Terrestrial sources of methylmercury in surface waters: The importance of the riparian zone on the Svartberget Catchment

The runoff of methylmercury (MeHg) from forested catchments to surface waters has been identified as a potentially significant input of MeHg to the aquatic ecosystem. Little, however, is known of the processes which control the transfer of MeHg from soils to surface waters. This study investigated the potential terrestrial sources of MeHg in runoff by sampling profiles of soil solution chemistry and determining the flux of water through those profiles into two tributaries on the Svartberget Catchment in northern Sweden. One study profile was from the podzol soil that covers most of the catchment area. The other profiles were taken in the riparian zone of each of the two tributaries. Soil solution was extracted from the soils by centrifugation. High catchment soil solution concentrations of MeHg (>1 ng l^?1) occur in the surface layers of the soil, but overland flow on the catchment is rare. MeHg concentrations in the podzol profile dropped to less than 0.2 ng l^?1 in the mineral soil just 5 cm below the mor layer. In the riparian soil profiles sampled in October, MeHg concentrations were higher (ca. 0.4 ng l^?1), but in a July sampling the concentrations in the riparian profiles were comparable to those in the podzol (i.e. < 0.2 ng l^?1). Very high concentrations of MeHg were found in the streambank sphagnum mosses (>2 ng l^?1) partially submerged within the stream. The concentrations of MeHg observed under the podzol soil were insufficient to sustain the concentration of MeHg in runoff from the forested subcatchments where podzol profiles cover more than 70% of the surface area. The only sources of additional MeHg that lie along major runoff flow pathways are the riparian soils and mosses on the streambanks. It is therefore hypothesized that output of MeHg from the forest areas of the catchment is controlled by the biogeochemical processes in the riparian zone.     

Analysis of runoff,sediment dynamics and sediment yield of subcatchments in the highly erodible Isábena catchment,Central Pyrenees

Purpose

The Isábena catchment (445 km²), Spain, features highly diverse spatial heterogeneity in land use, lithology and rainfall. Consequently, the relative contribution in terms of water and sediment yield varies immensely between its subcatchments, and also temporally. This study presents the synthesis of ~2.5 years of monitoring rainfall, discharge and suspended sediment concentration (SSC) in the five main subcatchments of the Isábena and its outlet.

Materials and methods

Continuous discharge at the subcatchment outlets, nine tipping bucket rainfall and automatic SSC samplers (complemented by manual samples), were collected from June 2011 until November 2013. The water stage records were converted to discharge using a rating curve derived with Bayesian regression. For reconstructing sediment yields, the data from the intermittent SSC sampling needed to be interpolated. We employed non-parametric multivariate regression (Quantile Regression Forests, QRF) using the discharge and rainfall data plus different aggregation levels of these as ancillary predictors. The subsequent Monte Carlo simulations allowed the determination of monthly sediment yields and their uncertainty.

Results and discussion

The stage–discharge rating curves showed wide credibility intervals for the higher stages, with great uncertainties associated with the discharge rates, especially during floods. The water yield of the subcatchments differed considerably. The entire catchment’s output was dominated by the northernmost subcatchment (~360 mm year^?1). The smaller, southern subcatchments featured much higher variability and lower runoff rates (55–250 mm year^?1). The SSCs exhibited a wide range and can exceed 100 g l^?1 for the central subcatchments, where most of the badlands are located. For the reconstruction of the sedigraphs, the QRF method proved suitable with Nash–Sutcliffe indices of 0.50 to 0.84. The specific sediment yield ranges from relatively low (32 t km^?2 year^?1) in the highly vegetated north to high values (3,651 t km^?2 year^?1) in areas with many badland formations.

Conclusions

The Isábena catchment shows high erosion dynamics with great variability in space and time, with stark contrasts even between adjacent subcatchments. The natural conditions make water and sediment monitoring and instrumentation very challenging; the measurement of discharge is particularly prone to considerable uncertainties. The QRF method employed for reconstructing sedigraphs and monthly yields proved well suited for the task.     

