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1.
《Geoderma》2007,137(3-4):466-476
Spatial variation is a typical feature of geochemical variables, providing a challenge for sampling design and environmental monitoring. It is generally qualitatively but not quantitatively described using spatial distribution maps. In this study, the feasibility of quantifying spatial variation is investigated using neighbourhood statistics within a GIS environment, using, as an example, near-total Ni concentrations in the surface soils of Northern Ireland. A total of 6138 topsoil samples were collected at an average sampling density close to 1 sample per km2. At this sampling density it was possible to calculate neighbourhood statistics directly from the raw data. Neighbourhood statistics of local mean, local standard deviation and local coefficient of variation were calculated using window sizes of 3 km × 3 km, 6 km × 6 km, 9 km × 9 km, 12 km × 12 km, 24 km × 24 km and 48 km × 48 km and visualized using GIS mapping techniques. The results showed that the highest soil Ni concentrations were located in the northern part of Northern Ireland where basalt is the main rock type. Lowest soil Ni concentrations were found in the western region of the Province on schist and limestone geologies. The granite area in the south-eastern region of Northern Ireland also displayed low soil Ni values. In terms of assessing the degree of spatial variation, high local standard deviation values were found to be associated with high local mean values thereby limiting the usefulness of local standard deviation as an indicator of spatial variation. This effect did not occur when local coefficient of variation values were used in place of local standard deviation so the coefficient of variation values are recommended as a more appropriate indicator to quantify spatial variation. The strongest spatial variations were observed on the western edge of the basalt area along the boundary of the basalt–sandstone areas and the schist area. Within each rock type, spatial variations were relatively weak and this was most clearly demonstrated in the basalt area. As the window size used for calculation of neighbourhood statistics was increased, so too was the resulting smoothing effect which led to clearer patterns but with loss of detail in the spatial variation observed. Neighbourhood statistics, coupled to a GIS, were found to be an effective way of quantifying and visualizing spatial variation in environmental geochemistry.  相似文献   

2.
In slopes of Mediterranean mid-mountain areas, land use and land cover changes linked to the abandonment of cropland activity affect soil quality and degradation and soil redistribution; however, limited attention has been paid to this issue at catchment scale. This paper evaluates the effects of cropland abandonment and post-land abandonment management (through natural revegetation and afforestation) on soil redistribution rates using fallout 137Cs measurements in the Araguás catchment (0.45 km2, Central Spanish Pyrenees). A total of 52 soil core samples, distributed in a regular grid, from the first 30–40 cm and 9 sectioned reference samples were collected across the catchment and soil properties were analysed. Fallout 137Cs was measured in a 5 cm sectioned references samples and in bulk grid samples. 137Cs inventories were used to estimate soil erosion and deposition rates across the catchment. Results show that the highest erosion rates were recorded under sparsely vegetated sites in the badland area, while the lowest rates were found in the afforested area, but no significant differences were observed between the different uses and covers in soil redistribution rates likely due to a long history of human intervention through cultivation in steep slopes and afforestation practices. However, the recovery of the soil organic matter in afforested areas suggest that afforestation can reduce soil degradation at long-term scale. The information gained achieve a better understanding of soil redistribution dynamics and provide knowledge for effective land management after cropland abandonment of agroecosystems in Mediterranean mountain areas.  相似文献   

3.
Phosphorus fertilizer contains contaminants that may increase the content in the soil and in plants. The relationship between soil P and soil uranium (U) was investigated to determine potential effects of P‐fertilizer use. This study is based on a long‐term experiment (38 years with 0, 15, and 30 kg fertilizer P ha–1 y–1) for beef production on grassland at Teagasc, Johnstown Castle, Wexford, Ireland and also on soils from a National Soil Database (NSD). The NSD soils were taken at fixed locations on a predetermined grid system at the density of one sample every 50 km2. Of the 1310 samples in the NSD, the 760 grassland mineral soils were selected for this study. The aim was to determine to what extent P fertilizer increases the content of U in the soil. The results showed that there was a small but significant increase in soil U in the high‐P treatments, which contained high levels of soil P, in the long‐term field experiment. The results from the NSD showed that there was not a significant relationship between extractable (Morgan's) soil test P (STP) and U. It is concluded that the use of chemical P fertilizer at normal rates used in agriculture in Ireland is not a major threat to U content of soil based on the results of this study. There was a significant relationship between total P and STP, in the NSD, with the latter making up approx. 1% of the former. Soil available P increased with soil pH, probably reflecting the use of chemical P fertilizer and lime on agricultural soils.  相似文献   

