基于水生态因子的沼泽安全阈值研究——以三江平原沼泽为例

在分析沼泽的蒸发,蒸腾,降雨,产流等水循环节和沼泽水量的季节动态基础上,利用系统动力学原理和方法对沼泽湿地蓄水量进行动态仿真,以预测沼泽蓄水量的动态变化;通过对比研究,分析沼泽的冷湿效应及其与治泽面积消长的相互关系,建立相关的统计模型;再通过植物生长的现场实验,研究沼泽代表植物对水分条件的依赖性,找出沼泽最小生态需水量临界;最后以沼泽最小生态需水量临界值为依据,结合统计模型和沼泽蓄水量动态仿真手段,计算沼泽的安全阈值,对三江平原沼泽湿地的案例分析验证了该方法的可行性。     

冻融作用对三江平原湿地土壤活性有机碳及酶活性的影响

为了研究冻融作用对不同类型土壤活性有机碳组分及酶活性的影响,选取三江平原未受干扰小叶章湿地（UDAW）,干扰小叶章湿地（DDAW）和水稻田（RP）土壤（0-10 cm,10-20 cm和20-30 cm）进行室内冻融模拟实验。实验设置（-10-10℃）和（-5-5℃）两个冻融幅度。将经过3次、6次、10次和15次冻融循环处理后的土壤活性有机碳和酶活性分别与未经过冻融处理的FTC（0）对比。结果表明：冻融循环增加了3种湿地土壤可溶性有机碳（Dissolved Organic Carbon,DOC）浓度。随着活动层深度的增加,同一类型土壤DOC增量降低,不同类型土壤DOC增量为UDAW最高,其次是DDAW,RP增量最低。与此相反,冻融循环均降低了土壤微生物量碳（Microbial Biomass Carbon,MBC）浓度和纤维素酶、蔗糖酶和淀粉酶的活性。随着土壤深度的增加,冻融循环对MBC和3种酶活性的影响逐渐减弱,不同类型间MBC浓度和3种酶活性降低幅度为UDAW高于DDAW,RP降低幅度最小。冻融幅度对DOC浓度的影响为-5-5℃大于-10-10℃,而对MBC浓度和3种酶活性的影响则是-10-10℃大于-5-5℃。冻融次数显著影响土壤活性有机碳组分（DOC与MBC）及3种酶活性（P < 0.05）。随着冻融次数的增加,DOC浓度先升高后降低,MBC浓度和3种酶活性则先降低后升高。此外,UDAW和DDAW土壤活性有机碳组分和土壤酶活性显著正相关（P < 0.01）,暗示DOC浓度的增加,MBC起着重要作用。而在RP土壤中,二者的相关性降低,或许与人类的强烈干扰有关。     

A comparison of soil carbon pools and profiles in wetlands in Costa Rica and Ohio

Wetlands are large carbon pools and play important roles in global carbon cycles as natural carbon sinks. This study analyzes the variation of total soil carbon with depth in two temperate (Ohio) and three tropical (humid and dry) wetlands in Costa Rica and compares their total soil C pool to determine C accumulation in wetland soils. The temperate wetlands had significantly greater (P < 0.01) C pools (17.6 kg C m⁻²) than did the wetlands located in tropical climates (9.7 kg C m⁻²) in the top 24 cm of soil. Carbon profiles showed a rapid decrease of concentrations with soil depth in the tropical sites, whereas in the temperate wetlands they tended to increase with depth, up to a maximum at 18–24 cm, after which they started decreasing. The two wetlands in Ohio had about ten times the mean total C concentration of adjacent upland soils (e.g., 161 g C kg⁻¹ were measured in a central Ohio isolated forested wetland, and 17 g C kg⁻¹ in an adjacent upland site), and their soil C pools were significantly higher (P < 0.01). Among the five wetland study sites, three main wetland types were identified – isolated forested, riverine flow-through, and slow-flow slough. In the top 24 cm of soil, isolated forested wetlands had the greatest pool (10.8 kg C m⁻²), significantly higher (P < 0.05) than the other two types (7.9 kg C m⁻² in the riverine flow-though wetlands and 8.0 kg C m⁻² in a slowly flowing slough), indicating that the type of organic matter entering into the system and the type of wetland may be key factors in defining its soil C pool. A riverine flow-through wetland in Ohio showed a significantly higher C pool (P < 0.05) in the permanently flooded location (18.5 kg C m⁻²) than in the edge location with fluctuating hydrology, where the soil is intermittently flooded (14.6 kg C m⁻²).     

