Manganese and land-use in upland catchments in Scotland

Manganese (Mn) in surface waters is a micronutrient, but elevated concentrations are toxic to fish and impair drinking water quality. In Scotland, undesirable Mn concentrations (> 0.05 mg l(-1)) occur predominantly in upland freshwaters because the acidic pH and organic nature of catchment soils favour Mn mobilisation. The relationship between upland land-use in Scotland and Mn concentrations in surface waters is reviewed. Conifer afforestation is associated with enhanced Mn in runoff. Mn is leached from conifer foliage and litter, and mature conifers enhance acid deposition and loss of Mn from acidified catchment soils. After harvesting, increased soil pools of water-soluble Mn and elevated Mn concentrations in runoff have been observed. Liming, fertiliser addition, drainage ditch construction and ploughing to improve upland pastures, and muirburn on grouse moors may also increase Mn concentrations in runoff, but the evidence is less clear-cut. The extent to which land-use influences Mn concentrations in upland catchments in Scotland is modified by catchment hydrology and soil type. Catchment geology, instream processes and standing water stratification are probably lesser influences on Mn concentrations in surface waters of upland catchments in Scotland. The location of land-use in upland catchments, especially in the riparian zone, is critical in determining its effect on Mn in runoff. Climate change is expected to increase Mn concentrations in runoff from upland catchments in Scotland because of predicted changes in soil hydrology.     

Analysis of catchment evapotranspiration at different scales using bottom-up and top-down approaches

Physically-based hydrological models are used to predict catchment water balance through detailed simulation of hydrological processes at small temporal and spatial scales. However, annual catchment water balance can also be easily and simply predicted using lumped conceptual model. Comparison between physically-based hydrological models and lumped conceptual models can help us understand the dominant factors on catchment water balance at different scales. In this paper, a distributed physically-based hydrological model (i.e., bottom-up approach) and a simple water-energy balance model (i.e., top-down approach) are used to predict actual evapotranspiration in nine sub-catchments, and the whole basin of the Luan River in northern China. Both simulations give very close values of annual evapotranspiration and show the same complementary relationship between actual and potential evapotranspiration at annual time scale. From the analysis at different time scales through comparison of the top-down and the bottom-up methods, it is shown that the annual catchment evapotranspiration is controlled mainly by annual precipitation and potential evapotranspiration, and the variability of soil water and vegetation becomes more important at a smaller time scale in the study areas. It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale but can be simplified to a linear relationship at hourly temporal and hillslope scales, which is commonly used in the physically-based hydrological models.     

A comparison of SWAT, HSPF and SHETRAN/GOPC for modelling phosphorus export from three catchments in Ireland

Recent extensive water quality surveys in Ireland revealed that diffuse phosphorus (P) pollution originating from agricultural land and transported by runoff and subsurface flows is the primary cause of the deterioration of surface water quality. P transport from land to water can be described by mathematical models that vary in modelling approach, complexity and scale (plot, field and catchment). Here, three mathematical models (soil water and analysis tools (SWAT), hydrological simulation program-FORTRAN (HSPF) and système hydrologique Européen TRANsport (SHETRAN)/grid oriented phosphorus component (GOPC)) of diffuse P pollution have been tested in three Irish catchments to explore their suitability in Irish conditions for future use in implementing the European Water Framework Directive. After calibrating the models, their daily flows and total phosphorus (TP) exports are compared and assessed. The HSPF model was the best at simulating the mean daily discharge while SWAT gave the best calibration results for daily TP loads. Annual TP exports for the three models and for two empirical models were compared with measured data. No single model is consistently better in estimating the annual TP export for all three catchments.     

