David V. D'Amore

Glaciers as a source of ancient and labile organic matter to the marine environment

Riverine organic matter supports of the order of one-fifth of estuarine metabolism. Coastal ecosystems are therefore sensitive to alteration of both the quantity and lability of terrigenous dissolved organic matter (DOM) delivered by rivers. The lability of DOM is thought to vary with age, with younger, relatively unaltered organic matter being more easily metabolized by aquatic heterotrophs than older, heavily modified material. This view is developed exclusively from work in watersheds where terrestrial plant and soil sources dominate streamwater DOM. Here we characterize streamwater DOM from 11 coastal watersheds on the Gulf of Alaska that vary widely in glacier coverage (0–64 per cent). In contrast to non-glacial rivers, we find that the bioavailability of DOM to marine microorganisms is significantly correlated with increasing 14C age. Moreover, the most heavily glaciated watersheds are the source of the oldest (∼4 kyr 14C age) and most labile (66 per cent bioavailable) DOM. These glacial watersheds have extreme runoff rates, in part because they are subject to some of the highest rates of glacier volume loss on Earth. We estimate the cumulative flux of dissolved organic carbon derived from glaciers contributing runoff to the Gulf of Alaska at 0.13 ± 0.01 Tg yr-1 (1 Tg = 1012 g), of which ∼0.10 Tg is highly labile. This indicates that glacial runoff is a quantitatively important source of labile reduced carbon to marine ecosystems. Moreover, because glaciers and ice sheets represent the second largest reservoir of water in the global hydrologic system, our findings indicate that climatically driven changes in glacier volume could alter the age, quantity and reactivity of DOM entering coastal oceans.

Changes in the concentration, biodegradability, and fluorescent properties of dissolved organic matter during stormflows in-coastal temperate .watersheds

percent BDOC decreased during both storms in the upland watershed, while percent BDOC increased in the three wetland streams. Parallel factor analysis (PARAFAC) modeling of fluorescence excitation-emission matrices further showed that as stream water DOM concentrations increased during stormflows in the upland watershed, the contribution of protein-like fluorescence decreased and humic-like fluorescence increased. However, the contribution of protein-like fluorescence increased and humic-like fluorescence decreased slightly in the three wetland streams. These results indicate that shifts in the biodegradability and chemical quality of DOM are different for upland and wetland watersheds. Taken together, our findings suggest stormflows are responsible for substantial export of BDOC from coastal temperate watersheds. Moreover, we found that PARAFAC modeling of fluorescent DOM is an effective tool for elucidating shifts in the quality of stream water DOM during storms.

Shifting Climate, Altered Niche, and a Dynamic Conservation Strategy for Yellow-Cedar in the North Pacific Coastal Rainforest

The extensive mortality of yellow-cedar along more than 1000 kilometers of the northern Pacific coast of North America serves as a leading example of climate effects on a forest tree species. In this article, we document our approaches to resolving the causes of tree death, which we explain as a cascade of interacting topographic, forest-structure, and microclimate factors that act on a unique vulnerability of yellow-cedar to fine-root freezing. The complex causes of tree mortality are reduced to two risk factors—snow depth and soil drainage—which are then used to model present and future cedar habitat suitability. We propose a dynamic, comprehensive conservation strategy for this valuable species on the basis of zones created by shifting climate, cedars ecological niche, and observed risk factors. Research on yellow-cedar decline is offered as a template for understanding and adapting to climate change for other climate—forest issues.

An evaluation of freezing as a preservation technique for analyzing dissolved organic C, N and P in surface water samples

Techniques for preserving surface water samples are recently in demand because of the increased interest in quantifying dissolved organic matter (DOM) in surface waters and the frequent collection of samples in remote locations. Freezing is a common technique employed by many researchers for preserving surface water samples; however, there has been little evaluation of the effects of freezing on DOM concentrations. Ten streams were sampled in southeast Alaska with a range of dissolved organic carbon (DOC) concentrations (1.5 to 39 mg C L(-1)) to evaluate the influence of freezing (flash and standard freeze) and filter pore size (0.2 and 0.7 mum nominal pore size) on dissolved organic C, N and P concentrations. We report a significant decrease in DOC (p<0.005) and total dissolved P (p<0.005) concentrations when streamwater samples were frozen, whereas concentrations of dissolved organic N did not significantly decrease after freezing (p=0.06). We further show that when surface water samples were frozen, there was a decrease in the specific ultraviolet absorbance (SUVA) of DOC that is particularly evident with high concentrations of DOC. This finding suggests that spectroscopic properties of DOC have the potential to be used as indicators of whether surface water samples can be frozen. Our results lead us to recommend that surface water samples with high DOC concentrations (>5 mg C L(-1)) and/or samples with high SUVA values (>3.5-4 L mg-C(-1) m(-1)) should be analyzed immediately and not frozen.

