Water Framework Directive: ecological classification of Danish lakes

Summary 1 The European Water Framework Directive (WFD) requires that all European waterbodies are assigned to one of five ecological classes, based primarily on biological indicators, and that minimum good ecological quality is obtained by 2015. However, the directive provides only general guidance regarding indicator definitions and determination of boundaries between classes. 2 We used chemical and biological data from 709 Danish lakes to investigate whether and how lake types respond differently to eutrophication. In the absence of well-defined reference conditions, lakes were grouped according to alkalinity and water depth, and the responses to eutrophication were ordered along a total phosphorus (TP) gradient to test the applicability of pre-defined boundaries. 3 As a preliminary classification we suggest a TP-based classification into high, good, moderate, bad and poor ecological quality using 0–25, 25–50, 50–100, 100–200 and > 200 µg P L−1 boundaries for shallow lakes, and 0–12·5, 12·5–25, 25–50, 50–100 and > 100 µg P L−1 boundaries for deep lakes. Within each TP category, median values are used to define preliminary boundaries for the biological indicators. 4 Most indicators responded strongly to increasing TP, but there were only minor differences between low and high alkalinity lakes and modest variations between deep and shallow lakes. The variability of indicators within a given TP range was, however, high, and for most indicators there was a considerable overlap between adjacent TP categories. Cyanophyte biomass, submerged macrophyte coverage, fish numbers and chlorophyll a were among the ‘best’ indicators, but their ability to separate different TP classes varied with TP. 5 When using multiple indicators the risk that one or more indicators will indicate different ecological classes is high because of a high variability of all indicators within a specific TP class, and the ‘one out – all out’ principle in relation to indicators does not seem feasible. Alternatively a certain compliance level or a ‘mean value’ of the indicators can be used to define ecological classes. A precise ecological quality ratio (EQR) using values between 0 and 1 can be calculated based on the extent to which the total number of indicators meets the boundary conditions, as demonstrated from three Danish lakes. 6 Synthesis and applications. The analysis of Danish lakes has identified a number of useful indicators for lake quality and has suggested a method for calculating an ecological quality ratio. However, it also demonstrates that the implementation of the Water Framework Directive faces several challenges: gradual rather than stepwise changes for all indicators, large variability of indicators within lake classes, and problems using the one out – all out principle for lake classification.

[1]  J. Barko,et al.  Shear stress and sediment resuspension in relation to submersed macrophyte biomass , 2004, Hydrobiologia.

[2]  S. Bayley,et al.  � 2003, by the American Society of Limnology and Oceanography, Inc. Do wetland lakes exhibit alternative stable states? Submersed aquatic vegetation and chlorophyll in western boreal shallow lakes , 2022 .

[3]  E. Donk,et al.  Impact of submerged macrophytes including charophytes on phyto- and zooplankton communities: allelopathy versus other mechanisms , 2002 .

[4]  Erik Jeppesen,et al.  Does high nitrogen loading prevent clear-water conditions in shallow lakes at moderately high phosphorus concentrations? , 2005 .

[5]  S. Körner.  Development of submerged macrophytes in shallow Lake Müggelsee (Berlin, Germany) before and after its switch to the phytoplankton-dominated state , 2001 .

[6]  Marten Scheffer,et al.  The determination of ecological status in shallow lakes - a tested system (ECOFRAME) for implementation of the European Water Framework Directive , 2003 .

[7]  D. Canfield,et al.  Wind-induced increases in trophic state characteristics of a large (27 km 2), shallow (1.5 m mean depth) Florida lake , 2001, Hydrobiologia.

[8]  L. J. Jackson.  Macrophyte-Dominated and Turbid States of Shallow Lakes: Evidence from Alberta Lakes , 2003, Ecosystems.

[9]  Erik Jeppesen,et al.  Seasonal dynamics in the concentrations and retention of phosphorus in shallow Danish lakes after reduced loading , 2002 .

[10]  L. Hansson,et al.  Effects of waterfowl and fish on submerged vegetation and macroinvertebrates , 2002 .

[11]  H. Sas,et al.  Lake restoration by reduction of nutrient loading: Expectations, experiences, extrapolations , 1990 .

[12]  S. H. Hosper.  Stable states, buffers and switches: An ecosystem approach to the restoration and management of shallow lakes in The Netherlands , 1998 .

[13]  B. Moss.  Brackish and freshwater shallow lakes — different systems or variations on the same theme? , 1994, Hydrobiologia.

[14]  R. Bjerring,et al.  Mid- to late-Holocene land-use change and lake development at Dallund Sø, Denmark: trophic structure inferred from cladoceran subfossils , 2005 .

