Seasonal response of nitrogen exchange fluxes to crab disturbance at sediment-water interface in coastal tidal wetlands

Coastal wetlands are hotspots for nitrogen(N)cycling,and crab burrowing is known to transform N in intertidal marsh soils.However,the underlying mechanisms remain unclear.This study conducted field experiments and used indoor control test devices to investigate the seasonal response of nitrogen to crab disturbance at the sediment-water interface in coastal tidal flat wetlands.The results showed that crab disturbance exhibited significant seasonality with large seasonal differences in cave density and depth.Due to crab disturbance,nitrogen fuxes at the sediment-water interface were much greater in the box with crabs than in the box without crabs.In summer,NH-N showed a positive flux from the sediment to the overlying water,but NO2-N and NOg-N showed positive fluxes from the sediment to the overlying water only in early stages.In winter,NH-N showed a positive flux from the sediment to the overlying water,but NO-N and NO,-N both exhibited positive and negative fluxes.These results indicated that the presence of crab burrows can cause the aerobic layer to move downward by approximately 8-15 cm in summer and directly promote nitrification at the sediment surface.

Analysis of heat pulse signals determination for sediment-water interface fluxes

The heat pulse signal is analyzed in a new way with the goals of clarifying the relationships between the variables in the heat transfer problem and simplifying the procedure for calculating sediment-water interface fluxes J. Only three parameters x0 λand pc l are needed to calculate J by the heat pulse data for this analysis method.The results show that there is a curvilinear relationship between the peak temperature arrival time and sediment-water interface fluxes and there exists a simple linear relationship between sediment-water interface fluxes and the natural log of the ratio of the temperature increase downstream from the line heat source to the temperature increase upstream from the heat source.The simplicity of this relationship makes the heat pulse sensors an attractive option for measuring soil water fluxes.

Impact of Rice-Catfish/Shrimp Co-culture on Nutrients Fluxes Across Sediment-Water Interface in Intensive Aquaculture Ponds

Exchange of nitrogen and phosphorus across sediment-water interface plays an important role in the management of nutrient recycling in the aquaculture pond. In this study, a plot experiment was conducted to study the effect of rice-catfish/shrimp co-culture on the micro-profile of oxygen (O2), pH and nutrient exchange across sediment-water interface in the intensive culture ponds. The results showed that rice-catfish co-culture increased the concentration and penetrating depth of O2, but decreased the pH value across the sediment-water interface, compared with catfish monoculture. Additional rice cultivation significantly reduced the flux rates of ammonium (NH4+) and nitrate (NO3-) across sediment-water interface in the catfish and shrimp ponds. The flux rates of NO2 - and soluble phosphorus (PO43-) showed no significant difference between rice-catfish/shrimp co-culture ponds and catfish/shrimp monoculture ponds. Rice only affected the dissolved inorganic nitrogen and phosphorus fractions in the sediment. The concentrations of NH4 + were significantly lower in the sediment of co-culture ponds than in the monoculture ponds. Additional rice cultivation also significantly reduced the content and percentage of dissolved inorganic phosphorus in the sediment of catfish ponds.

Experimental research on the impact of Corbicula flumineaon DIN exchange at a tidal flat sediment-water interface

Based on a simulative experiment and a comparison analysis, the effect of bivalve Corbiculafluminea activity on sediment-water exchange of dissolved inorganic nitrogen （DIN） is studied. The areas included three intertidal flat sites of the Changjiang （Yangtze） River estuary in China. The interface exchange flux of ammonium, nitrate and nitrite in the short experiment （6 h） was -46.4-40, -74.8-929.1 and 2.5-14.6 μmol/（m^2·h）, respectively. It was found that the burrowing activities of C. fluminea increased NH4 and NOi release from sediments to overlying water in the short-term experiment. During long-term incubation, NH4 and NOi released in turn from the sediments. At the beginning of incubation, bioturbation by C. fluminea could accelerate NH2 release from sediments 2-17 times in different sites, resulting in stronger nitrification and increased NOi concentrations in the overlying water. Sediment profile analysis post-incubation shows that organic matter mineralization and sediment-water NH4 exchange had been stimulated by C. fluminea bioturbation and bioirrigation during the experiment. Therefore, C. fluminea activities such as excretion, burrowing, irrigation and turbation can effectively alter nitrogen dynamics and accelerate and stimulate nitrogen exchange and cycling at the sediment-water interface.

