Simon Townsend - territorystories.nt.gov.au · a ,,,ere collected at approximately monthly...

Technical Report WRD94064

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Simon Townsend

Chemical Stratification in Darwin River Reservoir

Report 64/94

Water Quality Research and Evaluation Branch Water Resources Division DARWIN


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This report was presented at an international conference on tropical limnology held in Indonesia, July 1994. The paper will be included in the conference proceedings in a special edition of the journal Hydrobiologia.

This report shall not be copied without the permission of the author. Anyone quoting inforwation or data from this report and using that infoLHlation or data in any other document shall make proper written acknowledgement .


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.n.bstract

Oxygen depletion during stratification, which is

characteristic of eutrophic lakes in temperate regions, is

shown to occur in an oligotrophic, tropical reservoir. Deep

water deoX"ygenation in Darwin River Reservoir, Austral ia,

was highly responsive to thermal stratification. Rapid

oAy-gen depletion rates (maximlliLl 12.2 mg 1-1 month-I) and

long periods of anoxia (maximurn 20 1,o1eeks) 'iN"ere recorded in

the hypolirnnion and metalimrlion. DeoX"'ygenation vias

attributed primarily to the reservoir's elevated

temperatures (-25-30 'C) and its effect on microbial

metabolism. ~lorphometric influences ',-.rere considered

secondary. Periods of enoxia occu!'"red during the dt:.:~-\.;et

season transition end after wet season holomixis .. ilnoxia

calls'ed orl accurnulat lOr! ot iron, ma.nganese and arp!nonia In the

... ~, , me .... al.l.rru'l~on . P' -nospnorus release C~orn ~h'" sec'; men t c ho' --"e Y !..;... :t L. ~ ...... : ~~ ..... ·.·i~'/ _

was not detected due to its relatively 10''''; concentration end

immobilization. T'he efEect of terr.perature or. hypolimnetic

dissolved oX"y'gen depletion rates in lakes is rr.ore

significant than either morphometry or productivit.y.

2


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1. Introduction

'The hypolimnion of warm, tropical lakes is more susceptible

than that of temperate lakes to anoxia and pronounced

chemical stratification. This is due to the reduced

solubi 1 i ty of OA,},gen at higher temperatures coupled wi th

increased microbial metabolism. This paper describes

chemical stratification in Dar"vin River Reservoir {DRR} I a

tr"opical ;"-later body of low trophic status. Data collected

over a six year period sho\\' the effects of year to year

climatic variation on various stratification characteristics

including oxygen depletion rates. The reservoir, despite

its 10'''; trophic status, exhibits marked chemical

stratification with long periods - . or aDOXl.a.

2. Study site and methods

DP~~ (12' 54' S, 131· 00' E) is located 50 ~~ inland from the

coastal city of Dar.'lin. ~.t full capacity the ~;late!:' body has

a mean depth of 6~5 fit maxim~~ depth of 20 m and storage

Volu.lne of 260 x 10 6 m]. It is broad and shallm'/, with

c.pprox.::..mately 90% of the total reser~,,"'oir volume contained in

the upper 10 ID. The dfuTl'S catchment is dominated by eucalypt


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woodland, and managed by a "closed catchment policy" which

excludes almost all human activity.

The regions climate comprises of two seasons, the 'wet' and

the 'dry' > Cool, dry, south-easterly trade winds, of

continental origin, are the dominate feature of dr.t> season

weather {May - Oct}. In contrast, the wet season

(Nov - lmril) is characterised by ViaL"', moist winds, of

maritime origin. Monsoonal bursts end depressions produce

sustained rainfall lasting several days during the f7-.'iet!.

~Jater colu..rn.:.'"1 temperat.ure l dissolved oxy"gen,. conductivity end

pH were measured at one metre intervals a.t the deepest site

by a Nartek Nk XV or Hydrolab Surveyor 2 rnultiparameter

probe between ,.Julj/ 1985 and Jur~e 1991 .. "A. total of 237

profiles were measured, beti,<leen 09:30 and 10:30 hours , at

weekly or fortnightly intervals over most oE the study

period. The probes were calibrated prior to each field

according to the manufacturers direc:.ions. Rair;fall data for

Dar-ylin Jl.~irport was provided by the Aestralian Bureau of

Heteorology>

Water samples for analyses of total iron , total manganese,

total phosphorus, arr~onia, nitrate, nitrite and chlorophyll

a ,,,ere collected at approximately monthly intervals at

depths of 0, 41 St 12, 14, and 16 m~ In the last year of the

study/ Sful1pleS itlere taken for the analysis of


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nutrients and chlorophyll a. Once a year, samples were

collected from the surface and from 14 m depth for total

alkalinity analysis. For most of the study period, total

iron and manganese ",,,-ere analysed on unfiltered samples.

During the last three months, though, these metals were

determined by the SQm of their respective filterable and

residual components. The analytical methods used are

surrmarized in Table 1. k~~nia, nitrite and nitrate

concentrations are expressed as elemental nitrogen.