Pools and fluxes of mercury and methylmercury in two forested catchments in Germany

Mercury (Hg) and methylmercury (CH3Hg+) are global pollutants, but little information is available on rates of atmospheric input, distribution and mobility in soils and catchments of central Europe. The objectives of this study were to investigate input and output fluxes of these compounds in a deciduous and a coniferous catchment in NE Bavaria (Germany), and to estimate pools and mobility of total Hg (Hgtot) and CH3Hg+ at the catchment scale. Bulk precipitation, throughfall, litterfall and runoff were collected biweekly from April 1998 to April 1999. Several soil profiles were sampled to estimate pools of Hg compounds in the catchments. In both catchments highest contents of Hgtot were found in the Oa layer of the forest floor (up to 500 ng g(-1)) and the soil storage of Hgtot calculated for a soil depth of 60 cm was approximately 890 g ha(-1) in the coniferous and 190 g ha(-1) in the deciduous catchment. Highest contents of CH3Hg+ in upland soils were observed in the Oi layer of the forest floor, and soil storage of CH3Hg+ was 4.35 g ha(-1) in the coniferous and 0.59 g ha(-1) in the deciduous catchment. The annual total deposition of Hgtot (total deposition not measured directly but calculated from throughfall and litterfall) was 541 mg ha(-1) year(-1) in the coniferous and 618 mg ha(-1) year(-1) in the deciduous catchment. Total deposition rates of CH3Hg+ were 3.5 and 2.6 mg ha(-1) year(-1). The contribution of litterfall to the total deposition of Hgtot and CH3Hg+ was 55% in the deciduous catchment. In the coniferous catchment, the contribution of litterfall to total deposition was only 29% for Hgtot, but 55% for CH3Hg+. By far the largest proportion of the deposited CH3Hg+ and Hgtot remained in the catchments (85% in the coniferous, 95% in the deciduous). As compared to remote Swedish catchments, deposition and output via runoff of Hgtot, were higher, but deposition and output of CH3Hg+ were lower in our catchments. In contrast to other studies, the annual budget revealed no differences in the mobility between the two species at the catchment scale. However, temporal patterns of the runoff fluxes and converse gradients of CH3Hg+ and Hgtot contents in the forest floor indicated differences in mobility on shorter time scales.     

Runoff generation in small catchments under a native rain forest and a rubber plantation in Xishuangbanna,southwestern China

For the purpose of assessing the potential influence of tropical rain forest conversion to rubber plantation on catchment hydrology, a stable oxygen isotope was used as a tracer to identify the event water and prestorm water components of storm runoff during low‐ and high‐flow conditions in a native tropical rain forest catchment (TRFC) and an artificial rubber plantation catchment (ARPC) in SW China. Isotopic hydrograph separations for the storm of April and September 2004 reveal that the event water made up only a small proportion of discharge (29 and 31%, respectively) at peak flow in the TRFC, while it made up the dominant component at peak flow (62 and 69%, respectively) in the ARPC. The analyses suggest that in the ARPC, the universal presence of compacted terraced tracks associated with land management would encourage infiltration‐excess overland flow. This isotopic investigation demonstrates that tropical rain forest conversion to rubber plantation would markedly change the runoff generation processes in this area.     

Effect of ditching operations on stream-water chemistry in a boreal forested catchment.

The effects of ditching of boreal forest land on stream-water quality and quantity was assessed by comparing, over a 4-year-period, the physicochemical properties of the water in two small streams (western Finland), one whose catchment was ditched for forestry halfway through the sampling period and another nearby (control) stream whose catchment was not ditched ('paired catchment method'). While the artificial drainage did not have any significant effect on the hydrograph, it resulted in an increase in the aquatic concentrations of Mn, Ca, Mg, suspended material and alkalinity, a decrease in the concentrations of TOC and H3O+, while for Al and Fe there was a change in control mechanisms. The concentration and control changes after ditching are related to changes in hydrological pathways and to the exposure of both organic (peat) and inorganic (mineral soil) layers on the ditch slopes.     

