Modeling compensated root water and nutrient uptake

Plant root water and nutrient uptake is one of the most important processes in subsurface unsaturated flow and transport modeling, as root uptake controls actual plant evapotranspiration, water recharge and nutrient leaching to the groundwater, and exerts a major influence on predictions of global climate models. In general, unsaturated models describe root uptake relatively simple. For example, root water uptake is mostly uncompensated and nutrient uptake is simulated assuming that all uptake is passive, through the water uptake pathway only. We present a new compensated root water and nutrient uptake model, implemented in HYDRUS. The so-called root adaptability factor represents a threshold value above which reduced root water or nutrient uptake in water- or nutrient-stressed parts of the root zone is fully compensated for by increased uptake in other soil regions that are less stressed. Using a critical value of the water stress index, water uptake compensation is proportional to the water stress response function. Total root nutrient uptake is determined from the total of active and passive nutrient uptake. The partitioning between passive and active uptake is controlled by the a priori defined concentration value c_max. Passive nutrient uptake is simulated by multiplying root water uptake with the dissolved nutrient concentration, for soil solution concentration values below c_max. Passive nutrient uptake is thus zero when c_max is equal to zero. As the active nutrient uptake is obtained from the difference between plant nutrient demand and passive nutrient uptake (using Michaelis–Menten kinetics), the presented model thus implies that reduced passive nutrient uptake is compensated for by active nutrient uptake. In addition, the proposed root uptake model includes compensation for active nutrient uptake, in a similar way as used for root water uptake. The proposed root water and nutrient uptake model is demonstrated by several hypothetical examples, for plants supplied by water due to capillary rise from groundwater and surface drip irrigation.     

Is The Ca + K + Mg/Al Ratio in the Soil Solution a Predictive Tool for Estimating Forest Damage?

The ratio between (Ca +K +Mg) and Al in nutrientsolution has been suggested as a predictive tool forestimating tree growth disturbance. However, the ratiois unspecific in the sense that it is based on severalelements which are all essential for plant growth;each of these may be growth-limiting. Furthermore,aluminium retards growth at higher concentrations. Itis therefore difficult to give causal and objectivebiological explanations for possible growthdisturbances. The importance of the proportion ofbase-cations to N, at a fixed base-cation/Al ratio, isevaluated with regard to growth of Picea abies.The uptake of elements was found to be selective;nutrients were taken up while most Al remained insolution. Biomass partitioning to the roots increasedafter aluminium addition with low proportions of basecations to nitrogen. We conclude that the low growthrates depend on nutrient limitation in thesetreatments. Low growth rates in the high proportionexperiments may be explained by high internal Alconcentrations. The results strongly suggest thatgrowth rate is not correlated with the ratio in therooting medium and question the validity of usingratios as predictive tools for estimating forestdamage. We suggest that growth limitation of Picea abies in the field may depend on lowproportions of base cations to nitrate. It istherefore important to know the nutritional status ofthe plant material in relation to the growth potentialand environmental limitation to be able to predict andestimate forest damage.     

Element Removal in Harvested Tree Biomass: Scenarios for Critical Loads in Wallonia,South Belgium

The critical load concept is nowwidely used as a tool for developing emissioncontrol policies in Europe. As a signatorycountry of the Convention of Long-RangeTransboundary Air Pollution, critical loads foracidity, nutrient nitrogen, nitrogen and sulphurhave been calculated for the Flemish and Walloonregions in Belgium. This paper describes themethodology used for estimating critical loadsfor forest soils in the Walloon region accordingto the Steady-State Mass Balance equations. As anexample the methodology was applied to thecatchment `Waroneu', situated in a sensitive areaof the Haute Ardenne. Main input parameters tothe equations were derived from precipitation andrunoff data of the catchment study. Improvedestimates of nitrogen uptake (Nu) and base cationuptake (BCu) were obtained by intensive samplingof Picea abies and Quercus roburtrees. Nutrient contents (Ca, Mg, K, N) andnutrient to nitrogen ratios of Picea abiesreflected the poor soil quality at a site withhigh N deposition. Quercus robur nutrientcontents increased from stem to higher orderbranches with a high proportion of nutrientslocated in the bark. However the simulation ofstem only harvesting had a minor effect oncritical loads. Measured wood densities werelower than reported literature values with a maineffect on Nu and BCu estimates. The use ofrecommended default values and/or data derivedfrom the experimental site resulted in a widerange of critical loads, some of which werelargely overestimated. Results demonstrated theimportance of site specific data for criticalload calculations.     

农垦与放牧对内蒙古草原N2O、CO2排放和CH4吸收的影响

利用优选静态箱/气相色谱法(GC),首次对我国内蒙古草原典型地区进行了人类活动对N₂O、CO₂和CH₄交换通量影响的实验观测结果表明,农垦麦田N₂O平均排放通量比原始草原高出3倍,并改变了草甸草原为CO₂汇的性质,使其季节排放净通量以C计增加14.3 mg·(m²·h).随放牧强度的增加CO₂排放通量呈线性增长,轻牧会引起草原对CH₄吸收的大幅增加,而随着放牧压力的增大,增加值迅速回落.农垦麦田与草甸草原相比地-气间CH₄交换无显著变化,放牧强度对N₂O排放影响无显著规律.土壤湿度和温度是影响草原排放N₂O和CO₂、吸收CH4季节变化形式的关键因子,而人类活动仅影响排放强度.排放和吸收量年际间差异很大,但主要受降水的影响.N₂O和CO₂排放与CH₄吸收峰值相反现象普遍存在.     

