Bioclimatic influence on water chemistry and dissolved organic matter in shallow temperate lakes of Andean Patagonia: A gradient approach

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Land use and hydrologic flowpaths interact to affect dissolved organic matter and nitrate dynamics

The transport and transformation of dissolved organic matter (DOM) and dissolved inorganic nitrogen (DIN) through the soil profile impact down-gradient ecosystems and are increasingly recognized as important factors affecting the balance between accumulation and mineralization of subsoil organic matter. Using zero tension and tension lysimeters at three soil depths (20, 40, 60 cm) in paired forest and maize/soybean land uses, we compared dissolved organic C (DOC), dissolved organic N (DON) and DIN concentrations as well as DOM properties including hydrophilic-C (HPI-C), UV absorption (SUVA₂₅₄), humification index and C/N ratio. Soil moisture data collected at lysimeter locations suggest zero tension lysimeters sampled relatively rapid hydrologic flowpaths that included downward saturated flow through the soil matrix and/or rapid macropore flow that is not in equilibrium with bulk soil solution whereas tension lysimeters sampled relatively immobile soil matrix solution during unsaturated conditions. The effect of land use on DOC and DON concentrations was largely limited to the most shallow (20 cm) sampling depth where DOC concentrations were greater in the forest (only zero tension lysimeters) and DON concentrations were greater in the cropland (both lysimeter types). In contrast to DOC and DON concentrations, the effect of land use on DOM properties persisted to the deepest sampling depth (60 cm), suggesting that DOM in the cropland was more decomposed regardless of lysimeter type. DOC concentrations and DOM properties differed between lysimeter types only in the forest at 20 cm where soil solutions collected with zero tension lysimeters had greater DOC concentrations, greater SUVA₂₅₄, greater humification index and lower HPI-C. Our data highlight the importance of considering DOM quality in addition to DOC quantity, and indicate long-term cultivation reduced the delivery of relatively less decomposed DOM to all soil depths.     

Bacterial Community Structure in Patagonian Andean Lakes Above and Below Timberline: From Community Composition to Community Function

Lakes located above the timberline are remote systems with a number of extreme environmental conditions, becoming physically harsh ecosystems, and sensors of global change. We analyze bacterial community composition and community-level physiological profiles in mountain lakes located in an altitude gradient in North Patagonian Andes below and above the timberline, together with dissolved organic carbon (DOC) characterization and consumption. Our results indicated a decrease in 71 % of DOC and 65 % in total dissolved phosphorus (TDP) concentration as well as in bacteria abundances along the altitude range (1,380 to 1,950 m a.s.l.). Dissolved organic matter (DOM) fluorescence analysis revealed a low global variability composed by two humic-like components (allochthonous substances) and a single protein-like component (autochthonous substances). Lakes below the timberline showed the presence of all the three components, while lakes above the timberline the protein-like compound constituted the main DOC component. Furthermore, bacterial community composition similarity and ordination analysis showed that altitude and resource concentration (DOC and TDP) were the main variables determining the ordination of groups. Community-level physiological profiles showed a mismatch with bacteria community composition (BCC), indicating the absence of a relationship between genetic and functional diversity in the altitude gradient. However, carbon utilization efficiencies varied according to the presence of different compounds in DOM bulk. The obtained results suggest that the different bacterial communities in these mountain lakes seem to have similar metabolic pathways in order to be able to exploit the available DOC molecules.     

Long-term trends of epilimnetic and hypolimnetic bacteria and organic carbon in a deep holo-oligomictic lake

We analysed the long-term dynamics (1980–2007) of hypolimnetic and epilimnetic bacterial abundances and organic carbon concentrations, both dissolved (DOC) and particulate (POC), in the deep holo-oligomictic Lake Maggiore, included in the Southern Alpine Lakes Long-Term Ecological Research (LTER) site. During the 28 years of investigation, bacterial abundance and POC concentrations did not decrease with declining phosphorus concentrations, while DOC concentrations showed a pronounced decrease in the epi- and hypolimnion. We used the annual mean total lake heat content and total annual precipitation as climate-related variables, and in-lake total phosphorus as a proxy for trophic state. The model (forward stepwise regression, FSR) showed that reduced anthropogenic pressure was more significant than climate change in driving the trend in DOC concentrations. Bacterial dynamics in the hypolimnion mirrored the fluctuations observed in the epilimnion, but average cell abundance was three times lower. The FSR model indicates that bacterial number variability was dependent on POC in the epilimnion and DOC in the hypolimnion. In the hypolimnion, cell biovolumes for rod and coccal morphotypes were significantly larger than in the epilimnion.     

