UMBC Geography and Environmental Systems Department

Permanent URI for this collectionhttp://hdl.handle.net/11603/39

A hallmark of the Department of Geography & Environmental Systems is its broadly integrative nature, drawing on the expertise of faculty with diverse backgrounds but with a common mission. Research interests among current regular departmental faculty span a broad range of topics in earth systems science, ecosystem science, human geography and urban geography, and human dimensions of global change, with application of geospatial technology to research questions across all areas of interest. Despite the diversity of research and teaching interests, there is a common focus on the importance of coupled natural and human systems and on landscape pattern in relation to human activities and their environmental consequences, and we see this as a broad programmatic thrust for our graduate degree offerings. Research based in the Department of Geography and Environmental Systems involves interdisciplinary collaborative work of local, regional and international scope.

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Linking Biodiversity and Human Wellbeing in Systematic Conservation Assessments of Working Landscapes
(MDPI, 2023-06-21) Huber, Patrick R.; Baker, Matthew; Hollander, Allan D.; Lange, Matthew; Miller, Daphne; Quinn, James F.; Riggle, Courtney; Tomich, Thomas P.
Systematic land use planning to address environmental impacts does not typically include human health and wellbeing as explicit inputs. We tested the effects of including issues related to human health, ecosystem services, and community wellbeing on the outputs of a standard land use planning process which is primarily focused on environmental variables. We consulted regional stakeholders to identify the health issues that have environmental links in the Sacramento, California region and to identify potential indicators and datasets that can be used to assess and track these issues. Marxan planning software was used to identify efficient land use patterns to maximize both ecological conservation and human health outcomes. Outputs from five planning scenarios were compared and contrasted, resulting in a spatially explicit series of tradeoffs across the scenarios. Total area required to meet imputed goals ranged from 10.4% to 13.4% of the total region, showing somewhat less efficiency in meeting biodiversity goals when health outcomes are included. Additionally, we found 4.8% of residential areas had high greening needs, but this varied significantly across the six counties. The work provides an example of how integrative assessment can help inform management decisions or stakeholder negotiations potentially leading to better management of the production landscapes in food systems.
Accuracy differences in aboveground woody biomass estimation with terrestrial laser scanning for trees in urban and rural forests and different leaf conditions
(Springer, 2023-06-01) Arseniou, Georgios; MacFarlane, David W.; Calders, Kim; Baker, Matthew
Both rural and urban forests play an important role in terrestrial carbon cycling. Forest carbon stocks are typically estimated from models predicting the aboveground biomass (AGB) of trees. However, such models are often limited by insufficient data on tree mass, which generally requires felling and weighing parts of trees. In this study, thirty-one trees of both deciduous and evergreen species were destructively sampled in rural and urban forest conditions. Prior to felling, terrestrial laser scanning (TLS) data were used to estimate tree biomass based on volume estimates from quantitative structure models, combined with tree basic density estimates from disks sampled from stems and branches after scanning and felling trees, but also in combination with published basic density values. Reference woody AGB, main stem, and branch biomass were computed from destructive sampling. Trees were scanned in leaf-off conditions, except evergreen and some deciduous trees, to assess effects of a leaf-separation algorithm on TLS-based woody biomass estimates. We found strong agreement between TLS-based and reference woody AGB, main stem, and branch biomass values, using both measured and published basic densities to convert TLS-based volume to biomass, but use of published densities reduced accuracy. Correlations between TLS-based and reference branch biomass were stronger for urban trees, while correlations with stem mass were stronger for rural trees. TLS-based biomass estimates from leaf-off and leaf-removed point clouds strongly agreed with reference biomass data, showing the utility of the leaf-removal algorithm for enhancing AGB estimation.
