Trophic state evolution in a subtropical reservoir over 34 years in response to different management procedures

Abstract

Despite their importance for water management, long-term studies on trophic state are relatively scarce in subtropical reservoirs. We analyzed total phosphorus (TP), total nitrogen (TN) and chlorophyll a (Chl a) concentrations in the Billings Reservoir (Brazil) over time: Phase 1 (1977-1992, Tietê River water was pumped to Billings to increase energy generation, 100 m(3) s(-1)); Phase 2 (1992-2007, Tietê water was conveyed to Billings only in special cases for flood avoidance, 8 m(3) s(-1)); and Phase 3 (2007-2010, besides flood control, Billings received Tietê water treated by an in situ flotation system, 13 m(3) s(-1)). We compared our results with data from 12 reservoirs to evaluate current (2005-2009) enrichment conditions. Phosphorus and nitrogen concentrations decreased (p < 0.05, MANOVA) from Phase 1 to 2 and were stable thereafter. TN/TP ratios increment (1977-2010) indicated shift from N- to P-limitation in the reservoir, affecting the phytoplankton. Nutrient levels in Billings are currently between the expected concentrations in mesotrophic and eutrophic reservoirs (0.03 mg L(-1) < TP < 0.42 mg L(-1), 0.8 mg L(-1) < TN < 7.6 mg L(-1)) and Chl a concentrations exceeded 34 μg L(-1), median for the eutrophic waterbodies from the dataset. Although water quality in Billings has improved, nutrient inputs from Tietê River pumping episodes, diffuse and internal sources are still favoring biomass accrual and compromising water uses.

Water quality in four reservoirs of the metropolitan region of São Paulo, Brazil

“…PCA performed with eleven abiotic variables and chlorophyll a from the four reservoir corroborates TSI results, with the two eutrophic environments grouped in the left side of axis 1, related to higher concentrations of nutrients and chlorophyll a, and the other reservoirs grouped in the right side, with higher concentrations of dissolved oxygen and transparency. These results are in agreement with those presented by CETESB (2013) and other studies conducted in Billings (Cardoso-Silva et al, 2014;Wengrat & Bicudo, 2011;Cunha et al, 2011;Moschini-Carlos et al, 2010) and Guarapiranga (Fontana et al, 2014) reservoirs in different sampling sites.…”

Defining limits to multiple and simultaneous anthropogenic stressors in a lake ecosystem – Lake Kinneret as a case study

“…Comparing the results of N and P load scenarios at multiplication factors of Â0.1 to Â0.5, revealed lower CWQI values for the N load scenarios, since the N:P ratio is much lower (N load is multiplied by factor of 0.1 while the P load is constant at its baseline load). Numerous studies have discussed the importance of nutrient ratios in determining the plankton dominance by cyanobacteria (Havens et al, 2003;Havens, 2008;Lv et al, 2011;Cunha et al, 2011). Cyanobacteria, which include toxin producing and nitrogen fixing species, often become the dominant group in nutrient enriched lakes and may create surface scums along with taste and odor problems.…”

In situ Remediation Technologies Associated with Sanitation Improvement: An Opportunity for Water Quality Recovering in Developing Countries

“…A comprehensive monitoring program (148 water variables and more than 200,000 laboratory analyses) was delineated to assess the efficiency and feasibility of the pilot-scale prototype. Detailed information about the monitoring results in the Tietê and Pinheiros Rivers and in the Billings Reservoir may be found in some recent papers Cunha et al, 2011a andCunha et al, 2011b). The efficiency achieved by each flotation station and the overall effect for some variables is shown in Table 4.…”