Assessing dynamic soil properties in southern New England using an ecological site framework

An ecological site is defined as a distinctive kind of land based on recurring soil, landform, geological, and climate characteristics that differs from other kinds of land in its ability to produce distinctive kinds and amounts of vegetation and in its ability to respond similarly to management actions and natural disturbances. The primary objective of this study was to initiate provisional ecological site concepts for upland, riparian, salt marsh, and subaqueous soils in southern New England by comparing sites that share similar geomorphic settings, but differing soil types. For each system, I also determined how a specific disturbance or management scenario affected dynamic soil properties. In uplands, Merrimac (sandy) and Enfield (silty) soil components were compared to determine whether or not these soils are different ecological sites. My preliminary investigation showed that forest stands on these soils could be coniferous or deciduous. Therefore, within each upland soil type, three deciduous and three coniferous sites were investigated. Within the upper 50 cm, Merrimac soils averaged 61% sand, which was significantly greater than the 26% recorded for Enfield (p<0.01). Although this supports that these soils differ in drainage, soil texture did not seem to influence the 50 cm soil organic carbon pools between Merrimac (109 Mg C ha) and Enfield (101 Mg C ha; p=0.66). Even though the Merrimac soils are sandier and thus better drained than Enfield, the similarity in vegetation composition and tree productivity indicate that these soils have similar ecological potential. 15 years after the selective harvest of sites with either Enfield or Merrimac soils, soil carbon pools were determined to be resilient to change. I concluded that the 50% removal of overstory trees decreases carbon additions from litter by 28% (p=0.036), but that this reduction did not significantly impact the distribution of soil carbon within the soil profile in both Merrimac and Enfield soils. For riparian ecological sites, I aimed to develop concepts to differentiate poorly drained (Walpole) and very poorly drained (Scarboro) soils. Both the Walpole and Scarboro riparian sites had stands of Acer rubrum, but there were observable differences in the understory species composition that support separate ecological sites for these soil systems. Carex stricta and Symplocarpus foetidus were the two species that seemed to indicate the very poorly drained conditions of the Scarboro soils. Within the upper 50 cm, Scarboro soils averaged 210 Mg C ha, which was greater than the 116 Mg C ha recorded for Walpole (p=0.17). The higher water table found at the Scarboro sites is the likely cause of increased organic matter accumulation and thus the higher SOC pool that was observed in comparison to the other soils used in this study. In a plot enrichment study, I compared two levels of nitrogen additions (7.5 and 15 g N m yr) with a control to determine whether nitrogen enrichment alters dynamic soil properties in riparian sites with Scarboro soils. Root biomass, measured in the upper 20 cm, was 4.6 times greater in the high treatment when compared to the control (p=0.006). The low treatment showed a similar trend with 1.6 times more root biomass than the control (p=0.135). Thus, N may be a limiting nutrient for plant growth in these riparian soils. Although there were significant root biomass differences, above ground biomass values were similar across treatments. In salt marshes, Ipswich and Matunuck soils were investigated to determine how these soils respond to ditching and whether or not they are different ecological sites. The main difference between Ipswich (Histosols) and Matunuck (Entisols) soils is the thickness of organic materials. Based on the kind of vegetation present and the response of the vegetation to salt marsh ditching, these soils are the same ecological site. On both soils, Spartina patens and tall Spartina alterniflora were most common at or near the edge of the ditch and short S. alterniflora and salt marsh pannes occupied zones inward from the ditch. The productivity and distribution of individual salt marsh species is based on several factors including soil salinity, which is often a function of the distance of the pedon to the marsh-water interface. Four passive opentopped warming chambers (OTCs) were installed on an Ipswich soil to determine how increased temperature will effect soil carbon dynamics. I concluded that OTCs can successfully increase air temperatures, but modifications to the design used in this study may be necessary to achieve projected (1.5-4 °C) temperature increases. Postseason biomass was 32% greater in the OTC plots in 2012 (p=0.06) and 91% more in 2013 (p=0.01), suggesting higher temperatures could increase productivity in salt marshes. However, potential increases in carbon additions to the soil may be offset by increased decomposition. I used macroinvertebrate distributions to compare Massapog and Pishagqua soils to illustrate that subaqueous soils can be viewed through an ecological site framework. Massapog soils are part of the flood-tidal delta, a high energy environment near the estuary’s inlet. These soils are sandier and have less SOM compared to the Pishagqua soils, which form on the bay floor, an area protected from high energy deposition. Because of their different geomorphic settings, 94% of the invertebrate community sampled from the Massapog soils were filter feeders, while in the Pishagqua soils the benthic community mostly consisted of deposit feeders (78%). Invertebrate density was reduced in dredged sites by 97 and 71% for the Massapog and Pishagqua soils, respectively. In the Massapog soils, dredging increased water depths promoting eelgrass colonization. This change induced a shift from dominantly filter feeding organisms such as Mya arenaria and Clymenella torquata to deposit feeders including Nephlys picta and species in the Ampeliscidae family. The invertebrate community in the Pishagqua soils was similar between the dredged and control site, indicating that these soils likely respond differently to dredging. I found that water depth strongly influences the presence of eelgrass, likely because depth influences light availability. I believe that in most cases dredging lagoon bottom soils will inhibit their ability to support eelgrass because depth will be too great. In contrast, dredging in the floodtidal delta could inhibit or induce eelgrass presence. For both Massapog and Pishagqua dredging increased depth which resulted in finer textures and greater SOC accumulation.