Hydrology and riparian forests drive carbon and nitrogen supply and DOC:NO_3⁻ stoichiometry along a headwater Mediterranean stream

In forest headwater streams, metabolic processes are predominately heterotrophic and depend on both the availability of carbon (C) and nitrogen (N) and a favourable C:N stoichiometry. In this context, hydrological conditions and the presence of riparian forests adjacent to streams can play an important, yet understudied role determining dissolved organic carbon (DOC) and nitrate (NO3−) concentrations and DOC:NO3− molar ratios. Here, we aimed to investigate how the interplay between hydrological conditions and riparian forest coverage drives DOC and NO3− supply and DOC:NO3− stoichiometry in an oligotrophic headwater Mediterranean stream. We analysed DOC and NO3− concentrations, and DOC:NO3− molar ratios during both base flow and storm flow conditions at three stream locations along a longitudinal gradient of increased riparian forest coverage. Further, we performed an event analysis to examine the hydroclimatic conditions that favour the transfer of DOC and NO3− from riparian soils to the stream during large storms. Stream DOC and NO3− concentrations were generally low (overall average ± SD was 1.0 ± 0.6 mg C L−1 and 0.20 ± 0.09 mg N L−1), although significantly higher during storm flow compared to base flow conditions in all three stream sites. Optimal DOC:NO3− stoichiometry for stream heterotrophic microorganisms (corresponding to DOC:NO3− molar ratios between 4.8 and 11.7) was prevalent at the midstream and downstream sites under both flow conditions, whereas C-limited conditions were prevalent at the upstream site, which had no surrounding riparian forest. The hydroclimatic analysis of large storm events highlighted different patterns of DOC and NO3− mobilization depending on antecedent soil moisture conditions: drier antecedent conditions promoted rapid elevations of riparian groundwater tables, hydrologically activating a wider and shallower soil layer, and leading to relatively higher increases in stream DOC and NO3− concentrations compared to events preceded by wet conditions. These results suggest that (i) increased supply of limited resources during storms can promote in-stream heterotrophic activity during high flows, especially during large storm events preceded by dry conditions, and (ii) C-limited conditions upstream were gradually overcome downstream, likely due to higher C inputs from riparian forests present at lower elevations. The contrasting spatiotemporal patterns in DOC and NO3− availability and DOC:NO3− stoichiometry observed at the study stream suggests that groundwater inputs from riparian forests are essential for maintaining in-stream heterotrophic activity in oligotrophic, forest headwater catchments.

Following the Curve?

Output from a runoff generation models is compared here with information from field measurements, making use of 11 years data from rainfall and runoff events at the Sierra de Enguera Soil Erosion Experimental Station in Eastern Spain.. The model presented simulates overland storm flow on a sloping rough and unvegetated surface, representing an area of 320x320 m. Green-Ampt infiltration constants are randomly assigned to each cell in a 128x128 grid, and rectangular storms applied at a range of total amounts and intensities to simulate runoff at each transect across the area. A simple algebraic expression is developed to estimate total runoff and storage in terms of storm size and duration, and plot length, with parameters that reflect infiltration behaviour, and this expression is compared with the SCS curve number approach. Output of these simulations is compared with measured storm runoff data on bare runoff plots at the Sierra de Enguera experimental Station in SE Spain and gives further support to the proposed expression for storm runoff.

ANALYSIS OF QUERCUS SELECTION OBJECTS IN VORONEZH AND THE VORONEZH REGION

Ecosystem services provided by forest ecosystems are diverse: improving microclimate formation, storing carbon, reducing storm flow, and absorbing pollutants from the air. One of the scientific tools aimed at reforestation and obtaining high-quality forest products is forest-seed nurseries and selection objects. We analyzed the materials of world and Russian scientific research on forest tree selection. The most frequently used approaches to forest selection, aims, as well as data on oak selection objects in the Voronezh region are highlighted. According to international practices, promising selection objects were selected and the possibility of their further use was evaluated. The following parameters of breeding objects were studied: creation aims, origin of breeding material, species, age of breeding objects, fruiting. In the practice of world forest breeding, the consequences of the introduction of non-native tree plantations on natural ecosystems, the need to integrate artificial plantations, the question of breed (species) forest plantation composition, prevention of invasion of plantation species, morphophysiological assessment of geographical crop responses, the role of genetic adaptation and physiological plasticity, as well as test crops, selection of the most productive individuals. The following oak selection objects were selected in the Voronezh region: geographical crops, forest-seed plantation, clone archive, plus trees. All these objects are in good condition, productive and produce seed progeny. Thus, they can be implemented in modern scientific research of forest genetics and breeding in accordance with the tasks of the forest industry.

