Holbrook Bay Saltmarsh Skills Revision

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Aim

To investigate the changes in flora due to succession along a transect on a salt marsh, with respect to soil temperature, soil compaction, wind speed, salt marsh profile and plant biodiversity

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Theory

Succession - the process of change in the species structure of an ecological community over time

  • community begins with a few pioneering plants (green and brown algae - can tolerate being submerged in salt water - halophytes)
  • Pioneer species trap mud which eventually leads to the build up of soil and improvement of soil conditions which allows the establishment of other species
  • developed through increasing complexity until it becomes stable as a climax community - PLAGIOCLIMAX
  • initial pioneer species decay, improve soil = more species - taller etc, outcompete other species 
  • roots bind the soil = more compact
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Location

Holbrook Bay, River Stour Estuary, Suffolk

  • 10km South of Ipswich
  • 15km West of Felixstowe
  • 2km wide
  • lower course of the River Stour, almost at sea level
  • sheltered from the North Sea by wide meander and headlands - allows deposition
  • area of calm, slow moving water
  • protected by the Shotley Penninsula
  • Suffolk is mainly a farming county, supplies the river deposits due to run off from fields (mud and clay)
  • Flocculation - process by which individual clay particles aggregate to form small lumps. Occurs as result of a chemical reaction between clay and salt water - lumps of clay deposited to form salt marsh
  • 50 km from school - only need 1 day to carry out investigation
  • 20 mins from Flatford Mill FSC - able to use their equipment and facilities 
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Risk Assesment

Transport - wear seatbelts, take care in car parks

Wear suitable clothing - mud, wear wellies

DYNAMIC RISKS

Tides - check the tide times, carry out at low tide so not at risk from being swept away etc.

Weather - check weather forecast before leaving and wear/ bring suitable clothing (i.e. raincoat)

Nature of Saltmarsh - gulleys and patches of mud - learnt to avoid

Strangers + Dogwalkers - stay in groups of at least 2 

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Biotic Factors

Plant Abundance (increases)

  • decay improves soil
  • roots bind soil
  • as conditions of salt marsh improves, more species are able to establish

Plant Variety (increase)

  • conditions better for a wider variety of plant species
  • as soil is formed, plants spend less time submerged in salt water - not only halophytes grow
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Abiotic Factors

Wind Speed (decreases)

  • plants are taller - causes an increase in friction which reduces wind speed
  • plants intercept the wind

Soil temperature (increases)

  • more microbiological activity increase temperature
  • microbes, decomposers etc. respire and therefore cause an increase in temperature 

Soil compaction (increases)

  • roots bind particles
  • more silts inland, form soils

Marsh Profile (increase in height)

  • stabilising nature of vegetation trapping and building up material
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Methods: 1 - Transect and Sampling

Transect 

  • Representative of whole salt marsh
  • perpendicular to the River
  • 70m - length of transect

Systematic Sampling

  • representative
  • every 5m - generates 15 values which is enough data to complete statistical analysis (Spearman's Rank)
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Methods: 2 - Biotic Factors

Plant abundance

  • divided quadrat (50x50cm)
  • (25x25) squares - each square = 4%
  • evaluated percentage of each species at 5m intervals by counting squares

Advantages

  • measures plant variety at the same time

Disadvantages

  • difficult to estimate % of individual plant species
  • difficult to identify each species - would have been easier to identify if plants had been flowering (go at a different time of year) (sea purslane and sea lavender look v. similar)
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Methods: 3 - Abiotic Factors (1)

Marsh Profile

  • theodolite and ranging staff
  • halfway up transect, few metres away
  • human error
  • holding staff upright, heavy - sank into mud

Wind Speed

  • anemometer (handheld)
  • basic equipment - difficult to read, didn't record data, difficult to measure gusts
  • difficult to hold close to the ground - had to clear plants etc
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Methods : 3 - Abiotic Factors (2)

Soil Compaction 

  • penetrometer - place tip onto ground, push down and record measurement
  • difficult to use in mud
  • took a while to understand how to use

Soil Temperature

  • digital thermometer
  • used for 1 min.
  • 10cm probe
  • repeated - results more reliable
  • easy to use
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Data Presentation (Biotic)

Kite Graph

  • shows species change with distance along the transect
  • horizontal line = distance along transect
  • vertical line = percentage of ground covered by species - plot half of percentage either side of the horizontal line

Advantages 

  • Useful for displaying changes over distance
  • Visually clear and easy to interpret one category from another
  • Comparisons can be easily made

Disadvantages

  • Visually subjective as the scale influences visual effect
  • Only works with a specific range of data
  • Time-consuming to construct by hand
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Data Presentation (Abiotic)

Scattergraphs

IV = distance along transect

DV = wind speed / soil compaction / soil temperature / marsh profile (draw line)

Advantages

  • Shows a trend in the data relationship
  • Retains exact data values and sample size
  • Shows minimum/maximum and outliers 

Disadvantages

  • Hard to visualise results in large data sets  
  • Flat trend line gives inconclusive results  
  • Data on both axes should be continuous 
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Statistical Analysis - Biotic

Spearman's Rank

to find possible relationships between variables 

draw best-fit line on scattergraph - use spearman's rank to test strength of correlation

1. Set up table - rank high to low (1 = highest)

2. total difference^2

3. input into spearman's rank formula

4. compare spearman's rank value to critical values to prove that the correlation is not a coicidence 

My Values

99% certainty - correlation at 13 degrees of freedom of -0.83

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Results - Abiotic Factors

Wind speed

0m - 1.30 m/s                                     70m - 0.00 m/s

Soild Compaction

0m - 0.00 kg/cm^2.                            55m - 3.00 kg?cm^2                         70m - 0.28 kg/cm^2

Spearkmans Rank = 0.39 --> accept null hypothesis - NO CORRELATION

Soil Temperature

0m - 22.05 c                                       70m - 7.95 c

Spearmans Rank = 0.69 - critical value = 0.6 --> 95% confident that we can reject the null hypothesis

Salt Marsh Profile

0m - 0m                                              70m - 2.69m

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Results - Abiotic Factors

Distance                                               Species

0m                                                        Green Algae - 40%

                                                             Cord Grass - 0%

                                                             Sea Couch Grass - 0%

35m                                                      Green Algae - 50%

                                                             Cord Grass - 50%

                                                             Sea Couch Grass - 0%

70m                                                      Green Algae - 0%

                                                             Cord Grass - 0%

                                                             Sea Couch Grass - 50%

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Conclusions (Biotic)

Plant Abundance and Plant Species - INCREASE

  • greater variety in middle of the transect
  • excepted abundance to increase ( did for the first 9 sites) 
  • after 40m, dominant species (sea couch grass) takes over

--> species abundance increases, variety does not - didn't expect this

Explanation - taller sea couch grass may block out sunlight, therefore other plants are unable to grow

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Conclusions (Abiotic)

Soil Compaction - INCREASES

  • last 2 results - anomalies - thick vegetation made it difficult to read - human error

Soil Temperature

  • Strong correlation - not what expected
  • ANTECEDENT weather conditions - hot and sunny days before investigation - heat river - temp. closer to river is much warmer than in land
  • ALBEDO effect - dark surfaces absorb heat better - dark, exposed mud = warmer conditions
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