Drainage Basin Scale Research Articles

Steady‐State Bedrock Channel Width

AbstractThe increase in bedrock channel width and the decline in bedrock channel slope with increasing drainage area are fundamental characteristics of mountainous landscapes. Compared with slope, little is known about controls on steady‐state bedrock channel width. We model steady‐state bedrock channel width by iteratively solving models for bed and bank erosion by impacting bedload, using measurable physical parameters, including uplift rate, water discharge, sediment supply, grain size, rock strength, and bank angle. The results indicate that width is largely controlled by sediment flux, rather than water discharge. The commonly used width‐discharge scaling relation is an artifact of the covariance of sediment flux and water discharge. Scaling up from cross‐section to drainage basin scales, our model reproduces the width‐drainage area scaling relation and suggests that the scaling exponent is largely controlled by the downstream change in the fraction of total sediment supply transported as bedload.

Morphotectonic Features in the Middle Biferno River Valley: The Case of Ponte Liscione Dam (Central Italy)

This paper presents a morphometric and structural-geomorphological approach to identifying morphotectonic features across an area underlain by lithologies that do not easily record tectonic deformations but are widely affected by seismic activity. The middle Biferno River Valley (Central Italy) was chosen as a study area. It was investigated through analyses performed from the drainage basin scale (Biferno River) to the local scale (Ponte Liscione Dam). This methodological approach was applied to investigate the impact of morphotectonic processes in the study area, providing a geomorphology-based contribution to landscape evolution. The aim of the work was to discriminate the main morphotectonic elements acting in the complex tectonic framework of the study area by means of a combination of morphometric, morphotectonic, and structural-geomorphological analyses. The resulting data allowed us to identify three main systems of tectonic elements (F1, F2, and F3), which are attributable to compressive and extensional kinematics, as already reported in previous thematic studies. The tectonic setting reflects the geodynamic framework of the Periadriatic region, as highlighted by the distribution of seismogenic sources and the historical to recent seismicity. Finally, the present work could act as a valuable scientific tool for any geomorphological studies aimed at better defining the impact of morphotectonic processes in similar tectonically active regions hosting important and strategic artificial dams.

Technological Advances to Rescue Temporary and Ephemeral Wetlands: Reducing Their Vulnerability, Making Them Visible

Mediterranean temporary ponds are a priority habitat according to the Natura 2000 network of the European Union, and complete inventories of these ecosystems are therefore needed. Their small size, short hydroperiod, or severe disturbance make these ponds undetectable by most remote sensing systems. Here we show, for the first time, that the distributed hydrologic model IBER+ detects ephemeral and even extinct wetlands by fully exploiting the available digital elevation model and resolving many microtopographic features at drainage basin scales of about 1000 km2. This paper aims to implement a methodology for siting flood-prone areas that can potentially host a temporary wetland, validating the results with historical orthophotos and existing wetlands inventories. Our model succeeds in dryland endorheic catchments of the Upper Guadalquivir Basin: it has detected 89% of the previously catalogued wetlands and found four new unknown wetlands. In addition, we have found that 24% of the detected wetlands have disappeared because of global change. Subsequently, environmental managers could use the proposed methodology to locate wetlands quickly and cheaply. Finding wetlands would help monitor their conservation and restore them if needed.

Environmental predictors of lake fish diversity across gradients in lake age and spatial scale

