Land use and its effects on water quality using the BASINS model

Differences in land use have been shown to affect water quality. This is important because water is used for human consumption. High levels of nitrate, phosphate and sediments can have a negative impact on a person’s health. The objective of this research is to determine if best management practices (BMPs) would affect the water quality and lower the associated agrochemicals that come with an agriculturally predominant watershed. Best management practices would decrease nutrient and sediment loads when compared to a watershed’s baseline status. Filter stripping was implemented and nitrate, phosphate and sediment were modeled using the Environmental Protection Agency modeling tool, Better Assessment Science Integrating point and Non-point Source pollution, to determine if BMPs were efficient in reducing current total maximum daily loads (TMDL) below Sassafras River Association TMDLs. The BMP that was most efficient at removing nitrate, phosphate and sediment was compared to a baseline run and compared between drought, average and wettest year conditions to determine if rainfall was driving the nutrient and sediment concentration. It was concluded that the BMP implementation decreased the amount of nutrients and sediments transported throughout the watershed’s waterways.     

Silica Mass-Balance and Retention in the Riverine and Estuarine Scheldt Tidal System (Belgium/The Netherlands)

An annual budget for dissolved silica (DSi) and biogenic silica (BSi) was constructed for the Scheldt estuary and for the entire riverine and estuarine Scheldt tidal system (Belgium/The Netherlands) using previously published silica concentrations and fluxes for the period 2003–2005. The annual estuarine DSi mass-balance was established, based on seasonal fluxes estimated using measured DSi concentrations and (fully transient) model simulations of conservative transport. The annual BSi mass-balance was deduced from measured BSi contents in the suspended particulate matter and annual mud fluxes taken from the literature. The Scheldt estuary acted as a net sink not only for the BSi carried by the tidal river as well as that produced by diatoms in the estuary, but also for large amounts of BSi imported from the coastal zone. This results in the retention of dissolved and biogenic silica higher than that of DSi alone, which is in contrast with the classical consideration that rivers act as a source of BSi for the coastal zone. DSi and silica (DSi + BSi) retentions amounted to, respectively, 28 and 64 % in the estuary, and 33 and 66 % in the entire tidal system. This study highlights thus the predominant role of the estuary in the entire Scheldt tidal system when dealing with silica dynamics, as well as the importance of including BSi when investigating estuarine silica retention.     

Sulfide petrology of four nakhlites: Northwest Africa 817, Northwest Africa 998, Nakhla,and Governador Valadares

Abstract– The nakhlites contain small proportions of Cu‐Fe‐Ni sulfide minerals; we have studied these sulfides in Northwest Africa (NWA) 998, Nakhla, Governador Valadares, and NWA 817 with optical microscopy, scanning electron microscope, and electron microprobe. Modal abundances of magmatic sulfides, as estimated by image analysis on thin section, are uniformly low (0.02 to 0.05 ± 0.03 vol%), i.e., a factor 5 lower than in shergottites. Sulfides occur within the glassy mesostasis, as composite two‐phase Fe‐Ti oxide‐sulfide grains, intimately associated with interstitial grains or locally enclosed in postcumulus melt inclusions (e.g., Governador Valadares) in olivine. They exhibit a uniform low‐Ni monoclinic pyrrhotite composition ± chalcopyrite. There is a gradation of sulfide grain sizes and textures across the nakhlites flow(s): droplets in NWA 817; resorbed blebs in Governador Valadares; more massive, true intercumulus blebs in Nakhla and NWA 998. These nakhlites also show evidence for sulfide weathering. Hot desert finds (e.g., NWA 998 and NWA 817) show a few percent fracture‐filling iron (oxy) hydroxides of likely terrestrial origin. Original sulfides are 50% altered in our NWA 998 section, with iron (oxy) hydroxides at grain boundaries and as complete pseudomorphs. The compositions of unaltered pyrrhotites are homogeneous, close to that of the monoclinic endmember Fe₇S₈, and are too sulfur‐rich to have been in chemical equilibrium with the late magmatic redox state fixed by the fayalite‐magnetite‐quartz buffer. Therefore, the compositions of the pyrrhotites must have been altered during the later stages of magmatic crystallization, by assimilation of S‐rich regolith and hydrothermal circulation.     

Mapping saltcedar (Tamarix ramosissima) and other riparian and agricultural vegetation in the Lower Colorado River region using multi-spectral Landsat TM imagery

Saltcedar (Tamarix ramosissima), an invasive shrub species, has successfully invaded large extents of several riparian zones in the western United States and northern Mexico. Mapping the distribution and abundance of saltcedar over these large areas through a multi-seasonal, cost-effective monitoring approach using satellite remote sensing is very essential. Ground truth surveys were conducted at 79 locations where the spectral reflectance measurements of vegetation, type of plant species, plant heights, soil samples and GPS co-ordinates were recorded. All the sampling was designed to coincide with the satellite overpass period. The Landsat TM colour-composite spectral ratio image (normalized difference vegetative index (NDVI), R _1,5 and R _1,7 as green, blue and red) can clearly identify and map the areas infested with saltcedar. The Landsat image analysis shows that these spectral ratios can be applied to multiple satellite overpasses for monitoring the seasonal progression of the saltcedar growth over time.     

