After the Storm: Fate and Leaching of Particulate Nitrogen (PN) in the Fluvial Network and the Influence of Watershed Sources and Moisture Conditions

Large storms can erode, transport, and deposit substantial amounts of particulate nitrogen (PN) in the fluvial network. The fate of this input and its consequence for water quality is poorly understood. This study investigated the transformation and leaching of PN using a 56-day incubation experiment with five PN sources: forest floor humus, upland mineral A horizon, stream bank, storm deposits, and stream bed. Experiments were subjected to two moisture regimes: continuously moist and dry–wet cycles. Sediment and porewater samples were collected through the incubation and analyzed for N and C species, as well as the quantification of nitrifying and denitrifying genes (amoA, nirS, nirK). C- and N-rich watershed sources experienced decomposition, mineralization, and nitrification and released large amounts of dissolved N, but the amount of N released varied depending on the PN source and moisture regime. Drying and rewetting stimulated nitrification and suppressed denitrification in most PN sources. Storm deposits released large amounts of porewater N regardless of the moisture conditions, indicating that they could readily act as N sources under a variety of conditions. The inputs, processing, and leaching of large, storm-driven PN inputs become increasingly important as the frequency and intensity of large storms is predicted to increase with global climate change.

Ventspils apkārtnes apdzīvojums 17.–18. gadsimtā

The article deals with questions relating to the settlement in the area of Ventspils. Attention is gi-ven to environmental factors that could have had a greater or lesser influence on the settlement structure. The stream bank erosion along the River Venta had a relatively small impact on populated areas, while the wind erosion (sand deposition) caused the individual farms as well as villages to be abandoned. The Great Plague epidemic of 1710 was particularly devastating in the Ventspils area, during which about 40% of farms disappeared and most of them were not restored until the end of the 18th century. Final abandon-ment of farms, their renovation or addition of the former farmland to the land of the manor caused chan-ges in the population structure.

Can Understory Plant Composition and Richness Help Designate Riparian Management Zones in Mesic Headwater Forests of the Northeastern United States?

Riparian buffers implemented to minimize sediment, nutrients, and disturbance impacts on streams during forest operations vary greatly in the degree to which ecological criteria are used in their design. Because most forest operations are concentrated around headwater streams, our primary research objective was to identify a floristically based riparian boundary for headwater streams using plant species composition and indicator species to classify riparian environments distinct from the surrounding upland forest. Within three forested regions of the Northeast US, understory vegetation plots were sampled along perpendicular transects extending from the stream bank into the upland forest. At all sites, species richness was highest adjacent to the stream, decreasing exponentially within 6–12 m from the channel. Species composition closest to the stream was significantly different from all other lateral distances, but identified riparian indicator species were of limited practical use across all sites. However, changes in species richness can serve to identify a riparian area extent up to 6–12 m from headwater streams. Study Implications Riparian areas around headwater streams can be sensitive to forest management activities, particularly harvesting. Riparian management zone (RMZ) buffers around these streams vary in the degree to which they are based on ecological criteria; for example, fixed-width buffers may or may not adequately protect the riparian area. Our study within three forests of the Northeast detected a significant exponential decreasing trend in understory plant species richness within 6–12 m (20–40 ft) from the stream bank. We believe this ecologically based floristic zone closest to the stream represents the most sensitive part of the RMZ. This study recommends a 12 m (40 ft) zone to maintain the majority of the forest cover and minimize the impact of logging equipment. Foresters should be cognizant of this 12 m zone when implementing silvicultural activities and planning harvest access systems.

The effects of combined vegetation on the stream bank stability– numerical analyses of benchmark cases for a catchment in south-eastern Norway

<p>Vegetation is used as a nature-based solution (NBS) to restore rivers and mitigate water triggered processes along stream banks, such as soil erosion or floods. Furthermore, roots are well-known to improve the overall stability of slopes through hydro-mechanical reinforcement within the rooted zone. Vegetation based solutions require selection of species which are most suitable for specific locations, aimed at restoring the natural state and function of river systems in support of biodiversity, flood management and landscape development. Selecting a combination of different species (trees, shrubs and grasses) along different zones of the riverbank (upper part, along the slope, at the toe of the slope) can improve the conditions for the river system regarding biodiversity and flood management. However, how the combination of different plant species can improve the stability of the stream bank needs to be further studied. Relevant factors are both related to the improved mechanical strength of the soil from the roots and the changed pore pressure conditions. This work presents a methodological approach for slope stability modelling including vegetation. We present the results obtained from a series of slope stability analyses carried out by using the proposed methodology, for different topographical conditions (slope inclination), and different plant combinations for species typically found along streams in south-eastern Norway.</p><p>In this study, two types of tree species were selected, respectively Norway Spruce (<em>Picea Abies</em>) and Downy birch (<em>Betula pubescens</em>). The Goat willow (<em>Salix caprea</em>) was selected as shrub while a common mixed-grass was chosen as grass. Vegetation features were obtained from the literature. The plant combinations considered were: <em>i)</em> only grass, <em>ii)</em> grass and shrubs, <em>iii) </em>only trees, and <em>iv)</em> trees, shrubs and grass. The commercial software GeoStudio (GEO-SLOPE International, Ltd.) was used. The module SEEP/W was used for the hydrological modelling and the calculation of pore-water pressure distribution while SLOPE/W was used for the slope stability modelling and calculation of the safety factor through the rotational failure model proposed by Bishop.</p><p>Although one of the main outcomes is that the purely mechanical contribution of vegetation to slope stability could not be decoupled from the hydrological reinforcement (as the most critical shear surface occurred outside the rooted zone), the combinations including trees (both only trees and trees, shrubs and grass) gave the highest mechanical improvement to the stability. To assess the hydro-mechanical reinforcement played by the combined vegetation, two seasons of the year were analysed (spring and autumn) and it was found that the main reinforcement occurs in the spring season, due to the favourable weather (more days of drying and lower rainfall intensity), and for combinations including low height vegetation ( i.e. grass and shrubs) because of their better aboveground vegetation features. In conclusion, a mixed combination of vegetation (trees, shrubs and grass) is the most suitable for reaching the highest hydro-mechanical reinforcement of streambanks, and in the meantime boosting the ecosystem biodiversity. </p>

Morphology, Mineralogy, and Chemistry of Ocherous Precipitate Aggregates Downstream of an Abandoned Mine Site

Mineral precipitates forming downstream of abandoned and/or uncontrolled mine sites generally act as scavengers for heavy metals, such as As and Sb, leaking from the sites. This study reports the morphology of ocherous precipitate aggregates downstream of Ayuta, an abandoned antimony mine site in Tochigi Prefecture, Japan, because its morphology differs significantly from those reported previously. The morphology of this aggregate consists of stacked, small terraces enclosed by numerous connected rimstone dams, although on a smaller scale compared to typical terrace landscapes. The rimstone pools contained ocherous spheroids precipitates at the bottom. Additionally, stream water and ocherous aggregates collected from the site were investigated for mineralogy and chemistry. As (0.07–0.17 μg/L) and Sb (0.02 μg/L) levels in the stream water were determined, and the distributions of As and Sb in the mineral phases of the precipitate were estimated using a sequential extraction procedure. The investigations revealed that As was adsorbed by iron-bearing ocherous precipitate aggregates, especially ferrihydrite that formed on the stream bank at concentrations, comparable to those reported by other studies (85 mg/kg). This adsorption contributed to the natural attenuation of As in the stream. Sb in the aggregate consisted of ultra-fine silt and clay-size particles of stibnite ore transported from the surrounding area and/or secondary minerals transported by groundwater and surface water.