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Chemical runoff from pasture: Theinfluence of (Fertiliser and riparianzonesR. H. S. McColl aa DSIR , Soil Bureau , Private Bag, Lower Hutt, New ZealandPublished online: 30 Mar 2010.

To cite this article: R. H. S. McColl (1978) Chemical runoff from pasture: The influence of(Fertiliser and riparian zones, New Zealand Journal of Marine and Freshwater Research, 12:4,371-380, DOI: 10.1080/00288330.1978.9515764

To link to this article: http://dx.doi.org/10.1080/00288330.1978.9515764

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N.Z. Journal of Marine and Freshwater Research 12 (4): 371-80 December 1978

Chemical runoff from pasture: the influence of (Fertiliserand riparian zones

R. H. S. MCCOLL

Soil Bureau, DSIR, Private Bag, Lower Hutt, New Zealand

ABSTRACT

Runoff of phosphorus, nitrate, ammonium, calcium, magnesium, sodium, potassium,chloride, and sulphate was measured in 15 storms and at low flows in 3 "nested" experi-mental catchments converted from scrub to pasture. Multiple regression analysis suggested thatover 2½ y, fertiliser application had a cumulative effect on the concentrations of calcium,potassium, and sulphate in storm waters leaving the experimental basin, but only in theflood waters from the small wholly-grassed sub-catchment (Pukeiti) was there an increase inphosphorus concentrations. A similar pattern was observed at baseflows. Reactive phosphoruslosses of up to 1 kg.ha-1 left Pukeiti in post-fertiliser storm events but mean losses fromthe whole basin were only about 0.004 kg.ha-1 per storm and there was little evidence ofany fertiliser effect. The stream below Pukeiti has well developed riparian vegetation withmarsh and scrub.

The phosphorus losses from the basin seem of little significance agriculturally andenvironmentally. Although the losses from Pukeiti sub-catchment were of siufficient magnitudeto have a strong impact on water quality in waterways and lakes (mean total phosphorusconcentration in post-fertiliser floods 1.91 g.m-3) this sub-catchment appeared to have littleeffect on the quality of water eventually leaving the whole basin.

The results are discussed in relation to sub-catchment differences and it is suggested thatthey give support to the use of riparian zones along streams to reduce phosphorus runoff.

INTRODUCTION SITE DESCRIPTION

Agriculture undoubtedly increases the potentialfor plant-nutrient loss from land. Nutrient runoffconstitutes a loss of fertility and a threat to thequality of receiving waters. Both problems may beminimised by better land management but the tech-nology remains undeveloped or poorly understood.This is partly because nutrient losses from presentagricultural systems have been inadequately describedand quantified: there is even poor agreement on howthe losses occur.

This study examines the changes in chemical run-off that took place while three "nested" experi-mental catchments in Northland, New Zealand, wereconverted from scrub to pasture. McColl et al. (1975)measured the chemical losses during four storms inthe early stages of pasture development and esti-mated the fertiliser losses. The origin and outputof suspended and dissolved material was studied indetail by Schouten (1976). Here, the changes inwater quality as the fertility of the land was raisedby fertiliser application, and the differences betweenthe catchments, are examined in more detail.

The Puketurua Experimental Basin (NZMS 1, N/19 585015,Fig. 1), 21 km west of Whangarei, was established by theWater and Soil Division of the Ministry of Works andDevelopment as a contribution to the International Hydro-logical Decade. Annual reports of the hydrology have beenpublished (National Water and Soil Conservation Organisa-tion 1968, 1970, 1971). Stream flow from the whole 248 habasin is gauged at the Puke:itoi weir. The stream flow isalso gauged in two "nested" sub-catchments, Pukewaenga(38 ha) and Pukeiti (1.44 ha). The Puketitoi weir normallyhas perennial flow, Pukewaeriga stream is normally dry forseveral weeks each summer, and Pukeiti stream flows onlyin winter or during heavy rainfall. High intensity rainfallsare common in October, November, and December and heavyrainfall from tropical cyclones; can occur between Decemberand March. Annual rainfall has averaged 1392 mm sincemeasurements were started in 1964 and up to 1975.

Puketurua Experimental Basin, like much of the farmlandin Northland, is rolling to mcderately steep hill country withslopes commonly between 12° and 20°, but Pukeiti sub-catch-ment is an area of gentle relief with easy rolling slopes«10°). The Puketurua catchment ranges from 29 m a.s.l. atPuketitoi weir to 160 m a.s.l. at Puketurua hill. Pukewaengaand Pukeiti flumes are 45 m and 105 m a.s.l. respectively.

The soils of the experimental basin are northern yellow-brown earths dotted with poclzols developed under the kauritrees. The basin is underlain by shattered mudstone rock,which is exposed in gullies.