杉木人工林土壤可溶性有机质及其与土壤养分的关系

通过在福建省来舟林场对不同栽植代数杉木人工林土壤可溶性有机碳(DOC)和氮(DON)及土壤养分的研究,其结果表明,随着杉木栽植代数的增加林地土壤DOC和DON含量逐渐下降,在0～10cm土层内第3代杉木林土壤DOC和DON含量分别是第1代杉木林的83.9%和87.1%、第2代杉木林的90.6%和96.9%,在10～20cm土层内第3代杉木林土壤DOC和DON含量分别是第1代杉木林的80.2%和81.5%、第2代杉木林的81.8%和90.0%。在不同林地和土层内土壤DOC含量之间的差异性达到了显著或极显著水平,而DON含量之间的差异性不显著。不同栽植代数杉木林土壤养分的变化趋势与DOM一致,随着杉木连栽,土壤养分含量呈下降趋势。在0～10cm土层内第3代杉木林土壤全氮、全钾、铵态氮和速效钾含量分别是第1代杉木林的83.1%、60.4%、68.1%和44.3%,是第2代杉木林的84.6%、68.5%、74.4%和58.7%;在10～20cm土层内第3代杉木林土壤全氮、全钾、铵态氮和速效钾含量分别是第1代杉木林的74.0%、53.4%、57.6%和54.6%,是第2代杉木林的94.8%、59.5%、74.3%和65.5%。经相关性分析,在各土层内土壤DOC和DON含量与土壤全氮、全钾、铵态氮和速效钾等土壤养分含量存在着不同程度的相关性。     

隔离降雨对亚热带米槠天然林土壤可溶性有机质数量及光谱学特征的影响

全球气候变化背景下区域降雨格局变化可能深刻影响土壤可溶性有机质(DOM)的数量和质量.为了解亚热带森林土壤DOM对降雨减少的响应,通过6年不同强度(对照、-30%、-60%)的隔离降雨模拟试验,采用光谱技术,研究了降雨减少对亚热带米槠天然林不同深度土壤DOM数量和结构的影响.结果表明: 与对照相比,隔离降雨使0～10 cm土层中可溶性有机碳(DOC)和可溶性有机氮(DON)含量显著降低,其中-30%处理DOC下降幅度小于DON, 而-60%处理DOC下降幅度大于DON,0～10 cm土层中DOC和DON含量都显著高于10～20 cm土层.-30%处理土壤DOM中源于微生物代谢的芳香类腐殖质和烷烃比例上升;-60%处理土壤DOM中微生物代谢产物的相对贡献率减少.除了隔离降雨后水分变化等直接影响外,微生物活性也是本试验区影响DOM数量和结构的重要因素.     

Temporal and spatial distributions of dissolved organic carbon and nitrogen in two small lakes on the Southwestern China Plateau

