Applications of AnnAGNPS Model for Sediment and Nutrient Loadings for Funiu Mountain Area, China

The main goal of this study was to evaluate the performance of AnnAGNPS(Annualized AGricultural NonPoint Source)pollution model,in calculating runoff,sediment loading and nutrient loadings for Funiu Mountain area.Most of the model input parameters were sourced from Luanchuan Forest Ecology Station(LFES)in Funiu Mountain area.The data on 23 storms in 2018 was used to calibrate the model and the data on 33 storms in 2019 for validation.The whole evaluation consisted of determining the coefficient of determination(R^(2)),Nash-Sutcliffe coefficient of efficiency(E),and the percentage volume error(VE).Results showed that the runoff volumes were underpredicted by 5.0%with R^(2) of 0.93(P<0.05)during calibration and underpredicted by 5.3%with R^(2) of 0.90(P<0.05)during validation.But sediment loading was able to produce a moderate result.The model underpredicted the daily sediment loading by 15.1%with R^(2) of 0.63(P<0.05)during calibration and 13.5%with R^(2) of 0.66(P<0.05)during validation.Nitrogen loading was overpredicted by 20.3%with R^(2)=0.68(P<0.05),and phosphorus loading performance was slightly poor with R^(2)=0.65(P<0.05)during validation.In general,the model performed well in simulating runoff compared to sediment loading and nutrient loadings.

Coupling effects of hydrological characteristics and nutrient load in sediments on the trophic state of reservoirs

Currently,lakes and artificial reservoirs are increasingly threatened by eutrophication,which is the result of the combined action of many natural and anthropogenic factors.In the past,the effect of nutrient load on the trophic state of water bodies has attracted much attention,while few studies have addressed the effect of hydrological characteristics.Therefore,to reveal the coupling effects of hydrological characteristics and nutrient load in sediments on the trophic state of water bodies,this study collected relevant data from 36 lakes and reservoirs across China.Pearson correlation analysis showed that trophic level index was positively and significantly correlated with nutrient load in sediments and hydraulic retention time,while it was negatively correlated with mean depth and hydraulic load.The principal component analysis showed that the nutrient load was the first major component that influenced the trophic state of water bodies,followed by the mean depth and hydraulic retention time.Eutrophication was prone to occur in water bodies with mean depth less than 7 m and hydraulic retention time greater than 14 d,and the trophic level index regression equation with hydrological characteristics and nutrient load in sediments was derived by multiple regression analysis.This study revealed that the trophic state of water bodies influenced by both nutrient load and hydrological characteristics.It provides a new idea to reduce the occurrence of eutrophication in reservoirs by using the artificial hydrological regulation capacity of reservoirs.

Impact Assessment of Land-Use Changes on Nutrient Load in Song Cau Watershed Using Soil and Water Assessment Tool （SWAT） Model

The objective of this paper is to implement ＂Soil and Water Assessment Tool （SWAT）＂ model to assess the possible impact of land-use changes on nutrient yields from Song Cau watershed located in Northern Viet Nam. Organic nitrogen （N） as well as phosphorus （P） output due to nonpoint source erosion was estimated through SWAT. Parameters governing the mechanics of streamflow discharge, sediment yield, nitrogen, and phosphorus output in SWAT were calibrated in a distributed fashion. A five-year period of record for nutrient was used for model calibration, while a four-year period was used for model validation. Comparing measured versus simulated average monthly total N, and P loads for the calibration and validation periods; respectively, we found that SWAT model performed reasonably well for Song Cau watershed. Simulation results showed that monthly Nash-Sutcliffe coefficient of Efficiency （NSE） ranged from 0.65 to 0.83, observation＇s standard deviation ratio （RSR） and percent bias （PBIAS） ranged from 0.41 to 0.58 and -36.12 to 2.78, respectively. Additionally, SWAT simulation results also showed that land-use changes caused significant percentage of changes in sediment yield, total N, and P loads within Song Cau watershed.

