Organic Vegetation Research Articles

Exploring the factors influencing the carbon sink function of coastal wetlands in the Yellow River Delta

Understanding the mechanisms of the coastal wetland ecosystem carbon sink function is crucial for adapting to, mitigating, and predicting global climate change. Landscape metrics and Carnegie Ames Stanford Approach (CASA) model were used to quantify the spatiotemporal patterns of soil organic carbon (SOC) and vegetation carbon sequestration (VCS) in the Yellow River Delta (YRD). GeoDetector model was used to explore the effects of various factors influencing VCS. The results showed that: (1) From 1999 to 2020, the area of natural wetlands and non-wetlands decreased, while the area of artificial wetlands increased. (2) The SOC stock in the 0 ~ 100 cm depth in 1999 and 2020 were about 7.8871 Tg C and 7.0521 Tg C, respectively. The amount of VCS increased from 0.2309 Tg C in 2000 to 0.3681 Tg C in 2020, with a significant annual increase of 6532 Mg C. In the past 21 years, the total carbon sink in the YRD was 6.0952 Tg C. The amount of VCS was equivalent to 2.93% of SOC stock in 1999, rising to 5.22% by 2020. (3) Vegetation cover has the greatest influence on the carbon sink function in the YRD, followed by precipitation and biodiversity. From 2000 to 2020, the effect of biodiversity on the carbon sinks of natural wetlands and artificial wetlands increased. The synergistic effect of wetland type and vegetation cover on carbon sink effect was replaced by the synergistic effect of biodiversity and vegetation cover. The identification of the primary factors that influence VCS in the YRD is significant to the understanding of the spatiotemporal evolution of carbon sink effect in coastal wetland ecosystems, and to the guidance of the rational development and protection of coastal wetlands and promote sustainable ecosystem development.

Midge Paleo-Communities (Diptera Chironomidae) as Indicators of Flood Regime Variations in a High-Mountain Lake (Italian Western Alps): Implications for Global Change

Sediments of alpine lakes serve as crucial records that reveal the history of lacustrine basins, offering valuable insights into the effects of global changes. One significant effect is the variation in rainfall regimes, which can substantially influence nutrient loads and sedimentation rates in lacustrine ecosystems, thereby playing a pivotal role in shaping biotic communities. In this study, we analyze subfossil chironomid assemblages within a sediment core from an alpine lake (western Italian Alps) to investigate the effects of rainfall and flood regime variations over the past 1200 years. Sediment characterization results highlight changes in sediment textures and C/N ratio values, indicating phases of major material influx from the surrounding landscape into the lake basin. These influxes are likely associated with intense flooding events linked to heavy rainfall periods over time. Flooding events are reflected in changes in chironomid assemblages, which in our samples are primarily related to variations in sediment texture and nutrient loads from the surrounding landscape. Increased abundances of certain taxa (i.e., Brillia, Chaetocladius, Cricotopus, Psectrocladius, Cricotopus/Orthocladius Parorthocladius) may be linked to higher organic matter and vegetation inputs from the surrounding landscape. Biodiversity decreased during certain periods along the core profile due to intense flood regimes and extreme events. These results contribute to our understanding of alpine lake system dynamics, particularly those associated with intense flooding events, which are still understudied.

Ditch cleaning in boreal catchments: Impacts on water chemistry and dissolved greenhouse gases in runoff

Ditch cleaning (DC) is a forestry practice commonly conducted in boreal regions that aim to lower groundwater tables (GWT) in waterlogged soils, thereby maintaining or improving forest growth. However, there is limited information on the impact of DC on water chemistry and dissolved greenhouse gases (GHG) in draining ditch networks. Based on a repeated synoptic sampling of a paired catchment design we here evaluated water chemistry and GHG data in ditch waters from 25 cleaned sites (being cleaned 1–4 years prior to sampling) and 25 non-cleaned reference sites (REF). The sampled sites were further selected to test whether there were any differences in the DC effect if the operations were conducted in forested or clear-cut areas. Across all sites, we found that DC sites exhibited higher pH, sulfate and calcium concentrations than REF sites. Also, lower dissolved carbon dioxide and higher nitrous oxide concentrations were observed in DC sites. In forested areas, DC sites exhibited significantly higher calcium and potassium concentrations, along with reduced levels of methylmercury and carbon dioxide. In clear-cuts, sulfate concentrations were significantly elevated in the DC sites. We suggest that the observed differences in water chemistry and GHG´s between DC and REF sites were induced by the DC and largely driven by lower GWT following DC, resulting in deeper groundwater flow paths through more mineral-rich soil layers, and altered redox conditions. Also, the removal of organic rich sediments and vegetation from the ditches themselves may affect water chemistry and GHG´s e.g. by decreasing the formation of methylmercury and carbon dioxide.

