Solid waste

Two field visits were conducted in September–October 2007 and in May–June 2008 for quantitative characterization of accumulated solid waste, its spatial distribution, sources, and an assessment of components of the existing waste management scheme and disposal technologies. To cover the area of SNPBZ, a total of 35 major settlements situated along main trekking routes (Caroli 2008) were investigated. The households were categorized into residential (private houses), commercial (hotels and lodges), and institutional (schools, hospitals, local offices and monasteries). A random structure sampling technique (Sutherland 1996) to cover all household types was applied and a sample of 15% of the households overall (n  =  154) were sampled for waste generation quantification using a standardized questionnaire developed through consultation with the local stakeholders based on identified data gaps (Salerno et al 2010).

Rapid appraisal was also done whenever it was not possible to use standard questionnaires. In each selected household and for each household type, the number of members (inhabitants, customers, visitors) was recorded as well as the amount of both overall and per person solid waste generated per day for 14 different types of waste. These were subsequently grouped into 4 main waste categories: plastic, metal, glass, and “other” (including kitchen waste, paper, dust, etc). The quantification of solid waste produced was estimated during 7 consecutive days. Different disposal methods (ie burning, burying, incinerating, transporting outside, reusing, recycling) were identified and quantified per each type of solid waste produced. In addition, for some settlements a survey of existing waste dumping sites was conducted, collecting information about their location, volume, lifetime, and burning efficiency. Following the methods of Gupta (2000), environmental impacts of waste dumping sites on water, soil, and air quality were also assessed: samples were collected at different locations from drinking water sources (in 11 sampling sites along rivers), soil (in 22 sampling locations), and air (in Luckla and Namche) close to existing waste dumping sites, and analyzed by atomic absorption spectrometry (AAS) to assess possible heavy metal (ie Cu, Ni, Cd, Zn) contamination in water and soil and contents of inhalable suspended particles less than 10 µm diameter (PM₁₀) in the air.

Water quality

A comprehensive water quality survey to evaluate the current situation in SNPBZ was carried out by collecting 104 surface water samples—mostly from streams and rivers, but also from Gokyo, Imja, and Pyramid Inferior Lakes—taken along the major trekking routes during three field visits in October 2007, May 2008, and October 2008. Water samples were analyzed to determine hydro-chemical and physical variables (temperature, pH, conductivity, total dissolved solids, nutrients such as nitrogen [N] and phosphorus [P], macro-constituents, alkalinity) following Trivedy and Goel (1986) and Camusso and Galassi (1998), and microbiological parameters (total and fecal coliforms, bacterial composition), following APHA, AWWA, WPCF (2005) methods. Phytological analyses (aquatic algae presence, chlorophyll content) were done on water samples collected from the Gokyo Lakes series and Imja Lake. River and lake water samples from 11 different locations (including 3 Gokyo Lakes) were additionally tested for heavy metals (Fe, Pb, Ni, Zn) by means of an atomic absorption spectrophotometer (AAS) and volumetric methods. To determine the nutrient influx, N, P, and potassium (K) content of organic fertilizer, litter, and fresh as well as burnt waste from dump sites was also analyzed (altogether 100 waste samples) by Kjeldhal, Stannus Chloride, and flame photometer methods (Jackson 1967), respectively.

In addition, a field survey to identify potential and actual sources of water pollution and to analyze water quality was carried out by means of a structured standard questionnaire (Converse and Presser 1986) developed through consultation with the local stakeholders based on identified data gaps. Households were selected in major settlements along main trekking routes (Caroli 2008). The households were categorized into different functional categories (large lodge, small lodge, tea shop, residential house), and a random sampling technique was applied to each group (Sutherland 1996) to cover all these household types, resulting in a coverage of around 20% of all households in SNPBZ. The questionnaire survey collected information about production of organic human waste, construction details, operation and management of sanitation facilities and services, use of organic and chemical fertilizers, and location of garbage pits.

The solid waste management model

The solid waste management model describes the process of waste production, collection, and treatment, providing, for each time step (monthly), the amount of solid waste—divided into the 4 identified categories: glass, plastic, metal and “other”—produced, treated, and disposed on the soil. The model structure was repeated for 18 selected park settlements, for which a complete set of the necessary data collected on the field and from the literature was available.

