Note that yearly variations in collection methods exist. Following is a
summary of methods that have been used.
The dataset shows the locations where eelgrass was observed in the Great
Bay Estuary based on low-altitude aerial surveillance. The study area
includes the following waterbodies: Great Bay, the mouth of the Squamscott
River, the tidal portion of the Lamprey River, the tidal portion of the Oyster
River, the tidal portion of the Bellamy River, the Piscataqua River and
Portsmouth Harbor and its associated creeks. Aerial photographs are taken
of the study area at 3000 feet at low spring tide with roughly 60% overlap
on a calm day without preceding rain events and when the sun is at a low
angle to minimize reflection (between 7 am and 10 am). Photographs are
taken in late summer, usually late August or early September, depending on
tides and weather, to reflect the maximum eelgrass annual biomass. 35 mm film
(ASA 200) or a digital camera is used to acquire the images. Typically 300 images
are needed to cover the entire Great Bay Estuary. The orientation of the
photographs is near-vertical. This is a slight deviation from the NOAA
Coastal Change Analysis Program protocol, but follows a published method
(Short and Burdick, 1986). The photographs, in the form of 35mm slides or
digital computer images, are projected on a screen and the eelgrass images
are transferred to a base map. These maps are then digitized using GIS
software. The eelgrass habitat mapped from the aerial imagery is verified
using the ground truthing data by placing the ground-truthing locations
onto the digital image using GIS software. Ground-truthing is done
from a small boat during the same season as the photographs are taken.
Ground-truth observations are made at low tide. Samples are collected with
an eelgrass sampling hook. Positions are determined using GPS. The
ground-truth surveys assess 10-20% of the eelgrass beds mapped in the
estuary. The aerial survey is completed yearly. The first survey in the
series was completed in 1986.
Purpose:
The dataset was developed to monitor the distribution of eelgrass within the
Great Bay Estuary over time. The surveys have been completed yearly since 1986
to track trends over time. A quality assurance project plan is available at:
<http://prep.unh.edu/resources/qapps/unh_eelgrass_zostera-qapp-unh&des-10.pdf>.
Time_Period_of_Content:
Time_Period_Information: Single_Date_Time:
Currentness_Reference: Ground Date
Status:
Progress: Complete
Maintenance_and_Update_Frequency: Annually
Spatial_Domain:
Bounding_Coordinates:
West_Bounding_Coordinate: -70.911297
East_Bounding_Coordinate: -70.677157
North_Bounding_Coordinate: 43.153869
South_Bounding_Coordinate: 43.049923
Keywords:
Theme:
Theme_Keyword_Thesaurus: ISO 19115 Topic Category
Theme_Keyword: biota
Theme:
Theme_Keyword_Thesaurus: None
Theme_Keyword: Eelgrass
Theme:
Theme_Keyword_Thesaurus: None
Theme_Keyword: Estuary
Theme:
Theme_Keyword_Thesaurus: None
Theme_Keyword: Estuarine
Place:
Place_Keyword_Thesaurus: ISO 19115 Topic Category
Place_Keyword: oceans
Place_Keyword: Northeast
Place_Keyword: New England
Place_Keyword: New Hampshire
Place_Keyword: Great Bay
Place_Keyword: Little Harbor
Place_Keyword: Piscataqua River
Place_Keyword: Lamprey River
Place_Keyword: Oyster River
Place_Keyword: Bellamy River
Place_Keyword: Portsmouth Harbor
Place_Keyword: Squamscott River
Place_Keyword: New Castle
Place_Keyword: Rye
Place_Keyword: Portsmouth
Place_Keyword: Newington
Place_Keyword: Greenland
Place_Keyword: Stratham
Place_Keyword: Newfields
Place_Keyword: Newmarket
Place_Keyword: Durham
Place_Keyword: Dover
Place_Keyword: Madbury
Place_Keyword: Eliot
Place_Keyword: Kittery
Place_Keyword: Maine
Access_Constraints: None
Use_Constraints:
User is required to read metadata completely before using the data. The
information provided in this coverage is a subset of spatial databases
developed by the University of New Hampshire and used by the NH Department
of Environmental Services (NHDES). Development of these databases is an ongoing
project; they may not contain all existing and potential sites, stations, or
threats. The NHDES is not responsible for the use or interpretation of this
information, or for any inaccuracies in the site names, tax map and lot
information, or locations. All information is subject to verification.
