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The melting of the Greenland Ice Sheet is accelerating, with glaciers shifting from marine to land termination and potential consequences for fjord ecosystems downstream. Monthly samples in 2016 in two fjords in southwest Greenland show that subglacial discharge from marine-terminating glaciers sustains high phytoplankton productivity that is dominated by diatoms and grazed by larger mesozooplankton throughout summer. In contrast, melting of land-terminating glaciers results in a fjord ecosystem dominated by bacteria, picophytoplankton and smaller zooplankton, which has only one-third of the annual productivity and half the CO2 uptake compared to the fjord downstream from marine-terminating glaciers.

Plankton comprises a large diversity of organisms, from pico- to macro-sized classes, and spans several trophic levels, whose population dynamics are characterized by a high spatio-temporal variability. Studies integrating multiple plankton groups, in respect to size classes and trophic levels, are still rare, which hampers a more thorough description and elucidation of the full complexity of plankton dynamics. Here, we present a study on the spatial variability of five in-situ monitored plankton components, ranging from bacteria to meso-zooplankton, and using a complementary set of molecular, chemical and imaging tools, with samples obtained during the phytoplankton spring bloom in the hydrodynamically complex Southern Bight of the North Sea. We hypothesized that while generally recognized spatial gradients in e.g. salinity, turbidity and nutrients will have a strong impact on plankton spatial distribution patterns, interactions within the plankton compartment but also lag effects related to preceding bloom-related events will further modulate spatial structuring of the plankton. Our study indeed revealed an overriding imprint of regional factors on plankton distribution patterns. The dominant spatial pattern mainly reflected regional differences in dissolved inorganic nutrients and particulate matter concentrations related to differences in phytoplankton bloom timing between the two main regions of freshwater influence, the Thames and the Scheldt-Rhine-Meuse. A second major pattern corresponded to the expected nearshore-offshore gradient, with increasing influence of low turbidity and low nutrient Atlantic waters in the offshore stations. Environmental forcing on specific plankton groups and inter-plankton relationships also appeared to drive plankton distribution. Although the marine plankton comprises heterogeneous functional groups, this study shows that multiple planktonic ecosystem components can be parts of common spatial gradients and that often neglected s

Many estuaries exhibit seasonality in the estuary‐scale distribution of suspended particulate matter (SPM). This SPM distribution depends on various factors, including freshwater discharge, salinity intrusion, erodibility, and the ability of cohesive SPM to flocculate into larger aggregates. Various authors indicate that biotic factors, such as the presence of algae and their excretion of sticky transparent exopolymer particles (TEP), affect the flocculation and erosion processes. Consequently, seasonality in these biotic factors may play a role in the observed seasonality in SPM. Whereas the impact of abiotic factors on seasonality in SPM is well studied, the relative contribution of biotically induced seasonality is largely unknown. In this study, we employ two approaches to assess the aggregated importance of biotically induced seasonality in flocculation and erosion on seasonality in SPM in the Scheldt estuary. In the first approach, we focus on seasonality of in situ observations in the Scheldt estuary of turbidity, floc size, Chlorophyll‐a, and TEP, showing that the abiotic parameters show seasonality, while seasonality in TEP is ambiguous. The second approach concerns a reverse engineering method to calibrate biotically affected parameters of a coupled sediment transport‐flocculation model to turbidity observations, allowing us to compare the modeled SPM concentrations to the observations. Driven by seasonality in freshwater discharge, the model captures the observed seasonality in SPM without requiring biotically induced seasonality in flocculation and erosion, which is supported by the absence of seasonality in TEP.

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Salt marshes are important coastal areas that consist of a vegetated intertidal marsh platform and a drainage network of tidal channels. How salt marshes and their drainage networks develop is not fully understood, but it has been shown that the biogeomorphic interactions and feedbacks between vegetation development and channel formation play an important role. We examined the relationships among tidal channel sinuosity, marsh elevation and roughness, vegetation type (pioneer, Elymus athericus or Phragmites australis) and patch size at different spatial scales using a high‐resolution vegetation map (derived from aerial photography) and lower‐resolution satellite imagery processed with linear spectral mixture analysis (LSMA). The patch size distribution in all vegetation types corresponded to a power law, suggesting the presence of self‐organizational processes. While small vegetation patches are more dominant in pioneer vegetation, they were present in all vegetation types. The largest patch size is restricted to E. athericus. We observed an inverse logarithmic relationship between channel sinuosity and vegetation patch size in all vegetation types. The fact that this relationship is observed in both pioneer and later successional stages suggests that after the establishment of a drainage network in the dynamic pioneer stages of salt marsh development, the later stages of salt marsh succession largely inherit the meandering pattern of the early successional stages. Our study confirms recent evidence that no significant changes in the specific features of tidal channel networks (e.g., channel width, drainage density and efficiency) take place during the later stages of salt marsh development.

Benthic diatoms are important primary producers in intertidal marine sediments and form the basis of the food web in these ecosystems. In order to investigate the carbon flow within diatom mats, we performed in situ 13C pulse-chase labeling experiments and followed in detail the biochemical fate of carbon fixed by the diatoms for five consecutive days. These labeling experiments were done at approximately 2-monthly intervals during 1 yr in order to cover seasonal variations. The fixed carbon was recovered in individual carbohydrates including extracellular polymeric substances (EPS), amino acids, fatty acids, and nucleic acid bases. In addition, we assessed a variety of environmental parameters and photosynthetic characteristics. The fixed carbon was initially mainly stored as carbohydrate (glucose) while nitrogen-rich compounds (e.g., amino acids and RNA/DNA) were produced more slowly. During the year, the diatoms distributed the photosynthetically fixed carbon differently among the various carbon pools that were measured. In summer, the diatoms decreased carbon fixation and accumulated relatively more lipid as a storage compound (27% +/- 2% vs. 12% +/- 5% in other seasons). The percentage of fixed carbon that was excreted as EPS was lower in summer compared to other seasons, amounting 9% +/- 4% and 21% +/- 6%, respectively. Hence, it seemed that the physiology of the microphytobenthos was different during summer and caused by higher light intensity and a shift in nitrogen source.