Lakes in cold 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
Dissolved salts concentration
Ecoregion:
Cold and Warm
Category:
Physico-chemical
BQE:
Salinity
Indicators:
Dissolved salts concentration
Why measure:
Warmer winters cause extreme rainstorms and heavy sea-salt deposition together with increased evaporation in summer, might affect water chemistry and biotic structure
How to measure:
Direct measurments of salinity levels
DOC concentration
Ecoregion:
Cold
Category:
Physico-chemical
BQE:
Dissolved organic carbons
Indicators:
DOC concentration
Why measure:
Rising temperatures in combination with declining acid deposition cause increasing DOC concentrations
How to measure:
Direct measurments of DOC concentrations
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.
pH level
Ecoregion:
Cold
Category:
Physico-chemical
BQE:
Acidity
Indicators:
pH level
Why measure:
Acidification pulses occur due to droughts and increased runoff. Acidification pulses may cause changes in phytoplankton richness and biomass.
How to measure:
Direct measurments of pH levels; use of specific biological indicators for acidity (e.g. Diatoms)
Sulphate concentration
Ecoregion:
Cold
Category:
Physico-chemical
BQE:
Sulphate
Indicators:
Sulphate concentration
Why measure:
Elevated sulphate concentrations will result from the release of oxidized sulphate during drought, which is stored in the anoxic zones (wetlands), with subsequently high export rates.
How to measure:
Direct measurments of S concentrations
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
Macrophyte community
Ecoregion:
Cold
Category:
Biological
BQE:
Secondary production
Indicators:
Macrophyte community
Why measure:
Many northern lakes are regulated to enhance hydropower production and flood protection. This bears hydromorphological pressures which are important factors causing lowered ecological status. Water level fluctuation triggers erosion on the shoreline and, depending on fluctuation range, also affects species composition or disappearance of sensitive aquatic macrophytes.
How to measure:
A water level drawdown index (WIc) developted for Nordic lakes using macrophyte data. The index is based on the ratio between sensitive and tolerant macrophyte species.
References:
Marit Mjelde, Seppo Hellsten & Frauke Ecke (2013) A water level drawdown index for aquatic macrophytes in Nordic lakes. Hydrobiologia 704:141?151
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.