Karstentwässerung im Kaisergebirge (Tirol, Österreich) – Abgrenzung hydrographischer Einzugsgebiete durch Kombination hydrogeologischer Untersuchungen mit Isotopenmethoden und hydrologischer Modellierung

Water resources investigations in karstic mountainous regions face the difficulty that the hydrological catchment boundaries are usually not identical with the orographic catchment boundaries. In this study an integrative method is presented that combines different sources of hydrogeological information and results of distributed water balance modelling to identify hydrological catchment boundaries and subsurface water ways in a karstic mountainous region. The different information comprises, in addition to meteorological and hydrographic data, region-wide point measurements of discharge, field surveys, isotope data, tracer tests, spring discharge data, soil and geological surveys and mapping, etc. The study was set-up in the Kaisergebirge mountain range in Tyrol/Austria, using the well known model MIKE SHE. Based on the additional information, the original model structure was adjusted to the specific situation in the karst, e.g. by introducing a bypass-flow within the unsaturated zone. The modelling results based on the orographic catchments were evaluated in terms of closure and—equally important—non-closure of the water balance. Spatial patterns of simulated hydrologic quantities are interpreted in light of the different sources of information. As a result, a regional map of surplus and deficit between observed and simulated runoff was drawn and combined with the additional information to form a general conceptual model of karst water flow directions and the location and altitude of the contributing recharge area in the high-alpine region. The results of the study provide a valuable basis for the assessment and protection of karst water resources for water supply.     

Land management as a factor controlling dissolved organic carbon release from upland peat soils 1: Spatial variation in DOC productivity

The importance of soil storage in global carbon cycling is well recognised and factors leading to increased losses from this pool may act as a positive feedback mechanism in global warming. Upland peat soils are usually assumed to serve as carbon sinks, there is however increasing evidence of carbon loss from upland peat soils, and DOC concentrations in UK rivers have increased markedly over the past three decades. A number of drivers for increasing DOC release from peat soils have been proposed although many of these would not explain fine-scale variations in DOC release observed in many catchments.We examined the effect of land use and management on DOC production in upland peat catchments at two spatial scales within the UK. DOC concentration was measured in streams draining 50 small-scale catchments (< 3 km²) in three discrete regions of the south Pennines and one area in the North Yorkshire Moors. Annual mean DOC concentration was also derived from water colour data recorded at water treatment works for seven larger scale catchments (1.5-20 km²) in the south Pennines. Soil type and land use/management in all catchments were characterised from NSRI digital soil data and ortho-corrected colour aerial imagery.Of the factors assessed, representing all combinations of soil type and land use together with catchment slope and area, the proportion of exposed peat surface resulting from new heather burning was consistently identified as the most significant predictor of variation in DOC concentration. This relationship held across all blanket peat catchments and scales.We propose that management activities are driving changes in edaphic conditions in upland peat to those more favourable for aerobic microbial activity and thus enhance peat decomposition leading to increased losses of carbon from these environments.     

Monitoring a flood event in a densely instrumented catchment, the Upper Eden, Cumbria, UK

Multi‐day rainfall events appear to be an important cause of recent flooding in the UK. Hydrological data from an extensive, nested hydrometric network in the unregulated, predominantly rural Upper Eden catchment in northern England are presented for one such flood event. These highlight antecedent catchment conditions and the propagation of the multi‐day flood event during February 2004. An assessment of flood response is provided over varying scales and land use between the upland Gais Gill catchment (1.1 km²) and the larger Upper Eden catchment (616 km²). Large spatial variations in rainfall totals are identified from a dense raingauge network during the flood event and are principally related to catchment elevation. High cumulative rainfall totals for the 6‐day event, particularly at upland sites appear to be the exceptional feature of the flood event with return periods in the order of 100 years at some upland gauges. Resultant patterns of flood attenuation and translation are quantified in different areas of the catchment, highlighting the flashy response of the headwater catchments and the attenuated downstream response in the lowland environment. The study forms part of the national Catchment Hydrology And Sustainable Management (CHASM) programme.     

