tailieunhanh - RESTORATION AND MANAGEMENT OF LAKES AND RESERVOIRS - CHAPTER 9

Chuyên sâu nghiên cứu nhiều thập kỷ qua đã phát triển một sự hiểu biết về các yếu tố quy định phân phối, sự phong phú, năng suất, và thành phần loài thực vật phù du, đặc biệt là trong các hồ sâu (ý kiến Chọn và nạc, 1987; Hecky và Kilham, 1988; Kilham và Hecky, 1988, Seip năm 1994, trong số rất nhiều). Phương pháp phổ biến lâu dài kiểm soát của các loại tảo phiền toái là làm giảm nồng độ chất dinh dưỡng, một cách tiếp cận hỗ trợ bởi phòng thí nghiệm kiểm soát, bao vây. | 9 Biomanipulation INTRODUCTION Intensive research over many decades has developed an understanding of factors regulating distribution abundance productivity and species composition of phytoplankton especially in deep lakes reviews by Pick and Lean 1987 Hecky and Kilham 1988 Kilham and Hecky 1988 Seip 1994 among many . The common approach for long-term control of nuisance algae is to lower nutrient concentrations an approach supported by controlled experimental laboratory field enclosure and whole lake investigations demonstrating that phosphorus P and sometimes nitrogen N concentrations are causally linked especially on a long-term basis to algal production . Schindler 1977 Smith and Bennett 1999 . The link between P concentration and algal biomass is frequently illustrated with a log-log TP-chlorophyll regression indicating that most long-term changes in algal biomass are explained by changes in P concentration Figure . However when these data are plotted on a linear scale Figure especially on a short-term basis variances are apparent suggesting other factors in addition to nutrients can be important in determining algal biomass. For example Schindler 1978 found a highly significant correlation r between pelagic productivity and steady state lake P concentrations for 66 P-limited lakes shallow and deep ranging in latitude from 38 S to 75 N. The relationship however explained only about half of the variance meaning that P concentration and chlorophyll are highly correlated but that the relationship might be weak or non-existent for some lakes in some years or parts of years. Grazing mixing and or allelopathic materials might influence and or control algal biomass in these lakes. An example is Square Lake Minnesota Osgood 1984 a lake with a greater Secchi Disc SD transparency than expected from its TP concentration of about 20 pg P L mesotrophic . SD was more than 7 m during summer months a depth typical of oligotrophic lakes and apparently due .