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In recent decades, mussel beds in the northern Atlantic and Scandinavia have declined rapidly in extent due to anthropogenic impacts, similar to many other marine habitats. In this study, a large‐scale restoration experiment was conducted to identify major challenges that arise during restoration efforts on shallow subtidal mussel beds. Suspension‐grown mussels (Mytilus edulis) were relayed in two different treatments either directly on bare bottom sandy sediments, or on coir nets (Net), used as a proxy for suitable byssal attachment substrate. The treatments were monitored for 1.5 years and coverage (%), biomass (WW), and population dynamics were quantified. Two main challenges of shallow bed restoration were identified: (1) Lack of suitable attachment substrate resulting in dislodgment of individuals during storm events. The Net treatment had significantly higher coverage and biomass of Mytilus at the end of the monitoring period, clearly demonstrating the importance of suitable substrate at physically exposed locations. (2) High mortality of juvenile mussels. Population dynamics revealed a high mortality of juvenile Mytilus, which resulted in almost complete loss of relayed Mytilus individuals less than 30 mm within the first season. This was most likely due to high meso‐predator densities, as a result of declining top‐predator populations. The high mortality of juvenile Mytilus prevented successful annual recruitment, thereby making the population unsustainable long‐term. Both challenges need to be addressed to create stable beds during restoration. Additionally, the experiment demonstrated the viability of using suspension‐grown Mytilus as a seed‐source when restoring mussel beds. [ABSTRACT FROM AUTHOR]

The restoration of seagrass habitats is a relatively young field with several successful restoration attempts highlighting the feasibility of large‐scale restoration. Successful restoration of seagrass habitats requires an understanding of the most appropriate techniques to use for the target species and local conditions of restoration sites, however, there are currently limited studies on Zostera muelleri. Here, we conduct field trials to explore the use of seed‐ and shoot‐based restoration approaches for Z. muelleri in Victoria, Australia. We assessed the feasibility of collecting and germinating seeds in the field for restoration purposes and trialed the success of four shoot‐based transplanting techniques. We found that seed collections for Z. muelleri were highly successful and scalable, with seed collection rates improving from 489 to 1,939 seeds/hour over 2 years. In addition, in situ seedling germination increased from a maximum of 10.80–25.25% over 2 years. In contrast, shoot‐based restoration approaches were more variable, with plants transplanted with their sediment‐intact outperforming all bare‐rooted approaches. Shoot‐based transplanting approaches appear to have more limited application, but may be appropriate for some restoration sites, or used in combination with seeds to achieve the best restoration outcome. Seed‐based approaches have the potential to be viable and scalable for Z. muelleri given that large numbers of seeds can be collected and stored for at least 7 months before successfully germinating in the field. However, further studies are required to overcome the seedling survival bottleneck (approximately 4 months from emergence) and further increase in situ germination rates. [ABSTRACT FROM AUTHOR]

