Reference Watersheds Research Articles

Effects of excess nitrogen on biogeochemistry of a temperate hardwood forest: Evidence of nutrient redistribution by a forest understory species

Excess nitrogen (N) in terrestrial ecosystems can arise from anthropogenically-increased atmospheric N deposition, a phenomenon common in eastern US forests. In spite of decreased N emissions over recent years, atmospheric concentrations of reactive N remain high in areas within this region. Excess N in forests has been shown to alter biogeochemical cycling of essential plant nutrients primarily via enhanced production and leaching of nitrate, which leads to loss of base cations from the soil. The purpose of our study was to investigate this phenomenon using a multifaceted approach to examine foliar nutrients of two herbaceous layer species in one N-treated watershed (WS3—receiving aerial applications of 35 kg N/ha/yr as ammonium sulfate, from 1989 to the present) and two untreated reference watersheds at the Fernow Experimental Forest, WV, USA. In 1993, we analyzed foliar tissue of Viola rotundifolia, a dominant herb layer species and prominent on all seven sample plots in each watershed. In 2013 and 2014, we used foliar tissue from Rubus allegheniensis, which had become the predominant species on WS3 and had increased, though to a lesser extent, in cover on both reference watersheds. Foliar N and potassium (K) were higher and foliar calcium (Ca) was lower on WS3 than on the reference watersheds for both species. Magnesium (Mg) was lower on WS3 for Viola, but was not different among watersheds for Rubus. Results support the stream chemistry-based observation that excess N lowers plant-available Ca and, to a lesser degree, Mg, but not of K. Foliar manganese (Mn) of Rubus averaged >4 times that of Viola, and was >50% higher on WS3 than on the reference watersheds. A Mn-based mechanism is proposed for the N-meditated increase in Rubus on WS3. Data suggest that excess N deposition not only alters herb community composition and biogeochemical cycling of forest ecosystems, but can do so simultaneously and interactively.

Effects of Timber Harvest on Water Quantity and Quality in Small Watersheds in the Piedmont of North Carolina

This paired watershed study tested the effects of timber harvest on water quantity and quality in the North Carolina Piedmont physiographic region. Four headwater watersheds at Hill Demonstration Forest (HF1, HF2, HFW1, and HFW2) and two at Umstead Research Farm (UF1 and UF2) were continuously monitored for discharge and water quality from 2007 to 2013. The HF1 and UF1 watersheds were clearcut (treatment), leaving a 15.2-m vegetated riparian buffer around the streams to protect water quality as described in the North Carolina Neuse River Basin Riparian Buffer Rule. HF2 and UF2 were uncut and used as reference watersheds. Merchantable timber was selectively removed from the riparian buffer, reducing tree basal area by 27% in HF1 and 48% in UF1. HF1 and HF2 were nested within HFW1; thus, HFW1 was considered a partial cut where 33% of the watershed area was harvested, and HFW2 was the reference. We found that discharge in treatment watersheds increased dramatically, averaging 240% in HF1 and 200% in UF1 and 40% in HFW1 during the postharvest period, 2011–2013. Total suspended sediment export in the treatment watersheds also increased significantly in HF1 after harvest, probably due to the increase of discharge and movement of in-channel legacy sediment. Stormflow peak nitrate reached its maximum concentration during the first 2 years after harvest in the treatment watersheds and then declined, corresponding to the rapid regrowth of woody and herbaceous plants in the riparian buffer and uplands. We found that 36% of the UF1 streambank trees were blown down but did not cause a measurable increase in mean daily stormflow total suspended sediment concentration. Most buffer tree blowdown occurred during the first few years after a harvest. Bioclassification of benthic macroinvertebrates indicated that stream water quality remained good/fair to excellent in the treatment watersheds after the harvest. We conclude that the temporary increases in discharge were relatively large for the Piedmont region compared with those for other regions in the southeastern United States. However, the increases in channel sediment transport and nutrient exports associated with the hydrologic change did not have a measurable impact on the indicators of aquatic invertebrate community health or bioclassification rankings. Management and Policy Implications: There are three distinct land provinces across North Carolina: the mountains, Piedmont, and coastal plain. Understanding how region-specific watershed hydrology responds to land management and natural disturbances can provide useful information to land managers as they set flow targets needed to maintain ecological integrity in surface waters or to design riparian buffers for water quality protection. We found that after a clearcut timber harvest with a riparian buffer zone around the streams, the percent increases in annual discharge and mean nitrate concentrations tended to be higher in the Piedmont region than in the other two regions. Our study also found that tree blowdown in the riparian buffer was more likely to occur in the Piedmont Triassic region than in the Piedmont Carolina Slate Belt region. In the Triassic region, additional management activities should be part of the preharvest planning process as they may help mitigate windthrow and uprooting of streambanks and improve the overall riparian buffer functions and flow dynamics. For example, land planners or loggers should assess whether soils have Triassic or Slate Belt characteristics to determine if they need to refrain from creating gaps and retain more windfirm species within the riparian buffer. Although there was variation in blowdown occurrences among regions, Triassic soils comprise about 3.5% of North Carolina's total land area, so any statewide implications would be low and recommendations would be localized.

