed wetlands with realistic allocations and sizes may only have small impact on riverine nitrogen transport from land to sea. The overall experience is that actor games and numerical modelling are useful tools in landscape planning for analysing stakeholders’ behaviour and the impact of measures to reduce coastal eutrophication.     

Controls on the nutrient content of suspended sediment transported by British rivers

Recent studies of nutrient fluxes from river basins have emphasised the importance of sediment-associated transport. In order to develop an improved understanding of sediment-associated nutrient transport in UK rivers and of contrasts between individual rivers, attention has been directed to spatial and temporal variations in the nutrient (N and P) content of suspended sediment transported by four rivers, which embrace a representative range of British conditions. Bulk samples of suspended sediment were collected during storm events and these were analysed for both total N and P content and for individual fractions of these nutrients. Significant temporal and spatial variability in these various measures of the nutrient content of suspended sediment has been documented. Spatial variability has been linked to catchment characteristics, which in turn influence sediment sources. Patterns of temporal variability, which are reasonably consistent among the different rivers, have been related both to variations in other sediment properties and to hydrometeorological conditions.     

Phytoplankton,pelagic community and nutrients in a deep oligotrophic alpine lake: ratios as sensitive indicators of the use of P-resources (DRP:DOP:PP and TN:TP:SRSi)

The different use of P-resources between two sites in the deep oligotrophic Traunsee was studied by seasonal and vertical patterns of phytoplankton and nutrients from 12/1997 to 10/1998. The P-resources were evaluated from the proportion between the P-fractions, the dissolved reactive P (DRP), dissolved non-reactive P (DOP) and particulate organic P (PP) and from the stoichiometry between nutrients, the total N (TN), the total P (TP) and soluble reactive Si (SRSi). Significant differences between an inshore site impacted by industrial tailings (Ebensee Bay, EB) and an open water reference site (Viechtau, VI) were evident from vertical profiles of both the P-accumulation (%PP of TP) evaluated by DRP:DOP:PP and the distribution of phytoplankton assessed by Si-exhaustion (TN:TP:SRSi), but not from the seasonal patterns of phytoplankton composition, S:V ratios of the algal community or surface layer nutrient dynamics. Low TP and the stable stratification from May to September triggered the relative accumulation of epilimnetic P at VI as it was evident from both the higher portion of particulate P within TP (%PP of TP) and from the shift towards P-enrichment in nutrient stoichiometry of TN:TP:SRSi. The predominance of around 55-52% algal carbon over bacteria at the surface layer to 20m coincided spatially with the lowest Si content relative to N and P. The disturbances at the impacted site was summarised by: up to 11% less P accumulation by organisms at the surface, no stoichiometric shift towards TP in the epilimnion when compared with deeper layers and a reduction of the trophogenic zone to the top 10m. Reasons for this disturbance are seen in the unstable stratification, turbidity, higher TP and the metazoan dominated food chain. Both triple ratios, DRP:DOP:PP and TN:TP:SRSi, were sensitive indicators of the use of P-resources by plankton communities, while inorganic dissolved fractions (DIN:DRP:SRSi, DIN = dissolved inorganic N) provided only insufficient information on nutrient resources in Traunsee.     

陆海统筹视角下海岸带界定的景观方法 与工具：基于英格兰SCA实践研究

当前,中国海岸带界定体系尚不完善,海岸带保护与利用之间的矛盾尤为严峻,亟待探索适用于国土空间规划背景下海岸带界定的综合方法与工具。景观的跨尺度性、整体性与综合性为理解海岸带提供了新的途径。在系统梳理国际海岸带界定方法的基础上,总结了英格兰海景特征评估工具在多尺度海岸带界定工作中的创新应用与实践,即SCA方法可为落实不同尺度海岸带的核心目标提供相适宜的空间范围,其划分结果纵向可为不同层级海岸带政策的联动提供实体媒介,横向可建立跨陆海界面的空间与视觉链接,为海岸带保护与利用提供了综合的信息背景与空间框架,以期为我国国土空间规划体系下海岸带边界界定提供参考。     

