Fingerprinting the Origin of Fluvial

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Fingerprinting the Origin of Fluvial Suspended Sediment in Larger River Basins: CombiningAssessment of Spatial Provenance and Source TypeAuthor(s): Adrian L. Collins, Desmond E. Walling, Graham J. L. LeeksSource: Geografiska Annaler. Series A, Physical Geography, Vol. 79, No. 4 (1997), pp. 239-254Published by: Blackwell Publishing on behalf of the Swedish Society for Anthropology andGeographyStable URL: http://www.jstor.org/stable/521219Accessed: 29/05/2010 05:47

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FINGERPRINTING THE ORIGIN OF FLUVIALSUSPENDED SEDIMENT IN LARGER RIVER BASINS:

COMBINING ASSESSMENT OF SPATIALPROVENANCE AND SOURCE TYPE

BYADRIAN L. COLLINS', DESMOND E. WALLING' AND GRAHAM J.L. LEEKS2

'Department f Geography, University of Exeter, Devon UK2Institute f Hydrology, Wallingford, Oxfordshire, UK

Collins, A.L.,Walling,

D.E. and Leeks, G.J.L., 1998:Fingerprint-ing the origin of fluvial uspended ediment n larger iverbasins:

combining ssessment f spatial rovenance nd ource ype. Ge-ogr. Ann., 79 A (4): 239-254.

ABSTRACT: nvestigation f the potential or using sedimentfingerprinting o integrate both spatial provenance nd sourcetype nformation or larger drainage asins appears o be desira-ble. This contribution resents he results f adopting compositefingerprinting rocedure ncorporating tatistically erified mul-ticomponent ignatures nd a multivariate mixing model to pro-vide a preliminary ntegration f spatial provenance nd sourcetype nformation or the upper nd middle eaches f the drainagebasins of the Rivers Exe (601 km2) and Severn 4325 km2), UK.A nested approach s employed, whereby patial provenance s

addressed n terms of the distinct sub-basin ones constitutingeach study area as an entirety, nd source ype s then character-ised within each of these distinct patial ones n terms of surface(woodland, pasture, ultivated) and subsurface channel bank)materials. The results demonstrate hat the fingerprintingapproach ossesses considerable otential or integrating patialprovenance nd ource ype nformation, ndhence or mprovingthe resolution f existing sediment ource nformation or largerdrainage asins.

IntroductionAssembling detailed information oncerning hetime-variant ource of fluvial suspended ediment

continues to prove a difficult task for the fluvialgeomorphologist. Traditional direct monitoringtechniques based on the use of erosion pins andtroughs o estimate oil loss, a combination f pinsand surveying o document hannel bank contribu-tions, or monitoring f sediment o assess the rel-ative significance of sediment contributions romindividual nstrumented ub-basins o downstreamsuspended sediment loads, involve many opera-tional difficulties and sampling constraints, here-by largely restricting uch approaches o small-scale catchments Imeson 1974). In consequence,

the fingerprinting pproach as been increasingly

employed as an alternative ndirect monitoringtechnique (Peart and Walling 1988). Two basicsteps underpin he application f sediment inger-printing: irstly, he selection of diagnostic physicaland chemical properties which are capable of dis-criminating potential sediment sources in an un-equivocal manner; secondly, comparison of themeasurements f the same fingerprint roperty b-tained for suspended sediment samples with thecorresponding alues for source material amplesin order o determine he source of the transportedsediment.

The search for effective diagnostic fingerprintproperties as encompassed a wide range of min-eralogic (Klages and Hsieh 1975), mineral-mag-netic (Slattery et al. 1995), radiometric (Murray etal. 1993), chemical (Peart and Walling 1986), or-ganic (Peart 1995), isotopic (Douglas et al. 1995),and physical, e.g. absolute particle size (Lambert1986), parameters. However, he quest for a singlediagnostic property as now been recognised as be-ing likely to prove elusive, with the result that at-tention has focused upon improving he discrimi-natory capacity of the fingerprinting pproach t-

self. Two important developments have resultedfrom such efforts. The first nvolves he use of com-posite, as opposed to single-component, igna-tures, incorporating range of properties drawnfrom either specific property ubsets, e.g. severalmineral-magnetic roperties Oldfield and Clark1990), or from a range of subsets, e.g. several min-eral-magnetic, adiometric nd organic properties(Walling et al. 1993). Composite fingerprints n-crease the reliability of the results obtained andpermit he discrimination f a greater ange of po-tential sources. Thus, for example, the additional

information rovided by the use of a suite of prop-

Geografiska Annaler * 79 A (1997) ? 4 239



ADRIAN L. COLLINS, DESMOND E. WALLING AND GRAHAM .L. LEEKS

erties can help to resolve a situation where he val-ue for a particular ingerprint roperty measuredfor a suspended ediment ample could be indica-tive of either the dominance of a specific source

characterised y a similar value or, alternatively,contributions rom a number of potential sourcescharacterised y a range of values. The second de-velopment oncerns he replacement f qualitativeinterpretation ith more rigorous quantitative ro-cedures, encompassing both the statistical-verifi-cation of tracer parameters r source groupings,and the use of multivariate ediment-mixing mod-els for source ascription e.g.Yu and Oldfield 1989;Walling et al. 1993; Slattery et al. 1995; Collins etal. 1996, 1997).

Previous sediment fingerprinting tudies have

been predominantly oncerned with distinguishingthe precise types of source operating within smallcatchments, e.g. surface and subsurface sources(Peart ndWalling 1986) or surface oils under dif-ferent and uses and channel banks (Walling andWoodward 1992). This approach has proved essapplicable o larger iverbasins, however, s the ex-treme complexity observed n the spatial distribu-tion of different source types, coupled with thegreater heterogeneity f specific source materialsin such areas, enders he search or source ype n-formation more complex. Consequently, most

source ingerprinting ork n larger basins has fo-cused upon determining the spatial provenance oftransported ediment, haracterised n terms of therelative ontributions f sediment rom either ndi-vidual tributary ub-basins Caitcheon 1993; Col-lins et al. 1996) or distinct geological subareas(Klages and Hsieh 1975; Walling and Woodward1995). Consideration f spatial provenance cir-cumvents the inherent complexity in the spatialdistribution f individual ource ypes, by dividinglarger basins nto distinct patial units, e.g. geolog-ical zones or sub-basin ypes. However, althoughthis approach as proved successful n larger iverbasins, provenance scription s necessarily crudeand interpretation s consequently endered moredifficult. As a result, ntegration f spatial prove-nance and source ype assessment would appear obe desirable for providing more comprehensivesediment ource nformation or arger iverbasins.