The area was dug over for kauri gum, farmed in the1930s, and used as an artillery range during World War II.Afterwards it reverted to manuka scrub, parts of which inthe south-eastern headwaters have been burnt in recent years.The older scrub vegetation was dated in 1970 as being 22-25 yold.

It is important to note that no fertiliser had been usedon the are:i since 1940.

Received 3 June 1977; revision received 7 August 1978.

New Zealand Soil Bureau Publication 831.

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372 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH 12 (4), 1978

Before development, Puketurua Experimental Basin was anarea of low natural fertility, and, therefore, offered a goodbite for monitoring changes in water quality associated withland development and fertiliser application. Details of therecent development programme are given in Table 1. Floodsfollowing soon after fertiliser applications are referred to as"post-fertiliser" floods; floods occurring prior to fertiliserapplications are called "pre-fertiliser" floods.

METHODS

Water samples were collected manually by Min-istry of Works and Development staff in 500 mlpolyethylene bottles during 11 rain storms betweenNovember 1972 and May 1974 (Storms 5 to 15,Table 1). The samples were frozen as soon as pos-sible and airfreighted to the laboratory. On thawing,

TABLE 1—Land development, fertiliser application, and water sampling in the Puketurua Experimental Basin1970-74.

DATE TREATMENT STORM

30 Apr 1970-11 Feb 197128 May 197122 Nov 197123 Dec25 Ian13 Jan

19711972-1972

22-23 Jan 19723 Mar 1972

24 Feb 197226 Feb 1972

3 Mar5 Mar8 Mar

10 & 161 Apr

14 AprMay

30 Jun25 Aug29 Aug19 Sep23 Sep

Oct8-9 Oct

197219721972Mar 197219721972197219721972197219721972-19721972

11 Oct 197213-14 Oct 197225 Oct 1972

30 Nov 197211 Jan 1973

Feb 19739-11 Jun 197312 Jun 1973

13 Jun 197315-16 Jun 197316-19 Jun 1973

4 Nov9 Nov

19731973

23 Nov 1973Jan 197423 Feb 197418 Mar 19745-7 Apr 19745 May 19744 6 May 197422-23 May 197427-28 May 1974Aug 1974

Scrub vegetation burned off

First giant discing completed, stick racing, and further burningSamples collected during low flowsSamples collected during thunderstorm (20 mm rain in 50 min)Samples collected during storm recession (27.5 mm rain in 7 h)Samples collected during cyclone Carlotta (44.5 mm rain in 21 h)733 t lime applied aerially on whole catchment

Second giant discing, and heavy harrowing completed67 t15% potassic superphosphate applied aerially on 107 ha on SW sidePuketurua catchment including all of Pukewaenga and PukeitiSamples collected during lowest 1971/72 summer flowsSamples collected during major storm (41.5 mm rain in 10 hr)Samples collected during major storm (68.2 mm rain in 31 h)Samples collected during low flowApplication of a further 117 t superphosphate completedApplication of a further 687 t lime completedTandem discing and grass seed sowing completedStock introducedSamples collected during normal winter flow conditionsSamples collected during storm (17.5 mm rain in 24 h)Samples collected during average spring flow conditions112 t 15% potassic superphosphate applied aerially

Samples collected during storm (76.7 mm rain in 3 periods amounting to21.5h) following prolonged dry spell16 t 15% potassic superphosphate applied aeriallySamples collected during storm (11.7 mm rain in about 5 h)0.33 t calcium-ammonium-nitrate plus 100 kg reverted superphosphateapplied to PukeitiSamples collected during storm, Pukeiti only (28.7 mm rain)Samples collected during storm, Pukeiti only (17.2 mm of rain)6001 lime appliedSamples collected during storm (47.5 mm of rain)201 15% potassic superphosphate applied aerially, Pukewaengaand Pukeiti onlySamples collected during storm (25.7 mm of rain)85 t 15% potassic superphosphate applied aerially to remainderSamples collected during storm (24.5 mm of rain)(Much overland flow in Storms 7a-c)Samples collected during heavy thunderstorm901 30% potassic cobaltised superphosphate applied with extra 162 kgcalcium ammonium-nitrate on PukeitiSamples collected during storm, Puketitoi only7201 lime spreadSamples collected during storm, Puketitoi onlySamples collected during stormSamples collected during storm (120 mm rain in 24 h)90 t potassic cobaltised superphosphate appliedSamples collected during stormSamples collected during stormSamples collected during stormFencing of stream channel completed; eastern side of channel fenced muchearlier. Stock grazed these areas until August 1974, especially during summer

56

7a

7b

7c

101112

131415

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MCCOLL—CHEMICAL RUNOFF FROM PASTURE 373

samples were analysed for three forms of phosphorus,ammonium, nitrate, chloride, sulphate, magnesium,calcium, sodium, potassium, pH, and electrical con-ductivity. Samples from the first three rain stormswere analysed by the techniques used by McCollet al. (1975). Subsequently a Technicon Autoanalyserwas used for some analyses; ammonium was meas-ured by a modification of the method of Crooke &Simpson (1971); soluble phosphate and nitrate weremeasured by modifications of the methods of Strick-land & Parsons (1968).

