Catchment Erosion Research Articles

Modelling the inter-annual variability of sediment yields: A case study for the upper Lech River

Abstract Pulsing storms and prolonged rainfall events have been associated to floods, soil erosion and nutrient fluxes in many European river catchments. This motivated us to develop a parsimonious approach to model the climate forcing on sediment yields in a mountainous Austrian–German river catchment. The hydro-climatologic forcing was interpreted by the novel RAMSES (RAinfall Model for SEdiment yield Simulation) approach to estimate the annual sediment yields. We used annual data on suspended-solid yields at the gauge Fussen, monitored from 1924 to 2003, and monthly rainfall data. The dataset was split into the period 1924–1969 for calibration and the period 1970–2003 for validation. The quality of sediment yield data was critically examined, and a few outlying years were identified and removed from further analyses. These outliers revealed that our model underestimates exceptionally high sediment yields in years of severe flood events. For all other years, the RAMSES performed well against the calibration set, with a correlation coefficient (r) equal to 0.83 and a Nash–Sutcliffe Index (NSI) of 0.69. The lower performance in the validation period (r = 0.61, NSI = 0.36) has to be partly attributed to discontinuities in the monitoring strategy. For the calibration dataset, monthly precipitations proved nonetheless to be better predictors for annual sediment yields than annual values. These first results lay the foundation for reconstructing intra- to inter-decadal variability of sediment yields in river catchments where detailed precipitation records are not available as well as for the reconstruction of historical sediment yields.

Exposition professionnelle au trichloroéthylène et pathologies cancéreuses du col utérin, une étude cas témoins

This study addresses the problem of modelling sediment erosion at the catchment scale, in order to predict the possible impact of reservoirs and land use changes on sediment load in South East Asia. The investigated basin is the Lo river basin, (38,165 km2 in Viet Tri), a left tributary of the Red River, where the Thac Ba and the recently built Tuyen Quang reservoirs have already been changing downstream sediment load since 1971 and 2005 when they were, respectively, in operations. The RUSLE equation is adopted in a distributed GIS framework to assess catchment erosion, and is coupled with a sediment accumulation and routing scheme to model suspended sediment load in the Lo basin at a monthly scale. Monthly precipitation were collected and used as input to the model. Suspended sediment load data, measured at eight gauging stations in Vietnam, from 1959 to 2007, were compared with the model’s simulated sediment yield. Resulting average Nash–Sutcliffe efficiency is 0.45, ranging from 0.33 to 0.62 and bias is 5% at Vu Quang, close to the basin outlet, and results 1.4% by averaging biases at the eight stations, thus confirming that the model is adequate. Effects of reservoirs were analysed by modelling erosion and sediment yield passing from natural to impounded conditions and resulted in a suspended sediment load reduction of about 95% and 75% downstream, respectively, the Thac Ba reservoir in the Chay river and the Tuyen Quang reservoir in the Gam river. Land use change scenarios, parameterized on the basis of observed land use changes in the impounded basin and assuming that 20% of forest area is converted into rice and agricultural crops and 15% into bushes, shrubs and meadows, are expected to induce a 28% increase of suspended sediment load which can compensate, at least in part, sedimentation in reservoirs. Also agricultural and hillslope maintenance practices can modify sediment erosion in the basin.

Lake and catchment response to Holocene environmental change: spatial variability along a climate gradient in southwest Greenland

