The Dutch Delta Region (S-W Netherlands) originally consisted of interconnected estuaries, interfacing the rivers Rhine, Meuse
and Schelde with the North Sea. The ecosystems were immature, with physical rather than biological control of population dynamics.
Main functions were shipping and shellfisheries. An emergent function of the interconnected estuaries was the buffering and
upgrading of river-borne substances before they entered the sea.
Execution of the Delta Project in the period 1960–1986 resulted in isolation of several water systems disconnected from rivers
and sea, and loss of gradients within these systems. Population dynamics were now controlled by chemical and biological rather
than physical factors. Vulnerability to external perturbation increased. These changes also affected the buffering capacity,
i.e. reduced the utility of the area as stabiliser of the geosystem. Recreational use and appreciation of natural values increased,
potentially conflicting with shipping and shellfisheries.
Retrospective analysis of the environmental policy and management revealed three consecutive strategies in the Delta Project.
1. Reactive one-issue management, focusing on safety against flooding only. This strategy aimed at complete closure of the
estuaries thus transforming them into fresh water lakes. It has destroyed feed-backs and buffering between coastal and inland
waters. This strategy has not promoted sustainable development and has increased the vulnerability of the area to future catastrophes.
2. Protective bio-ecological management focused on the preservation of existing values of landscape and environment, and resulted
in the maintenance of saline conditions and preservation of marshes by shore protection measures. The drawback of this passive
orientation to existing values ?where they are now? is the necessity of continuous intensive care because the natural adaptive
ability is not being restored. 3. Constructive geo-ecological management is based on understanding functional properties within
and between ecosystems as integrated elements of the landscape structure. This strategy aims at environmental protection,
restoration and development of values ?where they must be?. Re-establishment of gradients by e.g. re-introducing tidal influence
and by restoring salt marshes should contribute to sustainable development. 相似文献
Effects of elevated N deposition on forest aboveground biomass were evaluated using long-term data from N addition experiments and from forest observation plots in Switzerland. N addition experiments with saplings were established both on calcareous and on acidic soils, in 3 plots with Fagus sylvatica and in 4 plots with Picea abies. The treatments were conducted during 15 years and consisted of additions of dry NH4NO3 at rates of 0, 10, 20, 40, 80, and 160 kg N ha−1 yr−1. The same tree species were observed in permanent forest observation plots covering the time span between 1984 and 2007, at modeled N deposition rates of 12-46 kg N ha−1 yr−1. Experimental N addition resulted in either no change or in a decreased shoot growth and in a reduced phosphorus concentration in the foliage in all experimental plots. In the forest, a decrease of foliar P concentration was observed between 1984 and 2007, resulting in insufficient concentrations in 71% and 67% of the Fagus and Picea plots, respectively, and in an increasing N:P ratio in Fagus. Stem increment decreased during the observation period even if corrected for age. Forest observations suggest an increasing P limitation in Swiss forests especially in Fagus which is accompanied by a growth decrease whereas the N addition experiments support the hypothesis that elevated N deposition is an important cause for this development. 相似文献
For biological nitrogen (N) removal from wastewater, a sufficient organic carbon source is requested for denitrification. However, the organic carbon/nitrogen ratio in municipal wastewater is becoming lower in recent years, which increases the demand for the addition of external organic carbon, e.g. methanol, in wastewater treatment. The volatile fatty acids (VFAs) produced by acidogenic fermentation of sewage sludge can be an attractive alternative for methanol. Chemically enhanced primary sedimentation (CEPS) is an effective process that applies chemical coagulants to enhance the removal of organic pollutants and phosphorus from wastewater by sedimentation. In terms of the chemical and biological characteristics, the CEPS sludge is considerably different from the conventional primary and secondary sludge. In the present study, FeCl3 and PACl (polyaluminum chloride) were used as the coagulants for CEPS treatment of raw sewage. The derived CEPS sludge (Fe-sludge and Al-sludge) was then processed with mesophilic acidogenic fermentation to hydrolyse the solid organics and produce VFAs for organic carbon recovery, and the sludge acidogenesis efficiency was compared with that of the conventional primary sludge and secondary sludge. The results showed that the Fe-sludge exhibited the highest hydrolysis and acidogenesis efficiency, while the Al-sludge and secondary sludge had lower hydrolysis efficiency than that of primary sludge. Utilizing the Fe-sludge fermentation liquid as the carbon source for denitrification, more than 99% of nitrate removal was achieved in the main-stream wastewater treatment without any external carbon addition, instead of 35% obtained from the conventional process of primary sedimentation followed by the oxic/anoxic (O/A) treatment.
