Variability In Moisture Conditions Research Articles

Seed Bank and Vegetation in a Closed Depression in Agricultural Landscape: Relation to Moisture Conditions and Soil Properties

The aim of the study was to estimate the effect of habitat factors such as moisture conditions and some physicochemical soil characteristics on the structure of the vegetation and the soil seed bank, and to compare species composition of the vegetation cover and the seed bank along the soil moisture and fertility gradients in closed depression in agricultural landscape. Based on the averaged results of the extent and time of stagnation of the water, along the transect four habitat moisture zones were distinguished (dry, periodically moist, moist, and wet). In eighteen study plots we analysed flora, soil seed bank, and contents of Ca, Mg, K, Mn, Fe and pH of the soil. The analysed closed depression is characterised by high variability in moisture conditions and in the physical and chemical properties of the soil. The most important factors affecting the diversity of the vegetation cover and seed bank were the duration of water stagnation and the content of Fe and Mn in the soil. The lowest plant species richness and the smallest seed resources were determined for the wet zone of the depression. An increase in the habitat moisture level was accompanied by a decline in the floristic similarity between the vegetation cover and the seed bank.

Spatial and temporal patterns of drought in Oklahoma (1901–2014)

This study uses the Standardized Precipitation Evapotranspiration Index (SPEI) at a 6‐month timescale to document the spatial and temporal patterns of drought in Oklahoma from 1901 to 2014. A principal component analysis (PCA) with a VARIMAX rotation was used to divide Oklahoma into four spatially contiguous regions with similar drought patterns that are located in northwestern, northeastern, southwestern and southeastern regions of the state. Droughts tend to occur more frequently in northwestern Oklahoma, but all four regions show that droughts in Oklahoma have substantial variability at decadal timescales. A Mann–Kendall trend test demonstrates that there has been a statistically significant increase in the SPEI in Oklahoma since 1901. This indicates that conditions are generally getting wetter in Oklahoma. However, there is substantial variability in moisture conditions that is evident at shorter timescales. Prolonged periods of drier than normal conditions occurred in the 1910s, 1930s, 1950s, 1970s and 1980s, while conditions from the 1980s to the 2000s have been wetter than normal. Recently, the SPEI has decreased, which suggests that Oklahoma may be at the beginning of another dry cycle. In addition, while most droughts during the study period were caused by decreases in precipitation, recent droughts, such as the severe drought in 2011, were caused by both decreases in precipitation and increases in potential evapotranspiration. This may be indicative of future drought conditions in Oklahoma.

The sensitivity of US wildfire occurrence to pre-season soil moisture conditions across ecosystems

It is generally accepted that year-to-year variability in moisture conditions and drought are linked with increased wildfire occurrence. However, quantifying the sensitivity of wildfire to surface moisture state at seasonal lead-times has been challenging due to the absence of a long soil moisture record with the appropriate coverage and spatial resolution for continental-scale analysis. Here we apply model simulations of surface soil moisture that numerically assimilate observations from NASA’s Gravity Recovery and Climate Experiment (GRACE) mission with the USDA Forest Service’s historical Fire-Occurrence Database over the contiguous United States. We quantify the relationships between pre-fire-season soil moisture and subsequent-year wildfire occurrence by land-cover type and produce annual probable wildfire occurrence and burned area maps at 0.25 degree resolution. Cross-validated results generally indicate a higher occurrence of smaller fires when months preceding fire season are wet, while larger fires are more frequent when soils are dry. This is consistent with the concept of increased fuel accumulation under wet conditions in the pre-season. These results demonstrate the fundamental strength of the relationship between soil moisture and fire activity at long lead-times and are indicative of that relationship’s utility for the future development of national-scale predictive capability.

