Hydrodynamic modelling and characterisation of a shallow fluvial lake: a study on the Superior Lake of Mantua

This paper presents a numerical modelling framework developed to simulate circulations and to generally characterise the hydrodynamics of the Superior Lake of Mantua, a shallow fluvial lake in Northern Italy. Such eutrophied basin is characterised by low winds, reduced discharges during the summer and by the presence of large lotus flower (Nelumbo nucifera) meadows, all contributing to water stagnation. A hydrodynamic numerical model was built to understand how physical drivers shape basic circulation dynamics, selecting appropriate methodologies for the lake. These include a 3D code to reproduce the interaction between wind and through-flowing current, a fetch-dependent wind stress model, a porous media approach for canopy flow resistance and the consideration of wave-current interaction. The model allowed to estimate the circulation modes and water residence time distributions under identified typical ordinary, storm and drought conditions, the hydrodynamic influence of the newly-opened secondary outlet of the lake, the surface wave parameters, their influence on circulations and the bottom stress they originate, and the adaptation time scales of circulations to storm events. Some probable effects of the obtained hydrodynamic characteristics of the Superior Lake of Mantua on its biochemical processes are also introduced

Model simulations of the ecological dynamics induced by climate and nutrient load changes for deep subalpine Lake Maggiore (Italy/Switzerland)

Climate warming affects lake ecosystems both through its direct effect on the phenology of species and through the alteration of the physical and chemical environments, which in turn affect community composition. In deep lakes, stratification enhancement and mixing reduction have already been observed, leading to hypolimnetic anoxia and to the rise of cyanophytes. The increase in stability depends on the rise of air temperature due to global emissions of greenhouse gases (GHG). Primary production could then either increase with rising epilimnetic temperature and buoyancy or decrease as fewer nutrients are upwelled from deep layers. The prevailing outcome, as well as the quantitative and temporal dynamics of all climate-induced modifications, depend on the specific lake characteristics. Individual analyses are then needed, one-dimensional coupled hydrodynamic-ecological numerical models being suitable tools for such predictions. Here, we simulated with GLM-AED2 (General Lake Model – Aquatic EcoDynamics) the 2020-2085 dynamics of the oligomictic and oligotrophic deep subalpine Lake Maggiore (Italy/Switzerland), according to the Swiss Climate Change Scenarios CH2011. Multiple realisations were performed for each scenario with random meteorological series obtained from the Vector-Autoregressive Weather Generator (VG), highlighting the uncertainties related to meteorology. Increase and decrease of nutrient loads were also tested. Results show that anoxia would occur in the hypolimnion regardless of nutrient input reduction, unless global GHG emissions were immediately reduced. Total phytoplankton biomass would be weakly affected by climate change, strongly depending on nutrient input, yet water warming would cause cyanophytes to compete with diatoms. Therefore, the fate of Lake Maggiore would be tied to both global and local environmental policies

Development and Multicenter Validation of a Novel Immune-Inflammation-Based Nomogram to Predict Survival in Western Resectable Gastric and Gastroesophageal Junction Adenocarcinoma (GEA): The NOMOGAST

Background. More than 50% of operable GEA relapse after curative-intent resection. We aimed at externally validating a nomogram to enable a more accurate estimate of individualized risk in resected GEA. Methods. Medical records of a training cohort (TC) and a validation cohort (VC) of patients undergoing radical surgery for c/uT2-T4 and/or node-positive GEA were retrieved, and potentially interesting variables were collected. Cox proportional hazards in univariate and multivariate regressions were used to assess the effects of the prognostic factors on OS. A graphical nomogram was constructed using R software’s package Regression Modeling Strategies (ver. 5.0-1). The performance of the prognostic model was evaluated and validated. Results. The TC and VC consisted of 185 and 151 patients. ECOG:PS > 0 (p < 0.001), angioinvasion (p < 0.001), log (Neutrophil/Lymphocyte ratio) (p < 0.001), and nodal status (p = 0.016) were independent prognostic values in the TC. They were used for the construction of a nomogram estimating 3- and 5-year OS. The discriminatory ability of the model was evaluated with the c-Harrell index. A 3-tier scoring system was developed through a linear predictor grouped by 25 and 75 percentiles, strengthening the model’s good discrimination (p < 0.001). A calibration plot demonstrated a concordance between the predicted and actual survival in the TC and VC. A decision curve analysis was plotted that depicted the nomogram’s clinical utility. Conclusions. We externally validated a prognostic nomogram to predict OS in a joint independent cohort of resectable GEA; the NOMOGAST could represent a valuable tool in assisting decision-making. This tool incorporates readily available and inexpensive patient and disease characteristics as well as immune-inflammatory determinants. It is accurate, generalizable, and clinically effectivex

