CE4505 – Surface Water Quality EngineeringLecture 2. Water in LandscapesA. The Landscape ConceptIn this lecture, we examine the interaction of lakes (and reservoirs) with the land, combining concepts of limnology (the study of lakes) and landscape ecology (the study of interactions between spatial patterns and ecological processes). Limnology explores the way in which chemical and physical processes mediate changes in lakes and reservoirs, including not only chemical conditions, but also biological populations and communities. The concept of landscape refers to patches, characterized by different organisms and environments and linked in a complex mosaic with terrestrial communities. By integrating these two disciplines, we may consider interactions between patches and the structure and function of ecological processes.B. Lake Origins – How Lakes Are MadeThe origin and life history of lakes provide information important to their protection and management. Glaciation is one of the most important modes of formation, contributing to the great wealth of such systems in our portion of the country. Other processes leading to the formation of lakes include erosion and sedimentation, tectonic and volcanic activity and animal behavior. Reservoirs are ‘lake-like’ environments created by human action.1) Glaciation: continental glaciers are caused by the accumulation of snow during cool periods and its compaction into ice. As the ice sheet forms, it slowly spreads out and advances over the ice landscape. Continental glaciation has been occurring for ~1.5 million years and is largely restricted to the northern hemisphere due to the shape of the continents. The last glacier, having an ice sheet as much as 2000-3000 meters thick, receded about 10,000 years ago. Most of the lakes in northern North America and southern South America are of glacial origin. Glaciers create lake basins by depositing sediment that dams valleys and streams, leaving icebergs in the deposited sediment and gouging, grinding and depressing the Earth’s surface.a) Glacial scouring – lakes were formed by scouring as the glaciers moved south. Because these features formed ahead of the advancing glacier, they are termed proglacial lakes. The Laurentian Great Lakes were formed in this way and are among the deepest systems in North America. The abundant, shallow lakes of northern Wisconsin lie on exposed bedrock and were also formed by scouring.b) Glacial depressions – glaciers are so massive that they depress the continental surface to about 1/3 the height of the glacier. After the glacier melts, the crust rebounds. Hudson’s Bay is at the approximate center of the depressed area in North America and is expected torebound an additional 75m, essentially draining the bay.c) Glacial dams and moraines – as the glaciers travel over bedrock, erosive action produces material called glacial till, a mixture of clay, sand, gravel, cobble and boulders. Piles of till (moraines) become deposited beneath (ground moraines), alongside (lateral moraines)CE4505 – Surface Water Quality Engineeringand at the tip (terminal moraines) of the glacier. Where moraines dam up valleys and streams, a lake may be formed. The Finger Lakes of New York were formed in this fashion.d) Alluvial dams – even after a glacier has melted, the remaining till may be carried by streams (alluvium) and deposited where a fast-moving stream meets a slower-moving one creating and alluvial dam. Lakes Pepin and St. Croix on the Mississippi River were formed by alluvial dams where the Chippewa and St. Croix Rivers entered the larger stream.e) Kettle ponds – as the glaciers retreated, large blocks of ice were left mixed in with the glacial till. When the ice melted, a small body of water remained. These systems are usually about 100m across and only 1-2m deep and thus are referred to as ponds. Kettle ponds are common in south-central Wisconsin.f) Plunge basin – at times, the retreat of the glacier slowed and water plunged off of the ice into a moraine creating deep plunge basins. Green Lake near Syracuse, New York was formed in this manner.2) Non-glacial formation – while glaciers are a dominant force in forming North American lakes,other processes may form lake basins as well.a) Oxbow lakes – as a river meanders in a low-gradient valley, the outer bank (where the current is strongest) erodes and sediment is deposited along the inner bank (where the current is slowest). This leads to formation of a wide loop which is eventually cut off as the stream cuts across the bottom of the loop forming an oxbow lake (which can be observed locally in the Sturgeon River system).b) Sinkholes – these lakes are formed in areas having a layer of partially-eroded limestone (karst) near the surface. Rainfall dissolves the limestone forming caverns which eventually collapse and fill with water resulting in a sinkhole lake.c) Frost polygons – permafrost in tundra regions thaws to a depth of ~1m and then freezes in winter. This freeze-thaw-freeze pattern creates shallow lakes termed frost polygons.d) Tectonic activity – continent-sized pieces of the Earth’s surface (tectonic plates) move slowly relative to one another. Where two plates meet, the surface will sometimes break with one plate moving relative to the other forming a fault or rift. The African rift lakes, e.g. Lake Tanganyika, extend along a major fault line that extends north to the Dead Sea and Lake Baikal. Rift lakes tend to be millions of years old and hundreds to thousands of meters deep.e) Volcanic activity – the explosion of a volcano can destroy the volcanic cone, forming a depression termed a caldera. When the magma (molten rock) subsides the caldera may fillwith water forming a lake. Crater Lake, Oregon is an example of such a system.CE4505 – Surface Water Quality Engineeringf) Biological activity – these include beaver ponds, wallows (formed by large animals) and reservoirs.C. Morphometry – Shape and Size in Lakes1) Shape: lake shape depends greatly on the surrounding geology and topography. Shoreline erosion tends to work toward forming a ‘round’ lake, but the shape may be more complex when influenced by bedrock substrate or heterogeneity in watershed erosion. Reservoirs have particularly irregular, dendritic (tree-like) outlines because the process of damming has flooded stream valleys.2) Area: lake area is an important feature of the