Search Results (9)

This study identifies the characteristics of water regions with negative normalized water-leaving radiance ($n{L}_w\left(\lambda \right)$) values in the satellite observations of the Second-generation Global Imager (SGLI) sensor aboard the Global Change Observation Mission–Climate (GCOM-C) satellite. SGLI Level-2 data, along with atmospheric and in-water optical properties measured by the sun photometers in the AErosol RObotic NETwork-Ocean Color (AERONET-OC) from 26 sites globally, are utilized in this study. The focus is particularly on Tokyo Bay and the Ariake Sea, semi-enclosed water regions in Japan where previous research has pointed out the occurrence of negative $n{L}_w\left(\lambda \right)$ values due to atmospheric correction with SGLI. The study examines the temporal changes in atmospheric and in-water optical properties in these two regions, and identifies the characteristics of regions prone to negative $n{L}_w\left(\lambda \right)$ values due to atmospheric correction by comparing the optical properties of these regions with those of 24 other AERONET-OC sites. The time series results of $n{L}_w\left(\lambda \right)$ and the single-scattering albedo ($\mathsf{\omega }\left(\lambda \right)$) obtained by the sun photometers at the two sites in Tokyo Bay and Ariake Sea, along with SGLI $n{L}_w\left(\lambda \right)$, indicate the occurrence of negative values in SGLI $n{L}_w\left(\lambda \right)$ in blue band regions, which are mainly attributed to the inflow of absorptive aerosols. However, these negative values are not entirely explained by $\mathsf{\omega }\left(\lambda \right)$ at 443 nm alone. Additionally, a comparison of in situ $n{L}_w\left(\lambda \right)$ measurements in Tokyo Bay and the Ariake Sea with $n{L}_w\left(\lambda \right)$ values obtained from 24 other AERONET-OC sites, as well as the inherent optical properties (IOPs) estimated through the Quasi-Analytical Algorithm version 5 (QAA_v5), identified five sites—Gulf of Riga, Long Island Sound, Lake Vanern, the Tokyo Bay, and Ariake Sea—as regions where negative $n{L}_w\left(\lambda \right)$ values are more likely to occur. These regions also tend to have lower $n{L}_w\left(\lambda \right)$ values at shorter wavelengths. Furthermore, relatively high light absorption by phytoplankton and colored dissolved organic matter, plus non-algal particles, was confirmed in these regions. This occurs because atmospheric correction processing excessively subtracts aerosol light scattering due to the influence of aerosol absorption, increasing the probability of the occurrence of negative $n{L}_w\left(\lambda \right)$ values. Based on the analysis of atmospheric and in-water optical measurements derived from AERONET-OC in this study, it was found that negative $n{L}_w\left(\lambda \right)$ values due to atmospheric correction are more likely to occur in water regions characterized by both the presence of absorptive aerosols in the atmosphere and high light absorption by in-water substances. Full article

The proposed study is focused on an ecological analysis of Latvian coastal lagoons, emphasizing their unique but vulnerable nature. Coastal lagoons are recognized as fragile ecosystems of significant ecological, social, and economic value, as recognized by the European Directive 92/43/EEC (Habitats Directive). Despite their protected status, the existence of these ecosystems can be threatened by morphological, hydrological, and anthropogenic changes. The uniqueness of these ecosystems can be determined by the large number of influencing factors and their dynamics. They are affected by seawater, their level of fluctuation, wind exposure, overgrowing with macrophytes, freshwater sources, and water flow generated streams affecting sediment transport and accumulation. All the influencing factors determine a highly trophic ecosystem, which in the studied lagoons is rated as medium to poor ecological status, which confirms the above-mentioned vulnerability and fragility. The aim of this study was to analyze two lagoons in the coastal area of the Baltic Sea in the Riga Gulf, by characterizing, for the first time, their current conditions and ecological parameters because understanding such ecosystems is only partial. The physicochemical composition of lagoon sediments and water shows the impact of seawater by increased electrical conductivity and the concentration of SO₄²⁻ and Cl⁻ in water, while the presence of detritus in sediments is almost non-existent; thus, the content of organic matter is low with relatively variable pH. The results show that the diversity of studied benthic macroinvertebrates, macrophytes, zooplankton, and even phytoplankton species is low, but there is higher diversity in lagoons and their parts with regular water exchange with the sea. The study provides valuable insight into the ecological dynamics of coastal lagoons in Latvia, shedding light on their current conditions, anthropogenic impact, and the need for sustainable management measures. Full article

