Physical Processes   I   Biological Interactions   I   Human Impacts and Restoration Science

Physical Processes

Sedimentary Processes, Stratigraphic Characteristics, Holocene Development and Impact of Sea Level Rise

Tidal marsh systems often contain a rich history of the Holocene development of coastal environments, processes occurring in surrounding watersheds, and insights to past climates. In addition, tidal marshes are a vital component of coastal ecosystems providing numerous functions such as nurseries, nutrient sources, sediment sinks and flood buffers. Due to the recognition of their value to coastal systems, tidal marsh restoration has become a priority in many regions.

Because of their intrinsic value and excellent sedimentary records for deciphering the Holocene record, we have conducted a number of research projects focused on the sedimentological characteristics, stratigraphic relationships, origin and development, and impact of sea level fluctuations on tidal marsh systems. An important goal of this work has been to develop an understanding of their sedimentological and physical processes and apply this knowledge to estuarine restoration science.

Examples of recent research include the following.

Palynology and Geochronology of Tidal Marsh Systems in Great Bay Estuary, New Hampshire

Spatial and Temporal Variability in Marsh Elevation and Accretion in Coastal and Estuarine Tidal Marshes in New Hampshire and Southern Maine

Tidal Marsh Change Analyses in the Great Bay Estuary, New Hampshire

Ice Rafting within the Great Bay Estuary

Ice may have an important influence on algae and grasses in tidal marshes of north temperate areas like the Great Bay Estuary. The effects of ice (damage) depends upon the duration, frequency and extent of ice cover, as well as local physical and topographic factors. The damaging effects of ice may include freezing, crushing, abrasion, and rafting of living material. Ice cover of 0.5 m or more is usually present within the inner reaches of Great Bay from late December through early March. Fragments of the fucoid brown alga Ascophyllum nodosum that are rafted in ice and deposited into salt marshes are a major source of the ecad scorpioides. They are also a major source of organic detritus that is an important food for diverse detritivores.

Biological Interactions

Range Extension in Marsh Plants

The number of plants growing in salt and estuarine tidal marshes is limited due to harsh and stressful conditions. Northern range extensions of more "southerly" flowering plants and some seaweeds have been documented. For example, the first record of Hibiscus moscheutos from New Hampshire was documented during 2003 in Hampton. A second population was found by Joann Hoy at the upper edge of a salt marsh in Great Bay. The New Hampshire populations appear to be northern range extensions from Massachusetts and may be due to a longer growing season associated with global warming. The full epithet is: Hibiscus moscheutos subsp. palustrus (L.) R.T. Clausen (=H. Palustris); the common name is Rose mallow. The introduced Asiatic seaweeds Codium fragile ssp. tomentosoides and Neosiphonia harvey are warm temperate species that also may be responding (expanding) due to enhanced thermal conditions. See Introduced Seaweeds below for further details.

Saltmarsh Fucoid Ecads

Fucoid ecads are conspicuous within Gulf of Maine salt marshes and other estuarine habitats, occurring as detached balls (Ascophyllum nodosum ecad mackii), entangled masses (A. nodosum ecad scorpioides, Fucus vesiculosus ecad volubilis, F. spiralis ecad lutarius and "mytili-type" F. vesiculosus), and dwarf embedded (i.e. limicolous) forms. All of these ecads are derived from attached parental plants after injury and breakage (e.g. ice pruning) and are associated with the halophytic marsh plants Spartina alterniflora and S. patens. The origin, ecology, and affinities of these various ecads have been studied via demographic evaluations, transplant studies, common garden assessments, and molecular comparisons. The dwarf muscoides-like Fucus in Brave Boat Harbor, York-Kittery, Maine mainly consist of hybrids between F. vesiculosus and F. spiralis, while F. vesiculosus ecad volubilis may arise through backcrosses between F. vesiculosus and other fertile hybrids.

Introduced Seaweeds

Rapid assessment studies of introduced species within the Northeast Coast of USA have documented the introduction and spread of several seaweeds within estuarine and saltmarsh habitats, including the Asiatic taxa Bonnemaisonia hamifera (including Trailliella intriccata), Codium fragile ssp. tomentosoides, Neosiphonia harveyi, Porphyra katadae, P. yezoensis, and the European taxon Lomentaria clavellosa. A combination of morphological, ecological, and molecular evaluations have been conducted with these taxa, documenting "cryptic" diversity of several species. For example, the two Asiatic Porphyra taxa were previously confused with the native taxon P. leucosticta . The origin and spread of C. fragile ssp. tomentosoides are also being evaluated with field ecological and molecular studies.