Starting from the number of tourists and inhabitants in each settlement (calculated in the Tourism and Population dynamics model, see ICIMOD 2009) and considering the amount of solid waste produced pro capita (obtained from the field survey on waste generation), the model calculates the amount of waste produced for each category (Figure 2). The waste produced and collected (disposed waste) is then assigned to six different treatment options (reusing, burying, burning, incinerating, recycling, and transporting outside) according to specific coefficients of repartition (disposal method distribution). The waste not collected is represented in the model by littered waste, while residual waste indicates all collected and treated waste left after the treatment (treatment efficiency), particularly burying, burning (ie waste burned on the soil in open dumping pits), and incinerating (ie waste burned in incinerators). We assumed in the model that buried waste and the remains of burned and incinerated waste (residual waste) as well as uncollected waste (littered waste) are accumulated in the soil compartment.

To reduce the amount of solid waste that ends on the ground (both littered and residual waste), the model offers the possibility of implementing 2 different management policies (policy levers). Particularly, in the case of SNPBZ, the following were implemented: one leading to reduction of waste production, and the other entailing a change of treatment typology per each waste category by choosing the more suitable disposal method (eg recycling for plastic, transporting outside for metal and glass, reusing, and/or incinerating for “other”) while enhancing collection efficiency. The model provided information on the tourism-related impact of solid waste management while also assessing the economic consequences caused by the application of the above-mentioned possible management levers.

The water pollution model

The water pollution model was developed with the aim, first, of evaluating nutrient (ie N and P) concentration in streams and then assigning an index (excellent, good, sufficient, poor, very bad) representing the water quality. As shown in Figure 2 (bottom part), the model is able to estimate the nutrient concentration in each river's section by considering the civil load of nutrients, deriving from civil point sources like organic human waste (feces and urine), and residual (burned, buried, and incinerated) and littered solid waste. The civil load is indeed influenced by both the littered waste and disposed waste, which are outputs of the solid waste management model, as well as by the number of inhabitants and number of tourists that, considering the pro-capita nutrient load, contribute to the nutrient load through human excreta. The aggregation of nutrients from civil load, natural load (nutrients from forests, rocks, precipitations) and agricultural load (nutrients from chemical and organic fertilizers) defines the potential load of nutrients in the park. Then, considering natural reduction factors such as percolation, the actual nutrient load is appraised. At this stage, the model estimates the nutrient concentration in the river section dividing the actual nutrient load by the experimental hydraulic discharge.

Location of sampling points was chosen with the aim of calibrating on the one hand the nutrient sources (agricultural, civil and natural loads) calculated by the model, and on the other hand their impacts on water quality in different sections of the main course, as represented in the map of SNPBZ with indication of the sampling sites (see Figure 1). To achieve the first aim, some samples were taken (during field research) in the closure point of small watersheds considered representative of each type of pressure. For instance, watersheds completely dominated by natural land cover classes, watersheds with a predominance of agricultural fields, or watersheds characterized by densely populated settlements were considered. Comparisons between the nutrient concentrations calculated by the model and those measured on the field allowed us to calibrate the model so that it could simulate the experimental concentrations. By comparing the simulated concentration of nutrients in the river section with national or international standard parameters, the river ecological status (ie water quality) can be assessed. As described later on, this model made it possible to estimate the water quality of the main river sections in SNPBZ, considering recent environmental regulations in the European Water Framework Directive, WFD 2000/60/CEE (international regulations such as the WHO guidelines regards just quality of drinking water). By acting on the management levers that allow for change of agricultural and civil nutrient loads, different sustainable or unsustainable water pollution scenarios were obtained and evaluated, which are presented below. Furthermore, the model allows calculation of the cost implied by the specific management policy lever.

Improving solid waste management

The household questionnaire survey revealed that more than any other environmental problem, solid waste was perceived by interviewed local people as the key challenge for SNPBZ (for more than 65% of respondents). As reported in Table 1, daily total waste generated in SNPBZ was empirically assessed to amounts of around 4.6 t day⁻¹ during the tourist seasons (October–November and April–May), when the waste quantification survey was conducted. We found that local people and tourists on average produce around 0.109 kg day⁻¹ and 0.123 kg day⁻¹ of solid waste per capita. Thus, compared with visitors, waste generated by local people living in the park and its buffer zones is 15%–20% less. However, because visitors spend on an average of 10 days in the park per year, the actual yearly average generated waste is only 3–4 g day⁻¹.

Table 1

Waste generation in different locations in SNPBZ, per different waste categories. For every investigated settlement, the total daily amount of solid waste generated is reported as well as the amount per capita.