Lake Maggiore bathymetry

The file contains Lake Maggiore bathymetry, with 1 m resolution

1D thermodynamic modelling of Lake Maggiore for thermal structure evolution predictions under climate change

The deep subalpine lakes have been characterised during the last decades by an oligomictic behaviour, full overturns being achieved only at the end of cold and windy winters. Since vertical mixing is essential for the chemical and biological dynamics, the study of how such behaviour will evolve with future climate change is strongly relevant. In order to investigate that on Lake Maggiore, we built a 1D thermodynamic model of the basin using the General Lake Model (GLM) (Hipsey et al., 2014). Calibration was performed reproducing the thermal evolution in the period 1998-2014, feeding the model with meteorological data measured at the Pallanza and Locarno-Monti weather stations and comparing the results against monthly temperature observations along the deepest water column at the Ghiffa limnological site. The availability of extended data series, spanning years with very different meteorological and hydrological features, allowed to obtain calibration coefficients that are less specific and suitable for predictions. Two versions of the model were initially developed, one with a closed and fixed-level lake approximation and another reproducing the complete hydrological and thermal balances, including inflows, outflow, and direct rainfall contributions. Daily discharges for the major tributaries and the emissary in the calibration period were available, while the daily temperatures of the inflows were computed from daily air temperatures using the air2stream model (Toffolon & Piccolroaz, 2015), calibrated using monthly available observations. We studied the effects of an evolving climate scenario, with a linear increase of air temperature of 4?C from 2014 to 2081, as predicted by the International Panel for Climate Change (IPCC). A weather generator was used to estimate the corresponding variations of the other meteorological and hydrological parameters in response to the temperature rise, producing multiple series of input data for the thermodynamic simulations, whose results were statistically analysed. This allowed to evaluate the possible evolution of the thermal structure of the lake, especially considering the hypolimnion heating, the trend in the vertical mixing frequency and the influence of the "climatic memory" of the present state over future conditions

Hydrodynamics of a Bordered Collar as a Countermeasure against Pier Scouring

Countermeasures against local scour at bridge piers and abutments can be grouped into two categories: (1) flow-altering and (2) bed-armouring countermeasures. In this work, long-term laboratory-scale experiments of clear-water scour at bridge piers with different configurations were performed in order to investigate the effects of an unprotected cylindrical pier, of a cylindrical pier with a classic collar countermeasure and of a cylindrical pier with a modified collar countermeasure. Tests were performed in a flume with movable sediment bed, and the scoured bathymetries at the equilibrium stage were acquired and used in numerical simulations of small-scale hydrodynamics at the piers. The modified collar countermeasure resulted in a significant reduction of the scour hole dimensions

Modelling flows in shallow (fluvial) lakes with prevailing circulations in the horizontal plane: limits of 2D compared to 3D models