Abstract Freshwater ecosystems have experienced a great loss of biodiversity in the recent century due to eutrophication and loss of habitats, particularly in agricultural lowlands. Some of these ecosystems have recently been re‐established, or entirely new lakes have been created to improve nutrient removal, biodiversity, and recreation. Fish have an important structuring role in lake ecosystems, but little is known about the temporal development of fish species richness or composition in new or re‐established lakes, especially in comparison with natural lakes. We investigated the influence of environmental variables and landscape features on fish species richness and fish assemblage in drainage basins and in 34 new (between 0 and 99 years) and 193 natural lakes in Denmark, using structural equation modelling. Fish species richness in drainage basins is influenced primarily by basin elevation, lake area, and salinity at the basin outlet; low‐salinity coastal regions are important migration pathways for many freshwater fish species, not just for anadromous or catadromous species. Land use does not appear to influence richness at the drainage basin scale, indicating that the influence of anthropogenic activities is minor or that significant effects thereof occurred a long time ago (decades to centuries). The drainage basin richness defines the apparent pool of species that may colonise lakes within the basin, but the actual number of species is particularly influenced by stream network connectivity. Disconnected lakes have fewer species, a deficit that is sustained over long time scales. In addition to the influence of stream connectivity, lake characteristics such as elevation, surface area, and water chemistry (alkalinity and pH) are also important predictors of fish species richness, whereas we did not find any effect of lake nutrient concentrations. The direct effect of land use was not evaluated. Ordination analysis shows that fish assemblage depends on both lake type (new/natural) and stream connectivity (connected/disconnected). Furthermore, species‐specific occurrences reveal some differences between new and natural lakes and indicate that stocking plays a role in new lakes. While new and natural lakes may initially differ in terms of both how many and which species they contain, they converge over time in a process that can be enhanced by improving stream connectivity.

Instructive Surprises in the Hydrological Functioning of Landscapes

Landscapes receive water from precipitation and then transport, store, mix, and release it, both downward to streams and upward to vegetation. How they do this shapes floods, droughts, biogeochemical cycles, contaminant transport, and the health of terrestrial and aquatic ecosystems. Because many of the key processes occur invisibly in the subsurface, our conceptualization of them has often relied heavily on physical intuition. In recent decades, however, much of this intuition has been overthrown by field observations and emerging measurement methods, particularly involving isotopic tracers. Here we summarize key surprises that have transformed our understanding of hydrological processes at the scale of hillslopes and drainage basins. These surprises have forced a shift in perspective from process conceptualizations that are relatively static, homogeneous, linear, and stationary to ones that are predominantly dynamic, heterogeneous, nonlinear, and nonstationary. ▪ Surprising observations and novel measurements are transforming our understanding of the hydrological functioning of landscapes. ▪ Even during storm peaks, streamflow is composed mostly of water that has been stored in the landscape for weeks, months, or years. ▪ Streamflow and tree water uptake often originate from different subsurface storages and from different seasons’ precipitation. ▪ Stream networks dynamically extend and retract as the landscape wets and dries, and many stream reaches lose flow into underlying aquifers.

Autogenic knickpoints in laboratory landscape experiments

Abstract. The upstream propagation of knickpoints in river longitudinal profiles is commonly assumed to be related to discrete changes in tectonics, climate or base level. However, the recognition that some knickpoints may form autogenically, independent of any external perturbation, may challenge these assumptions. We investigate here the genesis and dynamics of such autogenic knickpoints in laboratory experiments at the drainage basin scale, where landscapes evolved in response to constant rates of base level fall and precipitation. Despite these constant forcings, we observe that knickpoints regularly initiate in rivers at the catchments' outlet throughout the duration of experiments. The upstream knickpoint propagation rate does not decrease monotonically in relationship with the decrease in drainage area, as predicted by stream-power-based models, instead the propagation rate first increases until the mid-part of catchments before decreasing. To investigate the dynamics of the knickpoints, we calculated hydraulic information (water depth, river width, discharge and shear stress) using a hydrodynamic model. We show that knickpoint initiation at the outlet coincides with a fairly abrupt river narrowing entailing an increase in their shear stress. Then, once knickpoints have propagated upward, rivers widen causing a decrease in shear stress and incision rate, and making the river incision less than the base level fall rate. This creates an unstable situation which drives the formation of a new knickpoint. The experiments suggest a new autocyclic model of knickpoint generation controlled by river width dynamics independent of variations in climate or tectonics. This questions an interpretation of landscape records focusing only on climate and tectonic changes without considering autogenic processes.