Growth and nutrient accumulation of Phragmites australis in relation to water level variation and nutrient loadings in a shallow lake

Shallow lake eutrophication is a global environmental issue. This study investigated the effects of water level variation and nutrient loadings on the growth and nutrient accumulation of Phragmites australis （reed） by field samplings in Baiyangdian Lake, the largest shallow lake of northern China. The field samplings were conducted in two sites of different nutrient loadings during the whole growth period of reeds, and three types of zones with different water depths were chosen for each site, including the terrestrial zone with water level below the ground, the ecotone zone with the water level varying from belowground to aboveground, and the submerged zone with water level above the ground. The result showed that reed growth was more limited by water level variation than nutrient loadings. The average stem lengths and diameters in terrestrial zones were about 26.3%-27.5% and 7.2%-12.0% higher than those in submerged zones, respectively. Similarly, the terrestrial status increased the aboveground biomass of reeds by 36.6%-51.8% compared with the submerged status. Both the nutrient concentrations and storages in the aboveground reeds were mainly influenced by the nutrient loadings in surface water and sediment rather than the water level variation of the reed growth environment, and the nutrient storages reached their maxima in late August or early September. It was observed that the maximum nitrogen storage occurred in the terrestrial zone with higher nutrient loadings, with the value of 74.5 g/m2. This study suggested that water level variation and nutrient loadings should be considered when using reeds to control and remediate eutrophication of shallow lakes.

THEORETICAL ESTIMATION OF GROUNDWATER DISCHARGE AND ASSOCIATED NUTRIENT LOADING TO A LAKE WITH GENTLE SLOPE BOTTOM

A simple estimation model of groundwater discharge and nutrient flux from nearshore unconfined aquifer to lake was studied. It was supposed that the aquifer was permeable isotropic homogeneously and its thickness approximated to the depth of lake. Distribution of the hydraulic gradient and the specific discharge along the transect of the discharge zone were discussed. Results show that the groundwater discharge patterns vary with the inclination angle of lakeshore bottom. For a shallow lake with gentle slope bottom, the rate of discharge of groundwater to lake is not constant across a discharge zone, but the discharge is concentrated in a narrow portion of the littoral zone where the Dupuit assumptions are invalid. The width of the discharge zone is correlative with aquifer thickness and slope of the lake bottom. The distribution functions of hydraulic gradient and groundwater discharge rates accord exponentially with offshore distance.

External versus Internal Loads of Nutrients of an Urban Eutrophic Tropical Reservoir （Southeastern Brazil）

This study aimed to evaluate the external and internal fluxes of nutrients of an urban eutrophic reservoir （lbirit6 reservoir, SE-Brazil）. External loads were estimated in the tributaries （Pintados and Ibirit6 creeks） through nutrient concentrations and discharge measurements. Using Fick＇s law, internal loads were estimated in the reservoir from fluxes across sediment-water interface from nutrient concentration gradients between the pore water and the water. The Ibirit6 creek （urban sewage recipient） contributes with 72%-47% of ammonium （NH4^＋） and 100%-8% of SRP （soluble reactive phosphorus） of the total quantity entering the reservoir, whereas the Pintados creek （oil refinery effluent recipient） contributions are 20%-19% and 44%-100%, respectively. Despite the high external loads （130 and 2.2 ton-yr^-1 of NH4＋ and SRP, respectively）, internal loads （average flux of 120 and 2 mg·cm^-2yr^-1, respectively） correspond to 25% of the total external loads which may sustain a high productivity in the reservoir for a long time even if the external loads are controlled. The stocks of ammonium and SRP of the interstitial water （100 cm of sediment） would be released to the water in six years and five months, respectively, The release time would be extremely larger （〉 3,000 years） considering the stocks of total N and bioavailable P.

