Nutrient dynamics at the interface between surface waters and groundwaters

1. The surface water/groundwater (SW/GW) interface is a crucial control point for lateral nutrient fluxes between uplands and aquatic ecosystems and for upstream/downstream (longitudinal) processes in lotic ecosystems. 2. Hydrological and biogeochemical dynamics of the SW/GW ecotone are linked to the degree of channel constraint and the sediment characteristics of the floodplain and stream bed. 3. The availability of specific chemical forms of electron donors and electron acceptors affects the spatial distribution of biogeochemical processes at the SW/GW interface. Temporal change in discharge is also a major factor affecting the rate and extent of these processes. 4. The magnitude of SW/GW interactions in lotic ecosystems is predicted to be a major determinant of solute retention. Channel morphology, stream bed composition and discharge are predicted to be important controls on SW/GW interactions. 5. Interdisciplinary research involving hydrologists, geomorphologists, aquatic ecologists, microbial ecologists and landscape ecologists is needed to further our present understanding of this critical interface linking terrestrial and aquatic ecosystems.     

Comparative ecotoxicity of suspended sediment in the lower Rhone River using algal fractionation,Microtox® and Daphnia magna bioassays

The toxicity associated with suspended sediments from the Rhone River (Switzerland-France) was determined with three acute bioassays. Large volume water samples were centrifuged for recovery of suspended solids in November 1989; one sample was taken as a control upstream from Lake Geneva and the 9 remainder downstream from Geneva to the Mediterranean Sea, with a single sample of the major tributary the Saône at Lyon. Heavy metals (Hg, Cd, Cr, Cu, Ni, Pb, Zn) and organic contaminants (OCs, PCBs, PAHs) bound to sediment were analysed and extracted by elutriation with filtered lake water and by organic solvent (dichloromethane). Sediment water elutriates were tested with algal fractionation bioassays (AFB) using Lake Geneva ambient phytoplankton, with Daphnia magna and Microtox® acute toxicity tests, whereas organic extracts were utilized in the latter two bioassays to evaluate the potential sediment toxicity.The bulk analyses of the sediment together with elutriate metal concentrations indicated the highest contamination of sediment downstream of Lyon. Medium contamination appeared for the stations downstream of Geneva, in the Saône River and at the Rhone River mouth. The station upstream of Lyon had low concentrations, comparable to the values in the Upper Rhone. Organic contaminants are mainly observed downstream of Lyon and their concentrations decline onwards to the sea. The bioassays Microtox® on organic extracts and AFB on the elutriates show a similar toxicity trend, but differ in that Microtox was more sensitive to organics whereas the algal test responded predominantly to metals. This difference is believed to be due to the different extraction procedures used, rather than to the tests themselves. Daphnia magna was the least sensitive and appeared to give a broader band response to the observed contaminants in the sediment. The bioassay results when integrated confirm that the biotoxicity trends relate well to the composition of the sediment, a factor which emphasizes the need for battery testing in ecotoxicological assessment.     

Diurnal changes in pore water sulfide concentrations in the seagrass Thalassia testudinum beds: the effects of seagrasses on sulfide dynamics

The dynamics of the seagrass-sulfide interaction were examined in relation to diel changes in sediment pore water sulfide concentrations in Thalassia testudinum beds and adjacent bare areas in Corpus Christi Bay and lower Laguna Madre, Texas, USA, during July 1996. Pore water sulfide concentrations in seagrass beds were significantly higher than in adjacent bare areas and showed strong diurnal variations; levels significantly decreased during mid-day at shallow sediment depths (0-10 cm) containing high below-ground tissue biomass and surface area. In contrast, diurnal variations in sediment sulfide concentrations were absent in adjacent bare patches, and at deeper (>10 cm) sediment depths characterized by low below-ground plant biomass or when the grasses were experimentally shaded. These observations suggest that the mid-day depressions in sulfide levels are linked to the transport of photosynthetically produced oxygen to seagrass below-ground tissues that fuels sediment sulfide oxidation. Lower sulfide concentrations in bare areas are likely a result of low sulfate reduction rates due to low organic matter available for remineralization. Further, high reoxidation rates due to rapid exchange between anoxic pore water and oxic overlying water are probably stimulated in bare areas by higher current velocity on the sediment surface than in seagrass beds. The dynamics of pore water sulfides in seagrass beds suggest no toxic sulfide intrusion into below-ground tissues during photosynthetic periods and demonstrate that the sediment chemical environment is considerably modified by seagrasses. The reduced sediment sulfide levels in seagrass beds during photosynthetic periods will enhance seagrass production through reduced sulfide toxicity to seagrasses and sediment microorganisms related to the nutrient cycling.     