Loading, retention, and in-lake cycling of phosphorus (P), nitrogen, silica, and dissolved organic carbon (DOC) were studied 1 year before and 3 years after P-inactivation by aluminum (Al) hydroxide in Danish Lake Nordborg in 2006. Simultaneously, external P loading was reduced by 40% via establishment of precipitation ponds in two inlets. After Al treatment, the internal P loading (sediment P release) during summer declined 90%-94%, owing to adsorption to aluminum hydroxide. Also, silicate regeneration from the sediment was reduced by 69%-76%, and sediment oxygen uptake as well as ammonium release declined markedly. Consequently, lake water total P, dissolved inorganic P, silicate, and DOC decreased by 73%, 97%, 87%, and 46%, respectively. The Secchi depth increased in the summer period during the first post-treatment year, but declined afterwards to pre-treatment levels, even though the mean lake-water total P concentration during summer was reduced from ~240 µg x [L.sup.-1] before treatment to 26-65 µg x [L.sup.-1] in the first three post-treatment years. We conclude that a further reduction in external P loading is needed to obtain the full effect of the Al treatment in Lake Nordborg. Nous avons determine l'apport, la retention et le recyclage au sein meme du lac du phosphore (P), de l'azote, de la silice et du carbone organique dissous (DOC) un an avant et trois ans apres l'inactivation du P par l'hydroxyde d'aluminium (Al) dans le lac Norborg au Danemark en 2006. Au meme moment, la charge externe de P a ete reduite de 40% par l'etablissement d'etangs de sedimentation sur deux tributaires. Apres le traitement a Al, l'apport interne de P (liberation de P par les sediments) durant l'ete a decline de 90-94% a cause de l'adsorption a l'hydroxyde d'aluminium. De plus, la regeneration du silicate a partir des sediments a ete reduite de 69-76% et l'absorption d'oxygene par les sediments de meme que la liberation d'ammonium ont diminue de facon marquee. En consequence, le P total, le P inorganique dissous, le silicate et le DOC ont diminue dans l'eau du lac par respectivement 73%, 97%, 87% et 46%. La profondeur de Secchi s'est accrue durant la periode d'ete de la premiere annee apres le traitement, mais a decru ensuite pour atteindre les valeurs d'avant le traitement, meme si la concentration moyenne de P total a diminue de ~240 µg x [L.sup.-1] avant le traitement a 26-65 µg x [L.sup.-1] dans les trois premieres annees apres le traitement. Nous concluons qu'une reduction supplementaire de l'apport externe de P est necessaire afin d'obtenir le plein effet du traitement a l'Al dans le lac Norborg. [Traduit par la Redaction], Introduction Aluminum (Al) treatment has been widely used as a restoration tool in eutrophic lakes to precipitate phosphorus (P) in the lake water, and to reduce internal P release (e.g., [...]

Traditional monitoring (e.g., in-water based surveys) of eelgrass meadows and perennial macroalgae in coastal areas is time and labor intensive, requires extensive equipment, and the collected data has a low temporal resolution. Further, divers and Remotely Operated Vehicles (ROVs) have a low spatial extent that cover small fractions of full systems. The inherent heterogeneity of eelgrass meadows and macroalgae assemblages in these coastal systems makes interpolation and extrapolation of observations complicated and, as such, methods to collect data on larger spatial scales whilst retaining high spatial resolution is required to guide management. Recently, the utilization of Unoccupied Aerial Vehicles (UAVs) has gained popularity in ecological sciences due to their ability to rapidly collect large amounts of area-based and georeferenced data, making it possible to monitor the spatial extent and status of SAV communities with limited equipment requirements compared to ROVs or diver surveys. This paper is focused on the increased value provided by UAV-based, data collection (visual/Red Green Blue imagery) and Object Based Image Analysis for gaining an improved understanding of eelgrass recovery. It is demonstrated that delineation and classification of two species of SAV (Fucus vesiculosus and Zostera marina) is possible; with an error matrix indicating 86–92% accuracy. Classified maps also highlighted the increasing biomass and areal coverage of F. vesiculosus as a potential stressor to eelgrass meadows. Further, authors derive a statistically significant conversion of percentage cover to biomass (R 2 = 0.96 for Fucus vesiculosus, R 2 = 0.89 for Zostera marina total biomass, and R 2 = 0.94 for AGB alone, p < 0.001). Results here provide an example of mapping cover and biomass of SAV and provide a tool to undertake spatio-temporal analyses to enhance the understanding of eelgrass ecosystem dynamics. [ABSTRACT FROM AUTHOR]

