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首页> 外文期刊>Lakes & Reservoirs >Trophic evolution of Lake Lugano related to external load reduction: Changes in phosphorus and nitrogen as well as oxygen balance and biological parameters
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Trophic evolution of Lake Lugano related to external load reduction: Changes in phosphorus and nitrogen as well as oxygen balance and biological parameters

机译：卢加诺湖的营养演化与外部负荷减少相关：磷和氮的变化以及氧平衡和生物学参数

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摘要

Lake Lugano is located at the border between Italy and Switzerland and is divided into three basins by two narrowings. The geomorphologic characteristics of these basins are very different. The catchment area is characterized by calcareous rock, gneiss and porphyry; the population amounts to approximately 290 000 equivalent inhabitants. The external nutrient load derives from anthropogenic (85%), industrial (10%) and agricultural (5%) sources. The limnological studies carried out by Baldi et al. (1949) and EAWAG (1964) revealed early signs of eutrophication, with a phosphorous concentration of about 30–40 mg m–3 and an oxygen concentration of less than 4 g m–3 in the deepest hypolimnion. Subsequently Vollenweider et al. (1964) confirmed these data and was the first to point out the presence of a meromictic layer in the hypolimnion of the northern basin. From the 1960s, as a result of an increase in the population and internal migration, the lake became strongly eutrophic with the P concentration reaching 140 mg m–3 and the oxygen in the hypolimnion reduced to zero. Fifty-five per cent of the P was from metabolic sources and 45% from detergents and cleaning products. In 1976, a partial diversion of waste water from the northern to the southern basin was begun, and gradually eight waste water treatment plants came into operation using mechanical, chemical and biological treatments. In 1986, Italy and Switzerland began to eliminate the P in detergents and cleaning products. Since 1995, the main sewage treatment plants have improved their efficiency by introducing P post-precipitation, denitrification and filtration treatments. The recovery of the lake is due to be completed by the year 2005. Altogether, during the last 20 years recovery measures have reduced the external P load from about 250 to 70–80 tonnes year–1; the goal to be reached is 40 tonnes year–1. In-lake phosphorous concentrations have decreased from 140 to 50–60 mg m–3, with the target at 30 mg m–3. Dissolved oxygen concentration is satisfactory only between the depths of 0 and 50 m, falling rapidly to zero in the deepest layers. Below a depth of 90 m, high CH4, HS–, NH4+, Fe2+ and Mn2+ concentrations exist. Primary production has decreased from 420 to 310 g Cass m–2 year–1, notwithstanding an increase in the thickness of the trophogenic layer. Structure and dynamic biomass show marked changes: phytoplankton dry weight has decreased from 16 to 7 g m–2, while zooplankton dry weight has increased from 3 to 4.5 g m–2. Chlorophyll concentration has fallen from 14 to 9 mg m–3 and Secchi disk transparency has increased from 3.5 to 5.5 m. The current sources of the external load are uncollected small urban conglomerations, storm-water overflows from outfall sewers, and the residual load from sewage treatment plants, particularly those without P post-precipitation.
机译：卢加诺湖位于意大利和瑞士之间的边界，被两个狭窄区域分成三个盆地。这些盆地的地貌特征非常不同。集水区以钙质岩，片麻岩和斑岩为特征。人口大约为29万当量居民。外部营养负荷来自人为（85％），工业（10％）和农业（5％）来源。 Baldi等人进行的语言学研究。 （1949年）和EAWAG（1964年）揭示了富营养化的早期迹象，最深层次磷中的磷浓度约为30-40 mg m-3，氧浓度低于4 g m-3。随后Vollenweider等。 （１９６４）证实了这些数据，并且是第一个指出北部盆地下缘的铁质层的存在。从1960年代开始，由于人口增加和内部迁徙，该湖变得富营养化，磷浓度达到140 mg m–3，次纤毛中的氧气减少至零。磷的百分之五十五来自代谢来源，百分之四十五来自洗涤剂和清洁产品。 1976年，开始将废水从北部流向南部流域，并逐步通过机械，化学和生物处理方法运行了8个废水处理厂。 1986年，意大利和瑞士开始消除洗涤剂和清洁产品中的P。自1995年以来，主要的污水处理厂通过采用P后沉淀，反硝化和过滤处理提高了效率。该湖的恢复工作将于2005年完成。在过去的20年中，恢复措施已将第一年的外部磷负荷从大约250吨减少到70-80吨。第一年要达到40吨的目标。湖中磷的浓度已从140 mg m-3降至50-60 mg m-3，目标浓度为30 mg m-3。溶解氧浓度仅在0至50 m深度之间令人满意，在最深层迅速降至零。在90 m深度以下，存在高浓度的CH4，HS–，NH4 +，Fe2 +和Mn2 +。尽管生液层的厚度增加了，但第一年的产量已从420 g Cass m–2年–1下降到310 g Cass m–2。结构和动态生物量显示出显着变化：浮游植物干重从16减少到7 g m-2，而浮游动物干重从3减少到4.5 g m-2。叶绿素浓度已从14降至9 mg m-3，Secchi圆盘透明度已从3.5升高至5.5 m。当前外部负荷的来源是未收集的小型城市集团，排污口的雨水溢出以及污水处理厂的残余负荷，特别是那些没有磷后沉淀的污水处理厂。

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