Odense Fjord Research Articles

Beach Wrack Dynamics Using a Camera Trap as the Real-Time Monitoring Tool

As part of Blue Carbon ecosystems (BCEs), detached macrophytes can be transported to the coast due to current and wave actions, and then deposited on the shore as beach wrack. To date, the role of beach wrack in the material cycle in BCEs is still unclear. In order to track the fate of beach wrack, this study conducted a monitoring survey on a semi-sheltered beach in Odense Fjord (Denmark) using camera trap data. Deep learning with a VGG network architecture was used to classify the image dataset acquired by the camera trap. The VGG network demonstrated the capability to identify beach wrack from different beach scenes, and the method can provide results on large datasets within a short time (187 images analyzed within 5 min) compared to manual identification of images. By combining the VGG detection with color-based segmentation, beach wrack coverage was determined. To evaluate the impact of ambient conditions on wrack deposition on the shore and relocation back to the sea, wind (including speed and direction), water temperature, and tidal amplitude were analyzed as environmental variables. Partial least squares regression (PLSR) analysis revealed that micro-tidal action with an average amplitude of 0.41 m accelerated the movement of floating macrophytes between the shore and the sea. Despite being exposed to the prevailing southwesterly winds (average speed of 11 m/s), the beach was sheltered due to the location in the inner part of Odense Fjord, limiting the transport of drifting macrophytes from sea to the shore. By using the camera trap to conduct continuous monitoring, this study presents a labor-saving and practical approach to track the dynamics of detached macrophytes deposited on the shore. Furthermore, the application of deep learning in image identification provides a study case for using a large image dataset to assist in ecological studies of dynamic environments.

Sand-capping – A large-scale approach to restore organic-enriched estuarine sediments

Decades of eutrophication have deteriorated marine coastal habitats severely and has led to massive decline of eelgrass along European coastlines and impoverishment of benthic fauna. Although nutrient loadings were reduced and water quality increased decades ago, eutrophication in the past had enriched marine sediments in organic matter to an extent that is still affecting ecosystems today. Organic-rich sediments are readily resuspended, keeping shallow estuaries in a turbid state and benthic fauna communities remain low in density and diversity. Sand-capping of muddy sediments may restore such deteriorated estuaries and is in this study applied for the first time as a large-scale restoration approach. A 10 cm layer of sand was added on 1.0 and 1.4 ha muddy sediments at two locations in Odense Fjord, Denmark. The organic content of the mud at the sites was 8–9% and 3–5% before sand-capping. The sand-cap stabilized the mud without mixing the sand-mud interface, not even after one year. The associated lower resuspension of fine particle improved light conditions in the overlying water by up to 9 and 22% at the two locations. Benthic fauna recruitment improved after sand-capping, leading to a local shift from low to high diversity of the benthic community and increased ecosystem functionality.

Predicting the ecological status of rivers and streams under different climatic and socioeconomic scenarios using Bayesian Belief Networks

Freshwater systems have increasingly been subjected to a multitude of human pressures and the re-establishment of their ecological integrity is currently a major worldwide challenge. Expected future climate and socioeconomic changes will most probably further exacerbate such challenges. Modelling techniques may provide useful tools to help facing these demands, but their use is still limited within ecological quality assessment of water resources due to its technical complexity.We developed a Bayesian Belief Network (BBN) framework for modelling the ecological quality of rivers and streams in two European river basins located in two distinct European climatic regions: the Odense Fjord basin (Denmark) and the Sorraia basin (Portugal). This method enabled us to integrate different data sources into a single framework to model the effect of multiple stressors on several biological indicators of river water quality and, subsequently, on their ecological status. The BBN provided a simple interactive user interface with which we simulated combined climate and socioeconomic changes scenarios to assess their impacts on river ecological status.According to the resulting BBNs the scenarios demonstrated small impacts of climate and socioeconomic changes on the biological quality elements analysed. This yield a final ecological status similar to the baseline in the Odense case, and slightly worse in Sorraia. Since the present situation already depicts a high percentage of rivers and streams with moderate or worse ecological status in both basins, this means that many of them would not fulfil the Water Framework Directive target in the future. Results also showed that macrophytes and fish indices were mainly responsible for a non-desirable overall ecological status in Odense and Sorraia, respectively. The approach followed in this study is novel, since BBN modelling is used for the first time for assessing the ecological status of rivers and streams under future scenarios, using an ensemble of biological quality elements. An important advantage of this tool is that it may easily be updated with new knowledge on the nature of relationships already established in the BBN or even by introducing new causal links. By encompassing two case studies of very different characteristics, these BBN may be more easily adapted as decision-making tools for water management of other river basins.