Temporal and spatial distributions of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), chlorophyll-a and inorganic nitrogen were investigated in two small mountainous lakes (Lake Hongfeng and Baihua), on the Southwestern China Plateau, based on almost 2 years’ field observation. DOC concentrations ranged from 163 μM to 248 μM in Lake Hongfeng and from 143 μM to 308 μM in Lake Baihua, respectively, during the study period. DON concentrations ranged from 7 μM to 26 μM in Lake Hongfeng and from 14 μM to 47 μM in Lake Baihua. DOC showed vertical heterogeneity with higher concentrations in the epilimnion than in the hypolimnion during the stratification period. The DON concentration profiles appeared to be more variable than the DOC profiles. Apparent DON maxima occurred in the upper layer of water. In Lake Hongfeng, DOC concentration in the surface water was highest at the end of spring and early summer. DON concentration was 2–5 μM higher in May 2003 and in June 2004 than in adjacent months. DOC and chlorophyll-a concentrations were significantly correlated (r = 0.79, P < 0.05). The period of highest concentrations of DOC in Lake Hongfeng was also the season of concentrated rainfall. Algae activity and allochthonous input might result in an increase of DOC and DON concentrations together. In Lake Baihua, the maximum concentrations of DOC and DON in the surface water occurred simultaneously in May 2003 and February 2004. DOC concentrations were significantly correlated with DON (r = 0.90, P < 0.01), indicating the common sources. Allochthonous input, biological processes, stratification and mixing were the most important factors controlling the distributions and cycling of dissolved organic matter (DOM) and inorganic nitrogen in these two lakes. Inference from the corresponding vertical distributions of DOM and inorganic nitrogen indicated that DOM played potential roles in the internal loading of nitrogen and metabolism in the water body in these small lakes. The carbon/nitrogen (C/N) ratio showed a potential significance for tracing the source and biogeochemical processes of DOM in the lakes. These results are of significance in the further understanding of biogeochemical cycling and environmental effects of DOM and nitrogen in lake ecosystems.     

氮沉降对杉木人工幼林土壤溶液可溶性有机物质浓度及光谱学特征的影响

为探究氮沉降对亚热带杉木人工幼林土壤溶液可溶性有机物质(DOM)浓度及光谱学特征的影响,采用负压法,对0～15和15～30 cm土层土壤溶液DOM进行了2年的动态监测及光谱学特征研究.结果表明:氮沉降显著减少了各土层土壤溶液可溶性有机碳(DOC)浓度,增加了芳香化指数(AI)及腐殖化指数(HIX),但对可溶性有机氮(DON)无显著影响.土壤溶液DOM浓度存在明显的季节变动,夏秋季显著高于春冬季.傅里叶红外光谱结果表明,森林土壤溶液DOM在6个区域的相似位置存在吸收峰,其中1145～1149 cm^-1的吸收峰最强.三维荧光光谱表明,DOM主要以类蛋白质物质(Ex/Em=230 nm/300 nm)和微生物降解产物(Ex/Em=275 nm/300 nm)为主,施氮使0～15 cm土层类蛋白质物质减少.氮沉降可能主要是通过降低土壤pH、抑制土壤碳矿化和刺激植物生长等途径显著抑制土壤溶液DOC浓度,而表层被抑制的DOC成分以类蛋白质物质和羧酸盐物质为主.氮沉降短期可能有利于土壤肥力的储存,但随着氮沉降量的积累,土壤中营养物质将难以得到有效利用.     

Climate‐related changes of soil characteristics affect bacterial community composition and function of high altitude and latitude lakes

Lakes at high altitude and latitude are typically unproductive ecosystems where external factors outweigh the relative importance of in‐lake processes, making them ideal sentinels of climate change. Climate change is inducing upward vegetation shifts at high altitude and latitude regions that translate into changes in the pools of soil organic matter. Upon mobilization, this allochthonous organic matter may rapidly alter the composition and function of lake bacterial communities. Here, we experimentally simulate this potential climate‐change effect by exposing bacterioplankton of two lakes located above the treeline, one in the Alps and one in the subarctic region, to soil organic matter from below and above the treeline. Changes in bacterial community composition, diversity and function were followed for 72 h. In the subarctic lake, soil organic matter from below the treeline reduced bulk and taxon‐specific phosphorus uptake, indicating that bacterial phosphorus limitation was alleviated compared to organic matter from above the treeline. These effects were less pronounced in the alpine lake, suggesting that soil properties (phosphorus and dissolved organic carbon availability) and water temperature further shaped the magnitude of response. The rapid bacterial succession observed in both lakes indicates that certain taxa directly benefited from soil sources. Accordingly, the substrate uptake profiles of initially rare bacteria (copiotrophs) indicated that they are one of the main actors cycling soil‐derived carbon and phosphorus. Our work suggests that climate‐induced changes in soil characteristics affect bacterioplankton community structure and function, and in turn, the cycling of carbon and phosphorus in high altitude and latitude aquatic ecosystems.     

