3.1. Hydrologic Setting
Peak flow in the Upper Naryn occurs in late July or early August, while the Lower Naryn experiences an earlier peak in late May or early June. The Naryn River hydrograph shape across elevations demonstrates the transition from ice to snow melt sourced waters as the river progresses downstream. The upper gauge (Chong Naryn) exhibits a typical sustained late summer flow shape of a glacier sourced system, while the lower elevation gauge at Uch Terek shows more water mass and higher flows earlier in the year coincident with the spring snow melt season (Figure 2
). The “flashy” character of the annual hydrograph’s rising limb suggests a river system that is fairly responsive to the highly variable precipitation inputs over the course of the year (Figure 2
Rain during the drier months almost always comes in multi-day storms, and in the rainy months the intensity can vary by an order of magnitude from day to day. Based on the 14 years of MERRA precipitation data across nine 500 m elevation bands (500 m to 4500 m), 70% of the months record both rain and snow event within the same elevation band. This suggests rain-on-snow events may exacerbate the high magnitude response of stream flow to new precipitation inputs across elevations. Since glaciers play a role reducing both intra- and inter-annual flow variability by providing a consistent ice melt supplied baseflow through the melt (summer) season that is independent from storm spikes, depletion of ice mass in glacier systems will lessen the water they supply to river systems over the long term and may impose a hydrograph that is even more responsive to changes in weather.
A substantial baseflow of approximately 200 m3 s−1 is observed outside of the melt season at the regional basin scale shown at the Uch Terek gauge, while consistent but smaller baseflows are present in the Upper Naryn. A small run-of-river reservoir is located immediately upstream of Uch Terek flow gauge and may account for the highly consistent winter flow recorded at this point.
Precipitation across the basin averages 27.13 cm per year, with 63% falling as rain and 27% falling as snow, however above 3000 m the total precipitation inputs are approximately half rain and half snow. In relation to the way the basin is split in this paper for analysis, approximately 40% of precipitation in the Upper Naryn falls as snow. Within the Lower Naryn Basin, annual precipitation inputs are comprised on average of 89% rain.
In the Upper Naryn basin, 84% of the area (8632 km2
) has snow probability >30% while this figure applies to 54% (20,424 km2
) of the Lower Naryn basin area (Figure 3
). Glaciers are present at the headwaters and provide melt inputs to both headwater stems as well as to the Ak-Tal, a major tributary joining the Naryn River at Dostuk. Glacier ice covers 994 km2
, or 2% of the entire study domain.
3.2. Hydro Chemistry Elevation Gradient
Isotope variation of Naryn River waters across the elevation gradient show a strikingly consistent isotope value throughout the basin (Figure 4
O values for mainstem waters hover around −12‰ from the highest elevation sample all the way through to Toktogul Reservoir. Tributary sample δ18
O values vary more than the mainstem ranging from −13‰ to −9‰. Notably, crysopheric end member samples—Snow, ice, glacial outflow and high elevation groundwater—bracket the isotope values found in the Naryn River. In contrast, the rain sample acquired in the adjacent Kyzyl Suu basin has a δ18
O value of 0‰, suggesting that surface waters in the Naryn basin are dominated by melt water sources. With the exception of the groundwater spring at Kazarman Pass (2299 m, −16‰), groundwater isotopes throughout the basin (−13‰ to −11‰) also hover near the isotopic values of the high elevation melt water group and are discretely different than rain.
The ion concentration progression demonstrates the combined influence of groundwater contributions and mine discharge on the chemical signature of mainstem waters (Figure 4
b,c). The mine discharge sample provides exceptionally high levels of SO42−
(25,387 μeq L−1
) and Na+
(24,596 μeq L−1
) to the mainstem waters. However, it is Ca2+
poor (599 μeq L−1
) and does not account for the high Ca2+
values observed in both mainstem waters and tributaries that are hydrologically disconnected from the mine discharge waters (e.g., Bordu Stream and Arabel River). Extremely elevated levels of Ca2+
(4116 μeq/L, twice the level of Ca2+
in the mainstem) were found in the Bordu alpine groundwater sample that logically also contributes to high elevation river flow. These groundwaters are SO42−
poor (453 μeq L−1
and 238 μeq L−1
, respectively), and so there is intuitively a joint contribution from mine discharge waters and groundwater that accounts for the elevated ion profile of the Kumtor (Upper Naryn) River.
