Presentation is loading. Please wait.

Presentation is loading. Please wait.

Riparian Ecosystems By: David Gridley.

Similar presentations

Presentation on theme: "Riparian Ecosystems By: David Gridley."— Presentation transcript:

1 Riparian Ecosystems By: David Gridley

2 General Overview Riparian comes from the Latin word “ripa”, which means stream bank. A Riparian Ecosystem is a transitional system between aquatic and terrestrial ecosystems. These are either freshwater or marine and can lie near lakes, streams, pond, rivers, oceans or any body of water.

3 Zonation: Riparian systems are zoned just as many other types of ecosystems. Sedges and rush live on the banks at or above water level. These can frequently become submerged depending on what aquatic system is present. Shrubs live above the sedges and rush. Deciduous trees live above the bank and provide shade during the midday sun and a home for various species. The trees are the last plant species characterized in a Riparian system. The Upland system follows.


5 Soil types: There are a variety of soil types found in a Riparian system. Common soils are those which are found in wetlands (silts and clays). Sands and gravels are also common. These are highly porous which allow for water movement. Porosity allows for variability in the types of plants in the system. Zonation occurs in a small distance laterally. There is no general width to the system. It depends on the hydrology of the aquatic system.

6 Habitat: This is a very diverse ecosystem.
These areas are very rich in life. They are home to various animals and plant. Small mammals are able to nest on the banks underneath the vegetation while birds are able to nest in the vegetation. The various plant species create a food source as well as shelter for insects, birds, mammals, and even fish in the water.

7 Vegetation: Vegetation provides cover and a natural habitat for species.

8 Uses: The plants that live in these systems help to clean the water.
Stem densities near the shore can slow the water movement enough for suspended solids to settle out. The roots also bring in nutrients and metals from the water which help to improve the water quality.

9 Benefits: Natural undeveloped vegetated flood plain allow excess water to spread out and easily re-enter the channel or to be soaked up by the wetland soil. The vegetation provides various barriers against the flowing water. The natural ecosystem is beneficial for wildlife and they are aesthetically pleasing.

10 Human Influence: One problem is that humans tend to straighten and bend waterways at angles. This disrupts currents and creates areas of high erosion. Irrigation ditches are easily flooded because they are not able to handle excess water. High rains can cause them to flood creating more problems. Straight channels reduces surface area of banks and therefore reduces the amount of habitat available for animals. This in turn creates competition for space and food.

11 Human Influence: When buildings and unnatural structures are placed in a floodplain and near waterways reduce the ability of the soil to absorb the water. Buildings also impede the movement of the water and will be damaged by the excess water.

12 Problems Straightening or Channelizing waterways has turned them into a mechanical waterway instead of a healthy stream environment. When streams are straightened and direction is changed from its natural state inundation becomes a problem.

13 Problems cont: Acequias are found throughout the west because droughts are common in the area. Water divergence is a common practice which allows farmers to maintain crops through the dry season. This diverts water from its original source direction and into new areas.

14 Acequia:

15 Acequia cont: These are actually a man made irrigation ditches.
These bring water to areas that are normally dry and allow for vegetation to grow that would not normally have been there. Erosion is a problem that frequently occurs

16 Restoration: There are many restoration efforts underway that will return Riparian Ecosystems to there natural state. One major problem with this effort is that diverting the water back to its original habitat will only create more problems just as the original divergence did. The effort must take place where the water is presently routed.

17 Restoration: Terraced and vegetated canal banks are now being used as a way to prevent inundation and erosion in events of high water. Proper plant species such as oaks, willows, and cottonwoods are being used to create shade and help smaller plant species grow. The trees will also out compete weeds to help create a healthy habitat for all life forms.

18 Restoration:

19 Restoration: A portion of Bear Creek in Iowa.
This restoration took place in 4 years. It now has a healthy soil environment as well as a healthy habitat for the species that live here.

20 Another Success Gila River at Kelvin, AZ. Top picture is from 1945.
The bottom picture is from 2002. The difference in habitat is quite clear.

21 Southern Deepwater Swamps
Brian Simpson

22 Geographical extent Only found in freshwater environments not so much climate dependant as hydrology, generally found along rivers and streams in the Southeast Coastal Plain and along the Gulf Coastal Plain to southeastern Texas, and up the Mississippi River to southern Illinois. There a few areas with similar habitat and vegetation located in the northeast these are small in comparison.

