River Warnow Research Articles

Spatial and temporal variations in the isotope hydrobiogeochemistry of a managed river draining towards the southern Baltic Sea

The flow path of a river draining a lowland into the southern Baltic Sea, the Warnow River, was investigated to evaluate its freshwater composition and potential to be a source of dissolved substances for regional coastal waters. A spatial study was conducted in April 2019 to follow the variations from the source to the estuary. A temporal study of the composition, for five years (2017–2021), was carried out at a site just before the river reaches the estuary. Surface water was sampled to analyse major and trace elements, stable (H, C, O, S), and short-lived (Ra) isotopes. The results show that the composition of the Warnow River along the flow path is controlled by a complex interplay between in-situ processes, exchange with the atmosphere, diffuse groundwater, and surface water inlets. On a temporal scale, pH, nutrient, and redox-sensitive trace element concentrations are strongly impacted by pelagic primary production in spring. During summer and autumn, influences occurred due to benthic microbial activity, associated diffusive release from soils/sediments, and surface water inlets. Throughout the investigation period, the Warnow River was a source of isotopically light CO2 to the atmosphere and DIC to the estuarine waters. The delivered DIC concentrations seemed to vary with season due to changes in biological pelagic and benthic activities. DOC was derived from a mixture of dominated C3 organic sources and potentially from fertilizers. From concentration-discharge relationships, examples of dilution, mobilization, and chemostasis trends were found. Discharge-controlled seasonal trends were superimposed by system internal processes and the hydrological consequences of the river management. Our analysis thus provides new insights into the controls on the variations of water and solutes in a managed river at the land-sea interface as part of the regional hydrological cycle of a lowland catchment-coastal water system.

Design of a hydro sound intensity probe for quantification and localization of acoustic sources — Applied to a hubless marine rim drive

The reduction of hydro noise emission by ship propulsion systems is of importance since background noise levels in the oceans have increased by 21 dB in the past decades. Thus, the acoustical improvement of ship propulsion systems is a necessary and challenging task. It involves not only the ship propeller but also the components of the entire drive train like diesel or electrical engines, electrical inverters as well as gearboxes. Acoustical measurement systems for the quantification and localization of noise sources are essential for any kind of optimization and are state of the art in the airborne noise field. This is not the case in the hydro acoustic field and measurements are mostly limited to the recording of the hydro sound pressure using single hydrophones. The objective of this paper is the presentation of a new three dimensional hydro sound intensity probe capable of acoustical sound power quantification and noise source localization. The probe can be used for the determination of the hydro sound pressure, the 3D sound intensity vector and the sound power. Furthermore, the probe can be utilized for hydro sound source localization purposes using beamforming methods based on virtual acoustical arrays. The developed probe was used for hydro acoustic investigations of a full scale marine rim drive during a measurement campaign in the river Warnow in Rostock, Germany. The results indicate the different hydro sound generating mechanism of the rim drive.

MiniLab - Agile underwater platform with integrated sensors for environmental and visual applications

The Fraunhofer “Smart Ocean Technologies” (SOT) research team extends its range of services towards underwater technology by developing new internal infrastructure. To test sensor technology and materials, empirical underwater data is required to evaluate new technology within realistic conditions. Various external factors like swell, wind, and the underwater environment itself complicate stable framework conditions during the measurements. For this purpose, a test platform called MiniLab was developed which can be extended by modules with respect to common interfaces. It serves as a base frame for internal as well as external projects. The MiniLab consists of an underwater unit and an on-ground unit. Both are connected via a hybrid underwater cable. In addition to the environmental conditions, camera live streams can be transmitted. The MiniLab service platform is currently being used in the Warnow River and in the Digital Ocean Lab (DOL) in the Baltic Sea. However, it is available for observations in other waters (Fraunhofer, 2021a).

Potential of constructed wetlands to reduce nitrate pollution in agricultural catchments