HypolillL'1ion and metalimnion mean oxygen concentrations and

depletior~ rates are volume weighted end aSSLLrne cn epililnnion

Isopleth data for iron, w~nganese and a~~onia

concentrations are presented only for periods of detailed

data collection.

In June 1993, SCUBA divers collected three samples £rc~,,(l a

flocculent layer above the sediment {"'vater depth lS m} .

These sa."'TIples were oven dried at 105 ·C and analysed for

loss on ignition, kjeld.:.'1al nitrogen and total phosphorus by

the met~ods listed in Table 1. Total al~uiniurr~1 calcilli~;

iron and manganese concentrations in the sediment h,"ere

detelmined by inductively coupled spectrometry after

digestion with e~~al portions of concentrated nitric and

hydrochloric acids. A particle size analysis was performed

on one sediment saInple by sieving and suspension {Loveday

1974) for the following particle size fractions; clay


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«2 ~~), silt (2-20 pm), fine sand (20-200 ~~), coarse sand

(200-2000 ~~) and gravel (>2000 pm).

3. Results

3.1 Seasonal stratification and mixing.

Figure 1 shm..;s isothe!."ls for a two year peri.od I-Ihich

featured characteristic d0/ season stratification and mixing

but contras ting ,yet season thermal behaviour. The

wet seasons had total rainfalls ot 1180

and 2220 rmn, respectively. This is reflected in the

diffe~ent wcter level changes of the reservoir in Ja~ucry

and Feb!.'"uar.x".

Heat loss and strong south-easterly trade winds completely

mixed the reservo~r I for up to three weeks J each dr:! season

(Hay - August). During periods of rela;:ive calm, however,

the ~,.,ater body stratified with a maximuIn vertical

temperature range of 1-2 ·C~ MinimlUTI reservoir temperacu!."es

usually occurred in July~

Prolonged stratification, lasting several months, develoged

ae the beginning of the dr~-wet transition iAug, Sep).

Initially the reservoir stratified with a classical

layered theLllal structure {ego Aug 14 1986, Fig 21. The


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hypolimnion, however, ItlaS progressively eroded by the

metalirrUlion. rrne interface between the tViO layers was

marked by an change in the temperature gradient which

deepened during the dry-wet transition period (Fig. 2) and

ot.her periods of stratification. Most of the reservoir's

V01U!l1e (-90%) during stratification ItlaS contained within the

epili~,ion, which extended to 10-12 m depth.

Monsoonal weather caused t.he resec,,'oir to cool and

completely mix, usually for 2-3 days. This occurred every'

'",let season excluding the 1989/90 'wet I v/hen monsoonal

weather was brief and had little impact on the reservoir's

thermal structure I}. When weather conditions cieared l

the reservoir restratified. NaximtlJt1 ' .... ater temperat.ures ;,,-le:r:e

recorded towards the end of the wet season, generally in

March. The reser~.,.·oir then cooled over the wet-dry transition

(April} Hay} and either gradually destrac.ified or

eAyerienced alternating periods of deep vertical sixing and

stratification. A more detailed account of the reservoir' 5

~, 1 ,-Derma reglme is published elSEwhere (Tc'\'VTlsend et al.

1994 j •

3 ~ 2 Stratification of dissol vee oxygen

The pattern of the.:..lllal stratificat.ion \-laS reflected in the

distribution of dissol":led orygen (Fig. 3). The longest

period of stratification of dissolved oX""ygen occurred OVer


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the dry-wet transition (Aug/Sep - Dec/Jan). Between the

cornmencement of stratification and onset of anoxia, average

oX'.Igen depletion rates were 2.4 - 4.6 mg 1-1 month- 1 (mean

3.3 mg 1- 1 month-I); the maximum rate was

8~7 mg 1-1 month~l. At the epili~nion-metalimnion interface,

a pronounced oX'.Icline often developed coincident with a

small temperature discoI'.tinui ty (<1 . C m- I ; Fig. 2).

Hetallmrlion-hypolimrlion aI'.oxia over the drl'-wet trar,sition

lasting 5-20 weeks and usually

commencing in October. The earlier Grlset of therrnal

stratification, in August 1985, favoured a long period of

strat i f icet ion of dissolved o;.,.ygen (Fig. 3). On the other

hand, the timing and extent of monsoonal "t.'leather det.el~dined

\'let season holomixis and the end of this . • r perJ..oa 01.

stratification. This occurred in Dece:rrber or Januari each

Viet season except during the 1989/90 Iwet t when the

reservoir remained stratiEied until the transition oet\';€en

the wet and dry seasons in April.

Depletion rates of dissolved oxygen during the dr./-wet

transition were affected by variation.s in the rese:!':'loir's

vollli-ne. ~vater level fluctuations of 3.4 m caused the

metaLLmnion voltune to vary between 2.5 x 10 6 m3 and

1 - 106 3 ~h . ~h . l' . 1 x ill I ~ ouan ~~e epl~lmn~on to

rnetalimnion-hypolimnion ratio (- 10) remained constar:.t.

Depletion rates were inversely related to

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metalimnetic-h}~oli~~€tic volume. A Spearman rank

correlation test of mean oX'.fgen depletion rate and

metali~~ion volume for each year explained 36% of the total

variance (P<O.05).