Information on the physical and ecological state of streams along with an overview of the need for maintenance is traditionally a time-consuming manual field task with subsequent limitations in area coverage. Here we propose a novel approach to stream monitoring and management using a low-cost Unmanned Aerial Vehicle (UAV) platform to collect data comparable to that from traditional monitoring schemes. This technology provides high-resolution imagery while being easy to implement at a low cost along with providing data that represent the stream in both fine-scale and at landscape scale. The results show a significant correlation between results obtained by the two methods, with the largest difference in DFI values being 10, but in many cases being <5. The UAV-method is especially strong in supporting geographical measurements of stream width and course along with certain stream parameters such as physical variation, water flow and gravel coverage. The results indicate that UAV mapping of streams is a feasible alternative or support to the traditional mapping of certain open stream types with the possibility of covering more area with the same time-use. [ABSTRACT FROM AUTHOR]

Zostera muelleri , the dominant seagrass species along the eastern coastline of Australia, has declined due to anthropogenic stressors, including reduced water clarity. Water quality has improved in recent years, but restoration efforts are hampered by limited knowledge of transplantation methods. To support future restoration efforts, we tested multiple techniques for transplanting mature seagrass shoots: (1) sediment cores with intact seagrass plants (plug); (2) individual shoots anchored on frames (frame); (3) frame methods combined with subsurface mats to exclude bioturbating animals (mat + frame); (4) above-ground cages to exclude grazing fish (cage + frame); and (5) combined treatment of above-ground cages and subsurface mats (cage + mat + frame). Transplant success over 10 months showed considerable variability among locations. At one site, seagrass persisted in all treatments, with highest growth in the mat + frame treatment. At two locations, uncaged shoots were lost within 6–35 days of transplanting, presumably due to grazing by fish. In treatments with cages, growth was again highest in the mat + frame treatment. At the fourth location, all seagrass was lost due to physical stress. Thus, we conclude that transplantation success is highest using the mat + frame technique, but overall success depends on careful assessment of biotic and abiotic stressors at the chosen locations. The seagrass Zostera muelleri has, in recent decades, declined massively along the eastern coastline of Australia. To restore this important marine plant, we tested multiple techniques for transplanting mature adult seagrass shoots. Results showed that transplantation works best when shoots are anchored and bioturbating animals are excluded. However, in areas where grazing fish are present, the transplanted shoots should be further protected by placement of cages above the shoots. [ABSTRACT FROM AUTHOR]

The lacking recovery of eelgrass ( Zostera marina ) has been observed in many coastal areas throughout the world. Through a strategic field project we managed to characterize and quantify the impact of new and already known stressors and their thresholds on the recovery process. The stressing mechanisms were 1) Physical stress from wave and current action 2) low sediment anchoring capacity facilitate uprooting of eelgrass seedlings; 3) benthic light intensity 4) ballistic stress from drifting macroalgae are damaging seedlings, 5) too frequent resuspension impoverishing the benthic light climate and dispersing seeds to deeper areas not sufficiently supported with light, 6) lugworms burial of seeds, and uprooting or burial of seedlings. Based on the field and supporting laboratory studies we present a GIS-tool that from data on a suite of stressors are able to predict potential areas for recovery of eelgrass by transplantation actions and seed broadcast. Input data may be field data or model simulation results. Here we have used model results. These input data were reclassified into 5 ranges, according to how much it impacted the eelgrass recovery process: 1) Optimal recovery, 2) Good recovery, 3) Threshold for recovery, 4) Poor recovery and 5) Very poor recovery. Afterward a weighed overlay function was performed, ending up with an accumulated value for stress impact on the eelgrass recovery process in all location in the Danish estuary, Odense Fjord. The GIS-tool is able to calculate and visualize areas of individual and/or multi-stress situations at specific locations. It also managed to identify potential recovery area at the present loading and after a 30% reduction of the external nitrogen loading of the system. Further validation by field activities is needed to verify the precision of the tool. [ABSTRACT FROM AUTHOR]