Comparison of decadal water storage trends from common GRACE releases (RL05, RL06) using spatial diagnostics and a modified triple collocation approach

GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (Follow-On) satellites have provided unique insights into the evolution of Terrestrial Water Storage (TWS) in space and time. Despite such advancements, various GRACE solutions produced by different data centers display uneven spatial attributes with varying associated uncertainties. Via spatial diagnostics tools and a modified triple collocation (MTC) approach, this research evaluates the TWS (terrestrial water storage) trend estimations “on the grid-scale” from 11 gridded GRACE products of RL05 and RL06 releases between 2002 and 2017. Distinct from classic TCA (triple collocation analysis), the MTC employs a GWR (geographically weighted regression) scaling scheme with distinctive spatial coefficients. The spatial diagnostics analyses identified different autocorrelation patterns, clustering tendencies of hot (positive) and cold (negative) spots agglomeration at varying spatial width, and unique frequency distributions. The results indicated that within a 10-degree spatial radius the SHs (Spherical Harmonics) of RL05 and RL06 are highly autocorrelated compared to the mascons (mass concentration blocks) solutions. The spatial clustering results revealed that many solutions agreed on the overall directions and distribution of the hot and cold spots. The clustering among mascon products, however, reflected more localized mass anomalies. At the scale of drainage basins, the trend magnitude, as well as their associated uncertainties appeared to be driven by the occurrence of spatial clusters within the basin area. The MTC results showed that the uncertainty patterns follow the same spatial extent within each cluster. The MTC analysis underscored the added benefits of cluster analysis and the GWR scaling over the classic OLS approach.

The impact of the spatiotemporal structure of rainfall on flood frequency over a small urban watershed: an approach coupling stochastic storm transposition and hydrologic modeling

Abstract. The role of rainfall space–time structure, as well as its complex interactions with land surface properties, in flood response remains an open research issue. This study contributes to this understanding, specifically for small (<15 km2) urban watersheds. Using a flood frequency analysis framework that combines stochastic storm transposition (SST)-based rainfall scenarios with the physically based distributed Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model, we examine the role of rainfall spatial and temporal variability in flood frequency across drainage basin scales in the highly urbanized Dead Run watershed (14.3 km2), Maryland, USA. The results show the complexities of flood response within several subwatersheds for both short (<50 years) and long (>100 years) rainfall return periods. The impact of impervious area on flood response decreases with increasing rainfall return period. For extreme storms, the maximum discharge is closely linked to the spatial structure of rainfall, especially storm core spatial coverage. The spatial heterogeneity of rainfall increases flood peak magnitudes by 50 % on average at the watershed outlet and its subwatersheds for both small and large return periods. The framework of SST–GSSHA-coupled frequency analysis also highlights the fact that spatially distributed rainfall scenarios are needed in quick-response flood frequency, even for relatively small basin scales.

Changes in floodplain regimes over Canada due to climate change impacts: Observations from CMIP6 models

With the recent Coupled Model Intercomparison Project Phase 6 (CMIP6), water experts and flood modellers are curious to explore the efficacy of the new and upgraded climate models in representing flood inundation dynamics and how they will be impacted in the future by climate change. In this study, for the first time, we consider the latest group of General Circulation Models (GCMs) from CMIP6 to examine the probable changes in floodplain regimes over Canada. A set of 17 GCMs from Shared Socioeconomic Pathways (SSPs) 4.5 (medium forcing) and 8.5 (high end forcing) common to historical (1980 to 2019), near-future (2021 to 2060), and far-future (2061 to 2100) time-periods are selected. A comprehensive framework consisting of hydrodynamic flood modelling, and statistical experiments are put forward to derive high-resolution Canada-wide floodplain maps for 100 and 200-yr return periods. The changes in floodplain regimes for the future periods are analyzed over drainage basin scale in terms of (i) changes in flood inundation extents, (ii) changes in flood hazards (high and very-high classes), and (iii) changes in flood frequency. Our results show a significant rise (>30%) in flood inundation extents in the future periods; particularly intense over western and eastern regions. The flood hazards are expected to cover ~16% more geographical area of Canada. We also find that large areas in northern and western Canada and a few spots in the eastern parts of Canada will be getting flooded more frequently compared to the historical period. The observations derived from this study are vital for enhancing flood preparedness, optimal land-use planning, and refurbishing both structural and non-structural flood control options for improved resilience. The study instills new knowledge on revamping the existing flood management approaches and adaptation strategies for future protection.

