消落带生态系统氮素截留转化的主要机制及影响因素

消落带是陆地与水体(河流、湖泊、水库、湿地以及其他特殊水体)之间的生态过渡带,具有独特的生态水文学和生物地球化学过程,是截留和转化NH₄⁺、NO₃^-等非点源氮素进入水体的最后一道生态屏障.整合已有相关研究成果发现: 1)植物固持作用改变氮素在土壤-植被-土壤-大气中相对存在位置;2)微生物反硝化作用将氮素从系统内永久性地去除,是消落带生态系统氮素截留转化的主要机制,但其相对贡献率仍有很大的不确定性.在不同流域背景条件下,影响消落带生态系统氮素生物地球化学循环的主要生态因子变化较大,很难确定地下水位高低、植被状况、微生物属性和土壤基质等哪一个生态因子是驱动消落带生态系统氮素循环的关键因子.研究方法的局限性、大的时空尺度数据的缺乏及对植被宽度认识的模糊性,是导致消落带生态系统氮素截留转化结果变异性大的主要原因.因此,应在消落带生态系统具体研究区位环境因子基础上,利用数学模型、GIS、RS等分析方法及同位素示踪和气体联用测定等定量分析技术,从不同时空尺度研究消落带生态系统氮素的循环与转化规律,以实现消落带生态系统氮素截留转化最优化,为消落带生态系统的科学管理提供理论基础.     

冻融对土壤氮素损失及有效性的影响

土壤冻融交替是寒冷生态系统土壤氮素循环的重要驱动力。已有研究表明冻融交替作用能够促进氮素周转,从而缓解因土壤有效氮素缺乏而引起的植物生长限制。即便如此,冻融环境下土壤有效氮素供应量远高于其利用量,过剩的氮素会通过气态(N2O-N)排放、淋溶和径流等途径损失。论述了季节冻融环境和模拟冻融条件下土壤氮素损失状况;同时分析了影响冻融土壤N2O生产的相关因素、产生途径及冻融期N2O大量排放的机制;针对冻融交替过程中土壤氮素有效性问题,探讨了氮矿化、可溶性有机氮(DON)和微生物量氮(MBN)与氮素损失的关系。评述了土壤冻融研究中存在的不足,认为模型研究、土壤微生物功能、氮素转化中间产物、土壤-植物界面过程是未来值得关注和深入探讨的研究方向。     

湿地土壤硫氧化-还原过程及其与其他元素的耦合作用研究进展

湿地土壤硫(S)的氧化-还原过程是硫循环的重要环节,其对于维持湿地系统的稳定与健康具有重要意义。本文综述了湿地土壤S的氧化-还原过程及影响因素,并分析了其与其他元素耦合机制的研究进展。湿地土壤S氧化-还原过程的影响因素主要涉及生物因子(植物、微生物、底栖动物及人类活动等)和非生物因子(温度、水分和粒度等物理因素及pH、盐度、有机质等化学因素),而其与其他元素的耦合作用主要涉及碳(C)、氮(N)、磷(P)等生源元素以及铁(Fe)、锰(Mn)等金属元素。鉴于当前湿地土壤S氧化-还原过程影响机制揭示不深入、耦合作用研究不均衡及生态效应探讨不充分等问题,未来应重点加强S氧化-还原过程的关键功能微生物研究,强化其与痕量元素迁移转化的耦合机理研究,重视其与其他元素耦合作用的生态效应研究。     