三江平原典型环型湿地土壤-植被-动物系统的结构及功能研究

环型湿地是三江平原沼泽湿地的主要景观类型之一。由于微地貌的变化 ,形成了相应的高势能区和低势能区。随着势能的变化 ,形成了不同的水热分布带 ,因而也产生了不同的土壤、植物、动物的环型水平结构和垂直结构的特点。在水平结构上 ,环型湿地由中心向外缘 ,地势由低到高 ,水分由多渐少 ,温度由低到高分布。因此 ,也带来了土壤和动植物的变化 ,土壤由泥炭土向沼泽土和白浆土过渡 ;植物由沉水的小狸藻向浮水的漂筏苔草、挺水的大穗苔草 睡菜群丛、毛果苔草 -狭叶甜茅群丛、小叶章 -沼柳 -越菊柳以及外缘分布的蒙古栎 白桦岛状林发展。动物的水平结构也就有相应的变化。环型湿地每个水平分布带又都具有各自不同的垂直结构。环型湿地的特殊结构 ,使其有着巨大的储水功能和调节温度的功能。即使在高温干旱的季节 ,由于湿地表面的须根层有隔离的空间 ,阻止了温度的传导 ,减少了下层水的蒸发 ,在下层的泥炭中仍有大量的水分保持。同时 ,这里也是一个太阳能储存库和遗传基因库。深入了解环型湿地的结构与功能 ,对研究湿地生态系统的功能及其保护湿地 ,实现湿地资源的可持续利用都具有重要的意义     

Test of the first-order removal model for metal retention in a young constructed wetland

The first-order removal model is widely used in constructed wetland design. The suitability of this model was tested to predict metal retention in a young constructed wetland receiving agricultural and urban runoff. During two years, water samples for total and dissolved metal analyses were collected every third day at both the inlet and the outlet. The wetland retained metals best during summer and fall whereas during winter the retention of metals was significantly lower. The first-order removal model predicted Fe and Mn retention in the spring and dissolved Zn retention from spring to fall in both years. During those periods, hydraulic retention times (HRTs) greater than 7 days provided maximum retention for Fe, Mn, and dissolved Zn. However, first-order removal models failed to fit summer, fall and winter data for almost every metal under investigation (Fe, Mn, dissolved Cu, dissolved As) suggesting that HRTs (<1–25 days) did not affect metal retention during these seasons. The metal loading to the wetland was low and the input of metals through internal loading may be more significant consequently decreasing the metal retention. Therefore, the first-order removal model is inadequate to predict metal retention on a seasonal basis. Models used to design constructed wetlands under cold climates must consider seasonal changes that affect biological as well as hydrological variables.     

三江平原典型湿地植物中汞的分布与库存量

分析了三江平原典型植物中的总Hg浓度．结果表明,各种植物中总Hg浓度差别较大,苔藓>藻类>苔草>禾草>灌木;干湿环境是影响总Hg浓度的重要因素;湿地植物总Hg浓度高于水稻和玉米等农作物．较高的土壤总Hg浓度是近地面大气中Hg的重要来源,间接地影响到植物中Hg的浓度．植物各构件中总Hg浓度具有立枯>根>叶>茎的特点．在植物整个生长季总Hg浓度先增加后减少．估算了三江平原湿地植物Hg的库存量．小叶章湿地植物地上部分库存量为24．9μg·m^-2;毛果苔草湿地植物地上部分库存量为35．8μg·m^-2,高于加拿大实验湖泊湿地．     

