Tidal gates on Sybil Creek Mosquito ditching Some human impacts on salt marshes in Connecticut
Phragmites - invasive sp. Development
Filling in salt marshes Other notable impacts: undersized culverts beneath roads/bridges pollution in Long Island Sound tidal mill ponds (historical impact)
Tidal Wetlands Act, 1969 - Sec. 22a-28“Preservation of tidal wetlands. Declaration of policy. It is declared that much of the wetlands of this state has been lost or despoiled by unregulated dredging, dumping, filling and like activities and the remaining wetlands of this state are all in jeopardy of being lost or despoiled by these and other activities, that such loss of despoliation will adversely affect, if not entirely eliminate, the value of such wetlands as sources of nutrients to finfish, crustacea and shellfish of significant economic value; that such loss or despoliation will destroy such wetlands as habitats for plants and animals of significant economic value and will eliminate or substantially reduce marine commerce, recreation and aesthetic enjoyment; and that such loss or despoliation will, in most cases, disturb the natural ability of tidal wetlands to reduce flood damage and adversely affect the public health and welfare; that such loss or despoliation will substantially reduce the capacity of such wetlands to absorb silt and will thus result in the increased silting of channels and harbor areas to the detriment of free navigation. Therefore, it is declared to be the public policy of this state to preserve the wetlands and to prevent the despoliation and destruction thereof”.
Salt Marsh restoration in Connecticut - 1980, DEP Office of Long Island Sound Programs involved in restoration - uses federal transportation funding - impacts of road/bridge construction - ~1700 acres restored - increase coastal water productivity - increase fish production - enhanced use by herons, shorebirds, waterfowl - reduced mosquito-breeding areas - lessened fire hazards
Some agencies involved in restoration: - Connecticut Department of Environmental Protection - Iroquois Gas Transmission System - Ducks Unlimited - The Stewart B. McKinney National Wildlife Refuge - U.S. Fish and Wildlife Service - local government - Audubon Society - The Nature Conservancy
Restoration might consist of: - Phragmites australis removal (reed tolerant of low salinities (< 18 ppt) other invasives (Purple loosestrife, Typha) - plugging old grid ditches (former mosquito control), clearing natural channels - removing old impoundments - Integrated Marsh Management (creation of new ponds, channels, salt pannes) - sediment removal sediment sources - stormwater discharge - dredged navigational channels - recreational marinas - culvert and flood gate modifications
RESTORATION RULES OF THUMB • re-establishment of regular tidal flushing with • saltwater (over 18 parts per thousand of salt) • replacement of Phragmites by salt marsh plants • - conversion normally occurs over a 5-10 yr • period. • re-establishment of salt marsh plants proceeds • spontaneously if a nearby salt marsh is present to • supply a seed source. • - In most cases expensive planting or • transplanting programs are not necessary. • restoration of tidal flows to their pre-disturbance • volumes is not always desirable, especially in the • case of subsided wetlands. • - restoration reduces or eliminates mosquito breeding • in subsided marshes. • - restoration re-establishes scenic vistas.
Restoration at Long Beach, Stratford, Ct. Steward B. McKinney National Wildlife Refuge
Bioassessments - Biological integrity – “ability to support and maintain balanced, integrated, adaptive community of organisms having a species composition, diversity, functional organization comparable to those of natural habitats within the region” - use index of biological integrity - metrics – combination of: - native plant cover - algae - amphibians - birds - macroinvertebrates - fish Functional assessments – estimate functions – e.g. water storage, nutrient cycling
Approaches and methods of tidal restoration at 57 Connecticut DEP sponsored or permitted projects between 1975 and 1999.
Table 1. Salt marsh tidal restoration sites included in this study Study sites Warren et al. 2002. Salt marsh restoration in Connecticut: 20 years of science and management. Restoration Ecology 10:497-513
Recovery of salt marsh vegetation after tidal restoration measured as the loss of Phragmites cover up to 1995, the latest complete false color infrared air photo set available. Dominance by Phragmites decreases following tidal restoration.
