A Bird's-Eye View of the Environmental Health of the Great Bay Estuary
By David Sims, Institute for the Study of Earth, Oceans, and Space
and, By Dave Kellam, New Hampshire Estuaries Project
August 22, 2007
On a clear day this August, a small airplane will fly over the Piscataqua
River, Little Bay, and Great Bay to take pictures of the large, beautiful
estuary system. But it is not a sightseeing tour. The project is part of
a $70,000, multi-agency effort to understand the effect of increasing nutrients
on the complex Seacoast system.
The overall goal of the effort, which is being led by the New Hampshire
Estuaries Project, is to create a conceptual model to help determine the
sustainable amount of nutrients that can be released into the state’s
largest estuary. Based on this work, the NHEP will make recommendations
to the N.H. Department of Environmental Services (NHDES), which is ultimately
responsible for developing nutrient criteria to protect water quality and
ecosystems of the Great Bay Estuary.
This intense effort is being driven by concerns over rising levels of
nitrogen entering Great Bay. According the NHEP State of the Estuaries
Report, the amount of nitrogen in Great Bay has increased 59% in the past
25 years. This trend is troubling because too much nitrogen in an estuary
will cause algal blooms that cloud the water and disrupt the ecology of
the bay.
One species especially affected by high nitrogen levels and the resulting
cloudy water is eelgrass. Eelgrass is a vital habitat for aquatic creatures
and waterfowl; however, data indicate that eelgrass beds have diminished
by 17 % from 1996 to 2004 in Great Bay. A major factor that limits eelgrass
growth is the amount of sunlight penetrating the water. Water clarity is
reduced when nutrients feed phytoplankton and when suspended inorganic
particulates or dissolved organic matter in the water increases.
A Maryland company has been contracted to take the hyperspectral aerial
images that will record 64 wavelengths across the visible and near-infrared
spectrum. The resulting imagery will show colorful swirls of a variety
of suspended and dissolved materials in the water over the 17-square-mile
region.
To check the reliability of the image data, teams of researchers from
UNH and NHDES will be taking water samples in a variety of locations during
the flight. Additionally, a state-of-the-art buoy deployed in Great Bay
by the UNH Coastal Observing Center will make continuous measurements of
the hyperspectral water clarity as well as other physicochemical parameters,
including turbidity, chlorophyll-a, colored dissolved organic mater, and
nitrate.
The buoy is a prototype deployed as part of the national Integrated Ocean
Observing System (IOOS) with funds from NOAA Coastal Services Center and
was designed to answer management issues like water clarity. Information
from the buoy, together with flow-through surveys coinciding with the flight,
will be invaluable in piecing all the information together.
Phil Trowbridge, NHEP Coastal Scientist, believes this project is the
best way to enhance understanding of how the Great Bay Estuary system responds
to nutrient loading. “The Great Bay Estuary is unique because of
its geography and the degree of development throughout its watershed. Existing
models for nutrient loading don’t quite make sense for this system.
We need real data and observations from several sources to determine what
is happening.”
Ru Morrison, a bio-optical oceanographer of the Coastal Observing Center
within the EOS, concurs and explains the value of multiple data collection
approaches.
“To fully understand water clarity in the Great Bay Estuary we need
information from multiple sources. The buoy in Great Bay is great at collecting
long-term information at one spot but how does that compare to the rest
of the estuary? We need the aerial information corroborated or ‘ground
truthed’ with the spatial surveys to expand results from the buoy.
Synthesis of data from all these sources will provide valuable insight
into light penetration in the waters of the
Great Bay Estuary.”
Trowbridge notes that there is need for further research and monitoring. “This
project captures the conditions at one point in time. To understand how
the estuary reacts to changing environmental conditions, including climate
change and increased upland development, we must monitor these parameters
over the next 10 to 15 years so we have reliable data on which to base
decisions.”
The New Hampshire Estuaries Project, in cooperation with the Coastal Observing
Center, secured the funding for this project from the US EPA Regional Dedicated
Water Quality Program.
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