|
Effects of Elodea spp. and Sphagnum on the diurnal cycles of Dissolved Oxygen, pH, Conductivity, Temperature, Nitrogen and Phosphorous in the water with the presence of primary treated sewage.
Abstract
We are to find out how do different submerged aquatic vegetation influence the diurnal cycle of several water quality measurements with and without the treatment which is addition of sewage. Measurements includes dissolved oxygen, pH, conductivity, temperature, nitrogen and phosphorous. Each species has two samples. One is control, the other one will be assigned treatment. A course of three days will be scheduled to carry out the measurement at specific time points. Lamp lights are used to provide light as a representation of sun and they will be closed during the night time. Results shown that DO, pH and temperature have strong diurnal cycle whereas the conductivity excluding the Hydrogen ions does not show a diurnal cycle. Vegetations take up NH4+ and SRP in the sewage and produce NO2+NO3.
Introduction
One of the reason why wetland is such a precious ecosystem as a nutrient cycling mechanism is its ability to change the water chemistry on some key chemicals like nitrogen and phosphorous. The vegetation contributes a lot in this case as they take up these nutrients to grow in which processes they regulate the nutrient level. Therefore they can also function as a sewage treatment. In this experiment, we are using Elodea spp. and sphagnum as the experimental species and find out how do they change the water chemistry. Submersed macrophytes can be important for the N metabolism in NH super(+) sub(4)-rich freshwaters (e.g., wastewater treatment systems) by stimulating nitrification through providing surfaces for attached nitrifying bacteria and possibly also through diurnal changes in the water chemistry. (Dale H. Vitt. Et al. 2003) As a result, I predict the N and P concentrations in the sewage added will drop steadily throughout the experiment as the vegetation assimilates them as nutrients. However, their level could maintain. Since either N or P could become the limiting factors as a certain ratio between them is required for plants (R.H. Kadlec, 2008). Moreover, in addition to modify the N, P concentration in the water body, macrophytes and sphagnum also cause diurnal cycles in water bodies on DO, pH as a result of the diurnal cycle of the natural temperature change as well as the result of photosynthesis by these submerged vegetation. Photosynthesis will take up carbon dioxide and produce oxygen. Therefore DO is likely to increase during illumination whereas pH will increase during this period as the H2CO3 increases in the water. The opposite will happen during night time. We will also look at the conductivity difference them. As the nutrients are being taken up, I will assume the conductivity will drop as fewer ions are available in the water.
Materials and methods
Two species were used in this experiment. They are Elodea spp. and Sphagnum. Two water tanks of sample were set up for each of them with one being control experiment and the other one being treated experiment. The diurnal cycle of sun light is created by using lamp lights in the laboratory room. Students were asked to turn on the lamps when dawn came and to turn them off when dust came. Water quality measurements were recorded by using corresponding equipments on a length of three days onhttp://www.ukassignment.org/daixieAssignment/daixieyingguoassignment/ different time stamps. pH meter, EC meter and DO meter were used to accomplish the data collection.#p#分页标题#e#
Results
Graph 1 Graph 1. Diurnal Cycle of Water Temperature for Macrophytes Aquarium #1 and Sphagnum Aquarium #2 shows the two sets of data were generally following the same pattern of cycle that temperatures of the water peak at the dust and appeared to be the lowest at dawn. There was not much difference between the values of the two set of data. They ranged from 20℃ and 26 ℃.
Graph 2. pH and DO of Water for Macrophytes Aquarium #1 and Sphagnum Aquarium #2 showed the pH of Macrophytes Aquarium #1 water was slightly above neutral, ranging from pH7 to pH8.5 whereas Sphagnum Aquarium #2 water appeared to be acidic with its graph stayed steady around pH4.5 except for the second dust point at which it peaks at pH5. The Macrophytes Aquarium #1 graph showed that pH was the lowest at Dawn. DO for both of the samples showed strong pattern that the values peak at dust and at the lowest at dawn. Macrophytes Aquarium #1 water had a higher DO when comparing to Sphagnum Aquarium #2 as well as a greater fluctuation.
Graph 3. Conductivity excluding the conductivity due to hydrogen ions in the water for macrophytes Aquarium #1 and Sphagnum Aquarium #2 showed Macrophytes Aquarium #1 had a higher conductivity than Sphagnum Aquarium #2 overall. Fluctuations between these two are very closed and they all appeared to be peaking at Dawn.
Graph 4. DO of water for Macrophytes Aquarium #3 and Sphagnum Aquarium #4 showed Macrophytes Aquarium #3 had a higher DO in water than Sphagnum Aquarium #4 in general and they followed a pattern that the values peak at dust and at the lowest at Dawn except Macrophytes Aquarium #4 showed a higher peak at the second 11:00AM. Macrophytes Aquarium #3, ranging from 1-7, showed a greater fluctuation than Sphagnum Aquarium #4 which ranged from 0.5-2.5.