Ttlhen the.:...dtal stratification first developed in the early

dry-wet transition, dissol\red OA.:t'gen concentrations were

. , -1 . between 5.8 and 8.3 mg.l. A lugh initial oxygen

concentration would be expected to delay the development of

metali~~etic-hypoli~,etic anoxia because of the greater

amount of oxygen available. There was no significant

Spearman rank correlation (P>O.05) however between the

initial dissolved ox-y-;en concentration and time for

metal irrt'1ion-hypol imnion anoxia to develop. Other factors,

such as inter-annual differences in the degree of theLdlal

stratification, probably overvihell7l the influence of initial

OAygen concentrations.

.

Deep vertical mixing following a period of stratification

produced an OA.fgen sag through the water COllliUD (Fig. 3) due

to the ox~gen demand of the former metaliu~etic and

hy-polimnetic waters and dilution of the former o:.-...ygenc.ted

waters. This was most pronounced during ','~'et season holomixis

;',fhen surface oxygen concentrations decreased by as much as

- 1 1 - i ...::::. mg _ -, returning to pre-holomixis concentrations Vlithin

1-2 weeks.


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I'[nen the reservoir restrati f ied after wet season holomixis,

metallmnetic and hypolinmetic oxygen was quickly depleted,

often at rates higher (maximum 12.2 mg 1-1 month-I) than

those recorded over the dry-'ttet transition. p.~"lOxia, lasting

2-6 weeks, was reached during most wet seasons .. Longe~'

periods o-f: anoxia were prevented by deep vertical mixing and

Cl~c>ct-'r-ltl' f'f'ac' l'on o"er ~he W"'~ dry ..... r--.-:::it-ion '-' .... '-..-~(:.J, J......,. v L~ ~l.,..-,j.., '-_c:.!! .... _~_ •

Dr,i season holomixis produced water colunL,,! oxygen

concentrations of 80-100% saturation. wnen the south-east

trade winds eased however, thermal stratification developed

accompanied by hypolimnion oX"".:(gen depletion at rates similcr

to other periods of stratification. In July 1989 and 100 0 --'-' ,

for eXfu'11ple I oxygen concent rat ions Hi thin the hypol irnnion

decreased by 2.4 mg I _1

_ - over a one week period. Dry season

strati. f ication of dissolved OKy'gen pers isced for c maXlffiUIn

of 2-3 weeks, too brief a period to allow anoxia to develop.

3.3 Cherrdcal stratification.

Nitrate and nitrite were present in ~le;::-:! lO'd concentrations

in DK"' .. Nitrate concentrations were <0.001 - 0.002 mg 1-1 In

98% of sarr~les, whilst nitrite was not detected

«0.001 ma 1-1 ) in any samples. Nitrate would not therefore

haVe been a significant terminal electron acceptor in

microbial metabolism.


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Higher concentrations of ammonia at the sediment-water

interrace of DRR (Fig. 4) indicated conversion of organic

nitrogen in the sediment to fu-nrrlonia and its transportation

to overlying waters (Fig. 4). Concentrations of ammonia

decreased exponentially with distance from the

, _ 1) . sediment-ftlater interface {maximtun 1.3 mg .!. - to

undetectable amounts «0.01 mg 1 -1) at the ox-xcI ine.

Destratification and oxidation of arn.lTlonia caused temporary

high nitrate concentrations of 0.005 - 0.01 mg 1-1 through

che water colUITn.

Iron ane manganese acc~~ulated in the metali~nion of DRR

1.10 ,_'0 ~) .J , reaching concentrations 2-3 orders of magnitude

higher than typical epilirnnetic concentrations

-1 1-1 ) m' (0.05··0.10 mg 1 - Fe; 0.01-0.05 mg Hn. d1e maXlmu..rn

hypolimnetic concentrations of iron and manganese measured

\'lere, respectively, 7.1 mg 1- 1 and 1.5 mg 1- 1 , The ratio of

iron to manganese concentrations (3:1 - 10:1) in the

hy-polimnion was higher than their ratio in the sediment

(50:1; Table 2) because manganese is reduced at a higher

redox potential than iron {:tsfortirner 1941). 'flet season

holomixis distributed both metals through the water coll.lJ.-nD(

increasing surface concentrations 5-10 times for several

days until stratification re-established. Similar

concentrations of iron and manganese were occasionally

11


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measured during the dry-wet transition in the epilimnion due

to the entrainrr,ent of metalirnnetic waters.

In the latter part of the dry-wet transition, sulphide was

detected by smell in samples collected within 2.5 m of the

sediments. This field observation provides indirect evidence

of a minimum redox potential (corrected to pH 7) of

0.10 - 0.06 V in DRR (Hortimer 1941).

H}~oliunetic and metalinmetic total phosphorus

concentrations were similar to those mea.sured lD ox~{gena::ed

\vaters (0.002-0.006 mg 1-1), suggesting there is little

~elease of phosphorus from the sediments.