[15]  J. Wanzenböck,et al.  Ecological Integrity Assessment of Lakes Using Fish Communities - Suggestions of New Metrics Developed in Two Austrian Prealpine Lakes , 2003 .

[16]  E. Jeppesen,et al.  Impact of fish predation on cladoceran body weight distribution and zooplankton grazing in lakes during winter , 2004 .

[17]  Juan Bald,et al.  Implementation of the European water framework directive from the Basque country (northern Spain): a methodological approach. , 2004, Marine pollution bulletin.

[18]  T. V. Madsen,et al.  The impact of grazing waterfowl on submerged macrophytes: In situ experiments in a shallow eutrophic lake , 1996 .

[19]  Henri J. Dumont,et al.  The dry weight estimate of biomass in a selection of Cladocera, Copepoda and Rotifera from the plankton, periphyton and benthos of continental waters , 1975, Oecologia.

[20]  M. Scheffer,et al.  Alternative equilibria in shallow lakes. , 1993, Trends in ecology & evolution.

[21]  Søren E. Larsen,et al.  Does resuspension prevent a shift to a clear state in shallow lakes during reoligotrophication? , 2003 .

[22]  Chris Ellegaard,et al.  Assessing Reference Conditions According to the European Water Framework Directive Using Modelling and Analysis of Historical Data: An Example from Randers Fjord, Denmark , 2003, Ambio.

[23]  Ter Braak,et al.  Canoco reference manual and CanoDraw for Windows user''s guide: software for canonical community ord , 2002 .

[24]  Katja Fennel,et al.  Subsurface maxima of phytoplankton and chlorophyll: Steady‐state solutions from a simple model , 2003 .

[25]  P. Rioual.  Limnological characteristics of 25 lakes of the French Massif Central , 2002 .

[26]  Erik Jeppesen,et al.  Trophic structure, species richness and biodiversity in Danish lakes: changes along a phosphorus gradient , 2000 .

[27]  E. Nielsen.  Photosynthesis of aquatic plants with special reference to the carbon-sources , 1947 .

[28]  B. Cumming,et al.  A regional paleolimnological assessment of the impact of clear-cutting on lakes from the central interior of British Columbia , 2001 .

[29]  E. Jeppesen,et al.  Response of submerged macrophytes in Danish lakes to nutrient loading reductions and biomanipulation , 2003, Hydrobiologia.

[30]  R. Wetzel.  Limnology: Lake and River Ecosystems , 1975 .

[31]  K. Sand‐Jensen,et al.  Alkalinity and trophic state regulate aquatic plant distribution in Danish lakes , 2000 .

[32]  M. Hammershøj,et al.  Does the impact of nutrients on the biological structure and function of brackish and freshwater lakes differ? , 1994, Hydrobiologia.

[33]  Erik Jeppesen,et al.  The Structuring Role of Submerged Macrophytes in Lakes , 1998, Ecological Studies.

[34]  Helen Bennion,et al.  Assessing eutrophication and reference conditions for Scottish freshwater lochs using subfossil diatoms , 2004 .

[35]  Engineering and biological approaches to the restoration from eutrophication of shallow lakes in which aquatic plant communities are important components , 1990 .

[36]  E. Jeppesen,et al.  Phosphorus release from resuspended sediment in the shallow and wind-exposed Lake Arresø, Denmark , 2004, Hydrobiologia.

[37]  G. Chiaudani,et al.  Lake management in Italy: the implications of the Water Framework Directive , 2003 .

[38]  B. Kronvang,et al.  Nationwide monitoring of nutrients and their ecological effects: state of the Danish aquatic environment , 1993 .

[39]  E. Jeppesen,et al.  Pond or lake: does it make any difference? , 2005 .

[40]  K. Christoffersen,et al.  Measurements of chlorophyll-a from phytoplankton using ethanol as extraction solvent , 1987, Archiv für Hydrobiologie.

[41]  Erik Jeppesen,et al.  Role of sediment and internal loading of phosphorus in shallow lakes , 2003, Hydrobiologia.

[42]  M. Dokulil,et al.  Eutrophication and restoration of shallow lakes – the concept of stable equilibria revisited , 2003, Hydrobiologia.

[43]  Brian Kronvang,et al.  Lake and catchment management in Denmark , 1999 .

[44]  Jan Köhler,et al.  Lake responses to reduced nutrient loading - an analysis of contemporary long-term data from 35 case studies , 2005 .

[45]  J. Lachavanne,et al.  Does size matter? The relationship between pond area and biodiversity , 2002 .

[46]  H. Bottrell.  A review of some problems in zooplankton production studies , 1976 .

[47]  K. L. Cottingham,et al.  THE RELATIONSHIP IN LAKE COMMUNITIES BETWEEN PRIMARY PRODUCTIVITY AND SPECIES RICHNESS , 2000 .