华北驼绒藜种群数量动态与生殖特性的相关性

采用立木级法研究华北驼绒藜种群的大小级结构,利用各龄级的存活数编制种群静态生命表和存活曲线,构建时间序列预测图对种群数量动态过程进行预测,利用生活史特征观察结果分析其生殖对策,探讨了生殖特性与种群动态的关系。结果表明:华北驼绒藜种群幼龄和老龄级个体数较少,中龄级个体数量较多,呈稳定或衰退趋势;种群生命表和存活曲线的分析表明,尽管生境条件不同,但存活曲线基本接近DeeveyⅢ型;种群数量的时间序列预测表明,华北驼绒藜种群会随时间推移,呈现老龄级株数先增加后减少的趋势,种群稳定性长期维持困难;生活史特征表明,华北驼绒藜在长期进化过程中形成了兼具r-对策和k-对策的双重特性来维持种群的相对稳定。良好的生殖适应性是物种发展的关键,华北驼绒藜种群年龄结构、生命表、存活曲线以及时间序列预测图反映出其种群数量动态与生殖特性具有密切的相关性,传粉系统效率低、胚胎发育过程营养失调、种子向幼苗的转化率低以及种群更新对母株的依赖性强等生殖生物学特性与种群动态相吻合;生境恶劣和人为干扰也成为其种群发展的制约因素。     

Changes in dissolved and total Fe and Mn in a young constructed wetland: Implications for retention performance

Surface-flow wetlands are generally considered sinks for Fe and Mn but they may also export and affect the partitioning of these metals. This study was undertaken to evaluate the effect of a young constructed wetland on the retention and transformation of both dissolved and particulate Fe and Mn. Duplicate water samples were collected every three days at the inlet and outlet structures of the Monahan Wetland, Kanata, Ontario, from spring of 1997 to 1999. While on a yearly basis the wetland showed significant retention of the dissolved phase, the retention of total Fe and Mn was poor. There were strong seasonal differences in retention and, during the winter, the wetland was a source. The wetland transformed dissolved into particulate Fe and Mn from spring to fall whereas during the winter, dissolved Fe and Mn were released. Changes in pH, alkalinity and temperature could explain 11% and 40% of the outlet variation in the ratio of dissolved to total Fe and Mn respectively. Furthermore, from spring to late summer, planktonic algal biomass was negatively related to the ratio of dissolved to total Fe and Mn implying a role in Fe and Mn transformations in young wetlands where emergent and submerged vegetation have yet to dominate the system.     

三江平原自然湿地与人工湿地双向演替动态过程研究

基于遥感和GIS技术,分析1986～2005年三江平原自然湿地(湖泊、河流、沼泽湿地)与人工湿地(水田)的双向演替过程,统计分析自然地理环境背景(土壤类型、海拔高度、坡度和地貌类型)对此过程的影响。研究结果表明,1986～2005年间三江平原湿地双向演替过程以沼泽湿地与水田之间的相互转化为主。1986～1995年、1995～2000年和2000～2005年三时段内沼泽湿地转化为水田的面积占同期沼泽湿地转出总面积的比例分别为7.61%、37.99%和28.81%,相反,水田转化为沼泽湿地的面积占同期水田转出总面积的4.83%、13.69%和4.84%。三江平原发生沼泽湿地与水田双向演替过程的主要自然地理环境背景为土壤类型为草甸土和沼泽土,海拔高度为0～100 m,坡度为0～1°,地貌类型为低河漫滩、高河漫滩、洼地和一级阶地。     

三江平原沼泽湿地生态承载能力综合评价

从湿地水资源、土地资源、水环境、生物资源等多方面入手,研究湿地生态系统的承载能力,采用分级评价方法,建立分级评价指标和承载模式,评价了沼泽湿地生态系统的生态弹性度、资源与环境承载力和承载压力度。利用基于加速遗传算法的层次分析技术确定承载模型的权重,计算得出的排序权值具有结果稳定、计算精度高的特点。应用到三江平原沼泽湿地生态承载力的综合评价中,结果表明整个三江平原大部分生态系统处于中稳、较高承载、中低压区。这说明三江平原生态承载能力比较高,人口压力不大,但要进一步提高生态承载能力,则需改善沼泽湿地生态环境,提高水资源利用效率。     