Influential factors on the exchange rate of dissolved inorganic nutrients at the sediment-water interface in Jiaozhou Bay, China

Incubation experiments are carried out to study the exchange rates of dissolved inorganic nutrients including silicate, phosphate, ammonium, nitrite, and nitrate (vSiO3-Si, vPO4-P, vNH4-N, vNO2-N and vNO3-N) at the sediment-water interface in the Jiaozhou Bay. Major factors influencing the exchange rates are discussed in detail, which include the dissolved inorganic nutrient concentrations in porewater (Cpw), water and clay contents, and grain size of the sediments (CH2O, Cclay and GSsed). The results may provide insight into the dynamics of nutrient transport and the environmental capacity of nutrients in Jiaozhou Bay, and should be beneficial to solving the problems caused by excessive nutrient input this area.

Nitrogen and Phosphorus Diffusive Fluxes Across the Sediment-Water Interface in Estuarine and Coastal Tidal Flats

Nitrogen and phosphorus contents are analyzed in the overlying waters and pore waters taken from the Changjiang Estuary and Shanghai coastal tidal flats in this study. In addition, the diffusion fluxes of nitrogen and phosphorus across the sediment-water interface in tidal flats are estimated according to the nutrient concentration gradients at the interface. It has been indicated that the concentrations of ammonium, nitrite, nitrate and dissolved phosphorus in overlying waters range from 0.0082-2.56, 0.03-0.58, 0.69-5.38 and 0.035-0.53 mg/L, respectively, while 0.0025 - 1.35 mg /L for NH^-N, 0. 0055 ~0.20mg/L for NO2-N, 0.61-1.14 mg/L for NO3-N and 0.11~0.53mg/L for DP insurface pore waters.The findings have revealed that ammonium, nitrite, nitrate and dissolved phosphorus diffusionfluxes across the sediment-water interface are between -0.024~0.99, -0.39~ -0.0019, -3.09--0.12 and -0.48- 0.12 ug/ (cm.d ) respectively, showing that the sediment in tidal flats is the source of phosphorus and an important sink for nitrogen in the waters.

The diffusive fluxes of inorganic nitrogen across the intertidal sediment-water interface of the Changjiang Estuary in China

Ammonium and nitrate concentrations were analyzed in near-bottom water and pore water collected from ten stations of the intertidal flat of the Changjiang Estuary during April, July, November and February. The magnitudes of the benthic exchange fluxes were determined on the basis of concentration gradients of ammonium and nitrate at the near-bottom water and interstitial water interface in combination with calculations of a modified Fick＇ s first law. Ammonium fluxes varied from - 5.05 to 1.43 μg/（ cm^2·d） and were greatly regulated by the production of ammonium in surface sediments, while nitrate fluxes ranged from - 0. 38 to 1.36 μg/ （ cm^2·d） and were dominated by nitrate concentrations in the tidal water. It was found that ammonium was mainly released from sediments into water columns at most of stations whereas nitrate was mostly diffused from overlying waters to intertidal sediments. In total, 823.75 t/a ammonium-N was passed from intertidal sediments to water while about 521.90 t/a nitrate-N was removed from overlying waters to intertidal sediments. This suggests that intertidal sediments had the significant influence on modulating inorganic nitrogen in the tidal water.

The Influence of Element Diffusion at the Sediment-Water Interface on the Basic Chemical Composition of Overlying Water Mass in Lake Lugu, China

Little work has been done on the influence of sediments on the basic chemical composition of overlying water mass. This paper deals with the vertical profile of the basic constituents such as Ca2 +, K +, Na+, and HCO3, as well as of pH in the overlying water mass and sediment porewater of Lake Lugu-a semi-closed, deep lake in Yunnan Province. The results revealed that those basic constituents may diffuse and transport from bottom sediments to overlying water mass through porewater. In the paper are also quantitatively evaluated the diffusive fluxes and the extent of their influence on overlying water mass, indicating that the lake sediment-water interface diffusion plays an important role in controling the basic chemical composition of water in the whole lake.