Spatiotemporal distribution and inter-media transfer of polycyclic aromatic hydrocarbons in Shanghai, China: Historical patterns and future trends

Spatiotemporal distribution and inter-media transfer of polycyclic aromatic hydrocarbons in Shanghai, China: Historical patterns and future trends

Tracking Land-use Trajectory and Other Potential Drivers to Uncover the Dynamics of Carbon Stocks of Terrestrial Ecosystem in the Songnen Plain

Land-use change is an important factor affecting terrestrial carbon balance, and it is crucial to explore the response of terrestrial carbon stocks to land-use change, especially in the Songnen Plain, which faces a fierce conflict between the rapid growth of production activities and ecosystem degradation. In this study, we measured soil organic carbon and vegetation biocarbon stocks in the Songnen Plain based on IPCC-recommended methodologies, and explored the characteristics of carbon stock changes in land-use trajectories, land-use drivers, and specific land-use change scenarios (cropland cultivation, returning cropland to forests, the expansion of land for construction, deforestation, greening, and land degradation). The results showed that soil organic carbon stock in the Songnen Plain decreased by 1.63 × 105 t, and vegetation biocarbon stock increased by 2.10 × 107 t from 2005 to 2020. Human factors and natural factors jointly contributed to the land-use change, but the extent of the role of human factors was greater than that of natural factors. The increase in land-use trajectory led to the decrease in soil organic carbon stock and the increase in vegetation biocarbon stock. There was no difference in the effects of human-induced and natural-induced land-use changes on vegetation biocarbon stocks, but the effects on soil organic carbon stocks were diametrically opposite, increasing by 43.27 t/km2 and decreasing by 182.02 t/km2, respectively. The reclamation of arable land, returning cropland to forests, and greening led to a net increase in terrestrial carbon stocks (+813,291.84 t), whereas land degradation, deforestation, and land-use expansion led to a decrease in terrestrial carbon stocks (−460,710.2 t). The results of this study can provide a reference for the adjustment of land-use structure and the increase in terrestrial carbon stock in the Songnen Plain.

Burrow morphology of three species of fiddler crab (Uca) along the coast of Pakistan

Burrowing by crabs is an important component of their functional role in mangrove biotopes. The Fiddler crab (Uca) is one of the more conspicuous burrowing organisms in the mangrove areas of Pakistan. To evaluate interspecific differences in burrowing behaviour between three species of Uca (U. annulipes, U. chlorophthalmus and U. sindensis), we compared vegetation cover, sediment composition and burrow morphology by using plaster of Paris casts. Five burrow morphology characters were measured (burrow number, depth, length, volume, and diameter of the burrow openings). Nearly all the morphological characters of the burrows differed significantly between species. The burrow morphology variations were correlated with the tidal level (distance from the water mark during low tide), porosity, percent organic matter, vegetation cover and structure of the sediments. The species-specific differences in the burrows cautions against generalizing regarding the functional role of fiddler crabs along the coast of Pakistan.

Uncertainty in measuring the role of climate change on debris-flow triggering on volcanoes - bulk-density, temperature and moisture analysis at Unzen Volcano (Japan)

As climate change creeps into the 21st century, the intensity of debris flows due to heavy and concentrated rainfall has increased in mountainous regions of Japan and East Asia. However, the relationship between climate change and an increase in debris flows is likely to be non-linear. Rainwater infiltrates more quickly into porous material, and the lack of vegetation cover increases evaporation and the temperature of surface sediments. In addition, periodic gully collapses bring fresh layers of porous material that increase the distance between the surface and the vadose zone. Therefore, to understand the relationship between volcanic debris flows (or lahars), parameters such as density, porosity, temperature, and moisture retention must be captured in detail in both time and space. The aim of this paper is to assess the role of loose, coarse, and porous sediments in lahar triggering. The present study was conducted at Unzen volcano in the Tansandani Guly between 31 May and 1 June 2023, 30 years after the last eruption. The dacite material is composed of a matrix of sand and coarse sand mixed with larger fractions and blocks, therefore traditional density measurement methods could not be applied, and a photogrammetric based method was used. In the field, sets of SfM-MVS photographs were taken before and after digging a hole in the sediments so that the measured mass could be compared to the volume of the hole in the sediments. After the sediments were dried, the dry and wet density, bulk density and porosity of the sample were calculated. When compared to the temperature data collected in the field, the following results were obtained: (1) The porosity of the volcanic material was highest in the lower reaches, followed by the upper reaches, and lowest in the middle reaches. This may be because fine sand washed out of the upstream area by rainfall is currently stored in the midstream area, which may facilitate debris flow generation. In addition, the downstream area has a high porosity, which may be due to the surrounding vegetation preventing the influx of new fine sand from the channel wall. (2) Because of the higher porosity and the lack of organic matter and vegetation cover, the increase in temperature acts more directly on the decrease in water content than in mountainous areas. Consequently, empirical equations for the potential for mudslides in volcanic areas with respect to surface temperature and soil moisture need to be developed for hazard and disaster risk management purposes.

