Sources of dissolved and particulate organic material in Loch Vale Watershed,Rocky Mountain National Park,Colorado, USA

The sources of both dissolved organic carbon (DOC) and particulate organic carbon (POC) to an alpine (Sky Pond) and a subalpine lake (The Loch) in Rocky Mountain National Park were explored for four years. The importance of both autochthonous and allochthonous sources of organic matter differ, not only between alpine and subalpine locations, but also seasonally. Overall, autochthonous sources dominate the organic carbon of the alpine lake, while allochthonous sources are a more significant source of organic carbon to the subalpine lake. In the alpine lake, Sky Pond, POC makes up greater than one third of the total organic matter content of the water column, and is related to phytoplankton abundance. Dissolved organic carbon is a product of within-lake activity in Sky Pond except during spring snowmelt and early summer (May–July), when stable carbon isotope ratios suggest a terrestrial source. In the subalpine lake, The Loch, DOC is a much more important constituent of water column organic material than POC, comprising greater than 90% of the spring snowmelt organic matter, and greater than 75% of the organic matter over the rest of the year. Stable carbon isotope ratios and a very strong relation of DOC with soluble Al_(tot) indicate DOC concentrations are almost entirely related to flushing of soil water from the surrounding watershed during spring snowmelt. Stable carbon isotope ratios indicate that, for both lakes, phytoplankton is an important source of DOC in the winter, while terrestrial material of plant or microbial origin contributes DOC during snowmelt and summer.     

Chemical Characteristics of Particulate, Colloidal, and Dissolved Organic Material in Loch Vale Watershed, Rocky Mountain National Park

The chemical relationships among particulate and colloidal organicmaterial and dissolved fulvic acid were examined in an alpine andsubalpine lake and two streams in Loch Vale Watershed, Rocky MountainNational Park. The alpine lake, Sky Pond, had the lowest dissolved organiccarbon (DOC) (0.37 mgC/L), the highest particulate carbon (POC) (0.13mgC/L), and high algal biomass. The watershed of Sky Pond is primarilytalus slope, and DOC and POC may be autochthonous. Both Andrews Creekand Icy Brook gain DOC as they flow through wet sedge meadows. Thesubalpine lake, The Loch, receives additional organic material from thesurrounding forest and had a higher DOC (0.66 mgC/L). Elemental analysis,stable carbon isotopic compositon, and ¹³C-NMR characterizationshowed that: 1) particulate material had relatively high inorganic contentsand was heterogeneous in compositon, 2) colloidal material was primarilycarbohydrate material with a low inorganic content at all sites; and 3)dissolved fulvic acid varied in compositon among sites. The lowconcentration and carbohydrate-rich character of the colloidal materialsuggests that this fraction is labile to microbial degradation and may beturning over more rapidly than particulate fractions or dissolved fulvic acid.Fulvic acid from Andrews Creek had the lowest N content and aromaticity,whereas Sky Pond fulvic acid had a higher N content and lower aromaticitythan fulvic acid from The Loch. The UV-visible spectra of the fulvic acidsdemonstrate that variation in characteristics with sources of organic carboncan explain to some extent the observed non-linear relationship betweenUV-B extinction coefficients and DOC concentrations in lakes.     

Seasonal and spatial distribution of dissolved and particulate organic carbon and bacteria in the bank of an impounding reservoir on the Enns River, Austria

1. Interstitial bacterial abundance, production and ectoenzyme activity were investigated over an annual cycle in an Austrian river when infiltration of oligotrophic river water into a river-bank was artificially enhanced. These microbial parameters were related to porewater chemistry and the concentration of particulate (POC) and dissolved organic carbon (DOC).
2. Porewater chemistry reflected the hydrodynamic mixing of infiltrating river water with riparian groundwater. Seasonal fluctuations in the microbial parameters resulted mainly from changes in temperature and organic matter supply. Seasonal change in porewater chemistry in the river-bank was detectable laterally only within the first metre of the sediment and decreased rapidly with increasing distance from the sediment–water interface.
3. The DOC concentration decreased only slightly during lateral transport through the aquifer, while total organic carbon (TOC) concentration as well as abundance and activity of interstitial bacteria were reduced by up to one order of magnitude within the top metre of the sediment. Retention of incoming particulate matter structured the lateral distribution pattern of TOC concentration. The POC and not the DOC pool was the main source of carbon for interstitial bacteria and, therefore, the quality of POC determines the distribution of microbial metabolism within the riparian zone.     