The Kangerlussuaq area of southwest Greenland is a lake-rich landscape that covers a climate gradient: a more maritime, cooler and wetter coastal zone contrasts with a dry, continental interior. Radiocarbon-dated sediment sequences (covering ~11,200–8,300 cal year) from paired lakes at the coast and the head of the fjord were analysed for lithostratigraphic variables (organic-matter content, bulk density, Ti, Ca). Minerogenic and carbon accumulation rates from the four lakes were compared to determine catchment and lake response to Holocene climatic variability. Catchment erosion at the coast was dominated by cryonival processes, with considerable sediment production due to the limited vegetation cover and exposed rock faces. Input of minerogenic sediment at one site (AT4) was high (>1 gDW cm−2 year−1) during the period 5,800–4,000 cal year BP, perhaps reflecting intensification of cryogenic processes on northeast-facing slopes and rapid delivery to the lake. This period of erosional activity was not observed at the nearby, higher elevation site (AT1) due to the lower catchment relief; instead, there was an abrupt decline in carbon and minerogenic accumulation rates at ~5,800 cal year BP. Sediment accumulation rates at the inland sites were much lower (<0.005 gDW cm−2 year−1) reflecting greater catchment stability (more extensive vegetation cover), lower relief and substantially lower precipitation, but synchronous increases in mineral accumulation rates from ~1,200 to 1,000 cal year BP may reflect wind erosion associated with regional cooling and local aridity. Carbon-accumulation-rate profiles were similar at the two inland sites, with higher-than-average accumulation (~6–8 g C m−2 year−1) during the early Holocene and a subsequent decline after ~6,000 cal year BP. At the inland lakes, both mineral and carbon accumulation rates exhibited a stronger link to climate, driven by trends in effective precipitation and regional aeolian activity. Catchment differences (relief, altitude) lead to more individualistic records in both erosion history and lake productivity at the coast.

Catchment erosion and trophic status changes over the past century as recorded in sediments from Wudalianchi Lake, the northernmost volcanic lake in China

Abstract In June 2009, two short sedimentary cores, wdlc-3 and wdlc-5, were collected from Wudalianchi Lake (48°40′ N ∼ 48°47′ N, 126°06′ E ∼ 126°15′ E) in the north central of Heilongjiang Province, northeastern China, using a gravity corer. The catchment erosion and trophic status changes were studied by an interpretation of the variations of multi-proxies, including organic matter (loss on ignition (LOI 550°C ) and total organic carbon (TOC)), total phosphorus (TP), total nitrogen (TN), magnetic susceptibilities, organic carbon isotope (δ 13 C org ) and grain size. Sediment accumulation rates (SARs) and ages were determined using a composited model of the 210 Pb or 137 Cs methods, respectively. The results are as follows: 1) the average sediment rate was 0.28 g cm −2 y −1 (0.59 cm y −1 ) in wdlc-3 and 0.25 g cm −2 y −1 (0.55 cm y −1 ) in wdlc-5 over the past 100 years. The interaction of the large-scale land reclamation and rainfall were related to high sediment accumulation rates before the 1980s; after the 1980s, however, the changes of precipitation were most likely the main influencing factor on SARs. 2) The δ 13 C org values ranged from −26.78 to −25.79‰ in wdlc-3 and −25.82 to −21.95‰ in wdlc-5. The TOC and TN showed an upcore increasing tendency, and TN, TOC and TP showed a dramatic increase since the 1980s. Based on the multi-proxies, the sediments recorded the change of the aquatic plant community from macrophyte-dominant to algae-dominant in the third lake and to macrophyte and algae coexistence in the fifth lake, also reflecting the changes of trophic status over the past 100 years. 3) Large-scale reclamation was the main factor impact the lake environment before the 1980s; after the 1980s, enhanced agricultural activities such as extensive use of fertilizers and the discharge of domestic waste water resulted in dramatic changes in the lake environment.

Ancient harbors and Holocene morphogenesis of the Ras Ibn Hani peninsula (Syria)

