Calcium (Ca) depletion and increased bioavailability of aluminum (Al) are potential consequences of soil acidification caused by acidic deposition and other anthropogenic factors. Tree declines are associated with base cation depletion and increased Al toxicity in forest soils in North America, Europe, and Asia. Changes in soil Ca and Al availability may lead to increased oxidative stress and disruptions in carbohydrate relationships in forest trees, as well as to substantial alterations in the capacity for enzymatically controlled processes of decomposition and mineralization in forest soils. Assessments were made to determine if forest systems are prone to disruption associated with altered Ca and Al bioavailability. Foliar elemental concentrations, foliar antioxidant enzyme activities, foliar and woody shoot carbohydrates were measured in sugar maple (Acer saccharum, Marsh.), and soil extracellular enzyme activities (EEA) were assayed at a long-term nutrient perturbation study (NuPert) in the Hubbard Brook Experimental Forest, New Hampshire, USA. Treated plots received Ca to increase soil Ca above ambient depleted levels or Al to further reduce Ca availability. Additions of Ca to soil are associated with greater Ca concentrations in foliage compared to leaves from trees from control and Al-addition plots. Soil Aladditions are associated with lower foliar phosphorus concentrations in comparison with foliage from trees in Ca-addition plots. Additions of Al to soil are associated with higher antioxidant enzyme (glutathione reductase and ascorbate peroxidase) activities in foliage and lower shoot sugar (total sugars, sucrose, glucose and fructose) concentrations relative to trees in Ca-addition and control plots. Al accumulations in distal tissues likely triggered toxicity responses reported for leaves and stems. Soil EEA results highlight treatment-induced alterations to soil processes. Across soil enzyme systems, EEA levels are greatest in Al-addition soils in fall, but are elevated in Caaddition soils in spring compared with ambient conditions. Seasonal differences in EEA levels suggest a differential influence of soil treatments on specific soil communities. Within this native, mature northern hardwood forest, early indications of response in foundation species to Ca and Al manipulation are detected including Al-induced oxidative stress and resulting carbohydrate irregularities in sugar maple trees, and substantial seasonal swings in soil EEA: processes that could foreshadow broader ecosystem alterations as anthropogenic disruptions of soil Ca and Al availability continue.

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Atmospheric acidic deposition has negatively impacted many Appalachian watersheds in the eastern United States and soils play a key role in the biogeochemical processes that govern the fate and transport of the acidic pollutants. Thus, the collection of soil chemistry data, a previously lacking component, is essential to understand the soil processes related to the retention or release of basic and acidic ions and is imperative for the prediction of ecosystem recovery. Soil chemical properties related to acidification were characterized for 25 sites within eight acid-sensitive watersheds located in the Great Smoky Mountains National Park (GRSM). Relationships were identified by comparing soil chemistry to watershed characteristics including site location, soil characteristics, forest type, geomorphic factors and the presence of Anakeesta. The Walker Camp Prong watershed had significantly higher soil base saturation, calcium and magnesium than all other study watersheds as a result of the application of dolomitic limestone to roadways for wintertime traction control. Significant differences in soil chemistry between the spatially close watersheds of Cosby and Rock Creek demonstrated how local factors can substantially influence the watershed acidification response. The chemical properties of the six study soil types, representing 60% of the entire GRSM, had no significant differences, suggesting soil chemistry must be governed by external inputs and basin characteristics, more so than parent material. This idea was strengthen by the ability to relate many soil chemical properties to forest type and identifying other chemical properties as functions of elevation, slope and soil depth. Also, the presence of unexposed Anakeesta did not seem to have any significant effect on soil chemical properties because all significant differences could be linked to factors unrelated to surficial geology. The majority of the soils of the GRSM study watersheds seem to be experiencing the deleterious effects of long-term exposure to acidic deposition and it could be assumed that soils in many other areas of the park may be enduring the same. The results provide a comparative baseline dataset and important input parameters for biogeochemical modeling. The relationships identified among watershed factors and soil chemical properties can aid in future study designs.

