PlymouthCounty Soil Survey Update
FACTORSOF SOIL FORMATION
Soil Profile Development
PowerPoint presentation on Soil Formation
Link to Soil Formation/ClassificationNRCS Web Page
Soils are formed through the interaction of five major factors:time, climate, parent material, topography and relief, andorganisms. The relative influence of each factor varies fromplace to place, but the combination of all five factors normallydetermines the kind of soil developing in any given place. InPlymouth County parent material and relief as it relates todrainage, account for many of the differences among the namedsoils. The following are brief explanations of the factorscontributing to soil formation in Plymouth County Massachusetts.
Time:
The formation of soils is a continuing process andgenerally takes several thousand years for significant changes totake place. The soils of Plymouth County began to developimmediately after the ice retreat of the last glaciation (Pleistocene),approximately 14,000 years ago. The soils are considered to berelatively young soils with slight alteration of parent materialand weak soil horizon development. Most of the soil orders mappedin Plymouth County are Inceptisols, Entisols, and Spodosols.
Climate:
Climate, particularly temperature, precipitation andfrost action have a profound influence on the soil formingprocesses which occur within a region. The kind of climatelargely determines the nature of the weathering processes thatwill occur and the rates of these chemical and physical processes.It directly affects the type of vegetation in an area which inturn will affect those soil forming processes related tovegetation. Plymouth County is in a transitional climate zonewith conditions characteristic of both humid marine and humidcontinental climates. The winters are quite mild for New Englanddue to the moderating effect of the surrounding Atlantic waters.Temperature and precipitation (approximately 40 in/yr.) govern the rate of chemical andphysical weathering of the soils and allows for the accumulationof organic matter in the surface layer of the soils. Moisture issufficient enough to promote leaching of water-soluble materialdown through the soil. Cold winter temperatures allow for frostaction which physically break apart rock fragments.
Parent Material: Link to General Geologyof Plymouth County, Massachusetts
Parent material is the unconsolidated mineral andorganic deposits in which soils are developing. It determines themineralogical composition and contributes largely to the physicaland chemical characteristics of the soil. The kind of parentmaterial also influences the rate at which soil forming processestake place.
Due to the effects of the Wisconsinan glaciation, insufficienttime has elapsed to significantly alter the glacial deposits. Theinfluence of parent material is very apparent in the soils ofPlymouth County. Parent material is roughly divided into twobroad groups; glacial (Late Pleistocene) deposits and post glacial (Holocene)deposits. There are four general types of glacial depositsrecognized in the survey area, they are; till, fluvial, lacustrine, and ice-contact deposits. Postglacial deposits are sediments which were deposited after thelast glacial period which ended approximately 10,000 years ago.Post glacial deposits recognized in the survey area include,eolian silts and sands, alluvial (floodplain) deposits,freshwater and marine organic deposits, and coastal beaches andsand dunes desposits.
Glacial till is dominantly unsorted and unstratified sediments,deposited directly (beneath and within) by glacial ice. Till consists of aheterogeneous mixture of clay, silt, sand, gravel, stones andboulders. Two broad groupings of till have been recognized bysoil scientists in Plymouth County. One is referred to as denseor basal till and is characterized by a loamy texture, with amoderate percentage of coarse fragments, and a dense, firm,slowly permeable substratum; locally referred to as hardpan. ThePaxton and Montauk soils arerepresentative soils that developed in these sediments. The othertill referred to as ablation till, has a sandy texture, with ahigh percentage of coarse fragments, and a loose, permeablesubstratum. The Gloucester and Canton soils are representativesoils that developed in this material.
Glacial fluvial (outwash) material isstratified sand and gravel deposited by glacial meltwater streams.Soils that have developed in glacial outwash have a sandy orgravelly, loose, very permeable substratum. Glacial fluvial deposits are associated with aquifer recharge areas. Soils commonly mappedin glacial outwash areas include Carver, Hinckley andMerrimac soils. Click here for a glacial fluvial landform image.
Glacial lacustrine, commonly referred to as lakebed depositsare varied ranging from sands and gravels to silts and clays.These materials were deposited within glacial lakes which havesince drained or have filled with sediments. Soil patterns arecomplex within these areas and often vary dramatically, bothchemically and physically, over short distances. Soils that havedeveloped in glacial lakebed deposits include the Scio,Hinesburg,Raynham and Birdsallsoils.