载氧沸石对沉积物-水剖面氮去除的机制

以3种粉煤灰为原材料,制备了粉煤灰基载氧沸石,通过构建原位沉积物柱试验体系,探究了覆盖厚度为0.5,1.0和2.0cm的粉煤灰基载氧沸石对沉积物-水剖面氮的去除效果与机制.结果表明,粉煤灰基载氧沸石能通过吸附和释氧作用降低沉积物-水体系中的氮含量,并控制沉积物中氮的释放,改善效果与材料覆盖厚度正相关.覆盖25d后,0.5,1.0,2.0cm覆盖厚度处理组中沉积物-水界面处的溶解氧浓度分别为1.79,3.69,6.26mg/L,上覆水中总氮的去除率分别为22.77%､30.37%和39.10%,沉积物中氨氮释放通量相较于对照组分别削减了31.4%､47.00%和50.47%.此外,粉煤灰基载氧沸石提高了沉积物表层中参与硝化和反硝化作用的微生物丰度,并增加了硝化功能基因(amoA),反硝化功能基因(narG､napA､nirS和nirK)和好氧反硝化基因(napA)的丰度,表明在表面沉积物中发生了耦合的有氧-缺氧反硝化过程.研究结果有望为粉煤灰的资源化利用和水体内源污染治理提供新的视角.

Harmful algal blooms and eutrophication: "strategies" for nutrient uptake and growth outside the Redfield comfort zone

While many harmful algal blooms have been associated with increasing eutrophication, not all species respond similarly and the increasing challenge, especially for resource managers, is to determine which blooms are related to eutrophication and to understand why particular species proliferate under specific nutrient conditions. The overall goal of this brief review is to describe why nutrient loads are not changing in stoichiometric proportion to the "Redfield ratio", and why this has important consequences for algal growth. Many types of harmful algae appear to be able to thrive, and/or increase their production of toxins, when nutrient loads are not in proportion classically identified as Redfield ratios. Here we also describe some of the physiological mechanisms of different species to take up nutrients and to thrive under conditions of nutrient imbalance.

极端洪水导致的湖泊水位抬升和氮磷输入增加对苦草(Vallisneria natans)的复合影响

据全球气候变化模型预测,未来极端洪水事件将呈现增多和加剧态势。极端洪水对沉水植物功能性状、生长发育状况及整个生态系统均有深远的影响,研究极端洪水对沉水植物生长发育的影响对理解和预测气候变化过程中水生态系统的变化具有重要意义。本文针对极端洪水事件引起的水位急剧上升和营养负荷量增加双重效应,在实验周期90 d内设置对照(水位保持75 cm)、2种极端洪水条件(水位在第1天从75 cm快速上升至150 cm+NP输入、水位从75 cm逐步上升至150 cm+NP输入)以及水位保持75 cm+NP输入4项处理(后3项处理中营养输入总量相同),研究了极端洪水对沉水植物苦草(Vallisneria natans)生长、繁殖对策及生物量分配的影响,实验过程中还同步监测了浮游植物、附着藻类和水体营养状况(TN和TP)。在苦草的17个测定指标中,只有根生物量分配和有性繁殖分配在4个处理下无明显变化。从水位的单独作用看,相对于营养增加且水位恒定的处理,两种洪水条件(水位急剧上升和逐步上升)均降低了苦草的分株数、叶片数、间隔子数、间隔子总长、最大根长、花果数以及各器官生物量和总生物量,促进了人工基质表面附着藻类的生长。水位急剧上升时,植株对间隔子的生物量投资倾向于最小,而株高和植株对叶的生物量投资倾向于最大。从营养负荷的单独作用来看,相对于对照组,营养增加且水位恒定的处理中水体N浓度显著增加,促进浮游植物和苦草表面附着藻类的生长,但是从二者的Chl.a浓度来看,浮游植物遮光作用相对较大,抑制了苦草叶、根和间隔子的生长,但有性繁殖生物量无明显变化。从水位和营养负荷联合作用的模式来看,水位上升和营养负荷两个环境因素的联合作用会使入湖营养负荷加强水位上升对沉水植物生长的影响效应,二者的联合作用使叶、根、间隔子和有性繁殖生物量均大大降低。因此,极端洪水对沉水植物的不利影响较大,一方面水位抬升会直接影响沉水植物,另一方面会通过浮游植物间接影响沉水植物生长发育。