Effects of changes in land use and climate on aquatic ecosystems: Coupling of models and decomposition of uncertainties

To analyse the potential future ecological state of estuaries located in the temperate climate (here exemplified with the Odense Fjord estuary, Denmark), we combined end-of-the-century climate change projections from four different climate models, four contrasting land use scenarios (“Agriculture for nature”, “Extensive agriculture”, “High-tech agriculture” and “Market driven agriculture”) and two different eco-hydrological models. By decomposing the variance of the model-simulated output from all scenario and model combinations, we identified the key sources of uncertainties of these future projections. There was generally a decline in the ecological state of the estuary in scenarios with a warmer climate. Strikingly, even the most nature-friendly land use scenario, where a proportion of the intensive agricultural area was converted to forest, may not be enough to counteract the negative effects of a future warmer climate on the ecological state of the estuary. The different land use scenarios were the most significant sources of uncertainty in the projections of future ecological state, followed, in order, by eco-hydrological models and climate models, albeit all three sources caused high variability in the simulated outputs. Therefore, when projecting the future state of aquatic ecosystems in a global warming context, one should at the very least consider to evaluate an ensemble of land use scenarios (nutrient loads) but ideally also include multiple eco-hydrological models and climate change projections. Our study may set precedence for future attempts to predict and quantify uncertainties of model and model input ensembles, as this will likely be key elements in future tools for decision-making processes.

Stable C and N Isotope Composition of Primary Producers and Consumers Along an Estuarine Salinity Gradient: Tracing Mixing Patterns and Trophic Discrimination

The mixing pattern along a summer salinity gradient in the estuary Odense Fjord was evaluated using nutrient concentrations as well as 13C and 15N isotope signatures of suspended and sediment organic matter, immobile macrophytes (Fucus vesiculosus and Ruppia maritima), and benthic fauna (Mya arenaria, Hediste (Nereis) diversicolor, and Arenicola marina). Trophic discrimination (Δ13C and Δ15N) of the infaunal consumers (suspension feeders and detritivores) was assessed from the obtained mixing patterns along the estuarine gradient. Correspondence between salinity, DIC, and DIN in Odense Fjord implies conservative mixing as also evident from linear relationships between salinity and δ13C and δ15N signatures of most living organic pools. Isotope signatures of suspended organic matter (i.e., diatoms) indicate that the river to marine DIC and DIN end-members have daily/weekly δ13C and δ15N averages during summer from − 10 to 0‰ and 10–12 to 0–5‰, respectively. Stable isotope signatures of long-lived macrophytes stationary at specific locations in Odense Fjord showed δ13C levels that were about 7‰ higher than for suspended particles and 3–4‰ higher than for sediment organic matter, while no such difference was evident for δ15N. The food of invertebrate consumers (M. arenaria, H. diversicolor, and A. marina) determined from the estuarine δ13C and δ15N patterns provided the first ever reported trophic discrimination of these animals. Thus, Δ13C was 1.9, 1.6, and 1.3‰ and Δ15N was 4.4, 5.0, and 3.5‰ for the three species, respectively. Accordingly, benthic suspension and deposit feeders in Odense Fjord are largely supported by a diet consisting of benthic and pelagic microalgae, however, with a possible slight shift in diet proportions or to other food sources in the lower reaches of the estuarine gradient.

Agent Based Modelling (ABM) of eelgrass (Zostera marina) seedbank dynamics in a shallow Danish estuary