Stormwater ponds are a common way to handle urban runoff. Different pond designs have been tested for decades to retain as much water as possible. Lately also, retention of nutrients and organic matter has become increasingly important, to reduce the eutrophication of downstream aquatic systems and thereby, e.g. fulfil the European Water Framework Directive. We have examined the load of particulate and dissolved fractions of organic matter, phosphorus, nitrogen and iron in 66 Danish ponds to determine the importance of catchment type (66 ponds) and the retention efficiency of the ponds (39 ponds) dependent on their type, age, size and design. The results showed that discharge from nutrient enriched and industrial areas is the most polluted while urban and developing areas are the least polluted. Wet ponds combined with vegetated sand filters have higher retentions of the particulate fractions (40-80%) compared with traditional wet ponds (10-20%). Generally, optimized retention requires a ratio between pond volume and impermeable catchment area of >250 m3 red.ha (reduced or impermeable hectare). Young ponds have higher retention than older ones, especially regarding the particulate fractions of organic matter, phosphorus and nitrogen. Here, 40-50% is retained in ponds <5 years, 0-30% in 5-10-year-old ponds and almost nothing in ponds >10 years. For the dissolved fractions, the trend is the same, but with lower retentions. Therefore, management and maintenance should be considered for all ponds, to avoid problems of internal loading, filling and resuspension. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The heterogeneous nature of both groundwater discharge to a lake (inflow) and nitrate concentrations in groundwater can lead to significant errors in calculations of nutrient loading. Therefore, an integrated approach, combining groundwater flow and transport modelling with observed nitrate and ammonium groundwater concentrations, was used to estimate nitrate loading from a catchment via groundwater to an oligotrophic flow-through lake (Lake Hampen, Denmark). The transport model was calibrated against three vertical nitrate profiles from multi-level wells and 17 shallow wells bordering a crop field near the lake. Nitrate concentrations in groundwater discharging to the lake from the crop field were on average 70 times higher than in groundwater from forested areas. The crop field was responsible for 96% of the total nitrate loading (16.2 t NO3/year) to the lake even though the field only covered 4.5% of the catchment area. Consequently, a small change in land use in the catchment will have a large effect on the lake nutrient balance and possible lake restoration. The study is the first known attempt to estimate the decrease of nitrate loading via groundwater to a seepage lake when an identified catchment source (a crop field) is removed. [ABSTRACT FROM AUTHOR]

Heavy metals have toxic effects on flora and fauna in the aquatic environments and are of great concern in stormwater. Heavy metal runoff was studied in 37 stormwater ponds in Denmark with varying heavy metal load, catchment type and pond design. The studied metals were Cu, Cr, Cd, Pb, Ni and Zn. The concentrations varied considerably depending on the catchment type, with the highest concentrations coming from industrial areas and the lowest from uncultivated and rural areas. Ponds can effectively remove heavy metals in particulate forms through sedimentation processes, but the dissolved forms are more difficult to retain. The removal efficiency in the ponds varied considerably, with the highest retention of Pb, Ni and Zn due to higher particulate fraction. The retention increased with increased pond volume-to-reduced catchment area ratio. In addition, the pond age affected the efficiency; whereas ponds less than 1–2 years efficiently removed all metals, 30–40-year-old ponds only removed Pb, Ni and Zn, but steeply decreasing over the years. Physical parameters such as pond size, age and sedimentation patterns were found to play a more significant role in the removal compared with chemical parameters such as pH, oxygen and organic matter. Input of metals to the ponds was reflected in the sediment content, but not significantly for all heavy metals probably due to low or varying retention caused by mineralization and re-suspension. The heavy metal concentration in the outlets was reduced to non-toxic levels, except for Cu and Cr at a few study sites. [ABSTRACT FROM PUBLISHER]