Considering the rather small difference with regard to the amount of waste produced per visitor and local resident, at an annual scale the tourism industry is responsible for only around 10% of the accumulated waste, but the accumulation pattern is extremely unequally distributed over the year. Considering the distinct seasonal pattern of tourism-related activities, the overall waste production could be as low as 2 t day⁻¹ in the low season and is at a maximum during the 2 peaks in the tourist seasons (October–November and April–May).

Kitchen waste (“other”), largely composed of organic matter and preferably used for cattle feeding, amounts to around 88% of the waste generated, leaving the share of nondegradable waste categories at 7% for plastic, 3% for glass, and 1% for metals. Though the amount of plastic, metal, and glass generated is low if compared with largely biodegradable waste, these nonbiodegradable waste types create a great visual pollution problem on the landscape. They can cause environmental pollution and public health problems (eg ground and surface water pollution, air pollution caused by toxic gas emissions from burning, harmful effects on aquatic and terrestrial animals; see El-Fadel et al 1997; Hamer 2003; Pokhrel and Viraraghavan 2005). Particularly, plastic, and synthetic materials when burned easily generate charred residue solid ashes and toxic gas emissions that pollute the atmosphere (Kuniyal 2002; Valavanidis et al 2008).

With regard to the spatial distribution of the waste generation pattern, it is clear that since Luckla, Phakding, and Namche—the major settlements in SNPBZ located along the main route to Everest Base camp, Gokyo, and Thame—host a high number of hotels and service enterprises, daily waste generation for all types of households in these settlements is high, particularly in the tourism node of Namche. Glass and metal are accumulated predominantly in the BZ and Namche (first 7 settlements in Table 1). The ban on import of glass bottles (mainly beer) into the park initiated by the BZ Management Committee was successful in reducing the problem of glass accumulation in SNPBZ.

The only running incinerator in SNPBZ is located in Luckla. Its incineration capacity is theoretically around 30 kg⁻¹, producing 2.3 kg of ash from 30 kg of wastes. Leakages have been observed in the device, and maintenance of the incinerator is urgently required. Furthermore, most of the supporting technical components are not operating properly, so that the current use of the system resembles a “closed burning” practice. Because of a lack of alternatives, current waste disposal practices in the park, besides exporting, are limited to permanent storage of waste in open dumping pits (a total of 49 were found in the park), which are occasionally set on fire to reduce the volume of waste, and burning in the closed burning installations in Namche and Kumjung. Because degradable waste is commonly used by households as fodder or for composting, the waste in the open pits consists predominantly of nonsegregated nondegradable waste.

Although attempts have been made to manage glass and metal, plastic is currently the most problematic waste type in SNPBZ. It is accumulated in large quantities and is spatially widely distributed across the park. Furthermore, current disposal of plastic (open dumping or burning) is a great hazard for environmental and human health (Gatrell and Lovett 1992; Thompson et al 2009). Although around half of the plastic accumulated in SNPBZ is openly burnt, 40% is dumped in pits or scattered around. A small share is reused by local residents. Figure 3 shows percentages of disposed solid waste for each waste category according to both the current treatment practices (Figure 3A) (ie burning, burying, incinerating, transporting outside, reusing, recycling) as well as the best options identified (Figure 3B).

Figure 3A and 3B

(A) Current waste disposal practices in SNPBZ; (B) best options for each category of waste.