Ice contact deposits are varied ranging from till to boulderysand and gravel. These materials were deposited in contact withan ice mass. Examples of ice contact features include; kames,heads of outwash, and kettles. Soils that have developed in icecontact deposits include the Plymouth, Barnstable, Canton, andHinckley soils.
Post glacial eolian sediments are sand and silt deposited bywind during the period after the glacial ice melted from the areaand before a permanent vegetative cover was established,stabilizing the newly exposed land surface. Eolian sands and siltoccur as a discontinuous mantle or cap, variable in thickness,over glacial deposits. Most of the upland soils in Plymouth Countyare capped with an eolian mantle. Haven soilsdeveloped in areas where this mantle is thick (18 to 36 inches)and overlies glacial outwash. The loamy surface and upper solumof the Barnstable and Merrimac soils is the result of a thincapping of eolian material that has been mixed, through naturalprocesses, with the underlying material. Carver soils havea coarse sand eolian mantle.
Organic deposits are accumulations of plant materials ofvarying degrees of decomposition that have formed in wet areasand are 16 inches or greater in thickness. The Freetown andSwansea soils developed in freshwater organic deposits. TheIpswich andPawcatuck soils developed in organic tidal marsh deposits.
Alluvial deposits are recent material which has been depositedby flowing water. Alluvial deposits occur along the major riversof the county. The Winoski and Limerick soils are examples ofalluvial soils.
Beaches are unvegetated, wave washed accumulations of sandthat do not meet the criteria for a soil and are mapped as amiscellaneous area. Sand dunes are windblown deposits of sand.Hooksan soils developed within areas of sand dunes.
Topography and Relief
The shape of the land surface, its slope and positionon the landscape, greatly influence the kinds of soils formed. InPlymouth County soils that formed in similar parent materialswith the same climatic conditions exhibit differences as a resultof their position on the landscape. These differences are largelya result of varying drainage conditions due to surface runoff ordepth to water table.
Soils that developed on higher elevations and sloping areasare generally excessively drained or well drained. Depth togroundwater is generally greater than 6 feet and surface runoffis moderate or rapid. Soil profiles within these areas commonlyhave a bright colored strong brown to yellowish brown upper solumgrading to a lighter, grayer, unweathered substratum.
Soils that occur at lower elevations such as in swales,adjacent to drainage-ways and water bodies, and withindepressions generally receive surface runoff from higherelevations and often have a seasonal high water table at ashallow depth. Soil profiles within moderately well drained andpoorly drained areas are mottled with irregular spots of brown,yellow and grey colors. In very poorly drained areas, where thewater table is at or near the surface for prolonged periods, soilprofiles characteristically have a dark-colored organic ororganic rich surface layer underlain by a strongly mottled orgleyed (gray color indicating a reduced condition) subsoil andsubstratum.
Permeability of the soil material; as well as the length,steepness, and configuration of the slopes, influence the kind ofsoil that is formed in an area. The local differences in thesoils mapped in Plymouth County are largely the results ofdifferences in parent material and topography.
Organisms
All living organisms actively influence the soilforming process. These organisms include bacteria, fungi,vegetation and animals. Their major influence is the effect onthe chemical and physical environment of the soils.
Most, if not all of Plymouth County, was originally in nativeforest of mixed hardwoods and conifers in varying proportions.The mineral element content of leaves and branches variesdepending on the type of forest vegetation, and influences thecharacteristics of the soils that develop beneath it. Hardwoodscharacteristically take up bases (calcium, magnesium, andpotassium) from the soil and return them to the soil surface inthe form of organic litter; thus recycling the soil nutrients.Coniferous trees tend to be low in bases, consequently soilsdeveloped beneath them tend to be more acid. Bases are also moresusceptible to leaching beneath coniferous trees. Mixing of thesoil, due to tree throws, is also a characteristic of woodlandsoils.
Some types of micro-organisms promote acid conditions andchange the chemistry of the soil which in turn influences thetype of soil forming processes that take place. Microbial animalsdecompose organic materials and return the products ofdecomposition to the soil.
