Investigating biomass of Ulva lactuca (sea lettuce) in conditions of varying dissolved oxygen concentration and

current speed

Group 3: Rachael Bardfield, Karleena Corey, Ben Duncan, and Shannon Kelly

Research & MethodsOverarching Question: How do abiotic factors such as dissolved

oxygen concentration and current speed affect the biomass of aquatic plants?

Testable Question: How does the biomass of Ulva lactuca (sea lettuce) vary in conditions of differing dissolved oxygen concentration and current speed?

Methods:• two distinct sites in estuary were chosen: the first was in close proximity to the beach and the

second was at the end of the boardwalk and much farther inland and away from the coast• the two sites were visited twice, once at low tide in the morning and again at high tide in the

afternoon• at each visit, the following measurements were conducted:

- dissolved oxygen was measured three time using a DO probe, each time at the same water depth- current speed was measured by recording the time it took the current to carry an apple the length of a 6 m long piece of rope, which was placed on the shore. Basic unit analysis was then used to calculate the current speed in cm/s- five small samples of sea lettuce were taken from the site, stored in plastic bags, then brought back to school to be dried and measured. After drying, lettuce samples were cut into 2 square cm pieces and measured for biomass on a scale

B-WET!

Dissolved Oxygen (± 0.1 mg/l) Current Speed(±0.1 cm/s)

Biomass of Ulva Lactuca Samples (±0.01 g)

Site 1, 10:45am 0.8 0.9 15.1 10.8 11.1 0.26 0.11 0.08

1.0 Avg: 0.9 9.9 10.5 Avg: 11.1 0.20 0.18 Avg: 0.166

Site 1, 12:45pm 0.7 0.8 11.5 11.9 9.9 0.12 0.17 0.12

0.9 Avg: 0.8 12.3 11.2 Avg: 11.3 0.09 0.16 Avg: 0.132

Site 2,11: 00am

0.7 0.8 9.9 9.9 11.2 0.08 0.05 0.08

0.8 :Avg: 0.77 9.9 9.9 Avg: 11.3

0.07 0.11 Avg: 0.078

Site 2, 1:35pm 0.7 0.8 13.2 13.4 12.0 0.06 0.05 0.07

0.7 Avg: 0.73 10.8 14.3 Avg: 12.6 0.08 0.06 Avg: 0.64

Results

Conclusion

• Overall trend: biomass of Ulva lactuca was greater in areas of more concentrated oxygen. We believe that this is evidence of plant productivity: greater oxygen concentration indicates that plants are photosynthesizing more, meaning that they are producing more oxygen and organic molecules to help them grow, which would account for greater biomass

• Current speed was not correlated to either biomass of Ulva lactuca or dissolved oxygen. However, as expected, current speed did increase throughout the day as the tide got higher and water flow increased

Personal Skills & Teamwork

Methods/ Data Collection

Ben went in water to set up apple and retrieve it while Rachael recorded time.

- Karleena assisted Shannon with the DO probe and getting readings. Karleena and Ben worked together in collecting the right amount of samples from the right location. Each group member had the responsibility to:

Shannon - collect DO readings

Rachael - measure current speed

Karleena & Ben - collect sea lettuce samples, which were later

dried and measured at school

Conclusion

In order to draw conclusions, all four of us had to combine our data to analyze our results, find correlations, and subsequently make statements about the estuary ecosystem based on our results.

Limitations & ReflectionsShannon -

- discovered that DO probe had not been calibrated after it gave inaccurate readings

- even after calibration, the probe still gave readings that were not expected or logical: a DO concentration of 2 mg/L is considered lethal for most fish, but we observed tad-poles and other small fish in the area

Rachael -

- over time, the apple became saturated with water and ultimately added mass, which altered to speed at which the current carried it

- current pulled apple in a path that was no longer parallel to the line on the shore, leading to inaccurate measurements of current speed

- for future experiment, choose a variable that is more pertinent to this kind of experiment

Karleena & Ben -

- sometimes samples were taken from areas that weren't very close to where Shannon and Rachael took their readings

- lettuce samples were not cut into perfect squares (we did our best), leading to lack of consistency in methods

- some pieces of lettuce were not completely dry when their biomass was measured, which also contributed to lack of consistency in methods

- while measuring biomass, the scale would change readings because the table would shake, causing varying and perhaps inaccurate measurements