Hydrobiologia 176/177 : 1-5, 1989 .P. G . Sly and B . T. Hart (eds) Sediment/Water Interaction .

1© 1989 Kluwer Academic Publishers . Printed in Belgium .

Social choice, risk and determinism in water quality management

Peter CullenCanberra CAE, School of Applied Science, P.O . Box 1 ., Belconnen, ACT 2616, Australia

Key words: Flow regime, climate, nutrient loadings, eutrophication, management

Abstract

In attempting to predict the likely water quality of a lake following some intervention to control nutrientinflow, or in attempting to predict the likely water quality in a proposed new impoundment, it is importantto appreciate the probabilistic nature of such predictions . The OECD-Vollenweider models require anestimate of phosphorus inflow to the water body, and these inflows will be partly at least a function ofrunoff from the catchment. Since the rainfall, and hence runoff varies so much from year to year inclimates such as Australia, it seems unwise to base predictions on some average rainfall or runoff value,when the long term average may be experienced only very rarely . A better approach seems to be to lookat the range of runoff values, and apply the OECD-Vollenweider model to dry, normal and wet periods,and develop trophic state predictions for each such hydrologic state .

Since water quality is probabilistic, rather than deterministic as implied by the models, then levels ofacceptable risk have to be established. Is it acceptable for an impoundment to have a cyanobacteria bloomone year every decade? These are questions of social choice, and require the public to be involved inchoosing between the various possible performances of the water body . The trade-off between cost andacceptable water quality is not one that can be made by professionals alone . In such questions of socialchoice society can expect professionals to assist them to understand the various trade-offs, not to makepolitical choices under the guise of technical analysis .

Introduction

Management of a natural resource requires iden-tification of the desired condition of the resource,which is a matter of social choice . It requiresselecting appropriate indicators that can bemeasured to assess the resource condition, andsuch indicators are largely a matter of technicalchoice. It also requires identification of cost-effective actions by which the objectives can bemet. The identification of strategies is generally atechnical choice although the selection betweenvarious strategies may be partly a matter of social

choice . For example the choice between restrict-ing the demand for water using a pricing policyand the provision of more water by buildingfurther storage is as much a matter of socialchoice as it is one of technical analysis by eithereconomists or engineers . If communities are to beinvolved in making an effective choice, the level ofpublic education about water resources and theirmanagement needs to be increased .

Technical people have to make many choiceswhen assessing water quality problems . There arechoices of indicators, choices of samplingmethods and measuring techniques and choices

2

on the way in which the data are to be analysedand presented. These are technical issues bestmade in the light of peer review and acceptedpractice .There are other elements of water quality

management that are partly matters of profes-sional judgement but also matters of socialchoice. In particular, the standards adopted forinterpreting water quality may have limited tech-nical merit, although based on what professionalsthink the communities served should want . Selec-tion criteria based on the number of places thathave adopted them and how many times theyhave been published in available literature isunreasoned . Many water quality standards havebeen developed in other continents and for othercultures and yet are arbitrarily applied inAustralia .

Social choice in chlorophyll standards

The issue of what concentration of chlorophyll aconstitutes a nuisance and is undesirable is ofparticular interest in eutrophication research andmanagement . The chlorophyll a standard used toseparate eutrophic and mesotrophic waters devel-oped in the OECD Eutrophication program is8 mg m -3. This figure is a professional judge-ment. The assumption that this judgement is uni-versally useful and applicable is one that needsexamination . Is a chlorophyll standard developedin an environment such as Sweden appropriate inNew Guinea, South Africa and Australia? Withina country the size of Australia is the samestandard appropriate in Darwin and in Hobart?

The standard is not linked directly to waterquality problems caused by chlorophyll . Further,chlorophyll a is a poor indicator of algal biomassand a very indirect indicator of algal problemssuch as taste and odour or water treatmentrequirements. The particular algal species that aredominant need to be known to predict these sortsof problems. Recognition of the difficulties in try-ing to define trophic status by some specifiedconcentrations of chlorophyll a, or even phos-phorus, is leading towards the use of a more open

boundary system. This makes apparent the proba-bility of various outcomes rather than the predic-tion of a certain response . Chlorophyll a levelsfrom 2.7-78 are shown in the open boundary sys-tem for eutrophic water bodies (Vollenweider &Kerekes, 1982) .

The chlorophyll a standard is perhaps morestrongly linked to aesthetic criteria in that concen-trations above some specified level may be visibleto the eye, depending on cell sizes and clumpingof particular species . As such, the concentrationsof chlorophyll that individuals find unacceptableare a matter of social choice best made byindividuals considering the trade-off betweenwhat they see and what they would have to payto see something less green .