Spatial distribution of ant mounds and effects on soil physical properties in wetlands of the Sanjiang plain, China

Ants constitute a dominant element of soil mesofauna due to their biomass, abundance, richness of species and distribution within terrestrial ecosystems. They are important regulators of soil aggregate structure as they translocate large amounts of soil from the bottom to the soil surface. In doing so, they form biogenic structures (BS) made up of aggregates of different sizes and characteristics, i.e. ant mounds. These BS have varying characteristics according to the ant species and the soil where they carry their activities. Ants are considered soil engineers because of their effects on soil properties, availability of resource and flow of energy and nutrients in soil. Thus, it is important to gain information on their distribution and abundance. Relatively little is known about the spatial distribution of mounds and their role in the soil physical properties in wetlands of the Sanjiang plain, China. We conducted a survey of ant mounds and measured the density, height, and diameter and material composition of different ant mounds. The ecological characteristics of wetlands that ant mounds wide occurrence were also investigated, including soil type, hydrology characters and plant composition. Differences in soil particle composition, bulk density and soil moisture between ant mound and natural meadow were measured to assess the influences of ant mounds on soil physical properties. We also studied the effects of ant mounds on the microtopography of meadows. Ant mounds were found mainly in the transition zone between terrestrial and aquatic habitats, with wetland type, including Calamagrostis augustifolia wet meadow, C.augustifolia marsh meadow, shrubs marsh meadow and Carexmeyeriana–Carexappendiculata wetland, being a significant factor. Most of the mounds detected were inhabited by Lasius flavus Fabricius, Lasius niger Linnaeus and Formica sanguinea Latreille, which occupied 52.9%, 26.5% and 20.6% of the mounds surveyed, respectively. The density, height, diameter and mound composition were significantly different among the mounds of F. sanguinea Latreille, L. flavus Fabricius and L. niger Linnaeus. The average density and diameter of L. flavus mounds was significantly higher than those of other ant mounds. The average height of F. sanguinea mounds was highest among the mounds detected. Mound building activities changed soil particle size distribution, with the silt and clay content of mounds higher than for non-mound soil. Compared with adjacent, non-mound soil, the bulk density (0–30 cm) and water content (0–25 cm) of mound soil were significantly lower, but there were no significant differences between the mound soil of F. sanguinea Latreille and L. flavus Fabricius. The spatial distribution of ant mounds with different height and diameter also changed the micro-geomorphology of the soil surface, increasing the degree of fluctuation of the microtopography. The ant distribution characteristics and their ecological roles respond to a wide range of environmental alterations. The biogenic structures of ant and the specific environment associated with them have been defined as the “functional domain”, a sphere of influence that may significantly affect soil processes at certain spatial and temporal scales. Our results suggest that the distribution and structure of ant mounds can indicate wetland environmental changes, with mounds influencing ecosystem functions and enhancing wetland degradation.     

Spatial distribution of ant mounds and effects on soil physical properties in wetlands of the Sanjiang plain, China

