Crushed Oyster Shell Research Articles

Improvement on engineering properties of alkali-activated paste with calcined oyster shell ash and flue gas desulfurisation gypsum

To reduce environmental pollution and conserve natural resources, calcined oyster shell ash (COSA), class F fly ash (FFA) and flue gas desulfurisation gypsum (FGDG) were used in an attempt to improve the engineering properties of alkali-activated ternary cementitious paste. The COSA – obtained by calcining crushed oyster shells at 800°C for 3 h and then grinding to pass through a no. 100 sieve – was used to substitute FFA at rates of 2.5, 5.0 and 7.5 mass%. The alkali solution used was 10M sodium hydroxide and sodium silicate with a modulus of 2.5. The hardened paste with 7.5% COSA, 1% FGDG and ratio of weight of added water to dry binder of 0.09 at 56 days had the highest compressive strength of 62 MPa. Microstructural analyses (scanning electron microscopy and energy-dispersive X-ray spectroscopy) showed that the resulting calcium aluminosilicate hydrate gel was found to have a compact microstructure, which improved the compressive strength of specimens. In summary, COSA successfully replaced natural limestone as a calcium oxide activator to manufacture an alkali-activated ternary cementitious paste containing FFA and FGDG.

Granular Skeleton Optimisation and the Influence of the Cement Paste Content in Bio-Based Oyster Shell Mortar with 100% Aggregate Replacement

The purpose of this paper is to propose a methodology to optimise the granular skeleton assembly of cementitious materials containing non-spherical aggregates. The method is general and can be applied to any granular skeleton whatever the aggregate shape, size, or composition because it is simply based on the direct minimisation of the intergranular porosity to consequently increase the skeleton’s compactness. Based on an experimental design approach, this method was applied to and validated for bio-based oyster shell (OS) mortar with 100% aggregate replacement. First, the best combination of seven crushed oyster shell particle classes was determined and compared with a standardised sand skeleton (0/4 mm) and three other non-optimised OS gradings in terms of intergranular porosity. In particular, it is shown that simply mimicking a reference grading curve initially designed for spherical particles with non-spherical particles led to poor performances. Then, different mortars were cast with the standardised sand skeleton, the optimised OS grading, and the three other non-optimised OS gradings by keeping the water-to-cement ratio (0.5), the aggregate bulk volume, and the cement paste content constant. Mechanical tests in compression confirmed the higher performance of the optimised OS mortar, validating the global optimisation approach. However, the high elongation of the oyster shell aggregates led to high skeleton intergranular porosities—even after optimisation—and the cement paste content needed to be adapted. For a given granular skeleton and for a constant aggregate bulk volume, the increase of the cement paste content led to an increase of both the filling ratio and the mechanical properties (compressive and flexural strengths). Finally, it is shown that the proposed skeleton optimisation and a cement paste content adjustment allowed recovering good mechanical properties for an oyster shell mortar with 100% aggregate replacement, especially in flexural tension.

Comparative study on stabilized oyster shells adobes: Mechanical resistance, durability and GHG emissions assessment

Adobes are earth bricks made without compression or firing in casts, usually using local soil. To improve adobe´s durability and mechanical behavior, the adobes allow the addition of various materials to stabilize them. This work compares the technical and GHG (greenhouse gas emissions) of adobes stabilized with potassium hydroxide, commercial lime Portland cement, and cement with hydrated lime, room-temperature cured. The adobe formulation was inspired by traditional mud adobes from the Aveiro region (Portugal), composed of silty clay loam local soil (80 wt.%), stabilized with wheat straw fibers (10 vol.%) and crushed oyster shells as filler, incorporating bio-based material. The adobe samples were assessed after 28 days of curing and after accelerated aging cycles. The mineralogy of the stabilized adobes after 28 days was determined through X-ray fluorescence (XRF) and X-ray diffraction (XRD) analysis. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) compared changes after aging cycles. Compressive strength and water erosion tests were performed to assess the stabilization and durability of the adobes. GHG emissions (kgCO2-eq.) of the mixes were provided through the life cycle assessment (LCA) methodology. The results indicate that the adequate type of stabilizer can change regarding the application of the adobes in the building. Lime and cement provided better compressive strength and durability, allowing a broader range of applications with higher GHG in comparison to KOH adobes, which presented restricted applications. This study contributes to encouraging the use of LCA along with durability assessment in earthen materials to promote sustainability in the construction sector.