The social issue in regard to chlorophyll is `howgreen is too green?' . The colour of water than anindividual finds remarkable or offensive is ofcourse a learned response based on what they areused to, rather than a level in some text book . Insome parts of the world many water bodies aregreen most of the time, and the application ofstandards from more temperate regions may actu-ally stress local ecosystems and impose un-reasonable costs on local communities .

Risk and determinism in pollutant transfer

Present eutrophication models, such as theOECD-Vollenweider model, require measure-ment or estimates of annual phosphorus input tothe water body of concern . That this model hasbeen so successful in northern temperate climatesis probably related to the fact that mean annualinflow in such environments is reasonably con-sistent from year to year .

Water quality, however, is a function of boththe natural hydrological cycle and the activities ofsociety (Ward & Loftis, 1983), with a number ofintervening biological, physical and chemicalprocesses. Since rainfall is stochastic in nature,nutrient and sediment inputs to a water bodymust be dealt with in terms of probability ratherthan in terms of long term means . Also, the shortterm stochastic nature of the quantity and quality

of effluent discharges themselves must be recog-nised. Effluent discharges vary with industrialbreakdowns at source, treatment plant accidentsand failures, and the biological nature of treat-ment processes which are dependent on healthypopulations of organisms . Thus, it is no morepossible to predict precisely the pollutant loadfrom sewage treatment works on to aquatic eco-systems than to predict the flow of a river intowhich they may be discharged .

When water runs off the land it transportsmaterials that can be detached or dissolved suchas particles of soil, plant material, fertilizer andanimal excreta. It has been long recognised thatwater quality is integrally coupled with the geologyand land uses within a catchment, but it is lesswidely appreciated that the number, duration andvolume of runoff events in any particular periodwill also influence measured loads .

Reliability of rainfall and runoff

Experience in Australia and South Africa hasindicated that such average inputs mean verylittle . In much of Australia rainfall is low by worldstandards (the mean annual rainfall of Australiais 420 mm whereas that of the United States is660 mm) and mean annual runoff is even lower(45 mm in Australia relative to 260 mm in theUnited States) .

This paucity of rainfall and runoff is made evenworse by its lack of reliability . McMahon (1982)has shown that relative to mean annual runoff, themean peak annual floods in Australia are aboutan order of magnitude larger than world averages,and the variability of peak annual flows is muchgreater than for world rivers .

Countries such as Australia and South Africa,in particular, have low and unreliable rainfallallied with skeletal soils and poor vegetationcover. The drought-flood patterns they experiencemean, also, that the loads of nutrients and sus-pended particles that enter water bodies are highlyvariable from year to year .

In studies of Lake Burley Griffin, it was shownthat flood events were responsible for transporting

Table] . Phosphorus exports from rural lands to LakeBurley Griffin . (From Cullen & Rosich, 1979) .

1978

1837

26

2.83

1 .91979

518

9

2.47

4.0

3

69% of the phosphorus, although they only occu-pied 9 % of the study period . Non-point sources,in particular, were important when runoff wasoccuring, and sampling regimes need to reflectthis (Cullen & Rosich, 1979) .

To date, experiences have indicated that the useof some mean annual export figure for catchmentsin semi-arid areas is inappropriate, given thevariation in such figures from year to year . Thebest approach available appears to be to analysethe variation in streamflow regimes, and to esti-mate the volume of discharge in a series of dis-charge classes (low, normal and flood at the mostsimple). A mean concentration then needs to beapplied to each discharge class to calculate loads .This concentration may come from directmeasurements or, if necessary, from some form ofrating curve (Cullen, 1986) .

With this approach it is necessary to considerrunoff and hence nutrient exports from a catch-ment in terms of probability of export in anyparticular year .

Table 2 provides data that show the extremevariability in annual rainfall leads to quite dif-ferent lake behaviour . In the wet year of 1978 thewater clarity was reduced by suspended sedimentfrom runoff, and from algal growth stimulated by

Table 2 . Water quality in Lake Burragorang (annualmeans). (From Cullen & Smalls, 1981) .

Year Rainfall Total P

Chlorophyll a Secchi depth(mm)

(mgm-3) (mgm-3)

(m)

Rainfall regime Phosphorus exports kg ha-' yr-'

Total Particulate

Normal 0.010 0 .004Drought 0.002 0 .001Flood 1975 0.072 0.054Flood 1976 0.208 0.191Overall 0.292 0.250

4

various major nutrient inputs . In 1978, the peakchlorophyll a concentration was 32 mg m - 3 pro-duced by a Volvox bloom following a storm .

Catchment processes a further source of uncertainty

The condition of the land surface itself is also acontrolling factor, both in affecting the volume andrate of runoff as well as the potential for mobilizingphosphorus from the land surface . Land manage-ment practices influence both the material to betransported, and the volume of runoff. The use offertilizers (amounts, method of application, tim-ing), grazing regime (grass length and compactionaffect runoff) and fire regime all affect sedimentand nutrient exports from rural lands .