4.
A soil quality database (SQDB) is a collection of soil samples described by a given set of parameters, allowing farmers, scientists and other stakeholders to make informed decisions about practices, processes and policies for soil use and management. If each parameter is considered as a dimension of the space spanned by the SQDB, extracting information becomes a difficult task when the number of parameters is >3. A widely used approach to explore multidimensional data sets is the self‐organizing map (SOM) method, which is suitable for clustering, visualization and extraction of information from multidimensional data. We applied the SOM method as an exploratory technique to an unlabelled SQDB to extract knowledge – data patterns and data associations – from the data set (the time and location of each sample were unknown). The SQDB used in this study is a set of 1240 unlabelled samples within the Central Valley of Chile, covering ca 7500 km2. The predominant soils are Andisols with a large organic matter content (7–12%), small bulk densities (0.6–1.0 g/cm3) and large water‐holding capacity. We identified three patterns: (i) isolated region within the map with close neurons (smooth transitions), (ii) two or more regions with predominantly large or small values and (iii) homogeneous map with small values with an isolated region of large values. These patterns show that the data set represented more than two groups that were not necessarily related. For pH, no important associations with other investigated parameters were observed. Previous studies carried out by the local agricultural research station showed that pH values below 5.5 constrain nutrient uptake. Thus, locations presenting pH<5,5 should be subject to seasonal monitoring to assess management practices that mitigate soil acidity. The component plane for organic matter indicates that ca. 50% of the soil samples had contents <8% related to soil series characteristics and management practices. As the k‐means is initialized by random partitions, the two‐step approach (clustering the map representing the input data) is less sensitive to variations in the input data (subsamples) than is the direct application of k‐means to the input data, but it also reduces the computational cost. The ability of SOMs to visualize multidimensional data sets helps gain an understanding of the data in the exploratory phase, such as the association and integration of physical, chemical and biological parameters.  相似文献   

5.
李盟  方瑞  乐峰  吴芳  张雪 《水土保持通报》2018,38(4):228-233
[目的]对江苏省水土流失重点治理区和预防区代表县进行水土流失定量监测,以掌握该区水土流失情况,为该区水土流失动态监测提供技术方法和理论支持。[方法]收集江苏省徐州市铜山区和连云港市赣榆区2015年度高分一号遥感影像、DEM和降雨量,以中国土壤流失方程(CSLE)为基本算法。[结果]铜山区水土流失面积1 917.82km~2,轻度以上流失面积175.76km~2,占总流失面积的9.16%;赣榆区水土流失面积1 511.2km~2,轻度以上流失面积131.95km~2,占总流失面积的8.73%。[结论]本研究方法模型参数真实、客观,不受人为因素干扰,适合多期、大尺度水土流失动态监测,能为江苏省水土流失动态监测提供高效可行的技术方法。  相似文献   

6.
基于通用土壤流失方程(USLE)的基本原理,利用我国南北方各水蚀区的土壤流失量及其相关生态因子的大量实测数据,建立了适用于我国南北方的以3S(GIS、GPS和RS)技术为支持的水土流失定量监测方法。该系统方法在我国山东、福建、江苏、云南、北京、河北等地累计应用面积超过30万km~2,其在江苏南京的应用时间最长,最具代表性。应用该方法在1997—2015年期间对南京全市区域水土流失和治理状况进行长期定量监测研究,结果表明:19年间,南京全市平均年水土流失总量为2.765×10~6t,平均轻度以上年水土流失面积为863.7km~2,占全市总面积的13.0%。轻度以上水土流失面积所占比例较小,但水土流失量占总流失量80%以上,因此,仍是水土流失治理和区域生态环境保护的重点方向;与2000年之前的监测结果相比,轻度以上水土流失面积和年土壤流失总量均有显著降低。该方法建立了更符合实际的模型因子算法和原则,监测精度和可靠性较高,监测结果验证了近年来南京市水土流失治理措施和生态环保监督管理实施力度加大,取得了明显成效。  相似文献   