内源营养负荷对4种常见沉水植物生长、形态和资源分配策略的影响

为探明内源营养负荷对沉水植物生长、形态和资源分配的影响,研究通过控制沉积物的营养浓度,探究4种常见沉水植物苦草(Vallisneria natans)、黑藻(Hydrilla verticillata)、穗状狐尾藻(Myriophyllum spicatum)和竹叶眼子菜(Potamogeton wrightii)的多种功能性状对沉积物营养浓度的响应。结果表明:(1)内源营养负荷的增加促进了4种沉水植物的生长,其中苦草的种群数量和总生物量均高于其他沉水植物。然而,当沉积物营养含量过高时(C:73.33 mg/g;N:4.94 mg/g;P:0.68 mg/g)4种沉水植物的种群数量均有所下降。(2)沉水植物形态特征对沉积物营养含量变化的响应趋势并不一致,所有物种株高均逐渐升高,根长则无显著变化规律;苦草和竹叶眼子菜的单株鲜重持续升高,黑藻和穗状狐尾藻的单株鲜重先升高后降低。(3)内源营养物质含量的变化使4种植物的资源分配发生了显著变化,随着沉积物营养含量上升4种沉水植物的地上生物量占比显著升高(根冠比显著下降),光合色素含量显著升高,但过高的营养含量对光合色素合成产生负效应。总之,本研究结果表明苦草对沉积物营养负荷变化的适应能力最强,因此在富营养化水体的生态修复中选择苦草作为先锋种能有效提高沉水植物的修复效率。

Environmental effects of mariculture in China:An overall study of nitrogen and phosphorus loads

Eutrophication in coastal area has become more and more serious and mariculture potential is a main cause.Although there are some quantitative research on nutrient loads in national and global perspective,the calculation method problems make the results controversial.In this paper,the farming activities are divided into fed culture types(include cage culture and pond culture)and extractive culture types(e.g.seaweed,filter-feeding shellfish culture).Based on the annual yield of China in 2019 and feed coefficient of fed culture types and carbon(C),nitrogen(N),and phosphorus(P)content of extractive culture types,the annual nutrient loads was estimated.The results showed that to coastal region of China(1)annual nutrient released by fed culture types were about58451 t of N,9081 t of P,and annual nutrient removed by harvest of extractive culture types were 109245 t of N,11980 t of P and 1.86×10^(6)t of C.Overall,the net amount of nutrient removed annually by mariculture industry were 50794 t of N and 2901 t of P.(2)The nutrient released from mariculture industry influenced nutrient stoichiometry.Pond farming and seaweed farming had the potential of increasing the molar concentration ratio of N and P(N:P),while cage farming and bivalve farming decreased the N:P.(3)Due to different mariculture types and layouts in the coastal regions in China,N and P loading were regional different.Among the coastal regions in China,net release of nutrient from mariculture occurred only in Hainan and Guangxi regions,while in the other regions,N and P were completely removed by harvest.We suggest decrease the amount of fed culture types and increase the amount of integrated culture with extractive culture types.This study will help to adjust mariculture structure and layout at the national level to reduce the environmental impact.

Effects of Nitrogen Exponential Fertilization on Growth and Nutrient Concentration of Hydrangea macrophylla Seedlings

Slow growth rate restricts the development and growth of seedlings due to nutrients deficiency or nutrient imbalance.Exponential fertilization can enhance the internal nutrient reserves in seedlings at the nursery-stage and strengthen their resistance to adverse conditions.In this study,nitrogen requirements for producing Hydrangea macrophylla‘Hanatemari’that robust seedlings,nutrient dynamics,biomass and growth,was examined utilizing exponential fertilization.The potted seedlings were fertilized with urea under exponential regime at rates of 0.5,1.5 and 2.0 g nitrogen/plant(EF1,EF2,and EF3),respectively.In addition,an unfertilized group treated with equal volume of deionized water was used as control.The results showed that seedlings under 1.5 g N/plant(EF2)had the highest plant growth index and total biomass.The nutrient concentrations of different organs varied in different fertilization treatments.Based on the results of current study,it is concluded that 1.5 g N/plant(EF2)is suitable exponential fertilization treatment for the culture of hydrangea seedlings.Our treatments results showed that 2.0 g N/plant is not suitable for seedling culturing,because of serious nutrient toxicity.These findings will help to improve seedling quality and strengthen the production of H.macrophylla for plantation.