The heavy metal analysis of the river water samples taken from 11 locations near waste dump sites showed elevated concentrations of lead (Pb) in all samples (0.09–0.34 mg l⁻¹) and elevated iron (Fe) in 60% of the samples (5.07–14.43 m l⁻¹), whereas nickel (Ni) and zinc (Zn) at all sites never exceeded the Nepali guidelines for drinking water (Gov. of Nepal, 2005: National Drinking Water Quality Standard (NDWQS) limits: Pb  =  0.01 mg l⁻¹, Ni  =  0.02 mg l⁻¹, Fe  =  0.3 mg l⁻¹, Zn  =  3.00 mg l⁻¹). Analysis of soil quality at different locations near dumping sites also showed a contamination by heavy metals. Thus, copper (Cu) was above WHO standards (Cu = 0.1–2.5 ppm) only in the soil collected near Namche burning pit (5.44 ppm), while Zn exceeded WHO guidelines (Zn = 1.2–2.0ppm) in most of the sampling points, with the highest values found near Luckla's incinerator (262.70 ppm) and Namche's closed burning installation (153.78 ppm), but cadmium (Cd) and Ni never exceeded the WHO standards (20 ppm and 3–1000 ppm, respectively). As a reference condition (control), we referred to the paleolimnological study of Lami et al (1998) who reported that trace metal concentrations, particularly Cu, Zn, and Ni, found in sediment cores from 2 lakes situated in the Upper Khumbu Valley, were generally close to the world average for rocks. Given that these lakes are situated in a remote area where the human impact is very limited and receive primarily water from glaciers and snowfield, no evidence was found indicating an anthropogenic contribution to the observed metal loads, which most likely are of geological origin. On the contrary, high concentrations of Cu and Zn observed in this study in the sample form Luckla and Namche may be associated with the presence, respectively, of the nearby small-size incinerator and open burning installation (Yoo 2002). However, as these results are preliminary, further specific investigations would be needed to support this hypothesis. Similarly, PM₁₀ concentration in air samples collected close to the burning pits at Luckla and Namche were found to be from 2 to 4 times higher than the standard threshold in ambient air (120 µg m³). Natural reference conditions for PM₁₀ concentration were provided by the study of Decesari et al (2009), who reported on chemical composition data for PM₁₀ from the Nepal Climate Observatory-Pyramid (NCO-P) located at 5079 m at the foothill of Mt Everest, where air pollution is mainly caused by transport of anthropogenic aerosols and the average PM₁₀ mass measured was of the order of 6 µg m³.

Microbiological contamination (fecal coliform) was also found in water samples obtained near the waste dump site in Namche.

With the aim of investigating alternative solutions for reducing waste scattered after treatment on the soil (littered and disposed) and consequent impacts on the environment, the solid waste model was developed and implemented. Before presenting and discussing the modeling scenarios, we must state beforehand that, to individuate the management options to be implemented in the model, different suggestions for improvement of management of solid waste in SNPBZ that emerged during the November 2008 workshop in Namche (SES bounding section) with local stakeholders (including local policy- and decision-makers, park managers, SPCC staff, school teachers, and local lodge owners from some settlements) were evaluated. Those included the following: promotion of indigenous knowledge and practices for waste management through related training and capacity building activities; introduction of appropriate incineration technology in suitable locations (repairing and functioning maintained of the Luckla incinerator or installation of a new incinerator of greater capacity (100 kg hour⁻¹) in Namche or other nearby places to incinerate waste produced from Luckla and other settlements in lower Khumbu); promotion of better segregation and disposal of waste at different levels (SPCC's staff and households); introduction/installation of waste recycling equipment (eg recycling plants for plastic); improving export of nondegradable waste; and encouraging use of low waste generating materials.

At first, the model was run applying the current management policy adopted by SPCC in the park to have a reference condition, the so-called “business as usual” scenario, useful to understand the model's performance and assess how the system changed when an alterative waste management lever was implemented. The simulated “business as usual” scenario depicted the current situation in the park, providing results similar to those found in the field, as expected, because the model was calibrated at the actual time step under local conditions in the study area, based on data collected from field surveys.

An alternative scenario was then simulated by implementing the model with a management policy, foreseeing at the same time a 100% collection efficiency total and a waste disposal practice in accordance with the most appropriate treatment methods proposed per each waste category in contrast with the current practice. According to this proposed policy lever, all plastic waste would be preferably recycled (alternatively incinerated), glass and metal exported, while remaining solid waste (category “other”) would be mostly reused (80%) and partly incinerated (20%) (Figure 3A). As a result, both the littered waste on the soil and the residual waste after treatment would be zero: this may help to significantly reduce the civil nutrient loads—influenced also by burned, buried, and incinerated solid waste as well as uncollected waste littered on the soil—that goes into streams.

A broader management analysis required that the projected costs of operations (ie collection and exportation) and the infrastructure needed (ie small incinerator with 100 kg hour⁻¹) to properly dispose each waste category were considered. A preliminary cost assessment was initiated with regard to the different disposal treatment methods considered in the above-mentioned management scenario. For instance, at park level, the cost estimated for a 100% collection of all solid waste produced amounted to US$ 3000, while costs for exporting plastic, glass, and metal were found to be around US$ 2900, 3300, and 3000, respectively, including discounted air cargo charge and porter charge from Namche to Luckla. Costs for incineration of solid waste depend mainly on the capacity of the incinerator. Considering an incinerator with a medium capacity of 100 kg hour⁻¹, the cost to incinerate solid waste generated in the park has been calculated to be around US$ 126, which is relatively low but does not include the high costs of building and maintaining the incinerator (which, however, can be amortized over time).

