Eutrophication

This is the most pervasive water quality problem on a global scale, being a primary cause of lake deterioration.

Table 1 Major freshwater lakes

Volume

Area

Max. depth

Lake

(km3)

(km2)

(m)

Lake Baikal

22 995

31 500

1 741

Lake

18140

32 000

1 471

Tanganyika

Lake Superior

12100

82100

170

Lake Malawi

6140

22 490

706

Lake Michigan

4920

57 750

110

Lake Huron

3540

59 500

92

Lake Victoria

2700

62 940

80

Lake Titicaca

903

8559

283

Lake Erie

484

25 700

64

Lake

48.5

571

254

Constance

Lake Biwa

27.5

674

104

Lake Maggiore

37.5

213

370

Eutrophication (nutrient enrichment) represents the natural aging process of many lakes in which they gradually become filled with sediments and organic materials over a typically geologic timescale. Human activities in a drainage basin can, however, dramatically accelerate this process. Its primary cause is the excessive inflow of nutrients (mainly phosphorus, sometimes nitrogen, sometimes both) to a water body from municipal wastewater treatment plants and industries, as well as drainage or runoff from urban areas and agricultural fields. Most lakes in densely inhabited regions of the world suffer from eutro-phication, both in industrialized and developing countries. The impacts of the eutrophication process include heavy blooms of phytoplankton in a water body. These blooms will inevitably result in (1) reduced water transparency; (2) decreased oxygen concentration in the water column, particularly in the bottom layer (hypolim-nion), which can cause fish kills and the remobilization or resuspension of heavy metals and nutrients into the water column; and (3) significant declines in the biodiversity of the lakes, including the disappearance of sensitive aquatic species. In shallow lakes, eutrophication can also cause an enormous increase in the growth of submerged and emergent rooted aquatic plants, as well as floating plants. This can lead to dramatic changes in the ecosystem structure.

If the sources of nutrients are removed or reduced significantly, the eutrophication problems can be fully controlled (see Figures 3 and 4). Lake Constance, also known as Bodensee, gives very illustrative examples. After the Second World War, the phosphorus concentration in the lake was about 0.01 mgP1 and the lake was oligotrophic. In the year 1980, the lake was mesotrophic to eutrophic and the phosphorus concentration was about 0.08 m gl~\Due to a massive reduction in the discharge of phosphorus from all sources, wastewater, agricultural drainage water, and septic tanks, it has been possible to reduce the phosphorus concentration to about

removed by siphoning

Figure 3 Abatement of eutrophication requires often the use of several methods at the same time, as shown here: removal of phosphorus from wastewater, construction of wetland to remove phosphorus from the inflowing tributary, and removal of hypolimnic (bottom) water by siphoning.

removed by siphoning

Figure 3 Abatement of eutrophication requires often the use of several methods at the same time, as shown here: removal of phosphorus from wastewater, construction of wetland to remove phosphorus from the inflowing tributary, and removal of hypolimnic (bottom) water by siphoning.

Figure 4 Lake Bled, where restoration by siphoning hypolimnic water has been applied.

0.013 mgP1 today. Lake Biwa, Japan, is illustrative of a partial solution of the problem (Figure 5). The discharge of phosphorus from wastewater has been significantly reduced since the 1970s, but due to almost no reduction in the phosphorus coming from agricultural drainage water, it has only been possible to stabilize the eutrophi-cation level at a phosphorus concentration about 0.035 mgl-1. If on the other hand, the phosphorus in wastewater would not have been reduced, the eutrophi-cation level would have increased.

Was this article helpful?

0 0
Oplan Termites

Oplan Termites

You Might Start Missing Your Termites After Kickin'em Out. After All, They Have Been Your Roommates For Quite A While. Enraged With How The Termites Have Eaten Up Your Antique Furniture? Can't Wait To Have Them Exterminated Completely From The Face Of The Earth? Fret Not. We Will Tell You How To Get Rid Of Them From Your House At Least. If Not From The Face The Earth.

Get My Free Ebook


Post a comment