水电水库水力负荷对生源要素同化效率的调控作用

河流筑坝发电是目前最为显著的人为扰动河流事件,形成的水电水库阻断了河流连续体,改变了其中生源要素的生物地球化学循环过程,但相关的影响机制还不完全清楚。为此,本研究以乌江11座水电水库为研究对象,季节性调查了水库及相应河流的生源要素(CO_(2)、溶解态无机氮DIN、溶解态无机磷DIP和溶解态硅DSi)浓度及相关的理化因子,以了解河流水库化过程中生源要素浓度的变化过程及水动力条件的变化对其生物地球化学循环的影响机制。结果表明,河流区CO_(2)、DIN、DIP和DSi浓度均高于水库区,水库区内各理化因子间的关联度显著高于河流区。研究水库对各种生源要素的同化效率表现出显著的时空差异;其中对CO_(2)和DSi的同化效率最高,季度均值分别为50%和40%。库区中各生源要素的同化效率和分层强度均与水力负荷显著负相关,表明水电水库的水动力条件是调控其生物地球化学循环强度的关键因素;滞留时间较长和较深的水电水库有利于浮游植物同化生源要素和促进其在剖面上的季节性分层。研究将加深对筑坝河流元素生物地球化学循环过程的认识,有助于水电水库管理措施的制定。

我国羊养殖量及其粪尿资源化利用潜力分析

为了解我国各地区羊粪尿产量及其资源化利用潜力,本研究依据统计年鉴数据和粪尿产排污系数,估算了2021年我国各省份羊粪尿产生量、羊粪尿肥料化和能源化利用潜力,进一步测算了羊粪尿养分农田耕地负荷。结果表明,2021年全国羊粪尿总产生量达2.91亿t,其中总氮(TN)、总磷(TP)、总钾(TK)含量分别为91.08万、19.28万t和73.89万t,可有效替代氮肥(以尿素计)255.31万t、磷肥(以P_(2)O_(5)计)108.45万t、钾肥(以K_(2)O计)191.82万t,可产沼气165.95亿m^(3),具有较高的肥料化与能源化利用潜力。青海和西藏两省份农田耕地负荷居全国第一和第二,消纳羊粪尿时,应充分考虑耕地、农牧交错带、林地和草地等多种土地类型。

Evaluation of Non-Point Source N and P Loads in a Small Mixed Land Use Land Cover Watershed

Non-point source pollution (NPS) of water resources has become a major problem in recent years due to more human interactions and disturbances to natural landscapes. The problem can have more impacts in sub-humid subtropical regions where high intensity monsoon rains have greater effects on hydrologic proc-esses and thus the assessment of those effects is necessitated for strategic water resources and environmental management. Since spatial and temporal changes of NPS pollutants are difficult to assess on a watershed scale, the assessment can be done effectively using a suitable water quantity-quality model coupled with GIS and remote sensing that incorporates spatial variations. The objective of this study was to assess the N and P loads from a small mixed type watershed comprising different land use land covers with the aid of Soil and Water Assessment Tool (SWAT)-a hydrologic-water quality model. The model was calibrated for runoff and sediment transport and then simulation of associated N and P loads as NPS pollution was done and compared with measured values at the outlet of the watershed which is part of the DVC Command, Hazaribagh, India. The calibrated SWAT model was used to estimate the water soluble NO3-N, NH4-N, P, organic N and or-ganic P loads being transported as pollutants by runoff and percolated water. The estimates of these pollut-ants provided information on the extent of NPS pollution of water downstream. The results of the study re-veal that the NPS pollutant load in runoff varies with seasonal rainfall patterns and ranges from 2.57 to 4.52 kg/ha in case of NO3-N which accounts for a maximum load of 7661.40 kg of NO3-N in surface runoff from the watershed under study. The total loss of N from the watershed accounts for as high as 8.84 kg/ha, whereas the P load is 0.02 kg/ha. These losses can be as high as 14984.14 kg of total N and 50.85 kg of total P when estimated as NPS pollutants from the watershed. The study is therefore important to get an estimate of the extent of these pollutants and develop measures for mitigating the losses as nutrient as well as pollu-tion of water resources.