23 Southern Deepwater Swamps General overview
Sometimes referred to as southern freshwater forested swamp. Freshwater systems with standing water throughout all or most of the year. They can be nutrient-rich in alluvial river swamps or under nutrient-poor conditions such as in rainwater fed swamps. Primary production is closely related to hydrologic conditions.

24 Geomorphology Located in broad, flat floodplains or they can be in isolated basins. Deepwater swamps are located in floodplains where there are meandering river channels, adjacent to natural levees, oxbow lakes, and sloughs which represent areas of ponded water. (Leopold et al, 1964) Found in areas of very low relief, where slight changes in elevation (just a few cm) can produce quite different hydrologic conditions, soils, and plant communities. Brown 1972) Biogeochemical processes are strongly linked to hydrologic characteristics. The depth and duration of flooding, as well as whether the flood waters are flowing or stagnant, affect whether the wetlands serve as sinks, sources, or transformers of nutrients..(Brinson 1990)

25 Cypress swamps as sinks, possible transformers and sources
Sinks: reports of 50% reduction in P as overflow waters passed through a swamp. (Day et al) In some locations it has been found that they were effective as sinks for over 50 years runoff of partially treated wastewater. More effective however, at P that at N collection. Transformers: total inputs and outputs of nutrients remain similar yet there are noted net increases in organic N and P and a decrease in inorganic N and P. Transformations from inorganic to organic forms can be important for secondary productivity downstream.(Mitsch 1993) Sources: in situations where there is periodic outflow from the system deepwater swamps can act as a mechanism of nutrient conservation during dormant seasons and transferred to the system during the growing season.

26 Hydrologic conditions
Hydrology is the most important feature of deepwater swamp environments. Inflows are dominated by runoff from uplands and overflow from flooding rivers. (Mitsch and Gosselink 1993) Outflows are limited by controlled by substrate, and the swamps distance from adjacent streams Topographic features may impound water and cause flooding from rainfall rather than from stream overflow. Water levels vary seasonally and annually, with high water levels coinciding with winter and spring rains and melting snow. In the summer low levels occur due to high evapotranspiration and low rainfall (Wharton and Brinson 1979)

27 pH and Nutrients Wide range of acidity pH can vary from 3.5 in swamps fed by rainwater whereas the pH of many alluvial swamps can be 6 to 7. Cypress domes and dwarf cypress swamps are low in nutrients because of their hydrologic isolation. Sampling of (P) showed concentration of 50 to 160 µg/l Alluvial river swamps and lake edge swamps tend to have much greater input of nutrients. Sampling of (P) showed concentrations as high as 660µg/l(Mitsch et al.1977)

28 Sedimentation/ Primary Production
Sediment deposition occurs during flooding conditions The rate of sedimentation can control the rate of succession. A high rate of sedimentation is associated with occurrence of cypress and tupelo stands which grow to be years of age (Hodges 1994). Primary productivity seems to be greater in the mixed hardwood swamp environment. These swamps tend to have seasonal flooding rather than constant flooding or constantly drained.

29 Productivity vs. Flooding
The highest productivity occurs periodic/seasonal flooding situations, low productivity is characteristic in continuously flooded or drained.

30 Typical Vegetation Canopy vegetation:
Well adapted to a wet environment. Includes bald cypress, pond cypress, tupelo, red bay and various hardwoods. Spanish moss typical in deep south. Understory vegetation: (difficult to generalize due to lots of other variables) Dependant on light penetration through canopy. Woody shrubs, small trees, herbaceous veg., variations from nutrient rich to nutrient poor. Nutrient rich areas grow a mat cover.

31 Typical hardwoods in canopy, understory mat of duckweed, virginia willow.

32 Buttresses Swollen Buttress, Okeefenokee Swamp, GA Cypress with watermarks, Brunswick Co., NC. Good indicators of hydroperiod. Greatest swelling appears to be where there is continual wetting and soaking of the tree trunk. The actual function is unknown and thought to be a relic response.

33 Cypress Knees Extend from trunks to well above water level. Still unsure as to purpose. Thought to be anchors for the tree and/ or could be possible areas of gas exchange for the root system. (Ewel and Penfound)

34 Five subclasses Each have similar characteristics , however vary slightly (Wharton et al 1976) 1.Still water cypress domes 2.Dwarf cypress swamps 3.Lake-edge swamps 4.Slow-flowing cypress strands 5.Alluvial river swamps

35 Cypress Domes Rainfall and surface inflow.
Generally 1-10 hectares in size. Poorly drained to permanently wet, where they form dense cypress heads, composed almost entirely of cypress; within these heads, growth conditions are better towards the center. Sandy and clay soils, the cypress heads form a very distinctive dome shape and are called cypress domes, with progressively taller tress toward the center, attributed to greater peat accumulation.