Decades of eutrophication have increased water turbidity in Danish estuaries and led to light limitation of eelgrass (Zostera marina) growth. Former eelgrass areas are now denuded and consist of organic-rich muddy sediment with frequent resuspension events that maintain a high turbidity state. In addition, low anchoring capacity of eelgrass in the soft organic-rich sediments has contributed to eelgrass loss. When navigation channels in Danish estuaries are dredged, large amounts (~100.000 m3) of sandy sediment are shipped to remote dumping sites. Instead, we suggest that the dredged sand is used to consolidate adjacent muddy areas. We demonstrate in the present laboratory study that capping of fluid muddy sediment with 10 cm of sand is feasible without any vertical mixing and that this marine restoration approach potentially can lower the magnitude and frequency of resuspension events. Erosion of suspended solids change from 5 g m−2 min−1 above muddy sediment as to about 0.2 g m−2 min−1 after sand-capping, implying that the application of sand can improve light conditions. Moreover, since erosion thresholds increase from about 10–12 cm s−1 for mud to 40 cm s−1 for sand-capped mud the anchoring capacity of rooted vegetation is increased. However, the full potential of sand-capping to facilitate restoration of otherwise lost eelgrass habitats requires verification by large-scale field experiments. • The past 40 years of eutrophication have enriched estuarine sediments considerably in organic matter. • Sediments are no longer able to consolidate and resuspension has increased, keeping the water in a more turbid state. • Sand-capping muddy sediments significantly increased the thresholds for sediment erosion. • Sand-capping clearly consolidates muddy sediments, and the average benthic light intensity increases due to less resuspension. [ABSTRACT FROM AUTHOR]

The use of wetlands for processing nutrient- and organic-rich wastewater has proved effective to prevent coastal pollution in developing countries, mainly due to low running costs (low energy consumption and training requirements) and relatively high system filtration efficiency (difference of is flushed in the system minus what is flushed out, multiplied by 100). In this study we present a management model that simulate the fate of area specific organic carbon loadings in constructed mangrove wetlands (CMW). The model was calibrated and validated by measured data obtained from a newly established CMW system in Tanzania. Sewage from a nearby hotel was pumped to a primary stabilization pond with a residence time of 12h. Subsequently, sewage was discharged into 9 unvegetated cells and 9 cells planted with mangrove trees (Avicennia marina). Each group of 9 cells was split into 3 subgroups of 3 cells receiving seawater mixed with 0, 20 and 60% sewage for six months. Raw sewage was assumed to contain 0.5 (150mgBODL−1)person equivalent. The model provided a good simulation of oxygen, carbon and nutrient dynamics in the systems; primary production (by benthic microalgae and phytoplankton); and biomass change of important faunal groups (crabs and gastropods). High sewage loadings and reduced residence time decreased the system filtration efficiency. Thus a discharge of 100L of 1PE (300mgBODL−1)m−2 into the system requires a water residence time of about 60h within the CMW to achieve the Tanzanian emission standards (30mgBODL−1). Higher mangrove fauna biomass and abundance of biogenic structures (i.e. pneumatophores and crab burrows) increased carbon mineralization in the CMW sediment by up to a factor of 2. [Copyright &y& Elsevier]

The article presents a study which examines the five types of crushed concrete in the laboratory to measure the retention capacity of dissolved phosphorus (P). The study shows that all types effectively removed P, while the possible release of bound P differed between 0.4 and 4.6%. It reveals that crushed concrete can be an efficient tool in removing P in agricultural and urban runoff as filter material in infiltration/sedimentation ponds offered that potential of hydrogen (pH) in the treated water in diluted or neutralized before outlet to avoid undesired impacts due to the high pH.

