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1.
Sediment samples were collected from three seawater aquaculture ponds, and soil characteristics, sediment oxygen consumption (SOC), dissolved organic carbon (DOC) and nutrient fluxes were measured using chamber incubations at laboratory. The three ponds were each representing a specific monoculture or polyculture model of sea cucumber. Total organic carbon (TOC) and total nitrogen (TN) contents in the dry sediment ranged from 0.14 to 0.26% and 0.022 to 0.037%, respectively. Total phosphorus (TP) contents in the sediment were more spatially and temporally variable. SOC ranged from 15.29 to 45.86 mmol m–2 d–1 and showed significant differences among the three ponds (p < 0.05). TOC, total carbon (TC) contents, and SOC of the sediment in the pond polycultured with jellyfish increased with culture time, indicating that jellyfish farming enhanced the accumulation of organic matter in the sediments to some extent. Sediment showed net nitrate and ammonium uptake in most ponds and months, and significant differences were found among months (p < 0.05). Dissolved inorganic phosphate (DIP) was released from the sediments in all ponds with low flux rates. DOC was released from the sediment in all ponds and ranged from 0.67 to 1.74 g DOC m–2 d–1. The results suggested that non‐artificial‐feeding sea cucumber culture ponds could not only yield valuable seafood products, but also effectively remove nutrients from the aquaculture systems and consequently alleviate nutrient loadings of the nearby coast.  相似文献   

2.
Beavers, primarily through the building of dams, can deliver significant geomorphic modifications and result in changes to nutrient and sediment fluxes. Research is required to understand the implications and possible benefits of widespread beaver reintroduction across Europe. This study surveyed sediment depth, extent and carbon/nitrogen content in a sequence of beaver pond and dam structures in South West England, where a pair of Eurasian beavers (Castor fiber) were introduced to a controlled 1.8 ha site in 2011. Results showed that the 13 beaver ponds subsequently created hold a total of 101.53 ± 16.24 t of sediment, equating to a normalised average of 71.40 ± 39.65 kg m2. The ponds also hold 15.90 ± 2.50 t of carbon and 0.91 ± 0.15 t of nitrogen within the accumulated pond sediment. The size of beaver pond appeared to be the main control over sediment storage, with larger ponds holding a greater mass of sediment per unit area. Furthermore, position within the site appeared to play a role with the upper‐middle ponds, nearest to the intensively‐farmed headwaters of the catchment, holding a greater amount of sediment. Carbon and nitrogen concentrations in ponds showed no clear trends, but were significantly higher than in stream bed sediment upstream of the site. We estimate that >70% of sediment in the ponds is sourced from the intensively managed grassland catchment upstream, with the remainder from in situ redistribution by beaver activity. While further research is required into the long‐term storage and nutrient cycling within beaver ponds, results indicate that beaver ponds may help to mitigate the negative off‐site impacts of accelerated soil erosion and diffuse pollution from agriculturally dominated landscapes such as the intensively managed grassland in this study. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

3.
内陆水体是大气CO2收支估算的重要组成部分。农业流域分布着大量池塘景观水体,且具备蓄洪抗旱、消纳污染、水产养殖等多种功能。但是,农业流域不同功能的小型池塘CO2排放特征尚不清楚。本研究以极具农业流域代表性的烔炀河流域为研究对象,选取流域中用于水产养殖(养殖塘)、生活污水承纳(村塘)、农业灌溉(农塘)、蓄水(水塘)的4个功能不同的景观池塘,基于为期1年的野外实地观测,以明确农业流域小型池塘CO2排放特征。结果表明,不同功能池塘水体CO2排放差异显著,受养殖活动、生活污水输入和农田灌溉等人类活动影响,养殖塘((80.37±100.39) mmol/(m2·d))、村塘((48.69±65.89) mmol/(m2·d))和农塘((13.50±15.81) mmol/(m2·d))是大气CO2的热点排放源,其CO2排放通量分别是自然蓄水塘((4.52±23.26) mmol/(m2·d))的18、11和3倍。统计分析也表明,该流域池塘CO2排放变化总体上受溶解氧、营养盐等因素驱动。4个不同景观池塘CO2排放通量全年均值为(37.31±67.47) mmol/(m2·d),是不容忽视的CO2排放源,其中养殖塘和村塘具有较高的CO2排放潜力,在未来研究中需要重点关注。  相似文献   