36 Dwarf cypress swamps Pond cypress is the dominant tree but grows stunted and scattered throughout the freshwater marshes. These trees rarely grow over 7 m high and average only 3 m in height. The poor growing conditions, which are defined here as lack of significant substrate above the limestone, prevent larger trees from establishing themselves in this environment. Fires often occur here but usually do not kill the cypress due to the lack of combustible organic material accumulation.

37 Slow-flowing Cypress Strands
Diffuse freshwater stream flowing through a shallow forested depression on a gentle sloping plain (Wharton 1976). Substrate is primarily sand with a mixture of limestone and shell beds. Shallow peat layer. They have a seasonal hydroperiod(wet and dry cycle. Corkscrew Swamp, Fl

38 Lake edge swamps Generally bald cypress swamps found along lake margins in the Southeast. Also have tupelo and other water tolerant hardwoods. Seasonal fluctuations in water level. Nutrient rich due to runoff from lake and uplands. Also can act as filters that receive overland flow from the uplands and allows sediments to settle and chemicals to absorb into the sediments before discharge into the open lake .

39 Alluvial River swamps Found in floodplains of river and creeks of the southeast. Dominated by bald cypress and/ or water tupelo. Confined to permanently flooded depressions. Abandoned river channels(oxbows) or elongated swamps that usually parallel the river(sloughs). Sometimes referred to as backswamps. Nutrient rich because of river flooding and upland runoff.

40 Economic resources and environmental impacts
Cypress was a staple commodity during the ’s for new settlers of the south. These areas were logged extensively. Many deepwater swamps were lost due to clearcutting. Production increased from 495 million board feet 1899 to 1 billion board feet in1913. By 1925 stocks were running low, they had essentially cut all the old growth cypress and second generation cypress was not as well suited. It is still a valuable resource just not as widely marketed.

41 Hydrology models S.L. Brown developed a hydrology model depicting how drainage of the Green Swamp wetlands led to lower aquifers, drier streams, and greater flooding. Other models by Littlejohn and Weimoff have demonstrated storage capacities and groundwater protection capabilities of these areas.

42 Further research efforts
Studies should be done to improve long term predictive capabilities and knowledge of the fine structure of these systems in order to incorporate proper planning and management practices. Particularly in the area of hydrological function and any factors contributing to loss.

43 Pocosins

44 Topics Defining pocosins Geographic extent Soils Hydrology Vegetation
Low vs. high pocosin communities Fauna Succession Response to fire Development Management

45 Definitions Fresh water wetlands.
Algonquin word poquosin, roughly = “swamp-on-a- hill”. Early European settlers used the term to describe a variety of swampy or marshy land consisting of poorly drained, peaty soils supporting pond pines and evergreen shrubs. The Oxford English Dictionary defines a pocosin as a track of low swampy ground usually wooded in the southern united states.

46 Defintions Cont’d In 1875 W.C. kerr, the state geologist of NC in a geologic Survey of North Carolina, defined pocosins as “flatwoods with no natural drainage ways, different from swamps in that they are not alluvial, occurring on divides between rivers and sounds and frequently elevated above streams of which they are the source”.

47 Defintions Cont’d In 1928 Wells provided a more broad definition. According to Wells the defining factors of a pocosin include soil type, hydrology, topography, occurrence of periodic burning, and vegetation.

48 Wells described pocosins as wetlands occurring in broad shallow stream basins, drainage basin heads or broad flat upland areas of the coastal plains that are characterized by long hydroperiods, temporary surface water, periodic burning, and soils of sandy humus, muck, and peat. The dominant vegetation being broad leaved evergreen shrubs or low trees. Later defining of the term by other authors, generally followed this concept pocosins.

49 According to the U.S. fish and Wildlife wetland classification system pocosins are classified as follows: System: Palustrine Class: Scrub-shrub Sub-class: Broadleaved evergreen. Water regime: Saturated. Water chemistry: Fresh-acid Soil: Medisaprist

50 Geographic Extent Occur on the southeastern coastal plain spanning from Virginia to southern Florida. North Carolina possesses seventy percent of all pocosins. In 1962 there were approximately 2,243,550 acres of pocosins in NC.