There are a number of characteristics of phos-phorus export in semi-arid areas that are nowwidely accepted (Cullen & O'Loughlin, 1982) .a. Most export of phosphorus occurs during

runoff events .b. Most phosphorus is exported in the particulate

form associated with clay or organic material,c. A large proportion of the overall export of

phosphorus may occur in the short time periodof a major runoff event.

d. Receiving waters experience variable sizedpulses of nutrients rather than a steady input .

Where does runoff come from?

It is widely believed that loads measured in astream are derived uniformly from the entirecatchment if rainfall is uniform . Not only israinfall often uneven over a catchment, but thebasic model of Hortonian overland flow has beenfound to be inappropriate in some catchments .The relationships between rainfall and runoff arecomplex and there are various mechanisms whichcontribute to streamflow. In many catchments insemi-arid areas only a small proportion of thecatchment may generate most of the runoff that ismeasured. It is the land use, and the condition of

the land surface on these run-off generating orvariable source areas that determines the nutrientloads in a stream. The average or dominant catch-ment land use or surface condition may beirrelevant in contrast to conditions on the sourceareas .Observation in the Sherwood experimental

catchment near Canberra has identified thesevariable source areas using both groundwaterdepth (at or near the surface for runoff generatingareas) and vegetation indicators (related to watertable), a numerical method for identifying zonesof surface saturation from topographic informa-tion (O'Loughlin, 1986) has also been used . Thethree methods have given consistent results infield experiments on nutrient exports (Farmer,1987 ; Cullen, Farmer & O'Loughlin, 1987) .

Conclusions

Water managers and scientists have to make manyjudgements, some of which are of a technicalnature, but some of which are clearly matters ofsocial choice . In these areas it is necessary todevelop strategies to improve public educationabout water resources and to effectively involvethe public in selecting appropriate criteria .

Allied to uncertainties about appropriate crite-ria for eutrophication management, there are un-certainties about measurements of nutrient inputs .Especially in semi-arid areas, the unreliability ofrainfall and hence runoff and streamflow, togetherwith the variability of vegetation cover and sur-face soil condition in runoff generating areasmeans that deterministic models of pollutanttransfers into lakes, based on annual averageexports, are inappropriate in semi-arid areas . Thepulses of nutrients that enter lakes or rivers canonly be treated in terms of probability and phos-phorus exports from diffuse sources may best beconsidered in terms of, for example, 1 in 2, 5, 10and 25 year export events . Also, the response ofreceiving waters should be considered by a similarprobabilistic approach .

References

Cullen, P . W., N . R . Farmer & E. M . O'Loughlin, 1987 . Esti-mating Non-Point Sources of Phosphorus to Lakes . Int .Ver. Limnol . Verhandlungen . 23: 588-593 .

Cullen, P . W ., 1986 . Managing Nutrients in Aquatic Systems :the Eutrophication Problem in Limnology in Australia. InDe Decker, P. & W. D. Williams, (eds) CSIRO-Dr W .Junk, Melbourne : 539-554 .

Cullen, P . W. & E. M . O'Loughlin, 1982 . Non-point sourcesof pollution . In E . M . O'Loughlin & P . Cullen (eds) Predic-tion in Water Quality, Australian Academy of Science,Canberra: 437-453.

Cullen, P . W. & R. S . Rosich, 1979. Effects of rural and urbansources of phosphorus of Lake Burley Griffin . Prog . Wat .Tech . 11 : 219-230 .

Cullen, P . W. & I . Smalls, 1981 . Eutrophication in Semi-Arid

5

Areas : The Australian Experience . Wat. Quality Bull . 6 :79-83 .

Farmer, N . R ., 1987 . The Impact of Fertilizer Application onPhosphorus Exports from a Radiata Pine Forested Catch-ment. M. App . Sci . Thesis. College of Advanced Edu-cation, Canberra .

McMahon, T . A ., 1982. World Hydrology : Does AustraliaFit? Hydrology and Water Resources Symposium . TheInst . of Engineers Aust. Nat . Conf. Publ . 82/ 3 . Canberra .

O'Loughlin, E. M., 1986. Prediction of surface saturationzones in natural catchments by topographic analysis . Wat .Resour. Res . 22 : 794-804 .

Vollenweider, R . A . & J . J . Kerekes, 1982 . Eutrophication ofwaters. Monitoring, Assessment and Control . OECD,Paris, pp 154.

Ward, R. C . & J . C . Loftis, 1983. Incorporating the stochasticnature of water quality into management . J . Wat. Poll .Cont . Fed . 55 : 408-414.