Flow rate was noted from the continuous hydro-graph record at the time of sampling. The initial in-flexion of the hydrograph was taken as the start ofa flood. For the purpose of calculating chemical lossesthe floods were judged to have finished when therecession curve had almost flattened off. The periodfrom peak to this point on the recession variedbetween 14 and 48 h in Puketitoi, 13 and 37 h inPukewaenga, and 3 and 20 h in Pukeiti.

Regressions, correlation coefficients, and analyses ofvariance were computed by standard statistical tech-niques. The statistical errors of the estimates of chem-ical losses made using the regression models werecalculated using a technique recommended by Mr T.Darwin (Applied Mathematics Division, DSIR, Wel-lington) in which regression variance, and the vari-ance of the independent-variable data fed into theregression model to make the estimates, were com-bined. Logarithmic transformations (either In x orIn (x + 1) improved concentration/stream flow re-lationships and they were used to normalise flow-rate, time elapsed and chemical concentration data.Novak & Andelman (1974) found that log transfor-

PukeWe2 9

35°4O's\

\N

tl

Pukeiti Flume

S

1

li

i '

"X' ~ N.

\ ^

174°O5'E

LEGEND

, ' Calch

• How

. . - Intern

^S Gull,

I I Bush

\

\ Puketitoi • ~\ Catchme •

i\Pukew

\ i /

Pukeiti /Catchment

waenga'B± \ l

\ Catchment! '1i \

iPuketurua Hill -

me

reco

itte

Sc

t boundary

rding station

t stream

_^

500 m

ale

\

- \

FIG. 1—Location of streams, weir, and flumes in thePuketurua Experimental Basin.

mations of flowrate and chemical concentration im-proved the linearity of concentration/flowrate re-lationships in unpolluted waters

RESULTS

Data for the 1971 to 1972 period have alreadybeen reported (McColl et al. 1975). These data plusthe results of the present study cover the period from22 November 1971 (when the Puketurua Experimen-tal Basin lay fallow after burning, stick-raking, giant-discing, and harrowing) up to May 1974 when thebasin was fully operational pasture farm.

CHEMICAL COMPOSITION OF STREAM WATERS

Chemical analyses of samples collected during 15floods, and at low stream flows, show that the streamwaters tended to be acidic and high in sulphate(Table 2). This partly results from the oxidationof sulphides in the shattered claystone rocks exposedin eroding gullies (Schouten 1976). Mean concen-trations of ammonium, phosphorus, calcium, potas-sium, and sulphate were markedly higher in post-fertiliser floods than in the first two pre-fertiliserfloods (Table 2). The highest chemical concentra-tions recorded in Pukeiti Stream (Ca80g.nr3; K46g.nr3; Cl 93 g.nr3; SO4 156 g.m"3; soluble PO.-P 13.4g.m-3; total P 17.3 g.nr3) followed fertiliser applica-tions. These concentrations greatly exceeded thoseconcentrations found in the waters of the basin in1971 before any fertiliser had been used, and alsogreatly exceed those commonly reported for NewZealand freshwaters.

Peak concentrations of 24.7 g.m"s of nitrate-N and3.8 g.m"3 of ammonium-N followed the applicationof "calcium ammonium nitrate" fertiliser to Puke-iti in October 1972; another peak of ammonium-Nconcentration (2.9 g.m"3) occurred in the rainstormthat followed the second application of this fer-tiliser to Pukeiti in November 1973.

Mean chemical concentrations of most elementswere highest in Pukeiti Stream; downstream at Puke-titoi weir mean concentrations were lowest and leastvariable.

AMOUNTS OF CHEMICALS LOST

When there were sufficient data, the amounts ofchemicals lost in floods were estimated using mul-tiple regression techniques. Chemical losses duringintervals varying from 12 min to several hours wereintegrated over the flood hydrographs using regres-sion models of chemical concentration on flowrate,elapsed time, and cumulative discharge of water.Estimates of chemical losses in Storms 7a, 7b, and 7cwere made using a regression of the bulked dataand apportioning to the three floods. Statisticalerrors of the estimates (P<0.05) were calculated forStorms 8, 12, 14, and 15. The floods were categorisedas pre- or post-fertiliser floods according to fertiliser

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374 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH 12 (4), 1978

history (Table 1). Storm 12 (April 1974) was cate-gorised as post-fertiliser because it was the firstmajor storm following superphosphate application inNovember 1973 and lime application in January 1974.