Factors affecting soil loss at plot scale and sediment yield at catchment scale in a tropical volcanic agroforestry landscape

Tropical deforestation and land use change is often perceived as the major cause of soil loss by water erosion and of sediment load in rivers that has a negative impact on the functioning of hydropower storage reservoirs. The Sumberjaya area in Sumatra, Indonesia is representative for conflicts and evictions arising from this perception. The purpose of this study as part of a Negotiation Support System approach was to assess sediment yield both at plot and catchment scale and to relate it to a variety of possible clarifying factors i.e. land use, geology, soil and topography. Sediment yield at catchment scale per unit area, was found to be 3–10 times higher than soil loss measured in erosion plots. A stepwise regression showed that the dominant factors explaining sediment yield differences at catchment scale in this volcanic landscape were a particular lithology (Old Andesites) and slope angle followed by the silt fraction of the top soil. In lithologically sensitive areas soil loss at the plot scale under monoculture coffee gardens decreases over time from on average 7–11 Mg ha^? 1 yr^? 1 to 4–6 Mg ha^? 1 yr^? 1, mainly because of the development of surface litter layers as filters and top soil compaction in the areas without litter, but remains higher than under shade coffee systems or forest. The runoff coefficient under monoculture coffee remains on average significantly higher (10–15%) than under forest (4%) or under shade coffee systems (4–7%). In lithologically stable areas soil loss remained below 1.8 Mg ha^? 1 yr^? 1 and the runoff coefficient below 2.5% under all land use types, even bare soil plots or monoculture coffee gardens. Less than 20% of the catchment area produces almost 60% of the sediment yield. The reduction of negative off-site effects on e.g. the life time of a storage reservoir would benefit greatly from an improved assessment of the lithologies in volcanic landscapes and the consideration of potential sediment source and sink areas. In lithologically sensitive areas, a shift from sun to shade coffee systems may result in reducing surface runoff and soil loss, although water erosion at the plot scale is not the main contributor to sediment yield at the catchment scale. The quantification of land use effects on dominant erosive processes such as river bank and river bed erosion, landslides and the concentrated flow erosion on footpaths and roads can contribute to more targeted efforts and relevant incentives to reduce (or live with) sediment load of the rivers.     

Quantifying farmland shelterbelt impacts on catchment soil erosion and sediment yield for the black soil region,northeastern China

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.     

Sediment and Phosphorus Export from a Lowland Catchment: Quantification of Sources

Storm event and annual export of suspended sediment (SS) and particulate phosphorus (PP) was measured during three hydrological years (June 1993 to May 1996) in Gelbæk stream, a Danish lowland stream draining a 11.6 km² arable catchment area. The contribution of subsurface drainage water, surface runoff and stream bank and bed erosion to catchment SS and PP losses was estimated using three different strategies: 1) Simultaneous and comparative monitoring of subsurface water. 2) A mass-balance and budget approach dividing the Gelbæk catchment into two subcatchments. 3) Application of the fingerprinting technique to single storm events. Subsurface drainage water proved to be a significant SS and PP source. Subsurface drainage water from half of the catchment area accounted for 9.8–15% of the total annual SS loss from the Gelbæ catchment and 9.6–18.2%, of the annual PP loss. The mass-balance and budget approach showed stream bank and bed erosion to be the major source of SS and PP in this channelized and highly managed lowland stream. These findings were consistent with the fact that the annual loss of SS and PP from an upper culverted stream sub-catchment was significantly lower than that estimated from a mass-balance for a lower sub-catchment with an open stream channel. Comparison of the tracer content (e.g.¹¹⁷Cs) of SS collected during four storm events with that of topsoil and subsoil using a simple mixing model revealed subsoil to be a major source of SS.     