4.
Surface waters associated with peatlands, supersaturated with CO2 and CH4 with respect to the atmosphere, act as important pathways linking a large and potentially unstable global repository of C to the atmosphere. Understanding the drivers and mechanisms which control C release from peatland systems to the atmosphere will contribute to better management and modelling of terrestrial C pools. We used non‐dispersive infra‐red (NDIR) CO2 sensors to continuously measure gas concentrations in a beaver pond at Mer Bleue peatland (Canada); measurements were made between July and August 2007. Concentrations of CO2 in the surface water (10 cm) reached 13 mg C l?1 (epCO2 72), and 26 mg C l?1 (epCO2 133) at depth (60 cm). The study also showed large diurnal fluctuations in dissolved CO2 which ranged in amplitude from ～1·6 mg C l?1 at 10 cm to ～0·2 mg C l?1 at 60 cm depth. CH4 concentration and supersaturation (epCH4) measured using headspace analysis averaged 1·47 mg C l?1 and 3252, respectively; diurnal cycling was also evident in CH4 concentrations. Mean estimated evasion rates of CO2 and CH4 over the summer period were 44·92 ± 7·86 and 0·44 ± 0·25 µg C m?2s?1, respectively. Open water at Mer Bleue is a significant summer hotspot for greenhouse gas emissions within the catchment. Our results suggest that CO2 concentrations during the summer in beaver ponds at Mer Bleue are strongly influenced by biological processes within the water column involving aquatic plants and algae (in situ photosynthesis and respiration). In terms of carbon cycling, soil‐stream connectivity at this time of year is therefore relatively weak. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

5.
Floods have become increasingly important in fluvial export of water, sediment and carbon (C). Using high-frequency sampling, the export of water, sediment and C was examined in the Wuding River catchment on the Chinese Loess Plateau. With groundwater as an important contributor to runoff all year round, floods were relatively less important in the export of water. However, large floods were disproportionately important in exporting sediment and inorganic C (DIC) and organic C (DOC and POC). The three largest floods in each year transported 53.6–97.3 and 41.4–77% of the annual sediment and C fluxes, respectively. An extreme flood in 2017 alone contributed 94.6 and 73.1% of the annual sediment and C fluxes, respectively, in just 7 days, which included 20.3, 92.1 and 35.7% of the annual DOC, POC and DIC fluxes, respectively. A stable carbon isotope (δ13C) analysis of POC indicated that modern soils and C3 plants were its primary source. Furthermore, floods greatly accelerated CO2 degassing due to elevated gas transfer velocity, although stream water CO2 partial pressure (pCO2) exhibited a decreasing trend with flow discharge. Although these results illustrated that increasing runoff diluted pCO2, the timing and magnitude of floods were found to be critical in determining the response of pCO2 to flow dynamics. Low-magnitude floods in the early wet season increased pCO2 because of enhanced organic matter input, while subsequent large floods caused a lower pCO2 due to greatly reduced organic matter supply. Finally, continuous monitoring of a complete flood event showed that the CO2 efflux during the flood (2348 ± 664 mg C m–2 day–1) was three times that under low-flow conditions (808 ± 98 mg C m–2 day–1). Our study suggests that infrequent, heavy storm events, which are predicted to increase under climate change, will greatly alter the transport regimes of sediment and C. © 2020 John Wiley & Sons, Ltd.  相似文献   

6.
Soil CO2 flux is strongly influenced by precipitation in many ecosystem types, yet knowledge of the effects of precipitation on soil CO2 flux in semi‐arid desert ecosystems remains insufficient, particularly for sandy soils. To address this, we investigated the response of sandy soil CO2 flux to rainfall pulses in a desert ecosystem in northern China during August–September 2011. Significant changes (P < 0.05) were found in diel patterns of soil CO2 flux induced by small (2.1 mm), moderate (12.4 mm) and large (19.7 mm) precipitation events. Further analysis indicated that rainfall pulses modified the response of soil CO2 flux to soil temperature, including hysteresis between soil CO2 flux and soil temperature, with Fs higher when Ts was increasing than when Ts was decreasing, and the linear relationship between them. Moreover, our results showed that rainfall could result in absorption of atmospheric CO2 by soil, possibly owing to mass flow of CO2 induced by a gradient of gas pressure between atmosphere and soil. After each precipitation event, soil CO2 flux recovered exponentially to pre‐rainfall levels with time, with the recovery times exhibiting a positive correlation with precipitation amount. On the basis of the amounts of precipitation that occurred at our site during the measurement period (August–September), the accumulated rain‐induced carbon absorption evaluated for rainy days was 1.068 g C m?2; this corresponds approximately to 0.5–2.1% of the net primary production of a typical desert ecosystem. Thus, our results suggest that rainfall pulses can strongly influence carbon fluxes in desert ecosystems. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

