Maryland Coastal Bays Sediment Mapping Project: Surficial Sediment

Over the course of the project, several navigational systems were used during the collection of samples.  A Loran-C navigation system was used to locate sampling sites during the collection of the cores 9101 through 9114 and for surficial samples 91003 through 91008 ( in Isle of Wight and Assawoman Bays).  The accuracy of this system is ± 50 meters.  Loran coordinates were converted to Latitude and Longitude coordinates using correction technique described in Halka, J.P., 1987, LORAN-C Calibration in Chesapeake Bay: Maryland Geological Survey Report of Investigation No. 47, Baltimore, Maryland, 34 pp.

For the collection of cores 9501 through 9510, and 9601 through 9606, and for surficial sediment samples 95001 through 95302, a Garmin GPS 45 unit interfaced with a Garmin GBR 21 Beacon Receiver was used.  The report accuracy of this system is ± 5 to 10 meters.   A Magnavox MX300 GPS system with MX 50R DGPS Beacon (U.S. Coast Guard) Receiver was used for navigation during the collection of surficial sediment samples 93001 through 94178 and cores.  The reported accuracy of the system is ± 3 to 5 meters.

An Ashtech ACA-12 GPS receiver interfaced with a Starlink MRB-2A MSK Radiobeacon DGPS receiver was used to collect cores 9701 through 9705, and surficial samples 96003 through 96353.  The reported accuracy of the Ashtech DGPS system is ± 2 to 4 meters.

Water depths recorded at each sampling site were not adjusted for tide level.

This study was conducted by the Maryland Geological Survey, Darlene Wells, Principle Investigator; and funded in part by the U.S. Minerals Management Service, Continental Margins Program, and the University of Texas at Austin, Bureau of Economic Geology contract #14-35-0001-30643, and by the Coastal Zone Management Program of the Maryland Department of Natural Resources pursuant to National Oceanic and Atmospheric Administration awards # NA47OZ0132, #NA57OZ0301, #NA67OZ0302, and #NA77OZ0188.

Surficial sediment collection-Sediment samples were collected using a hand operated LaMotte stainless-steel dredge sampler which sampled a bottom surface area of 19 cm x 14 cm, to a depth 5 to 6 cm below the sediment surface.  Upon collection, the samples were visually described and then placed in Whirl-PakTM bags.   A sampling grid based on 1 kilometer by 500 meter spacing was used to determine sample locations for Isle of Wight and Assawoman Bays, and a sampling grid based on 500 by 500 meter spacing was used to determine sample locations for Sinepuxent and Newport Bays, and the Maryland portion of Chincoteague Bay.  Samples were collected in the major tributaries approximately every 500 meters and as far upstream as the first stream bifurcation.

Water content- The procedure for measuring water content consisted of weighing a 25-50 g split of the homogenized sample, drying the split at 65oC, and reweighing it.  Water content, in percent, was calculated as:
(water weight (g)/ wet weight of sediment (g)) x 100
where water weight is the difference between the wet and dry weights of the sample.
The procedure is based on the assumption that the sediment is 100% saturated with free water (water that is not bound up in the crystalline lattice of clay minerals).

Bulk density
Bulk density, in g/cm3, was calculated from the weights used in determining water content, as:
wet weight of sediments (g)/((dry weight of sediment (g)/2.72 (g/cm3)) + water weight (g))
The calculation is based on the assumption that the average grain density of the particulate matter is 2.72 g/cm3 and that all voids in the sediment are completely saturated with water.

Textural analyses-
Overview- 
The grain size composition of each sample was determined for sand-, silt-, and clay-sized particles, ranging in diameter from 0.00006 to 2 mm.  Particle size, expressed as cumulative weight percent, was measured on a logarithmic scale and grouped into dimensionless phi intervals: phi = negative log to the base 2 of the particle diameter in mm.  Example: 4 phi is equivalent to  1 / (2 to 4th power) mm or 0.0625 mm
Sediment samples were analyzed for water content and grain size (sand, silt, clay content).  Water content was calculated as the percentage of water weight to the weight of the wet sediment.  Water content was determined by weighing 30 to 50 grams of sediment, drying the sediment at 65°C, and then re-weighing the dried sediment.  Dried sediments were saved for chemical analyses. Sand, silt and clay contents were determined using the following process.  Sediment samples were first treated with 10% solution of hydrochloric acid (HCl) to remove carbonate material such as shells and then treated with a 6 or 15% solution of hydrogen peroxide (H2O2) to remove organic material.  The sediments were then passed through a 62 micron mesh sieve separating sand from the mud (silt + clay) fraction.  Mud fractions were analyzed using a pipette technique to determine silt and clay contents.  Weights of the sand, silt and clay fractions were converted to relative proportions (weight percentages).