亚热带常绿阔叶林和杉木人工林有机碳流失动态特征对降雨的响应

揭示亚热带森林土壤有机碳流失规律是制定相应措施以巩固和维持森林生态系统碳汇的关键。然而已有研究存在的监测对象单一、频率过低、时间过短等问题,导致对这一规律的认识仍然不足。选择亚热带典型的常绿阔叶林和杉木人工林为研究对象,每次降雨过后监测其径流量、泥沙量,分析径流和泥沙中的可溶性有机碳（Dissolved organic carbon,DOC）含量以及颗粒有机碳（Particle organic carbon,POC）含量。旨在比较两种森林DOC和POC流失量的差异,并分析二者与降雨量、降雨强度、5 min最大雨强和降雨侵蚀力四个降雨特征值的关联。拟验证以下两个问题：（1）杉木人工林的DOC和POC流失量是否高于常绿阔叶林;（2）降雨侵蚀力对DOC和POC的解释是否优于降雨量、降雨强度和5 min最大雨强。研究结果发现常绿阔叶林径流量、泥沙量、径流水中DOC浓度和POC浓度、DOC和POC流失量均显著高于杉木人工林。回归分析表明常绿阔叶林和杉木人工林DOC和POC流失量与降雨量、降雨强度和降雨侵蚀力呈显著的线性或幂函数相关,其中降雨量与DOC和POC流失量之间的拟合关系最优。常绿阔叶林产流和产沙量高于杉木人工林可能与前者的林下植被生物量较低有关,前者径流水中DOC浓度和POC浓度较高可归因于其较高的总生物量和土壤有机碳含量。在未来森林经营过程中应合理管理林下植被,尽量减少和避免林下植被的抚育伐,从而能够降低有机碳的水土流失,达到巩固和维持森林碳汇的目的。在未来气候变暖导致降水变化背景下,利用降雨量作为预测指标能够较好评估我国亚热带森林有机碳流失的风险。     

Differences in temperature, organic carbon and oxygen consumption among lowland streams

1. Temperature, organic carbon and oxygen consumption were measured over a year at 13 sites in four lowlands streams within the same region in North Zealand, Denmark with the objectives of determining: (i) spatial and seasonal differences between open streams, forest streams and streams with or without lakes, (ii) factors influencing the temperature dependence of oxygen consumption rate, (iii) consequences of higher temperature and organic content in lake outlets on oxygen consumption rate, and (iv) possible consequences of forecasted global warming on degradation of organic matter. 2. High concentrations of easily degradable dissolved (DOC) and particulate organic carbon (POC) were found in open streams downstream of plankton‐rich lakes, while high concentrations of recalcitrant DOC were found in a forest brook draining a forest swamp. Concentrations of predominantly recalcitrant POC and DOC were low in a groundwater‐fed forest spring. Overall, DOC concentration was two to 18 times higher than POC concentrations. 3. Oxygen consumption rate at 20 °C was higher during summer than winter, higher in open than shaded streams and higher in lake outlets than inlets. Rate was closely related to concentrations of chlorophyll and POC but not to DOC. The ratio of oxygen consumption rate to total organic concentrations (DOC + POC), serving as a measure of organic degradability, was highest downstream of lakes, intermediate in open streams and lowest in forest streams. 4. Temperature coefficients describing the exponential increase of oxygen consumption rate between 4 and 20 °C averaged 0.121 °C^?1 (Q₁₀ of 3.35) in 70 measurements and showed no significant variations between seasons and stream sites or correlations with ambient temperature and organic content. 5. Oxygen consumption rate was enhanced downstream of lakes during summer because of higher temperature and, more significantly, greater concentrations of degradable organic carbon. Oxygen consumption rates were up to seven times higher in the stream with three impoundments than in a neighbouring unshaded stream and 21 times higher than in the groundwater‐fed forest spring. 6. A regional climate model has calculated a dramatic 4–5 °C rise in air temperature over Denmark by 2070–2100. If this is realised, unshaded streams are estimated to become 2–3 °C warmer in summer and winter and 5–7 °C warmer in spring and, thereby, increase oxygen consumption rates at ambient temperature by 30–40% and 80–130%, respectively. Faster consumption of organic matter and dissolved oxygen downstream of point sources should increase the likelihood of oxygen stress of the stream biota and lead to the export of less organic matter but more mineralised nutrients to the coastal waters.     