A data pedigree system to support geospatial analyses of human-environment interactions in data poor contexts
(Taylor & Francis, 2024-12-18) Magliocca, Nicholas R.; Sink, Carter D.; Devine, Jennifer A.; Fagan, Matthew E.; Aguilar-González, Bernardo; McSweeney, Kendra; Mukherjee, Rohit; Nielsen, Erik A.; Sesnie, Steven E.; Tellman, Beth; Arellano-Thompson, Elise
Geospatial analyses of human-environment interactions are challenged by the multi-scale, multi-dimensional nature of human-environment systems. Research in such contexts must often rely on integrating multiple, independently produced data sources, which presents heterogenous data qualities and interoperability challenges. Understanding data quality and transparency becomes increasingly important in these contexts, and multi?granularity and context specific spatial data quality indicators are needed. We develop a data pedigree system that accounts for multiple data quality aspects, geospatial ambiguities that may hinder interoperability, and the fitness-for-use of each data source for indicating causal linkages between human activities and environmental change. We demonstrate its application to a particularly challenging and data sparse case study of identifying the location and timing of transnational cocaine trafficking, or ‘narco-trafficking’, in Central America with five spatial and temporal data quality indicators: geographic clarity, geographic interpretation, provenance, temporal specificity, and narco-trafficking certainty. The proposed data pedigree system provides a systematic and coherent analytical framework for interoperability, comparison, and corroboration of fragmented and incomplete data, which are needed to support advanced geospatial analyses, such as causal inference techniques. The study demonstrates the transferability and operationalization of the data pedigree system for examining complex human-environment interactions, especially those influenced by illicit economies.
Canopy composition drives variability in urban growing season length more than the heat island effect
(Elsevier, 2023-08-01) Alonzo, Michael; Baker, Matthew; Caplan, Joshua S.; Williams, Avery; Elmore, Andrew J.
The elevated heat of urban areas compared to their surroundings makes humid temperate cities a useful preview of future climate effects on natural forest phenology. The utility of this proxy rests on the expectation that trees in urban areas alter their phenology in response to warmer site conditions in spring and fall. However, it is possible that apparent lengthening of the growing season is instead governed by human-driven tree species selection and plant functional type (PFT; trees, shrubs, turfgrass) heterogeneity typical of managed landscapes. Without the use of highly spatially and temporally resolved remote sensing data, the roles of tree taxonomy and local site characteristics (e.g., impervious cover) in controlling phenology remain confounded. To understand the drivers of earlier start of season (SOS) and later end of season (EOS) among urban trees, we estimated individual tree phenology using >130 high-resolution satellite images per year (2018–2020) for ~10,000 species-labeled trees in Washington, DC. We found that species identity alone accounted for 4× more variability in the timing of SOS and EOS compared with a tree's planting location characteristics. Additionally, the urban mix of PFTs may be more responsible for apparent advances in SOS (by between 1.8 ± 1.3 and 3.5 ± 1.3 days) than heat per se. The results of this study caution against associating longer growing seasons in cities—observed in moderate to coarse resolution remote sensing imagery—to within-species phenological plasticity and demonstrate the power of high-resolution satellite data for tracking tree phenology in biodiverse environments.
Remotely mapping gullying and incision in Maryland Piedmont headwater streams using repeat airborne lidar
(Elsevier, 2024-06-15) Metes, Marina J.; Miller, Andrew J.; Baker, Matthew; Hopkins, Kristina G.; Jones, Daniel K.
Headwater streams can contribute significant amounts of fine sediment to downstream waterways, especially when severely eroded and incised. Potential upstream sediment source identification is crucial for effective management of water quality, aquatic habitat, and sediment loads in a watershed. This study explored topographic openness (TO) derived from 1-m lidar for its ability to predict incision in headwater streams and to remotely detect changes in incision over time. Field surveys were conducted in one forested and two recently urbanized headwater watersheds in the Maryland Piedmont physiographic province, USA to characterize the level of stream channel incision (none, moderate, or severe) in the main stem of each watershed. Predictions of the severity of stream channel incision derived from TO were compared against the field surveys. Channel incision was detected with an overall accuracy of 67�%, with best performance in reaches with either severe or no incision (79��% accuracy). The method was also applied to repeat lidar collected over the same area to model the extent of channel incision in 2002 before urban development began and in 2008 and 2013 during active construction in the urban watersheds. Results showed increasing incision over time in all three watersheds, with similar patterns in the forested and urban watersheds. This new method of remotely measuring channel incision can be used to identify potential sediment sources across a watershed, enhance water and habitat quality predictions, and detect changes over time where multiple years of overlapping lidar are available.