7.
Short‐lived fallout isotopes, such as beryllium‐7 (7Be), are increasingly used as erosion and sediment tracers in watersheds. 7Be is produced in the atmosphere and delivered to the Earth's surface primarily in precipitation. However, relatively little has been published about the variation in 7Be wet deposition caused by storm type and vegetation cover. Our analysis of precipitation, throughfall, and sediments in two forested, headwater catchments in the mid‐Atlantic USA indicates significant variation in isotope deposition with storm type and storm height. Individual summer convective thunderstorms were associated with 7Be activity concentrations up to 5.0 Bq l?1 in precipitation and 4.7 Bq l?1 in throughfall, while single‐event wet depositional fluxes reached 168 Bq m?2 in precipitation and 103 Bq m?2 in throughfall. Storms originating from the continental USA were associated with lower 7Be activity concentrations and single‐event wet depositional fluxes for precipitation (0.7–1.2 Bq l?1 and 15.8–65.0 Bq m?2) and throughfall (0.1–0.3 Bq l?1 and 13.5–98.9 Bq m?2). Tropical systems had relatively low activity concentrations, 0.2–0.5 Bq l?1 in precipitation and 0.2–1.0 Bq l?1 in throughfall, but relatively high single‐event depositional fluxes due to large rainfall volumes, 32.8–67.6 Bq m?2 in precipitation and 25.7–134 Bq m?2 in throughfall. The largest sources of 7Be depositional variation were attributed to storm characteristics including precipitation amount and maximum storm height. 7Be activity associated with fluvial suspended sediments also exhibited the highest concentration and variability in summer (175–1450 Bq kg?1). We conclude the dominant source of variation on event‐level 7Be deposition is storm type. Our results illustrate the complex relationships between 7Be deposition in precipitation and throughfall and demonstrate event‐scale relationships between the 7Be in precipitation and on suspended sediment. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

8.
The sinks/sources of carbon in the Yellow Sea(YS) and East China Sea(ECS), which are important continental shelf seas in China, could exert a great influence on coastal ecosystem dynamics and the regional climate change process. The CO_2 exchange process across the seawater-air interface, dissolved and particulate carbon in seawater, and carbon burial in sediments were studied to understand the sinks/sources of carbon in the continental shelf seas of China. The YS and the ECS generally have different patterns of seasonal air-sea CO_2 exchange. In the YS, regions west of 124°E can absorb CO_2 from the atmosphere during spring and winter, and release CO_2 to the atmosphere during summer and autumn. The entire YS is considered as a CO_2 source throughout the year with respect to the atmosphere, but there are still uncertainties regarding the exact air-sea CO_2 exchange flux. Surface temperature and phytoplankton production were the key controlling factors of the air-sea CO_2 exchange flux in the offshore region and nearshore region of the YS, respectively. The ECS can absorb CO_2 during spring, summer, and winter and release CO_2 to the atmosphere during autumn. The annual average exchange rate in the ECS was-4.2±3.2 mmol m~(-2) d~(-1) and it served as an obvious sink for atmospheric CO_2 with an air-sea exchange flux of 13.7×10~6 t. The controlling factors of the air-sea CO_2 exchange in the ECS varied significantly seasonally. Storage of dissolved inorganic carbon(DIC) and dissolved organic carbon(DOC) in the YS and the ECS were 425×10~6 t and 1364×10~6 t, and 28.2×10~6 t and 54.1×10~6 t,respectively. Long-term observation showed that the DOC content in the YS had a decreasing trend, indicating that the "practical carbon sink" in the YS was decreasing. The total amount of particulate organic carbon(POC) stored in the YS and ECS was10.6×10~6 t, which was comparable to the air-sea CO_2 flux in these two continental shelf seas. The amounts of carbon sequestered by phytoplankton in the YS and the ECS were 60.42×10~6 t and 153.41×10~6 t, respectively. Artificial breeding of macroalgae could effectively enhance blue carbon sequestration, which could fix 0.36×10~6–0.45×10~6 t of carbon annually. Organic carbon(OC) buried in the sediments of the YS was estimated to be 4.75×10~6 t, and OC of marine origin was 3.03×10~6 t, accounting for5.0% of the TOC fixed by phytoplankton primary production. In the ECS, the corresponding depositional flux of OC in the sediment was estimated to be 7.4×10~6 t yr~(-1), and the marine-origin OC was 5.5×10~6 t, accounting for 5.4% of the phytoplankton primary production. Due to the relatively high average depositional flux of OC in the sediment, the YS and ECS have considerable potential to store a vast amount of "blue carbon."  相似文献   