7.
Sampling plays an important role in acquiring precise soil information required in modern agricultural production worldwide, which determines both the cost and quality of final soil mapping products. For sampling design, it has been proposed possibile to transfer the relationships between kriging variance and sampling grid spacing from an area with existing information to other areas with similar soil-forming environments. However, this approach is challenged in practice because of two problems:i) different population variograms among similar areas and ii) sampling errors in estimated variograms. This study evaluated the effects of these two problems on the transferability of the relationships between kriging variance and sampling grid spacing, by using spatial data simulated with three variograms and soil samples collected from four grasslands in Ireland with similar soil-forming environments. Results showed that the variograms suggested by different samples collected with the same grid spacing in the same or similar areas were different, leading to a range of mean kriging variance (MKV) for each grid spacing. With increasing grid spacing, the variation of MKV for a specific grid spacing increased and deviated more from the MKV generated using the population variograms. As a result, the spatial transferability of the relationships between kriging variance and grid spacing for sampling design was limited.  相似文献   

8.
1999-2018年黄河源区水土流失动态变化   总被引：1，自引：1，他引：0  
[目的] 研究1999—2018年黄河源区土壤侵蚀强度等级变化及空间分布情况，为该区生态环境建设和水土流失治理提供数据支撑。[方法] 利用1999，2011，2018年水土流失动态监测成果，开展黄河源区水土流失动态变化分析。[结果] 黄河源区水土流失面积表现为先增加后减少，与1999年相比，2011年水土流失面积增加1.89×104 km2，增幅126%，2018年水土流失面积增加1.01×104 km2，增幅67.33%。从空间数据来看，与1999年相比，77.97%的区域土壤侵蚀强度等级未发生变化，19.33%的区域土壤侵蚀强度等级降低，2.7%的区域土壤侵蚀强度等级增加。[结论] 水土流失面积增加主要与区域暖干化和人类活动引起的草场退化有关。应实施一批重大生态保护修复和建设工作，提升草场质量，改善区域生态环境。  相似文献   

9.
A series of five papers compares the cost-effectiveness of different procedures for soil survey at medium scale. The first three are presented here. The whole trial area of 120 km2 in Berkshire, in south-central England, was mapped in soil series by free survey at 1:25 000 for publication at 1:63 360. Three contrasting sample areas of 1.26 km2 were resurveyed to the same legend by free survey at 1:10 560, and by grid survey at a range of scales between 1:20 000 and 1:70 000, to both general purpose (soil series) and fifteen–twenty different single-property legends. The direct costs of producing each map were recorded. The study confirmed how much the free survey procedure depended on the external features of soil boundaries to locate them. The density of soil observations required to map soil series by free survey at the same map scale in different terrains was approximately proportional to the length of mapped boundary/km2, or to the number of separately mapped soil occurrences/km2. The density was least where the soil boundaries had the clearest external expression. Survey effort/km2 increased in proportion to the density of observations but was also affected by local differences in the ease of cross-country access, or in the effort necessary (by spade or auger) to identify the soil at a point. For soil series grid surveys there are approximately linear relations between log(cost) and log(map scale) with gradients between 1.3 and 1.7. A map of soil series by grid survey is more expensive than a map of the same units, based upon the same density of observations by the same surveyor, by free survey. But a series map by grid survey by a scientific assistant is cheaper than a series map based on the same density of soil observations by free survey by a scientific officer (diplomate or graduate). The cost of an isoline map of a single soil property depends very much upon the cost of determining the property mapped, and to some extent upon the number of different isoline maps produced from a single set of samples or observations. Even at the unusually low costs of chemical analyses assumed here, an isoline map of one chemical property costs nearly twice as much as a series map by grid survey.  相似文献   

10.
As one part of the ‘Three Norths’ forest protection system, dense farmland shelterbelt networks in northeastern China could greatly modify water and sediment flows. In this paper, catchment soil erosion rate and sediment yield (SY) that are impacted by farmland shelterbelts were estimated using WaTEM/SEDEM model. The shelterbelts reduced catchment soil erosion and SY to some extent. The mean soil erosion rate and specific sediment yield (SSY; defined as the ratio of SY to catchment area; t km?2 yr?1) of the 25 reservoir catchments decreased from 351.6 and 93.9 t km?2 yr?1 under the supposed scenario without shelterbelts to 331.1 t km?2 yr?1 and 86.3% t km?2 yr?1 under the current situation with shelterbelts. The sediment trap efficiencies (STEs) varied from 0.01% to 23.6% with an average value of 7.6%. The STEs were significantly correlated with shelterbelt density, catchment perimeter, topographic factors, RUSLEP‐factor and land use patterns including patch density (PD), patch cohesion index (COHESION), Shannon's diversity index (SHDI) and aggregation index (AI). The multiple regression equation involving factors of catchment's topography and morphology and land use pattern has a satisfactory performance, and mean slope gradient (MSG) and AI explained most of the variability of shelterbelts’ STE. This information can help land managers to better design shelterbelts and to reduce water‐derived soil loss at catchment scale.  相似文献   