These data are to be used for planning purposes only; distribution is discouraged.
Point_of_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Matt Wood
Contact_Organization: New Hampshire Department of Environmental Services
Contact_Position: Water Quality Specialist
Contact_Address:
Address_Type: Mailing and Physical Address
Address: 29 Hazen Drive, PO Box 95
City: Concord
State_or_Province: New Hampshire
Postal_Code: 03302
Contact_Voice_Telephone: 603-271-8868
Native_Data_Set_Environment: Version 6.2 (Build 9200) ; Esri ArcGIS 10.3.1.4959
Data_Quality_Information:
Logical_Consistency_Report:
Note that yearly variations in collection methods exist. Following is a
summary of methods that have been used.
The eelgrass habitat mapped from the aerial imagery is verified using the
ground truthing data by placing the ground-truthing locations onto the
digital image using GIS software. Ground-truthing is done from a small
boat during the same season as the photographs are taken. Ground-truth
observations are made at low tide. Samples are collected with an eelgrass
sampling hook. Positions are determined using GPS. The ground-truth surveys
assess 10-20% of the eelgrass beds mapped in the estuary. Overlapping polygon
areas are identified and removed using a topology rule.
Completeness_Report: The dataset is complete. There are no known omissions.
Lineage:
Process_Step:
Process_Description:
The photographs, in the form of digital computer images, are projected
on a screen and the eelgrass images are transferred to a base map by hand
Process_Date: 2016
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Matt Wood
Contact_Organization: New Hampshire Department of Environmental Services
Contact_Position: Water Quality Specialist
Contact_Address:
Address_Type: Mailing and Physical Address
Address: 29 Hazen Drive, PO Box 95
City: Concord
State_or_Province: New Hampshire
Postal_Code: 03302
Contact_Voice_Telephone: 603-271-8868
Spatial_Data_Organization_Information:
Direct_Spatial_Reference_Method: Vector
Point_and_Vector_Object_Information:
SDTS_Terms_Description:
SDTS_Point_and_Vector_Object_Type: G-polygon
Point_and_Vector_Object_Count: 151
Spatial_Reference_Information:
Horizontal_Coordinate_System_Definition:
Planar:
Grid_Coordinate_System:
Grid_Coordinate_System_Name: State Plane Coordinate System 1983
Horizontal_Datum_Name: North American Datum of 1983
Ellipsoid_Name: Geodetic Reference System 80
Semi-major_Axis: 6378137.000000
Denominator_of_Flattening_Ratio: 298.257222
Entity_and_Attribute_Information:
Detailed_Description:
Entity_Type:
Entity_Type_Label: eelgrass2014
Entity_Type_Definition:
Each polygon of eelgrass habitat is assigned an attribute in the density
field of the attribute table. The values in the density field are
qualitative assessments of the eelgrass density in each polygon.
Entity_Type_Definition_Source: NHDES
Attribute:
Attribute_Label: FID
Attribute_Definition: Internal feature number.
Attribute_Definition_Source: ESRI
Attribute_Domain_Values:
Unrepresentable_Domain:
Sequential unique whole numbers that are automatically generated.
Attribute:
Attribute_Label: Shape
Attribute_Definition: Feature geometry.
Attribute_Definition_Source: ESRI
Attribute_Domain_Values:
Unrepresentable_Domain: Coordinates defining the features.
Attribute:
Attribute_Label: COVER
Attribute_Definition:
Qualitative assessments of the eelgrass density in
each polygon
Attribute_Definition_Source: UNH
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: d
Enumerated_Domain_Value_Definition:
Dense. Eelgrass covers 90-100% of the bottom. The bottom is not
visible in the aerial photos. The shoot density or biomass level for
eelgrass of this density is approximately 250 grams per square meter.
