大型水生植物—藻类混合型富营养湖泊的生态管理模式——以固城湖为例

Lake Gucheng is located in the southeast of Nanjing, with an area of 24.3 km², an average depth of 2 meters. The macrophytes of the lake were used to be abundant and their biomass was about 4.96 mg·m^-2. The annual average contents of total phosphorus (TP), total nitrogen (TN), PO^3- -P, COD_Mn and BOD₅ 0.03, 1.31, 0.005, 3.61 and 1.46 mg·L^-1, respectively. Thus, the water quality of this lake is quite well. Recently, the water quality in pari of the lake became worse because of some unreasonable exploitation and utilization of bioresources. The interactions between phytoplankton (N₁), macrophyte (N₂), fish (N₃), crab (N₄) were studied here. The macrophyte has great influences on both phytoplanktons, fish and crab, controlling the water quality and maintaining the fishery productivity. On the other hand, the phytoplankton, fish and crab also influence the macrophyte. It is key method of ecological management to maintain the macrophyte by fishery culture. Therefore, a modified Lotka-Volterra model has been established to estimate the interaction between N₁, N₂, N₃, N₄ and the influences of some water environmental parameters on these aquatic organism, environmental and economic effect. The main model consists four compart-mental models and four submodels, involved 12 external variables, 8 state variables, 19 universal constants and 11 parameters. The values of most parameters were found from our experiments and calibrated by the model and actually measured data. The model has been validated by comparison the computed and experimental data of phytoplankton and macrophyte. The theoretical outputs showed a good agreement with the measured data. This model predicated that if the standing crop offish and crab was higher than 2.65 ·m^-2 during springtime in this lake, macrophytes would not grow, chlorophyll a content would arrive 34.8 mg·m^-3 and the water quality would decrease. If the macrophyte grow well, the maximum fishery productivity would be about 1 600 t. In this case, the annually averaged phytoplankton chlorophyll a content should be 3.69 mg·m^-3, which is lower than the criterion (10 mg·m^-3) for eutrophic state. From 1991 to 1996, Lake Gucheng was managed with this model, its water quality maintain quite well, chlorophyll a content decreased from 3.51 (1991) to 1.89 mg·m^-3 (1994). Meanwhile, the fishery productivity increased and the economic effect heightened year by year.     

太湖：过去、现在和将来

The presence of roads, farm house foundations, wells and Liangzhu period cultural relics in the bottom of Lake Taihu attest to the fact that this shallow depression was probably dry between 4 and 5 thousand years ago. This interpretation is corroborated by the sudden disappearance of algal pigments at sediment depths carbon-14 dated at 4-5 thousand years before present.In winter, the stronger winds are predominantly from the northeast. These winds result in a powerful counterclockwise current that transports lake sediments and has altered the very shape of the lake over the last 300 years. Winds produce a complex mixing pattern in Lake Taihu with storm induced sediment deposition occurring near the lake''s center.During approximately 240 days of the year, the wind blows across Lake Taihu with sufficient force to mix it to its bottom. As a result, this polymictic lake rarely becomes anoxic and dissolved oxygen at the mud water interface is maintained at or above 4 mg·l^-1. The consequences of this high dissolved oxygen are quite impressive as high organic loading to the lake would otherwise render its bottom waters anaerobic killing many of its natural inhabitants.Because suspended solids reduce (attenuate) light penetration, the major primary production takes place in the top metre of the lake (mean Secchi Transparency-0.25 m). Suspended clays are slow to settle and wind mixing keeps fine-grained suspended solids in suspension in all but the most quiet backwaters of the lake.In the recent past about 23 000 metric tonnes of phytoplankton were produced in Lake Taihu. This large production represents only about 5% of the total influx of organic material entering the lake. In summer and fall, cyanobacteria such as Microcystis spp. and Anabaena spp. dominate most of the lake. Recently, however, mixotrophic flagellates displaced cyanobacteria as the dominant algae in parts of Lake Taihu with high bacteria and high suspended solids (e.g. Wuli and Meiliang Bay). In the future, facultative heterotrophs may come to dominate an ever larger portion of the lake waterc column.     