The Use of Pre-Wetting to Improve the Mechanical Behavior of Masonry Mortar Elaborated with Crushed Oyster Shell

In this research, the use of the pre-wetting technique is proposed as an ecological alternative to reduce water absorption in waste oyster shells used in the production of masonry mortar as a partial substitute for natural sand. An experimental study was conducted to assess the properties in both the fresh and hardened states of masonry mortars. Two mortar groups were prepared based on a control mixture, with natural aggregate replaced by crushed oyster shell (COS) in varying proportions. In one group, the COS was pre-wetted, while in the other group, the COS was used at its natural moisture content. The experimental results demonstrated that the pre-wetting process aided in reducing the water–cement ratio (w/c) in the mortar mixture, thereby improving its properties. In both mortar groups, favorable results were observed with respect to capillary water absorption. Although the compressive strength was affected by the incorporation of COS, pre-wetted mortars with substitutions of up to 30% achieved the reference value established in this research. The pre-wetting process proves to be a straightforward and cost-effective technique; it is environmentally friendly and will contribute to decreasing the accumulation of COS in landfills, thereby safeguarding natural material reserves.

Fundamental Study on the Application of Oyster Shell as an Aggregate for Concrete in Coastal/Marine Structures

This study uses oyster shells as an aggregate substitute for marine concrete structures. The initial strength of concrete according to the proper particle size composition of the crushed oyster shell was experimentally analyzed. The particle size of the crushed oyster shell obtained through the shredder is out of the range of general aggregates' standard particle size curve because the ratio of 5 mm or less exceeds 50%. It was confirmed that if less than 5 mm was left abroad, it was within the range of the standard particle size curve, and only these were applied as thick aggregate substitutes. The crushed oyster shells impair workability due to their relatively high absorption rate. This study attempted to overcome poor workability by using two methods: using the crushed oyster shells in a saturated-surface-dry (SSD) state and adding an air entraining agent (AE). The SSD case showed that the slump increased, but the strength decreased by about 40%. The AE added case showed a slight decrease in strength while the slump more than doubled.

Influence of Oyster Shell Pyrolysis Temperature on Sediment Permeability and Remediation

Permeability is an important aspect of sediment remediation. It is well-known that oyster shells can be used for sediment remediation, however the influence of pyrolysis temperature on sediment permeability remains unknown. In this study, we examined sediment permeability and remediation using crushed oyster shells of less than 5 mm in size that were pyrolyzed at 350 °C (POS350) and 600 °C (POS600) for six hours. Based on the results of the variable head permeability test, POS600 has greater sediment permeability than POS350. In addition, POS600 has greater than POS350 to reduce dissolved inorganic nitrogen (DIN; NH3-N, NO2-N, and NO3-N) and phosphate (PO4-P) from organically enriched sediment because of its higher Ca2+ elution. In conclusion, pyrolysis of oyster shells at 600 °C is more effective than pyrolysis at 350 °C. This finding is true because the transformation of CaCO3 to CaO, which is the source of Ca2+, stimulates pore water flow. Based on these findings, it can be concluded that pyrolyzed oyster shells are beneficial for increasing sediment permeability, thereby helping in the remediation of sediments.