Graph 5. Water pH for Macrophyte aquarium #3 and Sphagnum Aquarium #4 showed that Macrophytes Aquarium #3 had a higher pH than Sphagnum Aquarium #4 overall. Macrophyte aquarium #3 showed peaks at dusts and at the lowest at dawns whereas Sphagnum Aquarium #4 only showed a trough at the first dust.
Graph 6. Conductivity excluding the conductivity due to hydrogen ions in Macrophytes Aquarium #3 and Sphagnum Aquarium #4 showed that Macrophytes Aquarium #3 had a higher conductivity than Sphagnum Aquarium #4 in general. They did not show a strong diurnal pattern except Macrophytes Aquarium #3 showed peak around dawn.
Graph 7. NH4+ ,NO2+NO3 and TN level for Macrophytes Aquarium #3 and Sphagnum Aquarium #4 showed TN for Macrophytes Aquarium #3 decreased after treatment and increased a bit at 72 hours when comparing to 24 hours whereas Sphagnum Aquarium #4 showed a steady drope in TN over 72 hours. NH4+ level decreased steady after the treatment for both of them. NO2+NO3 level increased for Macrophytes Aquarium #3 but decreased for Sphagnum Aquarium #4. Macrophytes Aquarium #3 was higher in all three measurements than Sphagnum Aquarium #4.
Graph 8. SRP and TP level for Macrophytes Aquarium #3 and Sphagnum Aquarium #4 showed that the starting and ending TP and SRP were higher in Macrophytes Aquarium #3 while these two measurements dropped by approximately the same amount after 72 hours. The difference was SRP level in Macrophytes Aquarium #3 maintained for 24 hours before dropping whereas it dropped immediately for Sphagnum Aquarium #4 after applying the treatment. TP levels shared the same pattern of steady dropping after treatment.#p#分页标题#e#
Graph 9. Ratio between total N and P and the ratio between inorganic N and inorganic P for Macrophytes Aquarium #3 and Sphagnum Aquarium #4 showed that the TN:TP ratios in both of the treatments shared similar trend of dropping right after applying treatments and raised in a 72-hour period, however, Sphagnum Aquarium #4 had a higher starting value and ending value while it also showed the greater fluctuation. Although Sphagnum Aquarium #4 had a higher starting IN:IP value, it dropped steadily despite of treatment before increased between 24 hours and 72 hours whereas Macrophytes Aquarium #3 showed a slight increase of IN:IP value after applying the treatment then followed the same pattern as Sphagnum Aquarium #4 afterward.
Disccusion
Temperature in control experiments
The source of temperature is the radiation. We imitated the natural sun light and its diurnal cycle by using lamp lights and turning on and off at specific time of the day. Although this might seemed good from a time perspective, it was different from quality when comparing with the sun light. The intensity of sun light was the least at dawn and dust and the strongest at mid day. It was determined by the length of atmosphere it had to travel, therefore the longer it traveled, the less intensive it became. Lamp lights, on the other hand, were not able to imitate this variation. They emitted constant radiation all the time. Moreover, we did not imitate the cloud shadow which could also affect the radiation and consequently the temperature. The real temperature diurnal cycle would still follow the same cycle with the peak at dust and the trough at dawn but I would expect a curve with smooth variation. This pattern could be explained by the net radiation to earth. At dust, the net radiation was the highest whereas it was the lowest at dawn.
pH and DO in control experiments
Both the pH and DO showed a diurnal cycle that the peaks were at dust and the lowest at dawn for aquarium 1. DO of aquarium 2 showed the same pattern as well. However pH of aquarium 2 did not show a very clear diurnal cycle except for a peak at dust, the rest of it is pretty smooth. These diurnal cycles could be explained by two aspects, photosynthesis/respiration and temperature diurnal cycle. The process of photosynthesis is to take up carbon dioxide, water and other nutrients and produce oxygen and water whereas respiration was uptaking of oxygen and producing CO2. The produced oxygen increased the DO in the water. The consumption of carbon dioxide would convert the H2CO3 in the water to CO2 to maintain the equilibrium (J.P. Ondok, et al. 1984). H2CO3 is an acid, the reduction of it would raise the pH to a higher level. Since photosynthesis was an endothermic reaction, despite the radiation provided by lamps were constant, the rising temperature would increase the photosynthesis rate and during the night time, the opposition will happen. Therefore diurnal cycles were formed. The data suggested the macrophyte carried out more photosynthesis than the sphagnum as the overall level of DO in aquarium #1 was larger.#p#分页标题#e#
Conductivity in control experiment
The conductivity seemed to follow a pattern such that it increased as the time moved from dust to dawn and then peak around dawn which contrasted with my hypothesis that the conductivity would drop steadily over time as the nutrients were taken up by the vegetation. This trend could be explained by the presence of HCO- as vegetation released CO2 by respiration during night time.