土壤-植物-大气连续体系中氮的研究进展

氮素是植物最需要的重要养分元素之一.近年来,土壤-植物-大气这一连续体系(SPAC)中的氮循环成为研究的热点之一.大气中的氮素可以通过生物固定和N沉降等作用进入土壤和植物内,同时土壤和植物内的氮素又会以氨挥发和氮氧化物等方式排放到大气中.氮素通过生物固持和植物吸收等方式进入植物体内,植物器官脱落使植物损失一部分的氮素,另外雨水的淋洗和植物溢出液也会造成植物的N损失.植物氮素在植物体内的积累和分布随着生长时期和各营养器官而有所不同.另外,植物吸收氮素的过程又受到大气状况和土壤状况的制约.土壤中氮素经过矿化作用、硝化作用和反硝化作用进行转化,一部分把氮素转化成植物能吸收的营养形态,另一部分则从土壤中损失.凋落物的分解和N沉降能补充土壤中的氮素,而植物吸收、微生物固持、水文流失和N溢出等方式使氮素从土壤中损失出去.另外,凋落物的分解和根际土壤、CO2浓度和臭氧对氮素循环有着重要的作用.N污染、N沉降、碳氮循环的耦合作用是今后研究的热点问题.     

丛枝菌根真菌在土壤氮素循环中的作用

作为植物需求量最大的营养元素,氮素是陆地生态系统初级生产力的主要限制因子。丛枝菌根真菌能与地球上80%以上的陆生植物形成菌根共生体,帮助宿主植物吸收土壤中的P、N等矿质养分。目前,丛枝菌根真菌与氮素循环相关研究侧重于真菌对氮素的吸收形态以及共生体中氮的传输代谢机制,却忽略了丛枝菌根真菌在固氮过程、矿化与吸收过程、硝化过程、反硝化过程以及氮素淋洗过程等土壤氮素循环过程中所起到的潜在作用,并且越来越多的证据也表明丛枝菌根真菌是影响土壤氮素循环过程的重要因子。总结了丛枝菌根真菌可利用的氮素形态及真菌的氮代谢转运相关基因的研究现状;重点分析了丛枝菌根真菌在调控土壤氮素循环过程中的潜在作用以及在生态系统中的重要生态学意义,同时提出了丛枝菌根真菌在土壤氮素循环过程中一些需要深入研究的问题。     

中国典型生态脆弱区生态化学计量学研究进展

在人类活动和自然环境变化的相互作用下,生态脆弱区生态系统随之变迁,荒漠化、盐碱化、水土流失、植被生产力下降等是生态脆弱区面临的重要问题。生态化学计量学作为当前多学科交叉研究的热点领域,强调从生态系统能量与元素平衡角度,揭示元素生物地球化学循环和生态系统对环境变化的调控机制。为了促进对生态脆弱区碳（C）、氮（N）、磷（P）生态化学计量的深入理解,本文重点总结了近年来有关我国典型生态脆弱区植物、凋落物、土壤和土壤微生物量C、N、P生态化学计量及其对环境变化响应的研究成果,并展望未来研究方向,以期促进生态化学计量学的发展和生态脆弱区生态保护与恢复研究。研究表明,植物-凋落物-土壤-土壤微生物系统C、N、P化学计量具有较强相关性,并受土壤因子、气候因子、生物因子和人类活动的显著影响。在生态脆弱区,我国北方荒漠及荒漠化地区由于较高的N∶P比值易受P限制,而青藏高原脆弱区、西南岩溶石漠化地区和黄土高原脆弱区等生态脆弱区更易受N限制;随着植被恢复,养分限制逐渐由N限制向P限制转变。生态脆弱区相对较低的养分含量和C∶N∶P比值或许可在一定程度上解释植被生产力较低的原因,而具有较高N、P化学计量内稳性的植物在贫瘠环境中具有较强竞争力和更高稳定性。今后可加强多尺度、不同生态系统植物-凋落物-土壤-土壤微生物系统生态化学计量和长期、多因子交互控制实验的研究。     

