High elevation mountain watersheds are undergoing rapid warming
and declining snow fractions worldwide, causing earlier and
quicker snowmelt. Understanding how this hydrologic shift
affects subsurface flow paths, biogeochemical reactions, and
solute export has been challenging due to the entanglement of
hydrological and biogeochemical processes. Coal Creek, a
high-elevation catchment (2,700 3,700 m, 53 km2) in Colorado, is
experiencing a higher rate of warming than surrounding low-lying
areas. This warming corresponds with dynamic and increased
responses from biogenic solutes and dissolved organic carbon
(DOC), whereas the behavior of geogenic solutes and dissolved
inorganic carbon (DIC) has remained relatively unchanged. DOC
has experienced the largest concentration increase (>3x), with
annual average flow weighted concentrations positively
correlated to average annual temperature. This suggests
temperature is the main driver of increasing DOC levels.
Although DOC and DIC response to warming is influenced by many
drivers, the relative contribution of each remains unknown. DOC
and DIC were analyzed to incorporate both carbon component
products of soil respiration (DOC and CO2) and to represent high
solute concentrations transported by shallow (DOC) versus deep
(DIC) subsurface flow. The contrasting behavior of these carbon
solutes indicates climate change and warming are driving changes
in organic matter decomposition and soil respiration. Modeling
results from the process-based model HBV-BioRT show increased
temperatures cause earlier snowmelt and streamflow generation
and lower peak discharge. As stream flow generation occurs
earlier, so do DOC flushing and DIC dilution events.
Additionally, post-snowmelt periods show greater DOC production
and concentrations under warming scenarios. Results indicated
increased production of DOC in post-snowmelt periods. DOC is
then flushed out by earlier snowmelt partitioned through the
shallow soil zone. Most process-based studies lack a
watershed-scale understanding of carbon transformation and flow
path alterations. This work demonstrates complex hydrologic and
biogeochemical coupling at the watershed scale to illustrate how
water flow paths and chemistry are responding to a changing
climate in highelevation mountain watersheds.
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Impact of Channel Dredging and Straightening in an Atlantic White Cedar (Chamaecyparis thyoides L. (B.S.P.)) Freshwater Tidal Wetland
Once prominent up the eastern coast of the United States, freshwater wetlands with Atlantic white cedar (AWC; Chamaecyparis thyoides L. (B.S.P.)) are now vanishing due to saltwater intrusion and anthropogenic landscape alterations. This study utilizes a historic, anthropogenic disturbance to provide insight into the AWC response to salinization. A major straightening and dredging project in the 1920s, including 16 oxbow cuts, allowed brackish water to move upstream in the St. Jones River in Dover, Delaware, leading to the die-off of an AWC swamp. The sampled AWC experienced climate change, storms, hydrologic alterations, and sea-level rise. Annual ring width and suppression event chronologies were developed from dead AWC and were compared to groupings of climate variables in the pre disturbance (1895–1920) and post disturbance (1928–1958) periods. Results of the dendrochronological analysis indicate that the AWC in this study died at an average age of 49.3 years, earlier than typically expected for such species. After the
straightening and dredging, the AWC experienced changes in growth response to temperature while suppression events became positively correlated with elevated temperature (p ¼ 0.024) and high precipitation (p ¼ 0.019). The system also showed signs of becoming more sensitive to storm events in the post disturbance period.