11.
At the global scale peatlands are an important soil organic carbon (SOC) pool. They sequester, store and emit carbon dioxide and methane and have a large carbon content per unit area. In Ireland, peatlands cover between 17% and 20% of the land area and contain a significant, but poorly quantified amount of SOC. Peatlands may function as a persistent sink for atmospheric CO2. In Ireland the detailed information that is required to calculate the peatland SOC pool, such as peat depth, area and carbon density, is inconsistent in quality and coverage. The objective of this research was to develop an improved method for estimating the depth of blanket peat from elevation, slope and disturbance data to allow more accurate estimations of the SOC pool for blanket peatlands. The model was formulated to predict peat depth at a resolution of 100 ha (1 km2). The model correctly captured the trend and accounted for 58 to 63% of the observed variation in peat depth in the Wicklow Mountains on the east coast of Ireland. Given that the surface of a blanket peatland masks unknown undulations at the mineral/peat interface this was a successful outcome. Using the peat depth model, it was estimated that blanket peatland in the Wicklow Mountains contained 2.30 Mt of carbon. This compares to the previously published values ranging from 0.45 Mt C to 2.18 Mt C.  相似文献   

12.
Recognizing the importance of preserving biodiversity and ecosystem services, human society has established extensive protected area networks to conserve these resources in recent decades. Are protected areas working as expected? Empirical coarse-scale assessments of this question across large regions, or even globally, tend to answer “yes”, while fine-scale studies of individual protected areas often and repeatedly answer “no”. We conducted a first fine-scale analysis of Brazil’s extensive Amazonian protected area network (1.8 million km2) and have quantitatively estimated conservation effectiveness in light of changing human development pressures in the surrounding landscape. The overall network maintained intact forest cover for 98.6% of protected forest lands, largely agreeing with previous coarse-scale studies. However, detailed examination of 474 individual protected areas unveils a broad range of efficacy. Many protected areas (544,800 km2) experience default protection simply due to their remoteness. Many others (396,100 km2) have provided highly effective protection in the face of substantial human development pressure. Conversely, 12% (38) of protected areas have failed to protect the 27,300 km2 that they encompass, and another 7% (23) provide only marginal protection of 37,500 km2. Comprehensive landscape assessments of protected area networks, with frequent monitoring at scales matching the patterns of human-caused disturbances, are necessary to ensure the conservation effectiveness and long term survival of protected areas in rapidly changing landscapes. The methods presented here are globally adaptable to all forested protected areas.  相似文献   

13.
Red Lists are used to assess the extinction risk of species based on quantitative IUCN criteria. For the compilation of a new Red List of butterflies in Flanders (north Belgium), we collated ca 800,000 distribution records and applied the IUCN Red List criteria to this small region (ca 135,00 km2). We also explored the effect of spatial resolution on the outcome of the Red List assessment by alternatively using 1 × 1 km2 and 5 × 5 km2 grid cells for geographic range size and trend calculations. We determined conservation hot spots in Flanders based on the Red List status of the species composition in each grid cell. The new Red List classified 20 butterflies (out of 68 resident species) as Regionally Extinct, six as Critically Endangered, five as Endangered, seven as Vulnerable and seven as Near Threatened. The remaining 23 species were classified as Least Concern. Using coarse instead of fine grain grid cells would have classified ten species in a lower Red List category. Compared with the previous Red List, nine species were classified in a lower and 12 in a higher threat category. In total, 218 1 × 1 km2 grid cells were considered as (very) high butterfly conservation priority sites. The application of the new IUCN criteria in a small region such as Flanders resulted in a Red List that offered challenging opportunities for the conservation of butterflies in particular and biodiversity in general.  相似文献   

