17:15 〜 18:30
[MIS11-P06] High concentration phosphate and biological production in a wando
キーワード：ワンド、リン酸
The wand (backwater) is a semi-enclosed body of water in a river floodplain that is partly connected to the river. Abundant algae and aquatic plants thrive in the wand, and juvenile fish and other aquatic organisms use it as a refuge and habitat, making it a place with high biodiversity even in rivers (Denda et al. 2006). The importance of primary production and nutrient supply to support these organisms is noteworthy. However, there have been few studies on the behavior of nutrient in semi-enclosed water wands. Therefore, we conducted this study focusing on the productivity in the wand and the mechanism that supports nutritionally it.
A wand of about 300m in length in the middle reaches of the Tama River was chosen as the study site. Sampling was conducted almost every month from July to January. Surface water and bottom water were collected for filtration samples at four sites along the flow direction within the wand. Phosphate, silica, were measured by colorimetric method. Floating algae flowing out from the wand was collected using a 0.75 x 0.75 mm mesh trap in October to measure chlorophyll content. For a comparison of water quality of the wand, we referred to the phosphate concentration data measured in the main stream of the Tama River by the Tokyo Metropolitan Government Bureau of Environment at Sekido Bridge, about 700 m upstream from the study site. (Monthly from April 2000 to March 2020)
Phosphate concentrations in the wand measured in the present study ranged from 6.0 to 4.7, which was about 3.7-0.7 µmol/L higher than river phosphate concentrations (Fig. 1). The difference in concentration was larger in summer and smaller in winter. In addition, silica concentrations in respective observations tended to be higher than the main river water. There was a significant positive correlation between silica concentration and phosphate concentration in the upstream of the wand where the subterranean river water springs (Fig. 2). This suggests that silica and phosphate, which are derived by rock-weathering, dissolve into subterranean river water and they are supplied to the wand with spring.
The concentrations of phosphate measured at four sites along the wand during summer and autumn showed decreases from the upstream to the downstream. In the wand, we observed that algae detached from the riverbed and discharged from there. Therefore, we quantitatively collected the floating algae at the downstream end of the wand during the survey in October.
The amount of chlorophyll-a in the algae flowing out of the wand into the river was calculated to be about 68 µg/m2/day. Therefore, it was found that primary production by periphyton was actively occurring in the wand by taking up phosphate.
These results suggest that weathering-derived phosphate is supplied to the wand via subterranean river water, and active primary production is taking place with its phosphate.
A wand of about 300m in length in the middle reaches of the Tama River was chosen as the study site. Sampling was conducted almost every month from July to January. Surface water and bottom water were collected for filtration samples at four sites along the flow direction within the wand. Phosphate, silica, were measured by colorimetric method. Floating algae flowing out from the wand was collected using a 0.75 x 0.75 mm mesh trap in October to measure chlorophyll content. For a comparison of water quality of the wand, we referred to the phosphate concentration data measured in the main stream of the Tama River by the Tokyo Metropolitan Government Bureau of Environment at Sekido Bridge, about 700 m upstream from the study site. (Monthly from April 2000 to March 2020)
Phosphate concentrations in the wand measured in the present study ranged from 6.0 to 4.7, which was about 3.7-0.7 µmol/L higher than river phosphate concentrations (Fig. 1). The difference in concentration was larger in summer and smaller in winter. In addition, silica concentrations in respective observations tended to be higher than the main river water. There was a significant positive correlation between silica concentration and phosphate concentration in the upstream of the wand where the subterranean river water springs (Fig. 2). This suggests that silica and phosphate, which are derived by rock-weathering, dissolve into subterranean river water and they are supplied to the wand with spring.
The concentrations of phosphate measured at four sites along the wand during summer and autumn showed decreases from the upstream to the downstream. In the wand, we observed that algae detached from the riverbed and discharged from there. Therefore, we quantitatively collected the floating algae at the downstream end of the wand during the survey in October.
The amount of chlorophyll-a in the algae flowing out of the wand into the river was calculated to be about 68 µg/m2/day. Therefore, it was found that primary production by periphyton was actively occurring in the wand by taking up phosphate.
These results suggest that weathering-derived phosphate is supplied to the wand via subterranean river water, and active primary production is taking place with its phosphate.