The source of the Beas River is located in the Himalayas, central Himachal Pradesh, India; the river merges with the Satluj River at Harike in Punjab. The Beas River is one of the main tributaries of the Indus River system, which is critical for food, energy and economic development in India. Figure 1 shows the location of the Beas River Basin in North India. The Pong Dam reservoir is situated downstream in the basin; the dam is mainly used for hydropower generation and irrigation water supply.

Historic daily mean stream flow discharge data for the study area was made available by the Bhakra Beas Management Board (BBMB) for two gauging stations: Nadaun (from 1980 to 2017) and Thalout (from 1967 to 2007) (Fig. 2).

Time varying seasonal and decadal summary flow statistics were calculated to understand the long-term flow variability which may influence macroinvertebrates, and hence, the provision of supporting ecosystem services. These included mean monthly flows, the cumulative seasonal flow exceeded 10 % of the time (Q10) and the cumulative seasonal flow exceeded 90 % of the time (Q90). While Q10 is a measure of high flows, the Q90 is a measure of low flow. Seasons were defined as the following hydrological periods: Summer (pre monsoon) (March–May), Monsoon (June–September), Autumn (Post monsoon) (October–November) and Winter (December–February).

The macroinvertebrate sampling locations (historic and from 2017) are detailed in Fig. 2. The historic sampling sites are located on the tributaries of the Beas River whilst the 2017 sampling sites are located on the main stem.

Figure 3 depicts the decomposed time series of the mean monthly flows at both gauging stations. There are strong similarities in flow seasonality, with high flows during the monsoon season and low flows during the winter season. Overall, the mean monthly flows show a decreasing trend after the 1990s. The observed facet (Fig. 3) also shows trend change points in the 1990s, thereafter the flows appear to decrease.

Mean monthly flows from Nadaun gauging station are more variable compared to Thalout upstream; this is also reflected by irregularities in flows at Nadaun during the change point in the 1990s.

Similarly, analysis of seasonal cumulative flows shows a shift over time in both the Q90 and Q10 as revealed in Fig. 4.

As illustrated in Fig. 4, both gauging stations depict similar trends of decreasing cumulative flows over the four seasons, especially the monsoon flows. The Nadaun station recorded a noticeable decrease in Q10 and Q90 monsoon flows from the 1980s to 2017. On the other hand, the Thalout station shows a noticeable downward shift in Q10 and Q90 during the winter season from the 1960s to the 2000s.

These decreases in both mean monthly flows and seasonal cumulative flows in the Beas River could be the result of climatic change and human activity impacts linked to increases in abstraction activities and hydropower generation in the basin (Singhvi and Krishnan, 2014).

Figure 5 provides a comparison of the LIFE scores.

Despite differences in the spatial location and timing of sampling, similar patterns in macroinvertebrate diversity and abundance were observed; this is represented by the seasonal variations in LIFE scores. Previous studies e.g. Joshi et al. (2007) on macroinvertebrate assemblage in the Himalayas region also observed maximum macroinvertebrate densities during winter and lower densities during the monsoon. Overall, LIFE scores were generally high (7.7–9.3) during the winter and summer seasons and low (minimum of 4.5) during the monsoon period. See Supplement 2 for the LIFE scores per site. The lower diversities and LIFE scores could be the result of the high monsoon flows washing the macroinvertebrates away.

Macroinvertebrate community structure changes across the seasons. High LIFE scores (winter and summer seasons) indicate an abundance of macroinvertebrates with a preference for high flows; this represents a high potential for instream supporting ecosystem services delivery. During the monsoon season, changes in the flow impacts on the macroinvertebrate structure resulting in low LIFE scores. Although macroinvertebrate response to these seasonal changes in river flows could be a natural process, human induced changes in the flow regime could negatively impact on the macro invertebrate community structure and the potential for supporting ecosystem services delivery.

The observed seasonal variation in LIFE scores suggests that the macroinvertebrate community is responding to changes in river flow. This reflects the importance of the flow regime in the ecological health of rivers and their capacity to deliver ecosystem services (Vörösmarty et al., 2010). This implies that the observed decrease in temporal and seasonal river flows in the study basin could have a detrimental impact on macroinvertebrates and, consequently, the instream supporting ecosystem services. However, a greater understanding of the hydroecological relationship in the Beas River is required. To this end, the next steps in this study focus on hydroecological modelling, where numerical models are developed to explore the relationship.

Due to data limitations, long-term historic understanding of the macroinvertebrate community and LIFE in the basin are limited. Consequently, this narrows the scope within which the changes in LIFE scores could be assessed. Generally, research on macroinvertebrates in river systems in India has been limited (Mishra et al., 2013). Despite this, the successful application of the LIFE methodology and subsequent findings, helps to confirm the applicability of the methodology in snow fed river systems in India. Additionally, this study highlights the need for further work in the form of hydroecological modelling.