Tracking the sources and fate of nitrate pollution by combining hydrochemical and isotopic data with a statistical approach

This study contributes to identifying and spatializing the different types of nitrate sources by combining hydrogeochemical and isotopic data with principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE) multicriteria statistical methods. The methodology is applied to the strategic Mons Basin chalk aquifer (Belgium). The results are based on a whole dataset containing 72 water samples with analyses of the hydrogeochemical parameters (temperature, pH, electrical conductivity (EC), redox potential, dissolved O₂), alkalinity, total organic carbon (TOC), silica (SiO₂), major and minor ions (NO₃^–, NH⁴⁺, Ca²⁺, dissolved Fe and Mn, K⁺, Mg²⁺, Na⁺, Sr²⁺, Cl^–, F^–, SO₄^–_, B) and multiple stable isotope ratios (δ¹¹B, δ¹⁵N–NO₃^–, δ¹⁸O–NO₃^–). Compared to classical PCA, the recently developed t-SNE method, which considers nonlinear relationships between variables and preserves local-scale similarities in a low-dimensional space, showed much better performance in discriminating different groups of samples and related zones in the aquifer. t-SNE results combined with isotope ratios highlighted four zones in the aquifer (grouped as A–D) and the presence of denitrification fronts. Group A presents a manure signature (δ¹⁵N–NO₃^– – mean (μ) +12.78‰, standard deviation (σ) 6.48‰; δ¹¹B – μ 29.96‰, σ 6.91‰). Group B exhibits both manure and inorganic fertilizer signatures (δ¹⁵N–NO₃^– – μ 6.27‰, σ 2.55‰; δ¹¹B – μ 15.86‰, σ 9.69‰). Group C shows a contamination by sewage (δ¹⁵N–NO₃^– – μ 12.67‰, σ 5.60‰; δ¹¹B – μ 9.97‰, σ 7.08‰). Group D presents a mixed signature (δ¹⁵N–NO₃^– – μ 9.25‰, σ 2.94‰; δ¹¹B – μ 20.00‰, σ 6.70‰).

     

Orbit of an Astrometric Binary System

We present a new method to solve the problem of initial orbit determination of any binary system. This method is mainly based on the material available for an observer, for example relative positions at a given time of the couple in the “plane of sky”, namely the tangent plane to the celestial sphere at the position of the primary component. The problem of orbit determination is solved by splitting in successive stages in order to decorrelate the parameters of each other as much as possible. On one hand, the geometric problem is solved using the first Kepler’s law from a single observing run and, on the other hand, dynamical parameters are then inferred from the fit of the Kepler’s equation. At last, the final stage consists in determining the main physical parameters involved in the secular evolution of the system, that is the spin axis and the J₂ parameter of the primary if we assume that it is a quasi-spherical body. As a matter of fact there is no need to make too restrictive initial assumptions (such as circular orbit or zero eccentricity) and initial guesses of parameters required by a non-linear least-squares Levenberg–Marquardt algorithm are finally obtained after each stage. Such a protocol is very useful to study systems like binary asteroids for which all of the parameters should be considered a priori as unknowns. As an example of application, we used our method to estimate the set of the Pluto–Charon system parameters from observations collected in the literature since 1980.     

黑龙江嘉荫晚白垩世一鸭嘴龙亚科恐龙齿骨化石

鸭嘴龙科(Hadrosauridae)化石根据头骨特征等被划分为鸭嘴龙亚科(Hadrosaurinae,无头冠)和赖氏龙亚科(Lambeosaurinae,有头冠)。黑龙江嘉荫龙骨山晚白垩世渔亮子组保存了丰富的鸭嘴龙化石,其中黑龙江满洲龙Mandschurosaurus amurensis(Riabinin,1925)是最早在中国发现的恐龙,属鸭嘴龙亚科;嘉荫卡龙Charonosaurus jiayinensis(Godefroit et al,2000)也是在这里发现的,属赖氏龙亚科。本文描述了采自嘉荫龙骨山的部分左齿骨化石和一些牙齿化石,新的化石明显属于鸭嘴龙亚科,主要特征为:齿骨每个牙列有5个以上的牙齿,牙冠边缘小锯齿由乳头状小瘤构成。新发现的牙齿牙冠上发育有明显的第二、三副脊,这在鸭嘴龙中是罕见的。新发现的化石明显不同于产于同一地点的嘉荫卡龙,但由于黑龙江满洲龙模式标本没有保存牙齿,因此暂不能与之充分对比。