Predicting Urban Trees’ Functional Trait Responses to Heat Using Reflectance Spectroscopy
(MDPI, 2024-1) Kyaw, Thu Ya; Alonzo, Michael; Baker, Matthew; Eisenman, Sasha W.; Caplan, Joshua S.
Plant traits are often measured in the field or laboratory to characterize stress responses. However, direct measurements are not always cost effective for broader sampling efforts, whereas indirect approaches such as reflectance spectroscopy could offer efficient and scalable alternatives. Here, we used field spectroscopy to assess whether (1) existing vegetation indices could predict leaf trait responses to heat stress, or if (2) partial least squares regression (PLSR) spectral models could quantify these trait responses. On several warm, sunny days, we measured leaf trait responses indicative of photosynthetic mechanisms, plant water status, and morphology, including electron transport rate (ETR), photochemical quenching (qP), leaf water potential (?leaf), and specific leaf area (SLA) in 51 urban trees from nine species. Concurrent measures of hyperspectral leaf reflectance from the same individuals were used to calculate vegetation indices for correlation with trait responses. We found that vegetation indices predicted only SLA robustly (R2 = 0.55), while PLSR predicted all leaf trait responses of interest with modest success (R2 = 0.36 to 0.58). Using spectral band subsets corresponding to commercially available drone-mounted hyperspectral cameras, as well as those selected for use in common multispectral satellite missions, we were able to estimate ETR, qP, and SLA with reasonable accuracy, highlighting the potential for large-scale prediction of these parameters. Overall, reflectance spectroscopy and PLSR can identify wavelengths and wavelength ranges that are important for remote sensing-based modeling of important functional trait responses of trees to heat stress over broad ranges.
THE ROLE OF DISASTER SUBCULTURES IN LOCAL BUSINESS COMMUNITY PREPAREDNESS: A CASE STUDY OF STAKEHOLDERS IN COASTAL MONMOUTH COUNTY, NEW JERSEY
(MSAAG, 2024) Howell, Nyla; Leichenko, R.; Clemens, M.; Cann, K.; Madajewicz, M.; Solecki, W.; Kaplan, M.; Herb, J.
Extreme weather events are increasingly affecting coastal communities, often leading to economic and social disruption within these areas. The businesses located within coastal communities are especially vulnerable to climate-related shocks, yet relatively little is known about how the experience of prior disaster events affects business preparedness and planning for future extreme events. This study applies the concept of a disaster subculture to investigate whether and how prior extreme events affect climate resilience practices among small and mediumsized businesses in coastal New Jersey. The methods for the study entailed qualitative analysis of interviews conducted with businesses and related stakeholders during the Spring of 2022. The results of the study indicate that elements of four possible disaster subcultures are present in the region and that these subcultures are influencing business mitigation and preparedness practices and community recovery. A future research direction could consider disaster subculture influence on an individual level and how subcultures may influence household preparedness.