Automatic nutrient estimator: distributing nutrient solution in hydroponic plants based on plant growth.

The primary objective is to address the specific needs of plants at different growth stages by delivering precise nutrient concentrations tailored to their developmental requirements. Challenges such as uneven nutrient distribution, fluctuations in pH and electrical conductivity, and inadequate nutrient delivery pose potential hindrances to achieving optimal plant health and yield in hydroponic systems. By overcoming these challenges, the hydroponic farming community aims to enhance the accuracy of nutrient dosing, streamline automation processes, and minimize resource wastage. Hydroponics, a cultivation technique without soil, facilitates the growth of organic vegetation while concurrently minimizing water use and eliminating the necessity for pesticides. In order to achieve effective cultivation of hydroponic plants, it is essential to maintain a controlled environment that encompasses essential factors such as temperature, carbon dioxide (CO2) levels, oxygen availability, and appropriate lighting conditions. Additionally, it is crucial to ensure the provision of vital nutrients to maximize output and productivity. Due to the demanding nature of a hydroponic farmer's schedule, it is necessary to minimize the amount of time dedicated to nutrient management, as well as pH and EC adjustments. In order to determine and deliver the proper amount of vital nutrients, such as nitrogen, phosphorus, and potassium, based on the plant growth stage, we presented an automatic hydroponic nutrient estimator in this system. We noticed that the plant's nutrient consumption varies depending on its stage of growth according to plant psychology. Four peristaltic pumps with the necessary sensors are controlled by an Arduino board in the suggested system. Both filling and draining the water are done using each pump. To identify the plant stage, we apply the Plant Growth Stage Identification algorithm to encompass the seedling, vegetative, flowers, and fruit stages. The experimental results reveal that the Growth Stage Identification algorithm obtains 97.5% accuracy for the first 5 weeks with 1,715 ppm of nutrition ingestion, identifying the vegetative state. The flowering stage is identified with 97.5% accuracy in the 6-9th week with 2,380 ppm of nutrition consumption, and the fruiting location is determined with 99.4% accuracy in the last 10-15th week with 2,730 ppm of nutrition consumption.

Human risk to tick encounters in the southeastern United States estimated with spatial distribution modeling.

Expanding geographic distribution and increased populations of ticks has resulted in an upsurge of human-tick encounters in the United States (US), leading to an increase in tickborne disease reporting. Limited knowledge of the broadscale spatial range of tick species is heightened by a rapidly changing environment. Therefore, we partnered with the Forest Inventory and Analysis (FIA) program of the Forest Service, U.S. Department of Agriculture and used passive tick surveillance to better understand spatiotemporal variables associated with foresters encountering three tick species (Amblyomma americanum L., Dermacentor variabilis Say, and Ixodes scapularis L.) in the southeastern US. Eight years (2014-2021) of tick encounter data were used to fit environmental niche and generalized linear models to predict where and when ticks are likely to be encountered. Our results indicate temporal and environmental partitioning of the three species. Ixodes scapularis were more likely to be encountered in the autumn and winter seasons and associated with soil organic matter, vegetation indices, evapotranspiration, temperature, and gross primary productivity. By contrast, A. americanum and D. variabilis were more likely to be encountered in spring and summer seasons and associated with elevation, landcover, temperature, dead belowground biomass, vapor pressure, and precipitation. Regions in the southeast least suitable for encountering ticks included the Blue Ridge, Mississippi Alluvial Plain, and the Southern Florida Coastal Plain, whereas suitable regions included the Interior Plateau, Central Appalachians, Ozark Highlands, Boston Mountains, and the Ouachita Mountains. Spatial and temporal patterns of different tick species can inform outdoorsmen and the public on tick avoidance measures, reduce tick populations by managing suitable tick habitats, and monitoring areas with unsuitable tick habitat for potential missed encounters.

