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Urbanization profoundly impacts biodiversity and ecosystem function, exerting an immense ecological filter on the flora and fauna that inhabit it, oftentimes leading to simplistic and homogenous ecological communities. However, the response of soil animal communities to urbanization remains underexplored, and it is unknown whether their response to urbanization is like that of aboveground organisms. This study investigated the influence of urbanization on soil animal communities in 40 public parks along an urbanization gradient. We evaluated soil animal abundance, diversity, and community composition and related these measures to urban and soil characteristics at each park. The most urbanized parks exhibited reduced animal abundance, richness, and Shannon diversity. These changes were influenced by many variables underscoring the multifaceted influence of urbanization on ecological communities. Notably, contrary to our expectation, urbanization did not lead to community homogenization; instead, it acted stochastically, creating unique soil animal assemblages. This suggests that urban soil animal communities are concomitantly shaped by deterministic and stochastic ecological processes in urban areas. Our study highlights the intricate interplay between urbanization and soil animal ecology, challenging the notion of urban homogenization in belowground ecosystems and providing insight for managing and preserving belowground communities in urban areas.

 

Groundwater nitrate‐N isotopes (δ¹⁵N‐) have been used to infer the effects of natural and anthropogenic change on N cycle processes in the environment. Here we report unexpected changes in groundwater δ¹⁵N‐ for riparian zones affected by relict milldams and road salt salinization. Contrary to natural, undammed conditions, groundwater δ¹⁵N‐ values declined from the upland edge through the riparian zone and were lowest near the stream. Groundwater δ¹⁵N‐ values increased for low electron donor (dissolved organic carbon) to acceptor ratios but decreased beyond a change point in ratios. Groundwater δ¹⁵N‐ values were particularly low for the riparian milldam site subjected to road‐salt salinization. We attributed these N isotopic trends to suppression of denitrification, occurrence of dissimilatory nitrate reduction to ammonium (DNRA), and/or effects of road salt salinization. Groundwater δ¹⁵N‐ can provide valuable insights into process mechanisms and can serve as “imprints” of anthropogenic activities and legacies.

 

Residential landscapes are essential to the sustainability of large areas of the United States. However, spatial and temporal variation across multiple domains complicates developing policies to balance these systems’ environmental, economic, and equity dimensions. We conducted multidisciplinary studies in the Baltimore, MD, USA, metropolitan area to identify locations (hotspots) or times (hot moments) with a disproportionate influence on nitrogen export, a widespread environmental concern. Results showed high variation in the inherent vulnerability/sensitivity of individual parcels to cause environmental damage and in the knowledge and practices of individual managers. To the extent that hotspots are the result of management choices by homeowners, there are straightforward approaches to improve outcomes, e.g. fertilizer restrictions and incentives to reduce fertilizer use. If, however, hotspots arise from the configuration and inherent characteristics of parcels and neighborhoods, efforts to improve outcomes may involve more intensive and complex interventions, such as conversion to alternative ecosystem types.

 

The idea of green infrastructure (GI) has generated great interest and creativity in addressing a range of challenging and expensive environmental problems, from coastal resilience to control of combined sewer overflows (CSOs). The appeal of GI stems from its cost savings compared to traditional “gray” infrastructure and the multiple benefits it provides, including biodiversity, aesthetics, and carbon sequestration. For example, a “green” approach to controlling CSOs in New York City saved $1.5 billion compared to a “gray” approach. Despite these advantages, GI still does not have detailed design and reliability specifications as compared to engineered gray infrastructure, potentially hindering its adoption. In this paper, we review some of the potential applications of GI in modern environmental science and discuss how reliability and associated (un)certainty in net benefits need to be addressed to realize the potential of this new approach.

 

Land-use change is highly dynamic globally and there is great uncertainty about the effects of land-use legacies on contemporary environmental performance. We used a chronosequence of urban grasslands (lawns) that were converted from agricultural and forested lands from 10 to over 130 years prior to determine if land-use legacy influences components of soil biodiversity and composition over time. We used historical aerial imagery to identify sites in Baltimore County, MD (USA) with agricultural versus forest land-use history. Soil samples were taken from these sites as well as from existing well-studied agricultural and forest sites used as historical references by the National Science Foundation Long-Term Ecological Research Baltimore Ecosystem Study program. We found that the microbiomes in lawns of agricultural origin were similar to those in agricultural reference sites, which suggests that the ecological parameters on lawns and reference agricultural systems are similar in how they influence soil microbial community dynamics. In contrast, lawns that were previously forest showed distinct shifts in soil bacterial composition upon recent conversion but reverted back in composition similar to forest soils as the lawns aged over decades. Soil fungal communities shifted after forested land was converted to lawns, but unlike bacterial communities, did not revert in composition over time. Our results show that components of bacterial biodiversity and composition are resistant to change in previously forested lawns despite urbanization processes. Therefore land-use legacy, depending on the prior use, is an important factor to consider when examining urban ecological homogenization.

