A three part investigation into the effects of riparian reforestation on small streams demonstrated the timing, nature, and processes of morphologic change. First, measurements of two small streams in northeastern Vermont collected in 1966 and 2004 – 2005 documented considerable change in channel width following a period of passive reforestation. Channel widths of several tributaries to Sleepers River were measured in 1966 when the area had more non-forested riparian vegetation than today. A longitudinal survey in 2004 of two of these tributaries, followed by detailed measurements at specific reaches in 2005, provided information on channel size, large woody debris (LWD), and riparian vegetation. Reforested reaches have widened and incised markedly since 1966. Reaches with the oldest forest were widest for a given drainage area, and the non-forested reaches were substantially narrower. A conceptual model was developed that describes a multi-phase process of incision, widening, and recovery following riparian reforestation of non-forested areas. Second, a fixed-bed hydraulic model of one of the streams was developed to evaluate the impact of forested riparian vegetation on near-bank turbulence during overbank flows. Flume experiments with kinematic similitude and a 1:5 scale represented half a channel and its floodplain, mimicking the size of a non-forested reach. Two types of vegetation were simulated: non-forested, with synthetic grass carpet; and forested, where wooden dowels were added. Three-dimensional velocities were measured with an acoustic Doppler velocimeter. Velocities, turbulent kinetic energy (TKE), and Reynolds shear stress showed significant differences between forested and non-forested runs. Forested runs exhibited a narrow band of high TKE in the near-bank region that was roughly two times greater than in non-forested runs. Hydraulic characteristics of forested runs appear to create an environment with higher erosion potential, thereby indicating a possible driving mechanism for channel widening in reforesting stream reaches. Third, Light Detection and Ranging (LiDAR) data from Chittenden County were analyzed to develop a method capable of classifying riparian buffers into broad classes according to forest type and age. The geospatial characteristics of the LiDAR data in forested areas were explored using semivariogram analysis, and LiDAR-based metrics were derived in a geographic information system (GIS) to quantify vegetation height and variance. The LiDAR-based metrics were then used in two discriminant analysis procedures that distinguished: 1) forest type as deciduous or coniferous; and 2) forest age in four age classes. With the resulting linear discriminant functions, a GIS-based classification method was developed. The classification method was highly successful at determining forest type but only moderately successful at determining forest age.

Dissolved organic carbon (DOC) plays an important role in the global carbon (C) cycle because increases in aqueous C potentially contribute to rising atmospheric CO2 levels. Over the past few decades, headwater streams of the northern hemisphere have shown increased amounts of DOC coinciding with decreased acid deposition. Although the issue is widely discussed in the literature, a mechanistic link between precipitation composition and stream water DOC has not yet been proposed. In this study, the breakup of soil aggregates is hypothesized as the mechanistic link between reduced acid deposition and DOC increases in surface waters. Specific hypotheses state that soil aggregate dispersion (and the ensuing release of DOC from these aggregates) is driven by a decrease in soil solution ionic strength (IS, decreasing the tendency of flocculation) as well as a shift from divalent to monovalent cations (reducing the propensity for cation bridging) in soil solution. These hypotheses were tested on soil samples collected from several riparian zone and hillslope positions along three flagged transects in the acid-impacted Sleepers River Research Watershed in northeastern Vermont. To determine soil C content by landscape position, samples from transects spanning hilltop to hillslope and riparian area, as well as replicated hillslope and riparian samples (n=40) were analyzed. Aqueous soil extracts simulate the flushing of soils during hydrologic events (e.g. rain or snowmelt) and were used to test the effect of soil solution chemistry on DOC release. Extracts were prepared with solutions of varying IS (0-0.005M) and composition (CaCl2 and NaCl) on replicated soil samples (n=54) and changes in DOC release and aggregate size were monitored. As IS of the extraction solution increased, the amount of DOC in solution decreased, and aggregate size increased. This was presumably due to cations bridging and diffuse double layer effects. This effect was reversed in low ionic strength solutions where DOC release was significantly higher and average aggregate size was smaller. While extraction solution controlled the amount of C liberated, landscape position impacted the quality, but not quantity, of released DOC. This study is the first to propose a mechanistic link observed changes in DOC in surface waters and recovery from acidification and provides initial experimental evidence that soil aggregates indeed play a role in the generation of DOC.