Oliver Gabriel

Lake restoration by hypolimnetic Ca(OH)2 treatment: impact on phosphorus sedimentation and release from sediment.

A whole-lake hypolimnetic Ca(OH)(2) addition, that induced calcium carbonate precipitation, combined with deep water aeration has been applied to eutrophic Lake Luzin, Germany during 1996-1998. In this study we investigated the dynamic of phosphorus and its binding forms in seston and sediment before and during the treatment. The sedimentation rates of phosphorus increased within three years of induced calcite precipitation. The phosphorus binding forms shifted to the calcite-bound phosphorus in the settling matter. The increase of calcite-bound P in the settling material did not coincide with the maximum induced CaCO(3)-precipitation caused by the hypolimnetic addition of Ca(OH)(2). An impact of chemicals additions and pH on phosphorus binding forms in seston and surface sediments has been studied in laboratory experiments with sediment core incubations and slurry experiments. Laboratory studies showed that the lowest phosphorus flux from sediment was related to the experiment with pH=7 in overlaying water adjusted with Ca(OH)(2). The adjusting of pH with Ca(OH)(2) leads to a lower P flux of 2.3 mg Pm(-2)d(-1), while the highest P-flux is attributed to the experiment with the pH which was adjusted with NaOH. Phosphorus fraction which reflects phosphorus binding on carbonates in surface sediments increased within one year of treatment, enhancing the phosphorus retention capacity of sediments.

Sink or source? - The effect of hydrology on phosphorus release in the cultivated riverine wetland Spreewald (Germany)

The cultivated riverine wetland region Spreewald faces detrimental changes in the hydrological conditions due to a significant discharge reduction. With its dense network of impounded waterways and a forced tendency of sedimentation of soluble reactive phosphorus adsorbed to large amounts of FeOH/FeOOH available from mining water and groundwater discharges the 320 km2 region is favoured to accumulate large amounts of total phosphorus (TR) and thus act as an effective phosphorus sink. The change of conditions strongly challenges this function hereafter. This is especially important because eutrophication of lakes downstream the Spreewald region is controlled by phosphorus. Phosphorus balances at a testfield situated in a polder area typical for the central Spreewald region point out that hydrological and consequently hydraulic conditions are the key factors for the phosphorus sink or source behaviour. This is true for the main processes determine P retention and release at the sediment-surface water transition zone as well as for the dominant phosphorus release and retention pathways: groundwater emissions and sedimentation. In the context of hydrological changes in the Spree river catchment results from point scale and river reach scale point out the need for an adapted water management in the Spreewald region to prevent risk of extended eutrophication tendencies downstream due to forced SRP emissions.

Screening of prevailing processes that drive surface water quality of running waters in a cultivated wetland region of Germany - a multivariate approach.

The Spreewald wetland is a large, peaty, inland delta wetland in which the water level is managed by weirs in cascade belts across an extensive, partly channelized running water system. To model the quality of the water, 946 surface water samples from 43 sites were analyzed for 29 water quality parameters in two monitoring programs spanning a period of six years. In this study, we pursued a multivariate approach using nonlinear principal component analysis (Isomap) to identify the prevailing processes that control the water quality of the complex surface water system. The first four principal components explained 79% of the variance in the dataset. These components were interpreted as anthropogenic impact factors, such as groundwater exfiltration from degraded peat areas and the influence of coal mining drainage with respect to SO(4), as well as groundwater exfiltration from mineral aquifers, and phytoplankton growth and competition. A sub-area of the Spreewald wetland, characterized by a sandy aquifer overlain by degraded peat, had the greatest impact on downstream surface water quality for most of the investigated parameters. In order to achieve better water quality in the Spreewald wetland, pollutant input - particularly SO(4) input from the tributaries - must be controlled by enhancing the wetlands buffer capacity in the catchment, and peat mineralization and groundwater exfiltration must be minimized by raising the water table of the peatland area and receiving waters. The results show that Isomap is a very powerful tool for gaining a better insight into the dominating processes defining the surface water quality of complex wetland systems. Nevertheless, to be able to draw the right conclusions from multivariate statistical approaches such as Isomap it is necessary to possess basic knowledge of the structure of the system and of the processes that may occur.

Foam formation on an Austrian–Hungarian lowland river: reasons, methods and solutions

The occurrence of foam in a lowland river in Austria and shortly after the border with Hungary and the consequent protests from Hungarian inhabitants led to investigations concerning the reasons for foam formation. The aims of the study were (i) to specify objectively the scale of appearing of foam, (ii) to evaluate reasons for foam formation, and (iii) to develop abatement measures.

Upgrading Vienna's wastewater treatment plant – linking point source emissions to Environmental Quality Standards

The new water quality protection approach of the EU combines the control of emissions with instream Environmental Quality Standards (=EQS). Since 1 April 2006 and actually relevant in the version of 2010 in Austria, priority substances from list A of the EUROPEAN DIERECTIVE 76/464 and further EQS of relevant chemical substances (list B), identified by a national risk assessment, have to be reached to achieve a good ecological state in the surface water (Edict for Water Quality Standards, 2006; changes to the Edict for Water Quality Standards 2010). The practical assessment of these substances after point source emissions is prescribed in the Edict, but rarely carried out. In this paper, two substances, namely: (1) ammonium (list B); and (2) nonylphenol, an endocrine disrupting compound (list A) are presented to discuss: (i) the improvement of treatment efficiency due to the upgrade of a large Waste Water Treatment Plant (=WWTP); (ii) the relevance of mixing processes and modelling as a method to control EQS after point source emissions; and (iii) the improvement of water quality in the ambient surface waters. It is shown that the improved treatment in the case of nonylphenol leads to emission values which fall below the EQS, making an assessment unnecessary. In the case of ammonium emission, values are significantly reduced and violation of EQS is avoided, while mixing modelling is shown to be a suitable instrument to address the resulting instream concentrations at different border conditions.