Geohydrology of a Reference Mediterranean Catchment (Cilento UNESCO Geopark, Southern Italy)

In this paper, we studied the geo-hydrological structure and behavior of a reference catchment, located in the Cilento UNESCO Global Geopark, southern Italy, representative of the hilly, terrigenous and forested headwaters of the Mediterranean eco-region. Based on detailed hydrogeological and hydro-geomorphological surveys and geomorphometric analysis, starting in 2012, a hydro-chemical monitoring activity at the catchment and sub-catchment scale started, and a hydro-chemical dataset was progressively recorded at daily and sub-hourly time steps. Based on this dataset, the authors performed an original procedure to identify different runoff components, derived by applying cascade mass balance filtering. The integration of hydrological and geomorphological approaches allowed us to obtain an interesting conceptualization of the storm flow generation using hydro-chemical signatures related to different runoff components produced during the increasing–decreasing cycle of the flood event magnitude. The hydro-system activated progressively different runoff sources (i.e., groundwater, riparian corridor, hillslope and hollow) and involved various mechanisms (i.e., groundwater ridging, saturation-excess, infiltration-excess and soil pipe exfiltration). The geo-hydrological conceptualization was validated using a hysteresis Q-EC loop analysis performed on selected events that showed how hysteretic indices could be used to characterize the events in respect to their origins, mechanisms and pathways in similar catchments.

A look inside the Panola trenched hillslope - initial results of a tracer test

<p>Trenched hilsllope studies are logistically challenging but have provided valuable information on hillslope hydrological processes. For example, they have shown that subsurface stormflow can respond very quickly to rainfall and that subsurface storm flow often varies in a non-linear and threshold-like way with total rainfall or antecedent conditions. They have also highlighted the high spatial variability in subsurface stormflow due to surface or bedrock topography or spatial variability in soil and bedrock characteristics. However, still less is known about mixing and flow velocities along hillslopes.</p><p>Here we present the initial results of a tracer test at the Panola trenched hillslope in Georgia, USA. We applied chloride to the surface of the lower half of the hillslope and bromide as a line source. We measured the concentrations in subsurface flow at 2-m sections of the trench face and for two macropores during a five-month period that included two large rainfall events that caused subsurface flow, and several sprinkling experiments on parts of the hillslope. We used 20 lysimeter pairs and more than 50 wells and piezometers across the hillslope to track the transport of the tracer through the soil to the trench. The results highlight the variability in flow pathways, the considerable difference between celerity and velocity, as well as the fast tracer transport through the weathered bedrock</p>

Managing Tidal Inlets

Sandy inlets are in a dynamic equilibrium between wave-driven littoral drift acting to close them, and tidal flows keeping them open. Their beds are in a continual state of suspension and deposition, so their bathymetry and even location are always in flux. Even so, a nearly linear relationship between an inlet’s cross-sectional flow area and the inshore tidal prism is maintained - except when major wind and/or runoff events act to close or widen an inlet. Inlet location can be stabilized by jetties, but dredging may still be necessary to maintain a navigable channel. Armoring with rock large enough to resist erosion can protect an inlet bed or river mouth from excessive storm flow erosion. Armoring can also be used as a stratagem to close inlets.

Managing Tidal Inlets

Sandy inlets are in a dynamic equilibrium between wave-driven littoral drift acting to close them, and tidal flows keeping them open. Their beds are in a continual state of suspension and deposition, so their bathymetry and even location are always in flux. Even so, a nearly linear relationship between an inlet’s cross-sectional flow area and the inshore tidal prism is maintained - except when major wind and/or runoff events act to close or widen an inlet. Inlet location can be stabilized by jetties, but dredging may still be necessary to maintain a navigable channel. Armoring with rock large enough to resist erosion can protect an inlet bed or river mouth from excessive storm flow erosion. Armoring can also be used as a stratagem to close inlets.