Significance of riverine carbon transport: A case study of a large tropical river, Godavari (India)

Although riverine carbon fluxes are a minor component of the global carbon cycle, the transfer of organic carbon from land to ocean represents a flux of potential carbon storage, irreversible over 103 to 104 a. Future carbon transfers through river basins are expected to accelerate, with respect to both sources and sinks, because of the large-scale human driven land-use and land-cover changes. Thus, the increased amounts of carbon transported to and sequestered in marine sediments (through fertilization by river-borne inorganic nutrients) may be an important net sink for anthropogenic CO2. Particularly, the humid tropics of South Asia are regions very sensitive to this lateral C transport because of high precipitation and high rates of land use and cover change. In this paper we report on the role of upland tributaries in the transport processes influencing the lateral carbon and nitrogen fluxes of the Godavari, a large tropical river of India. By far, dissolved inorganic carbon (DIC) is the dominant form of carbontransport in the river basin. It constitutes as much as 75% to the total carbonload. Particulate and dissolved organic carbon (POC and DOC) fluxes account for21% and 4%, respectively. In the upper basin, DOC fluxes exceed that of POC dueto large-scale anthropogenic activities. In contrast, tributaries in the central basin are characterized by comparable fluxes of POC and DOC. However, downriver POC export is 35% less than the import from upriver and tributaries due to theentrainment of sediments in river channels and dam sites. We argue that for highly disturbed watersheds in tropical regions, downstream transport of sediments and carbon requires long-term sampling programmes.     

Particulate organic matter quality influences nitrate retention and denitrification in stream sediments: evidence from a carbon burial experiment

Organic carbon supply is linked to nitrogen transformation in ecosystems. However, the role of organic carbon quality in nitrogen processing is not as well understood. We determined how the quality of particulate organic carbon (POC) influenced nitrogen transformation in stream sediments by burying identical quantities of varying quality POC (northern red oak (Quercus rubra) leaves, red maple (Acer rubrum) leaves, red maple wood) in stream mesocosms and measuring the effects on nitrogen retention and denitrification compared to a control of combusted sand. We also determined how POC quality affected the quantity and quality of dissolved organic carbon (DOC) and dissolved oxygen concentration in groundwater. Nitrate and total dissolved nitrogen (TDN) retention were assessed by comparing solute concentrations and fluxes along groundwater flow paths in the mesocosms. Denitrification was measured by in situ changes in N₂ concentrations (using MIMS) and by acetylene block incubations. POC quality was measured by C:N and lignin:N ratios and DOC quality was assessed by fluorescence excitation emission matrix spectroscopy. POC quality had strong effects on nitrogen processing. Leaf treatments had much higher nitrate retention, TDN retention and denitrification rates than the wood and control treatments and red maple leaf burial resulted in higher nitrate and TDN retention rates than burial of red oak leaves. Leaf, but not wood, burial drove pore water to severe hypoxia and leaf treatments had higher DOC production and different DOC chemical composition than the wood and control treatments. We think that POC quality affected nitrogen processing in the sediments by influencing the quantity and quality of DOC and redox conditions. Our results suggest that the type of organic carbon inputs can affect the rates of nitrogen transformation in stream ecosystems.     

