Replicated, urban-driven exposure to metallic trace elements in two passerines

While there are increasing examples of phenotypic and genotypic differences between urban and non-urban populations of plants and animals, few studies identified the mechanisms explaining those dissimilarities. The characterization of the urban landscape, which can only be achieved by measuring variability in relevant environmental factors within and between cities, is a keystone prerequisite to understand the effects of urbanization on wildlife. Here, we measured variation in bird exposure to metal pollution within 8 replicated urbanization gradients and within 2 flagship bird species in urban evolutionary ecology: the blue tit (Cyanistes caeruleus) and the great tit (Parus major). We report on a highly significant, positive linear relationship between the magnitude of urbanization—inferred as either tree cover, impervious surface cover, or an urbanization score computed from several environmental variables, and copper, zinc and lead concentrations in bird feathers. The reverse relationship was measured in the case of mercury, while cadmium and arsenic did not vary in response to the urbanization level. This result, replicated across multiple cities and two passerine species, strongly suggests that copper, zinc, lead and mercury pollution is likely to trigger the emergence of parallel responses at the phenotypic and/or genotypic level between urban environments worldwide.

The power of community science to quantify ecological interactions in cities

Studying animals in urban environments is especially challenging because much of the area is private property not easily accessible to professional scientists. In addition, collecting data on animals that are cryptic, secretive, or rare is also challenging due to the time and resources needed to amass an adequate dataset. Here, we show that community science can be a powerful tool to overcome these challenges. We used observations submitted to the community science platform iNaturalist to assess predation and parasitism across urbanization gradients in a secretive, ‘hard-to-study’ species, the Southern Alligator Lizard (Elgaria multicarinata). From photographs, we quantified predation risk by assessing tail injuries and quantified parasitism by counting tick loads on lizards. We found that tail injuries increased with age and with urbanization, suggesting that urban areas are risky habitats. Conversely, parasitism decreased with urbanization likely due to a loss of hosts and anti-tick medications used on human companion animals. This community science approach generated a large dataset on a secretive species rapidly and at an immense spatial scale that facilitated quantitative measures of urbanization (e.g. percent impervious surface cover) as opposed to qualitative measures (e.g. urban vs. rural). We therefore demonstrate that community science can help resolve ecological questions that otherwise would be difficult to address.

The Power of Citizen Science to Quantify Ecological Risks in Cities

Urbanization is an extreme form of habitat modification that can alter ecological relationships among organisms, but these can be hard to study because much of the urban landscape is inaccessible private property. We show that citizen science can be a powerful tool to overcome this challenge. We used photo-vouchered observations submitted to the citizen science platform iNaturalist to assess predation and parasitism across urbanization gradients in a secretive yet widespread species, the Southern Alligator Lizard (Elgaria multicarinata), in Southern California, USA. From photographs, we quantified predation risk by assessing tail injuries and quantified parasitism rates by counting tick loads on lizards. We estimated urbanization intensity by determining percent impervious surface around each lizard observation. We found that tail injuries increased with age of the lizard and with urbanization, suggesting that urban areas are riskier habitats, likely because of elevated populations of predators such as outdoor cats. Conversely, parasitism decreased with urbanization likely due to a loss of mammalian hosts and anti-tick medications used on companion animals. Moreover, our citizen science approach allowed us to generate a large dataset on a secretive species extremely rapidly and at an immense spatial scale that facilitated quantitative measures of urbanization (e.g. percent impervious surface cover) as opposed to qualitative measures (e.g. urban vs rural). This study demonstrates that citizen science is allowing researchers to answer ecological questions that otherwise would go unanswered.

Integrating Activity-Based Geographic Information and Long-Term Remote Sensing to Characterize Urban Land Use Change

The land use structure is a key component to understand the complexity of urban systems because it provides a snapshot of urban dynamics and how people use space. This paper integrates socially sensed activity data with a remotely sensed land cover product in order to infer urban land use and its changes over time. We conducted a case study in the Washington D.C.–Baltimore metropolitan area to identify the pattern of land use change from undeveloped to developed land, including residential and non-residential uses for a period covering 1986–2008. The proposed approach modeled physical and behavioral features of land parcels from a satellite-based impervious surface cover change product and georeferenced Tweets, respectively. A model assessment with random forests classifiers showed that the proposed classification workflow could classify residential and non-residential land uses at an accuracy of 81%, 4% better than modeling the same land uses from physical features alone. Using the timestamps of the impervious surface cover change product, the study also reconstructed the timeline of the identified land uses. The results indicated that the proposed approach was capable of mapping detailed land use and change in an urban region, and represents a new and viable way forward for urban land use surveying that could be especially useful for surveying and tracking changes in cities where traditional approaches and mapping products (i.e., from remote sensing products) may have a limited capacity to capture change.

