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1.
A study has been made of weathering in Glendye, an upland catchement of heather moorland underlain mainly by granite with some gneiss in north-east Scotland. The concentrations of a range of elements and ions in precipitation and river water were measured over a twelve-month period. The total input and output of each element or ion was calculated. The resulting balances show net outputs of all species except hydrogen ion. Large net outputs of silicon (38.5 kg ha?1 a?1) and bicarbonate (48 kg ha?1 a?1) indicate considerable chemical weathering. A large net output of chloride (32 kg ha?1 a?1) indicates the importance of dry deposition of oceanic aerosols. When this is allowed for the rate of output of elements due to weathering is. Si>Ca>Na>Mg>K>Fe>Al. These results were compared with the abundance of elements in bedrock and differential weathering ratios calculated. These are compared with data from the Hubbard Brook study in New Hampshire. In both cases calcium is by far the most mobile element. The relative importance of the atmosphere and of chemical weathering as sources of each element was calculated, and the results compared with those of a study at Wet Sleddale in the Lake District. Similar patterns emerge in both cases.  相似文献   

2.
The chemistry of bulk precipitation and stream water was monitored in an acidic afforested catchment at Llyn Brianne in upland Wales between 1985 and 1990. Throughfall, stemflow and soil water chemistry were also monitored between 1988 and 1989. Marine-derived solutes dominated the ionic composition of precipitation and stream water, which had mean Cl concentrations of 113 μequiv. 1?1 and 245 μequiv. 1?1, respectively. The higher concentrations in stream water reflect occult and dry deposition on the forest canopy and the effect of interception and transpiration losses. Chloride variations in stream water (112-454μequiv. 1?1) were damped compared with bulk precipitation (28-762μequiv. 1?1) due to the mixing of event (‘new’) water with pre-event (‘old’) water in the catchment soils. A storm episode monitored in the catchment in April 1989 was associated with high sea salt inputs and Cl concentrations in throughfall (1466μequiv. 1?1) and storm runoff were exceptionally high (392μequiv. 1?1). The Cl signal in stream water during the episode was consistent with an event (‘new’) water contribution to the storm response. However, a short-term hydrochemical budget estimated that although Cl outputs from the catchment during the event (1.17 kg ha?1) were equivalent to 8% of inputs in throughfall and stemflow, the storm runoff was equivalent to 32% of effective precipitation. This indicates that pre-event (‘old’) water was the dominant source (> 75%) of storm runoff. Although sea salt inputs during the event had a marked impact on stream water chemistry, the anomalously high levels of acidity sometimes associated with sea salt events were not observed in this particular study.  相似文献   

3.
The effects of timber-cutting on sediment concentrations, soil loss and overland flow in an insigne pine (Pinus radiata) plantation were studied in a mountain watershed of the Cordillera de la Costa, central Chile. Soil formation rates for the lithological conditions of the watershed were estimated. Soil loss measurements on the plantation were taken in 100 m2 plots, equipped with Coshocton samplers, during the years 1991 and 1992. Treatments were: clear-cutting no residues/burned, clear-cutting with residues and undisturbed controls. First-year soil losses were greater from the no residues/burned (2128 kg ha?1) than from the residues (1219 kg ha?1) or undisturbed (48 kg ha?1) plots. During the second post-treatment year, soil loss was greater from the burned plots (1349 kg ha?1) than from the residues (243 kg ha?1) or the undisturbed (72 kg ha?1) plots. Sediment concentrations for the three treatments were 561, 340 and 59 mgl-1 during the first year, and 400, 150 and 83 mgl?1 in the second year. Runoff from the no residues/burned plots was greater than from residues or undisturbed plots during the two post-treatment years. Long-term soil losses were projected to average 240 kg ha?1 yr?1 from areas without residues/burned and 120 kg ha?1 yr?1 in areas with residues treatment, over a 25 year rotation period, whereas control areas were projected to average 60 kg ha?1 yr?1.  相似文献   