51 In fact, according to Wilson, at this time pocosins accounted for the primary land area type in several of the counties in North Carolina. Dare: 55.7% Tyrell: 54.2% Hyde: 53.4% Jones: 42.7% Pender: 36.1% Carteret: 34.7%

52 Wilson's data was later compared to 1979 LANDSAT imagery, and aerial photographs to determine the total amount of the pocosin land that had been altered or drained in the seventeen year period. It was determined that 1,503,000 acres of pocosins remained in However only 695,000 of these were left completely in their natural state.

53 740,000 acres (33%) of the pocosins had been completely developed.
Completely developed pocosins in this study were defined as those that have been drained and ditched, their natural vegetation removed, their soils prepared for agriculture, forestry, industry, etc, and that are clearly depicted on landsat imagery or other aerial photos.

54 The largest areas of Natural pocosins in North Carolina are located in Pasquotank and Dare counties in The northern coastal plain.

55 Pocosins are also still abundant in Carteret, Craven, and Jones counties, in the central part of the coastal plain.

56 Abundant still in Pender, Duplin, and, Brunswick counties in the southern portion of the coastal plain.

57 Pocosin soils At the end of the Wisconsin ice age (~ 10,000 years ago) sea level began to rise from a level approximately 122 m below it current elevation. As the large exposed continental shelf became submerged, stream flows on the eroding plain slowed, and water table rose.

58 Pocosin soils Deposition in the stream channels increased as did that of the inter-stream areas. With the aid of a more mild climate aquatic vegetation began to grow in shallow areas which in turn led to the accumulation of peat.

59 Pocosin soils Once the peat had begun to form in the low drainage areas it built up and out ward laterally across the inter-stream divides. At this point there is the beginning of a transition from a mineral soil to a peat soil.

60 Pocosin soils C-14 dating results have determined the age of the earliest deposited organic clay and over lying peat of the Chesapeake Bay and Dismal swamp to be approximately approximately 10,340 and 8,135 years before present, respectively. It is believed that the deposition of peat in the lower portions of the North Carolina coastal plain to have occurred around the same time.

61 Pocosin soils Medisaprist soils: Well decomposed organic soils (histosols) with an organic depth of greater than 40cm. To be considered a histosol a soil must have 20 % organic matter if there is no clay present, or at least 30% if there is up 60% clay. The organic surface horizon of a pocosin soil can be greater than 130 cm.

62 Pocosin soils Anaerobic environment
Preserves organics. Acidic, with pH ranging from Nutrient poor. Especially in P. Low cation exchange capacity. Water logged

63 Soils/hydrology Accumulation of organic matter causes the surface of a pocosin to become regionally elevated. As a result the water table within the peat will rise to a degree that it becomes isolated from the chemical influence of the groundwater system below. Rainwater thereafter is the dominant source of nutrients and minerals, thus a pocosin is ombrotrophic.

64 Soils/hydrology At this point there is a change in head force of the water and the net movement is downward through the peat to the underlying sediments. Recharge will occur under these conditions, though it will be very limited. Low conductivity of the peat. Small difference between the two water levels.

65 Soils/Hydrology The effects of the of the isolation of the water table within the peat and that of the ground water beneath the peat was observed by in study by C.C. Daniel III of the Pungo Wildlife refuge. The figure below shows the reduction of dissolved cations in the water of the shallow well that does not penetrate the peat/mineral soil contact vs. a deeper well that reaches to the groundwater within the mineral soil.

66 Soils/Hydrology

67 Soils/Hydrology Ca reacts with carbonic acid (H2CO3)
Forms calcium bicarbonate (Ca[HCO3]2) (Ca[HCO3]2) dissociates in water leaving the bicarbonate ion (HCO3-). Responsible for most of the buffering for natural water systems. This reflects the low pH and poor buffering capabilities of these organic soils.

68 hydrology The water budget of pocosins results in fairly static water levels.