Pollution tolerance, flight capacity and natural history explain metacommunity structure in high-altitude stream insects

Abstract: Aim To test how different taxonomic and functional groups of aquatic insects from high-altitude streams respond to environmental and spatial gradients at multiple scales in Southeast of Brazil. Methods Specimens were collected in 26 high-altitude streams distributed over a gradient of previously defined environmental quality. The taxonomic identification was made at the genus level and the functional classification was based on traits of flight capacity and pollution tolerance compiled from specific literature. We obtained local in situ data (limnological, sediments, and organic matter), as well as calculated land use at the riparian and drainage basin scale. A variation partitioning approach was used to explain species composition based on different response matrices deconstructed by both taxonomic groups and functional traits. The explanatory matrices encompassed environmental variables at three spatial scales and spatial variables extracted from Principal Components of Neighbor Matrices analysis. A linear model was applied to verify the possible correlation between spatial and environmental components. Results The contribution of the spatial and environmental components varied strongly between taxonomic and functional groups. For taxonomic groups, the pure environmental component was more important for Odonata and Trichoptera, while spatial variables were more important for Diptera (non-Chironomidae) and Chironomidae, Coleoptera, Ephemeroptera, Plecoptera and Megaloptera. The sensitive groups with good flight capacity showed a greater environmental signature while the tolerant groups with low flight capacity had a greater spatial signature. Moreover, the important variables for explaining community variation were from different spatial scale (local, riparian and watershed) depending either on the analyzed taxonomic or on functional groups. However, a general effect of forests was found in several groups. Conclusions It is necessary to consider the joint effect of evolutionary natural history of groups, as well as their functional traits in the structuring of metacommunities, since only taxonomic resolutions may not be sufficient to detect assembly processes at multiple spatial scales.

The surface albedo of the Greenland Ice Sheet between 1982 and 2015 from the CLARA-A2 dataset and its relationship to the ice sheet's surface mass balance

Abstract. The Greenland Ice Sheet is losing mass at a significant rate, driven in part by increasing surface-melt-induced runoff. Because the ice sheet's surface melt is closely connected to changes in the surface albedo, studying multidecadal changes in the ice sheet's albedo offers insight into surface melt and associated changes in its surface mass balance. Here, we first analyse the CM SAF Cloud, Albedo and Surface Radiation dataset from AVHRR data second edition (CLARA-A2) Surface Albedo (SAL), covering 1982–2015, to obtain decadal albedo trends for each summer month. We also examine the rates of albedo change during the early summer, supported with atmospheric reanalysis data from MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2), to discern changes in the intensity of early summer melt, and their likely drivers. We find that rates of albedo decrease during summer melt have accelerated during the 2000s relative to the early 1980s and that the surface albedos now often decrease to values typical of bare ice at elevations 50–100 m higher on the ice sheet. The southern margins exhibit the opposite behaviour, though, and we suggest this is due to increasing snowfall over the area. We then subtract ice discharge from the mass balance estimates observed by the Gravity Recovery and Climate Experiment (GRACE) satellite mission to estimate surface mass balance. The CLARA-A2 albedo changes are regressed with these data to obtain a summer-aggregated proxy surface mass balance time series for the summer periods 1982–2015. This proxy time series is compared with latest regional climate model estimates from the MAR model to perform an observation-based test on the dominance of surface runoff in the magnitude and variability of the summer surface mass balance. We show that the proxy time series agrees with MAR through the analysed period within the associated uncertainties of the data and methods, demonstrating and confirming that surface runoff has dominated the rapid surface mass loss period between the 1990s and 2010s. Finally, we extend the analysis to the drainage basin scale to examine discharge–albedo relationships. We find little evidence of surface-melt-induced ice flow acceleration at annual timescales.