Rating Curve Estimation of Surface Water Quality Data Using LOADEST

Measurement of the nutrient concentrations in the stream is usually done on weekly, biweekly or monthly basis due to limited resources. There is need to estimate concentration and loads during the period when no data is available. The objectives of this study were to test the performance of a suite of regression models in predicting continuous water quality loading data and to determine systematic biases in the prediction. This study used the LOADEST model which includes several predefined regression models that specify the model form and complexity. Water quality data primarily nitrogen and phosphorus from five monitoring stations in the Neuse River Basin in North Carolina, USA were used in the development and analyses of rating curves. We found that LOADEST performed generally well in predicting loads and observation trends with general tendency/bias towards overestimation. Estimated Total Nitrogen (TN) varied from observation (“true” load) by -1% to 9%, but for the Total Phosphorus (TP) it ranged from -2% to 27%. Statistical evaluation using R2, Nash-Sutcliff Efficiency (NSE) and Partial Load Factor (PLF) showed a strong correlation in prediction.

Nutrient Input and CO₂Flux of a Tropical Coastal Fluvial System with High Population Density in the Northeast Region of Brazil

The carbon dioxide flux through the air-water interface of coastal freshwater ecosystems must be quantified to understand the regional balances of carbon and its transport through coastal and estuarine regions. The variations in air-sea CO2 fluxes in nearshore ecosystems can be caused by the variable influence of rivers. In the present study, the amount of carbon emitted from a tropical coastal river was estimated using climatological and biogeochemical measurements (2002-2010) obtained from the basin of the Capibaribe River, which is located in the most populous and industrialized area of the northeast region of Brazil. The results showed a mean CO2 flux of +225 mmol·m-2·d-1, mainly from organic material from the untreated domestic and industrial wastewaters that are released into the river. This organic material increased the dissolved CO2 concentration in the river waters, leading to a partial pressure of CO2 inthe aquatic environment that reached 31,000 μatm. The months of April, February and December (the dry period) showed the largest monthly means for the variables associated with the carbonate system (, DIC, CO2(aq), CO32-, TA, temperature and pH). This status reflects the state of permanent pollution in the basin of the Capibaribe River, due, in particular, to the discharge of untreated domestic wastewater, which results in the continuous mineralization of organic material. This mineralization significantly increases the dissolved CO2 content in the estuarine and coastal waters, which is later released to the atmosphere.

高温干旱背景下太湖藻情变化特征及机制

2022年我国长江流域经历了长期的高温干旱,对湖泊水生态环境和湖内藻情态势产生了深远影响。但目前关于干旱环境下湖泊水华的响应特征研究较少。以太湖为例,基于2005—2022年湖体营养盐与叶绿素a浓度的长期监测数据,结合卫星遥感影像反演的蓝藻水华面积变化,探讨了2022年高温干旱对太湖蓝藻的影响特征及驱动机制。结果表明,2022年蓝藻水华高发季节(5—9月),太湖蓝藻水华的平均面积和最大面积均明显下降,其中5月的水华面积仅为近5年同期平均面积的20%;水样采集分析获得的水体叶绿素a浓度和微囊藻生物量在春季也明显下降。营养盐方面,2022年太湖的总氮和总磷均值分别为1.41和0.084 mg/L,较近5年均值分别下降了30.6%和27.3%,均为2005年以来的最低值。氮磷浓度空间分布的克里金插值显示,除西北湖区(竺山湾)受河流入湖影响外,大部分湖区的溶解态氮磷也都处于较低状态,冬季溶解性总磷浓度小于0.02 mg/L的水域面积占全湖面积的79%。随机森林分析表明,总磷、水温和风速是影响春季微囊藻和藻类生物量的关键因子。冬季湖体磷水平低,加上春季外源负荷较少,致使2022年春季太湖大范围湖区磷浓度较低,对微囊藻的生物量产生了限制作用。此外,在随后夏季连续高温的背景下,太湖蓝藻水华面积虽然发生了反弹,但并未明显高于往年,这与极端干旱导致外源磷补给低、湖体仍能维持大范围低氮低磷条件有关。综上表明,目前太湖部分湖区的藻类生物量对氮磷浓度变化敏感,外源营养盐负荷开始对蓝藻水华情势产生调控作用。坚持外源负荷削减,关注湖泊氮磷内源效应,调控湖体的生态系统结构,是有效降低太湖蓝藻水华强度,应对未来多变气候带来生态风险的重要途径。