This paper demonstrates he potential or usinga composite fingerprinting echnique, ncorporat-ing both statistically erified composite signaturesand a multivariate mixing model, to provide a pre-liminary integration of spatial provenance andsource type information or contemporary us-

pended ediment luxes rom he upper and middlereaches of the River Exe (601 km2) and River Sev-ern (4325 km2) basins, UK. A nested approach sadopted, whereby sediment origin is initially ad-

dressed n terms of the distinct spatial zones (sub-basin ypes) costituting ach study area, and hen nterms of the precise source types (surfaces underdifferent and uses and channel banks) within eachof these spatial zones.

Study basinsLocated n southwest England, he Exe basin s un-derlain by Devonian slates and grits), Carbonifer-ous (shales and sandstones) and Permian marls,breccias and sandstones) ock types. This geolog-

ical diversity s paralleled by the relief and topog-raphy, with elevations of over 400 m occurring nthe resistant Devonian strata n the north, but fall-ing to 50-200 m in association with the less resist-ant Carboniferous ndPermian trata urther outh.A range of soil types can be found, ncluding peaty,surface-water ley, ground-water ley, podzolicand brown earth associations. Pastoral farmingdominates n northern reas, where n recent yearsmore effective land drainage, ombined with theuse of NPK fertilisers nd general pasture mprove-ment, have encouraged xtended grazing periodsby ever-expanding ivestock units. Mixed farmingassumes greater mportance o the south, where herange of autumn and spring sown crops includesbarley, wheat, oats and oilseed rape. Typical annualsuspended ediment yields within he basin are es-timated o be in the range 16-58 t km-2 yr-1 Wall-ing and Webb 1987). The flow gauging station atThorverton was selected as the basin outlet, withmonitoring tations at Bickleigh (R. Dart), CrazeLowman R. Lowman), Bampton R. Batherm) ndBrushford R. Barle) providing ampling ocationson the key tributaries see Fig. 1). The total catch-ment area above Thorverton s 601 km2.

The Severn basin represents he argest drainagearea n England and Wales and s underlain y Pre-Cambrian lavas), Cambrian shales, sandstonesand quartzites), Ordovician (mudstones andshales), Silurian shales and grits), Devonian OldRed Sandstone), Carboniferous limestones andsandstones), Permo-Triassic (sandstones) andJurassic sandstones) strata. Relief generally de-creases rom west to east and from north o south,with elevations of 752 m at the source n the north-west, falling to 50-200 m in the southeast. A widerange of soil types are observed, ncluding aw or-

Geografiska Annaler * 79 A (1997) ?40



FINGERPRINTING THE ORIGIN OF FLUVIAL SUSPENDED SEDIMENT

Fig. 1. The Exe study basin out-let and tributary suspended sedi-ment sampling sites.

* Suspended sedimentsampling point

0 10kmI I

ganic, stagnogley, podzolic and brown earth asso-ciations. Pastoral farming, along with commercialconiferous forestry, is widespread in the northwest,whilst arable agriculture for a range of autumn andspring sown crops including oats, barley, wheat,potatoes, turnips and swedes is widespread furtherto the east. Emphasis was placed upon the upperand middle reaches of the basin, with the flowgauging station at Bewdley being selected as thebasin outlet (i.e. a catchment area of 4325 km2).Additional tributary ampling locations (see Fig. 2)were chosen at the Institute of Hydrology Trape-

zoidal Flume (R. Severn), Berriew (R. Rhiw),

Llanymynech (R. Vyrnwy), Mytton (R. Perry) andWalcot (R. Tern).

Fieldwork and laboratory analysisCharacterising spatial provenanceThe spatial provenance of the contemporary sus-pended sediment load of the Exe and Severn basinswas characterised in terms of distinct sub-basintypes, which were represented by bulk suspendedsediment samples (50-500 1) collected from thekey tributaries noted above. These tributary sam-

pling sites were chosen as being representative of




ADRIAN L. COLLINS, DESMOND E. WALLING AND GRAHAM J.L. LEEKS

* Suspended sedimentsampling point

different ub-basin areas within each study basin,with similar physiographic haracteristics o thoseof the actual ributaries ampled. n the Exe, these

sediment amples were used to characterise totalof four distinct ub-basin ypes. Samples collectedfrom the River Dart at Bickleigh were taken o berepresentative f sediment derived rom low alti-tude, steeply sloping pasture areas of the lower(southern) Exe (i.e. the Dart ub-basin ype). Thosecollected from the River Lowman at Craze Low-man were taken to be representative f sedimentoriginating rom the higher altitude, more gentlysloping mixed arable and pasture areas of the mid-dle Exe (i.e. the Lowman ub-basin ype). Samplescollected rom he River Batherm t Bampton were

used to characterise igher altitude ub-basin reas

Fig. 2. The Severn studybasin outlet and tributary

50 km suspended sediment sam-I pling sites.

0I

typical of the transition etween mixed agriculturalland and moorland n the ower reaches of the upperExe (i.e. the Batherm ub-basin ype). Those col-

lected from the River Barle at Brushford were tak-en to be representative f the high altitude moor-land sub-basin areas of the upper (northern) Exe(i.e. the Barle sub-basin ype). A total of 73 bulksuspended sediment samples were collected atthese sites, i.e. 44 at Bickleigh, 15 at Craze Low-man, 8 at Bampton and 6 at Brushford. At the sametime, a total of 42 bulk suspended ediment sam-ples were collected at the basin outlet, .e. Thorver-ton, during 15 individual lood events.

In the Severn, tributary uspended sedimentsamples were used to characterise ive distinct ub-

basin ypes. Samples collected rom he River Sev-

Geografiska Annaler * 79 A (1997) ? 442



FINGERPRINTING HE ORIGIN OF FLUVIAL SUSPENDED EDIMENT

em at Plynlimon were taken o be representative fhigh altitude, teeply sloping forest and moorlandsimilar o the source of the River Severn (i.e. thePlynlimon sub-basin ype). Those collected from

the River Rhiw at Berriew were used to character-ise steeply sloping moor/rough asture areas char-acteristic of the abrupt ransition rom higher tolower altitudes, mmediately downstream rom hesource i.e. the Rhiw sub-basin ype). Samples col-lected from the River Vymwy at Llanymynechwere taken o represent ess steeply sloping pastureareas at even lower altitudes i.e. the Vyrnwy sub-basin type), whilst those from the River Perry atMytton were used to represent more gently slop-ing, mixed land use sub-basin areas occurring ur-ther downstream i.e. the Perry sub-basin ype).Sediment samples from the River Tern at Walcotwere used to represent he lowest altitude, gentlysloping sub-basin areas n the east and southeast,dominated by higher levels of arable agriculture(i.e. the Tern ub-basin ype). A total of 25 bulk sus-pended sediment samples were collected fromthese tributaries, .e. 6 from Plynlimon, 6 from Ber-riew, 4 from Llanymynech, from Mytton and 5from Walcot, whilst 23 samples were collected dur-ing nine individual lood events passing the basinoutlet at Bewdley.