中亚热带不同类型米槠林凋落枝溶解性有机质动态及光谱学特性

以中亚热带不同类型米槠林为对象,研究了米槠天然林、次生林和人工林凋落枝在生产量持续增加阶段、高峰阶段、持续减少3种生产阶段溶解性有机质的动态及光谱学特性。结果表明:凋落枝生产阶段和森林类型显著影响米槠凋落枝溶解性有机质含量及光谱学特征。米槠天然林在凋落枝生产量持续减少阶段溶解性有机碳(DOC)含量较高,溶解性有机质在254、260和280 nm处的特征紫外吸光值(SUVA₂₅₄、SUVA₂₆₀、SUVA₂₈₀)较低,表明该阶段天然林凋落枝质量较高,具有较高的以溶解性有机质为载体的物质循环效率。米槠人工林在凋落枝生产量高峰阶段具有较高的总氮(TN)、总磷(TP)、溶解性总氮(TDN)和溶解性总磷(TDP)含量以及较低的DOC∶TDP和TDN∶TDP值,但次生林凋落枝溶解性有机质含量及其光谱学特征在各阶段无显著差异。米槠天然林和次生林凋落枝DOC、TDN和TDP与气温和降水量呈负相关,人工林凋落枝TDN、TDP与气温和降水量呈正相关。人工林凋落枝生产量在高峰阶段具有较高的养分含量,可能具有相对快速的物质循环效率,天然林在凋落枝生产量下降阶段以凋落枝溶解性有机质为载体的物质循环效率相对较高。     

Climate and landscape influence on indicators of lake carbon cycling through spatial patterns in dissolved organic carbon

Freshwater ecosystems are strongly influenced by both climate and the surrounding landscape, yet the specific pathways connecting climatic and landscape drivers to the functioning of lake ecosystems are poorly understood. Here, we hypothesize that the links that exist between spatial patterns in climate and landscape properties and the spatial variation in lake carbon (C) cycling at regional scales are at least partly mediated by the movement of terrestrial dissolved organic carbon (DOC) in the aquatic component of the landscape. We assembled a set of indicators of lake C cycling (bacterial respiration and production, chlorophyll a, production to respiration ratio, and partial pressure of CO₂), DOC concentration and composition, and landscape and climate characteristics for 239 temperate and boreal lakes spanning large environmental and geographic gradients across seven regions. There were various degrees of spatial structure in climate and landscape features that were coherent with the regionally structured patterns observed in lake DOC and indicators of C cycling. These different regions aligned well, albeit nonlinearly along a mean annual temperature gradient; whereas there was a considerable statistical effect of climate and landscape properties on lake C cycling, the direct effect was small and the overall effect was almost entirely overlapping with that of DOC concentration and composition. Our results suggest that key climatic and landscape signals are conveyed to lakes in part via the movement of terrestrial DOC to lakes and that DOC acts both as a driver of lake C cycling and as a proxy for other external signals.     

胶州湾滨海湿地土壤溶解性有机质的三维荧光特性

为了了解滨海湿地土壤中溶解性有机质的结构特征及来源,2014年1月在胶州湾采集光滩、碱蓬、芦苇和大米草湿地的土壤样品,测定土壤溶解性有机质(DOM)含量,利用三维荧光技术进行光谱分析.结果表明: 胶州湾4种湿地类型土壤溶解性有机碳(DOC)含量表现为大米草湿地＞光滩＞碱蓬湿地＞芦苇湿地,垂直剖面上随土层深度的增加DOC含量均呈减少的趋势.经光谱分析,胶州湾湿地土壤DOM的三维荧光光谱(3DEEMs)中出现了B、T、A、D和C等5种荧光峰,分别代表类酪氨酸、类色氨酸、类富里酸、类可溶性微生物副产物和类腐殖酸5种组分.利用荧光区域积分(FRI)法对5种组分进行定量分析,类色氨酸、类富里酸和类酪氨酸在DOM各组分含量中居前3位,类可溶性微生物副产物和类腐殖酸的含量次之,二者含量差异不显著.DOM的5种组分相互之间均呈显著正相关,与DOC含量呈显著正相关,与总磷、有效磷、总氮有不同程度的相关性.胶州湾4种湿地类型土壤DOM主要由生物相互作用内源产生,且腐殖化程度较低.     

