Holbrook Bay Saltmarsh Skills Revision
- Created by: eleanorwalker05
- Created on: 03-04-17 13:10
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
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
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
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
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
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
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)
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)
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
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
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
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
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
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
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%
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
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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