The study of spatial and temporal nutrient limitation in Meiliang Bay, Lake Taihu Longyuan Yang 1, Feizhou Chen 1, Yunling Zhang 1, Shixin Wang 2 (1 Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences; 2 Institute of Remote Sensing Applications, Chinese Academy of Sciences )

Purpose To measure nitrogen and phosphorus concentrations in Meiliang Bay, Lake Taihu, and analyze spatial and temporal variation of water quality parameters; To analyze the relationship between nutrient concentrations and dominant algae species. To study nutrient limitation status in Meiliang Bay, Lake Taihu.

Redfield Ratio If N:P ratio > 16, there is P limitation in the aquatic ecosystem; If N:P ratio < 16, there is N limitation in the aquatic ecosystem.

Background about limitation factor research in Lake Taihu Phosphorus is the limitation factor in Lake Taihu (traditional opinion); There is nitrogen limitation sites in some seasons and in some aquatic area (Martin Dokulil et al. 2000); There is a limitation factor change phenomenon that from Liangxi river discharge area to the main body of Lake Taihu (McCarthy et al. 2007)

Sampling sites Regular site: 25 (per 3 months) Add specific site: 20 (2 times in 2004) Total sites: 45

Distribution of sampling area NameSitesNL RangeS Number River discharge L0 K5 B3 B4 B6 B7 B Inner bay L1 L2 K2 K3 K4 K6 B5 B9 B10 B11 B Outer bay L3 L4 K1 K7 K8 B1 B2 B13 B14 B Open area L5 L6 K9 K10 K11 K12 K19 K Central area L7 L8 L9 K13 K14 K15 K16 K17 K

Function of Distribution NameFunctionDistance River Discharge Pollution area by point source from Liangxi and Lvjing River 0 km Inner B Near pollution source area of Bay 8 km Outer B Fare pollution source and near open area of Bay 16 km Open A Open area that connect with the Outer Bay 24 km Central A Main body of Lake Taihu 36 km

Results (Oct-2003 to Aug-2005) For whole research area

Spatial and temporal variation calculate of nutrients Spatial variation in research area were calculated by average of all sites in one distribution area; Annual variation were calculated by all sites in same distribution area and separated seasons.

Interval to Average Index (IA Index) I %=(C i -C m )*100/C m Where: I mean the IA index coefficient ; C i concentration of individual parameter; C m mean concentration of whole area

The ratio of nitrogen over phosphorus TN:TPWinSprSumFall MB MB MB MB MB

Annual variation characters summary In winter and spring seasons the mole ratio of TN:TP are more higher than Readfield ratio (16) ; but in summer and fall seasons the mole ratio of TN:TP are almost equal to Readfield ratio. So there is dominant P limitation in Winter and Spring seasons (Colder season, water temperature 20 o C ) except the P limitation in shore area of Lake Taihu. In open and central areas(B4 and B5) the mole ratio of TN:TP reduced serious than in river discharge area(B1) in whole year; so the open and central areas is the hot point for nitrogen limitation or nitrogen and phosphorus co- limitation mainly occur areas.

Dominant algae species in different areas (Oct. 27, 2003) AreaName% B1 Microcystis Merismopedia Scenesdesmus Cyclotella B2 Microcystis Chlamydomonas Euglena 8.08 Cyclotella 5.24 Cryptomonas 6.82 B3 Microcystis Merismopedia 1.81 Chlamydomonas 2.80 Scenesdesmus 2.12 B4 Merismopedia B5 Merismopedia Scenesdesmus 18.47

Conclusion There is a phenomenon that phosphorus limitation change to nitrogen limitation from Liangxi river discharge area to the main body (open area) of Lake Taihu; Summer and Fall seasons is the nitrogen Limitation occur season; especially in the area that far away from pollution river discharge area such as in central area of Lake Taihu The phenomenon that limitation factor changes may occur in all large shallow eutrophication lakes and estuaries in east part of China and other north temperate zones

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