Chronology of Gloomy Scale (Hemiptera: Diaspididae) Infestations on Urban Trees

Pest abundance on urban trees often increases with surrounding impervious surface. Gloomy scale (Melanaspis tenebricosa Comstock; Hemiptera: Diaspididae), a pest of red maples (Acer rubrum L.; Sapindales: Sapindaceae) in the southeast United States, reaches injurious levels in cities and reduces tree condition. Here, we use a chronosequence field study in Raleigh, NC, to investigate patterns in gloomy scale densities over time from the nursery to 13 yr after tree planting, with a goal of informing more efficient management of gloomy scale on urban trees. We examine how impervious surfaces affect the progression of infestations and how infestations affect tree condition. We find that gloomy scale densities remain low on trees until at least seven seasons after tree planting, providing a key timepoint for starting scouting efforts. Scouting should focus on tree branches, not tree trunks. Scale density on tree branches increases with impervious surface across the entire studied tree age range and increases faster on individual trees that are planted in areas with high impervious surface cover. There is a lag between the onset of pest infestations and a decline in tree condition, indicating that gloomy scale management should begin prior to a visible decline in tree condition. Our results inform management of gloomy scale in cities.

Evaluating the Impact of Urbanization on the Physiochemical Parameters of the Urban River System: A Study on Vaigai River, Madurai

The article attempts to investigate the impact of Madurai’s urban expansion on the River Vaigai at the confluence of six channels draining into the river from the urban watershed and at the causeways. Impervious surface cover (ISC) has impacted the river. Water samples were collected during 2017 in 15 stations in the urban stretch and two stations in the peri-urban stretch. Physical characteristics, namely, temperature, colour, odour and taste, and the intensity of chemical parameters, namely, pH, calcium, nitrates, total dissolved solids (TDS), total hardness (TH) and carbon dioxide demand (COD), were estimated. These estimations show that anomalous concentrations of physiochemical parameters in the river are much higher than the permissible standards prescribed by the Bureau of Indian Standards (BIS). The causeway recorded greater variations in TDS levels between the upstream and downstream zone. The study identifies two realities: first, variance in the intensity of physiochemical properties in the urban and peri-urban stretch and second, the impact of causeways on the flow characteristics of the river.

Stream restoration and sewers impact sources and fluxes of water, carbon, and nutrients in urban watersheds

An improved understanding of sources and timing of water, carbon, and nutrient fluxes associated with urban infrastructure and stream restoration is critical for guiding effective watershed management globally. We investigated how sources, fluxes, and flowpaths of water, carbon (C), nitrogen (N), and phosphorus (P) shift in response to differences in urban stream restoration and sewer infrastructure. We compared an urban restored stream with two urban degraded streams draining varying levels of urban development and one stream with upland stormwater management systems over a 3-year period. We found that there was significantly decreased peak discharge in response to precipitation events following stream restoration. Similarly, we found that the restored stream showed significantly lower (p < 0.05) monthly peak runoff (9.4 ± 1.0 mm day−1) compared with two urban degraded streams (ranging from 44.9 ± 4.5 to 55.4 ± 5.8 mm day−1) draining higher impervious surface cover, and the stream-draining stormwater management systems and less impervious surface cover in its watershed (13.2 ± 1.9 mm day−1). The restored stream exported most carbon, nitrogen, and phosphorus at relatively lower streamflow than the two more urban catchments, which exported most carbon and nutrients at higher streamflow. Annual exports of total carbon (6.6 ± 0.5 kg ha−1 yr−1), total nitrogen (4.5 ± 0.3 kg ha−1 yr−1), and total phosphorus (161 ± 15 kg ha−1 yr−1) were significantly lower in the restored stream compared to both urban degraded streams (p < 0.05), but statistically similar to the stream draining stormwater management systems, for N exports. However, nitrate isotope data suggested that 55 ± 1 % of the nitrate in the urban restored stream was derived from leaky sanitary sewers (during baseflow), statistically similar to the urban degraded streams. These isotopic results as well as additional tracers, including fluoride (added to drinking water) and iodide (contained in dietary salt), suggested that groundwater contamination was a major source of urban nutrient fluxes, which has been less considered compared to upland sources. Overall, leaking sewer pipes are a problem globally and our results suggest that combining stream restoration with restoration of aging sewer pipes can be critical to more effectively minimizing urban nonpoint nutrient sources. The sources, fluxes, and flowpaths of groundwater should be prioritized in management efforts to improve stream restoration by locating hydrologic hot spots where stream restoration is most likely to succeed.

Forecasting the Effects of Heat and Pests on Urban Trees: Impervious Surface Thresholds and the ‘Pace-to-Plant’ Technique

Trees provide ecosystem services that benefit humans and the environment. Unfortunately, urban trees often do not provide maximum services due to abiotic stress and arthropod herbivores and borers. These problems often originate from trees being planted in unsuitable conditions. Cities are warmer than natural areas because impervious surfaces absorb and reradiate heat. Higher temperatures can increase pest insect abundance and water stress, and reduce street tree condition relative to natural forests. For example, the gloomy scale insect [Melanaspsis tenebricosa Comstock (Hemiptera: Diaspididae)], a pest of red maple (Acer rubrum) street trees, is more abundant in warmer than cooler urban sites. Acer rubrum, at warmer urban sites with more M. tenebricosa, are typically in poor condition. Here, researchers demonstrate these relationships and illustrate how impervious surface cover can be used to predict the condition of A. rubrum street trees. impervious surface thresholds were then developed to define suitable planting sites that can be used by individuals with access to GIS software. Researchers present the pace-to-plant technique, which can be used by landscape professionals to quickly estimate impervious surface cover around a planting site. These thresholds predict future tree condition based on planting site impervious surface cover. The hope is that more informed planting will minimize pest infestations and maximize the future vigor and performance of street trees.