GEOGRAPHY OF SOILS AND GLACIAL GEOLOGY ...pfarrell/Soils/Soil Lab Files/Field Trip... · Web viewThe structure of the plant remains is quite indistinct although it is still possible

GEOGRAPHY OF SOILS FIELD TRIP

Themes of Field Trip: Soil Parent Materials derived from glaciers in Minnesota

Catena ConceptForest-Prairie Transition in Soils

Practice in Soil Description MethodsIntroduction to Great Soil Orders of the taxonomy

DAY ONE:Leave UMD and drive to Floodwood (a one hour drive). On drive, notice flat (low relief) landscape and abundance of bogs as we near Floodwood.Floodwood: Gas up and have overview discussion in Rest Stop. Drive to peat bog on Route 8.

First Soil Stop: PEAT BOG IN LAKE PLAIN OF GLACIAL LAKES AITKIN AND UPHAMGlacial history in this region of MN is complex. Several advances from different lobes) of the Laurentide Ice Sheet (Wadena, Rainy, Superior and Des Moines moved through this region.

Each lobe in each advance deposited moraines. One of the advances of the Superior Lobe left the Highland and the Mille Lacs moraines. The Highland moraine acted as a dam and water was ponded to form Glacial Lakes Upham I and Aitkin I. Later, the St. Louis sublobe (of the Des Moines Lobe) stagnated and Glacial Lakes Upham II and AitkinII formed . These lakes covered an extensive area of northeastern Minnesota.

The lakes stood at several levels, and formed strandlines at each level. The lake water also modified earlier deposits of till. On our drive to Floodwood and Jacobson, we traverse Upham and Aitkin beaches and wave-washed tills from this basin. Eventually, the lakes drained through St. Louis River around 9000 yrs. BP. You will notice numerous peat deposits on the lake plain, where closed depressions have filled with peat.

We will examine a core of peat from one of these closed depressions. The peat deposits in the glacial lake basins here are extensive and many, such as the Arlberg bog site in Floodwood, and have been mined to make peat fertilizer. The peat soil in the Arlberg bog has 5-6 meters of peat above very fine sand of glacial lake origin. Organic soils accumulate in these poorly drained old lake basins as a result of anaerobic conditions. These soils have extremely low bulk densities (0.2 – 0.3 g/cm3) and high porosity (80%). The minerals in organic soils are tied up in organic compounds and are not plant-available.

Important descriptive elements of organic soils are the botanical origin of the organic material (sphagnum, grasses, sedges, cattails, wood and leaf litter) and the extent of decomposition. A simple classification is:

Fibric (peat) <1/3 decomposed; >2/3 identifiable (Von Post H1 – H4)Hemic (mucky peat or peaty muck) moderately decomposed (Von Post H5 –H6)Sapric (muck) 2/3 decomposed; <1/3 identifiable (Von Post H7-H10)

A more detailed classification is given in the Von Post method (below). We will examine a core and use the Von Post method.

THE VON POST SCALE OF HUMIFICATION (source Ekono 1981)

Symbol Description

H1 Completely undecomposed peat which, when squeezed, releases almost clear water. Plant remains easily identifiable. No amorphous material present.

H2 Almost entirely undecomposed peat which, when squeezed, releases clear or yellowish water. Plant remains still easily identifiable. No amorphous material present.

H3 Very slightly decomposed peat which, when squeezed, releases muddy brown water, but from which no peat passes between the fingers. Plant remains still identifiable, and no amorphous material present.

H4 Slightly decomposed peat which, when squeezed, releases very muddy dark water. No peat is passed between the fingers but the plant remains are slightly pasty and have lost some of their identifiable features.

H5 Moderately decomposed peat which, when squeezed, releases very “muddy” water with a very small amount of amorphous granular peat escaping between the fingers. The structure of the plant remains is quite indistinct although it is still possible to recognize certain features. The residue is very pasty.

H6 Moderately highly decomposed peat with a very indistict plant structure. When squeezed, about one-third of the peat escapes between the fingers. The residue is very pasty but shows the plant structure more distinctly than before squeezing.

H7 Highly decomposed peat. Contains a lot of amorphous material with very faintly recognizable plant structure. When squeezed, about one-half of the peat escapes between the fingers. The water, if any is released, is very dark and almost pasty.

