LEARNING & EXPLORING
ORV Detail - Watershed Ecosystem
Additional Watershed Ecosystem Documents
- Eightmile Biodiversity Study - PDF from the Management Plan Appendices. (6.2 MB - high bandwidth only)
The following text is an excerpt from the Watershed Management Plan Chapter VI.
Display
Poster -
1. The Eightmile River Watershed – A Whole Greater Than the Sum of Its Parts
The Eightmile River Watershed ecosystem reflects the sum of the many interacting ecological features found throughout the watershed. The fact that each of these features are generally in excellent condition means that their sum at the ecosystem level is synergistic – “greater than the sum of the parts” - and that an outstanding overall ecosystem is the result. This quality can be summarized by looking at the condition of the Eightmile’s structure, function and landscape context.
Regarding structure, the Eightmile contains all of the critical components of a high quality watershed ecosystem and these components are in excellent condition. These include rare, diverse and abundant species and natural communities, extensive habitat which is intact and connected, limited presence of invasive species, high water quality, stream connectivity throughout most of the watershed, natural channel morphology, and extensive forest and vegetative cover throughout the watershed including riparian areas. Regarding function, the quality of key ecological processes is also excellent. The hydrology of the watershed is as natural and unimpaired as any in Connecticut. Sediment and scour characteristics are natural. Nutrient and energy cycles reflect an undisturbed system. The size of intact habitat and low level of system manipulation allows natural disturbance regimes such as flooding, hurricanes, and ice storms to occur within their natural range of variability where the system can respond and recover naturally.
The landscape context for the Eightmile is very good. Because the ecosystem is the watershed itself, it has by definition sufficient size to incorporate the full range of the system. Furthermore, immediately outside of the Eightmile Watershed, the landscape remains largely intact providing a good buffer for the Eightmile and greater overall ecological integrity. The Connecticut River meets and interacts with the mouth of the Eightmile River by providing generally high quality water during daily tidal cycles.
In short, each of the previous natural resource ORV’s (water quality, hydrology, geology, and unique species and natural communities) all contribute to making the watershed ecosystem an outstanding resource value Below is a more detailed summary of some of the most significant features which make the Eightmile River Watershed ecosystem an Outstanding Resource Value.
Naturally functioning hydrologic system
One over-arching component of a functioning watershed ecosystem is a naturally functioning hydrologic cycle. Un-natural perturbations of a watershed’s hydrology include dams, water diversions, stream channel encroachment and channelization, point source and non-point source discharges, and many other human actions. It was determined that the Eightmile River watershed has an essentially natural intact flow, a few minor impediments, a single known consumptive water diversion, the impact of which is currently not known to be significant. In the Eightmile watershed, there are a low percentage of impervious surfaces (3%), a low percentage of developed area, and a high percentage of forested land. These values for these parameters are in the ranges that are correlated empirically with high ground and surface water quality.
High Water Quality
Available chemical and biotic data indicate that surface water quality is high in Eightmile Watershed streams. Biotic data collected by the CT-DEP 1998-1999 indicate “exemplary ecological conditions” for the Eightmile River [mainstem] and very good conditions for the East Branch Eightmile River (Beauchene 2003). In the context of Connecticut, and especially in the context of coastal Connecticut, a high percentage of the watershed is forested. This is doubtless the primary reason for the high surface water quality and high ecological integrity of these rivers.
Presence of large unfragmented forest blocks
The high percentage of forested habitat in the Eightmile River is comparable in Connecticut only to watersheds in the northwest corner of Connecticut and the southeast border of Connecticut with Rhode Island, both areas that are recognized as having the highest known biodiversity in New England. Similarly, in a Connecticut context, a low percentage of Eightmile watershed is developed, and it has a low density of roads (2.62 mi/mi2), and percentage of watershed occupied by large roadless blocks (72% occupied by roadless blocks greater than 1000 ac). All three parameters are strong indicators of the high level of habitat connectivity and intactness. These values are exceeded only by watersheds in the two areas of highest diversity in New England.
A
large portion of the Eightmile watershed’s forested portion occurs
as large, unfragmented blocks (e.g., 33% in blocks greater than 1000
ac, 17% in blocks greater than 500 ac). The Eightmile watershed also
comprises the greatest part of a major New England concentration of
the Cerulean Warbler, a forest interior species that is considered to
be the most area-sensitive bird in North America, and which is experiencing
a rapid range wide decline. The high densities of the Cerulean Warbler
centered in the Eightmile Watershed are attributed to the combination
of the Eightmile watershed’s near-coastal (therefore warmer climate)
position, its high proportion of large forest blocks, and the type and
maturity of its forests. The Cerulean Warbler, besides being identified
by multiple conservation organizations as a continental conservation
priority, is both an indicator species and an umbrella species in the
Eightmile watershed ecosystem. Its high densities indicate that the
system has adequate resources, in this case forest blocks of adequate
quantity and quality, to support a species with high sensitivity to
both parameters. The Cerulean Warbler is an umbrella species in this
system, because if habitat quality is such that there are high densities
of Cerulean Warblers, we can expect that a large number of other area-sensitive
forest species should thrive as well.
Nutrient cycling
Excellent surface water quality is a strong indicator of intact, well-functioning nutrient cycling processes in an ecosystem, and steams in the Eightmile watershed have been shown to meet this criterion.
Level of impairment due to invasive species
One parameter often used to assess ecosystem integrity, function, and
stress is the relative abundance of non-native and/or invasive species.