Impacts of long-term acid deposition on soil and water chemistry are of particular concern in the Great Smoky Mountains National Park (GRSM), receiving some of the highest acid deposition rates in the eastern United States and limited by inadequate acid buffering capacity. In the GRSM, the Noland Divide watershed (NDW) has been monitored since 1991 for water chemistries of precipitation, throughfall, soil, and stream. The impacts of long-term acidic deposition on stream water quality in the NDW were investigated through: 1) development of an ion input-output budget; 2) analysis of trends and seasonal patterns for major ions; 3) comparison of net export rates between baseflow and stormflow periods; and 4) characterization of soil chemistry and transport properties for various potential acid deposition scenarios. Between 1991 and 2006, throughfall deposition remained unchanged and consisted of 1,735 eq ha-1 yr-1 of SO42-, 863 eq ha-1 yr-1 of NO3-, and 284 eq ha-1 yr-1 of NH4+. Net retention of sulfate was estimated at 61% being controlled by soil adsorption, and inorganic nitrogen was retained at 32% presumably due to plant uptake. Nitrogen retention increased by 44.30 eq ha-1 yr-1 over the study period. Besides deposition, soil acidity was increased by nitrification and precipitation-driven desorption of previously accumulated sulfate. To neutralize soil acidity, Ca2+, Mg2+ and Na+ were depleted from NDW by 77, 46 and 66 eq ha-1 yr-1, respectively. Due to the continuous addition of acidity, base saturation in soil was reduced to 4% at present. Mobilization of aluminum and other metals (Mn and Zn) may be enhanced by these geochemical processes, potentially causing toxic conditions to fish and other biota in the GRSM streams. Impacts of acidic deposition on streams were confirmed by measured stream pH below 6 and acid neutralizing capacity below 0.01 meq L-1. During stormflows pH and ANC depressions occurred primarily due to increases in sulfate transport, leading to episodic acidification events. This study provides new information on hydrological and biogeochemical processes that regulate stream acidification events in the southern Appalachian region, supporting improved management strategies for GRSM streams.

Concentrations of dissolved organic carbon (DOC) measured within water bodies have been increasing on a global scale over the last two decades. Changes in temperature and rainfall have been shown to increase the production and export of DOC from catchments with peat soils in the UK (Freeman et al., 2001). However it is not clear whether increases in DOC concentrations are caused by production increases induced by temperature changes or by a greater incidence of high flows induced by rainfall changes. Increases in both temperature and rainfall have been predicted in Scotland over the next few decades (Kerr et al., 1999) which may further increase current DOC concentrations and exports. The implications of this include both a decrease in water quality and an increase in mobility of metals in upland water bodies. The overall aim of the thesis is to determine if the relationship between dissolved organic carbon (DOC) concentrations and discharge has changed over a 20 year period in small stream catchments in Scotland, in order to better understand the role of hydrology, in driving changes in DOC concentration. To achieve this streams draining two coniferous forest sites and one moorland site were monitored intensively between June 2004 and February 2006. Analysis of the relationship between DOC and discharge, within the catchments, identified the importance of the amount of precipitation falling on the catchment, antecedent precipitation and season, on the concentration of DOC that was measured within the stream. Models were then developed using variables to represent these drivers in terms of both the production (seasonal sine values and 14 day average temperatures) and movement (log of discharge (log Q), days since previous storm event and rising or falling stage) of DOC. In the Ochil Hills catchment, the best predictive model, used 4 hour average discharge and 1 day average 30cm soil temperatures (R2= 0.88). In the Duchray and Elrig catchments, the best predictive models produced used discharge and seasonal sine values; the strength of the model was greater in the Elrig (R2= 0.80) than the Duchray (R2= 0.48) catchment. The strength of the regression models produced highlighted the importance of precipitation in the movement of DOC to the stream and temperature variables representing production in the surrounding catchment. To determine if dissolved organic carbon (DOC) concentrations had changed within the three study catchments, since previous research was conducted at the same sites in the early 1980s and 1990s (Grieve, 1984a; Grieve, 1994), then regression analysis conducted in the previous research was repeated, so changes in the DOC and discharge relationship could be identified. Analysis of the Ochil Hills regression equations identified higher log of discharge and lower temperature and seasonal sine values in the present study (2004-06), when compared to the previous study (1982-83). This suggests that more DOC is now available for movement from the soil, and that the difference between winter and summer DOC production has decreased, potentially because of increasing temperatures. This would explain the limited increase in DOC concentration within the Ochil Hills stream. In the Duchray and Elrig streams, a large increase in DOC was identified at all discharges when all the models produced were compared between the two sampling periods (1989-90 and 2004-06). The increasing trend in DOC concentrations is too large to have been produced by change in temperature alone and it is suggested that the measured reduction in acidic deposition has resulted in the increased DOC concentrations measured in the Duchray and Elrig. The results from this research have identified that concentrations of DOC have increased in Scottish streams over the last 20 years and that the increases in DOC have been induced, potentially by temperature changes in climate. However, changes in temperature are not the only driver of this change as the reduction in acidic deposition is potentially more important, specifically in areas with base poor geology such as the Duchray and Elrig catchments.