The conductivity of epilimnetic waters ranged from

6 _1

55 to ·5 ~S em -. h h'" .' . . t.lOUg. n~gner conauctlvltl.€S

{maximlllLl 140 !-is C1U- 1 } ;'\i'ere measured near the sediment-\'la.ter

total alkalinities were 30-40 mg 1-1 (as CaC03). Oxygen

depletion in the h}~oliIDnion end metalirrnion of D~~ was

accompanied by decreaSed pH (Fi-;; 6), ;'.t the cormnenC~\1ent of

thermc.l stratification, minimuzn pH values 'Here loca.ted at

the sediment-water interface. with cQmplece metalinmetic

. 1 t-' oxygen cep e_lon, pH miniIT~ were located higher in the

profile. near the oxic-anoxic interface, 0.1 - 0.2 pH units

less than those measured close to the sediment-IVater

interf~ce.

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The pilrticle size distribution of DEE's sediments indicilted

the follo·.,· ... ing composition: 36% clay, 16% silt, 35% fine sand

and 13% coarse sand and no gravel. Sediment loss on

ignition, an approximation of organic material, was 20%.

l-lean sediment concentrations for nutrients and metals in DRR

are Slli[~liarized in Table 2. Concentrations varied from the

mean by a maXlITtUm of 14%.

Chlorophyll a conce~trations in the e~photic zone of ORR 1

which extended to 10m cepth (Toy,'I1send et a 1. 1994), had a

median concentration· of 3.5 mg m- 3 , and 10 and 90 percentile

1 = - 0 . ~ 8 -3 va_ues o!....::. anc:J. mg m .

The t~ophic status of DRR, based on the totcl phosphorus

criteria of Carlson (1977), Sakamoto (1956), USSPA (1974)

c!:'iteria classify the reservoir as either ol.igotrophic

(USEP_~. l Q7d) o~ meso-ol;-o"rAp~;r (C-r'~A--" _ ~. ......'::! '-- "-' _._.... , c:. ......... v~l Sakamoto

1966) .

4. Discussion

Deep water oX1gen depletion is a functicn of la.ke

productivity, morphometry and water tempe!:"ature {Cha!.~lton

1980, vollenweider & Janus 1982). Rates of dissolved oxygen

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depletion in the hypoliITL""1ion tend to increase with the

trophic status oE a lake. Hypolimnetic anoxia typically

occurs in eutrophic I temperate lakes and is considered

characteristic of eutrophic conditions (Cole 1983, Goldmann

& Horne 1983, Wetzel 1983) .

The eEEect of DK"l's 1m., trophic stacus on oX"ygen depletion

rates is cDuntered to some extent by the reservoirrs

morphometry which has a large epilim.netic volu . .l.ue compared to

its hy-poliITh'1ion and metalirr~T1ion vollL."!,e. Such volili-netric

ratios f.a~lour rapid oXJgen depletioD because of the small

oxygen mass available for oxidation compared to a lak.e ',·lith

c relatively large hypolirr~ion and t~e same temperature and

productivity ratio Q£ the

hypolimnion volth'11e to sediment surfa::e area f a potentially

significant source of oxygen demand l is smaller than in

lakes with relatively large hypolinE:ions.

To assess the influence of lake trc;r-.ic s~atus anc

rnO'!..pnometry \..;::--~ilst accounting for tje i:1fluence of

teILtgerature, oX"},rgen depletion rates ~~:Gve been sta:"!dard,:,sed

to 4 ·C by seve:::-al authors t aSSlli7.i.::Q a Ql0 of 2

(eg. Charlton 1980 1 Vollenweider & Janus 1982, Ferris &

~yler 1992). D~q's Bean temperature corrected oxygen

depletion rate for the dry-wet trar:sition, vlhen hyorpoliIT'lnion

and metali~~ion temperatures 26 ·C, was 0.72 mg


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~h--l T'-IEont...._ _ nlS , l' h 1 h" h h ' lS S 19 t_y 19ner t.an t .. e temperacure

corrected median rate

(0.51, range 0.01 - 2.11 mg 1-1 month-I) for 21 north

l'.mer'ican and European lakes studied by Vollenweider & Janus

(1982). It is also higher than the long term mean for Lake

1 -1 h-1 ' Burragorang (0.58 mg mont. -; FerrlS & ~~ler 1992), a

deep !'eservoi:.c in temperate .p~ustralia of low trophic status ~

• The ::relatively high; temperature corrected oX""y'gen ciepletion

rate of DP~ is attributed to its high epiliwnion to

h~~olirrnion-metalirrL~ion vol~~e ratio rather than the

reservoir's trophic status.

The calculated relationship between tempe:rature ana mean

hypolimI1ion-metalimI1ion deplec.ion re.te in DR? durir!g the

is shown .In Figu!:E 7~ Because t!-le rate is

exponential, small t~'1lperature chan~es can have considerable

impact on depletion rates and the pe:-icd of anoxia . . ~.

hypolinL'I1ion-metalimnion te.-nperature of 13.5 ·C, \v'hich yields

1_, ,-1 l' me - mont~ - J WOU_G noe. produce

in DPR anoxia during the dry-wet transition. This

temperature is higher than that recc-~ded in most tempe::ate

monomictic, and all dimictic, lakes. Straskraba (1980)

predicts a bottom te~perature of 13.5 ·C in lakes 30 m deep •

to occur at latitude 24·. The trends SnO'NTl in Figure 7

, , h empnaS1.Ze t.e influence of t&uperatu=e on oxygen depletion

ra ~e<; 1.'" ~UD" the sam" rese"-"Toir _in,;.;, .......... !T' ..... e ..... ,=. .... e ..... ':m~i-o:l 1-.... .l.. "-"':;"1 ._.1.. '. _ ..... L.e;,!..,~ J... ..... L I"....l...l.., 0,1....."

