Phosphorus budget as a water quality management tool for closed aquatic mesocosms

Since the start-up of the St. Lawrence Mesocosm (SLM) at the Montreal Biodome in 1992, phosphorus has accumulated slowly, reaching about 18 mg P l(-1) in 2000. It was decided that this concentration should be lowered to about 2mg P l(-1) to maintain a safe nitrogen:phosporus (N:P) ratio of about 10. Before deciding what type of treatment to use for the removal of phosphorus, a P budget was estimated for 1998 in order to evaluate the different pathways of phosphorus in the mesocosm. The resulting budget had only a 1% difference between the inputs (CV = 12.9%) and the sum of the outputs and changes in P pools (CV = 12.5%). P inputs amounted to 40.5 kg for 1998: food for fish and invertebrates contributed 76% of the inputs while seabird guano contributed 20%. Filtration and general cleaning removed 51% of the inputs while water losses removed 22%. The slight but constant difference between total phosphorus and dissolved reactive phosphorus (DRP) in 1998 and previous years led us to believe that only DRP (mostly orthophosphate) accumulated in the system. The accumulation of DRP was 10% of the inputs in 1998. The budget showed that the importance of water losses is relative and depends on the DRP concentration in the SLM. Furthermore, it was possible to compare this P budget with an N budget of the SLM prepared in 1995. The comparison helped us understand why nitrate in closed-circuit mesocosms are characterized by a high, never-ending accumulation while DRP is characterized by a net increase in the first few years after start-up followed by a very small increase in the following years. Considering its low CV, this P budget was considered a useful water quality management tool in designing a P removal unit for the SLM. This budget may also serve as a guideline for managers of closed-circuit systems such as marine aquariums and aquacultures as well as for designers of P removal units.     

Critical budget of metal sources and pathways in the Seine River basin (1994-2003) for Cd, Cr, Cu, Hg, Ni, Pb and Zn

River basin metal pollution originates from heavy industries (plating, automobile) and from urban sources (Paris conurbation: 2740 km(2), 9.47 million inhabitants). The natural sources of metal have been found to be limited due to sedimentary nature of this catchment and to the very low river sediment transport (10 t km(-2) y(-1)). Several types of data have been collected to build the metal budget within the whole Seine River basin: field surveys, economical statistics and environmental models. Environmental contamination and related fluxes have been measured on atmospheric fallout, rural streams particles, and Seine River particles upstream and downstream of Paris and at river mouth. Metal pathways and budgets have been set up for (i) a typical cultivated area, (ii) a Paris combined sewer system, (iii) Paris conurbation and (iv) the whole catchment metal retention effect in floodplain and dredged material. Metal fluxes to the estuary have been decomposed into natural, urban domestic and other sources. The latter are within 1-2 orders of magnitude larger than waste water fluxes directly released into rivers according to an industrial census. These fluxes have been further compared to the annual use (1994-2003) of these metals. Metal excess fluxes exported by the river are now a marginal leak of metal inputs to the catchment (i.e. "raw" metals, metals in goods, atmospheric fallout), generally from 0.2 to 5 per thousand. However, due to the very limited dilution power in this basin, the contamination of particles is still relatively high. The Seine River basin is gradually storing metals, mostly in manufactured products used in construction, but also in various waste dumps, industrial soils, agricultural and flood plain soils.     

Nitrogen flux and sources in the Mississippi River Basin

Nitrogen from the Mississippi River Basin is believed to be at least partly responsible for the large zone of oxygen-depleted water that develops in the Gulf of Mexico each summer. Historical data show that concentrations of nitrate in the Mississippi River and some of its tributaries have increased by factors of 2 to more than 5 since the early 1900s. We have used the historical streamflow and concentration data in regression models to estimate the annual flux of nitrogen (N) to the Gulf of Mexico and to determine where the nitrogen originates within the Mississippi Basin. Results show that for 1980-1996 the mean annual total N flux to the Gulf of Mexico was 1,568,000 t/year. The flux was approximately 61% nitrate as N, 37% organic N, and 2% ammonium as N. The flux of nitrate to the Gulf has approximately tripled in the last 30 years with most of the increase occurring between 1970 and 1983. The mean annual N flux has changed little since the early 1980s, but large year-to-year variations in N flux occur because of variations in precipitation. During wet years the N flux can increase by 50% or more due to flushing of nitrate that has accumulated in the soils and unsaturated zones in the basin. The principal source areas of N are basins in southern Minnesota, Iowa, Illinois, Indiana, and Ohio that drain agricultural land. Basins in this region yield 800 to more than 3100 kg total N/km2 per year to streams, several times the N yield of basins outside this region. Assuming conservative transport of N in the Mississippi River, streams draining Iowa and Illinois contribute on average approximately 35% of the total N discharged by the Mississippi River to the Gulf of Mexico. In years with high precipitation they can contribute a larger percentage.     