Colloidal and dissolved organic matter in lake water: Carbohydrate and amino acid composition,and ability to support bacterial growth

Bacterial utilization of dissolved organic matter (DOM) was studied in water from a humic and a clearwater oligotrophic lake. Indigenous bacteria were inoculated into either 0.2 m natural filtered lake water, or lake water enriched fivefold with colloidal DOM >100 kD but below 0.2 m. Consumption of DOM was followed from changes in concentrations of total dissolved organic carbon (DOC), dissolved combined and free carbohydrates and amino acids (DCCHO and DFCHO, and DCAA and DFAA, respectively) and by uptake of monosaccharide and amino acid radioisotopes. DCCHO and DCAA made up 8% (humic lake) to 33–44% (clear-water lake) of the natural DOC pools, while DFCHO and DFAA contributed at most 1.7% to the DOC pools. Addition of >100 kD DOM increased the DOC concentrations by 50% (clearwater lake) to 92% (humic lake), but it only resulted in a higher bacterial production (by 63%) in the humic lake. During the incubations 13 to 37% of the DOC was assimilated by the bacteria, at estimated growth efficiencies of 4–8%. Despite the measured reduction of DOC, statistically significant changes of specific organic compounds, especially of DCCHO and DCAA, generally did not occur. Probably the presence of high molecular weight DOC interfered with the applied analytical procedures. Addition of radiotracers indicated, however, that DFAA sustained 17–58% and 29–100% of the bacterial carbon and nitrogen requirements, respectively, and that glucose met 1–3% of the bacterial carbon requirements. Thus, our experiments indicate that radiotracers, rather than measurements of concentration changes, should be used in studies of bacterial utilization of DOC in freshwaters with a high content of humic or high molecular weight organic matter.     

Export of DOM from Boreal Catchments: Impacts of Land Use Cover and Climate

Dissolved organic matter (DOM) is an important fraction in carbon (C) and nutrient budgets for aquatic ecosystems and can have broad effects on food webs and nutrient cycling. To look at the role land use cover and climate might play in DOM transport from the boreal region, the export of total organic carbon (TOC), total organic nitrogen (TON) and dissolved organic phosphorus (DOP) was estimated for Finnish main rivers and their sub-catchments, altogether 86 catchments, situated between latitudes 60° N and 69° N and covering 297,322 km², 88% of the total area of Finland. On an average, 94% of the TOC, 90% of the total nitrogen (TN) and 40% of the total phosphorus (TP) in Finnish rivers was in a dissolved form. The majority of the DOM export from Finnish catchments consists of organic C. The TOC export increased with increasing peatland proportion (r = 0.39, p = 0.003), while TON export increased with the increasing percentage of agricultural land (r = 0.60, p <0.001). Although upstream lakes covered only on average 9% of the catchment area, they were the most important predictor for TOC, TON and DOP export (r = −0.83, r = −0.82 and r = −0.61, respectively). The higher the upstream lake percentage, the lower the export indicating organic matter retention in lakes.     

