Patterns and Drivers of Zonation in Coastal Salt Marshes

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Introduction

Southern California’s salt marshes play an important role along the coastal estuaries by maintaining the delicate balance of nature. The salt marshes were created from glacial processes, melting of continental glaciers, during the ice ages. Soil, sand, and sediments washed ashore by waves, blown by the wind, and brought down by rivers gradually formed dunes and ridges on the leeward side of the shoreline forming salt marshes. Striking Zonation patterns exist in salt marsh plant communities across an elevational gradient (Nancy, Ewanchuk & Bertness, 2471). Experimental studies show that there is an emerging paradigm that mediates the patterns. 

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How physical factors such as inundation and salinity vary along the elevation gradient 

Salt marsh salinity is directly influenced with the elevation gradient because of tidal flow. At higher elation (high mash), there is less tidal flow thereby resulting in lower salinity levels thus resulting to more vegetation (Pennings & Ragan, 688). Annual tidal flow at the lower gradient (lower elevation) causes constant salinity of the soil due to everyday flow of water causing reduction of vegetation. Whereas in the upper marsh, there is variation in the soil salinity due to fluctuating climates, plant zonation increases with the increase in gradient.  

Inundation is more common on the lower side of the elevation gradient (Pennings, Grant & Bertness, 160). On the higher side, there is less flooding thereby nutrients that normally carried in the floods are less. Plants zonation on the higher elevation tends to less as there is minimal nutrient supply. Al lower elevation gradient, the level of plants zonation is more. When floods take place, they carry along with them which eventually settle at the lowest gradient thus supporting more plant growth. This increases plants population. 

The species commonly found in each zone of the marsh

High marsh zone

This area is commonly flooded with tides and is found above the mean high water mark and the most common salt marsh community (Pennings & Ragan, 688). Some of the species found here include Distichlis, Salicornia, Juncus, and stands of Spartina mixed with some mangrove species. 

Border marsh zone

It forms at the border where fresh water meets the salt marsh ecosystem. Vegetation in this zone consists both estuarine and marine plants that can tolerate low salinities. The plant’s species in this zone are Jamaica swamp grass, cattail, golden leather fern, and needle grass rush. 

Low marsh zone

Also known as salt pans. This is an area of low latitude and soil salinity is very high, reaching up to 100 ppt and more. Vegetation is bare and devoid (Pennings & Ragan, 688). Some salt-tolerant species found around this zone include Juncus spp, glassworts, and saltworts. 

How physical and biotic factors interact to control zonation patterns

Physical conditions like gradient affect zoning of plants. At the lower marsh, there is a limited range of plant species due to their tolerance to physical conditions whereas at the higher marsh, superiors who are more competitive exclude plants species thereby having a direct effect on the zonation patterns (Pennings, Grant & Bertness, 160). 

Biotic factors like competition come in two forms. Some species are good competitors thus compete and dominate the zones whereas others are stress tolerant thus compete actively to dominate the zone even during low supply nutrients or even when physical factors bite (Pennings & Ragan, 689). The tolerant species can actively compete even during high tidal strengths thereby securing their zonal distribution all year round. 

Field Trip research

Sampling Method

We did 16-30 meter transects. Each transect was 30 meters from the next transect. We had 4 rows of transect each with 4 lines, and the transect area was 240 meters by 240 meters because the four lines will be 80 meters apart. We placed one quadrat at the 5-meter point and the 25-meter point for each line.

First, we used the area that we thought would be a “typical” site. Then, within this large area, we conducted a systematic sampling method evenly distributed over a 240 square meter area.

The elevation cut I made was 0.11, which is (0, 1.11, 1.5). All species we met include Sarcocornia pacifica(Sp), Jaumea carnosa(Jc), Monanthochloe littoralis(Ml), Salicornia subterminalis(Ss), Frankenia salina(Fs), Cuscuta salina(Cs), Distichlis spicata(Ds), Limonium californicum(Lc), and bare soils. I chose the most common three species, which are Sarcocornia pacifica(Sp), Jaumea carnosa(Jc), and Monanthochloe littoralis(Ml).

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Discussion

Results analysis

Most studies have often established the fact that ecological interations vary due t0o differences in physical factors affecting a given geographical area. Physical stress on ecological interactions has proven to be the most studied in field studies. The results obtained from this study indicate the effects of salt marsh gradient on the ecological life around coastal regions. The three species show different ecological niches in which they thrive. Jaume carnosa shows dominance in elevation cut 0, 0.11 compared to the other cut. This means the species is more likely to be found close to the channel. 

As the distance increases away from the channel the population decreases significantly. The plant has succulent stems which makes it a halophytic adaptation to the salty marshes in places prone to flooding. This corresponds to the lower gradient areas of the coastline. Sacornica pacifica on the other hand adapts comfortably in all gradients. The slight variation in the mean values obtained for each elevation cut as well as the P value is 0.836 being greater than 0.05 indicates little variation which could be as a result of error in area of study. 

The plant is generally not affected by competition or flooding thus can survive together with other species such as the Jaume Carnosa in the low gradient and Monanthochloe littoralis which dominates in the high gradient areas as shown by the high mean in the 0.11, 1.11. This is because Monanthochloe littoralis is affected by salinity and prefers high elevation with a high gradient areas where there is little saline water deposited (Nancy, Ewanchuk & Bertness, 2471). The lower limit of Monanthochloe is therefore defined by salinity, while the upper limit of Jaume Carnosa is determined mainly by availability of water due to its physiological succulent stems and salinity (Pennings, Grant & Bertness, 160).

Method limitations

The method used in this research is predominantly based on sampling techniques which provides room for a lot of errors when analyzing the data. Considering the nature of study, plant zonation patterns along coastline are affected by very many factors which are widely distributed. As a result, sampling technique is limited to the sample area. In this method only a 240 by 240 area was studied. However, this eliminates other factors which are localized to specific regions around the coastline. Using multiple sample areas or increasing the sample size solves the problem.

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Moreover, plants take a lot of time to grow and produce populations worth research. In some areas therefore during sampling, the plants might not have had time to establish themselves thus leaving room for assumption. This can be corrected by using evenly distributed sample sizes where individual plants under comparison present the same amount of growth. Another challenge this method faces is the lack of prior research in the area. For research data and comparison to be effective, comparison has to be made from sources showing research data carried out by different researchers. The unique nature of the research makes it difficult to compare and identify variations in the data, thus hypotheses drawn during planning are less informed. The method used to collect data was also a limitation. Considering that some species such as the Jaume Carnosa grow from a rhizome system, it is difficult to identify specific individuals from the plants which affects the numbers used in data analysis. Using a collective number for instance taking the dry weight of a group would be more efficient in establishing the numbers of the plants in a given sample size.

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  1. Emery, Nancy C., Patrick J. Ewanchuk, and Mark D. Bertness. Competition and saltmarsh plant zonation: stress tolerators may be dominant competitors. Ecology 2001: 2471-2485. http://www.esf.edu/efb/schulz/seminars/emery.pdf
  2. Pennings, Steven C., and Ragan M. Callaway. Salt marsh plant zonation: the relative importance of competition and physical factors. Ecology 1992: 681-690.
  3. http://userwww.sfsu.edu/parker/bio529/pdfs/PCZonation92.pdf
  4. Pennings, Steven C., MaryBestor Grant, and Mark D. Bertness. Plant zonation in lowlatitude salt marshes: disentangling the roles of flooding, salinity, and competition. Journal of ecology 2005: 159-167. http://nsmn1.uh.edu/steve/CV/Publications/Pennings%20et%20al%20JEcol%20zonation %202005.pdf
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