Hydrologic Monitoring Plan of the Brazilian Water Producer/PCJ Project

Both Ecosystem-based Adaptation (EbA) and Payment for Ecosystem Services (PES) have a wide range of strategies that include different economic instruments for nature conservation. Although the generation and maintenance of payment for hydrologic ecosystem services (Water-PES) is expanding in Brazil, there are difficulties in the implementation of projects. Due to the complexity and non-linearity of the hydrological processes, also affecting both EbA and Water-PES goals, monitoring quali-quantitative aspects of streams have been here addressed as a useful management tool. This study presents the Hydrological Monitoring Plan (HMP) of the Water Producer/PCJ project, operating between 2009-2014, in order to: 1) evaluate the impact of project actions under water quali-quantitative aspects; and 2) promote the incorporation of HMP’s elements in water resources management. HMP of the Water Producer/PCJ project has been implemented following the conditions for efficiency (baseline, long-term scale compatible with the actions of the project, in the experimental and reference watersheds). In addition, HMP is being implemented from upstream to downstream in catchments with areas ranging from 17 to 130 km2. This proposal favors the quantification and valuation of hydrologic services that could be assessed by ecohydrologic monitoring and modeling. Thus, we look forward to the consolidation of the Brazilian information system of water resources, the reduction of modeling uncertainties and integrated assessment of the consequences of land-use/land-cover change that strongly impact goals of EbA and Water-PES initiatives.

Testing associations between tree species and nitrate availability: Do consistent patterns exist across spatial scales?

In forest ecosystems there are numerous factors that influence nitrate (NO3) availability and retention in ways that can significantly affect receiving waters. Unfortunately these factors often co-exist and interact making it difficult to establish the importance of each individually. Three reference watersheds at the Fernow Experimental Forest (FEF) provide a unique opportunity to evaluate the influence of tree species on soil NO3 availability across spatial scales because they differ in stream-water NO3 concentrations despite sharing the same macro-climate, geology, hydrology, dominant soils series, stand age, pollution regime, and land-use history.To test the strength of plant/soil associations inferred from previous work in two watersheds in the FEF, we measured NO3 availability and the composition of tree species in a third watershed that has intermediate stream-water NO3 concentrations. We also examined plant/soil relationships in these watersheds at the scale of individual trees.Across the spatial scales examined – from individual trees to small watersheds – there were consistent associations between tree species and soil NO3 availability. For individual trees, species with high underlying soil NO3 availability included Acer saccharum and Lireodendron tulipifera, whereas species with low underlying soil NO3 availability included Acer rubrum, Nyssa sylvatica, and Quercus prinus. For small plots we found plant/soil relationships that were consistent with those made apparent by sampling under individual trees of A. saccharum, A. rubrum, N. sylvatica, and Q. prinus. And at the scale of entire watersheds, those with higher stream-water NO3 had a greater importance of tree species associated with high NO3 availability at finer spatial scales than did the watershed with low stream-water NO3.The spatially-robust relationships between tree species and soil NO3 availability at the FEF suggest that well-characterized relationships between dominant tree species and soil properties should improve our understanding of how changes in the species composition of forest trees due to human activities, or natural causes, will alter rates of NO3 production and loss.