Nitrate (NO3−) concentrations and loads are still above ecologically acceptable levels in many open waters, including coastal seas. Agricultural measures aimed at reducing the nitrogen (N) surplus in fields usually only have an effect in the long term. A short-term reduction of N pollution can be achieved through technical solutions such as surface-flow constructed wetlands (SFWs). We analyzed the effect of SFWs to reduce nitrate‑nitrogen (NO3−-N) loads in the tile-drained agricultural Warnow river basin (approx. 3000 km2) in northeastern Germany. The aim of the study was to transfer the results from individual SFWs to the scale of the river basin. For this purpose, an eco-hydrological model (Soil and Water Assessment Tool) was used to reproduce streamflow and NO3−-N loads on a monthly basis for the basin outlet and six subbasins. Measured water and compound fluxes depicted well with the model, so that we could conduct a scenario analysis. 97 locations for the establishment of SFWs in tile-drained areas throughout the river basin were identified and integrated into the model environment. The results indicate that the NO3−-N loads for the entire basin could be reduced from 902,200 kg yr−1 to 842,900 kg yr−1, which corresponds to a NO3−-N reduction of 6.6%. NO3−-N removal rates varied widely between the subbasins, ranging from 5 to 86 g m−2 yr−1, and were positively correlated with NO3−-N input loads. We conclude that SFWs, if installed area-wide, can help to significantly reduce NO3−-N loads in a river basin and can be an important component of a comprehensive management strategy to reduce N loads in surface waters to acceptable levels. The installation of SFWs should be prioritized in hot-spot areas where the greatest benefit can be expected.

Impaired reproductive fitness despite high fecundity in European eel (Anguilla anguilla L.) from a Baltic Sea drainage area

The reproductive fitness of female European eels (Anguilla anguilla L.) from the Warnow River, Germany, Baltic Sea region, was evaluated by estimating fecundity and applying a spawning model. Individual fecundity ranged from 1,440,000 to 7,455,000 oocytes and mean relative fecundity equalled 5,956,015 oocytes kg-1 . Modelling suggests that 43% of eels hold insufficient energy storages or are within 10% of complete depletion. The fraction of eels with insufficient energy supply increases from 19% to 35% if the effect of parasitic infection is considered.

Emission, Transport, and Deposition of visible Plastics in an Estuary and the Baltic Sea\u2014a Monitoring and Modeling Approach

Aimwas to assess whether a comprehensive approach linking existing knowledge with monitoring and modeling can provide an improved insight into coastal and marine plastics pollution. We focused on large micro- and mesoplastic (1–25 mm) and selected macroplastic items. Emission calculations, samplings in the Warnow river and estuary (water body and bottom sediments) and a flood accumulation zone monitoring served as basis for model simulations on transport and behavior in the entire Baltic Sea. Considered were the most important pathways, sewage overflow and stormwater. The coastline monitoring together with calculations allowed estimating plastics emissions for Rostock city and the Warnow catchment. Average concentrations at the Warnow river mouth were 0.016 particles/m³ and in the estuary 0.14 particles/m³ (300 µm net). The estuary and nearby Baltic Sea beaches were hot-spots for plastic accumulation with 6–31 particles/m². With increasing distance from the estuary, the concentrations dropped to 0.3 particles/m². This spatial pattern, the plastic pollution gradients and the observed annual accumulation values were consistent with the model results. Indicator items for sewer overflow and stormwater emissions exist, but were only found at low numbers in the environment. The considered visible plastics alone can hardly serve as indicator for microplastic pollution (<1 mm). The use of up-scaled emission data as input for Baltic Sea model simulations provided information on large scale emission, transport and deposition patterns of visible plastics. The results underline the importance of plastic retention in rivers and estuaries.

Identification and quantification of microplastic particles in drinking water treatment sludge as an integrative approach to determine microplastic abundance in a freshwater river

Microplastic (MP) has been detected ubiquitously in freshwater systems. Until now MP sampling, however, is predominantly based on short-term net or pumping and filtration systems which can only provide snapshots of MP abundance; especially in flowing water bodies. To improve representativeness in the determination of MP occurrences in these aquatic compartments, an integrative approach that covers larger water volumes for a longer period of time is required. In this regard, surface water supplied drinking water treatment plants (DWTPs) represent an opportunity. In DWTPs, suspended solids from thousands of cubic metres of raw water are continuously removed over several hours and enriched in coagulation/flocculation and filtration processes. Our hypothesis was that MP is also removed to a full extent, like suspended solids, and that an integrative approach for identification and quantification in raw water can be derived from the analysis of MP in the treatment sludge. To prove this hypothesis, treatment sludge from a riverside DWTP (Warnow river, North-Eastern Germany) was analysed for MP > 50 μm. A sample purification protocol overcoming potential matrix effects caused by coagulants and flocculants was developed and validated. MP was analysed using micro-Raman spectroscopy. MP occurrence determined for the Warnow river was compared with in situ reference sampling using an established pumping and filtration system at relatively stable flow conditions. As result, the number of MP particles derived from treatment sludge was extrapolated to 196 ± 42 m−3 for the Warnow river and is statistically insignificantly different from 233 ± 36 m−3 identified by conventional water sampling. In addition, the polymer distribution and particles shape indicated the validity of the integrative concept. Consequently, the determination of MP abundance for freshwater systems based on DWTP treatment sludge represents an adequate method to estimate MP concentrations in flowing waters in an integrative way.