Ras Ibn Hani peninsula, a wave-dominated tombolo (800×1000m) on the Syrian coast, provides evidence for significant Holocene changes that can be linked to geological inheritance, rising post-glacial sea level, sediment supply and human impacts. Initial development of Ras Ibn Hani's coastal system began ~8000years ago when shallow marine environments formed in a context of rising post-glacial sea level. Following relative sea-level stabilization ~6000calyr BP, beach facies trace the gradual formation of a wave-dominated sandbank fronted by a ~2300×~500m palaeo-island whose environmental potentiality was attractive to Bronze Age societies. A particularly rapid phase of tombolo accretion is observed after ~3500calyr BP characterised by a two- to fourfold increase in sedimentation rates. This is consistent with (i) a pulse in sediment supply probably driven by Bronze Age/Iron Age soil erosion in local catchments, and (ii) positive feedback mechanisms linked to regionally attested neotectonics. Archaeological remains and radiocarbon datings confirm that the subaerial tombolo was probably in place by the Late Bronze Age. These data fit tightly with other eastern Mediterranean tombolo systems suggesting that there is a great deal of predictability to their geology and stratigraphy at the regional scale.

Integration of GIS and remote sensing for estimation of soil loss and prioritization of critical sub-catchments: a case study of Tapacurá catchment

Mapping of erosion risk areas is an important tool for the planning of natural resources management, allowing researchers to propose the modification of land use properly and implement more sustainable long-term management strategies. The objective of this study was to assess and identify critical sub-catchments for soil conservation management using the USLE, GIS, and remote sensing techniques. The Tapacura catchment is one of the planning units for water resource management of the Recife Metropolitan Region. Maps of the erosivity (R), erodibility (K), slope (LS), cover-management (C), and support practice (P) factors were derived from the climate database, digital elevation model, and soil and land-use maps. In order to validate the simulation process, total sediment delivery ratio was estimated. The results showed a mean sediment delivery ratio (SDR) of around 11.5 % and a calculated mean sediment yield of 0.108 t ha−1 year−1, which is close to the observed one, 0.169 t ha−1 year−1. The obtained soil loss map could be considered as a useful tool for environmental monitoring and water resources management. The methodology applied showed acceptable precision and allowed the identification of the most susceptible areas to soil erosion by water, constituting an important predictive tool for soil and environmental management in this region, which is highly relevant for the prediction of varying development scenarios for Tapacura catchment. This approach can be applied to other areas for simple and reliable identification of critical areas of soil erosion in catchments.

Comparison of empirical models to estimate soil erosion and sediment yield in micro catchments

Assessment of sediment yield in soil conservation and watershed Project and implementation plan for water and soil resources management is so important. Regarding to somewhere that doesn’t have enough information and statistical data such as upper river branches, Empirical models should be used to estimate erosion and sediment yield. However the efficiency and usage of these models before calibration isn’t clear. In this research, the measurement of erosion and sediment yield of 10 basins upstream of reservoirshas been estimated by RUSLE and MPSIAC empirical models.In order to compare means between measured and estimated datat-test method was applied.Theresults indicated no significant differences between means of measured and estimated sediment yield in MPSAIC model in 5% level. In contrast, T-test showed contrary results in RUSLE model. Then the applicability and priority of two models were examined by statistical methodssuch as MAE and MBE methods. By regarding to accuracy and precision, MPSIAC model placed in first priorityto estimate soil erosion and sediment yield and has minimum value of MAE=0.79 and MBE = -0.59.

Provenance of sediments deposited at paleolake San Felipe, western Sonora Desert: Implications to regimes of summer and winter precipitation during last 50 cal kyr BP

Rare earth element, major and trace element and mineralogy in the sediments representing last 50 cal kyr BP from the summer precipitation fed paleolake San Felipe identify the different association of minerals and selective transportation of different grain size fractions and relate them to the variation in pluvial discharge into the basin as well as aeolian activities in the western Sonora Desert. Period of lower pluvial discharge during 14–48 cal kyr BP is contemporary to the regime of dominant winter storms in the region. Transportation of coarser quartz and plagioclase during 40–48 cal kyr BP and dominant finer fractions during 14–40 cal kyr BP possibly mirror the variation in the frequency of winter storms. During 3–14 cal kyr BP, higher catchment erosion (sedimentation increased 4–12 times) and transportation of REE bearing heavy minerals into the basin indicate higher pluvial discharge. We relate this period to a regime of dominant summer precipitation associated with the North American Monsoon and tropical cyclones. Geochemical and mineralogical signatures of the sediments deposited during ca. 8, 12–13 and >48 cal kyr BP suggest selective mobilization of quartz and plagioclase from the surrounding sand dunes by the aeolian processes.