Diffuse nitrogen pollution control: Moving from riparian zone to headwater catchment approach—A tribute to the influence of Professor Geoff Petts

AbstractA lot of attention has been given to the importance of riparian zones as a nitrogen buffer during the last 30 years. Expectations were high and have resulted often in mismanagement practices. This paper aims at revisiting during this period the main research advancement, questions generated, and the progress in understanding the role of interactions between land and water in river system functioning. We describe how the seminal papers published in the 1980s on the role of riparian zone as nitrogen buffer have triggered several fundamental and applied questions related to the mechanisms at stake or their long efficiency in different hydrological and climatic contexts. We then address how this local riparian buffer capacity can be evaluated at the small drainage basin scale. We finally touch upon the restoration and protection of riparian zones in the context of climate change and especially its potential role on local and global water fluxes and other key aquatic ecosystem functions.

Spatially differentiated regulation: Can it save the Baltic Sea from excessive N-loads?

The Baltic Sea Action Plan and the EU Water Framework Directive both require substantial additional reductions of nutrient loads (N and P) to the marine environment. Focusing on nitrogen, we present a widely applicable concept for spatially differentiated regulation, exploiting the large spatial variations in the natural removal of nitrate in groundwater and surface water. By targeting mitigation measures towards areas where nature's own capacity for removal is low, spatially differentiated regulation can be more cost-effective than the traditional uniform regulation. We present a methodology for upscaling local modelling results on targeted measures at field scale to Baltic Sea drainage basin scale. The paper assesses the potential gain and discusses key challenges related to implementation of spatially differentiated regulation, including the need for more scientific knowledge, handling of uncertainties, practical constraints related to agricultural practice and introduction of co-governance regimes.

Paleo-Drainage Network, Morphotectonics, and Fluvial Terraces: Clues from the Verde Stream in the Middle Sangro River (Central Italy)

This work analyzes the role of paleo-drainage network, morphotectonics, and surface processes in landscape evolution in a sector of the transition zone between the chain and the piedmont area of Central Apennines. Particularly, it focuses on the Verde Stream, a tributary of the middle Sangro River valley, which flows in the southeastern Abruzzo area at the boundary with the Molise region. The Verde Stream was investigated through a drainage basin scale geomorphological analysis incorporating the morphometry of the orography and hydrography, structural geomorphological field mapping, and the investigation of morphological field evidence of tectonics with their statistical azimuthal distributions. The local data obtained were compared with the analysis of the middle Sangro River valley and the tectonic features of the Abruzzo–Molise area. This approach led us to also provide relevant clues about the definition of the role of karst features and paleo-landscapes in the general setting of the study area and to identify the impact of active tectonics, confirmed by recent and active seismicity. In conclusion, the paper contributes to defining the main stages of the geomorphological evolution of this area, driven by uplift and local tectonics and due to a combination of fluvial, karst, and landslide processes.

Quantitative analysis of crystal-interface frequencies in granitoids: Implications for modelling of parent-rock texture and its influence on the properties of plutoniclastic sands