 

Despite interest in the contribution of evapotranspiration (ET) of residential turfgrass lawns to household and municipal water budgets across the United States, the spatial and temporal variability of residential lawn ET across large scales is highly uncertain. We measured instantaneous ET (ET_inst) of lawns in 79 residential yards in six metropolitan areas: Baltimore, Boston, Miami, Minneapolis‐St. Paul (mesic climates), Los Angeles and Phoenix (arid climates). Each yard had one of four landscape types and management practices: traditional lawn‐dominated yards with high or low fertilizer input, yards with water‐conserving features, and yards with wildlife‐friendly features. We measured ET_instin situ during the growing season using portable chambers and identified environmental and anthropogenic factors controlling ET in residential lawns. For each household, we used ET_instto estimate daily ET of the lawn (ET_daily) and multiplied ET_dailyby the lawn area to estimate the total volume of water lost through ET of the lawn (ET_vol). ET_dailyvaried from 0.9 ± 0.4 mm d¹in mesic cities to 2.9 ± 0.7 mm d⁻¹in arid cities. Neither ET_instnor ET_dailywas significantly influenced by yard landscape types and ET_instpatterns indicated that lawns may be largely decoupled from regional rain‐driven climate patterns. ET_volranged from ∼0 L d⁻¹to over 2,000 L d⁻¹, proportionally increasing with lawn area. Current irrigation and lawn management practices did not necessarily result in different ET_instor ET_dailyamong traditional, water‐conserving, or wildlife‐friendly yards, but smaller lawn areas in water‐conserving and wildlife‐friendly yards resulted in lower ET_vol.

 

The compounding effects of anthropogenic legacies for environmental pollution are significant, but not well understood. Here, we show that centennial‐scale legacies of milldams and decadal‐scale legacies of road salt salinization interact in unexpected ways to produce hot spots of nitrogen (N) in riparian zones. Riparian groundwater and stream water concentrations upstream of two mid‐Atlantic (Pennsylvania and Delaware) milldams, 2.4 and 4 m tall, were sampled over a 2 year period. Clay and silt‐rich legacy sediments with low hydraulic conductivity, stagnant and poorly mixed hydrologic conditions, and persistent hypoxia in riparian sediments upstream of milldams produced a unique biogeochemical gradient with nitrate removal via denitrification at the upland riparian edge and ammonium‐N accumulation in near‐stream sediments and groundwaters. Riparian groundwater ammonium‐N concentrations upstream of the milldams ranged from 0.006 to 30.6 mgN L⁻¹while soil‐bound values were 0.11–456 mg kg⁻¹. We attribute the elevated ammonium concentrations to ammonification with suppression of nitrification and/or dissimilatory nitrate reduction to ammonium (DNRA). Sodium inputs to riparian groundwater (25–1,504 mg L⁻¹) from road salts may further enhance DNRA and ammonium production and displace sorbed soil ammonium‐N into groundwaters. This study suggests that legacies of milldams and road salts may undercut the N buffering capacity of riparian zones and need to be considered in riparian buffer assessments, watershed management plans, and dam removal decisions. Given the widespread existence of dams and other barriers and the ubiquitous use of road salt, the potential for this synergistic N pollution is significant.

 

Biological nitrogen fixation is the conversion of dinitrogen (N2) gas into bioavailable nitrogen by microorganisms with consequences for primary production, ecosystem function, and global climate. Here we present a compiled dataset of 4793 nitrogen fixation (N2-fixation) rates measured in the water column and benthos of inland and coastal systems via the acetylene reduction assay, 15N2 labeling, or N2/Ar technique. While the data are distributed across seven continents, most observations (88%) are from the northern hemisphere. 15N2 labeling accounted for 67% of water column measurements, while the acetylene reduction assay accounted for 81% of benthic N2-fixation observations. Dataset median area-, volume-, and mass-normalized N2-fixation rates are 7.1 μmol N2-N m−2 h−1, 2.3 × 10−4 μmol N2-N L−1 h−1, and 4.8 × 10−4 μmol N2-N g−1 h−1, respectively. This dataset will facilitate future efforts to study and scale N2-fixation contributions across inland and coastal aquatic environments. 

We appear to be at a shining moment for interactions between soils and society. Popular interest in soils has increased along with interests in urban gardening, carbon sequestration, recognition of the vast biodiversity in soils, and the realisation that soils are a finite resource whose degradation has serious consequences. This increase in interest creates both opportunities and challenges for soil science. While there is great potential for increasing the diversity of people involved with soil science, key scientific and communication challenges need to be addressed for interactions between soils and society to be useful and productive. Here, I present case study issues on the mechanisms and limitations of carbon sequestration in soils and the need to restore and/or create new soils for specific uses, including urban agriculture and green infrastructure, to illustrate the opportunities and challenges associated with new societal interest in soil science. Addressing these issues requires advances in both basic and applied science, new participatory approaches to the design, execution, and interpretation of research, collaboration with multiple disciplines, including the social sciences, and improvements in the two‐way flow of information between science and society. Careful attention to these issues will attract new people to soil science, advance awareness of the importance of and threats to soils across the globe, and produce improvements in the quality of life for diverse human populations. 

Hydrologic alterations associated with urbanization can weaken connections between riparian zones, streams, and uplands, leading to negative effects on the ability of riparian zones to intercept pollutants carried by surface water runoff and groundwater flow such as nitrate and phosphate. We analyzed the monthly water table as an indicator of riparian connectivity, along with groundwater NO3 and PO4concentrations, at four riparian sites within and near the Gwynns Falls Watershed in Baltimore, MD, from 1998 to 2018. The sites included one forested reference site (Oregon Ridge), two suburban riparian sites (Glyndon and Gwynnbrook), and one urban riparian site (Cahill) with at least two locations and four monitoring wells, located 5 m from the center of the stream, at each site. Results show an increase in connectivity as indicated by shallower water tables at two of the four sites studied: Glyndon and Cahill. This change in connectivity was associated with decreases in NO3 at Glyndon and increases in PO4 at Glyndon, Gwynnbrook, and Cahill. These changes are consistent with previous studies showing that shallower water table depths increase anaerobic conditions, which increase NO3 consumption by denitrification and decrease PO4 retention. The absence of change in the forested reference site, where climate would be expected to be the key driver, suggests that other drivers, including best management practices and stream restoration projects, could be affecting riparian water tables at the two suburban sites and the one urban site. Further research into the mechanisms behind these changes and site‐specific dynamics is needed.