华北平原典型农田氮素与水分循环

华北平原近几十年的粮食生产伴随着强烈的地下水开采和化肥投入.高强度的农业活动改变了农田生态系统原有的物质循环和能量过程,同时给地区水土资源乃至粮食安全带来潜在的风险.本文通过对近20年有关华北平原冬小麦-夏玉米典型农田氮素循环、水分循环研究的分析,并结合气象数据及田间试验观测结果,综合计算得到该一年两熟轮作农田生态系统氮水循环的主要通量.在氮素循环方面,华北平原小麦-玉米轮作体系农田每年经由化肥施入的氮素约为523 kg N·hm-2,有机肥施入74 kg N·hm-2,大气沉降23 kg N·hm-2,灌溉水带入12 kg N·hm-2,共632 kg N·hm-2;在主要的氮素输出项中,作物吸收289kg N·hm-2,土壤残留77 kg N·hm-2,淋失到根区外104 kg N·hm-2,氨挥发52 kg N·hm-2,硝化-反硝化过程损失10 kg N·hm-2,共计532 kg N·hm-2.由于各研究案例本身以及综合分析时纳入的不确定性,致使氮素收支并不平衡.在水分循环方面,年平均降水量557 mm,灌溉量340 mm,蒸散约762 mm,根区向下的入渗量约135 mm.鉴于氮水平衡过程的不确定性,应尽快开展多学科并举的大型农田氮水耦合试验研究,揭示氮素与水分在土壤-植物-大气系统的运移转化规律,以及两者相互影响制约的机制和特定生理化学过程的临界点/阈值的确定,以实现水土资源的可持续利用.     

土壤氮素转化的关键微生物过程及机制

微生物是驱动土壤元素生物地球化学循环的引擎.氮循环是土壤生态系统元素循环的核心之一,其四个主要过程,即生物固氮作用、氨化作用、硝化作用、反硝化作用,均由微生物所驱动.近10年来,随着免培养的分子生态学技术和高通量测序技术等的发展,在硝化微生物多样性及其作用机理、厌氧氨氧化过程和机理等研究方面取得了突破性进展.本文重点阐述了我国有关土壤硝化微生物方面的研究进展,在此基础上,简要介绍了反硝化微生物和厌氧氨氧化及硝酸盐异化还原成铵作用的研究进展,并对今后的研究工作提出了展望.今后土壤氮素转化微生物生态学的研究,应瞄准国际微生生态学发展的前沿,加强新技术新方法的应用,结合我国农业可持续发展、资源环境保护和全球变化研究的重大需求,重点开展以下几方面的工作:(1)开展大尺度上土壤硝化作用及氨氧化微生物分布的时空演变特征及驱动因子的研究;(2)加强氮素转化关键微生物过程与机理的研究,并与相关过程的通量(如氨挥发、N2O释放)和反应速率(如矿化速率、硝化速率)关联起来;(3)在特定生态系统中系统研究各个氮转化过程的耦合关系,构建相关氮素转化和氮素平衡模型,为定向调控土壤氮素转化过程,提高氮素利用效率并减少其负面效应提供科学依据.     

蒙古栎叶片及其土壤碳、氮同位素自然丰度对大气CO_2浓度升高的响应

大气CO_2浓度升高对土壤氮素转化过程产生重要影响,研究其变化有助于更好地预测陆地生态系统的固碳潜力.氮同位素自然丰度作为生态系统氮素循环过程的综合指标能够有效地指示CO_2浓度升高对土壤氮素转化过程的影响.本研究采用开顶箱CO_2熏蒸法研究连续10年的大气CO_2浓度升高对我国东北地区蒙古栎及其土壤和微生物生物量碳、氮同位素自然丰度的影响.结果表明:大气CO_2浓度升高改变了土壤氮循环过程,增加了土壤微生物和植物叶片δ~(15)N;促进了富~(13)C土壤有机碳分解,中和了贫~(13)C植物光合碳输入的效果,导致土壤可溶性有机碳和微生物碳δ~(13)C在CO_2升高条件下没有发生显著变化.这些结果表明,CO_2浓度升高很可能促进了土壤有机质矿化过程,并加剧了系统氮限制的状态.     