Generation of sediments from crystalline rocks is the result of a complex and incompletely understood suite of processes. The time evolution of the rock-fragment assemblage in sands derived from granitoids is determined by the relative strengths of crystal interfaces and their abundances in the parent rock. In this study we highlight the role of crystal-interface frequencies in granitoids. Strong evidence for non-random texture with significant implications for predicted interface frequencies have been reported in previous studies. We analysed available interface-frequency data from granitoids using methods of compositional data analysis, and connected our results to existing texture classifications. On average, granitoids display a high degree of ordering with significant depletion of isomineralic interfaces relative to expectations based on random texture. Analysis of 210 normalized interface frequency distributions from nine different granitoids reveals a consistent pattern of variation among interface frequencies, which suggests a single underlying petrogenetic process related to the combined effects of nucleation and textural equilibration (“coarsening”).In view of the large scatter of relative interface frequencies within and among granitoids, we propose to model their distribution empirically for the purpose of calibrating sediment-generation studies. Multivariate normal distributions of centred log-ratio transformed relative frequencies are capable of capturing ~95% of the observed variability with a limited number of dimensions. As a rule of thumb, the number of dimensions needed to approximate interface-frequency counts can be taken equal to the number of mineral classes, which is (much) smaller than the number of interface classes. Mathematical analysis shows that the joint variability of rock texture and composition may be factorized into three statistically independent measures: modal composition, crystal-size probability density functions, and normalized interface frequencies. The potential independence of these measures permits objective identification of petrogenetically significant correlations among them, which will be indicated by statistically significant cross-covariances. At this stage, inferences from microscopic texture analysis cannot be extrapolated to the scale of entire drainage basins in which sediments are generated, because insufficient data are available on the large-scale spatial heterogeneity of texture and composition of granitoid parent rocks.

Agricultural land use doubled sediment loads in western China’s rivers

Abstract Land use changes, such as deforestation and agricultural expansion, increase soil erosion on the scale of hillslopes and small drainage basins. However, the effects of these changes on the sediment load in rivers is poorly quantified, with a few studies scattered globally, and only 10 data points in the world’s most populous nation, China. At 20 different sites in western China, we compare contemporary fluvial sediment yield data collected daily over 4 to 26 years between 1945 and 1987 (median = 19 years) to long-term measures of sediment generation based on new isotopic measurements of in situ 10Be (beryllium-10) in river sediments. We find that median sediment yield at these sites exceeds background sediment generation rates by a factor of two (from 0.13 to 5.79 times, median 1.85 times) and that contemporary sediment yield is statistically significantly different from long-term sediment generation rates (p

Future export of particulate and dissolved organic carbon from land to coastal zones of the Baltic Sea

Abstract The Baltic Sea is a semi-enclosed brackish sea in Northern Europe with a drainage basin four times larger than the sea itself. Riverine organic carbon (Particulate Organic Carbon, POC and Dissolved Organic Carbon, DOC) dominates carbon input to the Baltic Sea and influences both land-to-sea transport of nutrients and contaminants, and hence the functioning of the coastal ecosystem. The potential impact of future climate change on loads of POC and DOC in the Baltic Sea drainage basin (BSDB) was assessed using a hydrological-biogeochemical model (CSIM). The changes in annual and seasonal concentrations and loads of both POC and DOC by the end of this century were predicted using three climate change scenarios and compared to the current state. In all scenarios, overall increasing DOC loads, but unchanged POC loads, were projected in the north. In the southern part of the BSDB, predicted DOC loads were not significantly changing over time, although POC loads decreased in all scenarios. The magnitude and significance of the trends varied with scenario but the sign (+ or −) of the projected trends for the entire simulation period never conflicted. Results were discussed in detail for the “middle” CO 2 emission scenario (business as usual, a1b). On an annual and entire drainage basin scale, the total POC load was projected to decrease by ca 7% under this scenario, mainly due to reduced riverine primary production in the southern parts of the BSDB. The average total DOC load was not predicted to change significantly between years 2010 and 2100 due to counteracting decreasing and increasing trends of DOC loads to the six major sub-basins in the Baltic Sea. However, predicted seasonal total loads of POC and DOC increased significantly by ca 46% and 30% in winter and decreased by 8% and 21% in summer over time, respectively. For POC the change in winter loads was a consequence of increasing soil erosion and a shift in duration of snowfall and onset of the spring flood impacting the input of terrestrial litter, while reduced primary production mainly explained the differences predicted in summer. The simulations also showed that future changes in POC and DOC export can vary significantly across the different sub-basins of the Baltic Sea. These changes in organic carbon input may impact future coastal food web structures e.g. by influencing bacterial and phytoplankton production in coastal zones, which in turn may have consequences at higher trophic levels.