Slope planting patterns are superior to ditch grassing in reducing ditch erosion load to rivers: Evidenced from a five-year study in an intensive sugarcane growth watershed

Slope planting patterns are superior to ditch grassing in reducing ditch erosion load to rivers: Evidenced from a five-year study in an intensive sugarcane growth watershed

Modelling the terrestrial nitrogen and phosphorus cycle in the UVic ESCM

Abstract. Nitrogen (N) and phosphorus (P) biogeochemical dynamics are crucial for the regulation of the terrestrial carbon cycle. In Earth system models (ESMs) the implementation of nutrient limitations has been shown to improve the carbon cycle feedback representation and, hence, the fidelity of the response of land to simulated atmospheric CO2 rise. Here we aimed to implement a terrestrial N and P cycle in an Earth system model of intermediate complexity to improve projections of future CO2 fertilization feedbacks. The N cycle is an improved version of the Wania et al. (2012) N module, with enforcement of N mass conservation and the merger with a deep land-surface and wetland module that allows for the estimation of N2O and NO fluxes. The N cycle module estimates fluxes from three organic (litter, soil organic matter and vegetation) and two inorganic (NH4+ and NO3-) pools and accounts for inputs from biological N fixation and N deposition. The P cycle module contains the same organic pools with one inorganic P pool; it estimates influx of P from rock weathering and losses from leaching and occlusion. Two historical simulations are carried out for the different nutrient limitation setups of the model: carbon and nitrogen (CN), as well as carbon, nitrogen and phosphorus (CNP), with a baseline carbon-only simulation. The improved N cycle module now conserves mass, and the added fluxes (NO and N2O), along with the N and P pools, are within the range of other studies and literature. For the years 2001–2015 the nutrient limitation resulted in a reduction of gross primary productivity (GPP) from the carbon-only value of 143 to 130 Pg C yr−1 in the CN version and 127 Pg C yr−1 in the CNP version. This implies that the model efficiently represents a nutrient limitation over the CO2 fertilization effect. CNP simulation resulted in a reduction of 11 % of the mean GPP and a reduction of 23 % of the vegetation biomass compared to the baseline C simulation. These results are in better agreement with observations, particularly in tropical regions where P limitation is known to be important. In summary, the implementation of the N and P cycle has successfully enforced a nutrient limitation in the terrestrial system, which has now reduced the primary productivity and the capacity of land to take up atmospheric carbon, better matching observations.

Generation of soil maps permeability. Case study in two cantons of Loja province, Ecuador

The generation of permeability maps is based on the analysis and interpretation of geology, environmental morphology, land use, and slope, which enables the selection of sampling areas with similar characteristics. The method represents the integration of the physical characteristics of the study area and then determines the infiltration capacity differences in the most representative geopedologic units. In determining the basic data, minidisc infiltrometers were used to perform seventy-two infiltration tests in different types of soils with varying organic matter content, texture, soil structure, and vegetation cover, which showed the spatial variability that exists in two cantons of Loja province, Ecuador. In addition, it was observed that the infiltration rate depended mainly on the content of the organic matter in the soil and is consistent with information collected on permeability worldwide. In this study, generated pedotransfer function (FTP) coefficient of determination R2 0.78, the determination of the coefficient indicates a satisfactory estimate of the permeability with the variables that were analyzed; in addition, the methodology for assessing the permeability was suitable for the conditions of this investigation. For this reason, the method described here should be tested in other areas of the country with a greater number of field trials and with more variable contents of organic matter and soil textural classes.