Prophylactic efficiency of the administration of vitamin, mineral and sorbent complexes on bone tissue in female rats against the background of chronic alcohol consumption

Among the general effects of alcohol use, it has a negative effect on the bone system, so the development of prevention methods is becoming an increasingly urgent problem. The present study was aimed at evaluating the efficiency of the preventive complexes for the bone system in chronic alcohol intoxication. The study was conducted on 2-month-old female rats for 104 days. Chronic alcoholism in animals was simulated by replacing drinking water with an ethanol solution, the concentration of which was gradually increased from 8–25%. The prophylactic was administered by introducing into the diet a complex of vitamins (P, C, D) and minerals (Cu, Mg, Zn, Se, Mn), the main component of which was crushed oyster shells processed with citric acid. The second prophylactic complex was the clay mineral montmorillonite in combination with vitamins P, C, D. The biochemical markers of resorption (elastase and acid phosphatase activity), osteogenesis (calcium content, alkaline phosphatase activity) and the state of the antioxidant system (catalase, superoxide dismutase, glutathione reductase activity, malondialdehyde content) were determined in bones (jaws and femurs). Chronic alcohol consumption led to an increase in the degree of atrophy of the alveolar process, a decrease in femur bone density due to a decrease in the mineral component in bone tissue, and did not affect the state of the lumbar vertebrae. Chronic alcohol intoxication led to a decrease in the level of calcium in the blood serum of rats, and to a decrease in the alkaline phosphatase activity and the calcium content in the bone tissue of the jaws and femur against the background of increases in the activities of acid phosphatase and elastase. A significant decrease in the activity of the main antioxidant enzymes (superoxide dismutase, catalase and glutathione reductase) in bone tissue of animals against the background of an increase in the malondialdehyde content under conditions of chronic alcoholization has been established. The use of the complex with crushed oyster shells effectively prevented atrophy ofthe alveolar process in the jaws, did not affect the morphometric parameters in the femur and vertebrae, but normalized the activities of serum alkaline phosphatase and catalase, bone elastase, acid phosphatase, superoxide dismutase and glutathione reductase against the background of restoring the levels of calcium and malondialdehyde both in the serum and in the bone tissue of rats subjected to chronic alcoholization. Prophylactic administration of the vitamin complex with montmorillonite had a much weaker effect on the studied indicators. The obtained research results allow us to conclude that the osteoprotective and antioxidant efficiency of the complex with crushed oyster shells is more pronounced than that of montmorillonite under conditions of chronic alcohol intoxication.

Solent oyster enhancement reef concrete colonisation trials

The Interreg funded project RECIF (2012-2015) developed waste shell concrete formulations specifically for artificial reefs. Its successor MARINEFF continues these evaluating further formulations to maximise both physical performance and endurance with biological attractiveness. Four formulations were produced by ESITC Caen for trials based on combinations of two cement types (CEM II and CEM IV) with either coarse aggregate or crushed oyster shells replacing 20% of the aggregate. The most extensive colonisation trials were carried out with 5x5x2cm blocks by both UK and French partners. These test blocks also had smooth and rough faces. This paper describes the results of Southampton biological colonisation trials. Four blocks, one of each formulation along with an oyster shell cut to the same area were secured in a framework and pairs of these were suspended vertically at 6 fully saline sites around the Solent region (Calshot, Beaulieu River, Hamble River, Itchen River, Portsmouth and Langstone Harbours) from May to August 2019. On recovery these were analysed for Total Biomass, Algae (PAM & %cover), Anemones (n), Ascidians (%cover), Barnacles (n & % cover), Bryozoans (%cover), Hydroids (%cover), Mytilus edulis (n), Pomatoceros sp. (n), Sponges (%), Spirorbis sp (n). There were considerable differences in colonisation between the sites which are described in detail, but overall in terms of overall biomass the formulation using CEM V and 20% oyster shell performed as well as the oyster shell. Given that it is accepted that oysters are attracted to natural shell substrate, this concrete was promising for the choice mix of the final oyster reef modules deployed at Calshot, September 2020.