漓江水陆交错带土壤理化性质及其分布特征

水陆交错带是水生生态系统与陆地生态系统之间的过渡带,是一种典型的生态交错区,承载着能量流动、物质循环和信息交换的重要作用。土壤作为水陆交错带系统的重要组成部分,是水陆交错带功能实现的基础之一。鉴于此,以桂林漓江水陆交错带纵向梯度(上游、中游、下游)不同植被覆盖条件下的土壤为研究对象,采用野外取样调查、实验分析与统计检验相结合,系统的分析了土壤理化性质及其分布特征,旨在为该区域退化生态系统恢复与重建提供依据。结果表明:11个土壤理化性质,其中5个指标(土壤含水量、全氮、全磷、速效氮和速效钾)在上游、中游和下游均差异性显著。不同梯度下的土壤理化性质的相关性及相关性大小也不尽相同,但在总体上存在一些较相似的变化规律,如上游、中游和下游的土壤容重和孔隙度均呈现显著负相关,土壤全磷和有机质与多数土壤化学性质呈显著正相关;土壤含水量在下游与多数土壤化学性质均显著相关,但在上游仅与土壤全磷显著负相关。PCA主成分分析表明,土壤容重、土壤孔隙度和土壤全磷含量的贡献均大于其他环境因子的平均贡献率,体现了它们是影响漓江水陆交错带土壤理化性质的重要环境因子。     

长白山落叶松和白桦-沼泽生态交错带群落演替规律研究

研究了长白山落叶松、白桦沼泽生态交错带群落演替规律,通过野外观测和建立斑块状态、林木蒸腾量与林木年龄的相关模型,利用相关模型定量地分析斑块和林木蒸腾量随林木年龄增长的动态变化过程,并分析了区域气候变化和群落演替的关系。探讨森林沼泽交错群落对湿地生境改造作用、湿地生境的中生化过程以及区域气候变暖对森林湿地演替的影响机制,揭示森林沼泽生态交错带群落的演替规律。结果表明,斑块宽度、高度、面积、体积随林木年龄增长均呈现三次式相关关系,林木蒸腾量随林木年龄增长呈现幂函数相关关系。落叶松、白桦沼泽交错群落经过60年左右时间发育,斑块将不断扩大,使地势平均升高0．405～0,590m;林木蒸腾量也不断增大,平均降低水位1．050～1．442m。森林湿地生境将演变为中生化的森林生境,同时,区域气候变暖与森林树种向湿地侵入存在密切关系,区域气候变暖将加快森林向湿地侵入进程,进而森林沼泽交错群落在相对较短的时间内(50～60年)将演替为森林群落。     

Biotic fluxes of matter and energy between aquatic and terrestrial ecosystems

This paper is an introduction to a special issue of the journal. A brief historical delineation of the question of studying interfaces between adjacent ecosystems (ecotones) is presented. High biodiversity of ecotones and their vulnerability to natural and anthropogenic impacts, including invasions of alien species, are noted. It is supposed that there is no contradiction between the ecotone and river continuum concepts. The important ecological role of amphibiotic animals and plants in interactions and functioning of the adjacent ecosystems is emphasized. The issue of studying the quantitative parameters of fluxes of matter and energy between ecosystems in conjunction with their qualitative parameters (chemical elemental and biochemical compositions) is considered in the present paper.     