Sediment and Phosphorus Loads from a Stream Draining Agricultural and Forest Lands in Northwest Spain

ABSTRACT

Transport of suspended sediment (SS) and phosphorus (P) via surface runoff from soils to surface waters is a major problem of water quality degradation in many European rivers and in other parts of the world. This problem is especially serious during wet periods, which can produce twice the P loads of dry periods. In this study, the SS load and particulate phosphorus (PP) exported from a small catchment located in NW Spain (in which cultivated soils had different degrees of vegetation cover) were analyzed during two rainy periods of February 2006 and February 2007. The SS and PP loads were calculated from the data of discharge, and SS and PP concentrations were measured in water samples collected at the catchment outlet. SS and PP loads were higher in 2006 than in 2007, while there was higher rainfall and stream flow in 2007. Differences in the degree of vegetation cover in the cultivated fields with good connectivity with the stream, which was the main source area of sediment in this catchment, explain the differences in SS and PP loads between the two periods. Soil losses caused during both rainy periods were low (0.02 Mg ha^?1); however, they may be detrimental to quality of the stream water due to the P linked to soil particles. PP concentrations were above the critical values of P for eutrophication during the study periods, highlighting the need to take conservation measures to reduce soil erosion and sediment delivery to watercourse.     

Sediment and phosphorus transfer in overland flow from a maize field receiving manure

Abstract. The transfer of suspended sediment (SS) and phosphorus (P) in overland flow from 30 m² field plots receiving either nil, surface‐applied or incorporated manure (slurry) were monitored to determine the vulnerability of land cropped to continuous forage maize to diffuse pollutant transfer in winter runoff. In the absence of slurry, P export was dominated by particulate forms, with up to 1 t SS ha^?1 and 0.75 kg total P ha^?1 collected from an individual storm event. Background concentrations of P in soluble (<0.45 μm) form were large (c. 0.5 mg L^?1) by eutrophication standards due to the previous build‐up of soil P, and largely independent of SS concentrations. Largest P exports (representing up to 23% of the slurry P applied) were measured when dairy slurry (3–13% dry solids) was surface‐applied. The P mobilized from the slurry accounted for up to 60% of total plot P export, with the majority occurring in a soluble bioavailable form during the first storm event. Initial P concentrations in runoff were in proportion to the amount of slurry P applied and significantly lower where rainfall was delayed after application. In one year, splitting the slurry application (3 × 10 kg ha^?1) reduced total P export by 25% compared to a single surface application (30 kg P ha^?1). In two years, incorporation of slurry, either by ploughing, or by tine cultivation, reduced the amount of overland flow by 50%, and the amount of P export by up to 60%, compared to the surface‐applied slurry treatments. Timeliness of slurry spreading to avoid periods of wet weather and simple cultivation of maize fields after harvest are practical and effective options to minimize SS and P transfer in land runoff from maize fields. The results also draw attention to the need to grow maize, and apply slurry to fields with a low P loss risk.     

Siltation and radiocesium pollution of small lakes in different catchment types far from the Fukushima Daiichi nuclear power plant accident site

The Fukushima Daiichi nuclear power plant accident caused radioactive pollution in northeastern Honshu Island, Japan. This study examined the influence of snowmelt and rainfall on soil erosion processes and siltation of small lakes in Miyagi Prefecture (150 km northwest of the power plant). Two sets of slopes and lakes, respectively in pasture and forest catchments, were examined. Snowpack thickness, soil infiltration, surface runoff volume, soil and sediment physicochemical properties, Cs concentration of precipitation, meltwater, and rainwater, and lake siltation rates were determined. The total radioactive Cs content in precipitation was 0.7–7.4 BqˑL⁻¹ and was below the Japanese standard (10 BqˑL⁻¹). Total radioactive Cs was at the allowable level in water flowing down the pasture catchment slope (0.1–9.2 BqˑL⁻¹) during snowmelt and rainfall, as well as in pasture (0.9–8.8 BqˑL⁻¹) and forest (0.7–5.2 BqˑL⁻¹) catchment lake water. There was no soil erosion (surface runoff) in the forest catchment. Soil losses in the pasture catchment were 23 due to rainfall and 9 kg ha⁻¹ yr⁻¹ following spring snowmelt. After snowmelt, a 0.5 and 0.2 mm thick layer of silt was deposited in pasture and forest catchment lakes, respectively, and 1.4 and 0.6 mm were deposited during the rainfall period. Average siltation rates were 1.9 and 0.8 mmˑyr⁻¹ for pasture and forest catchment lakes, respectively. The upper layer of lake bottom sediments is represented mainly by silt fractions (2–50 μm), with high organic matter (4.0–5.7%) and radiocesium (1100–1600 kgˑha⁻¹) contents.     