69 Hydrology There are four input out put events that influence water budget. 1. Precipitation Exclusive input of water. 2. Evapotranspiration Greatest portion of output during summer and fall high temperatures and low precipitation. 3. Runoff In form of sheet flow following rain events Greatest during winter and spring higher precipitation and consequent higher water table 4. Groundwater Discharge Very Low due to poor drainage of peaty soil

70 Vegetation In general structure and distribution of vegetation is controlled by interrelated environmental conditions. Thickness of peat Length of hydroperiod Severity of fire Nutrient availability

71 Vegetation Primary characteristic is presence of a dense shrub layer.
Also the pond pine (Pinus Serotina)is indicative of pocosins. Also the zenobia (Zenobia pulverulenta) is native to pocosins. Sphagnum moss Though herbs are not major part of a pocosin community they do sprout vigorously after fire.

72 Two pocosin vegetation types
Low vs. high pocosins

73 Low Pocosins Very nutrient poor.
Occur in the center of the domed peatlands. Usually on peat deposits1-5m deep. Plant roots can never reach mineral soil.

74 Low Pocosins Identified by low stature of shrubs(<1.5m).
Also by sparse distribution and low stature of trees.

75 Low Pocosins Completely ombrotpophic.
Low dense shrub layer usually dominated by fetterbush (lyonia Lucida), swamp cyrilla, or titi (Cyrilla racemiflora), or Zenobia, and frequently greenbrier (Smilax spp.). Trees usually include stunted pond pine , as well as swamp red bays, loblolly-bay, and sweetbay (Magnolia virginiana).

76 High Pocosins High pocosin vegetation types usually occur from the intermediate portion to the center of the domed peatland. Usually on peat deposits 1.5m thick or less. Peat is shallow and saturated enough for for roots to sometimes reach underlying mineral soil. Shrubs range m tall. Sparse distribution and short stature of trees are also characteristic.

77 High Pocosins Receive very little surface or ground water so are largely ombrotrophic. Vegetation species is similar to low pocosin. Taller shrub layer and trees. More nutrients.

78 Successional Patterns
Two contrasting theories. 1. Controls of pocosin succession are fire intensity and frequency. Low pocosin considered a pioneer stage succeeding to high pocosin and then bay forest. Climax within a few hundred years (without disturbance).

79 Successional Patterns
2. Succession is controlled by nutrient levels. Succession goes from marsh to swamp forest to bay forest to tall pocosin to short pocosin. Supported by pollen analysis.

80 Development As early as the 1700s swamp land in NC has been developed.
The early 1800s successful agriculture at lake Phelps and Mattamuskeet lead to the state draining swamp lands extensively. J. Paul Lilly sates in A History of swamp land development. “that essentially all swamp lands in North Carolina have been logged at least once, and have had some drainage imposed, either for agricultural development, or to aid in logging and reforestation”.

81 Development Drainage of pocosins and their use as agricultural land can lead to over 20x the phosphorus output of natural pocosins. Those converted to cattle operations have been shown to out put up to 70x the amount of P of a natural pocosin.

82 Development For example, the conversion of pocosins to agricultural land in the Albemarle Sound region was shown to output 3X as much N and 28X as much P s before its conversion. Increased nutrient outputs such as these are likely to facilitate the eutrophication process of near by water bodies. And in this case was linked to subsequent algal blooms in The Chowan River.

83 Development Negative consequences of pocosin drainage and development include but are not limited to. Habitat loss Loss of natural flood buffer Diminished water quality

84 Management/preservation
Preservation and smart management of pocosins is imperative for the maintenance of natural diversity in North Carolina. These areas have often been considered wastelands by managers. The continued existence of pocosins relies on these managers to realize their ecological importance, and mandate formal protective safeguards for these communities(Richardson, 1982).

85 Carolina Bays by Leighann Budde

86 Definition Isolated, elliptical, shallow depressions (~50’ deep) oriented in a NW-SE direction with a sand ring pronounced in SE: “Neptune’s Racetracks”. Ellipse generally narrows to SE. Often vegetated by bay trees Most depend on rainwater for moisture, nutrients, though some have stream flow. Vary from 50m – 8km in length From 6,000-60,000 years in age or more

87 Distribution source:

88 Distribution Were possibly ~ 500,000 total, but inventory difficult due to human alteration. Now possibly 10-20,000 remaining Largest given area of occurrence includes southern NJ to northern Fla. ~80% in N. and S. Carolina

89 Wetland Loss Estimated 97% of Carolina Bay wetlands in South Carolina have been lost due to : Draining for agriculture- 71% Logging – 34% Highways / development threaten many

90 Named for presence of bay trees: Loblolly bay, red bay, and sweet bay
Vegetation Depends on size, depth, hydrology, and soil characteristics From open water with pond cypress To thick, shrubby pocosin type areas on peat mats Named for presence of bay trees: Loblolly bay, red bay, and sweet bay

91 Some common soil types Ponzer Dominant in large bays
Rutledge Found along inside boundary of large bays, but is most of small ones Higher / dryer than Pozer High organic matter, but sandy Rimini Found on some rims, not extensive Thin “A” horizon over wide sandy layer “B” horizon full of organic acids Ponzer Dominant in large bays Anoxic, mostly organic matter Thick Black, organic rich “A” horizon over loamy material

92 Carolina Bay Orientations
Notable orientation was not realized until 1930’s and the advent of aerial photography. Smaller bays deviate more from preferred orientation.