\"'lould probably not develop anoxia aT!c pronounced chemical


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stratification, The affect of temperature in warm tropical

waters on .oX"Jgen depletion rates is probably more

significant than either morphometry' or productivity,

rapid development of stratification ~n the tropics, due to

high insolation rates and the relatively large density

dif fer-ential of vfaLd waters, further increases the

likelihood of OA1'ge1'. depletion in warm tropical waters

compared to temperate waters,

Vollenweider & Janus (1982) examined the statistical

relationship betvleen lake morphometry (maximum depths

26 - 406 m) and trophic status (chlorophyll a concentrations

1.1 - 17 mg m- 3 ) I and temperature corrected hypolimnion

depletion rates for: several temperate lakes. A

Iilultiplicative regression, using log transformed

Chlorophyll a concentration" euphotic depth and mean depth

was founc to explain 91% of the variability of o)..'ygen

depletion rates. Although D?~ falls outside the morphometric

range of the lakes examined by lilollenweider & Janus (1982) I

the regression predicts a temperatu~e corrected depletion

( Il C9 1 -1 ,-1) -' - 1 rate ~.C mg ~ montn c~mos~ equc_

average (0 ..,~

, ,L. --1 ,-I) mg 1. - montn .

Decreased hypoliM,ion pH is also characteristic of

r.. <"m,pe-"r.· A OT1tropi-l~c h 7-l-er'" ('\"er-_'7eJ 19B.-'\), hu·r as is ;::;:."ria'enlt _~. ;.. ..... ~J ...... -.... ~_.J. .1Ct- ..... 1 _____ ~-' ...,. _ _ __ _ _

from DRR data, low pH values can also occur in the

metaliITlJ."!.ion and hypoli!..llIlion of tropical lak.es of low trophic

16


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status. The pH profiles with minima in the upper layers of

the anoxic metalimnion recorded in D~q are classified acid

heterograde by Hutchinson (1957). These occur in watex's of

low buffering capacity and are due to the transport of

ferrous and manganous bicarbonates from the sediments to the

overlying waters, raising the alkalinity of these waters and

neutralising the acidity of carbonic and organic acids.

Reductive solublization of ferric iron "las not accompanied

by phosphorus release from DP<-.-R. r s sediments due to its 101,0.1

concentration and i~mobilization. Compared to the total

phosphorus concentration of othe:r- lake sediments \o;ith

concentrations of <0.10 - - 1. . . 10.1 mg g - or.! :,,"elgnt. (Bartleson

& Lee 1974, Bostrom 1984, Flanner.! et el. 1982 and Klap .. ·,rijk

,. . 1G8?' e~ al. _ ~), the phosphorus content of D~q sediment

(0.36 mg g-l) is relatively low. The different flux of iron

and phosphorus at t:he sediment-water interface is due t:o the

high sediment stoichometric ratio of. Fe:? {3S:1) ;·;hich is

considerably greater than the ratios (1:1 - 22:1) at t.he

sediments investigated by the above auc1:.ors. A large

proportion of DRR sediment phosphorus is probably

imrr~bilized as apatite, allliuini~~ pnosphctes t refractory

organic compounds, and sorbed to clay minerals and

h~T.ic-iron complexes (see Bostrom et al. 1982) .

• Stratification in DRR and the det·/elopmenc of anOXl.a resul:::ed

III a significant flux of nitrogen l but ~!detectable fuuounts


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of phosphorus, from the sediments. Holomixis, after

prolonged stratification, will increase the N:P ratio of the

reservoirs surface waters and may affect its phytoplankton

ccrrrrnunity. Such an effect, ho\.,rever I will be minimal in DRR

due to its relatively large epilirnnion to

hypolimnion-metalironion volumetric ratio, but mav' be . -significant in other oligotrophic, tropical water bodies of

di f ferent morphometry.

Acknowledgements

Dr K. Boland «dater ?esources Division, Northern Terri:ory

PO"IOY Cl-no' rA;ater 'uthorl· t-vl p. rof~_ssoT' n, '.-:r_~ ffl' >-hs ~ .... _ ... f"' •• : __ <~ _ _ -...., ~-'- .... '- (James

Cook University of North Queensland) and Dr J. Luong-Van

(Northern Territor,/' University) for COnlI71ents 0[1

an earlier draft of this paper,

Re£erences

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and wast.e .... Jaters, 16th ed. ~.merican Public Eealth

Associat ior., ;. .... '11erican ~'ljater liiorks Assoc., &uerican

Pollution Water Pollution Control '""'~ ,> rec.eraclon f

New York 1268 pp.


