penetration of seagrasses in eutrophic waters (National
Research Council, 2000; Burkholder et al., 2007;
McGlathery et al., 2007).
In BB-LEH, comprehensive investigations of seagrass
beds have documented significant declines in plant demographics (biomass, blade length, and areal cover) during
the 2004–2010 time period in response to nitrogen inputs
(Kennish et al., 2008; Kennish et al., 2010). For example,
after an extended progressive decline, Zostera marina
(eelgrass) mean aboveground and belowground biomass
values in 2010 were the lowest ever recorded in the estuary (7.5 and 26.7 g dry wt m
À2 , respectively), which were
87.3 % and 64.8 % lower than in 2004. Concurrently,
mean Z. marina areal cover decreased by 43.8 %, and
mean blade length declined by 33.7 %. In addition, mean
shoot density of Z. marina during 2004–2010
($240–495 shoots m
À2
) also decreased substantially
compared with earlier measurements (650–1,150 shoots
m
À2 in 1999, Bologna et al., 2000, and 500–1,000 shoots
m
À2 in 1982, Vaughan, 1982).
Concomitant with the loss of seagrass habitat over the
2004–2010 period, other impacts have been documented.
For example, macroalgal blooms increased during
2004–2010 as well; investigations of macroalgal blooms
in the estuary over this period revealed 55 occurrences
(2.23 blooms m
À2
) of early bloom (70–80 % macroalgal
cover) and full bloom (>80 % macroalgal cover) events
(Kennish et al., 2011). These resulted in increased mortality of seagrass leading to reduced biomass and barebottom areas within the beds. Furthermore, epiphytic
overgrowth on seagrass was elevated, with the mean percent cover of seagrass leaf surfaces ranging from 10.7 %
to 38.3 % during 2009 and 2010. The loss of seagrass habitat has eliminated essential habitat for hard clams, bay
scallops (Argopecten irradians), and other benthic and
demersal organisms. Seagrass now covers a 5,260-ha area
of the BB-LEH estuarine floor, but the biomass of the
seagrass beds is now significantly reduced (Kennish
et al., 2010; Fertig et al., 2013; Fertig et al., 2014).
The decline of seagrass beds is a serious concern in any
estuary because of the multiple ecosystem services that
they provide, notably major sources of primary production, food for waterfowl, essential habitat and nursery
areas for numerous fish and invertebrates, filters of chemical substances, agents in biogeochemical cycling, and
buffers against wave and current action as well as sediment erosion (Larkum et al., 2006; Orth et al., 2006;
Moore, 2009). These vascular plants are important indicators of overall ecosystem health of an estuary because they
integrate water quality and benthic attributes (Longstaff
and Dennison, 1999; Carruthers et al., 2002; Orth et al.,
2006; Burkholder et al., 2007; Kennish et al., 2008;
Kennish et al., 2010; Moore, 2009).
Management of eutrophication
The conversion of natural land covers to farmlands, housing developments, and industrial complexes facilitates
nutrient loading to nearby estuarine waters, leading to
cascading water quality, biotic, and habitat impacts as
well as diminished ecosystem services. Natural stressors,
such as hurricanes and other major storms as well as
floods and droughts, can exacerbate these effects (Paerl
et al., 2005; Paerl et al., 2007; Paerl et al., 2009). An array
of mid-Atlantic estuaries of the USA, most notably
coastal lagoons with restricted circulation and high water
residence times, has exhibited severely stressed
responses due to nutrient over-enrichment. Most
lagoonal estuaries in this region are now moderately
to highly eutrophic and rank among the most impacted
estuarine systems in the USA (Bricker et al., 1999;
Bricker et al., 2007). Watershed management strategies
to reduce nutrient loading in estuaries of this region
include upgrading stormwater controls, implementing
low-impact development and best management practices, advancing open space preservation, and generating
total maximum daily loads (TMDLs) for nutrient limitation. The effects of urbanization as a driver of nutrient
impacts in estuaries will continue to increase with
increasing coastal population growth, development, and
alteration of coastal watersheds, unless aggressive management actions and effective land use planning are
broadly implemented.
There is the need to scale up the magnitude of corrective actions in altered coastal watersheds where estuaries
are impaired from nutrient enrichment. The effort to protect an estuary from ongoing nutrient pollution must be
accelerated. Coastal population growth and development
have altered land use in the coastal zone and contributed
significantly to the ecological downspiral of many estuaries. Both point and nonpoint source inputs of nutrients to
estuaries continue to be problematic in both developed
and undeveloped countries, and the future projections for
improvement are not promising. In addition, engineering
controls have not been effective at correcting the serious
environmental impacts from the cumulative land
use-land cover changes in many coastal watersheds. More
aggressive management strategies and decisions are
needed to effectively address continued development
effects in watersheds, if the long-term remediation of estuarine eutrophication is to be achieved.
Another problem that must be effectively addressed is
atmospheric delivery of nutrients to estuaries. Atmospheric deposition of nitrogen on estuary and watershed
surfaces is substantial and detrimental (Paerl et al.,
2002). Nitrogen inputs from the atmosphere derive substantially from fossil fuel combustion, and it is important
to seek solutions for this problematic source.
Summary
Boesch et al. (2001) discussed the strategies used to control nutrient pollution in estuarine and marine systems.
They identified three principal strategies of nutrient pollution abatement: (1) nutrient control at the source (i.e.,
farms, animal feedlots, lawns, and fossil fuel power
308
EUTROPHICATION
Research Council, 2000; Burkholder et al., 2007;
McGlathery et al., 2007).