Nitrogen and phosphorus mineralization in three wetland types in southeast Alaska, USA

To improve our ability to predict how different wetland soils cycle nutrients, it is necessary to gain an understanding of N and P net mineralization rates. Since information on mineralization rates in southeast Alaska is limited, this study will improve our ability to predict how different wetlands affect soil nutrient processing. Net N and P mineralization rates were measured both in situ and via lab incubations to evaluate both actual and potential mineralization rates in three wetland types: bogs; forested wetlands; and riparian wetlands. Soil pH was an important controlling variable for both net N and P mineralization rates and soil phosphorus content significantly influenced net P mineralization rates. In situ net mineralization rates ranged from 410–1,710 μg N kg soil −1 day−1 for N and from 2–27 μg P kg soil−1 day−1 for P after 56 days. Lab incubations revealed mineralization potentials were 2–3 times greater than in situ rates. Net N and P mineralization potentials were greatest in the riparian wetlands and were significantly different from the bogs and forested wetlands. In contrast, the bogs mineralized a greater proportion of the total N and P soil pool (μg nutrient mineralized per gram nutrient) and indicates greater internal nutrient cycling within bogs. These results suggest that different wetland types of southeast Alaska process N and P differently and these wetland types should be evaluated separately in future evaluations of wetland ecosystem function.

Influence of Forest Canopy and Snow on Microclimate in a Declining Yellow-Cedar Forest of Southeast Alaska

Abstract Site factors predispose yellow-cedar (Chamaecyparis nootkatensis D. Don (Spach)) to a widespread climate-induced mortality in Southeast Alaska. We investigated the influence of canopy cover and snow on microclimate at two small watersheds across a range of declining yellow-cedar stands on Baranof and Chichagof Islands in Southeast Alaska. Two measures of canopy cover, derived from hemispherical photography and LiDAR, were correlated (r = 0.74 and 0.80) at the two sites; both had significant relationships (all R2 ≥ 0.61) with basal area of live trees on plots. Reduced canopy cover increases soil warming in spring and leads to rapid changes in air temperature. There is also a positive feedback where the loss of tree overstory due to yellow-cedar mortality contributes to open, exposed site conditions. Variable patterns of snow depth in late winter and spring at one of the sites, documented with daily remote photography, were associated with elevation and cover. Dead trees predominate where lethal shallow soil temperatures occurred but not where snow buffers these temperatures because of existing snow pack. Canopy cover estimates, landscape analysis, and snow modeling could provide the components for a regional risk model to identify areas in Southeast Alaska that are suitable and unsuitable for future conservation and management of yellow-cedar.

Compatible Management of Red Alder-Conifer Ecosystems in Southeastern Alaska

Forest clearcutting has been the primary timber management practice in forests of southeastern Alaska since commercial timber harvesting began in the 1950s, and the dense, even-aged conifer stands that subsequently developed have broad and undesirable consequences for some nontimber resources-most notably, fish and wildlife. Because a few earlier reports suggested that red alder (Alnus rubra Bong.) helps mitigate some negative effects of timber harvesting (Deal 1997, Wipfli 1997, Hanley and Barnard 1998), we studied the influence of red alder on a broad set of nontimber resources in young conifer forests (40-year-old; equivalent to early third stage of Appendix 1, Chapter 1) in southeastern Alaska (Figure 1). It is unclear what the ecological functions of red alder are in young forested ecosystems in southeastern Alaska. Key questions include: Does red alder affect forest understory development, tree growth, and timber production? How does red alder influence food and habitat for fish and wildlife? How does red alder function in stream and riparian habitats? Does red alder influence forest ecosystem diversity and productivity? Open image in new window

Microsatellite Primers for the Pacific Northwest Conifer Callitropsis nootkatensis (Cupressaceae)

Premise of the study: Microsatellite primers were developed for Nootka cypress (Callitropsis nootkatensis) to provide quantitative measures for gene conservation that can assist in guiding management decisions for a species experiencing climate-induced decline. Methods and Results: Using multiplexed massively parallel sequencing, we identified 136,785 microsatellite-containing sequences from 489,625 Illumina paired-end 80-bp reads. After stringent filtering, we selected 144 primer pairs and screened variation at these loci in five populations of C. nootkatensis. Loci show between three and 36 dinucleotide repeats per locus, with an average of 13. Screening of these markers in the Pacific Northwest relative Chamaecyparis lawsoniana demonstrated no marker transferability. This finding highlights the narrow taxonomic utility of microsatellite markers in Callitropsis. Conclusions: These microsatellites show high polymorphism and can be used for routine screening of natural variation in Callitropsis nootkatensis, and will be particularly helpful in identifying clones and inbred relatives at the stand-level.