Field study on short-term changes in benthic environment and benthic microbial communities using pyrolyzed oyster shells

To evaluate the effect of pyrolyzed crushed oyster shells (PCOS) on the remediation of sediments and microbial diversity, a field study was conducted in Buksin Bay, Tongyeong City, Republic of Korea. It was observed that after treatment with PCOS, the concentration of H2S in the sediment of the control site was 287 mg/L. Furthermore, it decreased up to 0 mg/L and remained so until the end of the field study, that is for a period of six months. Moreover, the concentrations of NO2-N + NO3-N, NH4-N, and PO4-P decreased sharply, and the oxidation-reduction potential (ORP) increased after PCOS treatment in pore water and overlying water. Regarding the diversity of microbial communities, the predominance of bacteria from phylum Chlorobi was observed in highly reduced (−410 mV; ORP) sediment, which is well known for the production of H2S. After PCOS treatment, the relative abundance of Chlorobi was sharply suppressed. On the other hand, the predominance of bacteria from the phyla Proteobacteria and Bacteroidetes was observed, and their relative abundance in the PCOS-treated sediment increased throughout the experiment, based on 16S rRNA sequencing. The results demonstrate that the abundance of bacterial communities in the PCOS-treated sediments of Buksin Bay is important for marine ecological functioning, especially for pollutant transformation.

Plant-growing performance of pervious concrete containing crushed oyster shell aggregate

Global warming is the gradual increase in global temperatures owing to trapping of heat in the atmosphere by greenhouse gases. As of January 2020, 121 countries and 1 region, including Japan, pledged to achieve carbon neutrality by 2050. One of the measures for achieving this goal is the promotion of low-carbon urban development, which includes urban greening. Oysters are produced in all districts of Japan but Hiroshima Prefecture is particularly famous for its high production levels. The production of oysters generates oyster shells as a by-product, which are used commercially as livestock feed and a soil conditioner. However, the reuse of oyster shells remains limited. Pervious concrete is a special type of concrete in which single-sized aggregates are bound together with cement paste or mortar and is considered an environmentally friendly material because of its high water permeability. Therefore, we investigated whether oyster shell pervious concrete (OyPC) containing crushed oyster shell aggregate would be suitable for growing plants for potential application as a planting foundation for urban greening. Zoysia tenuifolia sod or Kentucky bluegrass (Poa pratensis) seeds were directly placed or sown in soil on the surfaces of OyPC and crushed stone pervious concrete specimens, which were then placed in plastic containers for either 72 days (short-term planting tests) or 802 days (long-term planting test). OyPC had a higher plant-growing performance than crushed stone pervious concrete in both the short- and long-term planting tests and also pumped the water from the container to moisten the sod and the soil covering the seeds, assisting the growth of plants. The grass on OyPC that has a small particle size could grow without water retention material which is indispensable to crushed stone pervious concrete for greening. These findings indicate that OyPC would be feasible for application as a planting foundation for urban greening.

Performance of Sand-Crushed Oyster Shells Blended Fine Aggregates in Concrete: Waste Management Perspective in Nigeria

Pollution of our environment with wastes and the associated harm to our ecosystem and health is of great concern globally. In addition, the unabated mining of sharp sand for concrete with environmental degradation arising therefrom is worrisome. In the Niger Delta region of Nigeria, enormous quantities of oyster shells are being littered along the streets, riverbanks and landfills, after eating the fleshy part as meat. As a means of managing the waste and conserving sand, this study examines the properties of concrete made, using crushed oyster shells (COS) as partial replacement of sand. Sand was partially replaced in concrete with COS at the rate of 0, 5, 10, 15, 20 and 25%. The concrete matrix was cast in a metal cube mold of 150mm3 and cured for 3, 7, 14 and 28 days. A total of 72 cubes were cast in three replicates for each replacement level and each curing period, using a standard mix of 1:2:4 and water-cement ratio of 0.5. The results reveal that the addition of COS reduces the slump of the fresh concrete from 27 mm at 0% to 20 mm at 25%. The addition of COS up to 25% reduced the density of the concrete by 4.05%. The compressive strength slightly reduced as the percentage replacement increased from 0 to 25%. The findings recommend replacement not exceeding 15% that has true slump of 23.5 mm, lighter density of 25.17 kg/m−3 and compressive strength of 26.2 Nmm−2 which are good for concrete works. When sand is partially replaced with COS in concrete, we can confront the environmental degradation arising from indiscriminate disposal of oyster shells, as well as the depletion of sand as non-renewable component of concrete.

