Relationships between Phosphorus and Suspended Sediment Concentrations in a Stream Draining a Rural Area in NW Spain

This study assesses the possible use of suspended sediment as an indirect measurement of phosphorus (P) concentrations in a rural headwater catchment located in NW Spain. Particulate P accounted for about 70 percent of the P export, indicating that P transport is linked to sediment in this catchment. The relationship between P and suspended sediment concentrations showed that particulate P was strongly dependent on suspended sediment, although the relationship is not consistent throughout seasons. The particulate P–suspended sediment relationship behaved differently at low flow and runoff events; the relationship was only significant during runoff events. This is because low flow is dominated by dissolved P and by pathways that do not mobilize or transport sediment. The particulate P–suspended sediment ratio was lower during runoff events than during low flow, which is consistent with enrichment ratio effects.     

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.     

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.     

Amounts and relative significance of runoff types in the transport of nitrogen into a stream draining an agricultural watershed

The concentration and amounts of NO₃-N and TN transported in surface, accelerated subsurface, and subsurface runoff and stream flow draining a 20 ha pasture watershed were measured over a period of 3 yr. A slight decrease and increase of NO₃-N and particulate N concentrations, respectively, were obtained with increased flow of the runoff types and stream, due to dilution and increased sediment transport, respectively. The concentration of NO₃-N in surface, accelerated subsurface and subsurface runoff and stream flow averaged for the 3 yr was 0.3, 6.6, 4.8, and 4.6 mg 1^?1, respectively, amounting to 0.5, 9.4, 11.6, and 16.8 kg ha^?1 yr^?1, respectively, transported annually. Although NO₃-N accounted for only a minor proportion of the TN transported in surface runoff (10%) it was the main form of N (75%) transported in the other runoff types and in streamflow. Subsurface runoff contributed the major proportion of stream discharge (63%), and NO₃-N (69%), particulate N (44%) and TN (65%) loading of the stream. The results are discussed in terms of non-point pollution of surface waters by NO₃-N.     

Effectiveness of Grass Filters in Reducing Phosphorus and Sediment Runoff

Surface water contamination can often be reduced by passing runoff water through perennial grass filters. Research was conducted in 2006 to 2008 to evaluate the size of cool season grass filters consisting primarily of tall fescue (Festuca arundinacea Schreb) with some orchard grass (Dactylis glomerata L.) relative to drainage area size in reducing runoff sediment and phosphorus (P). The soil was Pohocco silt loam Typic Eutrochrepts with a median slope of 5.5?%. The grass filters occupying 1.1 and 4.3?% of the plot area were compared with no filter with four replications. The filters were planted in the V-shaped plot outlets which were 3.7?×?11.0?m in size. The filter effect on sediment and P concentration was determined from four natural runoff events when nearly all plots had runoff. Filter effect on runoff volume and contaminant load was determined using total runoff and composites of samples collected from 12 runoff events. Sediment concentration was reduced by 25?% with filters compared with no filter (from 1.10 to 1.47?g?L^?1), but P concentration was not affected. The 1.1 and 4.3?% filters, respectively, compared with having no grass filter, reduced: runoff volume by 54 and 79?%; sediment load by 67 and 84?% (357 to 58?kg?ha^?1); total P load by 68 and 76?% (0.58 to 0.14?kg?ha^?1); particulate P (PP) load by 66 and 82?% (0.39 to 0.07?kg?ha^?1); and dissolved reactive P (DRP) load by 73 and 66?% (0.2 to 0.07?kg?ha^?1), respectfully. A snowmelt runoff event had 56?% greater DRP concentration compared with rainfall-induced runoff events. Grass filters reduced sediment and P load largely by reducing runoff volume rather than reducing concentration. Well-designed and well-placed grass filters that occupy 1.0 to 1.5?% of the drainage area and intercept a uniform flow of runoff from a drainage area can reduce sediment and nutrient loss in runoff by greater than 50?%.     

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.     

