Lab Report:
Abstract
The tidal cycle of natural water bodies present challenges for sampling and interpreting physical, chemical and biological data. The Rainbow Channel at Morton Bay was the location for a field work project on sampling characteristics about the biota and about water quality parameters. Rainbow Channel experiences ocean flushing dependent on daily, monthly, seasonal, and annual at regular natural time intervals. Both daytime and night time sampling took place to better understand 24 hourly and daily cycles of nutrient concentrations, salinity, temperature, fluorescence and currents. Primary productivity takes place at different three different depths. The rate of productivity depends on the amount of light and nutrients available for phytoplankton at the channels surface and the relative seasonal changes (Lalli & Parson, 2006, p. 59). Seasonal changes effect at different depths and the vertical distribution of phytoplankton primary (Lalli & Parson, 2006, p. 70). The density of nutrients at the bottom (where light is limited) is at the nurticline so the largest change is nutrient concentration is located there. The sampling took place during the five-days from April 28, 2014 to May 2, 2014. These data showed a diurnal vertical migration for zooplankton; zooplanktons are carried into the area during high tides. The three species of zooplankton identified from the collection nets and counted were calanoid, cyclopoida and harpacticoid. The water system sampled at the Rainbow Channel in Moreton Bay is oligotrophic. Higher tides bring warm salt water into the channel so high tides have higher temperatures and higher salt concentrations. The temperature of the surface water was somewhat higher than temperature measurements taken within the water column. Land use next to the channel does not add nutrient run off in the form of nitrogen or phosphorus compounds.
Key words: Rainbow Channel at Moreton Bay, tidal cycle, water quality, zooplankton, productivity
Field work was carried out at the Moreton Bay Research Station (MBRS) during the week of April 29, 2014 to May 2, 2014. Brisbane Bar tides were adjusted for time, specifically to match the tide at Amity Point. Low tide was adjusted by subtracting 54 minutes and by subtracting 40 minutes from high tide. (See table A-1 and figure A-1) Samples were taken from Rainbow Channel, Moreton Bay in order to analyse biological characteristics of the channel including concentration of nutrients, zooplankton biomass, and chlorophyll-a concentration. Natural physical measurements taken were for the wind speed and direction, depth of visibility, and surface water velocity. Oceanographic measurements such as salinity and currents were also measured. The sampling data was used to determine parameters as a function of the tidal cycle at the location. Plankton samples were gathered, processed and analysed and measurements were graphed to show relationships with chemical and other biological data. The purpose of the field work was to learn how to sample plankton and take measurements at a site. The health of surface water can be determined by the measurements taken. The 2000 Water Framework Directive from the European Union defines “the ecological status of surface water . . . is an expression of the quality of the structure and functioning of aquatic ecosystems associated with surface waters. . .” (Solimini, Cardoso, & Heiskanen, 2006, p. v). Water is the most precious resource on earth so learning how to judge the water quality of water bodies is necessary. Phytoplankton abundance and visibility (transparency) are indicators for eutrophication, but a well-planned sampling trip that includes biological, chemical and physical parameter measurements is the only way to analyse water status reliably. The impacts on the channel are varied including land use of shore, ocean currents, and meteorological conditions at the time of sampling; therefore the dynamics of the ecological system are better understood when a variety of precise and accurate data is available.
Methodology
The sampling for biomass collection and for physical/chemical measurements took place at Rainbow Channel, Moreton Bay, on the east side. A CISRO research ship was used to collect the samples in the channel. The Moreton Bay Research Station laboratory, North Stradbroke Island was used to take measurements that were not done on the ship. Sampling took place during five days from April 28, 2014 to May 2, 2014.
Biomass collection
Two nets were used to collect zooplankton, one with 100 micron mesh and the other with 200 micron mesh. The nets were dragged behind the boat in order to record the current on a flowmeter and collect biomass samples. Two samples were carefully placed in containers place in an ice bath for the remainder of the boat trip. At the laboratory one sample was dried in the oven, the weight was recorded in order to record the changing biomass while the sample dried. The other sample was split into eight subsamples using a Folsom splitter. One of the subsamples was diluted to a volume of 100mL. Of this 100mL a Stempel pipette was used to take 1mL samples, and each was analysed in a Bogarov tray under a dissecting microscope in order to identify the species of zooplankton collected.