Effect of different land use on soil erosion in the pre-alpine fringe (North-East Italy): Ion budget and sediment yield

Data concerning ion budget from rainfall, runoff and soil loss measurements from two experimental plots located in North-East Italy, under different land cover (beech forest and vineyard, respectively), are reported. The chemical composition of rainfall, soil solution and runoff was determined to study the solute cycle within the soil, and the relationships between water, soil and vegetation. The forest ecosystem is more prone to acidification than the agricultural one; the elemental concentration of runoff water is considerably lower than that of soil solution. Comparing the ion input (rainfall) and output (runoff) at the two sites, it was possible to estimate the ion budget in the two soil-vegetation systems. The runoff amount and the ion balance are related to rainfall volumes and composition; the measured runoff under vineyard is 59% in comparison to the one under beech. The soil loss at the two experimental sites (170 kg/ha and 132 kg/ha, respectively) is quite limited. The measured sediment yield of the two catchments (0.24-0.19 t/ha/year, respectively) is consistent with data reported for native forests of western Europe. Comparing rainfall and soil loss at the two sites proved that maintenance of some form of land cover is advisable if runoff and erosion are to be minimized. In the European context, where the most important consequences of erosion are sedimentation downstream and loss of productivity, this type of data will yield valuable information for the understanding of such processes occurring at catchment scale, and will help policy-makers develop appropriate programs for the territory safeguard.     

May land use change reduce the water deficiency problem caused by reduced brown coal mining in the state of Brandenburg?

Surface mining alters the water regime not only locally, but also regionally. The reduced brown coal mining in the south-east of the state Brandenburg (Germany) leads to decreasing river discharge and consequently to a shortage in the water supply. Land use change is one possible option to counteract this development. In this simulation study, we explored the impact of temporary and permanent set-aside of arable land on Brandenburg’s regional water balance. Temporary and permanent set-aside were considered as major measures towards deintensification of agriculture. Simulations were performed using the regional ecohydrological model SWIM, which integrates hydrological processes, vegetation growth, erosion and nutrient dynamics. The model was used to simulate the consequences of different land use change scenarios on main components of the regional water balance. Changes in the use of arable land altered clearly its water balance. The impact of these changes on the regional water balance for Brandenburg did not exceed ±10% for its single components. Opposite tendencies were established in the simulations by contrasting effects of temporary and permanent set-aside of arable cropland. While temporary set-aside increased runoff from the whole area up to 6.7% due to lower evapotranspiration and higher soil moisture in arable land, the conversion of agricultural land within river corridors to meadows had an opposite effect on regional runoff (6.9% decrease) due to higher water retention coefficients and higher evapotranspiration losses. Therefore, only temporary set-aside may compensate to some extent for the anticipated decrease in river discharge.     

Analysis of catchment evapotranspiration at different scales using bottom-up and top-down approaches

Physically-based hydrological models are used to predict catchment water balance through detailed simulation of hydrological processes at small temporal and spatial scales. However, annual catchment water balance can also be easily and simply predicted using lumped conceptual model. Comparison between physically-based hydrological models and lumped conceptual models can help us understand the dominant factors on catchment water balance at different scales. In this paper, a distributed physically-based hydrological model (i.e., bottom-up approach) and a simple water-energy balance model (i.e., top-down approach) are used to predict actual evapotranspiration in nine sub-catchments, and the whole basin of the Luan River in northern China. Both simulations give very close values of annual evapotranspiration and show the same complementary relationship between actual and potential evapotranspiration at annual time scale. From the analysis at different time scales through comparison of the top-down and the bottom-up methods, it is shown that the annual catchment evapotranspiration is controlled mainly by annual precipitation and potential evapotranspiration, and the variability of soil water and vegetation becomes more important at a smaller time scale in the study areas. It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale but can be simplified to a linear relationship at hourly temporal and hillslope scales, which is commonly used in the physically-based hydrological models.     

Riparian zone influence on stream water chemistry at different spatial scales: a GIS-based modelling approach, an example for the Dee, NE Scotland

A geographical information system (GIS-ARC/INFO) was used to collate existing spatial data sets on catchment characteristics to predict stream water quality using simple empirical models. The study, based on the river Dee catchment in NE Scotland, found that geological maps and associated geochemical information provided a suitable framework for predicting chemical parameters associated with acidification sensitivity (including alkalinity and base cation concentrations). In particular, it was found that in relatively undisturbed catchments, the parent material and geochemistry of the riparian zone, when combined with a simple hydrological flow path model, could be used to accurately predict stream water chemistry at a range of flows (Q95 to > Q5) and spatial scales (1-1000 km2). This probably reflects the importance of the riparian zone as an area where hydrological inputs to stream systems occur via flow paths in the soil and groundwater zones. Thus, evolution of drainage water chemistry appears to retain the geochemical characteristics of the riparian area as it enters the channel network. In more intensively managed catchments, riparian land use is a further influential factor, which can be incorporated into models to improve predictions for certain base cations. The utility in providing simple hydrochemical models, based on readily available data sets, to assist environmental managers in planning land use in catchment systems is discussed.     

