Hydrologic Effects of a Changing Forest Landscape

Hydrologic Effects of a Changing Forest Landscape
Author: National Research Council
Publisher: National Academies Press
Total Pages: 181
Release: 2008-12-19
Genre: Science
ISBN: 0309121086

Of all the outputs of forests, water may be the most important. Streamflow from forests provides two-thirds of the nation's clean water supply. Removing forest cover accelerates the rate that precipitation becomes streamflow; therefore, in some areas, cutting trees causes a temporary increase in the volume of water flowing downstream. This effect has spurred political pressure to cut trees to increase water supply, especially in western states where population is rising. However, cutting trees for water gains is not sustainable: increases in flow rate and volume are typically short-lived, and the practice can ultimately degrade water quality and increase vulnerability to flooding. Forest hydrology, the study of how water flows through forests, can help illuminate the connections between forests and water, but it must advance if it is to deal with today's complexities, including climate change, wildfires, and changing patterns of development and ownership. This book identifies actions that scientists, forest and water managers, and citizens can take to help sustain water resources from forests.

Wildfire and Forest Harvesting Effects on Natural Organic Matter

Wildfire and Forest Harvesting Effects on Natural Organic Matter
Author: Shoeleh Shams
Publisher:
Total Pages:
Release: 2018
Genre:
ISBN:

This work was also the first to comprehensively demonstrate wildfire-associated changes in DOC character (by measuring HPO %, UV254, SUVA, FI, and FEEMs) and related DBP-FPs, at the watershed-scale and over multiple flow regimes. The disturbance impacts indicated by all of these quantitative, DOC-associated metrics were all statistically significant, except for FI. Qualitative FEEM results were consistent with these significant shifts. Notably, despite the continued development and promotion of various proxy indicators, UV254 offered the most precise linear correlation with THM-FP, with a coefficient of determination (R2) of 0.6 (in contrast to values of 0.47, 0.42, and 0.39 for DOC, SUVA, and HPO %). Thus, changes in the proxy indicators were related to changes in THM-FP; however, they could not adequately explain response variability, thereby demonstrating the need to 1) better understand relationships between disturbance-associated changes in DOC and their implications to DOC reactivity and 2) advance modeling approaches for describing these relationships. While the mass of various DOC fractions obtained using LC-OCD and HAA-FPs was not analyzed in this manner because of the limited size of the data sets, similar relationships were suggested. Overall, these data suggest that severe wildfire may lead to significant DOC-associated drinking water treatability challenges and that post-fire salvage logging may further exacerbate them-notably, UV254 is unequivocally the best available tool for monitoring these potential impacts at present. THM-FP is generally understood to be linearly correlated with aromatic NOM as measured by UV254 and/or SUVA. In Phase 4, simple strategies for enhancing the prediction of THM-FPs using NOM-associated proxy indicators were investigated. Specifically, the relationship between NOM aromaticity (HPO %, HS, UV254, and SUVA) and THM-FP was examined. Then, HPO and HS were re-analyzed after weighting by mass (DOC concentration)-this appreciably enhanced their prediction performance. This improvement was especially evident for HS, for which the coefficients of determination (R2) increased from 0.10 and 0.26, to 0.85 and 0.88 (Phase 2 and 3 data, respectively). Thus, data processing and reporting are critical to anticipating NOM reactivity; absolute quantities have superior prediction performance. Notably, regardless of these improvements, the relationships between DBP-FP and NOM proxy indicators can be quite variable spatially and temporally, and frequently site specific. More work is required to link source water quality to DBP-FP and drinking water treatability more broadly. In Phase 5, changes in DOC concentration and character and their relationships to regulated DBP-FPs were comprehensively characterized using multiple NOM characterization techniques in the two years during and immediately after forest harvesting in the eastern slopes of the Rocky Mountains in south-western Alberta. Several NOM fractions also were characterized by LC-OCD to inform the relative potential for membrane fouling and microbial regrowth in distribution systems. Like Phase 3, this work was conducted as part of the ongoing SRWP in which two watersheds that served as unburned-reference watersheds in Phase 3 were studied. They were fully calibrated for climate, streamflow, and water quality for 11 years [2004-2014]). Three sub-watersheds within one watershed were harvested using clear-cut with patch retention, strip-shelterwood cut, and partial cut. All possible best management practices (BMPs) were followed to minimize disturbance impacts on water quality. Samples were collected during the dominant regional streamflow regimes. Notably, no substantial impacts of forest harvesting on water quality and treatability were observed during the harvest and first post-harvest years. Thus, this work suggests that forest harvesting with careful implementation of BMPs for erosion control may mitigate the potentially catastrophic impacts of wildfire on drinking water treatability without significantly compromising it.

Contemporary Forest Harvesting Impacts on Drinking Water Quality and Treatability

Contemporary Forest Harvesting Impacts on Drinking Water Quality and Treatability
Author: Soosan Bahramian
Publisher:
Total Pages:
Release: 2019
Genre:
ISBN:

Forested watersheds supply ~75% of global accessible freshwater resources and serve as important sources of drinking water. Both natural and anthropogenic landscape disturbances in these regions can deteriorate water quality in downstream environments. Climate change-exacerbated increases in the frequency and severity of disturbances such as wildfires, floods, and hurricanes threaten global drinking water security because the deterioration and/or increased variability of drinking water source quality can challenge treatment plants beyond their design and/or operational capacity, resulting in increased infrastructure and operating costs, servies disruptions or potentially catatrophic service outages. The water quality impacts of such events can last for decades; thus, risk reduction startegies must be developed to ensure the uninterrupted provision of adequate amounts of safe drinking water. Althgouh forests have not been historically managed for water, forest harvesting has been proposed for pre-emptive mitigation of severe natural disturbance effects on source water quality and treatability; Depending on how it is implemented, however, it can also deteriorate source quality. Critically, the impacts of forest harvesting on drinking water treatability have not been investigated. Thus, the focus of this research was to investigate the impacts of contemporary forest harvesting on drinking water source quality and treatability. Three types of contemporary forest harvesting (clear-cut with patch retention, strip-shelterwood cut, and partial cut) were investigated at the watershed-scale over a range of flow conditions in the eastern slopes of the Rocky Mountains of southwestern Alberta, Canada. Reference and harvested stream water turbidity and various water quality metrics related to NOM (and associated DBP formation potentials) were evaluated during and over the first three post-harvest years. The correlations between THM- and HAA-FPs and several proxy indicators (particularly, aromaticity) were also investigated. Reported pre-disturbance data from the study watersheds were included in this analysis. Notably, no appreciable impacts of forest harvesting on water quality and treatability were observed during the harvest and three post-harvest years. Thus, contemporary forest harvesting approaches coupled with state-of-the-art BMPs for erosion control show promise as "green" source water protection (SWP) technologies for mitigating severe disturbance risks to drinking water treatability, even in source water regions rich with glacially-derived fine sediments (e.g., many parts of western North America). To maximize the impacts of forest management-based approaches to SWP and to develop climate change adaptation strategies-in lieu of traditional landscape-level, time series trend monitoring-focused paired catchment investigations that are designed as before-after-control-impact (BACI) studies are urgently needed.