亚热带米槠林不同更新方式对土壤可溶性有机质降解性的影响

可溶性有机质(DOM)的生物降解性影响着土壤有机质的存留和释放,对深入认识森林土壤养分循环意义重大。为探究森林更新对土壤DOM降解特征的影响,选取亚热带地区米槠天然林(NF)、米槠次生林(SF)和米槠人工促进天然更新林(AR)土壤DOM溶液为研究对象,进行室内降解(42 d)试验。结果表明: 1)3种林分土壤可溶性有机碳(DOC)的降解率和易降解DOC的比例均为SF>AR>NF;可溶性有机氮(DON)和微生物生物量碳(MBC)是显著影响易降解DOC比例的因子;2)难降解组分占3种林分土壤DOC的大部分(72.3%～94.6%),其周转时间长,有利于稳定土壤有机质(SOC)的形成;3)土壤DOM最初的腐殖化指数(HIX_em)会影响易降解DOC的周转时间。DOM光谱结构随降解过程呈现动态变化,说明DOM中易降解组分被消耗完后,微生物会转而降解芳香类和疏水性物质以获取碳源。综上,米槠天然林更新为次生林和人促林后增加了易降解DOC的比例,提高了土壤DOM生物可降解性,不利于SOC的积累。     

Detrital Controls on Soil Solution N and Dissolved Organic Matter in Soils: A Field Experiment

We established a long-term field study in an old growth coniferous forest at the H.J. Andrews Experimental Forest, OR, USA, to address how detrital quality and quantity control soil organic matter accumulation and stabilization. The Detritus Input and Removal Treatments (DIRT) plots consist of treatments that double leaf litter, double woody debris inputs, exclude litter inputs, or remove root inputs via trenching. We measured changes in soil solution chemistry with depth, and conducted long-term incubations of bulk soils from different treatments in order to elucidate effects of detrital inputs on the relative amounts and lability of different soil C pools. In the field, the addition of woody debris increased dissolved organic carbon (DOC) concentrations in O-horizon leachate and at 30 cm, but not at 100 cm, compared to control plots, suggesting increased rates of DOC retention with added woody debris. DOC concentrations decreased through the soil profile in all plots to a greater degree than did dissolved organic nitrogen (DON), most likely due to preferential sorption of high C:N hydrophobic dissolved organic matter (DOM) in upper horizons; percent hydrophobic DOM decreased significantly with depth, and hydrophilic DOM had a much lower and less variable C:N ratio. Although laboratory extracts of different litter types showed differences in DOM chemistry, percent hydrophobic DOM did not differ among soil solutions from different detrital treatments in the field, suggesting that microbial processing of DOM leachate in the field consumed easily degradable components, thus equalizing leachate chemistry among treatments. Total dissolved N leaching from plots with intact roots was very low (0.17 g m⁻² year⁻¹), slightly less than measured deposition to this very unpolluted forest (~s 0.2 g m⁻² year⁻¹). Total dissolved N losses showed significant increases in the two treatments without roots whereas concentrations of DOC decreased. In these plots, N losses were less than half of estimated plant uptake, suggesting that other mechanisms, such as increased microbial immobilization of N, accounted for retention of N in deep soils. In long-term laboratory incubations, soils from plots that had both above- and below-ground litter inputs excluded for 5 years showed a trend towards lower DOC loss rates, but not lower respiration rates. Soils from plots with added wood had similar respiration and DOC loss rates as control soils, suggesting that the additional DOC sorption observed in the field in these soils was stabilized in the soil and not readily lost upon incubation.     

Coupling dissolved organic carbon,CO2 and productivity in boreal lakes

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Nutrient and mineralogical control on dissolved organic C, N and P fluxes and stoichiometry in Hawaiian soils