4.
A mass balance model of the main Pb stores and fluxes for a typical organic‐rich upland catchment in the Peak District, UK, has been produced. The model, based on the Howden reservoir catchment, reveals that the majority of Pb in the catchment is stored within the soil (approximately 8·63 t km?2). Soil Pb levels are extremely high and can only be explained as the result of centuries of atmospheric Pb deposition from surrounding urban–industrial conurbations, and mining and smelting activity within the Peak District National Park. The atmospheric Pb flux onto the Howden catchment is approximately 107 kg a?1. The aquatic Pb flux is estimated at between 29·9 and 71·7 kg a?1; thus, at present, catchment soils are acting as a sink for Pb pollution. The Howden reservoir acts as a secondary store for Pb eroded and leached from catchment soils, with approximately 80% re‐deposited in its sediments. It is estimated that 2·3% of the catchment soil Pb pool has been retained in the reservoir sediments over its 91 year lifespan. Although the catchment is currently acting as a Pb sink, the rate of change in the soil Pb pool is very small. Future change in climate or deposition chemistry could, however, transform catchment soils into a significant source of Pb to the aquatic environment and water supply. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

5.
This study concerns the problem of water erosion in the Sahel. Surface water and sediment yields (suspended matter and bedload) were monitored for 3 years (1998–2000) at the outlet of a small grazed catchment (1·4 ha) in the northern part of Burkina Faso. The catchment consists of about 64% sandy deposits (DRY soil surface type), which support most of the vegetation, and about 34% of crusted bare soils (ERO soil surface type). The annual solid‐matter export is more than 90% suspended sediment, varying between 4·0 and 8·4 t ha?1. The bedload represents less than 10% of soil losses. In a single flood event (10 year return period), the sediment yield can reach 4·2 t ha?1. During the period studied, a small proportion (20 to 32%) of the floods was thus responsible for a large proportion (80%) of the solid transport. Seasonal variation of the suspended‐matter content was also observed: high mean values (9 g l?1) in June, decreasing in July and stabilizing in August (between 2 and 4 g l?1). This behaviour may be a consequence of a reorganization of the soil surfaces that have been destroyed by trampling animals during the previous long dry season, vegetation growth (increase in the protecting effect of the herbaceous cover) and, to a lesser extent, particle‐supply limitation (exhaustion of dust deposits during July). The particle‐size distribution in the suspended matter collected at the catchment outlet is 60% made up of clay: fraction ≤2 µ m. The contribution of this clay is maximum when the water rises and its kaolinite/quartz ratio is then close to that of the ERO‐type surfaces. This indicates that these surfaces are the main source of clay within the catchment. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

6.
Rill erosion is an important erosional form on agricultural soils in England, causing large losses of soil, particularly on cultivated slopes. This paper describes a rill system that developed in a small agricultural catchment in north Oxfordshire during the winter of 1992–93. The rill system comprised two components: a system of ‘feeder rills’ along the valley-side slopes, which were the result of flow concentration and erosion along wheelings, and a thalweg rill, which formed along a dry valley bottom as a result of surface runoff concentration from the feeder rills. Total volumetric soil loss from the rill system was 32·28 m3, equivalent to 3·01 m3, ha?1 for the rill catchment area, or 3·91 t ha?1. Mean discharge for the thalweg rill and feeder rills, calculated during a storm event, was 31·101s?1 and 1·171s?1, respectively. All flows were fully turbulent and supercritical. We emphasize the need for a spatially distributed approach to the study of runoff and erosion at the catchment scale.  相似文献   

7.
This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100–2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area‐weighted average rate of soil erosion by water in the catchment, measured over four years (1998–2001), is 14·8 t ha?1 y?1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha?1 y?1. Calculated sediment yield (5·6 t ha?1 y?1) is similar to sediment yield measured in nearby catchments. Seventy‐four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present‐day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