Nitrogen, carbon, sulfur (NCS) analyses-  Total nitrogen, carbon and sulfur, and organic and reactive carbon contents was determined using a Carlo Erba NA1500 analyzer.  All surficial and cores samples (except for some coarse sand samples) were analyzed for total NCS.  One hundred seventy-five sediment samples were selected for organic and reactive carbon analyses. A split of each dried sample was treated with 10% hydrochloric acid (HCl) to remove inorganic carbon (i.e., CaCO3 from carbonaceous minerals such as marble and limestone).   This treated sample was redried, reground, and analyzed for organic carbon content.  A second split of  dried sample (for fifty-five samples)  was treated with 30% hydrogen peroxide (H2O2) to remove "reactive" carbon.  This peroxide treated sample was redried, reground and analyzed for non-reactive carbon.

Dried sediments were pulverized in tungsten-carbide vials using a ball mill.  Approximately 10 to 15 mg of dried sediment were weighed into a tin capsule.  The exact weight (to the nearest ?g) of the sample was recorded.  To enhance complete combustion during the analysis, 15 to 20 mg of vanadium pentoxide (V2O5) were added to the sediment.  The sediment sample, contained in a tin capsule, was dropped into a combustion chamber where the sample was oxidized in an atmosphere of pure oxygen.  The resulting combustion gases, along with pure helium used as a carrier gas, were passed through a reduction furnace to remove free oxygen and then through a sorption trap to remove water.  Separation of the gas components was achieved by passing the gas mixture through a chromatographic column.  A thermal conductivity detector was used to measure the relative concentrations of the gases.

Metal analyses-  Dried sediment samples were  prepared for elemental analysis (Cd, Cr, Cu, Fe, Mn, Ni, P, Pb, and Zn) using the following microwave digestion technique modified from EPA Method #3051 (Soil Sample Digestion Procedure for Floyd Digestion Vessels).  Approximately 0.5 g dried, ground sediment, 2.5 ml concentrated HNO3, and 7.5 ml concentrated HCl were placed in the teflon digestion vessel. Digestion vessel was capped and placed in microwave.  The sediment and acid mixture was digested by irradiating the vessel according to the programmed steps recommended for the number of vessels in the microwave.  The vessel was allowed to cool to room temperature before opening.  The contents of the vessel was transferred to 100 ml volumetric flask and diluted with high purity water to 75 ml.  The resulting digestates were then analyzed using a Thermo Jarrel-Ash Atom Scan 25 sequential ICAP (Inductively Coupled Argon Plasma) unit. The wavelengths and conditions selected for the metals of interest were determined using digested bottom sediments from the selected sites in Maryland's Coastal Bays and reference materials from the National Institute of Standards and Technology (NIST SRM #1646 and #1646a--Estuarine Sediment; NIST SRM #2704--Buffalo River Sediment) and the National Research Council of Canada (PACS-1 and PACS-2--Marine Sediment).

Results of previous process steps were all incorporated into the same table, with each sediment sample location stored in a record.  Each record contained location information and results of sediment analyses.  The UTM coordinates were then used to import the table into ArcMap, using the Import X/Y Data tool.  The resulting event theme was then converted into a shapefile, and metadata created by the Maryland Geologic Survey was appended to the shapefile using ArcCatalog.

Internal feature number.

ESRI

Feature geometry.

ESRI

Identification number for the surficial sediment or core station.  Core stations are identified by 4 digit number with first two digit designating the year of collection and last two designating the sequence of collection for that year.  Surficial stations are identified by 5 digit number with the first two designating the year of collection and last three designating the sequence or order in which the sample was collected for that year.  Generally, stations were numbered across the bays from north to south and from downstream to upstream.

