Mark H. Stolt

COMPARISON OF SOIL AND OTHER ENVIRONMENTAL CONDITIONS IN CONSTRUCTED AND ADJACENT PALUSTRINE REFERENCE WETLANDS

Wetlands are created to compensate for the loss of natural wetlands as a result of human landuse activities. How well these constructed wetlands mimic natural wetlands is in debate. The goal of this study was to compare soil and other environmental conditions within constructed and adjacent reference wetlands to assess the progress of the constructed wetlands towards a functional wetland. Three constructed wetlands in Virginia, USA, 4 to 7 years old, were paired with adjacent palustrine forested and scrub-shrub reference wetlands to examine differences in topography, hydrology, soil properties, and other environment conditions such as soil temperature and redox potential. Degree of microrelief was greater in reference wetlands than in the associated constructed wetlands. Seasonal fluctuations in water-table levels were similar in both wetland types. Two of the paired wetlands showed considerable differences (15 to 20 cm) in the depth to the water table. Redox potentials were similar in reference and constructed wetlands. Paired wetlands with water-table levels at or near the soil surface throughout the year showed similar soil temperatures. At the site where the summer water levels were 80 to 100 cm below the soil surface, summer temperatures were substantially higher in the poorly shaded, constructed wetland. At the two sites with high water-table levels throughout the year, percent clay and silt, levels of organic C and N, and cation exchange capacity were significantly greater (p <0.05) in the reference wetlands. At the drier site, only 3 of the 16 soil parameters compared were significantly different. In this limited study, observed differences in soil and other environmental conditions between paired wetlands suggest that constructed wetlands may not function in the same capacity as adjacent reference wetlands.

8 – Redoximorphic Features

Publisher Summary Redoximorphic features have been referred to by various terms over the past decades. The terminology used to describe redoximorphic features is derived from sedimentary petrology and soil micromorphology. Redoximorphic features are common in most soils where water saturation occurs and their presence is used extensively in making land use decisions. Although redoximorphic features are visible in the field with both the naked eye and a hand lens, micromorphological analysis can further enhance our understanding of how these features form and how to interpret them correctly. These interpretations are best made when supportive information such as water table and climatic data are available, but they can to a large extent be based on extensive micromorphological data correlating redoximorphic pedofeatures to environmental conditions.

Denitrification Capacity in a Subterranean Estuary below a Rhode Island Fringing Salt Marsh

Coastal waters are severely threatened by nitrogen (N) loading from direct groundwater discharge. The subterranean estuary, the mixing zone of fresh groundwater and sea water in a coastal aquifer, has a high potential to remove substantial N. A network of piezometers was used to characterize the denitrification capacity and groundwater flow paths in the subterranean estuary below a Rhode Island fringing salt marsh.15N-enriched nitrate was injected into the subterranean estuary (in situ push-pull method) to evaluate the denitrification capacity of the saturated zone at multiple depths (125–300 cm) below different zones (upland-marsh transition zone, high marsh, and low marsh). From the upland to low marsh, the water table became shallower, groundwater dissolved oxygen decreased, and groundwater pH, soil organic carbon, and total root biomass increased. As groundwater approached the high and low marsh, the hydraulic gradient increased and deep groundwater upwelled. In the warm season (groundwater temperature >12 °C), elevated groundwater denitrification capacity within each zone was observed. The warm season low marsh groundwater denitrification capacity was significantly higher than all other zones and depths. In the cool season (groundwater temperature <10.5 °C), elevated groundwater denitrification capacity was only found in the low marsh. Additions of dissolved organic carbon did not alter groundwater denitrification capacity suggesting that an alternative electron donor, possibly transported by tidal inundation from the root zone, may be limiting. Combining flow paths with denitrification capacity and saturated porewater residence time, we estimated that as much as 29–60 mg N could be removed from 11 of water flowing through the subterranean estuary below the low marsh, arguing for the significance of subterranean estuaries in annual watershed scale N budgets.

