Cultivated exotic plants are often introduced for their aesthetic value and today comprise a substantial fraction of the flora of urban domestic gardens. Yet, their relative contribution to the functional diversity of domestic gardens and how it changes across different climate zones is insufficiently understood. Here, we investigated whether the effects of cultivated exotics on functional diversity of three plant traits related to plant aesthetics (that is, plant showiness, plant height, and leaf area) varied in suburban domestic gardens in three regions (Minnesota, USA; Alt Empordà, Spain; and central South Africa) that differ in aridity. For each garden, we calculated the mean and variance of each plant trait considering all co-occurring species and also splitting them into co-occurring cultivated exotics and natives. Our results revealed that mean plant showiness increased linearly with the proportion of cultivated exotics both across and within studied regions. Moreover, co-occ...

1. Despite high levels of disturbance and habitat modification, urban ecosystems still host substantial levels of biodiversity. The processes that maintain existing levels of diversity, however, remain understudied. Identifying the links between urban ecological processes and patterns has, therefore, become a fundamental research goal to support urban biodiversity and ecosystem functioning. 2. We conducted a study to determine how the diversity and composition of urban plant communities is affected by spatially and temporally variable land use legacies. We constructed a chronosequence of vacant lot properties covering a range of 3-22 years since demolition, in an urban neighbourhood in Baltimore, Maryland (USA). Surveys of herbaceous plant species abundance were conducted during the summers of 2012 and 2013 in sections of each vacant lot where the building previously stood (the "building footprint") and sections of the lot that was previously a backyard or garden (the "remnant garden"). 3. We found divergent patterns in plant community composition between areas of vacant lots with varying land use histories. This includes significant shifts in the functional composition of biotically vectored seed dispersal strategies, as well as an increase in seed mass and terminal velocity trait values of plant communities in building footprints over time. In addition, we found that plant communities in different sections of the same vacant lot tended to become more functionally dissimilar in seed dispersal strategies over time. In contrast, we found no significant changes in taxonomic diversity over time for any of our measures. 4. Policy implications. Our study suggests that regional-scale patterns of seed dispersal interact with diverse land use legacies to structure the plant communities of urban vacant lots. Although it has been suggested that highly altered local environmental conditions and competition from introduced species limit native plant diversity in urban environments, we find seed dispersal to be a more significant driver of urban plant community assembly patterns. Implementing management strategies that focus on habitat connectivity and enhancing species pools via seeding may present an effective strategy for promoting more successful establishment of diverse plant communities in urban environments.

Many studies have investigated species diversity patterns across space and time, but few have explored patterns of coexistence of tightly interacting species. We documented species diversity patterns in a hostparasitoid system across broad geographic location and seasons. We calculated species diversity (H and e H ′) and compared the relationship between community similarity and geographic distances of frugivorous Drosophila host (Diptera: Drosophilidae) and Leptopilina parasitoid (Hymenoptera: Figitidae) communities across Eastern North America, from New Hampshire to Florida, at two time points during the breeding season. We also analyzed the influence of environmental factors on species assemblages via constrained correspondence analysis and lastly calculated cluster dendrograms to identify potential host-parasitoid interactions. We found that the composition of Drosophila-Leptopilina communities varied significantly with latitude. Interestingly, diversity increased with increasing latitude, a trend counter to latitudinal patterns of diversity observed in many other taxa. We also found seasonal effects of monthly temperature range and precipitation on host biodiversity patterns across geographic locations. Cluster dendrograms nominated potential parasitoid-hosts and competitive interactions to be validated in the future studies. The present study fills an important gap of knowledge in North American Drosophila-Leptopilina species diversity patterns and lays the groundwork for future ecological and evolutionary studies in this system.

This paper resulted from the sUrBioCity working group funded by sDiv, the Synthesis Centre of the German Centre for Integrative Biodiversity Research(iDiv) Halle-Jena-Leipzig, funded by the German Research Foundation. CMS acknowledges support from NSF LTER grant no. DEB-1027188. The opinions and findings expressed in this paper are those of the authors and not of the National Science Foundation.

High nighttime urban air temperatures increase health risks and economic vulnerability of people globally. While recent studies have highlighted nighttime heat mitigation effects of urban vegetation, the magnitude and variability of vegetation-derived urban nighttime cooling differs greatly among cities. We hypothesize that urban vegetation-derived nighttime air cooling is driven by vegetation density whose effect is regulated by aridity through increasing transpiration. We test this hypothesis by deploying microclimate sensors across eight United States cities and investigating relationships of nighttime air temperature and urban vegetation throughout a summer season. Urban vegetation decreased nighttime air temperature in all cities. Vegetation cooling magnitudes increased as a function of aridity, resulting in the lowest cooling magnitude of 1.4 °C in the most humid city, Miami, FL, and 5.6 °C in the most arid city, Las Vegas, NV. Consistent with the differences among cities, the...