A range of physical and chemical propertieswere used with the composite fingerprinting p-proach to compare he tributary nd basin outletsuspended sediment samples collected in eachstudy area. This provided a basis for assessing hespatial provenance f the sediment oad sampled ateach basin outlet, defined n terms of the varioussub-basin ypes.

Characterising source typeAdditional source material sampling was under-taken n order o characterise he various potentialsource ypes within the areas associated with eachindividual ub-basin ype. This nvolved he collec-tion of surface oil from woodland, pasture ndcul-tivated areas and of subsurface material rom ac-tively eroding channel banks. Although error wasinevitably nvolved n the assignment f particularcatchment areas not encompassed by the actualtributary basins to specific sub-basin types, thisscheme provided a basis for integrating spatialprovenance and source type information or thestudy basins. Care was taken o ensure hat sourcematerial amples represented ither topsoil likelyto be eroded (i.e. 0-2 cm depth) from surficial

sources, or geological and colluvial material orm-ing actively eroding channel banks. Totals of 480and 256 source type samples were collected fromthe Exe and Severn basins respectively. The finger-

printing approach was then used to compare heproperties f the suspended ediment amples col-lected rom each tributary ith equivalent nforma-tion for the potential ource ypes within areas rep-resentative f corresponding ub-basin ypes. Thisprovided n assessment f the relative ontributionfrom ndividual ource types to the sediment oadsampled n the major ributaries sed to representeach sub-basin ype.

Fingerprint property analysis

All bulk water samples collected at the tributaryand basin outlet sampling ites were dewatered s-ing continuous-flow centrifugation, reeze-driedand stored ready for detailed aboratory nalysis.Sediment amples were found o consist almost ex-clusively (>90%) of clay and silt (i.e. <63 pm) par-ticles. All samples used to characterise otentialsource ypes within he individual ub-basin areaswere air-dried, ently disaggregated nd screenedthrough 63 pm sieve to aid direct omparison withthe corresponding ributary uspended sedimentsamples.

Laboratory nalysis of both the suspended ed-iment and source material amples encompassedwide range of potential ingerprint roperties om-prising several property ubsets, .e. trace metals(Fe, Mn, Al), heavy metals Cu, Zn, Pb, Cr, Ni, Co),base cations Na, Mg, Ca, K), other organic and n-organic constituents C, N, total P), as well as ra-diometric 137Cs) properties. The choice of proper-ty subsets and extraction echniques was governedby previous experience and by the desire to usesubsets with differing environmental behaviour.Extraction f Fe, Mn and Al involved both pyro-phosphate-dithionite Bascomb 1968) and oxalate(Deb 1950) methods, whilst heavy metal extractionwas accomplished sing direct acid (nitric and hy-drochloric) igestion Allen 1989). Acid ammoni-um acetate was used to extract base cations Qui &Zhu 1993). All extract concentrations were deter-mined using atomic absorption pectrophotometry(AAS) with either an air/acetylene r a nitrous ox-ide/acetylene lame. Direct determination f C andN was undertaken sing a Carlo Erba ElementalAnalyser, whilst total P was determined olorimet-rically using UV-visible spectrophotometry fterextraction with perchloric acid (Olsen and Dean

Geografiska Annaler ? 79 A (1997) ? 4 243



ADRIAN L. COLLINS DESMOND E. WALLING AND GRAHAM .L. LEEKS

Table 1. Significance evels for the Kruskal-Wallis -test.

Fingerprint roperty Exe * Severn

pyrophosphate e

dithionite epyrophosphate ldithionite Alpyrophosphate n

dithionite Mntotal of pyro. and dith. Fetotal of pyro. Al and dith. Altotal of pyro. Mn and dith. Mnoxalate Fe

oxalate Mnoxalate AlCuZnPb

CrCoNiNaMg

CaKtotal PCN137Cs

24.30

20.4023.519.32

29.37

31.526.28

28.6531.51

4.74

19.77

29.4631.7324.95

26.9819.4529.5428.4317.93

27.9722.5025.70

3.784.568.04

15.64

14.4314.9317.4317.39

16.9414.1916.8318.0711.47

15.959.96

14.5813.4115.53

16.8715.7816.9014.1016.67

16.6411.297.37

12.039.74

14.67

*Critical H-value = 7.82t Critical H-value = 5.692

1965). 137Cs ssay was undertaken by gamma spec-trometry using HPGe detectors. For the purpose ofcalculating a particle size correction factor, abso-lute particle size composition was measured usinga Malvern Mastersizer after sample pretreatmentwith hydrogen peroxide and sodium hexameta-phosphate.

Fingerprinting sediment originA quantitative approachThe use of a quantitative composite fingerprintingprocedure to provide a preliminary integration ofspatial provenance defined in terms of sub-basintypes and source type defined in terms of surfacesunder different land uses and channel banks forboth the Exe and Severn basins, involved the fol-lowing steps:

a) use of a statistical-verification procedure toidentify from an extensive list of individual fin-gerprint properties, composite fingerprints ca-

Table 2. Final results of the discriminant unction analysis oridentifying composite ingerprint apable of distinguishing heindividual ub-basin ypes within each study basin.

Cumulative % sub-basin ype

Fingerprint roperty sediment amples lassified orrectly

ExeNi 70.59oxalate Mn 76.75dithionite Fe 89.87Na 93.16Co 97.55Ca 100.00

SevernC 100.00Ca 100.00oxalate Fe 100.00

pable of distinguishing sub-basin types for eachstudy area;

b) use of a similar procedure to establish compositefingerprints capable of discriminating potentialsource types within the areas representative ofeach individual sub-basin type;

c) use of these composite fingerprints in combina-tion with a multivariate mixing model to quan-tify the relative contributions of the individualsub-basin types to the sediment load sampled atthe basin outlet, and the relative contribution ofthe various potential source types to the sedi-ment loads sampled in the tributaries represent-ing the individual sub-basin types.

Identification of composite signaturesThe two-stage statistical selection procedure pro-posed by Collins et al. (1996, 1997) was used tospecify composite signatures capable of discrimi-nating the individual sub-basin types within eachstudy area, and also composite signatures capableof distinguishing potential source types within theareas representative of these sub-basin types.