Soil infiltration, runoff and sediment yield from a shallow soil with varied stone cover and intensity of rain

Stones on the surface of the soil enhance infiltration and protect the soil against erosion. They are often removed in modern mechanized agriculture, with unfortunate side‐effects. We evaluated experimentally the influence of surface stones on infiltration, runoff and erosion under field conditions using a portable rainfall simulator on bare natural soil in semi‐arid tropical India, because modernization and mechanization often lead to removal of these stones in this region. Four fields with varied cover of stones from 3 to 65% were exposed to three rainfall intensities (48.5, 89.2 and 136.8 mm hour^?1). Surface stones retarded surface runoff, increased final infiltration rates, and diminished sediment concentration and soil loss. The final infiltration ranged from 26 to 83% of rainfall when the rainfall intensity was 136.8 mm hour^?1. The reduction in runoff and soil erosion and increase in infiltration were more pronounced where stones rested on the soil surface than where they were buried in the surface layer. The sediment yield increased from 2 g l^?1 for 64.7% stone cover with rainfall of 48.5 mm hour^?1 to 70 g l^?1 for 3.5% stone cover with rain falling at 136.8 mm hour^?1. The soil loss rate was less than 2 t ha^?1 hour^?1 for the field with stone cover of 64.7% even when the rainfall intensity was increased to 136.8 mm hour^?1. The effects of stones on soil loss under the varied rainfall intensities were expressed mathematically. The particles in the sediment that ran off were mostly of silt size.     

Oscillation of Three Phosphorus Forms and Suspended Solids Content from 1999 to 2007 in a Spanish Agroforestry Catchment under Atlantic Climate

Phosphorus (P) transfers may accelerate water eutrophication to waters. Increasing awareness of the role of diffuse P sources motivates land managers in different regions of Europe to undertake conservation programs that place emphasis not only on soil conservation but also on water quality and eutrophication risk. Fertilizer applications and wastes are the main sources of dissolved P in Galicia and in the Atlantic regions of Spain. The aim of this study was to assess the temporal changes in concentration of total P (TP), sedimentary P (SP), and total dissolved P (TDP) and suspended solids at the outlet of an agroforestry catchment located in northwestern Spain. The study datasets range from January 1999 to December 2007, with 992 water samples collected. The water-collection strategy was a stratified point sampling involving more frequent collections when flow was high. Phosphorus contents were assessed by inductively coupled plasma (ICP)–mass spectroscopy (MS), and suspended solids were measured by filtration. The content ranges of the different studied P forms and suspended solids were as follows: TDP between 1 and 672 mg L^?1, SP between 1 and 1064 mg L^?1, TP between 1 and 1111 mg L^?1, and suspended solids between 1 and 1044 mg L^?1. A few events of intense precipitation with peaks of TP greater than 200 mg L^?1 and in some cases even more than 1000 mg L^?1 were responsible for most of the P losses in the catchment studied. TP and SP, TP and suspended solids, and SP and suspended solids showed highly significant correlations during the entire study period, evidencing the erosive origin of P in this catchment.     

Modelling geochemistry and Lake pH since glaciation at Lake Gårdsjön

The soil acidification model SAFE was modified to calculate historical changes in geochemistry and runoff since the last glaciation ended at the Lake Gårdsjön F1 catchment 12 000 B.P. Changes in runoff pH and ANC, soil weathering rate, soil mineralogy, soil texture and base saturation was also calculated. The changes in mineralogy compared favorable to data. Modeled historic weathering rates were slightly higher than data suggest, while present weathering rate was somewhat to low, 37 mmol_c m^?2 yr^?1. The weathering rate was very high immediately after the last glaciation, and decreased as the smaller particles were consumed by weathering. The calculated runoff pH follows the pattern of the paleo-inferred pH. SAFE suggests a natural depletion of base cations in the C-layer.     

