Pollution of Lakes and Rivers

Chapter 2:How long is long

Copyright © 2008 by DBS

Contents

• History as a vehicle for exploration and study• How unusual are unusual events?• Managing Aquatic Ecosystems: a Matter of Time Scales• Importance of Time Scales in Separating ‘noise’ from ‘signal’• A Medical Analogy to ‘Ecosystem Health’• Critical and Target Loads for Pollutants’• Requirements for Effective Ecosystem Management• Sources of Information on Long-term Environmental Change

How Long is Long?History as a Vehicle for Exploration and Study

• History provides context – success and failure• Warning signs?• People tend to get more interested in history when they are worried

about the future• Long term data is useful in showing degradation/recovery of

systems– Used to set mitigation goals– Used to determine levels of disturbance that have elicited a negative

consequence

How Long is Long?How Unusual are Unusual Events?

• Unusual events – unanticipated natural phenomenon that affects the outcome of a study,

e.g. drought, flood, heat, cold, predation etc.

– How often do ecologists invoke the ‘unusual event’ clause?

– Are they truly unusual or a matter of perspective?

• Of 380 studies 1 in 10 used the term ‘unusual event’

• Longer-term studies show decreased ‘unusual events’

– Due to the perspective of a broader range of natural variability

‘…we tend to overestimate the importance of some unusual events when we lack the benefit of perspective provided by a longer study’(Weatherhead, 1986)

How Long is Long?Managing Aquatic Ecosystems: a Matter of Time Scales

• What type of data are used for environmental decisions?

• Short-term? Long-term?

Tilman (1989)623 observational + experimental ecological studies

40 % of observational studies were under 1 year

Terrestrial based scientific studies:

Abundance of short term data sets

How Long is Long?Managing Aquatic Ecosystems: a Matter of Time Scales

• 70 % of aquatic studies less than 1 year (Smol, 1995)• Ecologists, limnologists and environmental scientists use short-term data sets.

Duration of studies published:Environmental Monitoring and Assessment 1981 - 1993.

How Long is Long?Managing Aquatic Ecosystems: a Matter of Time Scales

• “Invisible Present” - The time-scale within which our responsibilities for planet earth are most evident

• Processes acting over decades are hidden in “the invisible present” (Magnuson, 1990)

• Most environmental decisions are based on “the invisible present”

• Little understanding of how the system evolved

Lake Mendota (WI) ice cover:In 1983 duration of ice cover was 40 days shorter than any of the 9 other years

Lake Mendota ice cover:Linked to El Nino

Lake Mendota ice cover:Warming trend (less duration of ice cover)

How Long is Long?Importance of Time Scales in Separating ‘noise’ from ‘signal’

• Almost all environmental assessments are done after-the-fact, after a problem has been identified

• e.g. Lake Erie • Phosphorus reduction (intentional) and zebra mussel invasion (unintentional)

– Both have reduced algae, improved water clarity

5-10 yr data the impact of zebra mussels more dramatic

On long-term arrival of zebra mussels barely noticeable (Nicholls, 1997)

How Long is Long?Importance of Time Scales in Separating ‘noise’ from ‘signal’

• Day-to-day monitoring is expensive and uninteresting• There are alternative methods for obtaining long-term data sets

Figure 2.2. Environmental monitoring – a matter of time scales. Ecosystem managers should ideally use a continuum of techniques, ranging from laboratory studies and bioassays (typically working on time scales of hours to days), to field studies (often representing seasonal or a few years of observations), to paleoenvironmental studies. With the tremendous advancements in techniques and increased temporal resolution available to paleolimnologists, these approaches can now be used to dovetail with neolimnological approaches, and so allow mangers to extend their sampling programs back in time. The time scales shown in the figure to the left are on a logarithmic scale; the figure to the right shows a more realistic representation of the relative amount of information potentially available from sedimentary deposits! (Modified from Smol, 1992).

How Long is Long?A Medical Analogy to ‘Ecosystem Health’

• Medical analogy (Smol, 1990)• The “retroscope” analogy

Ecosystem Human

Ecosystem manager Physician

Ecosystem history Medical history

Lake sediments Patients records

Healthy ecosystem Existence prior to human impacts

How Long is Long?A Medical Analogy to ‘Ecosystem Health’

• Ecosystem stress:

“…to denote any human agent that causes an ecosystem or community to respond in some way that is outside its natural range of variation…”

Schindler (1990)

• How do we know what is outside its natural range of variation?

• Are all patients are equally resistant to diseases?

- No, same is true of water bodies

• Establishing susceptibility of ecosystems to disturbances is an important management issue, e.g. establishment of critical loads (thresholds)

• Monitoring of recovery following treatment is important

How Long is Long?Critical and Target Loads for Pollutants’

• Determining the level of permissible pollution for an ecosystem forms a major part of environmental science and policy

Target load:takes into consideration national objectives, financial and social considerations

Critical load:highest load of pollutant that will not cause changes leading to long-term harmful effects (Nilsson, 1986)Nilsson, 1986

"We live forward but understand backwards"

"It is perfectly true, as philosophers say, that life must be understood backwards. But they forget the other proposition, that it must be lived forwards. And if one thinks over that proposition it becomes more and more evident that life can never really understood in time simply because at no particular moment can I find the necessary resting place from which to understand it—backwards.“

~ Søren Kierkegaard

How Long is Long?Requirements for Effective Ecosystem Management

1. What were the baseline conditions prior to human disturbances?

Gauging the extent of a problem is impossible without a basis for comparison.