Distribution and origin of biologically available phosphorus in the water of the Meiliang Bay in summer

The investigation and continuous monitoring with an innovative iron oxide embedded cellulose acetate membrane (FeO/CAM) on the concentrations of biologically available phosphorus (BAP) were conducted in the Meiliang Bay of the Taihu Lake during summer in 2004. The results showed that the concentrations of dissolved (FeO-DP), particulate (FeO-PP) and total bioavailable phosphorus (FeO-P) had similar horizontal distribution. The BAP concentrations were the highest in those estuaries in the northern bay. With the decrease of the distance to the estuary or long shore, there was little difference between BAP concentrations in an open lake area. During the observation period, algal blooms occurred in most waters of the northern bay, which was reflected from the high concentrations of chlorophyll a (Chl-a). While they were not highest in the estuarine waters of those major rivers, this is the case for the BAP concentrations. The concentrations of Chl-a had a significantly positive correlation with those of bioavailable phosphorus in the open area of the Meiliang Bay. With the sediment resuspension induced by wind and wave, BAP concentrations increased in a short-term, indicating that the riverine P inputs mainly contribute to the concentrations of BAP in the estuarine water while internal P release was the major source of BAP in the open lake area. In the eutrophic shallow lake, the blooms of alga may cause pH increase and further result in internal P release. The above results showed that the new membrane of FeO/CAM can be used to monitor the concentrations of BAP and provide the scientific justifications for the control strategy of the lake eu-trophication.     

中国太湖五里湖内不同凤眼莲密度圈闭内的沉降率

The dynamic model of physical-biological engineering for purifying water quality in Lake Taihu needs the parameter of sedimentation rate (SR). Especially, it is seldom reported how SR is influenced by interactions between algae and aquatic plant. So 6 enclosures with each area of 5×5 m² were constructed in Wulihu with 2 m depth, a small hypereutrophic bay of Taihu Lake, China. Enclosures, in which the original water quality was the same as that in surrounding lake, were input Eichhomia crassipes at various original densities from 0-6 kg·m^-2 on August 9, 1996. SR had been measured separately at depths of 0.6, 1.2f 1.8 m in each enclosure during 20 days. Main results were as follows:1) SR average in enclosures (17.3g·m^-2 d^-1) was as much as about 1/14 that in the surrounding lake; 2) The deeper was it, the higher rate was it in each enclosure, generally; 3) SR cures versus original densities of Eichhomia crassipes (ODE) in enclosures had the ship of "V" at different depths; SR minimuma were observed in the enclosure with original meso-density of Eichhomia crassipes (EMESO, 4kg·m^-2), the average of SR minimuma was about 8.55 g ·m^-2 d^-1) SR in enclosures with original hypo-density (EHYPO, 0-3kg·m^-2) were mainly negative related with water temperature and light intensity;while those with original hyperdensity (EHYPR, 5-6kg·m^-2) were mainly negative related with transparency (SD) instead.These SR-distribution characteristics may be explained by interactions between dead algae and relics of Eichhomia crassipes.     

The Calculation Method for the Volume of Landslides and Dammed Lake Sediments Triggered by a Strong Historical Earthquake in the Loess Plateau: A Case Study of Qiuzigou, Gansu Province, Northwest China

The quantitative calculation of the volume of large earthquake-triggered landslides and related dammed lake sediments is of great significance in the study of secondary disasters and focal parameters of strong historical earthquakes. In this study, the dammed lake induced by Qishan M7 earthquake (Lingtai County, Gansu Province, Northwest China) is selected as the research object. Based on the information collected from the 4 boreholes in the dammed lake area, we further take advantage of the low-level Unmanned Aerial Vehicle (UAV) photogrammetry and the morphology recovery method,to calculate the volume of the dammed lake and landslides, respectively. Finally, major conclusions are obtained as follows:① the AMS-¹⁴C age at the bottom of the Qiuzigou Dammed Lake sediments is 2 890±30 BP, which coincides with the 780 BC Qishan earthquake; furthermore, the Qiuzigou Landslides seem to have been triggered by the earthquake, forming an enclosed dammed lake deposition environment after the upstream sediments accumulate;② the Qiuzigou landslides are opposite-sliding landslides that have blocked the river valley; in detail, landslide volumes at the right and left banks are 235×10⁴ m³ and 229×10⁴ m³, respectively. The length of the dammed lake is 2.6 km, with a thickness of approximately 43 m near the landslides, and the total sedimentary volume is 573×10⁴ m³; ③the erosion rate of Qiuzigou Landslide Dammed Lake is 0.44 mm/a, the accumulation rate is 15.05 mm/a, and the soil erosion modulus is 593 t/(km²/a), characterized as slight erosion. Quantitative research on the formation of landslides and dammed lakes from strong historical earthquakes is vital for increasing our understanding of the vibrational characteristics and surface action processes of these types of earthquakes.     