Below the disappearing marshes of an urban estuary: historic nitrogen trends and soil structure

Marshes in the urban Jamaica Bay Estuary, New York, USA are disappearing at an average rate of 13 ha/yr, and multiple stressors (e.g., wastewater inputs, dredging activities, groundwater removal, and global warming) may be contributing to marsh losses. Among these stressors, wastewater nutrients are suspected to be an important contributing cause of marsh deterioration. We used census data, radiometric dating, stable nitrogen isotopes, and soil surveys to examine the temporal relationships between human population growth and soil nitrogen; and we evaluated soil structure with computer-aided tomography, surface elevation and sediment accretion trends, carbon dioxide emissions, and soil shear strength to examine differences among disappearing (Black Bank and Big Egg) and stable marshes (JoCo). Radiometric dating and nitrogen isotope analyses suggested a rapid increase in human wastewater nutrients beginning in the late 1840s, and a tapering off beginning in the 1930s when wastewater treatment plants (WWTPs) were first installed. Current WWTPs nutrient loads to Jamaica Bay are approximately 13 995 kg N/d and 2767 kg P/d. At Black Bank, the biomass and abundance of roots and rhizomes and percentage of organic matter on soil were significantly lower, rhizomes larger in diameter, carbon dioxide emission rates and peat particle density significantly greater, and soil strength significantly lower compared to the stable JoCo Marsh, suggesting Black Bank has elevated decomposition rates, more decomposed peat, and highly waterlogged peat. Despite these differences, the rates of accretion and surface elevation change were similar for both marshes, and the rates of elevation change approximated the long-term relative rate of sea level rise estimated from tide gauge data at nearby Sandy Hook, New Jersey. We hypothesize that Black Bank marsh kept pace with sea level rise by the accretion of material on the marsh surface, and the maintenance of soil volume through production of larger diameter rhizomes and swelling (dilation) of waterlogged peat. JoCo Marsh kept pace with sea-level rise through surface accretion and soil organic matter accumulation. Understanding the effects of multiple stressors, including nutrient enrichment, on soil structure, organic matter accumulation, and elevation change will better inform management decisions aimed at maintaining and restoring coastal marshes.

Soil respiration rates in coastal marshes subject to increasing watershed nitrogen loads in southern New England, USA.

Mean soil respiration rates (carbon dioxide efflux from bare soils) among salt marshes in Narragansett Bay, RI ranged from 1.7–7.8 μmol m−2 s−1 inSpartina patens in high marsh zones and 1.7–6.0 μmol m−2 s−1 inS. alterniflora in low marsh zones. The soil respiration rates significantly increased along a gradient of increasing watershed nitrogen (N) loads (S. alterniflora, R2 = 0.95, P = 0.0008;S. patens, R2 = 0.70, P = 0.02). As the soil respiration increased, the percent carbon (C) and N in the soil surface layer decreased in theS. alterniflora, suggesting that in part, the increased soil respiration rates are contributing to the increased turnover of labile organic matter. In contrast, there were no apparent relationships between the soil respiration rates in the high marsh and the soil C and N contents of the surface layer. However, there was a broad-scale pattern and significant inverse relationship between the high marsh soil respiration rates and the landscape belowground biomass ofS. patens. As more and more salt marsh systems are subjected to increasing nutrient loads, decomposition rates of soil organic matter may increase in marsh soils leading to higher turnover rates of C and N.

Soil Organic Matter

Publisher Summary This chapter discusses soil organic matter. Organic matter is universal to all soils. The form and distribution of soil organic matter is dependent upon a number of processes that may act independently or in concert. Most of these processes are related to the initial decomposition of the plant residues by a suite of soil fauna, and to the continued decomposition, transport and accumulation of the by-products. Descriptions of the forms, distribution and genesis of organic components in soils can range from quite simple to extremely complex. Micromorphological approaches to such descriptions are comparably varied. The most important issues that are faced are related to the effects of land-use change, global warming, pollution and invasive species on the soil environment. Because soil organic matter is the most dynamic of the soil components, effects of changing soil environment are often recorded first in the quality and distribution of organic matter.

Development and application of multi‐proxy indices of land use change for riparian soils in southern New England, USA

Understanding the effects of land use on riparian systems is dependent upon the development of methodologies to recognize changes in sedimentation related to shifts in land use. Land use trends in southern New England consist of shifts from forested precolonial conditions, to colonial and agrarian land uses, and toward modern industrial-urban landscapes. The goals of this study were to develop a set of stratigraphic indices that reflect these land use periods and to illustrate their applications. Twenty-four riparian sites from first- and second-order watersheds were chosen for study. Soil morphological features, such as buried surface horizons (layers), were useful to identify periods of watershed instability. The presence of human artifacts and increases in heavy metal concentration above background levels, were also effective indicators of industrial-urban land use periods. Increases and peak abundance of non-arboreal weed pollen (Ambrosia) were identified as stratigraphic markers indicative of agricultural land uses. Twelve 14C dates from riparian soils indicated that the rise in non-arboreal pollen corresponds to the start of regional deforestation (AD 1749 +/- 56 cal yr; mean +/- 2 SD) and peak non-arboreal pollen concentration corresponds to maximum agricultural land use (AD 1820 +/- 51 cal yr). These indices were applied to elucidate the impact of land use on riparian sedimentation and soil carbon (C) dynamics. This analysis indicated that the majority of sediment and soil organic carbon (SOC) stored in regional riparian soils is of postcolonial origins. Mean net sedimentation rates increased -100-fold during postcolonial time periods, and net SOC sequestration rates showed an approximate 200-fold increase since precolonial times. These results suggest that headwater riparian zones have acted as an effective sink for alluvial sediment and SOC associated with postcolonial land use.