Dilution of ions with decreasing elevation likely result from added ion-poor snowmelt contributions as the catchment expands to include major additional sub-basins adding significant alpine areas and snow cover to the basin. This dilution trend is observed until 3182 m in the Ca2+
profile (Figure 4
b), then reverses towards an increasing concentration pattern likely a result of groundwater contributing increasing proportions to the river flow.
3.3. EMMA Diagnostics and Mixing Model Results
3.3.1. Upper Naryn
Diagnostic tests for conservative tracers examining the randomness of residuals between actual and projected tracers suggest that the following tracers are conservative for the Upper Naryn: Ca2+
]. Solute concentration reconstructions using all of the tracers and two principal components rendered poor concentration reconstructions for Mg2+
so these tracers were dropped from the model and re-run with only Ca2+
18O. With this combination of tracers, 1 dimensional space (two end members explains only 64% of the variance in the data. Two principal components (three end members) explain 94% of the chemistry variation indicating three dimensions is a more appropriate model space (Figure 5
In the Upper Naryn, three end members were used to describe stream flow compositions for all samples, however a change in end member selection from mine discharge waters to snow is due to dilution of river water with downstream distance from the mine. Note that for the three samples influenced by the mine discharge, snow is not considered an end member. Conversely, for all other surface water samples in the Upper Naryn, mine discharge is not considered an end member.
End members were selected based on the quantitative tests described in Section 2
above. Decision-making rationale for end member selection is shown in Table 1
. Percent contributions of end members to river flow across the elevation gradient are shown in Figure 6
. The headwater reach is fed by Petrov Lake and deep upstream groundwater, with an influence from the mine discharge. Petrov Lake is in essence a modified version of glacial outflow because some combination of snow and ice melt, groundwater and rain—the same combination expected to produce glacial outflow—combine to run-off and fill Petrov Lake. While in Petrov Lake, ponded water has the potential to fractionate via evaporation, somewhat modifying the isotopic character of Petrov Lake as compared to glacial outflow samples that do not experience prolonged exposure to surface fluxes in an arid climate. Petrov Lake is considered a proxy to glacial outflow in the realm of source waters while acknowledging some difference between the two end members’ isotopic signatures.
Mine discharge and Upper Naryn groundwater sources are high in some ions but not in others. While these end members have relatively higher ion concentrations, meltwaters that do not travel through the subsurface have relatively lower ion concentrations. The source waters of the most upstream site (3587 m) are dominated by reacted upstream ground water and glacial outflow, with mine discharge contributions to river flow calculated to be 5% or less at all headwater sites (Figure 6
The gradual ion dilution effect observed across the elevation gradient is echoed by the gradual movement of the more downstream river samples in the EMMA diagram away from the mine discharge position (Figure 5
). After the confluence of the Chong Naryn and Kichi Naryn, river samples are sourced by snow, reacted upstream groundwater and Petrov Lake/glacial outflow. The rise of snow as an end member supports the idea of low-ion concentration dilution waters as the basin expands to include more snow covered area through to the confluence of the Chong Naryn and Kichi Naryn at the Chong Naryn gauge site (Figure 1
and Figure 3
). The inflow of the more reacted Kichi Naryn tributary waters mixes with the Chong Naryn and increases some ion concentrations once again. With decreasing elevation, river sources transition from being majorly sourced by glacial outflow with groundwater as a subsidiary contributor, to the inverse just above Naryn town (Figure 6
). Logically, the importance of glacial waters wanes with distance from the glacier.