Larger animals such as earthworms and burrowing animals mixthe soil and change its physical characteristics. They generallymake the soil more permeable to air and water. Their wasteproducts cause aggregation of the soil particles and improve soilstructure.
Man's activities have significantly altered many areas ofnatural soils in the county. The chemical and physical properties,particularly of the plow layer, have changed with cultivation andthe addition of lime and fertilizer. Artificial drainage andfilling have altered the environment of some naturally wet soils.Of all the animals, man can have the most beneficial or mostdetrimental impact on the soil forming processes.
Link to Power Point Presentation on Soil Horizons
The interaction of the five soil-forming factors; time,climate, parent material, topography, and plant and animal life,result in the development of a soil profile. A soil profile is avertical section of the soil beginning at the surface andextending down into the unconsolidated underlying material to adepth of 60 inches or more. A soil horizon is a layer of soil,approximately parallel to the soil surface, with distinctcharacteristics produced by soil-forming processes. The physicaland chemical characteristics observed within the soil profile arethe basis for differentiating one soil from another.
The majority of the soils within the survey area exhibit weaksoil profile development with little change or alteration ofparent material, due primarily to the relatively young age of thesoils. The depth of soil profile development varies between thedifferent soils and generally averages about 30 inches in thewell drained soils.
Soil profile development is generally shallower in the poorlyand very poorly drained soils, and may be absent or very weak inrecently deposited material, as in the case of the Hooksan soils.
Organic matter has accumulated on the surface of soils as O-horizonswith varying degrees of thickness and decomposition. Wherenatural mixing of humified organic material and the underlyingmineral matter has occurred, an A-horizon is present. The amountof organic matter added to the soils in the survey area varieswith the kind of vegetation, moisture, and drainage condition.The thick, mucky, organic deposits that the Freetown and Swanseasoils are developing in are the result of a very poorly drainedcondition where organic material accumulates within this very wetenvironment rather than being oxidized. In areas that have beencultivated, the surface organic layers and the upper solum of thesoil have been mixed to form an Ap-horizon.
The soil profile development characteristic of manyexcessively drained, well drained, and moderately well drainedsoils mapped in the survey area is the result of movement anddeposition of aluminum, iron, clay, and humified organic matterwithin the soil profile. Weak organic acids generated from thedecomposition of surface organic litter are percolated downwardthrough the soil by rainwater. Aluminum and iron within the upperportion of the soil profile are released into solution andleached downward, along with fine particles of humified organicmatter and small amounts of fine clay. The light gray color inthe E-horizon (surface mineral horizon below the O-layers or A-horizon)has resulted from this leaching and is more evident in thecoarser textured soils and often absent in the finer texturedsoils. With depth, the chemical environment within the soilchanges and the aluminum, iron, clay, and organic materialprecipitate out forming the B-horizons. The greatestconcentration of leached material precipitates out just below theE-horizon and often forms a strong brown Bhs or Bw1 horizon.Undisturbed soil profiles of Carver, and Montauk soils commonlyhave an E-horizon underlain by a brightly colored B-horizon. Thecharacteristic dark brown to yellowish brown color within thesubsoil is due primarily to iron oxide stains on the surfaces ofsand-size particles. Color within the subsoil generally fadeswith depth. The unweathered parent material in the C-horizon isoften light yellowish brown or light olive brown.
Where there is a water table that is within or fluctuateswithin the soil profile, there are soil color changes referred toas soil mottling. Soil mottles are the combination of gray andreddish spots produced by alternating aerated and saturatedconditions (oxidation-reduction process) within the soil profile.These spots are caused principally by migration, depletion orconcentration of iron within the soil (Soil Survey Manual).Gleying is a condition that develops when the soil is wet formost of the year and the soil matrix color is gray or bluish graydue to the removal of iron caused by prolonged reducingconditions. Soil mottling is common in the upper solum of thepoorly drained Ridgebury and Walpole soils; and in the lowerportion of the solum in the Scio, Scituate, Deerfield and Sudburysoils. Gleying is characteristic of the very poorly drained Birdsall soils.Induration of sand grains caused by the concentration of iron (ferric)occurs within the soil profile of some of the very poorly drainedBerryland soils.
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