Ants constitute a dominant element of soil mesofauna due to their biomass, abundance, richness of species and distribution within terrestrial ecosystems. They are important regulators of soil aggregate structure as they translocate large amounts of soil from the bottom to the soil surface. In doing so, they form biogenic structures (BS) made up of aggregates of different sizes and characteristics, i.e. ant mounds. These BS have varying characteristics according to the ant species and the soil where they carry their activities. Ants are considered soil engineers because of their effects on soil properties, availability of resource and flow of energy and nutrients in soil. Thus, it is important to gain information on their distribution and abundance. Relatively little is known about the spatial distribution of mounds and their role in the soil physical properties in wetlands of the Sanjiang plain, China. We conducted a survey of ant mounds and measured the density, height, and diameter and material composition of different ant mounds. The ecological characteristics of wetlands that ant mounds wide occurrence were also investigated, including soil type, hydrology characters and plant composition. Differences in soil particle composition, bulk density and soil moisture between ant mound and natural meadow were measured to assess the influences of ant mounds on soil physical properties. We also studied the effects of ant mounds on the microtopography of meadows. Ant mounds were found mainly in the transition zone between terrestrial and aquatic habitats, with wetland type, including Calamagrostis augustifolia wet meadow, C.augustifolia marsh meadow, shrubs marsh meadow and Carexmeyeriana–Carexappendiculata wetland, being a significant factor. Most of the mounds detected were inhabited by Lasius flavus Fabricius, Lasius niger Linnaeus and Formica sanguinea Latreille, which occupied 52.9%, 26.5% and 20.6% of the mounds surveyed, respectively. The density, height, diameter and mound composition were significantly different among the mounds of F. sanguinea Latreille, L. flavus Fabricius and L. niger Linnaeus. The average density and diameter of L. flavus mounds was significantly higher than those of other ant mounds. The average height of F. sanguinea mounds was highest among the mounds detected. Mound building activities changed soil particle size distribution, with the silt and clay content of mounds higher than for non-mound soil. Compared with adjacent, non-mound soil, the bulk density (0–30 cm) and water content (0–25 cm) of mound soil were significantly lower, but there were no significant differences between the mound soil of F. sanguinea Latreille and L. flavus Fabricius. The spatial distribution of ant mounds with different height and diameter also changed the micro-geomorphology of the soil surface, increasing the degree of fluctuation of the microtopography. The ant distribution characteristics and their ecological roles respond to a wide range of environmental alterations. The biogenic structures of ant and the specific environment associated with them have been defined as the “functional domain”, a sphere of influence that may significantly affect soil processes at certain spatial and temporal scales. Our results suggest that the distribution and structure of ant mounds can indicate wetland environmental changes, with mounds influencing ecosystem functions and enhancing wetland degradation.     

三江平原湿地生态系统P、K分布特征及季节动态研究

对三江平原毛果苔草,狭叶甜茅（Carex lasixarpa-Glyeria spiculosa)湿地和小叶章（Deyeuxia angusti,folia)湿地的值物,土壤和地表积水进行P,K含量测定,运用一元非线性回归分析对P,K元素含量季节动态特征进行了探讨,结果表明,不同种类的湿地植物,同种植物的不同器官其P,K含量存在的差异,但部特点是K含量高于P含量,说明湿地植物具有富集K的特性,两类湿地土壤P,K全量,速效果的剖面分布特征也不同,名层土壤全K含量均高于全P含量,植物,土壤和地表积水中P,K含量均有明的季节动态变化,一元非线性回归模拟均得到较理想的模拟模型,相关系数大多在0．9以上,F检验较显著。     

Effects of dissolved oxygen on extracellular enzymes activities and transformation of carbon sources from plant biomass: implications for denitrification in constructed wetlands

Dissolved oxygen (DO) concentrations have often been shown to be important to decomposition rates of plant litter and thus may be a key factor in determining the supply of dissolved organic carbon (DOC) and carbon-dependent denitrification in wetlands. During the 2 months operation, DOC accumulation in anaerobic condition was superior to aerobic condition due to higher activities of hydrolase enzymes and lower hydrolysates converted to gaseous C. Also, much higher denitrification rates were observed in wetland when using anaerobic litter leachate as the carbon source, and the available carbon source (ACS) could be used as a good predictor of denitrification rate in wetland. According to the results of this study, extracellular enzymes activities (EEAs) in wetland would change as a short-term consequence of DO. This may alter balance of litter carbon flux and the characteristics of DOC, which may, in turn, have multiple effects on denitrification in wetlands.     