Kruskal-Wallis H-test significance levels for theability of each individual potential fingerprintproperty to distinguish between the tributary sus-pended sediment samples collected to characterisethe individual sub-basin types within the two studybasins are presented in Table 1. For the Exe, thecritical value is 7.82. The values for the total of py-rophosphate and dithionite Fe, oxalate Fe, C and Nyield significance levels below this critical valueand therefore fail the test. For the Severn basin, the




FINGERPRINTING HE ORIGIN OF FLUVIAL USPENDED EDIMENT

Table 3. Mann-Whitney -test significance evels for the ability of each ndividual ingerprint roperty odistinguish otential urface/subsurface ource ypes within each sub-basin ype comprising he Exe basinstudy area critical P-value = 0.05).

Sub-basin ype spatial provenance

Property Dart Lowman Batherm Barle

pyrophosphate e 0.0006 0.0002 0.0004 0.0002dithionite Fe 0.0004 0.0002 0.0002 0.0002pyrophosphate l 0.0177 0.0002 0.0008 0.0004dithionite Al 0.0004 0.0002 0.0010 0.0008pyrophosphate Mn 0.0004 0.0004 0.0003 0.0003

dithionite Mn 0.0004 0.0002 0.0002 0.0012total of pyro. and dith. Fe 0.0004 0.0002 0.0002 0.0004total of pyro. and dith. Al 0.0008 0.0002 0.0004 0.0002total of pyro. and dith. Mn 0.0006 0.0002 0.0002 0.0002oxalate Fe 0.0006 0.0002 0.0002 0.0002

oxalate Mn 0.0004 0.0003 0.0002 0.0002Cu 0.0006 0.0002 0.0002 0.0002Zn 0.0006 0.0002 0.0002 0.0002Pb 0.0008 0.0002 0.0004 0.0002Cr 0.0088 0.0002 0.0002 0.0003

Co 0.0004 0.0001 0.0003 0.0005Ni 0.0002 0.0002 0.0004 0.0002total P 0.0008 0.0021 0.0002 0.0002C 0.0444 0.0304 0.0304 0.0304N 0.0444 0.0304 0.0294 0.0294

Na 0.0006 0.0002 0.0006 0.0002Mg 0.0020 0.0002 0.0002 0.0008Ca 0.0004 0.0017 0.0004 0.0015K 0.0009 0.0002 0.0002 0.0002137Cs 0.0004 0.0002 0.0002 0.0008

critical value is 5.692 and all parameters pass thetest. The final results of using multivariate discri-minant function analysis to identify from the pa-rameters successful in stage one, the composite fin-gerprint capable of correctly distinguishing 100%of the tributary suspended sediment samples for ei-ther study basin are presented in Table 2. Both com-posite signatures comprise properties from differ-ent subsets, thereby confirming the need for initiallaboratory analysis to include a wide range of po-tential fingerprint properties. Although for the Sev-ern, C alone correctly distinguishes 100% of thetributary sediment samples, Ca and oxalate Fe arealso included, in order to increase the reliability ofthe discrimination afforded by this particular sig-nature. This was justified by the fact that the lownumbers of suspended sediment samples collectedfrom each tributary identified in the Severn basincould explain the apparently powerful discrimina-tion of individual sub-basin types provided by C.

Mann-Whitney U-test significance levels forthe ability of each individual fingerprint property todistinguish source type on a simple surface (i.e.

woodland, pasture, cultivated material) versus sub-surface (i.e. channel bank material) basis areshown in Tables 3 and 4. In each case the critical P-value is 0.05. Properties yielding significance lev-els below the critical value were taken to be suc-cessful in distinguishing source type on this simplebasis and so were then included in stage two. Instage two, source type was considered on a moredetailed basis involving surfaces under differentland uses (i.e. woodland, pasture, cultivated) andchannel banks. The final results of this discrimi-nant function analysis are presented in Tables 5 and6. As before, the composite fingerprints generallycomprise individual properties from a range ofproperty subsets.

Use of a multivariate mixing modelThe multivariate sediment-mixing model proposedby Collins et al. (1996, 1997) was used in conjunc-tion with the composite signatures to establish therelative contributions of the areas representing in-dividual sub-basin types to the suspended sediment




ADRIAN L. COLLINS, DESMOND E. WALLING AND GRAHAM .L. LEEKS

Table 4. Mann-Whitney -test ignificance evels for he ability of each ndividual ingerprint rop-erty o distinguish otential urface/subsurface ource ypes within each sub-basin ype spatial prov-enance omprising he Severn basin study area critical P-value = 0.05).

Sub-basin ype spatial provenanceProperty Plynlimon Rhiw Vymwy Perry Tern

pyrophosphate e 0.0004 0.0294 0.0304 0.0606 0.0304dithionite e 0.0004 0.0304 0.0304 0.0304 0.0304pyrophosphate l 0.0066 0.0294 0.0304 0.0304 0.0294dithionite Al 0.0004 0.0304 0.0294 0.0304 0.0304pyrophosphate n 0.0056 0.0304 0.0606 0.0304 0.3123

dithionite Mn 0.0106 0.0304 0.1124 0.3123 0.3123total of pyro. and dith. Fe 0.0004 0.0304 0.0304 0.0304 0.0304total of pyro. and dith. A1 0.0002 0.0294 0.0304 0.0304 0.0294total of pyro. and dith. Mn 0.0103 0.0304 1.0000 0.3123 0.1939oxalate Fe 0.0004 0.0304 0.0304 0.0304 0.0304

oxalate Mn 0.0889 0.0294 0.1124 0.8852 0.3123oxalate Al 0.0012 0.0304 0.0304 0.0304 0.0304Cu 0.0004 0.0304 0.0304 0.0304 0.0304Zn 0.0004 0.0304 0.0304 0.0304 0.0304Pb 0.0260 0.0294 0.0304 0.0294 0.0304

Cr 0.0004 0.0304 0.3123 0.0304 0.0304Co 0.0002 0.0256 0.0256 0.0228 0.0256Ni 0.4776 0.0294 0.0304 0.0284 0.0294total P 0.0004 0.0284 0.0304 0.0265 0.0304C 0.2222 0.0304 0.0304 0.0304 0.0304

N 0.2222 0.0265 0.0265 0.0304 0.0304Na 0.0004 0.0304 0.0294 0.0304 0.0294Mg 0.0006 0.0304 0.0304 0.0294 0.0304Ca 0.0004 0.0294 0.0304 0.0304 0.0304K 0.0004 0.0304 0.0304 0.0304 0.0304137cs 0.0004 0.0265 0.0265 0.0294 0.1052

load sampled at the basin outlet and the relativecontribution f the individual ource types to thesuspended ediment oads sampled n the tributarysub-basins. The mixing model seeks to satisfy thefollowing constraints.

