B. Climate:
The climate of the region is characterized by prominent seasonal temperature changes that produce distinct winters and summers; precipitation is evenly distributed throughout the year. The project area is also strongly influenced by the proximity of Long Island Sound, which modifies both summer and winter temperature extremes. The mean annual temperature of the area is about 51F ( 10.5C). Average winter temperature is about 32F (0C) with a mean monthly minimum of 23F (-5C) in the coldest month. Mean annual minimum temperature is approximately 0F (-18C). The average seasonal snowfall accumulation is generally around 76 centimeters (30 inches), with lesser amounts closest to the coast (river mouth). Frost-free season averages between 180-190 days. Average summer temperature is about 21C (70F); the warmest month has a monthly mean maximum temperature of about 28C (82F). Annual precipitation ranges from 109-117 centimeters (43-46 inches) (Brumbach 1965).
C. Physiography/Geomorphology:
Figure 3 is a computer-produced map of the physiography of the project area showing the regional landscape through which the river flows in the State of Connecticut. At the northern, inland extent of the project area, the principally south-flowing Connecticut River abruptly veers off to the southeast, exiting the broad, flat Hartford Basin, or Central Valley, which consists of relatively soft sedimentary strata. The river in the Central Valley is slow-flowing and meandering, and the substrate has favored the development of broad floodplains. Once it leaves the Central Valley, the river crosses the Eastern Border Fault and enters into the Eastern Crystalline Highlands which are characterized by hard metamorphic rock (Bell 1985). The project area section of the river is for the most part located in the Crystalline Highlands region, where the resistant metamorphic rocks constrict the river and have permitted only narrow marshes to form along the mainstem and secondary drainages of the Connecticut River. Where it enters into Long Island Sound, the river at its mouth flows across a low, flat coastal plain, distinguished by expansive brackish marshes. Most of the core sites are discontinuous from one another and reflect local geological conditions where sufficient sediment accumulation has enabled marshes to form.
D. Hydrology:
The main stem of the Connecticut River is 660 kilometers (410 miles) long and drains an area of approximately 2.9 million hectares (7.1 million acres), making it the largest riverine ecosystem in the northeastern United States. The lower Connecticut River, which is the subject of this Ramsar designation, encompassess approximately the lowermost 58 river kilometers (36 miles) of the mainstem of the river from its mouth to the vicinity of Portland/Cromwell, or 9 percent of the river's total length. The drainage area of this section of the mainstem of the river and tributaries is approximately 46,647 hectares (115,263 acres), less than 2 percent of the total drainage area of the Connecticut River.
The Connecticut River has a mean freshwater discharge of 560 cubic meters/second, a rate comparable to that of major rivers such as the Hudson and Delaware. In contrast to the valleys of these rivers, the lower valley of the Connecticut River is tightly constricted by hills of crystalline bedrock. As a drowned river valley, the river is strongly influenced by Long Island Sound. Consequently, this section of the river functions as a narrow conduit to tidal currents induced by the rise and fall of waters in Long Island Sound. The Connecticut River provides nearly 70 percent of the freshwater input into the Sound and thus exerts a profound influence on this major East Coast estuary.
The river is tidal as far north as Windsor Locks, nearly 96 river kilometers (60 river miles) from its mouth. Figure 4 illustrates the position of mean high and mean low water with respect to national geodetic vertical datum (NGVD) from the mouth of the river to Hartford, approximately 85 kilometers (53 miles) inland. High slack water arrives first at the mouth, occurs one hour later at Hadlyme and nearly three and a half hours later at Hartford. The tidal wave progresses northward at an average rate of 45 kilometers/hour (28 miles/hour). The mean tidal range decreases progressively northward from 61 centimeters (2.0 feet) at the mouth at Old Saybrook to 33.5 centimeters (1.1 feet) at Hartford. The actual elevation of these tidal datums increases with increasing distance northward (upstream) and reflects the effect of freshwater discharge upon water level elevations. Thus, throughout much of its length, the Connecticut River in this area has a mixed tidal and nontidal hydrology.
The Connecticut River supports relatively little tidal volume flux because of its small cross-sectional area. Its ratio of tidal inflow volume to freshwater flow volume during the flood portion of the tidal cycle is about 0.5 for mean conditions, compared to 10 and 140 for the Hudson and Delaware rivers, respectively. The Connecticut River Estuary therefore falls into the type 4, or salt wedge, class. As such, it is unique among major rivers of the U.S. East Coast and is comparable in general character to that stem of the Mississippi River within its delta.
During times of peak freshwater discharge in the spring, in response to snowmelt, the water levels in the river rise significantly (see Figure 5). These rises are greatest in the northern section and least at the mouth of the river. Even during peak flood stage, there is a discernable, albeit minor, tidal signature to the water levels as far north as the Hartford vicinity. At times there may be two discrete seasonal freshets. The first is characterized by a small rise in water level and increased freshwater discharge volume associated with runoff from snowmelt in the minor drainage basins in the State of Connecticut. This is generally followed by significantly higher water levels associated with heavier snowfall amounts and snowmelt in the northern section of the drainage basin in the states of Massachusetts, New Hampshire, and Vermont.
Although there is this very distinct seasonal pattern of extremes from the high water spring freshet to low flow conditions during late summer and early autumn, river waters levels are also quick to respond to major daily precipitation events, wind set-up, and other factors.
An important parameter affecting the distribution of plants, animals, and habitat types on the river is salinity. The source of salt water to the Connecticut River estuary is Long Island Sound, which on average has a relatively consistent salinity of 26 to 28 parts per thousand (ppt). In contrast, salinity in the Connecticut River exhibits wide daily fluctuations due to tides as well as seasonal fluctuations due to freshwater river discharges. For plants, the most significant salinity conditions are those which exist during the growing season. Figures 6 and 7 illustrate the distribution of the major salinity zones for surface and bottom waters at slack high and low tide conditions in May and August. There are two broad categories of water in the river based upon the presence or absence of seawater. These are: mixohaline, i.e., brackish water with a salinity of 0.5 to 30 parts per thousand (ppt), and fresh, i.e., less than 0.5 ppt. Brackish water can be further subdivided into the following categories: polyhaline (18-30 ppt), mesohaline (5-18 ppt), and oligohaline (0.5-5 ppt).
At the beginning of the growing season in early May, when river flows are at their peak, there is no detectable salt water in the surface waters of the river estuary, regardless of the stage of the tide. As the summer season progresses and the river flow decreases, the penetration of salt water corresponding increases; by August, the freshwater boundary is located near the southern tip of Lord Cove. Thus, the freshwater/salt water boundary migrates approximately 8 kilometers (5 miles) four times daily in response to the semi-diurnal tidal cycle.
In addition to the horizontal distribution of salinity, there is also a discrete vertical zonation of salt and freshwater in the river. Since the density of freshwater is less than that of salt water, freshwater lies above the denser sea water, often as a discrete lens or salt wedge.
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