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De Jong M.F.,Netherlands Institute of Ecology | Baptist M.J.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | Lindeboom H.J.,Netherlands Institute of Ecology | Hoekstra P.,University Utrecht
Marine Pollution Bulletin | Year: 2015

We studied short-term changes in macrozoobenthos in a 20. m deep borrow pit. A boxcorer was used to sample macrobenthic infauna and a bottom sledge was used to sample macrobenthic epifauna. Sediment characteristics were determined from the boxcore samples, bed shear stress and near-bed salinity were estimated with a hydrodynamic model. Two years after the cessation of sand extraction, macrozoobenthic biomass increased fivefold in the deepest areas. Species composition changed significantly and white furrow shell (Abra alba) became abundant. Several sediment characteristics also changed significantly in the deepest parts. Macrozoobenthic species composition and biomass significantly correlated with time after cessation of sand extraction, sediment and hydrographical characteristics. Ecosystem-based landscaped sand bars were found to be effective in influencing sediment characteristics and macrozoobenthic assemblage. Significant changes in epifauna occurred in deepest parts in 2012 which coincided with the highest sedimentation rate. We recommend continuing monitoring to investigate medium and long-term impacts. © 2015 Elsevier Ltd. Source


de Jong M.F.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | Borsje B.W.,Deltares | Borsje B.W.,University of Twente | Baptist M.J.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | And 3 more authors.
Ecological Engineering | Year: 2016

The demand for marine sand in the Netherlands as well as globally is increasing. Over the last decades, only shallow sand extraction of 2m below the seabed was allowed on the Dutch Continental Shelf (DCS). To guarantee sufficient supply and to decrease the surface area of direct impact, the Dutch authorities started to promote sand extraction depths over 2m for sand volumes over 10 millionm3. The ecological effects of deep sand extraction, however, are still largely unknown. Therefore, we investigated short-term effects (0-2.5y) of deep sand extraction (20-24m) and compared these with other case studies such as, regular shallow sand extraction on the DCS (2m) and an 8m deepened shipping lane. For intercomparison between case studies we used tide-averaged bed shear stress as a generic proxy for environmental and related ecological effects. Bed shear stress can be estimated with a two-dimensional quadratic friction law and showed a decrease from 0.50 to 0.04Nm-2 in a borrow pit in 20m deep water and extraction depths up to 24m. Macrozoobenthos in a borrow pit with a tide-averaged bed shear stress of around 0.41Nm-2 is expected to return back to pre-extraction conditions within 4-6 year. When tide-averaged bed shear stress decreases below 0.17Nm-2 enhanced macrozoobenthic species richness and biomass can occur. Below a tide-averaged bed shear stress of 0.08Nm-2, increasing abundance and biomass of brittle stars, white furrow shell (Abra alba) and plaice (platessa platessa) can be expected. Below 0.04Nm-2, an overdominance and high biomass of brittle stars can be expected whereas demersal fish biomass and species composition may return to reference conditions. Next to changes in faunal composition, a high sedimentation rate can be expected. Ecological data and bed shear stress values were transformed into ecosystem-based design (EBD) rules. At higher flow velocities and larger water depths, larger extraction depths can be applied to achieve desired tide-averaged bed shear stresses for related ecological effects. The EBD rules can be used in the early-design phases of future borrow pits in order to simultaneously maximise sand yields and decrease the surface area of direct impact. The EBD rules and ecological landscaping can also help in implementing the European Union's Marine Strategy Framework Directive (MSFD) guidelines and moving to or maintaining Good Environmental Status (GES). © 2015 Elsevier B.V. Source


De Jong M.F.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | Baptist M.J.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | van Hal R.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | de Boois I.J.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | And 2 more authors.
Estuarine, Coastal and Shelf Science | Year: 2014