Human Impacts and Restoration Science

Gulf of Maine Assessment of Saltmarsh Restoration

With a concerted effort to stop continued degradation of the region’s tidal marshes, NOAA has led several programs to restore marshes by returning tides to hydrologically restricted sites and removing dredge spoil placed on marshes. Another restoration approach, which has been conducted on several US Fish and Wildlife refuges, has been to fill or plug the many drainage ditches dug in marshes to reduce mosquitoes during the Public Works Administration. Although mosquitoes could still breed, open water for fish and birds was lost. Working with the USGS and Wells National Estuarine Research Reserve, we have obtained funding from NOAA to organize and synthesize data contributed to a regional assessment.

Monitoring Protocols were produced to simplify and standardize data collection and reporting. The synthesized data has been presented at a workshop (September 2004, Wells, Maine) and submitted to a peer-reviewed journal. Although over 100 projects have occurred in the Gulf of Maine, only partial data sets from 36 projects were available for the synthesis. One outcome of the 2004 workshop is a revised set of core protocols (Revision to the Protocols.pdf). There is an urgent need to promote uniform monitoring at more sites so a complete structural and functional assessment of the restoration can be developed for the region.

Monitoring and Performance Assessment of Tidal Marsh Restorations

Evaluating restoration success often assumes an all-or-nothing approach, determining project success or failure without consideration of intermediate stages of development or functional values. Building upon the important and valuable work of many researchers within the Gulf of Maine and southern New England, our group is reviewing a series of coastal restoration projects in association with NOAA to demonstrate and quantify the net benefit by providing interim measures of relative success for various stages of restoration. The work will utilize several core Global Programme of Action Coalition (GPAC) protocols to formulate a uniform comparison of restoration performance across the sites. Uniform evaluation of relative restoration success towards reference end points will allow for a more meaningful performance assessment during the restoration process. Our objective is to enable project managers and the regulatory community to identify the need for (and potentially the type of) corrective measures required to maintain restoration projects along their designed trajectory.

Algal Indicators of Human Impacts and Stress

A variety of floristic evaluations have been conducted within estuarine and saltmarsh habitats, with these documenting historical and recent changes due to anthropogenic impacts. Many seaweeds respond quickly to human impacts (e.g. sewage inputs) and environmental conditions (e.g. temperature and salinity) and they can indicate habitat eutrophication and other types of disturbance. The dominance of opportunistic green algae versus perennial red and brown algae is also indicative of stressful euryhaline habitats. The Asiatic warm temperate species Codium fragile ssp. tomentosoides and Neosiphonia harveyi have recently expanded their distribution within the Gulf of Maine, possibly because of enhanced thermal conditions (global warming).

A comparison of mean number (± SD) of taxa/site in the main channel in Brave Boat Harbor and its four tributaries is summarized, plus 17 other estuaries. The species richness within Brave Boat Harbor habitats is less than in the Piscataqua River and Little Bay, it is approximately the same as the York River and Great Bay, and it exceeds several mid- and inner-estuarine sites, the Hampton-Seabrook Estuary, and the polluted Merrimack River Estuary. As there are varying levels of eutrophication and development in the five estuarine systems (York River, Brave Boat Harbor, Great Bay Estuary, Hampton-Seabrook, and Merrimack River) low species diversity patterns represent a typical response to pollution, development, and extreme hydrographic variability where only a few tolerant ulotrichalean algae dominate.

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Bibliography

Mathieson, A.C., C.A. Penniman, P.K. Busse and E. Tveter-Gallagher. 1982. Effects of ice on Ascophyllum nodosum within the Great Bay Estuary System of New Hampshire-Maine. Journal of Phycology 18:331-336.

Mathieson, A.C. and C.J. Dawes. 2001. A muscoides-like Fucus from a Maine salt marsh: its origin, ecology and taxonomic implications. Rhodora 103:172-201.

Mathieson, A.C., C.J. Dawes, M.L. Anderson and E.J. Hehre. 2001. Seaweeds of the Brave Boat Harbor salt marsh and adjacent open coast of southern Maine. Rhodora 103:1-46.

Mathieson, A.C., C.J. Dawes, L.G. Harris and E.J. Hehre. 2003. Expansion of the Asiatic green alga Codium fragile ssp. tomentosoides in the Gulf of Maine. Rhodora 105:1-53.

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