Soil Methane and Carbon Dioxide Fluxes from Cropland and Riparian Buffers in Different Hydrogeomorphic Settings
(Wiley, 2015-07-01) Jacinthe, P. A.; Vidon, P.; Fisher, K.; Liu, X.; Baker, Matthew
Riparian buffers contribute to the mitigation of nutrient pollution in agricultural landscapes, but there is concern regarding their potential to be hot spots of greenhouse gas production. This study compared soil CO₂ and CH₄ fluxes in adjacent crop fields and riparian buffers (a flood-prone forest and a flood-protected grassland along an incised channel) and examined the impact of water table depth (WTD) and flood events on the variability of gas fluxes in riparian zones. Results showed significantly (P < 0.001) higher CO₂ emission in riparian areas than in adjoining croplands (6.8 ± 0.6 vs. 3.6 ± 0.5 Mg CO₂–C ha⁻¹ yr⁻¹; mean ± SE). Daily flux of CO₂ and soil temperature were significantly related (P < 0.002), with Q₁₀ values ranging between 1.75 and 2.53. Significant relationships (P < 0.05) were found between CH₄ daily flux and WTD. Flood events resulted in enhanced CH₄ emission (up to +44.5 mg CH₄–C m⁻² d⁻¹ in a swale) under warm soil conditions (>22°C), but the effect of flooding was less pronounced in early spring (emission <1.06 mg CH₄–C m⁻² d⁻¹), probably due to low soil temperature. Although CH₄ flux direction alternated at all sites, overall the croplands and the flood-affected riparian forest were CH₄ sources, with annual emission averaging +0.04 ± 0.17 and +0.92 ± 1.6 kg CH₄–C ha⁻¹, respectively. In the riparian forest, a topographic depression (<8% of the total area) accounted for 78% of the annual CH₄ emission, underscoring the significance of landscape heterogeneity on CH₄ dynamics in riparian buffers. The nonflooded riparian grassland, however, was a net CH₄ sink (−1.08 ± 0.22 kg CH₄–C ha⁻¹ yr⁻¹), probably due to the presence of subsurface tile drains and a dredged/incised channel at that study site. Although these hydrological alterations may have contributed to improvement in the CH₄ sink strength of the riparian grassland, this must be weighed against the water quality maintenance functions and other ecological services provided by riparian buffers.
First results and on-orbit performance of the Hyper-Angular Rainbow Polarimeter (HARP2) on the PACE satellite
(SPIE, 2024-11-20) Martins, J. Vanderlei; Fernandez-Borda, Roberto; Puthukkudy, Anin; Xu, Xiaoguang; Sienkiewicz, Noah; Smith, Rachel; McBride, Brent; Dubovik, Oleg; Remer, Lorraine
The Hyper-Angular Rainbow Polarimeter-2 (HARP2) was launched on board the Plankton, Aerosol, Cloud and ocean Ecosystem (PACE) mission, in February 2024, for the global measurement of aerosol and cloud properties as well as to provide atmospheric correction over the footprint of the Ocean Color Instrument (OCI). HARP2 is designed to collect data over a wide field of view in the cross-track direction (+/-47deg) allowing for global coverage in about two days, as well as an even wider field of view in the along-track direction (+/-54deg) providing measurements over a wide range of scattering angles. HARP2 samples 10 angles at 440, 550, and 870nm focusing on aerosol and surface retrievals, and up to 60 angles at 670nm for the hyper-angular retrieval of cloud microphysical properties. The HARP2 instrument collects three nearly identical images with linear polarizers aligned at 0°, 45°, and 90° that can be converted to push-broom images of the I, Q, and U Stokes parameters for each angle, and each wavelength. The HARP2 technology was first demonstrated with the HARP CubeSat satellite which collected a limited dataset for 2 years from 2020 to 2022. HARP2 extends these measurements to a full global coverage in two days, seven days a week.
Tree plantations and forest regrowth are linked to poverty reduction in Africa
(Nature, 2024-11-20) den Braber, Bowy; Hall, Charlotte M.; Rhemtulla, Jeanine M.; Fagan, Matthew E.; Rasmusssen, Laura Vang
Numerous countries have adopted large-scale tree planting programs as a climate mitigation strategy and to improve local livelihoods. However, it remains poorly documented how the surge in tree plantations has altered local livelihoods. Here, we assess whether tropical tree plantation expansion and forest regrowth across 18 African countries are associated with local people’s living standards. By combining a recent map that distinguishes tree plantations from regrowth from 2000 to 2012 with multidimensional poverty measures from more than 200,000 households, we find a positive association between people's living standards and areas where tree plantations have expanded or, to a lesser extent, forest regrowth has occurred. Because tree plantations make up a large proportion of recent increases in tropical tree cover – and controversy remains about their potential impacts on both biodiversity and local people – our study provides broad empirical support for the idea that tree plantations and forest regrowth can be linked with reduced poverty in the short term.