Extensive displacement of native species by invasive species, and loss
especially of the rarer, more sensitive native species are considered
indicators of an impaired, stressed ecosystem. Regarding the relative
importance of invasive species in the Eightmile watershed, inadequate
scientific data does not permit a rigorous comparison of this watershed
to others, but the opinion of many naturalists and scientists familiar
with the area is that the Eightmile watershed has relatively low levels
of invasive species. Field observations (2003-2005) support this view,
especially considering the vast acreage of dry to mesic, relatively
acidic forest in the watershed, which is invasive-free or nearly so,
and naturally inhospitable to all or most invasive plants. If one uses
the presence/abundance of extant rare species as an indicator of ecosystem
impairment due to invasives, the Eightmile watershed ecosystem’s
integrity appears rather high. The density of extant rare species in
the Eightmile watershed (.08 sp/mi2) is substantially higher than all
other regional watersheds in Connecticut except for those in the northwest
corner and along the Rhode Island border that have the highest numbers
of rare species in New England. Thus, both subjective professional impressions
and data on extant rare species indicate that the Eightmile watershed
ecosystem is currently relatively unimpaired by invasives.
Disturbance regimes
Among the many important intact natural disturbance regimes in the Eightmile watershed is the seasonal high flow-low flow cycle, overlaid by the lower frequency very high flows associated with catastrophic storms, of the larger streams in the system. The Eightmile streams are free of flood control structures, and the larger streams, especially, have relatively little bank stabilization. Thus, there exist along the streams in abundance various riparian communities that are maintained by and dependent upon periodic flooding and natural scouring. Also, this allows natural changes in channel configuration that produce riparian habitat diversity.
See Map 7: Intact Ecosystem
2. How the Watershed Ecosystem is Threatened
The watershed ecosystem is an intact functioning system because its component parts including the ORVs of water quality, watershed hydrology and unique species and natural communities are of such high quality. Therefore as would be expected, all of the threats that pertain to the above mentioned ORVs would also affect the quality of the watershed ecosystem as a whole. As a result, the assessment of threats to the watershed ecosystem concluded that all of the 24 distinct threats considered in the comprehensive threat analysis exercise would have an impact on the watershed ecosystem.
The
highest threats again were found to derive from the impacts of development
activities including: impervious surface increases; suburban lawns;
habitat fragmentation; poor stormwater management; loss of riparian
function; altering or filling of wetlands or watercourses; and habitat
fragmentation.
Invasive species was another high ranking threat. A number of invasive plant species are established in the watershed, and a number of these, such as burning bush (Euonymus alatus) and autumn olive (Elaeagnus umbellata), are considered capable of causing significant degradation of existing intact natural communities within the next 10 years. They may be expected to increase stress on at least certain elements of the Eightmile ecosystem. Among these in particular are the less common and rare habitats that occupy a relatively small portion of the watershed, but harbor a large portion of the biodiversity.
One theme that continually was present in performing the threat analysis was the need for further information on the location, quality and vulnerability of resources. Such regularly updated information shared with local land use commissions in performing application reviews and land use planning activities is essential for the long-term well-being of the many parts of the watershed ecosystem.
3. Existing Protections and Gaps
As with the threats to the watershed ecosystem the existing protections and gaps associated with protecting the watershed ecosystem is a combination of all that has been identified in previous ORVs.
Some of the key protections currently being employed that are most beneficial to protecting the watershed ecosystem include:
- Open space conservation efforts by local land trusts, towns, the state and The Nature Conservancy.
- Implementation of net buildable area requirements in all three towns for new subdivisions reducing the density of housing and targeting areas most appropriate for new development to occur.
- Inland wetland and watercourse regulatory protections as well upland review areas ensure upland activities are not impacting wetland and watercourse functions and values.
- A 400 foot upland review area around vernal pools in East Haddam.
- Protection of the riparian area for upper and lower Hamburg Cove
associated with the Gateway Zone in Lyme.
• Implementation of the State Stormwater Quality Manual in East Haddam.
• Implementation of Conservation Subdivision design in East Haddam. - Gaps in overall watershed ecosystem protection include:
- Lack of riparian corridor protection
- Limited ability to control the growth or impacts of impervious cover
- No comprehensive invasive species inventory or management plan established
- Lack of ongoing biological and ecological inventorying and monitoring
- Lack of management strategy for open and semi-open habitats in the watershed.
- Limited resources to purchase open space or conservation easements
- Inconsistent management of stormwater quality among communities
4. The Watershed Ecosystem Protection Goal
To understand, promote and protect a watershed ecosystem that integrates exemplary water quality and hydrologic conditions with high quality, intact and unfragmented wetland, riparian and upland habitats, in order to support diverse and robust populations of native plant, animal and fish species.
5. Watershed Ecosystem Indicators
The indicators for the Watershed Ecosystem are a roll up of all the Indicators for the Hydrology, Water Quality and Unique Species and Natural Communities ORVs identified for the Eightmile River Watershed and include:
a. Impervious Cover
b. Dams and Flow Manipulation
c. Surface and Ground Water Diversions
d. Riparian Corridor Condition
e. Forest and Vegetative Cover
f. Aquifer Storage and Recharge
g. Channel Morphology
h. Sediment and Scour Characteristics
i. Energy Regime/Organic Matter Inputs
j. Biotic Interactions: Structure, Composition, Recruitment
k. Species and Natural Community Rarity, Diversity and Abundance
l. Presence of Large, Contiguous Habitat Blocks
m. Aquatic and Upland Habitat Connectivity
n. Nuisance Species
o. Point Source Pollution Discharges
p. Non-point Source Pollution Discharges
q. Chemical, Physical and Biological Characteristics (of Water Quality)