Measuring ecosystem capacity to provide regulating services: forest removal and recovery at Hubbard Brook (USA).

In this study, by coupling long-term ecological data with empirical proxies of societal demand for benefits, we measured the capacity of forest watersheds to provide ecosystem services over variable time periods, to different beneficiaries, and in response to discrete perturbations and drivers of change. We revisited one of the earliest ecosystem experiments in North America: the 1963 de-vegetation of a forested catchment at Hubbard Brook Experimental Forest in New Hampshire, USA. Potential benefits of the regulation of water flow, water quality, greenhouse gases, and forest growth were compared between experimental (WS 2) and reference (WS 6) watersheds over a 30-year period. Both watersheds exhibited similarly high capacity for flow regulation, in part because functional loads remained low (i.e., few major storm events) during the de-vegetation period. Drought mitigation capacity, or the maintenance of flows sufficient to satisfy municipal water consumption, was higher in WS 2 due to reduced evapotranspiration associated with loss of plant cover. We also assessed watershed capacity to regulate flows to satisfy different beneficiaries, including hypothetical flood averse and drought averse types. Capacity to regulate water quality was severely degraded during de-vegetation, as nitrate concentrations exceeded drinking water standards on 40% of measurement days. Once forest regeneration began, WS 2 rapidly recovered the capacity to provide safe drinking water, and subsequently mitigated the eutrophication potential of rainwater at a marginally higher level than WS 6. We estimated this additional pollution removal benefit would have to accrue for approximately 65-70 years to offset the net eutrophication cost incurred during forest removal. Overall, our results affirmed the critical role of forest vegetation in water regulation, but also indicated trade-offs associated with forest removal and recovery that partially depend on larger-scale exogenous changes in climate forcing and pollution inputs. We also provide a starting point for integrating long-term ecological research and modeling data into ecosystem services science.

Buffer effects of streamside native forests on water provision in watersheds dominated by exotic forest plantations

AbstractThe Valdivian rainforest ecoregion in Chile (35°–48°S) has a high conservation priority worldwide. These forests are also keys for social welfare as a result of their supply of timber as well as ecosystem services. Forests in the ecoregion have been extensively converted to fast growing Pinus radiata and Eucalyptus spp. plantations for timber production promoted by public policies and timber companies. This study describes the results of detailed measurements of hydrology and stream water chemistry in eight small watersheds in south central Chile, subjected to replacement of native temperate rainforest by exotic Eucalyptus plantations. In this system, watersheds have streamside buffers of native forest (SNFW) with varying widths. Results indicate that retention of SNFW counteracts hydrologic effects of Eucalyptus plantations, which are widely known to reduce water yields. A 1.4% rate of increase of the run‐off coefficient for each metre of increase of SNFW was observed. In addition, a decrease in the concentrations of total nitrogen, dissolved inorganic nitrogen (DIN), nitrate‐N, and different sized fractions of particulate organic matter were found in streams draining these plantations as a function of increasing SNFW. Streamside buffer widths of 17–22 m for total nitrogen and DIN concentrations and ≥36 m for sediments were required to provide comparable values to reference watersheds (100% native forest). The findings from this study suggest that SNFW may significantly reduce adverse effects from exotic species forestry plantations on water provision in an area of south central Chile where exotic forest plantations are rapidly expanding. Copyright © 2014 John Wiley & Sons, Ltd.