轮虫培育池生态系统各有机碳库储量及其日变化

2001年5～6月对辽宁省盘锦光合水产有限公司的两种模式轮虫培育池有机碳库储量及动态进行了研究.结果表明,静水池溶解有机碳（DOC）和颗粒有机碳（POC）库储量平均值分别为5.69±2.90 mg·L^-1和24.56 ± 2.12 mg·L^-1;流水池DOC和POC分别为9.61±3.17 mg·L^-1和24.13 ±2.91 mg·L^-1.流水池和静水池TOC、DOC和POC的比例分别为 1∶0.75∶0.25和1∶0.82∶0.18.POC含量高的池塘DOC含量也较高.流水池的POC、DOC周日变动幅度大,静水池昼夜变动幅度小.流水池POC含量白天(5:00～17:00)升高,静水池降低,夜间(15:00～23:00)两池POC含量均降低.从23:00至次日5:00上升,两池分别在17:00和5:00达到高峰.白天(5:00～17:00) 流水池DOC/POC升高,静水池降低;夜间(17:00～23:00)两池均上升,23:00 至次日5:00则呈下降趋势.     

The Role of Stream Water Carbon Dynamics and Export in the Carbon Balance of a Tropical Seasonal Rainforest,Southwest China

A two-year study (2009 ∼ 2010) was carried out to investigate the dynamics of different carbon (C) forms, and the role of stream export in the C balance of a 23.4-ha headwater catchment in a tropical seasonal rainforest at Xishuangbanna (XSBN), southwest China. The seasonal volumetric weighted mean (VWM) concentrations of total inorganic C (TIC) and dissolved inorganic C (DIC) were higher, and particulate inorganic C (PIC) and organic C (POC) were lower, in the dry season than the rainy season, while the VWM concentrations of total organic C (TOC) and dissolved organic C (DOC) were similar between seasons. With increased monthly stream discharge and stream water temperature (SWT), only TIC and DIC concentrations decreased significantly. The most important C form in stream export was DIC, accounting for 51.8% of the total C (TC) export; DOC, POC, and PIC accounted for 21.8%, 14.9%, and 11.5% of the TC export, respectively. Dynamics of C flux were closely related to stream discharge, with the greatest export during the rainy season. C export in the headwater stream was 47.1 kg C ha⁻¹ yr⁻¹, about 2.85% of the annual net ecosystem exchange. This finding indicates that stream export represented a minor contribution to the C balance in this tropical seasonal rainforest.     

温带森林不同海拔土壤有机碳及相关胞外酶活性特征

研究测定了老秃顶子温带森林生态系统7个海拔土壤不同形态碳和相关水解酶、氧化还原酶活性,分析了土壤有机碳及相关酶活性沿海拔梯度的影响因素.结果表明: 随海拔升高,土壤有机碳(SOC)、颗粒有机碳(POC)和可溶性有机碳(DOC)含量显著增加,而在海拔825～1233 m之间没有显著变化,DOC/SOC则显著下降;土壤α葡萄糖苷酶、β葡萄糖苷酶、木糖苷酶和纤维二糖水解酶活性显著增加;土壤SOC、POC、DOC、全氮(TN)含量及土壤含水量(SMC)与土壤水解酶活性呈显著正相关;过氧化物酶(POD)活性在低海拔(675 m)落叶松人工林显著低于其他海拔,POD活性与土壤碳氮(SOC、TN、POC、DOC)含量及SMC呈显著正相关,而土壤多酚氧化酶(PPO)活性在海拔947 m落叶阔叶林带和海拔825 m红松林中较高,且仅与土壤pH呈显著正相关,表明土壤酸度是驱动PPO酶活性的主要因素.在温带森林生态系统中,土壤养分含量和含水量是影响土壤水解酶海拔分布的重要因素.     