The estimates show no consistent differences be-tween catchments in the rates of ammonium, mag-nesium, sodium, potassium, chloride, and sulphaterunoff per unit area (Table 3). However, Pukeiticatchment had markedly higher reactive phosphorusrunoff per unit area than Pukewaenga or Puketitoi,especially in post-fertiliser storms. Rates of total phos-phorus and calcium loss from Pukeiti were also mark-edly higher in some storms. On the other hand ratesof "nitrate loss tended to be lowest from this catch-ment. As much as 1 kg.ha1 of reactive phosphoruswas lost from Pukeiti in one post-fertiliser storm.This rate of loss is equivalent to some annual valuesfor agricultural land reviewed by Ryden et al. (1973).Phosphorus losses from the basin as a whole (Puketi-toi) however, were usually small in both post- andpre-fertiliser storms (about 0.004 kg.ha x as reactivephosphorus; about 0.02 kg.ha~l as total phosphorus).The chemical losses in runoff water comprisematerial carried from the ground or its surface, eitherin solution or suspension, and the material originallydissolved or suspended in the rain. Schreiber et al.(1976) point out that a critical quantity of stormdischarge must be exceeded before net loss fromland occurs. Rain samples were collected on severaloccasions in plastic rain gauges which had beencleaned in dilute HC1 and distilled water. Mean con-centrations in the samples (Table 4) were used toestimate the approximate amounts of chemicals sup-plied in rain to the stream discharge during eachflood. With the exception of ammonium, it appearsthat the chemicals in flood discharge were derivedmostly from the ground or materials at the groundsurface. Compared to the rainfall the storm dischargecontained, on average, about 8 times more sodiumand chloride, about 15 times more total phosphorus,potassium, and sulphate, and about 60 times morecalcium and magnesium. Storm discharge sometimescontained less nitrate and ammonium, apparently,than the equivalent volume of rain, suggesting the

land was gaining these compounds from rain. Plottingthe ratio (amount of NH4-N + NO3-N lost): (esti-mated amount in an equivalent volume of rain)against time for each storm (Fig. 2) shows that therewas an apparent fluctuation between net loss andnet gain of nitrogen by the land during the studyperiod. This pattern can be interpreted cautiouslyas an initial net loss of nitrogen compounds result-ing from land clearance and poor vegetation cover(early 1972), a period of net gain of nitrogen fromrainfall when pasture was developing but nitrogenwas in short supply in the soil (late 1972, early1973), and a final phase of net nitrogen loss whenclover was well established in the pasture (late1973 onwards).

DISCUSSION

EFFECTS OF FERTILISER

Floods following fertiliser application to the land(post-fertiliser floods) tended to have higher chemi-cal concentrations than floods with no recent fertiliserevent (pre-fertiliser floods) (Table 2). This cannotbe attributed reliably to fertiliser treatment becausethe floods were of different sizes and chemical con-centrations are often proportional to flowrate. McCollet al. (1975) used multiple regression, and statis-tical comparison of observed and predicted concen-trations to identify the effect of fertiliser on waterquality while eliminating the effects of stream flow-rate and flood duration. This technique involved theextrapolation of pre-fertiliser flood regressions andwas not, as a result, very sensitive. They pointedout the difficulties of performing controlled runoffexperiments when climate, season, soil factors, andvegetation factors are involved.

One way of showing up any fertiliser effect is tocompare the regression formulae of individual pre-and post-fertiliser floods at a range of discharge con-ditions representative of the range of floods measured.Multiple regression formulae of chemical concen-tration on flowrate, elaped time, and cumulative dis-

TABLE 2—Means of chemical concentrations (g.m 3) in samples of stream waters from the Puketurua Experi-mental Basin, November 1971 to May 1974. The pre-fertiliser flood data are from Storms 1 & 3. Post-ferti-

PUKETITOIEarly pre fertiliser floodsPost-fertiliser floodsLow flows

PUKEWAENGAEarly pre-fertiliser floodsPost-fertiliser floodsLow flows

PUKEITIEarly pre-fertiliser floodsPost-fertiliser floodsLow flows

No. ofSamples

577013

516821

327112

pH

4.64.54.7

4.94.24.4

5.66.56.2

NH,-N

0.0080.110.015

0.0194.20.024

0.0400.730.15

NO.-N

0.120.440.011

0.164.20.018

0.110.280.14

ReactivePO4-P

0.0020.0470.003

0.0060.190.006

0.0141.390.097

Total dis-solved P

0.0030.051

0.0074.2

0.0261.49

Total P

0.0630.1220.024

0.140.440.061

0.0921.916.2

Ca

3.19.84.1

2.221.611.9

3.26 . 523.5

Mg

2.14.02.2

2.18.75.5

1.84.03.4

Na

8.311.510.3

8.113.112.4

9.59.8

16.7

K

1.85.31.4

1.66.03.3

2.47.75.0

Cl

1.823.71.4

1.624.93 . 3

18.624.031.0

SO*

164824

1614786

125226

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MCCOLL—CHEMICAL RUNOFF FROM PASTURE 375