Spatial and Seasonal Variations of Nutrients in Sediment Profiles and Their Sediment-Water Fluxes in the Pearl River Estuary,Southern China

Three cruises were launched in the Pearl River Estuary （PRE） in 2005 to investigate the biogeochemical cycling of nutrients associated with early diagenesis related to degradation of organic matter. Seasonal and spatial variations of pore water nutrient concentrations and profile patterns in sediments were studied. Nutrient fluxes at the sediment-water interface （SWI） were measured by incu- bation experiments, and we here discussed the accumulation and transformation processes of nutrients at the SWI. The nutrients generally decreased from the Pearl River outlets downstream, indicating an- thropogenic influences on the nutrient inputs in the estuary. NO3-N concentration was the highest of the three forms of DIN （dissolved inorganic nitrogen, the sum of NH4-N, NO3-N and NO2-N） in the overly- ing water, and NH4-N was the main component of DIN in pore water. The gradual increase of NH4-N and the rapid decrease of NO3-N with sediment depth provided the evidence for anaerobic conditions below the SWI. Negative fluxes of NO3-N and positive fluxes of NH4-N were commonly observed, sug- gesting the denitrification of NO3-N at the SWL The DIN flux direction suggested that the sediment was the sink of DIN in spring, however, the sediment was generally the source of DIN in summer and winter. PO4-P distribution patterns were distinct while SiO4-Si inconspicuously varied in sediment profiles in different seasons. The flux results indicated that PO4-P mainly diffused from the water column to the sediment while SiO4-Si mainly diffused from the sediment to the water column. Generally, the incu- bated fluxes were the coupling of diffusion, bioturbation and biochemical reactions, and were relatively accurate in this study.

The mechanisms of contaminants release due to incipient motion at sediment-water interface

Sediments in many rivers and lakes are subjected to resuspension due to a combination of hydrodynamics. However, the roles of contaminant-contained dissolved and particulate sediments during the resuspension release are rarely studied. This study focuses on the release quantity of contaminants in both water phase and solid phase. Conservative tracer （NaC1） and reactive tracer （Phosphorus） were respectively added to cohesive fine-grained sediments and non-cohesive coarse-grained sediments. A range of typical shear stress was conducted to characterize the time-depended release of contaminants in a laboratory flume. When the sediment started to move, the concentration of contaminant in the overlying water increased with the bed shear stress, but the dissolved contaminants responded faster than the particulate ones. The observed contaminant release process can be divided into three main stages： the initial two hours fast mixing： the release contribution of pore water could reach up to 75%; the middle 4-6 h adsorption： the partitioning coefficient of contaminant between water phase and solid phase decreased over the time, and the adsorption of contaminates from resuspended sediment dominated the negative release; the last equilibrium stage： the desorption and adsorption reached equilibrium, and the reactive contaminant made an impact on the water quality in the solid phase. The existing formulas to evaluate the release flux are far from practice meaning as the sediment contaminants undergo a very complex release process.

Seasonal release of Fe and Mn at the sediment-water interface in Aha Lake

The release of various harmful and poisonous elements from sediments to overlying water via pore water is one of the geochemical processes influencing and restricting the water quality of lakes. It is important for protecting and managing freshwater lakes to uncover and recognize the basic features and forming mechanism of this process.

水土保持生态建设下的黄土高原典型流域水沙响应

为探讨黄土高原多沙粗沙区流域水沙关系演变特征及其对水土流失治理的响应,以黄河中游无定河流域为研究对象,综合采用水沙关系曲线、数理统计等多种方法,系统分析1956—2019年间无定河流域水沙关系多时间尺度演变特征及其与水土流失治理的协同响应。研究结果表明:1)研究时段内,无定河流域年径流及年输沙量呈锐减趋势(P<0.05),且均在1970年左右发生减少突变;2)流域水沙关系在年际和场次洪水尺度上均发生深刻变化。2010年以后,暴雨频发导致流域内侵蚀物源头供应明显增加,流域河道泥沙输送能力小幅提高;3)水土保持措施实施对流域水沙锐减影响较大。2000年前后在相似降雨条件下,单位降雨量径流量和单位降雨量输沙量较20世纪70年代减少47%和62%。水土保持措施面积增加与流域径流输沙减少呈现较好的一致性,流域水土流失治理在提高黄河多沙粗沙区流域下垫面抗侵蚀能力等方面发挥重要作用。研究结果可为科学认知区域水土流失治理成效及入黄泥沙锐减成因提供参考。