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- Award ID(s):
- 1757353
- NSF-PAR ID:
- 10247291
- Date Published:
- Journal Name:
- Journal of coastal research
- ISSN:
- 1551-5036
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The sagebrush biome covers much of the western United States yet is at risk from ongoing disturbances. Physical disturbances such as fire often overcome the resistance of sagebrush communities to biological disturbances such as invasion by non‐native species, but the impact of burn severity or combined disturbance types on sagebrush community composition remains unclear. We examined the relationship between native functional groups and non‐native annual grass cover to the number of fires, burn severity, anthropogenic development, and vegetation treatments in northern Nevada, USA. We used Bureau of Land Management vegetation monitoring plots and existing climate, fire, and vegetation treatment databases to explore relationships using beta regression. After accounting for mean annual precipitation and temperature, and elevation, we quantified functional group mean cover related to levels of burn severity, numbers of fires, development, and vegetation treatments. Native herbaceous (grass and forb) groups were resilient to fire, but fire caused large declines in shrub and sagebrush cover. Non‐native annual grass cover was associated with higher burn severity and the first fire at a site. We did not find evidence that post‐fire restoration treatments were associated with increased native cover or decreased non‐native cover. However, shrub control and soil disturbing treatments (discing and chaining) were associated with decreased native perennial grass cover and increased non‐native annual grass cover. Functional groups displayed varying patterns related to anthropogenic development and fire. For example, development had a larger impact on non‐native cover at lower levels of burn severity, whereas forbs increased following fire only at lower levels of development. Although in some cases sagebrush communities showed resilience to disturbance, our results showed resistance to invasion by non‐native annual grasses can be overcome by combinations of disturbances at lower levels or by severe events.
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The 1988 Yellowstone fire altered the structure of the local forest ecosystem and left large non-recovery areas. This study assessed the pre-fire drivers and post-fire characteristics of the recovery and non-recovery areas and examined possible reasons driving non-recovery of the areas post-fire disturbance. Non-recovery and recovery areas were sampled with 44,629 points and 77,501 points, from which attribute values related to topography, climate, and subsequent soil conditions were extracted. We calculated the 1988 Yellowstone fire burn thresholds using the differenced Normalized Burn Ratio (dNBR) and official fire maps. We used a burn severity map from the US Forest Service to calculate the burn severity values. Spatial regressions and Chi-Square tests were applied to determine the statistically significant characteristics of a lack of recovery. The non-recovery areas were found to cover 1005.25 km2. Among 11 variables considered as potential factors driving recovery areas and 13 variables driving non-recovery areas, elevation and maximum temperature were found to have high Variance Inflation Factors (4.73 and 4.72). The results showed that non-recovery areas all experienced severe burns and were located at areas with steeper slopes (13.99°), more precipitation (871.73 mm), higher pre-fire vegetation density (NDVI = 0.38), higher bulk density (750.03 kg/m3), lower soil organic matter (165.61 g/kg), and lower total nitrogen (60.97 mg/L). Chi-square analyses revealed statistically different pre-fire forest species (p < 0.01) and soil order (p < 0.01) in the recovery and non-recovery areas. Although Inceptisols dominated in both recovery and non-recovery areas, however, the composition of Mollisols was higher in the non-recovery areas (14%) compared to the recovery areas (11%). This indicated the ecological memory of the non-recovery site reverting to grassland post-disturbance. Unlike conventional studies only focusing on recovery areas, this study analyzed the non-recovery areas and found the key characteristics that make a landscape not resilient to the 1988 Yellowstone fire. The significant effects of elevation, precipitation, and soil pH on recovery may be significant to the forest management and forest resilience in the post-fire period.more » « less
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Abstract Fertilization studies have elucidated basic principles of the role of nutrients in shaping plant communities and demonstrated the potential effects of anthropogenic nutrient deposition. Yet less is known about how these effects are mediated by interacting ecological factors, particularly in nutrient‐poor wetland habitats. In a long‐term experiment in a coastal plain wetland, we examined how fertilization and mowing affected the diversity and composition of a plant community as it reestablished after major disturbance. A drainage ditch in proximity to the experimental plots allowed us also to consider the influence of hydrology and its interactions with nutrient addition. Fertilization decreased species richness, with wetland specialist species showing especially great losses, and several lines of evidence suggest that the effect was mediated by competition for light. Altered hydrology via ditch drainage had effects that were similar to fertilization, with more rapidly draining plots showing lower diversity and decreased abundance of wetland species. Plant community diversity and dynamics were influenced by complex interactions between fertilization, disturbance, and hydrology. The negative effect of fertilization on species richness was initially mitigated by mowing, but in later years was more evident in mowed than in unmowed plots. In the absence of disturbance, nutrient addition increased the rate of transition to primarily woody communities. Similarly, drained plots experienced increased rates of succession compared to wetter plots. Our results suggest that these interactions need to be considered to understand the potential effects of anthropogenic nutrient addition and hydrologic alterations to wetland ecosystems.
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