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Bort1eson, G.C. & G.F. Lee, 1974. Phosphorus, iron and

manganese distribution in sediment cores in six

\'iisconsin lakes. Limnol. Oceanogr:. 19: 794-801.

Bostrom, B., 1984. Potential mobility of phosphorus in

different types of lake sediment. Int. Revue ges.

Hydrobiol. 69: 457-474.

Bostrom, B., Jansson, M. & C. Forsberg, 1982. Phosphorus

release from lake sediments. Arch. Eydrobiol. Beih.

E . . . • , 8 5 50 ... rgenn, LlrnIl0.l _ ..L: -,., .

Carlson I R.E., 1977. A trophic state index Eor lakes.

Charltonf

H.N., 1980 ~ Hypolimnion ox-Jgen consumption In

lakes: discussion of product i vi ty end morphometry

effects. Can. J. Fish. Aquat. Sci. 37: 1531-1539.

Cole, G_~ZI_" 1983. Textbook of lim.r101ogy. The C.V. Hosby

Co .. St. Louis, 464 pp.

Ferris, J .M. & P.A. TJ"ler, 1992. The effects of inflow and

outflo\·, on the seasonal behaviour of a stratified

~-s-~"o;r ;n temperate ~u~"r-;:-_>::::: t:: ..... \I ............ _ .U _ __ .... L Cl..i....i...C - a 20 year analysis.

Arch. Eydrobiol. 126: 129-162.


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20

Fla!1nery, H. S., Snodgrass, R. D. & T. J. K'1itmore, 1982.

Deep \>/ate~' sediments and trophic conditions in Florida

lakes. Hydrobiol. 92: 597-602.

Gol&~an, R.G. & A.J. Horne, 1983. Limnology. McGraw-Hill

International Book Co, Japan, 464 pp.

Hutchinson, G.S., 1957. A treatise on 1 iTImology , vol. 1

Geography, physics and chemistry. J. i/Jiley & Sons,

Nev.; York. 1015 pp.

Kl-O\'li";1~ S D ___ 0. -J!."., .... . J Kroon, J.M.W. & M-L. Meiier, 1982 .. ;vailable

phosphorus in the lake sediments in The NetherlaTIds.

Hydrobiol. 92: 491-500.

Loveday, J. , 1974. Methods o~ for irrigated soils.

Commonvrealth Bureau of .z:'.Qricultu::-e .. :O.ustralian

Goverlli-nent Publishing Se:r-vice, Canberra; 64 pp.

Mo "-" 'me- C U • _ .... ..1.." _: .,i.,i. • , 1941. The exchange of di22.o1vec. substances

'oP~"een m'ud -na.- • '-"e"- in i ake" ., ;:--0 1 ?9' 208 ,~Q _,-w ... ~ t C. .·.c~ _ _.:.~ ~ ....... I..... _ ...... _, ...... - _':'.J •

Saka~oto, M'l 1966. Primary production by phytoplankton

corrmunity In some Japa~ese lakes and its dependence on

lake depth. Arch. Hyarobiol. 62: 1-28.


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Straskraba, N., 1980 .. The effects of physical variables on

freshwater production: Fnalyses based on models. In

E.D. Le Cren & R.R. McConnell (eds) , The functioning

of freshwater ecosystems. Cambridge University Press,

England, 13-84.

Townsend, S.A., Boland, K.T. & J. Luong-Van, 1994. The

thermal regime of a medium sized water body

(Darwin River Reservoir) in the Australian wet/dr.!

tropics. submitted Arch. Eydrobiol.

USEPA, 1974. p_~ approach to the relative trophic index

system for classifying lakes and reservoirs. US

Environmental Protection Agency, National

Eutrophication Survey '/lorking Paper No. 22.

. l' . . '1 068 ",' ." " 1 c Yo_..Lenwe~cer, R.r..,....... . ,-,Clent~rlC runOfullenta S 0.1.

eutrophicat ion of lakes and flo\,iinc waters 1 ;,·.rith

par~icular reference to phosphorus and nitrogen

as ractors in eutrophication. Tech. Rep. OEeD Paris,

DAS/CSI!58-27: 1-159.

Vollenweider, R.A. & L.L. Janus, 1982. Statistical models

for predicting h:..rpoliTILTletic oxygen depletion rates.

,,. 1 ~ - 1 Id b' 1 40 1 2' ~~em .. _SL .. ~ca.. ro 1.0 '! _: - ':1.

21


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Wetzel, R.G., 1983. Li~~ology. Saunders College Publishing,

U.S.A., 767 pp.

22


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Table 1

Methods used for the analysis of waters and sediments.