Evaluating the Ecological Status of Fluvial Networks of Tropical Andean Catchments of Ecuador

In the tropical high mountains, human activities have strongly intensified in recent decades. Agricultural frontier movement toward higher elevations, river channel modifications, mining, and urban waste discharge threaten river ecosystem health, which is even more alarming when drinking water supply comes from surface water. The aim of the current study was to evaluate the ecological status of high mountain fluvial networks of tropical Andean catchments based on the definition of different river types. Physical–chemical variables and macroinvertebrate communities were sampled in 90 stations of seven tropical high mountain catchments. River habitat and riparian vegetation quality were further evaluated. K-means classification, using physical and hydro-morphological characteristics, identified six different river types. This classification was further refined to five river types by the analyses of macroinvertebrate communities through multidimensional scaling and analysis of similarity. The anthropogenic pressure gradients, present in the different river types, were inorganic (i.e., conductivity, turbidity), organic (i.e., fecal coliforms), river habitat, and riparian vegetation quality. Macroinvertebrate communities responded to different environmental variables in the páramo, mountain forest with humid shrub, urban, and Tarqui river types. Heterogeneous fluvial habitats and high altitude favored taxa such as Atanatolica, Mortoniella, Helicopsyche, Anacroneuria, Paltostoma, Helicopsyche, Paltostoma, Atopsyche, Pheneps, and Maruina. Chironomidae and Psychoda dipteran were associated with higher biochemical oxygen demand, lower oxygen concentration, high fecal coliforms, and total dissolved solids, while Haitia was linked to elevated nitrate concentrations. Integrated watershed management could benefit from a well-established biomonitoring network, considering different river types, which represents the natural variability of the ecosystems, as well as anthropogenic pressure gradients.

Nitrogenous and Phosphorus Soil Contents in Tierra del Fuego Forests: Relationships with Soil Organic Carbon, Climate, Vegetation and Landscape Metrics

Soil nitrogen (SN) and soil phosphorus (SP) contents support several ecosystem services and define the forest type distribution at local scale in Southern Patagonia. The quantification of nutrients during forest surveys requires soil samplings and estimations that are costly and difficult to measure. For this, predictive models of soil nutrients are needed. The objective of this study was to quantify SN and SP contents (30 cm depth) using different modelling approaches based on climatic, topographic and vegetation variables. We used data from 728 stands of different forest types for linear regression models to map SN and SP. The fitted models captured the variability of forest types well (R²-adj. 92–98% for SN and 70–87% for SP). The means were 9.3 ton ha−1 for SN and 124.3 kg ha−1 for SP. Overall, SN values were higher in the deciduous forests than those in the mixed evergreen, while SP was the highest in the Nothofagus pumilio forests. SN and SP are relevant metrics for many applications, connecting major issues, such as forest management and conservation. With these models, the quantification of SN and SP stocks across forests of different protection status (National Law 26,331/07) and national/provincial reserve networks is possible, contributing to the determination of nutrient contents at landscape level.

A Multi-Community Approach in Biodiversity Assessment of a Peat Bog in the Southern Carpathians (Romania) and Implications for Conservation.

Although natural peatlands have been recognized as an important type of wetlands because they support high biodiversity and provide important ecosystem services, the value of peatlands both in biodiversity research and conservation is still largely underestimated. Our study characterizes the biodiversity and conservation value of Peşteana peat bog, an upland mesotrophic peat bog, located in the Southern Carpathians, Romania. More specifically, we: (1) characterized the invertebrate (i.e., top soil, surface litter, and plant-dwelling) and plant communities along a humidity gradient in Peşteana peat bog and nearby habitats (i.e., treeline, ecotone, lowland and highland meadow, and forest), (2) assessed the main environmental factors driving the invertebrate community diversity and composition, and (3) determined the relationship between invertebrate community diversity and vegetation, focusing on the top soil invertebrates. Our study revealed a high diversity of invertebrates spanning over 43 taxonomic groups and a high number of plant indicator species, emphasizing the role of natural peatlands in preserving diverse communities in a small area. The results showed that the composition of top soil invertebrate community was determined by depth of organic layer, vegetation cover, and soil compaction. We found that the diversity of top soil invertebrate community was strongly influenced by habitat type and soil attributes and weakly by vegetation. Overall, the invertebrate and plant communities showed different responses to habitat conditions along the humidity gradient. This highlights the importance of using a multi-community approach to support the design of effective conservation and management actions beneficial for a wide range of taxa.

Soil bacterial community structure in the habitats with different levels of heavy metal pollution at an abandoned polymetallic mine.

Soil bacterial community structure in the habitats with different levels of heavy metal pollution at an abandoned polymetallic mine.