Effects of calcium treatment on forest floor organic matter composition along an elevation gradient

Calcium amendment is a restorative option for nutrient-depleted, acidic soils in the forests of the northeastern United States. We studied the effects of watershed-scale wollastonite (CaSiO3) application on the structural composition of soil organic matter (SOM) and hot-water-extractable organic matter (HWEOM) at the Hubbard Brook Experiment Forest in New Hampshire 7–9 years after treatment, along an elevation gradient. Soils in the high-elevation spruce–fir–birch (SFB) zone contained significantly greater amounts of HWEOM compared with lower elevation hardwood soils, likely due to differences in litter quality and slower decomposition rates in colder soils at higher elevation. The only significant difference in hot-water-extractable organic carbon concentration between reference and calcium-treated watersheds was in Oie horizons of the SFB zone, which also exhibited the greatest degree of soil chemical change after treatment. The 13C nuclear magnetic resonance (NMR) spectra showed no significant patterns in O-alkyl C abundance for either soil or HWEOM along the elevation gradient, suggesting that there were no elevation-related patterns in carbohydrate concentration. The general absence of long-term effects in this study suggests that effects of Ca amendment at this dosage on the composition of SOM were small or short-lived.

Evaluation of forest disturbance legacy effects on dissolved organic matter characteristics in streams at the Hubbard Brook Experimental Forest, New Hampshire

Dissolved organic matter (DOM) source and composition are critical drivers of its reactivity, impact microbial food webs and influence ecosystem functions. It is believed that DOM composition and abundance represent an integrated signal derived from the surrounding watershed. Recent studies have shown that land-use may have a long-term effect on DOM composition. Methods for characterizing DOM, such as those that measure the optical properties and size of the molecules, are increasingly recognized as valuable tools for assessing DOM sources, cycling, and reactivity. In this study we measured DOM optical properties and molecular weight determinations to evaluate whether the legacy of forest disturbance alters the amount and composition of stream DOM. Differences in DOM quantity and composition due to vegetation type and to a greater extent, wetland influence, were more pronounced than effects due to disturbance. Our results suggest that excitation-emission matrix fluorescence with parallel factor analysis is a more sensitive metric of disturbance than the other methods evaluated. Analyses showed that streams draining watersheds that have been clearcut had lower dissolved organic carbon (DOC) concentrations and higher microbially-derived and protein-like fluorescence features compared to reference streams. DOM optical properties in a watershed amended with calcium, were not significantly different than reference watersheds, but had higher concentrations of DOC. Collectively these results improve our understanding of how the legacy of forest disturbances and natural landscape characteristics affect the quantity and chemical composition of DOM in headwater streams, having implications for stream water quality and carbon cycling.

Differential Carbon and Nitrogen Controls of Denitrification in Riparian Zones and Streams along an Urban to Exurban Gradient.

Denitrification is an anaerobic microbial process that transforms nitrate (NO) to nitrogen (N) gas, preventing the movement of NO into coastal waters where it can lead to eutrophication. Urbanization can reduce the potential for denitrification in riparian zones and streams by altering the environmental conditions that foster denitrification (i.e., low oxygen and available C). Here we evaluated the factors limiting denitrification potential in forested and herbaceous riparian and stream pool and organic debris dam habitats in urban, suburban, exurban, and forested reference watersheds in the Baltimore, Maryland metropolitan area. Denitrification potential (with and without C and NO additions) and microbial biomass C and N content, potential net N mineralization and nitrification, microbial respiration, and inorganic N pools were measured in summer (June) and fall (November). Denitrification potentials were highest in the herbaceous riparian soils and lowest in pool sediments. Forested riparian soil denitrification potential was highest in the exurban watershed but in other habitats did not vary with watershed type. Nearly all variables were higher in June than in November. Overall, C was a more important driver of denitrification potential than N; potentials in unamended and N-amended treatments were very similar (<200 ng N g h) and were much lower than in the C-amended and C+N-amended treatments (>800 ng N g h). Our results suggest that efforts to enhance denitrification in urban watersheds need to focus on the differential controls of denitrification across habitats, urban land use types, and seasons.

