Impacts of Animal Herbivory and Water Depth on Seed Germination and Seedling Survival of Vallisneria natans (Lour.) Hara and Hydrilla verticillata (L. f.) Royle

Seed germination is an important reproductive pattern for submerged macrophytes. In order to investigate the effects of animal herbivory and water depth on seed germination and seedling survival of Vallisneria natans and Hydrilla verticillata, we conducted an in-situ field experiment at 3 water depths (0.5, 1, and 2 m) with net and non-net (control) groups in Hangzhou West Lake, China. The results showed that the highest germination rates appeared at 1 m water depth and the lowest germination rates appeared at 2 m water depth (p&lt;0.05) for both species. The mean time to germination (MTG) values that indicate the velocity of germination are greater at 2 m water depth than that at 0.5 m and 1 m water depths for both V. natans and H. verticillata. Net protection obviously promoted germination rates of both species at 0.5 m and 1 m depths, especially for H. verticillata at 1 m (p&lt;0.05). Germination rates of H. verticillata were higher than that of V. natans under any treatment (p&lt;0.05). In the control, seedlings of both species were greatly grazed by herbivorous animals and the remaining seedling number showed no significant difference at different depths (p&gt;0.05). Remaining seedling number in net group was significantly higher than that in control group (p&lt;0.05). Grazing rate of H. verticillata was significantly higher than that of V. natans in control group at all 3 depths (p&lt;0.05). Conclusively, both water depth and animal herbivory significantly influenced germination of V. natans and H. verticillata, and net protection proved to be an efficient method that could promote seedling survival for both species in the field.</p

Aluminum distribution heterogeneity and relationship with nitrogen, phosphorus and humic acid content in the eutrophic lake sediment

Increasing amount of aluminum (Al) gets into aquatic ecosystem through anthropogenic activity, but the knowledge about Al migration and relationships with sediments possessing different physico-chemical properties in eutrophic lakes is limited. Here, the Al migration rule and relationships with sediment nutritions in the Hangzhou West Lake, China was investigated, where a certain amount of residual Al-salts can enter because of the pre-treatment of the Qiantang River diversion project every day. Results revealed the obvious spatial distribution heterogeneity of Al in sediment vertical direction and horizontal direction following water flow. The Al content in sediment ranged 0.463-1.154 g kg(-1) in Maojiabu Lake, and ranged 9.862-40.442 g kg(-1) in Xiaonanhu Lake. Higher Al content distributed in upper layer sediment in lake with more disturbance. Total nitrogen (TN) contents were higher 0.917-3.387 mg g(-1) and 0.627-0.786 mg g(-1) in upper layer sediment than that in lower layer in Maojiabu Lake and Xiaonanhu Lake, respectively. Total phosphorus (TP) content ranged 0.779-2.580 mg g(-1), in which IP and Fe/Al-P contributed 24.9-80.8% and 17.0-51.6%, respectively. Correlations between Al content with nutrition, humic acid (HA) etc. of sediment regionally varied in Maojiabu and Xiaonanhu Lake. Spatial distribution of Al-salt in eutrophic lakes closely related with the physico-chemical characteristics of nutrients, humus, human disturbance and water division parameters. Results provides new insight into Al-salts migration and references for Al-risk evaluating in eutrophic lakes. (C) 2019 Elsevier Ltd. All rights reserved

Factors affecting palatability of four submerged macrophytes for grass carp Ctenopharyngodon idella

Grass carp can weaken the growth and reproductive capacity of submerged macrophytes by consuming valuable tissues, but factors affecting palatability of submerged macrophytes for grass carp rarely are considered. In this study, relative consumption rate of grass carp with regard to submerged macrophytes was in the following order: Hydrilla verticillata &gt; Vallisneria natans &gt; Ceratophyllum demersum &gt; Myriophyllum spicatum. Firmness of macrophytes was in the following order: M. spicatum &gt; C. demersum &gt; H. verticillata = V. natans, whereas shear force was M. spicatum &gt; C. demersum &gt; H. verticillata &gt; V. natans. After crude extracts of M. spicatum were combined with H. verticillata, grass carp fed on fewer macrophyte pellets that contained more plant secondary metabolites (PSMs). This indicated that structure and PSMs affected palatability of macrophytes. PSMs do not contribute to reduction in palatability through inhibition of intestinal proteinases activity, but they can cause a decrease in the abundance of Exiguobacterium, Acinetobacter-yielding proteases, lipases, and cellulose activity, which in turn can weaken the metabolic capacity of grass carp and adversely affect their growth. Thus, the disadvantages to the growth and development of grass carp caused by PSMs may drive grass carp to feed on palatable submerged macrophytes with lower PSMs