NONE

Arbitrary code designating general area or bay in which the core or surficial sample was collected.

None

Iron content calculated as percent sediment dry weight.

Manganese content units given as micro-gram per gram of dry sediment, or parts per million (ppm).

Nickel content units given as micro-gram per gram of dry sediment, or parts per million (ppm).

Lead content units given as micro-gram per gram of dry sediment, or parts per million (ppm).

Date on which sample or core was collected.  Date is represented by a value corresponding to number of days since January 1, 1900.  In ASCII text file, date is presented as MM/DD/YY where MM is month, DD is day of the month, and YY is last two digits of the year .

Latitude of sample location  (North American Horizontal Datum of 1983, NAD83)

Longitude of sample location (North American Horizontal Datum of 1983, or NAD83)

Distance, in meters, east of origin for Maryland State Plane Coordinate System, NAD83

Distance, in meters, north of origin for Maryland State Plane Coordinate System, NAD83

The easting is abscissa of coordinate pair in NAD83 Universal Transverse Mercator (UTM) coordinate system, Zone 18.  Easting is the eastward projected distance, in meters, of the position from the central meridian (W75 degree meridian, give a false easting value of 500,000) for zone 18 of UTM.

Northing is ordinate of coordinate pair in UTM coordinate system, Zone 18.  Northing is the northward projected distance of the point from the equator.

Chromium content units given as micro-gram per gram of dry sediment, or parts per million (ppm).

Copper content units given as micro-gram per gram of dry sediment, or parts per million (ppm).

Water content of the sediments calculated as percent water weight of the saturated sediment.

Bulk density = wet weight of sediment (g) / {[dry weight of sediment (g) / 2.72] + weight of water (g)}

Bennett, R.H., and Lambert, D.N., 1971, Rapid reliable technique for determining unit weight and porosity of deep-sea sediments:  Marine Geology, vol. 11, p. 201-207.

Classification of sediment based on relative percentages of the sand, silt and clay components (%Sand +%Silt +%Clay= 100%). Gravel content is not included in Shepard's classification.  Gravel represents a minor component in estuarine depositional environments.

Wentworth, C.K., 1922, A scale of grade and class terms for clastic sediments: Jour. Geology, v. 30, p. 377-392.

Zinc content units given as micro-gram per gram of dry sediment, or parts per million (ppm).

Sand content of the sediments calculated as percent weight of sand sized particles (i.e.- those particles with diameter between 2 mm and 0.0625 mm).

Wentworth, C.K., 1922, A scale of grade and class terms for clastic sediments: Jour. Geology, v. 30, p. 377-392.

Silt content of the sediments calculated as percent weight of silt sized particles (i.e.- those particles with  diameter between 0.0625 mm and 0.0039 mm).

Wentworth, C.K., 1922, A scale of grade and class terms for clastic sediments: Jour. Geology, v. 30, p. 377-392.

Clay content of the sediments calculated as percent weight of clay sized particles (i.e.- those particles with  diameter less than 0.0039 mm).

Wentworth, C.K., 1922, A scale of grade and class terms for clastic sediments: Jour. Geology, v. 30, p. 377-392.

Classification of sediment based on relative percentages of the sand, silt and clay components (%Sand +%Silt +%Clay +%Gravel = 100%)  %Gravel is not considered in Shepard's classification.  Gravel represents a minor components in estuarine depositional environments.

Shepard, F.P., 1954, Nomenclature based on sand-silt-clay ratios: Jour. Sed. Pet., v. 24, p. 151-158.

Total nitrogen content calculated as percent of sediment dry weight

Total carbon content calculated as percent of sediment dry weight.

Total sulfur, calculated as percent of  sediment dry weight.

Cadmium content units given as micro-gram per gram of dry sediment, or parts per million (ppm)

Total phosphorus content, calculated as percent of  ediment dry weight

Water depth, in meters, of sample at time it was collected; water depth not adjusted for tide stage.

Organic carbon content, i.e., that carbon not reacting with HCl (acid),  calculated as percent of  sediment dry weight.

Reactive carbon content, i.e., that carbon reacting with H2O2 (hydrogen peroxide), calculated as percent of  sediment dry weight.