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376 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH 12 (4), 1978

O Puketitoi

• Pukewaenga

A Pukeiti

FIG. 2—LOSS (L) of NH4-N plus NCvNin runoff from land "a ttic PuketuruaBasin expressed as a ratio of the esti-mated amount in an eouivalent volumeof rain (R); the apparent gain by landis expressed as a percentage of theamount supplied in rain. The curve isidealised; inferences of loss or gainshould be treated cautiously.

1972 1973

NORMAL SEASONAL PATTERN

charge from each individual flood in each individualcatchment were used to estimate soluble phosphateconcentrations in each catchment stream at floodpeak in hypothetical small (e.g., Storm 14), medium(e.g., Storm 7a), and large (e.g., Storm 12) floods.Excessive extrapolation of the formulae was avoided.The results (Fig. 3) suggest that Pukeiti Stream wasgreatly affected by fertiliser application, PukewaengaStream was less influenced, and Puketitoi Stream wasleast influenced, with phosphorus enrichment occur-ring in only one instance. Analysis of variance ofthe estimates of concentration in small and mediumsize floods showed that reactive phosphate concen-trations were significantly higher in post-fertiliserfloods than in pre-fertiliser floods (P< 0.001), andthat Pukeiti had significantly higher concentrationsthan the other catchments (P<0.05).

BUILD-UP IN CHEMICAL CONCENTRATIONS 1972-74

The above estimates of reactive phosphate (Fig.3) suggest that in Pukewaenga and Puketitoi catch-ments there was no increase in concentrations inpre-fertiliser floods between 1972 and 1974. In Puke-

iti, by contrast, reactive phosphate concentrationsapparently increased in successive pre-fertiliser floodssuggesting that fertiliser applications were havingan increasing residual effect on water quality duringfloods.

BUILD-UP IN FLOODWATERS

Multiple regressions of mean chemical concen-trations, in up to 15 floods, on mean discharge rate,on days elapsed since fertiliser was applied (limeor superphosphate as appropriate), and on cumula-tive quantity of that chemical element applied wereused to test for a relationship between successivefertiliser applications and a cumulative effect onfloodwater quality. Mean discharge rate was includedin the regressions to allow for differences in the sizeof floods. The chemicals examined were reactivephosphate, total phosphorus, calcium, potassium,chloride and sulphate.

In Puketitoi and Pukewaenga, the mean concen-trations of calcium, potassium, and sulphate in eachflood were significantly correlated (P < 0.05, f-tests

TABLE 4—Chemical concentrations (g.m 3) in some rainfall samples, Puketurua Experimental Basin 1972-74.(- = no data)

Date

8 & 9 Mar 19724 Nov 1973

6 Apr 197427 May 1974

MEAN

NH.-N

0.110.0430.0330.1320.005

_0.0860.068

NO3-N

0.0230.0270.018

_0.0050.0200.0040.016

ReactivePCvP

_0.0030.0010.0020.003

_0.0060.003

Total P_

0.0150.0130.0400.020

_0.0470.0 27

Ca

0.50.10.1

—0.10.10.10.16

Mg

0.050 . 10 . 1

_—_-

0.05

Na

0.33.00.2

_1.01.90.61.2

K

0.30.30.2

_0.10.60.10.27

Cl

3.08.50.3

0.12.00.12.3

SO*

3.51.40.1

_2.43.34.22.3

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MCCOLL—CHEMICAL RUNOFF FROM PASTURE 377

0-00112 15

FIG. 3—Estimates of reactivePO,-P concentrations at threetypical but hypothetical floodconditions (low, medium, andhigh discharge rates) using themultiple regression formulaederived from the pre-fertiliser(white histograms) and post-fertiliser (hatched histograms)floods. Reactive phosphoruspredictions from each regres-sion are thus compared understandard flood conditions.

Asterisks mark positions wherehistograms were omitted be-cause extrapolation of the re-gression formula was excessive1.

0-01 -

000112 14 15

0001

Storm Number

of regression coefficients) with the cumulative quan-tities of these chemicals applied in fertiliser between1972 and 1974; in Pukeiti, mean concentrations ofreactive phosphate, and calcium were correlatedwith cumulative chemical applied. Increases withtime in the concentrations of calcium, potassium, andsulphate leaving Puketurua Basin in floodwaters areapparently associated with the build-up of fertiliserchemicals in the soils. Only in Pukeiti, however, didsuccessive applications of fertiliser apparently resultin a significant increase in the concentration of phos-phate in runoff.