氧和氮等离子体改性细旦涤纶的清洁工艺比较

该文对氧、氮低温等离子体改性细旦涤纶进行了研究,分别探讨了氧、氮等离子体放电参数对提高细旦涤纶上染率的影响,得出了2种工艺的最佳放电参数。实验结果表明:经氧、氮等离子体改性后,细旦涤纶的上染率分别提高了17%和5%,说明氧等离子体改性可显著减少印染废水中的污染物排放量,有利于环境治理,氮等离子体改性效果次之。      

倒置AAO工艺聚磷微生物的吸磷行为

采用人工配水和市政污水研究了“缺氧-厌氧-好氧”(倒置AAO)脱氮除磷工艺中,聚磷微生物(PAOs)在低碳源、高硝酸盐环境下的释磷和吸磷行为.结果表明,在低碳源、高氮和磷环境中,尽管PAOs在缺氧厌氧段释磷程度低,如果适当延长厌氧段和好氧段的HRT、且好氧曝气较充分,仍能超量吸收磷.PAOs过量吸磷的能量来源不仅仅是厌氧段吸收与合成的胞内聚合物在好氧段的氧化,还来自好氧环境正常代谢过程中多余的能量.外加碳源的投加时间点对PAOs吸磷的影响不显著.PAOs在厌氧段后期出现过量吸磷现象,推测是细胞内有机物厌氧降解产生的ATP通过某种代谢途径被用于无机磷的吸收.     

低强度超声波改善污泥活性

采用城市污水处理厂的好氧活性污泥为试验材料,以好氧呼吸速率(OxygenUptakeRate,OUR)为指标,研究活性污泥在超声波强度0～1.2W/cm²、辐照时间0～40min处理后活性的变化.发现当采用超声波强度0.3W/cm²,辐照时间10min,对提高污泥活性的效果最为显著,不适当的处理时间与处理强度则不利于污泥活性的提高.因此,利用超声波激励污泥活性存在最佳的超声波强度和辐照持续时间.另外,研究了强度0.3W/cm²,辐照时间10min超声波辐射处理后0～48h中污泥活性的变化规律,发现超声辐照8h后污泥活性达到最大值,为辐射处理后初始活性的2倍,24h后超声波的强化作用基本消失.因此,可采用强度0.3W/cm²超声波每隔8h取反应器中的部分活性污泥辐照10min后再返回反应器,来提高生物反应器的处理效率.本文还对低强度的超声波改善污泥活性的可能机制进行了假说性解释.     

Denitrification and phosphorus uptake by DPAOs using nitrite as an electron acceptor by step-feed strategies

Denitrifying phosphorus accumulating organisms (DPAOs) using nitrite as an electron acceptor can reduce more energy. However, nitrite has been reported to have an inhibition on denitrifying phosphorus removal. In this study, the step-feed strategy was proposed to achieve low nitrite concentration, which can avoid or relieve nitrite inhibition. The results showed that denitrification rate, phosphorus uptake rate and the ratio of the phosphorus uptaken to nitrite denitrified (anoxic P/N ratio) increased when the nitrite concentration was 15 mg·L^-1 after step-feeding nitrite. The maximum denitrification rate and phosphorus uptake rate was 12.73 mg NO2-–N·g MLSS-1?h-1 and 18.75 mg PO43-–P·g MLSS-1?h-1, respectively. These rates were higher than that using nitrate (15 mg·L^-1) as an electron acceptor. The maximum anoxic P/N ratio was 1.55 mg PO43--P?mg NO2--N-1. When the nitrite concentration increased from 15 to 20 mg NO2--N?L-1 after addition of nitrite, the anoxic phosphorus uptake was inhibited by 64.85%, and the denitrification by DPAOs was inhibited by 61.25%. Denitrification rate by DPAOs decreased gradually when nitrite (about 20 mg·L^-1) was added in the step-feed SBR. These results indicated that the step-feed strategy can be used to achieve denitrifying phosphorus removal using nitrite as an electron acceptor, and nitrite concentration should be maintained at low level (<15 mg·L^-1 in this study).     

鱼吸收富集LAS的分析研究进展

LAS对鱼等水生生物均产生有害影响,会破坏鱼鳃上皮组织、影响其相关功能(如通透性等)。LAS经由鱼鳃吸收、并通过血液输送到鱼体中各组织。LAS疏水性越大,其在鱼体中生物富集系数越大。水硬度等影响鱼吸收、富集LAS。鱼体中LAS生物转化过程减小了LAS生物富集。鱼体中LAS及其生物转化产物大多是经过固相萃取或基质固相分散萃取后,采用HPLC或HPLC/MS等方法进行分析。