Gregory L. Bruland

Environmental and anthropogenic controls over bacterial communities in wetland soils

Soil bacteria regulate wetland biogeochemical processes, yet little is known about controls over their distribution and abundance. Bacteria in North Carolina swamps and bogs differ greatly from Florida Everglades fens, where communities studied were unexpectedly similar along a nutrient enrichment gradient. Bacterial composition and diversity corresponded strongly with soil pH, land use, and restoration status, but less to nutrient concentrations, and not with wetland type or soil carbon. Surprisingly, wetland restoration decreased bacterial diversity, a response opposite to that in terrestrial ecosystems. Community level patterns were underlain by responses of a few taxa, especially the Acidobacteria and Proteobacteria, suggesting promise for bacterial indicators of restoration and trophic status.

Factors influencing the sorption of oxytetracycline to soils.

Veterinary antibiotics such as oxytetracycline (OTC) increasingly are found in the environment and often come into direct contact with soils via the release of animal wastes. Oxytetracycline is known to sorb strongly to soils by interaction with soil organic matter, clay minerals, and metal oxides. However, current knowledge of the influence of soil properties on OTC sorption is limited, as is our ability to predict OTC sorption to soils. This work was aimed at identifying properties that most influence the extent of OTC sorption in a suite of soils from the eastern United States representing a wide range in soil properties. Thirty soils were well characterized, an OTC soil-water distribution coefficient (Kd) was determined for each soil, and statistical analyses were employed to determine appropriate soil descriptors of OTC sorption. Soil texture, cation exchange capacity, and iron oxide content seemed to most influence the extent of OTC sorption in soils with organic carbon (OC) content between 0 and 4%. Thus, the knowledge of these three soil properties would be key to anticipating the extent of OTC sorption and gaining insight into OTC fate within a given soil system. Notably, OC content appeared to influence OTC sorption only in a soil with 9% OC.

Effects of agriculture and wetland restoration on hydrology, soils, and water quality of a Carolina bay complex

We compared hydrology, soils, and water quality of an agricultural field (AG), a two-year-old restored wetland (RW), and two reference ecosystems (a non-riverine swamp forest (NRSF) and a high pocosin forest (POC)) located at the Barra Farms Regional Wetland Mitigation Bank, a Carolina bay complex in Cumberland County, North Carolina. Our main objectives were to: 1) determine if the RW exhibited hydrology comparable to a reference ecosystem, 2) characterize the soils of the AG, RW, and reference ecosystems, and 3) assess differences in water quality in the surface outflow from the AG, RW, and reference ecosystems. Water table data indicated that the hydrology of the RW has been successfully reestablished as the hydroperiod of the RW closely matched that of the NRSF in 1998 and 1999. Jurisdictional hydrologic success criterion was also met by the RW in both years. To characterize soil properties, soil cores from each ecosystem were analyzed for bulk density (Db), total carbon (Ct), nitrogen (Nt), and phosphorus (Pt), extractable phosphate (PO4w), nitrogen (Nex), and cations (Caex, Mgex, Kex, Naex), as well as pH. Bulk density, Pt, Caex, Mgex, and pH were greatly elevated in the AG and RW compared to the reference ecosystems. Water quality monitoring consisted of measuring soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate + nitrite (NOX), and total nitrogen (TN) concentrations in surface water from the AG, RW, and reference outflows. Outflow concentrations of SRP, TP, and NOX were highest and most variable in the AG, while TN was highest in the reference. This study suggested that while restoration of wetland hydrology has been successful in the short term, alteration of wetland soil properties by agriculture was so intense, that changes due to restoration were not apparent for most soil parameters. Restoration also appeared to provide water quality benefits, as outflow concentrations of SRP, TP, NOX, and TN were lower in the RW than the AG.

