changes in ecological character

8. CHANGES IN ECOLOGICAL CHARACTER:

Invasion by Phragmites australis: Common reed is displacing native tidal wetland vegetation in the lower Connecticut River marshes at an alarming rate. Recent estimates for the Great Island and Lord Cove area have determined that the spread of this species is occurring at a linear rate of 1 to 2 percent per year. It appears that this spread commenced in the late 1960's.

Although this grass is known to be native in North America, it has been speculated that the highly invasive and aggressive Phragmites in the project area and elsewhere along the coast may represent an introduced variety or spontaneous mutation from some other part of the globe. For the most part, Phragmites is not invasive into tidal wetlands where the soil salinity is greater than 18 ppt. Nearly all of the tidal wetlands in the Connecticut River, however, have soil salinities less than 18 ppt, which indicates that there may be no natural chemical barrier to prevent Phragmites' spread throughout this area.

It is projected that, unless action is taken fairly quickly to check and reverse the spread of this grass, the diversity of tidal wetland vegetation types will soon give way to the formation of a monoculture of Phragmites over nearly the entire extent of tidal wetlands in the project area. Efforts by the State of Connecticut, U.S. Fish and Wildlife Service and The Nature Conservancy are currently underway to not only study this problem in more detail, but also to restore marshes that have been invaded by Phragmites and to check its spread. Related to the spread of this grass is a concomitant decrease in plant community and species diversity. Dense stands of Phragmites pose a physical barrier to access by most wildlife species, which will likely result in an increasing diminishment in wildlife use and productivity over time. Decreased use and abundance of federal and state trust species will also likely occur as a consequence.

Other Invasive Plants: In addition to common reed discussed above, two other plants are commonly invasive in tidal wetlands and continuing to spread: indigo bush (Amorpha fruticosa) and purple loosestrife (Lythrum salicaria). There are several tidal wetland areas where these species are locally invasive and where future control practices may be warranted to preserve the natural diversity of these systems.

Mute Swans: The mute swan (Cygnus olor) is not native to North America, but has become thoroughly naturalized in this and many other areas in the U.S. The number of mute swans in the Northeast continues to increase, with the greatest increase occurring in coastal tidal areas. Since 1972, wintering swans in the State of Connecticut have increased from 505 to at least 1,300. The number of breeding pairs has increased in direct proportion to winter population numbers. Mute swans are largely non-migratory and large concentrations of individuals occur in both winter and summer in most of the major rivers near the coast, including the lower Connecticut River. In the summer of 1993, over 800 birds were observed in the lower Connecticut River alone. Swans are aggressive and compete with native waterfowl for food and space, especially during the breeding season. They have been observed to consume tidal wetland vegetation and submerged aquatic plants in large quantities, including rare plants such as golden club. The swans' long necks allow them to browse beds of submerged aquatic plants to a considerable depth, beyond the reach of native dabbling ducks.

B. Mosquito Ditching: Throughout much of the northeastern U.S. during the first half of the twentieth century, nearly all salt and brackish tidal wetlands, including the project area marshes, were ditched for mosquito control purposes. While ditching did not destroy tidal wetlands, it did drain the marsh of standing water and in so doing reduced or eliminated pool, panne, and stunted smooth cordgrass (Spartina alterniflora) habitats. Stunted Spartina habitat is now known to be a critical habitat for seaside sparrows (Ammodramus maritimus). Presently, seaside sparrows are listed as a species of special concern in the state and a federal species of management concern in the Northeast. The sparrows' low abundance probably reflects the reduced acreage of stunted smooth cordgrass associated with past ditching practices. There are virtually no natural pools and ponds occurring on ditched marshes in Connecticut. Studies have shown that wildlife diversity is greatest on those natural marshes containing pools and ponds, even through these critical habitat types originally covered only a small percentage of the total wetland area during prior to ditching.

