Nutrient dynamics of seasonal tanks in the dry zone of Sri Lanka in relation to their hydrological regimes

Village tanks are put to a wide range of uses by the rural communities that depend on them for their survival. As the primacy of irrigation has decreased under these tanks due to a variety of climatic and economic reasons there is a need to reevaluate their use for other productive functions. The research presented in this paper is part of a programme investigating the potential to improve the management of living aquatic resources in order to bring benefits to the most marginal groups identified in upper watershed areas. Based on an improved typology of seasonal tanks, the seasonal changes and dynamics of various water quality parameters indicative of nutrient status and fisheries carrying capacity are compared over a period of one year. Indicators of Net (Primary) Productivity (NP): Rates of Dissolved Oxygen (DO) change, Total Suspended Solids (TSS): Total Suspended Volatile solids (TVSS) ratios are the parameters of principle interest. Based on these results a comparative analysis is made on two classes of ‘seasonal’ and ‘semi-seasonal’ tanks. Results indicate a broad correlation in each of these parameters with seasonal trends in tank hydrology. Highest productivity levels are associated with periods of declining water storage, whilst the lowest levels are associated with the periods of maximum water storage shortly after the NW monsoon. This variation is primarily attributed to dilution effects associated with depth and storage area. During the yala period, encroachment of the surface layer by several species of aquatic macrophyte also has progressively negative impacts on productivity. The most seasonal tanks show wider extremes in seasonal nutrient dynamics, overall, with less favourable conditions than the ‘semi-seasonal’ tanks. Never the less all the tanks can be considered as being highly productive with NP levels comparable to fertilised pond systems for much of the year. This indicates that nutrient status is not likely to be amongst the most important constraints to enhancing fish production. Other potential management improvements based on these results are discussed. [PDF contains 19 pages

Performance evaluation of sub-surface flow constructed wetland systems under variable hydraulic loading rates

Wastewater treatment has given an immense attention in the field of pollution control throughout the world. This has become a challenge in developing countries due to the limitations of resources and expertise. Constructed wetlands where water, plants and microorganisms interact to improve the quality of water have been proven to be an effective low-cost wastewater treatment technology in many parts of the world, which does not necessarily require skilled personnel to run the system. However, these systems are not yet widely spread in developing countries due to lack of information. Constructed wetlands can be designed as surface flow or subsurface flow systems, depending on the level of the water column. This study compares the performance of vertical subsurface flow (VSSF) and horizontal subsurface flow (HSSF) constructed wetland systems at laboratory scale at tropical condition. This paper also evaluates the effects of Hydraulic Loading Rate (HLR) on treatment capacity of wastewater parameters such as Five day Biochemical Oxygen Demand (BOD5), Total Suspended Solids (TSS), Nitrate Nitrogen (NO3 —N), Phosphate (PO4 3-), Ammonia Nitrogen (NH4-N ), Fecal Coliforms (FC) and Total Coliforms (TC). Six wetland models of size 1.4 m x 0.5 m x 0.5 m (L x W x H) were constructed and arranged: 1) Two models as VSSF system with plants, 2) Two models as HSSF system with plants, 3) One model as a VSSF control without plants and 4) One model as a HSSF control without plants. An emergent macrophyte specie; cattail (Typha angustifolia), gravel media (size 10 – 20 mm) and synthetic wastewater with average concentrations of BOD5 ; 29.51 ± 4.21 mg/L, NO3 - - N ; 3.22 ± 1.25 mg/L, NH3 - - N ; 15.14 ± 2.65 mg/L, PO4 3- ; 6.78 ± 5.67 mg/L, Fecal Coliform 495.12 * 103 ± 307.12 * 103 counts/100 mL and Total Coliform 915.5 * 103 ± 719.83 * 103 counts/100 mL were used in this study. The HLR was increased from 2.5 – 25 cm/day at 12 days interval during two and a half months period. Sampling was carried out with each HLR from both influent and effluents of each wetland system after 12 days of constant flow rate, and wastewater quality parameters such as the BOD5, TSS, NH4-N, NO3 --N, PO4 3-, pH, Conductivity, FC and TC were measured in all samples. Results show that VSSF systems perform better than horizontal systems, but the treatment performance declines with the increasing HLR in all six wetland models

Assessment of the Variability of Soil Properties for OFC Cultivation under Minor Irrigation Systems

Combined paddy and other field crops (OFC) fields are unique from other wetland or upland soils, because of seasonal alternation of wetting and drying conditions resulting anaerobic and aerobic conditions. Therefore, objective of this study was to assess spatio-temporal variation of soil properties in paddy fields under minor tanks with respect to OFC cultivation. Soil samples were collected at two soil depths from 24 locations covering the entire command area of the Bayawa Minor Irrigation Tank (MIT), Sri Lanka. Soil properties were analyzed and mapped using Arc GIS. Hardpan depth (HPD) was also determined by collecting undisturbed core samples at 0, 15, 25, 30, 45 and 60 cm depths from the same locations Statistical analysis was done to identify spatio-temporal variability of each property. Results revealed that, Bayawa command area showed low coefficient of variation (CV) for pH and bulk density, but high CV for saturated hydraulic conductivity (Ks). HPD was found to be varied in each section within the effective root zone. Overall, low Ks, high clay content, high field capacity, poor drainage and the presence of hardpan are major obstacles to introduce OFC. Therefore, introduction of site specific OFC by considering the variability of soil properties is very important for sustainability of the MIT system