Significance of riverine carbon transport: A case study of a large tropical river, Godavari (India)

Although riverine carbon fluxes are a minor component of the global carbon cycle, thetransfer of organic carbon from land to ocean represents a flux of potential carbon storage, irre-versible over 10~3 to 10~4 a. Future carbon transfers through river basins are expected to accelerate,with respect to both sources and sinks, because of the large-scale human driven land-use and land-cover changes. Thus, the increased amounts of carbon transported to and sequestered inmarine sediments (through fertilization by river-borne inorganic nutrients) may be an important netsink for anthropogenic CO_2. Particularly, the humid tropics of South Asia are regions very sensitiveto this lateral C transport because of high precipitation and high rates of land use and cover change. In this paper we report on the role of upland tributaries in the transport processes influ-encing the lateral carbon and nitrogen fluxes of the Godavari, a large tropical river of India. By far,dissolved inorganic carbon (DIC) is the dominant form of carbon transport in the river basin. It con-stitutes as much as 75% to the total carbon load. Particulate and dissolved organic carbon (POC and DOC) fluxes account for 21% and 4%, respectively. In the upper basin, DOC fluxes exceedthat of POC due to large-scale anthropogenic activities. In contrast, tributaries in the central basinare characterized by comparable fluxes of POC and DOC. However, downriver POC export is 35%less than the import from upriver and tributaries due to the entrainment of sediments in river channels and dam sites. We argue that for highly disturbed watersheds in tropical regions, down-stream transport of sediments and carbon requires long-term sampling programmes.     

Dynamics of dissolved and particulate organic carbon in a saline and semiarid stream of southeast Spain (Chicamo stream)

Annual variations in the concentration of dissolved (DOC) and particulate organic carbon (CPOC = Coarse; FPOC = Fine; UPOC = Ultrafine) were studied in a 100 m-reach of the Chicamo stream, an intermittent saline stream in southeast Spain. DOC represented the most important fraction of organic carbon flowing in the Chicamo stream (>98%), with concentrations of about 1.7 mgC l^–1 during most of the year, reaching 2.5 mgC l^–1 in summer. One high flow episode during a rain storm in winter was characterized by a considerably increased concentration of DOC (9.4 mgC l^–1). CPOC was the dominant POC fraction. Positive and significant correlations were found for DOC and discharge, which support the idea of allochthonous inputs due to floods. There was no significant correlation between POC and discharge. No significant correlations were found for DOC or POC with the physico-chemical parameters measured, while a negative significant correlation was found between DOC and temperature. The export of total organic carbon from the drainage basin of the Chicamo stream was low (6.2 × 10^–4 gC m^–2 yr^–1) and typical of streams in arid and semi-arid regions. The results of a Principal Component Analysis defined three different phases. The first consisted of short periods, during which floods provide pulses of allochthonous organic carbon and nutrients, the second a dry phase (summer), defined by biotic interactions, during which the stream could acts as a `sink' of organic matter, and the third and final phase which is characterised by hydrological stability.     

Relationships between bacterial productivity and organic carbon at a soil—stream interface

Microbial communities at soil-stream interfaces may be particularly important in regulating amounts and forms of nutrients that leave upland soils and enter stream ecosystems. While microbial communities are thought to be responsible for key nutrient transformations within near-stream sediments, there is relatively little mechanistic information on factors that control microbial activities in these areas. In this study, we examine the roles of dissolved organic carbon (DOC) vs. particulate organic carbon (POC) as potential controls on rates of bacterial productivity (measured as incorporation of [3H]thymidine into bacterial DNA) and amounts of bacterial biomass (measured as fatty acid yield) in sediments along a transect perpendicular to a soil–stream interface. We hypothesized that spatial patterns in bacterial productivity would vary in response to strong and persistent patterns in pore-water concentrations of DOC that were observed along a soil-stream transect throughout a 2-year period. Our results did not support the existence of such a link between pore-water DOC and bacterial productivity. In contrast, we found bacterial productivity and biomass were related to small-scale spatial variations in sediment POC on 3 of 4 sample dates. While our results indicate that total bacterial productivity in near-stream sediments is not consistently linked to spatial variations in pore-water DOC, it is likely that DOC and POC are not mutually exclusive and the relative contribution of DOC and POC to sedimentary microbes varies temporally and spatially in different riparian habitats. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dial organic carbon fluctuations in a mangrove tidal creek in Sepetiba bay, Southeast Brazil