14.
Slurry injection below maize seeds is a rather new application technique developed to improve the nitrogen use efficiency of liquid organic manure. To enable the characterization of the spatial and temporal soil mineral nitrogen (SMN) dynamics after slurry injection, the present study aims to develop an appropriate soil sampling strategy. Three consecutive experiments were conducted. The first testing of the soil sampling approach was conducted in an existing field trial where the slurry was injected down to a depth of 12 cm (upper rim) below the soil surface. The soil profile (75 cm wide) centered below the maize row was sampled grid‐like to a depth of 90 cm. Around the injection zone, soil monoliths (SM) were sampled using a purpose‐built soil shovel. Below the SMs and in the interrow space (15 and 30 cm distance to the row) a standardized auger procedure was performed. The second experiment aimed at improving the sampling strategy with a focus on sample homogenization quality and necessary sample sizes per pooled sample. Furthermore, the risk of a carryover of slurry components along the soil core due to drilling an auger through a slurry band was analyzed. In the third experiment this improved sampling strategy was validated. Results from the first testing of the sampling procedure showed that the strategy is suitable, although some problems occurred (especially the high spread in values among the replications causing high coefficients of variation (CV) of mostly 40–60%). The improvement trial revealed that due to the high gradient of SMN concentration in the direct range of the injection zone an intensive homogenization of these samples is required. Suitable sample sizes (twelve auger samples and six soil monolith samples per pooled sample) have to be collected to obtain reliable SMN values. Drilling an auger through a slurry band to sample subjacent soil layers has to be avoided. Following this enhanced sampling strategy, in the final validation trial the spread in values were considerably reduced and resulted in CV values of mostly < 20%. The developed sampling strategy enables the characterization of the spatial and temporal SMN dynamics when slurry has been band‐injected below a maize row. The method can be transferred to other row crops and different slurry injection spacing.  相似文献   

15.
Over the past decades, numerous practical applications of Digital Soil Mapping have emerged to respond to the need of land managers. One important contribution to this effort is the release of regional‐scale soil maps from the GlobalSoilMap (GSM) project. While the GSM project aims at producing soil property predictions on a fine 90 × 90 m grid at the global scale, land managers often require aggregated information over larger areas of interest (e.g. farms, watersheds, municipalities). This study evaluated a geostatistical procedure aiming at aggregating GSM grids to a land management scale, thereby providing land suitability maps with associated uncertainty for the French region ‘Languedoc‐Roussillon’ (27 236 km2). Specifically, maps were derived from three GSM prediction grids (pH, organic carbon and clay content) by calculating the proportion of ‘suitable’ agricultural land within a municipality, where suitability was defined as having soil property values below or above a predefined threshold (pH < 5.5, OC < 10 g/kg, clay > 375 g/kg). Calculation of these nonlinear spatial aggregates and the associated uncertainty involved a three‐step approach: (i) sampling from the conditional probability distributions of the soil properties at all grid cells by means of sequential Gaussian simulation applied to a regression kriging model, (ii) transformation of soil properties to suitability indicators for all grid cell samples generated in the first step and (iii) spatial aggregation of the suitability indicators from grid cells to municipalities. The maps produced show large differences between municipality areas for all three land suitability indicators. The uncertainties associated with the aggregated suitability indicators were moderate. This approach demonstrated that fine‐scale GSM products may also fulfil user demands at coarser land management scales, without jeopardizing uncertainty quantification requirements.  相似文献   

16.
The metal content was determined in soil and vegetation around the eastern zone of the disused sulphur and copper mines at Avoca (southeast Ireland). A 250 m × 250 m grid survey was conducted covering a total area of 4 km2. The mining belt was in the centre of the investigated site and was sampled separately. Iron, Zn, Cu and Cd concentrations in soil and plant material were determined, in addition to soil organic matter content and soil pH. Soil samples taken from the spoil showed elevated Cu and Cd concentrations, and low soil pH and organic matter content. At least 50 per cent of the agricultural sites examined around the East Avoca Mine showed elevated soil Cu and Cd concentrations, whereas Zn and Fe soil concentrations were within the range for unpolluted soils. None of the vegetation analysed had elevated Zn, Cd, Fe or Cu concentrations. Overall there was no indication of serious metal contamination in either soils or vegetation surrounding the mine in spite of extensive dust deposition during open-pit mining activity 15–30 years ago. However, a plume of elevated Cu in the soil was identified, which originated from a large spoil heap and had been spread for some 2·0 km by the prevailing wind.  相似文献   