8.
Solute concentrations and fluxes in rainfall, throughfall and stemflow in two forest types, and stream flow in a 90 ha catchment in southern Chile (39°44′S, 73°10′W) were measured. Bulk precipitation pH was 6·1 and conductivity was low. Cation concentrations in rainfall were low (0·58 mg Ca2+ l?1, 0·13 mg K+ l?1, 0·11 mg Mg2+ l?1 and <0·08 mg NH4–N l?1), except for sodium (1·10 mg l?1). Unexpected high levels of nitrate deposition in rainfall (mean concentration 0·38 mg NO3–N l?1, total flux 6·3 kg NO3–N ha?1) were measured. Concentrations of soluble phosphorous in bulk precipitation and stream flow were below detection limits (<0·09 mg l?1) for all events. Stream‐flow pH was 6·3 and conductivity was 28·3 μs. Stream‐water chemistry was also dominated by sodium (2·70 mg l?1) followed by Ca, Mg and K (1·31, 0·70 and 0·36 mg l?1). The solute budget indicated a net loss of 3·8 kg Na+ ha?1 year?1, 5·4 kg Mg2+ ha?1 year?1, 1·5 kg Ca2+ ha?1 year?1 and 0·9 kg K+ ha?1 year?1, while 4·9 kg NO3–N ha?1 year?1 was retained by the ecosystem. Stream water is not suitable for domestic use owing to high manganese and, especially, iron concentrations. Throughfall and stemflow chemistry at a pine stand (Pinus radiata D. Don) and a native forest site (Siempreverde type), both located within the catchment, were compared. Nitrate fluxes within both forest sites were similar (1·3 kg NO3–N ha?1 year?1 as throughfall). Cation fluxes in net rainfall (throughfall plus stemflow) at the pine stand generally were higher (34·8 kg Na+ ha?1 year?1, 21·5 kg K+ ha?1 year?1, 5·1 kg Mg2+ ha?1 year?1) compared with the secondary native forest site (24·7 kg Na+ ha?1 year?1, 18·9 kg K+ ha?1 year?1 and 4·4 kg Mg2+ ha?1 year?1). However, calcium deposition beneath the native forest stand was higher (15·9 kg Ca2+ ha?1 year?1) compared with the pine stand (12·6 kg Ca2+ ha?1 year?1). Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

9.
This study was designed to improve our understanding of, and mechanistically simulate, nitrate (NO3) dynamics in a steep 9.8 ha rural headwater catchment, including its production in soil and delivery to a stream via surface and subsurface processes. A two‐dimensional modelling approach was evaluated for (1) integrating these processes at a hillslope scale annually and within storms, (2) estimating denitrification, and (3) running virtual experiments to generate insights and hypotheses about using trees in streamside management zones (SMZs) to mitigate NO3 delivery to streams. Total flow was mathematically separated into quick‐ and slow‐flow components; the latter was routed through the HYDRUS software with a nitrogen module designed for constructed wetlands. Flow was monitored for two years. High surface‐soil NO3 concentrations started to be delivered to the stream via preferential subsurface flow within two days of the storm commencing. Groundwater NO3‐N concentrations decreased from 1.0 to less than 0.1 mg l?1 from up‐slope to down‐slope water tables, respectively, which was attributed to denitrification. Measurements were consistent with the flushing of NO3 mainly laterally from surface soil during and following each storm. The model accurately accounted for NO3 turnover, leading to the hypotheses that denitrification was a minor flux (<3 kg N ha?1) compared to uptake (98?127 kg N ha?1), and that SMZ trees would reduce denitrification if they lowered the water table. This research provides an example of the measurement and modelling of NO3 dynamics at a small‐catchment scale with high spatial and temporal resolution. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

10.
Piping has been recognized as an important geomorphic, soil erosion and hydrologic process. It seems that it is far more widespread than it has often been supposed. However, our knowledge about piping dynamics and its quantification currently relies on a limited number of data for mainly loess‐derived areas and marl badlands. Therefore, this research aimed to recognize piping dynamics in mid‐altitude mountains under a temperate climate, where piping occurs in Cambisols, not previously considered as piping‐prone soils. It has been expressed by the estimation of erosion rates due to piping and elongation of pipes in the Bere?nica Wy?na catchment in the Bieszczady Mountains, eastern Carpathians (305 ha, 188 collapsed pipes). The research was based on the monitoring of selected piping systems (1971–1974, 2013–2016). Changes in soil loss vary significantly between different years (up to 27.36 t ha?1 yr?1), as well as between the mean short‐term erosion rate (up to 13.10 t ha?1 yr?1), and the long‐term (45 years) mean of 1.34 t ha?1 yr?1. The elongation of pipes also differs, from no changes to 36 m during one year. The mean total soil loss is 48.8 t ha?1 in plots, whereas in the whole studied catchment it is 2.0 t ha?1. Hence, piping is both spatially and temporally dependent. The magnitude of piping in the study area is at least three orders of magnitude higher than surface erosion rates (i.e. sheet and rill erosion) under similar land use (grasslands), and it is comparable to the magnitude of surface soil erosion on arable lands. It means that piping constitutes a significant environmental problem and, wherever it occurs, it is an important, or even the main, sediment source. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