Water Column and Sediment Phosphorus in a Calcareous Lowland River and Their Differential Response to Point Source Control Measures

Phosphorus control measures at two major (>10000 people equivalent, p.e.) sewage treatment works (STWs) were installed in the lowland calcareous basin of the River Wensum (England). In-stream phosphorus concentrations were monitored seasonally from subcatchments with different levels of phosphorus impacts, as well as before and after phosphorus control, above and below the two major STWs. Point source effluents raised in-stream soluble reactive phosphorus (SRP) concentrations from 9–15 μg L^?1 (agricultural sub-catchments) to 580–3270 μg L^?1. This was accompanied by an increase of the SRP relative to total phosphorus from 27% to 80–90%. The phosphorus content of the suspended sediment was high (0.2 to 7.7%). Molybdate unreactive phosphorus (1–29 μg L^?1) was surprisingly not affected by point source effluents. The river bed sediment bioavailable phosphorus concentrations were higher (4–18 μg g^?1 wet weight) downstream from the main effluents, compared to upstream (2–6 μg g^?1 wet weight). Phosphorus control at the STWs in 1999 has allowed to reduce in-stream soluble reactive concentrations to 140–280 μg L^?1 but has had no significant impact on bioavailable phosphorus in the sediment by 2001, suggesting that either net sediment desorption did not occur or that it is a much slower, longer term response. The relative contribution of the diffuse sources increased from 10% to 27% of the total phosphorus loads at Fakenham. The management of these rivers is therefore problematic.     

Sediment and Phosphorous Fluxes Analysis in Aquia Creek,a Sub-watershed of the Chesapeake Bay Basin,VA, USA

Decline in global surface water quality around the world is closely linked to excess sediment and nutrient inputs. This study examined sediment and phosphorus fluxes in Aquia Creek, a fourth-order sub-watershed of the Chesapeake Bay located in Stafford, Virginia. The Revised Universal Soil Loss Equation (RUSLE), sediment delivery ratio (SDR), field sediment traps, bank erosion pins, and LIDAR data, combined with historical aerial images, were used in quantifying rill and inter-rill erosion from the basin, as well as internally generated sediments. Stream water and stream bank soils were analyzed for phosphorus. RUSLE/SDR modeling estimates a basin total sediment flux of 25,247 tons year^?1. The greatest calculated soil losses were in deciduous forests and cropland areas, whereas medium and high-intensity developed areas had the least soil loss. Cut-bank erosion ranged from 0.2 to 27.4 cm year^?1, and annual bank sediment fluxes were estimated at 1444 Mg, with a corresponding annual mass of phosphorous of 13,760 kg year^?1. The highest bank loss estimates were incurred along reaches draining urban areas. Stream water total phosphorous levels ranged from 0.054 μg g^?1 during low flows to 134.94 μg g^?1 during high discharge periods in autumn and spring. These results show that stormwater management practices in urban areas are limiting runoff water and soil contact, reducing surficial soil loss. However, the runoff acceleration due to expansion of impervious surfaces is progressively increasing the significance of intrinsic sediment and phosphorous sources by exacerbating stream bank erosion and resuspension of internally stored sediments.     

Water flow paths in soil control element exports in an Andean tropical montane forest

We tested the hypothesis that concentrations of chemical constituents in stream water can be explained by the depth of water flow through soil. Therefore, we measured the concentrations of total organic carbon (TOC), NO₃‐N, NH₄‐N, dissolved organic nitrogen (DON), P, S, K, Ca, Mg, Na, Al and Mn in rainfall, throughfall, stemflow, litter leachate, mineral soil solution and stream water of three 8–13 ha catchments on steep slopes (1900–2200 m above sea level) of the south Ecuadorian Andes, from April 1998 to April 2003. Peak C (14–22 mg litre^?1), N (0.6–0.9 mg litre^?1), K (0.5–0.7 mg litre^?1), Ca (0.6–1.0 mg litre^?1), Mg (0.3–0.5 mg litre^?1), Al (110–390 μg litre^?1) and Mn (3.9–8.4 μg litre^?1) concentrations in stream water were associated with lateral flow (fast near‐surface flow in saturated topsoil) while the greatest P (0.1–0.3 mg litre^?1), S (0.3–0.7 mg litre^?1) and Na (3.0–6.0 mg litre^?1) concentrations occurred during low baseflow conditions. All elements had greater concentrations in the organic layer than in the mineral soil, but only C, N, K, Ca, Mg, Al and Mn were flushed out during lateral‐flow conditions. Phosphorus, S and Na, in contrast, were mainly released by weathering and (re‐)oxidation of sulphides in the subsoil. Baseflow accounted for 32% to 61% of P export, while > 50% of S was exported during intermediate flow conditions (i.e. lateral flow at the depth of several tens of cm in the mineral soil). Near‐surface water flow through C‐ and nutrient‐rich topsoil during rainstorms was the major export pathway for C, N, Al and Mn (contributing > 50% to the total export of these elements). Near‐surface flow also accounted for one‐third of total base metal export. Our results demonstrate that near‐surface flow related to storm events markedly affects the cycling of many nutrients in steep tropical montane forests.     

