| Compared with other nutrient elements which are essential for life, such as carbon, hydrogen and sulphur etc. under natural conditions, phosphorus is always the main limiting element for aquatic ecosystems. Such changes as its emission, migration and transformation are of great significance to the primary productivity of aquatic ecosystems. In this study, the Grand River, Ontario, Canada, the largest tributary of one of the Great Lakes, Eire, was chosen to evaluate the relationship between the seasonal variation of different forms of phosphorus and water physicochemical properties. Such methods as the isotope labeling and chemical sequential extraction and so on were applied to explore the activity of the three specific forms of phosphorus in water, that is, the dissolved organic phosphorus (DOP), orthophosphate (PO43-) and suspended particulate phosphorus (PP), and their involvement in water phosphorus cycling for better understanding of the three major processes of the water phosphorus cycling in watershed of the Grand River:the absorption and release of PO43-from of the plankton and the benthos, the acquisition of the conceptual model based on the involvement of the phosphorus in such aquatic organisms as the phytoplankton and bacteria by being prey to the zooplankton and the protozoa, as well as the contribution of the potentially biological available phosphorus released from the DOP and suspended PP due to changes in environmental conditions to the total phosphorus in water.The study is mainly composed of four parts.The first part is about the activity of the DOP in rivers and its involvement in water phosphorus cycling. Three sampling points were chosen in the midsection of the Grand (?) from the upstream to the downstream:Bridgeport, Victoria and Blair, to investigate the contribution of the DOP in water to the soluable reactive phosphorus (SRP), and the specific species of enzyme influencing the DOP concentration in water and their activities. The average DOP concentration in the three sampling points was11.24μg P L-1,16.73μg P L-1and40.19μg P L-1respectively. Due to the different exogenous input such as the sewage discharge and disposal from the sewage treatment plants etc., these three sampling points represent the natural water environment under different nutrition conditions. Comparing the influence of different filtration pressures (0mm Hg,100mm Hg,300mm Hg and500mm Hg) on the DOP concentration in water, it was found that there was a positive correlation between the filtration pressures of water samples and the DOP concentration of the filtrates (P<0.05), that is, the larger the filtration pressure, the higher the concentration of the DOP in the filtrates, which may due to the fact that some of the limbs of the zooplankton and phytoplankton, immersed into the filtrates through the filter membrance and became part of the DOP and also the cell membrance of part of active solid particles bursted under pressure, resulting in the penetration of such phosphorus substances as cell sap (mainly for RNA etc.) into the filtrates and influencing the DOP concentration in the filtrates. Exlporing the contribution of the DOP in natural water to the SRP, it was shown that the DOP concentration in natural water decreased gradually over time,and besides the decline of the DOP concentration in water of the Grand River in different sampling seasons was similar with the increase of the SRP (They changed similarly at the range less thatn2ug PL-1h-1). It was also shown through the following water enzyme assay that the alkaline phosphatase (AP) in water of the Grand River played an important part in the DOP degradation into the PO43-which indicates that the DOP can participate in the water phosphorus cycling and futhermore it is one source of the water SRP. Besides, the AP existed not only in bodies of the plankton in water but also in the extracellular free forms with strong activity in water, acconting for about50%of the total AP activity of the water body. With the involvement of the DOP, the turnaround time of water phosphorus in water of the Grand River was10to24hours. Thus it could be got through the comparison of the experimental results from former studies that the Grand River is one river of eutrophication, with fast water nutrient cycling, strong photosynthesis and active metabolism for the aquatic life.The second part discusses the relationship between the seasonal variation of different forms of phosphorus in water and water physicochemical properties. The watershed in the midsection of the Grand River and the Conestogo River, one important tributary of the Grand River, was studied. Results indicated that the average concentration of the total phosphorus (TP) in water of the Grand River and the Conestogo River in2012was individually87.42μg P L-1and82.15μg PL-1, which indicates clearly that these two rivers are of eutrophication. The correlation analysis indicated that the TP concentration variation in water of the Conestogo River had no impact on the TP in the Grand River (p=0.061), which implies that although the phosphorus in the water of the Conestogo River flowed into the main stream in the midsection it did not bring great impact on the nutrient concentration of water phosphorus. Thus it can be inferred that besides the input from the tributaries, for the water phosphorus in the midsection of the Grand River there are other input sources with high phosphours concentration, which may be due to the fact that there are sewage treatment plants of Waterloo which discharge waste water with abuandant nutrients directly into the Grand River at about15km along the river between the river mouth of the Conestogo River and the Bridgeport, the midsection of the Grand River. The annual average concentration of the SRP and the DOP in water of the midsection of the Grand River was9.77μg P L-1and10.85μg P L-1. That in the river mouth of the Conestogo River was10.14μg P L-1and16.28μg P L-1respectively. The correlation analysis showed that there was no good correlation between the SRP concentration and the DOP concentration at these two sampling points (P>0.05), which infers that besides the input from the Conestogo River, for the soluable phosphorus (SRP and DOP) there are input of the exogenous soluable phosphorus into water of the Grand River. The annual average concentration of the PP in water of the Grand River and the Conestogo River was67.51μg P L-1and55.30μg P L-1. It can be found through the correlation analysis that there was good correlation between the concentration of the suspended PP in midsection of the Grand River and the suspended PP concentration in the river mouth of the Conestogo River (P<0.05), thus it can be inferred that the suspended PP, accounting for67.09%of the TP in water