Landscape controls of surface-water/groundwater interactions on shallow outwash lakes: how the long-term groundwater signal overrides interannual variability due to evaporative effects

The spatial and temporal controls on variability of the relative contributions of groundwater within and between flow systems to shallow lakes in the low-relief glaciated Boreal Plains of Canada were evaluated. Eleven lakes located in a coarse glacial outwash, of varying topographic positions and potential groundwater contributing areas, were sampled annually for stable O and H isotope ratios over the course of 8 years. It was demonstrated that landscape position is the dominant control over relative groundwater contributions to these lakes and the spatial pattern of the long-term isotopic compositions attributed to groundwater overrides interannual variability due to evaporative effects. Lakes at low landscape positions with large potential groundwater capture areas have relatively higher and more consistent groundwater contributions and low interannual variability of isotopic composition. Isolated lakes high in the landscape experience high interannual variability as they have little to no groundwater input to buffer the volumetric or isotopic changes caused by evaporation and precipitation. An alternative explanation that lake morphometry (area and volume) control long-term isotopic compositions is tested and subsequently refuted. Landscape position within coarse outwash is a strong predictor for relative groundwater input; however, surface-water connections can short circuit groundwater pathways and confound the signal. A hydrogeological case study for three of the study lakes is used to contextualize and further demonstrate these results.

Effect of Slope Positions on Properties of Soils of some Forest reserves in South-West Nigeria

Topography has an influence on soil erosion and consequently on the properties of soils. The effect of slope position on soil properties is of great importance in soil suitability assessment. This study assessed the effect of topographic position on the characteristics of soil of basement complex rocks derived soils under Teak (Tectona grandis) and Gmelina (Gmelina arborea) plantations in Osun sacred grove, Onigambari and Omo forest reserves situated within South-West Nigeria. Three soil profiles were dug in each landuse type, sited at the upper, middle and lower slope positions along a toposequence. Soil samples were collected according to their pedogenetic horizons and were analyzed using standard methods. Results showed variations in colour, depth of soil profile, soil structure, texture, drainage and soil consistence. The high sand content dominated the particle size fraction in all the soils formed from the three locations, and base saturation was rated very high with values >90% irrespective of the toposequence or slope position. The result of correlation analysis between slope position and content of N, P, K and CEC showed a significant relationship irrespective of locations with N(r = 0.019< 0.05) respectively. Despite variation in soil properties as influenced by topography, the studied soils can sustain the current land use type. It was concluded that soils on different topographic positions should be managed differently.

Characterization and Taxonomy Classification of Soils of Hill Slope Land and Stream Terrace Land Located at North-Eastern Ghat Agro-Climatic Zone of Odisha, India

The present investigation was carried out to study the characterization, fertility status and taxonomic classification of some soils of North-Eastern Ghat Agro-Climatic zone of Odisha. Hill slope (pedon 1) and stream terrace land (pedon 2) two representative pedons of the Nayagarh district located in different topographic positions were studied for their physico-chemical characteristics and taxonomic classification. Results show that in pedon 1, percentage of sand, silt and clay range between 78.4 to 86.4, 3.2 to 3.4 and 10.4 to 17.4 respectively and in pedon 2, sand, silt and clay percentages range between 72 to 84, 3.2 to 7.2 and 10.8 to 18.8 respectively in different horizons. In pedons 1 and 2, pH increases along with depth from 4.80 to 5.82 and 5.80 to 7.60 respectively. Organic carbon content in pedons 1 and 2, ranges from 3.4 to 5.1 and 1.6 to 6.3 g kg-1 respectively. Cation exchange capacity decreases in pedon 1 from 13.25 to 8.66 c mol (p+) kg-1 and in pedon 2, range 7.66 to 16.65 c mol (p+) kg-1. The exchangeable sodium percentage in pedon 1 and 2, ranges from 4.53 to 9.23, and 2.56 to 6.53 per cent in different horizons respectively. The base saturation percentage in pedon 1, range from 58.11 to 98.15 per cent and in pedon 2, from 59.54 to 97.91 percent. The Hill slope (pedon 1) and stream terrace land (pedon 2) have little or no evidence of development of pedogenic horizons except ochric epipedon, therefore these soil are classified under the order Entisols. These soils have A-C profile with no distinct horizonation. Pedon 1, are classified under sub order Orthents, great group Ustorthents and sub group Typic Ustorthents. In case of pedon 2 the soils are put under the sub order Aquents, great group Fluvaquents and sub group Aeric Fluvaquents.