Hydrodynamical impact on biogeochemical processes in aquatic sediments

Boundary layer flow characteristics and sediment permeability control pathways and magnitude of material exchange in the surface layer of aquatic sediments. In fine-grained cohesive beds, bottom currents and sediment microtopography shape the diffusive boundary layer and locally produce areas where the interfacial solute fluxes are increased or reduced. Where sediment permeabilities exceed 10^–12 m², advective pore water flows driven by boundary flow–topography interaction dominate the sediment–water exchange of matter, with transport rates that exceed those of molecular diffusion by two orders of magnitude and more. The curved paths of the advective pore flows through the surface layers of such sandy beds generate complex three-dimensional biogeochemical patterns with extreme spatial and temporal variability ranging from millimeters to decimeters and seconds to seasons. High filtration rates, a bacterial community firmly attached to the mineral grains, rapidly changing biogeochemical zonations and winnowing of the sediment surface layers by frequent resuspension convert these beds into effective biocatalytical filter systems.     

Seasonal variation in the diversity and species richness of phytoplankton in a tropical eutrophic reservoir

The water chemistry, structure of sediment grain size, algal biomass, and patterns of nine bacteria physiological groups were studied monthly from May to October 1991 in an adjacent stream, ecotone, and reservoir zones (southern Poland). The distribution of five particulate organic carbon fractions was significantly different among the zones. Biomass of benthic algae demonstrated a maximum in the ecotone (22.74 g C m^–2). Most of the bacterial groups were more numerous in the stream sediments where aerobic heterotrophs prevailed (1.2–6.5 × 10¹¹ cells m^–2). The significant differences in density were found for anaerobic heterotrophs, anaerobic nitrogen fixing, amylolytic, and cellulolytic bacteria among the zones. The small density of bacteria in the ecotone was probably an effect of the rapid water fluctuations, accompanied by movement of fine sediments or/and an inhibitory effect of compounds secreted by the periphyton. The principal component analysis showed that the ecotone zone was more similar to the reservoir open water than to the stream.     

Properties of ecotones: Evidence from five ecotones objectively determined from a coastal vegetation gradient

Abstract. Several properties have been suggested to be characteristic of ecotones, but their prevalence has rarely been tested. We sampled five ecotones to seek evidence on seven generalizations that are commonly made about ecotones: vegetational sharpness, physiognomic change, occurrence of a spatial community mosaic, many exotic species, ecotonal species, spatial mass effect, and species richness higher or lower than either side of the ecotone. The ecotones were in a sequence from scattered mangroves, through salt marsh, rush‐marsh, scrub, woodland, to pasture. We developed a method to objectively define, by rapid vegetational change, the position and depth of an ecotone, identifying five ecotones. Their positions were consistent across three sampling schemes and two spatial grain sizes. One ecotone is a switch ecotone, produced by positive feedback between community and environment. Another is anthropogenic, due to clearing for agriculture. Two others are probably environmental in cause, and one may be largely a relict environmental ecotone. Sharp changes in species composition occurred. Three ecotones were associated with a change in plant physiognomy. In two, the ecotone was located just outside a woodland canopy, in the zone influenced by the canopy. Community mosaicity was evident at only one ecotone. There were few strictly ecotonal species; many species occurred more frequently within ecotones than in adjacent vegetation, but there were never significantly more ecotonal species than expected at random. There was little evidence for the spatial mass effect reducing ecotonal sharpness, or leading to higher species richness within ecotones. Species richness was higher than in the adjacent habitat in only one ecotone. It seems that supposedly characteristic ecotone features depend on the particular ecological situation, and the ecology of the species present, rather than being intrinsic properties of ecotones.     

Estimating the ecotone width in patchy ecotones using a sigmoid wave approach

Ecotones are zones of transition between two adjacent ecological systems and are characterized by a high rate of change compared to these adjacent areas. They are dynamic entities with both a spatial and temporal property, reflected in an ecotone width and location, which vary across time during succession or environmental change on both a local or global scale. Various techniques have been proposed to characterize ecotones, one of them being a sigmoid wave curve fit on the transects across the ecotone. In this paper, we test the robustness of a sigmoid wave model approach on simulated ecotone data with a varying degree of steepness, patchiness and transect length. An analysis of variance (ANOVA) provided us details on the sensitivity of the estimated ecotone width for the steepness, the transect length as well as for the patchiness of the ecotone. The statistics also allowed us to investigate the interaction between the different parameters on the resulting ecotone width. We conclude that the sigmoid wave curve-fitting algorithm provides a robust way to describe ecotones with various degrees of steepness and patchiness. Depending on the transect window size used, a sigmoid wave curve-fitting algorithm will pick up variations in ecotone steepness or in ecotone steepness and patchiness.     