A study was conducted to evaluate the performance of six advanced wastewater treatment facilities using biological nutrient removal processes as the primary mechanism for removing carbon, nitrogen, and phosphorus from domestic wastewater. One year of operating data was obtained from monthly operating reports provided by the Georgia Environmental Protection Division (EPD) in Atlanta. Additional information about facility operations and the types of chemicals used was gathered through review of EPD files and interviews with plant personnel. Data evaluated were: influent and effluent five-day Biochemical Oxygen Demand (BOD(5)); influent and effluent total suspended solids (TSS); influent Total Kjeldahl Nitrogen and effluent Total Nitrogen; and influent and effluent Total Phosphorus (TP). Although varying from plant to plant, effluent requirements for BOD(5), TSS, ammonia, and TP were met. Chemicals utilized, design capacity, and monthly effluent concentrations are presented in this study. 相似文献
Carbohydrate acid amides, diamides and polyamides have been proposed to be utilized as nitrogen plant fertilizers or fertilizer components, and experiments with Brassica rapa demonstrated a positive biological response when these compounds were used as the only source of fixed nitrogen for plant growth. The present study was carried out with the aim of elucidating the mechanism of degradation of these polymers in both soil/compost and in liquid media and the role of microorganisms in this process. The results obtained suggest that a major route of degradation of polyglucaramides in the environment is their abiotic hydrolysis/release of the diacid and diamine building block units of these polymers, which are then utilized for growth by microorganisms. In cell-free crude extracts from enrichment cultures obtained with different poly-D-glucaramides, no enzyme activities catalyzing the release of diamines from these compounds were detected. 相似文献
Parametric (propagation for normal error estimates) and nonparametric methods (bootstrap and enumeration of combinations)
to assess the uncertainty in calculated rates of nitrogen loading were compared, based on the propagation of uncertainty observed
in the variables used in the calculation. In addition, since such calculations are often based on literature surveys rather
than random replicate measurements for the site in question, error propagation was also compared using the uncertainty of
the sampled population (e.g., standard deviation) as well as the uncertainty of the mean (e.g., standard error of the mean).
Calculations for the predicted nitrogen loading to a shallow estuary (Waquoit Bay, MA) were used as an example. The previously
estimated mean loading from the watershed (5,400 ha) to Waquoit Bay (600 ha) was 23,000 kg N yr−1. The mode of a nonparametric estimate of the probability distribution differed dramatically, equaling only 70% of this mean.
Repeated observations were available for only 8 of the 16 variables used in our calculation. We estimated uncertainty in model
predictions by treating these as sample replicates. Parametric and nonparametric estimates of the standard error of the mean
loading rate were 12–14%. However, since the available data include site-to-site variability, as is often the case, standard
error may be an inappropriate measure of confidence. The standard deviations were around 38% of the loading rate. Further,
95% confidence intervals differed between the nonparametric and parametric methods, with those of the nonparametric method
arranged asymmetrically around the predicted loading rate. The disparity in magnitude and symmetry of calculated confidence
limits argue for careful consideration of the nature of the uncertainty of variables used in chained calculations. This analysis
also suggests that a nonparametric method of calculating loading rates using most frequently observed values for variables
used in loading calculations may be more appropriate than using mean values. These findings reinforce the importance of including
assessment of uncertainty when evaluating nutrient loading rates in research and planning. Risk assessment, which may need
to consider relative probability of extreme events in worst-case scenarios, will be in serious error using normal estimates,
or even the nonparametric bootstrap. A method such as our enumeration of combinations produces a more reliable distribution
of risk. 相似文献
A model of nitrogen and phosphorus cycles in the sediment of a lagoon has been developed. This model was applied to the Thau lagoon (southern France). Sediment was sliced in three layers to reproduce the oxygen profile, which is simulated within the model. Following an equilibrium hypothesis, the model was calibrated against field data. State variables and fluxes were estimated in the sediment and across the sediment-water interface. A Monte Carlo sensitivity analysis was performed to determine the most sensitive parameters and sediment state variables. A dynamic simulation with varying oxygen concentrations then showed the influence of anoxia on the phosphorus and nitrogen fluxes between water and sediment. 相似文献