Five‐year legacy of wildfire and salvage logging impacts on nutrient runoff and aquatic plant, invertebrate, and fish productivity

ABSTRACTEcohydrological linkages between phosphorus (P) production, stream algae, benthic invertebrate, and fish communities were studied for 4 years after severe wildfire in the Rocky Mountains (Alberta, Canada). Mean concentrations of all forms of P (soluble reactive, total dissolved, particulate, and total) were 2 to 13 times greater in burned and post‐fire salvage‐logged streams than in unburned streams (p &lt; 0.001). Post‐disturbance recovery of P was slow with differences in P‐discharge relationships still evident 5 years after the fire (p &lt; 0.001). Coupled P and sediment interactions were likely responsible for slow recovery of P regimes in fire‐disturbed watersheds. P loading was associated with strong ecological responses in stream biota. Annual algal productivity was 5 to 71 times greater in streams within burned watersheds than in reference watersheds and persisted for 5 years after the fire (p &lt; 0.001). Elevated algal production was associated with strong differences in benthic invertebrate community structure, including greater invertebrate densities, biomass, species diversity, and shifts in species composition. Monotonic shifts in invertebrate stable carbon and nitrogen isotope ratios indicated increased consumption of autochthonous food sources and effects on energy pathways for invertebrates from fire‐affected streams. Wildfire‐related changes at lower trophic lead to increases in size (weight and length) and growth rate (weight : age ratios) of cutthroat trout (Oncorhynchus clarki). This cascading series of effects of wildfire on stream productivity (primary production, secondary invertebrate consumers, and fish) may be long‐lived legacies of wildfire because of the slow recovery of P regimes. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Inorganic Nitrogen Retention by Watersheds at Fernow Experimental Forest and Coweeta Hydrologic Laboratory

Because elevated N loading can impair both terrestrial and aquatic ecosystems, understanding the abiotic and biotic controls over retention and export of dissolved inorganic N (DIN) is crucial. Long‐term research has been conducted on experimental watersheds at two U.S. Forest Service experimental forests in the Appalachian region: Fernow Experimental Forest (FEF) in West Virginia and Coweeta Hydrologic Laboratory (CHL) in North Carolina. While similar in vegetation and research history, FEF and CHL differ in climate, historic DIN deposition, and soils. We evaluated long‐term patterns of DIN inputs and exports from three watersheds at each location with similar treatments including clear‐cut harvest, conversion to conifer plantation (Norway spruce [Picea abies (L.) H. Karst.] at FEF and white pine [Pinus strobus L.] at CHL), as well as reference watersheds. We examined DIN export and retention in these watersheds, comparing treated and reference watersheds within each experimental forest and comparing similarly treated watersheds between the experimental forests. Despite current similar levels of N deposition, stream water DIN concentrations and exports were generally greater at FEF by almost an order of magnitude. We found differences between FEF and CHL in stream DIN concentrations, watershed export, and retention of DIN inputs not only in the untreated reference watersheds but also in the watersheds with similar disturbance treatment. We hypothesize that these differences are the result of site and vegetation differences as well as site history including long‐term patterns of DIN deposition. We document the switch from biogeochemical to hydrologic controls that occurred when N availability exceeded N immobilization, due to either N deposition or biological N inputs.

Clearcutting and pine planting effects on nutrient concentrations and export in two mixed use headwater streams: Upper Coastal Plain, Southeastern USA