Determinants of submerged macrophytes palatability to grass carp Ctenopharyngodon idellus

Submerged macrophytes reestablishment is one of key processes in restoration of water ecological system. However, adverse effect caused by grass carp on macrophyte communities is existed during the process of ecological restoration. At present, little is known about determinants of submerged macrophytes palatability to grass carp. In this study, we measured the relative consumption rates (RCR) of grass carp on four species of submerged macrophytes Hydrllla verticillata, Vallisneria natans, Ceratophyllum demersum, and Myriophyllum spicatum, analysed the correlation between macrophytes traits and RCR, then investigated the kinds of flavonoids in four species of submerged macrophytes and their effects on the palatability for grass carp. The results showed that RCR of grass carp on H. verticillata and V. natans were much higher than C. demersum and M. spicatum. And for each submerged macrophyte, RCR of grass carp declined in the order of July &gt; October &gt; May. Stepwise multiple liner regression analyses showed that water temperature and protein were positively correlated, and flavonoids were negatively correlated, with RCR of grass carp. Rutin, quercitrin, quercetin and kaempferol, as the typical kinds of flavonoids, were in different contents in four kinds of macrophytes. And rutin, quercetin and kaempferol can deter grass carp feeding. These results conducted that grass carp favoured macrophytes with high protein and ate less macrophytes with high flavonoids. And it is helpful to provide fundamental basis for administrators to select appropriate macrophytes in restoration of water ecological system

Effects of aluminate flocculant on turion germination and seedling growth of Potamogeton crispus

Aluminate flocculants are employed widely in water treatment for precipitating suspended solids and emergency treatment of algal blooms in eutrophic lake, but the residual aluminum (Al) may have phytotoxic effects on aquatic organisms after entering aquatic ecosystems. To elucidate the potential impacts of Al on turion germination and early growth in Potamogeton crispus, we conducted a mesocosm experiment using five Al concentrations (0 (control group), 0.3, 0.6, 1.2, and 1.5 mg/L) in alum solutions. The results showed that the germination of turions and the early growth of P. crispus were reduced and inhibited by Al. The maximum numbers of germinating turions and newly-formed seedlings occurred in the control group, and their numbers declined in the end of the experiment as the Al concentration increased. Al at a concentration of 1.5 mg/L decreased the number of germinating turions 3.0 times and the number of newly-formed seedlings 30.7 times compared with the control. The chlorophyll content and root activity decreased when the Al concentration increased. The maximum soluble protein contents in seedling tissues (1.953 mg/g fresh weight) occurred in the 0.6 mg/L treatment group, which differed significantly from the other treatment groups. The Al contents in the seedling tissues had a significant positive correlation with the Al treatment concentrations (P &lt; 0.05, r = 0.763), but negative correlations with the biomass, root number, stem weight, soluble protein, and root activity (r = -0.935, -0.975, -0.907, -0.721, -0.944, respectively). Persistent Al concentration 1.2 mg/L significantly decreased the germination of turions and seedling growth in P. crisp us. These results may facilitate the restoration of aquatic macrophytes and ecological risk assessments in Al-exposed lakes

Investigation on the adsorption of phosphorus in all fractions from sediment by modified maifanite

Sediment phosphorus (P) removal is crucial for the control of eutrophication, and the in-situ adsorption is an essential technique. In this study, modified maifanite (MMF) prepared by acidification, alkalization, salinization, calcination and combined modifications, respectively, were first applied to treat sediment P. The morphology and microstructure of MMF samples were characterized by X-ray fluorescence (XRF), Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET). Various adsorption parameters were tested, such as dosage of maifanite, time, operation pH and temperature. The adsorption mechanisms were also investigated and discussed. Results showed that CMMF-H2.5-400 (2.5 mol/L H2SO4 and calcined at 400 degrees C) exhibited the highest P adsorption capacity. Thus, it was selected as the in-situ adsorbent material to control the internal P loading. Under the optimal conditions of dynamic experiments, the adsorption rates of TP, IP, OP, Fe/Al-P and Ca-P by CMMF-H2.5-400 were 37.22%, 44.41%, 25.54%, 26.09% and 60.34%, respectively. The adsorption mechanisms analysis revealed that the adsorption of P onto CMMF-H2.5-400 mainly by ligand exchange. Results of this work indicated that the modification treatment could improve the adsorption capacity of maifanite, and CMMF-H2.5-400 could be further applied to eutrophication treatment

