Relative importance of P and N in macrophyte and epilithic algae biomass in a wastewater-impacted oligotrophic river

Abstract

The role of nutrient loading on biomass growth in wastewater-impacted rivers is important in order to effectively optimize wastewater treatment to avoid excessive biomass growth in the receiving water body. This paper directly relates wastewater treatment plant (WWTP) effluent nutrients (including ammonia (NH3-N), nitrate (NO3-N) and total phosphorus (TP)) to the temporal and spatial distribution of epilithic algae and macrophyte biomass in an oligotrophic river. Annual macrophyte biomass, epilithic algae data and WWTP effluent nutrient data from 1980 to 2012 were statistically analysed. Because discharge can affect aquatic biomass growth, locally weighted scatterplot smoothing (LOWESS) was used to remove the influence of river discharge from the aquatic biomass (macrophytes and algae) data before further analysis was conducted. The results from LOWESS indicated that aquatic biomass did not increase beyond site-specific threshold discharge values in the river. The LOWESS-estimated biomass residuals showed a variable response to different nutrients. Macrophyte biomass residuals showed a decreasing trend concurrent with enhanced nutrient removal at the WWTP and decreased effluent P loading, whereas epilithic algae biomass residuals showed greater response to enhanced N removal. Correlation analysis between effluent nutrient concentrations and the biomass residuals (both epilithic algae and macrophytes) suggested that aquatic biomass is nitrogen limited, especially by NH3-N, at most sampling sites. The response of aquatic biomass residuals to effluent nutrient concentrations did not change with increasing distance to the WWTP but was different for P and N, allowing for additional conclusions about nutrient limitation in specific river reaches. The data further showed that the mixing process between the effluent and the river has an influence on the spatial distribution of biomass growth.

Multiple challenges confront a high-effort inland recreational fishery in decline

“…High flow events leading to food supply limitations and subsequent population collapse were responsible for boom-and-bust population cycles in a tailwater rainbow trout fishery below the Glen Canyon Dam in Arizona (Korman et al 2017). However, this mechanism seems unlikely in the LBR, as substantial wastewater inputs have increased biological productivity (Sosiak 2002;Askey et al 2007), and these inputs have remained relatively constant throughout the study period (see Taube et al 2016). Intriguingly, abundance declined in both 2005 and 2013 according to postflood surveys (Fig.…”

Considering multiple anthropogenic threats in the context of natural variability: Ecological processes in a regulated riverine ecosystem

“…Potential eutrophication of the Bow River from WWTP effluents in Calgary has been a concern for decades (Culp et al, 1992;Sosiak, 2002;Taube, He, Ryan, & Valeo, 2016). Macrophyte and epilithic algae biomass assessments have been conducted by AEP in most years since 1981.…”

“…Macrophyte and epilithic algae biomass assessments have been conducted by AEP in most years since 1981. Spatial assessments have shown an increase in macrophyte and algal production downstream of the WWTP outflows, which were associated with increased productivity resulting from WWTP effluent inputs (Sosiak, 2002;Taube et al, 2016). Temporal assessments have demonstrated declines in macrophyte and algae production following upgrades to the City of Calgary WWTPs that have resulted in decreased phosphorus loads since 1982, and decreased nitrogen loads since the mid 1990s (Sosiak, 2002;Taube et al, 2016).…”

“…Spatial assessments have shown an increase in macrophyte and algal production downstream of the WWTP outflows, which were associated with increased productivity resulting from WWTP effluent inputs (Sosiak, 2002;Taube et al, 2016). Temporal assessments have demonstrated declines in macrophyte and algae production following upgrades to the City of Calgary WWTPs that have resulted in decreased phosphorus loads since 1982, and decreased nitrogen loads since the mid 1990s (Sosiak, 2002;Taube et al, 2016). High discharge has also been shown to limit aquatic vegetation (Chambers, Prepas, Hamilton, & Bothwell, 1991;Sosiak, 2002) with low end of season macrophyte abundances in years when annual maximum flow exceeds 400 m 3 /s (Taube et al, 2016).…”

“…Temporal assessments have demonstrated declines in macrophyte and algae production following upgrades to the City of Calgary WWTPs that have resulted in decreased phosphorus loads since 1982, and decreased nitrogen loads since the mid 1990s (Sosiak, 2002;Taube et al, 2016). High discharge has also been shown to limit aquatic vegetation (Chambers, Prepas, Hamilton, & Bothwell, 1991;Sosiak, 2002) with low end of season macrophyte abundances in years when annual maximum flow exceeds 400 m 3 /s (Taube et al, 2016). Conversely, algae biomass was not influenced by variations in annual maximum flow (Taube et al, 2016), presumably owing to the quicker regeneration of epilithic algae.…”