H8 Very highly decomposed peat with a large quantity of amorphous material and very indistinct plant structure. When squeezed, about two-thirds of the peat escapes between the fingers. A small quantity of pasty water may be released. The plant material remaining in the hand consists of residues such as roots and fibres that resist decomposition.

H9 Practically fully decomposed peat in which there is hardly any recognizable plant structure. When squeezed it is a fairly uniform paste.

H10 Completely decomposed peat with no discernible plant structure. When squeezed, all the wet peat escapes between the fingers.

B1 Dry peat

B2 Low moisture content

B3 Moderate moisture content

B4 High moisture content

B5 Very high moisture contentNote: The moisture regime of each peat sample is estimated using the above scale of 1-5 and symbol “B” (derived from Swedish blöthet = wetness).

After leaving the peat bog, we will drive to Jacobson and examine a cutbank of the Mississippi River. We will continue west on 2 and turn left on 200 (west) to Jacobson. Right after we turn left on 200, we cross a continental divide between Great Lakes drainage and Mississippi drainage.

Second Soil Stop: GLACIAL LAKES AITKIN AND UPHAM UNDERFLOW FAN AND LACUSTRINE DEPOSITS: JACOBSON LANDING, MISSISSIPPI RIVER CUTBANK

This site on the Mississippi River exposes underflow fan deposits of the glacial lakes and a sharp contact with the underlying gray lake clays. (If you look again at the figure of the Glacial Lakes above, the unlabeled, smaller star marks the site we are looking at).

In the cutbank of the river, you can see the lake sediments, with clear thin layers called rhythmites. These are rhythmic accumulations of sediments that form distinctive laminae. Annual cycles of deposition create rhythmites called varves in glacial lake sediment. Each varve includes a coarser-grained “summer” layer, produced by rapid ice melt in the warmer months and wave activity that keeps finer sediments in suspension, and a finer grained “winter” layer, deposited from suspension in quiet water while streams feeding the lake are frozen. Rhythmites can also be caused by periodic changes in sediment source.

There are three things to take note of here: the rhythmites, the cross-bedding produced by the underflow fan and the gleyed (grey) layers of lacustrine sediments at the base of the hill.

THINGS TO NOTICE ABOUT THE LANDSCAPE AS WE DRIVE TOWARDS HILL CITY AND BRAINERD:

As we drive west, follow our route on your color maps showing the landscapes through which we are driving. We continue to drive through the expansive, flat lake basin. Eventually we approach Hill City, presumably so-named because of the relatively high relief in the Des Moines Lobe end moraine, the “Sugar Hills Moraine”, in which Hill City lies. From Hill City, we head west to Remer and then south towards Brainerd. Along the way, we travel through a jigsaw puzzle of end moraines of the Rainy and Des Moines lobes and peat deposits in closed depressions.

Approaching Brainerd, we enter the pitted outwash plain, composed of outwash of Des Moines and Rainy lobes. Notice the shallow, lake-filled depressions, sandy sediments and droughty soils. Driving south from Brainerd, we follow the terraces of the Mississippi. This outwash deposit is pitted with kettles and is composed of meltwater sediment of both the Des Monies and Rainy lobes. Outwash spreads out beyond the till in the form of a broad outwash plain, created by the merging of the floodplains of many braided streams draining the ice. Long after the glacier melts, these plains are criss-crossed by shallow abandoned channels and may also be pock-marked by depressions or kettles formed by ice blocks which were rafted into the outwash, then melted away.

Outwash may also exist in more narrow valleys which cut through the sheets of till, in which case the resulting landform is referred to as a valley train. The Mississippi Valley in this area contains glacial outwash in the form of a valley train. Outwash plains and valley trains generally have different terrace levels developed along their margins, reflecting formation of floodplains and downcutting of the rivers into those floodplains as the volume of meltwater changes through time.

FROM BRAINERD TO STAPLES:As we head west on 210 and 10 towards Staples, you will see on your color maps, that we begin to leave the Rainy lobe deposits and enter the deposits of the Wadena Lobe.