Combined Approaches to Predict Microplastic Emissions Within an Urbanized Estuary (Warnow, Southwestern Baltic Sea)

Microplastic river emissions are known to be one of the major sources for marine microplastic pollution. Especially urbanized estuaries localized at the land-sea interface and subjected to microplastic emissions from various sources exhibit a high microplastic discharge potential to adjacent coasts. To adapt effective measures against microplastic emissions a more detailed knowledge on the importance of various microplastic sources is necessary. As field data is scarce we combined different approaches to assess microplastic emissions into the Warnow estuary, southwestern Baltic Sea. Resulting microplastic emission estimates are based on in-situ measurements for the catchment emissions, whereas for the remaining microplastic sources within the estuary literature data on microplastic abundances, and various parameters were used (e.g. demographical, hydrological, geographical). The evaluation of the different emission scenarios revealed that the majority of microplastic is likely discharged by the Warnow river catchment (49.4%) and the separated city stormwater system (43.1%) into the estuary, followed by combined sewer discharges (6.1%). Wastewater treatment plant emissions exhibit the lowest percentage (1.4%). Our approach to estimate anti-fouling paint particles emissions from leisure and commercial shipping activities was associated with highest uncertainties. However, our results indicate the importance of this source highlighting the necessity for future research on the topic. Based on our assumptions for microplastic retention within the estuary, we estimate a potential annual emission of 152–291 billion microplastics (majority within the size class 10–100 µm) to the Baltic Sea. Considering all uncertainties of the different applied approaches, we could assess the importance of various microplastic sources which can be used by authorities to prioritize and establish emission reduction measures. Additionally, the study provides parameters for microplastic emission estimates that can be transferred from our model system to other urbanized Baltic estuaries.

Inversions of Estuarine Circulation Are Frequent in a Weakly Tidal Estuary With Variable Wind Forcing and Seaward Salinity Fluctuations

AbstractThe hydrodynamics in estuaries is mainly governed by the competition between a horizontal density gradient, friction, and wind stress. The sensitivity of the estuarine exchange flow to the wind stress increases in the absence of tides, which is investigated here using the example of the weakly tidal Warnow river estuary in the southwestern Baltic Sea—the mouth of which is characterized by strongly varying salinities of 8 to 20 g kg−1. The interaction between a volatile salinity gradient and along‐estuary wind forcing is found to cause temporary inversions of the estuarine circulation. Despite the highly dynamic conditions, the applicability of recent theories for isohaline mixing, using the framework of Total Exchange Flow, and the strength of the exchange flow, using a non‐dimensional parameter space, could be confirmed. By analyzing salinity fluxes at the mouth of the estuary, a mixing completeness of 84% was calculated for the estuary. Furthermore, inversion of estuarine circulation was typically found for a local Wedderburn number (ratio of non‐dimensional wind stress to non‐dimensional horizontal density gradient) exceeding 0.33, indicating a high sensitivity to along‐estuary wind.

Lignipirellula cremea gen. nov., sp. nov., a planctomycete isolated from wood particles in a brackish river estuary

A novel planctomycetal strain, designated Pla85_3_4T, was isolated from the surface of wood incubated at the discharge of a wastewater treatment plant in the Warnow river near Rostock, Germany. Cells of the novel strain have a cell envelope architecture resembling that of Gram-negative bacteria, are round to pear-shaped (length: 2.2 ± 0.4 µm, width: 1.2 ± 0.3 µm), form aggregates and divide by polar budding. Colonies have a cream colour. Strain Pla85_3_4T grows at ranges of 10–30 °C (optimum 26 °C) and at pH 6.5–10.0 (optimum 7.5), and has a doubling time of 26 h. Phylogenetically, strain Pla85_3_4T (DSM 103796T = LMG 29741T) is concluded to represent a novel species of a novel genus within the family Pirellulaceae, for which we propose the name Lignipirellula cremea gen. nov., sp. nov.

Three novel Rubripirellula species isolated from plastic particles submerged in the Baltic Sea and the estuary of the river Warnow in northern Germany.