In BB-LEH, comprehensive investigations of seagrass
beds have documented significant declines in plant demographics (biomass, blade length, and areal cover) during
the 2004–2010 time period in response to nitrogen inputs
(Kennish et al., 2008; Kennish et al., 2010). For example,
after an extended progressive decline, Zostera marina
(eelgrass) mean aboveground and belowground biomass
values in 2010 were the lowest ever recorded in the estuary (7.5 and 26.7 g dry wt m
À2 , respectively), which were
87.3 % and 64.8 % lower than in 2004. Concurrently,
mean Z. marina areal cover decreased by 43.8 %, and
mean blade length declined by 33.7 %. In addition, mean
shoot density of Z. marina during 2004–2010
($240–495 shoots m
À2
) also decreased substantially
compared with earlier measurements (650–1,150 shoots
m
À2 in 1999, Bologna et al., 2000, and 500–1,000 shoots
m
À2 in 1982, Vaughan, 1982).
Concomitant with the loss of seagrass habitat over the
2004–2010 period, other impacts have been documented.
For example, macroalgal blooms increased during
2004–2010 as well; investigations of macroalgal blooms
in the estuary over this period revealed 55 occurrences
(2.23 blooms m
À2
) of early bloom (70–80 % macroalgal
cover) and full bloom (>80 % macroalgal cover) events
(Kennish et al., 2011). These resulted in increased mortality of seagrass leading to reduced biomass and barebottom areas within the beds. Furthermore, epiphytic
overgrowth on seagrass was elevated, with the mean percent cover of seagrass leaf surfaces ranging from 10.7 %
to 38.3 % during 2009 and 2010. The loss of seagrass habitat has eliminated essential habitat for hard clams, bay
scallops (Argopecten irradians), and other benthic and
demersal organisms. Seagrass now covers a 5,260-ha area
of the BB-LEH estuarine floor, but the biomass of the
seagrass beds is now significantly reduced (Kennish
et al., 2010; Fertig et al., 2013; Fertig et al., 2014).
The decline of seagrass beds is a serious concern in any
estuary because of the multiple ecosystem services that
they provide, notably major sources of primary production, food for waterfowl, essential habitat and nursery
areas for numerous fish and invertebrates, filters of chemical substances, agents in biogeochemical cycling, and
buffers against wave and current action as well as sediment erosion (Larkum et al., 2006; Orth et al., 2006;
Moore, 2009). These vascular plants are important indicators of overall ecosystem health of an estuary because they
integrate water quality and benthic attributes (Longstaff
and Dennison, 1999; Carruthers et al., 2002; Orth et al.,
2006; Burkholder et al., 2007; Kennish et al., 2008;
Kennish et al., 2010; Moore, 2009).
Management of eutrophication
The conversion of natural land covers to farmlands, housing developments, and industrial complexes facilitates
nutrient loading to nearby estuarine waters, leading to
cascading water quality, biotic, and habitat impacts as
well as diminished ecosystem services. Natural stressors,
such as hurricanes and other major storms as well as
floods and droughts, can exacerbate these effects (Paerl
et al., 2005; Paerl et al., 2007; Paerl et al., 2009). An array
of mid-Atlantic estuaries of the USA, most notably
coastal lagoons with restricted circulation and high water
residence times, has exhibited severely stressed
responses due to nutrient over-enrichment. Most
lagoonal estuaries in this region are now moderately
to highly eutrophic and rank among the most impacted
estuarine systems in the USA (Bricker et al., 1999;
Bricker et al., 2007). Watershed management strategies
to reduce nutrient loading in estuaries of this region
include upgrading stormwater controls, implementing
low-impact development and best management practices, advancing open space preservation, and generating
total maximum daily loads (TMDLs) for nutrient limitation. The effects of urbanization as a driver of nutrient
impacts in estuaries will continue to increase with
increasing coastal population growth, development, and
alteration of coastal watersheds, unless aggressive management actions and effective land use planning are
broadly implemented.
There is the need to scale up the magnitude of corrective actions in altered coastal watersheds where estuaries
are impaired from nutrient enrichment. The effort to protect an estuary from ongoing nutrient pollution must be
accelerated. Coastal population growth and development
have altered land use in the coastal zone and contributed
significantly to the ecological downspiral of many estuaries. Both point and nonpoint source inputs of nutrients to
estuaries continue to be problematic in both developed
and undeveloped countries, and the future projections for
improvement are not promising. In addition, engineering
controls have not been effective at correcting the serious
environmental impacts from the cumulative land
use-land cover changes in many coastal watersheds. More
aggressive management strategies and decisions are
needed to effectively address continued development
effects in watersheds, if the long-term remediation of estuarine eutrophication is to be achieved.
Another problem that must be effectively addressed is
atmospheric delivery of nutrients to estuaries. Atmospheric deposition of nitrogen on estuary and watershed
surfaces is substantial and detrimental (Paerl et al.,
2002). Nitrogen inputs from the atmosphere derive substantially from fossil fuel combustion, and it is important
to seek solutions for this problematic source.
Summary
Boesch et al. (2001) discussed the strategies used to control nutrient pollution in estuarine and marine systems.
They identified three principal strategies of nutrient pollution abatement: (1) nutrient control at the source (i.e.,
farms, animal feedlots, lawns, and fossil fuel power
308
EUTROPHICATION