The characteristics of stormwater need focus due to climate change. Paved areas and recipients receiving more stormwater have an enhanced need for treatment before discharge to remove suspended solids, nutrients and xenobiotics. To handle and treat stormwater efficiently, knowledge concerning first flush patterns is crucial. Therefore, we have studied 12 entire rain events and correlated water volume, suspended solids, and dissolved and particulate phosphorus to catchment characteristics and precipitation characteristics. We have mainly studied smaller rain events (average 12.6 mm), as nearly 90% of the events in the studied catchment are <10 mm. We revealed first flush tendencies in 50% of the rain events, concerning both suspended solids and phosphorus. We also found significant correlations between catchment size and discharged masses, and most importantly between precipitation patterns and discharged mass per volume. A long dry period and low amount of rain during the previous event, as well as high rain intensity, gives a high chance of first flush. We conclude that stormwater treatment should focus on the initial part of the event, especially in areas with a lack of space and/or economy to handle and treat the entire event. [ABSTRACT FROM AUTHOR]

Climate changes, intensive agricultural production, and expanding urban areas make the study of runoff and its possible impact on stream quality increasingly important. In this study, we examined large datasets concerning catchment type, stream quality, and invertebrate composition in a comprehensive geographic information system study. The aim was to examine correlations between land use type and quality of the receiving waters to detect possible differences in anthropogenic impacts. The studied area covered 937 km2, and the dataset included 1672 stretches of streams and data from 468 fauna sampling stations. Runoff from agricultural areas more negatively influenced the stream quality than runoff from urban areas. Considering urban catchments, the areas with separate sewer systems generally influenced the stream quality less than catchments with combined sewer systems. In conclusion, the catchment of any specific stream must contain an area with a minimum of 20–30% without agriculture or urban areas to obtain good ecological status; when focusing only on the riparian zone (10 m on each side of the stream), a minimum of 40–55% is needed to create a good ecological status. Therefore, management focus on the entire catchment is important and separate sewers should be preferred rather than combined sewers. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Seagrass global distribution has declined in the last decades due to many causes, and the implementation of recovery programmes as well as the development of new restoration techniques are needed. This work describes the development of an innovative restoration measure to enhance Zostera marina (eelgrass) seed germination and seedling survival in sediments inhabited by lugworms ( Arenicola marina ) and its validation in mesocosm experiments. The technique consists of placing 3 cm thick biodegradable coconut fibre mats (membrane) in the surface sediment to exclude the negative effects of sediment reworking (burial of seeds and destabilization/burial of seedlings). Two different flume mesocosm experiments were setup to test for: i) the effect of membranes on burial of Z. marina seeds; ii) the effect of membranes on survival and growth of Z. marina seedlings. The experiments were run for 8 and 10 weeks, respectively. Results show that the membrane was effectively preventing critical burial of Z. marina seeds as all seed mimics placed on the surface initially were recovered from 0 to 4 cm depth in the plots with membrane, while in the absence of the membrane, all seeds were buried to below the critical depth of 5–6 cm. The membrane also significantly enhanced the survival of Z. marina seedlings. The initial seedling density was in both cases 30/m 2 and the final density was 26.0 ± 3.3/m 2 with membrane versus 8.0 ± 1.6/m 2 without membrane. This new marine restoration measure showed to be effective on the reduction of the physical stress imposed by sediment reworking lugworms on Z. marina recovery, as a membrane keeps seeds at optimal depth for germination and protects seedlings from burial and erosion. In comparison to other measures, this new restoration technique is a low-tech nature-based solution. The results clearly show that this restoration technique can support Z. marina recovery through seeds and seedling protection. In this way, this technique contributes to decrease Z. marina vulnerability and increase its natural recovery potential and stability. [ABSTRACT FROM AUTHOR]