淡水养殖池塘水质评价及与底质相关性分析

在哈尔滨地区面积6 600 m^(2)、平均水深1.2 m、多年未清淤的泥沙底质典型淡水精养池溏中混养鲤(Cyprinus carpio)、鲇(Silurus asotus)、草鱼(Ctenopharyngodon idella)和鲢(Hypophthalmichthys molitrix),春季(4—5月)、夏季(6—8月)和秋季(9月)不同时间采集池塘水体和表层底泥样品,监测养殖周期内水质总氮(TN)、总磷(TP)、氨氮(NH_(4)^(+)-N)、亚硝酸盐氮(NO_(2)^(-)-N)、硝酸盐氮(NO_(3)^(-)-N)和总有机碳(TOC)含量及高锰酸盐指数(COD_(Mn))、p H的季节性变化,利用单项污染指数法、综合污染指数法评价水体污染程度,利用主成分分析法解析水质污染的主要驱动因子,并结合底质指标绘制网络关系图。结果表明:池塘水质整体处于严重污染水平,春季优于夏季和秋季。参与评价时池塘水质为Ⅳ类、Ⅴ类和劣Ⅴ类,水质超标数随着养殖时间延长而增加,TN在全养殖周期内均超出警戒水平;TN、TP、NH_(4)^(+)-N和COD_(Mn)是池塘水体的主要污染物。因子分析结果表明,池塘水质主要受鱼类的生长代谢、溶解氧和投饵的影响,污染物以N、P营养盐为主。水体TP、TN、NH_(4)^(+)-N和底泥NO_(2)^(-)-N呈极显著正相关关系(P<0.01),与底泥TOC呈显著正相关关系(P<0.05)。池塘水体和底泥中的有机物污染具有共现性,水体TOC和底泥TOC呈极显著正相关关系(P<0.01)。

液相色谱-串联质谱法测定土壤、沉积物和水中3种新型除草剂残留

除草剂在杂草和有害植物防控上发挥着重要的作用,但其有效利用率低,大量除草剂进入环境中,对生态环境和人类健康构成了潜在威胁,因此建立环境样品中除草剂的残留分析方法尤为重要。该文采用电喷雾正离子源模式,建立了液相色谱-串联质谱法(LC-MS/MS)测定土壤、沉积物和水中异噁唑草酮、吡唑草胺和苯嘧磺草胺残留量的方法。土壤和沉积物样品经乙腈振荡提取、盐析后经C18固相萃取小柱净化,水样过滤后经C_(18)固相萃取小柱净化;再用LC-MS/MS测定样品中异噁唑草酮、吡唑草胺和苯嘧磺草胺的残留量。实验优化了仪器检测和前处理条件,考察了方法的线性关系、基质效应、检出限和定量限,并选取4种土壤、2种沉积物和水样进行了方法验证。在0.0005~0.02 mg/L范围内,异噁唑草酮、吡唑草胺、苯嘧磺草胺的线性关系均良好,r≥0.9961。3种除草剂在土壤、沉积物和水中的基质效应为-10.1%~16.5%。异噁唑草酮、吡唑草胺和苯嘧磺草胺的检出限分别为0.05、0.02、0.01μg/kg,定量限分别为0.2、0.05、0.05μg/kg。异噁唑草酮、吡唑草胺和苯嘧磺草胺在土壤、沉积物和水样中3个水平(0.005、0.1、2.0 mg/kg)下的加标回收率分别为77.2%~101.9%、77.9%~105.1%、80.8%~107.1%;相对标准偏差(RSD)分别为1.4%~12.8%、1.2%~7.7%、1.5%~11.5%。结果表明:本方法操作简单,方法稳定,定量准确,实用性强,可用于土壤、沉积物和水中异噁唑草酮、吡唑草胺和苯嘧磺草胺残留量的检测。