9.
With the recovery of the European beaver (Castor fiber) and their capacity to engineer fluvial landscapes, questions arise as to how they influence sediment transport, including the spatio‐temporal trends and patterns of sedimentation in beaver ponds. The Chevral river (Ardennes, Belgium) contains two beaver dam sequences, which appeared in 2004. Volumes of sediment deposited behind the dams were measured, and grain‐size distribution patterns were determined. Flow discharges and sediment fluxes were measured at the inflow and outflow of each dam sequence. Between 2004 and 2011, 1710.1 m3 of sediment was deposited behind the beaver dams, with an average sediment thickness of 25.1 cm. The thickness of the sediment layer was significantly (p < 0.001) related to the area of the beaver ponds. Along the stream, beaver pond sediment thickness displayed a sinusoidal deposition pattern, in which ponds with thick sediment layers were preceded by a series of ponds with thinner sediment layers. A downstream textural coarsening in the dam sequences was also observed, probably because of dam failures subsequent to surges. Differences in sediment flux between the inflow and outflow at the beaver pond sequence were related to the river hydrograph, with deposition taking place during the rising limbs and slight erosion during the falling limbs. The 7‐year‐old sequences have filtered 190.19 ton of sediment out of the Chevral river, which is of the same order of magnitude as the 374.4 ton measured in pond deposits, with the difference between the values corresponding to beaver excavations (60.24 ton), inflow from small tributaries, and runoff from the valley flanks. Hydrogeomorphic effects of C. fiber and Castor canadensis activity are similar in magnitude. The detailed analysis of sedimentation in beaver pond sequences confirms the potential of beavers to contribute to river and wetland restoration, and catchment management. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

10.
Abstract

Agricultural land use in the area of water bodies is generally considered to increase the nutrient status of the water body water and sediments, but is this also the case for already nutrient-rich fish ponds? We studied 83 fish ponds in the Dombes region, France, where 1100 ponds are located in a heterogeneous agricultural landscape. Different water and sediment parameters were analysed for ponds and in ditches after rainfall events. Land use was studied in the primary catchment of ponds and in a 100-m zone around ponds. Soil parameters of different land-use types were analysed and farmers interviewed about agricultural practices. Increasing cropping area in the catchment of the ponds is significantly correlated to higher PO4 3- concentration of pond water and to a lower degree, also to NO3 ?, but only in certain years with higher rainfall and with a more uneven distribution in spring. Sediment parameters were not significantly influenced. High NO3- concentration in the water of a ditch during significant rainfall events was found for a cropland dominated catchment.

Citation Wezel, A., Arthaud, F., Dufloux, C., Renoud, F., Vallod, D., Robin, J., and Sarrazin, B., 2013. Varied impact of land use on water and sediment parameters in fish ponds of the Dombes agro-ecosystem, France. Hydrological Sciences Journal, 58 (4), 854–871.  相似文献   

