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A LIDAR‐DERIVED EVALUATION OF WATERSHED‐SCALE LARGE WOODY DEBRIS SOURCES AND RECRUITMENT MECHANISMS: COASTAL MAINE, USA
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In‐channel large woody debris (LWD) promotes quality aquatic habitat through sediment sorting, pool scouring and in‐stream nutrient retention and transport. LWD recruitment occurs by numerous ecological and geomorphic mechanisms including channel migration, mass wasting and natural tree fall, yet LWD sourcing on the watershed scale remains poorly constrained. We developed a rapid and spatially extensive method for using light detection and ranging data to do the following: (i) estimate tree height and recruitable tree abundance throughout a watershed; (ii) determine the likelihood for the stream to recruit channel‐spanning trees at reach scales and assess whether mass wasting or channel migration is a dominant recruitment mechanism; and (iii) understand the contemporary and future distribution of LWD at a watershed scale. We utilized this method on the 78‐km‐long Narraguagus River in coastal Maine and found that potential channel‐spanning LWD composes approximately 6% of the valley area over the course of the river and is concentrated in spatially discrete reaches along the stream, with 5 km of the river valley accounting for 50% of the total potential LWD found in the system. We also determined that 83% of all potential LWD is located on valley sides, as opposed to 17% on floodplain and terrace surfaces. Approximately 3% of channel‐spanning vegetation along the river is located within one channel width of the stream. By examining topographic and morphologic variables (valley width, channel sinuosity, valley‐ side slope) over the length of the stream, we evaluated the dominant recruitment processes along the river and often found a spatial disconnect between the location of potential channel‐spanning LWD and recruitment mechanisms, which likely explains the low levels of LWD currently found in the system. This rapid method for identification of LWD sources is extendable to other basins and may prove valuable in locating future restoration projects aimed at increasing habitat quality through wood additions.
key words: large woody debris; lidar; river restoration; habitat
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Effects of Flow Regulation on Shallow-Water Habitat Dynamics and Floodplain Connectivity
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Our study examined the effects of flow regulation on the spatiotemporal availability of shallow habitat patches with slow current velocity (SSCV patches) and floodplain inundation in the unregulated Yellowstone River and the regulated Missouri River in Montana and North Dakota. We mapped representative sites and used hydraulic models and hydrograph data to describe the frequency and extent of floodplain inundation and the availability of SSCV habitat over time during different water years. In the Yellowstone River the distribution, location, and size of SSCV patches varied but followed an annual pattern that was tied to the snowmelt runoff hydrograph. There was less variation in patch distribution in the Missouri River, and the pattern of habitat availability was influenced by flow regulation. Regulated flows and their effects on channel mor- phology and patterns of vegetation establishment resulted in 3.0–3.5 times less area of inundated woody vegetation during normal and dry years in the Missouri River compared with the Yellow- stone River. The differences we observed in SSCV patch dynamics between rivers may have implications for fish populations and community structure through affecting the survival of early life stages. At a larger scale, the smaller area of vegetation inundated in the Missouri River suggests that nutrient cycling and the ecological benefits associated with a moving littoral zone are reduced by the altered flow and sediment regime in that river. Accurate assessments of the effects of flow alteration and successful efforts to restore riverine ecosystems will require consideration of physical and biotic processes that operate at multiple spatial and temporal scales.
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Too late for two degrees? Low carbon economy index 2012
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Even doubling our current rate of decarbonisation would still lead to emissions consistent with 6 degrees of
warming by the end of the century. To give ourselves a more than 50% chance of avoiding 2 degrees will
require a six-fold improvement in our rate of decarbonisation.
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Human mining activity across the ages determines the genetic structure of modern brown trout (Salmo trutta L.) populations
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Humans have exploited the earth’s metal resources for thousands of years leaving behind a legacy of toxic metal contamination and poor water quality. The southwest of England provides a well-defined example, with a rich history of metal mining dating to the Bronze Age. Mine water washout continues to negatively impact water quality across the region where brown trout (Salmo trutta L.) populations exist in both metal-impacted and relatively clean rivers. We used micro- satellites to assess the genetic impact of mining practices on trout populations in this region. Our analyses demonstrated that metal-impacted trout populations have low genetic diversity and have experienced severe population declines. Metal-river trout populations are genetically distinct from clean-river populations, and also from one another, despite being geographically proximate. Using approximate Bayesian computation (ABC), we dated the origins of these genetic patterns to periods of intensive mining activity. The historical split of contemporary metal-impacted populations from clean-river fish dated to the Medieval period. Moreover, we observed two distinct genetic populations of trout within a single catchment and dated their divergence to the Industrial Revolution. Our investigation thus provides an evaluation of contemporary population genetics in showing how human-altered landscapes can change the genetic makeup of a species.
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Uncertainty in the response of transpiration to CO2 and implications for climate change
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While terrestrial precipitation is a societally highly relevant climate variable, there is little consensus among climate models about its projected 21st century changes. An important source of precipitable water over land is plant transpiration. Plants control transpiration by opening and closing their stomata. The sensitivity of this process to increasing CO2 concentrations is uncertain. To assess the impact of this uncertainty on future climate, we perform experiments with an intermediate complexity Earth System Climate Model (UVic ESCM) for a range of model-imposed transpiration- sensitivities to CO2. Changing the sensitivity of transpiration to CO2 causes simulated terrestrial precipitation to change by −10% to +27% by 2100 under a high emission scenario. This study emphasises the importance of an improved assessment of the dynamics of environmental impact on vegetation to better predict future changes of the terrestrial hydrological and carbon cycles.