Ecological resistance in urban streams: the role of natural and legacy attributes
(University of Chicago Press, 2016-03) Utz, Ryan M.; Hopkins, Kristina G.; Beesley, Leah; Booth, Derek B.; Hawley, Robert J.; Baker, Matthew; Freeman, Mary C.; L. Jones, Krista
Urbanization substantially changes the physicochemical and biological characteristics of streams. The trajectory of negative effect is broadly similar around the world, but the nature and magnitude of ecological responses to urban growth differ among locations. Some heterogeneity in response arises from differences in the level of urban development and attributes of urban water management. However, the heterogeneity also may arise from variation in hydrologic, biological, and physicochemical templates that shaped stream ecosystems before urban development. We present a framework to develop hypotheses that predict how natural watershed and channel attributes in the pre-urban-development state may confer ecological resistance to urbanization. We present 6 testable hypotheses that explore the expression of such attributes under our framework: 1) greater water storage capacity mitigates hydrologic regime shifts, 2) coarse substrates and a balance between erosive forces and sediment supply buffer morphological changes, 3) naturally high ionic concentrations and pH pre-adapt biota to water-quality stress, 4) metapopulation connectivity results in retention of species richness, 5) high functional redundancy buffers trophic function from species loss, and 6) landuse history mutes or reverses the expected trajectory of eutrophication. Data from past comparative analyses support these hypotheses, but rigorous testing will require targeted investigations that account for confounding or interacting factors, such as diversity in urban infrastructure attributes. Improved understanding of the susceptibility or resistance of stream ecosystems could substantially strengthen conservation, management, and monitoring efforts in urban streams. We hope that these preliminary, conceptual hypotheses will encourage others to explore these ideas further and generate additional explanations for the heterogeneity observed in urban streams.
What is the Point? Evaluating the Structure, Color, and Semantic Traits of Computer Vision Point Clouds of Vegetation
(MDPI, 2017-04-09) Dandois, Jonathan P.; Baker, Matthew; Olano, Marc; Parker, Geoffrey G.; Ellis, Erle C.
Remote sensing of the structural and spectral traits of vegetation is being transformed by structure from motion (SFM) algorithms that combine overlapping images to produce three-dimensional (3D) red-green-blue (RGB) point clouds. However, much remains unknown about how these point clouds are used to observe vegetation, limiting the understanding of the results and future applications. Here, we examine the content and quality of SFM point cloud 3D-RGB fusion observations. An SFM algorithm using the Scale Invariant Feature Transform (SIFT) feature detector was applied to create the 3D-RGB point clouds of a single tree and forest patches. The fusion quality was evaluated using targets placed within the tree and was compared to fusion measurements from terrestrial LIDAR (TLS). K-means clustering and manual classification were used to evaluate the semantic content of SIFT features. When targets were fully visible in the images, SFM assigned color in the correct place with a high accuracy (93%). The accuracy was lower when targets were shadowed or obscured (29%). Clustering and classification revealed that the SIFT features highlighted areas that were brighter or darker than their surroundings, showing little correspondence with canopy objects like leaves or branches, though the features showed some relationship to landscape context (e.g., canopy, pavement). Therefore, the results suggest that feature detectors play a critical role in determining how vegetation is sampled by SFM. Future research should consider developing feature detectors that are optimized for vegetation mapping, including extracting elements like leaves and flowers. Features should be considered the fundamental unit of SFM mapping, like the pixel in optical imaging and the laser pulse of LIDAR. Under optimal conditions, SFM fusion accuracy exceeded that of TLS, and the two systems produced similar representations of the overall tree shape. SFM is the lower-cost solution for obtaining accurate 3D-RGB fusion measurements of the outer surfaces of vegetation, the critical zone of interaction between vegetation, light, and the atmosphere from leaf to canopy scales.