11.
The objective of this study was to measure the effects of invertebrates on the physical characteristics and microbial processes in hyporheic sediments. We investigated the impacts of an assemblage of three taxa (asellids, chironomid larvae, and tubificid worms) on sediment distribution, water fluxes, sediment organic carbon, biofilm (attached bacteria) characteristics, and O2, dissolved organic carbon NO3?, NO2?, and NH4+ concentrations in slow filtration sand–gravel columns. The results showed that invertebrates clearly modified the distribution of particles in the sediment column, probably because of the structures (tubes, macropores, and faecal pellets) produced by the three taxa in the sediment. Our assessment of water fluxes indicated that invertebrate activities led to an increase in the porosity of the sediment columns. In addition, aerobic (O2 consumption) and anaerobic (denitrification and fermentative decomposition of organic matter) microbial processes occurring in the sediment were stimulated in the presence of invertebrates. Finally, the present study demonstrates that invertebrates can act as ecosystem engineers in heterogeneous sediments that are under the influence of an advective flux of water. The solute residence time increased in columns containing the faunal assemblage. Micro‐organisms used more dissolved organic matter and nutrients in the presence of invertebrates because invertebrate activities increased the contact between the biofilm and water. We conclude that engineering by invertebrates in natural conditions modifies characteristics of the hyporheic zone and thereby enhances both the porosity of the sediment and the solute transport across the benthic interface. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

12.
马松  魏榆  韩翠红  晏浩  刘再华  孙海龙  鲍乾 《湖泊科学》2021,33(6):1701-1713
为探究筑坝后不同水库物理、化学、生物过程对水化学和碳循环的影响,本研究对贵州三岔河流域的平寨水库、普定水库以及猫跳河流域的红枫湖水库进行研究,于2018年3月2019年1月分别在入库河流和库区采集了分层水样和沉降颗粒物,并探究水中主要离子及颗粒物通量的时空变化特征及其控制因素.结果表明,水体主要离子的主要来源受碳酸盐溶解影响,并且离子浓度受光合作用控制.红枫湖水库水体水化学类型为Ca-Mg-HCO3-SO4型,普定水库、平寨水库水化学类型均为Ca-HCO3-SO4.夏季藻类光合作用诱导碳酸盐沉淀导致水体表层Ca2+、HCO3-及溶解态Si浓度降低,其降低幅度分别为20.87%~44.25%、33.12%~51.18%、48.55%~96.34%.此外,藻类光合作用也影响C、N、Si等生源要素间的化学计量关系.Mg2+/Ca2+比值在水体垂向剖面上主要受碳酸钙沉淀的控制,而在不同水库之间则主要受流域岩性的控制.根据沉积物捕获器通量计算的平寨水库、普定水库、红枫湖水库夏季颗粒无机碳沉积通量分别为0.74、1.36、0.27 t/（km2·d）,而根据水体Ca2+浓度降低计算的通量分别为0.31~0.64、0.35~0.99、0.09~0.29 t/（km2·d）,根据水体HCO3-浓度降低计算的通量分别为0.30~0.65、0.29~1.26、0.12~0.33 t/（km2·d）.其红枫湖水库无机碳沉降通量的实测值与计算值接近,而平寨、普定水库实际沉降通量高于计算值,这可能是有外源输入导致.因此,利用水化学分层数据能对喀斯特水库中的无机碳沉降通量进行合理估算,并且能够得到较好的估算结果,从而指示碳循环的过程.  相似文献   

13.
The water quality of an urban pond in the thickly populated area of Varanasi city (5 km apart) was studied and compared with a rural pond in the Banaras Hindu University campus for transparency, conductivity and nutrient richness (Cl?, SO, PO? P, NO? N, organic carbon, Ca2+, Mg2+, K+, Na+) at three depths (surface, 1.5 m, 3 m) at monthly intervals between February 1982 and February 1983. This was done to assess the effects of urban surroundings of a very ancient city sector on pond water quality in reference to that of a rural pond. The rural pond had a lush growth of 12 macrophytic species, whereas the urban one had only such a growth with many phytoplanktonic species. Transparency was maximum in the winter season and the rural pond water was more transparent, while the electrolytical conductance was maximum in the rainy season, being higher in the urban pond. Electrolytical conductivity was negatively correlated to transparency: urban: EC = 1081.612–6.575 T, r2 = 0.897, F1,11 = 96, P <0.005; rural: EC = 728.981–4.328 T, r2 = 0.892, F1,11 = 91, P <0.005. Chloride and sulphate concentrations were highest in summer months, but the former was much higher in the urban pond while the latter in the rural pond. NO3–N was highest in the rainy season in the rural pond and in early winter in the urban one and showed a definite trend with change in depth. PO4–P also varied with depth and time and it was higher in late summer and the early rainy season in the rural pond and in early winter in the urban pond. But both these nutrients were much higher in the urban pond. The maximum organic carbon concentration was found in the rainy season in the rural pond and in summer months in the urban pond. The variation of organic carbon with depth was distinct. Both summer and winter seasons showed almost similar values of calcium concentration in the rural pond, but in the urban pond it was maximum in summer. Organic carbon and calcium were higher in the urban pond. The magnesium concentration was highest in rainy months in both the ponds, but the periodicity of the minimum differed. The distribution of calcium with depth was not well defined. The highest concentration of potassium was found in the winter season in both the ponds. The sodium concentration in the rural pond was observed maximum in summer and minimum in the rainy season, but in the urban pond the trend was different. The variation of potassium and sodium with depth was not well defined. Magnesium and sodium were also higher in the urban pond but potassium was almost at the same concentration in both the ponds. The effect of urbanisation may be one of the factors which might be responsible to the shift of the species composition towards phytoplanktonic flora.  相似文献   

