Lake Management Plan
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4.5 Soils
Soils influence a watershed determining the type and quantity of vegetation both aquatic and agricultural. They will also determine the type of septic systems installed.
Slope
The slope along with the soil type influences the amount of runoff. The less compact the soil, and the greater the slope the more potential there is for runoff erosion. Erosion adds to the total suspended solids in the water and increases eutrophication. The Pelican River generally flows through the flat or nearly flat regions of the watershed. The south east corner of Pelican Lake has the steepest slopes therefore it is a focused area for erosion control.
Land slope within the Pelican River watershed
Soil Dominance Suborder
The Pelican River watershed contains 2 dominant suborder soils, Udalfs (green), and Udolls (brown). Udalfs is a sub order of Alfisols. Udolls is a sub order of Mollisols.
Alfisols are a soil order in USA soil taxonomy. Alfisols form in semiarid to humid areas, typically under a hardwood forest cover. They have a clay and nutrient-enriched subsoil. Because of their productivity and abundance, the Alfisols represent one of the more important soil orders. Udalfs is the soil found in humid climates; udic moisture regime. The udic moisture regime is common to soils of humid climates which have well-distributed rainfall, or which have enough rain in summer so that the amount of stored moisture plus rainfall is approximately equal to, or exceeds, the amount of vapotranspiration. Water moves down through the soil at some time in most years.
Mollisols are a soil order in USA soil taxonomy. Mollisols form in semi-arid to semi-humid areas, typically under a grassland cover. They are most commonly found latitudinally in a band of 50 degrees north of the equator. Their parent material is generally limestone, loess, or wind-blown sand. The main processes that lead to the formation of grassland mollisols are melanisation, decomposition, humification and pedoturbation. They have deep, high organic matter, nutrient-enriched surface soil (A horizon), typically between 60-80 cm thick. This fertile surface horizon, known as a mollic epipedon, results from the long-term addition of organic materials derived from plant roots. The clayey B horizon may stem from the rainfall pattern causing chemical weathering of the parent material. They have a soft, granular, soil structure. Mollisols occur in savannahs and mountain valleys (such as the North American Great Plains). It was estimated that in 2003, between 14-26% of grassland ecosystems still remained in a relatively natural state (that is, they weren't used for agriculture due to the fertility of the A horizon). Because of their productivity and abundance, the mollisols represent one of the more economically important soil orders.
Vadose Zone
The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the water table, and is thus not considered groundwater ("vadose" is Latin for "shallow"). It comprises the unsaturated portion of the soil, regolith or bedrock, as well as the unsaturated portion of the capillary fringe above the water table. The pore spaces in the vadose zone are subject to atmospheric pressure, and so the water is held to the regolith and rock by adhesion ( funiculary groundwater ), and in pore spaces by capillary action ( capillary groundwater ). If the vadose zone envelops soil, the water contained therein is termed soil moisture.
Movement of water within the adose zone is studied within hydrology, particularly hydrogeology, and is of importance to agriculture and contaminant transport.
The Pelican River watershed is composed of clay/loam (maroon), and sand/sandstone (blue). Loam is soil composed of sand, silt, clay, and organic matter, with particles of various sizes, evenly mixed. Loams are gritty, plastic when moist, and retain water easily. They generally contain more nutrients than sandy soils. Clay is a generic term for an aggregate of hydrous silicate particles less than 4 µm (micrometres) in diameter. Clay consists of a variety of phyllosilicate minerals rich in silicon and aluminum oxides and hydroxides which include variable amounts of structural water. Clays are generally formed by the chemical weathering of silicate-bearing rocks by carbonic acid, but some are formed by hydrothermal activity. Clays are distinguished from other small particles present in soils such as silt by their small size, flake or layered shape, affinity for water and high plasticity index.
Compacted soil intended for cultivation can be made more loamy by turning under organic material such as manure, compost, or previous crops when the ground is prepared for the next growing season; it is not necessary to add sand as it will find its own way in as the organic materials decay. This enrichment process must be repeated every year until the aeration and nutrient qualities of the soil are permanently improved.
There are three main groups of clays: kaolinite-serpentine, illite, and smectite. Altogether, there are about thirty different types of "pure" clays in these categories, but most natural clays are mixtures of these different types, as well as other weathered minerals.
Sand is an example of a class of materials called granular matter. Sand is a naturally occurring, finely divided rock, comprising particles or granules ranging in size from 1 / 16 to 2 millimeters. An individual particle in this range size is termed a sand grain. The next smaller size class in geology is silt: particles below 1 / 16 mm down to 1 / 256 mm (0.004 mm) in size. The next larger size class above sand is gravel, with particles ranging up to 64 mm.
Sandstone is a sedimentary rock composed mainly of feldspar and quartz and varies in color (in a similar way to sand), through grey, yellow, red, and white. Since sandstones often form highly visible cliffs and other rock formations, certain colors of sandstone may be strongly identified with certain regions.
Rock formations that are primarily sandstone usually allow percolation of water, and are porous enough to store large quantities, making them valuable aquifers. Fine grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices such as limestones or other rocks fractured from seismic activity.
Soil Atlas - Landform Description
The Pelican River watershed contains only 2 major landforms, out washed plains (orange) and terminal moraines (green). Outwash plain is material from a terminal moraine that has been washed downstream and deposited over a relatively flat surface. Moraine is the general term for debris of all sorts originally transported by glaciers or ice sheets that have since melted away.
Terminal moraine: When balance is maintained between the melting of a glacier and its forward advance, the debris carried on (superglacial), within (englacial), and dragged along the bottom (subglacial) is dumped at that point and builds up a heterogeneous mass of the transported material called the terminal moraine. If a glacier is slowly retreating and makes successive halts farther and farther up the valley, a series of terminal moraines are formed which are spoken of as recessional moraines.
