Effects of epiphytic algae on biomass and physiology of Myriophyllum spicatum L. with the increase of nitrogen and phosphorus availability in the water body.

The disappearance of submerged vascular macrophytes in shallow eutrophic lakes is a common phenomenon in the world. To explore the mechanism of the decline in submerged macrophyte abundance due to the growth of epiphytic algae along a nutrient gradient in eutrophic water, a 2 × 3 factorial experiment was performed over 4 weeks with the submerged macrophyte (Myriophyllum spicatum L.) by determining the plant's biomass and some physiological indexes, such as chlorophyll (Chl) content, malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity in the leaves of M. spicatum L. on days 7, 14, 21, and 28, which are based on three groups of nitrogen and phosphorus levels in the water body (N-P [mg L-1]: NP1 0.5-0.05, NP2 2.5-0.25, NP3 4.5-0.45) and two levels of epiphytic algae (the epiphytic algae group and the control group). Epiphytic algal biomass was also assayed. The results indicated that epiphytic algal biomass remarkably enhanced in the course of the experiment with elevated levels of nitrogen and phosphorus in the water. Under the same level of nutrient condition, plants' biomass accumulation and Chl content were higher in the control group than that in the epiphytic algae group, respectively, while MDA content and SOD activity in the former were lower than that in the latter. The influences of epiphytic algae on the biomass accumulation and Chl content and MDA content became greater and greater with elevated levels of nutrients. In general, in this experiment, water nutrients promoted the growth of both epiphytic algae and submerged plants, while the growth of epiphytic algae hindered submerged macrophytes' growth by reducing Chl content and promoting peroxidation of membrane lipids in plants.

[Spatial and Temporal Distribution Characteristics of Different Forms of Phosphorus in Three Sorts of Rivers around Lake Taihu].

Different forms of phosphorus from the upper reaches of river to lower reaches of river in nine rivers were analyzed to clarify the pollution characteristics of industrial effluent, agriculture effluent and sanitary wastewater to Lake Taihu in February (low water period), May (average water period) and August (abundant water period) of 2009. The results showed that total phosphorus (TP) dissolved total phosphorus (DTP) and soluble reactive phosphorus ( SRP) mass concentration all showed decreasing trend while enzymatic phosphorus (EHP) mass concentration increased with the increase of algal biomass from low water period to abundant water period. Mass concentrations of several forms of phosphorus were all the highest in the rivers impacted by sanitary wastewater, but sanitary wastewater's self-purification capabity from the upper reaches of river to lower reaches of river was the best, and the pollution to Lake Taihu was the lowest. Pollution from rivers impacted by industrial effluent was the highest. Mass concentration of EHP was higher than that of SRP in most cases, so EHP played an important role in Cyanbacterial harmful algal blooms events in Lake Taihu.

The physiological responses of Vallisneria natans to epiphytic algae with the increase of N and P concentrations in water bodies.

To reveal the mechanism of submerged plants decline in progressively eutrophicated freshwaters, physiological responses of Vallisneria natans to epiphytic algae were studied in simulation lab by measuring plant physiological indexes of chlorophyll content, malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity based on a 2 × 4 factorial design with two epiphytic conditions (with epiphytic algae and without) and four levels of N and P concentrations in water (N-P[mg.L(-1)]: 0.5, 0.05; 2.5, 0.25; 4.5, 0.45; 12.5, 1.25). Compared with control (non-presence of epiphytic algae), chlorophyll contents of V. natans were significantly decreased (p < 0.01) for the presence of epiphytic algae under any concentrations of N and P in water bodies. While the presence of epiphytic algae induced peroxidation of membrane lipids, MDA contents of V. natans had significantly increased (p < 0.05) by comparing with control. SOD activity significantly enhanced (p < 0.05) with the presence of epiphytic algae in the treatments of T2 and T3 in the whole culture process by comparing with control, sometimes reaching an extremely significant level (p < 0.01). However, in the treatments of T1 and T4, SOD activity had no obvious change with the presence of epiphytic algae (p < 0.05) by comparing with control. At the end of the experiment, the effects of epiphytic algae on chlorophyll content and SOD activity in the leaves of V. natans were increased at first and then decreased with the concentrations of N and P in water, and MDA content became higher with the increase of N and P. concentrations. Repeated measurement data testing showed that the effects of epiphytic algae on the chlorophyll content and MDA content and SOD activity were significant, respectively (p < 0.001), the effects of epiphytic algae were combining with effects of concentrations of N and P (p < 0.001), respectively, and their interaction (p < 0.001). Our observations confirmed that this prediction: the growth of epiphytic algae directly produced adverse effects on physiology of V. natans and epiphytic algal biomass were positively correlated with nutrient available in the water column.