Biological mechanisms driving the seasonal changes in the internal loading of phosphorus in shallow lakes

Because of the obvious importance of P as a nutrient that often accelerates growth of phytoplankton (including toxic cyanobacteria) and therefore worsens water quality, much interest has been devoted to P exchange across the sediment-water interface. Generally, the release mode of P from the sediment differed greatly between shallow and deep lakes, and much of the effort has been focused on iron and oxygen, and also on the relevant environmental factors, for example, turbulence and decomposition, but a large part of the P variation in shallow lakes remains unexplained. This paper reviews experimental and field studies on the mechanisms of P release from the sediment in the shallow temperate (in Europe) and subtropical (in the middle and lower reaches of the Yangtze River in China) lakes, and it is suggested that pH rather than DO might be more important in driving the seasonal dynamics of internal P loading in these shallow lakes, i.e., intense photosynthesis of phytoplankton increases pH of the lake water and thus may increase pH of the surface sediment, leading to enhanced release of P (especially iron-bound P) from the sediment. Based on the selective pump of P (but not N) from the sediment by algal blooms, it is concluded that photosynthesis which is closely related to eutrophication level is the driving force for the seasonal variation of internal P loading in shallow lakes. This is a new finding. Additionally, the selective pump of P from the sediment by algal blooms not only explains satisfactorily why both TP and PO4-P in the hypereutrophic Lake Donghu declined significantly since the mid-1980s when heavy cyanobacterial blooms were eliminated by the nontraditional biomanipulation (massive stocking of the filter-feeding silver and bighead carps), but also explains why TP in European lakes decreased remarkably in the spring clear-water phase with less phytoplankton during the seasonal succession of aquatic communities or when phytoplankton biomass was decreased by traditional biomanipulation. Compared with deep lakes, wax and wane of phytoplankton due to alternations in the ecosystem structure is also able to exert significant influences on the P exchange at the sediment-water interface in shallow lakes. In other words, biological activities are also able to drive P release from sediments, and such a static P release process is especially more prominent in eutrophic shallow lakes with dense phytoplankton.     

Contributions of phosphatase and microbial activity to internal phosphorus loading and their relation to lake eutrophication

Phosphatase may accelerate the process of lake eutrophication through improving phosphorus bioavailability. This mechanism was studied in three Chinese eutrophic shallow lakes (Lake Taihu, Lake Longyang and Lake Lianhua). Phosphatase activity was related to the concentration of soluble reactive phosphorus (SRP) and chlorophyll a. Stability of dissolved phosphatase in reverse micelles may be attributed to molecular size, conformation and active residues of the enzyme. At the site with Microcystis bloomed in Lake Taihu, dissolved phosphatase activity was higher and more stable in micelles, SRP concentrations were lower in interstitial water, the contents of different forms of phosphorus and the amounts of aerobic bacteria were lower while respiration efficiency was higher in sediments. Phosphobacteria, both inorganic and organic and other microorganisms were abundant in surface water but rare in sediments. Therefore, internal phosphorus may substantially flux into water column by enzymatic hydrolysis and anaerobic release, together with mobility of bacteria, thereby initiating the bloom. In short, biological mechanism may act in concert with physical and chemical factors to drive the internal phosphorus release and accelerate lake eutrophication.     

Spatiotemporal variations of internal P-loading and the related mechanisms in the large shallow Lake Chaohu

Spatiotemporal variations of P species and adsorption behavior in water column, interstitial water, and sediments were investigated in the large shallow eutrophic Lake Chaohu. Ortho-phosphate (Ortho-P) and total phosphorus (TP) concentrations were significantly higher in the western part than in the eastern part of the lake, due to different nutrient inputs from the surrounding rivers. Moreover, paniculate phosphorus (PP) concentration was in a similar spatial pattern to Ortho-P and TP concentrations, and also showed significantly positive correlation with the biomass of Microcystis, indicating more uptake and store of phosphorus by Microcystis than by other algae. Increase of pH and intensive utilization of P by phytoplankton were the main factors promoting P (especially Fe-P) release from the sediment to interstitial water during the cyanobacterial blooms in Lake Chaohu. Spatial dynamics in TP concentration, P species and adsorption behavior of the sediment, coupled with the statistical analyses, suggested that the spatial heterogeneity of P contents in the sediment was influenced by various factors, e.g. human activities, soil geochemistry and mineral composition. In spite of similar TP contents in the sediments, increase in proportion of Fe-P concentration in the sediment may result in a high risk of P release.     

