Presentation on theme: "Primary Production measurements over a daily cycle in Clark’s Cove Ayan Chaudhuri, Lin Zhang, Anne-Marie Brunner MAR640 – Global Marine Biogeochemistry."— Presentation transcript:
Primary Production measurements over a daily cycle in Clark’s Cove Ayan Chaudhuri, Lin Zhang, Anne-Marie Brunner MAR640 – Global Marine Biogeochemistry
The aim of this experiment Measuring primary productivity in Clarks Cove using –Light bottle/dark bottle technique to measure O 2 with a Massspectrometer –d18O-Method –Organic Carbon and Nitrogen measurements –Nutrient measurements establishing a box model for carbon fluxes in this Cove
Clarks Cove It has an average water depth of 12ft (Very shallow) remains well mixed by tidal and wind events year round Hill, 1998 found nutrient levels lower in Buzzards Bay than in Narragansett Bay Hill, 1998 for Buzzards Bay measured a primary productivity in Nov/Dec between 8-26mgC m-3h-1(his figure 18, station 6) Source:
Measuring Primary Productivity – The Theory Light Bottle/Dark Bottle Oxygen –a. Light bottle O 2 minus initial O 2 concentration is net community production. In the absence of heterotrophs, the difference is net primary production. – b. Dark bottle O 2 concentration minus initial O 2 concentration is respiration – c. Light bottle minus dark bottle is gross community production. –Incubation time: 3hrs –Sampling every 3 hours during the day, 5hours at night –Using a massspectrometer for higher accuracy
d18O-Method During the incubation time the gross production produces O2 in the water with the same, enriched ratio as the water. Therefore, the ratio of 18O to 16O is enriched in the dissolved O2 pool, as the tagged O2 mixes with the large O2 pool. Thus, the change in the 18O of dissolved O2 can be used as a measurement of gross production. (Bender et al., 1987). The O2 consumed during respiration has a lower d 18O than the dissolved O2 18O/16O value of a gas with a d18O value, relative to SMOW (standard mean ocean water) would be
Conversion to primary productivity carbon (mg) * 32 * PQ = oxygen (mg) * 12; where PQ = photosynthetic quotient, the ratio of moles of oxygen released to moles of carbon fixed; its value depends on whether nitrate or ammonia is available as a nitrogen source, and varies from 1.0 to 1.3; here 1.2
Measuring Primary Productivity – The Experiment Starting at 7am on the 30 th of November we conducted the first sampling. Further sampling times were at 10am, 1pm, 4pm, 9pm, 2pm and 7am. Light Bottles (not at 4, 9 and 2), Dark Bottles and initial bottles were sampled and incubated in the seawater. At the first sampling, also dark and light bottles for the daylight cycle (9hrs) were incubated. Bottles were labeled with 18 O and some samples with 13 C for incubation.
Problems during the Experiment Weather conditions were good, although cloudy, it was calm. At 2am,1 st December, a storm started with increasing wind speeds and light drizzle until noontime, the second half of our experiment. Also, our setup for our bottle measurements started to fail around 2 am, so results are questionable during that time. Some data were lost for the bottles at 10am, 30 th November. Jellyfish were seen in the sampled water
Bottle Measurements Initial Bottle O2/Ar ratios, low at daybreak, moves up during the day, back to low at sunset and after. Light Bottle O2/Ar ratios, rises during day, should fall to zero by sunset. Dark Bottle O2/Ar ratios, falls during the day and rises after sunset
Calculations GPP mostly negative More respiration than production Average pools all light, dark and initial bottles into respective means NPP comparable to thesis by Hill TimeGPPNPPRES mg/C/hr Average
Summary System as a whole is net heterotrophic very less carbon is available for fixation Sources - Tidal Inflow - Sediment re-suspension - atmospheric deposits Sinks - Tidal outflushing
Del O18 Method 450 micL of H2O enriched in 18O The 18O enrichment of the dissolved O2 is taken to be a proportional measure of gross production 9% enrichment – biased estimate
Summary Like the concentrations of nutrients follow a daily cycle, the POM values generally coincident with a tidal cycle. However, the change of C/N values shows an opposite cycle to the tidal cycle, with incoming tides, the C/N ratio decreases, and increases with outgoing tides. The above results lead to a conclusion that the phytoplanktons carry out photosynthesis when there is available light and consume the nutrients in the seawater based on the Redfield ratio. So the concentrations of nutrients decrease during the day as we got from the experiment. But POM values didn’t increase as expected when there is photosynthesis. In the night, phytoplanktons consume O2 and release CO2, the concentrations of nutrients increased due to no consumption. There should be some productivity in the Cove from the above results.
Summary The results of quad method show some interesting differences. The O2/Ar ratio in the initial bottle increases during the day which means there is O2 released and decreases in the night which means respiration leads to a decreasing of O2. However, the ratio from light bottles is always increasing during the experiment period, indicating discrepancies during measurement. The result from dark bottles is also beyond expectation. The ratios dipped from a significant high all through the day, however steadily rising by evening. The whole results show a common trend in that the entire system seems to have more respiration than production, Which is totally opposite to the nutrients and POM analysis.