Odense Fjord (Denmark) has suffered from a drastic decline in eelgrass (Zostera marina) coverage during the last decades. In 1983 eelgrass still covered about 25% of the estuary, which in 2005 was reduced to less than 2%. The alarming decline in the past decades initiated preliminary restoration activities, where it was questioned whether the present low eelgrass biomass is able to produce a sustainable seed bank to support natural recovery. Field studies verified that the seed bank was hampered. Laboratory experiments were conducted to determine 1) seed dispersion along the sediment surface and in the water column; 2) settling rates of seeds and flowering shoots; 3) critical current speed for seed movement; 4) floating dynamic of flowering shoots and 5) seed dropping dynamics during transport of rafting shoots.These parameters supported the development of an agent based model (ABM) predicting seed movements in estuaries. The model handled two ways of seed dispersal: 1) seeds dropped in eelgrass beds and transport by hydrodynamic forces along the seabed 2) seeds released by rafting shoots. This setup allowed assessment of both eelgrass seed loss and potential connectivity between beds. Seed losses were divided into direct losses, such as seeds lost on land due to desiccation or external boundary, and indirect losses affecting seedling establishment.The model estimates that app. 92% of the seeds would be retained in the Odense fjord, while only 5.0% of the seeds ended up in areas supporting seedling establishment. Eelgrass seeds were also found in areas with insufficient light, high hydrodynamic pressure, excessive sediment reworking by lugworms or poor anchoring capacity. In addition, the model showed potential bed connectivity via rafting shoots, but also with individual seed movement along the bottom, when beds were not separated by deep areas, such as boating channels.

Quantifying the combined effects of land use and climate changes on stream flow and nutrient loads: A modelling approach in the Odense Fjord catchment (Denmark)

Water pollution and water scarcity are among the main environmental challenges faced by the European Union, and multiple stressors compromise the integrity of water resources and ecosystems. Particularly in lowland areas of northern Europe, high population density, flood protection and, especially, intensive agriculture, are important drivers of water quality degradation. In addition, future climate and land use changes may interact, with uncertain consequences for water resources. Modelling approaches have become essential to address water issues and to evaluate ecosystem management. In this work, three multi-stressor future storylines combining climatic and socio-economic changes, defined at European level, have been downscaled for the Odense Fjord catchment (Denmark), giving three scenarios: High-Tech agriculture (HT), Agriculture for Nature (AN) and Market-Driven agriculture (MD). The impacts of these scenarios on water discharge and inorganic and organic nutrient loads to the streams have been simulated using the Soil and Water Assessment Tool (SWAT). The results revealed that the scenario-specific climate inputs were most important when simulating hydrology, increasing river discharge in the HT and MD scenarios (which followed the high emission 8.5 representative concentration pathway, RCP), while remaining stable in the AN scenario (RCP 4.5). Moreover, discharge was the main driver of changes in organic nutrients and inorganic phosphorus loads that consequently increased in a high emission scenario. Nevertheless, both land use (via inputs of fertilizer) and climate changes affected the nitrate transport. Different levels of fertilization yielded a decrease in the nitrate load in AN and an increase in MD. In HT, however, nitrate losses remained stable because the fertilization decrease was counteracted by a flow increase. Thus, our results suggest that N loads will ultimately depend on future land use and management in an interaction with climate changes, and this knowledge is of utmost importance for the achievement of European environmental policy goals.