Third Soil Stop: WADENA DRUMLINS (Ron and Sue Storbakken’s farm)

There are approximately 1200 drumlins in the Wadena drumlin field. The drumlins are elongated hills of glacial till. They are quite evident on the topographic map. The long axes of drumlins are oriented in the direction of ice movement, with the less steep side of the drumlin pointing in the direction of ice movement. The Wadena drumlins suggest that the ice was moving from the northeast to the southwest. (See “Advance 4” in small figures). However, the source area for the the Wadena Lobe is thought to be from the northwest, from what is now SE Manitoba. Wadena lobe till is buff-colored, sandy, and calcareous. The common explanation has been that another ice lobe deflected the Wadena lobe to the southwest, resulting in the drumlins’ orientation. Recent research suggests that the Wadena lobe may have come from the northeast and is really an early phase of the Rainy Lobe.

The drumlins in the field we are visiting are composed of loose material that has been plastered into a very compact core. The bulk density of the core is very high, 1.9 – 2.0 g/ml. (For comparison, loamy soils have a bulk density of 1.1 – 1.5; concrete has a bulk density of 2.4). The core is encountered at approximately 4 – 5 feet below the surface (depth of frost). The core is so dense that it prohibits water penetration. The depth of redoximorphic features tells where the water is concentrated in the soil. We will examine a catena of soils on the slope of a drumlin. Moving downslope, the redox features are closer to the surface, the sediment becomes increasingly moist, and the texture changes because clay is moving downslope. (In spring, there are springs in the side of the slope).

Working in four groups, collect cores from four topo positions on the side of the drumlin. Core as deeply as you can and describe the core. Then we will place the cores side by side to compare them. Use the 4 soil description sheets that you printed, copy notes from the other groups, and answer the following questions in your field book.

QUESTIONS TO ANSWER ABOUT DRUMLIN CATENA:As a group, answer the following questions about the four soils:1. What changes in A horizon thickness did you observe in the profiles? To what doyou attribute these changes?2. What changes in color of the surface horizon did you observe in the profiles andto what do you attribute these changes?3. What changes in texture did you observe in the surface horizons of the profilesand to what do you attribute these changes?

4. What changes in chroma values did you observe in the subsurface horizons ofthe profiles and how do you explain these changes?5. What redoximorphic features did you observe in the profiles? How can youexplain their presence or absence in the various landscape positions?6. Did you observe any significant changes in soil pH in the profiles? Can youhypothesize as to the reasons for those changes?

Put 4 soil description sheets here and leave room to answer the above questions

ITASCA STATE PARK, UNIVERSITY OF MINNESOTA FIELD STATION

Itasca is the oldest park in Minnesota. It used to be called Omushkos, the Ojibwe word for “elk”. The first white explorer called it Itasca as a combination of “veritas” and “caput”, Latin for “true head”. We will look at some interesting things in the park, including the headwaters of the Mississippi. From its headwaters here in the park, the Mississippi travels 2,492 miles to the Gulf of Mexico, making it the third longest river system in the world.

DAY TWO: FOREST-PRAIRIE TRANSITION:

There are many theories attempting to explain the abrupt transition in Minnesota from forest to prairie. These theories range from climate change to fire patterns to changes in topography. Prairie and forest vegetation have existed in Minnesota since the Pleistocene glaciation. The prairie/forest transition was very dynamic and ever-changing before European settlement. The changing border was dictated by the frequency and severity of fires and weather patterns. Several different kinds of communities existed along this transition zone, including brush prairie and savanna.

Before settlement, the “Big Woods”, existing south and west of the Twin Cities, covered over 2 million acres in Minnesota. Currently the remaining acreage of the Big Woods is mainly comprised of the late-successional species of maple and basswood referred to as maple-basswood forest. The first trees to invade the prairies were oak, aspen and willow, followed later by elm.

Fires started by lightning and by American Indians were originally the primary obstacles to forest invasion into the prairie. Frequent fires spread easily over the prairie, killing most invading trees and shrubs, but were extinguished when they reached the moister forest regions. The prairie grasses would quickly regenerate after the burns but the large burr oaks were resistant to fire, and the willow and aspen regenerated quickly after burns at the transition. A later shift in climate to cooler, wetter conditions in the Big Woods likely ushered in the shift from oak and aspen to elm.