Liquid water path (LWP) is one of the most important cloud parameters and is crucial for global and regional climate modelling, weather forecasting, and modelling of the hydrological cycle and interactions between different components of the climate system: the atmosphere, the hydrosphere, and the land surface. Space-borne observations by the SEVIRI instrument have already provided evidence of the systematic difference between the cloud LWP values derived over the land surface in Northern Europe and those derived over the Baltic Sea and major lakes during both cold and warm seasons. In the present study, the analysis of this LWP land-sea contrast for the period 2011–2017 reveals specific temporal and spatial variations, which, in some cases, seem to be artefacts rather than of natural origin. The geographical objects of investigation are water bodies and water areas located in Northern Europe that differ in size and other geophysical characteristics: the Gulf of Finland and the Gulf of Riga in the Baltic Sea and large and small lakes in the neighbouring region. The analysis of intra-seasonal features has detected anomalous conditions in the Gulf of Riga and the Gulf of Finland, which show up as very low values of the LWP land-sea contrast in August with respect to the values in June and July every year within the considered time period. This anomaly is likely an artefact caused by the LWP retrieval algorithm since the transition from large LWP contrast to very low contrast occurs sharply, synchronically, and at a certain date every year at different places in the Baltic Sea. Full article

The aim of this study was to test and develop the indicators for the remote sensing assessment of cyanobacterial blooms as an input to the estimation of eutrophication and the environmental status (ES) under the Marine Strategy Framework Directive (MSFD) in the optically varying Estonian coastal regions (the Baltic Sea). Here, the assessment of cyanobacteria blooms considered the chlorophyll-a (chl-a), turbidity, and biomass of N₂-fixing cyanobacteria. The Sentinel-3 A/B Ocean and Land Colour Instrument (OLCI) data and Case-2 Regional CoastColour (C2RCC) processor were used for chl-a and turbidity detection. The ES was assessed using four methods: the Phytoplankton Intensity Index (PII), the Cyanobacterial Surface Accumulations Index (CSA), and two variants of the Cyanobacterial Bloom Indicator (CyaBI) either with in situ-measured cyanobacterial biomass or with satellite-estimated cyanobacterial biomass. The threshold values for each coastal area ES assessment are presented. During 2022, the NW Gulf of Riga reached good ES, but most of the 16 coastal areas failed to achieve good ES according to one or multiple indices. Overall, the CyaBI gives the most comprehensive assessment of cyanobacteria blooms, with the CyaBI (in situ) being the best suited for naturally turbid areas. The CyaBI (satellite) could be more useful than in situ in large open areas, where the coverage of in situ sampling is insufficient. Full article

The complexity of the marine environment and the increasing anthropogenic pressure create a necessity to expand existing monitoring approaches. The main goal of this study was to depict the effects of selected, seasonally varying environmental factors on a battery of biomarkers in the benthic amphipod Monoporeia affinis from the Gulf of Riga (GoR). Seasonal variability in acetylcholinesterase (AChE), catalase (CAT), glutathione reductase (GR), and glutathione S-transferase (GST) activities was investigated at six coastal stations (20–30 m) in August and November in 2020 and 2021. In addition, the biomarkers were measured at seven deep-water stations (>30 m) in November 2021. In general, the results indicated no significant influence of the measured environmental variables on the biomarker activities, except for deep-water stations, where chlorophyll a significantly affected enzymatic activity. The current study indicated that M. affinis has a higher GST, CAT and GR activity in summer compared to autumn in coastal stations, showing seasonal variability of these biomarkers. However, summarizing the biomarker levels recorded at each station and season, the integrated biomarker response (IBR) index showed the most stressed health status of the M. affinis populations in the deep-water stations 135 and 107 and coastal regions in the north-eastern part of the GoR (station 160B). This suggests that the impact on enzymatic responses of benthic organisms could be due to port activities leading to the accumulation of pollutants in muddy sediments regionally. Moreover, for the monitoring of biological effects of contaminants there is a need to establish the background levels of biomarkers, i.e., responses to the different natural environmental factors in the GoR region. Full article