A statistical approach for landfill classification in Sri Lanka based on waste characteristics

Several parameters have been used to characterize wastes in dumping sites. It is not possible to measure all the parameters and also those parameters are not equally important for management options which are decided on priority basis. In fact some parameters are closely related to other parameters. Therefore, parameters have to be clustered for classifying the wastes in dumping sites. A study was conducted to develop a statistical procedure using available tools to cluster landfills based on landfill waste characteristics. Five waste samples were collected from three landfills in the central province of Sri Lanka to compare the waste characteristics followed by the use of data to elaborate the clustering procedure. Correlation diagrams, principle component and cluster analysis have been applied for eight parameters; Moisture content, Ash content, Unit Volume mass, Lower heating value, Particle density < 2mm, Plasticity index, pH and Electrical Conductivity. Statistical analysis was able to extract two main principle components as primary, and secondary which accounted for 92.1 % of the total variability establishing two main classes which can be further improved to be more representative and precise with the increased number of samples subjected to the analysis

Investigation of landfill suitability based on semi quantitative risk matrix and GIS

Open dumping is the most widely practiced method in Sri Lanka to dispose municipal solid waste (MSW) because it is the cheapest and easiest method compared to other methods available to manage MSW.Currently, there are no guidelines available for a proper selection of landfill dump site which may minimize the environmental, social and economic problems in the country. Site selection for landfill sites is an important aspect from both environmental conservation and social/economical point of view. Data was collected from the Udapalatha area for analyzing. Considering priority of all criteria in comparison with others, a specific risk rate was decided to each criterion according to their total influence on the whole process of decision making. Suitable landfill site was analyzed by using the Geographic Information System (GIS) together with risk assessment. To identify appropriate landfill areas in the study area, five input map layers including surface water bodies, distance from transportation routes, distance from urban areas, land use/land cover, and elevation were used in the mapping. Based on these data a risk assessment wascarried out with a semi-quantitative matrix. The findings obtained from this study could be used for preliminary information to develop criteria for new landfill site selection. Finally, suitable low-risk regions in the area have been proposed for solid waste landfill disposal

Biodiversity Assessment of Paddy Field Ecosystem using Birds as a Biodiversity Indicator

Biodiversity assessment is considered in making decisions concerning declaration ofprotected areas, management of nature reserves and assessment of the success ofmanagement decisions within a particular area. Biodiversity indicators are used as measuresof biodiversity. Degree of disturbance or fragmentation of a definite habitat can be measuredusing specific indicator species. A variety of invertebrates and vertebrates are widely used asindicators of biodiversity. Birds are one of the best species for the national and internationalbiodiversity schemes to be used as a biodiversity indicator.This study focused on the use of birds as an ecological indicator to assess the paddy fieldecosystem. The study was carried out in a minor irrigation system in Awlegama AgrarianService area in Wariyapola Divisional Secretariat. Bayawa was the selected tank with nearlya 38 ha of command area. A standard fixed-radius point count method with the radius set at25 m was used to sample birds in the paddy field ecosystem. Shanon index was used toexplain the results. During a single rice cycle, rice plants undergo three main phenologicalstages namely; vegetative, reproductive and ripening. All these stages are influenced byfarming practices such as tillage, irrigation, crop establishment, agrochemical application andweeding. Different stages with different farming practices create distinct habitats for variousbird species. According to the results, the highest Shanon index value (highest diversity) wasrecorded during the vegetative stage. Birds‟ diversity had a significant, strong (p=0.05)negative correlation with the age of the paddy. Initial land preparation and vegetative stagesprovide more food sources for the predatory birds who feed on worms, insects and snails;some of whom act as pests of paddy. Mixing of upper and the sub-soil layers in landpreparation stages supply more feed for predatory birds. Cattle Egret, Red Wattled Lapwing,Intermediate Egrets, Indian Pond Heron, Black Necked Stroke were in abundance at landpreparation and vegetative stage. Yellow crowned woodpecker and White throated muniawere recorded during the later stages. A variety of management practices such as landpreparation, crop establishments, irrigation, nutrient and pest management, harvesting withinthe paddy field facilitate to create different habitats with different eco systems and suitablefood for bird species. The birds as a biodiversity indicator, symbolise the ecosystem and itreflects the existing condition of an ecosystems. A detailed study will reveal how these birdswould help to manage different pests in the paddy fields to bring benefits to the farmers.Keywords: Biodiversity indicator, Ecosystem, Paddy field, Birds, Cattle Egre

Land preparation water management by canal simulation in a paddy estate.

A canal simulation study was conducted in an intensively cultivated paddy estate in Malaysia. CanalMan software was applied to main and selected secondary canals that have difficulty in land preparation supply within the scheduled time periods. The study revealed that the CanalMan is capable of simulating different scenarios possible in the project area. Canal simulations also revealed that the land preparation supply management could be completed in three days, which is two days less than the current practice, when the canals are supplied with design discharges. Canal simulations combined with a water balance study revealed that a minimum of 20 mm of effective rainfall is needed to complete land preparation within the desired period. When the water levels along main canal drops, the required rainfall is much higher. This forces the management to start supply by pumping or shift land preparation water management in critical blocks to the drainage period soon after seeding in other blocks