Jinge Zhu

Variation in the Efficiency of Nutrient Removal in a Pilot-Scale Natural Wetland

This two-year study focused on mechanisms of nutrient removal efficiency and variation in this efficiency in a pilot-scale natural wetland with different macrophyte species. Effects of plant harvesting and the differences among plant species (Ceratophyllum demersum, Nelumbo nucifera, Zizania latifolia, Hemarthria sibirica, Phragmites communis, and Typha orientalis) were investigated. Results show that the mean retention of total nitrogen (N), total dissolved N, ammonia N, nitrite N, total phosphorus (P), total dissolved P, and phosphate P in the second year was generally lower than that found in the first year. Harvest of above-ground macrophytes had a beneficial effect on retention capacity, especially for total dissolved N and ammonia N, whereas an increase in nutrient concentration was observed in zones that were not harvested. The total N removal efficiency had a positive relationship with inflow loading. A mixture of Z. latifolia and T. orientalis demonstrated the best potential for both N and P retention.

The effects of water depth on the growth and reproduction of Potamogeton crispus in an in situ experiment

Aims Water level is one of the most important determinants of the distribution and composition of submersed aquatic vegetation in shallow lakes. Without changes in nutrient loading, large-scale declines in submerged macrophytes in shallow lakes are largely attributed to strong external or internal forces, including changes in water level. As a winter-active submerged macrophyte, Potamogeton crispus has important functions in aquatic ecosystem. The objectives of our study were to reveal the effects of water depths on the germination, growth, reproduction and morphological changes of P. crispus under natural environmental conditions; identify the optimum water depth range for colonization of P. crispus; and predict the succession course for P. crispus in Lake Taihu. Methods A long-term in situ experiment was performed to study the effects of water depth on the growth and morphology of P. crispus across the entire life cycle. Plants were grown in the improved cross type of rhizotrons for 30 weeks at three different water depths (60, 120 and 200 cm) in Dongtaihu Bay of Lake Taihu. We measured the plant height, root length, the length and width of leaves and counted the numbers of leaves, ramets, turion spikes and roots of each plant on each observation day during the experiment. Important Findings Water depths ranging from 60 to 120 cm were favourable for aboveground vegetation growth, root tissue growth and the reproductive ability of P. crispus. At water depth of 200 cm or beyond, the distribution of P. crispus will be limited in the following year because of the lack of turion formation and the severe inhibition of ramet production. The relationship between above-ground biomass and growth time at three different water depths fits a logistic growth curve well (P < 0.001). The rapid growth and distribution with high density of P. crispus at water depth near 60 cm during the reproductive stage is not favourable for growth of other submerged species. So a continuous water depth of ~60–120 cm is the optimum growth depth range for the conservation and restoration of P. crispus in Lake Taihu. In addition, the morphological parameters values acquired can replace or provide the ranges for the value of GmaxSB (the maximum growth rate of submerged plants, in the unit of d−1) obtained via calibration in the control equations of submerged plant growth in the Eco-Taihu model, which is a three-dimensional ecological model of Lake Taihu.

A new collector for in situ pore water sampling in wetland sediment

Currently available pore water samplers generally do not allow continuous monitoring of temporal variations in pore water composition. Therefore, a new type of pore water collector was designed and constructed. These collectors were constructed of polyvinyl chloride (PVC) materials, including PVC tubing with one end sealed and another end topped with a removable PVC screw-cap. A row of holes was drilled 10 cm from the sealed end of each collector. These new collectors were deployed in different layers of the sediment in a constructed wetland in Lake Taihu, China, to reveal variations in the nutrient composition of pore water with high spatial and temporal resolution. Specifically, the collectors were driven into the sediment, and the pore water flowed into the tubing via gravity. The pore water was then sampled from the PVC tubing using a portable vacuum pump, and then was taken to the lab within 20 min for analysis of the dissolved oxygen (DO) and nutrient concentration. The DO concentration of the pore water was below the detection limit for all samples, indicating that the pore water was probably not influenced by the air and that the water in the collector tube was representative of the pore water. These findings suggest that the collector is capable of measuring the temporal and spatial variations in the nutrient concentrations in pore water. Furthermore, the inexpensive material, ease of construction, minimal disturbance to the sediment and applicability for wetland sediments are advantages of the collector presented here compared with traditional pore water sampling techniques.