Lakes in temperate ecoregions - indicators for climate change
The raising temperatures and changes in precipitation patterns due to climate change will result in complex cause–effect chains, linked by many interacting environmental parameters. The degree of ecosystem response will depend on the ecoregion (cold, temperate or warm) and ecosystem type (lakes, rivers or wetlands), and on species-specific adaptations of different organisms.
The purpose of this section is to suggest indicators for the effects of climate change on lake, river and wetland ecosystems that reflect the direction of their pathways, relative importance, and magnitude of change.The term ‘indicator’ is used here simply to describe a detectable signal of a complex process that can be used as an early warning of ecosystem change. Indicators may be chemical, hydrological, morphological, biological or functional parameters, which reflect key processes influenced by climate change and are relatively simple to monitor.
The purpose of this section is to suggest indicators for the effects of climate change on lake, river and wetland ecosystems that reflect the direction of their pathways, relative importance, and magnitude of change. It addresses the three ecosystem types and the three climatic regions always with four categories of indicators: (a) abiotic variables; (b) primary producers; (c) macroinvertebrates; and (d) fish.
Physico-chemical
Duration of summer stratification as reflected by water temperature
Ecoregion:
Cold and Temperate
Category:
Physico-chemical
BQE:
Stratification
Indicators:
Duration of summer stratification as reflected by water temperature
Why measure:
Higher temperatures result in earlier onset and prolongation of summer stratification. As a result, changing mixing processes occur and systems may change from dimictic to warm monomictic. A lack of full turnover in winter might lead to a permanent thermocline in deeper regions
How to measure:
Water temperature reflects the status of lake stratification.
Hydrological parameters
Ice-cover duration, timing of ice break-up, ice thickness
Ecoregion:
Cold and Temperate
Category:
Hydrological parameters
BQE:
Ice cover
Indicators:
Ice-cover duration, timing of ice break-up, ice thickness
Why measure:
Higher air, and thus higher water temperature, leads to a shorter ice cover period. The relationship between air temperature and timing of lake ice break-up shows an arccosine function. This nonlinearity results in marked differences in the response of ice break-up timing to changes in air temperature between colder and warmer regions
How to measure:
Ice cover duration is simple to monitor, e.g. by remote sensing
Biological
Alien species
Ecoregion:
Temperate and Warm
Category:
Biological
BQE:
Secondary production
Indicators:
Alien species
Why measure:
Higher temperatures often favour alien fish, macrophytes or macroinvertebrate species. These may have a negative impact on local biota, including increased predation and competition for food and habitat.
How to measure:
Share of alien species in the community (macrophyte, macroinvertebrates, fish)
Macroinvertebrate groups
Ecoregion:
Temperate
Category:
Biological
BQE:
Secondary production
Indicators:
Macroinvertebrate groups
Why measure:
Southern species are more adapted to warmer waters and drier conditions
How to measure:
Number and abundance of southern species of Odonata (dragonflies and demselflies) in the macroinvertebrate assemblage
References:
Ott J. (2010). Dragonflies and limatic change - recent trends in Germany and Europe. BioRisk 5: 253?286.
DOI:
doi: 10.3897/biorisk.5.857
Macrophyte properties
Ecoregion:
Temperate and Warm
Category:
Biological
BQE:
Primary production
Indicators:
Macrophyte properties
Why measure:
Inter-annual variation in water temperature results in deeper macrophyte colonization, greater wet weight biomass, and an increase in whole lake biomass.
How to measure:
Macrophytes can be sampled routinely using WFD methodologies or using remote sensing techniques.
References:
Bucak T., Saraoglu E., Levi E.E., Tavsanoglu U.N.Y., Idil Çakiroglu A., Jeppesen E. & Beklioglu M., 2012. The role of water level for macrophytes growth and trophic interactions in Mediterranean shallow lakes: a mesocosms experiment with and without fish. Freshwater Biology 57(8): 1631-1642.?(2)
Phytoplankton biomass and composition, cyanobacterial algal blooms
Ecoregion:
Cold and Temperate
Category:
Biological
BQE:
Primary production
Indicators:
Phytoplankton biomass and composition, cyanobacterial algal blooms
Why measure:
Increasing water temperatures lead to shifts from a dominance of diatoms and cryptophytes to cyanobacteria. This effect is especially pronounced at temperatures > 20°C, since cyanobacteria (especially large, filamentous) and green algae are favored at higher temperatures.
How to measure:
The shift in community composition gives information about the response of biota to changed lake characteristics as water temperatures. Phytoplankton community composition is routinely monitored for the Water Framework Directive.
References:
Kosten, S., V. L. M. Huszar, E. Bécares, L. S. Costa, E. Donk, L.-A. Hansson, E. Jeppesen, C. Kruk, G. Lacerot, N. Mazzeo, L. Meester, B. Moss, M. Lürling, T. Nõges, S. Romo, & M. Scheffer, 2012. Warmer climates boost cyanobacterial dominance in shallow lakes. Global Change Biology 18: 118?126, http://doi.wiley.com/10.1111/j.1365-2486.2011.02488.x.
Adrian, R., C. M. O?Reilly, H. Zagarese, S. B. Baines, D. O. Hessen, W. Keller, D. M. Livingstone, R. Sommaruga, D. Straile, E. Van Donk, G. a Weyhenmeyer, & M. Winder, 2009. Lakes as sentinels of climate change. Limnology and oceanography 54: 2283?2297, http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2854826&tool=pmcentrez&rendertype=abstract.
Tolerant/sensitive fish species
Ecoregion:
Cold and Temperate
Category:
Biological
BQE:
Secondary production
Indicators:
Tolerant/sensitive fish species
Why measure:
Higher water temperatures (especially in the epilimnion) lead to the progressive reduction of thermal habitats for cold-water species that will disappear from littoral areas in spring and summer. Furthermore, higher water temperatures will reduce reproduction success of cold-water species and increase parasitic and predator pressure on the egg and young life stages.
How to measure:
The shift in community composition gives information about the response of biota to changed lake characteristics as water temperature, food avilability and water quelity. Fish community composition is routinely monitored for the Water Framework Directive.
Zooplankton biomass and composition, size classes
Ecoregion:
Temperate
Category:
Biological
BQE:
Secondary production
Indicators:
Zooplankton biomass and composition, size classes
Why measure:
Higher water temperature leads to shifts in zooplankton community composition. Higher, earlier population growth rates of Daphnia and earlier summer decline occur due to higher spring temperatures. As a result, higher Daphnia biomass leads to earlier phytoplankton suppression and a shift from a dominance of large-bodied to smaller species.
How to measure:
The response of zooplankton (although not monitored for the Water Framework Directive) might be a good indicator for changes in food web dynamics due to temperature increase.
References:
Angeler, D. G., & S. Drakare, 2012. Tracing alpha, beta, and gamma diversity responses to environmental change in boreal lakes. Oecologia , http://www.ncbi.nlm.nih.gov/pubmed/23229393.