Benthic fluxes of nutrients and some trace metals in the Tamar estuary,SW England

Pore water concentration gradients and fluxes of chemical components have been studied in sediments from six intertidal sites in the Tamar Estuary, SW England over the course of a year. Fluxes of nutrients (ammonia, nitrate, nitrite, phosphate and silicate) and trace metals (iron, manganese, zinc, copper and cadmium) were determined using a laboratory microcosm incorporatingin situ pore water samplers. Nutrients (except nitrate) were transported out of the sediment throughout the year, but nitrate fluxes were directed into the sediment in the summer (denitrification) and out of the sediment in the winter (nitrification). The activities of benthic macrofauna resulted in enhanced fluxes but these differed between sites depending on population structure and density and whether irrigation or sediment reworking predominated. Fluxes of trace metals were seasonally and spatially variable and specific differences were observed that could be attributed to both chemical and biological activity.     

The complex effects of the invasive polychaetes Marenzelleria spp. on benthic nutrient dynamics

The effects of the polychaetes Marenzelleria sp. (Polychaeta, Spionidae), nonindigenous, rapidly increasing species in the Baltic Sea, on benthic nutrient fluxes, denitrification and sediment pore water nutrient concentration were studied in laboratory experiments using a flow-through setup with muddy sediment from coastal regions of the Gulf of Finland. In addition, different forms of sediment phosphorus (P), separated by chemical fractionation, were studied in three sediment layers. At a population density corresponding to about half the highest measured in the northern Baltic Sea, Marenzelleria sp. increased the fluxes of P and ammonium to the water column. No effect could be recorded for denitrification. Since the previously dominant species of the area, Monoporeia affinis, can enhance denitrification and lower the amount of dissolved P in the pore water, the replacement of M. affinis with Marenzelleria spp. may lead to increased P flux to the water column and decreased denitrification, further increasing the ammonium flux to the water column. However, sediment reworking by Marenzelleria spp. also oxidizes the surface sediment in the long run, improving its ability to retain P and support nitrification. Therefore, the impact of Marenzelleria spp. on sediment nutrient release may not be as drastic as the initial reactions seen in our experiments suggest.     

Sediment‐phosphorus dynamics can shift aquatic ecology and cause downstream legacy effects after wildfire in large river systems

Global increases in the occurrence of large, severe wildfires in forested watersheds threaten drinking water supplies and aquatic ecology. Wildfire effects on water quality, particularly nutrient levels and forms, can be significant. The longevity and downstream propagation of these effects as well as the geochemical mechanisms regulating them remain largely undocumented at larger river basin scales. Here, phosphorus (P) speciation and sorption behavior of suspended sediment were examined in two river basins impacted by a severe wildfire in southern Alberta, Canada. Fine‐grained suspended sediments (<125 μm) were sampled continuously during ice‐free conditions over a two‐year period (2009–2010), 6 and 7 years after the wildfire. Suspended sediment samples were collected from upstream reference (unburned) river reaches, multiple tributaries within the burned areas, and from reaches downstream of the burned areas, in the Crowsnest and Castle River basins. Total particulate phosphorus (TPP) and particulate phosphorus forms (nonapatite inorganic P, apatite P, organic P), and the equilibrium phosphorus concentration (EPC₀) of suspended sediment were assessed. Concentrations of TPP and the EPC₀ were significantly higher downstream of wildfire‐impacted areas compared to reference (unburned) upstream river reaches. Sediments from the burned tributary inputs contained higher levels of bioavailable particulate P (NAIP) – these effects were also observed downstream at larger river basin scales. The release of bioavailable P from postfire, P‐enriched fine sediment is a key mechanism causing these effects in gravel‐bed rivers at larger basin scales. Wildfire‐associated increases in NAIP and the EPC₀ persisted 6 and 7 years after wildfire. Accordingly, this work demonstrated that fine sediment in gravel‐bed rivers is a significant, long‐term source of in‐stream bioavailable P that contributes to a legacy of wildfire impacts on downstream water quality, aquatic ecology, and drinking water treatability.     