黄河下游花园口以上河段滞沙能力分析

黄河下游河床调整主要取决于来水来沙和河床边界条件,河床调整沿程不均衡特征明显,花园口以上河段床演变对水沙条件的变化响应尤为突出,泥沙冲淤调整幅度最大。基于河道冲淤及水沙演进特性、滞沙可行性、河槽几何特性等分析,提出了花园口以上河段可作为泥沙天然反调节“库”概念,结合黄河下游实测洪水资料,采用水力计算方法,计算了花园口以上河段的河槽排洪能力及不同河槽规模条件下河槽允许滞沙量,提出了反调“库”滞沙能力,可为小浪底水库排沙指标的确定提供依据,对维持小浪底水库有效库容、弥补后续清水河床沙源不足、改善黄河下游河槽冲淤不均衡现象具有重要意义。

环境因子对河流底泥-水界面氮释放规律影响

潮白河作为北京重要城市河流水源之一,其顺义减河河段属于典型的再生水回补河道。研究不同点位代表的自然河段与再生水河段中底泥-水界面的养分释放规律及其影响因素,对河道水质改善具有重要意义。该研究通过室内土柱模拟实验,分析不同p H、溶解氧(DO)和温度条件下河道不同断面底泥氨氮释放规律,估算了底泥-水界面氨氮释放通量。结果表明:(1)下游汇流(S1)、潮减交汇处(S2)和自然河道(S3)上覆水和间隙水中NH4+-N呈明显的释放趋势,再生水河道中段(S4)和再生水排水口(S5)释放不明显或发生NH4+-N吸附作用。(2)不同断面土柱模拟中,间隙水中NH4+-N通量为上覆水的2.5~66.7倍,验证了底泥氮先释放到间隙水再扩散到上覆水的过程。(3)不同环境因子(p H、DO和温度)对底泥NH4+-N释放的影响呈现出不同规律:随p H升高,底泥NH4+-N释放通量先降低后增加,在p H=7时达到最低值;随DO浓度增加,底泥NH4+-N释放通量减小,DO浓度为3 mg/L时NH4+-N释放通量最大;温度越高,NH4+-N释放通量越大。潮白河水体在酸性或碱性条件下,DO浓度越低,温度越高,NH4+-N释放通量越大,该研究结果可为潮白河水质改善提供参考。

地形地貌变化对调水调沙期间黄河口沉积格局的影响

自2002年实施调水调沙以来,由于入海径流、沉积物的通量和组成发生变化,黄河现行河口三角洲叶瓣不断向海淤积造陆,水下三角洲坡度变陡。地形地貌变化对调水调沙期间入海泥沙沉积格局的影响成为黄河口研究的重要科学问题。本文基于Delft3D模型系统,利用岸线、水深和河流水沙数据构建三维水沙数值模型,对2002年、2008年、2014年和2019年调水调沙期间现行河口近岸海域泥沙的输运和沉积过程进行模拟。结果表明,随着水深、岸线的变化,黄河口近岸海域动力环境增强,泥沙的横向输运增强,纵向输运相应减弱;进而导致黄河入海泥沙堆积体的横向长度增加约30%,纵向长度减小约27%,厚度、形态也相应变化。本研究揭示了地形地貌变化条件下,黄河调水调沙期间入海泥沙在河口的沉积格局及动力机制,对深入理解黄河口近岸海域水动力-地貌耦合系统有重要参考价值。

黄河下游高效输沙指标及输沙水量研究

研究提出黄河下游高效输沙的定义和内涵,依据小浪底水库运用方式和黄河不同时段河道水量的功能定位,将汛期的洪水水量定义为狭义输沙水量,汛期的平水期和非汛期水量的主要功能为满足生态、灌溉、发电等需求,不作为输沙水量。建立了单位输沙水量与排沙比及流量含沙量之间的定量关系,提出了高效输沙流量和含沙量指标的定量计算方法,在现状下游河道过流能力条件下,计算了满足高效输沙要求的流量与含沙量搭配指标。提出了维持下游河道全年一定冲淤水平的利津断面狭义输沙水量计算方法,当进入下游年沙量为3亿t时,维持下游河道全年冲淤平衡的利津断面洪水输沙水量为56.2亿~69.6亿m^(3)。