The carbon (C) concentration and flux, as dissolved organic carbon (DOC), particulate organic carbon (POC) and macrodetritus (MD), were quantified through 4 tidal cycles in a mangrove tidal creek in Southeastern Brazil. DOC was the major fraction of the total C concentration, accounting for 68 and 61% of the total C concentration during ebb and flood periods respectively. Concentrations of DOC (Ebb = 3.41 +/- 0.57 mgC.L-1 and Flood = 3.55 +/- 0.76 mgC.L-1) and POC (Ebb = 1.73 +/- 0.99 mgC.L-1 and Flood = 1.28 +/- 0.45 mgC.L-1) were relatively similar during the four tidal cycles. Macrodetritus presented a wide variation with concentration peaks probably related to external forces, such as winds, which enrich the ebb flow with leaf litter. DOC and POC fluxes depended primarily on tidal and net water fluxes, whereas MD fluxes were not. The magnitude of the DOC and POC fluxes varied with the area flooded at high tide, but not the MD fluxes. DOC was the major form of carbon export to Sepetiba Bay. During the four tidal cycles, the forest exported a total of 1.2 kg of organic carbon per ha, mostly as DOC (60%), followed by POC (22%) and MD (18%).     

虾池生态系各有机碳库的储量

1997年6～8月于山东省海阳市黄海集团公司养虾场,采用围隔实验生态学方法研究了虾池生态系各有机碳库的储量,结果表明:溶解有机碳(DOC)、颗粒有机碳(POC)库储量(mgC/l)平均分别为9.95±2.04及3.10±1.60,DOC/POC比值平均为3.21.POC库中,腐质颗粒碳为总浮游生物碳的2倍.浮游植物碳、浮游动物碳、浮游细菌碳平均分别占总浮游生物碳的53%、13%及34%.腐质碳、总浮游生物碳平均分别占总有机碳(TOC)的92%及8%,腐质碳为总浮游生物碳的11.08倍.     

Distribution and characterization of dissolved and particulate organic matter in Antarctic pack ice

Distribution and composition of organic matter were investigated in Antarctic pack ice in early spring and summer. Accumulation of organic compounds was observed with dissolved organic carbon (DOC) and particulate organic carbon (POC) reaching 717 and 470 μM C, respectively and transparent exopolymeric particles (TEP) up to 3,071 μg Xanthan gum equivalent l⁻¹. POC and TEP seemed to be influenced mainly by algae. Particulate saccharides accounted for 0.2–24.1% (mean, 7.8%) of POC. Dissolved total saccharides represented 0.4–29.6% (mean, 9.7%) of DOC, while dissolved free amino acids (DFAA) accounted for only 1% of DOC. Concentrations of TEP were positively correlated with those of saccharides. Monosaccharides (d-MCHO) dominated during winter–early spring, whereas dissolved polysaccharides did in spring–summer. DFAA were strongly correlated with d-MCHO, suggesting a similar pathway of production. The accumulation of monomers in winter is thought to result from limitation of bacterial activities rather than from the nature of the substrates.     

不同土地利用类型下土壤活性有机碳库的变化

分析了中国科学院沈阳生态试验站不同土地利用类型长期定位试验土壤0～40cm活性有机碳含量,结果表明:0～20cm土层内荒地土壤有机碳、易氧化碳、微生物生物量碳、溶解性有机碳和轻组有机碳含量高于割草地和裸地,而割草地颗粒有机碳含量略高于荒地;在20～40cm土层,割草地土壤有机碳、易氧化碳和颗粒有机碳含量较高,而荒地微生物量碳、溶解性有机碳和轻组有机碳含量较高。不同土地利用类型土壤活性有机碳含量均随着土层加深而递减。土壤微生物量碳、溶解性有机碳和轻组有机碳的分配比例为荒地>割草地>裸地,易氧化碳和颗粒有机碳的分配比例为割草地>荒地>裸地。土壤活性有机碳的分配比例随土层加深而下降,但溶解性有机碳的分配比例变化趋势相反。     

