Download Animals in the Neponset - BIOEEOS660-f12

Kristin Bulpett
Thursday November 13, 2014
EEOS 660
Restoring the Neponset River: The Role of Animals
Salt marshes are afflicted by ranging salinity, temperature, humidity and
inundation (Nixon, 1982). These characteristics determine the zonation of marsh
halophytic plants due to their varying tolerances of physical parameters; ultimately
influencing the densities and distributions of marsh animal species (Haslett, 2006).
Despite the harshness of the intertidal zone, marshes are highly productive
ecosystems and are home to many species of insects, fish, birds, small mammals and
invertebrates—each leading important roles in marsh ecosystem functioning and
production (Nixon, 1982).
Healthy New England salt marshes are breeding grounds for many species of
insects, particularly mosquitos but also flies, spiders and mites (Nixon, 1982). In
salt marshes, insects control vegetation processes including growth, seed
production, reproduction, productivity and survivorship; affecting the abundances
of marsh plants (Sala et al., 2008).
Commercial fishery species such as winter flounder, herring, clams, bay
scallop, conch, dogfish shark, spiny shark and skate all depend on the salt marsh as a
nursery and feeding grounds (NRWA, 2012). In addition, salt marshes serve as a
habitat for several migratory fish species (American shad, blueback herring and
alewife) and waterfowl (ducks, herons and sparrows) (NRWA, 2012). Predator
species, such as these, regulate plant biomass and primary production of salt
marshes through a “trophic cascade” by preying on the marsh grazers (Silliman and
Bertness, 2002).
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Foundation species facilitate entire communities through habitat creation,
thereby influencing the dispersal and abundances of their associated organisms
(Altieri et al., 2009). In Narragansett Bay, for example, cordgrass prevents solar
stress and provides an attachment surface for mussels, which in turn, provide a safe
habitat space for other organisms—largely influencing the distribution of organisms
of that region (Altieri et al., 2009).
Since certain organisms can also largely influence the physical nature of
habitats, fluxes of elements in biogeochemical cycles and the productivity of
ecosystems, the loss of these particular species could significantly alter the structure
and functioning of entire ecosystems (Cardinale et al., 2012; NRWA, 2012).
Biodiversity also helps to maintain the stability of ecosystem functioning because
some species are able to functionally offset for others so that any changes to
ecosystem processes also accelerates as biodiversity loss increases (Cardinale et al.,
2012; Palmer et al., 1997).
However, despite the importance of animal biodiversity in salt marshes,
many marshes like the Neponset River Salt Marsh, are plagued by pollution, low
water levels, altered wildlife habitats and invasive species posing serious threats to
natural communities and marsh sustainability (Silliman and Bertness, 2004, NRWA,
2012). Before the Clean Water Act in 1972, factories would release their untreated
wastewater directly into the Neponset River (NRWA, 2012). Today, pollution still
reaches the Neponset from leeching of PCB-laced soils from these former industrial
properties or by entering the streams of the watershed directly from runoff ridding
the streets of animal waste, garbage, oil and toxic heavy metals (NRWA, 2012). In
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addition, there are still some instances of sewage pipes leaking into the
groundwater or when a building`s waste is accidently directed to the Neponset
River instead of the wastewater treatment facility (NRWA, 2012).
Increasing
nitrogen availability increases tissue quality, which can lead to increased herbivory;
dramatically shifting the competitive balance between healthy S. alterniflora and
Phragmites australis (Silliman and Bertness, 2004, Sala et al., 2008).
With urbanization in the Neponset came an increase in impervious surfaces
so that precipitation across the watershed is carried to Boston Harbor instead of
replenishing the local streams (NRWA, 2012). Simultaneously, the people living in
these communities are extracting water from the watershed and their wastewater is
transported to Deer Island for treatment (NRWA, 2012). In addition, groundwater
leaks into poorly sealed sewer pipes in a process known as infiltration; comprising
of an estimated 52%—or 7 billion gallons—of MWRA`s total annual sewer flow
(NRWA, 2012). Low water levels can result in concentrated levels of pollution,
bacteria and nutrients as well as a decrease in the size and quality of habitats
(NRWA, 2012).
Throughout the history of the Neponset watershed, developers have installed
roads, dikes and several dams throughout the river which block or restrict tidal flow
to salt marshes (NRWA, 2012; Raposa, 2008). Tidal restrictions result in altered
hydrology and biogeochemistry and degraded water quality by the creation of
warm, stagnant water thereby reducing the river`s ability to support a more diverse
range of species (NRWA, 2012). These changes to marshlands restrict aquatic
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animals from access to other habitats, potential mates, escape from predators and
restrict fish migration (NRWA, 2012; Raposa, 2008).
Alterations to the Neponset Watershed landscape also occurred by
converting lands for agricultural, industrial or residential purposes through
dredging or filling in marshlands to increase acreage (NRWA, 2012). These lands
served as vital buffers against eutrophication by intercepting polluted terrestrial
runoff (Silliman and Bertness, 2004). These changes to the landscape directly
degrade and reduce wildlife habitats but also increase the risk of other disturbances
such as pollution loading or the success of an invasive species (NRWA, 2012).
Exotic, invasive species displace native species through competition of
resources thereby degrading the natural habitat and reducing local biodiversity
(NRWA, 2012). The Neponset River Watershed Association (NRWA) has eradicated
several exotic, invasive species as apart of restoration efforts but is particularly
troubled by the invasive Phragmites australis (NRWA, 2012). Phragmites australis
were introduced to the Neponset due to increased nutrient loading and upland
vegetation removal (Silliman and Bertness, 2004). The Phragmites out-compete
native S. alterniflora in acquiring nitrogen resulting in aggressive crowding and
stress of the native vegetation (NRWA, 2012; Silliman and Bertness, 2004).
