Coastal groundwater discharge – an additional source of phosphorus for the oligotrophic wetlands of the Everglades

In this manuscript we define a new term we call coastal groundwater discharge (CGD), which is related to submarine groundwater discharge (SGD), but occurs when seawater intrudes inland to force brackish groundwater to discharge to the coastal wetlands. A hydrologic and geochemical investigation of both the groundwater and surface water in the southern Everglades was conducted to investigate the occurrence of CGD associated with seawater intrusion. During the wet season, the surface water chemistry remained fresh. Enhanced chloride, sodium, and calcium concentrations, indicative of brackish groundwater discharge, were observed in the surface water during the dry season. Brackish groundwaters of the southern Everglades contain 1–2.3μM concentrations of total phosphorus (TP). These concentrations exceed the expected values predicted by conservative mixing of local fresh groundwater and intruding seawater, which both have TPμM. The additional source of TP may be from seawater sediments or from the aquifer matrix as a result of water–rock interactions (such as carbonate mineral dissolution and ion exchange reactions) induced by mixing fresh groundwater with intruding seawater. We hypothesize that CGD maybe an additional source of phosphorus (a limiting nutrient) to the coastal wetlands of the southern Everglades

L'atelier du CCETT. Bilan et perspectives d'avenir

SIGLECNRS RP 254 (5) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Impact de l'outil videographique sur la motivation des graphistes et la conception de produits (etude menee aupres de graphistes et analyse de cas)

SIGLECNRS RP 254 (6) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

International Journal Of Communication Systems

This paper develops a new modelling approach to evaluate saturation performance of the AIr protocol based on conditional probability arguments rather than bi-dimensional Markov chains. Moreover, we extend performance studies in former literature papers by providing an intuitive AIr packet delay analysis assuming error-free transmissions and a fixed number of stations. Using OPNET simulation results, we validate our mathematical analysis and we show that the proposed model predicts AIr packet delay performance very accurately. Utilizing the derived mathematical analysis, we determine the significance of both link layer and physical parameters, such as burst size, minimum CW size value and minimum turnaround time on AIr packet delay performance. Finally, we propose suitable values for both backo# and protocol parameters that reduce average packet delay and, thus, maximize performance. Copyright # 2005 John Wiley & Sons, Lt

International Journal Of Communication Systems

This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput e#ciency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backo# procedure parameters and to give insights on the issues a#ecting IEEE 802.11 DCF performance. Copyright # 2005 John Wiley & Sons, Lt