The urban landscape is a collective outcome of both natural and anthropogenic forces. These forces strongly influence the structure and functioning of urban biotic communities, often in unique and unexpected ways. Contrary to prevailing assumptions, cities are capable of hosting a high diversity of plant species, which often represent distinct suites of functional strategies. Although this pattern has been identified across cities globally, few generalities about the processes responsible for driving plant community assembly patterns and the expression of functional traits in urban environments have been established. Using a metacommunity approach, this dissertation investigates the effects of local and regional processes on plant community assembly and functional trait patterns in urban vacant land habitats. Chapter 1 summarizes the literature, highlighting key ecological concepts and theories and how they apply to novel urban ecosystems. Chapter 2 presents results from an observat...

Despite a growing literature-base devoted to document biodiversity patterns in cities, little is known about the processes that influence these patterns, and whether they are consistent over time. In particular, numerous studies have identified the capacity of cities to host a rich diversity of plant species. This trend, however, is driven primarily by introduced species, which comprise a large proportion of the urban species pool relative to natives. Using an experimental common garden study, we assessed the relative influence of local assembly processes (i.e., soil environmental filtering and competition from spontaneous urban species) on the taxonomic and functional diversity of native plant communities sampled over four seasons in 2016-2018. Taxonomic and functional diversity exhibited different responses to local processes, supporting the general conclusion that species-and trait-based measures of biodiversity offer distinct insights into community assembly dynamics. Additionally, we found that neither soil nor competition from spontaneous urban species influenced taxonomic or functional composition of native species. Functional composition, however, did shift strongly over time and was driven by community-weighted mean differences in both measured traits (maximum height, Hmax; specific leaf area, SLA; leaf chlorophyll a fluorescence, Chl a) and the relative proportions of different functional groups (legumes, annual and biennial-perennial species, C4 grasses, and forbs). By contrast, taxonomic composition only diverged between early and late seasons. Overall, our results indicate that native species are not only capable of establishing and persisting in vacant urban habitats, they can functionally respond to local filtering pressures over time. This suggests that regional dispersal limitation may be a primary factor limiting native species in urban environments. Thus, future regreening and management plans should focus on enhancing the dispersal potential of native plant species in urban environments, in order to achieve set goals for increasing native species diversity and associated ecosystem services in cities.

An extensive saline plume (>250 km 2 ) within the regionally important uncon®ned aquifer in the Neogene Ogallala Formation overlies the Panhandle oil and gas ®eld in the Southern High Plains, Texas, USA. Relative to upgradient Ogallala water, the plume waters have d 18 O (À6.7 to À8.8-) and dD (À42 to À88-) values that tend to be depleted and have higher Cl (>150 mg/l) and SO 4 (>75 mg/l) concentrations. Various end-member-mixing models suggest that the plume composition re¯ects the presence of paleowaters recharged during Middle to Late Wisconsinan time rather than salinization associated with petroleum production. Paleowaters probably mixed with salt-dissolution zone waters from the underlying Upper Permian formations before discharging upward into the Ogallala Formation. Cross-formational discharge is controlled primarily by the geometry of the underlying units, as in¯uenced by the Amarillo uplift, pinch-out of the laterally adjoining con®ned aquifer in the Triassic Dockum Group, variations in the saturated thickness of the Ogallala aquifer and the presence of potential pathways related to salt dissolution. #

Tracer tests have been widely used in studies of solute transport, gas exchange, and nutrient cycling in streams. However, the use of tracer tests to assess natural attenuation of ground-water-derived contaminants in streams, particularly from point sources, has been limited. We used tracer tests in conjunction with stream gauging and contaminant analyses to study the fate of trichloroethene (TCE) and technetium-99 ( 99 Tc), which seep from industrial contaminant plumes into a channelized, first-order stream in the Coastal Plain of western Kentucky. Six tests were conducted over a 20-month period along a 300-m reach downstream of contaminated springs. Bromide, rhodamine WT, and nitrate were introduced as slug tracers to assess dilution, sorption, and reduction, respectively. Propane was added as a continuous, volatile tracer. Tracer transport was modeled as onedimensional, with transient storage and first-order mass loss. Results indicate that (1) TCE is attenuated by volatilization; (2) TCE sorption, TCE reduction, and 99 Tc reduction are negligible or absent; and (3) dilution is negligible along the study reach.