93 Meteorites! Prouty (1952), Melton and Schriever(1933), etc.
Meteorites coming in at a low trajectory from the northwest or one broke apart and debris fanned out over Carolinas. Impact direction pushed up sand into southeast rims Problems: No meteoric material found, no shatter cones or SiO2 polymorphs, what about “ghost bays”? different ages of bays?

94 Comet: Eyton & Parkhurst, 1975
Refute marine ideas because Carolina Bay types were found in Va. Piedmont ’ above SL = no known marine terraces above 350’. Refute meteor or asteroid ideas after studying impact mechanics of Baldwin (1965) and determining that the crater would be roughly 1000 feet deep rim heights of 150 feet rim width of 1000 feet

95 Carolina Comet Eyton & Parkhurst, 1975
Approached from NW, fragmented Cohesiveness of clay rich surficial sediments lessened crater depth Volatile content in nucleus of fragments caused them to explode Led to shock waves which created depressions

96 “Tunguska event” did it happen again?
June 30th, Near the Tunguska River, Siberia. Explosion leveled 2000 sq km of tundra and left felled trees radiating 9 miles from one area. Others left branchless. No meteorites found: Proposed that a small comet vaporized before impact, but the heat/energy caused by shockwave affected surface Many shallow, funnel shaped depressions left. By 1928 these were filled with swampy vegetation Weeks afterward sky was bright: comet tail Knocked guy off his porch 29 miles away

97 Modern Oriented Lakes Kacrowski, 1977
Found similar features in: East Texas, Chile and the North Slope of Alaska Was able to recreate oriented bays with a wind machine and a sand box But: -Why do we need to go to the ends of the earth to find similar if it’s just winds? Why are winds in Carolinas able to do this? Soils anchored by roots are too stable for winds Why has this process stopped? What about bays within bays and overlapping bays? (Savage, H., Mysterious Carolina Bays)

98 Artesian Spring Hypothesis Johnson, D.A. 1942
Vast amount of artesian springs eroded sediments or dissolved karst leaving a pool of surface water that appeared elongated as the artesian spring migrated along regional dip. Northwesterlies furthered the elliptical shape.

99 Carolina Bays and the Shapes of Eddies Cooke, C.W. 1954
Carolina Bays are of marine origin Originally hollows in marine terrace Sand rims are bars / spits / dunes built by tidal eddies in former estuaries or tidal flats on Pleistocene age marine terraces.

100 Cooke Refutes: Artesian spring hypothesis: too many bays, bays are above artesian flow, too hard to maintain artesian head in surficial sediments Rounding effects of waves: bays are too perfect, orientation is too perfect Rotation of earth must be involved!

101 Tidal currents often create stationary eddies b/c they often flow into wide, quiet water bodies.
Stationary eddies should leave impression on surface. Incoming tide scours sand and drops it in bars. Wave activity pushes it up into crescent beach ridge around the eddy, which may become vegetated. The eddy slows/stops with growth of beach ridge and the bay begins to silt and become marsh-like. A fall in sea level will result in transition into a freshwater bog, a Carolina Bay.

102 cot(bearing) = cos(lat)
Gyroscopic Eddies Fixed Precessing b:a=sin(lat) b is oriented N450W b:a=cos(lat) cot(bearing) = cos(lat) The rotation of the earth has a gyroscopic effect on already rotating bodies of water, or eddies, causing them to change shape from a circle to an ellipse.

103 Halfmoon Island, Chesapeake Bay,Va.
Based on Cooke’s equations for a precessing eddy,at latitude 37049’ the ratio of long and short diameters should be 0.79, and direction of long axis should be N 51041’ W.