O< P, 1

n

s= I

(3)

(4)

a) The contributions f the individual sub-basin A linear equation s constructed or each tracertypes to the sediment oad sampled at the outlets property comprising each composite signatureof the two study basins must all be non-negative used to distinguish either spatial provenance de-and must sum to unity, .e. fined in terms of sub-basin ype (see Equation ),

or the potential ource types within the areas rep-0 < Pt ? 1 (1) resented by each sub-basin ype (see Equation ).

The resultant et of linear equations pertaining on each signature s generally ver-determined, nd so

E Pt = 1 (2) optimisation f the values representing he estimat-t= 1 ed percentage contributions from either the indi-

vidual sub-basin types or the individual sourceb) The contributions f the individual ource ypes types s achieved by minimising he sum of squares

to the sediment oads of the tributaries sed to of the relative errors:characterise he sub-basin ypes must all be non-negative and must sum to unity, .e.





Table 5. Final results of the discriminant unction analysis oridentifying composite ingerprint apable f distinguishing o-tential and use and channel bank source ypes within each sub-basin ype comprising he Exe basin study area.

Cumulative % sourcetype samples lassified

Sub-basin ype Property correctly

Dart P 87.50Cu 92.50Cr 95.00Na 95.00oxalate Mn 100.00

Lowman Ni 95.00C 87.50Co 95.00N 97.50Cu 100.00

Batherm Ni 75.00N 82.50C 87.00K 90.00dithionite Mn 95.00dithionite e 100.00

Barle K 67.50dithionite Fe 92.50N 97.50Pb 97.50Zn 95.00Co 100.00

{[Ci-(PtlSitlZtlOtl+Pt2Sit2Zt20t2+---

Ptn SitnZtnOtn)]/Ci}2 Wi (5)

n

E {[Ci-(PWSiwwOw+PpSipzpOp+PcSic

ZcOc + PcbSicbZcbOcb)]/Ci}2 W (6)

where:

Ci = concentration f tracer parameter i) in ba-sin outlet (Equation 5) or tributary Equa-tion 6) suspended ediment ample;

Ptl = percentage ontribution rom each sub-ba-sin type;

Px = percentage ontribution rom each potentialsource ype within he area epresentative feach sub-basin ype:w = woodland, p = pasture, c = cultivated,cb = channel bank;

Sitl = mean concentration of tracer property (i) for

Siweach sub-basin ype;

= mean concentration f tracer roperty i) for

Table 6. Final results of the discriminant unction analysis oridentifying composite ingerprint apable f distinguishing o-tential and use and channel bank source ypes within each sub-basin ype comprising he Severn basin study area.

Cumulative % sourcetype samples lassified

Sub-basin ype Property correctly

Plynlimon Cr 76.67Cu 80.00Zn 96.67Ca 100.00

rhiw pyrophosphate n 81.25Ca 93.75K 100.00

vyrnwy N 68.75Na 87.50Zn 81.25Pb 93.75oxalate Al 100.00

Perry Ca 68.75Zn 85.50Na 100.00

Tern Co 81.25Ni 87.50dithionite e 100.00

each potential source type within the arearepresentative f each sub-basin ype;

Ztl = sub-basin ype particle size correction ac-tor ratio of the mean specific surface rea ofall sediment samples collected at the basinoutlet o the mean specific surface area of allsediment amples collected from each trib-utary);

Zw = source type particle size correction actor(ratio of the mean specific surface area of allsediment amples collected from each trib-utary o the mean specific surface area foreach potential source type within the arearepresentative f the individual sub-basintypes);

Otl = sub-basin type organic matter content cor-rection actor ratio of the mean organic ar-bon content of all sediment amples collect-ed at the basin outlet to the mean organiccarbon ontent of all sediment amples col-lected from each tributary);

0w = source type organic matter content correc-tion factor ratio of the mean organic arboncontent of all sediment samples collected





Table 7. Mean particle ize correction actors or each sub-basintype constituting he Exe and Severn basins.

Sub-basin ype Correction actor

ExeDart 0.99Lowman 0.95Batherm 1.07Barle 1.11

SevernPlynlimon 0.96Rhiw 1.16Vyrnwy 1.04Perry 0.97Tern 0.97

from each tributary o the mean organic ar-bon content for each potential source typewithin he area epresentative f the ndivid-ual sub-basin ypes);

Wi = tracer pecific weighting.

The tracer data pertaining o each sub-basin ypeand to each potential source type within the indi-vidual sub-basin ypes, are aggregated o provide asingle mean value which s then used n the relevantmixing model calculations.

A particle size correction factor (Ztl, Zw) is in-cluded n the optimised mixing model to permit adirect comparison etween samples with contrast-ing particle size characteristics see Collins et al.1996, 1997). During he mixing model calculationsfor assessing spatial provenance n terms of sub-basin type, the ratios of the mean specific surfacearea of all suspended ediment samples collectedfrom the basin outlet to the mean specific surfacearea of the sediment samples collected from eachindividual ributary sed to characterise patial or-igin, was employed see Table 7). During he mix-ing model calculations or assessing source typecontributions, he ratios of the mean specific sur-face area or each set of tributary uspended edi-ment samples o the mean specific surface area oreach individual ource ype within the area repre-sented by the corresponding ub-basin ype wasused (see Table 8).

An organic matter ontent orrection actor Otl,Ow) s also used to ensure more direct comparabil-ity of the values used in the mixing model calcula-tions (see Collins et al. 1996, 1997). Organic ar-bon content s used as a surrogate measure or or-

Table 8. Particle ize correction actors or the potential and useand channel bank source ypes associated with each sub-basintype constituting he Exe and Severn basins.

Source ype

Sub-basin ype Woodland Pasture Cultivated Bank

ExeDart 1.04 1.09 1.11 1.18Lowman 1.05 1.13 1.23 1.26Batherm 1.08 1.02 1.06 1.13Barle 1.05 1.06 1.01 1.13

SevernPlynlimon 1.05 1.11 - 1.20Rhiw 1.03 1.06 1.07 1.18Vyrnwy 1.20 1.24 1.10 1.18Perry 1.28 1.15 1.13 1.20Tern 1.19 1.15 1.16 1.25

ganic matter ontent Peart ndWalling 1986), andthe correction actor s calculated n the same man-ner as for particle ize (see Tables 9 and 10).

Tracer pecific weightings Wi) are used to en-sure that he property roviding he greatest preci-sion within each composite signature exerts thegreatest nfluence upon he optimised mixing mod-el estimates relating o that signature see Collinset al. 1996, 1997). Weightings or the fingerprintproperties dentified n the composite signaturesused for this study are presented n Table 11.