氮素类型和剂量对寒温带针叶林土壤N2O排放的影响

大气氮沉降输入会增加森林生态系统氮素有效性,进而改变土壤N_2O产生与排放,然而有关不同氮素离子(氧化态NO_3~--N与还原态NH_4~+-N)沉降对土壤N_2O排放的影响知之甚少。以大兴安岭寒温带针叶林为研究对象,构建了3种类型(NH_4Cl、KNO_3、NH_4NO_3)和4个施氮水平(0、10、20、40 kg N hm~(-2)a~(-1))的增氮控制试验,利用流动化学分析仪和静态箱-气相色谱法4次/月测定凋落物层和矿质层土壤无机氮含量、土壤-大气界面N_2O净交换通量以及相关环境因子,分析施氮类型和剂量对土壤氮素有效性、土壤N_2O通量的影响探讨氮素富集条件下土壤N_2O通量的环境驱动机制。结果表明:施氮类型和剂量均显著影响土壤无机氮含量,土壤NH_4~+-N的积累效应显著高于NO_3~--N。施氮一致增加寒温带针叶林土壤N_2O排放,NH_4NO_3促进效应最为明显,增幅为442%-677%,高于全球平均水平(134%)。土壤N_2O通量与土壤温度、凋落物层NH_4~+-N含量正相关,且随着施氮水平增加而增加。结果表明大气氮沉降短期内不会导致寒温带针叶林土壤NO_3~--N大量流失,但会显著促进土壤N_2O的排放。此外,外源性NH_4~+和NO_3~-输入对土壤N_2O排放的促进作用具有协同效应,在未来森林生态系统氮循环和氮平衡研究中应该区分对待。     

Structural and functional loss in restored wetland ecosystems

Wetlands are among the most productive and economically valuable ecosystems in the world. However, because of human activities, over half of the wetland ecosystems existing in North America, Europe, Australia, and China in the early 20th century have been lost. Ecological restoration to recover critical ecosystem services has been widely attempted, but the degree of actual recovery of ecosystem functioning and structure from these efforts remains uncertain. Our results from a meta-analysis of 621 wetland sites from throughout the world show that even a century after restoration efforts, biological structure (driven mostly by plant assemblages), and biogeochemical functioning (driven primarily by the storage of carbon in wetland soils), remained on average 26% and 23% lower, respectively, than in reference sites. Either recovery has been very slow, or postdisturbance systems have moved towards alternative states that differ from reference conditions. We also found significant effects of environmental settings on the rate and degree of recovery. Large wetland areas (>100 ha) and wetlands restored in warm (temperate and tropical) climates recovered more rapidly than smaller wetlands and wetlands restored in cold climates. Also, wetlands experiencing more (riverine and tidal) hydrologic exchange recovered more rapidly than depressional wetlands. Restoration performance is limited: current restoration practice fails to recover original levels of wetland ecosystem functions, even after many decades. If restoration as currently practiced is used to justify further degradation, global loss of wetland ecosystem function and structure will spread.     

退化湿地生态系统恢复的一些理论问题

湿地是陆地和水生生态系统间的过渡带,作为一种重要的自然资源,湿地是野生生物的栖息地,可调控区域内的水分循环和C、N等元素的生物地球化学循环;其生物生产力可为人类提供食物和商品,还能过滤和分解所吸纳的污染物,由于湿地的功能未受到足够的重视。全世界的湿地因大量围垦和干扰而丧失或退化,在退化湿地的恢复过程中,可用自我设计和设计理论、演替理论、入侵理论、河流理论、洪水脉冲理论、边缘效应理论和中度干扰假说等理论作指导,湿地恢复的方法包括：尽可能采用工程与生物措施相结合的方法,恢复湿地的供水连接,利用水文过程加快恢复,控制污染物的流入,修饰湿地的地形或景观,改良湿地土壤,在最佳位置重建湿地的生物群落,减少人类干扰,提高湿地的自我维持能力,建立缓冲带以保护自然的和恢复的湿地,建立湿地稳定性和持续性的评价体系并予以监控。     

