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Many lakes have experienced a transition from a clear into a turbid state without macrophyte growth due to eutrophication.
There are several measures by which nitrogen (N) and phosphorus (P) concentrations in the surface water can be reduced. We
used the shallow lake model PCLake to evaluate the effects of three measures (reducing external nutrient loading, increasing
relative marsh area, and increasing exchange rate between open water and marsh) on water quality improvement. Furthermore,
the contribution of different retention processes was calculated. Settling and burial contributed more to nutrient retention
than denitrification. The model runs for a typical shallow lake in The Netherlands showed that after increasing relative marsh
area to 50%, total phosphorous (TP) concentration in the surface water was lower than the Maximum Admissible Risk (MAR, a
Dutch government water quality standard) level, in contrast to total nitrogen (TN) concentration. The MAR levels could also
be achieved by reducing N and P load. However, reduction of nutrient concentrations to MAR levels did not result in a clear
lake state with submerged vegetation. Only a combination of a more drastic reduction of the present nutrient loading, in combination
with a relatively large marsh cover (approximately 50%) would lead to such a clear state. We therefore concluded that littoral
marsh areas can make a small but significant contribution to lake recovery. 相似文献
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Hauke Reuter Ulrike Middelhoff Frieder Graef Richard Verhoeven Thomas Batz Martin Weis Gunther Schmidt Winfried Schröder Broder Breckling 《Environmental science and pollution research international》2010,17(8):1479-1490
Background, aim and scope
European legislation stipulates that genetically modified organisms (GMO) have to be monitored to identify potential adverse environmental effects. A wealth of different types of monitoring data from various sources including existing environmental monitoring programmes is expected to accumulate. This requires an information system to efficiently structure, process and evaluate the monitoring data. 相似文献3.
Cohesive sediments besides their typical heterogeneity are characterised by structural discontinuity. Particularly, organic
consolidated muds are a good example of sediments that consist of vast aggregates, pore water and gaseous products. The texture
of a cohesive sediment bed is a result of a number of mutually affecting factors, such as deposition history, mineral and
organic composition, kind of biota and oxygen uptake. The presented work attempts to quantify the effect of sediment physical
properties and sediments structure on the sediment erosion potential, considering incipient motion and erosion rate. This
quantification is made on the basis of comparative testing of both unremoulded and remoulded samples of a river mud. Due attention
is paid to sediment handling to preserve the delicate structure of the sediment for the laboratory experiments. Mud with two
degrees of consolidation has been examined in a tilting flume under different flow situations. The test results show a typical
increase of erosion strength with dry matter concentration of the mud. It has also been found that the structural properties
increase the erosion strength for the less consolidated mud. An opposite effect has been recorded for a more consolidated
deposit. As a consequence, due to the sediment structure, the original beds differ much less in erosion resistance in relation
to the dry mass concentration than their disturbed analogues. Finally, the erosion resistance of the examined mud is compared
with data from the literature. 相似文献
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Sonneveld MP Schröder JJ de Vos JA Monteny GJ Mosquera J Hol JM Lantinga EA Verhoeven FP Bouma J 《Journal of environmental quality》2008,37(1):186-195
Dutch regulations for ammonia emission require farmers to inject slurry into the soil (shallow) or to apply it in narrow bands at the surface. For one commercial dairy farm in the Netherlands it was hypothesized that its alternative farming strategy, including low-protein feeding and surface spreading, could be an equally effective tool for ammonia emission abatement. The overall objective of the research was to investigate how management at this farm is related to nitrogen (N) losses to the environment, including groundwater and surface water. Gaseous emission of ammonia and greenhouse gasses from the naturally ventilated stables were 8.1 and 3.1 kg yr(-1) AU(-1) on average using the internal tracer (SF(6))-ratio method. Measurements on volatilization of ammonia from slurry application to the field using an integrated horizontal flux method and the micrometeorological mass balance method yielded relatively low values of ammonia emissions per ha (3.5-10.9 kg NH(3)-N ha(-1)). The mean nitrate concentration in the upper ground water was 6.7 mg L(-1) for 2004 and 3.0 mg L(-1) for 2005, and the half-year summer means of N in surface water were 2.3 mg N L(-1) and 3.4 mg N L(-1) for 2004 and 2005, respectively. Using a nutrient budget model for this farm, partly based on these findings, it was found that the calculated ammonia loss per ton milk (range 5.3-7.5 kg N Mg(-1)) is comparable with the estimated ammonia loss of a conventional farm that applies animal slurry using prescribed technologies. 相似文献
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Determination of the Manning roughness coefficient influenced by vegetation in the river Aa and Biebrza river 总被引:1,自引:0,他引:1
L. De Doncker P. Troch R. Verhoeven K. Bal P. Meire J. Quintelier 《Environmental Fluid Mechanics》2009,9(5):549-567
The aim of this study was to investigate the variation of channel bed roughness in two rivers, as important parameter in hydraulic
modelling especially with regard to flood control. The universities of Ghent (UG) and Antwerp (UA) are conducting scientific
research in the river Aa in Belgium and the Biebrza river in Poland in order to better understand the phenomena involved and
to come to a more accurate determination of the different parameters influencing flow. In this paper, the determination of
the roughness coefficient ‘n’ from the Manning equation is used. This coefficient is not easy to determine and is varying constantly. It is influenced
by the meandering character of the river, the bed material and the average grain size, the channel bed forms, the channel
obstructions, the geometry changes between sections and the vegetation in the channel. Furthermore, due to these parameters,
the roughness of the channel is not equally distributed over the channel, the banks and the floodplains. So, using literature
data does not always lead to satisfactory results, due to the different situation in the field (Werner et al. J Hydrol 314:139–157,
2005). Therefore, measurements are necessary to determine the variation of the Manning coefficient. The Manning coefficient
is a function of the discharge, but will also vary over the time due to the mentioned influences. In a multidisciplinary research
project on the fundamental exchange processes in river ecosystems, hydraulic measurements were performed on a regular base
in the river Aa. During these measurement campaigns, velocity and discharge measurements were carried out in multiple cross-sections.
Once a month, the discharge and the water levels were measured at the upstream and the downstream end of the test stretch.
On the river Biebrza, similar intensive measurement campaigns took place along a 6 km stretch in the upstream part of the
river. An accurate determination of the Manning coefficient according a seasonal variation is an important tool in hydraulic
modelling. 相似文献
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