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Skudra M.,Tallinn University of Technology | Skudra M.,Latvian Institute of Aquatic Ecology | Lips U.,Tallinn University of Technology
Oceanologia | Year: 2016

Available CTD profiles from the Gulf of Riga (May-August, 1993-2012) were analyzed to study inter-annual and long-term changes in temperature, salinity and density in relation to river runoff and atmospheric forcing (e.g. Baltic Sea Index). To describe temporal changes in vertical stratification, the upper mixed layer (UML) and deep layer (DL) parameters were estimated. On average the UML depth increases from 8.7m in May to 9.0, 11.5 and 13.7m in June, July and August, respectively, and the UML temperature increases from 8.0°C to 12.5, 18.7 and 18.6°C (May, June, July and August) while the UML salinity increases from 4.90gkg-1 to 5.14, 5.28 and 5.38gkg-1, respectively. High correlation (r =-0.82) was found between the inter-annual changes in river runoff (spring) and mean salinity in the UML in August as well as between DL mean salinity (r =0.88) and density (r =0.84) in the Irbe Strait and DL mean salinity and density in the Gulf of Riga. Inter-annual changes in the UML depth as well as in DL salinity and density had a significant correlation with the changes in Baltic Sea Index. The strongest stratification (August) can be observed in the years with the highest UML temperature and the highest river run-off in spring. We suggest that the predicted increase in water temperature and changes in river run-off due to the climate change would result in faster development of the seasonal thermocline in spring and stronger vertical stratification in summer. © 2016 Institute of Oceanology of the Polish Academy of Sciences.


Lips U.,Tallinn University of Technology | Zhurbas V.,Tallinn University of Technology | Zhurbas V.,RAS Shirshov Institute of Oceanology | Skudra M.,Tallinn University of Technology | And 2 more authors.
Continental Shelf Research | Year: 2016

A regional model of the Gulf of Riga (GoR) with horizontal grid spacing of 0.5 nautical miles was applied to study the features and driving forces of the whole-basin circulation in the GoR. The initial conditions and atmospheric forcing were taken from the operational models High Resolution Operational Model for the Baltic (HIROMB) and High Resolution Limited Area Model (HIRLAM), respectively. The wind stress curl is shown to be a major contributor to the whole-basin circulation pattern. An anticyclonic circulation pattern in the summer is determined by a combined effect of the negative wind stress curl, thermal density stratification and bottom topography. Positive values of the wind stress curl and a cyclonic circulation pattern prevail during the cold period of the year when seasonal thermocline is absent. During calm periods, the anticyclonic type of circulation is established due to a combined effect of the river runoff, saltier water inflow into and mixed water outflow from the GoR. Two seasonal baroclinic jet-like currents are identified in the summer: the Northward Longshore Current in the western GoR and Southward Subsurface Longshore Current in the eastern GoR. The alteration of the circulation pattern in the GoR from cyclonic in the cold period of the year to anticyclonic in the summer, and vice versa, was shown to be observed not every year due to inter-annual variability of wind forcing. © 2015 Elsevier Ltd.


PubMed | Institute of Food Safety, Leibniz Institute for Baltic Sea Research, University of Stockholm, Finnish Environment Institute and 3 more.
Type: Journal Article | Journal: PloS one | Year: 2016

The European Marine Strategy Framework Directive requires the EU Member States to estimate the level of anthropogenic impacts on their marine systems using 11 Descriptors. Assessing food web response to altered habitats is addressed by Descriptor 4 and its indicators, which are being developed for regional seas. However, the development of simple foodweb indicators able to assess the health of ecologically diverse, spatially variable and complex interactions is challenging. Zooplankton is a key element in marine foodwebs and thus comprise an important part of overall ecosystem health. Here, we review work on zooplankton indicator development using long-term data sets across the Baltic Sea and report the main findings. A suite of zooplankton community metrics were evaluated as putative ecological indicators that track community state in relation to Good Environmental Status (GES) criteria with regard to eutrophication and fish feeding conditions in the Baltic Sea. On the basis of an operational definition of GES, we propose mean body mass of zooplankton in the community in combination with zooplankton stock measured as either abundance or biomass to be applicable as an integrated indicator that could be used within the Descriptor 4 in the Baltic Sea. These metrics performed best in predicting zooplankton being in-GES when considering all datasets evaluated. However, some other metrics, such as copepod biomass, the contribution of copepods to the total zooplankton biomass or biomass-based Cladocera: Copepoda ratio, were equally reliable or even superior in certain basin-specific assessments. Our evaluation suggests that in several basins of the Baltic Sea, zooplankton communities currently appear to be out-of-GES, being comprised by smaller zooplankters and having lower total abundance or biomass compared to the communities during the reference conditions; however, the changes in the taxonomic structure underlying these trends vary widely across the sea basins due to the estuarine character of the Baltic Sea.