太湖水质及其保护

Lake Taihu, the third largest fresh water lake in China, with a surface area of 2 338 km², is located in the Changjiang River Delta, the most advanced economic zone in China. During the last two decades, the rapid economic development of local agriculture and industry both in the urban and rural areas of the region has made great advances. Great quantieis of pollutants have been discharged into the lake, its nutrient content has increased continuously, and phytoplankton blooms have occurred in some areas. Water quality protection in Lake Taihu is very important because of its close relation with economical development and people''s daily life. It is urgent to have comprehensive pollution control in Lake Taihu. Based on water quality monitoring data in Lake Taihu from 1987 to 1994, the dynamic variations of water quality and eutrophication trends have been analyzed, showing obvious spatial and temporal variations. The main water quality factors were compared with the standard for drinking water and indicate considerable change with the seasons. Some basic strategies to protect water quality and prevent eutrophication are discussed.     

Nano-and microphytoplankton community characteristics in brown tide bloom-prone waters of the Qinhuangdao coast,Bohai Sea,China

Since 2009, the newly recorded species Aureococcus anophagefferens has successively induced brown tides in the Qinhuangdao coastal waters of the Bohai Sea. Here, we focus on the phytoplankton community structure in this region and try to point out the biological background characteristics of the outbreaks of successive brown tides. We analyzed species composition,cell abundance, diversity indices and size-fractionated chlorophyll a(Chl-a) concentration monthly from March 2013 to January2014. The phytoplankton community, as observed by microscopy, underwent succession from nano-celled chained diatoms to dinoflagellates in the spring and summer, and then to micro-celled diatoms and nano-celled chained diatoms as the most prominent groups in the subsequent autumn and winter. Canonical correspondence analysis revealed that changes in the abundance of diatoms were related to nutrient availability, especially of nitrogen, while water temperature was the crucial factor influencing the abundance of dinoflagellates and A. anophagefferens. Considering the contribution of nano-celled chained species to the micro-sized Chl-a,small phytoplankton(20 μm) composed the majority of total Chl-a and were generally abundant during our study. Abundant and diverse small phytoplankton seemed to serve as a background or seedbank for the formation of blooms of A. anophagefferens and other small-celled algae.     

垂向归纳模型下鄱阳湖丰、枯水期初级生产力特征及与环境因子相关性分析

于2014年1月(枯水期)、7月(丰水期)对鄱阳湖湖水进行采集,测定相应的理化参数、叶绿素a浓度和光合有效辐射,结合初级生产力垂向归纳模型估算浮游植物初级生产力,分析湖区初级生产力特征及与环境因子的相关性.结果表明,鄱阳湖枯水期浮游植物初级生产力波动范围为83.50~355.43 mg C/(m~3·d),平均值为193.33 mg C/(m~3·d),初级生产力空间分布特征主要受水体类型的影响,枯水期初级生产力与氮、磷营养盐浓度呈负相关,其中与铵态氮浓度呈显著负相关,枯水期不会出现营养盐限制现象;丰水期浮游植物初级生产力波动范围为113.80~1134.06 mg C/(m~3·d),平均值为412.12 mg C/(m~3·d),初级生产力空间分布主要受河流注入的影响,丰水期浮游植物初级生产力与总磷及悬浮物浓度呈显著正相关,由于悬浮物对浮游植物生长的促进作用大于抑制作用,鄱阳湖丰水期会出现磷营养盐的限制;鄱阳湖整体平均流速约为0.28 m/s,易于浮游植物的生长,南鄱阳湖平均流速约为0.21 m/s,而北鄱阳湖平均流速约为0.35 m/s,所以南鄱阳湖比北鄱阳湖更容易发生水体富营养化并暴发水华.     