Channel response to sediment release: insights from a paired analysis of dam removal
(Wiley, 2017-01-13) Collins, Mathias J.; Snyder, Noah P.; Boardman, Graham; Banks, William S.L.; Andrews, Mary; Baker, Matthew; Conlon, Maricate; Gellis, Allen; McClain, Serena; Miller, Andrew; Wilcock, Peter
Dam removals with unmanaged sediment releases are good opportunities to learn about channel response to abruptly increased bed material supply. Understanding these events is important because they affect aquatic habitats and human uses of floodplains. A longstanding paradigm in geomorphology holds that response rates to landscape disturbance exponentially decay through time. However, a previous study of the Merrimack Village Dam (MVD) removal on the Souhegan River in New Hampshire, USA, showed that an exponential function poorly described the early geomorphic response. Erosion of impounded sediments there was two-phased. We had an opportunity to quantitatively test the two-phase response model proposed for MVD by extending the record there and comparing it with data from the Simkins Dam removal on the Patapsco River in Maryland, USA. The watershed sizes are the same order of magnitude (10² km²), and at both sites low-head dams were removed (~3–4 m) and ~65 000 m³ of sand-sized sediments were discharged to low-gradient reaches. Analyzing four years of repeat morphometry and sediment surveys at the Simkins site, as well as continuous discharge and turbidity data, we observed the two-phase erosion response described for MVD. In the early phase, approximately 50% of the impounded sediment at Simkins was eroded rapidly during modest flows. After incision to base level and widening, a second phase began when further erosion depended on floods large enough to go over bank and access impounded sediments more distant from the newly-formed channel. Fitting functional forms to the data for both sites, we found that two-phase exponential models with changing decay constants fit the erosion data better than single-phase models. Valley width influences the two-phase erosion responses upstream, but downstream responses appear more closely related to local gradient, sediment re-supply from the upstream impoundments, and base flows. Copyright © 2017 John Wiley & Sons, Ltd.
Scope#10: Methodology for developing high-resolution stream and waterbody datasets for the Chesapeake Bay watershed
(2018-10) Baker, Matthew; Saavedra, David; Norton, Michael
Thresholds in forest bird communities along woody vegetation gradients in the South American Dry Chaco
(Wiley, 2019-02-11) Macchi, Leandro; Baumann, Matthias; Bluhm, Hendrik; Baker, Matthew; Levers, Christian; Grau, Héctor Ricardo; Kuemmerle, Tobias
World-wide, tropical savannas and dry forests are under increasing pressure from land use. The environmental impacts of agricultural expansion into these ecosystems have received much attention, yet subtler changes in natural vegetation remain severely understudied. We explored how bird communities vary along gradients of woody vegetation in the South American Dry Chaco by combining high-resolution, satellite-based tree, shrub and total woody cover with field data on the frequency of 82 bird species surveyed in 167 plots. We identified change points along woody cover gradients where the relative frequency of individual bird species dropped most strongly. Based on this, we identified forest indicator species and assessed evidence for community-level thresholds. Most forest birds (71%) had clear change points in their frequencies along vegetation gradients, starting as high as 38% total woody cover. Many (41%) forest species declined drastically at woody cover levels of less than 11%. This general pattern was similar for tree and shrub cover. Only 7% of our study area had woody cover levels where we detected no response in forest bird communities. In contrast, 68% of the area had woody cover levels with incremental declines in forest bird species, and 25% of the study area had woody cover levels below the forest bird community threshold. We identified 11 indicator species strongly related to woody cover, with highest frequencies in the eastern and western Dry Chaco. Spatial distributions of these species corresponded well with areas above and below woody vegetation thresholds. Synthesis and applications. We found evidence for critical thresholds for forest birds along woody cover gradients in dry forests and implemented tools to map where these thresholds have been crossed. For the Chaco, we highlight the importance of maintaining woody cover levels above about 40%, such as in certain silvopastoral systems that can be much more wildlife-friendly than other forms of agriculture. We identify remaining areas of potentially intact forest bird communities. More broadly, this study highlights the value of combining species-level (indicator species' distributions) and ecosystem-level (satellite-based, continuous woody cover maps) surrogates for understanding biodiversity patterns and threats.
