Origin and Pathways of Dissolved Organic Carbon in a Small Catchment in the Lena River Delta

The Arctic is rich in aquatic systems and experiences rapid warming due to climate change. The accelerated warming causes permafrost thaw and the mobilization of organic carbon. When dissolved organic carbon is mobilized, this DOC can be transported to aquatic systems and degraded in the water bodies and further downstream. Here, we analyze the influence of different landscape components on DOC concentrations and export in a small (6.45 km2) stream catchment in the Lena River Delta. The catchment includes lakes and ponds, with the flow path from Pleistocene yedoma deposits across Holocene non-yedoma deposits to the river outlet. In addition to DOC concentrations, we use radiocarbon dating of DOC as well as stable oxygen and hydrogen isotopes (δ18O and δD) to assess the origin of DOC. We find significantly higher DOC concentrations in the Pleistocene yedoma area of the catchment compared to the Holocene non-yedoma area with medians of 5 and 4.5 mg L−1 (p < 0.05), respectively. When yedoma thaw streams with high DOC concentration reach a large yedoma thermokarst lake, we observe an abrupt decrease in DOC concentration, which we attribute to dilution and lake processes such as mineralization. The DOC ages in the large thermokarst lake (between 3,428 and 3,637 14C y BP) can be attributed to a mixing of mobilized old yedoma and Holocene carbon. Further downstream after the large thermokarst lake, we find progressively younger DOC ages in the stream water to its mouth, paired with decreasing DOC concentrations. This process could result from dilution with leaching water from Holocene deposits and/or emission of ancient yedoma carbon to the atmosphere. Our study shows that thermokarst lakes and ponds may act as DOC filters, predominantly by diluting incoming waters of higher DOC concentrations or by re-mineralizing DOC to CO2 and CH4. Nevertheless, our results also confirm that the small catchment still contributes DOC on the order of 1.2 kg km−2 per day from a permafrost landscape with ice-rich yedoma deposits to the Lena River.

Torrent Monitoring and Early Warning Systems Development

The level of sustainability of a modern society is associated with the ability to manage unwanted stressors from the environment, regardless of origin. Torrential floods represent a hydrological hazard whose frequency and intensity have increased in recent years, mainly due to climate changes. In order to effectively manage the risks of torrents, it is necessary to apply early warning systems, since torrential floods are formed very quickly, especially on the watercourses of a small catchment area. The early warning system is part of a comprehensive torrential flood risk management system, seen as a technical entity for the collection, transformation, and rapid distribution of data. Modern early warning systems are the successors of rudimentary methods used in the past, and they are based on ICT and mobile applications developed in relation to the requirements of end users. The chapter presents an analysis of characteristic examples of the use. The main conclusion of the chapter indicates the need to implement early warning systems in national emergency management structures.

Assessing discharge periodicity in mountain catchments using classified environmental conditions (Tatra Mountains, Poland)

The periodicity of a river expressed in cycles of various lengths (monthly, seasonal, multiannual) is a result of climatic factors and overlapping environmental conditions within its catchment. In uncontrolled or poorly surveyed catchments, it is very difficult to determine the duration of a stream’s hydrological activity. This is especially relevant for catchments with complicated water circulation in karstic rocks. The present study concerns the small catchment of the Strązyski Potok river located in the area of the Tatra National Park, in the Western Tatras. The observation period covered the 2015 hydrological year, which differed hydrologically from average conditions. This study aims to develop a simple method to explain the processes shaping the mountain stream discharge periodicity. The research employed periodic field observations linked with climatic and non-climatic factors. Environmental conditions were assessed as four classes reflecting their influence on appearance or disappearance of mountain stream water. Class boundaries were the values of quartiles. The degree of correspondence between environmental factors and stream field observations was described via the Index DC (Degree Correspondence Index) approach. Complete correspondence (Index DC =0) was found in 23% catchments, a weak relationship between conditions favouring discharge and actual condition (Index DC= -1, +1) was noted within 11 catchments, while in 9 catchments, no such relationship was found (Index DC = -2, +2). The obtained results indicate a correspondence or lack thereof between the environmental potential of the catchment and its discharge periodicity. The discrepancies between the assessment of the influence of climatic and non-climatic factors and the data collected during field observations provide a basis for more detailed studies. Continuation of these studies based on the proposed classifications will allow for a more complete explanation of water disappearance in river channels and the determination of their short- and long-term discharge periodicity.

