Lake environments - Environmental Sedimentology

Geoscience Reference

In-Depth Information

4

Lake environments

Lars Håkanson

4.1

There is no generally accepted terminology as

to what is a lake, a pond or an inland sea, except,

of course, that ponds are small and inland seas

large. From Table 4.1, however, one can note that

there are 227,000 ponds, small lakes, lakes and

large lakes in Sweden alone and that ponds are

smaller than 1 ha and objects larger than 100 km 2

may be called large lakes. The primary focus of

this chapter is to discuss the role of sediments

and suspended particulate matter (SPM) in lakes.

How do sediments and SPM influence the sedi-

mentological and ecological function of lake

systems? What are the sedimentological controls

on the distribution and effects of environmental

pollutants? These could be, and have been, dis-

cussed from many perspectives and scales. This

chapter focuses on general principles and pro-

cesses, many of which are analogous to those

described in the chapters on riverine, coastal and

marine environments. The format of the chapter

will be to first discuss schemes for lake classifica-

tion and controls on lake forms (section 4.1).

Section 4.2 discusses sediment sources and the

resulting products. Section 4.3 focuses on natural

and anthropogenic disturbances on lake sediment-

ary systems; section 4.4 focuses on sediment

INTRODUCTION AND BACKGROUND

Lakes are important sedimentological environ-

ments. When a river enters into a lake, the section

area becomes wider, hence the flow velocity of

the running water is reduced and the particles

suspended in the water end up in a much calmer

environment where they can settle out. The

coarse and heavy particles carried by the river will

settle more rapidly than the smaller, less dense

particles. As a result, lakes function as 'sediment

traps' for materials and pollutants transported

in rivers. The consequences of this are that lakes

accumulate and retain pollutants, that lake sedi-

ments may be heavily contaminated and that

lake sediment cores are excellent for studies of

the historical development of contamination.

In addition, lake sediments are good records

of temporal changes in the landscape and are

important systems for studying the ecosystem

effects of pollutants. Lakes are also extremely

important freshwater resources, important for

recreation and totally dominate the landscape

of certain regions. As a result, there are many

reasons why lakes are target systems for research

and management.

Table 4.1 The number of lakes

in Sweden arranged by size

(1 km 2

Area (km 2 )