Monitoring purposes determine the selection of variables, location of sampling sites, and sampling frequency. The selection should provide the best signal to noise ratio for the parameters of interest. For trend and surveillance monitoring, the deepest point of a lake, where different inputs to the lake are integrated, is frequently selected. However, the representativeness of a single site is often questioned, especially for large lakes. Based on data collected from 10 sampling points during 11 survey expeditions in August 2001–2011 to the large shallow Lake Võrtsjärv, Estonia, we studied the spatial and annual variability of environmental and phytoplankton variables and analysed the representativeness of a permanent sampling station for the whole lake conditions. The two southernmost stations under the influence of the main tributary deviated clearly from the homogeneous group of the other eight stations, which we termed ‘Võrtsjärv Proper’. Among the stations of Võrtsjärv Proper, the year-to-year variability dominated strongly over the spatial variability, the latter being almost negligible for most of the variables. Surface water temperature and water level explained approximately half of the total variability in parameters commonly used in ecological status assessment of lakes. This has serious implications for using these variables to detect human impacts in Võrtsjärv. Our study showed that the deep sampling site, which was characterized by the lowest average variability of the parameters measured and was representative of more than 90% of the lake aquatory, possesses all necessary qualities required of a permanent surveillance monitoring station.
Blank, K., Laugaste, R. & Haberman, J. 2010. Temporal and spatial variation in the zooplankton:phytoplankton biomass ratio in a large shallow lake. Estonian J. Ecol., 59, 99–115.
http://dx.doi.org/10.3176/eco.2010.2.02
Cavanagh, N., Nordin, R. N., Pommen, L. W. & Swain, L. G. 1998. Guidelines for Designing and Implementing a Water Quality Monitoring Program in British Columbia. Ministry of Environment, Lands and Parks. Government Publication No. 7680000554. http://www.ilmb.gov.bc.ca/ risc/pubs/aquatic/ (visited 2012-04-27).
EC. 2000. Directive 2000/60/ EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy. OJ L 327, 22.12.2000.
Ellis, J. & Adriaenssens, V. 2006. Uncertainty Estimation for Monitoring Results by the WFD Biological Classification Tools. WFD Report. Environment Agency, Bristol.
EPA. 1997. Guidelines for Preparation of the Comprehensive State Water Quality Assessments (305(b) Reports) and Electronic Updates: Supplement. EPA-841-B-97-002B. U.S. Environmental Protection Agency, Washington, DC.
Feldmann, T. & Mäemets, H. 2004. Macrophytes. In Lake Võrtsjärv (Haberman, J., Pihu, E. & Raukas, A., eds), pp. 185–205. Estonian Encyclopaedia Publishers, Tallinn.
Feldmann, T. & Nõges, P. 2007. Factors controlling macrophyte distribution in large shallow Lake Võrtsjärv. Aquat. Bot., 87, 15–21.
http://dx.doi.org/10.1016/j.aquabot.2007.01.004
Fore, L. S., Karr, R. & Conquest, L. L. 1994. Statistical properties of an index of biotic integrity used to evaluate water resources. Can. Fish. Aquat. Sci., 51, 1077–1087.
http://dx.doi.org/10.1139/f94-107
George, D. G., Maberly, S. C. & Hewitt, D. P. 2004. The influence of the North Atlantic Oscillation on the physical, chemical and biological characteristics of four lakes in the English Lake District. Freshwater Biol., 49, 760–774.
http://dx.doi.org/10.1111/j.1365-2427.2004.01223.x
Grasshoff, K. (ed.). 1976. Methods of Seawater Analysis. Verlag Chemie, Weinheim and New York.
Hering, D., Feld, C. K., Moog, O. & Ofenböck, T. 2006. Cook book for the development of a Multimetric Index for biological condition of aquatic ecosystems: experiences from the European AQEM and STAR projects and related initiatives. Hydrobiologia, 566, 311–324.
http://dx.doi.org/10.1007/978-1-4020-5493-8_22
IPCC. 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (Solomon, S. et al., eds). Cambridge Univ. Press, Cambridge, U. K.
Järvet, A. 2004. Pollution load to Lake Võrtsjärv. In Lake Võrtsjärv (Haberman, J., Pihu, E. & Raukas, A., eds), pp. 151–171. Estonian Encyclopaedia Publishers, Tallinn.
Järvet, A., Karukäpp, R. & Arold, I. 2004. Location and physico-geographical conditions of the catchment area. In Lake Võrtsjärv (Haberman, J., Pihu, E. & Raukas, A., eds), pp. 11–26. Estonian Encyclopaedia Publishers, Tallinn.
Jeffrey, S. W. & Humphrey, G. F. 1975. New spectrophotometric equations for determining chlorophylls a, b, c1 and c2 in higher plants, algae and natural phytoplankton. Biochem. Physiol. Pfl., 167, 191–194.
Karr, J. R. & Chu, E. W. 1997. Biological Monitoring and Assessment: Using Multimetric Indexes Effectively. EPA 235-R07-001. University of Washington, Seattle.
Kivimaa, R., Huttula, T. & Podsetchine, V. 1998. Hydrodynamical studies. In Present State and Future Fate of Lake Võrtsjärv. Results from Finnish–Estonian Joint Project in 1993–1997 (Huttula, T. & Nõges, T., eds). Vol. 209, pp. 60–77. The Finnish Environment, Helsinki.