The first documented interpretation of the regional-scale hydrostratigraphy and groundwater flow is presented for a ∼21,000-km 2 area of the arsenic-affected districts of West Bengal [Murshidabad, Nadia, North 24 Parganas and South 24 Parganas (including Calcutta)],

Stable isotopes of H 2 O are used to define the hyporheic-hypolentic boundary in Ledbetter Creek as it discharges to Kentucky Lake, a constructed reservoir in western Kentucky, USA. High-resolution (centimeterscale) sample collection and analysis were utilized to determine one-dimensional variations in δ 2 H and δ 18 O of H 2 O and chloride (Cl − ) across the boundary. During reservoir low stand in winter, the hyporheic-hypolentic zone contains water from Ledbetter Creek and groundwater separated by an interface at~10 cm below the channel bottom. Following reservoir-stage increase in spring and summer, water from Kentucky Lake infiltrates into the hyporheic-hypolentic zone to a depth of at least 18 cm below the channel bottom. Reservoir-stage decline in autumn causes source-water mixing, largely obscuring the hyporheic-hypolentic boundary. Stable isotopes provide an effective complement to conventional tracers for delineation of water masses within the hyporheic-hypolentic zone. 18 cm bajo el límite hiporreico-hipoléntico. Los isótopos estables aportan un complemento efectivo a los trazadores convencionales para la delimitación de masas de agua dentro de la zona hiporreica-hipoléntica.

Although arsenic (As) contamination of groundwater in the Bengal Basin has received wide attention over the past decade, comparative studies of hydrogeochemistry in geologically different sub-basins within the basin have been lacking. Groundwater samples were collected from sub-basins in the western margin (River Bhagirathi sub-basin, Nadia, India; 90 samples) and eastern margin (River Meghna sub-basin; Brahmanbaria, Bangladesh; 35 samples) of the Bengal Basin. Groundwater in the western site (Nadia) has mostly Ca-HCO 3 water while that in the eastern site (Brahmanbaria) is much more variable consisting of at least six different facies. The two sites show differences in major and minor solute trends indicating varying pathways of hydrogeochemical evolution However, both sites have similar reducing, postoxic environments ( p e : +5 to −2) with high concentrations of dissolved organic carbon, indicating dominantly metal-reducing processes and similarity in As mobilization mechanism. The trends of various redox-sensitive solutes (e.g. As, CH 4 , Fe, Mn, NO 3 − , NH 4 + , SO 4 2− ) indicate overlapping redox zones, leading to partial redox equilibrium conditions where As, once liberated from source minerals, would tend to remain in solution because of the complex interplay among the electron acceptors.

In arid and semi-arid environments, artificial recharge or reuse of wastewater may be desirable for water conservation, but NO y contamination of underlying aquifers can result. On the 3 Ž . semi-arid Southern High Plains USA , industrial wastewater, sewage, and feedlot runoff have been retained in dozens of playas, depressions that focus recharge to the regionally important High Ž . Plains Ogallala aquifer. Analyses of ground water, playa-basin core extracts, and soil gas in an 860-km 2 area of Texas suggest that reduction during recharge limits NO y loading to ground 3 water. Tritium and Cl y concentrations in ground water corroborate prior findings of focused 15 Ž . recharge through playas and ditches. Typical d N values in ground water ) 12.5‰ and correlations between d 15 N and ln C y suggest denitrification, but O concentrations G 3.24 NO -N 2 3 mg l y1 indicate that NO y reduction in ground water is unlikely. The presence of denitrifying and 3 NO y -respiring bacteria in cores, typical soil-gas d 15 N values -0‰, and decreases in NO y -3 3

Samples of deep groundwater, river water and rainwater were collected for d 18 O and d 2 H analyses from an area of $22,000 km 2 in the arsenic-affected districts of West Bengal, India, in order to examine groundwater recharge. A plot of d 18 O versus d 2 H of groundwater falls subparallel to the constructed local meteoric water line (d 2 H = 7.2 d 18 O + 7.7), suggesting a predominance of meteoric recharge with some evaporation. The stable isotopic signature of groundwater from the deeper part of the semiconfined main aquifer is similar to that of shallower groundwater, which suggests that deeper groundwater has been recharged in the present-day climatic regime, mostly from monsoonal rainfall. Groundwater in deeper isolated aquifers falls within the isotopic range observed for the main aquifer. A trend of isotopic depletion of groundwater that extends northward and westward from the Bay of Bengal (the monsoonal moisture source area) indicates a rain-out process following Rayleigh-type distillation. Some recharge may have taken place from the rivers Ganges and Bhagirathi-Hoogly, with minimal inflow from other rivers (Jalangi and Ichamati).