Settlement of the transition area brought with it extensive fire control to protect buildings, crops, livestock, and the surrounding woodlands. Constructed railroads and highways served as fire breaks. This fire suppression has and continues to lead to the invasion of the forest into the remaining native prairie lands. Prescribed burning is now used to manage the remaining native prairie.

Fourth Soil Stop: BAD MEDICINE LAKE ESKER: FOREST SOIL (ALFISOL) IN WADENA LOBE DEPOSIT

(As we drive to the first stop today, we will be crossing another continental divide between Hudson Bay drainage and Mississippi drainage).

We will look at two forest soils, one in Wadena lobe deposits and the second one in Des Moines Lobe till. The first deposit is on an esker. An esker is a long, winding, narrow ridge made up of stratified sand and gravel, deposited by a subglacial

meltwater stream. This esker formed at the margin of the Wadena lobe and is composed of coarse gravelly material.

This soil is an Alfisol. We will compare the forest soils to the prairie and the forest-prairie transition soil. Notice all of the characteristics of this soil that make it a forest soil.

Fifth Soil Stop: FOREST SOIL (ALFISOL) IN DES MOINES LOBE DEPOSIT

The next three sites show changes that occur traversing the transition zone between prairie and forest. All 3 sites occur in the same parent material, Des Moines lobe till. This site is still in the Des Moines lobe till, which is finer-textured and more carboniferous than the Wadena lobe till. This area is in a stagnation moraine, which formed in a body of ice, cut off from the main glacier, which melted in place, leaving the irregular topographic moraine surface. This alfisol formed in a forest. Note all the features of this soil that make it a forest soil.

Sixth Soil Stop: FOREST/PRAIRIE TRANSITIONAL SOIL

We are now in an area that has experienced both deciduous forest and prairie influences over the past 10,000 years. The soils here have characteristics of both Alfisols and Mollisols: a thick dark A horizon, a thin E horizon, an argillic horizon, and moderate depth to carbonates. This soil is called a “Mollic Hapludalf”.

Seventh Soil Stop: PRAIRIE SOIL

Prairie vegetation dominates landscapes to the west on Des Moines lobe ground moraine, which has relatively low relief. Here the landscape is made up of beach ridges, inter-ridge complexes and lacustrine sediments.

The topographically higher landscapes are dominated by forests and are composed of Itasca End Moraine (from the Wadena Lobe) and the Big Stone Stagnation Moraine (from the Des Moines Lobe).

The prairie soil that we will look at is a Mollisol, with the typical deep, dark, mollic epipedon characteristic of grassland soils. Working in groups, we will describe a prairie soil here.

PASTE A SOIL PROFILE DESCRIPTION SHEET HERE.

LAKE AGASSIZ : BEACH RIDGE AND LACUSTRINE SEDIMENTS

Glacial Lake Agassiz was formed as the retreating ice towards the end of the Wisconsin glaciation blocked the northward flowing drainage towards Hudson Bay. During this time, the lake had multiple stages and multiple outlets. The primary outlet was over the Big Stone Moraine (in the vicinity of Brown’s Valley, MN), which created Glacial River Warren that formed the current channel of the Minnesota River. The various lake stages left a series of continuous beach ridges along the perimeter of the lake. The beach ridges are composed of sand and gravel and often show cross-bedded strata. The beach ridges are often mined for sand and gravel, being the only local sources. The inter-beach areas trap water and are quite wet.

The lake sediments themselves form Vertisols in deep deposits of silty clay. The lake plain itself is extremely flat, with relief in some places only one inch per mile. Ditching in this region can be seen on the topo maps. It removes water from the surface, and has led to productive agriculture, especially of sugar beets and small grains. But the ditching has increased peak flows to the Red River and may be partly responsible for severe flooding in recent years.

Eighth Soil Stop: BEACH RIDGE

The Beach Ridge we are going to see is in the Twin Valley Prairie Scientific and Natural Area. This prairie remnant is 339 acres and is dominated by big bluestem and prairie cordgrass. Sandhill cranes stop here on their migration and prairie chickens boom here during mating season.

Ninth Soil Stop: LAKE CLAY

We will drive to a cutbank of the Red River and look at the soils developed on lacustrine sediments of glacial Lake Agassiz. Locally, these clayey soils are called “gumbo soils”.