Frequency–magnitude relationships for precipitation,stream flow and sediment load events in a small Mediterranean basin (Vallcebre basin,Eastern Pyrenees)

Precipitation, discharge and suspended sediment concentrations were continuously measured during 10 years (1995–2004), at the Ca l'Isard sub-basin (1.32 km²) of the Vallcebre experimental catchments. Daily precipitation record is 22 years long. When the ranks of the events obtained with the diverse variables considered (precipitation depth, peak discharge, runoff depth, suspended sediment concentration and sediment load) were compared, the results confirmed the complexity of the response of the catchment and demonstrated that precipitation is an irregular criterion for ranking the main sediment transporting events. When the partial duration series corresponding to the 10% major events were analysed, daily precipitation, peak discharge and sediment concentration series showed good fits with log-normal distributions, but event precipitation, runoff and sediment load series needed bi-modal log-normal distributions. This behaviour may be attributed to the fact that event mass magnitudes depend not only on event intensity but also on its duration.     

Dynamic changes of nitrogen and phosphorus losses in ephemeral runoff processes by typical storm events in Sichuan Basin, Southwest China

This study was carried out in the Xujiawan watershed in Sichuan Province, China. The area is characterized by easy weathering of bedrock (sedimentary sandstone and shale) and vulnerability to erosion due to coarse soil texture and weak soil structure. The objective of this study was to understand the dynamics of nitrogen (N) and phosphorus (P) losses during typical storm events. The results showed that runoff generation was sudden and ephemeral, giving rise to flash floods with sharp, narrow hydrographs and short time lags in this type of agricultural ecosystems. The time lag effect of runoff formation depended on soil conditions before storm events. Suspended solids (SS) concentration peaks occurred at the beginning of the storm flow and decreased as rainfall progressed. Meanwhile, SS losses increased at the beginning of runoff flow, then decreased due to flow volume change. Concentrations of NO₃⁻-N were four times higher than NH₄⁺-N in runoff. NO₃⁻-N concentrations first decreased as runoff volume increased until reaching relatively low concentrations, then increased again as runoff volume decreased. Both NH₄⁺-N and dissolved phosphorus (DP) in runoff remained at low concentrations with a small magnitude of variation. Suspended particulate nitrogen (SN) was the dominant N form. Losses of NO₃⁻-N were higher than NH₄⁺-N in the dissolved nitrogen (DN). Suspended particulate nitrogen losses were several times higher than DN in the early period of runoff formation, but the ratio of SN/DN decreased gradually as rainfall progressed, and by the end of the storm event the rate was lower than 1, indicating DN took the main form after the early physical flush. In the early period of storm events, suspended particulate phosphorus (SP)/DP was above 70 and decreased as rainfall progressed, but remained higher than 1, which showed that SP was the main form of P loss. The transport of N, and particularly P, was intimately linked to sediment in the runoff, indicating an obvious soil erosion-associated nutrient transport, especially in relation to P loss.     

Relationships among rainfall, runoff, and suspended sediment in a small catchment with badlands

The Araguás Catchment of the Central Spanish Pyrenees has been monitored since 2004 to study weathering, erosion, and the hydrological and sediment response to rainfall events in order to understand the hydromorphological dynamics of a badland area in a relatively humid environment. This small catchment (0.45 km²) shows highly active processes of physical and chemical weathering related to seasonal variations in temperature and moisture. Erosion and sediment transport are widely studied in badlands within Mediterranean environments because they represent the dominant sediment source. To obtain information about suspended sediment and discharge, a gauging station was installed within the Araguás Catchment during the summer of 2005. The aim of this work is to determine the relationships among rainfall, runoff, and suspended sediment in this badland area. Towards this goal, we analyze the relationships between suspended sediment concentration and discharge during rainfall events.From a hydrological viewpoint, the Araguás Catchment reacts to all rainfall events with torrential flow being the most characteristic hydrological response. The results obtained between October 2005 and April 2007 reveal extremely high concentrations of suspended sediment, with values frequently exceeding 100 g l^{<modINS>−<!--[/INS]"> 1} and reaching a maximum of 1200 g l^{<modINS>−<!--[/INS]"> 1}. Three different types of hysteretic loops were observed: clockwise (22 events, 28%), counter-clockwise (27 events, 34%), and figure-eight (12 events, 15%). Moreover, 23% of events were classified as complex hysteretic loops and removed from the analysis due to their complexity. Clockwise hysteretic floods are characterized by their long duration and the highest hydrological and sedimentological responses; counter-clockwise hysteretic floods are characterized by their short duration and moderate hydrological and sediment responses; finally, figure-eight hysteretic floods are related to multiple peaks in suspended sediment, coinciding with oscillations in discharge associated with the highest rainfall intensities within each event and moderate hydrological and sediment responses.     