The Anti-Landscape ed. by David E. Nye and Sarah Elkind

Reviewed by: The Anti-Landscape ed. by David E. Nye and Sarah Elkind Timothy James LeCain (bio) The Anti-Landscape. Edited by David E. Nye and Sarah Elkind. Amsterdam and New York: Rodopi, 2014. Pp. 218. $65. J. B. Jackson defined "landscape" as the "infrastructure or background for our collective existence." By contrast, David Nye explains in the opening essay to this collection, an "anti-landscape" is a space that does not sustain human life in either a biological or sociocultural sense. Nye and co-editor Sarah Elkind suggest that this anti-landscape concept provides a useful extension of Jackson's earlier fusing of the human and non-human. The movement between landscape and anti-landscape might further bring together materialist and constructivist approaches under the capacious banner of the environmental humanities. It is an ambitious goal, not easily realized with such an eclectic collection of essays. Nye and Elkind provide some useful organizational structure by dividing the volume into three sections. The first, "The Threatened Landscape," most squarely pursues the idea of the anti-landscape as a degradation of the eco-social potentialities of a previously useful landscape. James Fleming's essay perhaps most successfully unites the cultural and material by surveying visual representations of what he terms "skyscapes" and "anti-skyscapes." By its literally transparent nature, Fleming notes that the sky is often both materially and culturally transparent. Yet some artists have developed new ways of making the invisible visible, as with a French duo's use of laser lights to outline the emissions from a power plant in a noxious green. On the more material side, the historian of irrigation technology Maurits Ertsen analyzes the relationship between British colonial irrigation canals in Pakistan, which raised water tables, and subsequent farmer-initiated tube wells, which lowered them. Such complex historical evolutions challenge our tendency to see irrigation systems as leading in any simple way towards either civilizational progress or collapse. Ertsen thus seems to suggest that the line between nurturing landscape and sterile anti-landscape is decidedly fluid. [End Page 1101] Section II, "Anti-Landscapes," pursues a more cultural turn rooted mostly in literary studies. Anna Flügge treats the anti-landscape mostly metaphorically in her analysis of two prominent American novels, The Great Gatsby and The Big Sleep. These examples of a "melancholic modernism" suggest that their authors believed that an unproductive anti-landscape gives rise to a largely meaningless and unsustainable modern culture. The characters Nick Carraway and Philip Marlowe both sense the inadequacy of the sterile anti-landscape, yet are equally incapable of escaping it. Treating the landscape somewhat more concretely, Øyunn Hestetun's perceptive analysis of Cormac McCarthy's post-apocalyptic novel The Road suggests an intimate connection between the cultural and material: the non-human landscape has the power to both nurture and destroy what we wrongly think of as a solely human-created identity and culture. McCarthy's evocation of a horrific "landscape of fear," Øyunn argues, reveals an environment that can no longer nurture either biological or moral survival. A degenerate anti-landscape creates a degenerate culture, McCarthy seems to suggest, effectively collapsing the modernist division of the material and the cultural. In the third section, "Recoveries," the volume returns to more concrete material examples of various attempts to remediate anti-landscapes. Anna Storm's insightful analysis of an abandoned open pit mine and a nuclear power plant, in Sweden and Lithuania respectively, admits that practical remediation of the environmental damage and pollution at such sites is extraordinarily difficult. Nonetheless, even these badly wounded sites might yet be turned to productive social and cultural purposes when used for historical and cultural heritage. Nikolet Jensen's fascinating history of the transformation of an abandoned elevated rail line in New York City into a popular green linear parkway offers perhaps the most optimistic story in the volume, demonstrating how urban and environmental preservation can at times be united. In her "Afterword," Elkind examines recent efforts to transform a former dump along Denmark's Odense fjord into a recreational area. While the project has been reasonably successful, Elkind raises a hard question. If the remediation of an anti-landscape succeeds only in making it...

Modelling stressors on the eelgrass recovery process in two Danish estuaries

Eelgrass (Zostera marina L.) depth limit is used as an environmental indicator in Danish coastal waters in the Water Framework Directive (WFD) to evaluate coastal waters and their ecological condition. Even after decades of reduced nutrient loadings the reestablishment of eelgrass has not yet succeeded. The mechanisms hindering/delaying eelgrass recovery were recently identified: 1) lack of sediment anchoring capacity, 2) resuspension created by drifting ephemeral macroalgae, 3) seedling uprooting created by current and wave forces, 4) ballistic stress from attached macroalgae and 5) burial of seeds and seedlings by lugworms. These processes were quantified and introduced to an ecological MIKE 3D model. The developed model was calibrated and validated on two Danish estuaries, Odense Fjord and Roskilde Fjord. Analyses of the simulations were performed on area distribution maps. The parameterized stressors impact has been investigated over a three-year period.The results indicate accumulated effects from multiple stressors weakening the capability of eelgrass to recolonize. Combining all stressors in the model decreased the total area covered by eelgrass 83.72% in Odense Fjord and 80.30% in Roskilde Fjord compared to simulation without stressors. Eelgrass peak biomass declined in both fjords from 33.4 to 4.55 tonCkm−2 in Odense Fjord and from 24.42 to 5.58tonCkm−2 in Roskilde Fjord. Combining lugworm burial of seeds and seedlings with resuspension from macroalgae and wave forcing had the second strongest negative impact on eelgrass growth, area reduction of 78.31% and 73.14% in Odense and Roskilde Fjord was seen. Ballistic stress from attached macroalgae also reduced growth drastically. Light conditions, sediment organic content along with shear stress at the sediment surface impact the ability of eelgrass to cope with above mentioned stressors. The spatial resolution of the model setup made it possible to generate maps where eelgrass is exposed to lowest stress, revealing areas for potential eelgrass recovery. The developed eelgrass model is now used as a national tool to predict areas where eelgrass restoration effort may be initiated.