Comparison of soil organic matter in created, restored and paired natural wetlands in North Carolina

Soil organic matter (SOM) content is a key indicator of soil quality and is correlated to a number of important soil processes that occur in wetlands such as respiration, denitrification, and phosphorus sorption. To better understand the differences in the SOM content of created (CW), restored (RW), and paired natural wetlands (NWs), 11 CW/RW-NW pairs were sampled in North Carolina. The site pairs spanned a range of hydrogeomorphic (HGM) subclasses common in the Coastal Plain. The following null hypotheses were tested: (1) SOM content of paired CW/RWs and NWs are similar; (2) SOM content of wetlands across different HGM subclasses is similar; and (3) interactions between wetland status (CW/RW vs. NW) and hydrogeomorphic subclass are similar. The first null hypothesis was rejected as CW/RWs had significantly lower mean SOM (11.8 ± 3.9%) than their paired NWs (28.98 ± 8.0%) on average and at 10 out of the 11 individual sites. The second and third null hypotheses were also rejected as CW/RWs and NWs in the non-riverine organic soil flat subclass had significantly higher mean SOM content (31.08 ± 14.2%) than the other three subclasses (8.18 ± 2.5, 11.18 ± 8.2, and 10.38 ± 4.2%). Individual sites within this fourth subclass also had significantly different SOM content. This indicated that it would be inappropriate to include the organic soil flat subclass with either the riverine or non-riverine mineral soil flat subclasses when considering restoration guidelines. These results also suggested that if there is a choice in mitigation options between restoration or creation, wetlands should be restored rather than created, especially those in the non-riverine organic soil flat subclass.

SPATIAL VARIABILITY OF DENITRIFICATION POTENTIAL AND RELATED SOIL PROPERTIES IN CREATED, RESTORED, AND PAIRED NATURAL WETLANDS

To gain a better understanding of the spatial patterns of denitrification potential and related soil properties in created (CW), restored (RW), and natural wetlands (NWs), four CW/RW-NW pairs in North Carolina, USA were sampled. These site pairs spanned a range of hydrogeomorphic (HGM) settings common in the Coastal Plain. It was hypothesized that denitrification enzyme activities (DEAs) and related soil properties of CW/RWs would have less spatial variability than DEAs and soil properties of NWs, as prior land-use and mitigation activities tend to homogenize soil properties. Cochran’s C tests indicated that variances were significantly lower in CW/RWs than in NWs for most soil properties, and that for nitrate (NO3-N), variances were significantly lower in CW/RWs across all HGM settings. Interpolated maps of the soil properties revealed homogeneous distributions of NO3-N across the CW/ RW plots compared to much more heterogeneous distributions of NO3-N across the NW plots. Multiple stepwise regressions confirmed that either NO3-N or soluble organic carbon were significant predictors of the DEA at each plot. Interpolated maps of predicted DEA generally showed similar patterns to those of NO3-N. While some nitrate and DEA hotspots were observed in the CW/RWs, more were present in the NWs. These results indicated that spatial distributions of soil chemical properties and DEAs were considerably different in CW/RWs than in paired NWs. This is the first study to document such differences, suggesting that CWs and RWs with homogeneous soil chemical distributions may not develop the full range of soil biogeochemical processes that occur in NWs.

SPATIAL VARIABILITY OF SOIL PROPERTIES IN CYPRESS DOMES SURROUNDED BY DIFFERENT LAND USES

Anthropogenic activities affect self-organization in wetlands, in turn affecting spatial patterns of soil properties such as pH, nutrient concentrations, and soil organic matter content. To better understand the effects of anthropogenic disturbance in wetlands, we examined soil patterns in wetlands subject to a gradient of human impact. Four cypress domes in north Florida representing reference/ unmanaged, forest plantation, improved pasture, and urban land uses were sampled (n = 60 site−1) for soil pH, organic matter (OM), and total phosphorus (TP). Mean values varied significantly both within and among sites, with low pH, SOM, and TP at minimally impacted and plantation sites, and high values at pasture and urban sites. Within-site variability was large for SOM and TP in all sites (average coefficient of variation = 48% and 62%, respectively), and small for pH (average CV = 7%). Strong radial patterns for SOM and TP in minimally impacted and plantation sites were observed. In contrast, at pasture and urban sites linear/quadratic trends in pH were observed. We quantified spatial patterns by soil property for each site, observing significant structure (long range, low nugget:sill) for TP and SOM in minimally impacted and forest plantation sites. We infer a transition from endogenous to exogenous drivers with increasing anthropogenic influence. Our findings indicate that, for pH, a small number of samples (n < 3 for characterization within 10% of true mean) are needed, while more (n = 11–33) are needed for SOM and TP; sampling density requirements increase with the scale of spatial structure. Our results allow the definition of the necessary sampling intensity and design to achieve effective monitoring.