Planctomycetes are a unique and important phylum containing mostly aquatic bacteria, which are often associated with phototrophic surfaces. A complex lifestyle, their potential for the production of bioactive small molecules, their unusual cell biology and a large number of giant and hypothetical genes in their genomes make these microorganisms a fascinating topic for further research. Here, we characterise three novel planctomycetal strains isolated from polystyrene and polyethylene particles that were submerged in the German part of the Baltic Sea and the estuary of the river Warnow. All three strains showed typical planctomycetal traits such as division by polar budding and formation of rosettes. The isolated strains were mesophilic and neutrophilic chemoheterotrophs and reached generation times of 10-25h during laboratory-scale cultivation. Taxonomically, the three strains belong to the genus Rubripirellula. Based on our analyses all three strains represent novel species, for which we propose the names Rubripirellula amarantea sp. nov., Rubripirellula tenax sp. nov. and Rubripirellula reticaptiva sp. nov. The here characterised strains Pla22T (DSM 102267T = LMG 29691T), Poly51T (DSM 103356T = VKM B-3438T) and Poly59T (DSM 103767T = LMG 29696T) are the respective type strains of these novel species. We also emend the description of the genus Rubripirellula.

Rhodopirellula heiligendammensis sp. nov., Rhodopirellula pilleata sp. nov., and Rhodopirellula solitaria sp. nov. isolated from natural or artificial marine surfaces in Northern Germany and California, USA, and emended description of the genus Rhodopirellula.

Expanding the collection of Planctomycetes by characterisation of novel species is key to better understanding of their complex lifestyles, uncommon cell biology and unexplored metabolism. Here, we isolated three novel planctomycetal strains from a kelp forest on the California Coastline at Monterey Bay or from plastic surfaces submerged in the Baltic Sea and the estuary of the river Warnow in the northeast of Germany. According to our phylogenetic analysis, the isolated strains Poly21T, Pla100T and CA85T represent three novel species within the genus Rhodopirellula. All three show typical planctomycetal traits such as division by budding. All are aerobic, mesophilic chemoheterotrophs and show genomic features comparable to other described Rhodopirellula species. However, strain CA85T is exceptional as it forms cream colonies, but no aggregates, which is a notable deviation from the pink- to red-pigmented and aggregate-forming Rhodopirellula species known thus far. We propose the names Rhodopirellula heiligendammensis sp. nov., Rhodopirellula pilleata sp. nov., and Rhodopirellula solitaria sp. nov. for the novel strains Poly21T (DSM 102266T = LMG 29467T = CECT 9847T = VKM B-3435T), Pla100T (DSM 102937T = LMG 29465T) and CA85T (DSM 109595T = LMG 29699T = VKM B-3451T), respectively, which we present as the respective type strains of these novel species.

Spatial and seasonal variations in phosphorus speciation along a river in a lowland catchment (Warnow, Germany)

Losses of phosphorus (P) from arable land lead to P enrichment in surface waters and thus to eutrophication. To gain deeper insights into riverine P processing and transport, the temporal and spatial changes of P compounds along the lowland river Warnow and its tributaries were investigated. Surface water samples were taken monthly between August 2016 and August 2017 and analyzed for the four P fractions: dissolved reactive (DRP), dissolved nonreactive (DNP), particulate reactive (PRP) and particulate nonreactive (PNP) phosphorus. P-composition differed between the courses of the upper Warnow and the impounded middle Warnow due to differences in their hydrological conditions. In the catchment of the upper course, riverine lakes were the sources of PNP and DRP during the summer and autumn. From the catchment of the middle course, mainly PRP and DRP had been introduced into the river. The negative relationship between PRP and the chlorophyll (Chla) concentration (rho = −0.43, p < 0.001) indicated that this P fraction is potentially bioavailable. During the rainy summer of 2017, substantially higher amounts of DRP occurred in the whole Warnow river. The potentially bioavailable P fractions (DRP, PRP, DNP) supported phytoplankton growth in the middle course, and the PNP loads increased with increasing biomass. Total phosphorus (TP) loads increased along the Warnow flow path, due to increasing discharge volume. The annual TP load of 40 t to the estuary was dominated by DRP (32%) and PNP (31%), with smaller contributions by PRP and DNP (19% and 18%, respectively). Our results demonstrate that detailed information on P fractions are helpful to understand P-cycling in rivers and its influence on eutrophication processes. This knowledge should be included in the development of effective management strategies for the improvement of water quality.