To assess the goodness-of-fit fforded y the op-timised mixing model solutions, a comparison wasundertaken etween he actual ingerprint ropertyconcentrations measured n the basin outlet or trib-utary suspended ediment samples and the corre-sponding values predicted by the model based onthe sum of the estimates of the percentage ontri-

Table 9. Mean organic matter ontent orrection actors or each

sub-basin ype comprising he Exe and Severn basins.

Sub-basin ype Correction actor

ExeDart 1.11Lowman 1.11Batherm 1.11Barle 0.75

SevernPlynlimon 1.05Rhiw 0.47Vyrnwy 0.69Perry 0.34Tern 0.36

Geografiska Annaler ? 79 A (1997) ? 448




Table 10. Mean organic matter ontent orrection actors or po-tential and use and channel bank source ypes associated witheach sub-basin ype constituting he Exe and Severn basins.

Source ype

Sub-basin ype Woodland Pasture Cultivated Bank

ExeDart 1.03 1.01 1.94 1.78Lowman 1.62 1.20 1.73 1.51Batherm 1.62 1.20 1.73 1.51Barle 1.77 1.30 1.80 1.98

SevernPlynlimon 0.99 1.18 - 1.30Rhiw 0.81 1.33 1.62 1.22Vymwy 1.21 0.77 1.66 1.59Perry 1.26 1.70 1.56 1.93Tern 0.83 1.34 1.20 1.60

butions from each sub-basin type to the former andfrom each source type to the latter (see Collins etal. 1996, 1997). Values of relative error associatedwith the mixing model estimates for sub-basin typeare typically of the order of ?11% (see Table 12),whilst those associated with the estimates for indi-vidual source types are typically less than ?+10%(see Table 13).

Table 11. Tracer pecific weightings.

Fingerprint roperty Weighting

Ni 0.140oxalate Fe 0.272dithionite Fe 0.140C 0.222

total P 0.623Cr 0.285oxalate Mn 0.146Co 0.758N 0.459K 0.783

Pb 0.200Cu 0.664Zn 0.353Ca 0.415oxalate Al 0.221

pyrophosphate Mn 0.473dithionite Mn 0.503Na 0.783

Table 12. Mean elative rrors or he estimates f sediment rop-erties obtained rom he mixing model based on the contributionsfrom he individual ub-basin ypes n each study basin.

Study basin Mean % error SE mean

Exe 9.38 2.08Severn 8.70 3.74

Results and discussionThe Exe Basin

Figure 3 presents the mean results of the mixingmodel calculations for the relative contribution ofsediment from each sub-basin type to the sedimentload sampled at the outlet of the Exe basin. Themean contribution from the Lowman sub-basintype (42.0%) is most important, followed in de-scending order by the Dart (28.0%), Barle (20.0%)and Batherm (10.0%) sub-basin types. These re-sults demonstrate that all parts of the larger catch-ment provide significant contributions to the sedi-ment load at the basin outlet. Using these estimatesand the areas of the Exe basin above the outlet atThorverton represented by each sub-basin type (i.e.Dart = 17.5%, Lowman = 19.5%, Batherm = 20.5%and Barle = 42.5%), the specific sediment yieldsfrom each sub-basin type are estimated to be in theratio 1 (Batherm sub-basin type): 1 (Barle sub-ba-sin type): 3.4 (Dart sub-basin type): 4.6 (Lowmansub-basin type). These estimates indicate that thecentral portions of the Exe basin represented by theLowman sub-basin type generate the highest spe-cific sediment yields and are therefore consistent

Table 13. Mean elative rrors or he estimates f sediment rop-erties obtained rom he mixing model based on the contributionsfrom potential ource ypes associated with each sub-basin ype

constituting he Exe and Severn basins.

Sub-basin ype Mean % error SE mean

ExeDart 6.3 0.88Lowman 6.9 0.93Batherm 7.2 0.82Barle 7.0 0.62

SevernPlynlimon 6.5 0.93Rhiw 8.8 0.79Vyrnwy 7.7 0.80Perry 7.1 0.92Tern 8.3 0.76




ADRIAN L. COLLINS, DESMOND E. WALLING AND GRAHAM J.L. LEEKS

50-

40-

S30-

0 20-

10-I""

i'

Dart type Lowman type' Batherm type' Barle type

Fig. 3. Mean relative contributions from each sub-basin type tothe suspended sediment load sampled at the outlet of the Exe studybasin.

with existing knowledge of sediment productionfrom different parts of the basin provided by directmonitoring programmes cf. Walling and Webb1987). However, t is important o recognise thatthe mixing model calculations incorporate noweighting actor for the relative magnitude of thesuspended ediment oad transported hrough hebasin outlet at the time of each flood event sample.As a result, hese results may not provide an accu-rate ndication of the real contribution f each in-dividual sub-basin ype to the annual suspendedsediment oading at Thorverton.

Figure 4 presents he mean results of the mixingmodel calculations for the relative contributionfrom each potential ource ype within he area ep-resented by each sub-basin ype constituting heExe. These estimates were obtained by averagingthe results of the mixing model calculations oreach suspended sediment sample collected fromthe individual ributary ampling sites. Contrastsare mmediately pparent or the four spatial zonesunder scrutiny. Mean contributions rom pasture

100-

80-c0a 60-

o 40-

20-

0-

sources are highest in the Batherm 87.0%) andBarle 85.5%) ub-basin ypes, reflecting he wide-spread occurrence of pasture n northern reas ofthe Exe represented by these two spatial zones.

Surface erosion in pasture areas is promoted bypoaching associated with intensive ivestock arm-ing (Findlay et al. 1984; Heathwaite 1994). Meancontributions rovided by surface erosion of culti-vated areas are highest for the Lowman (40.0%)and Dart 11.0%) sub-basin ypes. This reflects heimportance of arable cultivation on the mixedfarms within he more southern reas of the Exe ba-sin represented y these particular patial zones.Cultivation esults in bare soils being exposed torainsplash nd surface runoff erosion during boththe autumn nd spring owing periods. The highest

mean contribution rom cultivated reas s provid-ed by the Lowman sub-basin ype. This particularzone is characteristic f the more gently sloping ar-eas of the middle Exe, which represent he mostsuitable and for cultivation n the Exe basin studyarea. The mean contribution rom cultivated ourc-es within the Dart sub-basin ype is lower, as thiszone represents he more steeply sloping areas ofthe southern Exe basin which are less suitable orcultivation urposes. Mean contributions rom sur-face erosion in woodland areas are low for eachsub-basin ype, reflecting he protection of wood-

land soils from erosion by litter and vegetation ov-er and the general absence of surface runoff inwoodlands. The highest mean woodland contribu-tion (6.0%) s provided by the Barle sub-basin ype,which represents northern reas of the Exe basinwhere woodland oppices are commonly observedin riparian reas.