17.
Understanding the erosion and deposition rates is very important for designing soil and water conservation measures. However, existing methods of assessing the rates of soil loss present many limitations and are difficult to apply to in karst areas, and there is still very little data in this areas. Karst depressions comprise geomorphologically important sources and sinks for sediments and can provide the long‐term history records of environmental changes. But there have been few similar studies focused on its sediments in the world. In this paper, the Cs‐137 technique was employed to estimate the sediment deposition rate of karst depression to assess the surface erosion. The results indicate that the average deposition rate, deposition amount and specific deposit yield for the Yongkang catchments since 1963 were estimated to be 4·32 mm y−1, 3·16 t y−1and 20·53 t km−2 y−1, respectively. The results obtained were consistent with the actual monitoring data of local runoff plots, and confirm the validity of the overall approach. So it was suggested that the mean specific sediment yields of 20 t km−2 y−1 can be representative of the soil loss rates in the regions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

18.
平顶山市丘陵区面积2607.36km2,占总面积的29.6%,该区沟壑纵横,地形支离破碎,水土流失严重,特别是风化层较厚的花岗岩、片麻岩及黄土覆盖丘陵区,沟蚀极为发育,冲沟密布、沟头前进、沟岸扩张、沟床下切、崩塌滑坡,致使沟道荒芜。沟头是沟道与坡面之间由缓变陡的转折处,是沟掌与沟道的衔接处,是溯源侵蚀发生与发展的关键部位。沟头防护治理是小流域综合治理的重要组成部分,然而在群众性的水土保持小流域治理中,沟头防护工程数量少、质量差,缺乏生物措施配置,甚至往往被忽视。本研究采用当地适宜的乔、灌木经济植物作不同处理,通过对降水量、沟头前进、沟岸护张、沟道下切、土壤侵蚀量、生物量、土壤养分变化观测,取得了大量的成果资料,应用水土保持学、植物学、土壤化验分析的理论,进行对比分析研究,探索出了平顶山市丘陵区沟头防护生物措施配置最佳方式,旨在运用简便、经济、利于环境效益的生物措施防护途径,扼制由于坡面径流冲刷而引起的沟头溯源侵蚀的发生与发展,为丘陵区沟头防护建设提供科学依据。  相似文献   

19.
Many national and regional databases of soil properties and associated estimates of soil carbon stock consider organic, but not inorganic carbon (IC). Any future change in soil carbon stock resulting from the formation of pedogenic carbonates will be difficult to set in context because historical measurements or estimates of IC concentration and stock may not be available. In their article describing a database of soil carbon for the United Kingdom published in this journal, Bradley et al. [Soil Use and Management (2005) vol. 21, 363–369] only consider data for organic carbon (OC), despite the occurrence of IC‐bearing calcareous soils across a substantial part of southern England. Robust techniques are required for establishing IC concentrations and stocks based on available data. We present linear regression models (R2 between 0.8 and 0.88) to estimate IC in topsoil based on total Ca and Al concentrations for soils over two groups of primary, carbonate‐bearing parent materials across parts of southern and eastern England. By applying the regression models to geochemical survey data across the entire area (18 165 km2), we estimate IC concentrations on a regular 500‐m grid by ordinary kriging. Using bulk density data from across the region, we estimate the total IC stock of soil (0–30 cm depth) in this area to be 186 MtC. This represents 15.5 and 5.5% of the estimated total soil carbon stock (OC plus IC) across England and the UK, respectively, based on the data presented by Bradley et al. [Soil Use and Management (2005) vol. 21, 363–369]. Soil geochemical data could be useful for estimating primary IC stocks in other parts of the world.  相似文献   

20.
Abstract. Because of the observed variability in soil available P (Olsen) contents, phosphorus budgets were used to predict changes in the soil P status of an intensively managed 6 ha grassland catchment in Northern Ireland. The P accumulation rate of approximately 24 kg/ha/y suggested an increase of soil available P (Olsen) of 1.0 mg P/kg/y. Soluble reactive phosphorus concentrations in drainflow measured on a daily basis for a two year period (January 1981 — December 1982) were compared with the two year period January 1990 — December 1991. The median concentration had increased by 10.0 μg P/1 in 1990/91 compared with 1981/82. This difference was only apparent in mean concentrations for the two time periods, after data associated with high flow events, which were more frequent in 1981/82, were excluded from the comparison. This rate of increase of 1.1 μg P/1/y, which was interpreted as reflecting an increase in soluble reactive phosphorus concentration in soil solution, is comparable to the increase in background soluble reactive phosphorus of 1.5 ± 0.54 μg P/1/y which was reported recently over a 17 year period from diffuse sources in the much larger (4400 km2) Northern Ireland catchment of Lough Neagh.  相似文献   

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