富营养化初期湖泊放养鲢(Hypophthalmichthys molitrix)、鳙(Aristichthys nobilis)控藻生态效果的初步评估

放养鲢（Hypophthalmichthys molitrix）、鳙（Aristichthys mobilis）控制富营养化湖泊蓝藻水华暴发是当前最有效的手段之一.为评估富营养化初期湖泊鲢、鳙控藻的生态效果,2016年在洱海红山湾开展原位围栏鲢、鳙控藻实验,对围栏内外的浮游生物群落结构及水环境因子的变化进行对比分析,同时测定了围栏内鲢、鳙的生长及摄食节律.结果表明：围栏内鲢、鳙呈现匀速生长,围栏生存环境适宜.根据Egger''s模型估算鲢、鳙的日摄食量分别为24.96%和18.18%,鲢的日粮高于鳙;滤食率结果表明,鲢对浮游植物的摄食率高于鳙（分别为3.01和2.19 L/（g·h）,而鳙对浮游动物的滤食率高于鲢（分别为18.61和13.54 L/（g·h））.研究期间,围栏内外水体理化因子无显著差异;但围栏内外微囊藻生物量差异明显,并且在7月达到生物量峰值（围栏内为1.7 mg/L,围栏外为2.4 mg/L）.鲢、鳙对浮游植物的优势种类——微囊藻和隐藻有明显的削减效果,6-8月逐渐上升并在8月达到最高（64%）;当浮游植物优势种由微囊藻替换为硅藻门和绿藻门的种类时,鲢、鳙的削减效率不明显（10-11月为负值）.此外,鲢、鳙放养显著降低了浮游甲壳动物的总生物量和枝角类生物量.因此,结合实验结果得出,鲢具有更高的控藻能力,尤其对微囊藻水华,但同时具备了较高对浮游甲壳动物的削减能力,需要进一步分析富营养化初期湖泊——洱海中实施非经典生物操纵的适宜性.     

Spring and summer blooms of phytoplankton (SeaWiFS/MODIS) along a ferry line in the Bay of Biscay and western English Channel

The seasonal cycle of chlorophyll concentration in the Bay of Biscay and western English Channel has been examined using satellite data (chlorophyll, sea surface temperature (SST), photosynthetically available radiation (PAR) and wind) along the line of the ferry Pride of Bilbao (Bilbao to Portsmouth). The spring phytoplankton bloom develops regularly in the oceanic region of the Bay of Biscay from mid March to the beginning of May with peak chlorophyll concentrations ranging 2–4 mg m^?3. Low wind turbulence is a major factor allowing the development of productivity pulses in the Bay of Biscay during spring. Exceptional blooms of phytoplankton take place in summer (July–August) in the western English Channel with chlorophyll concentrations as high as 40 mg m^?3. Some environmental factors (SST, wind, pressure and tide) are examined. Autumn blooms of phytoplankton (1–2 mg m^?3) are also detected in the northern Bay of Biscay, shelf-break and Celtic Sea in October. A 11 years pluri-annual synthesis of SeaWiFS satellite measurements is presented.     

Validation of SeaWiFS chlorophyll a in Massachusetts Bay

Massachusetts Bay, a semi-enclosed embayment (50×100 km) in the Northwest Atlantic, is the focus of a monitoring program designed to measure the effects of relocating the Boston Harbor sewage outfall to a site 15 km offshore in Massachusetts Bay. The Massachusetts Water Resources Authority (MWRA) in situ monitoring program samples selected stations up to 17 times per year to observe seasonal changes in phytoplankton biomass and other water quality variables. We investigated the feasibility of augmenting the monitoring data with satellite ocean color data to increase the spatial and temporal resolution of quantitative phytoplankton measurements. In coastal regions such as Massachusetts Bay, ocean color remote sensing can be complicated by in-water constituents whose concentrations vary independently of phytoplankton and by inaccurate modeling of absorbing aerosols that tend to be concentrated near the coast. An evaluation of in situ and sea-viewing wide field-of-view sensor (SeaWiFS) measurements from 1998 to 2005 demonstrated that SeaWiFS overestimated chlorophyll a mainly due to atmospheric correction errors that were amplified by absorption from elevated concentrations of chlorophyll a and colored dissolved organic matter. Negative water-leaving radiances in the 412 nm band, an obvious artifact of inadequate atmospheric correction, were recorded in approximately 60–80% of the cloud-free images along the coast, while the remaining portions of the Bay only experience negative radiances 35–55% of the time with a clear nearshore to offshore decrease in frequency. Seasonally, the greatest occurrences of negative 412 nm radiances were in November and December and the lowest were recorded during the summer months. Concentrations of suspended solids in Massachusetts Bay were low compared with other coastal regions and did not have a significant impact on SeaWiFS chlorophyll a measurements. A regional empirical algorithm was developed to correct the SeaWiFS data to agree with in situ observations. Monthly SeaWiFS composites illustrated the spatial extent of a bimodal seasonal pattern, including prominent spring and fall phytoplankton blooms; and the approximate 115 cloud-free scenes per year revealed interannual variations in the timing, magnitude and duration of phytoplankton blooms. Despite known artifacts of SeaWiFS in coastal regions, this study provided a viable chlorophyll a product in Massachusetts Bay that significantly increased the spatial and temporal synoptic coverage of phytoplankton biomass, which can be used to gain a comprehensive ecosystem-wide understanding of phytoplankton dynamics at event, seasonal and interannual timescales.     