LONG-TERM PLANT-GROWING PERFORMANCE OF POROUS CONCRETE WITH VARYING AMOUNTS OF OYSTER SHELL AGGREGATE

Oysters are produced in each district in Japan, and Hiroshima Prefecture is especially famous as a high producing district. Accordingly, the production of oysters has created oyster shells as a by-product. Oyster shell porous concrete (OyPoC) is porous concrete using crushed oyster shells as aggregates. In previous researches, it was found that OyPoC with finely crushed oyster shell had high plant-growing performance. However, all of the planting test periods were less than three months; the long-term plant-growing performance of OyPoC had not been clear. In this study, the plant-growing performance of OyPoC was investigated by conducting long-term planting tests over one year. OyPoC and hybrid porous concrete (HyPoC), which was combined with OyPoC and crushed stone porous concrete, were prepared for the planting tests. From the test results, the plant-growing performance of OyPoC was higher than that of HyPoC because OyPoC had much higher oyster shell aggregate than HyPoC. In contrast, there was a risk of the severe summer drought withering the grass on OyPoC and the watering in the summer was found to be important.

Modified Crushed Oyster Shells for Fluoride Removal from Water

Elevated concentrations of fluoride ions (F−) in natural groundwater are a worldwide problem. Discarded oyster shells were ground to ≤100 µm particle size to produce oyster shell powder (OS). A subset of the OS was heated to produce calcined oyster shell (COS). A subset of the COS was further treated with 1 M phosphoric acid to produce phosphoric-acid-treated oyster shell (POS). OS and COS were combined with phosphoric acid (1.6 mM and 3.2 mM) to produce OS + P (oyster shell with phosphoric acid) and COS + P (calcined oyster shell with phosphoric acid). OS and COS removed 46% and 50% (10 g/L of sorbent dose) but POS, OS + P and COS + P removed 96%, 100% and 76% (1 g/L of sorbent dose) when the initial concentration of fluoride was 10 mg/L. The sorption kinetics of POS, OS + P and COS + P followed second-order reaction rates, and sorption isotherms of all sorbents were well-described by the Freundlich sorption isotherm. These results indicate that oyster shells can be an effective sorbent for fluoride removal, with the added benefit of re-use of a waste product.

Biogas production from high solids anaerobic co-digestion of food waste, yard waste and waste activated sludge

High-solids anaerobic co-digestion (HS-AcD) has the potential to recover energy and reduce environmental impacts of the organic fraction of municipal solid waste and waste activated sludge. We investigated the impact of substrate to inoculum (S/I) ratios, alkalinity sources (sodium bicarbonate and oyster shells), co-substrate mixing ratios and inoculum acclimation on HS-AcD of food waste, yard waste, and waste activated sludge using batch studies. Long-term HS-AcD performance was evaluated under the optimal conditions through a semi-continuous biodigester study with leachate recirculation. The digester with S/I = 1 using a mixture of crushed oyster shells and sodium bicarbonate as alkalinity sources had the highest methane yields (183 mL CH4/g VS). Addition of waste activated sludge to food waste and yard waste alleviated acidification (pH 6.86 ± 0.12) during the start-up period, which and improved digester stability. Mixtures with FW/YW/WAS = 0.8:1.7:0.5 had higher methane yields (134 ± 15 mL CH4/gVS) than mixtures with FW/YW/WAS = 1:1:1, but required a longer time (10 days) for self-recovery from volatile fatty acid inhibition. The use of an acclimated inoculum eliminated the lag time during start-up and produced 38% higher methane yield. In the semi-continuous biodigester, an average volatile solids reduction of 38% and methane yield of 186 mL/gVS was achieved. Improved performance in the semi-continuous biodigester compared with batch reactors was likely due to leachate recirculation, which can improve mass transfer of substrates to the microbial community. Digestate produced from HS-AcD of waste organics had a 1.7–2.3 fold higher nitrogen, similar phosphorous and 0.2–0.3 fold lower potassium content than commercially available bioorganic fertilizer.

