Phosphorus Status: Phosphorus enrichment
appears to be more widespread than nitrogen enrichment with few sites
meeting the seagrass threshold. View total phosphorus status map.
Where do nutrients come from?
inputs to the Coastal Bays are dominated by non-point sources (e.g.,
surface runoff, groundwater, atmospheric deposition and shoreline
erosion). The amount of nutrients coming from an area is largely
dependent on the predominant land use - agriculture and developed land
versus wetlands and forests.
budgets are a tool managers use to organize diverse nutrient data sets.
The essential parts of simple budget include inputs (point,
diffuse, atmospheric) and exports (denitrification, burial in sediment,
oceanic exchange, fisheries harvest).
Additional elements that should be included are nitrogen storages
in the sediments, eroding marshes (a form of inputs) and nitrogen fixation
(another potential input).
22, 2004 The Maryland
Coastal Bays Program Scientific and Technical Advisory Committee,
STAC, held a one day workshop to refine the nutrient loading
budget for the MD Coastal Bays. In the past few years there
has been an abundance of data collected related to nutrient inputs
to the bays that can be used to verify (or challenge) the modeling
estimates that have been calculated. The goal of the workshop was
"to develop an updated nutrient budget for the Coastal Bays
(including VA and DEL) based on locally collected data."
from the workshop are available online and a synthesis of the
results will be completed by June 2005.
How Excess Nutrients Harm
the Coastal Bays
Excess amounts of nutrients are the
most extensive pollution problem affecting the Maryland Coastal Bays. Just
as nutrient fertilizers are used to promote plant growth on our lawns and
farm fields, nutrients in streams and the bays encourage the growth of
aquatic plants. Although some aquatic
plants are beneficial and provide food, oxygen, and habitat, excessive
nutrients may result in thick growths of aquatic plants (especially algae)
that contribute to an unhealthy environment. These
algae blooms block light needed by
seagrasses (submerged aquatic
vegetation, or SAV), either by clouding the water column or coating the
grasses themselves. In addition, when algae die, they
settle to the bottom and are consumed by bacteria during the decomposition
process. This process consumes oxygen, depleting it from bottom waters.
The resulting low
dissolved oxygen concentrations drive fish and blue
crabs from their preferred habitat and can kill clams, worms, and other
small bottom organisms on which crabs feed.
The most important nutrients affecting
aquatic plant growth are nitrogen and phosphorus. Plant and animal matter
(including animal and human waste), fertilizer, and even car and power
plant exhaust, all contain nutrients. When these nutrient sources are not
controlled, excess nutrients find their way into the groundwater, creeks,
rivers and, eventually, the open bays.
Nutrients can have detrimental effects on these tributary systems as
Definition of nutrient
loads versus nutrient concentrations
The nutrient load
refers to the total amount of nitrogen or phosphorus entering the water
during a given time, such as "tons of nitrogen per year."
Nutrients may enter the water from runoff, groundwater, or the air (in the
form of wet deposition such as rain or snow as well as dry deposition).
The nutrient concentration refers to the amount of nitrogen
or phosphorus in a defined volume of water (such as milligrams of nitrogen
per liter of water). Total nitrogen concentration is the total amount of
nitrogen in one liter of water; total nitrogen includes both dissolved
nitrogen in the water column and particulate nitrogen contained in algal
cells and in organic detritus such as degrading leaves from trees. Like
nutrients, concentrations of oxygen, algal abundance (measured as
a), and total
suspended solids are a measure of how much oxygen, chlorophyll a,
or total suspended solids are in a defined volume of water. The
relationship between nutrient concentration and nutrient load can vary and
depends on the flow, the volume of water in the river, and watershed
Although water quality goals refer to
decreasing nitrogen and phosphorus loads, concentrations are generally
used as thresholds because laboratory analyses of water samples are reported in terms of
concentration with a known level of precision and accuracy. The Maryland
Coastal Bays Scientific and Technical Advisory Committee (STAC) developed
criteria for threshold categories based on living resources indicators,
most notably seagrasses.
Living resource objective
|Better than seagrass
|Meets seagrass objective
|Does not meet seagrass
|Does not meet STAC
|Does not meet any