Julie K. Cronk

Macrophyte productivity and community development in created freshwater wetlands under experimental hydrological conditions

Abstract Macrophyte biomass production and species richness were monitored from 1988 through 1991 in four freshwater wetlands constructed on the floodpain of the Des Plaines River, Lake County, Illinois, USA. The wetlands were constructed in 1988 and pumping of river water began in 1989 under two differentd hydrologic regimes: two wetlands received high water inflow (equivalent to 40 cm wk −1 of water depth) and two received low flow (11 cm wk −1 ). Biomass production showed no relationship to the hydrologic inflows after two years of experimentation, with both the highest and lowest production occuring in low flow wetlands. Rates of primary production increased between 1990 and 1991 under low flow conditions and decreased under high flow conditions, primarily as a result of the initial composition of the plant community. The change from dry conditions in 1988 to flooded conditions in 1989 altered the species composition in each wetland to include almost 100% wetland-adapted species. Similarity in species composition among the four wetlands diverged from 1988 to 1989 as the plant community adjusted to flooded conditions and then converged in both 1990 and 1991 as the wetlands developed.

Aquatic metabolism in four newly constructed freshwater wetlands with different hydrologic inputs

To determine the effect of two different hydrologic flows on aquatic metabolism in constructed freshwater riparian marshes, we measured diurnal changes in dissolved oxygen concentrations during two growing seasons. Average gross primary productivity of water column producers (phytoplankton, periphyton, and submerged macrophytes), estimated from the daily shift in dissolved oxygen concentration, was generally higher in the high-flow wetlands (84 kJ m−2 d−1 in 1990; 69 kJ m−2 d−1 in 1991) than in the low-flow wetlands (73 kJ m−2 d−1 in 1990; 46 kJ m−2 d−1 in 1991). Detailed comparisons of one high-flow and one low-flow wetland at 16 sample sites in each wetland twice the solar efficiency in the high-flow wetland (0.6 vs. 0.3%). Depth profiles indicated that the dissolved oxygen concentration decreased by as much as 60% from 15 cm below the waters surface to 50 cm below. Chlorophyll a concentration did not correlate to productivity. Water column primary producers contributed an estimated 17 to 67% of the net aboveground carbon production of each wetland.

Periphyton productivity on artificial and natural surfaces in constructed freshwater wetlands under different hydrologic regimes

Four constructed freshwater marshes in midwestern USA were subjected to two hydrologic regimes of turbid river water. Two wetlands (high flow) received 41 cm of water depth per week and the other two wetlands (low flow) received 6–9 cm week. Periphyton samplers near the inflow and outflow of all four wetlands measured dry weight, organic dry weight and chlorophyll a every 2 weeks for one growing season. We also estimated periphyton growth on the dominant macrophytes (Polygonum amphibium L., Polygonum pennsylvanicum L., Phalaris arundinacea L., Typha angustifolia L. and Typha latifolia L.) three times in all four wetlands. Periphyton growth on artificial surfaces was higher in the high flow wetlands (P<0.10). Inflow samplers in all wetlands had higher average chlorophyll a (0.4 vs. 0.2 μg cm−2), dry weight (3.0 vs. 1.0 mg cm−2) and organic dry weight (0.7 vs. 0.4 mg cm−2) than outflow samplers (P<0.10). Epiphyte chlorophyll a, dry weight and organic dry weight, were highest on Polygonum spp. and lowest on Typha spp. (P<0.10). Net epiphyte productivity ranged from 2 to 85 g carbon m−2 per year and was highest in a high flow wetland. Higher productivity in high flow wetlands and near the inflow was attributed to higher nutrient availability.

Ecological engineering - contrasting experiences in China with the West

Abstract Ecological engineering is a concept which has been used informally in China for centuries and formally for the past 25 years. A definition of ecological engineering in China is “…a specially designed system of production process in which the principles of the species symbiosis and the cycling and regeneration of subtances in an ecological system are applied…” Specific case studies in China are described for agro-ecological engineering (over 2000 sites in China), integrated fish ponds, water pollution control, salt marsh restoration, and wetland management. Differences between Western and Chinese systems relate to design principles, objectives, human manipulation of ecosystem structure, and recognized values and economics.

EFFECTIVE MODELLING OF A MAJOR INLAND OIL SPILL ON THE OHIO RIVER

Abstract A model of a large (2700 m 3 ) inland oil spill on the Monongahela/Ohio River System, U.S.A. on 2 January 1988 is developed to estimate the fate and transport time of the oil for 600 km downstream. The emphasis is on developing an effective modelling procedure that balances accuracy with simplicity, is user friendly, and is easily applicable to future spills. Model calibration with oil concentration data suggests that loss of oil due to sedimentation was important. After calibration, the model estimates that 1400 m 3 or 52% of the spilled oil ended up in the sediments, most of it in the first few reservoir pools along the river. Both the model and field data agree on similar peak concentrations of oil of between 1.0 and 2.5 ppm (by volume) in the river pools between 130 and 240 km downstream of the spill. The model was further validated by comparing the output with the actual time of travel of the oil spill. Other simulations include the use of resuspension of oil during high flow conditions and an investigation of the role of storms on the time of travel of the oil spill. Model results suggest that the location of the most significant ecological impact was not at the spill site but was between 130 and 240 km further downstream of the greater exposure time there.