Effects of Crushed Oyster Shell on Strength and Durability of Marine Concrete Containing Fly Ash and Blastfurnace Slag

A large quantity of oyster shell is generated every year in coastal regions. Instead of being dumped as waste, after crushing or grinding, oyster shell may be recycled for use in concrete. Herein, the use of crushed oyster shell (COS) in conjunction with fly ash (FA) and blastfurnace slag (BS) to produce marine concrete was studied. By varying the COS, FA and BS contents in the marine concrete, the combined effects of COS, FA and BS on the cube compressive strength, water penetration, cyclic wetting-drying chloride attack and long-term seawater attack resistances were evaluated. The results showed that the addition of proper amounts of COS, FA and BS has positive effects on the strength and durability of marine concrete, but excessive COS may have negative effects. Hence, the combined addition of COS, FA and BS up to a certain optimum COS content is a promising way of producing a higher performance and greener marine concrete.

Effects of Crushed Oyster Shell on Strength and Durability of Marine Concrete Containing Fly Ash and Blastfurnace Slag

Effects of Crushed Oyster Shell on Strength and Durability of Marine Concrete Containing Fly Ash and Blastfurnace Slag

Root exudation of low-molecular-mass-organic acids by six tree species alters the dynamics of calcium and magnesium in soil

Soils in plantations of Cryptomeria japonica in Japan have ∼threefold more exchangeable Ca compared with soils in other types of forest vegetation even in a Ca-poor environment. To explain mechanisms underlying this phenomenon, we determined the effect of root exudation rate of low-molecular-mass organic acids (LMMOAs) on exchangeable cations in soil. We conducted a pot experiment using C. japonica and five dominant tree species in Japan, and measured the root exudation rates of LMMOAs and exchangeable nutrient concentrations in the soils. To estimate whether the root exudation rate of LMMOAs is elevated in response to Ca deficiency, we created variation in Ca availability by adding different amounts of crushed oyster shells. The root exudation rates of LMMOAs were two to five times higher for C. japonica than for other tree species, but did not differ significantly among the different quantities of oyster shell. Exchangeable Ca and Mg were significantly higher in the soils with C. japonica and significantly correlated with the root exudation rate of LMMOAs (R2 > 0.24) at high and moderate quantities of oyster shell. Therefore, variation among species, in terms of root exudation of organic acids, might be one important factor affecting the cation dynamics in soil.

A Tire-Sulfur Hybrid Adsorption Denitrification (T-SHAD) process for decentralized wastewater treatment

Nitrogen discharges from decentralized wastewater treatment (DWT) systems contribute to surface and groundwater contamination. However, the high variability in loading rates, long idle periods and lack of regular maintenance presents a challenge for biological nitrogen removal in DWT. A Tire-Sulfur Hybrid Adsorption Denitrification (T-SHAD) process was developed that combines nitrate (NO3−) adsorption to scrap tire chips with sulfur-oxidizing denitrification. This allows the tire chips to adsorb NO3− when the influent loading exceeds the denitrification capacity of the biofilm and release it when NO3− loading rates are low (e.g. at night). Three waste products, scrap tire chips, elemental sulfur pellets and crushed oyster shells, were used as a medium in adsorption, leaching, microcosm and up-flow packed bed bioreactor studies of NO3− removal from synthetic nitrified DWT wastewater. Adsorption isotherms showed that scrap tire chips have an adsorption capacity of 0.66 g NO3−–N kg−1 of scrap tires. Leaching and microcosm studies showed that scrap tires leach bioavailable organic carbon that can support mixotrophic metabolism, resulting in lower effluent SO42− concentrations than sulfur oxidizing denitrification alone. In column studies, the T-SHAD process achieved high NO3−–N removal efficiencies under steady state (90%), variable flow (89%) and variable concentration (94%) conditions.