Figure 2. (A) Mean percent cover and frequency of occurrence of Spartina alterniflora (Sa) and Phragmites australis (Pa) along three Mumford Cove transects sampled in 1992 and 1997, 2 and 7 years after restoration. Cover (Tukey's test p> 0.05) and frequency (chi-square p> 0.05) increased for Sa but not for Pa. (B) Mean elevations (datum = 1992 local mean lower low water) of points along three Mumford Cove transects sampled in 1992 and 1997 that supported (cover 1%) Sa and Pa and points that were essentially free of these species (cover < 1%). Spartina increases in percent cover and frequency by 7 years.
(A) Total mean percent cover and frequency of occurrence for all salt marsh angiosperms along 1996 restoration transects versus transect mean salinity. Both measures increase with salinity and regressions are significant. (B) Mean percent cover and frequency of occurrence for Phragmites australis along 1996 restoration transects versus transect mean salinity. Both measures decrease with salinity and regressions are significant. Frequency drops sharply above 26%; curve fitted by hand. (C) Mean end of season height and stem density of Phragmites australis at transect soil water wells (n = 27). Height drops with salinity with maximum salinity ca. 26%; curve fitted by hand. Stem density does not correlate with salinity. Changes in plants track salinity changes
Figure 4. Relative abundance of Melampus bidentatus in recovering versus reference regions (mean density on restoration area/associated reference marsh) of four marshes at Barn Island in relation to the number of years of recovery. Although these marshes differ from one another in ways other than years of recovery, data indicate a long trajectory for full recovery of Melampus populations Abundance of a salt marsh snail
Figure 5. Relative abundance (recovering/reference) of birds considered salt marsh specialists (triangles) and salt marsh generalists (circles) at two recovering Barn Island (BI) marshes (solid) and at Mumford Cove (MC, open) plotted against years of restoration at the time counts were conducted. Although these marshes differ from one another in ways other than years of restoration, data indicate that it may take a decade for restoration sites to support equivalent populations of marsh specialists. Also, marsh generalists, whose use declines over time, rapidly occupy restoration sites. Marsh generalists decrease, specialists increase through time
Mean recovery rates, seasonal soil water well and peat salinities, and depths to water table for the three rapidly recovering (Hammock River, Long Cove, and Great Meadows) and two slowly recovering (Barn Island and Great Creek) systems. Slower recovering sites have lower salinities and deeper depths to water table
Mean density (no./m2± SE) of six macroinvertebrates in recovering and reference regions of three marshes at Barn Island, Connecticut that have been in the process of restoration for different periods of time.
Fishes and crustaceans caught within mosquito control ditches at Barn Island in the recovering marsh (IP1) and the adjacent reference marsh (HQ) below impoundment dike 21 years after restoration and in recreated creeks of the restored Mumford Cove marsh 8 years after return of tidal flooding.
Abundance of birds (average number of individuals observed per visit) at the reference marsh, HQ, and the restoration marshes, IP1, IP3 sites at Barn Island and the MC Marsh during surveys conducted in the summers of 1994, 1995 and 1999.
Results • Restoration of tidal flow initiated decline in • Phragmites and Typha re-establishment of tidal salt • marsh species • - some sites had rapid recover, others slow • - important influences • - salinity & hydroperiod (major factor) • - slow sites had reduced • hydroperiods due to • flooding frequency • constraints • -> altered chemistry
Some salt marsh macroinvertebrates were • present in < 5 years; others might require • several decades for establishment • Characteristic fish species might return early in • restoration (8-13 years); many might require a • longer period of time to achieve population sizes • characteristic of reference salt marshes. • - diets appeared similar between restored and • reference sites, though quantity • of food (gut contents) differed.
Marsh generalists birds were present ~ 4-5 years • following restoration (increased abundance + • diversity). • - ~ 10 years, Marsh specialists were present, • but less abundant than generalists. • - Specialists increase through time.. 5. Species have different and often independent recovery rates.
Take-home message: • With appropriate substrate, hydrology, propagules • in vicinity functioning salt marshes can develop, • in time… • - reestablishing tidal connections are key. • - final equilibrium conditions often • unrealistic goal. • best to start trajectory, • recognize it might take • decades to attain marsh • with conditions similar • to reference sites