Mass Balance Study on Phosphorus Removal in Constructed Wetland Microcosms Treating Polluted River Water

A number of studies have showed that the mass removal rates of phosphorus (P) in different constructed wetlands (CWs) varied significantly, and it is essential to quantify the contributions of major P removal processes in order to improve system design. The objective of this study was to investigate the effects of vegetation, hydraulic retention time (HRT), and water temperature on P removal from polluted river water and to quantify the contributions of different P removal pathways in surface CWs. Results showed that the average total P removal rates ranged between 2.69 and 20.84 mg/(m² day) in different seasons and were influenced significantly by vegetation, HRT, and water temperature. According to the mass balance approach, plant uptake removed 4.81–22.33% of P input, while media storage contributed 36.16–49.66%. Other P removal processes such as microbiota uptake removed around 0.26–4.13%. Media storage and plant uptake were identified as the main P removal processes in surface CWs treating polluted river water. This illustrated the importance of selecting media and plants in CWs for future practical application.     

Impact of elevated levels of CO2 on animal mediated ecosystem function: The modification of sediment nutrient fluxes by burrowing urchins

A mesocosm experiment was conducted to quantify the relationships between the presence and body size of two burrowing heart urchins (Brissopsis lyrifera and Echinocardium cordatum) and rates of sediment nutrient flux. Furthermore, the impact of seawater acidification on these relationships was determined during this 40-day exposure experiment. Using carbon dioxide (CO₂) gas, seawater was acidified to pH_NBS 7.6, 7.2 or 6.8. Control treatments were maintained in natural seawater (pH ≈ 8.0). Under normocapnic conditions, burrowing urchins were seen to reduce the sediment uptake of nitrite or nitrate whilst enhancing the release of silicate and phosphate. In acidified (hypercapnic) treatments, the biological control of biogeochemical cycles by urchins was significantly affected, probably through the combined impacts of high CO₂ on nitrifying bacteria, benthic algae and urchin behaviour. This study highlights the importance of considering biological interactions when predicting the consequences of seawater acidification on ecosystem function.     

Net ecosystem metabolism of a coastal embayment fertilised by upwelling and continental runoff

O₂, N, P and Si net ecosystem metabolism of the Ría de Ares-Betanzos (NW Iberian upwelling system) was estimated during two 3-wk periods of contrasting summer downwelling and autumn upwelling conditions by means of a transient 2-D kinematic box model. The subtidal circulation was positive in both situations, although it was depressed during downwelling and enhanced during upwelling. Concurrently, the ría was fertilised mainly by shelf bottom waters, which introduced from 69% (under downwelling) to almost 100% (under upwelling) of the limiting N nutrients. The ría was an efficient nutrient trap: about 70% of the N nutrients that entered the embayment were retained under downwelling conditions (average flushing time, 9 days) and about 50% under upwelling conditions (average flushing time 3 days). Although the trapping efficiency was lower, the net ecosystem production (NEP) was much higher under upwelling (from 1.0±0.3 to 1.5±0.4 g C m⁻² d⁻¹), than under downwelling favourable winds (from 0.2±0.1 to 0.3±0.1 g C m⁻²). The stoichiometry of NEP suggests that P and N compounds recycled faster than C compounds, specially in the inner segment of the ría. The net degree of silification was twice in the inner than in the outer segment of the ría.     

Land use and topography as predictors of nutrient levels in a tropical catchment

The influence of landscape on nutrient concentration and yield was analyzed in a tropical catchment, the Guare River in northern Venezuela. Spatial and temporal variation in nitrate, SRP and total P were determined in 15 sites located along the river mainstem and tributaries. Higher nitrate concentrations and yields were reported from upper sites and both decreased in the downstream direction along the river mainstem. These trends appear to be related to more pronounced slopes and larger proportions of agricultural and forest lands in subcatchments located in the upper part of the basin, and dense algal mats in the lower reaches. Nitrate values were higher during periods of high discharge, suggesting that nitrate is primarily transported by shallow subsurface flow. SRP represented between 60 and 80% of total P. Phosphorus concentrations were homogeneous along the river mainstem and showed little seasonal variation, while yields were higher in the upper basin. Multiple regression identified slope, runoff and agriculture as primary predictors of nitrate and phosphorus across the watershed, which suggests that both natural and anthropogenic landscape characteristics have a strong influence on nutrient levels in the Guare catchment.     

Geographic variations in shell growth rates of the mussel Diplodon chilensis from temperate lakes of Chile: Implications for biodiversity conservation

The Chilean lake district includes diverse lentic ecosystems along ca. 700 km of the country (36°–43°S), including the “Nahuelbutan lakes”, “Araucanian lakes” and “Chiloe lakes”. This area is recognized as an important “hot spot” of benthic freshwater biodiversity in Southern South America. In Chilean temperate lakes, increased nutrient loads of P and N caused eutrophication, particularly in the Nahuelbutan Lakes. The freshwater Hyriidae mussel Diplodon chilensis (Gray, 1828) which is one of the most abundant species in Chilean temperate lakes, is known to be very susceptible to eutrophication. This species presents a clear reduction in its geographic ranges and is considered to be a threatened species in many Chilean lakes. In this study, we used a correlative approach to determine how eutrophication-driven changes in the food supply and in geographical parameters of different Chilean lakes affected the shell growth rates of D. chilensis. The results obtained from sclerochronological analyses of the mussel shells suggest an association with a group of environmental variables, including geographical types (negative), such as latitude and altitude, and limnological types (positive), especially phosphorous and turbidity. However, the D. chilensis populations under extreme conditions of turbidity in eutrophic and hypertrophic lakes are extinct or nearly so. The high positive correlation of the mean D. chilensis growth rates with orthophosphate (R=0.76; P<0.05), in relation to dissolved inorganic nitrogen, suggests that P is the major limiting factor of the primary productivity in Chilean temperate lakes. We discuss some implications of our results in terms of the conservation of biodiversity in temperate lake ecosystems at different taxonomic levels.     