For the seaward harbour extension of the Port of Rotterdam in the Netherlands, approximately 220 million m3 sand was extracted between 2009 and 2013. In order to decrease the surface area of direct impact, the authorities permitted deep sand extraction, down to 20m below the seabed. Biological and physical impacts of large-scale and deep sand extraction are still being investigated and largely unknown. For this reason, we investigated the colonization of demersal fish in a deep sand extraction site. Two sandbars were artificially created by selective dredging, copying naturally occurring meso-scale bedforms to increase habitat heterogeneity and increasing post-dredging benthic and demersal fish species richness and biomass. Significant differences in demersal fish species assemblages in the sand extraction site were associated with variables such as water depth, median grain size, fraction of very fine sand, biomass of white furrow shell (Abra alba) and time after the cessation of sand extraction. Large quantities of undigested crushed white furrow shell fragments were found in all stomachs and intestines of plaice (Pleuronectes platessa), indicating that it is an important prey item. One and two years after cessation, a significant 20-fold increase in demersal fish biomass was observed in deep parts of the extraction site. In the troughs of a landscaped sandbar however, a significant drop in biomass down to reference levels and a significant change in species assemblage was observed two years after cessation. The fish assemblage at the crests of the sandbars differed significantly from the troughs with tub gurnard (Chelidonichthys lucerna) being a Dufrêne-Legendre indicator species of the crests. This is a first indication of the applicability of landscaping techniques to induce heterogeneity of the seabed although it remains difficult to draw a strong conclusion due the lack of replication in the experiment. A new ecological equilibrium is not reached after 2 years since biotic and abiotic variables are still adapting. To understand the final impact of deep and large-scale sand extraction on demersal fish, we recommend monitoring for a longer period, at least for a period of six years or even longer. © 2014 The Authors. Source


de Jong M.F.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | Baptist M.J.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | Lindeboom H.J.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | Hoekstra P.,University Utrecht
Marine Pollution Bulletin | Year: 2015

We studied short-term changes in macrozoobenthos in a 20. m deep borrow pit. A boxcorer was used to sample macrobenthic infauna and a bottom sledge was used to sample macrobenthic epifauna. Sediment characteristics were determined from the boxcore samples, bed shear stress and near-bed salinity were estimated with a hydrodynamic model. Two years after the cessation of sand extraction, macrozoobenthic biomass increased fivefold in the deepest areas. Species composition changed significantly and white furrow shell (Abra alba) became abundant. Several sediment characteristics also changed significantly in the deepest parts. Macrozoobenthic species composition and biomass significantly correlated with time after cessation of sand extraction, sediment and hydrographical characteristics. Ecosystem-based landscaped sand bars were found to be effective in influencing sediment characteristics and macrozoobenthic assemblage. Significant changes in epifauna occurred in deepest parts in 2012 which coincided with the highest sedimentation rate. We recommend continuing monitoring to investigate medium and long-term impacts. © 2015 Elsevier Ltd. Source


Meriac A.,Wageningen University | Meriac A.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | Eding E.H.,Wageningen University | Kamstra A.,IMARES Wageningen UR Institute for Marine Resources and Ecosystem Studies | And 3 more authors.
Aquaculture | Year: 2014

Denitrification on internal carbon sources offers the advantage to control nitrate levels in recirculating aquaculture systems (RAS) by using the fecal carbon produced within the husbandry system. However, it is not clear to which extent fecal carbon can be utilized by the microbial community within a denitrification reactor. Especially fibers can hamper the bioavailability of carbon in fecal waste. Therefore, this study investigated the nitrogen removal capacity of a denitrification reactor using fecal waste with a high fiber content as the only carbon source in RAS. Furthermore, we investigated to which extent fibers were utilized as a carbon source within the reactor.Four identical small-scale RAS (V. = 460. L) were stocked with 25 rainbow trout of ~. 110. g, and operated at a water exchange rate of ~. 200. L/kg of feed DM. Two RAS served as controls without denitrification and two RAS were upgraded with an upflow sludge blanket denitrification reactor (V. = 10.5. L). During the six weeks of experiment, we determined COD (chemical oxygen demand, measure for organic carbon) and N balances for all systems and analyzed the composition of the collected solids. The denitrification reactors were able to remove 19. g. N/kg of feed DM, or 48% of the metabolic nitrogen waste produced by the fish. Based on the COD balances, 44% of the supplied fecal COD was degraded in the reactor. Hemicellulose and cellulose degradability was ~. 50%, accounting for 45% to the total degraded COD. Under steady state conditions, 4.4. g of biodegradable COD needed to be oxidized to reduce 1. g of nitrogen, indicating respiratory COD losses of approximately 50%.This experiment successfully demonstrated that denitrification on internal carbon sources using a high fiber diet could remove half of the nitrogen waste produced by the fish. Although fibers limited carbon bioavailability, half of the cellulose and hemicellulose present in the fecal waste was utilized in the denitrification reactor. © 2014 Elsevier B.V. Source

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