Sea-Air Exchange of Methane in Shallow Inshore Areas of the Baltic Sea

We report sea-air fluxes of methane in physically and biologically distinct inshore habitats of the Baltic Sea with the goal to establish empirical relationships that allow upscaling of local site-specific flux measurements. Flux measurements were conducted using floating chambers with and without bubble shields, and by using a boundary layer gas transfer model before, during, and after an annually occurring algal bloom from June to October 2019. Water and air temperature, salinity, wind, sediment organic content, and organic content of floating algal biomass were found to successfully discriminate the different habitats in terms of methane flux, both over periods of days and over a season. Multivariate statistical analysis was used to establish the relative environmental forcing of methane emissions over one growth season for each flux method. Floating algal biomass carbon and sediment organic content were identified as the most important controlling factors for methane emissions based on flux chamber measurements over a period of days to weeks, whereas water and air temperature and wind velocity were the most important factors based on the gas transfer model on these time scales. Over the season, water and air temperature were the most important controlling factors with both methods. We present a first attempt how our observations can be extrapolated to determine the coastal methane emission along the coastline.

BED SEDIMENT DISTRIBUTION IN THE RIVER ESTUARY AND COASTAL SEA OF MALILI (SOUTH SULAWESI, INDONESIA)

Bed sediment characteristics and distribution is one of the important parameters in determining the management plan and utilization of estuarine and coastal waters. The objective of this study was to analyze sediment distribution and determine dominant oceanographic factors controlling the distribution of bed sediment in the river estuary and coastal sea of Malili. Sediment samples were collected using a grab sampler at ten stations, namely four stations in the river estuary and six stations in the adjacent coastal sea for grain size and sediment organic content analysis. The results showed that the bed sediment along the river estuary consisted of silt, very fine sand, fine sand, and medium sand with organic content varying from 1.31 to 7.18 %. In the coastal sea, bed sediment was dominated by silt with a higher organic content of 2.25 - 7.31%

Historical development of three man-made reservoirs in a mining region: A story told by subfossil chironomids

Chironomid stratigraphic changes were studied in three man-made reservoirs situated in a region intensely used for mining in the past (Banska Stiavnica, Central Europe) The reservoirs were built in the first half of the 18th century and are remnants of a former hydro-energetic system that provided water for operating mining and smelting facilities until the 1920s. The dated sequence of sediment cores span the last 170–200 years, however the oldest sediments were not identified. A total of 58 taxa were recorded with the most common taxa being Cladotanytarsus mancus-type, Polypedilum nubeculosum-type, Procladius spp. and Tanytarsus spp. Changes in the subfossil assemblages suggest that all reservoirs followed similar developmental trends. The low number of chironomid remains and the prevalence of littoral and rheophilic taxa characterize the initial phase of reservoirs connected with severe water level fluctuations and unproductive conditions. A dramatic shift in both qualitative and quantitative structure of the chironomid assemblages correspond to the documented decline of mining activities in the region. The second period of the reservoir development is also connected to changes in sediment composition and an increase of sediment organic content. In this phase, chironomids indicate nutrient enrichment, developed profundal zone with oxygen depletion and a complexity of littoral habitats. Since the 1970s, changes in the assemblage structure indicate the reduction of the profundal fauna and increasing importance of littoral taxa. Despite the significantly different usage of the reservoirs after the mining phase (recreation and angling vs drinking water supply) the chironomid succession trajectories were fairly similar.

Relationships between shallow-water cumacean assemblages and sediment characteristics facing the Iranian coast of the Persian Gulf

During two sampling campaigns carried out in August 1998 and November 2002, 232 cumaeans from eight species belonging to the families Bodotriidae and Nannastacidae were collected. This paper presents the first ecological data on a shallow water tropical cumacean assemblage from the Persian Gulf, where 50% of the existing species were recently described as new for the science. Neither the environmental conditions (except for the sediment organic content) nor the cumacean assemblage descriptors differed between the two sampling periods. However, two different species dominated in each period (i.e. Eocuma travancoricum and Heterocuma inerme in 1998 and 2002, respectively) and the MDS analysis revealed differences in the assemblage composition between periods, particularly for the deepest sampling stations. An increasing density together with the increase in gravel content, and a decreasing density together with the increasing silt content characterized the distribution pattern of both the whole cumacean assemblages and the two dominant species, the latter being also positively correlated with the mean grain size and negatively correlated with depth and organic matter (E. travancoricum) and with depth (H. inerme).

Sediment pH and Redox Potential Affect the Bioavailability of Al, Cu, Fe, Mn, and Zn to Rooted Aquatic Macrophytes

We have evaluated the role of sediment pH (4.7–7.1) and redox potential (88–305 mV) in determining the bioavailability of five metals to four species of isoetoid macrophytes. The four species (Eleocharis acicularis, Eriocaulon septangulare With., Isoetes sp., and Sagittaria graminae) did not differ significantly in the relationship between the contents of metals in plants and sediment. When data for all species were pooled, 28–80% of the variation in the log of plant metal content was explained by the log of sediment metal (Al, Fe, and Mn) or by the log of sediment organic content (Cu and Zn). Sediment pH explained 45% (Al), 10% (Cu), 20% (Fe), 5% (Mn), and 12% (Zn) variation over and above that explained by the sediment metal content. These results demonstrate that lower sediment pH, in the presence of mildly oxic redox conditions, increases the bioavailability of these five trace metals to rooted aquatic plants. Rooted macrophytes subject to acidification contain higher metal concentrations which may be transferred by grazing to higher trophic levels.