Mean chemical concentrations in the floodwaterswere negatively correlated with the time elapsed sincelime or superphosphate application. The inverse re-lationship was most significant in the cases of calciumin Puketitoi (P < 0.01), calcium and potassium in

Pukewaenga (P < 0.1 and P < 0.01 respectively),and of reactive phosphate (P < 0.001), total phos-phorus (P < 0.001), calcium (P < 0.1), and sul-phate (P < 0.01) in Pukeiti.

The multiple regressions were used to estimate thisrate of decrease at the mean flowrate, In (x + 1),and the mean cumulative chemical quantity for eachcatchment. The regressions suggested that chemicalconcentrations in Pukeiti floodwaters had the highestinitial response to fertiliser application (Day 0) butthe most rapid decline afterwards; Puketitoi res-ponded least (Fig. 4). In Pukeiti, at the time when0.19 tonne of superphosphate phosphorus had beenapplied, the mean reactive phosphate P likely tooccur in a flood of 2.6 mm.l r1 mean discharge woulddecrease from 2360 mg.m'3 on the day of fertiliserapplication to 380 mg.m~a 100 d after application. In

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378 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH 12 (4), 1978

Puketitoi the expected decrease in reactive phos-phate P under equivalent conditions would be from7 to 3.5 mg.irr3. Mean calcium concentrations infloodwaters would be expected to decline at a rateof about 30% per hundred days following fertiliserapplication in all three catchments. Mean chloridewould be expected to decline least rapidly.

Results from Pukeiti (Fig. 4) suggest that meanreactive phosphate concentrations in floods might bearound 40% less if heavy rain held off for 1 monthafter fertiliser application but unfortunately NewZealand's changeable climate makes effective controlof fertiliser loss by this means a faint hope.

BUILD-UP AT BASEFLOWS

Multiple regression of chemical concentrations offlowrate and elapsed time (months elapsed since fer-tiliser was first applied) suggests that concentrationsin baseflows increased between 1971 and 1974. Therewere limited baseflow samples especially from Puke-iti and samples taken in the late stages of floodrecessions were included. In view of this, the conclu-sions should be treated with caution. In addition,no account was taken of seasonal variation whichSchouten (1976) found had a major effect on elec-trical conductivity in the waters of the basin.

The results of the regressions (Table 5) suggestthat significant increases of calcium occurred in allcatchments, presumably in response to liming, withthe largest increases in Pukeiti. Large increases insulphate apparently occurred in Puketurua andPukewaenga. While this could result from superphos-phate application, the possibility of increased erosion

of sulphide bearing rock in gullies makes this con-clusion tentative. Ammonium increased in all catch-ments although the increase was not statistically sig-nificant in Pukeiti. Total phosphorus increased sig-nificantly in Pukewaenga and there was a large butnon-significant increase in Pukeiti. Phosphorus levelsat baseflows in Puketurua apparently remained un-changed between 1971 and 1974.

These increases over the study period represent adoubling of magnesium, sodium, potassium, chloride,and sulphate, a 5-to 13-fold increase of calcium, as24-fold increase of total phosphorus in Pukeiti, andan up to 50-fold increase in ammonium. They sug-gest that agricultural development can have a markedinfluence on groundwaters and background levels instreams. Losses of phosphorus and sulphur in base-flows might be controlled by adjusting fertiliser rateaccording to soil adsorption properties but this is aremote possibility since fertiliser requirements willnormally be judged by pasture performance ratherthan stream quality.

DIFFERENCES BETWEEN CATCHMENTS

Phosphorus levels in Pukeiti Stream respondedmost to fertiliser treatment whereas levels in Puketi-toi responded least or not at all. This is surprising asPuketitoi Stream is fed by Pukeiti catchment and arange of other small wholly grassed catchments.McColl et al. (1975) noted that in Storms 2 and 4more reactive phosphate left Pukeiti (1.44 ha) alone,than apparently arrived at Puketitoi weir (24 ha)during these storms, and suggested that much phos-phate was removed from solution on passing down-stream. While this process partly explains the obser-

00 200 300

Potassium

100 200 300 100 200 300

Time (d)

FIG. A—Curves, derivedusing multiple regres-sion formulae, show-ing the rate ofdecrease in the meanconcentration of chem-icals likely to occur infloodwaters in thethree catchments inthe Puketura Experi-

200 300 mental Basin followingfertiliser application.