Phosphorus losses from arable land in England

Abstract. Concentrations and annual loadings of molyhdate reactive P (MRP) and total (including particulate) P (TP) are reported from field drainage, catchment and erosion experiments in England. Annual losses through field drains and in catchment runoff were 0.037-0.74 kg MRP/ha and 0.37-2.64 kg TP/ha, but those in surface runoff from experimental plots measuring erosion were generally much greater (often > 3 kg MRP/ha and up to 32 kg TP/ha in a wet year). Amounts of TP in drainflow and catchment runoff depended upon factors influencing soil dispersibility, such as particle size distribution and calcium carbonate content. The results to date suggest that P losses in surface runoff and erosion from arable fields to water are best limited by: (a) maximizing crop cover, using minimal cultivation practices and where possible planting crop rows across rather than up and down the slope, (b) avoiding cultivation practices that result in dispersion of soil particles, and (c) avoiding application of P fertilizer to wet soils when rainfall is likely soon after application. Consideration should he given to maintaining field drains below peak efficiency to reduce subsurface P losses.     

Effect of surface-casting earthworms on the transport of phosphorus and nitrogen in surface runoff from pasture

Treatment of a soil under permanent pasture with carbaryl (a broad spectrum carbamate biocide) resulted in a 2-fold increase in the volume of surface runoff. This was attributed to a 3-fold reduction in infiltration rate as a result of litter accumulation at the soil surface in the absence of surface-casting earthworm activity. The amounts of dissolved inorganic P (DIP), NH⁺₄-N, and NO^?₃-N in surface runoff from pasture treated with carbaryl (1.18, 9.53 and 4.25 kg ha^?1 yr^?1, respectively) were appreciably greater than those from untreated pasture (0.31, 1.63 and 0.52 kg ha^?1 yr^?1). This was attributed to the large amounts of DIP, NH⁺₄-N, and NO^?1₃-N released from decomposing litter. Following incubation at 4°C for 18 days the release of DIP, NH⁺₄-N and NO^?₃-N from litter was 160, 1600 and 950 μg g^?1, respectively. Losses of particulate P and sediment in surface runoff were lower in the absence (0.31 and 290 kg ha^?1 yr^?1, respectively) than in the presence (0.56 and 1120 kg ha^? yr^?1) of surface casts, pointing to the importance of surface casts as a source of sediment. Surface casts accounted for 45 and 75%, respectively, of the annual loading of particulate P and sediment in surface runoff. Nevertheless, the total loss in surface runoff of P and N forms was increased substantially when the production of earthworm casts was eliminated     

An evaluation of the pesera soil erosion model and its application to a case study in Zakynthos, Greece

Abstract. The Pan‐European Soil Erosion Risk Assessment (pesera ) model was evaluated using existing soil erosion data collected under various types of climate, vegetation, landscape and soil conditions. The data used represent a variety of typical Mediterranean land uses such as winter wheat, vines, olives and bare, stony land prevailing in hilly areas. Using this data, the model was calibrated for sediment transport by overland flow and results compared to measured soil erosion values from runoff plots and a watershed on a monthly basis. The performance of the model was assessed statistically, showing that it can be satisfactorily used for predicting soil erosion rates under the conditions included in the study. The overall model estimate including all the available experimental data was 0.69 t ha^?1 yr^?1 with a maximum error of 1.49 t ha^?1 yr^?1. After validation, the model was applied to a small watershed (60 ha) of great ecological importance for the sea turtle Caretta caretta. For this purpose, soil and vegetation maps were compiled from all the necessary data for applying the model. The model was run for three years using daily data from an existing nearby meteorological station. The predicted and measured soil erosion rates for a 7‐month period were 0.31 t and 0.18 t, respectively. Application of the model to each mapping unit showed the over‐riding importance of land use for sediment generation under the given climatic conditions. Bare land, occupying 5.5% of the watershed area, generated up to 69% of the total sediments estimated for the watershed. It is concluded that the pesera model can be used as a regional diagnostic tool under a range of soil, topographic and climatic conditions for identifying the best land use type and vegetation cover to protect hilly areas from soil erosion. The calculated overall root mean square error for the model is 0.06 t ha^?1 yr^?1, compared to a soil erosion rate of 0.04 t ha^?1 yr^?1, which can be tolerated for protecting the area for the sea turtle.     