Timber harvest temporarily increases water yield; however, relationships between hydrologic and nutrient chemistry changes have not been consistent. This study quantified the effects of forest harvesting and site preparation without fertilization and with modern best management practices on nutrient concentrations and yields in small headwater streams of the Southeastern Coastal Plain. We monitored two watershed pairs for 2 years prior to and 1 year following timber harvest and for 2 more years following site preparation and planting. Treatment watersheds were clearcut, and downstream portions of streamside management zones were thinned in Fall 2003. Site preparation (herbicide application and burning) and planting followed a year later. All operations followed 1999 Georgia forestry best management practices. Previously published research revealed a large increase in water yield following harvest. Nutrient concentrations varied significantly within and between monitoring periods, even in reference watersheds. Silvicultural activities had no discernible effect on phosphorus and ammonium concentrations; however, statistically significant increases in nitrate/nitrite (67–340 µg L−1) and total nitrogen concentrations (100–400 µg L−1) in treatment watersheds followed stand re-establishment. Nutrient yields increased after timber harvest largely as a result of increased water yields, although increased nutrient yields were small relative to inter-annual and inter-watershed variability and variability. Annual water yield largely explained the variability in annual nitrogen and phosphorus export from reference and treatment streams (r2 values from 0.65 to 0.98). High NOx concentrations coming from an upstream agricultural area decreased 1600–1800 µg L−1 over several hundred metres in the treatment streams by dilution, uptake or denitrification. Copyright © 2013 John Wiley & Sons, Ltd.

Restoring Soil Calcium Reverses Forest Decline

Forest decline in the northeastern United States has been linked to the effects of acid deposition on soil nutrients. To test this link, we added a calcium silicate mineral to a paired watershed at the Hubbard Brook Experimental Forest, New Hampshire, in an amount designed to gradually replace the estimated amount of calcium lost as a result of human activity in the 20th Century (primarily because of acid deposition). The experimental restoration resulted in a recovery of tree biomass increment. The improved calcium nutrition also promoted higher aboveground net primary production and increased the photosynthetic surface area in the treated watershed relative to that in the reference watershed. These results demonstrated that soil acidification accelerated by acid deposition has contributed to the decline of forest growth and health on naturally acidic soil in the northeastern United States and that decline can be reversed by the addition of calcium.

Evaluation of stream chemistry trends in US Geological Survey reference watersheds, 1970–2010

The Hydrologic Benchmark Network (HBN) is a long-term monitoring program established by the US Geological Survey in the 1960s to track changes in the streamflow and stream chemistry in undeveloped watersheds across the USA. Trends in stream chemistry were tested at 15 HBN stations over two periods (1970-2010 and 1990-2010) using the parametric Load Estimator (LOADEST) model and the nonparametric seasonal Kendall test. Trends in annual streamflow and precipitation chemistry also were tested to help identify likely drivers of changes in stream chemistry. At stations in the northeastern USA, there were significant declines in stream sulfate, which were consistent with declines in sulfate deposition resulting from the reductions in SO₂ emissions mandated under the Clean Air Act Amendments. Sulfate declines in stream water were smaller than declines in deposition suggesting sulfate may be accumulating in watershed soils and thereby delaying the stream response to improvements in deposition. Trends in stream chemistry at stations in other part of the country generally were attributed to climate variability or land disturbance. Despite declines in sulfate deposition, increasing stream sulfate was observed at several stations and appeared to be linked to periods of drought or declining streamflow. Falling water tables might have enhanced oxidation of organic matter in wetlands or pyrite in mineralized bedrock thereby increasing sulfate export in surface water. Increasing sulfate and nitrate at a station in the western USA were attributed to release of soluble salts and nutrients from soils following a large wildfire in the watershed.

Alterations on flow variability due to converting hardwood forests to pine

Flow variability is a potential indicator of land use impacts on aquatic ecosystems and a dominating factor for lotic habitats. Vegetation management effects on the stream habitat conditions must be better understood to propose forest management activities that are compatible with general ecosystem management objectives (integrity, diversity, sustainability, etc.). In our study, we used long term flow data (1936-2004) from four gauged experimental watersheds (W1, W2, W17, W18) of Coweeta Hydrologic Laboratory in US to assess the impacts of pine conversion on flow characteristics by using paired watershed experimentation. In W1, all trees and shrubs were cut and burned in 1956-57 and white pine (Pinus strobus) was planted in 1957. In W17, white pine was planted in 1956. W2 and W18 have been kept untreated as reference watersheds for W1 and W17, respectively. After analyzing long-term daily flow series with flow duration curves and frequency analyzes, we found that the timing and magnitude of 7Q flows were changed significantly due to conversion but flow variability was not affected. Overall findings revealed that pine conversion has significantly influenced some flow characteristics but stream habitat conditions were not affected potentially.