Importance of bank erosion for sediment input, storage and export at the catchment scale

Purpose

The importance of bank erosion was quantified during three periods (October 2006–April 2007, May 2007–April 2008 and May 2008–April 2009) in the 486 km² catchment area of River Odense, Denmark. A catchment sediment budget was established including other sediment sources such as tile drains and surface runoff, in-channel and overbank sinks and storage and the resulting bed load and suspended sediment load exported from the catchment.

Material and methods

Bank erosion and sedimentation were measured using ca. 3,000 erosion pins established in 180 pin plots, each consisting of three vertical lines of pins. Thirty-six representative reaches, each with a length of 100 m, were selected by a stratified random procedure in GIS. Bed load and suspended sediment export from the catchment were measured using a bed load sampler and from continuous measurements of turbidity at the outlet gauging station.

Results and discussion

The gross sediment input from bank erosion during the three study periods amounted to 21,100–25,200 t in the River Odense catchment, which is considerably higher than the estimated input of sediment from tile drains and surface runoff, which amounted to 220–500 t and 0–100 t, respectively. The measured bed load (20–490 t) was five to 60 times lower than the suspended sediment export from the catchment (1,240–2,620 t) during the three study periods, with the largest difference occurring in the driest year. Sediment sinks and storage were of high importance for the catchment sediment budget as the measured in-channel storage of sediment on stream banks was as high as 16,200–20,100 t, and the overbank sediment sink was estimated at 360–3,100 t.

Conclusions

Bank erosion was the dominant sediment source (90–94 %) in the River Odense catchment during the three study years. In-channel and overbank sediment sinks and storage dominated the sediment budget as 79–94 % of the sediment input from all sources was not exported from the catchment during the three study years. Such a large attenuation of sediment in river channels and on floodplains is extremely important for fluvial habitats and ecology. Moreover, it has strong implications for attempts to document changes in sediment export following implementation of mitigation measures.     

Factors Controlling Mercury Transport in an Upland Forested Catchment

Total mercury (Hg) deposition and input/output relationships were investigated in an 11-ha deciduous forested catchment in northern Vermont as part of ongoing evaluations of Hg cycling and transport in the Lake Champlain basin. Atmospheric Hg deposition (precipitation + modeled vapor phase downward flux) was 425 mg ha-1 during the one-year period March 1994 through February 1995 and 463 mg ha-1 from March 1995 through February 1996. In the same periods, stream export of total Hg was 32 mg ha-1, respectively. Thus, there was a net retention of Hg by the catchment of 92% the first year and 95% the second year. In the first year, 16.9 mg ha-1 or about half of the annual stream export, occurred on the single day of peak spring snowmelt in April. In contrast, the maximum daily export in the second year, when peak stream flow was somewhat lower, was 3.5 mg ha-1 during a January thaw. The fate of the Hg retained by this forested catchment is not known. Dissolved (< 0.22 µm) Hg concentrations in stream water ranged from 0.5-2.6 ng L-1, even when total (unfiltered) concentrations were greater than 10 ng L-1 during high flow events. Total Hg concentrations in stream water were correlated with the total organic fraction of suspended sediment, suggesting the importance of organic material in Hg transport within the catchment. High flow events and transport with organic material may be especially important mechanisms for the movement of Hg through forested ecosystems.     

Quantifying suspended sediment sources during runoff events in headwater catchments using spectrocolorimetry

Purpose

Understanding hydro-sedimentary dynamics at the catchment scale requires high temporal resolution data on suspended sediments such as their origin, in addition to the common measurements of sediment concentrations and discharges. Some rapid and low-cost fingerprinting methods based on spectroscopy have recently been developed. We investigated how visible spectra could be used to predict the proportion of various source materials in suspended sediment samples, paying particular attention to the potential alteration of spectrocolorimetric signatures between soils and suspended sediments during transport.