Disentangling spatial and environmental determinants of fish species richness and assemblage structure in Neotropical rainforest streams

Abstract Freshwater ecology templates were developed in temperate streams, but whether they also apply to tropical streams that harbour a higher biological diversity than their temperate counterparts remains uncertain. This is particularly true for tropical fish assemblages inhabiting small streams that have been less studied than larger, higher‐order lowland streams. Here, we disentangled the strength of spatial (longitudinal and environmental) drivers, and scale‐specific (drainage basin, reach and local scale) determinants of species richness and composition of freshwater fish assemblages inhabiting small streams in French Guiana. We found that species richness increased from upstream to downstream but also with increasing local habitat structural diversity independently of stream position in the upstream–downstream gradient. This pattern was shared by the two most speciose fish orders (Characiformes and Siluriformes), demonstrating that species addition rather than species replacement shaped species richness in these assemblages. Species composition of fish assemblages was determined equally by their spatial structure within drainage and by the environment, and assemblages differed both with distance and along an upstream–downstream gradient. The environmental effect on species assemblages indicated by the fact that almost all environmental descriptors had slight but nonetheless significant effects on assemblage composition, probably reflecting species‐specific responses to the local environment. In contrast, despite a strong micro‐endemism between drainages for some taxa, assemblages were only slightly affected by river drainage identity, since widespread species were a common constituent of assemblages in all rivers. We identified five species assemblages characterising different local habitat features from torrential areas to lowland muddy areas. We also distinguished fish assemblages from confluence areas with larger rivers, which differed from the other five assemblages. The fish zonation patterns we report can constitute a benchmark for future studies measuring the impact of anthropogenic disturbances on Neotropical forest streams.

Ecological and human land-use indicator value of fungal spore morphotypes and assemblages

The value of non-pollen palynomorphs (NPPs) to complement reconstructions of past communities and environments has led to the identification of an increasing number of microfossil morphotypes. Unfortunately, limited knowledge about their specific ecological indicator values still restricts the interpretation of NPP accumulation rates or assemblage variations. Here, a comparison with classical palaeoecological proxies along a sedimentary sequence has been tested to improve the ecological indicator values of NPP morphotypes. Pollen, geochemical and NPP analyses performed on the same samples all along the Holocene sedimentary sequence of Lac de Moras (France) were compared using principal component analysis to identify statistical relationships and to establish correlations between all these parameters. Ecological indicator values were obtained for some morphotypes such as UG-1097 which is related to specific taxa (Corylus sp.), or Diporotheca rhizophila defined as an indicator of the local presence of alder swamp habitat. However, most of the NPP morphotypes can be combined in two opposite NPP assemblages reflecting the change from natural to managed ecosystems at the drainage basin scale and over the Holocene. It more specifically illustrates a change in the source of organic matter transferred to the lake system provided from the plant debris of woodland cover (litter) to organic matter from animal excreta (dung and manure).

The significance of the geological strata on desert runoff agriculture: Indications for stable desert environment over the last 1600 years in southern Israel

Large distribution of historical agricultural installations in the desert zone of the southern Levant, mainly from the Byzantine - Early Muslim periods (1600–1000 y BP) indicates that the region was highly productive in the past. That could have been achieved either because of a more humid climate, or by sophisticated runoff harvesting techniques utilized by the ancient farmers under a desert climate. Among all, the most important factor enabling the existence of the desert agriculture was runoff harvesting. Our study assess a multi-disciplinary approach testing the relationship between diverse geological strata, their ability to cause runoff and the possible preferences made by the ancient farmers to utilize these rock properties. Utilizing GIS methods we generated high-resolution maps, highlighting the present runoff potential both on a single lithology slope level and on the drainage basin scale. By applying this methodology we show that high correlation (80%) exists when testing the spatial emplacement of runoff-farming installations constructed during the Byzantine - Early Muslim periods on the present best runoff yielding drainage basins under the present climatic conditions. This hints at the long stability of the environmental and probably climatic conditions in the southern Levant regions during the late Holocene.