The role of <Emphasis Type="Italic">Campsurus notatus</Emphasis> (Ephemeroptera: Polymitarcytidae) bioturbation and sediment quality on potential gas fluxes in a tropical lake

About 30% of the total area of Lake Batata (Amazon) was impacted by the disposal of bauxite tailings originated from the process of washing bauxite. This effluent, composed by fine particles of clay and water, settled on top of the natural sediment, originating a new substratum with a different physical and chemical composition. This phenomenon created a new distinct habitat (impacted sediment) influencing the benthic community. The aim of this study was to evaluate the impact of bioturbation by Campsurus notatus (Ephemeroptera: Polymitarcytidae) on potential gas fluxes in the sediment of natural and impacted areas of the lake. The natural sediment had a significantly higher methane concentration when compared to the impacted one. In incubated sediment cores, the presence of C. notatus nymphs resulted in a significant increase in oxygen consumption and methane and carbon dioxide release to the water column. The effect of the presence of nymphs on methane was ambiguous. The C. notatus nymphs strongly decreased methane concentration in natural sediment samples, probably because of the enhancement of the oxic sediment area. However, this effect was not observed in impacted samples. Finally, the new substratum of Lake Batata decreased methane concentration in sediment and water column. C. notatus nymphs demonstrated to have a significant role on gas flux (methane and CO₂) from sediment to water column as well as on oxygen consumption in Lake Batata, consequently influencing the carbon cycle in this lake. Handling editor: S. M. Thomaz     

Relationships between Solutes,Nutrients, and the Biofilm in Sediments of Floodplain Karstic and Alluvial Springs

Two pairs of springs were surveyed in the floodplain of the Upper Rhône River. Each pair included a karstic (upstream) and an alluvial (downstream) spring in the same catchment. Various physical, chemical, and biological factors were measured in the water and the sediment. The study showed karstic and alluvial spring typology. In each pair, the karstic springs were characterized by higher alkalinity, whereas alluvial springs were fed both by karstic groundwater and Rhône River water with higher sulphate content. Organic matter dynamics and retention processes were different in each spring. The distribution and abundance of fine sediment played a prominent role in the storage of particulate organic carbon and the development of microbial biomass and activity. The hydrological cycle governed organic and inorganic nutrient fluxes, and was, with temperature, the main factor influencing microbial and macroinvertebrate dynamics. The high amount of organic matter in one alluvial spring was correlated with high microbial biomass and activity.     

Novel patch–matrix interactions: patch width influences matrix use by birds

This study investigated the influence of the width of patches of native eucalypt forest on bird occurrence in stands of exotic radiata pine ( Pinus radiata ) forests that surrounded such patches. Boundaries between eucalypt and pine forests were surveyed to examine bird occurrence and species richness at different distances in the pine matrix from eucalypt forest edges. Birds were counted by the area search method within 0.5 ha quadrats at 32 study sites (where sites spanned the boundaries of pine and eucalypt forests). Data were examined using generalised linear mixed models. Species richness and occurrence of particular species in quadrats located within pine forests decreased with increasing distance from eucalypt patches. This resulted, in part, from the fact that several species found in native patches also use pine plantations as additional foraging areas. Species richness decreased more quickly with distance from eucalypt patches in younger than in older pine stands. The width of native forest patches also influenced bird occurrence in adjacent pine forest matrix. Bird species richness decreased more rapidly in exotic plantations adjacent to wide rather than narrow patches of native forest. To the best of our knowledge, no studies have previously reported that dimensions of patches can influence the use of surrounding matrix. We introduce the term "halo effect" for the influence of patch attributes on the differential use of matrix adjacent to native patches. These patterns highlight that conservation efforts in patchy environments should protect not only native patches but also adjacent areas of matrix into which animals extend their home ranges.     