Filter-feeding zoobenthos and importance of hydrodynamics in the shallow Odense Fjord (Denmark) - earlier and recent studies, perspectives and modelling

Filter-feeding zoobenthos and importance of hydrodynamics in the shallow Odense Fjord (Denmark) - earlier and recent studies, perspectives and modelling

Organic N and P in eutrophic fjord sediments – rates of mineralization and consequences for internal nutrient loading

Abstract. Nutrient release from the sediments in shallow eutrophic estuaries may counteract reductions of the external nutrient load and prevent or prolong ecosystem recovery. The magnitude and temporal dynamics of this potential source, termed internal nutrient loading, is poorly under\\-stood. We quantified the internal nutrient loading driven by microbial mineralization of accumulated organic N (ON) and P (OP) in sediments from a shallow eutrophic estuary (Odense Fjord, Denmark). Sediments were collected from eight stations within the system and nutrient production and effluxes were measured over a period of ~ 2 years. Dissolved inorganic nitrogen (DIN) effluxes were high initially but quickly faded to low and stable levels after 50–200 days, whereas PO43− effluxes were highly variable in the different sediments. Mineralization patterns suggested that internal N loading would quickly (< 200 days) fade to insignificant levels, whereas internal PO43− loading could be sustained for extended time (years). When results from all stations were combined, internal N loading and P loading from the fjord bottom was up to 121 × 103 kg N yr−1 (20 kg N ha−1 yr−1) and 22 × 103 kg P yr−1 (3.6 kg P ha−1 yr−1) corresponding to 6 (N) and 36% (P) of the external nutrient loading to the system. We conclude that the internal N loading resulting from degradation of accumulated ON is low in shallow eutrophic estuaries, whereas microbial mineralization of accumulated OP is a potential source of P. Overall it appears that, in N-limited eutrophic systems, internal nutrient resulting from mineralization of ON and OP in sediments is of minor importance.

Influence of benthic macrofauna community shifts on ecosystem functioning in shallow estuaries

We identify how ecosystem functioning in shallow estuaries is affected by shifts in benthic fauna communities. We use the shallow estuary, Odense Fjord, Denmark, as a case study to test our hypotheses that (1) shifts in benthic fauna composition and species functional traits affect biogeochemical cycling with cascading effects on ecological functioning, which may (2) modulate pelagic primary productivity with feedbacks to the benthic system. Odense Fjord is suitable because it experienced dramatic shifts in benthic fauna community structure from 1998 to 2008. We focused on infaunal species with emphasis on three dominating burrow-dwelling polychaetes: the native Nereis (Hediste) diversicolor and Arenicola marina, and the invasive Marenzelleria viridis. The impact of functional traits in the form of particle reworking and ventilation on biogeochemical cycles, i.e. sediment metabolism and nutrient dynamics, was determined from literature data. Historical records of summer nutrient levels in the water column of the inner Odense Fjord show elevated concentrations of NH4+ and NO3- (DIN) during the years 2004-2006, exactly when the N. diversicolor population declined and A. marina and M. viridis populations expanded dramatically. In support of our first hypothesis, we show that excess NH4+ delivery from the benthic system during the A. marina and M. viridis expansion period enriched the overlying water in DIN and stimulated phytoplankton concentration. The altered benthic-pelagic coupling and stimulated pelagic production may, in support of our second hypothesis, have feedback to the benthic system by changing the deposition of organic material. We therefore advice to identify the exact functional traits of the species involved in a community shift before studying its impact on ecosystem functioning. We also suggest studying benthic community shifts in shallow environments to obtain knowledge about the drivers and controls before exploring deep-water environments.

Cost-efficient reductions in nutrient loads; identifying optimal spatially specific policy measures

Abstract Nitrogen leakage from agriculture contributes significantly to eutrophication of freshwater and marine ecosystems, and numerous studies have focused on finding cost-effective ways to mitigate this effect. This article utilizes high-resolution data to identify a spatially targeted cost-effective reduction of nitrogen leakage, optimizing over measures as well as over locations. The use of discrete optimization techniques ensure that mutually exclusive measures are not applied on the same plot of land. The analysis is based on a case study of Odense Fjord, where spatially explicit data capture the spatial heterogeneity of the effects and costs of abatement measures. The differences in retention capacity; soil types; and current land use are particularly important factors for the spatial variation in costs and effects. The analysis highlights the importance of applying discrete optimization techniques in spatially specific analyses. We find that no unambiguous ranking of measures or spatial pattern of abatement effort can be given. Hence, landscape scale models are needed to identify optimal abatement effort. The results show that spatial targeting offers substantial improvements in cost-effectiveness compared to a uniform regulation.

