This should involve a survey of the study area to determine the nature of the saltmarsh vegetation present, its condition and the general state of key parameters that may influence the success of management (i.e. distinct changes in saltmarsh width, erosion/accretion or the type/orientation of coastal defences). The Box below describes the main tasks that should be undertaken as part of such a survey. However, also see Appraisal of available options with respect to the influence the nature of your problem or decision can have on the amount of detail you may require.
Baseline survey tasks |
Measure (or estimate) and record vegetated width
Look for signs of erosion
Estimate whether the rate of erosion is slight, moderate or rapid
Look for signs of accretion
Estimate whether the accretion is slight, moderate or rapid
Where available, analyse historic maps and aerial photographs to determine rate and nature of change in saltmarsh extent and distribution |
The presence and extent of desirable conditions for successful saltmarsh development should also be established, as far as this is possible (see the table below). In many cases this will need to be estimated from observations made of the site during the survey, however, there may be more detailed information available from other studies (e.g. research studies, coastal defence strategies, Shoreline Management Plans, CHaMPs and data from other schemes conducted in the area).
The information gained from baseline data collection can then be used to define the status of your saltmarsh.
Desirable physical and chemical conditions for successful saltmarsh development
Characteristic |
Constraints |
Exposure to waves and currents |
Saltmarsh species will not establish or survive in exposed sites; protection against waves and strong currents will almost always be required at such sites (i.e. with a fetch greater than 2000m, sometimes less); a breakwater, for example, may be needed to “trip” waves moving inshore in order to prevent undercutting/slumping |
| Tidal prism |
It is difficult to establish and maintain vegetation in areas of high velocity and scour; particular problems may exist around points of tidal entry and exit; good tidal circulation is nonetheless essential to transport fine sediment (sand and mud) onto the saltmarsh surface |
Elevation relative to the tide |
Mean sea level to extreme high water level will generally provide suitable elevations for many saltmarsh species (precise needs vary according to the species); elevation which is too low or too high will inhibit species establishment, survival and community diversity/development |
Slope and drainage |
Steep slopes drain well but do not attenuate wave energy; poor drainage causing standing water can kill off existing species or prevent species from establishing; the best slopes are generally 3-5% downwards from landward to seaward; inadequate tidal flushing may lead to ponded water and the accumulation of toxins, or cause hypersaline salt pans |
Sedimentation regime |
Most saltmarsh species withstand sedimentation rates of 3 to 10mm per annum; in excess of 25mm/year may smother some (especially pioneer) plants; rapid sedimentation will cause the evolution from low or mid zone saltmarsh to high zone saltmarsh |
Sediment grain size and depth; compaction |
Plant establishment can be easier and more successful in well oxygenated sandy sediments with a firmer foundation (although note that planting is not a widely used technique); sandy soils may require higher energy to erode; although many low zone species can be found in much finer grained sediments. Shallow sediment depth can restrict vegetation growth; compacted soil will inhibit root growth (so it is recommended to use low ground pressure equipment when undertaking work) |
Nutrient levels |
Adequate nutrient levels (nitrogen, phosphorus, potash) can promote rapid vegetation establishment, although there are no long term benefits of fertilisation. Excessive nutrient levels can lead to eutrophication and algal mats smothering vegetation |
Salinity |
Some seeds and young seedlings may be sensitive to full strength salinity; conversely, undesirable species such as alga may establish if salinity is too low. A number of saltmarsh species are semi-halophytic, that is they require fresh water to survive, and may show signs of stress or die in prolonged dry weather (lack of fresh water input) or where empounded (sea or brackish) water evaporates, such as in pans or saline lagoons. |
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