On the dynamics of 3-D single thermal plumes at various Prandtl numbers and Rayleigh numbers

Three-dimensional (3-D) numerical simulations of single turbulent thermal plumes in the Boussinesq approximation are used to understand more deeply the interaction of a plume with itself and its environment. In order to do so, we varied the Rayleigh and Prandtl numbers from Ra?～?10⁵ to Ra?～?10⁸ and from Pr?～?0.025 to Pr?～?70. We found that thermal dissipation takes place mostly on the border of the plume. Moreover, the rate of energy dissipation per unit mass ε _T has a critical point around Pr?～?0.7. The reason is that at Pr greater than ～0.7, buoyancy dominates inertia and thermal advection dominates wave formation whereas this trend is reversed at Pr less than ～0.7. We also found that for large enough Prandtl number (Pr?～?70), the velocity field is mostly poloidal although this result was known for Rayleigh–Bénard convection (see Schmalzl et al. [On the validity of two-dimensional numerical approaches to time-dependent thermal convection. Europhys. Lett. 2004, 67, 390--396]). On the other hand, at small Prandtl numbers, the plume has a large helicity at large scale and a non-negligible toroidal part. Finally, as observed recently in details in weakly compressible turbulent thermal plume at Pr?=?0.7 (see Plourde et al. [Direct numerical simulations of a rapidly expanding thermal plume: structure and entrainment interaction. J. Fluid Mech. 2008, 604, 99--123]), we also noticed a two-time cycle in which there is entrainment of some of the external fluid to the plume, this process being most pronounced at the base of the plume. We explain this as a consequence of calculated Richardson number being unity at Pr?=?0.7 when buoyancy balance inertia.     

Evaluating DEM source and resolution uncertainties in the Soil and Water Assessment Tool

DEMs as important input parameters of environmental risk assessment models are notable sources of uncertainties. To illustrate the effect of DEM grid size and source on model outputs, a widely used watershed management model, the Soil and Water Assessment Tool (SWAT), was applied with two newly available DEMs as inputs (i.e. ASTER GDEM Version 1, and SRTM Version 4.1). A DEM derived from 1:10,000 high resolution digital line graph (DLG) was used as a baseline for comparisons. Eleven resample resolutions, from 5 to 140?m, were considered to evaluate the impact of DEM resolution on SWAT outputs. Results from a case study in South-eastern China indicate that the SWAT predictions of total phosphorus and total nitrogen decreased substantially with coarser resample resolution. A slightly decreasing trend was found in the SWAT predicted sediment when DEMs were resampled to coarser resolutions. The SWAT predicted runoff was not sensitive to resample resolution. For different data sources, ASTER GDEM did not perform better than SRTM in SWAT simulations even it was provided with a smaller grid size and higher vertical accuracy. The predicted outputs based on ASTER GDEM and SRTM were similar, and much lower than the ones based on DLG. This study presents potential uncertainties introduced by DEM resolutions and data sources, and recommends strategies choosing DEMs based on research objects and maximum acceptable errors.     

Natural and artificial recharge investigation in the Zéroud Basin,Central Tunisia: impact of Sidi Saad Dam storage

Hydrochemical and isotopic data of waters from the Zéroud aquifer have been used to potentially provide a means for locating occurrences and to trace movements of a variety of natural and anthropogenic recharge waters in the Zéroud Basin, Central Tunisia. Geochemical data have been measured during the dam water release, from May to September 2005, with a sampling time step of 15 days. An implication of dam water has been demonstrated that is noticeable up along the main flow path to a distance of 10 km far from the injection site. Environmental isotopes ²H, ¹⁸O and ³H of water molecule were studied to investigate the effect of dam water on the hydrological system, and an isotope balance was established to compute the contribution of water storage component in groundwater. Based on isotopic mass balance, we assess that an average of 13% of total groundwater in the upper aquifer came from dam water storage. Three distinctive recharge waters in the aquifer can be determined. Water from local rainfall (pre-dam Zéroud River) that infiltrated into the boundaries of the Draa Affane Mountain was easily distinguished from the water influenced by anthropogenic recharge located in the Zéroud right rivulet. Distinguishable isotopic signatures of native wadi Zéroud recharge due to “recent lineal recharge” through the riverbed were also identified.     

Longitudinal and temporal thermal patterns of the French Rh?ne River using Landsat ETM+ thermal infrared images

Understanding the thermal regime of rivers is a key issue for predicting ecosystem change in the context of global warming. However, water temperature is not only influenced by air temperature. To better highlight relative contribution of factors controlling water temperature, we used satellite thermal infrared (TIR) images from Landsat ETM+ to investigate longitudinal and temporal variations in thermal patterns of the French Rh?ne River. Because satellite TIR remote sensing is limited to large rivers, we used an automated water extraction technique to remove pixels contaminated by terrestrial surfaces. We calculated water surface temperatures of the 500?km long reach for 83 dates between 1999 and 2009. The average accuracy and uncertainty of our data, ±1.1 and ±0.4°C for reaches with more than 3?pixels across and ±1.4 and ±0.5°C for reaches with one to 3?pixels across, are comparable to other satellite TIR studies of rivers. Our results confirmed previous studies on the thermal impacts of tributaries and nuclear power plants on the Rh?ne, providing an understanding of their seasonal pattern and their longitudinal impact. We showed temperature differences of 0?C2°C within the largest hydroelectric bypass facilities between the bypass section and the canal, with Montélimar and Caderousse showing the most pronounced differences. Discussion points concern the potential impacts of tributaries and nuclear power plants on the spatio-temporal thermal patterns, as well as the factors responsible for thermal differences in the bypass facilities: length and minimum flow of the bypass section, and tributaries coming into this reach.