104 Halfmoon Island Chesapeake Bay, Va.
Formed on “Silver Bluff” a late Pleistocene marine terrace named for oolite cliff in Biscayne Bay, Miami (called the Kapapa strand in Hawaii). SL was 6’ above 1954 level. Beach ridge 5’ above high tide, continues subaqueously. Narrow, 10’ deep channel in Thorofare, but you can wade out to it. Weak, clockwise drift observed on either side of channel. Bar was probably built when the eddy was stronger due to greater tidal range in Chesapeake which speeded currents (and eddies) in Pokomoke Sound.

105 New Constraints on the Evolution of Carolina Bays from GPR – Grant, J
New Constraints on the Evolution of Carolina Bays from GPR – Grant, J.A. et al. 1998 Savannah River Site: ~190 Carolina Bays preserved in 803 sq km. Bays are located along terraces and interfluves of the Savannah River. Most bays are small w/ a long axis of ~ m. Some have ponds of ha which may dry seasonally. Used GPR, Cores, and archeological data to track evolution of 4 Carolina Bays: Flamingo, Mona and Woodward, and Thunder Bays

106 Varying Hyrdrologies Flamingo Bay: innundated up to 164 cm in spring. Shallows through summer, fall. Thunder Bay: holds water for 6-9 mo., wettest in spring and summer. Mona / Woodward Bays: hold water for 3-6 mo., wettest in spring and summer.

107 Vegetation Interiors dominated by aquatic or herbaceous wetland species: smartweed, American lotus, panic grasses, blackgum, etc. Basin-Rim transition zone has facultative hardwoods: sweetgum, red maple, blackgum Rims are dominated by slash pine and loblolly pine plantations

108 Stratigraphy Bay interior Regional quartz sand sheet:
Grades from sandy sediment with little organics interbedded with silt / clay near the edge to organic rich, silty clays of a Rembert sandy loam soil towards the center Bay fill is mostly mid to late Holocene in age. Regional quartz sand sheet: Thin (1-3m), moderate sorting Absent from within bay, but thickens to SE side  likely present before bay formation

109 Stratigraphy ~cont. Upland Unit underlies sand sheet.
Poorly sorted, but finer than sand sheet. Surface lies above that of basin interiors (likely there before basin formation) Flat lying under east and south rims but outcrops on northern rim of Flamingo Bay  excavation of sand sheet  depression in upland unit and sand reworked into SE rims?

110 Grant’s Model GPR indicates multiple reactivation surfaces on base of rim sediments Evolution didn’t involve much modification of the underlying Upland unit During fluctuating water conditions (though still open) sediments were exposed for deflation and rim accretion Rim sediments were deposited into standing vegetation  ESE facing parabolic dune w/ no stratification and moderate sorting

111 Grants Model ~cont. Slow erosion of shoreline from WNW side provided sediment for basin infill Infill led to colonization of emergent vegetation  less open water time/year  less wave E to modify shoreline rims stop accreting Some sediments transferred back into basin through alluvial activity (sand wedges found grading down to basin)

112 Grant’s Model Problems: scouring of bay margins needs southwesterlies and parabolic rim on ESE needs northwesterlies Answers: Southwesterlies dominate bay orientation b/c they are most common during spring and summer when water level is highest  minimum exposure of sediments to wind. Northwesterlies are dominant during fall and winter when water levels are low  more deflation and downwind rim accretion

113 Not to be confused with…
GRANT, C A biological explanation of the Carolina Bays. Sci. Monthly 61:

114 Lake Waccamaw, NC Stager and Cahoon (UNCW), 1987
Largest of Bay lakes,marine bluffs along north shore, location at major river indicate tectonic genesis. Wind / Waves caused orientation Colder winters during Pleistocene moist phase  Ice  pushed sand ridges up Multiple ridges  multiple shoreline positions Genesis at end of pleistocene Unique due to endemic species Found to be young ~15,000 yBP = young for endemics

115 Conclusion Carolina Bays remain another wonder of the world. General belief seems to be that existing wet depressions were further scoured by winds into preferred orientation. Theories abound: None fully accepted Modern technology could break the story Must protect them for further study

116 “Given a confident belief that the answers are indeed out there in the sand, we come then to the true shame of the Carolina Bay story: the willingness of the current geophysical research community to tolerate and admit such a profound ‘mystery’ in their midst….The study of the Carolina Bay origin is the ‘crazy aunt in the attic’ of the Coastal Plain researcher” -George Howard

Download ppt "Riparian Ecosystems By: David Gridley."

Similar presentations

Ads by Google