The numerical modelling of circulations in shallow lakes is a relevant tool for all environmental applications in which flow advection processes are of interest, e.g. for studies on nutrients, microorganisms, pollutants and sediment dynamics. While three-dimensional (3D) models are needed to properly describe the flow fields of basins with the main circulations in the vertical plane, two-dimensional (2D) models are commonly deemed to yield adequate results for lakes with prevailing horizontal circulations. However, the depth-averaged approximation is more limiting for wind-driven flows than for gravity-driven ones, such as rivers, as the driving force is a surface rather than a volume one, distributed along the depth through turbulence. In this work, the effects of such inaccuracy on the reproduction of circulation layouts are evaluated through compared simulations between a 2D Shallow Water solver and a 3D Reynolds-Averaged Navier-Stokes one. The models are first applied to a simple enclosed elliptical test basin and then to the real case of the Superior Lake of Mantua, a shallow fluvial lake in Northern Italy, thereby also investigating the influences of the interaction of wind with a riverine current and of a complex bathymetry on the compared results

Estimation of long-term series of total nutrient loads flowing into a large perialpine lake (Lake Como, Northern Italy) from incomplete discrete data by governmental monitoring

Continuous series of nutrient loads released into a water body are essential for nutrient budgeting, water quality modelling and watershed management activities. A quintessential example of pursued data are the series of total nutrient loads flowing from multiple tributaries into a lake. However, except for extraordinary cases in which high-frequency monitoring (HFM) stations are installed for both discharge and concentrations, measured nutrient loads are available on a discrete basis. Such observations are typically obtained by governmental agencies for environmental monitoring purposes, with an at best monthly resolution, yet commonly with gaps spanning years. Usually, monitoring activities are limited to major inflows, neglecting minor ones. However, the latters can play a more relevant role in nutrient load budgets than in hydrological ones, in response to different natural features and pollution among tributary watersheds. In this work, we present a methodology we developed to estimate long-term series of total nutrient loads flowing into a water body, employing as case study Lake Como, a large deep lake in the Italian Alps with manifold monitored and unmonitored tributary watersheds. The method uses observed long-term relationships between discharges and concentrations (Q – C) and available discharge measurements and hydrological estimations to estimate continuous load series for the monitored basins. For the unmonitored watersheds, Q – C relationships are estimated from those of the monitored basins, given the observed dependence of the power-law coefficients on basin hydromorphological parameters. This equals to extending the regionalisation approach applied in hydrology for rainfall and discharges to the ecohydrological field for nutrient load estimation. The application of the method to the case study led to overall annual load estimations congruent to traditional techniques and revealed interesting Q – C watershed dynamics at interannual time scales which could not be disclosed through previous approaches. This work represents an exploratory development and application of ecohydrological regionalisation techniques, whose future development is fostered

Relevance of inflows on the thermodynamic structure and on themodeling of a deep subalpine lake (Lake Maggiore, NorthernItaly/Southern Switzerland)

tAtmospheric exchanges largely dominate the heat budget of deep lakes in temperate regions. Heat importand export by through-flows is of much lower entity and has been neglected or simplified in many numer-ical thermodynamic models of lakes. This is often due either to the unavailability of data for inflows andoutflows, or to the difficulties in forecasting the evolution of their discharge and temperature in cli-mate change studies. While disregarding through-flows may seem correct, riverine intrusions can bringwarmer water than the deep hypolimnetic one to the lower metalimnion and upper hypolimnion, wheresunlight does not penetrate and mixing is poor. For holomictic lakes with significant inflow contribu-tions, this can affect the thermal structure at intermediate depths, hampering any numerical modelwhich neglects through-flows. This study focuses on a relevant basin under such aspect, Lake Maggiore(Northern Italy/Southern Switzerland), which drains the rainiest watershed of the Southern Alps. First, wequantify to what extent a one-dimensional fixed-level model ignoring through-flows is able to predict theobserved evolution of the thermal structure of the lake and the improvements resulting from reproducingthe main inflows and outflows. Then, we directly discuss the influence of through-flows on the thermo-dynamic structure of Lake Maggiore. The General Lake Model (GLM) was here adopted, reproducing the1998–2014 period, spanning years with different meteorological and hydrological features. Results showthat a calibrated enclosed-lake model can give satisfactory results only if it employs an unrealisticallylow light extinction coefficient to allow heating of the deep metalimnion and hypolimnion, whose realwarming strongly depends on interflows