Reprint of “Mapping of nitrogen risk areas”

Loading of nitrogen (N) from diffuse sources to Danish marine waters was reduced by 41% in the period 1990–2012 by a suite of general measures. However, further reductions in N loading are required if the ambitious quality goals of the EU Water Framework Directive are to be achieved. Measures will be more effective if they are implemented in N loss hot spots or risk areas. Additionally, the highly variable N reduction in groundwater and surface waters needs to be taken into account as this strongly influences the resulting effect of mitigation measures. The objectives of this study were to develop and apply an N risk tool to the entire agricultural land area in Denmark. The purpose of the tool is to identify high risk areas, i.e. areas which contribute disproportionately much to diffuse N losses to the marine recipient, and to suggest cost-effective measures to reduce losses from risk areas. In the N risk mapping part of the tool, we combined a modelled root zone N leaching with a catchment-specific N reduction factor which in combination determines the N load to the marine recipient. N leaching was calculated using detailed information of agricultural management from national databases as well as datasets of percolation and soil parameters as input parameters to an empirical N leaching model. The developed N risk tool showed that the Danish agricultural area is distributed almost evenly between N retention classes (N retention being divided into classes of <40%; 40–60%; 60–80% and >80% N retention). Hot spots for marine N loading are, however, mainly located in catchments with N retention less than 80%. Hot spots for N leaching from the root zone are mainly located in the western part of Jutland, while hot spots for marine N loading are found in all regions and especially in small catchments close to the coast. In a case study for the catchment of the Danish Odense Fjord estuary, we demonstrated how the tool facilitates cost-effective implementation of measures and how measures can be combined to reach a given reduction target for an estuary.

Mapping of nitrogen risk areas

Loading of nitrogen (N) from diffuse sources to Danish marine waters was reduced by 41% in the period 1990–2012 by a suite of general measures. However, further reductions in N loading are required if the ambitious quality goals of the EU Water Framework Directive are to be achieved. Measures will be more effective if they are implemented in N loss hot spots or risk areas. Additionally, the highly variable N reduction in groundwater and surface waters needs to be taken into account as this strongly influences the resulting effect of mitigation measures. The objectives of this study were to develop and apply an N risk tool to the entire agricultural land area in Denmark. The purpose of the tool is to identify high risk areas, i.e. areas which contribute disproportionately much to diffuse N losses to the marine recipient, and to suggest cost-effective measures to reduce losses from risk areas. In the N risk mapping part of the tool, we combined a modelled root zone N leaching with a catchment-specific N reduction factor which in combination determines the N load to the marine recipient. N leaching was calculated using detailed information of agricultural management from national databases as well as datasets of percolation and soil parameters as input parameters to an empirical N leaching model. The developed N risk tool showed that the Danish agricultural area is distributed almost evenly between N retention classes (N retention being divided into classes of <40%; 40–60%; 60–80% and >80% N retention). Hot spots for marine N loading are, however, mainly located in catchments with N retention less than 80%. Hot spots for N leaching from the root zone are mainly located in the western part of Jylland, while hot spots for marine N loading are found in all regions and especially in small catchments close to the coast. In a case study for the catchment of the Danish Odense Fjord estuary, we demonstrated how the tool facilitates cost-effective implementation of measures and how measures can be combined to reach a given reduction target for an estuary.

Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 503:41-58 (2014) - DOI: https://doi.org/10.3354/meps10747 Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries Thomas Valdemarsen1,*, Cintia O. Quintana1,2, Erik Kristensen1, Mogens R. Flindt1 1Institute of Biology, University of Southern Denmark, 5230 Odense M, Denmark 2Institute of Oceanography, University of São Paulo, São Paulo 05508-070, Brazil *Corresponding author: valdemarsen@biology.sdu.dk ABSTRACT: Sediments in eutrophic estuarine ecosystems may become heavily enriched with organic carbon (OC). This OC is primarily of low reactivity and, therefore, has moderate effects on sediment biogeochemical cycling. Nonetheless, OC levels of >1% reduce sediment stability and cause frequent resuspensions and high water turbidity, which affect the recovery of ecosystem functioning. Significant reduction of sediment OC content to <1% is, therefore, needed before ecosystems can fully recover. It was investigated whether organic-rich sediments with 2.5 to 4.4% OC (180–310 mol m–2) from the eutrophic Odense Fjord (Denmark) can recover by microbial degradation. Defaunated sediment cores from various habitats were subjected to long-term (~2 yr) degradation experiments. Total OC content was measured initially and OC degradation was measured regularly from CO2 effluxes and closed anoxic sediment incubations. OC degradation was high initially, but faded exponentially at all stations before stabilizing at 6 to 15 mmol OC m-2 d-1 after 100 to 150 d. Hence, over the 2 yr experiment OC degradation corresponded to only 3 to 5% reduction of initial OC. Temporal degradation patterns analyzed by exponential decay models suggested that sedimentary OC consisted of 2 pools with different reactivity plus a non-reactive pool. OC with the highest turnover (k = 0.5 × 10-2 to 5.5 × 10-2 d-1) was quantitatively the least important (0.3-4.3% of total OC), while OC with lower reactivity (k = 0.1 × 10-3 to 2.0 × 10-3 d-1) constituted a higher proportion (4-58% of total OC in organic-rich sediments). Furthermore, 43 to 95% of sediment OC was non-degradable. Our results suggest that partial recovery (5-57% reduction of initial OC) may occur within 23 to 50 yr. However, complete recovery of organic-rich sediments to <1% OC seems unlikely due to large pools of non-reactive OC. Eutrophication, therefore, leads to irreversible OC accumulation in sediments, which prolongs the recovery time for estuarine ecosystems after reductions in nutrient loading. KEY WORDS: Organic matter · Degradation · Mineralization · Oligotrophication · Recovery time · Exponential decay · G-model Full text in pdf format PreviousNextCite this article as: Valdemarsen T, Quintana CO, Kristensen E, Flindt MR (2014) Recovery of organic-enriched sediments through microbial degradation: implications for eutrophic estuaries. Mar Ecol Prog Ser 503:41-58. https://doi.org/10.3354/meps10747 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 503. Online publication date: April 29, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Macrobenthic community response to the Marenzelleria viridis (Polychaeta) invasion of a Danish estuary

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 461:83-94 (2012) - DOI: https://doi.org/10.3354/meps09821 Macrobenthic community response to the Marenzelleria viridis (Polychaeta) invasion of a Danish estuary Matthieu Delefosse1,*, Gary T. Banta2, Paula Canal-Vergés1,3, Gil Penha-Lopes 1,4, Cintia O. Quintana1, Thomas Valdemarsen1, Erik Kristensen1 1Institute of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark 2Department of Environmental, Social and Spatial Change, Roskilde University, Universitetsvej 1, 4000 Roskilde C, Denmark 3DHI Water Environment Health, Agern Allé 5, 2970 Hørsholm, Denmark 4Laboratório Marítimo da Guia, Centro de Oceanografia, Faculdade de Ciências da Universidade de Lisboa, Avenida Na Senhora do Cabo, 939, 2750-374 Cascais, Portugal *Email: matthieu.delefosse@gmail.com ABSTRACT: We investigated the invasion of the non-native polychaete Marenzelleria viridis in a shallow Danish estuary, Odense Fjord. Three datasets with different spatial and temporal resolution were examined to describe the invasion of M. viridis and to investigate its effect on the native benthic community with focus on the 2 common polychaetes, Nereis (Hediste) diversicolor and Arenicola marina. Marenzelleria viridis colonized Odense Fjord rapidly, and within 3 yr it had spread to ~50% of the estuary. The population development of M. viridis in Odense Fjord followed the ‘boom-bust’ pattern that is typical for many invaders. M. viridis is now firmly established and has reached an overall abundance of 100 to 200 individuals (ind.) m−2 with local maxima of up to 1200 ind. m−2. Its distribution is apparently regulated by abiotic parameters that prevent its establishment in the oligohaline and more silty parts of Odense Fjord. There was a positive interaction between M. viridis and the native A. marina. Otherwise the introduction of M. viridis was synchronous with a decrease of several macroinvertebrates species, especially N. diversicolor. The latter is still the dominant species in Odense Fjord, but its density has decreased by >60% in areas colonised by M. viridis. We do not expect that N. diversicolor disappears completely in this estuary, but it will probably be displaced to refuge areas where M. viridis cannot survive. Decrease in the population size of a key native species such as N. diversicolor might have significant ecological implications at the ecosystem level with respect to biodiversity and nutrient cycling. KEY WORDS: Invasive species · Marenzelleria viridis · Nereis (Hediste) diversicolor · Arenicola marina · Benthic communities · Biological interactions · Polychaetes · Regime shift Full text in pdf format PreviousNextCite this article as: Delefosse M, Banta GT, Canal-Vergés P, Penha-Lopes G, Quintana CO, Valdemarsen T, Kristensen E (2012) Macrobenthic community response to the Marenzelleria viridis (Polychaeta) invasion of a Danish estuary. Mar Ecol Prog Ser 461:83-94. https://doi.org/10.3354/meps09821 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 461. Online publication date: August 08, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Burial of seeds and seedlings by the lugworm Arenicola marina hampers eelgrass ( Zostera marina) recovery