Hydrochemical processes controlling arsenic and selenium in the Changjiang River (Yangtze River) system

The hydrochemistry of arsenic and selenium in the Changjiang (Yangtze River) was studied, based on continuously monitored data at Nantong station (i.e. 180 km inland from river mouth), the main Changjiang channel and 10 major tributaries. The dissolved inorganic arsenic (DIAs) and selenium (DISe) concentrations of the Changjiang are related to water discharge, rock type of drain basin, anthropogenic influences etc. The DIAs and DISe levels vary over an order of magnitude throughout the basin (i.e. 6.95-68.9 nmol/L for DIAs, 1.16-9.92 nmol/L for DISe). Source rock composition is the primary control on the concentrations of DIAs and DISe in the Changjiang. Several tributaries (e.g. Xiangjiang River, Minjiang River and Tuojiang River) are contaminated by human activities. Flux calculations from hydrographic data at Datong (the most downstream main channel station without tidal influence) indicate that the Changjiang transports 234.8 x 10(5) mol/yr of DIAs and 49.6 x 10(5) mol/yr of DISe to the East China Sea.     

长江入海流量减少对陈行水源地影响预测及对策措施

上海自来水要全面达到欧盟标准,必须以优质、稳定的原水为前提。开发利用量大质优的长江水,是改变上海水源地结构不合理、水质不稳定的最佳选择。但是,陈行水源地虽依托长江大水体供水,因水库库容偏小,目前已出现了一系列问题。大自然的变化、长江流域重大蓄水和引水工程等因素的调整,又朝着减少长江入海流量和加剧长江口盐水入侵的方向发展,对陈行水源地形成更为不利的影响。因此,必须采取扩大现有陈行水库库容,调整取水口位置等措施,改变上海水质型缺水城市的现状,让老百姓喝上更多更好的长江水。     

Phosphorus dynamics along a river continuum

Changes in phosphorus concentration and form along 110 km of the River Swale in Northern England were examined over a 2-year period during 1998-2000. This study aimed to use these data to identify the importance of within-channel storage on phosphorus dynamics and to determine the changes in longitudinal transport of phosphorus along a river continuum. The catchment was divided into three contrasting zones: the upland, dominated by sheep farming; a transitional zone, and an intensively-farmed lowland, impacted by sewage inputs. Samples, taken at the downstream extent of each zone at approximately 2-day intervals, were analysed for total phosphorus (TP), total dissolved phosphorus (TDP) and soluble reactive phosphorus (SRP), all of which increased in concentration downstream. SRP concentrations were highest in summer and during low flows, although 92% of phosphorus was exported between autumn and spring. The TDP in the upper and transitional zones consisted of both soluble reactive and un-reactive phosphorus, but in marked contrast was almost entirely in soluble reactive form in the lowland. The majority (85%) of phosphorus exported from the catchment was generated within the lowland, due to sewage inputs and losses from intensive agricultural land. It was predominantly particulate-bound, due to interactions of dissolved phosphorus with suspended sediment. The upland contributed less than 5% to the TP annual budget. Intensive river water monitoring highlighted that the lowland dominated phosphorus export during the rising stage of storms (indicating a rapid mobilisation of fine phosphorus-rich sediment), whereas the transitional zone became dominant on the falling stage (due to greater diffuse phosphorus input).     