极端酸性矿山环境微生物基于CRISPR系统的适应性免疫机制

【目的】通过对酸性矿山环境中嗜酸硫杆菌属(Acidithiobacillus)、脱硫弧菌属(Desulfovibrio)、钩端螺旋菌属(Leptospirillum)、硫化杆菌属(Sulfobacillus)、酸原体属(Acidiplasma)和铁质菌属(Ferroplasma)的100株冶金微生物基因组中CRISPR-Cas系统的结构特征和同源关系进行生物信息学分析,在基因组水平上解析冶金微生物基于CRISPR系统对极端环境的适应性免疫机制。【方法】从NCBI网站下载基因组序列,采用CRISPR Finder定位基因组中潜在的CRISPR簇。分析CRISPR系统的组成结构与功能:利用Clustal Omega对重复序列(repeat)分类;将间隔序列(spacer)分别与nr数据库、质粒数据库和病毒数据库比对,获得注释信息;根据Cas蛋白的种类和同源性对酸性矿山环境微生物的CRISPR-Cas系统分型。【结果】在100株冶金微生物基因组中共鉴定出415个CRISPR簇,在176个c CRISPR簇中共有80种不同的重复序列和4147条间隔序列。对重复序列分类,发现12类重复序列均能形成典型的RNA二级结构,Cluster10中的重复序列在冶金微生物中最具有代表性。间隔序列注释结果表明,这些微生物曾遭受来自细菌质粒与病毒的攻击,并通过不同的防御机制抵抗外源核酸序列的入侵。冶金微生物细菌的大部分CRISPR-Cas系统属于I-C和I-E亚类型,而古菌的CRISPR-Cas系统多为I-D亚类型,两者基于CRISPR-Cas系统的进化过程中存在显著差异。【结论】酸性矿山环境微生物的CRISPR结构可能采用不同免疫机制介导外源核酸序列与Cas蛋白的相互作用,为进一步揭示极端环境微生物的适应性进化机理奠定了基础。     

Advancing the use of minirhizotrons in wetlands

Background

Wetlands store a substantial amount of carbon (C) in deep soil organic matter deposits, and play an important role in global fluxes of carbon dioxide and methane. Fine roots (i.e., ephemeral roots that are active in water and nutrient uptake) are recognized as important components of biogeochemical cycles in nutrient-limited wetland ecosystems. However, quantification of fine-root dynamics in wetlands has generally been limited to destructive approaches, possibly because of methodological difficulties associated with the unique environmental, soil, and plant community characteristics of these systems. Non-destructive minirhizotron technology has rarely been used in wetland ecosystems.

Scope

Our goal was to develop a consensus on, and a methodological framework for, the appropriate installation and use of minirhizotron technology in wetland ecosystems. Here, we discuss a number of potential solutions for the challenges associated with the deployment of minirhizotron technology in wetlands, including minirhizotron installation and anchorage, capture and analysis of minirhizotron images, and upscaling of minirhizotron data for analysis of biogeochemical pools and parameterization of land surface models.

Conclusions

The appropriate use of minirhizotron technology to examine relatively understudied fine-root dynamics in wetlands will advance our knowledge of ecosystem C and nutrient cycling in these globally important ecosystems.     

Opportunistic wetland formation on reconstructed landforms in a sub-humid climate: influence of site and landscape-scale factors

Initiation of wetland features is integral to sustaining landscape eco-hydrological function and meeting defined goals in surface mine reclamation. Within the sub humid climate of the Athabasca Oil Sands, Canada, the water generation mechanisms (external water sources, internal feedback mechanisms) that enable wetlands to form opportunistically on recently reconstructed landscapes are currently unknown, restricting the flexibility in mine closure planning. To address this knowledge gap, we interpret site and local physical characteristics of opportunistic wetlands within the Athabasca Oil Sands through a synoptic survey. Wetlands formed in ~?8% of the random survey transect areas designed and planted for forestlands. Wetlands had vegetation structures characteristic of woody Salix spp. swamps and narrow-leaved Carex spp. marsh wetland types, with minor coverage of open water marshes. Wetlands formed opportunistically over a range of slopes, aspects and topographic positions, across contrasting fine and coarse-textured landforms. However, different wetland establishment and maintenance controls exist on fine and coarse-textured landforms. On coarse-textured landforms with large groundwater transmissivity, wetland formation was influenced by landscape-scale factors; wetlands were restricted to the toes of slopes and areas intersecting groundwater. On fine-textured constructed landforms, small and large wetlands occurred on lower landscape elevations with the potential for the external (cumulative) water sources, and in hydrologically isolated locations with little potential for runoff contribution from adjacent forestlands (saturation and wetland formation through internal feedback mechanisms). Regardless of landscape position, wetlands formed on flat areas and in shallow inward draining endorheic pans with clay rich soils where low water storage potential promotes frequent surface saturation. These findings have important implications in landscape reclamation design, suggesting that passive techniques that support internal feedback mechanisms may offer a more cost effective reclamation approach compared to more active, expensive techniques that aim to develop wetlands with external water sources.