11.
The increase of the nitrate concentration in surface waters used as water supply resources has been investigated with a view to the effects of agricultural activities and atmospheric precipitation. The nitrate concentration increased beyond the acceptable limit for infants after 1975, when due to the permanent augmentation of the synthetic fertilizer rates the organic humus quantities decreased to a minimum. The variability of nitrate concentrations in atmospheric precipitation is dependent on the magnitude of precipitation and the intensity of industry in the given region. At an average value of atmospheric precipitation the nitrogen value in agricultural regions varies within 6 to 12 kg · ha?1 · a?1, in regions with extended industries up to 24 kg · ha?1 · a?1.  相似文献   

12.
In Lutzito catchment on Barro Colorado Island, Panama, extraordinarily high suspended‐sediment yields of 1–2 Mg ha?1 year?1 were generated despite the dense forest cover coinciding with erosion‐resistant soils. We hypothesized that ant mounding activity is an important zoogeomorphological mechanism in this area, providing relevant quantities of easily transportable material at the soil surface. To test this hypothesis, all ant mound material was collected collected for dry mass determination from thirty 4 m2 plots installed in the study area every 1–3 days during the 39‐day sampling period. Additionally, three ground‐nesting ant species responsible for mounds in the study area, Ectatomma ruidum, Trachymyrmex cornetzi and Strumigenys marginiventris, were identified. On the basis of the total of 1.38 kg of material collected in the wet season of 2011, the estimate for the whole 8 months wet season amounts to 725 kg ha?1. As this value is in the same order of magnitude as sediment output, it shows that ants may act as important ecosystem engineers and contribute to sediment production here by providing large quantities of fine‐grained, readily erodible material at the soil surface for subsequent transport to the streambed. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

13.
Nitrogen (N) fertilization may profoundly affect soil microbial communities. In this study, a field fertilization experiment was conducted in temperate grassland in Inner Mongolia, China to examine the effect of N fertilization on soil microbial properties and the main factors related to the characteristics of soil microbial community. Soil microbial biomass carbon (MBC) and microbial functional diversity along an N gradient were measured over three months (June to August). The result showed that N fertilization significantly decreased MBC under high N treatment (N200, 200 kg N ha?1 y?1) compared with the control (N0, 0 kg N ha?1 y?1) in the three months. Microbial functional diversity in July and August were significantly increased by low N treatment (N50, 50 kg N ha?1 y?1). Among the three fertilization treatments, microbial functional diversity under N200 in the three months was significantly lower than that of N50. The decrease of MBC and functional diversity under N200 were mainly due to the significant decline of plant belowground biomass under high N treatment. The increase of functional diversity under N50 treatment was due to the higher plant aboveground biomass as a result of the higher soil moisture availability. This finding highlighted that the higher N fertilization (N200) was not suitable for the growth and improvement of functional diversity of the soil microbial community, and that site and plant community play an important role in regulating the characteristics of soil microbial community.  相似文献   