Water quality of lake Qarun,Egypt

The River Nile is the main source of water for agricultural, industrial, and municipal purposes in Egypt. A large number of canals transfer river water; there are separate drains for transporting agricultural (and at times sewage) run‐off. Lake Qarun is a closed basin with a high evaporation rate. The only source of water in the lake is the agricultural and municipal drainage from the surrounding communities. The drainage waters are high in solids, nutrients, pesticides, heavy metals and organics. Little information is available on the water quality of Lake Qarun, and its fisheries resources. The objective of this research was to study the water quality characteristics of Lake Qarun and compare these with the quality of water in the River Nile and its canals. Lake Qarun's surface water – 3Km south of National Institute of Oceanography and Fisheries – is alkaline (pH 8.4), with high conductivity (95 mS/m) and a high total dissolved solids (TDS, 2.8 g/L), chloride (Cl, 164 ppm)), and ammonium‐N (9.2 ppm). The dissolved oxygen (DO) content at a depth of 3m is 3.5 ppm. Compared to River Nile and its canals, the water quality of Lake Qarun has significantly deteriorated from the large input of agricultural and domestic wastewaters.     

Anthropogenic impacts on mercury concentrations and nitrogen and carbon isotope ratios in fish muscle tissue of the Truckee River watershed, Nevada, USA

The lower Truckee River originates at Lake Tahoe, California/Nevada (NV), USA and ends in the terminal water body, Pyramid Lake, NV. The river has minimal anthropogenic inputs of contaminants until it encounters the cities of Reno and Sparks, NV, and receives inflows from Steamboat Creek (SBC). SBC originates at Washoe Lake, NV, where there were approximately six mills that used mercury for gold and silver amalgamation in the late 1800s. Since then, mercury has been distributed down the creek to the Truckee River. In addition, SBC receives agricultural and urban nonpoint source pollution, and treated effluent from the Reno-Sparks water reclamation facility. Fish muscle tissue was collected from different species in SBC and the Truckee River and analyzed for mercury and stable isotopes. Nitrogen (delta(15)N) and carbon (delta(13)C) isotopic values in these tissues provide insight as to fish food resources and help to explain their relative Hg concentrations. Mercury concentrations, and delta(15)N and delta(13)C values in fish muscle from the Truckee River, collected below the SBC confluence, were significantly different than that found in fish collected upstream. Mercury concentrations in fish tissue collected below the confluence for all but three fish sampled were significantly greater (0.1 to 0.65 microg/g wet wt.) than that measured in the tissue collected above the confluence (0.02 to 0.1 microg/g). Delta(15)N and delta(13)C isotopic values of fish muscle collected from the river below the confluence were higher and lower, respectively, than that measured in fish collected up river, most likely reflecting wastewater inputs. The impact of SBC inputs on muscle tissue isotope values declined down river whereas the impact due to Hg inputs showed the opposite trend.     

An advanced modelling tool for simulating complex river systems

The present paper describes MOHID River Network (MRN), a 1D hydrodynamic model for river networks as part of MOHID Water Modelling System, which is a modular system for the simulation of water bodies (hydrodynamics and water constituents). MRN is capable of simulating water quality in the aquatic and benthic phase and its development was especially focused on the reproduction of processes occurring in temporary river networks (flush events, pools formation, and transmission losses). Further, unlike many other models, it allows the quantification of settled materials at the channel bed also over periods when the river falls dry. These features are very important to secure mass conservation in highly varying flows of temporary rivers. The water quality models existing in MOHID are base on well-known ecological models, such as WASP and ERSEM, the latter allowing explicit parameterization of C, N, P, Si, and O cycles. MRN can be coupled to the basin model, MOHID Land, with computes runoff and porous media transport, allowing for the dynamic exchange of water and materials between the river and surroundings, or it can be used as a standalone model, receiving discharges at any specified nodes (ASCII files of time series with arbitrary time step). These features account for spatial gradients in precipitation which can be significant in Mediterranean-like basins. An interface has been already developed for SWAT basin model.     

确保上海黄浦江大桥取水口的取水安全--引江济太试验引发的思考

鉴于全球变暖、海平面上升以及未来长江口沿江抽引水量大幅上升,长江枯季入海流量下降,将导致长江口盐水入侵增强,上溯距离增加,威胁黄浦江大桥取水口的水质安全。建议利用太浦河泵站冲盐,将入侵盐水阻止在大桥取水口下游,以保护取水口的水质安全。