Of note, the shallow “quickflow” groundwater appears to be a similarly good fit as an end member as snow in both Euclidean distances and EMMA diagrams (Figure 5
). Utilizing shallow groundwater instead of snow as an end member yields a much poorer reconstruction, including an inverse relationship between modeled versus observed isotopes. Snow as an end member appears indispensable for the mainstem above Naryn town. Tracer concentration reconstructions show significant linear fits (p
< 0.01 for all tracers, R2
> 0.9 except for Cl−
and isotopes) (Table 2
), but there are some biases in the model with both under and over prediction of concentrations across tracers.
3.3.2. Lower Naryn
As with the upper basin, Ca2+
O were deemed to be conservative as per the diagnostic tests from Hooper [10
]. Also as with the Upper Naryn, two principal components were selected for analysis as they explain 94% of the data as compared to 78% variance explanation with 2 end members (1 dimension) (Figure 5
Naturally, the Naryn River inflow from the Upper basin feeds the downstream reach and is an obvious end member selection for the Lower Naryn. While we treat the Naryn River inflow as an end member in and of itself, it is important to recall the composition of these waters derived from the Upper Naryn mixing model: 67% reacted groundwater, 24% glacial outflow and 9% snow. Meltwater plays an inherent role in this end member. Along with Naryn River inflow, deep reacted downstream groundwater and shallow lateral flow groundwater are the other end members. While we acknowledge that the deep groundwater point does not appear to be a geometrically tight fit to the EMMA diagram, the Euclidean distances for other end members ruled them out as compared to the selected point (Table 1
The Naryn River immediately below Naryn town is naturally dominated by the Upper Naryn inflow end member at Naryn town. The system progresses to a river flow roughly equally partitioned into water coming from the Upper Naryn (51%) and downstream groundwater sources (49%) just above Toktogul Reservoir (Figure 6
Concentration reconstructions perform soundly for the Lower Naryn samples (p
< 0.01 for all tracers, R2
> 0.84 except for NO3
) (Table 2
) however under prediction and some minor over prediction of solutes/isotopes is observed.
3.3.3. Mixing Model Validation
Primarily mixing model validation was performed via concentration reconstructions to assess adequate performance by comparing the modeled concentrations to the observed values (Table 2
Model validation was also afforded on a conceptual basis by contrasting model results between diurnal samples collected at (1) the Bordu River tributary site adjacent to Bordu glacier and (2) on the mainstem Naryn above Kazarman. On the Bordu River samples were collected at 6 p.m. and 6 a.m. at a site 3622 m in elevation. While isotope values are similar during both times, lower ion concentrations in the evening support the notion of the afternoon being a time when higher melt rates contribute more snow and ice melt transferred directly to the river composition relative to other times. The 6 a.m. sample has ion higher concentrations by a factor of 3–4 as compared to the 6 p.m. sample. This agrees with our general understanding of diurnal fluctuations in glacial systems where melt-sourced groundwater makes up a larger portion of river flow in the early morning, after cold nights mitigate overland flow melt inputs to the channel.
Similarly, at 1328 m in the Lower Naryn basin, samples were collected at 6 p.m. and 10 a.m. on the Naryn River upstream of Kazarman town. In contrast to the diurnal hydrologic behavior of Bordu glacial stream, the Naryn River near Kazarman shows no significant variation in chemistry between early evening and mid-morning. This is an expected result given the groundwater dominated source waters of the mainstem Naryn River at this location. The agreement between these results and what we know about glacial melt patterns and larger river systems contributes to validation of Upper and Lower Naryn mixing models.
Further validation of our two-regime hypothesis is provided by poor model performance when using all samples to derive a single source water separation for the entire glacier-to-plains study domain.
3.4. Socio-Hydro Results
Survey results indicate a common response across all communities relating to an overall decrease in water access over the last 15 years. Survey participants stated that water availability depends not on the physical water supplies but primarily on water management and infrastructure investment for both municipal and irrigation systems. Much of the water stress stems from agricultural reorganization after the Soviet collapse from large collective farm structures to individual, small private farms. This transition lies at the root of many factors contributing to current water stress across Naryn River basin communities. The deputy water manager in Naryn province summarized several factors, including:
Gaps in knowledge. Farmers accustomed to single task jobs associated with large scale farming practices lacked knowledge about crop rotation, irrigation techniques suitable for the climate and soils of the Naryn basin, and the complete cycle of agricultural production needed for productive small-plot farming.