We measured DOM fluxes from the O horizon of Hawaiiansoils that varied in nutrient availability and mineralcontent to examine what regulates the flux ofdissolved organic carbon (DOC), nitrogen (DON) andphosphorus (DOP) from the surface layer of tropicalsoils. We examined DOM fluxes in a laboratory study from N, P and N+Pfertilized and unfertilized sites on soils that rangedin age from 300 to 4 million years old. The fluxesof DOC and DON were generally related to the % Cand % N content of the soils across the sites. Ingeneral, CO₂ and DOC fluxes were not correlatedsuggesting that physical desorption, dissolution andsorption reactions primarily control DOM release fromthese surface horizons. The one exception to thispattern was at the oldest site where there was asignificant relationship between DOC and CO₂flux. The oldest site also contained the lowestmineral and allophane content of the three sites andthe DOC-respiration correlation indicates arelationship between microbial activity and DOC fluxat this site. N Fertilization increased DON fluxes by50% and decreased DOC:DON ratios in the youngest,most N poor site. In the older, more N rich sites, Nfertilization neither increased DON fluxes nordecreased DOM C:N ratios. Similarly, short termchanges in N availability in laboratory-based soil Nand P fertilization experiments did not affect the DOMC:N ratios of leachate. DOM C:N ratios were similar tosoil organic matter C:N ratios, and changes in DOM C:Nratios with fertilization appeared to have beenmediated through long term effects on SOM C:N ratiosrather than through changes in microbial demand for Cand N. There was no relationship between DON andinorganic N flux during these incubations suggestingthat the organic and inorganic components of N fluxfrom soils are regulated by different factors and thatDON fluxes are not coupled to immediate microbialdemand for N. In contrast to the behavior of DON, thenet flux of dissolved organic phosphorus (DOP) and DOMC:P ratios responded to both long-term P fertilizationand natural variation in reactive P availability. There was lower DOP flux and higher DOM C:P ratiosfrom soils characterized by low P availability andhigh DOP flux and narrow DOM C:P ratios in sites withhigh P availability. DOP fluxes were also closelycorrelated with dissolved inorganic P fluxes. PFertilization increased DOP fluxes by 73% in theyoungest site, 31% in the P rich intermediate agesite and 444% in the old, P poor site indicating thatDOP fluxes closely track P availability in soils.     

Dissolved organic matter in small streams along a gradient from discontinuous to continuous permafrost

The Yenisei river passes every type of permafrost regime, from south to north, being characterized by increasing continuity of the permafrost and by decreasing thickness of the active layer. We used that situation to test the hypothesis that amounts and properties of dissolved organic matter (DOM) in small streams draining forested catchments respond to different permafrost regimes. Water samples were taken from eight tributaries along the Yenisei between 67°30′N and 65°49′N latitude. The samples were analysed for dissolved organic carbon (DOC) and nitrogen (DON) and DOM was characterized by its chemical composition (XAD‐8 fractionation, sugars, lignin phenols, amino acids, protein, UV and fluorescence spectroscopy), and its biodegradability. Most properties of the tributary waters varied depending on latitude. The higher the latitude, the higher were DOC, DON and the proportion of the hydrophobic fraction of DOC. The contribution of hexoses and pentoses to DOC were higher in southern tributaries; on the other hand, phenolic compounds were more abundant in northern tributaries. Mineralizable DOC ranged between 4% and 28% of total DOC. DOM in northern tributaries was significantly (P<0.05) less biodegradable than that in southern tributaries reflecting the differences in the chemical properties of DOM. Our results suggest that the differences in DOM properties are mainly attributed to differences of permafrost regime, affecting depth of active layer, soil organic matter accumulation and vegetation. Soil organic matter and vegetation determine the amount and composition of DOM produced in the catchments while the depth of the active layer likely controls the quantity and quality of DOM exported to streams. Sorptive interactions of DOM with the soil mineral phase typically increase with depth. The results imply that a northern shift of discontinuous permafrost likely will change in the long term the input of DOM into the Yenisei and thus probably into the Kara Sea.     

Dissolved organic matter quantity and quality from freshwater and saltwater lakes in east-central Alberta

Concentrations of dissolved organic matter (DOM) in surface waters of sub-humid to semi-arid lakes in east-central Alberta increase with increasing salinity and water residence time from about 20 to 330 mg L^–1 as dissolved organic carbon (DOC). This pattern is opposite to that observed among freshwater lakes spanning a gradient in water residence times, and is probably caused by evaporative concentration of refractory DOM. The proportion of total DOC, operationally defined as humic substances using XAD-8 resin, was high, though similar to surface waters typically referred to as "humic", and independent of salinity. Very long water residence times (hundreds of years) in saline lakes favors evapoconcentration of low-color, low molecular weight DOM, with N-content characteristic of allochthonous DOM.