Laas, A., Nõges, P., Kõiv, T. & Nõges, T. 2012. High-frequency metabolism study in a large and shallow temperate lake reveals seasonal switching between net autotrophy and net heterotrophy. Hydrobiologia, 694, 57–74.
http://dx.doi.org/10.1007/s10750-012-1131-z
Lindenmayer, D. B. & Likens, G. E. 2009. Adaptive monitoring: a new paradigm for long-term research and monitoring. Trends Ecol. Evol., 24, 482–486.
http://dx.doi.org/10.1016/j.tree.2009.03.005
Nõges, P. & Laugaste, R. 1998. Seasonal and long-term changes of phytoplankton in L. Võrtsjärv. Limnologica, 28(1), 21–28.
Nõges, P., Kägu, M. & Nõges, T. 2007. Role of climate and agricultural practice in determining the matter discharge into large shallow Lake Võrtsjärv, Estonia. Hydrobiologia, 581, 125–134.
http://dx.doi.org/10.1007/978-1-4020-6158-5_14
Nõges, P., Nõges, T., Haberman, J., Laugaste, R. & Kisand, V. 1997. Tendencies and relations in the plankton community and pelagic environment of Lake Võrtsjärv during three decades. Proc. Estonian Acad. Sci. Biol. Ecol., 46, 40–57.
Nõges, P., Laugaste, R. & Nõges, T. 2004. Phytoplankton. In Lake Võrtsjärv (Haberman, J., Pihu, E. & Raukas, A., eds), pp. 217–231. Estonian Encyclopaedia Publishers, Tallinn.
Nõges, P., Mischke, U., Laugaste, R. & Solimini, A. G. 2010a. Analysis of changes over 44 years in the phytoplankton of Lake Võrtsjärv (Estonia): the effect of nutrients, climate and the investigator on phytoplankton-based water quality indices. Hydrobiologia, 646, 33–48.
http://dx.doi.org/10.1007/s10750-010-0178-y
Nõges, P., Nõges, T. & Laas, A. 2010b. Climate-related changes of phytoplankton seasonality in large shallow Lake Võrtsjärv, Estonia. J. Aquat. Ecosyst. Health Manage., 13(2), 154–163.
http://dx.doi.org/10.1080/14634981003788953
Nõges, T., Kisand, V., Nõges, P., Põllumäe, A., Tuvikene, L. & Zingel, P. 1998. Plankton seasonal dynamics and its controlling factors in shallow polymictic eutrophic lake Võrtsjärv, Estonia. Int. Rev. Ges. Hydrobiol., 83(4), 279–296.
Nõges, T., Nõges, P. & Laugaste, R. 2003. Water level as the mediator between climate change and phytoplankton composition in a large shallow temperate lake. Hydrobiologia, 506–509, 257–263.
http://dx.doi.org/10.1023/B:HYDR.0000008540.06592.48
Nõges, T., Tuvikene, L. & Nõges, P. 2010. Contemporary trends of temperature, nutrient loading, and water quality in large lakes Peipsi and Võrtsjärv, Estonia. J. Aquat. Ecosyst. Health Manage., 13(2), 143–153.
http://dx.doi.org/10.1080/14634981003788987
Pall, P., Vilbaste, S., Kõiv, T., Kõrs, A., Käiro, K., Laas, A., Nõges, P., Nõges, T., Piirsoo, K., Toomsalu, L. & Viik, M. 2011. Fluxes of carbon and nutrients through the inflows and outflow of Lake Võrtsjärv, Estonia. Estonian J. Ecol., 60, 39–53.
http://dx.doi.org/10.3176/eco.2011.1.04
Patil, G. P. 1991. Encountered data, statistical ecology, environmental statistics, and weighted distribution methods. Environmetrics, 2, 377–423.
http://dx.doi.org/10.1002/env.3770020402
Rachamim, T., Stambler, N., Zohary, T., Berman-Frank, I. & Gal, G. 2010. Zooplankton contribution to the particulate N and P in Lake Kinneret, Israel, under changing water levels. Hydrobiologia, 655, 121–135.
http://dx.doi.org/10.1007/s10750-010-0413-6
Raukas, A. 1995. Estonia. In Nature. Valgus, Tallinn.
Raukas, A. & Tavast, E. 2002. The Holocene sedimentation history of Lake Võrtsjärv, Central Estonia. Geol. Quart., 46(2), 199–206.
Reckhow, K. H. & Chapra, S. C. 1983. Engineering Approaches for Lake Management. Volume 1. Data Analysis and Empirical Modeling. Butterworth Publishers, Boston.
Roberts, K. A. 1991. Field monitoring: confessions of an addict. In Monitoring for Conservation and Ecology (Goldsmith, F. B., ed.), pp. 179–212. Chapman & Hall.
http://dx.doi.org/10.1007/978-94-011-3086-8_10
Tammert, H. & Kisand, V. 2004. Bacterioplankton. In Lake Võrtsjärv (Haberman, J., Pihu, E. & Raukas, A., eds), pp. 207–215. Estonian Encyclopaedia Publishers, Tallinn.
Timm, T. (ed.), 1973. Võrtsjärv. Valgus, Tallinn.
Toming, K., Arst, H., Paavel, B., Laas, A. & Nõges, T. 2009. Spatial and temporal variations in coloured dissolved organic matter in large and shallow Estonian waterbodies. BER, 14, 959–970.
Tuvikene, L., Nõges, T. & Nõges, P. 2011. Why do phytoplankton species composition and “traditional” water quality parameters indicate different ecological status of a large shallow lake? Hydrobiologia, 660, 3–15.
http://dx.doi.org/10.1007/s10750-010-0414-5