Enumerated_Domain_Value_Definition_Source: UNH
Enumerated_Domain:
Enumerated_Domain_Value: sb
Enumerated_Domain_Value_Definition:
Some bottom. Eelgrass covers 60-90% of the bottom. Some bottom is
visible in the aerial photos but the majority is covered by eelgrass.
The shoot density or biomass level for eelgrass of this density is
approximately 85 grams per square meter.
Enumerated_Domain_Value_Definition_Source: UNH
Enumerated_Domain:
Enumerated_Domain_Value: h
Enumerated_Domain_Value_Definition:
Half. Eelgrass covers 30-60% of the bottom. Approximately half the
bottom is visible in the aerial photos. The shoot density or biomass
level for eelgrass of this density is approximately 55 grams per square meter.
Enumerated_Domain_Value_Definition_Source: UNH
Enumerated_Domain:
Enumerated_Domain_Value: p
Enumerated_Domain_Value_Definition:
Partial. Eelgrass covers 10-30% of the bottom. Eelgrass is present but the
majority of the bottom is still visible in the bed. The shoot density or biomass
level for eelgrass of this density is approximately 25 grams per square meter.
Enumerated_Domain_Value_Definition_Source: UNH
Enumerated_Domain:
Enumerated_Domain_Value: pr
Enumerated_Domain_Value_Definition:
Present. Eelgrass is present but the density could not be determined.
Enumerated_Domain_Value_Definition_Source: UNH
Enumerated_Domain:
Enumerated_Domain_Value: unk
Enumerated_Domain_Value_Definition:
Present. Eelgrass is present but the density could not be determined.
Enumerated_Domain_Value_Definition_Source: UNH
Enumerated_Domain:
Enumerated_Domain_Value: r
Enumerated_Domain_Value_Definition:
Ruppia. Ruppia maritima is a different species of submerged aquatic
vegetation than the Zostera marina that is mapped for this program.
Ruppia can be found in the Great Bay Estuary at low levels, particularly
in association with salt marsh pannes and in the upper reaches of the
estuary. Ruppia was mapped if it appeared in large beds in parts of the
tributaries where eelgrass could be expected.
Enumerated_Domain_Value_Definition_Source: UNH
Enumerated_Domain:
Enumerated_Domain_Value: NULL
Enumerated_Domain_Value_Definition:
No eelgrass. Polygon represents an island or area without eelgrass.
Enumerated_Domain_Value_Definition_Source: UNH
Attribute:
Attribute_Label: FT2
Attribute_Definition: Eelgrass area in square feet.
Attribute_Definition_Source: UNH
Attribute_Domain_Values:
Unrepresentable_Domain: Calculated value.
Attribute:
Attribute_Label: ACRES
Attribute_Definition: Acreage of the eelgrass area.
Attribute_Definition_Source: UNH
Attribute_Domain_Values:
Unrepresentable_Domain: Calculated value.
Distribution_Information:
Distributor:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: Earth Systems Research Center, University of New Hampshire
Contact_Person: GRANIT Database Manager
Contact_Position: GRANIT Database Manager
Contact_Address:
Address_Type: mailing and physical address
Address: Morse Hall, University of New Hampshire
City: Durham
State_or_Province: NH
Postal_Code: 03824
Contact_Voice_Telephone: 603-862-1792
Contact_Facsimile_Telephone: 603-862-0188
Contact_Electronic_Mail_Address: granit@unh.edu
Hours_of_Service: 8:30AM-5PM. EST
Resource_Description: Downloadable Data
Distribution_Liability:
Digital data in NH GRANIT represent the efforts of the contributing agencies
to record information from the cited source materials. Earth Systems Research Center, under contract
to the NH Office of Energy and Planning, and in consultation with cooperating agencies, maintains a
continuing program to identify and correct errors in these data. OEP, ESRC, and the cooperating agencies
make no claim as to the validity or reliability or to any implied uses of these data.
