Walter Rast, Texas State University &

Vice-Chair, ILEC Scientific Committee

IWScience ConferenceIWScience ConferenceBangkok, Thailand, Sept. 24, 2012Bangkok, Thailand, Sept. 24, 2012

Lakes and Reservoirs:Lakes and Reservoirs:Challenges and ConsiderationsChallenges and Considerations

Lakes in the WorldLakes in the World• ~5.3 million lakes - >1 ha in size~5.3 million lakes - >1 ha in size• Overall, lakes hold Overall, lakes hold ~~100,000 km100,000 km33 of freshwater of freshwater

>90% of liquid freshwater on Earth >90% of liquid freshwater on Earth surface is in lakes/reservoirs;surface is in lakes/reservoirs;

Lakes (lentic) used for wider range of Lakes (lentic) used for wider range of ecosystem services than other types ecosystem services than other types of water systems of water systems also greatest also greatest potential for water use conflictspotential for water use conflicts

Mirror LakeMirror Lake

44

66

‘Sink” buffer function very important: Lakes as ‘barometers’ of human activities inside/outside basin;

Often ‘trigger’ for initiation of remedial actions

• Integrating Nature (Everything comes together)

→ 1. Issues are mostly inseparable• Long Retention Time (Problems remain long, and

solving them also takes long time) → 2. Changes are gradual and mostly invisible

• Complex Response Dynamics (Everything affects everything

else in waterbody) → 3. Often unpredictable and uncontrollable

Unique Unique FeaturesFeatures of Lakes of Lakes

System won’t fully recover

(or Regime Shift may set in)

Hysteresis

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Lake Taihu, ChinaLake Taihu, China

M. Nakamura, RCSE Shiga University, Chairman ILEC Scientific Committee

1919

ConsiderationsConsiderations Only 4 ‘lakes’ in GEF IW portfolio;Only 4 ‘lakes’ in GEF IW portfolio;

No global-scale data bases for lakes;No global-scale data bases for lakes;

Although within river basins, most Although within river basins, most river studies do not explicitly river studies do not explicitly consider lakes; different spatial/ consider lakes; different spatial/ temporal scales temporal scales management management implications; implications;

ConsiderationsConsiderations

Other hydrologic linkages Other hydrologic linkages (groundwater; LMEs) often ignored (groundwater; LMEs) often ignored (management implications);(management implications);

‘‘Translating’ scientific results for Translating’ scientific results for decision-makers vs. decision-makers decision-makers vs. decision-makers communicating management needs;communicating management needs;

differing ‘languages’ & temporaldiffering ‘languages’ & temporal scalesscales

ConsiderationsConsiderations

Haven’t yet integrated science with Haven’t yet integrated science with science (lakes, rivers, aquifers, etc) science (lakes, rivers, aquifers, etc) or policy with policy (different water or policy with policy (different water Ministries with different mandates; Ministries with different mandates; little coordination; fragmentation of little coordination; fragmentation of authority and responsibility);authority and responsibility);

Resource Provision Service

Regulating Service

Cultural Service

Supporting Service

Ecosystem Services

We all want this value

We tend to forget these values

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• … ….Thanks for your kind .Thanks for your kind attention. attention.