Emergent zooplankton data were also collected over a 24 hour period at the end of the jetty. The 100 micron net was dragged back and forth 5 times to gather the samples.
Instruments for chemical and physical parameter measurements
A Secchi disk was placed in the water to the depth were visibility ended to measure the transparency of the water. CTD-F, an oceanographic instrument uses electronic sensors to measure temperature, salinity and fluorescence (emitted light). Niskin bottles were used to do the collection of sea water samples for surface water quality and chlorophyll-a concentration and in conjunction with instruments such as the CTD-F. Surface current direction and speed was measured by ‘drifters’ that were allowed to drift on the surface in five minute intervals. An anemometer was used for recording wind speed. Detailed techniques for using these methods can be found in the MARS3012 Moreton Bay field trip manual.
Results
The amounts of nutrients in the water are directly correlated to the amount of Eutrophication. The average concentrations of phosphates, nitrates, nitrites and ammonia were measured at Rainbow Channel and compared to a river (UQ) and an aquapond. (See fig. 1) The error bars indicate standard error from the mean (average).
Figure 1 Nutrient comparison between three locations
Figure 3 shows the relationship per day between the tidal height and the biomass weight. The laboratory results for biomass weights are presented in Table A-2. The amount of the average weight (grams) per sample as abundance (per meter3) compared to the ebb and flow of the tidal cycle.
Figure 2 Tidal height graphed with biomass measured in seven trips
The emergent zooplankton composition was determined by measuring the number of copepods per two-hour interval for a 22 hour period from Wednesday noon to Thursday morning at 10 a.m. (See fig. 3) The three species of zooplankton were identified as calanoid, cyclopoida and harpacticoid. No linear trend can be identified because of the currents. The highest number measured was of cyclopoida with about 117 counted from the 10 a.m. sampling. The range of variation for the number of cyclopoida was from two at 2 p.m. to approximately 38 at 4 a.m. Calanoids were the highest at 10 p.m. and 4 a.m. when the count was approximately 85 and 82, consecutively. The hapracticoid were not as numerous as the others; their numbers ranged for zero at 4 p.m. to approximately 38 at 10 p.m. The counts for calanoids were greatest from 10 p.m to 6 a.m and then 4 hours later at 10 a.m.
Figure 3 Emergent zooplankton composition sampled every two hours from
Noon Wednesday to 10 a.m. Thursday (22 hours)
Figure 4 gives a better picture of the zooplankton composition over time. Calanoids were in greatest number, especially from 1:00 p.m. to 3 p.m. on the second day.
Figure 4 Species of zooplankton sampled during a 24+hour sampling period
Samples gathered of the zooplankton were weighted and dried in the laboratory in order to report biomass weights. The dry weight of the sampled zooplankton biomass was measured in grams. Figure 5 graphs the zooplankton biomass dry weight (grams) collected in Samples 1-7 over time (hours). Sample 0 was the control sample.
Figure 5 The dry weight of biomass as samples were dried over time.
Discussion
A low phosphate average concentration was measured at Rainbow Channel, 0.4 μM/L (See fig. 1). The highest concentration nitrogen compound in Rainbow Channel was the nitrate concentration, 13.64 μM/L. Nitrite and ammonia concentrations were negligible to none being measured in the Rainbow Channel, the average nitrite concentration equalled 1.03 μM/L and no ammonia was measured Phosphorus and nitrogen are the two main ingredients of agricultural fertilizer, which can enter water bodies in land run-off. The amount of all the measured nutrients was higher in the aquapond and in the river than in Rainbow Channel. This could indicate that agricultural run-off is impacting the river and the aquapond. The values of the concentrations of phosphorus and nitrogen compounds in the Rainbow Channel are unlikely to cause eutrophication.
The three species of zooplankton identified from the collection nets and counted were calanoid, cyclopoida and harpacticoid. The tidal cycle in a 24-hour period demonstrated larger numbers and greater diversity of zooplankton during the night time. Diel vertical migration (DVM) is also called the diurnal vertical migration because it refers to the movement in the currents of zooplankton during the night. (See fig. 2) The epiplegaic zone is the water’s surface; it receives the most sunlight so it is the primary area of production (because of photosynthesis). It is only about 200 meters deep. The layer under that is the mesopligaic layer from about 200 to 1000 meters deep. It is in the mesoplagaic layer that fluorescent creatures may sometimes be seen. The tidal cycle is important for the creatures living in the mesoplagaic area because the tide allows them to feed during the night.