Analysis of moisture conditions in the lowland areas using high resolution spectral data from the Sentinel-2 satellite and the GIS tools

Research concerning agricultural drought issue mainly focuses on the methods based on long-term atmospheric data, temperature, precipitation and evaporation measurements. On the other hand, the scientific bibliography shows the possibilities of using spectral data for description the state of plants. The general availability and increasing resolution of the spectral and temporal data create a chance for monitoring and forecasting deficiencies of soil moisture based on spectral images. Paper presents the results of analysis of the moisture conditions in soil-plant environment in the lowland catchment area using the spectral data obtained from the Sentinel-2 European Space Agency satellite for period February-November 2016. These spectral data were used for the calculation the Normalized Differential Vegetation Index (NDVI) which provided information about moisture conditions in the soil-plant environment. Then, the values of NDVI index were compared with the data obtained from the field investigations. The analyses have showed the spatial and temporal variability of moisture conditions in the soil-plant environment determined on the background of the spectral indicators and the existence of some dependences between climatic and spectral indicators characterizing soil-plant environment.

Northern peatland Collembola communities unaffected by three summers of simulated extreme precipitation

Extreme climate events are observed and predicted to increase in frequency and duration in high-latitude ecosystems as a result of global climate change. This includes extreme precipitation events, which may directly impact on belowground food webs and ecosystem functioning by their physical impacts and by altering local soil moisture conditions.We assessed responses of the Collembola community in a northern Sphagnum fuscum-dominated ombrotrophic peatland to three years of experimentally increased occurrence of extreme precipitation events. Annual summer precipitation was doubled (an increase of 200mm) by 16 simulated extreme rain events within the three months growing season, where on each occasion 12.5mm of rain was added within a few minutes. Despite this high frequency and intensity of the rain events, no shifts in Collembola density, relative species abundances and community weighted means of three relevant traits (moisture preference, vertical distribution and body size) were observed. This strongly suggests that the peatland Collembola community is unaffected by the physical impacts of extreme precipitation and the short-term variability in moisture conditions. The lack of response is most likely reinforced by the fact that extreme precipitation events do not seem to alter longer-term soil moisture conditions in the peat layers inhabited by soil fauna.This study adds evidence to the observation that the biotic components of northern ombrotrophic peatlands are hardly responsive to an increase in extreme summer precipitation events. Given the importance of these ecosystems for the global C balance, these findings significantly contribute to the current knowledge of the ecological impact of future climate scenarios.

Ecology of testate amoebae in a North Carolina pocosin and their potential use as environmental and paleoenvironmental indicators

Testate amoebae inhabiting Sphagnum peatlands are sensitive indicators of substrate-moisture content. However, ecological data from a range of peatland types is needed to assess their indicator-value in other peatland systems. We examined testate amoeba communities and species—environment relationships at 40 locations within a pocosin of North Carolina. Primary objectives were to provide baseline data on the ecology of testate amoebae in pocosins, compare communities with those of northern peatlands, and assess the potential of using testate amoebae as environmental indicators in these systems. Results indicated that pH, substrate-moisture content, and conductivity were important controls on community composition. Communities that were relatively similar and dissimilar to those of northern peatlands were encountered, and the ecology of species with respect to water-table depth was similar in both peatland types. Cross validation of transfer functions for pH and water-table depth suggests that pocosin testate amoebae can be used as indicators for these variables. However, water-table depth was poorly inferred from communities at several dry sites characterized by high bulk density. These sites may experience large seasonal or interannual variability in moisture conditions because of differences in peat structure, suggesting that research is needed on the influence of short-term variability in shaping community structure.

Changing growing conditions for crops during the Near Eastern Bronze Age (3000–1200 BC): the stable carbon isotope evidence

The analysis of carbon isotope discrimination (Δ 13C) in crop plant remains from seven Bronze Age sites in northern Mesopotamia and the Levant shows clear differences in water availability between the different geographic areas and throughout the different periods (3000–1200 BC). Amongst the different moisture variables modelled precipitation minus evaporation (P-E—using a macrophysical climate model (MCM)) results in very high correlation (0.74) with Δ 13C values in barley, supporting the significance of climate parameters (effective moisture) in carbon fixation in this species. The comparison of Δ 13C values of different crops in different periods confirms increased aridity during the Middle Bronze Age (2000–1600 BC), compared to the later Early Bronze Age (2700–2000 BC) particularly in the north-eastern Syrian territory with generally lower Δ 13C values during the Middle Bronze Age, as has been documented in palaeoclimate proxies, and in agreement with the MCM. Standard deviation in Δ 13C values from grains or seeds of one species originating from different samples of an individual site may be understood as variability in moisture conditions during the grain-filling period around the considered location. Large standard deviations occur preferably in sites with low mean annual precipitation (e.g. at Emar) and suggest that in these sites, at least some of the crops were irrigated.