[Variation of water quality and trophic state of Lake Tianmu, China].

Water quality survey was carried out in 2006 and 2007 in Lake Tianmu (Shahe Reservoir) of China in order to make clear the eutrophication reasons of urban lake-type reservoirs in the middle and lower reaches of Yangtze River, and then put forward the corresponding control measures for such reservoirs. The survey frequency was once a month in 2006 and once two months from May 2007 to Dec. 2007. The results indicate that total nitrogen (TN) and total phosphorus (TP) average concentrations were 1.49 mg/L and 0.06 mg/L respectively in 2006, which are 2.7 and 2 times those of 2001-2002. The average permanganate index was 3.68 mg/L in 2006 and it is a little higher than that of 2001-2002. Secchi disk depth (SD) was 1.2 m in 2006 and it is 25 cm lower than that of 2001-2002. The average algal biomass of 2006 was 46.39 mg/L. All of these show that Lake Tianmu has been situated meso-eutrophication in 2006 from the meso to meso-eutrophication in 2001-2002. Control measures of Lake Tianmu were put forward according to the joint survey results of water quality, sediments, fishery, plankton, benthos etc. in 2006, which considered exogenous, endogenesis and substance cycle of the lake ecosystem in together. The measures pointed out that it was needed to control the pollution of agriculture, river, tourism, soil and water erosion as well as fishery etc. in order to increase SD of the reservoirs. TN and TP average concentrations in 2007 were 1.25 mg/L and 0.05 mg/L respectively, and the average algal biomass of 2007 was 22.56 mg/L. Water quality variation between 2006 and 2007 showed that the control measures had effect on reducing nutrients contents and phytoplankton biomass of the lake.

[Release of colloidal N and P from sediment of lake caused by continuing hydrodynamic disturbance].

The course of continuing hydrodynamic disturbance and succeeding long time settlement of lake water was simulated to study the release of nitrogen (N) and phosphorus (P) from lake sediment. It was showed in the experiment that the hydrodynamic disturbance caused abundant release of particulate and colloidal phosphorus and nitrogen. The concentration of total nitrogen (TN) and total phosphorus (TP) in water reached the highest values of 2.106 mg/L and 0.272 mg/L, respectively, when the water was disturbed for 0.5 d, and the concentration of colloidal nitrogen (CN) and colloidal phosphorus (CP) in water reached the highest values of 0.452 mg/L and 0.052 mg/L, respectively, when the water was disturbed for 1 day. Then, the concentration of TN, TP, CN and CP turned to decrease despite the continuing disturbance, for the particles and colloid deposited exceeded that suspended. During the settling phase after disturbance, the bigger suspended particles deposited quickly while the tiny colloid deposited much slower, and the concentration of CN and CP did not decrease until the water was settled for 1 day. The concentration of ultra-filtrated dissolved nitrogen (UDN) and ultra-filtrated dissolved phosphorus (UDP) increased much more in the settling phase than in the disturbing phase. It can be drawn that the adsorption of colloid limited the increase of dissolved N and P in lake water in the disturbing phase and prolonged the time of suspended N and P stayed in water. And the N and P adsorbed by colloid could also be released into water in the settling phase after disturbance, which delayed the elimination of nutrition and improvement of water quality.