Many samples and measurements were taken during the field trip. This proved to be very important for understanding the complex dynamics that impact the water quality of the Rainbow Channel. The results that depended on non-interference from sand and silt in the muds were the least reliable. That was the main problem for taking reliable and accurate measurements because of the possibility for sample contamination. The currents are strong so turbulence takes place that is strong enough to mix bottom sediments in the water column.
The water system sampled at the Rainbow Channel in Moreton Bay is oligotrophic and zooplanktons are carried into the area during high tides. Higher tides bring warm salt water into the channel so high tides have higher temperatures and higher salt concentrations. The temperature of the surface water was somewhat higher than temperature measurements taken within the water column. Land use next to the channel does not add nutrient run off in the form of nitrogen or phosphorus compounds.
Sources of error
Accuracy and precision are the goals for collecting data that will pass quality control rules. Accurate measurements are as close to the true value as can possibly be measured. Precision is how well repeating the same measurement can be reproduced. Precision is an indicator of the reliability of measurements. Errors in accuracy and precision are avoided as much as possible. Since the field work was a learning experience, many errors were possible due to lack of experience and mistakes made using the instruments.
Measurements with a Secchi disk can vary at the same location if the person taking the sample is different, because the measurement is subjective. The Secchi disk measures visibility so the time of the day also gives a different Secchi disk measurement because of different light angles striking the level of turbidity.
The field work gathered many types of data in order to better understand the dynamics of the tidal cycle and the biomass movements as well as the water status in reference to chemical compounds. The larger number of variables measured can give a bigger picture of the parameters in a system but they can also allow more opportunities for error. The two largest limitations of the field work data are the inexperience of the students and the short time period for sampling.
References
Alamazan, G. & Boyd, C.E. (1978) “An evaluation of Secchi Disk visibility for estimating plankton density in fish ponds.” Hydrobiologia, 61(3), 205-208.
Bis, B., Zdanowicz, A., & Zalewski, M. (2000) Effects of catchment properties on hydrochemistry, habitat complexity and invertebrate community structure in a lowland river. Hydrobiologia, 422, 369-387.
Lalli, C. & Parsons, T.R. (2006; 1993) Biological Oceanographic: An Introduction. 2nd ed. Burlington, MA: Elsevier Butterworth-Heinemann.
Glibert, P., Heil, C., O'Neil, J., Dennison, W., and O'Donohue, M.H. (2006) Nitrogen, phosphorus, silica, and carbon in Moreton Bay, Queensland, Australia: Differential limitation of phytoplankton biomass and production. Estuaries and Coasts 29(2), 209-221.
Greenwood, J.G. (1982) Dominance, frequency and species richness patterns in occurrences of calanoid copepods in Moreton Bay, Queensland. Hydrobiologia 87(3), 217-227.
Lalli, C. & Parsons, T.R. (2006; 1993) Biological Oceanographic: An Introduction. 2nd ed. Burlington, MA: Elsevier Butterworth-Heinemann
O'Donohue, M.J., Glibert, P.M., and Dennison, W.C. (2000) Utilization of nitrogen and carbon by phytoplankton in Moreton Bay, Australia. Marine and Freshwater Research 51(7), 703-712.
Solimini, A.G., Cardoso, A.C. & Heiskanes, A-S. (2006) Indicators and methods for the ecological status assessment under the Water Framework Directive. European Commission Joint, Research Centre. pp. 262
Water Quality & Ecosystem Health Policy Unit. (July 2010) Environmental Protection (Water) Policy 2009) Moreton Bay environmental values and Basin No. 144 (part) and adjacent basins 141, 142, 143, 145 and 146, including Moreton Bay, North Stradbroke, South Stradbroke, Moreton and Moreton Bay Islands. Water Quality & Ecosystem Health Policy Unit, Department of Environment and Resource Management, pp. 42. https://www.ehp.qld.gov.au/water/policy/pdf/documents/moreton-bay-ev-2010.pdf
Appendix
The tides were adjusted as recorded in Table A-1.
Figure A- 1 Brisbane Bar Tides times adjusted Amity Point (MARS3012 Field Trip, 1st Semester 2014, GPEM-UQ)
The data for biomass weight and time for laboratory measurements are presented in Table A-2.
Table A- 2 Data for biomass weight and time for laboratory measurements