Jurgensone I.,Latvian Institute of Aquatic Ecology | Carstensen J.,University of Aarhus | Ikauniece A.,Latvian Institute of Aquatic Ecology | Kalveka B.,Latvian Institute of Aquatic Ecology
Estuaries and Coasts | Year: 2011

Trends in phytoplankton monitoring data (1976-2008) from the Gulf of Riga were investigated and linked to environmental factors. Annual means of spring phytoplankton biomass correlated to phosphorus input from land and shifts between diatoms and dinoflagellates were attributed to potential Si limitation and time of sampling relative to the spring phytoplankton succession. The summer phytoplankton biomass, which more than doubled over the study period, was related to the abundance of summer copepods that similarly declined. Cyanobacterial blooms proliferated in summer and the proportion of diatoms similarly declined when the winter-spring inorganic N/P ratio was low. The chlorophyte proportion in summer increased over the study period, and this was linked to increasing temperatures favoring their higher growth rates. The dinoflagellate proportion appeared to decrease with temperatures above a threshold of 15. 5°C. Although nutrient inputs and their ratios are important factors for the phytoplankton community, this study suggests that climate change and overfishing could be equally important. © 2011 Coastal and Estuarine Research Federation.


PubMed | AKTiiVS Ltd., University of Warsaw, University of St. Andrews and Latvian Institute of Aquatic Ecology
Type: | Journal: The Science of the total environment | Year: 2017

The ecological status of coastal and marine waterbodies world-wide is threatened by multiple stressors, including nutrient inputs from various sources and increasing occurrences of invasive alien species. These stressors impact the environmental quality of the Baltic Sea. Each Baltic Sea country contributes to the stressors and, at the same time, is affected by their negative impacts on water quality. Knowledge about benefits from improvements in coastal and marine waters is key to assessing public support for policies aimed at achieving such changes. We propose a new approach to account for variability in benefits related to differences in socio-demographics of respondents, by using a structural model of discrete choice. Our method allows to incorporate a wide range of socio-demographics as explanatory variables in conditional multinomial logit models without the risk of collinearity; the model is estimated jointly and hence more statistically efficient than the alternative, typically used approaches. We apply this new technique to a study of the preferences of Latvian citizens towards improvements of the coastal and marine environment quality. We find that overall, Latvians are willing to pay for reducing losses of biodiversity, for improving water quality for recreation by reduced eutrophication, and for reducing new occurrences of invasive alien species. However a significant group within the sample seems not to value environmental improvements in the Baltic Sea, and, thus, is unwilling to support costly measures for achieving such improvements. The structural model of discrete choice reveals substantial heterogeneity among Latvians towards changes in the quality of coastal and marine waters of Latvia.


Andersson A.,Umeå University | Jurgensone I.,Latvian Institute of Aquatic Ecology | Rowe O.F.,Umeå University | Simonelli P.,University of Bergen | And 3 more authors.
PLoS ONE | Year: 2013

A common and established view is that increased inputs of nutrients to the sea, for example via river flooding, will cause eutrophication and phytoplankton blooms in coastal areas. We here show that this concept may be questioned in certain scenarios. Climate change has been predicted to cause increased inflow of freshwater to coastal areas in northern Europe. River waters in these areas are often brown from the presence of high concentrations of allochthonous dissolved organic carbon (humic carbon), in addition to nitrogen and phosphorus. In this study we investigated whether increased inputs of humic carbon can change the structure and production of the pelagic food web in the recipient seawater. In a mesocosm experiment unfiltered seawater from the northern Baltic Sea was fertilized with inorganic nutrients and humic carbon (CNP), and only with inorganic nutrients (NP). The system responded differently to the humic carbon addition. In NP treatments bacterial, phytoplankton and zooplankton production increased and the systems turned net autotrophic, whereas the CNP-treatment only bacterial and zooplankton production increased driving the system to net heterotrophy. The size-structure of the food web showed large variations in the different treatments. In the enriched NP treatments the phytoplankton community was dominated by filamentous >20 μm algae, while in the CNP treatments the phytoplankton was dominated by picocyanobacteria <5 μm. Our results suggest that climate change scenarios, resulting in increased humic-rich river inflow, may counteract eutrophication in coastal waters, leading to a promotion of the microbial food web and other heterotrophic organisms, driving the recipient coastal waters to net-heterotrophy. © 2013 Andersson et al.


Muller-Karulis B.,Latvian Institute of Aquatic Ecology | Muller-Karulis B.,University of Stockholm | Aigars J.,Latvian Institute of Aquatic Ecology
Journal of Marine Systems | Year: 2011

The long term dynamics of nitrogen, phosphorus, and phytoplankton in the Gulf of Riga were simulated with a biogeochemical box model that resolved seasonal cycles. The model was calibrated using a numerical optimization procedure that adjusted 37 parameters to maximize the model data fit for field observations from 1973 to 2000 and validated with an independent dataset covering 2001-2007. Both the long-term increase and subsequent decline in winter nitrogen concentrations, as well as the continuous increase in winter phosphate levels were well reproduced by the model, which also gave reasonable representations of the seasonal dynamics of nutrients and phytoplankton. Starting from the mid-1990s, the model simulated an increase in cyanobacteria growth sustained by internal phosphorus loading. While nitrogen was efficiently removed by denitrification from the Gulf of Riga, comparatively slow export to the Baltic Proper was the main removal pathway of phosphorus. Modeled residence times were 5.4. years for nitrogen and 38. years for phosphorus. Scenario simulations indicated that the Gulf of Riga responds to phosphorus load reductions with a gradual decrease in primary production and cyanobacteria growth, while the effect of nitrogen load reductions is largely offset by nitrogen fixation. © 2011 Elsevier B.V.