Phragmites invasions change the nitrogen fluxes which increases herbivory and
lowers plant diversity, altering the animal composition dependent on the native
vegetation (Windham and Meyerson, 2003).
Restoration efforts should focus on reducing pollution to the watershed by
working with communities to repair sewage pipes, decrease nutrient and heavy
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toxins usage and filter contaminated water runoff before it reaches the streams
(NRWA, 2012). If a restoration site is still experiencing pollution or eutrophication
that exceeds the native`s plants tolerance levels, the marsh, let alone biodiversity,
will fail to recover (Zedler, 2000).
Watershed communities should also work to reduce water usage, remove
waterway obstructions such as dams and large debris and repair drinking water
pipes (NRWA, 2012). The removal of two of the most downstream dams on the
Neponset River—the Baker Dam and the Tileston and Hollingsworth Dam—would
restore water quality with cooler water temperatures, higher dissolved oxygen
levels, reduced pollution levels and grant access to habitat, food and mates (NRWA,
2012). Hydrologic restoration of the Potter Pond marsh in Rhode Island resulted in
reduced Phragmites height and cover and increased abundances and distributions of
S. alterniflora; quickly improving the ecological conditions after a year of
restoration, with more gradual improvements later (Raposa, 2008).
Exotic species also prevent the reestablishment of native species at
restoration sites (Palmer et al., 1997).
Reestablishing natural habitat borders,
minimizing disturbances as well as limiting the use of fertilizers and freshwater
runoff to marshes are the best ways to limit Phragmites australis expansion, thereby
enabling native marsh vegetation growth (Silliman and Bertness, 2004). Removal of
the established Phragmites can be accomplished by cutting or application of
herbicides (Silliman and Bertness, 2004).
The shape and size of healthy habitats as well as the ease of mobility between
patches is also important in maintaining biodiversity and therefore, marsh health
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(Palmer et al., 1997). The unnatural distribution of vegetation at some restoration
sites occurs when seedlings or plants of uniform size are introduced to large areas
and often attracts herbivores (Zedler, 2000). In contrast, ‘self-design’ restoration
occurs when natural vegetation develops in patches and expands from the wetland
edges (Zedler, 2000). Given that environmental heterogeneity is associated with
increased species diversity, it can be assumed that the rehabilitation of physical
diversity will lead to the restoration of biological communities (Palmer et al., 1997).
Ecological responses to salt marsh restorations are, to an extent, site-specific
making responses difficult to generalize (Raposa, 2008). In order to maximize the
outcomes of restoration efforts, ecological monitoring is needed to show how each
of these threats affect coastal food webs and how animals will respond to
restoration efforts in order to better guide future restoration projects (Zedler, 2000;
Raposa, 2008).
References:
Altieri, A., van Wesenbeeck, B. K., Bertness, M. D., and Silliman, B. R. 2009.
Facilitation cascade drives positive relationship between native biodiversity
and invasion success. Ecology 91: 1269-1275.
Cardinale, B. J., Duffy, J. E., Gonzales, A., Hooper, D. U., Perrings, C., Venail, P.,
Narwani, A., Mace, G. M., Tilsman, D., Wardle, D. A., Kinzig, A. P., Daily, G. C.,
Loreau, M., Grace, J. B., Larigauderie, A., Srivastava, D. S., Naeem, S. 2012.
Biodiversity loss and its impact on humanity. Nature 486: 59-66.
Haslett, Simon K. 2006. Topographic Variation of an estuarine salt marsh: Northwick
Warth (Seven Estuary, UK). Bath Spa University Occasional Papers in
Geography 3: 1-17.
Neponset River Watershed Association. Neponset River Watershed Association, 2012.
Web. 10 Nov. 2014. <http://www.neponset.org>
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Nixon, S.W. 1982. The Ecology of New England High Salt Marshes: a Community
Profile. U.S. Fish and Wildlife Service, Office of Biological Services 55: 70 pp.
Palmer, M. A., Ambrose, R. F., Poff, N. L. 1997. Ecological Theory and Community
Restoration Ecology. Restoration Ecology 5: 291-300.
Raposa, Kenneth B. 2008. Early Ecological Responses to Hydrologic Restoration of a
Tidal Pond and Salt Marsh Complex in Narragansett Bay, Rhode Island.
Journal of Coastal Research 10055: 180-192.
Sala, N. M., Bertness, M. D. and Silliman, B. R. 2008 The dynamics of bottom-up and
top-down control in a New England salt marsh. Oikos 117: 1050-1056.
Silliman, Brian R. and Bertness, Mark D. 2002. A trophic cascade regulates salt
marsh primary production. PNAS 99: 10500-10505.
Silliman, Brian R. and Bertness, Mark D. 2004. Shoreline Development Drives
Invasion of Phragmites australis and the Loss of Plant Diversity on New
England Salt Marshes. Conservation Biology 18: 1424-1434.
Windham, L. and Meyerson, L. A. 2003. Effects of Common Reed (Phragmites
australis) Expansions on Nitrogen Dynamics of Tidal Marshes of the
Northeastern U. S. Estuaries 26: 452-464.
Zedler, Joy B. 2000. Progress in wetland restoration ecology. Trends in Ecology and
Evolution 15: 402-407.
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