The capacity of urban forest patches to infiltrate stormwater is influenced by soil physical properties and soil moisture
(Elsevier, 2019-09-15) Phillips, Tuana H.; Baker, Matthew; Lautar, Katie; Yesilonis, Ian; Pavao-Zuckerman, Mitchell A.
Forest patches in developed landscapes perform ecohydrological functions that can reduce urban stormwater flows. However, urban forest patch contributions to runoff mitigation are not well understood due to a lack of performance data. In this study, we focus on the potential of urban forest patch soils to infiltrate rainfall by characterizing rates of unsaturated hydraulic conductivity (K) in 21 forest patches in Baltimore, Maryland. Soil bulk density, organic matter, soil moisture, percent of coarse fragments (≥2 mm), and texture were evaluated at the same locations to assess drivers of K. The K was significantly higher in soils with high sand content and related positively with the percent of coarse fragment material in the soil. Forest patch size did not impact K. We estimate that 68 percent of historic rainfall could be infiltrated by urban forest patch soils at the measured K rates. Continuous monitoring at one forest patch also showed that K is dynamic in time and influenced by antecedent soil moisture conditions. We conservatively estimate that unsaturated urban forest patch soils alone are capable of infiltrating most rain events of low to moderate intensities that fell within these forest patches in the Baltimore region. Considering this ecohydrologic function, the protection and expansion of forest patches can make substantial contributions to stormwater mitigation.
An Introduction to TITAN2
(2023-11-14) Baker, Matthew; King, Ryan; Kahle, David
The purpose of this vignette is to walk users through the basic functionality of the package TITAN2 for analysis of taxon-specific contributions to community change along an environmental gradient. The Everglades data for this vignette was described in Baker and King (2010) first published by King and Richardson (2003).
Mercury dynamics in groundwater across three distinct riparian zone types of the US Midwest
(Royal Society of Chemistry, 2013-10-04) G. Vidon, Philippe; J. Mitchell, Carl P.; Jacinthe, Pierre-André; Baker, Matthew; Liu, Xiaoqiang; R. Fisher, Katelin
Although the intense biogeochemical gradients present in riparian zones have the potential to affect mercury (Hg) cycling, Hg dynamics in riparian zones has received relatively little attention in the literature. Our study investigated groundwater filtered total mercury (THg) and methylmercury (MeHg) dynamics in three riparian zones with contrasting hydrogeomorphic (HGM) characteristics (till, alluvium, outwash) in the US Midwest. Despite high Hg deposition rates (>16 μg m⁻²) in the region, median THg (<1.05 ng L⁻¹) and MeHg (<0.05 ng L⁻¹) concentrations were low at the study sites. Methylmercury concentrations were significantly (p < 0.05) correlated to THg (R = 0.82), temperature (R = 0.55), and dissolved organic carbon (DOC) (R = 0.62). THg also correlated with groundwater DOC (R = 0.59). The proportion of MeHg in THg (%MeHg) was significantly correlated to temperature (R = 0.58) and MeHg (R = 0.50). Results suggest that HGM characteristics, the presence of tile drains, and the propensity for overbank flooding at a riparian site determined the extent to which stream water Hg concentrations influenced riparian groundwater Hg levels or vice versa. Differences in hydrogeomorphic characteristics between sites did not translate however in significant differences in groundwater MeHg or %MeHg. Overall, widespread Hg contamination in the most common riparian hydrogeomorphic types of the US Midwest is unlikely to be a major concern. However, for frequently flooded riparian zones located downstream from a potentially large source of Hg (e.g., concentrated urban development), Hg concentrations are likely to be higher than at other sites.