14.
The precipitation of freshwater carbonates (tufa) along karstic rivers is enhanced by degassing of carbon dioxide (CO2) downstream of karstic springs. However, in most karstic springs CO2 degassing is not enough to force the precipitation of tufa sediments. Little is known about the role of dissolution of gypsum or dolomite in the hydrochemistry of these systems and how this affects the formation of tufa deposits. Here we present a monitoring study conducted over a year in Trabaque River (Spain). The river has typical karst hydrological dynamics with water sinking upstream and re‐emerging downstream of the canyon. Mixing of calcium–magnesium bicarbonate and calcium sulphate waters downstream of the sink enhances the dissolution of carbonates and potentially plays a positive role in the formation of tufa sediments. However, due to the common‐ion effect, dissolution of dolomite and/or gypsum causes precipitation of underground calcite cements as part of the incongruent dissolution of dolomite/dedolomitization process, which limits the precipitation of tufa sediments. Current precipitation of tufa is scant compared to previous Holocene tufa deposits, which likely precipitated from solutions with higher saturation indexes of calcite (SIcc values) than nowadays. Limited incongruent dissolution of dolomite/dedolomitization favours higher SIcc values. This circumstance occurs when waters with relatively high supersaturation of dolomite and low SO42? composition sink in the upper sector of the canyon. In such a scenario, the process of mixing waters enhances the exclusive dissolution of limestones, preventing the precipitation of calcite within the aquifer and favouring the increase of SIcc values downstream of the springs. Such conditions were recorded during periods of high water level of the aquifers and during floods. This research shows that the common‐ion effect caused by the dissolution of gypsum and/or dolomite rocks can limit [or favour] the precipitation of tufa sediments depending on the occurrence [or not] of incongruent dissolution of dolomite/dedolomitization. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

15.
The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365 mg m−2 d−1, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (Cphyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546 mg m−2 d−1 and 22 mg chl a m−2 d−1, respectively) and minimum values during winter (22 mg m−2 d−1 and 0.1 mg chl a m−2 d−1, respectively). The contribution of Cphyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of Cphyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, Cphyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal Cphyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension.  相似文献   

16.
Cosmogenic 7Be is a natural tracer of short‐term hydrological processes, but its distribution in upland fluvial environments over different temporal and spatial scales has not been well described. We measured 7Be in 450 sediment samples collected from perennial channels draining the middle of the Connecticut River Basin, an environment that is predominantly well‐sorted sand. By sampling tributaries that have natural and managed fluctuations in discharge, we find that the 7Be activity in thalweg sediments is not necessarily limited by the supply of new or fine‐grained sediment, but is controlled seasonally by atmospheric flux variations and the magnitude and frequency of bed mobilizing events. In late winter, 7Be concentrations in transitional bedload are lowest, typically 1 to 3 Bq kg?1 as 7Be is lost from watersheds via radioactive decay in the snowpack. In mid‐summer, however, 7Be concentrations are at least twice as high because of increased convective storm activity which delivers high 7Be fluxes directly to the fluvial system. A mixed layer of sediment at least 8 cm thick is maintained for months in channels during persistent low rainfall and flow conditions, indicating that stationary sediments can be recharged with 7Be. However, bed mobilizing rain on snowmelt events in late Spring can ‘reset’ 7Be amounts and concentrations in the channel as previously buried ‘old’ sediment with low 7Be is mixed into the thalweg. We conclude that given proper temporal and spatial sampling, 7Be is a valuable tracer of seasonal‐timescale mass transport and exchange in coarse‐grained fluvial systems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