Eelgrass ( Zostera marina) used to dominate the vegetation in Odense Fjord, Denmark, and covered > 17 km 2 of the shallow fjord in 1983. Decades of excessive nutrient loading has lead to decreased eelgrass distribution, and only ~ 2 km 2 is covered at present. The state of low eelgrass coverage has not changed despite significant improvements of water quality in the past > 10 years, and lugworms, Arenicola marina, have colonized the former eelgrass areas (1–8 ind. m −2). It was hypothesized that the lack of eelgrass recovery was due to A. marina, which was investigated by a combined field and laboratory approach. At a study site where eelgrass used to dominate, a seasonal study of lugworm population dynamics and sediment reworking activity was performed. Additionally, density dependent burial of eelgrass seeds and seedlings due to sediment reworking by A. marina was investigated in mesocosm experiments. Our results indicate that A. marina may negatively impact eelgrass recovery, since sediment reworking lead to rapid burial of eelgrass seeds and seedlings; within 1–2 months, 95% of seeds and 75% of seedlings were buried below critical depth. Considerations based on empirical modeling suggest that negative impact occur even at low A. marina density (5–10 ind. m −2). Therefore the spread of A. marina into former eelgrass areas is critical, since eelgrass recovery may be severely impaired, even when water quality favors eelgrass recolonization.

Vulnerability of Zostera marina seedlings to physical stress

Eelgrass coverage in Odense Fjord (Denmark) has declined by 90% since 1983, due to eutrophication and its associated pressures, and the state of low eelgrass coverage has remained sta- ble despite 10 to 15 yr of reduced nutrient loading and improved water quality. We hypothesize that the survival of eelgrass seedlings, and thus recolonization through reproductive dispersal, is nega- tively affected by physical disturbances. The 3 most likely physical mechanisms involved are uproot- ing or burial through drifting macroalgae, Arenicola marina sediment reworking and current-driven sediment resuspension. Our hypothesis was tested by field observations during the summer of 2009, when the mortality of seedlings was followed through time. The density of seedlings decreased dra- matically by 80% during the first month of observations, and no seedlings survived past August, cor- responding to an average seedling mortality of 1.5% d -1 . This was >3 times higher than the mortal- ity for seedlings protected from physical disturbance by enclosures (0.4% d -1 ), indicating that physical disturbance contributed to high seedling mortality. A significant correlation (p = 0.02) between macroalgal drift and seedling mortality suggested that ~40% of seedlings were lost due to the physical disturbance of drifting algae. In contrast, no correlations were found between A. marina reworking or resuspension and seedling mortality, despite a mobility of up to 400 cm 3 sediment m -2 d -1 by these mechanisms. Given the observed intensity of macroalgal drift, we speculate that this

Resuspension created by bedload transport of macroalgae: implications for ecosystem functioning

Previous studies suggest that current-driven plant transport in shallow lagoons and estuaries is associated with increased turbidity. Our hypothesis is therefore that macroalgae erode surface sediment while drifting as bedload. This ballistic effect of moving plants on surface sediment was tested in a series of controlled annular flume experiments, where simultaneous measurements of macrophytes transport and turbidity were conducted at increasing current velocities. Sediment erosion always started earlier in experiments with plants than in control experiments without plants. Turbidity increased immediately when plants started to move at current velocities of 2–4 cm s−1. From a background concentration of 7–10 mg SPM l−1, turbidity increased to 30–50 mg SPM l−1 for Ceramium sp., Ulva lactuca and Chaetomorpha linum, while the more rigid Gracilaria sp., caused much higher turbidities (50–180 mg SPM l−1). Such plant induced sediment erosion at low current velocity can explain the observed appearance of turbid waters in estuaries and lagoons in the absence of strong wind and wave action. Based on 3-D hydrodynamic modelling, it was determined that plant driven erosion occurs during most of the growth season in a shallow eutrophic estuary (Odense Fjord, Denmark).