Comment on “Wetland drying and succession across the Kenai Peninsula Lowlands, south-central Alaska”Appears in Can. J. For. Res. 35: 1931-1941 (2005).

2011 ◽  
Vol 41 (2) ◽  
pp. 425-428 ◽  
Author(s):  
Michael B. Gracz

Klein et al. (2005, Can. J. For. Res. 35: 1931–1941) compare aerial photographs and report dramatically lower lake levels on the northern Kenai Peninsula, Alaska. They hypothesize that the lower lake levels may be caused by a decline in moisture surplus driven by climate change. However, the reported decline in surplus appears to be insufficient to explain the lower lake levels. Here I develop a simple sensitivity analysis to test their hypothesis and also show how tectonic processes such as the Great Alaskan earthquake could dramatically lower lake levels by fracturing an underlying aquitard. Tectonic processes, therefore, could potentially alter forest succession and wetland ecosystems by inducing hydrologic changes that mimic changes in climate.


2011 ◽  
Vol 41 (2) ◽  
pp. 429-433 ◽  
Author(s):  
Eric S. Klein ◽  
Edward E. Berg ◽  
Roman Dial

Gracz (2011, Can. J. For. Res. 41: 425–428) proposes that the Good Friday earthquake of 1964 caused falling lake levels and drying wetlands on Alaska’s Northern Kenai Lowlands (NKL). His hypothesis states that the earthquake increased hydraulic conductivity by fracturing a leaky confining layer, accelerating drainage of surface water into regional aquifers. We counter that a single model of draining does not apply across the heterogeneity of geomorphology and soils on the NKL. In particular, the NKL’s glacial history precludes uniform application of a subsurface hydrologic model for lake draining and the nature of peat-based wetlands precludes its application to wetland drying. Instead, small, yet cumulative, climatic reductions in moisture surplus explain both observed lake level declines and vegetation changes. Moreover, and unlike a climatic hypothesis, a seismic hypothesis fails to explain lake drying elsewhere in Alaska. Although it is likely that the earthquake influenced some hydrologic features in the NKL, it is unlikely that a single hydrologic model based on a simple mechanical cause, e.g., downward drainage, adequately explains the changes observed across the whole NKL. Conversely, we maintain that the uniformity of the vegetation response seen across different landscapes, including wetlands, forests, and alpine areas, throughout the state of Alaska strongly supports a climatic hypothesis.





1995 ◽  
Vol 32 (5-6) ◽  
pp. 95-101
Author(s):  
D. R. Weston ◽  
G. Quibell ◽  
W. V. Pitman

Lake St Lucia is one of Africa's largest coastal lakes, and is one of South Africa's most important wetland ecosystems. However, like many ecosystems, it is under threat from increased demands for water in its catchment area. Reduced runoff primarily impacts on the salinity regime of the lake. At low lake levels there is a net inflow of seawater to the lake. Evaporation concentrates the salts, and lake salinities rise to several times that of seawater. In water periods, lake levels rise and there is a net outflow toward the sea. Under these conditions salinities are low. The lake therefore naturally experiences a range of salinities associated with wet and dry cycles. Increased water use in the catchment will, however, impact on this natural salinity regime. This paper introduces a suite of models which will be used to facilitate management of the water resources of the catchment. The preliminary work presented demonstrates the ability of the models to provide meaningful input into a catchment management decision-support system.



Forests ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 593
Author(s):  
Janet E. Nichol ◽  
Sawaid Abbas

Global trends predict a continuous increase in the proportion of forest occupied by plantations up to the end of the 21st century, while a dramatic loss of biodiversity is foreseen as a result of anthropogenic exploitation and climate change. This study compares the role and performance of plantation policies in Hong Kong, with natural regeneration of secondary forest, using detailed spatio-temporal data extracted from a previous study. The study extends over a 70-year period from 1945 to 2014 using aerial photographs and satellite images of five time periods to document spatio-temporal trends in plantation forestry and natural forest succession. Field data on species richness and woody biomass at different stages of forest succession are compared with available data from plantations in the same study area. Results indicate that plantation forests support relatively few native species in the understory, with much lower species richness than naturally regenerated forest, even after 6 to 7 decades. Time-sequential maps of habitat change show that natural forest succession from barren grassy hillsides, progressed at an annual rate of 7.8%, from only 0.2% of the landscape post WWII, to over 37% today. Plantation forestry on the other hand has been less successful, and has even acted as a barrier to natural forest regeneration, as mono-cultural plantations from the late 1960s to 1980s are still plantations today, whereas other similar areas have succeeded naturally to forest. The theory of plantations acting as a nurse crop for a woody native understory is not supported, as Pinus massoniana plantations, destroyed by two deadly nematodes during the 1970s, apparently had no woody understory, as they were seen to have reverted to grassland in 1989 and are still mainly grassland today.





2021 ◽  
Author(s):  
Wanderson Luiz-Silva ◽  
Pedro Regoto ◽  
Camila Ferreira de Vasconcellos ◽  
Felipe Bevilaqua Foldes Guimarães ◽  
Katia Cristina Garcia

<p>This research aims to support studies related to the adaptation capacity of the Amazon region to climate change. The Belo Monte Hydroelectric Power Plant (HPP) is in the Xingu River basin, in eastern Amazonia. Deforestation coupled with changes in water bodies that occurred in the drainage area of Belo Monte HPP over the past few decades can significantly influence the hydroclimatic features and, consequently, ecosystems and energy generation in the region. In this context, we analyze the climatology and trends of climate extremes in this area. The climate information comes from daily data in grid points of 0.25° x 0.25° for the period 1980-2013, available in http://careyking.com/data-downloads/. A set of 17 climate extremes indices based on daily data of maximum temperature (TX), minimum temperature (TN), and precipitation (PRCP) was calculated through the RClimDex software, recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI). The Mann-Kendall and the Sen’s Curvature tests are used to assess the statistical significance and the magnitude of the trends, respectively. The drainage area of the Belo Monte HPP is dominated by two climatic types: an equatorial climate in the north-central portion of the basin, with high temperatures and little variation throughout the year (22°C to 32°C), in addition to more frequent precipitation; and a tropical climate in the south-central sector, which experiences slightly more pronounced temperature variations throughout the year (20°C to 33°C) and presents a more defined wet and dry periods. The south-central portion of the basin exhibits the highest temperature extremes, with the highest TX and the lowest TN of the year occurring in this area, both due to the predominant days of clear skies in the austral winter, as to the advance of intense masses of polar air at this period. The diurnal temperature range is lower in the north-central sector when compared to that in the south-central region since the first has greater cloud cover and a higher frequency of precipitation. The largest annual rainfall volumes are concentrated at the north and west sides (more than 1,800 mm) and the precipitation extremes are heterogeneous across the basin. The maximum number of consecutive dry days increases from the north (10 to 20 days) to the south (90 to 100 days). The annual frequency of warm days and nights is increasing significantly in a large part of the basin with a magnitude ranging predominantly from +7 to +19 days/decade. The annual rainfall shows a predominant elevation sign of up to +200 mm/decade only in the northern part of the basin, while the remainder shows a reduction of up to -100 mm/decade. The duration of drought periods increases in the south-central sector of the basin, reaching up to +13 days/decade in some areas. The results of this study will be used in the future as an important input, together with exposure, sensibility, and local adaptation capacity, to design adaptation strategies that are more consistent with local reality and to the needs of local communities.</p>







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