The Gulf of Riga stock of Baltic herring (Clupea harengus membras L.) has been maintained through several management tools. One such tool is the restriction of vessels’ main engine power (<221 kW). This restriction was implemented in the early 1990s and is based on the vessel types available in the area and on the assumption that the gear size used in trawl fishery depends on the vessel size (power). In the current study, we compared vessels with different engine powers using the same gears currently allowed in the gulf, to identify whether vessel power had any relation to catch structure. The results showed that engine power did not explain the differences in catch structure, which were more dependent on season and depth of water. Easing the power restriction of the trawl vessels in the Gulf of Riga will most likely not have a major negative impact on the sustainable management of the herring population. However, vessels with higher engine power should not use larger trawl gear than is currently used in the gulf. Full article

Passive acoustic monitoring (PAM) is widely used as an initial step towards an assessment of environmental status. In the present study, underwater ambient sound recordings from two monitoring locations in marine-protected areas (MPAs) of the Gulf of Riga were analysed. Both locations belong to the natural habitat of pinnipeds whose vocalisations were detected and analysed. An increase of vocal activity during the mating period in the late winter was revealed, including percussive signallings of grey seals. The ambient sound spectra showed that in the current shallow sea conditions ship traffic noise contributed more in the higher frequency bands. Thus, a 500 Hz one-third octave band was chosen as an indicator frequency band for anthropogenic noise in the monitoring area. It was shown that changes in the soundscape occurring during the freezing period create favourable conditions for ship noise propagation at larger distances. Based on the monitoring data, the environmental risks related to the anthropogenic sound around the monitoring sites were considered as low. However, further analysis showed that for a small percentage of time the ship traffic can cause auditory masking for the ringed seals. Full article

Zooplankton as an essential component in the pelagic food web are directly linked to pelagic ecosystem functioning. Therefore, comprehension of zooplankton functional diversity (FD) and its responses to environmental changes is crucial for ecosystem-based view. To identify FD responses to environmental drivers, we analysed 25 years of summer data on the brackish mesozooplankton community (including rotifers, cladocerans, copepods, and meroplankton) from the eutrophied, shallow Gulf of Riga (Baltic Sea). We established that within the Gulf of Riga, open waters are notably different from coastal regions based on the dynamics of hydrological conditions (temperature, salinity), cyanobacterial dominance, abundance of mesozooplankton functional groups, and mesozooplankton FD indices. Competition over resources in combination with hydrodynamic features and predation by adult herring were seemingly the central structuring mechanism behind the dynamics of FD metrics (richness, evenness, divergence, and dispersion) within coastal mesozooplankton communities. Whereas predation by young herring was an important driver only for the mesozooplankton communities in the open waters. Cyanobacterial dominance, used as a proxy for food quality and availability, had no effect on summer mesozooplankton FD metrics. Full article

The present study examines the seasonal and decadal changes of the variance of the synoptic (periods from 2 days to 30 days) and mesoscale (periods from 2 h to 2 days) sea level oscillations in the Baltic Sea. Long-term hourly sea level records were used at 12 tide gauges located in different parts of the sea. We used spectral analysis to estimate the variance for different time scales. The spectral density of sea level oscillations in the Baltic Sea has maximum values in winter when the cyclonic activity in the atmosphere is more intensive. The maximum variances of synoptic ${\sigma }_{syn}^2$ and mesoscale ${\sigma }_{mes}^2$sea level oscillations are observed in winter, except for the heads of the Gulf of Finland (Gorny Institute) and Gulf of Riga (Pärnu), where the absolute maximum of ${\sigma }_{syn}^2$ is reached in November. The variances ${\sigma }_{syn}^2$ and ${\sigma }_{mes}^2$from November to February are 2–3 and 5 times higher than in the summer. The values of ${\sigma }_{syn}^2$ and ${\sigma }_{mes}^2$ are characterized by high correlation up to 0.7–0.75 with wind variations and atmospheric indices (NAO, AO, and SCAND) in winter and low correlation in summer. The zonal wind and ${\sigma }_{mes}^2$ in Gorny Institute are characterized by wide areas of high coherence at periods of 0.7–4 years. At Gedser, ${\sigma }_{syn}^2$decreased by 19%, and at Ratan it increased by 17% over 90 years. The values of ${\sigma }_{mes}^2$ over 90 years increased by 32% at Klagshamn, 36% at Ratan, and up to 60% at Kungsholmsfort. Full article