17.
Sediment movement during erosion, transport and deposition greatly affects the ecosystem of river basins. However, there is presently no consensus as to whether particular river basins act as carbon dioxide (CO2) sources or sinks related to these processes. This paper introduces a rule‐of‐thumb coordinate system based on sediment delivery ratio (SDR) and soil humin content (SHC) in order to evaluate the net effect of soil erosion, sediment transport and deposition on CO2 flux in river basins. The SDR–SHC system delineates CO2 source and sink areas, and further divides the sink into strong and weak areas according to the world‐average line. The Yellow River Basin, most severely suffering soil erosion in the world, only appears to be a weak erosion‐induced CO2 sink in this system. The average annual CO2 sequestration is ~0·235 Mt from 1960 to 2008, a relatively small value considering its 3·1% contribution to the World's sediment discharge. The temporal analysis shows that the Yellow River Basin was once a source in the 1960s, but changed its role to become a weak sink in the past 40 years due to both anthropogenic and climatic influences. The spatial analysis identifies the middle sub‐basin as the main source region, and the lower as the main sink. For comparison, sediment‐movement‐related CO2 fluxes of eight other major basins in four continents are examined. It is found that the six basins considered in the Northern Hemisphere appear to be sinks, while the other two in the Southern Hemisphere act as sources. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

18.
A numerical model (sediment trap efficiency for small ponds—STEP) is developed to simulate sediment deposition in small ponds (i.e. <1 ha) and to calculate the sediment trap efficiency (STE). The algorithms are kept simple to allow the model to simulate larger time periods (i.e. several years). Eight runs with an experimental pond were executed to test the model. The STEP model produces reasonable predictions of STE as well as the shape and magnitude of the effluent sediment concentration graph. The model efficiency of STEP for the prediction of STE equals 0·38 and the root mean square error equals 4·7%. Similar models, such as DEPOSITS and CSTRS, were inefficient in predicting the experimental results. The STEP model was used to simulate the long‐term (33 years) STE of small retention ponds in central Belgium using 10‐min rainfall data. For a typical pond (1000 m2) with a catchment area of 25 ha, annual STE can vary from 58 to 100%, with a long‐term STE of only 68%. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

19.

Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were −7.4 and 5.4 g·m−2·d−1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were −12.8 and 5.8 g·m−2·d−1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m−2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m−2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m−2·s−1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature.

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20.
Spatial and temporal variability of hydrological responses affecting surface water dissolved organic carbon (DOC) concentrations are important for determining upscaling patterns of DOC export within larger catchments. Annual and intra‐annual variations in DOC concentrations and fluxes were assessed over 2 years at 12 sites (3·40–1837 km2) within the River Dee basin in NE Scotland. Mean annual DOC fluxes, primarily correlated with catchment soil coverage, ranged from 3·41 to 9·48 g m?2 yr?1. Periods of seasonal (summer–autumn and winter–spring) DOC concentrations (production) were delineated and related to discharge. Although antecedent temperature mainly determined the timing of switchover between periods of high DOC in the summer‐autumn and low DOC in winter‐spring, inter‐annual variability of export within the same season was largely dependent on its associated water flux. DOC fluxes ranged from 1·39 to 4·80 g m?2 season?1 during summer–autumn and 1·43 to 4·15 g m?2 season?1 in winter–spring.Relationships between DOC areal fluxes and catchment scale indicated that mainstem fluxes reflect the averaging of highly heterogeneous inputs from contrasting headwater catchments, leading to convergent DOC fluxes at catchment sizes of ca 100 km2. However, during summer–autumn periods, in contrast to winter–spring, longitudinal mainstem DOC fluxes continue to decrease, most likely because of increasing biological processes. This highlights the importance of considering seasonal as well as annual changes in DOC fluxes with catchment scale. This study increases our understanding of the temporal variability of DOC upscaling patterns reflecting cumulative changes across different catchment scales and aids modelling of carbon budgets at different stages of riverine systems. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

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