Soil moisture observation in a forested headwater catchment: combining a dense cosmic-ray neutron sensor network with roving and hydrogravimetry at the TERENO site Wüstebach

Cosmic Ray Neutron Sensing (CRNS) has become an effective method to measure soil moisture at a horizontal scale of hundreds of meters and a depth of decimeters. Recent studies proposed to operate CRNS in a network with overlapping footprints in order to cover root-zone water dynamics at the small catchment scale, and, at the same time, to represent spatial heterogeneity. In a joint field campaign from September to November 2020 (JFC-2020), five German research institutions deployed 15 CRNS sensors in the 0.4 km2 Wüstebach catchment (Eifel mountains, Germany). The catchment is dominantly forested (but includes a substantial fraction of open vegetation), and features a topographically distinct watershed. In addition to the dense CRNS coverage, the campaign featured a unique combination of additional instruments and techniques: hydro-gravimetry (to detect water storage dynamics also below the root zone); ground-based and, for the first time, airborne CRNS roving; an extensive wireless soil sensor network, supplemented by manual measurements; and six weighable lysimeters. Together with comprehensive data from the long-term local research infrastructure, the published dataset (available at https://doi.org/10.23728/b2share.afb20a34a6ac429ca6b759238d842765) will be a valuable asset in various research contexts: to advance the retrieval of landscape water storage from CRNS, wireless soil sensor networks, or hydrogravimetry; to identify scale-specific combinations of sensors and methods to represent soil moisture variability; to improve the understanding and simulation of land-atmosphere exchange as well as hydrological and hydrogeological processes at the hill-slope and the catchment scale; and to support the retrieval soil water content from airborne and spaceborne remote sensing platforms.

Using Geochemical Fingerprints for Assessing Sediment Source Apportionment in an Agricultural Catchment in Central Argentina

In the hilly semi-arid region of central Argentina, where the agricultural frontier expands at the expense of natural ecosystems, soil erosion is one of the most alarming environmental problems. Thus, obtaining knowledge about the dynamics of erosive processes and identifying erosion hotspots constitutes a primary scientific objective. This investigation is focused on estimating the apportionments of main sources of sediments, at the mouth of a small catchment called Durazno del Medio, located in the province of San Luis, Argentina. Elemental Analysis, measured by Energy Dispersive X-ray Fluorescence (EDXRF), was used to select potential geochemical fingerprints of sediment. The unmixing model MixSIAR was applied to approximate the contribution of each identified source in the sediment accumulation areas at the mouth of the catchment. Potential sediment sources were selected using two criteria: (i) a hierarchical approach to identify the main geomorphological units (GUs) and (ii) the main land uses (LU), recognized by examining satellite images and field recognitions. The selected geochemical tracers were able to distinguish sources located in the Crystalline basement hills with loess-patched (CBH) as the main sediment contributors.

Dissolved organic matter characterization in soils and streams in a small coastal low-arctic catchment

Ongoing climate warming in the western Canadian Arctic is leading to thawing of permafrost soils and subsequent mobilization of its organic matter pool. Part of this mobilized terrestrial organic matter enters the aquatic system as dissolved organic matter (DOM) and is laterally transported from land to sea. Mobilized organic matter is an important source of nutrients for ecosystems as it is available for microbial breakdown, and thus a source of greenhouse gases. We are beginning to understand spatial controls on the release of DOM as well as the quantities and fate of this material in large arctic rivers. Yet, these processes remain systematically understudied in small, high-arctic watersheds, despite the fact that these watersheds experience the strongest warming rates in comparison. Here, we sampled soil (active layer and permafrost) and water (porewater and stream water) from a small catchment along the Yukon coast, Canada, during the summer of 2018. We assessed the organic carbon (OC) quantity (using dissolved (DOC) and particulate OC (POC) concentrations and soil OC content), quality (δ13C-DOC, optical properties, source-apportionment), and bioavailability (incubations, optical indices such as slope ratio (Sr) and humification index (HIX)) along with stream water properties (T, pH, EC, water isotopes). We classify and compare different landscape units and their soil horizons that differ in microtopography and hydrological connectivity, giving rise to differences in drainage capacity. Our results show that porewater DOC concentrations and yield reflect drainage patterns and waterlogged conditions in the watershed. DOC yield (in mg DOC g soil OC−1) generally increases with depth but shows a large variability near the transition zone (around the permafrost table). Active layer porewater DOC generally is more labile than permafrost DOC, due to various reasons (heterogeneity, presence of a paleo-active layer, and sampling strategies). Despite these differences, the very long transport times of porewater DOC indicate that substantial processing occurs in soils prior to release into streams. Within the stream, DOC strongly dominates over POC, illustrated by DOC/POC ratios around 50, yet storm events decrease that ratio to around 5. Source-apportionment of stream DOC suggests a contribution of around 50 % from permafrost/deep-active layer OC, which contrasts to patterns observed in large arctic rivers (12 ± 8 % Wild et al., 2019). Our 10-day monitoring period demonstrated temporal DOC patterns on multiple scales (i.e. diurnal patterns, storm-events, and longer-term trend) underlining the need for high-resolution long-term monitoring. First estimates of Black Creek annual DOC (8.2 ± 6.4 t DOC yr−1) and POC (0.21 ± 0.20 t yr−1) export allowed us to make a rough upscaling towards the entire Yukon Coastal Plain (447 ± 313 t DOC yr−1 and 8.95 ± 9.7 t POC yr−1). With raising arctic temperatures, increases in runoff, soil OM leaching, permafrost thawing and primary production are likely to increase the net lateral OC flux. Consequently, altered lateral fluxes may have strong impacts on the arctic aquatic ecosystems and arctic carbon cycling.