Eelgrass is a key indicator for the water quality in Europe ( WFD , European Union, 2000 ). However, although water quality has been improved in most Danish water bodies, the eelgrass population does not seem to be recovering. In this study, we validate and further develop a GIS tool designed by Flindt et al. (2016) , to evaluate the potential of eelgrass reestablishment in Danish waters. The GIS tool was tested in two large broads of the Limfjorden, Løgstør and Lovns broad (Denmark), where two scenarios are run. The first scenario was set up including modelled data, whereas the second scenario included both monitored and modelled data. All scenarios were validated with monitored data collected over a 5 years period in the two broads. The developed GIS tool highlights areas with eelgrass potential, both for vegetative growth and sexual reproduction, in accordance with those found in situ in the period 2009–2013, in the two investigated broads. A combination of modelled and monitored data was found to be optimal to achieve accurate predictions for eelgrass development in the Limfjorden using this GIS tool. In order to implement the current model or to use this GIS tool in other locations, it is needed to have detailed knowledge of the area in focus, especially on the controlling ecosystem parameters and pressures. This eelgrass GIS tool is been proven to be especially beneficial as site selection tool for marine spatial planning e.g. in relation to the implementation of the WFD and the ICZM directives ( WFD , ICZM ), to help assessing anthropogenic/targeted environmental impacts e.g. assessing mussel fisheries impacts and is as well a powerful tool to optimize monitoring cost efficiency. Finally, the described GIS tool, originally set for Odense fjord (Denmark) by Flindt et al. (2016) , has been validated with data from Limfjorden, corroborating the efficiency of the studied tool in Danish waters. [ABSTRACT FROM AUTHOR]

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 ton C km −2 in Odense Fjord and from 24.42 to 5.58 ton C km −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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Phosphorous removal was studied in filters with sand and crushed concrete. [•] Set-up of a dynamic model for a combined sedimentation and infiltration pond. [•] We can simulate removal of phosphorous and suspended particulate matter. [•] Model based design of ponds optimize the phosphorous removal efficiency. [•] Dissolved phosphorous is ineffective removed in wet ponds, but what about filters? [ABSTRACT FROM AUTHOR]

Highlights: [•] An agent based model was developed to simulate unattached macroalgae in a fjord. [•] Bottom drifting macroalgae generate sediment resuspension and reduce light availability. [•] The reduced light availability at the seabed and the ballistic effect generated by drifting macroalgae negatively affect eelgrass populations. [•] The model simulates the monitored macroalgae distribution. [•] The model simulates the location of hot spots where eelgrass recovery is affected by macroalgae stress. [Copyright &y& Elsevier]

Abstract: Eelgrass (Zostera marina) used to dominate the vegetation in Odense Fjord, Denmark, and covered >17km2 of the shallow fjord in 1983. Decades of excessive nutrient loading has lead to decreased eelgrass distribution, and only ~2km2 is covered at present. The state of low eelgrass coverage has not changed despite significant improvements of water quality in the past >10years, and lugworms, Arenicola marina, have colonized the former eelgrass areas (1–8ind.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 1–2months, 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 (5–10ind.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. [Copyright &y& Elsevier]

Abstract: In many shallow coastal areas worldwide, several species of opportunistic macroalgae (mainly Chlorophyta) have an excessive growth, as a consequence of eutrophication processes. Therefore, bloom-forming macroalgae become the dominant primary producers within these coastal systems. However, frequently the ecology and the ecophysiology of adult macroalgae have been insufficient to explain their seasonal abundances. Thus, it is essential to understand the factors that regulate the germination and growth of spores of opportunistic green macroalgae. In the present work, we assessed the effects of nutrients (N and P), salinity and light on the germination and growth of Enteromorpha spores. Overall, the results highlight the fact that, such as for adult macroalgae, spore germination and growth are adversely affected by low salinities. Growth of the spores is significantly decreased at 5 psu, while salinities of 20 and, especially of 35 psu, clearly promote the spore growth. Additionally, Enteromorpha spores seem to be particularly sensitive to PO4–P limitation and to NH4–N toxicity, which suggests a higher sensitivity to the variation of external nutrient concentrations than adult macroalgae. The present results contribute to increase the understanding about the factors that control macroalgal growth at its early phases of development. In particular, the results suggest that the growth of spores from opportunistic green macroalgae is strongly salinity-dependent. Consequently, in highly hydrodynamic systems such as most shallow estuaries, salinity variations may play a determinant role in the yearly abundances of green macroalgae, since it controls macroalgal growth from the spores to the adults. [Copyright &y& Elsevier]