Converting tropical rain forest to forest plantation in sabah,malaysia. Part I. Dynamics and net losses of nutrients in control catchment streams

Streamwatcr chemistry was monitored for five years in six streams in a paired catchment experiment in Mendolong, Sabah, Malaysia, including controls in rain forest and secondary vegetation after the [Borneo fire] of 1982–3 and comparing the effects of different ways of establishing forest plantations with Acacia mangium. Three catchments were covered with selectively logged lowland hill dipterocarp forest (W4-W6) and three (W1-W3) with secondary vegetation after forest fires. The control catchments, W3 and W6 reported in this paper, had no treatments applied. Reference monitoring at all streams was for 25 months and the total period of study reported here is 64 months. The soils in the catchments were mainly Orthic Acrisol in W3 and Gleyic Podsol in W6 and a mix of both soil types in the other catchments. Element baseflow concentrations were generally low and not significantly different from stormflow concentrations for all streams during the reference period. Concentrations were also generally consistently low for the two control streams during the whole period of measurement. Chemical inputs as wet deposition were low as a result of a high input from local convection. The rain forest on the Podsol had a tight nutrient circulation indicated by small net losses of macronutrients. The Podsol was found to have poorer conditions for soil mineralization and more surficial runoff, resulting in higher loads of S, C and N in the organic phases, with higher organic C/N ratio, in the discharge. Nitrogen was found to accumulate in both catchments. An almost double accumulation of N in W3 was attributed to a larger biomass accumulation continuing after the forest fire 3–8 years earlier. On the other hand, the Acrisol in W3 had much larger net losses of S, Si, K, Ca, Mg and Na. Most of differences could be attributed to differences in weathering between the soils and local mineralogical differences.     

Simulations of Annual Cycle of Phytoplankton Production and the Utilization of Nitrogen in the Yellow Sea

A nutrient dynamic model coupled with a 3D physical model has been developed to study the annual cycle of phytoplankton production in the Yellow Sea. The biological model involves interactions between inorganic nitrogen (nitrate and ammonium), phosphate and phytoplankton biomass. The model successfully reproduces the main features of phytoplankton-nutrient variation and dynamics of production. 1. The well-mixed coastal water is characterized by high primary production, as well as high new production. 2. In summer, the convergence of tidal front is an important hydrodynamic process, which contributes to high biomass at frontal areas. 3. The evolution of phytoplankton blooms and thermocline in the central region demonstrate that mixing is a dominant factor to the production in the Yellow Sea. In this simulation, nitrate- and ammonium-based productions are estimated regionally and temporally. The northern Yellow Sea is one of the highly ranked regions in the Yellow Sea for the capability of fixing carbon and nitrogen. The annual averaged f-ratio of 0.37 indicates that regenerated production prevails over the Yellow Sea. The result also shows that phosphate is the major nutrient, limiting phytoplankton growth throughout the year and it can be an indicator to predict the bloom magnitude. Finally, the relative roles of external nutrient sources have been evaluated, and benthic fluxes might play a significant role in compensating 54.6% of new nitrogen for new production consumption.     

东海赤潮高发区营养盐时空分布特征及其控制要素

东海长江口、舟山渔场附近海域是我国近海赤潮爆发严重的区域之一。在影响该海域营养盐分布的水团中 ,长江冲淡水向表层输入了大量的氮、磷、硅营养盐 ,台湾暖流主要对底层和长江口外上升流区有贡献 ,苏北沿岸水、闽浙沿岸水主要影响近岸区域。同时 ,营养盐在海水 -沉积物界面的交换作用 ,大气湿沉降作用等也影响着该海域营养盐的时空分布。结合2002年4月～2003年3月对29°00′～32°00′N、122°00′～124°00′E海域四季航次调查的营养盐分布规律 ,该海域可分为三片区域 ,由岸边向外海分别为高营养盐、低浮游植物区 ,较高营养盐、高浮游植物区和较低营养盐、低浮游植物区。随着近年来营养盐输入通量的增加 ,富营养化程度加大 ,受化学、物理、生物等因素综合作用 ,高浮游植物区赤潮爆发频率和规模逐年增加 ,已为中国近海典型的赤潮高发区     

Mise en évidence expérimentale des facteurs nutritifs limitants de la production du micro-nanoplancton et de l'ultraplancton dans une eau côtière de la Méditerranée orientale (Haïfa,Israël)

Enrichment experiments were carried out on seawater samples from the Israeli coast to characterise the nature of nutrient limitation. Phytoplankton chlorophyll, ATP, PC, PN, PP and bicarbonate and orthophosphate uptake rates indicate that phosphorus limitation is more extreme than that of nitrogen. A large increase in total nitrogen observed with P enrichment suggests that a substantial nitrogen fixation is mediated by picocyanobacteria in this kind of oligotrophic mediterranean waters.