An Empirical Approach for Assessing the Relationship Between Nitrogen Deposition and Nitrate Leaching from Upland Catchments in the United Kingdom Using Runoff Chemistry

Samples were collected from 13 upland sites (main inflow and loch outflow) in the UK along an N deposition gradient of 12-50 kg ha^-1 yr^-1 to determine the relationship between N deposition and NO₃ ^- concentrations in surface waters. There was no direct correlation between NO₃ ^- leaching and soluble inorganic N deposition at these sites, but a significant relationship with NO₃ ^- was found using a deposition function incorporating dissolved organic carbon (DOC) flux from each catchment. A similar but less significant relationship was found between NO₃ ^- concentration and DOC:DON ratio in runoff water. Catchments showed evidence of N saturation, i.e., when mean NO₃ ^- concentration exceeded 5 µeq L^-1, when the mean DOC:DON ratio fell below an approximate value of 25. Five other large loch sites (LLS) with multiple subcatchments were used to test these relationships and for four of these mostly heathland sites the predicted NO₃ ^- concentrations closely matched measured values. At the fifth site, where most subcatchments were forested, the deposition function and DOC:DON ratios gave conflicting predictions and both methods generally underestimated measured NO₃ ^- concentrations. If the capacity of these catchments to retain deposited N is determined by C supply then many upland catchments in the UK may experience increasing NO₃ ^- concentrations in runoff in the future at current or increased levels of N deposition.     

Some effects of tramlines on surface runoff, sediment and phosphorus mobilization on an erosion-prone soil

Although introduced into UK farming to help ensure more even application of agrochemicals, tramlines (marked wheelways through crops) are a potential cause of surface runoff and transfer of diffuse pollutants, including sediment and phosphorus (P), into watercourses. To help quantify these potential effects, the impact of tramlines on sediment and P movement in surface runoff was assessed on an erosion‐prone sloping (5°) fine sandy soil over two successive winters. Three replicate and hydrologically isolated runoff plots measuring 15 m long and 2 m wide, and either with, or without, a tramline, were established on field demonstration areas which had received different soil (traditionally ploughed vs. reduced cultivated) and crop (early vs. late drilling) management practices. Reduced cultivation (minimum tillage) consisted of heavy discing (5–8 cm depth) instead of ploughing (20–25 cm depth). Over monitoring periods ranging up to 5 months, plots with tramlines running up and down the slope generated, on average, 46% more runoff (+1–2 mm) compared with plots without tramlines on ploughed soils. This extra runoff resulted in up to fivefold greater sediment loss (+0.4 t ha^?1) and up to fourfold greater total P loss (+0.3 kg ha^?1) from the plots. However, the presence of tramlines had no significant impact on runoff, or sediment and P transfers, where the soil received reduced cultivation. Plots with tramlines that were partially crop covered, or which ran across the slope rather than up and down the slope, produced the same amount of runoff, sediment and P transfer as plots without tramlines. Greatest entrainment of sediment and P in runoff occurred where tramlines coarsely indented the soil, or caused erosion rills to form. Establishing tramlines in dry soils reduced the degree of soil indentation and the risk of channelled runoff causing sediment and P entrainment. The data suggest that tramlines can be managed more sensitively on erosion vulnerable soils to help minimize the risk of sediment and P pollution of our surface waters, and various options are discussed.     