Behaviour, escapement and mortality of female European silver eels within a regulated lowland river draining into the Baltic Sea

AbstractMigration patterns of 146 female silver eels on their way through fresh and brackish water stretches of the Warnow River into the Baltic Sea were studied using acoustic telemetry. The majority of eels (77%) regained their expected downstream migration behaviour after a median rehabilitation time of 2 days. Positive rheotactic behaviour was observed for 23% of tagged eels after release, probably influenced by experimental procedures. The observed silver eel escapement rate was 63%. Two migratory groups were classified by significantly different migratory speed, time of residence in brackish waters and biometric silvering characteristics. Although the classification of silvering stages is based on these measures, the proportions of these stages did not reflect the observed differences in migratory behaviour. In the context of a permanent silver eel descent in the freshwater part of the Warnow River, a permanent escapement was likewise occurring into the Baltic Sea.

Spatio-temporal analysis of phosphorus concentrations in a North-Eastern German lowland watershed

Study regionThe Warnow River Basin, an agriculturally dominated lowland watershed in North-Eastern Germany with a considerable extent of artificial drainage. Study focusWe analyzed a 21-year data set (1990–2010) of dissolved reactive (DRP) and total phosphorus (TP) concentrations in surface waters to evaluate trends and seasonality of phosphorus (P) concentrations and pathways of P losses from soils. New hydrological insights for the regionPhosphorus concentrations were moderately spatially variable over the investigation period and mean DRP and TP concentrations ranged from 57 to 132 mg l−1 and 114 to 184 μg l−1 respectively. The mean annual DRP and TP loads ranged from 0.04 ± 0.01 to 0.15 ± 0.05 and 0.12 ± 0.05 to 0.27 ± 0.06 kg ha−1 a−1, respectively. We detected significant negative temporal trends of P concentrations and loads in the decade 1990–2000. In the 21st century, the TP concentrations and loads tend to increase moderately. The results underline the importance of baseflow for DRP export and storm flow events for TP export, and emphasize the importance of artificial drainage systems modifying the hydrological regime of soils and surface waters alike. The P export rates during storm events and the proportion of particulate phosphorus in artificial drainage systems should be monitored at a higher temporal resolution to obtain a comprehensive database necessary for developing management strategies to reduce P loads in agricultural used landscapes.

Microplastics alter composition of fungal communities in aquatic ecosystems.

Despite increasing concerns about microplastic (MP) pollution in aquatic ecosystems, there is insufficient knowledge on how MP affect fungal communities. In this study, we explored the diversity and community composition of fungi attached to polyethylene (PE) and polystyrene (PS) particles incubated in different aquatic systems in north-east Germany: the Baltic Sea, the River Warnow and a wastewater treatment plant. Based on next generation 18S rRNA gene sequencing, 347 different operational taxonomic units assigned to 81 fungal taxa were identified on PE and PS. The MP-associated communities were distinct from fungal communities in the surrounding water and on the natural substrate wood. They also differed significantly among sampling locations, pointing towards a substrate and location specific fungal colonization. Members of Chytridiomycota, Cryptomycota and Ascomycota dominated the fungal assemblages, suggesting that both parasitic and saprophytic fungi thrive in MP biofilms. Thus, considering the worldwide increasing accumulation of plastic particles as well as the substantial vector potential of MP, especially these fungal taxa might benefit from MP pollution in the aquatic environment with yet unknown impacts on their worldwide distribution, as well as biodiversity and food web dynamics at large.

Phosphorus fractions in discharges from artificially drained lowland catchments (Warnow River, Baltic Sea)

Understanding phosphorus (P) dynamics, from inland sources to the sea, is essential for developing strategies to reduce P loads. In this study, we examined concentrations, fractions, and association of P with other elements at a tile-drain outlet, the adjacent ditch and brook, further downstream from the brook, and in the river itself. The study was conducted in a sub-basin of the Warnow River catchment from 1 November 2013 to 30 April 2014 covering a mild and dry winter. Total phosphorus (TP) concentrations were lowest at the tile-drain effluent and increased in the ditch and brook, as a result of elevated dissolved reactive phosphorus (DRP), particulate reactive (PRP) and organic (POP) phosphorus. Dissolved organic phosphorus (DOP) concentrations remained constant. Further increase of TP along the brook and in the river reflected the increase in DRP+DOP along the first 2.5km and the doubling of PRP along the 6.5km thereafter. In the river, phytoplankton growth transformed P into POP in early spring. Total loads of DRP, PRP+POP, and DOP emitted during the study period were 4.3–5.6, 3–7, and 1–2gha−1 respectively, with an increasing tendency downstream. Despite their low P content (0.7–3.9%), clay minerals and Fe(hydr)oxides particles were the most important carriers because they formed 68–90% of all P-containing particles. A shift from Ca-phosphate to Fe-phosphate occurred from winter to spring and there was a variation in composition of P-containing particles along the flow course. Our results underline the importance of particulate P in discharge and show that the brook Zarnow following the drain outlet and the ditch is a location of P-enrichment and modification probably due to other inputs. The entire flow course has to be considered to assess nutrient inputs from agricultural land because P-composition and loads are changing in time and space.