滨海景观带园林植物的选择及应用研究--以山东省基岩海岸城市为例

城市滨海景观带是指城市临海的、海陆相互作用而产生的，具有一定景观价值的特定区域。植物对改善其生态环境，软化、强调或衬托硬质景观，提高景观带的综合效益，具有重要作用。通过对山东省六座基岩海岸城市景观带内，园林植物利用现状的调查研究，对其存在的问题提出了对策及建议。     

Evaluating river water quality through land use analysis and N budget approaches in livestock farming areas

This study was carried out to evaluate the quality of river water by analysis of land use in drainage basins and by estimating the N budgets. The drainage basins of Shibetsu River (Shibetsu area) and Bekkanbeushi River (Akkeshi area) in eastern Hokkaido, Japan were selected for a case study, and the evaluation of water quality was up-scaled to the regional level in Hokkaido by using the Arcview/GIS and statistical information. Water sampling was carried out in August 2001 and May 2002 in the Shibetsu and Akkeshi areas, respectively. The proportions of major land uses in drainage basins such as upland field, forest, urban area, wetland and wasteland for each sampling site were estimated by using topographic maps scaled at 1:25,000. The linear regression results showed that the correlation between NO3-N concentration and the proportion of upland in the drainage basins was highly and positively significant for both the Shibetsu area (r = 0.84, n = 57) and the Akkeshi area (r = 0.71, n = 73) at < 0.001 significance level. The regression coefficients or impact factors of river water quality were 0.015 and 0.0052 for the Shibetsu and Akkeshi areas, respectively. A comparison of these results with that of the previous study results in Hokkaido indicated that the impact factors were highest for intensive livestock farming areas (0.040), medium for mixed agriculture and livestock farming (0.020-0.030), and the lowest for grassland-based dairy cattle and horse farming areas (0.0052-0.015). The results of a simple regression analysis showed that the impact factors had a significant positive correlation with the cropland surplus N (r = 0.93, P < 0.01), chemical fertilizer N (r = 0.82, P < 0.05), and manure fertilizer N (r = 0.76, P < 0.05), which were estimated by using the N budget approach. Using the best-correlated regression model, impact factors for all cities, towns and villages of the Hokkaido region were estimated. The NO3-N concentrations for all major rivers in Hokkaido were predicted by multiplying the estimated impact factors by the proportion of uplands. The regression analysis indicated that the predicted NO3-N concentrations were significantly correlated (r = 0.62, P < 0.001, n = 203) with the measured NO3-N concentrations, reported previously. It can be concluded that estimating the proportions of upland fields in drainage basins, and calculating cropland surplus N enables us to predict river water quality with respect to NO3-N concentration.     

Impact of selected agricultural management options on the reduction of nitrogen loads in three representative meso scale catchments in Central Germany

Nitrogen inputs into surface waters from diffuse sources are still unduly high and the assessment of mitigation measures is associated with large uncertainties. The objective of this paper is to investigate selected agricultural management scenarios on nitrogen loads and to assess the impact of differing catchment characteristics in central Germany. A new modelling approach, which simulates spatially distributed N-transport and transformation processes in soil and groundwater, was applied to three meso scale catchments with strongly deviating climate, soil and topography conditions. The approach uses the integrated modelling framework JAMS to link an agro-ecosystem, a rainfall-runoff and a groundwater nitrogen transport model. Different agricultural management measures with deviating levels of acceptance were analysed in the three study catchments.N-leaching rates in all three catchments varied with soil type, the lowest leaching rates being obtained for loess soil catchment (18.5 kg nitrate N ha^− 1 yr^− 1) and the highest for the sandy soils catchment (41.2 kg nitrate N ha^− 1 yr^− 1). The simulated baseflow nitrogen concentrations varied between the catchments from 1 to 6 mg N l^− 1, reflecting the nitrogen reduction capacity of the subsurfaces. The management scenarios showed that the highest N leaching reduction could be achieved by good site-adapted agricultural management options. Nitrogen retention in the subsurface did not alter the ranking of the management scenarios calculated as losses from the soil zone. The reduction effect depended strongly on site specific conditions, especially climate, soil variety and the regional formation of the crop rotations.