Evaluating the Effect of Fire on Cultivated Tropical Peat Properties: Lessons Learned from Observation in East Kutai Peatlands

Fire and its associated impact highly affect peatland, particularly the peat properties, the plant cultivated above it, and its surrounding environment. Despite much research focused on fire monitoring or susceptibility assessments, peat consumption during fire occurrence, emissions from burned peat, and rehabilitation or restoration of burned peat, little attention is given to studying the changes of peat bio-physicochemical after burning. This small-scale study aims to examine the fire’ effect on the upper 30 cm of peat’s bio-physicochemical properties two months after being burned, using unburned peat as a reference. The result of this study indicated that fire-affected peat at all of our sampling depths. The impacted changes on peat chemical variables were varied. This study also found that sampling methods, fire magnitude and severity, peat physicochemical properties, laboratory determination, and statistical analyses were paramount in examining the fire effect on peat properties. This study also promotes the combination approach that represents both local and global phenomena to analyze and interpret the change of burned peat properties from its initial unburned state. More efforts are required to verify the initial results reported in this study and to gain in-depth information concerning the intricate relationships of organic materials, climate, hydrology, and vegetation across spatial and temporal scales in cultivated tropical peat as affected by fire events.

Use of pulp mill biosolids to stimulate forest plant growth on an industrial footprint with marginal soil

Land application of biosolids may be an effective strategy to improve soil quality and better support the establishment of native vegetative cover on an industrial footprint with marginal soil. Biosolids can influence the C sequestration potential of impacted soils at the onset of reclamation activities by facilitating soil development processes and enhancing primary productivity, thereby leading to an increase in soil organic carbon (SOC) accumulation.The objective of this study was to examine the ameliorative effects of biosolids originating from a regional pulp and paper company on soil and vegetation development at a reclaimed airstrip in NW Alberta with limited topsoil replacement. Three biosolids application treatments (0 [control], 6.2, and 15.5 T ha−1) were established and vegetation was monitored by measuring percent cover and woody species density, height, biomass, and total nitrogen in aboveground biomass. The effects of biosolids on soil bulk density, various chemical properties including total organic carbon (TOC), nitrate (NO3), phosphorous (P), soil organic matter (SOM) and vegetation growth and establishment were evaluated over five growing seasons after initial application.One-time application of biosolids at 15.5 T ha−1 decreased soil bulk density, significantly increased other soil chemical properties (e.g., TOC, NO3, SOM), and improved native species vegetation establishment and growth significantly over the five growing seasons. These findings have implications for improving the efficiency and reducing the cost of reclamation in industrial footprints with marginal soil properties (high bulk density, low total organic carbon and nitrogen) using a by-product from forestry companies to ameliorate the soils

Assessing the sustainability of land uses in Driefontein and Intunjambili wetlands, Zimbabwe

Assessing the sustainability of land uses in Driefontein and Intunjambili wetlands, Zimbabwe

Urban runoff and stream channel incision interact to influence riparian soils and understory vegetation.

Riparian soil processes and vegetation are sensitive to water availability. Urbanization can alter riparian water availability by modifying stream flows and stream channel morphology. In cities, runoff from impervious surfaces tends to increase stormflow magnitudes, causing stream channels to incise, or downcut. This change in channel morphology has been linked to lowered water tables and drier conditions in temperate urban riparian zones, leading to shifts in riparian nitrogen (N) cycling and vegetation communities. In Mediterranean climates with distinct wet and dry periods, there is an additional dynamic to consider: runoff from urban water use can cause streams to flow when they would otherwise be dry. This dry-season stream flow could create increased, rather than decreased, water availability in urban riparian zones. However, channel incision may counteract this effect. We asked whether dry-season stream flow interacted with channel incision to influence riparian soil characteristics and understory vegetation along streams in Sacramento, California, which has a Mediterranean climate with an intense summer dry season. At 40 stream reaches that varied by severity of downcutting and presence of dry-season flow, we sampled soils and vegetation on top of stream banks and at the margin of the low-flow channel, an important location for nutrient cycling in dry climates. We measured soil moisture, organic matter, and ∂15 N, as well as total and perennial understory vegetation cover. We found that channel characteristics associated with incision limited the influence of dry-season stream flow on soil moisture, and this interaction appears to have lasting effects on soil organic matter and perennial vegetation on bank tops. At the stream margin, channel downcutting was associated with reduced soil organic matter and vegetation cover, while dry-season flow was associated with increased vegetation cover. Values of soil ∂15 N pointed to limited hydrologic linkage between stream flows and riparian bank soils along incised streams. Our findings suggest that channel incision could limit the ability of urban riparian ecosystems to mitigate low-flow water quality. However, where streams are not incised in Mediterranean climates, dry-season flows from urban runoff may actually increase riparian productivity and N cycling above historical levels.