Advances in variable selection methods II: Effect of variable selection method on classification of hydrologically similar watersheds in three Mid-Atlantic ecoregions

Hydrological flow predictions in ungauged and sparsely gauged watersheds use regionalization or classification of hydrologically similar watersheds to develop empirical relationships between hydrologic, climatic, and watershed variables. The watershed classifications may be based on geographic proximity, regional frameworks such as ecoregions or classification using cluster analysis of watershed descriptors. General approaches used in classifying hydrologically similar watersheds use climatic and watershed variables or statistics of streamflow data. Use of climatic and watershed descriptors requires variable selection to minimize redundancy from a large pool of potential variables. This study compares classification performance of four variable groups to identify homogeneous watersheds in three Mid-Atlantic ecoregions (USA): Appalachian Plateau, Piedmont, and Ridge and Valley. The variable groups included: (1) variables that define watershed geographic proximity; (2) variables that define watershed hypsometry; (3) variables selected using causal selection algorithms; and (4) variables selected using principal component analysis (PCA) and stepwise regression. The classification results were compared to reference watersheds classified as homogeneous using three streamflow indices: Slope of flow duration curve; Baseflow index; and Streamflow elasticity using a similarity index (SI). Classification performance was highest using variables selected by causal algorithms (e.g., HITON-MB method, SI=0.71 for Appalachian Plateau, SI=0.90 for Piedmont, and SI=0.72 for Ridge and Valley) compared to variables selected by stepwise regression (SI=0.72 for Appalachian Plateau, SI=0.87 for Piedmont, and SI=0.64 for Ridge and Valley) and PCA (SI=0.71 for Appalachian Plateau, SI=0.76 for Piedmont, and SI=0.57 for Ridge and Valley).

Soil bacterial communities of a calcium-supplemented and a reference watershed at the Hubbard Brook Experimental Forest (HBEF), New Hampshire, USA

Soil Ca depletion because of acidic deposition-related soil chemistry changes has led to the decline of forest productivity and carbon sequestration in the northeastern USA. In 1999, acidic watershed (WS) 1 at the Hubbard Brook Experimental Forest (HBEF), NH, USA was amended with Ca silicate to restore soil Ca pools. In 2006, soil samples were collected from the Ca-amended (WS1) and reference watershed (WS3) for comparison of bacterial community composition between the two watersheds. The sites were about 125m apart and were known to have similar stream chemistry and tree populations before Ca amendment. Ca-amended soil had higher Ca and P, and lower Al and acidity as compared with the reference soils. Analysis of bacterial populations by PhyloChip revealed that the bacterial community structure in the Ca-amended and the reference soils was significantly different and that the differences were more pronounced in the mineral soils. Overall, the relative abundance of 300 taxa was significantly affected. Numbers of detectable taxa in families such as Acidobacteriaceae, Comamonadaceae, and Pseudomonadaceae were lower in the Ca-amended soils, while Flavobacteriaceae and Geobacteraceae were higher. The other functionally important groups, e.g. ammonia-oxidizing Nitrosomonadaceae, had lower numbers of taxa in the Ca-amended organic soil but higher in the mineral soil.