By taking account of the mean contributions s-timated for each sub-basin ype and aggregatingthe mean contributions stimated or each source

_l Woodland

Pasture

Cultivated

Channel bank

Lowman'

Batherm

Sub-basin type

barle

Fig. 4. Mean relative contributionsfrom each potential source type tothe suspended sediment loads fromareas representative of each sub-

basin type in the Exe study basin.




FINGERPRINTING THE ORIGIN OF FLUVIAL SUSPENDED SEDIMENT

80-

70-

c60-

m 50-

c 40-o0 30-

20-

10-

0-

50-

40-

0*30-

-0

0o 20-

10-

Woodland Pasture 'Channel bank'

Fig. 5. Mean total contribution from potential source types to thesuspended sediment load of the entire Exe study basin.

type within he different ub-basin ypes, it is pos-sible to calculate he total contribution f individ-ual source ypes to the suspended ediment oad ofthe overall basin see Fig. 5). The erosion of surfacesoils under pasture s most important 71.7%), ol-lowed n descending rder by the erosion of surfacesoils under arable and use (20.4%), he erosion ofchannel banks (5.3%) and finally the erosion ofsurface soils beneath woodland (2.6%). Usingthese estimates and he percentage f the Exe basinunder ach and use (i.e. woodland = 4.2%, pasture= 86.6% and cultivated = 9.2%), t is possible o es-

timate hat he mean specific sediment yields fromthe different and uses are n the ratio 1 (woodlandsoils): 1.4 (pasture soils): 3.9 (cultivated soils).These figures ndicate hat although pasture ourc-es are estimated o be the most significant meansource type for the entire Exe basin, the specificsediment ields from eroding pasture oils are ow-er than hose from eroding cultivated oils.

The Severn Basin

Figure 6 examines he mean results of the mixing

model calculations for the relative contributionfrom each sub-basin ype to the sediment oad sam-pled at Bewdley. The contribution rom the Vyrn-wy sub-basin ype (47.5%) s most significant, ol-lowed in descending order by the Tern (43.0%),Perry 5.0%), Rhiw (3.0%) and Plynlimon 1.5%)sub-basin ypes. As with the Exe, sediment ourcesappear o be distributed hroughout he Severn ba-sin study area. Using these estimates and the areasof the Severn basin above the outlet at Bewdleyrepresented y each sub-basin ype (i.e. Plynlimon= 3.5%, Rhiw = 7.2%, Vyrnwy = 37.0%, Perry =

9.8% and Tern = 42.5%), the specific sediment

Plynlimon'

Rhiw type Vyrnwy 'Perry type'

Tern typetype type

Fig. 6. Mean relative contributions from each sub-basin type tothe suspended sediment load sampled at the outlet of the Severnstudy basin.

yields from each sub-basin ype are estimated o bein the ratio 1 (Rhiw sub-basin ype): 1.1 (Plynli-mon sub-basin ype): 1.2 (Perry sub-basin ype):2.9 (Tem sub-basin ype): 3.2 (Vymwy sub-basintype). However, s with the Exe, no weighting ac-tor is incorporated nto the mixing model calcula-tions for the suspended ediment oads at the timeof sample collection at the basin outlet and so theseestimates must be treated with caution.

Figure 7 illustrates he mean results of the mix-ing model calculations or the relative ontributionfrom each potential ource ype within he area ep-

resented by each sub-basin type costituting theSevern basin. As with he Exe, marked ontrasts reobserved n the source ype contributions ssociat-ed with the individual patial zones. The mean rel-ative contributions rom woodland are far greaterfor the Plynlimon ub-basin ype (i.e. 22.0%) hanfor the other patial ones (generally . 1.5%). Thisreflects he severe disturbance f forest soils in theextreme western areas epresented y the suspend-ed sediment sampling at Plynlimon, associatedwith the ogging activities of the Forestry Commis-sion (Leeks and Roberts 1987). Pasture mean con-

tributions are greatest or the Rhiw and Vymwysub-basin ypes (i.e. 90.0% and 84.0%), reflectingthe surface erosion of the widespread pasturesources observed n the western areas haracterisedby these sub-basin ypes. Surficial rosion of pas-ture soils is promoted y the high-energy illslopefluvial system which characterises he west, and bypoaching n association with intensive sheep andcattle grazing (Thomas 1964; Rudeforth et al.1984). Mean contributions rom surface rosion ncultivated areas are ow for the Rhiw and Vymwysub-basin ypes (2.0% and 3.5% respectively), butfar greater or the Perry 22.5%) and Tern 52.5%)




ADRIAN L. COLLINS , DESMOND E. WALLING AND GRAHAM J.L. LEEKS

_ Woodland

Pasture

Cultivated

Channel banlk Fig. 7. Mean relative contributionsfrom each potential source type tothe suspended sediment loads fromareas representative of each sub-basin type in the Severn study ba-sin.

sub-basin ypes. This reflects the influence of thewidespread mixed arable/pastoral arming ound n

eastern areas. Intensive arming of wheat, barley,oats, potatoes, urnips nd swedes n such areas x-poses bare soils to erosion processes during bothautumn and spring. Channel bank mean contribu-tions are greater n the west, e.g. 12.0% for thePlynlimon ub-basin ype. Severe bank erosion hasbeen noted n the area characterised y this partic-ular spatial zone in association with forest drains,log jams and debris dams in commercial orests,and in response to the local high-energy-efficientfluvial system n general Leeks and Roberts 1987;Lawler and Leeks 1992).

Aggregation of the source type estimates foreach sub-basin ype again provides a useful meansof estimating the contributions rom individualsource types for the basin as a whole (see Fig. 8).Eroding urface oils beneath pasture are most m-portant 65.3%), ollowed in descending order byeroding surface soils beneath arable land use(25.4%), he erosion of channel banks (7.5%) anderoding surface soils beneath woodland (1.8%).

Woodland Pasture Cultivated 'Channel bank'

Fig. 8. Mean total contribution from potential source types to the

suspended sediment load of the entire Severn study basin.

Using these estimates and taking nto account heproportions f the Severn basin beneath each land

use (i.e. woodland = 3.4%, pasture = 76.0% andcultivated = 20.6%), the specific sediment yieldsfrom the areas under different and uses are esti-mated to be in the ratio 1 (woodland soils): 1.5(pasture oils): 2.8 (cultivated oils). As with theExe basin, hese figures mply that although he es-timates or the mean total contribution rom eachindividual ource type to the suspended edimentload sampled at the basin outlet reveal the overallsignificance of pasture ources, specific sedimentyields are higher or the cultivated reas n the Sev-ern basin.