A sedimentary record of Holocene surface runoff events and earthquake activity from Lake Iseo (Southern Alps, Italy)

This study presents a record of Holocene surface runoff events and several large earthquakes, preserved in the sediments of pre-Alpine Lake Iseo, northern Italy. A combination of high-resolution seismic surveying, detailed sediment microfacies analysis, non-destructive core-scanning techniques and AMS 14C dating of terrestrial macrofossils was used to detect and date these events. Based on this approach, our data shed light on past seismic activity in the vicinity of Lake Iseo and the influence of climate variability and human impact on allochthonous detrital matter flux into the lake. The 19 m long investigated sediment sequence of faintly layered lake marl contains frequent centimetre- to decimetre-scale sandy-silty detrital layers. During the early to mid Holocene, these small-scale detrital layers, reflecting sediment supply by extreme surface runoff events, reveal a distinct centennial-scale recurrence pattern. This is in accordance with regional lake-level highstands and minima in solar activity and thus apparently mainly climate-controlled. After c. 4200 cal. yr BP, intervals of high detrital flux occasionally also correlate with periods of enhanced human settlement activity. In consequence, deposition of small-scale detrital layers during the late Holocene apparently reflects a rather complex interplay between climatic and anthropogenic influences on catchment erosion processes. Besides the small-scale detrital layers, five up to 2.40 m thick large-scale detrital event layers, composed of basal mass-wasting deposits overlain by large-scale turbidites, were identified, which are supposed to be triggered by strong earthquakes. The uppermost large-scale event layer can be correlated to a documented Mw=6.0 earthquake in ad 1222 in Brescia. The four other large-scale event layers are supposed to correspond to previously undocumented local earthquakes. These occurred around 350 bc, 570 bc, 2540 bc and 6210 bc and most probably also reached magnitudes in the order of Mw = 5.0–6.5.

Detection of Hot Spots of Soil Erosion and Reservoir Siltation in Ungauged Mediterranean Catchments

The long-term average, distributed parameter PhosFate model was applied for erosion hot spot identification in unmonitored Mediterranean catchments. Based on experiences of previous case studies in well-monitored watersheds, the model was tested in a study over the entire area of Albania with success. The model results were validated by the sporadically available data on river discharge and sediment loads. With an optimization method cost effective interventions were planned to efficiently reduce soil erosion. The optimization algorithm is based on a simple sediment transport model and it minimizes the necessary area of interventions. In accordance with the critical source area concept, it was shown that intervention with better management practices on properly selected, a few percent of the total area is sufficient to reach a significant reduction in soil loss, reservoir siltation and consequently an improvement in water quality.

A RUSLE approach to model suspended sediment load in the Lo river (Vietnam): Effects of reservoirs and land use changes

Summary This study addresses the problem of modelling sediment erosion at the catchment scale, in order to predict the possible impact of reservoirs and land use changes on sediment load in South East Asia. The investigated basin is the Lo river basin, (38,165 km 2 in Viet Tri), a left tributary of the Red River, where the Thac Ba and the recently built Tuyen Quang reservoirs have already been changing downstream sediment load since 1971 and 2005 when they were, respectively, in operations. The RUSLE equation is adopted in a distributed GIS framework to assess catchment erosion, and is coupled with a sediment accumulation and routing scheme to model suspended sediment load in the Lo basin at a monthly scale. Monthly precipitation were collected and used as input to the model. Suspended sediment load data, measured at eight gauging stations in Vietnam, from 1959 to 2007, were compared with the model’s simulated sediment yield. Resulting average Nash–Sutcliffe efficiency is 0.45, ranging from 0.33 to 0.62 and bias is 5% at Vu Quang, close to the basin outlet, and results 1.4% by averaging biases at the eight stations, thus confirming that the model is adequate. Effects of reservoirs were analysed by modelling erosion and sediment yield passing from natural to impounded conditions and resulted in a suspended sediment load reduction of about 95% and 75% downstream, respectively, the Thac Ba reservoir in the Chay river and the Tuyen Quang reservoir in the Gam river . Land use change scenarios, parameterized on the basis of observed land use changes in the impounded basin and assuming that 20% of forest area is converted into rice and agricultural crops and 15% into bushes, shrubs and meadows, are expected to induce a 28% increase of suspended sediment load which can compensate, at least in part, sedimentation in reservoirs. Also agricultural and hillslope maintenance practices can modify sediment erosion in the basin.

