organized by Rafaela Schramm, Prof. Edgar Nehlsen, Dr. Kai Wellbrock, Prof. Dr. Norbert Reintjes, Prof. Dr. Christoph Külls, Dr. Ozgur Kisi, Prof. Dr. Wilfert

The conference program includes eight presentations by student groups of the MAEH supervized by Prof. Dr. Edgar Nehlsen, Dr. Kai Wellbrock, Prof. Dr. Norbert Reintjes, Prof. Dr. Christoph Külls with Dr. Ozgur Kisi

Program and list of presentations

Single case studies, no policy yet, lack of adressing small rivers. Mapping of river quality (Phase 1990-2000), Policy (2000) and Inception (2005), Implementation. There are different levels: science, technology, economy, sociology.

Technological phases: Limit, reduce pollution (laws, technology, waste water treatment, industrial water treatment, municipal water treatment), creation of legislation and administration bodies. Basin oriented management and basic data, creation of IWRM bodies, structural transformation.

Comparison of Near-Natural Watercourse Design (strategies, approaches, measures) in Germany and China: Comparison of river restoration. Two river restoration projects in Schwartau and Yangtze were compared based on a literature review and research. The key components of river restoration were introduced. The Schwartau river restoration was presented as a combination of measures including landscape remodeling, bridge redesign, ecohydrological service improvement. The Yangtze restoration project was introduced focusing on a more technological approach with river bank reconstruction (geotextiles, concrete, gravel, sand). A timeline of water governance in China was presented, starting in 4000 B.C. with King Yu the Great, continuing to largte scale engineering projects. In 2010 a paradigm shift occurred with a concept of ecological civilization (2012). River chiefs were introduced, ecology was embedded in the constitution and in 2021 the Yantse Rivere Protection Law as introduced. In Europe, after the deterioration of rivers and especially after the single event of the Sandoz accident, a paradigm shift occurred in the 1990ies (mapping), leading to the WFD and the SDGs, followed by the National Water Strategy. Democratic versus Authoritarian Environmentalism while in both contries there is a paradigm shift towards ecological governance.

Presentation on recent developments such as pilot-scale Ozonation showing a reduction of 50 % of total persistent and mobile fractions, working well against PM substances with electron -rich functional groups. The Ozonation followed by Filtration (GAC) showed 31.6 % of removal rates and was effective both PAC. The presentation included also electrical energy demand for the different measures and the cost analysis. About 25 % of the cost are electrivity cost and 50 % are personnel cost. The analysis shows that a combination of methods is best to first reduce pollutants with cheaper methods and then gradually add methods for higher efficiency in the order of their cost (ascending).

The study presents the decentralized wastewater treatment case study in Hamburg. The project was presented in contrast to a conventional urban drainage system. In these the water is centralized and transported to a treatment and discharge poiint. The JenFelder Au in contrast presents the case of a decentral treatment unit for 835 living units, 1000 households on 11 hectares that is operational since 2019. It features a partial flow treatment a) from the toilet to produce biogas with a biological treatment with a fixed bed bioreactor, b) a special filtration with an ultrafiltration membrane and c) a separation of greywater from block water.

The system is based on a separation of rainwater, blackwater and greywater. Greywater accounts for 80 % of sewwage in Germany. The blackwater treatment having a very large proportion of organic matter and requires-energy intensive purification processes. For the treatment of black water a fermentation plant can be used to form biogas by anaerobic treatment with other biomass such as organic waste. Biogas in turn can be used to gnerate renewable energy for the district.

The environmental factors and cynobacterial bloom dynamics are presented (Davis's experiment) showing the factors for blooms are higher temperature and higher growth rate leading to toxic blooms. In low N/P ratios nitrogen-fixing cynobacteria can fix nitrogen, non-nitrogen-fixing cynobacteria require a N:P ratio of 16:1 (the Redfield ratio). High temperature, hihg availabiltiy of light, high nutrient availability and long duration of blooms are critical factors. Any cooling or any flood can break the bloom duration. An overview was given using machine learning algorithms such as decision trees, random forests, and boosting techniques. A combination of sensor monitoring data is required (satellite imagery and environmental predictors). EPA has developed a Baysian modeling approach. Latest develpments are presented: a) coupling of climate change models with water quality modeling, b) individual-based modeling, c) generalized linear mixed models, d) coupling hydrodynamics and buyoancy regulation models. The mechanisms of ultrasound suppression of algae are presented affecting the regulation of buyoncy.

Potential new developments were presented as bioplastics, biofuel, medicine and agriculture.

MAAs are polyphenolic and bioactive compounds, there are about 30, contain N. The Shikimate pathway and the pentose phosphate pathway exist. They produce Macosporine-glycine. Why are MAAs important: a) block UV radiation preventing photoxidative damaging, they block Thymine-Thymine dimers, act as intracellurlar nitrogen reservoirs and aid in osmoregulation of cells within hypersaline environments. Can be harvested from prphyra umbilicalis. Production can be increased by genetic engineering and high exposure to UV light. Harvesting can be done through gravity sedimentation, preserving the integrity and being scalable, b) by floatation, which is energy-intensive, having a high efficiency, c) centrifugation offers a high efficiency and high specificity but requires a lot of energy. Finally membrane filtration requires less energy and seems to be the most suitable. All extraction methods were compared and evaluated in terms of efficiency, scalability and costs. A potential extraction method was presented: Membrane Filtration being rapid and efficient involves a sequence of microfiltration, ultrafiltration and nanofiltration resulting in a 48 % recovery of the MAAs.

Degradation of wetlands occurred for several centuries. Map of Wetland loss by Etienne Fluet-Chouinard (Nature). Main factors were agriculture, forestry, peat extraction, urbanization and wetland loss, the overall function of wetland rewetting is reconstructed by blocking channels, naturally regenerate and manage water. Rewetting causes a transitional increase of temperature due to $CH_4$ release but leads to a stabilization at lower levels. The nature of the Schaalsee region was introduced as a hot spot of biodiversity in transitional zones and ecotones. The Schaalsee region has significant land use compartments formed by bogs and fens. 72 % of land was drained, peat was mined for many years, and water was diverted to the Farchau power plant. This lead to a loss of groundwater levell and the disruption of natural hydrology due to changes in the water balance. The perspectives of rewetting were presented: Rewetting is obtained by closure of drainage ditches, dams and trenches, river renaturation. The wetland vegetation is protected by buffer strips, fences and diversion schemes. The restoration of water balance plays and important role. 1500 ha of mooreland have been restored. A methodology is presented to monitor the restoration of water balances.

Schaalsee receives 3681 kg/year of P. Several Moore restoration projects have been implemented (Neuendorf Moor, Kuhlrader Moor, Reoggendorf Moor). Project to map algal bloom dynamics in Schaalsee. Looking for a connection between water level fluctuations and algal blooms. GLDAS 2.1 was used and the Harmonized Sentinel 2 MSI Multispectral Instrument, Level-2A. An algal bloom area analysis was carried out. The algae bloom area could be visualized as a film and correlated well with water level area but less with precipitation. The algal bloom area correlates with lake water surface area. The correlation between precipitation and algal bloom area is limited to weak. Piecewise regression leads to a negative regression at a threshold of about 100 mm per month.