2. What is the range of natural variability?

Ecosystems are naturally “noisy”. Is a new trend within the range of natural variation or a sustained and significant trend?

3. At what point in time and at what level of disturbance or contamination did negative impacts become apparent?

Need to know the level of stress that a system can encounter before it cannot recover.

Historical perspectives put present and predicted changes into context. They can assess whether a change is occurring, as well as the direction, magnitude, and rate of change. They help us identify and understand the mechanisms and driving forces of change.

How Long is Long?Sources of Information on Long-term Environmental Change

• Historical measurements: – Direct measurements, observational and instrumental– Often sparse, rarely sufficient quality or duration

• Space-for-time substitution:– i.e. comparing conditions in affected lakes to those in similar but unaffected lakes– For example: comparing an acidified lake with a non-acidified lake in a similar

setting (geology, climate, vegetation)– Unaltered lake is considered an analogue for the “pre-impact” conditions– Assumes other stressors have not altered the lakes used to estimate “pre-

impact” conditions• Hindcasting using Models:

– Based on present day conditions and processes• Paleoenvironmental reconstructions:

– Focus of this course

How Long is Long?Sources of Information on Long-term Environmental Change

• Four major sources• Each has pros/cons

Paleoenvironmental approaches provide critical data that cannot be directly attained from other approaches. For example, rarely were ecosystems studied before impacts had occurred, nor has the trajectory of change been recorded.

How Long is Long? Model Evaluation Using Paleolimnology

• How do we evaluate model outputs?

– Wait and see approach – obviously not good for policy makers

– Hindcasting using paleolimnological data

How Long is Long? Summary

• The environment constantly changes

• Both natural and man-made

• Short-term data not very useful

• Knowledge of background conditions is poor

• Difficult to determine how a system has changed and by what amount

• There is no time machine but records can be reconstructed using proxy data archived in lake sediments

References

• Anderson, N.J. and Battarbee, R.W. (1994) Aquatic community persistence and variability: A paleolimnological perspective. In Giller, P.S., Hildrew, A.G. and Raffaelli, D.G. (eds.), Aquatic Ecology: Scale, Pattern and Process. Blackwell Scientific Publications, Oxford, pp. 233-259.

• Bennion , H. and Battarbee, R.W. (2007) The European Union Water Framework Directive: opportunities for paleolimnology. Journal of Paleolimnology, Vol. 38, pp. 285-295.

• European Commission (2003) Common Implementation Strategy for the Water Framework Directive (2000/60/EC), Guidence Document No. 10, Rivers and lakes – Typology, Reference Conditions and Classification Systems. Produced by Working Group 2.3 – REFCOND. Luxembourg: Office for Official Publications of the European Communities.

• Frey, D.G. (1974) Paleolimnology. Mitteilungen Internationale Vereinigung Limnologia, Vol. 20, pp. 95-123.

• Magnuson, J. (1990) Long-term ecological research and the invisible present. Bioscience, Vol. 40, pp. 495-501.

• NAPAP Aquatic Effects Working Group (1991) National Acidic precipitation Assessment Program 1990 Integrated Assesment Report. Washington, DC: National Acid precipitation Program.

References

• Nicholls, K.E. (1997) Planktonic green algae in western lake Erie: the importance of temporal scale in the interpretation of change. Freshwater Biology, Vol. 38, pp. 419-425.

• Nilsson, J. (ed.) (1986) Critical Loads for Nitrogen and Sulphur. The Nordic Council of Ministers Report 1986: 11, Copenhagen.

• Schindler, D.W. (1990) Experimental perturbations of whole lake as a test of hypotheses concerning ecosystem structure and function. Oikos, Vol. 57, pp. 25-41.

• Smol, J.P. (1990a) Are we building enough bridges between paleolimnology and aquatic ecology? Hydrobiologia, Vol. 214, pp. 201-206.

• Smol, J.P. (1990b) Paleolimnology – Recent advances and future challenges. Memoire dell’Istituto Italiano di Idrobiologia, Vol. 47, pp. 253-276.

• Smol, J.P. (1992) Paleolimnology: an important tool for effective ecosystem management. Journal of Aquatic Ecosystem Health, Vol. 1, pp. 49-58.

• Smol , J.P.(1995) Paleolimnological approaches to the evaluation and monitoring of ecosystem health: providing a history for environmental damage and recovery. In Rapport, D., Gaudet, C. and Calow, P. (eds), Evaluating and Monitoring the Health of Large-Scale Ecosystems. NATO ASI Series, Volume 128. Springer-Verlag, Stuttgart, pp. 301-318.

• Tilman , D. (1989) Ecological experimentation: Strengths and conceptual problems. In Likens, G.E. (ed.), Long Term Studies in Ecology: Approaches and Alternatives. Springer Verlag, New York, pp. 136-157.

• Weatherhead , P.J. (1986) How unusual are unusual events? American Naturalist, Vol. 128, pp. 150-154.