PerspectiveThe preceding discussion has demonstrated hesuccessful use of a composite ingerprinting roce-dure o provide a preliminary ntegration f spatialprovenance and source type information or thecontemporary uspended ediment oads of the up-per and middle River Exe and Severn basins. Usinga nested approach, ediment origin has initiallybeen assessed in terms of the distinct sub-basintypes costituting ach study area as an entirety and

then in terms of the contributions rom individualpotential ource ypes within each of these spatialzones. Integration f spatial provenance nd sourcetype information mproves he level of source res-olution provided by existing large-scale sedimentprovenance nvestigations, which, odate, have pri-marily ocused upon the identification f spatiallydefined sources. This inevitably assists the inter-pretation f sediment rigin data or arger iverba-sins by revealing n more detail, he nfluence of en-vironmental ontrols such as land use upon sedi-ment supply. Ultimately, he desire o integrate pa-tial provenance and source type data could point


100-

80-c0

= 60-.0_

0o 40-

20-

0-Plynlimon

Sub-basin typePerry

80-

70-

C60-0'g 50-

oo 30-

20-

10-

0-

252



FINGERPRINTING HE ORIGIN OF FLUVIAL USPENDED EDIMENT

towards the adoption of a stringent hierarchicalmethodology or sediment ingerprinting tudies nlarger river basins. Initial source area depictioncould focus upon spatial provenance, ollowed by

more detailed discrimination f the actual sourcetypes within each spatial origin. Scope clearly ex-ists for further mproving the use of the fingerprint-ing approach o synthesize patial provenance ndsource type information for larger river basins. Inparticular areful consideration must be directedtowards source material sampling strategies andhence towards he structure f the fingerprint rop-erty database. Where possible, the assembly of asingle source material database yielding both spa-tial provenance and source type information forsuspended sediment samples collected at the basin

outlet should be sought (cf. Walling and Woodward1995). This would overcome the problem of usingboth tributary uspended ediment and soil/chan-nel bank source material amples o provide he in-tegration achieved in this study.

AcknowledgementsThe support f the Natural Environment ResearchCouncil and the Institute of Hydrology in fundinga CASE Research Studentship ALC) s gratefullyacknowledged. Staff at Plynlimon (I.H.), David

Rowlands, and Mike Avrill provided valuable as-sistance with suspended ediment ampling. HelenJones produced he diagrams.

Dr A.L. Collins and Professor D.E. Walling, De-partment of Geography, University of Exeter, Exe-ter, Devon, EX4 4RJ, UK.

Mr G.J.L. Leeks, Institute of Hydrology, Walling-ford, Oxfordshire, OXO1 8BB, UK.

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Blackwell. Oxford. 368 p.Bascomb, C.L., 1968: Distribution f pyrophosphate-extractable

iron and organic arbon n soils of various roups. . Soil Sci.,19: 251-268.

Caitcheon, G.G., 1993: Applying environmental magnetism osediment racing. n: Peters, N.E., Hoehn, E., Leibundgut,Ch., Tase, N. andWalling, D.E. (eds): Tracers n hydrology.IAHS Press. Wallingford. AHS Publ. no. 215. 285-292.

Collins, A.L., Walling, D.E. and Leeks, G.J.L., 1996: Compositefingerprinting f the spatial ource of fluvial suspended ed-iment: a case study of the Exe and Severn River Basins, UK.Geomorphologie: elief, Processus, Environnement, : 41-54.

Collins, A.L., Walling, D.E. and Leeks, G.J.L., 1997: Source ype

ascription or fluvial suspended ediment ased on a quanti-tative composite ingerprinting echnique. Catena, 29: 1-27.

Deb, B.C., 1950: The estimation f free iron oxides n soils andclays and heir removal. . Soil Sci., 1: 212-220.

Douglas, G.B., Gray, C.M., Hart, B.T. and Beckett, R., 1995: A

strontium sotopic investigation f the origin of suspendedparticulate atter SPM) n the Murray-Darling iver ystem,Australia. Chem. Geol., 59: 3799-3815.

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Leeks, G.J.L. nd Roberts, G., 1987: The effects of forestry n up-land treams with special eference o water quality nd ed-iment ransport. n: Good, J.E.G. ed.): Environmental spects

of plantation orestry n Wales. nstitute f Terrestrial colo-gy. Grange-over-Sands. -24.

Murray, A.S., Olive, L.J., Olley, J.M., Caitcheon, G.G., Wasson,R.J. and Wallbrink, .J., 1993:Tracing he source f suspend-ed sediment n the Murrumbidgee iver, Australia. n: Peters,N.E., Hoehn, E., Leibundgut, h.,Tase, N. and Walling, D.E.(eds): Tracers n hydrology. AHS Press. Wallingford. AHSPubl. no. 215. 293-302.

Oldfield, F. and Clark, R.L., 1990: Lake sediment-based tudiesof soil erosion. n: Boardman, ., Foster, .D.L. and Dearing,J.A. (eds): Soil erosion on agricultural and. Wiley. Chiches-ter. 201-228.

Olsen, S.R. and Dean, L.A., 1965: Phosphorous. n: Black, C.A.(ed.): Methods f soil chemical nalysis. Part . American o-ciety of Agronomy. Madison, Wisconsin, 1035-1049.

Peart, M.R., 1995: Fingerprinting ediment ources: An examplefrom Hong Kong. n: Foster, .D.L., Gumell, A.M. and Webb,B.W. (eds): Sediment nd water quality n river catchments.Wiley. Chichester. 79-186.

Peart, M.R. and Walling, D.E., 1986: Fingerprinting edimentsource: he example of a drainage asin n Devon, UK. In:Hadley, R.F. (ed.): Drainage asin sediment delivery. AHSPress. Wallingford. AHS Publ. no. 159. 41-55.

- 1988:Techniques or establishing uspended ediment ourc-es in two drainage asins n Devon, UK: a comparative s-sessment. n: Bordas, M.P. and Walling, D.E. (eds): Sedimentbudgets. AHS Press. Wallingford. AHS Publ. no. 174. 269-279.

Qui, X-C. and Zhu, Y-Q., 1993: Rapid nalysis f cation xchangeproperties n acidic soils. J. Soil Sci., 155: 301-308.

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Ch. (ed.): Tracer technologies for hydrological ystems.IAHS Press. Wallingford. AHS Publ. no. 229. 143-151.Thomas, T.M., 1964: Sheet erosion by sheep n the Plynlimon r-

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Walling, D.E. and Webb, W.B., 1987: Suspended oad n gravelbed rivers: UK experience. n: Thorne, C.R., Bathurst, .C.and Hey, R.D. (eds): Sediment ransportation n gravel-bedrivers. Wiley. Chichester. 91-723.

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Manuscript received May 1997, revised and accepted Sept. 1997


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