Materials and methods

The 22-km² Galabre catchment, France, is composed of black marls, limestones, molasses, undifferentiated deposits and gypsum. Forty-eight source materials were sampled and 328 suspended sediment samples were collected at the outlet during 23 runoff events. Measurements were taken with a diffuse reflectance spectrophotometer on dried samples. As the erosion processes are particle size selective, five particle size fractions of source material were measured in order to assess the potential alteration of the fingerprint signatures. As the biogeochemical processes occurring in the river could also affect the signatures, source materials were immersed in the river for durations ranging from 1 to 63 days and subsequently measured. Finally, partial least-squares regression models were constructed on 81 artificial laboratory mixtures to predict the proportions of source materials.

Results and discussion

The spectrocolorimetric measurements discriminated the primary source materials but not the Quaternary deposits. As the gypsum was not conservative, only the black marls, molasses and limestones were used in the fingerprinting procedure. The construction of the partial least-squares regression models led to a median absolute error of 1.1%. This error increased to 3.9% when the models were applied to source samples with: (1) different particle sizes; (2) different durations spent in the river; or (3) different origins than those used for their construction. The effect of particle size on the fingerprinting procedure was larger than the effect of biogeochemical reactions or the spatial variability of the spectrocolorimetric signatures. Half of the 23 runoff events analysed exhibited huge variations in the source proportions from one sediment sample to another.

Conclusions

The spectrocolorimetric fingerprinting approach was able to quantify routinely the proportion of primary source materials in all suspended sediment samples collected during runoff events. The high temporal resolution of the predicted proportions revealed that only analysing three or four suspended sediment samples during a runoff event could lead to a misunderstanding of the hydro-sedimentary processes for more than half of the investigated runoff events.     

Long-term erosional responses after fire in the Central Spanish Pyrenees: 1. Water and sediment yield

This paper reports the results of a study on how fire effects water and sediment losses in the Central Spanish Pyrenees where land abandonment results in an increase of the scrubland and fire-affected surfaces. In 1991, two plots (control and burnt) were installed to collect runoff, suspended sediments and solutes. One of the plots was burnt (burnt-1) and the other was covered by shrubs and herbs (control). During 1993, another burnt plot was installed (burnt-2). Data was collected from the three plots until 1999 and is used as the basis for assessing the soil erosion changes after the fire. Runoff, solute and suspended sediment concentration and erosion rates were slightly greater during the first 2 years following fire on burnt-1 compared to the control plot. The average runoff coefficients during the 8-year study period were 4.2% and 7%, the total sediment concentrations were 189 and 181 mg l⁻¹, and the erosion rates were 89 and 143 kg ha⁻¹ year⁻¹ for the control and burnt-1 plots, respectively. In contrast, burnt-2 plot responded differently than burnt-1 plot to fire, although these two plots were designed to be replicated treatments. The average runoff coefficient for burnt-2 plot was two times greater than that for the control plot. Likewise, total sediment concentration was 649 mg l⁻¹ and erosion rate was 566 kg ha⁻¹ year⁻¹, which are 3.6 and 4.5 times greater than the control plot. Differences between burnt and control plots were analysed at hourly, daily, monthly and yearly temporal scale. Both burned plots began to recover after the fire. However, burnt-1 plot had a recovery time of 2 years compared to burnt-2 plot; while 7 years after the fire, the runoff sediment concentration and erosion rates from burnt-2 were higher than those for the control plot. Water and sediment losses from the two burnt plots were markedly different.     

Research on the sedimentation and erosion problem of the Ergene River Basin in Western Turkey and precautions to control it