Mapping Shallow Coastal Ecosystems: A Case Study of a Rhode Island Lagoon

Abstract In order to effectively study, manage, conserve, and sustain shallow-subtidal ecosystems, a spatial inventory of the basic resources and habitats is essential. Because of the complexities of shallow-subtidal substrates, benthic communities, geology, geomorphology, and water column attributes, few standard protocols are fully articulated and tested that describe the mapping and inventory processes and accompanying interpretations. In this paper, we describe a systematic approach to map Rhode Islands shallow-subtidal coastal lagoon ecosystems, by using, integrating, and reconciling multiple data sets to identify the geology, soils, biological communities, and environments that, collectively, define each shallow-subtidal habitat. We constructed maps for these lagoons via a deliberate, step by step approach. Acoustics and geostatistical modeling were used to create a bathymetric map. These data were analyzed to identify submerged landforms and geologic boundaries. Geologic interpretations were verified with video and grab samples. Soils were sampled, characterized, and mapped within the context of the landscape and geologic boundaries. Biological components and distributions were investigated using acoustics, grab samples, video, and sediment profile images. Data sets were cross-referenced and ground-truthed to test for inconsistencies. Maps and geospatial data, with Federal Geographic Data Committee (FGDC)-compliant metadata, were finalized after reconciling data set inconsistencies and made available on the Internet. These data allow for classification in the revised Coastal and Marine Ecological Classification Standard (CMECS). With these maps, we explored potential relationships among and between physical and biological parameters. In some cases, we discovered a clear match between habitat measures; in others, however, relationships were more difficult to distinguish and require further investigation.

Evaluating methods to create a base map for a subaqueous soil inventory

Topographic maps are often used as base maps for soil survey investigations and inventories. On these maps landscape units, based on slope, land-surface shape, and landscape/landform associations can be easily visualized and delineated. These landscape units provide the first approximation of the distribution of soils across an area. In the submerged environment, observing landscape units in water that are greater than a meter is nearly impossible, so reliable topographic maps of the submerged topography are necessary for conducting subaqueous soil surveys. In this study, bathymetric data collected by NOAA using acoustic soundings were compared with direct measurement of the submerged topography of a coastal lagoon in Rhode Island in order to evaluate the usefulness of the NOAA data for creating a topographic base map for a subaqueous soil inventory. Direct measurements were made using traditional surveying equipment and innovative methods. Although the data were 40 years old, the topographic map (1:10,000) created from the NOAA data resembled closely the contour map created from the more recent survey data. These results strongly suggest that subaqueous landscape units in coastal lagoons may be stable for a relatively long period of time. Our study suggests that available NOAA bathymetric data, augmented with elevation data collected with traditional and innovative methods, may be a useful approach to create a base map for subaqueous soil inventories.

Soils-Based Rapid Assessment for Quantifying Changes in Salt Marsh Condition as a Result of Hydrologic Alteration

Wetland condition can be severely altered as a result of a change in hydrology. In this study, we examined several soil-based methods to quantify and assess changes in salt marsh condition as a result of tidal restriction. Soil properties were compared between two tidally restricted and two (paired) unrestricted salt marshes. Organic horizon morphology provided a qualitative metric of marsh peat decomposition. Quantitative measures of the degree of decomposition included stable plant fragment content and bearing capacity. Soil pH provided simple metrics of changes in soil chemistry. Bulk density was measured to estimate marsh peat collapse and soil organic matter content provided a measure of carbon dynamics. Neither marsh showed significant differences in soil organic matter or bulk density relative to their paired reference marsh. In contrast, soil pH, stable plant fragment content, and bearing capacity were significantly different between restricted and reference marshes. With the exception of incubation pH, these soil properties can be simply and rapidly measured in the field to quantify physical, chemical, and biological changes in the wetland condition of salt marshes as a result of tidal restriction. Further studies should be conducted to develop a rapid protocol for measuring incubation pH in the field.