岩石边坡植被护坡系统的水分平衡及控制

 通过对植被护坡系统水分动态平衡的分析,提出岩石边坡植被护坡系统根层土壤贮水量的基本要求。采用现场降雨试验等方法研究岩石边坡植被护坡系统水分运移的规律,对影响植被护坡系统水分平衡的根层土壤初始贮水量、植被截留量、坡表径流量、边坡坡角、坡表蒸散量及根层土壤萎蔫贮水量等因子进行分析。试验结果表明：若客土配比合理,其渗透性能良好,客土能在较短的时间内获得较大的贮水量,客土中添加适量保水剂、泥炭可明显减缓客土层水分的蒸散,此外,客土中添加保水剂还可降低客土的萎蔫持水量,使客土层中更多的水分成为可供植物利用的有效水;覆盖良好的坡面植被对降雨的截留量不可忽视;为提高降雨的入渗量,须选择适宜的边坡坡角。研究成果可为岩石边坡植被护坡系统的水分平衡及控制提供依据。     

Export of dissolved organic matter in relation to land use along a European climatic gradient

The terrestrial export of dissolved organic matter (DOM) is associated with climate, vegetation and land use, and thus is under the influence of climatic variability and human interference with terrestrial ecosystems, their soils and hydrological cycles. We present a data-set including catchments from four areas covering the major climate and land use gradients within Europe: a forested boreal zone (Finland), a temperate agricultural area (Denmark), a wet and temperate mountain region in Wales, and a warm Mediterranean catchment draining into the Gulf of Lyon. In all study areas, DOC (dissolved organic carbon) was a major fraction of DOM, with much lower proportions of DON (dissolved organic nitrogen) and DOP (dissolved organic phosphorus). A south-north gradient with highest DOC concentrations and export in the northernmost catchments was recorded: DOC concentrations and loads were highest in Finland and lowest in France. These relationships indicate that DOC concentrations/export are controlled by several factors including wetland and forest cover, precipitation and hydrological processes. DON concentrations and loads were highest in the Danish catchments and lowest in the French catchments. In Wales and Finland, DON concentrations increased with the increasing proportion of agricultural land in the catchment, whereas in Denmark and France no such relationship was found. DOP concentrations and loads were low compared to DOC and DON. The highest DOP concentrations and loads were recorded in catchments with a high extent of agricultural land, large urban areas or a high population density, reflecting the influence of human impact on DOP loads.     

海河流域山西省段土地利用变化研究

为了探讨土地利用变化对天然降水产流．过程的影响，对海河流域山西省段的土地利用变化进行分析，以便研究海河流域山西省段的洪水特性及其变化趋势。     

Interaction of nitrogen deposition and land use on soil and water quality in Scotland: issues of spatial variability and scale

Over large areas of the Scottish uplands anthropogenic sulfur (S) deposition is declining in response to stringent national and European controls on S emissions. At the same time, however, the relative contribution of nitrogenous (N) compounds to the total anthropogenic deposition loading has increased. To investigate the significance of N deposition on the potential acidification of surface waters, national, regional, and catchment databases were developed to assess the relationships between N deposition, soil C/N ratios, land use and surface water NO3 concentrations. National classification schemes for land use and soils were used as only limited empirical data are available at such large spatial scales. Data were screened to eliminate areas where N inputs are dominated by non-atmospheric sources. From these screened datasets, it was apparent that areas with the highest risk of N leaching were situated predominantly in the upland areas of south-west and west Scotland (areas with low soil C/N ratios). At the regional scale, surface-water NO3 concentration in afforested catchments was negatively correlated with soil C/N ratios below 20. This relationship was not evident in moorland catchments, where NO3 leaching was strongly related to N deposition and the loch/catchment ratio, rather than the soil C/N ratio. Temporal trends of regional water quality highlighted as increasing loch NO3 concentrations between 1988 and 1996-1997, presumably reflecting an increase in N deposition, enhanced leaching losses from the terrestrial component of the catchment, or altered in-lake processes. The hydrochemical records for two catchments in NE Scotland (Lochnagar and Allt a Mharcaidh) highlight the importance of within catchment process in controlling the nitrogen response observed in surface waters. The potential mechanisms through which vegetation and soils may modify incoming deposition are discussed.     