C. Stormwater Discharges: For many years, stormwater discharges were considered to have little or no impact upon wetlands and waters. It is now well documented that stormwater discharges, in fact, can cause water quality degradation and loss of aquatic habitat through the deposition of sediment. Equally important in an estuary such as the Connecticut River are the dilution effects caused by stormwater discharges. While dilution effects upon estuarine organisms are not well documented, it is known that dilution of the salt content in the soils of brackish and salt marshes can facilitate the spread of Phragmites australis. In addition, the deposition of waterborne sediment can increase site elevations, thereby increasing the distance between the soil surface and water table, creating habitat disturbance and conditions ideally suited for the spread of Phragmites. The specific areas of the Connecticut River and its wetlands which have been lost, degraded, or altered as a result of stormwater discharges have not been quantified.

D. Dredging and the Disposal of Dredged Sediments: There are two general categories of dredging in the project area. The first is maintenance dredging of the federal navigation channel between the mouth of the river and Hartford. There are approximately 20 shoal areas within the project area that have been subject to dredging for commercial navigation purposes. Oil barges are currently the primary commercial vessels using this channel. The frequency of maintenance dredging is highly variable and is controlled, in large part, by the volume and velocity of waters discharged during the spring freshets.

The authorized depths of the navigation channel are 4.5 meters (15 feet). With the exception of the five southernmost channel segments, all shoal areas are sandy and dredging in these areas does not significantly alter the depth or sediment type. In the southernmost five segments, however, the sediments are fine textured silts and clays, coarser in texture than the adjacent river margin sediments.

Historically, dredged sediments were disposed of in a number of ways. At one time, sandy sediments were deposited on certain tidal wetland areas such as Nott Island and Calves Islands. While this practice of disposal is no longer permitted, it appears that some of these created upland sandy habitats which have become critical habitats for federal and state trust species such as bald eagles and northern diamondback terrapins.

Upland and wetland disposal was subsequently replaced by in-river disposal at certain designated mid-depth sites. While this practice continues today, in the last five years field studies have revealed that several of the in-river disposal sites are concentration areas for the federally-listed endangered shortnose sturgeon. As a result of these studies, no disposal has been allowed at the sturgeon concentration areas. The fine-textured sediments derived from the five southernmost shoal areas are now deposited at the Cornfield Shoals disposal site located southwest of the mouth of the river.

At this time, it appears that the minimal dredging done for the maintenance of the federal channel has not significantly altered habitat conditions in the river and is probably not causing any significant water quality problems. The dredged sediments are relatively free of contaminants and are not known to contain contaminants at levels to cause toxic effects in estuarine organisms.

The second category of dredging in the project area estuary is that done for recreational purposes, specifically for marinas and anchorage areas, e.g., at North Cove in Old Saybrook. Although no detailed investigations have been conducted at these sites, it is very likely that dredging has changed the benthic sediment type from sand to fine silts, clays, or muds. It is not known whether the conversion of the otherwise shallow North Cove to a deepwater anchorage is causing water quality degradation as a result of reduced tidal flushing and increased biological oxygen demand from the organic material that accumulates in the bottom waters. The marina basin for Ragged Rock Marina in Old Saybrook was excavated from tidal wetlands prior to the passage of Connecticut's Tidal Wetland Act in 1969. Although there is some freshwater drainage from the upland that flows through the outer channel, this marina is largely a cul-de-sac, and water quality degradation is likely due to reduced tidal flushing and a decrease in dissolved oxygen in bottom waters. Aside from these examples, many of the marina facilities in the project area are located on the mainstem of the river where flushing is maximal and water quality degradation is minimal and short-lived or non-existent. The sediments dredged from recreational marinas are primarily fine-textured in nature and are deposited in Long Island Sound at designated disposal sites.

E. Water Quality: Over the last few decades there have been tremendous improvements in the water quality of the Connecticut River. Many of these improvements are due to the establishment of secondary sewage treatment plants (STPs) for the major metropolitan areas, particularly Hartford in the late 1960's and Springfield in the late 1970's. Coupled with this were improved treatment for and sewage treatment tie-ins by industrial facilities. On a more localized basis, the establishment of STPs in Chester in the early 1980's and Deep River in the late 1980's and combined sewer overflow (CSO) corrections in Middletown and Portland, have improved the water quality in those estuarine segments of the river. Long-term water quality monitoring has shown reductions in turbidity, total organic carbon, total phosphorus, dissolved iron, dissolved zinc, dissolved nickel, and fecal coliforms. Oxygen levels have improved and nitrogen concentrations have increased slightly.

Return to table of contents