Improving water quality management

The water quality analysis revealed that the nitrate content of all water samples was within the threshold for drinking water, according to WHO and Nepali guidelines (Gov. of Nepal, 2005), ranging between 0.14 and 1.94 mg l⁻¹. We found that P content in collected river water samples ranged between 0.02 and 0.66 mg l⁻¹ whereas USEPA (2000) criteria for streams and river water is 0.1 mg l⁻¹, and for streams entering lakes is 0.05 mg l⁻¹. P concentration measured in water samples collected from lakes (four Gokyo Lakes, and Imja and Pyramid Inferior Lakes) ranged from 0.01 to 0.42 mg l⁻¹, thus exceeding USEPA (2000)'s standard, which set a range between 0.01 and 0.03 mg l⁻¹ for lake reservoirs, and indicating high probability of algae blooming (Stevenson et al 2009). Particularly, the elevated P concentrations found in the first and second lake of Gokyo (0.24 and 0.27 mg l⁻¹) are most likely caused by anthropic pressure caused by the nearby presence of touristic lodges: They discharge a mixture of greywater and even excreta-contaminated wastewater into the water body, thus contributing significantly to degradation of its water quality. Altogether 62 species of aquatic algae were recorded from lake waters in the study area; 10 were new records for Nepal. Chlorophyll content in algae ranged between 0.17 and 0.72 mg g⁻¹.

Reynolds et al (1998) analyzed sodium content at 1.61 mg l⁻¹, whereas this study found lower contents with an average of 0.2–6.4 mg l⁻¹. However, the highest values found for magnesium was 1.2 and 8.7 mg l⁻¹, showing higher values than those found by Reynolds et al (0.11 and 0.52 mg l⁻¹). However, as the dominant sources of Na and Mg are geochemical (moraine deposits), differences in their concentration are more likely associated with the different geological settings (described in Bortolami, 1998) of the investigated areas rather than the presence of waste dumping sites. Moreover, Mg concentration found in this study can be explained by means of geochemical origins as a result of the scour of the rocks and the pedogenetic layer.

Total dissolved solids, pH, sodium, magnesium, lead, and manganese were found to be everywhere within the limits for safe drinking water. Regarding the data collected on conductivity, the water quality in the Khumbu Region was still excellent. Analysis of heavy metals found that Fe and Cu content in water samples from 6 and 8 sampling sites, respectively, was above the WHO and Nepali standards for drinking water, which sets thresholds for Fe at 0.3 mg l⁻¹ and for Cu at 1.0 mg l⁻¹.

Regarding the use of fertilizer, total annual production of organic fertilizers was estimated to be about 2000 tons in SNPBZ. A farming household produces on average 1.7 t year⁻¹, used at a rate of 82 kg m⁻² on farmland. Different types of organic fertilizers are used: decomposed litter or litter mixed with animal or human waste from a single pit—one of the most widely used sanitation technologies: excreta, along with anal cleansing materials (water or solids) are deposited into a pit (Tilley et al 2008).

To meet the high demand for vegetables from the tourism industry (especially potatoes), farmers are tempted to use excessive amounts of organic fertilizers. Considering the N and P content of analyzed samples, the average ratio of organic fertilizer to area was 80 t ha⁻¹, which is higher than the recommended dose. At this rate, N, P, and K are brought out on the field at around 97, 54, and 137 kg ha⁻¹ respectively, whereas the recommended dose of organic fertilizer in potato crop is 70 kg ha⁻¹ for N, 50 kg ha⁻¹ for P, and 40 kg ha⁻¹ for K (Salerno et al 2009). Only 2 interviewed households in Namche were found to use chemical fertilizer, which is not sold on the markets of SNPBZ.

Elevated levels of microbiological contamination by fecal coliform bacteria (Escherichia coli and Streptococcus faecalis) were found in the water at 6 sampling points (see Figure 1). For business reasons, tourism services and facilities are preferably provided and situated directly along the trekking trails, which in turn often follow the river sections draining the valleys along the valley bottom. Consequently, rivers and streams are contaminated by human excrement, which leaches into the groundwater or is discharged and piped directly into the rivers and streams from open toilets and lodging facilities.

Three types of septic tanks were observed in SNPBZ: with cemented walls, stone walls (noncemented), and single pits (including litter toilet) (Figure 4). Only 5% of the inspected toilets had a septic tank with cement walls, while 47% consisted of a single pit and 48% had stone walls. Twenty percent of the houses in SNPBZ did not have a septic tank and were generally situated along the trekking routes.