of the Conestogo River, entered into the water body of the Grand River, flowed into the downstream and did great contribution to the suspended PP in the Grand River. The suspended PP in watershed of the midsection of the Grand River mainly came from the input from the tributaries.The third part is the geochemical properties analysis of suspended particulate phosphorus in water.Chemical approaches could be used to extract5kinds of potentially mobile phosphorus in the water particulate phosphorus in the Grand River and its tributary, Conestogo River. The variation trend of these five kinds was BD-SRP>85℃NaOH-SRP> NH4C1-SRP> HC1-SRP> NaOH-SRP,which indicates that the average concentration of BD-SRP in suspended particulate phosphorus was the highest, and it was even several times higher than that of NaOH-SRP. As the BD-SRP was the phosphorus fragment which combined with such metal ions as the iron ion, the aluminum ion and the manganese ion etc., and was quite sensitive to the redox state in water, it could be speculated that in this area in water of the main stream of the Grand River as well as its tributaries, the geochemical properties of the substances with phosphorus particles received from the terrestrial ecosystems were similar. It was possible that the soil in the watershed developed from the basic rock parent material abudant in such metal ions as iron, magnesium manganese and aluminum and so on. The correlation analysis showed that in each extraction fragment from the suspended particulate phosphorus in water of the Grand River, there was a good correlation between the NH4C1-SRP and the total water suspended PP, implying that with the increase of the water suspended PP, the NH4C1-SRP, representing bioactive phosphorus in instable combination, could make the potentially mobile phosphorus in water increase accordingly. Simultaneously, compared with the concentration of other extraction fragments, that of the85℃NaO-SRP was relatively high and it was in good correlation with the DOP in water, which stated that the water suspended PP in the Grand River mostly existed in organic forms and indicated that in Grand River the biomass was abundantly available and the activity of the aquatic life was strong. In the five potentially active fragments the concentration of the NaOH-SRP was the lowest. As it represented phosphorus organisms existing in humus or gathering in microorganisms, it could be concluded that water of the Grand River and the Conestogo River, was poor in such organic particulate matters as small bacteria and algae combined with soil and rock,humus and small bacteria and algae absorbed by the humus. The activity of the aquatic life in particles such as the algae etc. in water of the Grand River and the Conestogo River was strong. Such aquatic life as the bacteria, the alge and the protozoa were abundant and grew vigorously. As in different water bodies, the water environment such as the population quantity of the aquatic life (for example, the conten of the humus, the bacteria and the algae etc.) may have impact on the release and the absorption of the potentially available phosphorus fragments in water suspended PP with the seasonal variation, the high and low value of the average concentration of each potentially active phosphorus fragment in the water suspended PP in Grand River and the Conestogo River were various in different seasons. Thus it could be conculded that for the Grand River there was difference in the water environment between the main stream watershed and the watershed of its tributariesThe fourth part concerns the absorption and release of orthophosphate by the aquatic life. The isotope labeling (32P) was used to discuss several aspects of the orthophosphate cycling in river ecosystem. In water of the Grand River, there are two different kinds of aquatic lives:the aquatic organisms at the surface of pebbles in the riverbed (including the suface algae living at the surface of pebbles at the bottom of rivers as well as the microbenthons), and the aquatic lives in suspended particles (such plankton as the blue algae). It was showed through the experiment about the absorption of the orthophosphate labelled by the32P,(namely32P-PO43-) in water that the amount of the32P in these two kinds of aquatic lives increased sharply the first two hours after adding32P-PO43-.However, as time went on, the aquatic organisms at the surface of pebbles in the riverbed gradually accounted for the vast majority of the absorption of32P-PO43-in water and the amount of32P in the acquatic organisms in suspended particles in water decreased due to such factors as its absorption by the aquatic lives at the surface of pebbles in the riverbed and other aquatic organisms. The absorption rate of orthophosphate (PO43-) for the epilithion of the riverbed and acquatic organisms in suspended paritcles in water was the maximum in such season as summer with high to(?)perature,especially in August, namely0.33and0.24μg P cm-2h-1and in December it was quite the opposite with the absorption rate as0.036and0.034μg P cm-2h-1During the study of the contribution of aquatic lives with different sizes in water to the absorption of PO43-it could be found that despite the seasonal changes, the ultraplankton with the size from0.2to2μm in water of the Grand River was the main acquatic species absorbing the PO43-. Furthermore, the trunaround time of PO43-in water decreased with the increase of temperature. In August, it was the shortest as0.75h and in winter it was relatively longer as2.67h. Gel chromatography was used to explore the release and regeneration form of the32P-PO43-in water abosrbed and utilized by the aquatic lives. It could be found that the release of32P by the acquatic lives in the Grand River was mainly in the form of the dissolved PO43-with small molecular weight (≥200MW).To sum up, the study concerns the seasonal variation of different forms of phsophorus in the water ecosystem, their transformation organisms, the potential bioavailability of the suspended PP in water and the transformation between biofacies and non-biofacies of the orthophosphate and so on. The conceptual model of water phosphorus cycling was put forward to better understand the water phosphorus cycling in the Grand River, help with the ecological environment protection in the watershed of the Grand River and provide reference for similar studies about water phosphorus cycling in rivers. However, it must be mentioned that water in rivers is in a constant state of motion and variation. Thus there are massive changes for the water ecology. Different conclusions can be drawn at different time, so only by continuous and long-term monitoring and study in the river ecosystem can rules and conclusions be drawn. |
PDF Full Text Request