三江平原恢复湿地土壤种子库特征及其与植被的关系

通过幼苗萌发法和样方调查相结合的方法对三江平原不同演替恢复阶段的种子库特征及其与植被的关系进行了研究。将开垦湿地、不同演替恢复阶段湿地以及天然湿地不同土壤层次(0-5、5-10 cm和根茎)的种子库在两种水分条件下(湿润、淹水10 cm)进行萌发处理。结果表明: 随着演替恢复阶段的进行, 种子库的结构和规模逐渐扩大, 地表群落表现出由旱生物种占优势的群落逐渐演变成以小叶章(Calamagrostis angustifolia)占优势的湿生群落的演替趋势。恢复7年湿地、恢复14年湿地、天然湿地土壤种子库萌发物种数分别为24种、29种、39种, 植被物种数为21种、25种、14种。湿地类型、水分条件和土壤层次均显著影响种子库萌发的物种数及幼苗数(p < 0.01)。种子库具有明显的分层现象, 天然湿地0-5 cm土层种子库种子萌发密度是5-10 cm土层的4倍左右, 而恢复湿地仅1.3倍左右, 且土层间萌发物种相似性系数较低。湿润条件下的萌发物种数显著高于淹水条件, 且两种水分条件下萌发物种的生活型不同。由于恢复时间较短, 不同演替恢复阶段的种子库与植被相似性维持在30%以下。湿地中根茎分蘖出大量的湿地物种, 对于小叶章等优势物种的繁殖具有重要作用。研究表明, 在开垦湿地退耕后的次生演替阶段, 种子库能够保持大量的湿地物种, 通过对湿地种子库与植被的关系研究, 能够为三江平原湿地群落演替与湿地恢复提供策略指导。     

A comparison of microbially and chemically reducible iron in three soils

Microbially reducible iron (water-soluble plus exchangeable forms) in three soils represented about 20% of the chemically reducible iron. The amount of iron reduced by microorganisms increased for about ten days to two weeks following flooding and thereafter remained constant. A similar trend was observed for the release of added Fe-59 in the soils following flooding, except that the reduction of labelled iron began earlier. In the more weathered soil, a higher proportion of the total iron was reduced by citrate-dithionite than in the relatively unweathered alluvial soils. Of labelled iron added, sequential reduction showed approximately 70% in the three soils was microbially reducible, an additional 20% was reduced by citrate-dithionite, and 10% of the labelled iron had moved into the residual form.     

Chemical and carbon isotopic evidence for the source and fate of dissolved organic matter in the northern Everglades

Surface waters in the Florida Everglades contain high levels ofdissolved organic carbon (DOC) compounds. ¹³C values of DOCsamples collected from the northern Everglades indicate that less than about23%of the DOC was derived from sugarcane (the dominant agricultural crop in thearea), and the amount of DOC from sugarcane was greater during the dry period.Most of the DOC (> 50%) in the northern Everglades was in the low molecularweight (< 1000 Dalton) fraction (LMW-DOC). The relative amount of highmolecular weight DOC (HMW-DOC) was higher in the wet period than in the dryperiod. Radiocarbon ages of the DOC ranged from > modern toabout 2400 years B.P., indicating that DOC was derived from both historic peatdeposits and modern vegetation. At each site, the HMW-DOC had older radiocarbonages than the LMW-DOC, and therefore contained a greater fraction of DOCderivedfrom the historic peat deposits. It appears that at least some of the old DOCcompounds from the historic peat deposits were decomposed during theirresidencein the surface water system in the northern Everglades, and the LMW-DOC wasmoremicrobially labile than the HMW-DOC. Our analysis suggests that accelerateddecomposition of organic matter in the historic peat deposits (due to land-usechange) could be a significant source of DOC and nutrients in the northernEverglades. Our data also suggest that the radiocarbon signature of DOC couldbeused as a sensitive indicator of the overall effectiveness of a wetlandrestoration project.     