Soil Available Phosphorus Investigated for Spatial Distribution and Effect Indicators Resulting from Ecological Construction on the Loess Plateau, China

Soil phosphorus is a major determinant and indicator of soil fertility and quality, and is also a source of nonpoint-source pollution. In order to control soil and water loss in the Loess Plateau, a series of soil and water conservation measures have been taken, resulting in changes in land use and differences in spatial distribution. It is necessary to study soil available phosphorus (SAP) to evaluate land productivity and environmental quality. In this study, the spatial distribution of SAP in different land uses was investigated in a small catchment area of Loess Plateau, and the field-influencing factors were determined on five layers with soil depth of 20 cm. The results show the minimum and maximum SAP content occurred at 20–40 cm and 80–100 cm soil depth and reach a value of 27.26 mg/kg and 29.37 mg/kg at catchment scale, respectively. There is significant difference among the SAP of the five soil layers (p < 0.01). The SAP of different land uses is, in order: forestland < slope farmland < dam farmland < terrace < grassland. Different land uses’ topographies make a difference to the spatial distribution of SAP. Slope and soil texture are the domain factors influencing the SAP concentration at the catchment.

Investigation into Settlement Behaviour of Mussels and the Hydrology of a Selected Area with a View to Farming the Shellfish

<p>Physical observations in the Beatrix Basin, Marlborough Sounds, New Zealand, revealed four distinct regions: a partially exposed northern region with moderate water currents, low rainfall, small catchment area and scant freshwater inflow; a central highly exposed region with strong currents, moderate rainfall, no land catchment area and no direct freshwater inflow; an eastern region with a high degree of exposure and strong water movement, moderate rainfall, extensive catchment and seasonally high freshwater inflow; a southern sheltered region with sluggish water movement, comparatively high rainfall, extensive catchment and the highest rainfall in the study area. Differences between the four regions in monthly mean temperature and salinity were slight and there was an indication of more mixing in the central region than elsewhere. No thermocline was observed and surface water temperature demonstrated a diurnal rhythm in summer. Mean winter temperature fell to 10 degrees C and rose to 17 degrees C in summer. Mean salinity ranged from 32.8 degrees C in winter to 34.8 degrees C in summer and no halocline was present. Salinity fell occasionally after heavy rain, but tidal currents soon dissipated the freshwater except in the southern region where it persisted for a short time. The reproductive cycles of Perna canaliculus and Mytilus edulis aoteanus, the occurrence of their larvae in plankton samples, their season of settlement and peaks in settlement activity, were monitored. Physical environmental conditions preceeding or accompanying spatfall were recorded. A broad temporal relationship was found between spawning adult mussels, pelagic larvae, environmental conditions, and settlement of Perna canaliculus in Elie Bay. It appears that P. canaliculus spawned in early summer and in autumn when the water temperature was 18 plus-minus 0.5 degrees C. However, it was not possible to predict spatfall since the duration of the pelagic phase was not known and settlement is a function of larval survival and dispersal, as well as the presence of a suitable substrate. Accurate spatfall prediction is required to facilitate timed immersion of spat-collecting ropes while ensuring "seasoning" and avoiding fouling. As it was not possible to predict settlement by relating it to other biological or physical phenomena, this study sought an alternative spat-collecting material not so susceptible to fouling but still attractive to mussels. Carbon black fibrillated polypropylene film proved to be such an alternative. The determination of available food for mussels within the study area was attempted using particulate organic nitrogen as the indicator. The problems encountered are discussed. The concentration of particulate organic nitrogen was 11.78 microgram at N/litre. The larvae of Mytilus edulis aoteanus and Aulacomya maoriana were reared in the laboratory to the late veliger stage. The most likely causes of their failure to metamorphose were a too high larval density, an excess of food organisms and the lack of a suitable substrate for settlement. It was not possible to induce spawning of Perna canaliculus under controlled conditions.</p>