Impact of no-tillage agricultural systems on sediment yield in two large catchments in Southern Brazil

Purpose

The impact of agriculture on water resources has long been a problem associated with the formation of runoff, the siltation of lakes and reservoirs, and overall depletion of water quality. In Brazil, these problems are mainly related to soil degradation by water erosion. However, studies of catchment-scale erosion are still rare particularly in grain-producing regions which have adopted conservative tillage systems for soil protection. In order to contribute to a better understanding of the impact of conservation agriculture on water resources, this study determined the runoff coefficient and sediment yield for two agricultural catchments.

Materials and methods

Hydrological and sedimentological monitoring was conducted in two catchments: the Conceicao catchment is characterized by grain production in weathered soils and a gently sloping landscape, while the Guapore catchment is characterized by heterogeneous soils and topography. Both catchments have problems associated with water erosion.

Results and discussion

The magnitudes of annual runoff coefficients and sediment yield were high, even if compared to similar agricultural regions, including a catchment with widespread adoption of no-tillage. The sediment yield was 140 t km^?2 year^?1, and the runoff coefficient was 14 % for the Conceicao catchment, while the sediment yield was 270 t km^?2 year^?1, and the runoff coefficient was 31 % for the Guapore catchment. The results indicate that problems such as gullies, soil compaction, runoff, floods, siltation, and water quality depletion associated with the misuse of agricultural areas in terms of soil conservation and water use are still evident and important even in regions with widespread adoption of no-tillage systems.

Conclusions

The magnitudes of both runoff and sediment yield clearly indicate the need to adopt complementary practices of soil conservation measures, such as mechanical runoff control.     

Organic amendments as a source of phosphorus: agronomic and environmental impact of different animal manures applied to an acid soil

Phosphorus (P) is a non-renewable resource highlighting the significance of developing and using alternative P sources for a sustainable agriculture. The work aims to compare the effects of different organic amendments (OA) and a mineral P fertiliser as reference on P use efficiency by the crop, and on P losses to runoff waters and eroded sediments. A two-year field trial was conducted in a Dystric Regosol with Lolium sp. Treatments were: cattle manure compost (CM), solid fraction of swine (SS) and duck (DS) slurries and triple superphosphate (TSP), each applied at 50 kg P ha^?1 year^?1. Olsen P (mg P kg^?1) increased from ≈ 19 at the beginning to ≈ 30 (TSP, CM), 45 (SS) and 62 (DS) after the experiment. Most of applied P remained in soil, between 92% (SS) and 96% (TSP), plant uptake ranged from 5% (CM) to 3.5% (TSP) and total P loss in runoff and sediments ranged between 0.2% (CM) and 4% (SS). OA increased P-use efficiency by the ryegrass crop compared with mineral P fertilizer. Composted cattle manure showed the best agronomic and environmental behaviour, simultaneously increasing P-use efficiency and decreasing P losses by runoff and erosion.     

Crop production impacts on soil phosphorus removal and soil test levels

An 8-year field study documented the impact of tillage, crop rotations, and crop residue management on agronomic and soil parameters at Brookings, South Dakota. The greatest annual proportion of above-ground biomass phosphorus (P) removed was from the grain (78–87% of total) although crop residue removed some P as well. Greater above-ground total biomass P (grain P + crop residue P) was removed from corn than from soybean and spring wheat crops mainly due to the greater corn grain biomass harvested. Cumulative above-ground biomass P removal was greatest for the corn-soybean rotation (214 kg P ha^?1), while it was lowest for the soybean-wheat rotation (157 kg P ha^?1). Tillage treatments within crop rotation or residue management treatments did not influence annual or cumulative P removal rates. Olsen extractable soil orthophosphate-P levels declined consistently through time from a mean of 40 µg g^?1 (2004) to 26 µg g^?1 (2011). Biomass P removal was calculated to be 15.7 ha^?1 yr^?1 to decrease Olsen extractable soil orthophosphate-P levels by 1 µg g^?1 yr^?1 over 8 years of the study.