     

Tracing sources and pathways of dissolved nitrate in forest and river ecosystems using high-resolution isotopic techniques: a review

Nitrogen inputs into stream and river ecosystems, and the factors influencing those inputs, are important for various ecological and environmental concerns. Reliable information on where and how nitrogen compounds flow into aquatic ecosystems is indispensable to understanding the nutrient status of these ecosystems. Such information should include the biogeochemical mechanisms and hydrological controls of nutrient leaching into rivers from terrestrial systems such as forests, agricultural fields, and urbanized areas. Advancements in stable isotopomer measurements over the past two decades have expanded the variety of target substances and the precision with which they can be investigated. The high-throughput microbial denitrifier method allows for simultaneous measurement of nitrogen and oxygen isotope ratios and can provide high-resolution spatiotemporal information on both nitrate sources and biogeochemical processes. Although advanced techniques of stable isotope analysis have been used extensively to detect sources and estimate the relative contributions of multi-source systems in various rivers, there are still new horizons in investigating nitrogen transformations. For example, stable isotopes of oxygen (¹⁸O and ¹⁷O) occurring in nitrate due to atmospheric deposition can be used as natural tracers for evaluating internal nitrogen cycling; these isotopes are distinct from the oxygen within microbially generated nitrate in soils and water bodies. Another future challenge is improved use of nitrous oxide isotopomers in evaluating the relative contributions of nitrification and denitrification. Such analysis could provide insight into the nitrogen transformation that occurs under redox conditions at the boundary between terrestrial and aquatic systems, where nitrification and denitrification often occur simultaneously in soil and aquatic environments.     

湿地生物地球化学过程研究进展

1　湿地生物地球化学过程的概念及内涵营养物质在生态系统之间的输入和输出以及在生物各圈层之间进行的物质和能量交换称为生物地球化学循环 (ｂｉｏｇｅｏｃｈｅｍｉｃａｌｃｉｒｃｕｌａｔｉｏｎ) [4 ] ,它实质上是指生物有机体及其产物与无机环境之间进行的物质交换和能量转换过程。湿地是介于陆地生态系统和水生生态系统之间的过渡地带[3 ] ,它是一种特殊的生态系统 ,其独特多样的生物条件显著影响着生物地球化学过程。这些过程不仅改变了物质的化学组成 ,而且使它们在湿地内发生空间位移以及生物地球化学转化。湿地生物地球化学过程是…     

Dissolved Organic Matter Characteristics Across a Subtropical Wetland’s Landscape: Application of Optical Properties in the Assessment of Environmental Dynamics

Wetlands are known to be important sources of dissolved organic matter (DOM) to rivers and coastal environments. However, the environmental dynamics of DOM within wetlands have not been well documented on large spatial scales. To better assess DOM dynamics within large wetlands, we determined high resolution spatial distributions of dissolved organic carbon (DOC) concentrations and DOM quality by excitation–emission matrix spectroscopy combined with parallel factor analysis (EEM–PARAFAC) in a subtropical freshwater wetland, the Everglades, Florida, USA. DOC concentrations decreased from north to south along the general water flow path and were linearly correlated with chloride concentration, a tracer of water derived from the Everglades Agricultural Area (EAA), suggesting that agricultural activities are directly or indirectly a major source of DOM in the Everglades. The optical properties of DOM, however, also changed successively along the water flow path from high molecular weight, peat-soil and highly oxidized agricultural soil-derived DOM to the north, to lower molecular weight, biologically produced DOM to the south. These results suggest that even though DOC concentration seems to be distributed conservatively, DOM sources and diagenetic processing can be dynamic throughout wetland landscapes. As such, EEM–PARAFAC clearly revealed that humic-enriched DOM from the EAA is gradually replaced by microbial- and plant-derived DOM along the general water flow path, while additional humic-like contributions are added from marsh soils. Results presented here indicate that both hydrology and primary productivity are important drivers controlling DOM dynamics in large wetlands. The biogeochemical processes controlling the DOM composition are complex and merit further investigation.     