氮负荷增强对闽江河口芦苇残体分解及其养分释放的影响

选择闽江河口鳝鱼滩西北部的纯芦苇湿地为研究对象,基于野外氮负荷增强分解试验,探讨了氮负荷增强对芦苇残体分解及其养分释放的影响。试验设置了4个氮负荷水平,即NL0(无氮负荷处理,0 g N m^(-2)a^(-1))、NL1(低氮负荷处理,12.5 g N m^(-2)a^(-1))、NL2(中氮负荷处理,25.0 g N m^(-2)a^(-1))和NL3(高氮负荷处理,75.0 g N m^(-2)a^(-1))。结果表明,不同氮负荷处理下残体的分解速率整体表现为NL2(0.00284 d^(-1))>NL1(0.00263 d^(-1))>NL0(0.00257 d^(-1))>NL3(0.00250 d^(-1)),低氮和中氮负荷总体促进了残体分解,而高氮负荷抑制了残体分解,原因主要与不同处理下残体分解过程中基质质量及pH的明显改变有关。不同氮负荷处理下,残体中的全碳(TC)含量在分解期间均呈不同波动变化特征;全氮(TN)和全磷(TP)含量均在分解初期(0-30 d)骤然降低,之后则呈不同波动变化,其中TN含量呈波动上升变化,而TP含量呈小幅波动变化。残留率是影响不同氮负荷处理下残体分解期间碳(C)、氮(N)和磷(P)净释放的共性因素,而氮负荷增强导致的残体基质质量(C/N、C/P、N/P)和主要环境因子(pH、电导率(EC))改变影响了其释放强度。研究发现,在氮负荷增强背景下残体养分的累积与释放发生了明显改变,闽江河口氮负荷水平的增加整体将抑制芦苇残体中C、N养分的释放,但其在分解中后期(90-240 d)可能对P养分释放具有较为明显的促进作用。

耦合营养负荷的查干湖全季节适宜生态水位阈值研究

适宜生态水位作为反应湖泊水文情势的重要指标,是维持湖泊生态系统稳定的关键要素。已有研究大多集中于水文过程对生态系统影响,缺乏耦合考虑湖泊营养负荷的全季节生态水位阈值研究。本研究在刻画恢复天然水位情势的基础上,综合考虑了人类活动导致湖泊营养负荷的季节性波动以及冰封期的最小生态水位,构建了适用于季节性冰封湖泊全季节的适宜生态水位阈值获取的综合框架,确定了年内不同时期适宜生态水位阈值。结果表明,查干湖入湖口非冰封期的总氮(TN)浓度与平均水位均呈上升趋势,总磷(TP)浓度呈下降趋势;6月湖内TN和TP滞留量最高,分别达到1044.36和23.61 t;确定了查干湖全季节不同时期的适宜生态水位,冰封期(11月—次年4月)为129m,汛期(6—9月)为130.15~130.86 m,非汛期(5和10月)为130.08~130.57 m。研究结果可为季节性冰封湖泊的适宜生态水位研究提供方法支撑,也可为湖泊的水环境管理提供理论支撑。