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Freshwater pearl mussels (Margaritifera margaritifera) are vital bioindicators in river ecosystems, with their population health reflecting broader environmental conditions. Mussel population declines are well documented across Europe, and in Estonia, Pudisoo River supports the last remaining population. Long-term monitoring also indicates a significant decline in Pudisoo River, but the causes remain underexplored. This study aimed to assess how geology, geomorphology, and land use changes could impact pearl mussel population trends and distribution. We conducted field surveys, bioindication tests, and hydrological and morphometric analyses to evaluate physicochemical and environmental parameters in the Pudisoo River. The study revealed a declining but stabilizing population, concentrated in river sections with higher gradients and coarser riverbed substrates. Sediment transport and accumulation, influenced by both natural and human-induced factors, significantly affect habitat suitability, especially for juvenile mussels. Positive correlations were found between mussel populations and river sinuosity, suggesting that the varied microhabitats created by sinuosity, such as gradients in flow velocity and sediment deposition, play an important role in supporting the species. This finding highlights the importance of directing in-channel restoration efforts towards enhancing channel morphology to create more diverse habitats. Research on sediment dynamics and hydrological connectivity will be crucial for developing effective habitat management strategies for the species, especially considering the impacts of land use and climate change. [ABSTRACT FROM AUTHOR]

This study presents a method that could be used to assess the in‐situ saturated vertical hydraulic conductivity of deeper and more decomposed peat layers. Deeper peat layers may exhibit very low permeability comparable to clayey sediments, where measurements and sediment sample collection are very difficult. More traditional measurement methods, such as slug‐tests and permeameter tests, have proven difficult to carry out in these conditions, necessitating an alternative method. For surpassing these possible constraints, this paper introduces a field method to quantify vertical hydraulic diffusivity, capitalizing on naturally occurring hydraulic pressure fluctuations measured with buried pressure sensors. The determined diffusivity values are used to calculate vertical hydraulic conductivity of peat using separately measured compressibility and specific storage values. Our research demonstrates the feasibility of using this method to evaluate vertical hydraulic diffusivity in lower peat layers. Calculated diffusivity values, combined with peat compressibility measurements, yield reasonable estimates of vertical hydraulic conductivity for dense fen peat comparable with more widely used in‐situ and laboratory methods. It also shows potential for vertical hydraulic characteristics parametrization in the upper less decomposed and compacted peat layers; however, further research is needed to understand the method's limitations in such conditions. Our approach provides a potential method for measuring in‐situ vertical hydraulic properties of less accessible peat layers, often overlooked, while also providing a way to surpass the scale‐dependency constraints inherent in peatlands' heterogeneous structure. Such information is necessary when studying the hydraulic interactions between groundwater aquifers and peatlands. [ABSTRACT FROM AUTHOR]

Understanding the seasonal oscillation of peatland surface height initiated by changes in water table level (known as 'bog breathing') is key to improving spatial models of the water balance of bogs and their greenhouse gas exchanges with the atmosphere. Bog breathing has been studied locally via point-based measurements by telmatologists as well as over wider areas by the remote sensing community, in the latter case often without or with limited ground-truth validation. We aim to bring the two disciplines together by assessing the feasibility of validating Synthetic Aperture Radar (SAR) data from the Sentinel-1 satellite with in situ ground levelling data from nanotopes with different drainage status in two hemiboreal raised bogs. We demonstrate the continuous measurement of bog breathing using automatic ultrasonic levelling devices which shows that, during one growing season, bog breathing amounted to 11.6-14.7 cm in hollows, 6.9-7.5 cm in hummocks and 9.5-11.6 cm in haplotelmic nanotopes. Accounting for such relatively large vertical surface deformations remotely using the SAR Differential Interferometry (DInSAR) technique is prone to estimation errors owing to the so-called estimation ambiguity that occurs when deformation exceeds half the wavelength of the radar signal (2.77 cm for Sentinel-1). We approach the ambiguity problem by estimating deformation between consecutive SAR acquisitions (time separation 6 or 12 days) only. Remote and in situ measurements of bog breathing correlate moderately to very strongly (rs = 0.82-0.93 in hummocks) even though, from time to time, all nanotopes except hummocks show surface deformations in just a single day that exceed the ambiguity threshold. This indicates that DInSAR surface deformation estimates contain useful information despite under-estimating larger changes, and DInSAR has high potential for the assessment of bog breathing. Our findings imply that DInSAR estimates in peatlands without ground validation should be interpreted with caution. To take full advantage of the plentiful data from Sentinel-1, the introduction of contextual information (e.g. temperature, precipitation and/or evapotranspiration data) could guide ambiguity resolution, as we demonstrate up to moderate correlation (rs = 0.59 in a hollow) between precipitation and bog surface height. [ABSTRACT FROM AUTHOR]

We present early to mid-Holocene palaeocoastline reconstructions for the Tolkuse-Rannametsa area on the eastern coast of the Gulf of Riga. Radiocarbon-dated sediment stratigraphies and diatom analyses, supported by ground-penetrating radar data and GIS-based modelling, were used in the palaeogeographical reconstructions to strip back younger sediments and landforms from the Li DAR-derived digital elevation model. The reconstructions show an open coast environment during the Ancylus Lake stage and the formation of a peatland after the lake drainage at about 9000-8600 cal. a BP. The waters of the Litorina Sea flooded the study area between 8200 and 7700 cal. a BP, forming a 25-km-long and up to 5.5-m-deep lagoon with two connections to the sea. This brackish water lagoon existed in the area for about 4000 years and terminated around 3800-3500 cal. a BP as a result of isostatic uplift and growth of the barrier spit. The reconstructions illustrate the relationships between the lagoonal system and three Mesolithic and Neolithic settlement sites found in the study area. A comparative analysis which besides palaeogeographical and ecological data included a data set with more than 100 Stone Age sites from the eastern Baltic region, was used to propose the most suitable locations for coastal settlements in the Tolkuse-Rannametsa area. However, some of these areas are presently covered by a peat layer that is several metres thick, which may explain the relative scarcity of the archaeological finds on the shores of the palaeo-lagoon. The proposed multiproxy approach has the capability to delimit the areas that would have been favourable for prehistoric habitation, but might not be observable in the present-day topography. In return, this increases the likelihood of locating any well-preserved preserved settlement sites and artefacts that are buried under the protective sediment layer. [ABSTRACT FROM AUTHOR]

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