Parasitation of sea trout (Salmo trutta trutta L.) from the spawning ground and German coastal waters off Mecklenburg-Western Pomerania, Baltic Sea.

A total of 52 sea trouts, Salmo trutta trutta, were studied for parasites, originating from German freshwater streams and coastal waters of the Baltic Sea. While 35 specimens were caught mainly close to the shoreline in the Baltic Sea, 17 were sampled during their spawning migration in Warnow River and other neighboring rivers in Mecklenburg-Western Pomerania. A total of 12 different metazoan parasite species were found in sea trout originating from the Baltic Sea, including five digeneans, two cestodes, three nematodes, and two acanthocephalans. Marine and freshwater species were found. In the migratory trout, seven different parasite species were recorded (one digenean, two cestodes, one nematode, and one acanthocephalan), demonstrating lower parasite diversity and load during the spawning migration compared with the fish from the Baltic Sea. The anisakid nematodes Anisakis simplex (sensu stricto), Contraceacum rudolphii, and Hysterothylacium aduncum were identified by molecular analyses of the ITS-1, 5.8S, ITS-2, and flanking sequences of the rDNA. Together with the digenean Derogenes varicus, Hemiurus communis and H. luehei, and the cestode Diphyllobothrium dendriticum seven new host records for sea trout from the German part of the Baltic Sea are made.

Solar UV-Assisted Pretreatment of River Water Samples for the Voltammetric Monitoring of Nickel and Cobalt Ultratraces

The application of solar UV radiation as sample digestion method is reported. The method is employed in adsorptive stripping voltammetric determination of nickel and cobalt in river water samples. The river water samples were collected from downstream of Warnow River (Germany) and acidified to pH of 2±0.2 by addition of ultrapure 65% HNO3. Furthermore, 3.4 mgL−1 ultrapure hydrogen peroxide solution was added to the samples as photochemical reaction initiator. The samples were transferred to UV-A transparent polyethylene terephthalate bottles and put in the sunshine for UV irradiation for six and 12 hours at a UV-A intensity of 3.90 mW/m2. The comparison of the concentration values showed that, 6 hours of solar UV irradiation at 3.90 mW/m2 UV-A intensity is not sufficient to complete the digestion process though it yields much better results than the undigested original sample. However, 12 hours of solar UV-A irradiation under similar conditions is almost as effective as a 30 W artificial UV lamp (254 nm) and can be applied to the digestion of dissolved organic carbon in trace nickel (II) and cobalt (II) analysis in natural waters such as river water, lake waters, and well waters.

Downstream migration dynamics of female and male silver eels (Anguilla anguilla L.) in the regulated German lowland Warnow River

AbstractIn the light of the European wide efforts to increase the spawning biomass of the European eel, a reliable measurement of the escapement of mature silver eel is necessary to prove the effectiveness of the conservation management measures. The seaward migration of mature eel is commonly viewed as a seasonal phenomenon with concentrated migration peaks occurring in spring and autumn. To verify the assumed seasonal silver eel migration events for regulated lowland rivers, a stow‐net system was installed in the Warnow River located in north‐eastern Germany. Between 2008 and 2011, the stow‐net system was operated from March to December each year. The eel harvest was documented on a weekly base including the documentation of weight and length, the silvering stage and the tissue sampling for the molecular identification of the eel species. During the 4 year monitoring period, a continuous downstream migration of female and male silver eels was observed. Additionally, single migration peaks were recorded in each year occurring between April and December. Moreover, female and male silver eels showed varying downstream migration dynamics. Based on a Chi‐squared Automatic Interaction Detection (CHAID) tree analysis, it was shown that during periods of a daily minimum air temperature over 10.4 °C, increased discharge levels and increased wind speeds, higher weekly migration rates of silver eels were likely. Furthermore, the results indicated that both sexes differed in their responses to migration triggering environmental factors. The presented results might be helpful to design more efficient eel conservation management strategies in regulated lowland rivers.