The objective of this study was to asses the rainfall-runoff-sedimentation relationship from directly measured data since 1972, to find out the effect of the present land use and soil cultivation techniques on the sediment yield, and to offer practical solutions to the problems in the Ergene River Basins located in the European Part of Turkey. The suspended sediment yield was calculated by multiplying the daily average discharged water by the average sediment concentration, while the eroded coarse sediment yield was computed using a regression equation developed by the Japanese Ministry of Construction. The relationship between the runoff and suspended sediment rates was explained exponentially as S = 1.99 Q _A ^1.62 (P > 0.01 and R ² = 0.846) (S is the suspended sediment rate in t d^?1, and Q _A is the average daily runoff rate in m³ s^?1). The suspended sediment rates of the Ergene Basin can then be predicted from the flow rate at any time of the year using this produced regression equation. According to the results, 70% of the basin’s soil (9534 km² and occupying 81.76% of the total area of the region) is under erosion hazard varying in intensity, namely, 25.3% light, 34.6% moderate, 8.6% strong, and 1.5% very strong. 47.09% of the average 604 mm precipitation falls in the critical period of October–January in terms of the sedimentation. The coarse and suspended sediment yield was 74.040 t km^?2 per year, which was well below the average for Turkey. However, it was 2 and 2.5 times larger than the average for Europe and Africa, respectively. Because 76.93% of the eroded land is in the 1rst, 2nd, and 3rd class, the severity of the sedimentation situation is proved. The causes of the high sediment yield were identified, and a series of precautions were suggested to minimize them.     

Source areas of phosphorus transfer in an agricultural catchment,south-eastern Norway

Abstract

The strategy to mitigate phosphorus (P) losses in areas of arable cropping in Norway has focused on measures to reduce erosion. Risk assessment of erosion has formed the basis for implementation of the measures. The soil P content has increased during recent decades, motivating an evaluation of its effect on P transfer in the landscape. The present study describes the spatial variability of runoff P concentrations from an agricultural dominated catchment (4.5 km²), representative for agriculture in south-eastern Norway. The concentrations of suspended sediments (SS), total P (TP) and dissolved reactive P (DRP) in runoff from 22 subcatchments (0.3–263 ha) during one year (monthly and during runoff-events) were evaluated. Contributions from point sources were 38 kg TP yr^?1 compared to a total P loss of 685 kg yr^?1 from the whole catchment. During low flow, mean diffuse TP concentration in runoff from subcatchments varied from 28 to 382 µg l^?1. The mean low flow TP concentration was 39 µg l^?1 from the housing area (only diffuse runoff) and 33 µg l^?1 from the forested area. During high flow the highest diffuse TP concentration was measured in an area with high erosion risk and high soil P status. At the subcatchment level the transfer of SS varied from 25 to 175% of the whole catchment SS transfer. Correspondingly for TP, the transfer varied from 50 to 260% of the whole catchment TP transfer. For each of five agricultural subcatchments the slope of the relationship between TP and SS concentrations reflected the mean soil P status of the subcatchment. Erosion risk estimates were closely related to the SS concentration (R²=0.83). The study illustrates that soil P status in addition to soil erosion is an important factor for P transfer.     

Suspended matter and associated contaminants in Danish streams: a national analysis

Purpose

Suspended matter (SM) in streams is usually considered of minor importance in Danish environmental management. However, SM has some ecological effects as it may (1) clog fish spawning grounds and (2) act as an important agent for transport and exposure of biota to chemical substances, such as phosphorus and toxic inorganic (e.g. heavy metals) and organic (e.g. pesticides) substances.

Materials and methods

A large national data set of >?100,000 water samples analysed for SM and loss on ignition was investigated for spatial concentration patterns, sediment yields and temporal trends. Moreover, the importance of SM as a transport agent for phosphorus and heavy metals in streams was investigated through a correlation analysis.

Results and discussion

The mean suspended matter concentration (SMC) (including organic matter) amounted to 12 mg l^?1, with an organic content of 4.9 mg l^?1 (41%). A clear difference in SMC temporal trends over the sampling period was found between geographical regions. Sediment yields were calculated for all major catchments revealing low sediment yields (1–15 t km^?2 year^?1) compared to neighbouring countries and showed clear geographical patterns. Statistically significant relationships were established between SMCs, suspended sediment concentrations (SSCs) (excluding organic matter) and organic matter concentrations (OMCs) and particulate phosphorus (PP) concentrations, and again spatial patterns appeared. However, it was clearly shown that SMC/SSC/OMC could not be used as a robust, nationwide, indicator for PP concentrations. Analyses of the relationship between SMC and particle-bound heavy metal concentrations generally revealed weak correlations except for Pb and Ni (median R²?>?0.3).

Conclusions

Relatively low SM concentrations and sediment yields were found. SM is, in some geographical regions, an important transport agent for PP. Clear geographical patterns occurred in the relationships between SMC/SSC/OMC and both river water discharge and PP, as well as for sediment yields and for temporal trends in SMC.