Late Holocene environmental history on Tristan da Cunha, South Atlantic, based on diatom floristic changes and geochemistry in sediments of a volcanic crater lake

A late Holocene diatom stratigraphy of Bottom Pond (37°05′S, 12°17′W) was studied and interpreted to infer paleolimnological and climate changes on Tristan da Cunha, South Atlantic. The diatom flora of Bottom Pond is dominated by meroplanktonic Aulacoseira alpigena and A. distans and a benthic/epiphytic flora including Achnanthes spp., Naviculadicta spp., Eunotia taxa and Frustulia rhomboides. The flora also includes an important terrestrial and aerophytic component, consisting of several Diadesmis spp., Navicula lapidosa, Nitzschia terrestris and some Pinnularia spp., at times dominating the flora. Peaks of high terrestrial diatom abundances and low abundances and concentrations of Aulacoseira spp., correspond to periods of increased magnetic susceptibility and are interpreted to be the result of increased catchment erosion and/or precipitation leading to enhanced in-wash of species living in the soils around the lake. The diatom record of Bottom Pond most likely registers both local responses to increased erosion in the catchment as well as climatic change of a more regional character. Comparisons with the geochemical record in 2nd Pond on Nightingale Island show a correspondence between the two data sets at 2,000–1,750 cal yrs BP, most likely evidence of increased precipitation in the Tristan da Cunha region. The Tristan da Cunha archipelago is situated at the northern limit of the Southern hemisphere west wind belt and stronger and/or a northward shift of the westerlies, are probably the main causes of the precipitation changes.

SOIL EROSION RATES IN SOUTH AFRICA COMPARED WITH COSMOGENIC 3HE-BASED RATES OF SOIL PRODUCTION

Soil erosion has been considered a major problem in South Africa since the early 20th Century, yet the degree to which rates of soil erosion may exceed rates of soil production has not been well constrained by previous studies. Here we present 22 cosmogenic 3He-based maximum denudation rates of Karoo dolerite bedrock surfaces, and interpret these values as local rates of soil production. These generally low soil production rates (<4 m/Myr measured over a 105 yr timescale) are in all instances lower than various literature estimates for the corresponding rates of soil erosion in the same catchments, by up to two orders of magnitude. This significant contrast between long term rates of soil production and short term rates of soil erosion suggests that current agricultural practices are unsustainable under prevailing geological conditions.

Sediment source tracing in a lowland agricultural catchment in southern England using a modified procedure combining statistical analysis and numerical modelling