The Biomass and Physiological Responses of Vallisneria natans (Lour.) Hara to Epiphytic Algae and Different Nitrate-N Concentrations in the Water Column

Increasing N concentration and the high density of epiphytic algae are both key factors leading to the decline of submerged macrophytes in many eutrophic lakes. In order to investigate the impacts of increased nitrate-N concentration and the growth of epiphytic algae on the decline of submerged vegetation, we conducted a 2 x 4 factorial experiment with the submerged macrophyte Vallisneria natans (Lour.) Hara by measuring the biomass of plants and some physiological indexes in leaves of V. natans under four nitrate-N concentrations in the water column (0.5, 2.5, 5, and 10 mg/L) and two epiphytic groups (epiphytic algae group and no epiphytic algae group). The results suggested that epiphytic algae could impose adverse effects on the biomass accumulation of V. natans, while the increasing nitrate-N concentration (0.5-10 mg/L) could oppositely promote this process and counteract the adverse effect of epiphytic algae. When nitrate-N concentration was 5 mg/L, the total chlorophyll content in leaves of V. natans in the epiphytic algae group was prominently lower compared with the no epiphytic algae group, while MDA, free proline, and anti-oxidant enzyme (SOD, POD, CAT) activities were significantly higher. Overhigh nitrate-N concentration in the water column also directly imposed adverse effects on the physiology of V. natans. When nitrate-N concentration was over 5 mg/L, the total chlorophyll content and free proline decreased in the no epiphytic algae group, while soluble carbohydrates and soluble proteins decreased when nitrate-N was over 2.5 mg/L. Meanwhile, epiphytic algae and nitrate-N content imposed a synergetic effect on the anti-oxidant enzyme activities of V. natans. When nitrate-N concentration was over 5 mg/L, SOD, POD, and CAT activities kept constant or decreased, which indicated that the oxidation resistance of V. natans was inhibited by stress. Our results indicate that epiphytic algae and increasing nitrate-N concentration in the water column could severally or synergistically impose adverse effects on the physiology of submerged macrophytes and are both key factors leading to the decline of submerged macrophytes

Upslope inflow, hillslope gradient and rainfall intensity impacts on ephemeral gully erosion

Ephemeral gullies (EGs) are major contributors to sediment loss and land degradation on cultivated lands. However, the topography and rainfall impacts on EG development processes are still unclear, especially on steep loessial hillslopes such as the Loess Plateau. A series of laboratory rainfall simulation experiments were conducted to investigate the impacts of topographic characteristics (3 typical slope gradients (S): 26.8%, 36.4%, and 46.6%; and 5 upslope drainage areas (A): 16, 32, 64, 96, and 128m(2)) and rainfall intensities (3 representative erosive rainfall intensities 50, 75, and 100mmhr(-1)) on EG erosion on a steep loessial hillslope. A large slope adjustable soil pan (8m-long, 2m-wide, and 0.6m-deep) and a side-sprinkler rainfall simulation system were used in this study. The results showed that soil loss increased when rainfall intensity, slope, and upslope drainage area increased. Upslope topography and inflow had great impacts on downslope EG erosion, and the contribution percentages ranged from 52.2% to 74.1%, from 48.3% to 71.4%, and from 29.5% to 66.7% for the 50, 75, and 100mmhr(-1) rainfall treatments, respectively. Runoff velocities with upslope inflow were 22.7% to 79.4% larger than those without inflow, and the upslope inflow was more effective than rainfall intensity in increasing runoff velocities in EG channels, thus caused more soil erosion. Soil loss equation based on rainfall intensity and AS(2) (product of the upslope drainage area and the square of the local slope gradient) was established and validated. The determination coefficient (R-2) and Nash-Sutcliffe simulation efficiency (E-NS) were 0.80 and 0.87, which showed satisfactory accuracy. This equation can be used to predict the EG erosion in various topographic and rainfall conditions on steep loessial hillslopes