Considerations for analyzing ecological community thresholds in response to anthropogenic environmental gradients
(University of Chicago Press, 2010-09) King, Ryan S.; Baker, Matthew
The goal of this paper is to help managers better understand implications of using aggregate community metrics, such as taxon richness or Indices of Biotic Integrity (IBI), for detecting threshold responses to anthropogenic environmental gradients. To illustrate, we offer an alternative analytical approach, Threshold Indicator Taxa ANalysis (TITAN), geared toward identifying synchronous changes in the distribution of multiple taxa as evidence of an ecological community threshold. Our approach underscores the fundamental reality that which taxa are affected by stressors is important, both from a conservation standpoint and because taxon-specific life-history traits help us understand relevant mechanisms. First, we examine macroinvertebrate community response to an impervious cover gradient using a well-studied biomonitoring data set to show that representative community metrics are relatively insensitive to synchronous threshold declines of numerous individual taxa. We then reproduce these response relationships using a simulated community data set with similar properties to demonstrate that linear or wedge-shaped responses of community metrics to anthropogenic gradients can occur as an artifact of aggregating multiple taxa into a single value per sampling unit, despite strong nonlinearity in community response. Our findings do not repudiate the use of community metrics or multimetric indices, but they challenge assumptions that such metrics are capable of accurately reflecting community thresholds across a broad range of anthropogenic gradients. We recommend an alternative analysis framework that begins with characterization of the responses of individual taxa and uses aggregation only after distinguishing the magnitude, direction, and uncertainty in the responses of individual members of the community.
Spatial Considerations for Linking Watershed Land Cover to Ecological Indicators in Streams
(Wiley, 2005-02-01) King, Ryan S.; Baker, Matthew; Whigham, Dennis F.; Weller, Donald E.; Jordan, Thomas E.; Kazyak, Paul F.; Hurd, Martin K.
Watershed land cover is widely used as a predictor of stream-ecosystem condition. However, numerous spatial factors can confound the interpretation of correlative analyses between land cover and stream indicators, particularly at broad spatial scales. We used a stream-monitoring data set collected from the Coastal Plain of Maryland, USA to address analytical challenges presented by (1) collinearity of land-cover class percentages, (2) spatial autocorrelation of land cover and stream data, (3) intercorrelations among and spatial autocorrelation within abiotic intermediaries that link land cover to stream biota, and (4) spatial arrangement of land cover within watersheds. We focused on two commonly measured stream indicators, nitrate-nitrogen (NO₃–N) and macroinvertebrate assemblages, to evaluate how different spatial considerations may influence results. Partial correlation analysis of land-cover percentages revealed that simple correlations described relationships that could not be separated from the effects of other land-cover classes or relationships that changed substantially when the influences of other land-cover classes were taken into account. Partial Mantel tests showed that all land-cover percentages were spatially autocorrelated, and this spatial phenomenon accounted for much of the variation in macroinvertebrate assemblages that could naively be attributed to certain classes (e.g., percentage cropland). We extended our use of partial Mantel tests into a path-analytical framework and identified several independent pathways between percentage developed land and in-stream measurements after factoring out spatial autocorrelation and other confounding variables; however, under these conditions, percentage cropland was only linked to nitrate-N. Further analyses revealed that spatial arrangement of land cover, as measured by areal buffers and distance weighting, influenced the amount of developed land, resulting in a threshold change in macroinvertebrate-assemblage composition. Moreover, distance-weighted percentage cropland improved predictions of stream nitrate-N concentrations in small watersheds, but not in medium or large ones. Collectively, this series of analyses clarified the magnitude and critical scales of effects of different land-cover classes on Coastal Plain stream ecosystems and may serve as an analytical framework for other studies. Our results suggest that greater emphasis should be placed on these important spatial considerations; otherwise, we risk obscuring the relationships between watershed land cover and the condition of stream ecosystems.

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