Catchment erosion, soil losses and resulting sediment pressures continue to represent cause for concern with respect to the ecological vitality and amenity value of riverine systems, including those in the agricultural catchments of southern England. Given that the sources of fine-grained sediment are typically diffuse in nature, it is essential to adopt a catchment-wide perspective to corresponding management strategies and sediment source tracing procedures have proved useful in assisting such planning. There remains, however, scope for further refining sediment sourcing procedures and on that basis, a recent study in the upper River Kennet (~214km2) catchment in southern England, provided an opportunity for designing and testing a refined statistical procedure for sediment source discrimination with composite fingerprints using Genetic Algorithm (GA)-driven Discriminant Function Analysis, the Kruskal–Wallis H-test and Principal Components Analysis. The revised statistical verification of composite signatures was combined with numerical mass balance modelling using recent refinements including a range of tracer weightings and both local and GA optimisation. Comparison of the local and global optimisation increased confidence in the outputs of local optimisation and the goodness-of-fit for the predicted source contributions using the optimum composite signatures selected from the revised statistical testing ranged from 0.914 to 0.965. Overall relative frequency-weighted average median source type contributions were estimated to be 4% (agricultural topsoils; predicted deviate median inputs 1–19%), 55% (unmetalled farm track surfaces; predicted deviate median inputs 9–91%), 6% (damaged road verges; predicted deviate median inputs 4–42%), 31% (channel banks/subsurface sources; predicted deviate median inputs 5–41%) and 4% (urban street dust; predicted deviate median inputs 0–20%). The study provides further evidence of the importance of eroding farm tacks as a catchment scale sediment source and confirms the utility of tracing for assembling information on sediment inputs from both the agricultural and urban sectors.

Siltation of river-influenced coastal environments: Respective impact of late Holocene land use and high-frequency climate changes

The aim of this study is to unravel the respective influence of land use and high-frequency climate changes on the siltation of a river-influenced coastal environment. An 8.4 m long sediment core was recovered in the Pertuis Charentais (western France). An accurate 14C Bayesian age model was developed to perform a depth to time conversion of high-resolution sedimentological data obtained on the core. Forest loss and precipitation changes that occurred on the related catchments were reconstructed from data gathered in the literature. A sharp increase in winter rainfall (1700–1750 AD) intensified erosion of catchments previously sensitised by increased forest loss (1640–1710 AD), which resulted in a massive supply of silt to the coast from ca. 1775 AD onwards. A review of articles reporting similar mud layers is also proposed. Depending on their age, some major phases of mankind migration history could be traced back, which confirms the predominant influence of human activities on the siltation of river-influenced coastal environments. We therefore propose to group these mud layers into the “Anthropogenic System Tracts”, in reference to widely used sequence stratigraphy nomenclature, and we suggest that it might help to identify a Holocene to Anthropocene stratigraphic boundary in coastal areas.

Effect of recent climate change on Arctic Pb pollution: A comparative study of historical records in lake and peat sediments

Historical changes of anthropogenic Pb pollution were reconstructed based on Pb concentrations and isotope ratios in lake and peat sediment profiles from Ny-Ålesund of Arctic. The calculated excess Pb isotope ratios showed that Pb pollution largely came from west Europe and Russia. The peat profile clearly reflected the historical changes of atmospheric deposition of anthropogenic Pb into Ny-Ålesund, and the result showed that anthropogenic Pb peaked at 1960s–1970s, and thereafter a significant recovery was observed by a rapid increase of 206Pb/ 207Pb ratios and a remarkable decrease in anthropogenic Pb contents. In contrast to the peat record, the longer lake record showed relatively high anthropogenic Pb contents and a persistent decrease of 206Pb/ 207Pb ratios within the uppermost samples, suggesting that climate-sensitive processes such as catchment erosion and meltwater runoff might have influenced the recent change of Pb pollution record in the High Arctic lake sediments.

Reconstruction of metal pollution and recent sedimentation processes in Havana Bay (Cuba): A tool for coastal ecosystem management

Since 1998 the highly polluted Havana Bay ecosystem has been the subject of a mitigation program. In order to determine whether pollution-reduction strategies were effective, we have evaluated the historical trends of pollution recorded in sediments of the Bay. A sediment core was dated radiometrically using natural and artificial fallout radionuclides. An irregularity in the 210Pb record was caused by an episode of accelerated sedimentation. This episode was dated to occur in 1982, a year coincident with the heaviest rains reported in Havana over the XX century. Peaks of mass accumulation rates (MAR) were associated with hurricanes and intensive rains. In the past 60 years, these maxima are related to strong El Niño periods, which are known to increase rainfall in the north Caribbean region. We observed a steady increase of pollution (mainly Pb, Zn, Sn, and Hg) since the beginning of the century to the mid 90s, with enrichment factors as high as 6. MAR and pollution decreased rapidly after the mid 90s, although some trace metal levels remain high. This reduction was due to the integrated coastal zone management program introduced in the late 90s, which dismissed catchment erosion and pollution.

