Subfossil pollen from two co‐existing Betula species in Iceland, B. nana and B. pubescens, is frequently found in sediments and peat. Interpretation of the findings often depends on the ability to differentiate between the two species according to pollen size and structure. Fresh pollen samples were prepared from 70 individual trees/shrubs which had been identified to species by chromosome number. Grain diameters and pore depths were measured and ratios of grain diameter to pore depth (D/P ratios) were calculated. The mean grain diameters of pollen from diploid B. nana and tetraploid B. pubescens were 20.42 and 24.20 µm, whereas mean pore depths were 2.20 and 2.81 µm respectively. Mean D/P ratios were therefore 9.55 for B. nana and 8.85 for B. pubescens. The difference between species was statistically significant for all three pollen parameters. Grain diameter appeared to be the most useful parameter, as only about 20% of the samples were in the overlapping region of the species distributions. Pollen size (grain diameter) was also positively correlated to tree morphology, which was evaluated using species‐specific botanical characters. Pollen samples from different locations/populations in Iceland varied slightly in mean size and ratio. The size difference between pollen of B. nana and B. pubescens in this study is less than other papers have reported, which may be due to the effect of introgressive hybridisation between the two birch species in Iceland.

Aquaponics is a sustainable method of food production, whereby aquaculture and hydroponics are combined in one circular system. A few aquaponics startup companies are emerging in Europe with a limited production area of a few hundred or a few thousand square meters, whereas hydroponics is a common practice in a commercially viable manner most often with production units of several hectares. In Iceland, greenhouse farmers operate on relatively small production units, often between 2000 and 5000 m². The aim of the present study was, therefore, to develop and design aquaponic production systems towards integration into small greenhouse farming strengthening economic viability and sustainability. Since the local market in Iceland is small and import is relatively expensive due to the distance from other markets, the suitability of commercially available fish feed and the selection of plant species were assessed in relation to production efficiency and available market and resources. The effects of water flow on plant growth and on nutrient utilization in culture water were measured and evaluated. Four aquaponics test systems were designed, built and operated, and results were used to develop a pilot commercial aquaponics system implemented for greenhouse farming in Iceland. One of the test systems was a media filled flood and drain system and the other three were deep water culture systems. Tilapia (Oreochromis niloticus), one of the most popular fish in aquaculture, was reared in all systems, while different leafy greens and fruiting vegetables were grown in the hydroponics. The fish was fed with commercial aquaculture feed made for cod and charr. The feed conversion ratio (FCR) was used to assess the effectiveness of feed on fish growth. The FCR observed in this research was between 0.9 and 1.2, within the typical values for tilapia growth in aquaculture. The production of the leafy green plants (e.g., pak-choi) was approximately four times, by weight, that of the production of fish, a similar yield as shown in other researches in the field. The continuous rise of nitrate and phosphate concentrations in the aquaponic system indicated the potential to support even higher crop yield. Long daylength in the summer in Iceland is clearly beneficial for crop production in aquaponics. Based on the results, it is concluded that aquaponics can be a feasible opportunity for greenhouse farming at least to diversify the current business model. Not only can the fish provide an extra income but also the effluent from the aquaculture is easily used as fertilizer for the plants, thus the circular production system offers new innovative ideas for diversifying and value-adding the business further, for example into crayfish production and/or into educational and experience tourism.

Birch has a key role in the Holocene vegetation history of northern Europe and in sub‐arctic climates dwarf birch and tree birch co‐exist. In Iceland, triploid hybrids between diploid Betula nana (dwarf birch) and tetraploid B. pubescens (downy birch) are common and therefore likely to contribute to pollen deposition. Pollen from 22 triploid trees/shrubs from ten woodlands in Iceland was examined and its size and shape compared with pollen from the parental species. The mean diameter of pollen grains from the triploid hybrids was not statistically different from that of B. nana pollen, but was significantly smaller than the mean value of B. pubescens pollen. On the contrary, the size of the vestibulum was similar to that of B. pubescens, which was significantly greater than that of B. nana, and therefore the diameter‐pore depth ratio was lower than the values from either species. The pattern of size distribution within plants indicated that triploid hybrids might have produced two sizes of triporate pollen grains, but the small B. nana size was far more prevalent than the larger B. pubescens size. Several anomalies in pollen morphology were common among the hybrid pollen grains: four or more pores were the most frequent type of abnormality. Characteristics of the pollen of triploid Betula hybrids, especially structural anomalies, may provide a means to reveal periods of interspecific hybridisation in the analysis of sub‐fossil pollen.