Estimating phosphorus retention of existing and restored coastal wetlands in a tributary watershed of the Laurentian Great Lakes in Michigan,USA

Simulation modeling with uncertainty analysis was applied to the question of nonpoint source pollution control through extensive wetland restoration. The model was applied to the Quanicassee River basin, a tributary stream to Saginaw Bay on Lake Huron in northeastern Michigan, USA. An estimate of the role of the existing 695 ha of riverside and lake-side wetlands in the lower Quanicassee River basin suggests that they retain 1.2 metric tons of phosphorus per year (mt P/yr), or 2.5% of the total phosphorus load from the basin. A simple Vollenweider-type model of phosphorus retention by created wetlands, calibrated with 3-years of data from two wetland sites in Midwestern USA, was used to estimate the effect of major wetland restoration in the basin. For a wetland restoration project involving 15% of the Quanicassee River basin or 3,120 ha of wetlands, an estimated 33 mt P/yr could be retained, assuming a proper hydrologic connection between the wetlands and the river. This would represent a reduction of two-thirds of the existing phosphorus load to the Bay from the Quanicassee River basin. Large-scale wetland restoration appears to be a viable management practice for controlling phosphorus and other nonpoint source pollution from entering Saginaw Bay. It is an alternative that meets two major resource goals – developing wetland habitat and controlling pollution to the Great Lakes.     

Effects of monocot and dicot types and species richness in mesocosm constructed wetlands on removal of pollutants from wastewater

The effects of planting type and species richness on removal of BOD5, COD, nitrogen and phosphorus were studied in mesocosms with monocot alone (M), dicot alone (D) and mixed planting of M+D, where each planting type had four species richness levels. Above- and below-ground plant biomasses increased with the M and M+D species richness as shown by one-way ANOVA. The M+D type had the highest above-ground biomass, whereas the M type had the highest below-ground biomass among planting types. Carbon, nitrogen and phosphorus in the microbial biomass increased with the richness of the M and M+D type. Removals of BOD5, COD, inorganic P and total P did not change with the richness, but removals of NH4-N, NO3-N increased. Planting type impacted only removal of inorganic P, with higher removal of inorganic P in the M type.     

The ecological condition of geographically isolated wetlands in the southeastern United States: The relationship between landscape level assessments and macrophyte assemblages

Geographically isolated wetlands (GIWs) are common features of the Dougherty Plain physiographic region in southwestern Georgia. Due to lack of protection at the state and federal levels, these wetlands are threatened by intensive agricultural and silvicultural land uses common in the region. Recently, the ecological condition of such GIWs was assessed for the southeastern United States using the Landscape Development Intensity Index (LDI), a practical assessment tool that relies on remotely sensed land use and land cover (LULC) data surrounding isolated wetlands to rapidly predict wetland condition. However, no assessments have been attempted for GIWs in the Dougherty Plain specifically. Our goal was to develop a framework to guide and refine remote assessment of wetland condition within this agriculturally intense region of the southeastern USA. In this study, we characterized human disturbances associated with isolated wetlands in the Dougherty Plain, and paired the rapid assessment of GIWs using LDI with an intensive assessment of wetland plant communities. Specifically, we: (1) examined how macrophyte assemblages and vegetation metrics vary across a human disturbance gradient in the Dougherty Plain; (2) compared multiple condition assessment outcomes using variations of the LDI method that differed in spatial extent and resolution of LULC categories; and (3) determined the predicted condition of GIWs in the Dougherty Plain as indexed by LDI and compared with region-wide assessments of GIWs of the southeastern USA. Generally, the relationship between wetland plant communities and surrounding land use supported the assumptions of the LDI index in that wetlands surrounded by agricultural land use classes featured distinct plant communities relative to those surrounded by forested land use classes. Our results indicated that finer spatial resolution of LULC data improved the predictive ability of LDI. However, based on incongruence between wetland vegetation composition and LDI scores in some forested landscapes, this study identified limitations of the LDI assessment method, particularly when applied in regions in which prescribed fire is an important ecological driver of vegetation and habitat. Thus, we conclude that LDI may be biased toward an overestimation of reference condition GIWs, even though the habitat may be functionally degraded by the absence of natural processes such as fire. Regardless, relative to the assessment of the entire southeastern US, a greater proportion of total GIWs of the Dougherty Plain were identified as impaired due to the intensity of irrigated agricultural land use.