14.
Gullying has been widespread in the Ethiopian Highlands during the 20th century. It threatens the soil resource, lowers crop yields in intergully areas through enhanced drainage and desiccation, and aggravates flooding and reservoir siltation. Knowing the age and rates of gully development during the last few decades will help explain the reasons for current land degradation. In the absence of historical written or photographic documentation, the AGERTIM method (Assessment of Gully Erosion Rates Through Interviews and Measurements) has been developed. It comprises measurements of contemporary gully volumes, monitoring of gully evolution over several years and semi‐structured interview techniques. Gully erosion rates in the Dogu'a Tembien District, Tigray, Ethiopia, were estimated in three representative case‐study areas. In Dingilet, gullying started around 1965 after gradual environmental changes (removal of vegetation from cropland in the catchment and eucalyptus plantation in the valley bottom); rill‐like incisions grew into a gully, which increased rapidly in the drier period between 1977 and 1990. The estimated evolution of the total gully volume in the other areas show patterns similar to those of the Dingilet gully. Average gully erosion rate over the last 50 years is 6·2 t ha?1 a?1. Since 1995, no new gullies have developed in the study area. Area‐specific short‐term gully erosion rates are now on average 1·1 t ha?1 a?1. The successful application of the AGERTIM method requires an understanding of the geomorphology of the study area and an integration of the researchers with the rural society. It reveals that rapid gully development in the study area is some 50 years old and is mainly caused by human‐induced environmental degradation. Under the present‐day conditions of ‘normal’ rain and catchment‐wide soil and water conservation, gully erosion rates are decreasing. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

15.
An overall approach to assess the effectiveness of soil conservation measures at catchment scale is the comparison of sediment budgets before and after implementation of a catchment management programme. In the May Zeg‐zeg catchment (187 ha) in Tigray, north Ethiopia, integrated catchment management has been implemented since 2004: stone bunds were built in the whole catchment, vegetation was allowed to re‐grow on steep slopes and other marginal land, stubble grazing abandoned, and check dams built in gullies. Land use and management were mapped and analysed for 2000 and 2006, whereby particular attention was given to the quantification of changes in soil loss due to the abandonment of stubble grazing. Sediment yield was also measured at the catchment's outlet. A combination of decreased soil loss (from 14·3 t ha–1 y–1 in 2000 to 9·0 t ha–1 y–1 in 2006) and increased sediment deposition (from 5·8 to 7·1 t ha–1 y–1) has led to strongly decreased sediment yield (from 8·5 to 1·9 t ha–1 y–1) and sediment delivery ratio (from 0·6 to 0·21). This diachronic comparison of sediment budgets revealed that integrated catchment management is most effective and efficient and is the advisable and desirable way to combat land degradation in Tigray and other tropical mountains. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

16.
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17.
Prompt location of areas exposed to high erosion is of the utmost importance for soil and water conservation planning. Erosion models can be useful tools to locate sources of sediment and areas of deposition within a catchment, but the reliability of model predictions of spatial patterns of erosion at catchment scale has seldom been validated against observations. This study aimed to evaluate the performance of a simple empirical model (Morgan, Morgan and Finney model, MMF) in predicting spatial patterns of erosion at two small catchments in the East African Highlands: Kwalei (Tanzania) and Gikuuri (Kenya). Erosion maps predicted by the MMF model were compared with erosion maps obtained by direct survey. In Kwalei, erosion features were especially frequent in fields of annual crops. In Gikuuri, slope was the critical erosion factor, with estimated erosion rates >10 kg m?2 a?1 on slopes >18 per cent. Predicted erosion rates were mainly transport‐limited and ranged from <0·01 to 13·50 kg m?2 a?1 in Kwalei and 9·29 kg m?2 a?1 in Gikuuri. The performance of the MMF model in predicting the spatial patterns of erosion was acceptable in Kwalei, but poor in Gikuuri. However, by excluding the elements at the valley bottoms in Gikuuri Catchment, the performance of the model improved dramatically. The spatial pattern of erosion predicted by the MMF model was driven by the accumulation of surface runoff, which did not consider the possibility of re‐infiltration along the slope. As a result, the MMF erosion patterns predicted by the model increased invariably from the ridges to the valley bottoms, hampering the model suitability for locating areas subjected to high and very high erosion. It is concluded that the model predictions could be substantially improved by introducing a more realistic hydrological component for the prediction of surface runoff along the hill‐slope. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