生态交错带及其研究进展

生态交错带研究对探索自然生态规律和保护环境有重要意义。近30a来,有关生态交错带的论文数平均年增57%,显示其得到了愈来愈广泛的关注。回顾了生态交错带概念的产生与发展,区分了它与边缘、生态边界层与生态过渡带等概念的异同;简述了其7个基本属性,即高生物多样性、丰富的特有种、大量外来种、频繁的物质流动、敏感的时空动态性、结构的异质性和脆弱性;总结提炼了生态交错带的基本原理和假说;综述了生态交错带的生物多样性产生机制、对全球变化的响应与反馈、生态设计与管理以及生态交错带模型发展和整合的研究进展。提出今后需要大力发展理论研究、多尺度模型转化和多因子综合分析,以完善生态交错带理论并支持生态学机理的探索。     

Measuring the abruptness of patchy ecotones – A simulation-based comparison of landscape pattern statistics

The use of statistics of landscape pattern to infer ecological process at ecotones requires knowledge of the specific sensitivities of statistics to ecotone characteristics. In this study, sets of patch-based and boundary-based statistics were evaluated to assess their suitability as measures of abruptness on simulated ecotone landscapes. We generated 50 realizations each for 25 groups of ecotones that varied systematically in their degree of abruptness and patchiness. Factorial ANOVA was used to evaluate the sensitivity of statistics to the known differences among the simulated groups. Suitability of each index for measuring abruptness was evaluated using the ANOVA results. The statistics were then ranked in order of their suitability as abruptness statistics based on their sensitivity to abruptness, the consistency of the relationship, and their lack of sensitivity to patchiness. The two best statistics for quantifying abruptness were those we developed based on lattice delineation methods, and are called cumulative boundary elements and boundary element dispersion. The results of this research provide support for studies of ecotone process that rely on the interpretation of patch or boundary statistics.     

Against the flow: chemical detection of downstream predators in running waters

In running waters, chemical cues have generally been assumed to always come from upstream locations. Here, we present field and laboratory evidence that Gammarus pulex can use chemical cues from downstream predators to adaptively adjust drifting behaviour. In the field, significantly fewer Gammarus migrated into stream enclosures where brown trout (Salmo trutta) were present than into control enclosures. In a subsequent laboratory experiment, Gammarus actively avoided live trout and trout chemicals placed downstream in an artificial stream, whereas no effects were found in response to control or visual cues. We suggest that the mechanism explaining the ability of Gammarus to detect downstream predators is use of backflows, which locally transport fish chemicals against the main flow. Such backflows are both created by the Gammarus itself and by surrounding substrate heterogeneity. These results profoundly affect the way in which we view the chemical environment of running waters and have important implications for empirical and theoretical work evaluating predator effects in running waters, as they demonstrate that prey immigration rates can depend on downstream predator densities.     

Multiple Stressors in Agricultural Streams: A Mesocosm Study of Interactions among Raised Water Temperature,Sediment Addition and Nutrient Enrichment

Changes to land use affect streams through nutrient enrichment, increased inputs of sediment and, where riparian vegetation has been removed, raised water temperature. We manipulated all three stressors in experimental streamside channels for 30 days and determined the individual and pair-wise combined effects on benthic invertebrate and algal communities and on leaf decay, a measure of ecosystem functioning. We added nutrients (phosphorus+nitrogen; high, intermediate, natural) and/or sediment (grain size 0.2 mm; high, intermediate, natural) to 18 channels supplied with water from a nearby stream. Temperature was increased by 1.4°C in half the channels, simulating the loss of upstream and adjacent riparian shade. Sediment affected 93% of all biological response variables (either as an individual effect or via an interaction with another stressor) generally in a negative manner, while nutrient enrichment affected 59% (mostly positive) and raised temperature 59% (mostly positive). More of the algal components of the community responded to stressors acting individually than did invertebrate components, whereas pair-wise stressor interactions were more common in the invertebrate community. Stressors interacted often and in a complex manner, with interactions between sediment and temperature most common. Thus, the negative impact of high sediment on taxon richness of both algae and invertebrates was stronger at raised temperature, further reducing biodiversity. In addition, the decay rate of leaf material (strength loss) accelerated with nutrient enrichment at ambient but not at raised temperature. A key implication of our findings for resource managers is that the removal of riparian shading from streams already subjected to high sediment inputs, or land-use changes that increase erosion or nutrient runoff in a landscape without riparian buffers, may have unexpected effects on stream health. We highlight the likely importance of intact or restored buffer strips, both in reducing sediment input and in maintaining cooler water temperatures.