Puketitoi Pukewaenga - • • • -Pukeiti - - -

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MCCOLL—CHEMICAL RUNOFF FROM PASTURE 379

vations, unless removal is very rapid, it cannotexplain why pasture closer to Puketitoi weir alsoappears to contribute insignificant quantities of re-active phosphate to basin runoff. The explanationmay be found in the catchment hydrology and vege-tation pattern. Pukeiti is a dished, grass-covered areawithout a well-defined stream channel. Flows arerecorded at Pukeiti weir only in winter or as aresult of heavy rain. Puketitoi and Pukewaengahave well-defined stream channels which have beenfenced from stock but are periodically grazed. Thevalley floor on either side of Puketitoi Stream sup-ports marsh or scrub vegetation and there is scrubvegetation alongside Pukewaenga Stream. The fencedarea near the streams, because it is partly moist andluxuriant, is better able to trap and biologically fixapplied nutrients. It may also receive less fertiliser.The channel area in Pukeiti, by contrast, is undergrazed pasture. Fertiliser would remain undissolvedfor longer because of the drier conditions, fixation bysoil and plants would be slower, and under grazingthere would probably be more nutrients present atthe surface in dung and urine.

In smaller floods, where much of the runoff isgenerated in the channel regions, these differencesbetween catchments would be clearly emphasised. Inwinter floods in the Puketurua Basin, when wide-spread surface runoff predominates in the flood hydro-graph, the marsh region of the stream channel acts asa "reservoir" area ponding runoff from the surround-ing sub-catchments (Schouten 1976), and allowingsettlement of particulate matter and intimate contactof the runoff waters with the luxuriant vegetation.

The combination of chemical adsorption duringdownstream transport and hydrological differences inthe stream channel regions could explain the differ-ences in phosphorus runoff between catchments.

ENVIRONMENTAL AND AGRICULTURAL SIGNIFICANCE

This study of a Northland basin demonstrates thatsignificant changes in water quality followed conver-sion to pasture with associated fertiliser application.Schouten (1976) drew a similar conclusion from hisstudy. The concentrations of most chemicals ap-parently increased in baseflows over the period Nov-ember 1971 to May 1974, and increases in chemicalconcentration in floodwaters often correlated withthe amount of that chemical applied in the fertiliser.

The chemical runoff comes from the atmosphere,eroding gullies (see Schouten 1976), and soil, aswell as from fertiliser. The losses however, can becompared to the amount of fertiliser applied as aguide to the fertility losses. On average in post-fer-tiliser floods, less than 0.9% of the fertiliser phos-phorus was lost from Pukeiti as reactive phosphateand less than 1.2% as total phosphorus (Table 6).The percentage losses from the basin as a whole(Puketitoi) were even smaller. Calcium losses inpost-fertiliser floods were also a small proportion ofthe amount applied in fertiliser (less than 3.4%)and potassium losses were about 6%.

Since the potential for fertiliser loss will tend todecrease with time after application (Fig. 4), it isunlikely that phosphorus and calcium losses of thisorder will be of significance to farmers. Sulphatelosses, however, were on average 36-60% of theamount applied in fertiliser and this may give someconcern.

However, any increase in phosphorus loss from landmay have environmental significance, and phosphoruslosses of the magnitude of those in Pukeiti couldhave strong influence on waterways and lakes. Puke-iti Stream had concentrations of reactive phosphateas high as 13.4 g.nr3 and Pukeiti catchment lost asmuch as 1 kg.ha * in a single storm. Concentrationsleaving the Puketurua Basin as a whole, however,were considerably lower. With the exception of aheavy storm, which occurred the day after fertilisertopdressing operations, when concentrations averaged0.52 g.nr3 for about 3 h, concentrations of reactivephosphate leaving the basin fell in the range 0.001-0.035 g.nr3. The greatest quantity of reactive phos-phate lost from the whole basin in any of the floodsmeasured was about 0.018 kg.ha * and the mean losswas estimated to be only 0.004 kg.ha"1. It can be con-cluded that although partis of Puketurua Basin suchas Pukeiti catchment have the potential to releaseconcentrations and quantities of phosphorus whichcould have considerable impact on the trophic stateof receiving waters, the basin as a whole after 2i yof agricultural use released! phosphorus at rates lowerthan those from some natural and undisturbed catch-ments.