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Increasing Northern Hemisphere water deficit
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A monthly water-balance model is used with CRUTS3.1 gridded monthly precip- itation and potential evapotranspiration (PET) data to examine changes in global water deficit (PET minus actual evapotranspiration) for the Northern Hemisphere (NH) for the years 1905 through 2009. Results show that NH deficit increased dramatically near the year 2000 during both the cool (October through March) and warm (April through September) seasons. The increase in water deficit near 2000 coincides with a substantial increase in NH temperature and PET. The most pronounced increases in deficit occurred for the latitudinal band from 0 to 40°N. These results indicate that global warming has increased the water deficit in the NH and that the increase since 2000 is unprecedented for the 1905 through 2009 period. Additionally, coincident with the increase in deficit near 2000, mean NH runoff also increased due to increases in P. We explain the apparent contradiction of concurrent increases in deficit and increases in runoff.
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Seeing the landscape for the trees: Metrics to guide riparian shade management in river catchments
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Rising water temperature (Tw) due to anthropogenic climate change may have serious conse- quences for river ecosystems. Conservation and/or expansion of riparian shade could counter warming and buy time for ecosystems to adapt. However, sensitivity of river reaches to direct solar radiation is highly het- erogeneous in space and time, so benefits of shading are also expected to be site specific. We use a network of high-resolution temperature measurements from two upland rivers in the UK, in conjunction with topo- graphic shade modeling, to assess the relative significance of landscape and riparian shade to the thermal behavior of river reaches. Trees occupy 7% of the study catchments (comparable with the UK national aver- age) yet shade covers 52% of the area and is concentrated along river corridors. Riparian shade is most ben- eficial for managing Tw at distances 5–20 km downstream from the source of the rivers where discharge is modest, flow is dominated by near-surface hydrological pathways, there is a wide floodplain with little land- scape shade, and where cumulative solar exposure times are sufficient to affect Tw. For the rivers studied, we find that approximately 0.5 km of complete shade is necessary to off-set Tw by 18C during July (the month with peak Tw) at a headwater site; whereas 1.1 km of shade is required 25 km downstream. Further research is needed to assess the integrated effect of future changes in air temperature, sunshine duration, direct solar radiation, and downward diffuse radiation on Tw to help tree planting schemes achieve
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Downstream Warming and Headwater Acidity May Diminish Coldwater Habitat in Southern Appalachian Mountain Streams
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Stream-dwelling species in the U.S. southern Appalachian Mountains region are particularly vulnerable to climate change and acidification. The objectives of this study were to quantify the spatial extent of contemporary suitable habitat for acid- and thermally sensitive aquatic species and to forecast future habitat loss resulting from expected temperature increases on national forest lands in the southern Appalachian Mountain region. The goal of this study was to help watershed managers identify and assess stream reaches that are potentially vulnerable to warming, acidification, or both. To our knowledge, these results represent the first regional assessment of aquatic habitat suitability with respect to the combined effects of stream water temperature and acid-base status in the United States. Statistical models were developed to predict July mean daily maximum water temperatures and air-water tem- perature relations to determine potential changes in future stream water temperatures. The length of stream considered suitable habitat for acid- and thermally sensitive species, based on temperature and acid neutralizing capacity thresholds of 20°C and 50 μeq/L, was variable throughout the national forests considered. Stream length displaying temperature above 20°C was generally more than five times greater than the length predicted to have acid neutralizing capacity below 50 μeq/L. It was uncommon for these two stressors to occur within the same stream segment. Results suggested that species’ distributional shifts to colder, higher elevation habitats under a warming climate can be constrained by acidification of headwater streams. The approach used in this study can be applied to evaluate climate change impacts to stream water resources in other regions.
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Experimental studies of dead-wood biodiversity — A review identifying global gaps in knowledge
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The importance of dead wood for biodiversity is widely recognized but strategies for conservation exist only in some regions worldwide. Most strategies combine knowledge from observational and experimental studies but remain preliminary as many facets of the complex relationships are unstudied. In this first global review of 79 experimental studies addressing biodiversity patterns in dead wood, we identify major knowledge gaps and aim to foster collaboration among researchers by providing a map of previous and ongoing experiments. We show that research has focused primarily on temperate and boreal forests, where results have helped in developing evidence-based conservation strategies, whereas comparatively few such efforts have been made in subtropical or tropical zones. Most studies have been limited to early stages of wood decomposition and many diverse and functionally important saproxylic taxa, e.g., fungi, flies and termites, remain under-represented. Our meta-analysis confirms the benefits of dead-wood addition for biodiversity, particularly for saproxylic taxa, but shows that responses of non-saproxylic taxa are heterogeneous. Our analysis indicates that global conservation of organisms associated with dead wood would benefit most by prioritizing research in the tropics and other neglected regions, focusing on advanced stages of wood decomposition and assessing a wider range of taxa. By using existing experimental set-ups to study advanced decay stages and additional taxa, results could be obtained more quickly and with less effort compared to initiating new experiments.
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A Chinese cave links climate change, social impacts, and human adaptation over the last 500 years
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The collapse of some pre-historical and historical cultures, including Chinese dynasties were presumably linked to widespread droughts, on the basis of synchronicities of societal crises and proxy-based climate events. Here, we present a comparison of ancient inscriptions in Dayu Cave from Qinling Mountains, central China, which described accurate times and detailed impacts of seven drought events during the period of 1520–1920 CE, with high-resolution speleothem records from the same cave. The comparable results provide unique and robust tests on relationships among speleothem δ18O changes, drought events, and societal unrest. With direct historical evidences, our results suggest that droughts and even modest events interrupting otherwise wet intervals can cause serious social crises. Modeling results of speleothem δ18O series suggest that future precipitation in central China may be below the average of the past 500 years. As Qinling Mountain is the main recharge area of two large water transfer projects and habitats of many endangered species, it is imperative to explore an adaptive strategy for the decline in precipitation and/or drought events.
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