Brigitte Nixdorf, Jacqueline Rücker, Ingo Henschke, Ronny Hämmerling BTUCottbus, 1 IGB Berlin, Water quality and biodiversity in Lake Scharmützelsee from 1993 to 2005 Lakepromo October 2005

1.Since 1990 a drastic reduction of the external P load was calculated and measured 2.The current external P load of lake Scharmützelsee with 0.8 t a -1 P, estimated by the MONERIS model, is very low compared with the internal P release with 6.75 t a -1 P. 3.L. Scharmützelsee shows the tendency to better ecological quality. Is this observation confirmed by ecological water quality components (phytoplankton biomass and diversity, macrophytes, fish)? Results from April 2005/ Question in Oct. 2005:

1.1 Quality elements for the evaluation of lakes and ecological status – present state in Germany – Practical tests in 2005/2006

Lake Scharmützelsee region : Urban areas 15.8 % Agricultural crop land 13.7 % Grassland 3.8 % Forrest 53.2 % Surface waters 10.6 % Wetlands 2.1 %

External phosphorus inputs into the lake Scharmützelsee by point sources (sewage effluent, military hospital) and diffuse sources 1969 and 2001 No further reduction of external loads!

Input of phosphorous (TP) from different sources into lake Scharmützelsee from 1996 to 2000 calculated by MONERIS-model Groundwater TP- concentration between µg/L

Dynamics of phosphorus: Decreasing trend in TP, but high internal P-release Precipitation of P?

Phytoplankton

Phytoplankton dynamics in lake Scharmützelsee Data: Zippel, Hoehn – LBH)

Good ecological status for lake Scharmützelsees (Phytoplankton Report (/2005) Biovolume [mm 3 L -1 ] *:0.5 – 2 Chl a [µg L -1 ] *:2.5 – 10 Considering the trophic state from good ecol. state means: Reduction of phytoplankton biomass by at least 50% Increase in Secchi depth by more than 100% to more than 2 m during the vegetation period

Assessment of ecological state of lake Scharmützelsee acc. to LAWA (1999) and WFD (2000) LAWA (1999) Reference state (morphometry) mesotroph Natural nutrient input mesotroph Present statee2e1m e2m* Assessment321231#1# WFD (2000) - Phytoplankton Biovolume (BV) [mm 3 L -1 ]* 3,45,3 – 8,61,16,39,91,4 # Assessment acc. to BV

Number of phytoplankton taxa in L. Scharmützelsee and trendline from 1993 to 2005 (between per sample) Person A Person C/D Person B

Macrophytes

Distribution of species groups (macrophytes) within one lake type across a degradation gradient

Dominant species of macrophytes in L. Scharmützelsee 1994 and 2005 Increase in dominant species number from 5 to 12, good species (Nittellopsis, Stratiotes, Najas) as well as bad species (Elodea, Ranunculus)

Fish ( z.B. Gründling, Steinbeißer im Litoral des Müggelsees)

Number of fish taxa in L. Scharmützelsee (historical reports and before 1990 and now): Increase from about 15 to 28 (acc. to the reference state)

External nutrient inputs (TP) have been reduced during the last 15 years by more than 90 % Main nutrient pathways are internal P-release from the sediments and input from the groundwater as well as atmospheric deposition. Species numbers for macrophytes and fish increased, diversity for phytoplankton depends on taxonomic knowledge L. Scharmützelsee reached a threshold for TP – reduction in phytoplankton biomass and composition – but shows annual fluctuations mainly due to: Climatic influences, Biological food web interaction, Low silica concentrations favouring cyanobacteria Summary

Kenngrößen Phytoplankton nach trophiebasierter Voreinstufung und typspezifischen Referenzzuständen Biomassesindex Indikatortaxa Chlorophyll a Gesamt- biovolumen Algenklassen Einzelmetrics gelten für ausgewählte Seen-Typen und Bewertungszeiträume Phytoplankton-Taxa-Seen-Index a - - 2b - - 2c Taxonomische Zusammensetzung - Bewertung Summe Indices 1-3(4)/ (Summe F x ) = Trophischer Index Indices GFBiomasse- Bewertung planktische Diatomeen Profundal nur für Tieflandseen, wenn Diatomeenanalyse Plankton fehlt und/oder weniger als 4 Indikatortaxa ( 4 ) x F 1 x F 2 x F 4 Mittelwert aus Einzelmetrics 2 x F 3

Klassengrenzen für Gesamtbiovolumen schlecht 5 >20 >30 >40 >25

Lake types in the German lowlands and phytoplankton biomass

Degradation of lakes in Germany acc. to the lake types (phytoplankton biomass) Number of lakes