Control of geomorphic processes on 10Be concentrations in individual clasts: Complexity of the exposure history in Gobi-Altay range (Mongolia)

The dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre-deposition inheritance from the post-deposition history of the clasts in the studied marker. Moreover, estimating catchment-scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local/regional relationships between rock exhumation and transport through space and time. This is still poorly known for timescales of tens of thousand years. In order to document the evolution of clast exhumation and transport rates through time, we analyze in situ 10Be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in Gobi-Altay, Mongolia, strongly affected by global climatic changes during the Pleistocene–Holocene period. Samples were collected on bedrock, abandoned alluvial deposits, active colluvia and alluvia. Our results show a large 10Be scattering in the active river bed, consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision. On the contrary, pre-exposure signal within abandoned terraces is much more homogeneous, consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport. These results show that exhumation/transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations. The occurrence of abrupt climatic changes during short periods of time recorded by 10Be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers. On the other hand, strong and short erosion events limit and homogenize the pre-exposure 10Be signal in associated deposits like debris-flows, making them particularly suitable markers for dating in active tectonic and paleoclimatic studies.

Post-Messinian drainage changes triggered by tectonic and climatic events (eastern Southern Alps, Italy)

The Messinian–Quaternary history of tectonic and climatic control on sedimentation in the eastern Southern Alps, northern Italy, was reconstructed using an integrated petrographic and sedimentological analysis of five sedimentary successions. These units mainly consist of fluvial conglomerates of the Tagliamento sequence, deposited within the eastern Southern Alps since the Upper Miocene (“Messinian Salinity Crisis”). At that time, the closure of marine gateways between the Atlantic Ocean and the Mediterranean Sea caused a drop in sea level, causing exchanged fluvial erosion and widening of the Alpine catchments. Sediment composition in the Upper Miocene to Lower Pliocene units shows an abrupt change in the source areas: from sediments characterized by carbonate rock fragments to detritus rich in low-grade metamorphic grains. In spite of tectonic activity within the eastern Southern Alps, no major modifications in sediment supply took place during the Pliocene–Early Pleistocene time span. In the Middle Pleistocene the first major expansion of the Alpine glaciers triggered a change in drainage patterns and a marked increase in erosion rates. Predominantly climatic control on sedimentation in the Tagliamento basin and the erosion of the Carnic Alps produced sediments rich in quartz, siltstone and metamorphic rock fragments, deposited in the Upper Pleistocene unit and in modern river sediments.

Land use and ostracod community structure

Ostracods are important members of the benthos and littoral communities of lake ecosystems. Ostracods respond to hydrochemistry (water chemistry) which is influenced by climatic factors such as water balance, temperature, and chemicals in rainfall runoff from the land. Thus, at local scales, environmental preferences of ostracods and characteristics of lakes are used to infer changes in climate, hydrology, and erosion of lake catchments. This study addresses potential drivers of ostracod community structure and biodiversity at multiple spatial scales using NMS, CART®, and multiple regression models. We identified 23 ostracod species from 12 lake sites. Lake area, maximum depth, spring conductivity, chlorophyll a, pH, dissolved oxygen, sedimentary carbonate, and organic matter all influence ostracod community structure based on our NMS. Based on regression analysis, lake depth, chlorophyll a, and total dissolved solids best explained ostracod richness and abundance. Land uses are also important community structuring elements that varied with scale; locally and regionally agriculture, wetlands, and grasslands were important. Nationally, using regression tree analysis of lakes sites in the North American Non-marine ostracod database (NANODe), row-crop agriculture was the most important predictor of biodiversity. Low agriculture corresponded to low species richness but greater landscape heterogeneity produced sites of high ostracod richness.