Effects of Watershed History on Dissolved Organic Matter Characteristics in Headwater Streams

Dissolved organic matter (DOM) is recognized as a major component in the global carbon cycle and is an important driver in aquatic ecosystem function. Climate, land use, and forest cover changes all impact stream DOM and alter biogeochemical cycles in terrestrial environments. We determined the temporal variation in DOM quantity and quality in headwater streams at a reference watershed (REF), a watershed clear-cut 30 years ago (CC), and a watershed converted to a white pine plantation 50 years ago (WP) at the US Forest Service, Coweeta Hydrologic Laboratory, in the Nantahala Mountains of western North Carolina, USA. Average stream dissolved organic carbon (DOC) concentrations in CC or WP were 60 and 80% of those in REF, respectively. Stream DOM composition showed that the difference was mainly due to changes in humic-like components in chromophoric DOM. In addition, excitation–emission matrix fluorescence data with parallel factor analysis indicate that although the concentration of protein-like components did not differ significantly among watersheds, their relative abundance showed an enrichment in CC and WP compared to REF. The ratio of humic acid-type to fulvic acid-type components was highest and lowest at REF and WP, respectively. Our data suggest that forest ecosystem disturbance history affects the DOM quantity and quality in headwater streams over decades as a result of changes in watershed soil organic matter characteristics due to differences in organic matter inputs.

Calcium addition at the Hubbard Brook Experimental Forest increases the capacity for stress tolerance and carbon capture in red spruce (Picea rubens) trees during the cold season

Red spruce (Picea rubens Sarg.) trees are uniquely vulnerable to foliar freezing injury during the cold season (fall and winter), but are also capable of photo- synthetic activity if temperatures moderate. To evaluate the influence of calcium (Ca) addition on the physiology of red spruce during the cold season, we measured concentrations of foliar polyamines and free amino acids (putative stress- protection compounds), chlorophyll (a key photosystem component), and sapwood area (a proxy for foliar bio- mass), for trees in Ca-addition (CaSiO3 added) and Ca- depleted (reference) watersheds at the Hubbard Brook Experimental Forest (NH, USA). Ca-addition increased concentrations of the amino acids alanine and c-aminobu- tyric acid (GABA) and the polyamines putrescine (Put) and spermidine (Spd) in November, and Put in February rela- tive to foliage from the reference watershed. Consistent with increased stress protection, foliage from the Ca- addition watershed had higher total chlorophyll and chlo- rophyll a concentrations in February than foliage from the reference watershed. In contrast, foliage from the reference watershed had significantly lower glutamic acid (Glu) and higher alanine (Ala) concentrations in February than foli- age from the Ca-addition watershed. Imbalances in Ala:Glu have been attributed to cold sensitivity or damage in other species. In addition to concentration-based differences in foliar compounds, trees from the Ca-addition watershed had higher estimated levels of foliar biomass than trees from the reference watershed. Our findings suggest that Ca- addition increased the stress tolerance and productive capacity of red spruce foliage during the cold season, and resulted in greater crown mass compared to trees growing on untreated soils.

Development, sensitivity and uncertainty analysis of LASH model

Many hydrologic models have been developed to help manage natural resources all over the world. Nevertheless, most models have presented a high complexity regarding data base requirements, as well as, many calibration parameters. This has brought serious difficulties for applying them in watersheds where there is scarcity of data. The development of the Lavras Simulation of Hydrology (LASH) in a GIS framework is described in this study, which focuses on its main components, parameters, and capabilities. Coupled with LASH, sensitivity analysis, parameter range reduction, and uncertainty analysis were performed prior to the calibration effort by using specific techniques (Morris method, Monte Carlo simulation and a Generalized Likelihood Uncertainty Estimation -GLUE) with a data base from a Brazilian Tropical Experimental Watershed (32 km²), in order to predict streamflow on a daily basis. LASH is a simple deterministic and spatially distributed model using long-term data sets, and a few maps to predict streamflow at a watershed outlet. We were able to identify the most sensitive parameters which are associated with the base flow and surface runoff components, using a reference watershed. Using a conservative threshold, two parameters had their range of values reduced, thus resulting in outputs closer to measured values and facilitating automatic calibration of the model with less required iterations. GLUE was found to be an efficient method to analyze uncertainties related to the prediction of mean daily streamflow in the watershed.