Caution is therefore needed in extrapolating theresults of small catchment or runoff plot studies tolake catchment investigations. Farm development inthe Puketurua Basin up to May 1974 apparently

TABLE 5—Estimated increment of change in mean chemical concentration in streams at baseflows, PuketuruaExperimental Basin, November 1971 to May 1974. Increments were estimated from simple regressions ofconcentration on elapsed time (* = P < 0.05, ** = P < 0.01, *** = P < 0.001, NS = not significant)

ReactiveData NH4-N NOs-N PCvP Total P Ca Mg Na

Catchment points (mg.nr3) (mg.m-3) (mg.nr3) (mg.nr:!) (g.nr3) (g.nr3) (g.m 3)Puketitoi 15 +57 c - 3 +5 +7.2 +2.2 +2.4

K(g.nr3)+ 4.3

Cl SO*(g.nr3) (g.nr3)+ 7.1 +44.1

Pukewaenga 14 + 39

Pukeiti 10 +180NS

NS+ 94NS

+ 777

NS0

NS+ 99NS

NS

+ 756NS

+ 13.3

+ 43

+ 5.6

+ 0.7NS

NS+ 0.7NS

+ 5.1NS

+ 1.8 -2 .3NS NS

+ 2.7NS

+ 14.6NS

+ 96

+ 20.4NS

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380 N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH 12 (4), 1978

TABLE 6—Means of the estimated chemical losses (%) in post-fertiliser floods expressed as a percentage of theamount of the chemical spread in the preceding application of fertiliser, Puketura Experimental Basin,1971-74.

PUKETITOIMeanRange

ReactivePO4-P

0.014(0.001-0.02)

PUKEWAENGAMeanRangePUKEITIMeanRange

0.11(0.002-0.39)

0.9(0.55-1.6)

Total P

0.36(0.02-1.4)

0.49(0.26-0.65)

1.2(0.8-1.9)

Cal

1.1(0.5-1.7)

1.8(0.5-3.6)

3.4(0.5-7.4)

K

5.9(1.3-14)

6.8(2.3-15)

5.9(0.9-13)

Cl

47(8.4-146)

35(11-86)

30(6-63)

48(16-122)

60(24-102)

36(17-57)

caused minimal phosphorus enrichment downstream.The findings of this study provide strong support

for the use of buffer strips of vegetation along streamchannels as a means of protecting streams from phos-phorus losses. Attention to hydrological properties ofthe catchment and preservation of stream bank vege-tation could result in a significant reduction innutrient loss from land. This study provides strongevidence that it is runoff water which flows directlyfrom pasture to receiving water without the interven-tion of stream bank or channel reserve that poses thegreatest risk to water quality.

ACKNOWLEDGMENTS

I am very grateful to Ministry of Works andDevelopment staff, particularly Dr C. J. Schouten whocollected most of the samples and provided valuablecomments on the manuscript. Mr M. Downes andMiss B. Don of Ecology Division, DSIR, kindlycarried out a large part of the analytical work andMr A. R. Gibson, Soil Bureau, DSIR, performedmuch of the computer work. This work was initiatedin co-operation with Dr E. White and Mr J. R. Waughwhile I was a member of Ecology Division, DSIR.

LITERATURE CITED

CROOKE, W. M. & SIMPSON, W. E. 1971: Determina-tion of ammonium in Kjeldahl digests of crops byan automated procedure. Journal of the Science ofFood and Agriculture 22: 9-10.

MCCOLL, R. H. S., WHITE, E. & WAUGH, J. R. 1975:Chemical runoff in catchments converted to agri-cultural use. N.Z. journal of Science 18: 67-84.

NATIONAL WATER & SOIL CONSERVATION ORGANISA-TION 1968: Hydrological Research Annual Report13, Puketurua 1 (up to December 1966). Ministryof Works, Wellington, N.Z.

1970: Hydrological Research Annual Report14, Puketurua 2, (1967-1968). Ministry of Works,Wellington, N.Z.

1971: Hydrological Research Annual Report16, Puketurua IHD Experimental Basin (3-4 for1969-70). Ministry of Works, Wellington, N.Z.

NOVAK, S. M. & ANDELMAN, J. B. 1977: Analysis ofthe effect of stream flow on nitrogen and phos-phorus in the Ohio River. Pp. 379-98 in Suffet, I.H., (ed.) "Fate of Pollutants in the Air and WaterEnvironments" Part I. Wiley, New York. 506 pp.

RYDEN, J. C, SYERS, J. K. & HARRIS, R. F. 1973:Phosphorus in run-off and streams. Advances inAgronomy 25: 1-45.

SCHOUTEN, C. J. J. H. 1976: Origin and output ofsuspended and dissolved material from a catchmentin Northland (New Zealand), with particular ref-erence to man-induced changes. PhD thesis lodgedin the library of the University of Amsterdam.180 pp.

SCHREIBER, J. D., DUFFY, P. D., & MCCLURKIN, D. C.1976: Dissolved nutrient losses in storm runofffrom five southern pine watersheds. Journal ofEnvironmental Quality 5: 201-5.

STRICKLAND, J. D. H. & PARSONS, T. R. 1968: Apractical handbook of seawater analysis. FisheriesResearch Board of Canada Bulletin 167. 311 pp.

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