Dry conditions disrupt terrestrial–aquatic linkages in northern catchments

Aquatic ecosystems depend on terrestrial organic matter (tOM) to regulate many functions, such as food web production and water quality, but an increasing frequency and intensity of drought across northern ecosystems is threatening to disrupt this important connection. Dry conditions reduce tOM export and can also oxidize wetland soils and release stored contaminants into stream flow after rainfall. Here, we test whether these disruptions to terrestrial–aquatic linkages occur during mild summer drought and whether this affects biota across 43 littoral zone sites in 11 lakes. We use copper (Cu) and nickel (Ni) as representative contaminants, and measure abundances of Hyalella azteca, a widespread indicator of ecosystem condition and food web production. We found that tOM concentrations were reduced but correlations with organic soils (wetlands and riparian forests) persisted during mild drought and were sufficient to suppress labile Cu concentrations. Wetlands, however, also became a source of labile Ni to littoral zones, which was linked to reduced abundances of the amphipod H. azteca, on average by up to 70 times across the range of observed Ni concentrations. This reveals a duality in the functional linkage of organic soils to aquatic ecosystems whereby they can help buffer the effects of hydrologic disconnection between catchments and lakes but at the cost of biogeochemical changes that release stored contaminants. As evidence of the toxicity of trace contaminant concentrations and their global dispersion grows, sustaining links among forests, organic soils and aquatic ecosystems in a changing climate will become increasingly important.     

Building a potential wetland restoration indicator for the contiguous United States

Wetlands provide key functions in the landscape from improving water quality, to regulating flows, to providing wildlife habitat. Over half of the wetlands in the contiguous United States (CONUS) have been converted to agricultural and urban land uses. However, over the last several decades, research has shown the benefits of wetlands to hydrologic, chemical, biological processes, spurring the creation of government programs and private initiatives to restore wetlands. Initiatives tend to focus on individual wetland creation, yet the greatest benefits are achieved when strategic restoration planning occurs across a watershed or multiple watersheds. For watershed-level wetland restoration planning to occur, informative data layers on potential wetland areas are needed. We created an indicator of potential wetland areas (PWA), using nationally available datasets to identify characteristics that could support wetland ecosystems, including: poorly drained soils and low-relief landscape positions as indicated by a derived topographic data layer. We compared our PWA with the National Wetlands Inventory (NWI) from 11 states throughout the CONUS to evaluate their alignment. The state-level percentage of NWI-designated wetlands directly overlapping the PWA ranged from 39 to 95%. When we included NWI that was immediately adjacent to the overlapping NWI, our range of correspondence to NWI ranged from 60 to 99%. Wetland restoration is more likely on certain landscapes (e.g., agriculture) than others due to the lack of substantive infrastructure and the potential for the restoration of hydrology; therefore, we combined the National Land Cover Dataset (NLCD) with the PWA to identify potentially restorable wetlands on agricultural land (PRW-Ag). The PRW-Ag identified a total of over 46 million ha with the potential to support wetlands. The largest concentrations of PRW-Ag occurred in the glaciated corn belt of the upper Mississippi River from Ohio to the Dakotas and in the Mississippi Alluvial Valley. The PRW-Ag layer could assist land managers in identifying sites that may qualify for enrollment in conservation programs, where planners can coordinate restoration efforts, or where decision makers can target resources to optimize the services provided across a watershed or multiple watersheds.