Barda I.,University of Latvia | Purina I.,Latvian Institute of Aquatic Ecology | Rimsa E.,University of Latvia | Balode M.,Latvian Institute of Aquatic Ecology
Journal of Marine Systems | Year: 2014

Biomarkers are often regarded as "early warning" signals of environmental pollution; however seasonal changes are mentioned as one of the most important factor that influences the activity of biomarkers. The aim of our study was to assess the importance of seasonal variation of selected contaminant biomarkers in Macoma balthica to provide background information for further environmental surveys in the Gulf of Riga. Seasonal variation of biomarkers (acetylcholinesterase (AChE), catalase (CAT), glutathione reductase (GR) and glutathione. S-transferase (GST)) was measured in infaunal clam M. balthica from the southern part of the Gulf of Riga. The majority of biomarkers (GST, CAT and GR) showed strong seasonal variability; however only CAT and GR were found to be significantly related to environmental factors (near-bottom oxygen, salinity and temperature). Integrated biomarker response (IBR) index indicated that the most stressed condition of M. balthica is during August and May. The highest values of IBR were found near the mouth of the River Daugava, suggesting the impact of environmental pollution on the benthic animals. © 2013 Elsevier B.V.


Jurgensone I.,Latvian Institute of Aquatic Ecology | Aigars J.,Latvian Institute of Aquatic Ecology
Estuarine, Coastal and Shelf Science | Year: 2012

Nutrient inputs from catchments with intensive agriculture are mostly dominated by inorganic nutrients, whereas the contribution of organic nutrients from catchments with natural forests can be considerable but there is a pooere understanding of this nutrient source. Consequently this study investigated spring, summer and autumn phytoplankton community responses to enrichment by riverine dissolved organic matter (DOM). Dissolved organic substances were extracted from the Daugava River, fractionated into three molecular size classes: 1) 5-100. kDa, 2) 100-1000. kDa, and 3) >1000. kDa, and added to a microcosm with natural assemblages from the Gulf of Riga. During the spring the phytoplankton community was dominated (97%) by diatoms and the species composition did not change over the course of the experiment. Specific species and functional groups of the summer and autumn phytoplankton communities responded positively to these treatments. Small-celled cyanobacteria and Monoraphidium contortum responded to almost all size fractions of DOM for the summer and autumn experiments. Oocystis spp. characteristic for the summer and Chaetoceros wighamii, Cyclotella spp.,Thalassiosira baltica for the autumn responded to treatment by two and three size classes of organic substances, respectively, while Merismopedia spp. shifted from one food source to another during the summer experiment. © 2012 Elsevier Ltd.


Strode E.,University of Latvia | Balode M.,University of Latvia | Balode M.,Latvian Institute of Aquatic Ecology
Crustaceana | Year: 2013

Benthic organisms are important components of aquatic ecosystems and have been widely used to assess environmental pollution. Being very sensitive to a wide range of toxicants amphipods are often used as test objects in eco-toxicological studies. The aim of this study was to compare toxico-resistance of various Baltic amphipod species to exposure of heavy metals. The acute toxicity (48-h LC50 and 96-h LC50) of cadmium (CdCl2), copper (CuSO4) and zinc (ZnSO4 • 7H2O) was detected experimentally, using juveniles and adults of brackish water amphipods, Monoporeia affinis, Bathyporeia pilosa, Gammarus tigrinus, Pontogammarus robustoides and the freshwater amphipod Gammarus pulex as test objects. Amphipods were collected in Latvian territorial waters of the Open Baltic Sea, the Gulf of Riga and in a freshwater body (Kalkugrava canal). Sensitivity of native amphipod species was compared to Hyalella azteca (a species widespread in North America; a strain obtained from the Chesapeake Culture Collection, Hayes, VA, U.S.A.). High sensitivity of all tested amphipod species, except M. affinis, to heavy metals was observed. A two-way ANOVA analysis showed significant differences in toxico-resistance of selected test objects (p≤0.05). The highest toxico-resistance was shown by the brackish water amphipod M. affinis (96-h LC50: Cd 5.16 mg/l; Cu 5.68 mg/l; Zn 11.31 mg/l), but the lowest by the freshwater species G. pulex and H. azteca (96-h LC50 for Cd 0.005 and 0.007 mg/l, accordingly). Cadmium was the most toxic from the tested heavy metals, followed by copper and zinc. © Koninklijke Brill NV, Leiden, 2013.

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