A comparison of the vegetation and soils of natural, restored, and created coastal lowland wetlands in Hawai'i.

The loss of coastal wetlands throughout the Hawaiian Islands has increased the numbers of created (CW) and restored (RW) wetlands. An assessment of these wetlands has yet to occur, and it has not been determined whether CWs and RWs provide the same functions as natural wetlands (NWs). To address these concerns, vegetation and soil characteristics of 35 wetlands were compared within sites along hydrologic gradients and among sites with different surface water salinity and status (i.e., CW, RW, NW). Only 16 of 85 plant species identified were native and three of the four most abundant species were exotic. Vegetative characteristics differed primarily across salinity classes, then along hydrologic zones, and to a lesser extent among CWs, RWs, and NWs. Soil properties exhibited fewer differences across salinity classes and along hydrologic zones and greater differences among CWs, RWs, and NWs. The dominant presence of invasive species in coastal Hawaiian wetlands suggests that it will be difficult to locate reference sites that can be used as restoration targets. Differences in edaphic characteristics suggested that RWs/CWs do not exhibit the same functions as NWs. Future restoration and creation should include planting of native vegetation, controlling invasive vegetation, and alleviating inadequate soil conditions.

Landscape Patterns of Significant Soil Nutrients and Contaminants in the Greater Everglades Ecosystem: Past, Present, and Future

The primary goal of this review and synthesis effort is to summarize present landscape patterns of key soil constituents such as carbon (C), phosphorus (P), sulfur (S), and mercury (Hg), all of which are of historical and present interest with respect to Everglades restoration. A secondary goal is to highlight the importance of landscape scale monitoring and assessment of soils in the Everglades Protection Area (EPA) with respect to present and future restoration efforts. Review of present information derived from the two independent landscape scale studies revealed significant patterns of soil thickness, organic matter, and P in the EPA. Two soil constituents of concern, Hg (biological toxicity) and S (linked to increased P cycling), also exhibit spatial patterns at the landscape scale, suggesting a need for focused efforts of restoration. Significant patterns of soil enrichment and change suggest a dynamic interaction between environmental stressors and soil biogeochemical properties across the landscape. Trends and patterns at the landscape scale in the EPA suggest that landscape scale monitoring and assessment is necessary and critical to determining the success of restoration efforts. However, several key questions, surrounding appropriate temporal and spatial sampling scales, the standardization of sampling methods, and the significance of short range variability must be addressed to facilitate future landscape scale assessment efforts.

Expanding Distance Education in the spatial sciences through Virtual Learning Entities and a Virtual GIs computer Laboratory

In this paper we describe the implementation of an emerging virtual learning environment to teach GIS and spatial sciences to distance education graduate students. We discuss the benefits and constraints of our mixed architecture with the main focus on the innovative hybrid architecture of the virtual GIS computer laboratory. Criteria that were used to develop the virtual learning environment included: (i) Facilitating student-instructor, student-computer, and student-student interactivity using a mix of synchronous and asynchronous communication tools; (ii) Developing a liberal online learning environment in which students have access to a suite of passive and active multi-media tools; and (iii) Allowing student access to a mixed Web-facilitated/hybrid architecture that stimulates their cognitive geographic skills and provides hands-on experience in using GIS.