A lack of agricultural, economic, educational and hydrologic infrastructure needed to service small-plot farmers. Farmers were ill-equipped without financing options, reliable irrigation and water distribution, and appropriate machinery. As a result, yields declined and irrigation systems deteriorated leading to greater inefficiencies.
Complete absence of new irrigation technologies.
Inadequate government support for struggling farmers due to understaffed water management offices in the region. A shortage of qualified specialists was largely attributed to low compensation.
The impacts to the agricultural sector due to the transition between large-to-small scale farming demonstrates a shift in water-human experiences from one that was nationally regulated to one where communities are largely responsible for addressing water needs. Some communities responded to water supply stress by installing groundwater wells, especially for drinking water. The survey results show that changes to water supply sources (surface water versus groundwater well) are not dependent on water availability or location within the basin. For example 2 out of 6 surveyed communities with heavier reliance on groundwater are unregulated upstream communities, Naryn and Kazarman, communities one may expect to be more heavily tied to the surface flows of the Naryn River. Water quality—not quantity—motivated the increase in groundwater use.
In contrast to these two communities’ adaptive responses, the regulated downstream communities near Toktogul preferred tributary surface water sources and traditional Soviet community based water systems such as gravity fed canals and water storage. Despite these preferences, upon relocation reservoir communities were provided with electric pumps to extract lower-lying water to service the village. These pumps were a common gripe among survey respondents, as they require continual maintenance and are notoriously prone to failure, decreasing overall reliable access to water.
A comparison of survey results shows that source of income was one of the most obvious differences over time in unregulated upstream versus regulated downstream communities. Income shifted from salaries paid by state run organizations in 2000 to small businesses, water-efficient crops and livestock in unregulated upstream communities while in regulated downstream communities income increasingly comes from labor migration and associated remittances. Downstream survey participants indicated that factors contributing to this difference include smaller land plots per household and less water supplies in regulated downstream communities, which are not enough to provide food for households.
Apart from these changes, it was obvious that even though the price of water increases in downstream communities, at some point the price of water does not really matter in light of much bigger issues faced by regulated river basin communities near Toktogul reservoir. The biggest issues in the Toktogul district are limited water availability, land and funds scarcity, and lack of trust in government, all of which were being perceived by the local communities as a direct result of communities’ relocation and hydropower development in the region in 1960s. As a result, survey respondents in regulated river basin communities indicated that there were no positive socio-economic changes within their communities in the last 15 years.
This observation is strikingly different from the survey replies in the upstream communities where survey respondents were much more optimistic in their ability to change things, turn things around, or earn enough income with existing resources. One survey response summarizes the general attitude in the upstream communities: “If there will be another dry season (no rain and less water flow in the river), we will farm a different crop, like wheat, that requires less water.” Indeed, respondents in all communities noted that the majority of farmers shifted agricultural production from water-intensive crops grown under Soviet rule (e.g., vegetables and fruits), to less water-intensive crops such as alfalfa and barley to feed livestock.
Survey respondents in all communities brought up the topic of climate change, albeit with different emphasis. Upstream communities are aware that warmer temperatures may threaten their normal agricultural production cycle, including an observed shift in peak flows that they attribute to climate changes now misaligns water arrival with the height of the growing season. The survey respondents in regulated downstream communities acknowledged climate change but it was a lesser focus as compared to their counterparts in upstream communities.
In summary the survey found that Naryn basin communities responded to changes in water supplies, water flow, hydropower and irrigation projects at various levels. The responses suggest that the overall impact in communities is a mixture of actions on mainly household, farm, private firm and organization levels. These actions include a heavier reliance of some municipalities on groundwater, shifting to less water-intensive crops and/or livestock, and transitioning from agricultural sources of income to labor migration and associated remittances.