Chemical stabilization of cadmium in acidic soil using alkaline agronomic and industrial by-products

In situ immobilization of heavy metals using reactive or stabilizing materials is a promising solution for soil remediation. Therefore, four agronomic and industrial by-products [wood biochar (WB), crushed oyster shell (OS), blast furnace slag (BFS), and fluidized-bed crystallized calcium (FBCC)] and CaCO3 were added to acidic soil (Cd = 8.71 mg kg−1) at the rates of 1%, 2%, and 4% and incubated for 90 d. Chinese cabbage (Brassica chinensis L.) was then planted in the soil to test the Cd uptake. The elevation in soil pH caused by adding the by-products produced a negative charge on the soil surface, which enhanced Cd adsorption. Consequently, the diethylenetriamine pentaacetic acid (DTPA)-extractable Cd content decreased significantly (P < 0.05) in the incubated soil. These results from the sequential extraction procedure indicated that Cd converted from the exchangeable fraction to the carbonate or Fe-Mn oxide fraction. The long-term effectiveness of Cd immobilization caused by applying the 4 by-products was much greater than that caused by applying CaCO3. Plant shoot biomass clearly increased because of the by-product soil amendment. Cd concentration in the shoots was < 10.0 mg kg−1 following by-product application, as compared to 24 mg kg−1 for plants growing in unamended soil.

Unsuitable habitat patches lead to severe underestimation of dynamics and gene flow in a zooplankton metapopulation

Migration and re-colonization enable organisms to persist in metapopulations. Re-colonization success may be limited by the number of arriving migrants or by patch quality. In a well-studied rock pool Daphnia metapopulation, it is frequently assumed that re-colonization is limited by the number of arriving migrants, and that all patches are equally suitable for colonization. This assumption strongly influences how observations about dynamics, epidemiology and population genetics for the entire metapopulation are interpreted. Here we test this assumption. In 627 rock pools, we found that high pH, high Ca(++) and high water conductivity were positively correlated with the presence of D. magna. The experimental release of D. magna into randomly chosen natural pools revealed the highest colonization success in pools with high pH. Next, we elevated pH and Ca(++) concentrations in natural pools by adding a system-specific natural source of calcium carbonate (either from crushed oyster shells or from eider duck droppings, which contain blue mussel shells). These treatments led to a rapid increase in pH and Ca(++) and strongly raised the likelihood that introduced D. magna would establish persistent populations. Therefore, we conclude that low pH and Ca(++) result in unsuitable colonization conditions in two-thirds of the untreated pools. A further experiment revealed that natural colonization rates were about five times higher in calcium-treated pools than in untreated pools. Finally, we observed that eider droppings are more frequently found in the catchment area of occupied pools, than they are in those of unoccupied pools, suggesting that the blue mussel shells contained in the eider droppings play an important role in making pools suitable for colonization and in enabling D. magna to persist. Thus, eider ducks are ecosystem engineers in this system. We recalculate typical metapopulation parameters to account for the unsuitable pools, resulting in a much more dynamic picture of this metapopulation than previously believed, with colonization rates and gene flow three to five times higher. These results have strong implications for metapopulation persistence, local and global genetic diversity, genetic rescue, gene flow and local adaptation. Our results emphasize that without verifying patch suitability, estimated rates of metapopulation dynamics can severely underestimate the true rates.