Parameter

nitrite

Ammonia

Kjeldahl nitrogen

Total phosphorus

Total iron and manganese

Filterable iron

Residual iron and nanganese

Alkalinity

Chlorophyll a

Loss on ignition

Hethod

automated cadmium reduction (418F)

automated phenate method (417G)

s~lphuric acid digestion, automated phenate method (420A,417G) (deionised water .added to sediment s~mple before digestion)

persulphate acid digestion l

ascorbic acid method (424F) (deionised \'later added to sediment sample before digestion)

nitric acid digestion and fourfold evaporative concent~etion, flame atomic absorption spectrometry f;n3l>.) \ -' '-' --

0.2 lJ,nl filtriCtion, gra<;Jnite furnace {<D.OS mg l-J.. Fe l i-'t • .n} or: flai'.e atomic absorption spectrometr:/ on f i 1 trate (303A,304)

nitric acid digestion of resid~al retained on a D42 1J-TTI filter, ar.cohite furnace «0.05 mg 1- 1 Fe, t-!..:. ... d ~ or- flame ~ , 'e' " (-0-;' al....-oml.C aDsorp,-~on specJ....-rometrlf .) J~.,

304)

titration to pH 4.5 (403)

extraction in 90% acecone by ul j-,.-- -son).' cal- i on r' u·or,....,..-.c. .... 'Y"l,..... ...... _0- '-_ ~t __ V!.I.!'-zL __ "-

deteLluinatiop. corrected for phaeophytin (l002Gj

weight loss (%) of oven arled sediment after 24 hours at 550 ·C.

Parentheses contain the mechod number according to ~non. (1985) .

2L.


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Table 2

The mean total nutrient and metal concentrations (mg g-l dry weight) of three Darwin River Reservoir sediment samples collected in June 1993.

-----------------------------------------p N Fe Ca Al

------------------------------------------0.36 Q '7

~ . , 23 0.51 2.5 7.0 ------------------------------------------

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Fig. 1 'remperature isopleths ('C) for. Darwin River Reservoir.. northern Australia, July 1989 to June 1991. 'l'riangles pointing downwards from the top x-axis i.ndicate sample dates.

~ ~ E" Fl . ., I • j , •• .MyTYY..,-Y,.y9' .. "yY")'yV-Y"""T1'"V .. vrvv¥v-YV y .... l'l' .. v-"r'f"-".y·VVTf.""'"v ... yy" ....... vv"'l"""y.,-v., ••• E

~ ·\!Vl'~rlr ~ ~ " ~rr-[ II I I nnTITnrrJ;-llmn-TrI'-'[)J1P ~ t:J r II V .,,]

.~~L-~~ __ ,L _ x-t~_,_.11UJ .... :J; JASONOJfMAMJJASONDJFMAMJ:C

1969 1990 1991

}J of

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Aug 14- Sep 1 1 Oct 1 Nov 6 o~

...--. 4-E

'--'

..c 8 .'J CL III

o 12

16 1-9 .j~

Temp 24 28

DO .1

0 3

Dec 2 • , 0.--___o ., 0,

Gl~ 0

1 ----n'i 0, ~~ 0

4 (- 4 4

J ~. 4- -1

j 8 8 - 8 8 - 8 ~/ -~ --~ .... ~~ . - 1 2 - 12 /

l 1 2 - 1 2 12

,LJ 16 LLL_,- 16 I

- 1 G 1 6 _I~ . 1 6 --,--L.l , 32

I - ..J

6 9 0

24 28 32 24 28 32 24 28 32 24- 28 32 l,----------L -'--' __ ' __ 1. .1 '~I , . ~_~l 3 6 9 0 3 6 9 0 3 6 9 0 3 G 9 0 Temperature (Temp), °C • Dissolved oxygen (DO), mg 1- 1

Fig. 2 'J'emperature and dissolved oxygen depth profiles for Darwin River Reservoir for the 1986 dry-wet season transition.

0

Dec 31

-L~

J ~ - 0

1 , 1

24 28 32 Temp

3 6 '. DO 9

I-J tfJ

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•

Fig. 3 Isopleths of the percentage saturation of dissolved oxygen concentrations for Darwin Reservoir. July 1985 to July 1991.

•

River

~~ ,..-"-,, , •• •• ,,........-,.-....T-,--vy".n'i.,......,....."'YY"Y.,'<..-.,..'n"YV __ fY,,.".....-..." ... y,,.---,.W_"(_~ ... h ... ·.~v-.-y-~T"'''fr-Tll .1

",. [ " .. "

lD ,.

" l~ l..Jl,·q·"j"'.o

.11 ,til! JlJJ1j

J A SON 0 J F M A tJ J J A oS 0 N 0 J F M A M J ..-., 1965 1911G 11HH ""::' E E ~ ~ -;;; "r~'" .. ~-,~m~~.,~ry .. n~~~'n.m .. n~".m··"-'~~"-~Fl~~"iii

III .- ......---- ,- __ • ... III . -~.~ . - " ,\" 2 "f --1"--"" ~ -.r----:Oj·' I . "-o "/\ I • , - "\ •

" ~" " > o .£ll~ a

-·~l~ IL. I. C', ';U J A S 0 X 1967

N o J I: " A " J J A 1 90 II

5 o

a "

" V>

" > o ·,~o .0

o

-LflIIL.1UUIJ.JUh .. :::'JL • .J.J" :c N 0 J F M A M J ,2"