DO in treated experiments
I was expecting higher overall DO level in treated experiment than the control ones. Since sewage contains more N and P which were usually limiting growth elements for vegetation. With sufficient supply of these nutrients, more photosynthesis should occur and higher DO as a result. However, The DO diurnal cycles in treated experiment were very similar with the control experiment with regard to the pattern and the value. They both peaked at dust and dropped to the lowest at dawn, with macrophyte having a higher overall DO than sphagnum.
pH in treated experiments
Same as the DO, the pH values and cycles were hard to tell any difference between the treated experiment and the control experiment. The macrophyte samples were peaking at dust and were dropping to the lowest at dawn while the sphagnum showed a relatively linear unchanged level over time.
Conductivity in treated experiments
While the conductivity curves between the treated experiment and the control experiment were similar in the pattern, the treated macrophyte had a higher conductivity level than the control macrophyte sample. Whereas there were not much difference between treated and control experiment for sphagnum. An increased in conductivity met my hypothesis that more nutrients in water would lead to higher conductivity as more ions were available. However, the diurnal cycles on this measurement were not very strong. This may due to that the amount of sewage added was not significant to allow clear observation.
NH4+, NO3-+NO2, TN, TP, TN:TP and IN:IP in treated experiments
The NH4+ level in both aquarium showed sharp increasing just after treatment and gradual decreasing after that whereas the NO3-+NO2 level showed gradual increasing throughout the whole experiment. The sharp increase was explained by the nitrogen in sewage existed in the form of ammonia. The gradual decreasing was due to the uptaking of ammonia by plants as well as the nitrification process carried out by bacteria in the water. The increasing NO3-+NO2 showed that there were not denitrification to convert them to N2. The explanation for this could be the submerged vegetation released a lot of O2 by photosynthesis or simply by roots. The released of O2 expanded the oxic environment and stimulated more nitrification, on the other hand, the denitrification was hard to occur, the level of NO3-+NO2 built up.(N. R. Peterson, K. Jensen. 1997) Total nitrogen showed a reasonable declining trend in both the aquarium #3 and aquarium #4, as nitrogen acted as an critical nutrient in vegetation grow. However the TN for aquarium #3 had a slight increasing after 24 hours, this could be contributed by the decomposition of algae in the water. TP also showed a reasonable decline after applying the treatment as they were used by the vegetations and the algae. SRP, however, showed an unexpected rose in level for aquarium #3 in a 24-hour period after applying the treatment whereas aquarium #4 showed an expected declined in TP. Couple with the SRP trend for aquarium #3, we can deduce that it was the organic P that was raising whereas the inorganic P was still decreasing after the treatment. The increasing organic P could be contributed by the decomposition by bacteria. By looking at the TN:TP ratio, we could understand that both of the vegetation demanded more P than N. In other words, the limiting factors here were P. since the ratio for aquarium was 12:1 and 6.5:1 before the treatment respectively, and it became 6:1 and 5.5:1 right after treatment, indicating that P was limiting. As the uptaking of P by vegetation and decomposition happened, the ratio restored to the earlier level gradually with P became limiting again while N was supplied by decomposition. Another explaination would be the decomposition by bacteria was occurring fast. Knowing that the IN:IP raised whereas TN:TP dropped, we could conclude that the organic nitrogen was decreasing. Since the sewage provided a lot of nutrients for the growth of vegetation, photosynthesis released a fair amount of O2 which encouraged the decomposition.#p#分页标题#e#
Citation
Nordin. (2009) Ecophysiological adjustment of two Sphagnum species in response to anthropogenic nitrogen deposition. New Phytologist 181:1, 208-217
Dale H. Vitt. Et al. (2003) Response of Sphagnum Fuscum to Nitrogen Deposition: A Case Studyof Ombrogenous Peatlands in Alberta, Canada. The Bryologist 106(2):235-245.
An experimental study on effects of submersed macrophytes on nitrification and denitrification in ammonium-rich aquatic systems
R.H. Kadlec. (2008) The effects of wetland vegetation and morphology on nitrogen processing. Ecological Engineering Volume 33, 126-141
N. R. Petersen, K. Jensen. (1997) Nitrification and denitrification in the rhizosphere of the aquatic macrophyte lobelia dortmanna L. Limnology and oceanography 42:3, 529-537
|