Interacting Flooding and Competition Negatively Affect Growth of Riparian Species Dominating a Reservoir Shoreline

Plant–plant interactions change in response to environmental conditions, and riparian species are commonly influenced by flooding. This study tested whether flooding affects the intraspecific and interspecific competition of two riparian species and whether such effects depend on the topographic positions where plants have established. Seeds of the riparian species Polygonum hydropiper were collected from both low and high positions within the shoreline of the Three Gorges Reservoir. Groups of P. hydropiper seedlings from each position were either grown alone (i.e., without competition), with another group of P. hydropiper seedlings (i.e., intraspecific competition), or with a group of seedlings of the companion species Xanthium sibiricum (i.e., interspecific competition). Each group comprised six replicates. In total, 288 plants of P. hydropiper and 84 plants of X. sibiricum were selected for the experiment. Seedlings were subjected to control and flooding treatments for 60 days. Irrespective of competition type (i.e., intra- or interspecific), both flooding and competition negatively affected the growth and/or photosynthetic capacities of P. hydropiper. Flooding only interacted with competition to explain total biomass. Flooding reduced total biomass in a larger proportion in the absence of competition, and, to a lesser extent, with intraspecific competition, compared to interspecific competition. However, such interaction effects were independent of the positions where the seeds that originated from the plants were collected from. Interspecific competition significantly decreased the chlorophyll content and photosynthetic efficiency of plants, while intraspecific competition did not. In general, plants from lower positions had higher total chlorophyll content than plants from higher positions. These results suggest that flooding may regulate the population dynamics of P. hydropiper by altering its competitive interactions.

Pedogenic forms and distribution of potassium in soils along a complex toposequence within Forestry Research Institute of Nigeria, Ibadan

The study was designed to examine the forms and pedogenic distribution of potassium in soils formed along a toposequence within Forestry Research Institute of Nigeria, Ibadan. Four (4) profile pits were established, described and sampled. Particle size, soil reaction and organic matter were determined in addition to exchangeable K, solution K and Fixed K which were determined using flame photometer. Results of particle size analysis showed that the silt content is low and varied randomly within the profiles possibly due to their location on the topography. The clay content was relatively high in the genetic B horizons. The exchangeable K, solution K, fixed K and total K varied randomly across the profiles, and this can also be attributed to the topographic positions. Results also showed that there is a high correlation between clay and exchangeable K and between total K and organic matter. This is an indication that soils with high clay content are likely to be rich in exchangeable K and where organic matter in the soil is high, the soil is likely to have a high value of total K Key words: Toposequence, Pedogenic, Potassium

BIOGEOQUIMICA ESPAÇO-TEMPORAL DA LITEIRA EM AMBIENTE DE FLORESTA NATURAL NA AMAZÔNIA CENTRAL

SPACE-TEMPORAL BIOGEOCHEMISTRY OF THE LITTER IN A NATURAL FOREST ENVIRONMENT IN THE CENTRAL AMAZON. This research was aimed to evaluate the concentration of 15 chemical elements as a reference base for the quality of the litter in a forest in the central region of the Amazon. The sampling of the litter was performed monthly in two topographic positions for one year. For the quantification of the elements, digestion by nitroperchloric solution and reading by ICP OES were performed. The mean of macronutrient contents in the litter in decreasing order were Ca>K>Mg>Na. For micronutrients, the order was Al>Mn>Fe>Sr>Zn>Cu>Ba>Cr>Ni>Co>Cd for the Plateau and Al>Mn>Fe Sr>Zn>Cu>Ba>Cr>Ni>Cd>Co for the Baixio. Among the fractions, calcium had its highest concentration in the woody material, potassium in the reproductive material, while magnesium, sodium, and aluminum showed higher concentrations in the leaf fraction. Also, it was observed that the return of the elements to the soil by litter was greater in the dry period of the region, due to the greater fall in plant material. Calcium differed significantly within the same area, obtaining the highest concentrations compared to the other elements, while aluminum and zinc differed significantly between the areas studied, with a higher return for both elements on the Plateau.

Floristic Survey of Meethirigala Forest Reserve in Gampaha District

Meethirigala forest reserve consists of approximately 384 ha. It is the largest forest reserve in Gampaha District managed by the Forest Department. It has different topographic positions such as ridges, midslopes and valley areas close to the Kelani River. The present study was conducted to enumerate plant species found in all three topographic positions of the reserve. Plots were demarcated purposively to sample woody perennials equal or greater than 5 cm dbh (diameter at breast height) in 18 plots (5×100 m, rectangular shape). Seedlings greater than 1 m tall were sampled in 18 plots (5×5 m). Shannon diversity indices were calculated to compare dominance of particular species in different topographic positions. A total of 360 individuals of woody perennials belonging to 73 species in ridge, 368 individuals of woody perennials belonging to 100 species in midslope and 272 individuals of woody perennials belonging to 69 species in valley were recorded. And 132, 123 and 100 individuals of seedlings were enumerated in ridge, midslope and valley respectively. In ridge 58 generas, 28 families, in midslope 83 generas, 35 families and, in valley 68 generas, 29 families were observed. 28 species were found in all three different altitudes of the reserve. Forest species in study sites gave a total of 138 plant species belonging to 113 tree species, 11 climber species, 14 shrub species, 109 generas and 46 families. Of this total 138 species, 34 (25%) species are endemic to Sri Lanka. Highest endemism was recorded in the ridge (41.6%). Stratification of the ridge showed a very similar pattern to a Dipterocarp forest type. Highest diversity was recorded in midslope (1.7290) and lowest recorded in ridge (1.5626) of the forest. 18 threatened species were observed (3-Endangered and 15-vulnerable species). As a conclusion, Meethirigala forest reserve can be considered as an important refuge for wet zone forest species.