1969 :r:

u rvv-v~~"-v-"'-'''--''-'~''YTY'''''~'''''n''...-~.""" .... ~ ~ ~".,. ... ~ • ...-...... ". ~"""""'''T..--y.'rY>'Y '"'',TV''''' h'''VI'Y,..T''''''''''I''"1 " _ .. ~·-n ~

\[-- .. " "

" n .... _- ____ ---~---.~.---,,~ ....... ' ......... ----."'-'-'--JIJ ~~

J A SON 0 J r- )J A M J .J A SON D J F M A M J \90U 1090 19!J1

).J ()'

Technical R

eport WR

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, ..

i:: p~-'-~-C-~'-'~Y=~'-'-'-~--~-~~n-'-l: I " · . " • j o :c JO

.2' • "' "

o • " . • ~ A

" Jq •• ~ ~ .,

LUJ_.I_....l_'----~U.l__LL._.J; 'LL_l.l~l-..-J ~~ :x

DJI'MAMJJASONOJfMAMJJASONDJfMAMJJA

Fig. 4

1 991 1900 190 {)

Isople1hs De ammonia ni.trogen concentrations (mg 1- ) for Darwin River Reservoir, December 1986 to August pB8. Isopleth values 0.01, 0.10 and 0.25 mg 1- . Light shaded area: 0.10 < NH3-N ~ 0.25 mg 1-1 . Dark shaded area: > 0.25 mg 1-1 Triangles pointing downwards from the top x-axis indicate sample dates.

~

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'. •

Fig. 5 (a) Isop1eths for total iron concentrations

E

• > • • • • • > 0

I>

• ., "' '" • X

(mg 1-1) for Darwin River Reservoir. Decenmer 1985 to April 1988, Iyopleth values: 0.05. 0.10, 0.20, 0.50, 1.00 109 1 '.~, Light shaded area: 0,50 <: toral Fe < 1.00 109 1- 1 . Dark shaded area> 1.00 109 1-' (b) Is~pleths for total manganese concentrations (mg 1- ) for Darwin River Reservoir, December 1985 to April 1~88. Isopleth values: 0,01, 0.05, 0.10, 0.25 109 1- . Li2ht shaded area: 0.10 <: totlll Mn"" 0.25 mg 1- , Dark shaded area> 0,25 mg 1- 1 . Triangles pointing downwards from the top x-axis of the Fe isopleth figure indicate Fe and Mn sample dates.

(u) rotal Iron

"F "'~' 'ii' i' :~ ~1l'FTI4Iii-:-~~:-~~:~I:: .0

"

" " " " JO

Q·.hl

0 JFMAMJJAtl:ONDJFMAMJJAS

lO-G

~o "Z >

. . ~L.aH~L.1J l'

ONDJFMA:

~J I O~IlI-Lll!'!JjJ~.J/ .....

I _. ___ ~ :=1" . . 10 I 11\ ~(\" 'r<.-r.-:--: " I>

" -

OJFMAMJJAS

1906

• ~

" " '" • )0 To

.. t .1!--4J u o N 0 .J f~ tJ A M J J A SON 0 J F M "

100" 1 D 6 fj

)..J

00

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eport WR

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~

E ~

.c ~

0, .. Cl

o I if T'; I T'Tl 0

H If;}.1 1 ~ 4 .. ---- r,.'<1 i

8 ~ I /' I r 1 p/ ! -I B

12

{,I f ,! J ,\ ,\ , J pH

1 6 ,-

6

o I---'--~ ,...., , ' )--r, E " I r,--'-~ 1" _ .... , 0 r I

.c; 8 • r ,I •• _ .' T " fr /,,_!)}1 -j 4

Cl .,' r----'/ • 1 2 - .. / . ..--"-- _/ ':if >-__ .-==.-L' -I 8

-I 1 2. f,,- 1

16 1- l 1 h ± 16

o 2 6 8 .'-----'-_-L_~ , '~--~:----'- ..

4 '

Dissolved oxygen (mg 1-')

Legend:

• August 21 o September 8 • Doptember 1 9 y October 2

October 31 o November 13

November 28

•

Fig. 6

Darwin River Reservoir pH and dissolved oxygen profiles for tile 1985 dry-wet transition. ('J'hree dissolved oxygen pl:ofiles have been omitted for: clarity). Note: x-axis has a movin9 scale.

~ ..--0


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•

rig. 7

I

Mean 4- i-/ - 4-

oxygen depletion

-12

rate 2 -

~ (mg 1- 1

1 month-I) 0 ,

0 0 10 20 30

/ • 80 i- 180 Meon / •

period / ! J LO / of 40

onoxlo I 1 0

• (doys)

0 ,I

0 1 0 20 30

Temperature (OC)

The effect of temperature on Darw'in River Reservoir mean hy~olirnnion and metalimnion dissolved oxygen depletion rates and. period of anoxia during the dr.:r-t,-i€t transition.

o~xgen depletion rates have been corrected for temperature by;

actual depletion ratei2 «Temp-4) 110)

The period of anoxia = (actual period of oxygen depletion and anoxia) - (period of ta~perature corrected o~xgen depletion), Mean values are based on data for 1985 - 1990~

Simon Townsend - territorystories.nt.gov.au · a ,,,ere collected at approximately monthly...

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