The effect of drawdown on suspended solids and phosphorus export from Columbia Lake,Waterloo, Canada

This study examines the effect of drawdown on the timing and magnitude of suspended solids and associated phosphorus export from a 12 ha reservoir located in an urbanized watershed in southern Ontario, Canada. Water level in Columbia Lake was lowered by 1·15 m over a 2‐week period in November 2001. The total phosphorus (TP) concentrations ranged from 63 to 486 µg L^?1 in Columbia Lake and 71 to 373 µg L^?1 at its outflow. All samples exceeded the Provincial Water Quality Objective of 30 µg TP L^?1. Outflow concentrations of suspended solids and TP increased significantly with decreasing lake level and were attributed to the resuspension of cohesive bottom sediments that occurred at a critical threshold lake level (0·65 m below summer level). Suspended solids at the outflow consisted of flocculated cohesive materials with a median diameter (D₅₀) of c. 5 µm. Particulate organic carbon accounted for 8·5% of the suspended solids export by mass. A total mass of 18·5 t of suspended solids and 62·6 kg TP was exported from Columbia Lake, which represents a significant pulse of sediment‐associated P to downstream environments each autumn during drawdown. The downstream impacts of this release can be minimized if the water level in Columbia Lake is lowered no more than 0·5 m below summer levels. Copyright © 2004 John Wiley & Sons, Ltd.     

江汉平原长湖浮游植物初级生产力的季节性变化及其驱动因子

为探究长江中下游富营养化浅水湖泊的浮游植物初级生产力季节性演替特征及其驱动因子,本研究于2020年4月(春)、8月(夏)、10月(秋)及2021年1月(冬)对湖北长湖浮游植物进行采样调查,同时运用黑白瓶测氧法及VGPM模型估算法分别估算了其浮游植物生产力水平,并探究驱动初级生产力季节性变化的主要环境因子。结果显示,4个季节共鉴定出浮游植物194种,其中绿藻门(95种,49%)和硅藻门(40种,21%)居绝对优势地位;黑白瓶法测得浮游植物水柱总生产力(P_t)季节变化为:夏季((1841.24±345.93) mg C/(m²·d))>秋季((1324.14±208.34) mg C/(m²·d))>春季((847.50±247.72) mg C/(m²·d))>冬季((711.43±133.52) mg C/(m²·d)),其中M2站位在夏季采样时(2424.66 mg C/(m²·d))水柱总生产力最高;在垂直空间上,浮游植物总生产力(G...     

Hydrobiological Investigations of the Water Quality of the Water Supply Reservoirs Husinec and Římov

The two eutrophicated reservoirs Husinec (2.6 km³, 35 ha, z_max 18 m, MQ 1.87 m^3/s) and ?ímov (34.5 hm³, 216 ha, z_max 44 m, MQ 4.14 m^3/s) show concentrations of total phosphorus of 10… 50 mg/m³ and chlorophyll contents of 7… 36 mg/m³ in the summer season. For both reservoirs a good correlation exists between the chlorophyll concentration and the density of the phytoplankton (20 · 10³… 13 · 10⁶ ind./l). With average concentrations of 10… 20 mg/m³ chlorophyll a in summer, the water can be treated for producing drinking water only at a higher expenditure. The water quality will be improved by a reduction of the phosphorus load.