Figure 4

Types of toilets in SNPBZ. From left to right: (A) and (B) 2 toilets using litter, the most common type of toilet in the lower part of the park; (C) a temporary toilet at Everest Base Camp; (D) the toilet of a hotel showing waste flowing out on the surface from a septic tank. (Photos by Pramod Kumar Jha, Bharat Babu Shrestha, and Narayan Prasad Ghimire)

The impermeability of septic tanks depends on the depth of the tank, soil texture (high if soil texture is fine) and material used for the tank wall (cement or stones). In addition, the distance of the tank from the water source influences the time for the fecal matter to reach the water body by leaching. Stone-walled septic tanks have a permeability of 40%–50%. Although tanks with cement walls have an average permeability of less than 10%, the cost for construction material is relatively high because of the high cost of transportation and the cold climate, hindering the cementing process. For this reason, only a few lodges have such a tank. Septic tanks built out of stone are the most viable option for tourism enterprises in SNBPZ. This kind of septic tank has the advantage of low construction costs, also for tanks with a high volumetric capacity, as required for such enterprises.

Findings from field surveys gave a picture of the current situation in SNPBZ, which was also reflected in the “business as usual” scenario simulation by running the model without implementing any policy lever. As previously explained, the “business as usual” scenario represented the current condition in the study area (data collected on the field were used to calibrate the model at actual time) and provided a reference condition to understand the performance of the model. By evaluating such scenarios depicting the current situation in the park (where no policy levers are implemented) and considering the classes for water quality set in the European WFD, the water quality in the section of Dudh Kosi River below Surke village (BZ) was found sufficient on a yearly average. However simulation modeling showed that it became very bad during dry months.

The application of different policy levers allowed us to estimate the possible benefits of each policy on the river water quality. The model was run by implementing a policy lever to foresee the upgrading of already existing stone-wall septic tanks to cemented-wall ones with greater permeability or construction of a new cement wall, as possible management actions to reduce the leaking of fecal matter (human organic waste) into surface water bodies and groundwater that is a major source of water contamination, as previously stated. We obtained a simulation scenario showing that the river water quality in the same section became good in general on a yearly time scale, although it was sufficient during the driest months (April–May) when the pressures on water quality are greatest given that river flow is at a minimum and the weather is most favorable for tourist trekking.

As an overall result of the application of the above-mentioned management lever in SNPBZ, the water quality in the river section considered in general would improve, even if differently, during dry season—from very bad (Class V) to sufficient (Class III)— as well as the rest of the year—from sufficient (Class III) to good (Class II). The average estimated cost to realize this scenario in all selected settlements in SNPBZ was around US$ 1.4 million (NRs 110 million) and included both the costs of construction materials for cement wall septic tanks with a tank capacity of 1000 cubic feet (below 4000 m, US$ 2000  =  NRs 150,000; above 4000 m, US$ 1100  =  NRs 80,000) as well as the transportation costs (higher at higher altitudes). Because of the high transportation costs of construction material for cemented-wall septic tanks, they do not seem economically viable for small lodges and tea shops, especially at high altitudes (here stone-wall septic tanks could be the best option), but they can be constructed for bigger lodges and hotels.

Another alternative management option is related to the fact that local people living inside the park commonly use domestic animal excrement as organic fertilizer. According to Hatfield and Cambardella (2001), whether N source is animal manure, as in the case of SNPBZ, or commercial fertilizer, over-application of either source can provide too much plant-available N and increase the potential for NO₃ leaching and leakage into water resources, which can contribute to surface water and groundwater degradation. Among management strategies for reducing nonpoint NO₃ loss from cultivated fields through drainage, the establishment of riparian buffer zones, wetlands, or biofilters can contribute to nitrate removal and minimizing nitrate contamination of water resources (Dinners et al 2002). Given this background, we explored the possibility of introducing streamside forested buffers on one side of a cultivated field to reduce nitrate leaching and drainage caused by runoff from field applications of animal manure. Streamside forested buffers may indeed attenuate N inputs to aquatic ecosystems through plant uptake, microbiological denitrification, soil storage, and dilution (Haycock and Pinay 1993; Balestrini et al 2006; Dosskey 2001). By implementing this management lever, although the water quality in the considered river section would remain poor in the dry season, it would be good during most of the year. The model also estimated that the necessary surface of trees to be planted at park level would be at least 40 ha, for a total cost of US$ 19,000 (NRs 1.5 million).