Enzymatic Activities and Prokaryotic Abundance in Relation to Organic Matter along a West–East Mediterranean Transect (TRANSMED Cruise)

The distribution of extracellular enzymatic activities (EEA) [leucine aminopeptidase (LAP), ?-glucosidase (GLU), alkaline phosphatase (AP)], as well as that of prokaryotic abundance (PA) and biomass (PB), dissolved organic carbon (DOC), particulate organic carbon and particulate total nitrogen (POC, PTN), was determined in the epi-, meso-, and bathypelagic waters of the Mediterranean Sea along a West-East transect and at one Atlantic station located outside the Strait of Gibraltar. This study represents a synoptical evaluation of the microbial metabolism during early summer. Decreasing trends with depth were observed for most of the parameters (PA, PB, AP, DOC, POC, PTN). Significant differences between the western and eastern basins of the Mediterranean Sea were found, displaying higher rates of LAP and GLU and lower C/N ratios more in the eastern than in the western areas. Conversely, in the epipelagic layer, PA and PB were found to be higher in the western than in the eastern basins. PB was significantly related to DOC concentration (all data, n = 145, r = 0.53, P < 0.01), while significant correlations of EEA with POC and PTN were found in the epipelagic layer, indicating an active response of microbial metabolism to organic substrates. Specific enzyme activities normalized to cell abundance pointed out high values of LAP and GLU in the bathypelagic layer, especially in the eastern basin, while cell-specific AP was high in the epi- and bathypelagic zone of the eastern basin indicating a rapid regeneration of inorganic P for both prokaryotes and phytoplankton needs. Low activity and abundance characterized the Atlantic station, while opposite trends of these parameters were observed along the Mediterranean transect, showing the uncoupling between abundance and activity data. In the east Mediterranean Sea, decomposition processes increased probably in response to mesoscale structures which lead to organic matter downwelling.     

Carbon flow in a small turbid man-made impoundment

A shallow turbid man-made impoundment was studied intensively for five years. The carbon (C) budget indicated a well balanced system, where phytoplankton productivity and respiratory losses accounted for the major inputs and outputs. The carbon content was dominated by dissolved organic carbon, followed by detritus > fish > phytoplankton > bacteria > zooplankton > zoobenthos.From an analysis of a matrix flow model, three dominant components of C-flow in the system were identified, i.e. dissolved inorganic carbon (DIC), particulate organic carbon (POC) and fish. Phytoplankton and detritus were the important components of POC. The largest flow of C was through the largest pool, dissolved inorganic carbon (DIC), whilst the second largest flow was through the fifth largest pool, the phytoplankton. Phytoplankton was very important in determining the structure of the system, and variations in phytoplankton primary productivity influenced the entire system. This also applied to the input of organic material from macrophytes, but not to variations in the inflow and outflow of water from the impoundment.The input of detrital material from a littoral macrophyte community also markedly influenced the system. DOC was identified as a carbon buffer in the system, and differential flow occurred through this component upon variations in phytoplankton productivity.     

广东省北江流域河流有机碳浓度历史重建

根据河流颗粒有机碳浓度(CPOC)、溶解有机碳浓度(CDOC)与河流总悬浮物含量(CTSS)和流量(Q)的关系,构建广东省北江流域河流有机碳浓度估算模型分别为:CPOC=0.0195×CTSS+0.0589和CDOC = 0.0047×CTSS+0.0027×Q+0.9087.由上述模型重建了北江流域河流有机碳浓度变化历史,结果发现,北江流域河流有机碳主要以颗粒有机碳形式存在;年内分布表现为汛期高于平水期;年际变化多样,但总体上均表现出下降趋势;空间分布上表现为自上游往下有机碳浓度有所下降,但在三水站有所回升.