18.
Reliable assessment of the spatial distribution of soil erosion is important for making land management decisions, but it has not been thoroughly evaluated in karst geo‐environments. The objective of this study was to modify a physically based, spatially distributed erosion model, the revised Morgan, Morgan and Finney (RMMF) model, to estimate the superficial (as opposed to subsurface creep) soil erosion rates and their spatial patterns in a 1022 ha karst catchment in northwest Guangxi, China. Model parameters were calculated using local data in a raster geographic information system (GIS) framework. The cumulative runoff on each grid cell, as an input to the RMMF model for erosion computations, was computed using a combined flow algorithm that allowed for flow into multiple cells with a transfer grid considering infiltration and runoff seepage to the subsurface. The predicted spatial distributions of soil erosion rates were analyzed relative to land uses and slope zones. Results showed that the simulated effective runoff and annual soil erosion rates of hillslopes agreed well with the field observations and previous quantified redistribution rates with caesium‐137 (137Cs). The estimated average effective runoff and annual erosion rate on hillslopes of the study catchment were 18 mm and 0.27 Mg ha?1 yr?1 during 2006–2007. Human disturbances played an important role in accelerating soil erosion rates with the average values ranged from 0.1 to 3.02 Mg ha?1 yr?1 for different land uses. The study indicated that the modified model was effective to predict superficial soil erosion rates in karst regions and the spatial distribution results could provide useful information for developing local soil and water conservation plans. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

19.
Abstract

A field experiment was conducted on a sloping grassland soil in southwest England to investigate the downslope transport of nitrogen in soil water following the application of cattle manure, slurry and inorganic fertilizer. Transport of nitrogen (N) species was monitored on hydrologically isolated plots. Manure (50 t ha?1), slurry (50 m3 ha?1) and fertilizer (250 kg N ha?1) were applied in February/March 1992. Subsurface water movement, by both matrix and preferential flow, was the dominant flow route during the experiment. Subsurface and surface nutrient flow pathways were monitored by analysing soil water and surface runoff for NO3-N, NH4-N and total N. Subsurface flow chemistry was dominated by NO3-N, with concentrations usually between 2 and 5 mg NO3 ?N dm?3. Differences between fertilizer and manure treatments and the untreated control were not significant. Significantly elevated NO3-N concentrations were observed in soil water in the buffer zone, indicating the importance of a buffer zone at least 10 m wide between manure spreading zones and an adjacent water course.  相似文献   

20.
Mesoscalic estimation of nitrogen discharge via drainage systems   总被引：2，自引：0，他引：2  
A complex approach has been developed for estimating mesoscalic nitrogen discharges via drainage systems using spatial information about land use, drainage areas, nitrogen balances and soil and site characteristics. Determining the total drainage area involves certain difficulties for larger areas, as on the one hand, the available databases are incomplete, and on the other hand the localisation and digitalisation of large subsurface drainage areas is a very time-consuming process. Knowledge of the history and causes of drainage systems in landscapes is required. To solve this problem a method has been developed to calculate the drainage areas for large catchments. In order to obtain a complete data set of subsurface drainage areas, representative areas were selected to enable the proportion of subsurface drainage area to be determined for various soil and site characteristics. These proportions were extrapolated to the entire area and the approach tested in the Mulde River Catchment Area in Germany.The rate of drained arable land is about 25.2% of the total area, which can be broken down into grassland (19.0%) and arable land (27.4%). The results differ for sandy soils with up to 8% drained areas and 57.8% for stagnant soils. This shows that the proportion of drained land is highly dependent on the nature of the soil in the catchment area, which has profound implications for approaches to nitrogen modelling.Average nitrogen discharge for the whole catchment area via drainage water was 33 kg ha−1 yr−1 in the 1980s and 10 kg ha−1 yr−1 in the 1990s. The nitrogen discharge varies from one soil type to another: in regions with sandy substrate (11,900 ha) discharge was 34 kg ha−1 yr−1 in the 1980s (14 kg ha−1 yr−1 in the 1990s), while in areas with loess lessivé soils (89,200 ha) it was about 26 kg ha−1 yr−1 in the 1980s (9 kg ha−1 yr−1 in the 1990s). The reduction can be explained by the complete change in farming strategy since the demise of the former German Democratic Republic (GDR).The approach shown is well suited to future model approaches on a regional scale. By creating and integrating new data sets derived from modern GIS operations the approach reduces the uncertainty of water and nitrogen modelling. This gives us a better understanding of nitrogen discharges into surface and groundwater and temporal discharge dynamics. The discharge data are highly valuable to predict environmental protection measurements for streams, lakes, coastal waters and groundwaters.  相似文献   

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