Characterizing the spatial and temporal variability of June–July moisture conditions in the Canadian prairies

AbstractPalmer's moisture anomaly index (Z‐index) was used to characterize the frequency, severity, and spatial extent of June–July moisture anomalies for 43 crop districts across the Canadian prairies during 1920–99. In addition, the main modes of spatial and temporal variability in moisture conditions were identified and used to elucidate the physical mechanisms responsible for causing these moisture anomalies to occur. The crop districts were divided into five relatively homogeneous moisture regions using cluster analysis, and moisture anomaly statistics were analysed for each region.The single most severe June–July drought on the Canadian prairies occurred in 1961. This drought covered more than 86% of the study region and had a mean severity (Z‐index) of −5.67. Other severe June–July droughts occurred in the Canadian prairies (in order of severity) in 1988, 1936, 1929, and 1937. The results demonstrated that the severity and spatial extent of moisture anomalies on the Canadian prairies are strongly correlated, indicating that the more severe events tend to affect larger areas. The most drought‐prone regions experienced moisture conditions detrimental to crop production in approximately one year out of every six years.The spatial analysis revealed the existence of three preferred spatial patterns of moisture variability on the Canadian prairies and each pattern can be attributed to a unique set of atmospheric and oceanic forcings. The temporal analysis verified the presence of coherent periodicities (in particular quasi‐2, ‐4, and ‐10–15 year oscillations) in the moisture time series. Copyright © 2005 Royal Meteorological Society

Isolated wetlands: State-of-the-science and future directions

In Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC), the U.S. Supreme Court held that isolated, intrastate, non-navigable waters could not be protected under the Clean Water Act based solely on their use by migratory birds. The SWANCC decision has created a need to compile and make available scientific information for post-SWANCC policy development. In response, this article reviews the state of our scientific understanding of isolated wetlands, based on the major findings of papers contributed to this special issue of Wetlands. Because the term “isolated wetland” has not been used consistently in the scientific literature, we recommend that geographically isolated wetlands be defined as “wetlands that are completely surrounded by upland,” as proposed by Tiner, for the purposes of scientific studies. Geographically isolated wetlands are not homogeneous but have a broad range of functional response, partly due to their occurrence over a wide range of climatic and geologic settings. One major question addressed through this special issue is the role that isolation plays in the function of geographically isolated wetlands. It appears that isolation is not a primary factor and that many of the functions performed by isolated wetlands are also performed by non-isolated wetlands and non-wetland ecosystems. Variability in moisture conditions plays an important role in the function of many geographically isolated wetlands. However, hydrologic isolation may affect moisture conditions, and biotic isolation could be important for certain populations. Depending on the factor being considered, geographically isolated wetlands are not entirely isolated but are better viewed as occurring within an isolation-connectivity continuum that has both hydrologic and biotic expressions. The juxtaposition of isolation and connectivity occurring in geographically isolated wetlands may represent a semi-isolated state that uniquely shapes these wetlands and their functions. Comprehensive data, designating the number, total area, and functional classification of isolated wetlands, would provide the foundation for monitoring impacts to isolated wetlands. Studies are needed to examine and quantify how isolated wetlands, wetland complexes, and other potentially impacted waters contribute hydrologically, chemically, and biologically to waters of the U.S. Methods to assess and map the degree of connectivity between geographically isolated wetlands and waters of the U.S., based on ground-water travel time, recurrence frequency of intermittent surface-water connections, and home ranges of species that require both types of waters, could be useful for regulators. Whatever policies are developed, scientific input and technical information will continue to play a crucial role in the policy and regulatory arena. Maintaining and enhancing the dialogue among wetland scientists, policy-makers, and regulators will ensure that critical information is developed and communicated and also continue to invigorate wetland science.