Impacts of climate and land‐cover changes on water resources in a humid subtropical watershed: a case study from East Texas,USA

This study investigates the response of water resources regarding the climate and land‐cover changes in a humid subtropical watershed during the period 1970–2009. A 0.7°C increase in temperature and a 16.3% increase in precipitation were observed. Temperature had a lower increase trend, and precipitation showed definite increasing trend compared to previous studies. The main trend of land‐cover change was conversion of vegetation and barren lands to developed and crop lands affected by human intervention, and forest and grass to bush/shrub which considered to be caused by natural climate system. Hydrologic responses to climate and land‐cover changes resulted in increases of surface run‐off (15.0%), soil water content (2.7%), evapotranspiration (20.1%) and a decrease in groundwater discharge (9.2%). We found that surface run‐off is relatively stable with precipitation, whereas groundwater discharge and soil water content are sensitive to changes in land cover, especially land cover brought about by human intervention.     

Skalenübergreifende Prozess-Studien zur Abflussbildung in Gebieten mit periglazialen Deckschichten (Sauerland, Deutschland)

Based on studies at different scales, runoff processes in the catchment “Bohläse” (Sauerland, Germany) were analysed during several rainfall-runoff-events. Using hydrological tracers and hydrometric methods, the influence of periglacial cover beds was determined for runoff at the catchment scale and for soil water flux at the point scale. The results show that the influence of the base layer depends on the current water content. If the water content in the base layer is low, vertical water movement is impeded. On the other hand, if the water content is high, the base layer becomes a preferential flow path for interflow. Due to the spatial variability of the soil physical properties, the base layer functions as a preferential flow path for interflow only if the bulk density is low. The results confirm the importance of periglacial cover beds for runoff processes in low mountain regions and represent an experimental basis for hydrological regionalisation depending on the spatial distribution of periglacial cover beds.     

Stream water hydrochemistry as an indicator of carbon flow paths in Finnish peatland catchments during a spring snowmelt event

Extreme hydrological events are known to contribute significantly to total annual carbon export, the largest of which in Arctic and boreal catchments is spring snowmelt. Whilst previous work has quantified the export of carbon during snowmelt, the source of the carbon remains unclear. Here we use cation hydrochemistry to trace the primary flowpaths which govern the export of carbon during the snowmelt period; specifically we aim to examine the importance of snowpack meltwater to catchment carbon export. The study was carried out in two forested peatland (drained and undrained) catchments in Eastern Finland. Both catchments were characterised by base-poor stream water chemistry, with cation concentrations generally decreasing in response to increasing discharge. Streamflow during the snowmelt period was best described as a mixture of three sources: pre-event water, snowpack meltwater and a third dilute component we attribute to the upper snow layer which was chemically similar to recent precipitation. Over the study period, pre-event water contributed 32% and 43% of the total stream runoff in Välipuro (undrained) and Suopuro (drained), respectively. The results also suggest a greater near-surface throughflow component in Suopuro, the drained catchment, prior to snowmelt. CO₂ and DOC concentrations correlated positively with cation concentrations in both catchments indicating a common, peat/groundwater flowpath. CH₄ concentrations were significantly higher in the drained catchment and appeared to be transported in near-surface throughflow. Meltwater from the snowpack represented an important source of stream water CO₂ in both catchments, contributing up to 49% of total downstream CO₂ export during the study period. We conclude that the snowpack represents a potentially important, and often overlooked, transient carbon store in boreal snow-covered catchments.